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Full text of "Projection Engineering (Jan 1932-Mar 1933)"



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Scanned from the collections of 
The Library of Congress 




AUDIO-VISUAL CONSERVATION 
at The LIBRARY of CONGRESS 




Packard Campus 

for Audio Visual Conservation 

www.loc.gov/avconservation 

Motion Picture and Television Reading Room 
www.loc.gov/rr/mopic 

Recorded Sound Reference Center 
www.loc.gov/rr/record 



IN THIS ISSUE 



UAL 



DRESS AND RADIO 
1 IN THE WAL- 
RIA HOTEL 



N PICTURES IN MEDICAL 
AL PRACTICES 




OF 



BALANCE IN 
AUDITORIUMS 



OUND-ON-FILM 
UND-ON-DISC 





Photo courtesy T hc Rauland Corpn 



Mundelein College, Chicago, equipped with Rau- 
land Sound Apparatus. Insert shows control 
panel for radio broadcast reception, phono- 
graph and microphone services to sixty 
rooms. 






journal of me Sound and Light Prqjecf ion Industries 

JANUARY, 1932 




«HW 



II 



FOREST 

RECTIFIERS 



for Good Projection Everywhere 



Until recently it was the general practice to use batteries or motor genera- 
tors to supply direct current to sound systems. Today Forest Rectifiers are 
used to replace troublesome storage batteries and motor generators. 

Forest rectifiers save current, are efficient, supply unfailing non-fluctuating 
current, require no attention or attendance and are always ready for 
service. 

Every NEW sound installation should have a Forest Rectifier. Every OLD 
installation should be modernized for greater saving and better sound. 

The finest sound installation is made better with a 
Forest Rectifier. There is a Forest Rectifier for every 
type of sound installation. 



m 




"bSS Model 77 illustrated is ^ 
for supplying 7'/2 amperes to 
exciter lamp and 1 ampere to 
amplifier filaments. Models 
are made for every direct- 
current requirement. 




MODEL 77, FRONT VIEW 



MODEL 77, INSIDE VIEW 



FOREST 



ELECTRIC CORP. 



NEWARK 



NEW JERSEY 



THE FOREST ELECTRIC CORP., 

New Street, 
Newark, New Jersey. 

Gentlemen: 

I am interested in hearing more about Forest Rectifiers for use in 
sound system installations. 

Name 

Address 

State 



i^ 



so 






3 

JANUARY, 1932 Page I 

Leadership is Progress 

I NATIONAL Projector Carbons hold recognized 
leadership for all types of projection equipment. 

Leadership is achieved and maintained only 
through progress. The Motion Picture Industry 
has attained its high rank in the business world 
as a result of steady progress . . . Improved qual- 
ity of direction and photography . . . Larger and 
more beautiful theatres . . . Higher standards of 
service . . . Sound . . . Color . . . Better screen 
illumination. The march of PROGRESS. 

National Projector Carbons keep pace with 
the progress of the industry. Backed by splendid 
research and manufacturing facilities, they meet 
or anticipate each new demand. The new National 
S R A Carbons and Pre-Cratered High Intensity 
Carbons are recent improvements making possible 
better projection and steadier screen illumination. 

Use National Projector Carbons in your the- 
atre. You will find the ste*ady brilliance of screen 
illumination pleasing to your audiences and a 
source of increased patronage. 
NATIONAL 

PROJECTOR CARBONS 

. . . Sold exclusively through distributors and dealers. 
National Carbon Company will gladly cooperate with the 
producer, exhibitor, machine manufacturer or projectionist 
on any problem involving light. 

NATIONAL CARBON COMPANY, INC. 

Carbon Sales Division » Cleveland, Ohio 

Unit of Union Carbide [j jjjj and Carbon Corporation 
Branch Sales Offices: New York Pittsburgh Chicago San Francisco 






Projection 

Engineering 

Member, Audit Bureau of Circulations 



Donald McNicol 
Editor 

Jas. R. Cameron 
Associate Editor 

Ulmer G. Turner 
Western Editor 

F. Walen 
Managing Editor 



Sound Pictures 

Visual Projection 

Sound Recording 

Audio Amplifiers 

Public-Address Systems 

Photography 

Facsimile Recording 

Television 

Photo-Voltaic Cells 

Circuit Measurements 

Automatic Music 

Acoustic Engineering 

Radiant Energy Devices 

Electric Recording 

Phototubes 

Home Talkies 

Theatre Engineering 

Amplifier Tubes 

Sound Reproducers 

Screen Engineering 

Electric Power for Projec- 
tion 

Recording Studio Engi- 
neering 

Location Sound Equipment 

Rectifier Tubes 

Industrial Tube Applica- 
tions 



Vol. IV 



JANUARY 
1932 



Number 1 



Contents 

PAGE 

Editorial 4 

The Public-Address and Radio Program System in the 
Waldorf-Astoria Hotel By Robert C. Sturgeon 7 

Motion Pictures in Medical and Surgical Practices, 

By Gordon S. Mitchell 1 1 

Thermionic Tube Control of Theatre Lighting. 

By Burt S. Burke 14 

Sound Absorption Balance in the Acoustics of Audi- 
toriums, By H. V. Schlenker 17 

The Trend of Sound, 1932 By Carl M. Weber 22 

Improved Disc Recording . .* 23 

Answers to Questions Nos. 21-25 23 

A British View of Sound-On-Film Versus Sound-On-Disc, 

By John Wilson 24 

Departments 

New Developments and News of the Industry 26 

Index of Advertisers 30 



Bryan S. Davis 
President 

James A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

52 Vanderbilt Avenue 

New York City 



E. M. Bacon 
Advertising Manager 

J. E. Nielson 
Circulation Manager 



Chicago Office— 333 N. Michigan Ave.— Charles H. Farrell, Mgr. 

St. Louis Office— 503 Star Bldg.— F. J. Wright. 

Kansas City Office— 306 Coca Cola Bldg.— R. W. Mitchell. 



San Francisco Office — 15S Sansome St. — R. J. Birch. 
Los Angeles Office — 846 S. Broadway— R. J. Birch. 
New Zealand — Tearo Book Depot — Wellington. 
Australia — McGill' s Agency — Melbourn e. 



Entered as second class matter August 15, 1931, at the post office at New York, N. Y., under Act of March 3, 
1879. Yearly subscription rate $2.00 in U. S. Yearly subscription rate $3.00 in Canada and foreign countries. 



JANUARY, 1932 



Page 3 




BtLL 35 M.M. SOUND on-FILM PROJECTOR 

A A TRULY PROFESSIONAL sound-on-film projector that is in the fullest sense of the word A 

JLJL portable. The entire equipment disassembles into compact, easily handled units, no one 
/ \of which weighs over 65 lbs. Can be easily transported in the back of a standard sedan 
automobile and handled by one man. 

BELL Equipment is easily in a class by itself in such important features as ease and certainty 
of control, freedom from fire hazards, full automatic lubrication, quality of sound projection, 
compactness and portability. 

Designed by acknowledged experts with a full knowledge of the rigid requirements in the 
portable field, BELL Equipment is far in advance of all competition in adaptability to every 
reasonable condition possible to encounter. 



THE BELL SINGLE or Industrial Unit is provided with 1,000- 
ft. or 2,000-ft. reels and magazines, and consists of one 
right projector, 5-stage Amplifier and Uni-Remote-Control, 
mounted in metal case and two dynamic speakers mounted 
in carrying case. The total weight is 150 lbs. complete 
with legs, carrying cases and accessories. Price, $1,250 
complete. 

THE BELL TANDEM UNIT is designed in right and left 
projectors and can be set up with 18 in. between lenses 



or 20 ft. apart. The Uni-Remote control of exclusive BELL 
design provides smooth "changeover" and individual opera- 
tion of either projector. The BELL Tandem Unit consists 
of one right projector, one left projector, 5-stage amplifier 
and Uni-Remote-Control mounted in metal case and 2 
Dynamic Speakers mounted in carrying case. The total 
weight is 215 lbs. complete with legs, carrying cases and 
accessories. Price, $2,150 complete, F.O.B. Factory, Derby, 
Conn. 



Write for Descriptive Literature 



Demonstration by appointment at oar New York Showroom 



BELL EQUIPMENT CORPORATION 

Suite 605 .. . 729 SEVENTH AVENUE . . . NEW YORK 

Phone: BRyant 9-9890 FACTORY: Hershey Metal Products Co., Derby, Conn. 



Edit 



i a 



JANUARY, 1932 



BIG YEAR FOR JHE year 1932 is sure to 
PUBLIC ADDRESS | be a profitab le year for 
manufacturers of public- 
address equipment and for 
installation engineers who make a business 
of renting portable systems. 

In addition to the increment of business 
accruing- from the natural extensions of a 
comparatively new art there will be thou- 
sands of temporary installations employed 
during the months preceding the presiden- 
tial election. 

Auditoriums, halls, picnic grounds, fan- 
g-rounds, outdoor overflow areas, et cetera, 
will be widely subjected to the advantages 
of public-address facilities. 

There is opportunity for one or more con- 
cerns in 40,000 municipalities throughout 
the country to participate in some degree in 
this approaching business gain. 

Complete public-address systems, and the 
elements of systems are now available for 
use in every possible situation. 



THE YEAR 
1931 



ryj) i 



progress in the sound- 
picture projection art in 
more than one respect par- 
alleled the advance of broadcast radio at 
about the same number of years after its 
commercial advent. Refinements have been 
the noteworthy steps during the year. 

Outstanding among the forward steps 
have been the introduction into widespread 
service of the all a-c. operated standard and 
special size equipments, and the new port- 
able reproducing apparatus. In the success- 
ful transcription of sound on film a new rib- 
bon microphone, introduced by R.C.A. 
Photophone, Inc., played an important part. 

Progress was made also in developing suc- 
cessful equipment for the suppression of the 
heretofore troublesome "ground" noise. 

The past year has witnessed the exten- 
sion in service of the high speed "Pan" 
films, and in color cinematography a new 
additive screen process is reported to have 
been demonstrated successfully. 

A trend appears to have set in calling for 
projection lamps of higher amperage — bet- 
terment changes in other elements making 
this an advantage. 

From a mass of reports from manufac- 

Page 



turers' laboratories may be gleaned the in- 
formation that during a year of subnormal 
sales advantage has been taken of slack per- 
iods to lay foundations of developments of a 
technical nature which may be capitalized 
profitably when the business tide turns. 

▲ 

THE OUTLOOK rv TJRING 1931 there was 
B°OA T DCAST ° N D I ™*ed improvement 

ENTERTAINMENT m tne technique of radio 
broadcast entertainment. 
In response to the demand for novelty and 
variety the large stations and the chains 
have progressively introduced betterments, 
both in matter and manner, which almost 
continuously bring into the homes of the 
country a grade and quality of entertain- 
ment such as insures sustained interest. 

There is no doubt that dramatically pre- 
sented mystery stories, concerts by sym- 
phonic orchestras, amusing sketches of the 
vaudeville type, radio adaptations of min- 
strel shows, and so on, to an increasing ex- 
tent are lessening the desire to go abroad 
in the evening in search of entertainment. 

The situation is such that silent moving- 
picture shows would now have a struggle 
for existence. Talking pictures are better 
able to compete with the home radio, but 
the competition compels the picture house 
to present pictures of unquestionable merit. 
The allure must be next to irresistible. 

The leaders in the moving picture indus- 
try are not overlooking the probable or the 
possible advent of broadcast television — 
and the extent to which television in the 
home might make further inroads upon at- 
tendance in theatres. 

Perhaps for the moment no more inform- 
ing forecast can be presented than that sug- 
gested in NBC's annual report just issued. 
This reads, in part: 

"NBC engineers are conducting, tests that 
must lead eventually to the inauguration of 
public television service on a plane com- 
parable with station synchronization and im- 
proved transoceanic broadcasting." 






j> 



mJj^mziUc 



orL 



Editor 



JANUARY, 1932 



Page 5 



AMPLION 




AMPLION 

OCTOPHASE 

GIANT DYNAMIC 

AIR COLUMN UNIT 

Weight 15 lbs. 

Height 5% in. 

Diameter 5% in. 

Field Coil Resistance 5 

ohms. 
Field Coil Supply 6 volts 

D. C. 
Field Current Consumption 

1.8 amperes. 
Voice Coil impedance 16 

ohms. 
Maximum Capacity 25 

watts. 
Permanent Capacity 6 

watts. 
Shipping Weight 21 lbs. 
Shipping Dimensions 

12x12x12 in. 
This unit Is also supplied 
with 1500 ohm field coil. 
Field Supply 110 volts 
D.C. Field Current Con- 
sumption 75 milliamperes. 



OCTOPHASE 

SPEAKERS 

OF ALL THE EQUIPMENT IN 
THE THEATRE THE LOUD 
SPEAKER IS ALL YOU HEAR 

Give your amplifiers a chance 

It is those overtones from 5000 to 8000 cycles which give char- 
acter to speech. Can you afford to nullify your entire equipment 
by employing speakers which can not reproduce these frequencies. 

for 

AUDIBILITY - INTELLIGIBILITY - DURABILITY 
EFFICIENCY and FREQUENCY RANGE 

Choose the Amplion 

OCTOPHASE 



It is so much finer yet costs so little more 



CONSTRUCTION 



In this unit, the area over a scientifically domed 
diaphragm encased in a scientifically shaped air 
chamber, is divided into eight divisions. The cen- 
ters of gravity of each of these divisions are 
exactly equi-distant from the throat of the unit 
and since all operate under identical pressures, 
the sound impulses from each division reach the 
throat of the horn in perfectly timed synchronism 
with the arrival of sound impulses from all the 
other divisions. From these eight divisions, this 
reproducer derives its name OCTOPHASE. 



AMPLION 
PRODUCTS 
CORPORATION 

38 West 21st Street 
New York, N. Y. 



AMPLION NINE FOOT THEATRE HORN JW-9 

The JW-9 Horn is especially designed for 
theatre and indoor use. No horn of such 
great clarity and wide frequency range has 
ever been concentrated into so small a space. 
It covers the full speech 
range perfectly pre- 
venting over resonance 
and muffling on base 
notes. As a reproducer 
of music, it possesses a 
brilliancy impossible of 
attainment in horns 
made of soft materials. 
Its nine foot air column 
and wide bell, assure 
excellent performance 
on the low notes. 

List Price $95.00 

Air Column 108" 

Bell 3*" x 86" 

Bell Area 720 sq. Inches 

Weight S3 lbs. 

Shipping: Wgt. 70 lbs. 

Shipping Dimensions 

38" X 33%" x 39" 

Angle of Spread measured 

at lip of bell 36° 

Height 42" Width 34" 

Depth 87" 




Page 6 



PROJECTION ENGINEERING 



NEW Samson CINE-PAN 



N> 




HAS SURPRISING 
FEATURES 

For use as portable or permanent booth 
installation of sound-on-film talking pic- 
ture equipment. 

It is highly prized by those connected 
with theatre management. It is only 
28% inches long by 20'4 inches high 
and 10 !4 inches deep, weighs but 
104 lbs. 

Any panel can be removed by 
taking out 4 screws without 
breaking a soldered connection 
as all connections are made 
with flexible wire and plugs. 

2 15-ft. lengths of shielded 
cable from foto cell in the 
sound head to the Cine 
Pam are provided and 
can be increased to 25' 
lengths without any 
noticeable loss in 
high frequencies. 

Your biggest sur 
prise will be the re- 
markable crisp- 
ness of dialogue 
— heretofore 
sadly lacking 
in most 
sound-on- 
film am- 
plifiers. 



Tubes 
can be 
exposed 
for re- 
placement 
by remov- 
ing 4 thumb 
screws. 

There are 2- 
224's, one 280, 2- 
281's,one245,and 

2-250's. 



Variable output im- 
pedance allows use 
of any speakers you 
already have in your 
theatre. 

Visual volume indicator 
gives operator more ac- 
curate volume control 
than aural indication. Field 
current and voice energy 
are also provided for moni- 
tor speaker if wanted. 

The Cine-Pam is entirely AC 
operated and supplies photo-cell 
voltage and exciter lamp current. 
No batteries of any kind are re- 
quired. 

Sold only through manufacturers 

or jobbers of talking motion picture 

equipment. Ask them for literature 

on the Cine-Pam — or write us for 

Folder No. PE16. 



amson. 



Manufacturers Since 1882 



Main Office: 

Canton, 

Mass. 



Factories : 

Canton and Water - 

town, Mass. 



Projection Engineering 



JANUARY, 1932 



The public-address 
and radio program 
system in the 
Waldorf-Astoria Hote 



By Robert C. Sturgeon 



FOR nearly half a century the name 
Waldorf-Astoria has been synony- 
mous with the highest ideals of 
hotel excellence. With the con- 
struction of this new hotel at Park 
Avenue and Forty-Ninth Street, New 
York City, the same traditions have 
been carried out. 

Among the many and varied appoint- 
ments provided by the Waldorf-Astoria 
for the convenience, comfort and en- 
tertainment of their guests is the most 
elaborate and complete system for the 
electrical distribution of entertainment 
ever brought together under one roof. 

The radio control room or nerve cen- 
ter of this intricate system, located on 
the sixth floor of the hotel, is a large, 
well lighted room that becomes a show- 
place where guests see how they are 
supplied with good radio reception. 
The radio room contains not only all 
the equipment for radio pickup, public- 
address amplifiers, etc., but houses an 




Fig. 1. Distributing panels. 



up-to-date sound motion picture booth 
equipped like a modern theatre. 

The radio system provides in gen- 
eral facilities for : 

1. The distribution of six programs 
to the 1940 guest rooms. These six 
programs may be radio entertainment 
from broadcast stations or music orig- 
inating in the hotel, such as dinner 
programs for the dining rooms. The 
loudspeakers in the bedrooms have a 
selector switch and volume control 
mounted in the speaker housing itself, 
thus allowing the guest to select and 
control any one of the six programs. 

2. The reproduction of programs in 
the public rooms throughout the hotel. 
This may be an organ recital originat- 
ing in the grand ballroom or an ad- 
dress by President Hoover coming 
from Washington by direct wire. There 
are 24 public rooms throughout the 
hotel equipped with loudspeakers suf- 
ficiently large to handle the volume 
required. 

3. A centralized antenna system 
which enables permanent guests in the 
140 residential suites to connect their 
individual radios to a common antenna. 

4. The re-enforcement of speech and 
music in the public rooms. For ex- 
ample, a dinner is held in the grand 
ballroom where many notables are 
speaking. A public-address system am- 
plifies the voices of these speakers so 
that everyone hears each word perfectly 
without the knowledge that the voices 
are actually being amplified. After 
dinner the assembled guests retire to 
the reception rooms and the grand ball- 
room is made ready for dancing. The 
orchestra tunes up and presently the 
dance begins. A vocalist steps up to 
the microphone and begins to sing. The 

Page 7 




Fig. 2. Remote control panel. 

dancers hear his solo much more 
clearly and naturally than if he had 
used a megaphone. 

5. The showing of sound motion 
pictures. As well as two permanent 
machines for use in the ballroom, there 
are two portable machines in the 
smaller public rooms. 

6. The picking up of programs in- 
tended for broadcasting which are 
monitored, amplified, and sent out by 
line to remote points such as broad- 
cast transmitters or key stations. 

Before going into details let us sum- 
marize the huge amount of equipment 
installed in the Waldorf-Astoria. Let 
us first look at the apparatus installed 
in the control room. There are 39 audio 
amplifiers in all ; everything from small 
speech amplifiers delivering a few mil- 
liwatts to several large power ampli- 
fiers each capable of delivering 12 
watts of undistored output. These 39 
audio amplifiers require 190 vacuum 
tubes of various types such as vapour 
arc-rectifiers for changing a-c. to d-c. 
which is used for plate supply, as well 
as large and small tubes used in the 
various circuits of the audio amplifiers. 
Associated with these amplifiers are 
mixers, gain controls, volume indi- 
cators and a host of other necessary 
control devices. 

Throughout the hotel are 72 con- 
denser microphone outlets each sup- 
plied with filament and plate current 
from the control room. Special circuits 



Page 8 



PROJECTION ENGINEERING 



were designed for these microphone 
outlets such as relays operated by 
patching up the microphone termina- 
tion to the mixer and thereby putting 
power on the lines connected to the 
outlet. 

After the audio-frequency signal, 
which has been picked by the conden- 
ser microphone, goes through the vari- 
ous amplifiers, it is fed to six distri- 
bution panels. Each distribution panel 
is capable of feeding and controlling 
the signal to eight large dynamic loud- 
speaker units of the W. E. 581 or 
similar type. Here again, special cir- 
cuits were designed so that both mag- 
netizing current and speech current are 
fed to the public room loudspeakers 
through relays which are operated 
when the correct jacks are patched 
up from the distribution panel to the 
loudspeaker termination. The speech 
current relay is operated by a key which 
is located on the loudspeaker key panel 
near the operator's desk. 

A novel feature incorporated in the 
system is a power panel that remotely 
controls two 240 volt d-c. motors driv- 
ing 15 kw., 115 volt, single phase alter- 
nators which are located in the gen- 
erator room on the seventh floor. Asso- 
ciated with this panel is a duplicate 
set of ammeters, voltmeters, and fre- 
quency meters to give the operator an 
indication of the a-c. load supplied to 
the audio amplifiers, radio receivers, 
and reproducer sets. The alternators 
are equipped with exciters and ar- 
ranged with automatic starters for each 
set. In addition to rheostats which are 
manually operated, there is automatic 
speed and voltage regulating equipment 
mounted on the main control panel in 
the generator room. In the remote 
control panel, Fig. 2, which is a part 
of the main board of the radio room, 
can be seen a set of pilot lamps to in- 
dicate which set is in operation. The 
alternator switching is so arranged as 
to allow only one machine to be con- 
nected to the load at a time. 

The battery room contains two 280 
ampere-hour, 12 volt Exide batteries 
supplying filament current to the con- 
denser microphones and the seven 
vacuum tube voltmeters or volume in- 
dicator panels. A charging panel 



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Fig. 6. Typical con- 
denser transmitter 
circuit. 




having the necessary switches for the 
transfer of the one battery to load and 
the other to the charging position pro- 
vides resistances for controlling the 
current to the 12 volt batteries from a 
110 volt d-c. supply. A necessary piece 
of apparatus should be associated with 
all battery panels and that is an ampere 
hour meter. 

Between the 20th and 42nd floors 
of the hotel are located 140 radio- 
frequency amplifiers for the use of 
guests in the residential suites who wish 



l" J'— I Hill llll- 

1 > 'i—A """" , " iii- 



Fig. 3. Fidelity characteristics of No. 10-A 
radio receiver. 



Fig. 4. Automatic gain control characteristics 
of No. 10-A radio receiver. 



to operate their own receivers. The 
centralized antenna system consists of 
a radio antenna located between the 
two towers some 600 feet above the 
street level. Three aerials are provided, 
one for the use of the six radio re- 
ceivers located in the radio room on 
the sixth floor, and two for the radio 
frequency amplifiers — seventy to each 
aerial. To insure a strong signal, free 
from noise, to the r-f. amplifiers as well 
as the control room radio sets, the 
aerial is connected to a low impedance 
transmission line which is loaded at 
proper intervals thus keeping down to 
a minimum, interference between the 
various sets. The r-f. amplifiers which 
are inserted between the antenna and 
the apartment radio jacks, make up for 
transmission loss and thereby insure 
a good quality of reception, removing 
the necessity of erecting unsightly 
aerials. 

The Western Electric 10A radio re- 
ceiver used in the Waldorf-Astoria for 
program pickup has been designed 
primarily for the purpose of high qual- 



ity reproduction that is not possible 
to obtain from any commercial receiver 
on the market today. 

This receiver has been designed for 
rack mounting in keeping with the ap- 
pearance and general layout of the 
other equipment. In Fig. 1 it will be 
noticed that the six receivers are 
mounted on the first two racks. Prac- 
tically all the wiring is on the front of 
the panel. This arrangement of equip- 
ment not only permits high electrical 
efficiency and accessibility of apparatus, 
but improves the stability of the radio- 
frequency system. 

Electrical Characteristics 

The circuit of this receiver consists 
of a three-stage tuned radio-frequency 
amplifier aperiodically coupled to a 
three-element biased grid detector and 
to a three-element gain control tube. The 
amplifier coupling elements consist of 
three sets of two tuned coupled circuits, 
employing a six gang variable tuning 
condenser. The variable band-pass 
filters are coupled to the amplifier plate 
circuits by a combination of two prim- 
aries, one of which resonates below the 
broadcast spectrum and one above. The 
coupling between the tuned circuits of 
each band-pass filter consists of a con- 
denser and reversed mutual inductance. 

The input circuits are so designed 
to permit the coupling of several of 
these receivers in multiple to the same 
aerial or the same antenna transmis- 
sion system in such a manner that the 
operation of any one receiver will be 
independent of the adjustment of the 
others. The selectivity of the prese- 
lector is sufficient to prevent appreci- 
able modulation or cross-talk in the 
first tube. 

The sensitivity of the receiver is 
such that a standard output of 50 mil- 
liwatts will be obtained from the re- 
ceiver used in conjunction with an 
amplifier having a gain of 47 decibels 
with an input voltage at the antenna of 
approximately 10 microvolts (2.5 



JANUARY, 1932 



Page 9 



microvolts per meter). The variation 
in sensitivity over the broadcast band 
(550 to 1500 kilocycles) is 5 db., 
which is more than adequate for either 
local or distant reception. 

Fidelity of reproduction is one of the 
distinctive features of the receiver. Its 
overall audio characteristic shows a 
band from 25 to 7,000 cycles with only 
a 4 db. variation. A band width ad- 
justment consisting of a low-pass fil- 
ter, incorporated in the detector output 
circuit, will reduce the band width as 
shown in Fig. 3. This adjustment will 
permit operation through abnormal in- 
terference or noise. 

The automatic gain control circuit 
will hold the output level constant 
within 6 db. over a range of input sig- 
nal of approximately 60 db. Fig. 4 
shows the characteristics of the auto- 
matic gain control circuits indicating 
that an increase in the strength of the 
incoming signal from 100-100,000 mi- 
crovolts (60 db.), will increase the 
audio output only 6 db. The automatic 
gain control circuit operates essentially 
by changing the sensitivity of the re- 
ceiver in accordance with the varia- 
tions in the intensity of the received 
carrier. A sensitivity switch is incor- 
porated in the receiver to prevent the 
overloading of the gain control system 
from a signal of greater than 150,000 
microvolts in the antenna. This switch 
permits a 34 db. reduction in signal 



input voltage to the first r-f. tube. A 
visual tuning meter permits a more 
accurate means of tuning than by aural 
methods. 

Description of Circuits 

Input : The antenna input circuit 
consists of resistances Rl, R2, and R3, 
which are so arranged as to provide 
for a constant input impedance of about 
1400 ohms irrespective of the tuning 
of the receiver. The 10-A receivers 
Fig. 5, used in the Waldorf-Astoria 
are energized from a low impedance 
transmission line and the coupling be- 
tween this line and the first filter is 
effected by inductance LI and the 
transformer L2. The primary of L2 
is in series with LI while the secondary 
forms part of the first tuned circuit. 
The constants of these coils provide 
a substantially constant voltage step-up 
ratio of 7-1. The first tuned circuit is 
formed by condenser CI, the secondary 
of the transformer L2, and L3 and C9. 
The second tuned circuit consists of 
condenser C2, the inductance coil L4, 
and L3 and C9. Thus, L3 and C9 
are common to both tuned circuits of 
the first band-pass filter or preselector. 
It is this combination of mutual induc- 
tance and capacity for the common cir- 
cuit of the filter, that effects constant 
band width throughout the broadcast 
range. 



Interstage Coupling 

The interstage coupling between the 
first and second radio-frequency ampli- 
fier tubes and between the second and 
third tube, is a similar band-pass filter 
except that the connection to the plate 
circuits of each tube is made by means 
of a three-circuit transformer. This 
transformer is designed to give sub- 
stantially constant gain throughout the 
tuning range of the receiver. The third 
radio frequency amplifier works into 
an input transformer, the secondary of 
which connects to the grids of the de- 
tector and automatic gain control tubes 
which are connected in parallel. 

Detector Circuit 

The three-electrode tube used as a 
detector is operated at a moderately 
high level. The automatic gain control 
circuit maintains a constant level to 
the input of the detector which is of 
the plate demodulator type, thus afford- 
ing a large undistorted output. The 
output transformer and output circuit 
network transforms the detector out- 
put impedance to 200 ohms thereby 
permitting direct connection to the 
audio amplifiers used in p-a. and radio 
distribution systems. 

Output Circuit 

The potentiometer PI, connected di- 
rectly to the secondary of the output 
transformer affords a continuous vari- 



i»o r 
WTJV 



GROUND SIDE 




00+I.2UIL5 




R20 
2000 U 



T 



To25MF 




0.25 UF ui L " CI8 

0.25 MF 



=i=C22 -> 
0.25MF< Rl8 

,100,000 <-< 



Fig. 5. Schematic diagram of No. 10-A radio receiver. 



Page 10 



PROJECTION ENGINEERING 



able change in output level of 70 db. 
without any change in impedance of 
the receiver output. The output cir- 
cuit includes band adjustment circuits 
which reduces the upper limit of the 
band to 4,000 cycles and further to 
2,000 cycles. The normal band width 
of the receiver is from 25 to 7,000 
cycles, but the reduction in band width 
permits tuning through abnormal in- 
terference due to static or local distur- 
bances. 

Other Circuit Elements 

It will be noticed from an examina- 
tion of the schematic Fig. 5 that since 
the grid return to cathode of the first 
two radio-frequency amplifier grid cir- 
cuits is through both R18 and R19 
while the last radio tube is through 
R18 only, the control voltage applied 
on the last r-f. tube is only half the 
value of the control voltage on the first 
and second r-f. tubes. This affords 
smooth operation of the control circuits 
and prevents distortion in the third r-f. 
tube where the received signal is 
strongest. The values of the capacities 
and resistances both in the plate cir- 
cuit of the control tube and in the re- 
spective grid circuits (R4, R7 and 
R10) are chosen to provide the proper 
time constant. Thus the period of 
operation of the control circuits is 
sufficiently long to prevent any effect 



on the quality of reproduction. The 
resistances R4, R7 and R10 with their 
associated by-pass condensers also act 
as grid filters, preventing any tendency 
toward regeneration. 

The radio-frequency choke coils L14, 
L16 and L18, are used as a means of 
applying grid bias to the radio fre- 
quency tubes without affecting the 
radio frequency potential of the band- 
pass filters. The choke coils L15, L17 
and L19 are used to isolate the cath- 
odes (at radio frequencies) from the 
voltage divider to which the cathodes 
must be connected to obtain their 
proper direct current potential. 

In the arrangement of the automatic 
gain control circuit, neither the grid 
nor the cathode of the radio frequency 
tubes can be connected directly to the 
ground. The direct-current potential 
of each cathode, grid, and screen with 
respect to ground is indicated at the 
voltage divider as shown in Fig. 6. 
The mid-point of the heater winding 
is not returned to ground but to a mid- 
point that reduces the voltage between 
the heaters and cathodes to about 46 
volts. Potentiometer P2 provides a 
means of adjusting the potential be- 
tween the cathode and grid of the con- 
trol tube, thus adjusting its sensitivity. 
The grid of the automatic control tube 
returns to ground through the input 
transformer winding 3-4, while the 

AAA 



cathode is connected to the variable 
arm of P2. 

General 

Fig. 3 shows fidelity curves of the 
10- A receiver taken at 600, 1,000, and 
1,400 kilocycles with the band width 
adjustment normal. Fig. 4 shows the 
characteristics of the automatic gain 
control circuits. The 10-A receiver 
obtains its plate supply from an exter- 
nal source ; in the case of the Waldorf- 
Astoria the set obtains its plate supply 
from the channel amplifier (59-B). 
The plate current drain is clearly 
shown in Fig. 5. 

There are several sources of signal, 
chief among which are radio, conden- 
ser, microphone, pickup, phonograph 
recording and signal from a remote 
point handled by direct wire. 

Fig. 6 is a schematic diagram of a 
typical condenser transmitter circuit 
of which there are seventy-two (72) 
throughout the hotel. The speech cir- 
cuit of each microphone is terminated 
on a tip, ring and sleeve jack located 
on the input switching panel. When 
the jack is patched up to the mixer 
the sleeve of the jack and cord com- 
plete the 12 volt battery circuit, thereby 
pulling up the two relays which put 
filament and plate supply on the micro- 
phone circuit running to the micro- 
phone outlet. 



Technical papers on various sound picture 
and public-address subjects 



FOLLOWING is a list of the com- 
plete technical articles which 
have appeared in the issues of 
Projection Engineering during 
the last six months of 1931. 

There is a limited number of copies 
of these issues on hand. 

July 1931 : Control of theatre stage 
light effects; portable recording 
equipment for police requirements ; 
television projector for screen pic- 
tures; design and assembly of out- 
door p-a. system; new sound record- 
ing system for producers of motion 
pictures. 

August 1931 : Applying p-a. equip- 
ment to indoor use; acoustic treat- 
ment of auditoriums and halls; what 
happens within the bulb of a radio 
tube; output matching to loud- 
speaker; early movies; supersensi- 
tive panchromatic safety film for 
16mm. cameras; sound systems in 
public schools; measuring screen 
brightness; portable 16mm. camera; 
use of positive film in sound record- 
ing. 



September 1931: Adjustments for 
light valve recording ; increasing the 
usefulness of theatre sound equip- 
ment; splices at sound track; Madi- 
son Square Garden sound system ; 
sound projection practice: nitrocellu- 
lose motion picture film ; new port- 
able sound unit. 

October 1931 : Sound motion pic- 
tures and education ; moving coil 
microphone; new uses for thermo- 
couple; high power for p-a. systems; 
indoor applications of air-column 
horns; monitoring and sound control 
in theatres; more about the Seleno- 
phone — home reproducing equipment 
(sound-on-film recording). 

November 1931 : Film and wax 
records — advantages and disadvan- 
tages ; influence of American films ; 
acoustics and its relation to seating; 
magnetic pickups and loudspeakers; 
educational sound motion pictures; 
thyratron reactor lighting control in 
movie theatre field. 

December 1931 : Standardization 
of aperture for sound pictures ; sell- 



ing p-a. equipment and service; skat- 
ing rink music problem; new sys- 
tem of color television; some 
aspects of a modern soun$ recording 
system; p-a. finds various uses; p-a. 
system on new steamship ; portable, 
battery-operated, separate film sound 
recording system; Eastman super- 
sensitive motion picture negative 
film ; calculation of supply voltage 
and load impedance for a vacuum 
tube ; installation of "sound" in 
Great Britain ; new talking movies. 
A 

THEATRES IN CANADA WIRED 
FOR SOUND 

A TOTAL of 727 houses, or approxi- 
mately 80 per cent of the 899 regu- 
larly-operated theatres in the Dominion 
of Canada, are now wired for sound, 
according to the latest survey. The 
situation, by provinces, is now as fol- 
lows : Alberta, 96 out of 1 10 wired ; 
British Columbia, 81 out of 103; Mani- 
toba, 105 out of 139; Maritime Prov- 
inces, 62 out of 90; Ontario, 258 out 
of 300; Quebec, 125 out of 157. 



JANUARY, 1932 



Page I I 



Motion pictures in 
medical and surgica 
practices 




By Gordon S. Mitchell^ 



IN addition to its very important po- 
sition in the field of entertainment, 
the sound motion picture finds a 
place of importance in many far 
removed fields, not the least of which 
is the medical. As a means of furnish- 
ing medical knowledge, both in instruct- 
ing students in the medical schools and 
in aiding scientific research, the motion 
picture is inherently far ahead of any 
other method. 

The human body is in a state of per- 
petual motion during life, a fact which 
has created a tangible lack in any medi- 
cal still pictures which might be made. 
This lack may definitely be eliminated 
by the motion picture camera provided 
a proper care is exercised in the photog- 
raphy and production of the medical 
picture. Heretofore, the medical mo- 
tion picture has been concerned prima- 
rily with the showing of deformities of 
the extremities, although there have 
been some excellent pictures made 
showing surgical technique. 

Due to a variety of reasons, the 
medical motion picture has not taken 
the strides which were predicted for it 
during the first years after the develop- 
ment of the motion picture camera. Ac- 
cording to some medical authorities, 
this has been due to the antipathy with 
which the medical motion picture is 
viewed by those in authority in the stu- 
dios. 

A definite lack of a financial scheme 
has tended to materially retard progress. 
The doctor who is interested in outside 
activity and has the time to devote to 
extraneous matters after the demands 
of his practice have been met with 
may, with very little expenditure, turn 
to the preparation of medical papers 
and articles for the medical journals. 
These works return him at least a meas- 
ure of financial reward for the time 
and effort expended. 



* Universal Pictures Corp. 



However, the production of a medi- 
cal motion picture, should the doctor be 
aroused in interest to such a point that 
he might desire to produce one, entails 
a considerable expense in preparation, a 
necessity for cooperation from various 
sources, and a doubtful return after 
completion. In view of the very limited 
distribution, the production of medical 
films on 35 mm. stock has been almost 
prohibitively expensive. The advance- 
ments of 16 mm. photography have al- 
leviated this condition somewhat. 

According to the statements of sev- 
eral doctors who have seen the possi- 
bilities of the medical motion picture, 
it has been almost impossible to arouse 
enthusiasm in the motion picture pro- 
ducers towards this type film, due in no 
small measure to the very limited mar- 
ket offered. 

Several private enterprises have be- 
come interested in the possibilities of 
the medical motion picture and are car- 
rying on a definite work of production 
and distribution. The Harvard Univer- 
sity Film Foundation, established for 
the purpose of "providing a center for 
the production and collection of scien- 
tific and educational films in collabora- 
tion with the Harvard University fac- 
ulty" has placed many such pictures 
in circulation. Their collection of films, 
dealing with biology, anthropology, ge- 
ology and kindred scientific subjects is 
at the disposal of libraries, colleges, 
hospitals, associations and interested 
groups. The Rockefeller Institute of 
Medical Research is carrying on an ex- 
tensive work in the field of microcine- 
matography. 

Classroom Work 

Probably one of the most tedious fea- 
tures of the medical student's life are 
the many, many pages of material which 
must be committed to memory. It has 
been said that if the pages of Gray's 



In this article is presented an account of the present 
status of moving picture photography in surgical prac- 
tice, including information relative to equipment and 
types of film employed. 



The Russell "Fono- 

faryngoskop" as used in 

the photography of the 

laryngeal cavity. 



Courtesy of the Electro 

Surgical Supply Co., 

Rochester, N. Y. 



"Anatomy," which every student is ex- 
.pected to memorize during a three 
months' course, were extended word 
after word in a straight line that line 
would be forty-eight miles long. This 
task would, of course, be impossible 
were it not for the aid offered the mem- 
ory by charts, drawings and illustra- 
tions. While it is not to be expected 
that such a mass of material will be 
retained in the mind for long, the use 
of the motion picture as an aid to the 
study of this one course alone helps 
materially in fixing important points of 
the book in the mind and thus results 
in its retention for a longer period. 

The knowledge is not only more cer- 
tainly acquired, but is more easily ac- 
quired as well. Many apparati have 
been developed as an aid to the memory 
during the centuries since it first be- 
came desirable to remember, but no 
other has been as efficient as the mo- 
tion picture. 

The characteristics of any medical 
treatment or surgical operation are such 
that in order to gain materially from 
witnessing the procedure the spectator 
must be close to the point of activity. 
The motion picture method of witness- 
ing these processes gives every specta- 
tor the advantage of a ringside seat 
provided the picture has been properly 
photographed. 

Keeping Up To Date 

In addition to its value in instructing 
the student doctor the medical motion 
picture has potentialities for great use- 
fulness in aiding the practicing phy- 
sician and surgeon to keep up with cur- 
rent developments in his field. The 
monetary cost of travel as well as the 
possible loss of practice while he is 
away deters many a doctor from pur- 
suing post graduate courses at the cen- 
ters of medical learning and make it 
necessary for the interested doctor to 
depend upon the medical periodicals for 
current education. Sound motion pic- 
tures, dealing with the latest develop- 
ments in medicine made available to 
doctors or groups of doctors would in 
effect bring the teacher to the student. 
These pictures might be shown in the 
hospital staff room, the laboratory or 



Page 12 



PROJECTION ENGINEERING 



even in the individual doctor's own li- 
brary. Thus, fine points of procedure 
and technique would be brought out to 
the small-town or country doctor, plac- 
ing him on a more nearly equal foot- 
ing with the city doctor whose location 
in close proximity to the medical cen- 
ters gives him a distinct advantage over 
his rural contemporary. 

Anatomical still photographs are of 
increased value due to the fact that 
color representation is possible, thus 
bringing out many fine points which 
would otherwise be lost. Arterial blood, 
venous blood, nerves, muscles, bones, 
etc., may be accurately shown by a dif- 
ferentiation of color in the still pic- 
ture. The fact that most of the colors' 
encountered in anatomical photography 
lie in the red end of the spectrum has 
offered a difficulty which has been par- 
ticularly pronounced; especially as it is 
this end of the spectrum which has of- 
fered most difficulty in the development 
of color motion pictures. Due to the 
specific type of subject, in which details 
of structure are given particular em- 
phasis by fine color gradations, color 
medical motion pictures offer a pro- 
nounced advantage over the black and 
white picture. 

Some Problems 

In addition to the problem of color 
recording, the production of a medical 
motion picture offers several problems 
which have so far been only partially 
solved. Camera placement, in order that 
shadows and the hand or instruments of 
the surgeon may not obscure the subject 
has proven a difficulty which seems to 
be only partially capable of solution. 
The necessity for haste during a sur- 
gical operation eliminates the possibility 
of a changed camera setup during the 
actual operation, while the progress of 
the operation and the changing posi- 
tions of the surgeon may make such a 
change in setup vitally necessary if a 
satisfactory picture is to be obtained. 
The use of a cadaver presents an ad- 
vantage from "this standpoint; and also 
from the fact that there is a complete 
absence of blood during the operation 
which in a living body tends to obscure 
the area of operation. 

Correct lighting for satisfactory pho- 
tography of the medical motion picture 
presents points which do not arise in 
the ordinary run of motion picture pro- 
duction. The medical motion picture 
is a combination of correct .camera 
placement (mounting the camera and 
photographing an operation are de- 
rcribed in considerable detail in Pro- 
jection Engineering for March, 
1931) and the proper direction of light 
of sufficient intensity to illuminate the 
subject. A flat light with no heavy 
shadows should be the result towards 
which the medical cinematographer 



aims. As a practical point, it might be 
mentioned that this lighting may be 
more easily obtained with two or more 
light sources than with a single lamp. 

Light Sources 

Obviously, carbon arc lamps cannot 
be used in the operating room due to 
proximity to explosive vapors used as 
anesthetic. Incandescent lights recom- 
mend themselves for this work for sev- 
eral reasons. Any amount of light may 
be obtained by a multiplication of 
sources, this light may be directed 
closely to any portion of the operating 
area by means of portable light units, 
and an absolute duplication of exposure 
may be obtained at any time later. 

The light radiated from an incan- 
descent tungsten filament possesses a 
continuous spectrum suited to color 
photography and the lamp is entirely 
safe for lighting in rooms where Ethy- 
lene or other inflammable anesthetic is 
used. The amount of light radiated as 
well as the color relations in the light 
are both functions of the current pass- 
ing through the lamp. If a tungsten 
filament lamp be burned at over-voltage, 
the temperature, of course, will be 
higher and the light will contain a 
greater percentage of violet and blue 
rays, which makes it rather unsatis- 
factory for color photography. How- 
ever, if the light be operated at cor- 
rect filament voltage the light is of 
suitable spectroscopic composition for 
this work. 

The Eastman Kodak Company has 
perfected a 500-watt tungsten filament 
lamp mounted in a spot frame which is 
especially adaptable to the lighting of 
surgical cases for motion picture pho- 
tography. The lamp is so mounted that 
the light passes through a water cell 
which removes most of the heat from 
the radiated wave without affecting the 
intensity of the actinic rays which are 
necessary for successful photography. 
The light radiated from this lamp may 
truthfully be called a "cold" light. 

For black and white pictures, an il- 
lumination of 400 foot-candles is neces- 
sary for adequate exposure, while for 
color pictures 3,200 foot-candle illumi- 
nation is necessary. From these fig- 
ures it can be seen that the introduc- 
tion of color into the field of medical 
pictures considerably complicates the 
lighting problem, making necessary an 
intensity of illumination eight times 
that needed for black and white photog- 
raphy. (These figures are given purely 
for purposes of comparison, and should 
not be taken as an arbitrary pronounce- 
ment. The actual intensity of illumina- 
tion for any given case, of course, de- 
pends upon several factors, among 
which might be listed the depth of ex- 
posure desired, the coloration of the 
subject and the depth of the cavity.) 



Flesh Burns 

It is an interesting practical point in 
connection with the subject of medical 
motion pictures that it has been found 
that in cases where iodine or mercuro- 
chrome are used as antiseptic about the 
area of operation, bad flesh burns result 
due to the absorption of heat from the 
lights by these compounds. Alcohol or 
Kalmerid have been found satisfactory 
from this standpoint, in addition to be- 
ing colorless and thus introducing no 
false impressions to the picture. 

Certain types of surgical operations 
are, on account of their location on the 
human frame, difficult of access. In 
all cases where the operating surgeon 
has difficulty in seeing the affected area, 
difficulty will be experienced in light- 
ing for photography. All deep incisions 
as well as areas of the nose, throat and 
bodily cavities will present difficulties 
of this nature. 

Body Functions in Action 

For purposes of scientific research 
and to further both medical and physi- 
cal knowledge it was the self-assigned 
problem of Prof. G. O. Russell of Ohio 
State University and Clifton Tuttle of 
the research laboratory of the Eastman 
Kodak Company to obtain moving pic- 
ture photographs of the human vocal 
chords in action. Of the many difficul- 
ties presented, not the least was that 
of obtaining sufficient light in the throat 
to satisfactorily impress the image upon 
the film. The insertion of any optical 
system into the subject's throat imme- 
diately caused muscular action which 
eliminated the possibility of free vocal 
action. The old style laryngoscopic 
mirror, while it placed sufficient light 
inside the throat, prevented a natural 
articulation due to its restriction of the 
tongue movement. This particular 
problem was finally solved by the use 
of the Russell "Fonofaryngoskop," 
which consists essentially of a tube 135 
mm. long and 13 mm. inside diameter 
with a mirror at each end tilted so that 
the vocal cords become visible. 

For the ordinary uses to which the 
device is put a small half-watt, local 
battery operated lamp is provided which 
gives 12 foot-candles intensity of il- 
lumination. For motion picture photog- 
raphy, this intensity of illumination was 
of course insufficient. An intensity of 
250 foot-candles was finally obtained by 
the use of a quartz rod in contact with 
the glass bulb of a six-volt, 18-ampere 
ribbon filament lamp. In order to con- 
duct the light from its source to the 
laryngeal cavity, it was necessary to 
bend the rod in two places. One bend, 
with a total deflection of 55 degrees, 
was made in a circular arc the radius 
of which was such that the critical an- 
gle of the quartz was always exceeded 
and there was no light loss at the bend. 



JANUARY, 1932 



Page 13 



The other bend was of such sharp angle 
that a portion of the rays were inci- 
dent at an angle less than the critical 
angle of the quartz resulting in approxi- 
mately 70 per cent loss of light at that 
point. This made it necessary to op- 
erate the source lamp at a considerable 
overload (22 amperes) during the short 
periods of actual photography. 

Frame-to-Frame Inspection 

In addition to the advantages enumer- 
ated which result from motion picture 
photography of medical processes and 
surgical operations based upon the as- 
sumption that the pictures will be pro- 
jected upon the screen, much knowledge 
may be gained from a frame-to-frame 
inspection of the film. Especially is this 
true in the case of a picture such as 
the vocal chord film discussed wherein 
a frame-to-frame inspection might in- 
dicate facts about the motion of the 
chords which would pass unnoticed on 
the screen. 

The addition of sound to the motion 
picture has proven to be of little im- 
portance to the medical film, whose pur- 
pose is principally to visually indicate 
conditions. The addition of voice syn- 
chronized to the picture, much in the 
manner of the travel pictures seen lately 
in the theatre wherein an announcer 
audibly points out points of interest 
about the picture as it unfolds across 
the screen, may increase the utility of 
certain types of medical film. How- 
ever, in this type of picture as few 
words as possible should be used. The 
descriptive dialogue should be care- 
fully written and all unnecessary words 
deleted. As phonetic a description as 
possible should at all times aim to cen- 
ter the inind of the audience upon the 
subject of the picture and the action 
taking place upon the screen. The addi- 
tion of the spoken word to the medical 
motion picture should never in any way 
distract attention from the photographed 
subject. 

While motion pictures which show 
details of operating technique are of 
great value to the medical profession, 
action pictures showing the heart beat- 
ing, the lungs expanding or the stomach 
digesting food would be of incalculable 
value not only to the medical profes- 
sion, but would also be of interest to 
the lay public. Many medical men, be- 
coming impatient with the X-ray still 
picture, have desired an X-ray motion 
picture, and several have devoted con- 
siderable time and effort towards the 
development of this kind of cinematog- 
raphy with, however, little success. 

X-ray Pictures 

From the very nature of the problem 
several difficulties are presented which 
necessitate considerable research before 
a satisfactory X-ray motion picture will 



be possible. The X-ray picture, which 
is in the nature of a shadowgraph, is 
produced by the invisible Roentgen rays 
falling upon a fluorescent screen which 
fluoresces in a corresponding degree to 
the transparency of the subject. In or- 
der to obtain an X-ray motion picture, 
this screen with its image must be pho- 
tographed. 

Voltages of an order of magnitude of 
120,000 have been used in an effort to 
obtain satisfactory actinic radiation to 
impress the image upon the film, with 
small success. The fact that human 
flesh tissue, when subjected to the dis- 
charge of such high voltage tubes burns 
in from four to six seconds presents a 
difficulty of importance. Even with an 
X-ray discharge of such intensity fluor- 
escence is so deficient in actinic light 
that normal film exposure is far too 
short to produce a negative of any- 
where near rea:onable printable density. 

In order to work around the harmful 
effect of such intense rays upon human 
flesh, experimentation has been car- 
ried on with a view towards perfecting 
an intermittent flash discharge of high 
intensity. Such photography takes ad- 
vantage of a certain "lag" of fluores- 
cence of the screen. While this method, 
by a synchronization of the camera 
shutter with the flash of the X-ray tube 
eliminates the possibility of burning the 
subject, it also presents another problem 
in that the fluorescent screen after about 
five seconds becomes "tired" and photo- 
graphically inactive. Work is now be- 
ing carried on in this phase of the prob- 
lem in several hospitals in the United 
States. 

Film Stock 

Of the several types of negative stock 
experimented with, orthochromatic film 
seemed to give a denser negative than 
panchromatic. Many color filters have 
been tried, a red filter with panchro- 
matic film giving the best negative. 
However, the best of the negatives ob- 
tained was of insufficient density to give 
what might be termed a satisfactory 
positive print. According to several 
medical cinematographers who have 
spent considerable time on the problem 
of the X-ray motion picture, a specially 
prepared negative stock rendered super- 
sensitive to the particular rays emitted 
by the fluorescent screen is needed for 
this work. From indications given that 
the screens themselves are not uniform 
as regards photographic properties, it 
would seem that research aimed at im- 
proving the screens from this standpoint 
would result in improved photography. 

Difficulties presented by the lack of 
sufficient exposure have been obviated 
in a measure by a Paris experimenter, 
Mons. Laboshey, with a lens of his own 
manufacture working at about f/0.75 
used with 16-mni. film. The pictures 



obtained with this lens have been the 
most satisfactory of any so far obtained. 
However, on account of difficulties with 
the glass, M. Laboshey considers it im- 
possible to manufacture another lens of 
such size. 

High Voltages 

On account of the extremely high 
voltages necessary for the production 
of X-rays electrical equipment of con- 
siderable size is necessary. Difficulties 
are introduced by the fact that this 
equipment will not stand up for long un- 
der the high operating voltages and the 
very high cost price of the equipment 
presents an obstacle to a commercial 
organization which might experiment 
with the problem, and proves to be 
prohibitive to all but endowed research 
organizations. However, this fact not- 
withstanding, research is being carried 
on in several centers and satisfactory 
X-ray motion pictures are ultimately 
expected. 

Considerable research is being car- 
ried on in Austria at this time, both in 
the photography of X-ray motion pic- 
tures and in the perfection of surgical 
photography. Prof. Pernkopf of Vienna 
has achieved marked success in photo- 
graphing surgical operations using ca- 
davers prepared beforehand entirely for 
subject matter. 

The production of medical motion 
pictures is a problem which presents 
great inherent possibilities; a problem 
the satisfactory solution of which will 
result in the future increase of the sum 
total of human knowledge and, conse- 
quently, is entirely worthwhile. 



DECISION INVOLVES PHOTO- 
ELECTRIC CELL WIDELY 
USED FOR SOUND 

A DECISION having an important 
bearing on the future of sound pic- 
tures was given recently at Washing- 
ton in District Supreme Court by Judge 
Jesse C. Adkins when, after months of 
study, he ruled that a patent on an in- 
vention sought by the American Tri- 
Egon Co., and refused by the Patent 
Office, should be granted. 

The invention involves a tiny photo- 
electric cell such as is in general use 
for reproduction of sound films, and 
granting of the patent gives to Tri- 
Egon the right to demand royalties 
from all persons or firms now using 
its invention. 

Justice Adkins ruled in a 24-page 
decision against the assertion of the 
patent office that the cell is merely a 
development or refinement of an exist- 
ing invention, and held that the cell, as 
embodied in plans and specifications 
filed in the patent office, is an entirely 
new invention. 



Page 14 



Thermionic tube contro 
of theatre lighting -t 



By Burt S. Burke^ 



This modern system of theatre lighting control provides 
flexibility in circuit selection and in light intensity changes 



DURING the past 15 years the 
equipment for controlling il- 
lumination in theatres has de- 
veloped from the simple knife- 
switch type of switchboards to the com- 
plex arrangement of circuits and dim- 
mers which are required by the elabo- 
rate stage productions of the present 
day. Two general qualities are essential 
in a modern theatre switchboard, flexi- 
bility in selection of circuits and flexi- 
bility in controlling the light intensity 
of these circuits. The first has been 
well provided for in the various 
types of multi-preset switchboards which 
have been built for the past sev- 
eral years. The second requirement, as 
provided for in the dimmer systems, 
which are built into the usual multi- 
preset switchboard leaves much to be 
desired. 

In the past three years, a new means 
for controlling the intensity of the light 
circuit has become available. The de- 
velopment of thermionic devices (for 
industrial uses has made possible new 
systems for accomplishing the complex 
lighting effects required in modern the- 
atres. Architects, illuminating engi- 
neers and theatrical producers are now 
able to use lighting in ways that have 
never before been possible. 

The thermionic tubes used in theatre 
lighting equipment have been of the 
hot cathode grid-glow type whose out- 
put may be regulated by properly con- 
trolling the grid circuit of the tube. 
The whole control system consists 
briefly of a reactance type dimmer, sim- 
ilar to the reactance dimmers which 
have commonly been in use for many 
years, a. thermionic tube unit for sup- 
plying direct current to saturate the 
reactance dimmer and a control means 
consisting of a network of potentio- 



iPaper presented before the convention of the 
Society of Motion Picture Engineers, Swampscott, 
Mass., October 5-9, 1931. 

* Switchboard Engineer, Westinghouse Electric 
and Manufacturing Company. 



meters for properly controlling the out- 
put of the tube unit. 

A system of this type was used for 
the control of the stage and auditorium 
lighting of the new Los Angeles theatre, 
which was opened January 30, 1931. 
This article will describe this equip- 
ment which is typical of the thermionic 
tube type of control for theatre lighting. 

Installation in Service 

The Los Angeles theatre, similar to 
many theatres of this size, is equipped 
for both motion pictures and stage pre- 
sentations. On this basis, the control 
switchboard was split into two parts, 
one of which was located in the pro- 
jection room for controlling the audi- 
torium lights and the second of which 
was located at the stage floor for con- 
trolling the stage lights. On the stage 
floor is also located a remote panel, 
which allows the operator to obtain 
color master control of the auditorium 
circuits as well as control of the five 
scene preset arrangement which will be 
described later. Dual control for the 
footlights, the first border, the orchestra 
floods and the stage floods is provided 
so that these circuits may be controlled 
either from the stage floor or from the 
projection room. A transfer scheme 
is used to transfer these controls from 
one place to the other so that no inter- 
ference of control is possible. 

Each of these two switchboards con- 
sists essentially of a reactance dimmer 
bank, a set of tube units for use in 
connection with the direct-current coils 
of these reactors and a control board 
used to control the output of the tube 
unit thus indirectly controlling the in- 
tensity of the lighting circuit. 

The reactance dimmers are similar to 
the standard theatre duty reactance 
dimmer in that they consist of alternat- 
ing-current coils and a direct-current 
coil mounted on an iron core. The re- 
actance of the dimmer is varied by 
changing the amount of direct current 
in the d-c. leg of the reactor thus vary- 



PROJECTION ENGINEERING 

ing the saturation of the iron. With 
no direct current in this coil, the iron 
is unsaturated and of very high re- 
actance thus dimming out the light cir- 
cuit with which it is associated. By in- 
creasing the amount of direct current, 
the iron becomes saturated so that the 
reactance of the dimmer becomes lower 
thus increasing the voltage across the 
lamps and bringing them up to full 
brilliancy. 

Filament and Plate Power 

The direct current supplied to the 
coil of the reactance dimmer comes 
from the thermionic tube unit which con- 
sists essentially of two grid-glow type 
tubes, a control tube and the necessary 
transformers for supplying the proper 
filament and plate voltages for the 
above tubes. This tube unit receives its 
power from the 115 volt, 60 cycle single 
phase mains. This is applied to the two 
grid-glow tubes, through a suitable 
transformer, in order to obtain the 
proper voltage on the plates of these 
tubes. This voltage is rectified by these 
tubes and impressed on the coil of the 
reactor and rectified alternating cur- 
rent. The magnitude of the direct-cur- 
rent output of the tube unit is varied 
by means of changing the relationship 
of the grid voltage to the plate voltage 
of the grid-glow tubes. This is accom- 
plished by means of the control tube, 
which is a vacuum tube similar to the 
standard UX-226 tube used in radio 
circuits. The output of this control tube 
is varied by means of a system of 
potentiometers located on the control 
board which will be described later on 
in this article. One set of these tube 
units was mounted on the reactor bank 
located in the projection room for the 
auditorium lights and a second set of 
the tube units was mounted on the re- 
actor rack located in the basement 
which was for the stage lights. 

The two control switchboards, one 
located in the projection room for the 
auditorium circuits and the second lo- 
cated on the stage floor for the stage 
circuit are similar except for the cir- 
cuits controlled and may be briefly de- 
scribed as follows : 

Circuit Control 

For the control of each individual 
circuit there is provided a pilot switch, 
a selector switch, an indicating lamp, 
5 preset potentiometers, and an in- 
dividual control potentiometer. In ad- 
dition to this there is provided at the 
rear of the board for each circuit a 
scene- fader by which it is possible to 
fade from one effect into the next suc- 
ceeding effect, giving a gradual transi- 
tion from one to the other. These faders 
are ganged together and have a com- 
mon drive either operated by a hand- 
wheel or a motor. 

The pilot switch serves a purpose 



JANUARY, 1932 



Page 15 



similar to that of the pilot switch on 
the standard switchboard. That is, one 
throw of the pilot switch connects the 
circuit directly to a hot-bus connection 
so that the circuit may be controlled 
independent of any of the master set- 
ups. A second position of this switch 
connects the circuit through a color 
master control so that it is possible to 
control an entire color by means of a 
single color master. The middle posi- 
tion of the switch is the "off" position. 
The pilot lamp is wired in connection 
with the pilot switch so as to indicate 
when the circuit is hot, that is, when 
the pilot switch is thrown directly to 
the hot-bus position or when the pilot 
switch is thrown to the color master 
position and the color master is en- 
ergized. 

The selector switch is used for trans- 
ferring the control from the individual 
potentiometer to the preset potentio- 
meter. In one position of this switch 
the grid lead from the tube circuit is 
connected to the moving arm of the 
individual potentiometer. In this posi- 
tion, the output of the tube circuit may 
be controlled by manipulating the in- 
dividual potentiometer and it is not af- 
fected by any changes made in the 
preset potentiometer. In the second 
position of the selector switch the grid 
lead is connected through the fader to 
the preset potentiometer. In this posi- 
tion the circuit, is controlled through 
the preset control by means of which 
the intensities of the circuit may be 
set up for five scenes in advance. 

Preset 

Regarding the operation of the pre- 
set potentiometer, let us first go back 
to the operation of the tube unit. As 
has been previously stated, the output 
of the tube unit and consequently the 
intensity of the lighting circuit is 
changed by means of changing the grid 
potential on the control tube. This grid 
potential is obtained through a system of 
potentiometers from the direct-current 
control source as indicated in Fig. 1. 
Thus to preset the intensities of the 
lighting circuit for a number of scenes 
in advance, it is necessary to be able 
to preset the potential applied to the 
grid circuit of the tube unit. This is 
accomplished as follows : for the Los 
Angeles job, the five-scene preset type 
of switchboard was supplied. In order 
to obtain these five presets, five small 
slider type of potentiometers were sup- 
plied, one for each preset. In addition 
to this a flashing arrangement was sup- 
plied whereby it was possible for the 
operator to immediately flash from one 
scene to another by simply operating 
a push-button, which operates relays 1, 
2, 3, 4 or 5 as indicated. Relay (1) has 
its contact closed whenever all of the 
other five relays are in the open posi- 



tion. The normal position of the re- 
lays for operating the scene master 
fader is to have relays 1 to 5 open and 
relay (1) closed. Now to set up cir- 
cuit No. 1 for full intensity the slider 
of preset potentiometer No. 1 is moved 
to the positive end of the potentiometer. 
To set up circuit No. 2 for black-out 
the slider is moved to the negative end. 
In order to obtain intermediate inten- 
sities on the other scenes, the sliders 
are moved to intermediate positions 
corresponding to the intensities desired. 

Now assuming that the switchboard 
is operating on scene No. 1, the pointer 
of the dimming fader will be connected 
to Point No. 1 on this piece of appara- 
tus. In order to transfer to scene No. 
2, the dimming fader, which consists 
of a unit for each circuit to be con- 
trolled on a common drive, is moved 
either by a hand-wheel or by means of 
a motor drive to position No. 2. It 
can be seen therefore that since point 
No. 1 of the dimming fader is con- 
nected to the slider of preset potentio- 
meter No. 1, and is therefore at the 
same potential as its preset for this 
scene, and since point No. 2 is connect- 
ed to the slider of preset potentiometer 
No. 2, there is a gradual transmission 
from the potential set for preset No. 1 
to that for preset No. 2. This gives a 
gradual change in the potential im- 
pressed on the grid circuit of the tube 
unit and, therefore, a proportional 
change in the lighting circuit. 

A similar operation is also perform- 
ed to transfer from scene 2 to scene 3. 
It is furthermore possible with this 
type of equipment to set up the scenes 
not in use for additional effects with- 
out affecting the scene in progress. 



Scene Flashing 

The purpose of the scene flashing 
equipment is to allow the operator to 
transfer immediately from the effect 
that may be set up from one scene to 
the effect set up for any other scene 
and have all the lighting circuits come 
to the desired preset intensity. This 
is accomplished by means of the relays 
1, 2, 3, 4 and 5, Fig. 1, which operate 
to disconnect the grid lead from the 
scene fader and connect it to the pre- 
set potentiometer associated with the 
relay selected. Thus the potential which 
has already been set up on this potentio- 
meter is applied to the grid lead of the 
tube unit and a corresponding intensity 
of the lighting circuit results. When 
any other relay is operated, the relay 
previously closed is automatically dis- 
connected by means of the switch keys 
which are interlocked. 

In order to obtain color master 
operation of any of the circuits as has 
been previously described, the pilot 
switch is thrown to the color master 
position. This transfers the lead to the 
positive end of the control potentio- 
meter from the positive bus and con- 
nects it to the sliding arm of the color 
master potentiometer. Thus it may be 
seen that the voltage on all of the po- 
tentiometers connected to this particu- 
lar color master is varied by moving 
its sliding arm. Consequently, a pro- 
portional change in the voltage im- 
pressed on the sliding arm of the in- 
dividual potentiometers is obtained 
which results in a proportional change 
in the lighting intensity of the circuits 
connected to these controls. Thus if 
one of the circuits connected to this 



SCHEMATIC DIA&RAM OF SCENE FLASH/KG CONTROL 
THERMIONIC Type THEATRE SWITCHBOARD 

PRESET POTENTIO METERS 

s scenes 




inoiviDuAL 

potentiometer 



^gHil ' r v v \ o £ 



risk* circuit V 



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1 SW . ! SH . ! 3* . . I J* . . I *<v. 

\neri \Keri \Ktrj Ucr« \kiy s 

H h H h h 



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OTHER 
CIRCUITS 
SAME AS 

c/R~/i2- 



MUL Tl CON TACT R£L ATS 
Fig. 1. Control switchboard for theatie lighting. 



Page 16 



PROJECTION ENGINEERING 



color master is at full brilliancy, a sec- 
ond at Y\ brilliancy, a third at y 2 bril- 
liancy, etc., should these circuits be 
dimmed out by the color master, they 
will start dimming at the same time 
and proportionally change so that they 
reach the blackout position at the same 
time. This is in contrast to the opera- 
tion of the standard interlock type 
of color master in which a similar 
operation would result in the circuit 
at full brilliancy being dimmed until 
it corresponded to the one at % bnl~ 
liancy at which point the second circuit 
would interlock with the color master 
and both these circuits travel until they 
reached half brilliancy where the thirf' 
circuit would interlock and finally all 
would block out together. This often- 
times resulted in a spotty effect and is 
undesirable. By using an electrical 
color master rather than a mechanical 
color master, a proportional dimming 
effect is accomplished as previously 
described. 

Master Control 

In order to obtain grand master con- 
trol, the pilot switch on the color mas- 
ter section is transferred from the hot- 
bus position to the grand master posi- 
tion which connects the circuits on the 
color master to a master generator. By 
varying the voltage on this master gen- 
erator, the potential impressed on the 
color master is varied, thus causing a 
proportional change similar to that pre- 
viously described for all the circuits 
connected to the grand master. 

Motor operation is provided for the 
dimming fader on the Los Angeles the- 
atre job so that it is possible for the 
operator to change from one effect to 
another by simply pushing a small tele- 
phone switch starting the motor drive. 
This motor drive is so provided with 
limit switches that it will travel to the 
next succeeding scene at which point 
it will stop and will not restart again 
until the operator pushes the "start" 
button. This allows an easy means of 
obtaining remote control of the inten- 
sity of all the lighting circuits in the 
theatre. In the old type of multi-pre- 
set board it was entirely possible to 
obtain remote control scene changes, 
but it was impossible to obtain a pre- 
set of the intensities, it being necessary 
for the operator to set the dimmers be- 
forehand or to change when changing 
from one effect to the other. By using 
the thermionic tube control, it is pos- 
sible to preset the dimming as well as 
to preset the circuits which are to be 
used and furthermore, obtain remote 
control of these circuits if it is desired. 
This is of special advantage in some 
moving picture houses where it is de- 
sirable to control the light from the 
projection room and at the same time 
have a switchboard on the stage floor 



which can be used in case of stage 
presentation work. 

Remote Control 

In the Los Angeles theatre, the re- 
mote control board at the stage floor 
allowed the stage switchboard operator 
to have full control of the color masters 
for the auditorium circuit and in addi- 
tion to this allowed him to change the 
lighting effects in the auditorium for 
five presets, which had previously been 
determined by means of the switch- 
board located in the projection room. 
Furthermore, by means of the color 
masters, it was possible for the opera- 
tor to dim out any particular color from 
any scene that had previously been pre- 
set thus giving a very flexible control. 

The previous description covers the 
tube type switchboard which was in- 
stalled in the Los Angeles theatre and 
is typical of this type of control. Due 
to the rapid development in this art, 
at least one other scheme has already 
been conceived. Instead of a grid-glow 
type tube, a vacuum tube of a rather 
large plate capacity is used and a 
motor-generator set supplies 500 volts 
direct current to the plates. The out- 
put is regulated by grid control of 
these tubes. That is, the 500 volts 
from the generator is connected in 
series with the vacuum tube and the 
direct-current coil of the reactor. Thus 
by varying the impedance of the vac- 
uum tube by change of grid potential, 
the amount of direct current that is 
allowed to pass through the d-c. coil 
of the reactor is changed. The control 
equipment, that is, the potentiometer 
setup is practically a duplicate of that 
used for the Los Angeles theatre, the 
new developments affecting the tube 
units rather than the control. 

Scene Changes 

Another advancement has been in 
the method of control by which it is 
now possible for a switchboard to be 
built wherein the operator may change 
from any one scene to any other scene 
and get a gradual shading effect from 
one to the other or obtain a flashing 
effect as previously described. The Los 
Angeles theatre was built before this 
development so that in this job it was 
necessary to fade from one scene to the 
next succeeding scene. This new de- 
velopment allows a much more flexible 
means of control due to the fact that 
in stage presentation work it is often 
desirable to repeat an effect and with 
this type of control, it is possible to 
do this as often as is desired and to 
fade into this effect from any other 
that may be in progress. 

Another interesting development that 
has recently been brought forth, the 
first application of which is for the 
control lighting of the Buckingham 



Fountain in Chicago, provides a con- 
tinuous preset program which is laid 
out in advance for an evening's per- 
formance. This is accomplished by 
means of an insulating track on which 
there has been drawn a conducting 
path. This moves and is continuously 
in contact with a potentiometer similar 
to the control potentiometers for the 
tube units. Thus by varying the loca- 
tion of the conducting strip on the mov- 
ing track, a variable preset potential is 
obtained which correspondingly changes 
the output of the tube unit and a 
change in the intensity of the lighting 
circuit results. While this is developed 
for floodlighting control, it may be 
used for such an application as vary- 
ing the lighting of a theatre according 
to a definite program for the overture. 
It could also be used for providing a 
light change program for the patrons 
at the time between the opening of the 
house and the beginning of the per- 
formance. This program is motor 
driven and can be started and allowed 
to run for a definite period of time 
after which by means of a transfer re- 
lay, the control could be transferred 
back to the regular stage switchboard 
for use in connection with the picture 
or the stage presentation. 

In summarizing, it may be said that 
the application of thermionic tubes to 
theatre dimming has made possible a 
stage board giving the following very 
desirable features : 

1. Presetting of intensity for any de- 
sired number of scenes. 

2. Proportional dimming. 

3. A light compact board using tele- 
phone switches thus insuring ease of 
operation with added insurance of 
proven reliability of this type of equip- 
ment. 

4. Low control voltage (less than 
50 v. d-c.) allows use of telephone 
cable for control wiring. 

5. Remote control easily added. 

In fact, the field of the application 
of tube control to lighting, is in its 
very infancy and due to the rapid de- 
velopment in tubes, as we have wit- 
nessed in the past in the radio field, 
a great deal may be expected from 
this type of equipment. 



SPRING MEETING OF S. M. P. E. 

The Board of Governors of the 
Society of Motion Picture Engineers 
has voted that the spring meeting of 
the society shall be held in either 
Washington or New York City, with a 
tentative date set for May 9 to 12. 
Choice between these two cities will be 
made by the members of the Society 
and ballots have been mailed to the 
members for their votes, according to 
W. C. Kunzmann, chairman of the con- 
vention committee. 



JANUARY, 1932 



Page 17 



Sound absorption 
balance in the acoustics 
of auditoriums + 



By V. A. SCHLENKER^ 



In this paper is presented new studies of the relation 

between reverberation and articulation, as employed in 

sound transmission in auditoriums 



A REGRET expressed by engi- 
neers now delving into archi- 
tectural acoustics is that the 
father of modern acoustics is 
no longer living. Professor Wallace 
Clement Sabine was never content to 
consider any phase of acoustics a closed 
book. He was always willing to re- 
open and continue with any investiga- 
tion where there was hope of extending 
experimetal data in a practical way. 

Unfortunately, many of his successors 
have shown a tendency to assume that 
his contributions were sufficient for the 
solution of practically all acoustical 
problems which the engineer encount- 
ers. Without detracting in the least 
from the monumental pioneer work of 
Professor Sabine, it can truthfully be 
said that his contributions are not en- 
tirely adequate to arm the present en- 
gineer to successfully cope with the 
acute conditions caused by sound pic- 
tures, radio, and television. Had Sabine 
lived he would no doubt still be the 
leader in experimental investigation 
with our present electro-acoustical in- 
struments. That he was able to make 
such accurate and intricate measure- 
ments with the crude equipment avail- 
able in his time is beyond the compre- 
hension of most of us. 

The most common assumption made 
by the young acoustician is that his 
job is done when he adjusts the rever- 
beration of an auditorium to the so- 
called "optimum." Just what or why 
there is or should be an optimum pe- 
riod of reverberation has always been 
somewhat obscured with a veil of mys- 
tery. That music is enhanced with 
some reverberation is well known and 
it follows that a definite period, not too 
long and not too short, can be deter- 



mined by the sensing of artists who 
react positively to the variation of the 
reverberation as it is adjusted. Pro- 
fessor Sabine reported that "a difference 
of five per cent in reverberation is a 
matter for approval or disapproval on 
the part of musicians of critical taste." 
(P. 80) Collected Papers on Acoustics.) 

In the case of speech, however, it is 
not so simple. In a general way, the 
clarity should increase as the reberbera- 
tion is reduced. At the same time the 
intensity at the ear of the listener is 
reduced by the introduction of acoustic 
absorption which is employed to reduce 
the reverberation. In small audi- 
toriums the attenuation is not especially 
objectionable so long as the intensity is 
well within the limits o f audibility. 
Therefore, if there are no other factors 
in control no optimum period of re- 
verberation can be determined. 

In the case of the large auditorium 
we have two essentially opposite effects 
on the quality of speech — one tending to 
increase, the other tending to reduce 



'",; ' 

1\ 

5Peccn ,„ Titf*TKC 'A' 
/if ren r#r*rrtrnr 






*mm 



Fig. 2. Effect of reverberation on speech. 

the reverberation. If there were no 
other important factors, naturally, a 
compromise or optimum would result. 

It is quite apparent, in the small in- 
closure, at least, that some other im- 
portant factor must be in control to 
account for the optimum period of 
reverberation. 

The reverberation of a room is 
usually measured by timing the decay 
of sound. Present methods involve a 
microphone to pick up the sound and a 
chronographic means of recording the 
time required for the sound intensity to 
drop a certain number of decibels. 
The number of seconds required for a 
60 decibel reduction in level is uni- 
versally designated as the period of 
reverberation regardless of frequency. 

An oscillographic trace of such decay 
of sound can be seen in Fig. 1. The 
two traces are recorded simultaneously 
— the lower one is monitored on the 
upper channel electrically but set at an 
adjustable number of decibels above it 
in gain. In this particular case, the 
lower trace was recorded at 24 db. 
above the other. The distance between 
the points of equal amplitude on the 
two traces is a measure of the time for 
the sound to decay 24 db. By multi- 
plying this figure by 2 l / 2 the period of 
reverberation is obtained. The differ- 
ence of level chosen is determined by 
the noise level and the maximum inten- 



Fig. 1. Oscillographic 

trace of decay of 

sound. 



f Presented before the Radio Club of America, 
November 11, 1931. 

* Consulting Acoustical Engineer, Chanin Bldg., 
New York City. 




Page 18 



PROJECTION ENGINEERING 




Fig. 3. 

sity level of the test tone which is 
available. 

The method just described was de- 
veloped by the writer to avoid the pos- 
sibility of error which is apt to enter 
when other methods are employed 
which involve the operation of mar- 
ginal relays. Furthermore, the exact 
manner in which the decay takes place 
is at all times known when the oscillo- 
graphic trace is made. This facility is 
very important for the research worker 
who must be on the look-out for new 
and unexpected phenomena. 

The effect of reverberation on speech 
is shown in an interesting way in Fig. 
2. In this case, two microphones were 
set up in a particular theatre. One was 
placed about four feet in front of the 
loudspeaker behind the picture screen 
giving the lower trace, while the other 
was positioned out in the auditorium, 
giving the upper trace. In this way a 
direct comparison between the sound as 
it comes out of the horn can be made 
with the sound as it is received by the 
listener out in the audience. The last 



three syllables are "VI-TA-PHONE." 

Although the distortion is abundant 
because of reverberation it was worse 
before this house was acoustically 
treated, as will be seen in Fig. 3. The 
reverberation is so great that the indi- 
vidual syllables are scarcely discernible. 

When the reverberation is measured 
in the auditorium the investigator at 
once discovers that there is a consider- 
able variation, depending on the fre- 
quency. Some typical curves are given 
in Fig. 4. The curve marked T-l has 
an excessive period of 4.0 seconds at 
128 c.p.s., while at 4096 c.p.s. the period 
is only 1.5 seconds, which is a ratio of 
almost 2.7. The curve T-3 from a 
theatre which has been treated acous- 
tically has a period of 3.5 at 128 c.p.s. 
and 1.0 at 4,096 c.p.s. Here the ratio is 
even greater — 3.5. Curve T-2 has the 
smallest ratio — 3.2 to 1.8 seconds, which 
is approximately 1.8. 

At once, one is led to the suggestion 
that perhaps the relative slope of the 
reverberation curve may be of con- 
siderable importance. In other words, 
the fact that low-frequency sound is ab- 
sorbed less efficiently than the high 
frequency may be most valuable in de- 
termining the degree of intelligibility 
with which speech is understood. 

In Fig. 5 (lower right portion), is 
given the reverberation curve of a par- 
ticular average theatre with a seating 
capacity of 1,800. It will be noted that 
the reverberation at the higher fre- 
quency depends upon the relative 
humidity of the air. Recent investiga- 
tion by Dr. Knudsen and others have 
established the absorption of the air at 
different values of relative humidity. 
Their findings have been quite startling 



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but entirely in accord with the experi- 
mental as collected by competent ob- 
servers. Professor Sabine, himself, rec- 
ognized the fact that the moisture 
content of the air is a factor in the 
dissipation of acoustic energy but he 
concluded that (to quote from p. 171 
of his Collected Papers), "this form of 
dissipation instead of being an im- 
portant factor, is an entirely negligible 
factor in any actual auditorium." If 
the bounding surfaces of this audi- 
torium were perfect reflectors the re- 
verberation at 4,000 c.p.s. would be 4.4 
seconds due to the absorption of the air 
at a relative humidity of 20 per cent 
and room temperature of 70° F. On 
the other hand, if the humidity is 70 
per cent the period is almost twice as 
great — the absorption at 4,000 c.p.s. 



o 
?2 

6 



> 1 



THREE TYPICAL THEATERS 

1,000 to 1,500 Seats — i — 




_ Without balcony - 
treatea 1 with material with 
coefficient similar to A 



178 



256 



512 1,024 2,048 

Frequency, C.P.S 



4,096 



Fig. 5. Reverberation curves. 



Fig. 4. Reverberation curves of three typical 
theatres with different acoustical treatment. 



being almost negligible for all prac- 
tical purposes. In fact, this no doubt 
accounts for Sabine's failure to detect 
the effect of humidity, since he may 
have done practically all his work in 
humid air. 

The effect of dry air must be taken 
into consideration since most of the 
theatres have very dry air in the winter 
time. I have been informed by the Car- 
rier Engineering Corporation that the 
humidity will run as low as 25 per cent 
in the winter where no air conditioning 
is provided. The practical ideal for 
winter is 35 to 40 per cent as is main- 
tained by the air conditioning equip- 
ment. It can be concluded that at fre- 
quencies above 2,000 c.p.s. the relative 
humidity must be considered in deter- 
mining the acoustical absorption and its 
effect on reverberation. 

In the upper right-hand portion of 
Fig. 5 is given the absorption as cal- 
culated from the reverberation given in 
the curve immediately below. It will 
be noted that the curve has an alarming 
slope at a relative humidity of 70 per 
cent. At an average humidity of 45 
per cent the total absorption is 12,000 
units at 4,000 c.p.s. and only 6,000 units 
at 125 c.p.s — a ratio of 2.0. For pur- 
poses of later consideration the units of 



JANUARY, 1932 



Page 19 



absorption required to give a flat curve 
are given in the left portion. In other 
words, if a balanced condition is de- 
sired in this theatre the absorption must 
be added in largest amounts at low fre- 
quencies. 

In the last analysis of the acoustic 
problem, the final judge which must be 
satisfied is the human ear. It is well 
known that the ear is limited in tonal 
range or frequency. It is also limited 
in the range of intensities. The very 
faintest sound is sensed at the "thres- 
hold of audibility" while the very loud- 
est sound is sensed at the "threshold of 
feeling." Both the frequency and in- 
tensity ranges can be represented on a 
chart by a certain area as shown in 
Fig. 6. 

A smaller area can be used to repre- 
sent average or normal speech. The 



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Fig. 7. Records of street noises. 

average extends from 200 c.p.s. to 8,000 
c.p.s. for the important components. 
The speech area, then, will extend from 
200 to 8,000 along the frequency axis 
and about 25 decibels along the intensity 
axis. The speech area can be further 
divided into the vowel and consonant 
portions. The vowels occupy the region 
of low frequency and high intensity 
while the consonants are found in the 
region of high frequency and low in- 
tensity. 

Taking the total speech power as 10 
microwatts for average speech (p. 67, 
Fletcher, "Speech and Hearing"), the 
speech intensity is 1 microwatt per 
square centimeter at a distance of one- 
half inch from the mouth of the speaker, 
since the power is divided over the 10 
sq. cm. of surface of the hemisphere 
whose radius is .5 inch. The intensity 
of 1 microwatt per sq. cm. is taken as 
zero level. 

If sound continues to radiate into un- 
confined space the intensity will diminish 
according to the inverse square of the 
distance. At a distance of 12.5 feet the 
intensity will be 50 db. lower than the 
"initial level" which is taken at a dis- 
tance of .5 inch bv definition. 




Fig. 6. Frequency and intensity ranges. 



On the auditory chart the effect of 
the listener moving from .5 inch to 12.5 
feet can be represented as a 50 db. 
vertical drop of the speech area. When 
the listener moves to a distance of 125 
feet a further drop of 20 db. is experi- 
enced. At this distance, the speech area 
is then touching the minimum audibility 
level. 

Some idea of what this means in 
terms of the dimensions of a theatre can 
be gained by the curve and sketch 
shown in the left portion of Fig. 6. It 
will be seen that if a person spoke on 
the stage with a speech power of 1 
microwatt, it would be just audible in 
the rear of the theatre, assuming that 
no reflections took place from the walls, 
ceiling, and floor. If there is noise 
present a portion will be masked. In 
the shaded portion of the auditory sen- 
sation area is represented the space oc- 
cupied by a 30 db. level of noise which 
has its components below 500 c.p.s. The 
masking extends well up in the higher 
frequency range as has been determined 
at the Bell Telephone Laboratories. If 
this noise were present as is frequently 
the case, the speaker could not be heard 
in the remote portion of the balcony. 
In other words, the one microwatt voice 
with an initial intensity level of — 10 
db. would have to be raised 30 db. to 
1,000 microwatts to give an initial level 
of -+20 db. This would insure a — 50 
db. level at a distance of 125 feet with- 
out the aid of reflections. 

In the actual theatre the reflections 
raise the level of sound, immensely. 
For the purpose of comparison the in- 
tensity levels have been calculated for 
different absorption conditions. For an 
average coefficient of absorption of 0.10 
the intensity level of approximately 50 
db. below 1 microwatt per sq. cm. 
(zero level) would be established by a 
sustained sound. 

The nature of the room noise which 
is ever present should be known with 
some degree of accuracy. Not only the 
intensity should be known, but its fre- 
quency distribution as well. Fig. 7 
•nves a record of the street noise which 



filtered into the theatre which we have 
been considering as typical. The elec- 
trical circuits were arranged with 
special filters so that the entire fre- 
quency range was divided into three 
bands — low, middle, and high. The 
distribution of the noise is fairly uni- 
form over the three bands when picked 
up on the street. After finding its way 
into the lobby the middle and high fre- 
quencies are attenuated somewhat as 
can be seen in the left half of the traces. 
A special switching device automatically 
switches the circuits over to another 
microphone located in the foyer. This 
switching is accomplished in much less 
time than it takes the sound to travel 
from one microphone to the other. The 
traces from the noise in the foyer show 
an entirely different distribution of 
energy over the three bands. In the 
foyer, which is really a part of the 
orchestra itself, the noise is almost en- 
tirely made up of frequencies below 
500 c.p.s. This fact is important in de- 
termining the characteristics of any 
acoustical treatment which is pre- 
scribed for noise abatement. The type 
of auditorv masking which it causes is 




Fig. 8. 



Traces made in an acoustically 
treated theatre. 



Page 20 



PROJECTION ENGINEERING 



also determined by its frequency 
characteristics. 

Fig. 8 shows an interesting com- 
parison of two traces which were taken 
In a studio which was heavily treated 
acoustically. The upper trace shows 
the room noise which runs as low as 
30 c.p.s. up to 200 c.p.s. The lower 
trace shows the same room noise with 
high frequency noise of a motion pic- 
ture camera superposed. These traces 
were taken separately but within 15 
minutes of each other. Once more the 
room noise is found to be made up of 
low frequency components. 

It has been noted how multiple re- 
flections build up the sound intensity 
when a single tone is sustained long 
enough for a steady state condition to 
be established. In dealing with speech, 
however, the duration of the individual 
component is very short. The time of 
the average vowel is 0.3 second while 
the average consonant can be taken as 
0.05 second. Inasmuch as the vowels 
and consonants are entirely different in 
frequency, duration, and intensity, it 
seems reasonable that each should be 
considered separately. For purposes of 
diagnosis, the writer has developed an 
electrical syllable which can be used to 
simulate a component of speech. If its 
frequency is set at, say, 250 c.p.s. with 
a length of 0.30 second, it will represent 
a vowel. If its frequency is set at, say, 
4,000 c.p.s., with a length of 0.05 second, 
it will represent a consonant. 

In this way an auditorium may be 
tested by acoustically projecting the 
vowel and the consonant separately and 
recording the sound as it is picked up 
in various parts of the house by a 
microphone. 



Fig. 10. Intensity 

level of vowel above 

intensity level of 

consonant: 

tv = .30 sec. 

tc = .05 sec. 





























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3.0 SEC 




A« 














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Ac COEFFICIENT OF ABSORPTION FOR CONSONANT Ac 



Four different oscillograms are re- 
produced in Fig. 9. These were taken 
as suggested in the last two para- 
graphs. In fact, they were all taken 
in the same theatre but in differ- 
ent positions. The traces on the left 
were taken in the center of the orchestra 
while the ones on the right were taken 
on one side of the orchestra. Space will 
not permit more than a glance, but it is 
obvious that a great wealth of infor- 
mation may be gained from a careful 
study of such soundings in an audi- 
torium. The particular orientation of 
the horns will also control to some de- 
gree whether the high frequency pro- 
jection will "clean cut" like the one at 
"M-2" or ragged like the one at "M-5." 

After a careful consideration of the 
properties of speech and its interpreta- 
tion by the ear, the writer has finally 
concluded that the true relation between 
reverberation and articulation can be 
traced to the short length of the funda- 



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Fig. 9. Traces made in an acoustically treated theatre. 



mental speech sounds. If the vowels 
are assigned a duration of 0.3 second 
and the consonants 0.05 second with a 
difference of 15 decibels in power we 
will have a good average representa- 
tion. The vowel can have a frequency 
of 250 c.p.s. while the consonant can 
be assigned 4,000 c.p.s. The inten- 
sity to which each will build up can 
then be calculated where the average 
coefficient of absorption of the room is 
known for each frequency. It is at 
once apparent that the consonant will 
build up to only a small fraction of the 
steady state value because it is so 
short in duration. On the other hand, 
the vowel which is six times longer will 
attain a much greater fraction of its 
steady state value. 

As has been seen, the vowels are 
about 15 db. higher than the consonants. 
One can then proceed to calculate the 
difference in level as determined by the 
duration of the sound, the absorption at 
the particular frequency of the vowel or 
consonant, the volume, and total surface 
of the room. 

Fig. 10 shows the results when all the 
possible coefficients of absorption are 
assigned to the vowels and consonants, 
respectively. The true vertical distance 
represents the intensity level of the 
vowel above that of the consonant for 
any particular value of the consonant 
coefficient. For example, take the point 
marked 0.8 second on the chart for the 
room with a volume of 9,000 cubic feet. 
This represents a consonant with a co- 
efficient of 0.20 and a vowel with -a 
coefficient of 0.20 also ; the level of the 
vowel being 17 db. above the con- 
sonant. The 0.8 second is the re- 
verberation for this particular coeffi- 
cient. The dotted line passing through 
this point is a locus of all conditions in 
which the vowels and consonants have 
the same coefficient. In other words, 
this line represents a balanced absorp- 
tion with respect to frequency. 

The upper dotted line represents the 
condition in which coefficient of absorp- 
tion for the vowels (Av) is only one- 



JANUARY, 1932 



Page 21 



half that for the consonants (Ac). 
Likewise, the lower dotted curve con- 
tains all the points in which the vowel 
absorption is twice that for the con- 
sonant. In brief, the area above the 
middle dotted line represents unbal- 
anced absorption of the usual kind while 
the area below represents a reversed 
absorption unbalance which is most un- 
usual. 

Many interesting deductions can be 
made from this chart. Perhaps the most 
interesting thing to note is that the 
condition of unbalanced absorption 
causes the vowels to rise far above the 
normal level for initial speech which is 
bound to decrease the articulation. On 
the other hand, the reversed unbalance 
causes the vowels to be much lower in 
level and in some cases to be below the 
normal level. Further experiment will 
show that the articulation will be im- 
proved in a corresponding way. 

The effect of the size of the room is 
strikingly shown when the same cal- 
culations are made for a room with a 
volume of 410,000 cubic feet. Here 
there is less opportunity to keep the 
level of the vowels at or below the nor- 
mal level of initial speech. However, 
the reversed absorption condition is far 
superior to even the balanced condition. 

In the application of acoustical treat- 
ment, one must not lose sight of the fact 
that coefficients of absorption which are 
available, are painfully limited. Prac- 
tically all the materials on the market 




256 



511 ..OTA 

Frequency, C.P S 



TfiAb 



4,096 



Fig. 11. Coefficients of, absorption curves of 
well known materials for different frequencies, 
also one material of special design to correct 
unbalanced absorption in acoustic treatment. 



have absorption curves similar to those 
which are shown in Fig. 11. The slopes 
of these curves are of special interest 
in view of the data given in the chart 
presented. The absorption at high fre- 
quencies which controls the consonants 
is between twice and three times that 
at low frequencies which controls the 
vowels. These curves have the usual 
unbalance which results in the vowels 
being intensified in excess of the con- 
sonants. The net effect is to lower the 
articulation. 

The new acoustic treatment which is 
indicated by the curve "X" in this figure 
is designed to aid in the correction of 
the unbalanced condition. The cost of 
treatment which will give the extreme 



slope of one-fifth is considerably more 
than a modified treatment on the same 
principle which has a slope of one-half. 

Referring again to Fig. 10, the 
smaller room gave an articulation of 
79 per cent when the reverberation was 
adjusted to a period of 1.2 seconds for 
a sensation level of 72 db. (J. C. Stein- 
berg, J. A. S.., Oct., 1929). In this 
room (whose dimensions were 20 x 30 
x 15 feet), the coefficients Av and Ac 
were approximately equal to 0.12. Read- 
ing the chart, it will be noted that the 
vowels are about 3 decibels above the 
normal, or a total of 18 db. above the 
consonants. If this room were treated 
with the new material with a reversed 
absorption curve, the average coefficient 
for the vowels Av could be adjusted 
to 0.30 keeping the A c at 0.12. The 
result would be to bring the vowel level 
completely down to the normal for initial 
speech, thereby enhancing the intelligi- 
bility. 

In conclusion, the method of acoustic 
treatment of auditoriums which employ 
a new material with maximum absorp- 
tion at low frequencies has unusual 
possibilities for improving the articula- 
tion of speech. That there is a sound 
scientific basis for such a conclusion in 
addition to experimental confirmation 
is most reassuring to the engineer who 
desires to determine the specifications of 
acoustic treatment to give a certain per- 
centage of articulation at a prescribed 
acoustic intensitv level. 



AAA 



WUNDER LEAVES ACADEMY 

AT a meeting of the Board of 
Directors of the Academy of 
Motion Picture Arts and Sci- 
ences on Nov. 11, Dr. Clinton 
Wunder resigned as executive vice- 
president. He announced that he had 
accepted the invitation of the Institute 
of Religious Science and Philosophy 
of Los Angeles, to share the leader- 
ship of the Institute with Ernest 
Holmes, its founder, and to become edi- 
tor of the magazine, "The Science of 
Mind," beginning his new duties De- 
cember 1. 

M. C. Levee, president of the Acad- 
emy, made the following statement : 
"The resignation of Dr. Wunder was 
accepted with regret as in the two years 
that he has been executive head of the 
Academy he has gained the thorough 
confidence of the board of directors 
and of our membership. His qualities 
of leadership, distinguished standing as 
a student of public affairs and his abil- 
ity as a speaker have exercised a genu- 
inely helpful influence throughout the 
motion picture industry." 

Previous to his association with the 



MORE TECHNICAL QUESTIONS 

Continuing the series of examination 
questions introduced in the October 
issue of Projection Engineering, 
herewith are presented questions No. 
26 to 32. The correct answers will be 
published in the February issue. 

26. State what is meant by self-in- 
duction. 

27. What percentage of light is lost 
between the arc and the screen and 
where is this percentage lost? 

28. What precautions must be taken 
in mounting lamps for mazda projec- 
tion? 

29. Can you use a prismatic con- 
denser for projection stero slides? 

30. Give four reasons for low volume 
from horns when using sound-on-film. 

31. Give three reasons for low vol- 
ume from horns when using sound- 
on-disc. 

32. Give a full description of the 
input and voltage amplifier panels 
Type "B" as used by R.C.A. What 
type tubes are used on this panel ? 



Academy, Dr. Wunder was for ten 
years minister of the Baptist Temple of 
Rochester, New York, one of the larg- 
est churches in the Protestant denomi- 
nation. In this position he established 
a national reputation as a liberal in re- 
ligion and philosophy. For the past 
fifteen years he has lectured in all parts 
of the United States on the social and 
educational aspects of the motion pic- 
ture. 

Through the Academy, Dr. Wunder 
has had opportunity to extend his study 
of the relation of the motion picture to 
religious and secular instruction. He 
plans to continue his interest in this 
field and in the public relations pro- 
gram of the industry. 
A 

BOOK REVIEW 

"TALKING PICTURES," by Bernard 
Rroiv-n. 305 pp. Isaac Pitman & Sons. 
2 West 45 St., New York, 1931. 
Mr. Brown has succeeded in produc- 
ing a thoroughly practical and popular 
account of the principles of construc- 
tion and operation of the apparatus used 
in producing and showing sound pic- 
tures. The price of the book is $3.00. 



Page 22 



The trend 

of sound, 1932 



By Carl M. Weber 



IT is only by analyzing the develop- 
ment of sound in the past year that 
one can visualize the trend for 1932. 
1931 saw a change from disk to 
sound-on-film. 

This change is for the better, not 
only from the angle of better sound, 
but also of reducing the cost of handling 
sound pictures. 

The developments for sound-on-film 
have been remarkable in the last year, 
not only in improved recording but 
also improved reproduction. The most 
marked improvement has been in re- 
production. This has been possible by 
the remarkable improvement in photo- 
cells, tubes and amplifiers. The optical 
system has also had a large share to- 
ward better sound reproduction. The 
lenses used in the better grades of 
optical systems are of as high a quality 
as the finest camera lens and in many 
cases the lens system used in the sound 
head is of greater precision and quality 
than the lens used in the projector. 

All in all, the year of 1931 has been 
a year of development in the sound in- 
dustry. Not only has the quality of 
all units involved been greatly improved, 
but prices have been reduced. Price 
reduction has not only been possible by 
improved manufacturing methods, but 
by keen competition of many equip- 
ment manufacturers. 

Four major units are involved for 
perfect sound reproduction, namely, the 
sound head, amplifiers, speaker units 
and acoustics. Each one of these units 
is more or less complex as each one 
is an assembly of other units that must 
function properly in order that the 
whole may perform as it should. Per- 
fect sound consists of the perfection 
of small details, any one of which may 
make or break the entire set up. Up 
to the present time the weakest link 
in the chain of perfect sound has been 
the speaker unit. The larger the fre- 
quency range, the better the reproduc- 
tion and up to the present time there 
has been no speaker available that 
would handle the full range of frequen- 
cies recorded and passed through the 
associated apparatus. While this may 
be true, the modern horn and unit give 
remarkable results if associated appara- 
tus is of the proper quality. 



Sound iri the theatre has passed the 
experimental stage and today it is only 
a matter of proper equipment, properly 
installed. The present trend is toward 
all a-c. operated equipment in prefer- 
ence to battery operated. A-C. equip- 
ment has simplicity of operation in its 
favor, also fewer parts which have a 
limited life and which must be replaced 
periodically. 

In changing over to a-c. operated 
theatre sound equipment, we are going 
through the same stages of development 
as radio, but at a faster pace. All a-c. 
operated equipment is the ultimate goal, 

• 
A 



PROJECTION ENGINEERING 

but there is a necessity for improve- 
ment before all a-c. operated equip- 
ment will give as good sound as prop- 
erly built battery equipment. 

The records of all sound companies 
show a continued decline in service as 
the requirements for sound apparatus 
have been better understood and all 
units are built with larger safety fac- 
tors which reduces the number of break- 
downs. Projectionists are now more 
familiar with sound apparatus and can 
handle all minor difficulties without 
assistance. Therefore, service is not 
the vital factor that it was a few years 
ago. 

Summarizing, the year 1932 may not 
see radical changes in sound equipment. 
There will be a gradual change from 
battery operated to all a-c. There will 
be a stabilizing of the industry. The 
weaker companies will be eliminated 
and only the companies with a reliable 
product will be able to stay in the field. 
The mystery is rapidly being eliminated 
from sound, and sound apparatus will 
soon be classed as any other equip- 
ment in the theatre. 

A A 




Scene in a section of the lobby, 



(Courtesy General Electric Co.) 
Earl Carroll Theatre, New York City. 






JANUARY. 1932 

Improved 

disc 

recording 



AN epochal advance in sound re- 
cording and reproducing was 
demonstrated on December 10 
to 1500 engineers at a meeting 
of the Society of Motion Picture En- 
gineers and the Institute of Radio En- 
gineers, in the Engineering Societies' 
auditorium, New York, by Halsey A. 
Frederick. Using disc records cut by 
the vertical method, a new high power 
amplifier and the latest types of loud- 
speakers, Mr. Frederick produced an 
extraordinarily faithful reproduction of 
organ, orchestral, and vocal music, 
which his audience could scarcely dis- 
tinguish from the original in either 
quality or volume. 

Speaking also before the meeting, 
Leopold Stokowski, director of the 
Philadelphia orchestra, explained ■ the 
problems connected with recording 
music from the standpoint of the mu- 
sician. 

The vertical method of recording on 
wax discs differs from the so-called 
lateral method which is standard prac- 
tice in the phonograph and sound pic- 
ture industries in that the groove in- 
stead of wavering back and forth along 
an otherwise spiral path is a true spiral 
whose depth varies in a perfect pat- 
tern of the sound waves which have 
been recorded. Such a method was the 



original conception of Edison but lack- 
ing modern electrical technique, it was 
superseded by the lateral method. With 
the availability of microphones, ampli- 
fiers, and other electrical adjuncts to 
modern recording the old method now 
finds itself in the forefront of progress. 
Among reasons for its excellence is 
that the needle is no longer thrown 
from side to side by the vibrations, with 
the resulting over-travel and wear on 
the groove, but rather rides smoothly 
up and down. A close fit of the repro- 
ducing point in the groove — a requisite 
of the old method — was secured by in- 
corporating a certain amount of abra- 
sive material into the disc which would 
soon wear the steel needle to an ap- 
proximate fit. This fit is not required 
in the new method and hence a per- 
manent sapphire point is used in the 
reproducer with a resultant saving in 
weight of the steel needle and its clamp- 
ing device. A further saving in weight 
is effected by an electrical reproducer 
whose moving system consists only of 
the tiny sapphire point, a coil of flat 
wire about an eighth of an inch in 
diameter, and a bit of thin metal to 
hold the whole in alignment. On ac- 
count of its lightness, the moving ele- 
ment is able to follow vibrations up to 
10,000 per second with entire fidelity. 

Needle Scratch 

On account of the abrasive material 
embodied in the older records, the re- 
producing system was designed to elim- 
inate from the output those frequencies 
above about 3,500 cycles, where "needle 
scratch" was especially conspicuous. A 
new method of preparing the original 
wax for recording, and the use of a 
finer grained material for the ultimate 
commercial records make the new rec- 

A A ▲ 



Page 23 

ord extraordinarily free from this 
source of noise and thereby brings 
about a much greater range in volume 
from the level at which surface noise 
would intrude on the program to the 
point at which the moving parts would 
be overloaded. Further increase in vol- 
ume is enabled by the use of a vertical 
groove in which there is no danger, 
in the louder parts of the program, of 
the recording stylus overcutting into 
the adjoining groove. 

In copying from the original wax 
record, it has been the commercial 
practice to dust the wax with very 
finely powdered graphite. The particles 
of graphite were still large enough to 
contribute to the surface noise so that 
method has been abandoned in favor of 
depositing a molecular film of gold 
thrown down by an electrical discharge 
in a vacuum. On this gold film a layer 
of copper is electroplated and the whole 
is then backed up by a lead alloy. Fur- 
ther operations of pressing the discs 
are carried out much as in the present 
process but the ultimate records are 
pressed in cellulose acetate which has 
a surface texture extremely fine. 

The power amplifier, which is the 
last of several stages of amplification, 
consists of two 1,000 watt vacuum tubes 
connected in push-pull. Mr. Frederick 
explained that although its full 2,000 
watts could be drawn upon if necessary, 
the reason for the use of such large 
tubes was in order that they might be 
very lightly loaded. With loudspeakers 
responding to frequencies as high as 
12,000 cycles, the spurious tones pro- 
duced by a heavily loaded vacuum tube 
are distressingly perceptible and for 
this reason none of the tubes in the am- 
plifying system are worked at more 
than a small part of their rated capacity. 



Answers to Questions Nos. 21-25 



CONTINUING the examination 
begun in the October issue of 
Projection Engineering, here- 
with are given answers to ques- 
tions 21 to 25 presented in the De- 
cember issue, page 23. 

21. a. The lens combination which 
gathers the light from source and 
brings same to a point of focus on 
aperture in gate. 

b. An appliance for storing up elec- 
trical energy, made of a number of thin 
sheets of tin foil laid on top of each 
other and separated from each other 
by an insulator. 

c. This is generally known as an "A" 
condenser. The chemical condenser is 
best suited for low voltage work. 

22. The Western Electric system 
employs a three-stage amplifier mounted 
directly on the projector with output 



rated to be approximately equal to the 
output of the electromagnetic pickup 
without amplification. 

The R.C.A. system on the other hand 
does not employ a special amplifier other 
than that regularly used in the system 
and the energy from the photoelectric 
cell is carried to the regular amplifier 
rack there to be passed into the am- 
plifiers. 

With respect to the W. E. photo- 
electric cell amplifier, one of these am- 
plifying tubes is located in the cell hous- 
ing and the other two tubes are located 
beneath the chamber which houses 
the photoelectric cell. The cell is re- 
sistance-coupled to the first amplifying 
tube, a 239 A. Another stage of re- 
sistance-coupling links this tube with 
the second stage, another 239 A and 
the third stage is transformer-coupled 



operating into a third 239 A tube. The 
output of the amplifier is transformer- 
coupled with a 500 ohm output im- 
pedance. 

23. Motor starting rheostats or start- 
ing boxes are designed to start a motor 
and bring it gradually from rest to full 
speed. They are not intended to regu- 
late speed and must not be used for that 
purpose. Failure to observe this cau- 
tion will result in burning out the re- 
sistance which in a motor starter is 
sufficient to carry the current for a lim- 
ited time only, whereas in a speed regu- 
lator sufficient resistance is provided to 
carry the full load continuously. 

24. From 9 1 /- to 10 amperes. 

25. Because the voltage is higher and 
the current lower than if the dynamos 
were in multiple. There is a savins: 
also of machinery. 



Page 24 



PROJECTION ENGINEERING 



A British view of 
sound-on-film 
versus 
sound-on-disc 

By John Wilson* 



THERE is a section of the trade 
today which holds the opinion that 
the day of the disc is fast waning 
and the ever-increasing number of 
sound-on-film releases with a corre- 
sponding decrease in disc releases cer- 
tainly lends color to this belief. I, for 
one, however, do not share this popular 
opinion since I am of the firm convic- 
tion that there still exists a wide field 
in which the disc can be used to greater 
advantage than the film for the purpose 
of reproduction. 

Technically speaking, and from a 
surface viewpoint, sound-on-film does 
possess considerable advantages over 
sound-on-disc, but a careful considera- 
tion of the matter tends to make one 
discount some of the alleged advan- 
tages of sound on film. Granted, one 
can cite against the disc two distinct 
disadvantages, firstly transport charges 
and the ever-present risk of the discs 
going astray from the film in transport 
to the confusion and annoyance of the 
exhibitor and secondly, the necessity of 
a fresh start in the case of a film break. 
Those are, however, the principal dis- 
advantages in connection with sound-on- 
disc, and at the same time which cannot 
be cited against sound-on-film. 

Now, on the other hand, sound-on- 
film, with all its advantages, possesses 
one great disadvantage. To be better 
able to appreciate that one great dis- 
advantage which looms so large against 
sound-on-film we must be able to 
appreciate fully also the position of the 
small exhibitor. The small exhibitor is, 
in this country, the backbone of the 
trade, and according to the size of his 
hall he is much in the same position as 
the member of a large family of very 
small means in which for economic rea- 
sons the mantle of an elder member of 
the family descends through successive 
stages of wear to the youngest member 
of the family whose nakedness is finally 
hidden beneath what might at one time 

"Chief Engineer of Gramo-Radio, Ltd. 



have been a model of sartorial elegance, 
but which has become through much 
hard wear merely a tolerably wearable 
garment. The exhibitor will immedi- 
ately see the analogy. A sound film 
commences its comparatively short life 
at some super house, and from there is 
passed along by stages to the youngest 
member of the cinema family, namely, 
the smallest exhibitor. 

The deterioration of a sound film com- 
mences the first time it is run through 
a projector, but this deterioration is 
slow and hardly discernible, while the 
film remains amongst the elder brethren 
— the large halls — since their projectors 
are of the very latest type, and for the 
most part air-cooled, which is a vital 
point as we shall see in a moment. 
When the film commences to be passed 
down to the younger brethren, however, 
deterioration becomes more rapid and 
for that one simple reason that the pro- 
jectors of the younger brethren are not 
air-cooled, which brings me to my argu- 
men against sound-on-film as a method 
of reproduction for the small exhibitor. 
In passing, before the gate of the pro- 
jector the sound film is subject to the 
intense heat of the arcs which softens 
the emulsion on the film and conse- 
quently the film passing on its way to 
the bottom spool box in this softened 
state is scratched by dust and dirt on 
those parts of the projector with which 
it comes into frictional contact. This 
scratching may not be very apparent on 
the picture itself, but on the sound track, 
owing to the microscopic proportions of 
this latter havoc is worked, and thus 
deterioration continues as it passes 
through the hands of the younger bre- 
thren, with the consequence that the 
small exhibitor offers to his patrons a 
tolerably good picture with sound marred 
by extraneous noises which make speech 
unintelligible, and distort music. 

No blame attaches to the renter in 
this connection because he cannot be ex- 
pected to furnish to the small exhibitor 



a brand new copy, since returns will not 
warrant it, and thus the small exhibitor 
has to offer to his patrons who are often 
more critical than those of any West 
End cinema a picture that does not leave 
a great deal to be desired with sound 
that leaves practically everything to be 
desired. Excellent sound and a poor 
picture is likely to meet with greater 
tolerance than indifferent sound, and a 
good picture, and so the small exhibitor 
who confines himself exclusively to 
sound-on-film is going to find himself 
with an empty hall. 

The small exhibitor who has turn- 
tables installed is in a much better posi- 
tion since his sound is independent of 
his film and he may, either for nothing 
or at the most for ten dollars obtain a 
brand new set of discs with this film so 
that he is able not only to offer to his 
patrons an excellent picture, but also 
sound as perfect as that put over at the 
London premiere, and for that reason I 
contend that sound-on-disc, despite its 
disadvantages, is a much more profitable 
nroposition for the small exhibitor. 

Further, we must not lose sight of the 
fact that Technicolor productions are 
still being produced on disc, and as has 
happened in the past so in the future 
will brilliant Technicolor productions 
come along, of which the small exhibitor 
will not be able to avail himself and 
reap the advantage unless he has tables 
installed. Again, despite appearance 
there is really no actual dearth of disc 
productions, as any exhibitor who goes 
into the matter fully will find, and I 
would, therefore, counsel every small ex- 
hibitor who would run his cinema on the 
lines most profitable to himself, to show 
as many disc productions as possible, 
since only on disc can he offer to his 
patrons perfect sound, and by keeping 
alive the demand for disc productions, so 
will the supply be influenced. — Cine- 
matograph Times, London. 

(In the United States at the present 
time about 20 per cent of the equipped 
theatres employ disc sound systems. — 
Editor.) 



WM. C. ELLIOTT SUCCEEDS 
CANAVAN 

WILLIAM C. ELLIOTT of Cin- 
cinnati has been elected president 
of the I. A. T. S. E. and M. P. 0., 
succeeding William F. Canavan. 

Mr. Elliott has been first vice-presi- 
dent of the organization. 

This move also advances John P. 
Nick to the post of first vice-president, 
and William J. Harper to third vice- 
president. Joseph C. Campbell becomes 
fourth vice-president, and William T. 
Madigan becomes fifth vice-president, 
while Floyd M. Billingsley becomes 
sixth vice-president. 



JANUARY, 1932 



Page 25 



YOU'RE GIVING BIGGER VALUE 
FOR THE SAME MONEY 

X. HE majority of current productions are being photographed 
on Eastman Super-sensitive Panchromatic Negative. Amazing in 
its qualities, limitless in its possibilities, this new film is bring- 
ing you better - directed, better - acted, better - photographed, 
better - finished pictures. In tune with the times, you are now 
able to give your patrons bigger value than ever . . . for the same 
money as before. And that fact is bound to mean better business 
for your theatre. 

EASTMAN KODAK COMPANY 

J. E. Brulatour, Inc., Distributors 

New York Chicago Hollywood 





SUPER AUDIO SYSTEMS 

FOR SOUND DISTRIBUTION 

Complete Sound Systems or Power Amplifiers are offered with 
undistorted power output of 15, 50 or 100 watts or more. 

Rauland Power Amplifiers and Sound Equipment reflect the highest 
quality in design and manufacture behind which is twelve years of 
specialization in the science of audio amplification. 

A typical Sound System for schools having an undistorted power 
output of 15 watts is illustrated which furnishes radio broadcast, 
phonograph, and microphone service to upwards of sixty rooms. 

We welcome the opportunity to supply technical information. Our 
staff of expert engineers are eager to help in any sound problem. 
Write for information. — Now. 

THE RAULAND CORPORATION 

3341 BELMONT AVE. CHICAGO, ILL. 



Page 26 



PROJECTION ENGINEERING 



New Developments 

and 

News of the Industry 



S 



BIG P-A. JOBS TO SAMSON 

The Samson Electric Company, Canton, 
Mass., reports receiving orders for one of 
the largest group address jobs so far 
planned covering the new recreational 
building of Louisiana State University, and 
the Fine Arts Building of Louisiana State 
University, both of these buildings being 
on the campus at Baton Rouge, Louisiana. 

The total net amount of Samson equip- 
ment at contractors' prices used for this 
installation is $51,000.00. Both of these 
installations are very elaborate, particu- 
larly the Fine Arts Building, where they 
have two theatres in the building. There 
are microphones to a total of 24 in the 
installation, most of which are condenser 
microphones. In both installations are re- 
producing microphone pickup, phonograph 
records and radio programs throughout the 
building. In the Fine Arts Building it is 
possible to pick up a program by micro- 
phone in any one of the rooms of the 
building, and transmit it to any or all of 
the other rooms of the building. The 
equipment is all special, and will take ap- 
proximately 3 months to build. 



NEW SOUND HEAD 

The Goodall Electric Company, Ogalalla, 
Neb., announces a new sound head. 

There are no moving parts in this sound 
head, no springs or gates, yet the film when 
passing in front of the light beam main- 
tains a perfect semi-circle, thus keeping 
the film in focus against the light beam at 
all times regardless of how badly buckled 
the film may be. 

By a special arrangement, the film is 
pulled past the sound aperture at a con- 
stant, even speed thus eliminating all "flut- 
ter" and uneven tones. Standard exciter 
lamps of any size are used. A special opti- 
cal system throwing a light beam of .0007 
inches is used. The GM caesium P. E. 
cell is entirely shielded, both electrically 
and from stray lights, by a hollow alumi- 
num cell house in which the P. E. cell is 
always held at the proper tension and po- 
sition. 

Another novel feature is the adjustable 
aperture plate and guide roller making it 
possible to adjust either the film or the 
aperture plate while the equipment is in 
operation. 

CONDENSER MICROPHONE 

The Shure Brothers Company, 337 West 
Madison St., Chicago, with reference to 
their new condenser microphone, state : 

"This instrument is designed to meet 
the most exacting requirements for high 
quality radio broadcasting, sound record- 
ing, and sound measurement tests. Its out- 
standing characteristic is its relatively uni- 
form response to all frequencies from 40 
to 10,000 cycles. In the special design of 
its amplifier are combined the advantages 
of high output level with extreme wealth 
of richness in tone quality. Its reproduc- 
tion is so realistic as to make it difficult 



for even the trained ear to discern the use 
of the instrument between the original 
source of sound and the listening ear." 
▲ 
MODEL 603 ILLUMINOMETER 

An instrument has recently been devel- 
oped which reads illumination intensities 
with the same ease and facility as reading 
ammeters and voltmeters. This instrument 
was developed by the Weston Electrical 
Instrument Corp. of Newark, N. J. and is 
know as their Model 603 Illuminometer. 

It consists of an indicating instrument 
and a light target assembled in a portable 
case. The light target is on the end of a 
flexible cord so that it may be placed in 
any position. This light target or search- 
ing unit has two Photronic cell units which 
convert light energy directly into electrical 
energy without the use of batteries or 
other auxiliary voltage. They maintain 
constant output over long periods of time 
and there is no dark current. The output 
from the Photronic cell units is consider- 
able, allowing the use of a rugged porta- 
ble instrument calibrated directly in foot- 
candles. 

There are three ranges on the instru- 
ment, namely 10, 50 and 250 foot-candles. 




A range changing switch is provided for 
the selection of the desired scale. Other 
combinations of ranges are being added to 
the line and will be available shortly. The 
light target may be placed at a distance 
from the" observer so that shadows and 
lights reflecting from light clothing will 
not cause errors in readings. Light may be 
read from all angles and the light target 
may be placed in relatively inaccessible 
places, in show cases, windows, etc. The 
absorption of light by painted walls, screens, 
draperies, etc. can be measured directly by 
turning the light target so that it faces 
the surface. 

A 

MOVABLE SWITCHBOARD FOR THEATRES 

One of the difficulties the smaller theatre 
producers often meet with when leasing a 
theatre or auditorium for their season's 
presentation is either the absence of, or an 
inadequate, switchboard installation with 
proper dimmer equipment. To provide ad- 
ditions to the existing equipment or order 
the erection of a new switchboard not only 
puts an added burden of expense upon the 
producer, but the very nature of the equip- 
ment is such that it becomes a fixture of 
the building under the terms of the lease, 



and the tenant must leave it behind when 
he moves out at the close of the season. 

This disadvantage has been overcome by 
a semi-portable switchboard built by Kliegl 
Bros., New York — which while having all 
the gradations of control to be found in 
permanent equipment, as well as being ex- 
tremely flexible in the matter of circuit 
connections and combinations, can also be 
removed from the premises as a complete 
unit, and used again at the next location 
by simply connecting the feeder cable to 
the source of supply. 

While primarily intended for little the- 
atre producers, this semi-portable switch- 
board may also be used to advantage by 
national exhibitors, novelty display adver- 
tisers, and others requiring equipment of 
this character — its design being modified 
to meet their particular needs. 



NEW AMPLIFIER TUBES 

Jenkins and Adair, 3333 Belmont Ave., 
Chicago, have brought out three new 
tubes suitable for the Standard C amplifier 
panel, C monitor panel and C volume in- 
dicator panel. These tubes are particularly 
adapted to speech frequency amplification. 
The characteristics of these tubes are: 

Fila- Fila- 

ment merit Plate Plate 

Current Volts Plate Current Hesist- 

Type Amp. V. Volts M.A. Mu ance 

J&A 102 .98 2/2.5 135 V. .5/1.0 28/30 50.000 

.7&A 205 1.6 4.5/5 350 Max. 20/35 6.5/7 3,500 

J&A 211E 2.5 10 750 Max. 65 12/14 4.000 



ARCTURUS REDUCES PRICE OF SCREEN- 
GRID TUBE 

Effective December 14 the Arcturus 
Radio Tube Company, Newark, N. J., 
announced that it reduced the list price 
of the Type 122 d-c. screen grid tube to 
$3.00. 



CONDENSERS WITH 2000 VOLTS D-C. TEST 

1, 2 and 4 microfarad condensers which 
stand a 2,000 volts d-c. test, 1 to 4 micro- 
farad condensers of 1,500 volts d-c. test, 
and .01 to 4 microfarad condensers which 
pass a 500 volt of d-c. test are being mar- 
keted to the sound laboratories, studios 




and projection booths by Morrill and Mor- 
rill, 30 Church St., New York. The com- 
pany also handles a dependable line of 
a new type of carbon resistors. 



JANUARY, 1932 



Page 27 



For Your Own 



Protection ♦ ♦ ♦ 



For your convenience National 
keeps a large stock of GENU- 
INE repair parts on hand all 
the time. Day or night service 
— right at your telephone. 



demand GENUINE 
Repair Parts 

The projectionist who insists on genuine repair parts for the 
maintenance and repair of his equipment is wise. It's a sate plan 
to follow. The projectionist is, or certainly should be, responsible 
for results in. the projection room. He takes a long chance when 
he repairs with bootleg parts, which have been known to seriously 
affect the performance of the entire mechanism. Play safe and 
fair with yourself, your employer and the manufacturer by always 
saying "No" to the seller of spurious parts. 

NATIONAL THEATRE SUPPLY COMPANY 





n 



Get Aboard the 

Large Picture 

'Xrend with 

Super Cinephor! 





There's no denying the trend to larger pictures, and their 
appeal to the public must be recognized by every theater 
operator. The modern theater must be prepared for wide 
film and wide screen requirements while continuing to give 
the best in the way of standard screen projection. 

Super Cinephor and the new B&L Condensing System meet 
this demand exactly. Super Cinephor is the first true anastigmat. 
Corrected for wide angle projection, and made in focal lengths 



down to 2 inches, it produces sharp, clearly defined images to 
the very margin of the screen. 

It distributes the light so efficiently that even on wide or giant 
screens the image has exceptional brilliance. It's got a projection 
punch that means profits. Are you missing this opportunity to 
make a moderate investment that will put your showings out in 
front? 

Catalog E-16 gives complete description and valuable infor- 
mation for the projectionist. Bausch & Lomb Optical Co., 
681 St. Paul Street, Rochester, N. Y. 



BAUSCH & LOMB 



Page 28 



PROJECTION ENGINEERING 



CAPACITORS AND RESISTORS 

The Federal Telegraph Company, 200 
Mount Pleasant Avenue, Newark, N. J., 
announces a new line of wire wound vi- 
treous enamelled resistors, and a line of 
paper-wax and paper-oil capacitors. Harry 
C. Gawler, is sales manager of the com- 
pany. Mr. Gawler was formerly with the 
De Forest Radio Company at Passaic, N. J. 
▲ 

MALLORY PURCHASES YAXLEY 

On October 15, 1931, P. R. Mallory & 
Co. Inc., Indianapolis, pioneers in the de- 
velopment of dry electrolytic condensers 
sold under the trade name "Elkon," 
purchased the Yaxley Manufacturing 
Company of Chicago. The "Yaxley" name 
has been for twenty-five years identified 
with a line of quality electrical parts 
known throughout the world. The Yax- 
ley company will receive full benefit of 
the Mallory company's engineering, chemi- 
cal and metallurgical facilities. 

Ray F. Sparrow will remain in his 
executive capacity as sales manager, in 
full charge of service in all its aspects 
to the many Yaxley customers. 

RCA-RADIOTRON COMPANY, INC., 

AND E. T. CUNNINGHAM, INC., 

ANNOUNCE PHOTOTUBE 

RCA-Radiotron Company, Inc., and E. 
T. Cunningham, Inc. have recently made 
available to experimenters a phototube des- 
ignated as Radiotron RCA-868 and Cun- 
ningham CX-868. 

This tube is of particular interest because 
of its use for sound movies in the home 
and because of its adaptability to many 
novel experimental uses with light. 

This phototube is an electronic device 
and consists of two electrodes enclosed in 
a glass bulb. One electrode, the cathode, 
has a sensitized surface which emits elec- 
trons when the surface is exposed to light. 
The other electrode, the anode, acts as a 
collector for these electrons when a bat- 
tery is connected across the cathode and 




View, showing 
arrangement of 
cathode and 
anode, of RCA- 
868 and CX-868 
phototubes. 



anode terminals. The anode or collector, 
is, of course, connected to the positive ter- 
minal of the battery so as to assist the flow 
of electrodes from the cathode to the an- 
ode. This circuit is not unlike that of 
the usual vacuum tube except that the 
electrons are emitted from a light sensi- 
tive surface instead of from an incandes- 
cent cathode. 

The current flowing in the phototube 
circuit is dependent on the amount of light 
received by the sensitized surface. The 
phototube, like a vacuum tube, has prac- 



tically no time lag, so that variations in 
light intensity instantaneously affect the 
amount of current passing through the 
tube. 

The cathode of the 868 is a semi-cylin- 
drical sheet of metal and is coated with a 
thin film of caesium. The anode or col- 
lector consists of a small wire placed in 
the axis of the cathode surface. A small 
amount of gas is used in this tube to pro- 
duce high sensitivity. 

The 868 is sensitive to light over the en- 
tire visible spectrum and also to radiation 
in the near infra-red zone. The large re- 
sponse in the red and infra-red region 
makes this tube very well adapted to sound 
reproduction and television work where 
incandescent lamps are used for light 
sources. 

Ordinarily, the output of an 868 requires 
further amplification. This may be ac- 
complished by a suitable tube amplifier re- 
sistance coupled to the phototube circuit. 



CONDENSER MICROPHONES 

Three new models of condenser micro- 
phones for every requirement of broad- 
casting, recording and public - address 
operation are announced by the Gates 
Radio and Supply Co., Quincy, Illinois. 
Bulletin No. 6 describes these new units. 



RESISTORS 

Ohmite Manufacturing Company, 636 N. 
Albany Avenue, Chicago, announces the 
publication of a new stock list, Bulletin 
No. 10, which illustrates and describes 
Carbohm and Wirohm resistors. 

The bulletin lists 75 different values of 
carbon resistors in both 1 watt and H watt 
sizes, as well as 42 different values of wire- 
wound resistors. These wire-wound resis- 
tors, called Wirohms, are of special inter- 
est because of their high wattage rating 
and very small size. 



A NEW PHOTO-TUBE 

An announcement from the Cable Radio 
and Tube Corpn., 84 N. 9th Street, Brook- 
lyn, N. Y., reads : 

"Speed Fotoelectric tubes are the cul- 
mination of years of experimental research 
work conducted both in this country and 
abroad. 

"They have two zones of maximum sen- 
sitivity. The first extends into the near 
ultra-violet, peaking at approximately 3500 
Angstroms but falling off rapidly below 
this point due to glass absorption. 

"The second zone has a much broader 
peak extending into the red and infra-red 
region and peaking from 7500 to 8500 
Angstroms. The great sensitivity at this 
point taken in conjunction with the fact that 
radiation from an incandescent lamp source 
is largely in this region gives a large over- 
all sensitivity. . 

"Because of trie uniformly high sensitiv- 
ity brought about by a special cathode 
treatment, it has been found practical to 
supply Speed Fotoelectric tubes with a 
somewhat higher ionizing voltage than that 
generally obtainable. This allows increased 
latitude in pickup adjustment, in addition 
to minimizing tube damage from accidental 
ionization during adjustment, while still 
retaining gain equivalent to that obtain- 
able from other photoelectric tubes at sim- 
ilar operating voltages. 

"These photoelectric tubes have an 
ionization voltage of 108 ± 8 volts and 
are designed for operation at 90 volts. 
However, tubes having other operating vol- 
tages are regularly stocked and may be 
obtained without delay. 

"No photoelectric tube should be oper- 



ated at voltages above ionization for more 
than a few seconds, although speed Foto- 
electric tubes will safely handle hundreds 
of microamperes for short periods without 
serious damage. 

"It is recommended that these tubes be 
protected against intense illumination or 
excessive heat, to avoid shortening of life, 
under light of moderate intensity they will 
retain their sensitivity for long periods of 
time. 

"While the gas-filled Fotoelectric tube is 
supplied as standard equipment, vacuum 
Fotoelectric tubes may be obtained to spe- 
cial order. Their sensitivity, however, is 
only a fraction of that obtained from gas- 
filled tubes and thus their use is restricted 
to applications where extreme constancy is 
of prime importance, such as quantitative 
measuring, etc. 

"Particular attention has been given in 
the design of these tubes to a sturdy an- 
chored construction, insuring noiseless non- 
microphonic operation, free from transient 
disturbances. 

"Speed Fotoelectric tubes, without ap- 
preciable loss of sensitivity, have an ex- 
pected life in excess of one year, provided 
they are not subjected to abuse. They are 
guaranteed against defects in workmanship 
or material for a period of six months from 
date of purchase." 



NEW BALL-BEARING MOTOR WITH 
BUILT-IN SPEED REDUCER 

A new line of fractional-horse-power 
motors with worm-gear speed reducers has 
been developed by the Bodine Electric 
Company, 2264 W. Ohio St., Chicago, 111. 
These motors are built into the new Bodine 
Type N-5 frame, which is of three-piece 
construction with pleasing contour lines. 
The ventilating ducts and fan have been 
enlarged and the ratings increased. 

Gear reductions of 10-1, 20-1, and 40-1 
are available, which afford slow shaft 
speeds of 28, 43, 56, 86, 112, and 172 r.p.m. 
at standard motor speeds of 1125 and 
1725 r.p.m. The speed reducer consists of 
a separable nitralloy steel worm and an 
oversize bakelite gear, mounted in a grease- 




tight housing forming an integral part of 
the end shield of the motor. 

Double ball bearings absorb the end 
thrust on the rotor shaft and preserve 
alignment of the gears after long service. 
The ball bearings are packed in grease be- 
fore the motor is shipped and require no 
further attention for several years. The 
slow-speed shaft runs in leaded bronze 
bearings with wool-packed lubrication. 

These motors are rated from 1/20 to Y% 
h. p., and they are available in two types : 
Type NSIR for alternating current, and 
Type NSHR for direct current. 



FELT FEET DON'T SCRATCH 

The T. R Brawley Felt Company, Inc., 
279 20th St., Brooklyn, N. Y., manufacture 
felt feet for four types of chassis, cabinet, 
loudspeaker, amplifier and other assemblies. 
Samples will be sent upon request. 



JANUARY, 1932 



Page 29 



The key to better 
sound projection 




— for operators 
on all types of 
equipment. 



This new book makes easy the 
successful operation and repair 
of all makes of sound projec- 
tion apparatus, by explaining 
simply and clearly the funda- 
mentals of sound reproduction 
and projection upon which all 
types of equipment are based. 

— Just published — 

PROJECTING 
SOUND PICTURES 

By AARON NADELL 

Publix Theatre Corporation; Formerly of Electrical 
R^seTch Products, Inc. 

265 pages, 6x9, 100 illustrations, $2.50 

Whether you are a sound projectionist by profession or only 
occasionally work on sound equipment, you will find this an 
invaluable handbook, presenting the fundamentals that will 
enable you to understand the problems arising in the oper- 
ation and repair of all makes of sound equipment. 

Beside explaining the theory of 
sound reproduction on disc and 
film, the book takes up each 
unit of the sound equipment, 
explaining the underlying the- 
ory and principles, showing by 
description and illustration how 
these are applied in various 
types of apparatus. 
At the same time the author 
points out the common trou- 
bles associated with each unit 
and the remedies for them. In 
addition a chapter is devoted to 
precautions to take to prevent 
trouble and another on tracing 
trouble and correcting it. 
Because of its value in forming a clear understanding of the 
operation of tubes and photo-electric cells, the electron theory 
of the nature of currents is explained, in a surprisingly sim- 
ple way. The book is thorough, authoritative, practical. It 
minimizes constructional details of various makes of equip- 
ment in favor of the basic facts that will enable you to 
understand all makes. 

See it 10 days free — Send this coupon 



Mc Graw-mill 



FREE EXAMINATION COUPON 

i 

| McGraw-Hill Book Co., Inc., 330 W. 42nd St.. New York. N. Y. 

Send me Nadell— PROJECTING SOUND PICTURES, $2.50 for 

10 days' free examination. I will return the book in 10 days or 
remit for it then. 



NOTE: Questions, 
with answers, at the 
end of each chapter, 
a Precaution Index, 
and a Trouble Index, 
form the equal of an 
invaluable "trouble- 
shooting" chart; a 
quick means of look- 
ing up the cause and 
cure of every projec- 
tion trouble. 



Name 

Address 

City and State. 

Position 

Company 



Here's 
"PROF 

for You . 



T 




fees' 



The New Webster-Chicago 

Midget Portable 

Public Address System 

Think of it — a complete powerful voice or 
music system that you can carry in one 
hand! And priced so low that it will pay 
for itself in a few evenings' rentals. 

It is well built, practical, dependable. One 
carrying case includes the complete outfit 
consisting of: 

(1) Powerful push-pull amplifier employ- 
ing screen grid and pentode tubes. 

(2) Phonograph turntable, driven by syn- 
chronous motor — plays either 33 1/3 
or 78 R.P.M. records. 

(3) One microphone. Control provides 
for mixing of phonograph and micro- 
phone, allowing musical background 
for vocal announcements. 

(4) One high-grade dynamic speaker. 
Provision is made for plugging in 
one additional speaker. 

(5) 15 ft. of microphone cable. Polar- 
ized plugs prevent possibility of 
wrong connections. 

(6) 30 ft. of speaker cord. 

(7) Complete power supply for I 10 or 
220 volts, 50-60 cycle alternating 
current. 

Write for descriptive bulletin So. 115. 

WEBSTER M 
CHICAGO 

The WEBSTER Company 

Sound Amplifiers for Every Purpose 

854 Blackhawk St. Chicago, III. 



Page 30 



PROJECTION ENGINEERING 




For perfect results 
in your recorder 
try this improved 
glow lamp. 

Every recording is 
noiseless when 
made with a Cine- 
glow 3-element. 

Prices on Request. 



Every 

CINEGLOW 

Recording 
is noiseless 

Gineglow Re- 
corders are per- 
forming satisfac- 
torily in studios 
throughout the 
world. The am- 
plifier is licensed 
and is the last 
word in modern 
efficiency. Learn 
more about Gine- 
glow Recorders. 



Any Special Equipment Made to Order 
Single System Double System 

Newsreel Type Studio Type 

Write, Wire or Cable for Particulars 

Cineglow Sound Systems 

MANUFACTURED BY 

BLUE SEAL SOUND DEVICES, Inc. 
130 West 46th St., New York City 

Cable Address: SOUNDFILM, New York 
European Representative: N. V. World Industrial Co., Hague, Holland 



Your Customers 
Will Welcome — 

Brawley Felt Feet are being used by progres- 
sive manufacturers in the Sound and Light 
Industries — giving these manufacturers an 
impressive sales talking point. Let us advise 
you in the case of your products. 

Machine screw, nail, 

rivet and reverse 

rivet types. 



®lLi\L 




IS 



MC 



Free sample o\ any 
type you want 




IT. R. BRAWLEY FELT COMPANY, INC. 

279— 20th Street, Brooklyn, N. Y. 



For Best Results — 

You Need the Best Materials! 

SIEMENS & HALSKE 

Condensers and Resistors are 
standard with exacting sound 
engineers the world over. 




Sole U. S. A. 
Distributors 



Condensers Condenser Kits 

Resistors Resistor Kits 

Microphones Mike Buttons 

Interference Eliminators 

Write for Bulletin P 

Morrill & Morrill 

30 Church St., New York City 




Sell Portable Talkie Sound on Film 

To Theatres, Schools, Churches, Clubs, etc. 

Write for Manufacturers Prices on Soundheads, 
. Photocells, Optical Systems, Rectifiers, Ampli- 
fiers, Horns, Faders, Synchronous Motors, Pro- 
jectors, Lamphouses, Screens, Microphones, etc. 
Used and rebuilt equipment supplied. 



SOS Corp., Dept. PE, 1600 B'way, N. Y. C. 

Cable Address: SOSOUND 



WAX RECORDING EQUIPMENT 

For Sound Pictures, Broadcast, and 
Commercial Recording 

R. W. NICHOLLS 

119-28 27th Ave., College Point, L. I., N. Y. 



PROJECTION ENGINEERING 

has the largest paid 
circulation of any 
technical publication 
in the projection or 
theatrical fields. 

See latest report of the 
Audit Bureau of Circulations 
and Standard Rate and Data 



INDEX TO ADVERTISERS 



Amplion Products Corp 5 

B 

Bausch & Lomb Optical Co 27 

Bell Equipment Corp 3 

Blue Seal Sound. Devices, Inc 30 

Brawley Pelt Co., Inc., T. R 30 



Cameron Publishing Co 32 

B 
Eastman Kodak Co 25 



F 

Forest Electric Corp Second Cover 

L 
Leeds Radio Co 31 

Mc 
McGraw-Hill Book Co 29 

M 
Morrill & Morrill 30 

N- 

National Carbon Co., Inc 1 

National Theatre Supply Co 27 

Nicholls, R. W 30 



Racon Electric Co., Inc Back Cover 

Rauland Corporation, The 25 



Samson Electric Co 6 

Shure Bros. Co 31 

Silver-Marshall, Inc Third Cover 

S.O.S. Corporation 30 

Strong Electric Co., The 31 



W 

Weber Machine Corp 31 

Webster Company 29 



JANUARY, 1932 



Page 31 



General Radio 
Volume 
Control 

employing an entirely 
new circuit and 
mechanical construction 
at low cost. 





Contacts of Advance metal (using same wire for its resis- 
tance). Noise level is low and may be used in circuits at 
levels as low as 60 to 80 decibels without introducing noise 
in the circuit. 



Type 
652 M.A. 
652 M. B. 
652 M. C. 



Impedance 

50 ohms 

200 ohms 

500 ohms 



Price 

$12.50 
12.50 
12.50 



Let us assist you in your requirements 



r 




-nheHome of RADIO. J 

45 VESEY STREET NEW YORK CITY 




IIII I IIIIII M I , III M i ll M ll i lll h ■H. ll III I i iiiiiiiiiiiiiTniiiiiiiiiiiiiiitM i 



Investigate These Sound Heads 
for Simplex or Powers — 

=SYNCR0FILM "B"= 




Designed especially for 
small theatres where low 
priced equipment is de- 
sirable. 

Compact and sturdy 
in construction, sim- 
ple to operate, per- 
fect in efficiency. 
Smooth, quiet, posi- 
tive drive assures 
even tone quality 
without distortion. 
Furnished complete 
and include all nec- 
essary attachments 
for projector. 



EASY TO 
INSTALL 



$275 



complete 
per pair 



MONEY BACK 
GUARANTEE 



WEBER MACHINE CORP. 

I 59 RUTTER ST. ROCHESTER, N. Y. 

Export Dept.: 15 Laight St., New York City 



SHURE 

CONDENSER 
MICROPHONE 



ANNOUNCING AN EX- 
CEPTIONAL INSTRUMENT 

The product of years of devel- 
opment and laboratory experi- 
mentation. Designed to meet 
the most exacting requirements 
for high quality radio broad- 
casting, sound recording, sound 
measurement tests, and public 
address work. Frequency re- 
sponse remarkably uniform com- 
bined with high output level 
and extreme wealth of richness 
in tone quality. 

WRITE FOR DETAILS 

Send for descriptive literature 
giving full details regarding the 
fidelity of the condenser head, 
the special 2-stage amplifier 
built into the case, and all 
other electrical and physical 
characteristics. 

GUARANTEE 

Each instrument is backed by a liberal 
one year guarantee which gives assurance 
of the high quality in spite of the low 
price. 



SHURE BROTHERS COMPANY 

. Manufacturers-Engineers 
S.N. SHURE. Pre.. 

337 WEST MADISON ST CHICAGO. ILLINOIS 






Demanded 1 1 ! 




Portable Type 
Reflector Arc Lamp 



Designed for projection of 35 or 16 mm. fijm. 
Especially valuable with sound equipment, giving 
a brilliantly illuminated picture as large as 8 to 
12 feet wide, even on porous screens. 

Operates from any lamp socket with current 
from S to 16 amps. 

Weighs less than 25 lbs. Size 19" x 12" x 10". 

Extremely simple in operation. 

A new rectifier unit as companion to this lamp 
is also available. 

For Sale by Independent Supply Dealers 

<3he Strong Electric Corporation 

2501 LAGRANGE ST., TOLEDO, OHIO 

Export Office: 44 Whitehall St., New York, N. Y. 



Page 32 

Here's News 



PROJECTION ENGINEERING 



Any Cameron Book Sent You for 

A ONE DOLLAR BILL 




HOTIONPICTlltf SMNDPICTURIS J 

5222 «•*— * mm 

smrun „ CA MER0N'S 
SOUND ENCYCLOPEDIA 

ON 
WllDMOIIOdPlCtllMS 



JA M1S R . QMERON CAMERON &RIDER 



F °URTH EDITION 



JAMESR-CAMHR"" 



PRICE 6^0 PRlCE7«fo PRICE5£ro p R1CE 3fB 
c *MfR0N PUBLISHING CO. ^hERON PUBLISHING Cft C/w 



We are now offering for the first time the 
famous Cameron books on an easy payment 
plan. Remember these books carry the en- 
dorsement of the United States Govern- 
ment and every trade paper published in 
this country. The Cameron books have 
been used by the motion picture industry 
throughout the English speaking world for 
Fourteen Years and are the standard works 
on the subject. 

These four books make up a complete 
library on the making and showing of 
sound motion pictures and equipment nec- 
essary for same. Fill in the coupon. Send 
us ONE DOLLAR for each book you order. 
We'll see they are mailed you by return. 



ENCLOSE ONE DOLLAR FOR EACH BOOK ORDERED 



CAMERON PUBLISHING COMPANY 
WOODMONT, CONN. 

Enclosed find the sum of send me the books I have checked below, I agree to pay mailman 

$1.98 for each book on delivery, plus postage, the balance I will send you in three equal monthly 
instalments. 

NAME I ADDRESS 

EMPLOYERS NAME 
CITY & STATE & ADDRESS 



SOUND PICTURES TROUBLE SHOOTER'S MANUAL.... 7.50 
CAMERON'S ENCYCLOPEDIA SOUND PICTURES 3.50 



MOTION PICTURE PROJECTION 6.00 

MOTION PICTURES WITH SOUND 5.00 




COVERING A 
4000 SEAT HOUSE WITH 



A PORTABLE AMPLIFIER 



Leo Salkin, expert show- 
man and manager of The Ori- 
ental, one of Chicago's great 
Loop theatres, wanted a stunt 
for one of his shows. He 
needed a microphone offstage, 
a speaker in an ordinary radio 
cabinet and an amplifier with 
sufficient "bang" to cover his 
4,000-seat house. 

An S-M 686 Portable Ad- 
dress System did the job with 
power to spare. It is an ideal 
showman's kit. Can be used 
to announce coming shows on 
the sidewalk or in the lobby. 
Can be used for voice with an 
organ and innumerable other 
ways. Also for banquets, 
speeches, dances, etc. 




The Famous Oriental Theatre in the Loop, Chicago 
Leo Salkin, Manager 




Silver-Marshall now offers Power Amplifier panels 
and equipment for any class of service or type of 
system. 

Write to Mr. Gray for literature and the new Novem- 
ber catalog. 



The 686 Portable Address Unit weighs 
75 lbs. complete, contains a five-tube 
push-pull Pentode Amplifier having a 
gain of 90 DB and an undistorted output 
of 7 to 8 watts. It is entirely free from 
hum. Its fidelity curve shows a variance 
of only 2 DB, plus or minus, from 40 to 
8,500 cycles. 

Built into the case (half of which 
serves as an excellent baffle) is a 10' 2" 
S-M 855B Electro Dynamic Speaker with 
25 feet of cord. The speaker may, how- 
ever, be operated at any distance from 
the amplifier. 

A double-button microphone completely 
mounted and with 12 feet of cord is in- 
cluded. 

Cost (110-120V, 50-60 cvcle), complete, 
with tubes, etc., $119.70 net. 

25 cycle slightly higher. 



SILVER-MARSHALL, Inc. 

6401 West 65th Street, Chicago 

Canadian Division: 75 Sherbourne St., Toronto 

Export Division: 41 Water St,, New York City, U. S. A. 



H V* * M Vi 1 0j i .* HAW* 



rr'nunifffiii 



When Better Speakers A re Made 

they will be 
made by 




The finest sound installations employ RACON HORN 
SPEAKERS and UNITS because of their outstanding perform- 
ance, efficiency, and long life of uninterrupted service. 



RACON now offers 5 new, im- 
proved types of dynamic speaker 
units. Wider frequency response 
[particularly on highs) — and re- 
duced prices are the more impor- 
tant features. There is a RACON 
HORN and UNIT for 
purpose. 



every 



RACON urges you to see, hear 
and learn more about these new 
speakers and units. The best sound 
installation will be improved by 
RACON or it will cost you 
nothing. 



Theatres Churches Schools 
Hotels Airports Parks 

have learned that RACON HORNS and UNITS are better 

RACON HORNS AND UNITS ARE 

▲ COVERED BY U. S. PATENTS NOS. -A, 

1,507,711 1,501,032 1,577,270 73,217 73,218 ^^ 

1,722,448 1,711,514 1,781,489 1,832,608 

1,834,327 1,835,739 

Write for Racon's Catalog P. E. 1. Catalog and price list will be 
cheerfully sent on request. 

RACON ELECTRIC CO., Inc. 



FACTOR 

18-24 WASHINGTON PLACE 

TORONTO, CANADA 



E S 



NEW YORK CITY 
LONDON, ENGLAND 






New Type Small Theatre Horn No. 2115 



New Type Cone Speaker Baffle 




New Super Giant Dynamic Unit 




New Baby Dynamic Unit 




THIS ISSUE 



IONALIZING TALKING 
PICTURES 

y Or. Alfred Gradenwita 

AUSES OF FILM MUTILATION 
By Sylvan Harris 

OUTPUT STAGE IN SOUND 
TRANSMISSION 

By Gilbert Smiley 

OF SOUND RECORDS 
By Charles Felstead 

BUTTONHOLE MICROPHONE 



Fourth Year 
Of Servii 





IJ LUW ITIIT1 


* 


MTTuTSWff 


II 


/ OuND -•- VI/UAL 

■ 




. 






Photo Courtesy Rola Company 
Public-Address on American Troop Transport. 



^H 



journal of Ine Sound and Light Prqjecf ion Industries 




FEBRUARY, 1932 



ma 



Real Sensitivity— Greater Naturalness 
Freedom from Battery Bondage 



with 



Samson Condenser Microphone & Power Supply 




.... These features are obtained for you without 
undue noise level encroachment or a hum level that 
approaches audibility. 

The Samson Condenser Microphone yields the highest 
possible interest on your sound investment through 
coordination of engineered design — and precision con- 
struction of the finest materials to get a maximum of 
fidelity and a minimum of internal noise level. 



Bullet Type 




Desk Type 



Its use is indicated where carbon-button 
microphones are inadequate for the instal- 
lation in question. The light weight, com- 
pact, Samson Condenser Microphone Power 
Supply unit, type S. U. 42, is 110 volt, 60 
cycle, a. c. operated and does away with all 
batteries when used with a Samson Con- 
denser Microphone. 

Pioneers in the a. c. operation of Micro- 
phones and associated sound system equip- 
ment, Samson is proud to announce this 
Condenser Microphone Power Supply as a 
further step in the liberation of the sound 
reproduction art from battery bondage. 
Send for P. E. No. 17 for complete details 
on these and other new products. 




Power Supply Unit 



AMPLIFIER DIVISION 




\amson 



feToy 



Manufacturers since 1882 



Main Office: 
Canton, Mass. 



Factories: Canton and 
Watertown, Mass. 



FEBRUARY, 1932 



Page I 





BELL 35 M.M. SOUND on-FILM PROJECTOR 

A A TRULY PROFESSIONAL sound-on-film projector that is in the fullest sense of the word A 

Ll portable. The entire equipment disassembles into compact, easily handled units, no one 
# \ of which weighs over 65 lbs. Can be easily transported in the back of a standard sedan 
automobile and handled by one man. 

BELL Equipment is easily in a class by itself in such important features as ease and certainty 
of control, freedom from fire hazards, full automatic lubrication, quality of sound projection, 
compactness and portability. 

Designed by acknowledged experts 1 , with a full knowledge of the rigid requirements in tho 
portable field, BELL Equipment is far in advance of all competition in adaptability to every 
reasonable condition possible to encounter. 



THE BELL SINGLE or Industrial Unit is provided with 1,000- 
ft. or 2,000-ft. reels and magazines, and consists of one 
right projector, 5-stage Amplifier and Uni-Remote-Control, 
mounted in metal case and two dynamic speakers mounted 
in carrying case. The total weight is 150 lbs. complete 
with legs, carrying cases and accessories. Price, $1,250 
complete. 

THE BELL TANDEM UNIT is designed in right and left 
projectors and can be set up with 18 in. between lenses 



or 20 ft. apart. The Uni-Remote control of exclusive BELL 
design provides smooth "changeover" and individual opera- 
tion of either projector. The BELL Tandem Unit consists 
of one right projector, one left projector, 5-stage amplifier 
and Uni-Remote-Control mounted in metal case and 2 
Dynamic Speakers mounted in carrying case. The total 
weight is 215 lbs. complete with legs, carrying cases and 
accessories. Price, $2,150 complete, F.O.B. Factory, Derby, 
Conn. 



Write for Descriptive Literature 



Demonstration by appointment at our New York Showroom 



BELL EQUIPMENT CORPORATION 



Phone: BRyant 9-9890 



Suite 605 .. . 729 SEVENTH AVENUE . . . NEW YORK 

FACTORY: Hershey Metal Products Co., Derby, Conn. 



Projection 

Engineering 

Member, Audit Bureau of Circulations 



Donald McNicol 
Editor 

Jas. R. Cameron 
Associate Editor 

Ulmer G. Turner 
Western Editor 

F. Walen 
Managing Editor 



Sound Pictures 

Visual Projection 

Sound Recording 

Audio Amplifiers 

Public-Address Systems 

Photography 

Facsimile Recording 

Television 

Photo-Voltaic Cells 

Circuit Measurements 

Automatic Music 

Acoustic Engineering 

Radiant Energy Devices 

Electric Recording 

Phototubes 

Home Talkies 

Theatre Engineering 

Amplifier Tubes 

Sound Reproducers 

Screen Engineering ■ 

Electric Power for Projec- 
tion 

Recording Studio Engi- 
neering 

Location Sound Equipment 

Rectifier Tubes 

Industrial Tube Applica- 
tions 



Vol. IV 



FEBRUARY 
1932 



Number 2 



Contents 



Editorial 

Internationalizing Talking Pictures. 

By Dr. Alfred Cradenivitz 

Causes of Film Mutilation By Sylvan Harris 

The Output Stage in Sound Transmission. 

By Gilbert Smiley 

Voice Training on a Scientific Basis 

Types of Sound Records By Charles Felstead 



PAGE 

4 



9 
14 
15 



Commercial 1 6 MM. Sound-On-Film 17 

The Buttonhole Microphone By W. C. Jones 1 9 

Talking Picture Productions for College Alumni. ... 20 

Standards for Electrical Reproduction and Recording 

of Sound 22 

Fader Attenuation Circuits for Public Address and 

Recording By W. S. Parsons 24 

Departments 

New Developments and News of the Industry 26 

Index of Advertisers 30 



Bryan S. Davis 
President 

James A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

52 Vanderbilt Avenue 

New York City 



E. M. Bacon 
Advertising Manager 

J. E. Nielson 
Circulation Manager 



Chicago Office— 333 N. Michigan Ave.— Charles H. Farrell, Mgr. 

St. Louis Office- 505 Star Bldg— F. J. Wright. 

Kansas City Office— 306 Coca Cola Bldg— R. W. Mitchell. 



San Francisco Office — 155 Sansome St. — R. J. Birch. 
Los Angeles Office-r-846 S. Broadway— R. J. Birch. 
New Zealand— Tearo Book Depot— Wellington. 
Australia — McGill's Agency — Melbourne. 



Entered as second class matter August 15, 1931, at the post office at New York, N. Y., under Act of March 3, 
1879. Yearly subscription rate $2.00 in U. S. Yearly subscription rate $3.00 in Canada and foreign countries. 



FEBRUARY, 1932 



Page 3 



STOPS 

BOX-OFFICE 

REFUND! 




WESTON MODEL 564 

• Recently ... a big Mid-western city ... a crowded 
House . . . middle of the evening show . . . suddenly the 
Sound went dead. 

• Frantic projectionists inspected connections, switches, 
tubes . . . two minutes . . . three . . . five. Impatient, the 
audience began to file out. Ticket refunds were de- 
manded and given. Eight minutes . . . ten. Still no 
Sound. Then a hurry call for the manufacturer's 
service man. 

• Seven minutes later he arrived. His handy, portable 
Volt-ohmmeter went to work. In three minutes the 
show was on! The cause of the twenty-minute break- 
down had been located and fixed . . . Another example 
of the importance and value of portable testing instru- 
ments in the projection booth. 

• The modern projection booth must be equipped with 
adequate portable testing instruments to prevent break- 
downs — costly interruptions of performances. By check- 
ing circuits, tubes, batteries and other apparatus reg- 
ularly, failure is anticipated, reproduction quality 
maintained — replacement or repair effected before 
failure occurs. Good instruments are insurance — your 
protection from breakdowns. 

• For this work Weston recommends Model 564 Volt- 
ohmmeter or Model 595 Sound Equipment Tester. 
Complete information about these instruments— vitally 
important in modern projection maintenance — will be 
gladly sent on request. 

WRITE TODAY! 



ELECTRICAL INSTRUMENT CORP. 



608 FRELINGHUYSEN AVENUE . . . NEWARK, N. J. 



FOREST 

RECTIFIERS 

^\i — ■ — ^/A 




GOOD PROJECTION 



Forest Rectifiers are de- 
signed and constructed 
to meet the need for 
dependable rectification 
equipment. They are 
silent, and may be oper- 
ated in the projection 
booth with sound ap- 
paratus. 

The Forest M.P. 25-25 Rectifier, illus- 
trated above, supplies steady, direct 
current of from 15 to 25 amperes to 
two projectors continuously. 



Announcement of the 

NEW 3-PHASE RECTIFIER 

will be made next month 



All Types of Rectifiers in 15 amps., 25-25 amps., 
30, and 65 amps., Sizes 

Write Today for Literature! 

Forest Electric Corp, 

New and Wilsey Sts., Newark, N. J. 



Edit 



i a 



FEBRUARY, 1932 



NO longer ago than eigh- 
teen months he was a 
SYSTEMS sanguine manufacturer who 

announced that 50 watt am- 
plifiers for sound systems were practicable, 
with passable loudspeaker reproduction. To- 
day, there are installations going in with 
powers of 100 watts and higher. This is real 
progress along lines which vastly extend fields 
of application for sound transmission and re- 
production systems. 

While 15 watt to 50 watt installations are 
yet largely in the majority, serving short range 
needs in interiors, the availability of higher 
powers broadens usefully the utility of audio 
systems — in very larg'e auditoriums, from air- 
planes, dirigibles, at airports, stadiums, parks, 
race tracks, skating rinks, ball parks, dance 
halls, for army and navy uses, on ship board, 
in factories, and in no end of locations hereto- 
fore thought to be of such large areas as to 
necessitate the installation of numerous units 
when amplifiers of lower powers only were 
available. 

No doubt there shall always be conditions 
which will be best served by a properly deter- 
mined distribution of speaker units of 15 to 50 
watts power, but the arrival of amplifier sys- 
tems of the super power order opens up a new 
vista of opportunity for designers of sound 
systems and for installing organizations. 
Henceforth we expect to learn of new applica- 
tions of and new uses for sound systems as 
technical improvement progresses. 



TALKING 
PICTURES 
IN AUSTRALIA 



IT was but a matter of 
time when the enterprising 
Australians would catch up 
with progress in the produc- 
tion of talking pictures. Australians have now 
commenced production of their own talking 
films. The first program of all- Australian 
talkies from the studio of Efftee Film Produc- 
tions, Melbourne, was recently disclosed at the 
Plaza Theatre, and will be screened in the 120 
Hoyts theatres in Australia. With this project 
American film interests are associated. 

In past years desultory attempts were made 
to produce screen presentations, but due to lack 



of studio equipment the success achieved was 
not such as to interfere with the regular flow 
of 80 per cent American films into Australia. 
To overcome this technicians were lent by Hol- 
lywood to train Australian operators. The fea- 
ture of the first program, "Diggers," a humor- 
ous story of life among the Australian soldiers 
in France, is the first Australian film to be sub- 
ject to comparison on the standards of produc- 
tion here and in Europe. Photography, lighting 
and recording are regarded as excellent. 

During the next eighteen months the Austra- 
lian producers hope to produce twelve films, 
each to run forty minutes. Australian actors 
will be engaged and encouragement will be 
given to Australian scenario writers. A recent 
scenario competition resulted in a flood of 
scripts from all sections of the country. 



MATERIAL FOR 
THE SCREEN 



C UPPORT of high grade 
^ entertainment broadcasts 
in Canada follows custom in 
the United States. Manufac- 
turers of products of national sales possibilities 
are sponsoring broadcasts by paying for time 
"on the air." There is a present demand for 
dramatic and historical features of a Canadian 
character. 

In a bid for the Canadian film market the 
wonder is that producers have so far drawn so 
little upon the pageantry and romance of early 
exploration in Canada. 

The French occupation of Canada continued 
until Washington's time. For three hundred 
years a civilization, now viewed as venturesome 
and picturesque, continued north of the St. 
Lawrence. 

There are in the libraries various versions 
of many stirring events participated in by cour- 
ageous gentlemen and brave women — which 
may again be enacted on the screen, and in 
abbreviated form from broadcast studios. 



o3 



mJj^stttZfUc 



<rL 



Editor 



FEBRUARY, 1932 



Page 5 



Easy to Get 

but mighty hard to get along without! 



National Service has created a new idea of what projec- 
tion men have a right to expect from an equipment and 
supply house. Intelligent, speedy, always dependable 
attention to the mechanical needs of the projection room 
has convinced our customers and friends that while Na- 
tional Service is easy to get, it would be mighty hard to 
get along without it. 



Trade 

where you're 
always treated 

RIGHT! 






NATIONAL THEATRE SUPPLY COMPANY 




YOUR LOGICAL OH SUPPLY HOUSE 



BLUE SEAL SOUND DEVICES, INC. 




Portable Double System 
Dry Battery Operated 



offer 

CINEGLOW SOUND 
SYSTEMS 

Quality sound-on-film, recording systems priced 
within the reach of all. 

Single systems for Bell & Howell 

or Akeley Audio Cameras. 

Double systems — battery operated 
portable — for any camera with 
Bell & Howell motor adaptor. 

Double systems — studio 
production type. 

Manufacturers of the famous 

CINEGLOW 
THREE ELEMENT RECORDING LAMP 

(Patent Pending) 
Suitable for any glow lamp recording system. 

"^^ nbe ^yT ro misew ' th _ 

Write or wire your requirements for specifica- 
tions and prices — fares to New Yorlc de- 
ductible from purchase price of a system. 

BLUE SEAL SOUND DEVICES, INC. 

130 W. 46th Street New York, N. Y. 

Cable Address: SOUNDFILM. New York 



Page 6 



PROJECTION ENGINEERING 




from your light socket! 

— for condenser microphones 

— for sound'On'film 

— for recording and reproduction 







Webster-Chicago Style R-ll 

High and Low Voltage 

Power Unit 

Here, for the first -rime, is a practical, compact 
power supply, fully dependable, that eliminates 
"A", "B", and "C" batteries, charging apparatus, 
and trouble. Every theatre, recording studio, and 
broadcasting station needs one. Low in cost, easy 
to install, nothing to maintain. 

The Webster-Chicago Power Unit, operating from 
either 110 or 220 volt A.C., furnishes all necessary 
filament, plate, grid and polarizing potential current 
without noise or fluctuation. The output includes: 

Filament supply variable from 2 volts at 
60 m.a. to 5 volts at 2 amperes, 

190 volts for photoelectric cell or micro- 
phone, 

90 to 135 volts for pre-amplifier circuit, 

to -8 volts grid bias. 

The high voltages are rectified through a standard 
280 type tube, the low voltage through a durable 
copper-oxide rectifier which will operate for years 
without attention. Output may be regulated pre- 
cisely through efficient, noiseless resistors. An ef- 
ficient filter system removes all audible A.C. hum. 

Install a Webster-Chicago Power Unit and forget 
power supply troubles — permanently! 

Write today for Bulletin 116 

WEBSTER M 
CHICAGO 

The WEBSTER Company 

Sound Amplifiers for Every Purpose 

854 Blackhawk St. Chicago, III. 



T. 



_ HE Group Subscription 
Plan for Projection Engi- 
neering enables a group of 
engineers, executives, projec- 
tionists or technicians to sub- 
scribe at one-half the yearly 
rate. , 

The regular individual rate 
is $2.00 a year. In groups of 
4 or more the subscription 
rate is $1.00 a year. (In 
Canada and foreign countries 
$2.00.) 

The engineering depart- 
ments of hundreds of manu- 
facturers and scores of the 
M. P. M. O. U. locals in the 
projection and allied indus- 
tries have used this Group 
Plan extensively, in renew- 
ing their subscriptions to 
Projection Engineering. 



Each subscriber should print 
his name and address clearly 
and state his occupation — 
whether an executive, engi- 
neer, department head, con- 
tractor, installation man, pro- 
jectionist or technician, etc. 



Remember this Group 
Plan when Your 
Subscription Expires 



( Projection Engineering ) 

Bryan Davis Publishing Co., Inc. 

52 Vanderbilt Ave., 

N. Y., N. Y. 

Los Angeles Chicago Cleveland 



Projection Engineering 



FEBRUARY, 1932 



Internationalizing 
talking pictures 



By Dr. Alfred Gradenwitz 



WHEN the now famous Re- 
marque film, "Nothing New 
at the Western Front," a 
short time ago created such 
a stir in Berlin, spectators did not ^ask 
how the German version of this Ameri- 
can picture had been produced. So 
naturally did the German phrases seem 
to flow from the lips of American 
actors that no doubt of its German 
origin occurred to the average lookers- 
on. 

Still, the film had originally and ex- 
clusively been turned in English, and 



dp 1 




J? 






§4' 


* _l 


■■■mi ■iiiiuTf 


1 



The rhythmographic method. A group of actors 
recording a scene of "Nothing New at the West- 
ern Front." 



the German text had been added after- 
wards, with such perfect agreement of 
rhythm that spectators were not even 
conscious of the typically. Anglo-Saxon 
faces of the artists. 

This unprecedented result was brought 
about by a new method which is bound 
to revolutionize the talking film indus- 
try, putting the "talkie" on the same 



footing, economic and technical, and 
making it as international as its pre- 
decessor the silent film. This "rhyth- 
mographic" method is the invention of 
Carl Robert Blum, of Berlin, and is, 
even outside the film industry, likely to 
prove useful. 

The method is based on a new means 
of rhythmic remote control securing 
synchronism, i. e., perfect agreement 
of rhythm between any number of elec- 
trical devices. Unlike the familiar 
synchronous motor, it is independent 
of the actual speed of motion. 

According to the new method, the 
picture film is turned just as in the case 
of a silent film ; without regard to the 
text, music and noises. These, the 
acoustic part of the 'talkie," are after- 
wards recorded on a "band" moving in 
front of the operator in an electrical re- 
corder (or "rhythmograph") in per- 
fect rhythmical agreement with the 
picture film. 

The original record is eventually 
checked up by several consecutive re- 
hearsals, in the course of which it is 
compared with the picture film, on the 
one hand, and a recital of the various 
roles, on the other. Any correction can 
thus be made very easily, so that the 
"rhythm band" ultimately produced se- 
cures absolute rhythmic agreement. In 
fact, the text and music are, on this 
band, accurately spaced in accordance 
with the rhythm of the picture, so that 
actors have only to read their re- 
spective parts from the band as it passes 
in front of them, to be sure of perfect 
agreement between picture and speech 
(as well as music). 

An apparatus called rhythmoscope is 



A new rhy+hmoscopic method of recording sound effects 

enables picture directors to nationalize in language, 

talking pictures produced in foreign tongues. 









JK 


.^H 




. ■ 


Oi '^? 






,)"""5 


^?*—-5/ 






/ 


: . 






ft *-. - 







Carl Robert Blum, inventor of the rhythmographic 

method, working at the rhythmograph, where the 

text is inscribed on rhythmic bands. 



used to prepare from the original 
rhythmic band, comprising the whole 
text, the various bands containing the 
part of each artist. Several lengths of 
tape are in front of the operator, pass- 
ing in uniform motion ; in rhythmic 
agreement between one another as well 
as with the picture, and the operator is 
all the while checking them with a 
phonograph record. 

Each artist's rhythm band is fitted 
into a rhythmonome of his own, in the 
window of which there appears the 
text of his part as it moves along — 
always in rhythmical agreement with 
the remaining roles and the picture. 

After these preparations the acoustic 
part of the film is turned, each artist 
speaking into a microphone the text 
read from his rhythmonome, as the band 
is moving past a mark in front of him. 
His phrases are thus in permanent 
agreement with gestures and movements 
of his lips. 

The same process can, of course, be 
repeated in as many languages as there 
(Concluded on page 23) 




Erich Dunskus. of the Berlin State Theatre, 
reading his role from his rhythmic band. 



Page 8 



PROJECTION ENGINEERING 



Causes of 

film 

mutilation 

By Sylvan Harris 



ACCORDING to various esti- 
mates, the cost which the mo- 
tion picture industry is called 
upon to bear because of the 
amount of film that is mutilated in pro- 
jection, due to the maladjustment of 
projector parts, wearing of the parts, 
and the use of incorrect tensions and 
tolerances, runs into hundreds of thou- 
sands of dollars. Anything that can be 
done to alleviate this serious condition 
will, of course, be greatly appreciated 
by the entire industry, especially during 
the difficult period through which it is 
now passing. 

Realizing the seriousness of the sit- 
uation, the Projection Practice Commit- 
tee of the Society of Motion Picture 
Engineers has undertaken an intensive 
study of the factors that contribute to 
the mutilation of prints, with the view 
of considering what means may be taken 
to correct the difficulty. The causes of 
film mutilation are many, and for this 
reason it is difficult to judge what cause 
is the most important. At any rate, it 
is clear that they may easily be divided 
into two categories which, together, will 
include all the causes. These are: (a) 
the condition of the film, and (b) the 
condition of the projector. It is un- 
necessary to introduce a third category, 
relating to the conditions under which 
the film and the equipment are handled 
or operated, respectively, as these may 
be understood to be included in the 
categories (a), and (b). 

At the present time, film may be re- 
ceived at the theatres either "processed" 
or "unprocessed," according to the usual 
acceptation of the terms, which refer 
to the buffing, waxing, or oiling of the 
prints. In the case of "unprocessed," 
or improperly treated film, the photo- 
graphic emulsion is likely to accumulate 
at the projector gate and at the sound 
gate, giving rise to severe strains on 
the film at the sprocket holes, due to the 
increase of tension at the gates. On 
this account the film may become dam- 



aged and may be displaced somewhat 
from the focal plane of the lens struc- 
ture, impairing both' the definition of 
the picture and the quality of the repro- 
duced sound. 

When oil or wax is used for "pro- 
cessing" the film, similar difficulties may 
arise due to the spreading of the wax 
or oil under the action of the heat ra- 
diated by the projector lamp, and the 
consequent accumulation of dirt in va- 
rious parts of the projector. 

The Projection Practice Committee 
considers the solution of the "process- 
ing" problem, the determination of the 
best method of "processing," to be of 
utmost importance to the industry, and 
extends its invitation to producers and 
exchanges to cooperate in devising and 
standardizing such a method of treating 
positive prints. The tentative recom- 
mendation is made that a process be de- 
vised for hardening or fixing the emul- 
sion so as to prevent "shedding" and 
consequent accumulation at various 
points in the machine, rather than to 
prevent this from happening by apply- 
ing oil or wax. 

A summary of the subject reveals the 
following facts : 

1. It has been shown quite definitely 



PROJECTIONISTS and others 
who are interested in the 
problems of motion picture -engi- 
neering are invited to write to the 
Editor of Projection Engineer- 
ing, or to the editorial office of 
the Society of Motion Picture En- 
gineers, 33 West 42nd Street, 
New York, N. Y., for informa- 
tion which they may need in solv- 
ing their problems, or for infor- 
mation regarding membership in 
the Society or subscription to the 
Journal. 



that more trouble is experienced at the 
projector and sound gates with first-run 
film than with film that has been run 
a number of times. 

2. New film, in passing through fric- 
tion devices, causes an accumulation of 
deposits in the device which produce 
the effects described. 

3. The accumulation of these deposits 
not only influences the quality of the 
projected picture and the reproduced 
sound, but results in scratching of the 
film as well. 

4. In searching for a method of alle- 
viating these difficulties, it should be 




The Projection Practice Committee of the Society of 
Motion Picture Engineers inaugurates program of in- 
quiry into the causes of film mutilation 



SYLVAN HARRIS 
Editor-Manager, S. M. P. E. 

borne in mind that the film, when pass- 
ing through the sound gate, is at a 
rather high temperature, due to its ex- 
posure to the radiation of the projector 
lamp, as it passes the picture gate. Any 
method which may be devised for treat- 
ing the film should be such that the 
film remains in suitable condition for 
use at the high temperatures thus en- 
countered. 

In connection with the fourth item, 
it has been claimed that the heating of 
the film by the high-intensity arcs 
causes the film to become dry and brit- 
tle, and to buckle or break. This effect 
is said also to occur in hot and dry 
weather. Further, as the film is wound 
upon the lower magazine, it is quite 
warm ; upon cooling, it contracts, and it 
has been said that this, too, is one of the 
causes of the damage done to film. The 
suggestion has several times been made 
that the film be cooled by a blast of air 
before it enters the lower magazine. 

No less important than the effects of 
heating the film and the treatment giver, 
it prior to projection, is the conditior, 
of the projection machine, on the 
amount of film that is damaged in use 
And, in turn, the condition of the ma 
chine is dependent upon the tensions 
applied, the clearances allowed, and the 
amount of wearing experienced at two 
dozen or more points of the mechanism. 
Accordingly, the Projection Practice 
Committee set about determining the 
correct tensions and clearances to be 
maintained at the various points in the 
projector, and to determine, wherever 
possible, the extent to which wearing of 
the various moving parts may be toler- 
ated before replacements or repairs are 
necessary. 

Starting at the upper magazine spin- 
dle, and following the path of travel of 
(Concluded on page 23) 



FEBRUARY, 1932 



Page 9 



The output stage 

in sound transmission 



IMPEDANCE 
40,000 



By Gilbert Smiley* 



THE purpose of this article is to 
cover the needs for and uses of 
certain recent additions to audio- 
frequency equipment. The appa- 
ratus described comprises two items, 
output transformers and push-pull inter- 
stage transformers. First, however, it 
is thought best to consider certain fun- 
damental principles upon which the 
electrical amplification and reproduc- 
tion of sound depend. 

The Reproduction of Speech and 
Music 

In order to produce the proper illu- 
sion of reality in the reproduction of 
broadcast speech and music it is essen- 
tial that there be sufficient volume to 
bring to the listener a signal of such 
strength that it approximates the orig- 
inal sound as the listener would hear it. 
This, of course, does not imply that the 
loudspeaker must carry the full volume 
of a symphony orchestra as it would 
be heard by a listener located beside 
the microphone, but there must be 
enough intensity of sound to duplicate 
the effect upon a listener located within 
the hall in which the music originates 
at a distance of, say, some ten rows 
back. 

Few people appreciate the importance 
of this volume requirement, or, if they 
do, they still keep the volume low in 
order that the program may serve as 
a background for some other activity. 
Yet, by so doing, they create an un- 
mistakable quality of artificiality. The 
music takes on a thin, "tinny," un- 
pleasant sound, associated in the popu- 
lar mind with radio in general, an atti- 
tude which greatly maligns the present 
excellent equipment. 

These remarks presuppose the exist- 
ence of a receiving set of sufficient ex- 
cellence to handle any reasonable vol- 
ume of sound without perceptible dis- 

*Samson Electric Company. 



PLATE 




tortion due to the inability of the appa- 
ratus to reproduce faithfully a station 
.signal of more than the lowest intensity. 
By distortion is meant that the signal 
suffers in naturalness when passed 
through the apparatus. 

It is well at this point to discuss dis- 
tortion and its causes in order that 
there be a clear understanding of this 
subject on the part of the reader. 
Briefly, distortion is due either to the 
extraction of certain vital components, 
or the addition of certain other com- 
ponents not present in the original sig- 
nal. The most common of these effects 
is the first and is known as frequency 
distortion. It is found in most of the 
older receiving sets, and the cause may 
lie in one, several, or all of the follow- 
ing places. 

First there is the tuning system, 
which, if it be overly selective, will 
cause an uneven response, accentuating. 
the lower tones and suppressing the 
higher. This effect is called "cutting 
of sidebands," and is prevalent in sets 
designed with too great a sharpness of 
tuning. Within reason, the broader the 
tuning of the ordinary receiving set, 
the less danger there is of this form 
of distortion. For those who might 
otherwise take exception to this state- 
ment it might be well to state that sets 
securing selectivity through a "band- 
pass" action are free from such trouble 
if properly designed. 

Secondly there is frequency distortion 
due to the failure of the audio system 
to respond equally to all frequencies. 
Many amplifiers have a tendency to 
"peak" or over-amplify a narrow band 
of tones. Obviously, if reproduction 
of the whole musical range is desired, 




the amplifier must handle each note 
impartially. To demonstrate the im- 
portance of even amplification, it is a 
fact that the loss of frequencies above 
three thousand cycles per second seri- 
ously affects the intelligibility of speech 
by removing the consonant sounds, 
while loss or attenuation of the lower 
frequencies destroys the "depth" of 
music. 

The third cause of frequency distor- 
tion lies in the loudspeaker and is due 
in turn to several factors. Practically 
any object is prone to vibrate more 
readily at certain frequencies than at 
others, and the behavior of the cone or 
diaphragm of a loudspeaker will be 
no exception to this rule. This effect 
may be minimized by careful design, 
and each year sees improvement in 
loudspeakers. 

Since the deeper musical tones re- 
quire a relatively greater displacement 
of air for proper reproduction, the ef- 
fective area of the loudspeaker must be 
large or these tones will be slighted. 
Which, without going into theory, ex- 
plains the trend towards larger cones 
— or cones placed in a large "baffle" — 
and the long exponential horns with 
large bell openings. 

In conjunction with resonance effects 
there is another cause of frequency dis- 
tortion in loudspeaking devices. This 
is the varying impedance of many units, 
which allows a maximum energy trans- 
fer from tube to loudspeaker to occur 
at but one frequency. It is not neces- 
sary to go into the details of a discus- 
sion on this subject, but it would be 
well to mention the fact that any device, 
such as a vacuum tube, will deliver 
maximum energy to an external circuit 



PLATE 



Fig. 2. Coupling Device. 
Fig. 3. Transformer Connections. 



SPEAKER 



FIG. 2. 



PWR. 




FIG. d. 



Page 10 



PROJECTION ENGINEERING 



output a 

IMPEDANCE i. MFD. 




PLATE 



when the impedance of the external 
circuit is equal to the impedance of the 
device itself. Since the impedance of 
practically all armature, or, magnetic, 
type units varies with frequency, being 
low at low frequencies, and, similarly, 
high at high frequencies, while the im- 
pedance of a vacuum tube remains es- 
sentially constant over the entire audible 
range, it is obvious that the two im- 
pedances cannot be equal at all places. 
An illustration of this is found in Fig. 
1, which shows the impedance of a well- 
known loudspeaker plotted against fre- 
quency, with the impedance of a stand- 
ard medium power tube on the same 
scale. Compensation for this disparity 
is made in many units by combining 
the effects of resonance and impedance 
so that the sum of the two will be fairly 
constant. A considerable improvement, 
from the standpoint of impedance, is 
found in the "dynamic" speaker, though 
this does not imply that either the mag- 
netic or dynamic type of loudspeaker 
is, in itself, superior. 

One other form of frequency distor- 
tion occurs in certain horns, and, to a 
lesser extent, in cones. In this case 
the higher frequencies set up interfer- 
ing vibrations in such a fashion that all 
or part of the energy representing these 
frequencies is lost, never appearing as 
sound. 

Distortion 

The other general type of distortion 
is known as waveform, or harmonic, 
distortion. In every case this repre- 
sents a condition of overloading; that 
is — the apparatus is forced beyond the 
proper limits of operation. Waveform 
distortion is manifested by an unpleas- 
ant quality in the received sounds 
which is not present at lower volume 
levels. Generally it is caused by the 
attempts of the set owner to secure 
more volume from the apparatus than 
it is capable of delivering. Flagrant 
offenders in this field are overloaded 
detector tubes — especially those which 
use the conventional grid leak and con- 
denser — forced loudspeakers, and an 
amplifying tube of insufficient power in 
the final stage of audio amplification. 
Less common causes of this trouble are 
poorly designed audio-frequency trans- 
formers, or other coupling devices, im- 
proper voltages on tubes, or output 



Fig. 4. Output Circuits. 

Fig. 6. Connections when trans- 
former substituted in place of. im- 
pedance. 



transformers of faulty design or con- 
struction. 

Having discussed distortion in gen- 
eral, it would be well to get down to 
cases, and, as the title of this paper 
suggests, the case in question is the 
output stage. Assuming that a good 
loudspeaker and a good amplifying sys- 
tem have been provided as a matter 
of course, the output stage may still 
prove the weak link in the chain be- 
tween microphone and ears. 

It takes considerable power to fill a 
room with undistorted sound, so the 
first consideration of the. output stage 
leads us to the problem of the tube or 
tubes to be employed, in order that the 
requirements of the listener may best 
be met. A rough scale of comparison 
may be found from the following "rule- 
of-ear" ratings. With fair efficiency in 
the loudspeaker, a power tube of the 
227 type will handle the speaking voice 
at normal volume. A tube of the 171 
type will permit the speaker to become 
more vehement, he may even shout, 
while a 245 tube can safely handle an 
output of sound energy representing 
Chaliapin's voice at full volume. Put- 
ting any of these tubes in parallel 
doubles the available output, if proper 
circuit changes are made. Two tubes 
in push-pull will deliver twice the vol- 
ume of a single similar tube, again 
allowing for proper circuit changes. 
The advantage of push-pull over paral- 
lel connection of tubes lies in the fact 
that a greater input voltage may be 
impressed upon the tubes in push-pull, 
as the effects of distortion due to over- 
loading are reduced when the push-pull 
connection is employed. Since a greater 
input voltage means an equally in- 
creased output voltage, the apparent 
power output is increased by such a 
procedure. 

Fortunately, or unfortunately, the hu- 
man ear is a most inaccurate instru- 
ment. It does not respond directly to 
an increase of sound energy, but re- 
quires several times the power in order 
that the volume may seem twice as 
great. This fact may well be remem- 
bered when comparing amplifiers or 
loudspeakers. 

As power tubes are rated in watts 
of undistorted power output under rated 
conditions, and as watts are not readily 
translatable into terms of volume, the 
average listener has little means of tell- 




ing what tube or tubes will best fit his 
requirements. Reference to the second 
preceding paragraph gives some slight 
idea of the power output of certain 
standard tubes. An idea of the com- 
parison between voice intensity and 
power rating may be gained from the 
fact that the power output ratings of 
the same tubes are as follows. The 227 
is rated at 0.165 watt; the 171, 0.7 
watt; the 245, 1.6 watts. In addition 
there is the 250, which trebles the power 
of the 245, giving 4.60 watts as a 
maximum, and there are special pur- 
pose tubes, the ratings of which may 
be had from the literature of the manu- 
facturers. 

Theory of Power Tubes 

As a matter of interest it might be 
well to go into the theory of power 
tubes to some extent. The three-elec- 
trode tube has three factors from which 
it is possible to determine its undis- 
torted power output. These factors are 
the amplification coefficient, or p, of 
the tube, the plate impedance, and the 
grid bias at which the tube is to be 
operated, all these factors being ob- 
tained under the same set of conditions. 
In order that tube distortion shall not 
occur, the strongest signal the tube 
should receive must be just insufficient 
to cause the grid to become positive at 
the peak of the cycle, for, if there be 
rectification in the grid circuit, wave- 
form distortion will result. Peak volt- 
age refers to the maximum instantane- 
ous value of an alternating voltage, and 
bears a relation to the voltmeter read- 
ing expressed by the factor V2. The 
voltmeter reading is known as the 
root-mean-square value, commonly des- 
ignated by r.m.s., and, in a sine wave, 
is equal to the peak voltage divided by 
the V2. Thus the maximum alternat- 
ing voltage that can be applied to the 
grid circuit is equal to the grid bias 
in volts, E c , divided by V2. This alter- 
nating voltage is called V g . Under these 
conditions the total voltage' appearing 
in the plate circuit will be the alternat- 
ing grid voltage times the amplification 
coefficient, or ^Vg. 

In an earlier paragraph it was stated 
that the maximum transfer of energy 
between a tube and a load such as a 
loudspeaker would occur when the im- 
pedance of the external circuit was 
equal to the plate impedance of the tube. 



FEBRUARY. 1932 



Page I I 



This is true, and strict adherence to 
this principle would yield the best re- 
sults if the tube had an absolutely 
"straight" characteristic in the opera- 
tional region. Though some tubes 
closely approximate the ideal over a 
considerable portion of their character- 
istic curve, none are actually free from 
a slight curvature in this respect, a con- 
dition which leads to a certain amount 
of distortion at all times. Thus the 
theoretically perfect ideal of matched 
impedances cannot be achieved in 
vacuum tube practice, for, though there 
may be a maximum energy transfer, 
there will also be a sensible amount of 
waveform distortion. It has been de- 
termined empirically that the best con- 
ditions exist when the external load 
has twice the impedance of the vacuum 
tube, for an increase in load impedance 
tends to straighten out the undesirable 
curvature. The two to one impedance 
ratio is an attempt to combine . this 
effect with the condition for maximum 
energy transfer, minimizing distortion, 
but not overly reducing the possible 
power output. These remarks apply 
to three-electrode tubes. 

With this in mind the discussion of 
power tube theory may be continued. 
Under the conditions that the load im- 
pedance be twice the plate impedance, 
the voltage appearing across the loud- 
speaker terminals will be two-thirds of 
the total alternating voltage appearing 
in the plate circuit of the tube, or 
0.67fi\/ g . Since this is the output volt- 
age, and power is equal to volts squared 
over resistance, the power output is the 
square of 0.67/W e divided by twice the 
plate impedance, r p . Since V g is equal 
to E c -r- V2, the final expression is 

W = 0.1iyE c 2 -4- r p 
where W is the undistorted power out- 
put in watts, fi is the amplification co- 
efficient of the tube, E c is the grid 
bias in volts, and r p is the plate im- 
pedance in ohms. 

If the same discussion be followed 
for a load impedance equal to the plate 
impedance of the tube, the expression 
will be the same with the exception 
that the factor, 0.111, will become 0.125. 
However, the reduction of distortion 
due to a greater load impedance allows 
the tube to be somewhat overloaded 
with no apparent ill effects upon the 



Schedule showing proper transformer to 
use under various conditions. 









FIG.5. 








TYPE Of 
TUBE 


TYPE OF CONNECTION 
SINOLE PUSH - PULL PARALLEL 


201-A 


1-, 0HM3 EMPLOY 


r, 0HM3 EMPLOY 


r,.OWMS EMPLOY 


10.000 


0-3,0-7 






3,000 


0-4.0-8 


112-A 


3,000 


0-4,0-4 


10.000 


0-3,0-7 


2,300 


0-9.0-10 


171-A 


2,000 


0-9, OlO 


4,000 


0-4, o-a 






210 


3,000 


0-4,0-8 


10,000 


0-3,0-7 


2400 


0-9.0-10 


230 


i.aoo 


0-»,0-10 


3,«00 


0-4,0-a 






12 O 


6,300 


0-4,0-6 


12.6O0 


0-3,0-7 


3,150 


0-9,0-10 


226-221 


7,000 


0-3,0-7 


14,000 


0-3,0-7 


3.S00 


0-4,0-8 


NOTES" THE 0-3, 0-4, 0-» TRANSFORMERS OPERATE 
WITH ALL STANDARD LOUDSPEAKERS. 

THE 0-7, 0-8, 0-10 TR.ANSr0P.MER3 ARE FOR 
OPERATION DIRECTLY INTO THE MOVING 
COIL OF DYNAMIC LOUD-SPEAKERS. 

BLANK SPACES INDICATE A CONNECTION 
NOT COMMONLY" RECOMMENDED. 

1 



quality of the signal, which more than 
compensates for the slight reduction in 
energy transfer. 

Practical Considerations 

From the above discussion it has no 
doubt been made plain that, for the 
best results, a loudspeaker should have 
an impedance which bears a definite 
relation to the plate impedance of the 
tube with which it is to be used. Un- 
fortunately it is impossible to stop at 
this simple statement, as the plate im- 
pedances of different types of tubes dif- 
fer widely, and loudspeakers, in addi- 
tion to their individual idiosyncrasies, 
have impedances varying with varying 
types as well. The only solution of the 
problem is to assume that a loudspeaker 
•has a characteristic of impedance of 
some general order, determined from 
the average characteristic of desirable 
types. This still leaves the problem of 
an impedance which varies with fre- 
quency, and forces the conclusion that 
the desirable relation can be secured 
at only one point, preferably in the use- 
ful range. The effect of differences be- 
tween loudspeaker and tube impedances 
can be reduced by the use of proper out- 
put devices, and, if the frequency at 
which the desired relation occurs is 
carefully chosen, the results will closely 
approximate the ideal to the imperfect 
human ear. 



Applications of Theory to Practice 

With low impedance tubes such as 
the 245 and 250, a suitable coupling 
device is illustrated in Fig. 2. The out- 
put impedance serves to protect the 
loudspeaker windings from the unde- 
sirable effects of the comparatively 
heavy direct current in the plate cir- 
cuit of the tube, while the alternating 
signal current is passed on to the loud- 
speaker through the condenser. The 
efficiency of the device is high, and 
excellent results will be secured if the 
impedance of the loudspeaker fits that 
of the tube, which will be the case with 
most existing good loudspeakers. There 
is one objection to this form of coup- 
ling, which is that, if the blocking con- 
denser breaks down, the full "B" volt- 
age of the last tube will appear across 
the loudspeaker terminals, probably 
damaging the unit. This condition can 
be prevented by connecting the return 
circuit of the loudspeaker to B+ rather 
than to F— , which connection intro- 
duces other objections, as the loud- 
speaker leads are at the same voltage as 
the plate of the power tube and can 
give the user a serious shock, and 
coupling between the plate circuits of 
the last and preceding tubes may de- 
velop through the common impedance 
of the plate supply device. This output 
coupling allows no control of the im- 
pedance ratio of loudspeaker and tube. 



-orkczr 




SPEAKER 



ft+4 no.7. A 



WITH PROPER TRANSFORMER 
L = 0.015 r P HENR1E5 AT lp 
G=10.00CHr P MICROFARADS. 
WHERE r P ISTUE PLATE IM- 
PEDANCE AND lp THE PLATE 
CURRENT OF THE TUBE. 



Fig. 7. Method of 

keeping excessive d-c, 

cut of transformer 

windings. 



Fig. 8. Single tube 

coupled to push-pull 

stage. 



-TJL.CD 




B+ 1 c-1 FIG. 8. 



Page 12 



PROJECTION ENGINEERING 



V. P. 1NTGK5TA&E 
TRANS. 

-njucn — i i — oil 



— r LTk □ 



PLATE , , &RID 
1MPEDANCE5 IMPEDANCESr 




FIG. 9. 



With the above considerations in mind 
there have been developed output trans- 
formers which isolate the loudspeaker 
from both the direct current and volt- 
age of the tube, and allow a proper re- 
lation of impedances in order that the 
most satisfactory results may be ob- 
tained along the lines indicated in the 
preceding discussion. The connections 
of these transformers, as substituted for 
an output impedance, are shown in 
Fig. 3. 

Push-pull amplification has been ad- 
vocated for many years. The results 
obtained from this form of amplifica- 
tion have justified its introduction 
many times over. In addition to the 
consideration of greater allowable in- 
put voltage, with consequently increased 
power output, . push-pull amplification 
has other distinct advantages over other 
circuits. Chief among these advantages 
is the reduction of hum when alternat- 
ing current devices are employed as a 
power supply. Since the tubes in a 
push-pull stage are so connected that 
there will be no output across the plates 
unless dissimilar conditions exist in the 
tubes, any disturbance arising simul- 
taneously in both will cancel out. This 
allows the use of raw alternating cur- 
rent on the filaments, and also permits 
the plate and grid supply to have a 
considerable ripple without the intro- 
duction of undesirable hum. 

An output impedance is commonly 
employed to couple the plate circuits of 
push-pull tubes to the loudspeaker, as 
illustrated in Fig. 4. It is satisfactory, 
provided the impedances of the tubes 
and of the loudspeaker are properly 
related, though here again there is the 
objection that, in many cases, no ade- 
quate provision can be made for the 
maintenance of a proper impedance ra- 
tio. Fig. 4 also illustrates a method of 



Fig. 9. Coupling two push-pull 
stages. 

Fig. 10. Impedance coupling 
between stages. 




coupling that removes all danger of a 
direct current shock if a person should 
come into contact with the leads to the 
loudspeaker, which has been another 
valid objection to the use of an output 
impedance with push-pull tubes. The 
dotted lines illustrate a method by which 
all but the alternating voltage can be 
kept from the loudspeaker. 

The use of an output transformer re- 
moves the disadvantages of an output 
impedance as mentioned above, assum- 
ing, always, that the unit is carefully 
designed and constructed. There are 
several types, intended for use with 
tube impedances of two, five and ten 
thousand ohms. The transformers fall 
into two general classes, one class 
working with all standard loudspeakers, 
and the other class working directly 
into the moving coil of a dynamic loud- 
speaker with no intermediate trans- 
former required. All the units allow 
the most favorable relation between 
tube and loudspeaker impedances, with 
maximum efficiency at the lower fre- 
quencies. Fig. 5 shows the proper 
transformer to use under various con- 
ditions. Figs. 6 and 7 show the con- 
nections to these transformers when 
substituted for output impedances. Fig. 
7 illustrates a method whereby too high 
a value of direct current may be kept 
out of the transformer windings. 

In addition it is well to note the fact 
that the high plate impedance of the 
226, 227, and 120 types of tubes makes 
any but parallel operation undesirable, 
in which case the impedance may be 
calculated by dividing the impedance of 
a single tube by the number of tubes 
in parallel. It is understood that these 
remarks apply to the output stage only. 

It has been assumed that the reader 
knows of the methods of obtaining an 
input to a push-pull amplifier. For 



-'Uli.CD 



TJIj.O- 




this purpose there is a transformer 
known as the Type Y, which may be 
used to couple a single tube to a push- 
pull stage, or to couple two push-pull 
stages. Figs. 8 and 9 illustrate these 
connections. Fig. 10 shows a similar 
circuit with impedance coupling be- 
tween stages. 

Double push-pull amplification is new 
and many seem to find its use of benefit. 
Before attempting to employ this type 
of amplification, however, it is well to 
consider when and where its applica- 
tion is beneficial or detrimental. A list 
of advantages versus disadvantages 
might be of help. 

Advantages 

1. Minimization of disturbances in- 
troduced by power supply. 

2. Greater voltage available for op- 
eration of last stage with no increase 
of supply voltages. 

3. Reduction of saturation effects of 
primary current. 

4. Cancellation of even harmonic 
components of distortion introduced in 
first push-pull stage. 

5. Reduced tendency to "motor-boat" 
when operated from high impedance 
power sources. 

Disadvantages 

1. Lowered overall quality due to 
increased impedance of primary supply 
source unless low impedance tubes are 
used or an interstage transformer with 
a higher primary impedance is em- 
ployed. Impedance coupling also ob- 
viates this difficulty. 

2. Increased instability of system. 
This difficulty is more apparent with 
good apparatus than with poor, and is 
due to resonance effects plus an in- 



Fig. 11. The — 250 tube is on the 
right. 

Fig. 12. Connection when consider- 
able distance from amplifier to 
loudspeaker. 



TUBE TO LINE TUBE TO LINE 



b + I c-4 FIG. 11. 




FEBRUARY. 1932 



Page 13 



crease of "feedback" due to the high 
impedance plate load introduced by a 
good transformer. The higher the plate 
impedance external to the tube, the 
greater the tendency to oscillate at a 
frequency determined by the unavoid- 
able tuning of the transformers. This 
seems to be an inherent characteristic 
of double push-pull amplifiers, but the 
use of resistance equalizers across the 
secondaries of the push-pull transform- 
ers is an effective remedy. 

With the advantages and disadvan- 
tages listed above well in mind, the 
subject of double push-pull amplification 
resolves itself into whether the particu- 
lar needs of a given case are best met 
by it, or by some other system. If it is 
wished to use direct-current tubes with 
an alternating-current filament supply, 
double push-pull amplification is indi- 
cated, but the tubes must be carefully 
matched in all essential points. With 
a "motorboating" or humming ampli- 
fier double push-pull will often prove 
an effective cure. Again, where an 
abnormally high secondary voltage is 
required, as when push-pull 250s are 
to be supplied, double push-pull is often 
the solution. 

When an abnormally high secondary 
voltage is desired, and double push- 
pull amplification -is not desired, a semi- 
power tube may be used on the Type Y 
primary. For the supply of push-pull 
250s a 112 with the maximum allow- 
able voltages will just about do the job. 
The plate current should not exceed ten 
milliamperes, and, under these condi- 
tions, the lower plate impedance of the 
112 will more than compensate for the 
decreased inductance of the transformer 
windings due to the saturation effect 
of the high primary current. 

As an example of the above state- 
ments consider Fig. 11. Here is a two 
stage amplifier with a 250 tube in the 
last stage, preceded by a 227. The 
standard method of measuring amplifi- 
cation with a vacuum tube voltmeter is 
to treat the transformer and the pre- 
ceding tube as a unit. The overall 
amplification is the voltage ratio be- 
tween the grid of the tube following 
the transformer and the grid of the 
tube preceding the transformer. The 
amplification so determined is called 
the "grid to grid gain." In Fig. 11 



this factor is the ratio of V 3 to Vi. 
With a three to one ratio transformer 
and a tube having an amplification co- 
efficient of eight, the grid to grid gain 
will be on the order of twenty, pro- 
vided the transformer is correctly de- 
signed to work with the tube in ques- 
tion. In Fig. 11 the bias on the 250 
is 84 volts, which means that the peak 
value of alternating current that may 
be applied to the input of this tube is 
84 volts. As the peak values of alter- 
nating voltages are in the same ratio 
as their root-mean-square values, and 
the amplification between the grid of 
the 227 and the grid of the 250 is 
roughly twenty, the peak value of 
' voltage on the grid of the 227 neces- 
sary to operate the 250 at maximum 
output is 36 -=- 20, or 1.8 volts. 4.2 
volts is well within the limit of the 9 
volt bias on the grid of the 227, so 
there is no danger of over-loading the 
tube preceding the 250. 

Analysis of the circuit by parts yields 
the same results, but may be considered 
as a point of interest. The 84-volt bias 
on the 250 means an allowable alter- 
nating voltage of 84 -f- y/2, or 59.2 
volts. The three to one ratio of the 
transformer may be assumed to mean 
that the approximate voltage across the 
primary need be but 59.2 -*- 3, or 19.7 
volts. Since the amplification coeffi- 
cient of the 227 is eight, and nearly the 
full amount of this coefficient is realized 
with a good transformer, it is safe to 
assume an amplification of approxi- 
mately seven in the 227. The full am- 
plification of eight could be realized if 
the primary impedance of the coupling 
transformer were infinite, a desirable 
but, unfortunately, impractical condi- 
tion. With an amplification of seven, 
however, the signal voltage on the grid 
of the 227 need be but 19.7 -=- 7 or 2.8 
volts to secure the full output of the 
250. 2.8 X V2 is the peak voltage, 
approximately equal to the peak volt- 
age indicated by the grid to grid 
method, the only difference being in 
the assumption of an amplification of 
twenty in one place and three times 
seven in the other. Both methods in- 
dicate that a 227 can be used to operate 
a 250 with transformer coupling of the 
type indicated without the slightest 
danger of overloading the 227. 



Along the same lines there is an- 
other consideration against the use of 
a power tube to precede a power tube, 
the overloading of the coupling trans- 
former. If too high a value of alter- 
nating voltage be applied to an audio 
transformer primary, distortion will be 
introduced, due to the saturation of the 
core of the transformer. This effect 
becomes most marked at low frequen- 
cies where the flux density for a given 
voltage is greatest. Too high a value 
of direct current in the primary, in 
addition to overheating the windings, 
is apt to reduce the primary inductance 
to such a degree that the net loss in 
quality is more than the gain derived 
from the use of a tube which takes a 
high plate current, and, probably, has 
a low plate impedance. 

Many times it is considered desirable 
to operate a loudspeaker at a consider- 
able distance from an amplifier. For 
this purpose, when the loudspeaker is 
several hundred feet away, a tube-to- 
line transformer should be used at the 
output of the amplifier, and a similar 
transformer should be used at the other 
end of the line. Refer to Fig. 12. 
These transformers, however, are un- 
suited to carry an extremely heavy load 
and should be used with discretion. 

In broadcast and group address work 
it is sometimes necessary to use tubes 
of higher rating than those which have 
been under discussion here. In order 
to operate these tubes it is often essen- 
tial to have higher voltages than can be 
obtained from general purpose tubes. 
The Type Y transformer here finds an 
application following a push-pull stage, 
the secondary delivering the necessary 
grid voltage for modulators or power 
amplifiers. This application is illus- 
trated in Fig. 13. 

It is often necessary to operate sev- 
eral loudspeakers from one amplifier. 
If the plate impedance of the tube or 
tubes in the output stage be known, 
and the impedance of the type of loud- 
speakers to be used be also known, the 
problem is one of connections only. 
If impedance output coupling be used, 
the loudspeakers should be connected 
so that their total impedance is twice 
that of the tube or tubes in the output 
stage. This impedance ratio is to be 
(Concluded on page 23) 



P.P. INTERSTAGe 
TRANS. 




Fig. 13. Type Y transformer follow- 
ing a push-pull stage. 

Fig. 14. Connections in case ampli- 
fier intended for single speaker. 



FIG.13. 




FIG. 14 



Page 14 



Voice training on a 
scientific basis 



TRANSMITTING, recording, re- 
producing, and amplifying of 
sound by mechanical, electrical, 
and photographic devices have 
brought an industrial need for an ex- 
act science of sound. In 10 years of 
research with modern instruments and 
laboratory methods, and with the latest 
knowledge of physiology, enough has 
been learned to establish principles for 
training a voice understandingly al- 
though much additional research is 
needed. 

Hundreds of tests were made upon 
voices, trained and untrained; for ex- 
ample, an investigation of the expul- 
sion of breath during phonation. The 
singer put on a French gas mask; in 
its eye-piece was a telephone transmit- 
ter; rubber tubing went from the mask 
to a spirometer and to the air. Flutter 
valves allowed breathing in from the 
outer air and out into the spirometer, 
but stopped ' escape into the outer air 
or out of the spirometer. The specially 
designed transmitter was connected to a 
special amplifier and thence to an oscil- 
lograph. The singer sang several tones 
on different vowels at various pitches 
and intensities, each tone held 8 to 12 
seconds. Readings of the volume of air 
expelled per second were taken. 

Observation of great singers has 
shown that they never produce a "dead" 
steady tone except at pianissimo. The 
tone fluctuates in intensity with perfect 
regularity. This fluctuation, very wide 
at high intensity, is accompanied with 
a slight fluctuation of pitch. This vi- 
brato is the result of an impulse period- 
ically applied to all the muscles which 
coordinate in the act of phonation. Its 
frequency is about six per second, but 
can be increased. Thus all the time the 
singer is phonating he actually is alter- 
nately singing and silent, rapidly and 
regularly. As the intensity rises the 
"on" impulse is more vigorous and the 
swing of the vibrato increases. Since 
at mezzo forte, when the technic is good, 
the intensity of the tone should increase 
as the pitch rises nearly up to the top 
of the singer's range, the vibrato should 
increase in amplitude as the scale is 
ascended. The vibrato decreases as the 
intensity drops until a point is reached 
at which a stream of air actuates the 

XFrom "Research Narratives," June 15, 1931, 
published by The Engineering Foundation, 29 West 
39th Street, New York, N. Y. Based upon in- 
formation contributed by Douglas Stanley, M.S., 
Assoc. City Guilds of London Inst., Fel. Acousti- 
cal Society of America, N. Y. 



vocal chords, when it disappears alto- 
gether. This concept of an "on" and 
"off" impulse is very different from the 
old notion of steady control of a stream 
of breath. 

A great voice is not due to anatomi- 
cal peculiarities but to mental and emo- 
tional capacity and tractability. The 
human voice is a sound-producing in- 
strument governed by the laws of sound 
and of physiology; it consists of a mo- 
tive force (the pressure of the breath), 
a vibrator (the vocal chords), and a re- 
sonator (a set of adjustable cavities in 
the head and throat). Voice starts in 
a mental concept which brings the 
necessary muscles into action. A sing- 
er must have a mental concept of the 
pitch which he is about to sound. If 
this concept or the receiving mechanism 
of the ear, be faulty, a pupil cannot be 
made to sing, although his speaking 
voice may be trained. Two groups of 
muscles, one of seven and the other 
(far stronger) of two, bring the vocal 
chords into tension and hold them there. 
When a mental concept initiates the 
nerve impulses supplied to the larynx, 
these muscles come into action and the 
vocal chords are set to the proper length, 
tension, and position. If the singer 
starts from pianissimo, where the breath 
pressure is at a minimum, and increases 
the intensity and therefore the breath 
pressure or the amplitude of the vibrato 
to fortissimo, the muscles must take on 
additional tension. The lighter muscle 
group should take tension to a point at 
which it would overload ; then tension 
of the stronger group must be increased. 

So long as the vocal chords are held 
in tension against pressure of the breath 
by means of additional tension on the 
lighter muscles, the singer or speaker 
is using the "upper register" (falsetto) ; 
as soon as the stronger muscles start to 
take on added tension, he is using the 
"lower register." Registration provides 
the proper method of controlling the in- 
tensity, not the pitch. The registers 
should be isolated and trained separate- 
ly; only when fully developed should 
they be coordinated. Improper coordi- 
nation of the laryngeal muscles accounts 
for the partial or total loss of voice of 
most of the great singers at an age at 
which they should be in their prime. 

From "breath expulsion-intensity" 
curves, a person trained in this new sci- 
ence will be able to make an accurate 
technical criticism of a voice without 



PROJECTION ENGINEERING 

having heard it. The "breath control" 
doctrines, long accepted, are fallacies. 
Tremolo is caused by a fluttering of the 
walls of the resonating cavities. The 
vibrato is the means for moving the 
voice correctly from tone to tone; it 
allows the singer to keep perfect time 
and rhythm; it can be improved and 
controlled by training. 

The range of every properly produced 
voice should be at least three octaves ; 
some persons may attain nearly four. 
Faulty registration and resonance ad- 
justment can curtail the range 50 per 
cent or more; also reduce the power to 
an incredible degree. The mouth 
should not be used as resonator. When 
a person is phonating the muscles used 
in the act of phonation should not be 
relaxed but in proper tension balance. 

There is no fundamental difference 
between the singing and speaking voices 
except in so far as vowels are more sus- 
tained in singing. There is no vibrato 
in speech. In singing the intensity is 
far greater (thus the general pitch is 
far higher), the range far wider, and ar- 
ticulation much stronger than in speech. 
In speech, low tones are most effective ; 
hence all normal speech should be in 
the pure lower register. 



NATURAL COLOR MOVIES OF 
NORTHERN LIGHTS 

After exhaustive tests, Colorcraft 
film, produced by the Colorcraft Cor- 
poration, 122 East 42nd Street, New 
York City, has been accepted by the 
American Polar Expedition, members 
of which, under Captain Flavel M. 
Williams, commander, are now work- 
ing out of a base established at Port 
Churchill, Canada, in an attempt to 
make motion pictures of the aurora bo- 
realis in natural colors. 

Laboratory tests, made with colored 
light reflected at intensities as low as 
five candlepower, proved the Colorcraft 
film to give 92 per cent fidelity over the 
entire spectrum, and to be 2 l / 2 times as 
fast as ordinary black and white film 
or the next fastest color film, and eight 
times as fast as the average color film. 

The film is treated by a special proc- 
ess developed by William Hoyt Peck, 
who in his fifteen years of work with 
color motion pictures has spent approxi- 
mately $980,000 in experimentation. It 
is- used in a standard bi-pack camera, 
and prints are made on specially treated 
and developed standard color positive. 
Peck is one of America's pioneers in 
color motion picture work and has thir- 
ty-six patents and applications on his 
processes. 

If the attempts to photograph the 
Aurora are successful, it will be the 
first time in thirteen years of trials by 
various companies that satisfactory re- 
sults have been had. 



FEBRUARY, 1932 



Page 15 



Types of 

sound 

records 

By Charles Felstead* 



A review of the various 
methods employed in re- 
cording sound for repro- 
duction with synchronized 
pictures 



EVEN to motion picture projection- 
ists, the various types of sound 
records used in motion picture 
work are confusing. The term 
sound record is applied here compre- 
hensively to motion picture sound rec- 
ords in general, regardless of the kind 
of medium on which the sound is 
recorded. With the present-day record- 
ing systems, the two recording media 
that are used are positive motion pic- 
ture film stock and the soft wax record 
blank. In the case of the film, the 
sound energy is recorded on it as a 
narrow "sound track," approximately 
one-tenth of an inch wide, near one 
edge. The sound track on the wax rec- 
ord is a narrow, wavy spiral groove 
running uninterruptedly from near the 
center of the flat disc to almost the out- 
side edge. These are the two types of 
sound records ; but there is a variation 
in them that is caused by the method 
employed in making this permanent rec- 
ord of the sound energy. 

There are four sound recording sys- 
tems in general use: the Warner 
Brothers' Vitaphone, the RCA Photo- 
phone, the Fox Movietone, and the 
Western Electric system. The first 
mentioned system records on wax rec- 
ords alone ; the next two systems record 
only on film; and the Western Electric 
system employs either, or both, film and 
wax as its recording media. There are 
two distinctly different types of film 
sound tracks produced by these systems ; 
but on the photoelectric cell "eye" of the 
reproducing system, a light shining 
through either of these two sound tracks 
has exactly the same effect. The wax 
records produced by the two systems 
that record on wax are identical, be- 

"Sonnd Engineer, Universal Pictures Corpora- 
tion. 



cause almost exactly the same recording 
equipment is used in both systems. 

The finished wax records turned out 
by the Vitaphone and Western Electric 
systems of recording are similar in ap- 
pearance to the records used on ordinary 
phonographs, except that they are six- 
teen inches in diameter instead of 
twelve inches and that they are some- 
what thicker. They are of a hard, black 
wax composition ; and they are caused 
to revolve at a speed of 33 1/3 r.p.m. 
in recording and reproducing. The 
electro-mechanical recording device 
operates a sharp stylus that cuts a 
groove of constant depth and width in 
the original soft, soapy wax record from 
which the final hard wax records are 
later derived by a method called "proc- 
essing." This cutting stylus moves at 
a steady rate of speed from a point near 
the center of the record to the outside, 
producing a spiral groove. As it moves 
steadily forward in this spiral path, the 
stylus also oscillates from side to side 
under the influence of the speech cur- 
rents. This causes the stylus to trace 
in the soft wax a groove that undulates 
about a fixed spiral. The amplitude of 
the side to side movement of the cutting 



Sound track of 
variable density- 
fixed area type 
produced by the 
Western Electric 
recording system. 




stylus is governed by the strength of 
the speech currents producing the 
movement, and the rapidity of the move- 
ment is regulated by the frequency of 
the speech currents. A turntable geared 
to the projection machine and an elec- 
trical reproducer are used in reproduc- 
ing the sound from the records. 

Types of Film Records 

The two types of film sound records 
are known as the variable density-fixed 
area track, which is produced by the 
Fox Movietone and Western Electric 
recording systems, and the fixed density- 
variable area track that is created by the 
RCA Photophone system. Examples of 
these sound tracks may be seen in the 
accompanying illustrations. As has 
been said, these sound tracks have a 
similar effect on the reproducing sys- 
tem, because in the first case the in- 
tensity of the light that passes through 
the track at any instant is governed by 



The picture half 
of, a section of 
composite film. 




the density of the track at that point, 
and in the other case the amount of 
light that is permitted by the track to 
pass is regulated at any particular point 
bj the proportion of the sound track 
that is transparent. The output voltage 
of the photoelectric cell in the projection 
machine is directly proportional to the 
amount and intensity of the light fall- 
ing on the sensitive surface ; so it is 
immaterial to the cell whether the in- 
tensity of the light reaching it is gov- 
erned by the density of the film through 
which the light passes, or whether the 
amount of light striking it is regulated 
by the area of the sound track that is 
transparent. The overall width of both 
types of tracks is very nearly the same, 
and they are recorded in identical posi- 
tions on the film. 

The variable density-fixed area film 
sound track is made up of an infinite 
number of very fine parallel striations, 
or bands, of varying exposure but of 
fixed lengths lying transversely across 
the sound track. These striations vary 
in all shades of gray from almost pure 
white to nearly jet black, but there is 
no variation of density in them in the 
transverse direction. They are pro- 
duced in the Western Electric system 
by shutting off more or less of the light 
that falls on the moving film from a 
light source of constant intensity. This 
is accomplished by means of a special 
slit, the width of which is modulated 
by the speech currents, through which 
the light reaches the film, and which is 
called the "light valve." It is made up 



A strip of com- 
posite, or "movie- 
tone," film. 




Page 16 



PROJECTION ENGINEERING 




Wide sound 
track of variable 
density-fixed area 
type used with 
double film re- 
leases. 



of a loop of narrow duralumin ribbon 
held under tension in a frame, the two 
sides of the loop forming the two sides 
of the slit. The slit opens and closes 
and continually changes in width with 
variations in the speech currents flow- 
ing through the loop of ribbon. In the 
case of the Fox Movietone, the same 
type of track is produced by a light 
source that varies in intensity, or 
nickers, with variations in the speech 
currents. The lamp producing this light 
of varying intensity is known as an 
"Aeolight." The slit through which the 
light from this lamp shines on the film 
is of fixed and constant dimensions. In 
the Western Electric system, the light 
is focused directly on the varying slit ; 
but with the Fox Movietone system, the 
light is allowed to fall on the fixed slit 
and is not focused on it. An equivalent 
effect on the moving film is obtained 
with either arrangement. 

Variable Area 

The RCA Photophone is the only 
recording system that produces a sound 
track having an exposure on the film of 
fixed density and variable area. The 
overall w<dth of the track is slightly 
less that that of the tracks of the other 
systems — seventy mils instead of one- 
tenth of an inch — but the portion that 
is actually exposed in this case varies 
in width with the instantaneous ampli- 
tudes of the speech currents. The 
track appears on the film as an ir- 
regular, black saw-tooth edge. The 
higher the frequency of the speech cur- 
rents (the shriller the sound), the 
closer together will be the points ; and 
the greater the amplitude of the speech 
currents (the louder the sound), the 
higher will be the saw teeth. This vari- 
able area of exposure is produced on 
the film by light from a source of con- 
stant intensity that is reflected by a 
tiny mirror through a slit of fixed di- 
mensions onto the film. The mirror is 
delicately suspended in an electromag- 
netic field of force, which reacts with 
the varying field of force set up by the 
changing speech currents flowing 
through a very small winding on the 



back of the mirror. This causes the 
mirror to vibrate, or swing, from side 
to side, exposing more or less of the 
sound track space on the film. When 
there is no speech current flowing, the 
mirror comes to rest in such a position 
that it exposes just one-half of the 
sound track width. In this system the 
light reflected from the mirror is fo- 
cused sharply on the fixed slit. 

Sound records are released to the- 
atres in three forms : on hard wax 
records, on film in composite, or 
"movietone," prints, and on film as a 
separate sound track print. The wax 
records have been described in detail 
and will not be taken up again, except 
to say that there is a start mark on the 
record and a start mark on the picture 
film accompanying it, and that these 
marks must be properly lined up when 
the projection equipment is started in 
order that the sound and picture will 
be in synchronism. The picture shown 
with a wax record is somewhat larger 
than the picture projected from a movie- 




1 1 1 u s t r ation of 
full-width picture 
released with disc 
recording and 
with double film. 



f 



tone print, because the space taken up 
on the edge of the film by the sound 
track subtracts just that much from the 
size of the picture. Also, the shape of 
the picture projected with a wax rec- 
ord sound release is generally con- 
sidered more pleasing to the eye than 
is the nearly square picture on a movie- 
tone print. This difference in picture 
dimensions will be evident from an ex- 
amination of the accompanying illus- 
trations. 

In recording, the picture is photo- 
graphed by a standard motion picture 
camera and the sound is recorded 
simultaneously with the picture on a 
recording machine generally situated at 
a little distance from the camera. The 
recording machine and the camera start 
and stop together and are kept running 
ar exactly the same speed by "inter- 
locked" motors and a speed control ar- 
rangement. An exception to this is the 
Fox Movietone, because in that system 
the Aeolight is usually mounted directly 
on the picture camera. For projection, 
the picture and sound track are printed 
on a single piece of film, which is then 



given the name of composite, or movie- 
tone, print because it combines then: 
both. These two — hard wax record and 
movietone print — are the standard forms 
of releases for sound motion pictures. 

Separate Films 

On a rare occasion, however, the 
sound and action are released on separ- 
ate films, which have start marks to 
permit proper synchronization. This 
form of release is not often employed 
because it necessitates the presence in 
the projection room of a "dummy" ma- 
chine, which is ordinarily a standard 
sound and picture projection machine 
with the picture head removed. Slight- 
ly better sound quality can usually be 
obtained by this means, because the 
sound and picture films can be de- 
veloped and printed separately without 
having to effect any sort of compromise 
between them in laboratory develop- 
ment. Another advantage of this ar- 
rangement is that a picture covering the 
full width of the film can be employed. 
Double film release is hardly worth the 
extra expense and labor involved, how- 
ever, and is it never used except for 
"super" productions, and then only 
while they are being shown at the best 
theatres. It is sometimes employed 
when pictures in natural colors are re- 
leased and it is not thought desirable 
to release them on wax, because the 
color stain on the film has somewhat 
of a derogative effect on the sound 
quality. 

Movietone Releases 

The motion picture companies using 
Western Electric recording equipment 
release their pictures on both film and 
wax ; but the companies using the other 
types of recording systems can release 
only on the 'medium on which their 
equipment permits them to record. The 
movietone form of release is coming 
more and more into universal use be- 
cause it is less bulky and easier to 
handle than hard wax records, it is 
not so fragile, it does not wear out 
so quickly, the sound frequency and 
sound volume range that it will carry 
(Concluded on page 23) 



Sound track of 
fixed density- 
variable area, 
' 'saw-tooth,' ' 
type. 



1 

at 
> 







FEBRUARY, 1932 



Commercial 16 mm. 
sound-on-fiim 



THERE has recently been placed 
on the market a new 16 mm. 
sound-on-film process, under 
which process the sound track is 
printed alongside the picture exactly 
as with 35 mm. and is in every respect 
an exact miniature of the standard 35 
mm. sound-on-film. 

The film used is standard 16 mm. 
film, runs at 36 feet a minute, uses both 
sets of sprocket holes, has 40 frames to 
the foot, projects 1,440 pictures upon 
the screen a minute, has a sound track 
whose width is twenty thousandths of an 
inch running alongside picture — inter- 
posed directly between picture and per- 
foration — (exactly as in 35 mm.) and 
reproduces voice and music with all 
fidelity, clearness and volume of its 
larger brother the 35 mm. 

It has been determined that the fol- 
lowing principles must be adhered to 
strictly, basing the following outstand- 
ing points wholly on commercial con- 
siderations ; limitations considered 
necessary if the 16 mm. talking motion 
picture is to be commercially successful. 

1. Nothing but standard 16 mm. film 
must be employed, and sound-on-film, 
and not disc, must be employed. 

2. That a double set of perforations 
must be retained, and no split frames 
allowed. 

3. That the sound track must be 
photographed on the film exactly as is 
done in 35 mm. and that sound track 
must not take away from the picture 
more picture space than the 35 mm. 
sound, or namely, not to exceed forty- 
five thousandths (.045 inch) of an inch 
in width. 

4. That the sound track must be 
capable of reproducing all frequencies 
found in 35 mm. recording with as fine 
a fidelity, clearness and volume as the 
35 mm. 

5. That the speed of the film must be 
legulated to run at 36 feet per minute, 
which would give exactly the same 
number of frames (pictures), namely, 
1,440 per minute as in the 35 mm. film. 

6. That all pictures to be photo- 
graphed must be taken on 35 mm. and 
means of optically reducing to 16 mm. 
be perfected, that sharpness of detail 



Description of a new 16 

mm. sound-picture system 

using sound-on-film 



and reduction of film grain be obtained 
to allow for commercial projection of 
16 mm. pictures upon a sufficiently 
large screen in auditoriums, seating at 
least 300 to 400 persons, so that all 
present can see the picture clearly and 
without eye strain. 

7. That the recording process and 
apparatus must be so refined and com- 
mercialized that trained operators can 
consistently turn out the highest stand- 
ard of work, both in studios and trucks. 

8. That simple, well-made, sturdy 
projection must be perfected, together 
with suitable amplifying apparatus 
which would, in the hands of careful 
persons, project both sound and pic- 
ture consistently, and give satisfactory 
results, under the most difficult and 
trying conditions. 

9. That the price of apparatus and 
equipment must be kept down to rea- 
sonable figures, so that schools, 
churches, clubs, and other educational, 
industrial and amusement interests may 
become a ready market for the 16 mm. 
picture. 

Development 

Retaining both sets of sprocket holes, 
while requiring much additional work 
to develop the sound track with such 
small dimensions as to keep within the 
required .045 inch width, has proven 
sound. Where only one set of sprocket 
holes is used the wear and tear on film 
in projection shortens life of print to a 
point which makes single sprocket film 
impractical and non-commercial. 

Should the split-frame method have 
been adopted, the wear and tear on film 
would have been tremendous, and while 
by printing split-frame pictures, i. e., 
wherein a blank space, the size of one 
picture is left out after each picture 
frame, 1,440 frames of pictures would 
have been retained, and, in addition, 
would have 1,440 blank frames spaced 
alternating with the picture, thereby 
giving 72 feet a minute surface speed 
of film for the sound track. The de- 
sired commercial advantage might not 
have been gained inasmuch as twice 
the correct amount of film would have 
been required with the additional 
double cost of film as well as the break- 
age factor of pulling the film two frames 
in place of one. 

The three-dimensional sound track 
which track has, together with the de- 



Page 17 

velopment of a new process of photo- 
graphing the sound variations, made it 
possible to re< ord all harmonics and 
music usually recorded where 35 mm. 
is used, within as small a width track 
as ten one-thousandths (.010 inch) of 
an inch, whereas the standard 35 mm. 
sound track, measures one-tenth CI 00 
inch) inch, or ten times as wide as the 
smallest 16 mm. track. Manufacturers 
have standardized the 16 mm. sound 
track with a width of twenty thous- 
andths (.020 inch; of an inch, with the 
reproducing aperture set at fifteen 
thousandths (".015 inch) of an inch, 
thereby allowing for (.0025 inch) 2j^ 
thousandths of an inch cutoff, which 
makes the 16 mm. sound track one-fifth 
the width of standard 35 mm. track. 

In the development of the 16 mm. 
sound track it has been possible to re- 
tain the pureness of and clearness and 
volume of the 35 mm. sound film, in 
every respect. 

The reason for standardizing 16 mm. 
film, so that it should run at thirty-six 
feet per minute, or 1,440 frames, was 
due to the fact that a great portion of 
all 16 mm. film for a long time to come 
will be taken from 35 mm. pictures al- 
ready made, and all 35 mm. film is 
photographed and projected, today, at 
a speed of ninety feet per minute, which 
means that 1,440 frames of pictures 
will pass the projection lens each 
minute. In 16 mm. there are forty (40) 
frames of picture to each foot of film, 
and so, when running at thirty-six feet 
per minute, we have 1,440 frames pass- 
ing the aperture each minute. 

It is well known in the art that, 
optically-reduced 35 mm. to 16 mm. 
pictures give prints of far greater 
sharpness, detail and finer grain, than 
contact prints, and by using frame for 
frame, a 900 foot reel of 35 mm. (hav- 
ing 16 pictures to the foot and 1.440 
frames to 90 feet) will optically reduce 
to 360 feet, on 16 mm. It remains only 
to record the sound track upon 360 foot 
of positive 16 mm. film to match for 
contact printing with the optically-re- 
duced 35 mm. picture. 

In the case where sound has been 
recorded on 35 mm. film, the picture is 
optically reduced, frame for frame, and 
the sound track picked up — inputted 
through pre-amplifiers, through record- 
ing amplifier and re-recorded at 36 
feet per minute on 16 mm. film. 

In the case of synchronized discs — 
pictures are optically reduced as above, 
while sound is picked up from 3>i 1/3 
r.p.m. turntable, inputted through re- 
cording amplifier and re-recorded at 36 
feet per minute on 16 mm. film. Where 
direct picture is being photographed and 
sound recorded over microphones, or 
pickups, or both, the picture is short 
or photographed on 35 mm. film, which 
runs at the standard speed of () feet 



Page 18 



PROJECTION ENGINEERING 



per minute, and the sound recorded upon 
a seperate 16 mm. film (as is the stand- 
ard practice of 35 mm. film), which is 
running at 36 feet per minute. The 
picture is now optically reduced, frame 
for frame, to 16 mm. for sharpness, de- 
tail and reduction of grain, and the 
sound track contact-printed, as above. 

This method of optically reducing 
from a larger size film to a Smaller is 
not new and' is quite extensively used 
daily, from 65 to 35 mm. with marked 
improvements over contact-printing of 
65 to 35 mm. Optically reduced pic- 
tures allow, due to this sharpness, de- 
tail and reduced grain, far greater 
screen enlargement, retaining a much 
clearer and better-defined picture, and 
meet all requirements. 

Any recording operator can with 
very little training become proficient in 
the handling of the recording appara- 
tus, and can deliver consistently the 
highest quality of work. Any com- 



mercial 16 mm. film laboratry can, with- 
out changing their equipment, solution 
or process, handle these film develop- 
ments. Printing machines which op- 
tically reduce a picture from 35 mm. to 
16 mm. and at the same operation print 
16 mm. sound track, are now ready for 
delivery, to film laboratories. Syn- 
chronizing sound-track apparatus has 
also been developed to assist the 
laboratories. 

Projection apparatus to operate the 
sound film has been designed in several 
models, using standard makes of ampli- 
fying equipment and loudspeakers. It 
will be possible for users of this equip- 
ment to have their choice of styles and 
models which will best meet their re- 
quirements, with prices ranging up to 
four hundred dollars ($400.00) for the 
complete equipment, ready to operate 
by merely plugging into any light 
socket. 

Apparatus powerful enough to fill a 

AAA 



hall, seating 300 or 400 persons, with 
screen 7 inches x 9 inches, or even 
larger, giving a picture clear and dis- 
tinct, with sufficient amplification to 
give a full, clear reproduction, powerful 
enough to properly fill an auditorium, 
has been perfected. 

Field of Operation 

It would be impossible to satisfy all 
fields wishing to adopt 16 mm. sound- 
on-film at the start. It is expected that 
the following fields will be thoroughly 
covered : educational field ; industrial 
field ; amusement field ; home field. 

Studios and trucks will be equipped 
as soon as possible, so that 35 mm. 
pictures as well as new subjects may 
be made into 16 mm. pictures in quan- 
tities. 

The new system herein described has 
been placed on the market by the Jones 
Research Sound Products, Inc., 729 
Seventh Avenue, New York. 



Answers to technical questions Nos. 26—32 



HEREWITH are presented the 
answers to Questions Nos. 26 
to 32, which appeared in the 
January issue of Projection 
Engineering: 

26. This is a characteristic of alter- 
nating-current circuits, where the cur- 
rent tends to create a counter electro- 
motive force. Self-induction varies 
greatly with conditions, depending upon 
the arrangement of the circuit, the me- 
dium surrounding the circuit, the de- 
vices or apparatus supplied or connect- 
ed into the circuit. For example, if a 
coil having a resistance of 100 ohms 
is included in the circuit, a current of 
one ampere can be passed through the 
coil with an electric pressure of 100 
volts, if direct current is used; while it 
might require a potential of several 
hundred volts to pass a current of one 
ampere if alternating current is used, 
depending upon the number of turns in 
the coil and whether it is wound on 
iron or some non-magnetic substance. 

27. A little leeway must be allowed 
in the answering of this question. Sev- 
eral factors must be taken into consid- 
eration, but let us assume that the glass 
surfaces of condensers and lenses are 
perfectly clean and that the maximum 
of light is being picked up by the con- 
densers from the arc lamp. Take the 
crater of the arc as 100 per cent, only 
approximately 33 per cent of this is 
picked up by the condensers on d-c, 
while on a-c. the percentage is a great 
deal less. There is a reflection loss 
amounting to 4 per cent at each of the 
four glass-to-air surfaces of condensers, 
plus an absorption loss which can be 



reckoned as 6 per cent per inch, assum- 
ing the condenser combination to have 
an axial thickness of \y 2 inches, then 
the total loss by absorption will amount 
to 9 per cent, or a total loss of 25 per 
cent passing through the condenser 
combination. Thus only about 25.75 per 
cent of the light from the arc reaches 
the film being projected, the light loss 
due to film density will of course vary 
greatly, but it is safe to assume that the 
loss amounts to 50 per cent, which 
leaves us with only 12.85 per cent of 
the original 100 per cent. In its passage 
through the objective lens this is re- 
duced some 25 per cent — 4 per cent re- 
flection loss at each of the 6 glass-to- 
air surfaces ; therefore only 9.65 per 
cent emerges from the objective lens. 
This is again cut 50 per cent by the 
flicker shutter, leaving only 4.80 per 
cent of the original 100 per cent. Other 
factors cut this percentage down, dis- 
tance to screen, effective aperture of 
objective, etc. 

28. Mazda motion picture lamps are 
designed for operation base down with- 
in 25 degrees of the vertical, at any 
greater angle performance will be im- 
paired. They are made for use at con- 
stant current rather than constant volt- 
age. The lamps must be operated at 
their rated current — for instance, at 31 
amperes the life of the 30 ampere lamp 
will be reduced about one-half. 

29. A prismatic condenser cannot be 
used when showing slides because the 
risers of the prisms deflect the light so 
much that dark rings appear in the 
beam near the condenser where the 
slide would have to be placed to be cov- 



ered by the light beam, although they 
are filled in by the crossing of the rays 
further out in the beam. 

30. Exciter lamp currents not cor- 
rect, storage battery discharged, exciter 
lamp out of focus, photocell defective, 
sound gate aperture clogged. 

31. Pickup defective, one power am- 
plifier defective, voltage amplifier de- 
fective, storage battery discharged. 

32. The input and voltage amplifier 
panel is made as a single unit and is 
similar to the two panels used in type 
A equipment. Duplicate controls on the 
panel are provided for two projectors. 
They consist of two exciter lamp rheo- 
stats, with meter jacks, two projector 
control switches, with pilot lamps to 
denote which projector is connected to 
the amplifier, a single test meter with 
extension cord and jacks for reading 
plate current and bias voltage. In the 
type B equipment the voltage amplifier 
has the gain control following the sec- 
ond stage. Tubes used are first and 
third stages UX-210 and the second 
stage UX-841. 

As previously announced many of the 
sets of answers to this series of ques- 
tions are not worded the same as the 
answers that are published each month. 
This does not mean that the answers ■ 
sent in are not substantially correct. 
The purpose of the questions is to give 
projectionists an opportunity to test 
their knowledge by attempting in their 
own language to answer the questions 
presented monthly and then, later, check 
their answers against the set of answers 
published. 



FEBRUARY, 1932 



Page 19 



The 

buttonhole 

microphone 



By W. C. Jones* 

A 

Mike fastened to coat 
lapel enables speaker to 
move around on rostrum 



MANY speakers, unfamiliar with 
the use of the conventional 
stationary microphone, mar 
the public address programs 
in which they take part by straying 
away from the instrument. To permit 
the speaker to move about more freely, 
a microphone has been developed which 
is worn on his clothing and moves with 
him. This microphone is an adapta- 
tion to public-address use of the essen- 
tial elements of a transmitter recently 
developed for operators. It is only 
about an inch in diameter and weighs 
about one and one-half ounces. A thir- 
ty-foot length of flexible cord provides 

*Transmission instruments development engi- 
neer, Bell Telephone Labs. 




^INSULATING 
HOUSING 

Fig. 2. The lapel microphone is of the 
granular carbon type, with an un- 
stretched cone-shaped diaphragm of 
aluminum. The two electrodes are sta- 
tionary and are electrically insulated 
from the diaphragm. 




Fig. 3. Associated with the lapel microphones, an input circuit attenuates 
the lower frequencies which the microphone picks up from the speaker's 
chest, and prevents clicks when the microphone is cut in or out of circuit. 



the connection to the amplifier of the 
public-address system. 

The diaphragm is made of thin alu- 
minum, formed into a cone to provide 
sufficient stiffness to cause it to vibrate 
as a unit throughout the frequency 
range of interest. A number of im- 
pregnated paper rings, about four ten- 
thousandths of an inch thick, support 
the edge of the diaphragm. The dimen- 
sions of the recess into which these 
rings fit are such that the rings sepa- 
rate slightly from one another. This 
not only provides a resilient support for 
the diaphragm, but also adds a certain 
amount bf damping which reduces the 
effect of -resonance and improves the 
response characteristics. 

Unlike the carbon microphones now 
in use in public-address work, in which 
the diaphragm forms one of the elec- 
trodes, the diaphragm of the lapel mi- 
crophone is insulated by a coating of 
phenol varnish from the granular car- 
bon. Electrical connection to the car- 
bon is made through two stationary cyl- 
indrical electrodes, insulated from each 
other by a ceramic barrier which also 
serves to define the current path 
through the carbon. In order to in- 
crease the life of the microphone and 
reduce the noise which results from 
moving it about, the space between the 
electrodes is filled practically full of 
carbon. 

A rubber covering for the micro- 
phone eliminates the disturbing noise 
which would otherwise result from rub- 
bing against the speaker's clothing, or 
would be picked up through the clip 
which is provided for attaching it to 
the clothing. The clip is so arranged 
that the microphone can be attached to 
either the inside or outside of the 
breastpocket of a coat, or to the lapel. 
The latter position is preferable, for it 
brings the microphone closer to the 



speaker's lips and increases the inten- 
sity of the speech without adding to the 
interfering noise. In the case of a wo- 
man, the clip can be fastened to her 
dress with a pin. 

The frequency response characteris- 
tics of the lapel microphone compare 
favorably with those of the stretched 
diaphragm type now in use. Owing to 
the smaller size of the lapel model, less 
sound field distortion is introduced. 
When worn on the speaker's clothing, 
however, the instrument picks up sound 
as the result of chest vibration in ad- 
dition to that reaching it through the 
air. The part due to chest vibration is 
rich in low frequencies, and if unatten- 
uated results in a "deep" unnatural 
quality of transmission. A special in- 
put circuit has therefore been provided 
for connecting the microphone to the 




Fig. I. H. L. Lundberg demonstrates 

how, when the lapel microphone is in 

use, the jack and plug are placed in 

the coat pocket. 



Page 20 



PROJECTION ENGINEERING 



public-address amplifier. This circuit 
attenuates the low frequencies suffi- 
ciently to correct for the effect of chest 
vibration. Provision is' also made in 
this circuit for supplying direct current 
to the microphone, and suppressing 
clicks when it is switched in and out of 
circuit. 

Complete equipment, consisting of 
the microphone, the flexible cord and 
the apparatus unit which contains the 
input circuit is shown in Fig. 3. The 
unit shown is arranged for connecting 
only one microphone at a time and is 
provided with a lamp which lights 
when the microphone is connected in 
circuit and is ready for use. Another 
unit permits a number of microphones 
to be connected at one time, of which 
any one can be selected at will. A plug 



and jack are provided in the cord so that 
the microphone can be disconnected if 
desired. The plug contains a small con- 
denser to prevent the cohering of the 
carbon granules which would otherwise 
occur were the plug withdrawn from 
the jack while the microphone is con- 
nected in circuit. When in use, the plug 
and jack are placed in the coat pocket. 
This prevents mechanical vibration 
from being transmitted through the 
cord to the microphone and introduc- 
ing noises. 

S. P. Grace was the first to use this 
microphone. His audiences have mar- 
veled at the loudness and clearness 
with which his voice reached them, 
even in large auditoriums, and for the 
most part have been unaware that he 
was using a microphone. They have 



only realized its part when he called 
to their attention that he had concealed 
the microphone in his coat pocket, and 
the cord by passing it down his trouser 
leg. The portability of the instrument 
has enabled him to move about freely 
while demonstrating his apparatus, in 
a way which would otherwise have 
been quite impossible. 

It is expected that the lapel micro- 
phone will find application in churches, 
convention halls, banquet rooms, lec- 
ture rooms, and the like. The instru- 
ment will be a boon to speakers who 
depend on gestures for effective deliv- 
ery, who must turn to explain lantern 
slides or use a blackboard, or who find 
it difficult to put their personality into 
their message if their position is re- 
stricted. 



Talking picture productions for college alumni 



THERE has just been completed a 
production of a three-reel talking 
picture "Life on the Quadrangles," 
for the University of Chicago. 
The university has been seeking for 
some years the most effective means of 
satisfying requests of its alumni and of 
high schools for information concern- 
ing its activities, and adopted the sound 
picture medium as providing the most 
vivid and satisfactory method. 

Touching on all phases of college 
activities, the picture presents realis- 
tically the student life of the University 
of Chicago. It takes the audience into 
the lecture room, the conference room, 
and the laboratory. It enables them to 
hear President Robert Maynard Hutch- 
ins explain the new educational plan 
Among other notables seen and heard 
are Thornton Wilder, the novelist, ad- 
vising a student writer, and director 
A. A. Stagg, the famous "Old Man" of 
. Chicago athletics, talking to his foot- 
ball team before it takes the field in an 
important game. 

There is a representative selection of 
campus activities, among them scenes 
showing women's athletics, archery, 
hockey, and swimming, the staff of the 
student newspaper at work, dramatic 
rehearsals, and informal views of dormi- 
tory and fraternity life. A scene of un- 
usual beauty in the University chapel 
emphasizes the spiritual life of the Uni- 
versity. 

While the picture maintains a tone of 
dignity throughout, it moves swiftly 
and holds interest to the final fadeout. 
The voice of Quin Ryan, of radio fame, 
makes running comment on outstand- 
ing features of the picture. The "Alma 



Mater," sung by the University choir, 
furnishes an attractive accompaniment 
to the title footage. Staging of scenes 
was avoided in producing the picture 
and the action is consistently natural. 

Pre-views Well Received 

Several previews of the picture were 
held to test audience response of the 
groups toward which the picture is di- 
rected, and the University authorities 
were greatly pleased with the reaction. 
Three different high school student 
bodies, totaling 2,500, were keenly in- 
terested in the picture, and alumni clubs 
have been enthusiastic in their recep- 
tion. A special preview at the Univer- 
sity of Chicago for the benefit of the 
unemployed packed Mandel Hall, and 
netted $900. 

A portable sound projector, operated 
by Kenneth A. Rouse, assistant to the 
dean, and former Chicago football cap- 
tain and winner of the Tribune trophy. 
is being used to show the picture be- 
fore high schools and alumni in the 
middle-west. The University is now 
planning to have the picture reduced 
to 16 mm. for use before small groups 
at distant points where it is not con- 
venient to send the present equipment. 

"Life on the Quadrangle" was pro- 
duced at the University and the Vitalgo 
Studios, under the direction of Avery 
B. Chereton. The photography and 
sound are theatrical in character and 
of a quality not ordinarily found in 
straight commercial productions. An 
enormous amount of incandescent light- 
ing was used on a number of the Uni- 
versity scenes. 

The Vitaglo Corporation formerly de- 



voted their entire efforts to the manu- 
facture of recording and reproducing 
apparatus for the major production 
studios, but on discovering the tremen- 
dous field existing for the production 
of commercial and educational pictures, 
suspended manufacturing operations 
and are now devoting their entire facil- 
ities to the making of pictures. 



HARVARD TO TEST VALUE OF 
FILMS IN EDUCATION 

EXPERIMENTS to determine the 
value of talking films in education 
are to be begun in three Massachusetts 
cities. 

The tests, which will continue over a 
six weeks' period, were devised by the 
Harvard Graduate School of Education, 
working with a $25,000 grant from the 
Carnegie Foundation for the Advance- 
ment of Teaching. The junior high 
schools of Lynn, Quincy and Revere 
were selected for the tests. 

Three hundred students will receive 
film instruction as well as instruction 
with textbooks. A large "control 
group" will be instructed with text- 
books alone. At the end of the period 
both groups will be given tests which 
have been devised especially to deter- 
mine the comparative effectiveness of 
both types of instruction. 

Eight films will be used. They deal 
with physiography and biology and pre- 
sent the fundamentals of each subject as 
covered in the last-year course of junior 
high schools. 



FEBRUARY, 1932 



Page 21 



P-A.. SPECIFICATIONS 

HEREWITH is a form of ques- 
tionnaire suitable to forward 
to persons desirous of procur- 
ing equipment or an installa- 
tion for public-address uses. With the 
answers 1 to these questions in hand the 
manufacturer is in position to advise 
and to quote. 

1. Is the installation for the purpose 
of reaching : 

a. Indoor audiences? 

b. Outdoor audiences ? 

c. Both indoor and outdoor audi- 
ences ? 

2. If an indoor installation, what are 
the dimensions and what is the cubical 
content (width x length x height) of 
the, room or space to be covered? 

3. What are the acoustic properties 
of the room or space to be covered? 
Answer the following questions : 

a. Are the walls bare ? State 
whether wood, plaster, stone, brick 
or beaver-board. 

b. Are there many draperies in the 
room? 

c. Has the room been treated for 
acoustical defect? 

d. When the room is filled, nor- 
mally, is there apt to be a good deal 
of space around the audience? In 
other words, does the seating capac- 
ity take- up all the available space 
outside of the aisles ? 

e. Is the height of the room 
greater than its length or breadth ? 
Give dimensions. 

f. Is there a balcony seating an 
audience ? 

4. Are the loudspeakers desired at 
one end of the hall or are they to be 
located in the center of the room, or 
suspended from the ceiling? If any 
special speaker placement is particu- 
larly desired, so state. 

5. Are additional speakers required 
to serve sound to other rooms or out 
of doors? If so, how many, and state 
whether indoor or outdoor. If indoor, 
give same information for this room as 
was asked under question 3 for the 
main room. If outdoor, mention area 
to be covered and advise if there is an 
unusual amount of noise in the vicinity. 

6. If an outdoor installation, state 
the exact area to be covered by. sound. 

7. Is the location of the outdoor in- 
stallation noisy? Are there nearby any 
of the following: Car lines, heavy.auto- 
mobile traffic, machinery in operation ? 
If so, describe the sound effect of this 
extraneous noise upon the location to 
be served. 

8. Is the installation desired for 
speech only, or will it be used for the 
following as well : 

a. Reproduction of music, played 
by an orchestra on premises. 



b. Reproduction of music or speech 
from phonograph records. 

c. Radio reproduction. 

9. What type of electric current sup- 
ply is available ? Specify : 

a. Voltage. 

b. Alternating or direct current. 

c. Frequency, if alternating cur- 
rent. 

10. Describe in detail, location of 
sound pickup with respect to loud- 
speakers. 

a. Voice. 

b. Music from orchestra. 

c. Phonograph reproduction. 

d. Radio reproduction, and if so 
give make and model number of radio 
set. 

Send a pencil sketch of the rooms 
and spaces to be served with sound. 



LARGE P-A. SYSTEM FOR HIGH 
SCHOOL IN NEW YORK 

THE first step in the recently an- 
nounced program to test the po- 
tentialities of the sound motion 
picture as an aid in teaching in 
the New York public schools was taken 
on January 15 when contracts were 
signed for the installation of RCA Pho- 
tophone sound reproducing equipment 
in the new Samuel Gompers industrial 
high school for boys, 145th Street and 
Wales Avenue, Bronx, New York, 
which is now under construction and 
which will be open in September. The 



equipment, one of the recently intro- 
duced all a-c. operated types, will be 
installed in tin assembly room which 
will have a seating capacity of 724 per- 
sons. 

Provisions for the installation of mo- 
tion picture apparatus having been 
made when the plans for the new build- 
ing were drawn, the projection booth 
and necessary wiring throughout to 
the loudspeaker apparatus behind the 
screen, will be modern to the most min- 
ute detail. 

Dr. Eugene A. Colligan, associate 
school superintendent in charge of the 
visual instruction activities of the New 
York board of education recently an- 
nounced that he had suggested experi- 
menting with sound pictures and it is 
said that other installations will be 
made in high schools within the next 
few months. 

Dr. Charles Pickett will be principal 
of the new Samuel Gompers high 
school, which will have a pupil enroll- 
ment capacity of 1,696 boys. In addi- 
tion to sound motion picture apparatus, 
the new school will be equipped with a 
complete radio communication system 
with outlets and speakers in all parts 
of the building. A radio control room 
will adjoin the principal's desk and 
through the medium of a microphone, 
the principal will be able to speak to 
one or all rooms or even to students 
upon the outdoor courts. Seventy-six 
loudspeakers will be located at various 
points of vantage. 



AAA 




Left: Front view of rack and panel equipment for public address recently installed 

in St. Paul Auditorium, St. Paul. Minn. 

Right: Rear view of panel installation. (Made by Samson Electric Co.. Canton. Mass.) 



Page 22 



Standards for 
electrical reproduction 
and recording 
of sound 



ALTHOUGH projectionists are 
quite generally familiar with 
the application of the trans- 
mission unit, known as the de- 
cibel, to the discussion of the electrical 
reproduction and recording of sound, 
there is no doubt that they are often 
perplexed as to whether to include the 
photographic characteristics of the film 
in such discussions. For a given input 
to the microphone at the recording stu- 
dio, and knowing the electrical charac- 
teristics of the microphone, amplifiers, 
light valves, and loudspeakers, it should 
be easily possible to calculate the out- 
put of the loudspeakers, basing the en- 
tire calculation on the transmission 
characteristics of the electrical circuit. 
However, the system is not a complete 
electrical transmission system, but is 
broken approximately at its middle by 
the motion picture film. The problem 
is, how to include the photographic 
characteristics of the film in the dis- 
cussion. 

Fortunately, the photographic char- 
acteristics of film are logarithmic in na- 
ture, exactly as are the transmission 
characteristics of electrical circuits. The 
density of an exposed light-sensitive 
emulsion is a logarithmic function of 



S. M. P. E. Committee 
recommends aperture di- 
mensions 



the quantity of light to which it has 
been exposed. 

Again, fortunately, the current out- 
put of a photoelectric cell bears a linear 
relation to the light incident upon it; 
and, finally, the luminous output of a 
light valve or glow-lamp is a linear 
function of the electric power operating 
the one or the other. So, the phenomena 
found in motion picture systems operate 
according to two laws, one of which is 
linear, the other of which is logarith- 
mic. By converting the logarithmic 
functions into decibels, it is possible to 
consider them as a group, and the pho- 
tographic characteristics of the film may 
be regarded in terms of equivalent elec- 
trical characteristics. 

The transparency (or transmission) 
of motion picture film is a linear func- 
tion of its exposure, and its ability to 
transmit light is a linear function of its 
transparency. But the density of mo- 
tion picture film is a logarithmic func- 
tion of the transparency, so that in or- 
der to define the characteristics of the 
film in decibels we have to consider the 
logarithm of the transparency, or sim- 
ply the density. 

V. C. Hall in the March issue of the 
Journal of the Society of Motion Pic- 
ture Engineers, explains very clearly 
the manner of including the characteris- 
tics of the film in making calculations 
of the performance of the entire system. 
If the transparency of the film at two 
points is Tj and T 2 , respectively, and 



PROJECTION ENGINEERING 

the. corresponding densities are Dj and 
D 2 , the change of response of the sys- 
tem as the film passes from one point 
to the other is calculated in decibels 
either by 20 log (T 2 — Ti) or simply 
by 20 (Di — D 2 ). By employing densi- 
ties, therefore, instead of transparen- 
cies, the calculation is greatly simpli- 
fied. 



Much time has been spent by the 
standards committee of the S. M. P. E. 
during the past several months, on the 
problem of establishing dimensional 
standards for projector apertures. When 
sound was introduced into the picture, 
a portion of the frame of the film was 
taken up by the sound track, so that 
the photographer had to restrict the 
scene he was photographing conform- 
ably to the reduced area of the film 
which was available for photographic 
purposes. 

Likewise, the projectionist, in order 
to preserve on the screen a pleasing 
shape of picture, was forced to mask 
the top and bottom of the projector 
aperture, and so was unable to project 
to the screen the part of the action in- 
cluded in the masked portions of the 
film. 

On account of these difficulties the 
S. M. P. E. standards committee recently 
recommended that the width of the 
aperture be increased from the present 
width of 0.800 inch to 0.825 inch, 
changing the height by only 0.010 inch 
in order to assure a pleasing shape of 
picture in theatres employing large an- 
gles of projection. 

On May 9 to 12 inclusive, the 
Spring, 1932, Convention of the S. M. 
P. E. will be held at Washington, D. C, 
with headquarters at the Wardman 
Park Hotel. An extremely interesting 
program of papers is being planned, 
and arrangements are being made to 
hold an attractive exhibition of newly 
developed motion picture apparatus. 
Coming at the time of the Washington 
Bi-Centennial, there will be much to 
attract attendance to the convention, 
and everyone is cordially invited to at- 
tend. 



AAA 



Answers to Projectionists' Examination Questions 

It is a good sign to see so many projectionists taking the time to study the questions appearing in the 
successive issues of PROJECTION ENGINEERING. Some sets of answers are not correctly worked out, but 
in all replies sent in there is evidence of a desire to learn. The presentation of a series of technical questions 
monthly gives each projectionist reader an opportunity to test his knowledge. 

Sets of answers received to questions 21 to 25, which appeared in the December, 1931, issue, 
include those sent in by C. L Merrell, Selmer, Tenn.; Robert A. Passmore, Valdosta, Ga.; Frank Griesel 
Regina, Sask.; Albert Bolze, New Glasgow, N. S., Canada; Kirk Buchak, Minneapolis, Minn.; Wilbur N. 
Leamon, Marion, Ind.; W. Hoy, Calgary, Alberta. 






FEBRUARY, 1932 



Page 23 



S.M.P.E. TO HOLD SPRING MEET- 
ING IN WASHINGTON, D. C. 

The Society of Motion Picture Engi- 
neers will hold its Spring Meeting in 
Washington, D. C, May 9-12, accord- 
ing to an announcement made by the 
Board of Governors of the Society. 
Washington was selected by the Board 
of Governors following a majority vote 
for this city by the membership. 

W. C. Kunzmann, chairman of the 
convention committee, and O. M. Glunt, 
chairman of the papers committee, will 
prepare the program of arrangements 
for the meeting which will be held 
during the height of the Washington 
Bi-Centennial activities. 
▲ 
INTERNATIONALIZING TALKING 
PICTURES 
{Concluded from page 7) 
are to be different versions of the film, 
care being taken to avoid by a proper 
choice of words, any actual discrepancy 
between speech and the movements of 
the lips. That this is quite feasible was 
proved in the case of "Nothing New at 
the Western Front" throughout the 
whole length of which there is perfect 
agreement of German speech with the 
lip movements of English speaking 
actors. 

An additional advantage of the 
rhythmographic process is the fact that 
the actors, being able to concentrate 
upon the phonetic parts of the roles, 
will do much better than in the case of 
an ordinary talking film record made 
at the same time as the picture is being 
produced. 

A further development of the new 
method, which is likely soon to ma- 
terialize, is the "radio talkie," in the 
course of which the text (read from 
rhythm bands) is transmitted by radio 
broadcasting to any number of cinemas 
communicating among one another and 
operating in mutual agreement. 
▲ 

CAUSES OF FILM MUTILATION 
{Concluded from page 8) 
the film through the machine, all the 
way to the takeup spindle, a chart was 
constructed which enumerated in suc- 
cession all the points in the projector 
which would admit of study with regard 
to tension, clearance, and wear, and the 
bearing which these have upon the mu- 
tilation of film and the successful pro- 
jection of high-quality pictures. This 
chart is actually a program of the work 
which the committee has undertaken; 
to obtain the information requisite for 
completing the chart, whether or not the 
values of tension, clearance, and wear 
found in practice are justified by exper- 
ience, and are compatible with high 
quality projection and are economical 
of film. 



SIX MORE TECHNICAL QUESTIONS 
FOR PROJECTIONISTS 

Correct answers will appear in the 
March issue of Projection Engineer- 
ing. 

33. State how you would go about 
setting up for reproduction using 
sound-on-film. 

34. What is the object of the excit- 
ing lamp, how is it adjusted? 

35. Describe a shunt motor, state 
how it is constructed. 

36. State what you know of the re- 
cording of sound-on-disc for use with 
sound pictures. 

37. Give six reasons for lamp not 
lighting, when using Mazda lamps for 
projection. 

38. How would you locate a ground- 
ed coil in generator ? 



THE ANGSTROM 

An angstrom is a unit of length which 
is used to express very short lengths, 
especially those of wavelengths of light. 
There are 100 million angstrom units 
in one centimeter, or ten billion in one 
meter. Hence a wave of 5,000 angstrom 
units long is 0.0005 centimeter long. 
▲ 

THE OUTPUT STAGE IN SOUND 
TRANSMISSION 

{Concluded from page 13) 
taken at some arbitrary frequency, 
though a good rule is to match im- 
pedances at the lowest frequency de- 
sired. If the amplifier is designed to 
work with a single loudspeaker, th^ 
units should be connected as shown 
in Fig. 14, which duplicates the im- 



pedance of a single loudspeaker. If 
more than four units are required, the 
number necessary will increase as the 
squares of whole numbers, four, nine, 
sixteen, etc. There should always be 
as many series groups in parallel as 
there are single units in each series 
group. Where it is impossible or im- 
practical to follow these suggestions 
always have the speakers arranged so 
that the load impedance is greater than 
the impedance of a single unit, not less. 
▲ 

TYPES OF SOUND RECORDS 

{Concluded from page 16) 
are greater, and there is no possibility 
that the sound and action will get out 
of synchronism. It must be under- 
stood that the designation "movietone" 
as applied to this form of composite 
sound and action print is merely a 
nickname and does not necessarily mean 
that the sound was recorded by the 
Movietone recording system. All of 
the better theatres are equipped to use 
either film or disc sound records ; but 
many of the smaller theatres are 
equipped as yet for reproduction from 
hard wax records alone. This is be- 
cause the disc equipment is not so 
thoroughly covered by patents as the 
film equipment, and so small inde- 
pendent companies can manufacture and 
market disc reproducing equipment at 
a greatly reduced cost. It is needless 
to say that often the quality of repro- 
duction obtained with this equipment 
leaves very much to be desired indeed. 
The trend seems to indicate conclusive- 
ly that eventually sound pictures will be 
released only on movietone prints. 

Photographs courtesy Universal Pic- 
tures Corporation and RKO Studios. 



▲ ▲ ▲ 



Chemical stages 
in the manufac- 
ture of. film. 




Cdhdase WW« Solution 

"DOPE" 



Pthn Supporl 



Emulsion 



1 



Finish* 1 *! Film 



Courtesy Eastman Kodak Co., Roci-crcr, X. V. 



Page 24 



PROJECTION ENGINEERING 



Fader attenuation circuits 
for public address 
and recording 

By W. S. Parsons* 



AFIELD with unlimited oppor- 
tunities and growing with the 
passing of each day is to be 
found in sound projection. 
Large outdoor public-address systems 
are no longer a novelty, but the appli- 
cation of this type of service can be 
turned to other innumerable uses. 
Churches, schools, hospitals, funeral 
parlors, public ballrooms, lodge halls, 
factories, apartment hotels, and many 
other similar places, are all prospective 
customers for good sound equipment. 
This field offers a profitable business 
for both dealer and serviceman. There 
are several manufacturers offering good 
amplifiers to meet the various needs of 
this market, but the control of the in- 
put system and selection of controls and 
speaker arrangement of the output sys- 
tem are left to the ingenuity of the per- 
son installing the equipment. 

In the following paragraphs no at- 
tempt will be made to discuss the vari- 
ous amplification systems. That, after 
all, would be a duplication of the recom- 
mendations of any manufacturer of such 
equipment. Therefore, we will confine 
our remarks to a non-technical discus- 
sion of the use of attenuation units as 
controls in both input and output cir- 
cuits. 

The requirements of sound projection 
are divided into two classes : 

First, a system of perfect fidelity, 
where both voice and music must be 
one hundred per cent. Installations of 
this type are necessary in schools, 

^Engineer, Central Radio Laboratories, Mil- 
waukee, Wis. 



I~1A D 




hotels, ballrooms, etc., where quality is 
primary and extreme volume secondary. 
Second, a class of equipment where 
volume is essential and fidelity only a 
necessity over the range of voice fre- 
quencies. This type of equipment is for 
announcing and call systems or out- 
door public address where the major 
requirement is volume. 

Input Control 

Let us consider a typical input system 
for a requirement of the first class such 
as a centralized school installation. A 
microphone for announcements, pickup 
for recorded entertainment or educa- 




traranrar 
> 








> 






VVWNA, 

— Vvwjv- O 
-WwIa, 


vwyy^ — 
— ^vwvw CP 
VWWA 





Fig. 1. 



Fig. 2. 

tional subjects, and a radio set for 
broadcast features of interest to pupils. 
These three instruments must be prop- 
erly mixed and controlled before input 
to the power amplifier to assure com- 
plete fidelity of the reproduced sound. 
See Fig. 1 illustrating connections. Al- 
so see Fig. 2 for connections for a 4 
microphone mixer. A proper control 
at A, B and C. Fig. 1, is "T" pad No. 
93-003, 200 ohms ; Fig. 2, A, B, C and 
D is "T" pad No. 93-005, 50 ohms. 

In the same type of mixer system as 
we have just described, the require- 
ments may call for a double turntable 
installation for continuous recorded 
transmission. It is then necessary to 
provide a fader from one pickup to the 
other. See Fig. 3 for method of con- 
nections. A proper control is fader No. 




Fig. 3. 

83-004 200 ohms. The pickups should 
be of 200 ohms impedance to match the 
200 ohm fader. The secondary of the 
transformer in Fig. 3 should be 200 
ohms for a 3-circuit mixer system and 
50 ohms for a four-circuit mixer. 

A representative system of the sec- 
ond class would be a call system, of the 
type used in depots and factories, or a 
public address system devoted to an- 
nouncements. 

The use of less expensive equipment 
will prove satisfactory in this type of 
installation as the prime requisite is am- 
ple volume, with fidelity necessary only 
over a relatively small part of the audio 
spectrum. 

Fig. 4 illustrates a four-microphone 
mixer panel providing a control for 
each microphone by means of an "L" 
pad. Four 50 ohm transformers in 
series feeding into a 200 ohm input 
transformer. A proper control for each 
microphone is "L" pad No. 96-005, 50 
ohms. If a three-circuit control is de- 
sired, then the transformers should each 
be 200 ohms and feed into a 600 ohm 
input transformer, and the individual 
control "L" pad No. 96-006. 200 ohms. 

To summarize input mixer circuits, it 
must be remembered that the individual 
generator units such as microphone, 
pickup, radio set or other device, must 
be connected through transformers or 
direct in the case of pickups where they 
are of the same impedance value as the 
individual sections of the mixer, to in- 
dividual controls. These controls are 
connected in series to match the stan- 
dard line impedance values of 100 ohms. 
200 ohms, and 500 or 603 ohms. The 




FEBRUARY, 1932 



Page 25 



mixer panel should never exceed four 
individual sections. 

Output Control 

The control of the output of an am- 
plification system is as necessary as 
proper input control. To obtain the 
best results, an individual control of 
speakers is essential. The number of 
speakers which can be successfully 
operated from an amplifier of certain 
size and power output, depends on the 
manufacturer's rating. 

The output of the majority of com- 
mercial amplifiers is provided with im- 
pedance adjusting transformers to meet 
the requirements of multiple speaker 
output. 

Dynamic speakers for use on high 
power equipment eliminate the usual 



transformer and depend on a direct con- 
nection to the voice coil from the line. 
The impedance of dynamic voice coils 
vary with each manufacturer of speak- 
ers. The range extends from 2 ohms 
to 20 ohms. However, the majority of 
speakers have a voice coil impedance 
between 10 and 15 ohms. Fig. 5 il- 
lustrates the individual control of three 
dynamic speakers connected in series. 

The speakers are from 10 to 15 ohms, 
and the total impedance of the group is 
30 to 45 ohms, and should be fed from 
a line of the same impedance value. A 
proper control for each speaker is "L" 
pad No. 94-001 rated at 10 watts for 
use with amplifiers of high power out- 
put, or "L" pad No. 96-001 rated at 4 
watts for use with amplifiers of moder- 
ate power output. 

It is possible to connect dynamic 




Fig. 5. 

speakers in multiple by series and par- 
allel connections to obtain any desired 
impedance value. Thus, for a multiple- 
connection of four dynamics of 10 ohms 
each, parallel two sets of two each and 
then connect the two sets in series, the 
resulting total impedance value is 10 
ohms. If all four were connected in 
series the total impedance would be 40 
ohms, while if all four were parallel the 
result would be 2y 2 ohms. 



AAA 



HEARINGS IN MARCH ON PATENT 

SUITS COVERING TALKING 

PICTURES AND RADIO 

TEN suits involving the motion 
picture and radio industries listed 
in the United States district 
court at Wilmington, Del., before 
Judge John P. Nields in the December 
term were continued until the next term 
in March. The suits continued are : 

Western Electric Company, Inc., 
Electrical Research Products, Inc., and 
American Telephone and Telegraph 
Company against the Stanley Company 
of America. 

De Forest Radio Company against 
the Duovac Radio Tube Corporation. 
The suit may be dismissed. 

United States of America, represented 
by L. E. Wales, United States Attorney, 
against Radio Corporation of America, 
General Electric Company, American 
Telephone and Telegraph Company, 
Inc., Westinghouse Electric and Manu- 
facturing Company, RCA Photophone, 
Inc., RCA Radiotron Company, Inc., 
RCA Victor Company, Inc., General 
Motors Radio Corporation and General 
Motors Corporation. 

American Tri-Ergon Corporation, 
Tri-Ergon Holding A. G., Josef Engl, 
Joseph Massolle and Hans Vogt against 
General Talking Pictures Corporation, 
DeForest Phonofilms, Inc., and Lee 
DeForest. 

Joseph Lopiano and Henry Frank, 
Jr., receiver of American Reproducer 
Corporation, against Pilot Radio & 
Tube Corporation. 

General Talking Pictures Corporation 
and DeForest Phonofilms, Inc., against 
RCA Photophone, Inc. 

General Talking Pictures Corporation 



and DeForest Phonofilms, Inc., against 
RKO Radio-Pictures, Inc. 

John M. Miller against National 
Broadcasting Company, Inc. 

John M. Miller against RCA Com- 
munications, Inc. 

The suits of General Talking Pictures 
Corporation and DeForest Phonofilms, 
Inc., vs. RCA Photophone, Inc., and 
General Talking Pictures Corporation 
and DeForest Phonofilms, Inc., vs. 
RKO Radio Pictures, Inc., may be tried 
in February. 

A 

DR. GOLDSMITH FAVORS AID FOR 
PROJECTIONISTS 

THE work of the projection practice 
committee of the Society of Motion 
Picture Engineers, when com- 
pleted, will be a valuable contri- 
bution to the motion picture industry, 
according to Dr. A. N. Goldsmith, presi- 
dent of the society. 

"When I recall that the driver of a 
five hundred dollar automobile has at 
his command an oil gauge, a speed- 
ometer, an ammeter, a radiator ther- 
mometer, and what not, with which to 
'feel the pulse and take the temperature' 
of the machine continuously while oper- 
ating it, I look with astonishment and 
sympathy at the projectionist, who is 
obliged to project pictures night after 
night before a one thousand box office 
house, in a two-hundred thousand dollar 
theatre, literally, as it were, in the dark, 
and partially ignorant of the condition 
of the projector until its condition be- 
comes so bad that the effect is seen upon 
the screen and is heard in the sound," 
said Dr. Goldsmith at the meeting. 

"Then it is too late — the audience has 
seen the effect, consciously or uncon- 



sciously, the audience carrie> away a 
feeling of dissatisfaction, the magnitude 
of which depends upon the seriousness 
of the circumstance, and may look else- 
where for better pictures and better 
sound. 

"When the projection practice com- 
mittee will have completed its work of 
determining all the tolerances, clear- 
ances, and tensions for all moving parts 
of the projector, as it has set out to do, 
and of determining the amount of wear 
to which these parts may be subjected 
with safety, it will have completed an 
invaluable piece of work. 

"But the final economic results of the 
work will have been achieved when the 
committee successfully indicates the 
simple means to be used by the projec- 
tionist to check these things, and the 
design of a cheap and simple kit of 
tools which he may use to do so. The 
Society of Motion Picture Engineers 
should do its best to make it easy for 
the projectionist to determine the exact 
condition of the projectors and to prove 
the occasional and timely need for re- 
placement parts to the properly eco- 
nomical exhibitor. This means money 
in the exhibitor's pocket through better 
audience reaction, and also a more sat- 
isfactory and dignified position for the 
projectionist. 

"Flicker, shaking of the picture on 
the screen, out-of-focus effects, poor 
sound reproduction, all of which can be 
caused by the wearing or the malad- 
justment of parts, will then be under 
the control of the projectionist, who 
will be able to check and to readjust or 
replace the faulty parts before they are 
allowed to annoy the audience, irritate 
the theatre owner, and drive away the 
patrons." 



Page 26 



PROJECTION ENGINEERING 



New Developments 



nd 



News of the Industry 



THEATRE AMPLIFIERS 

The Webster Electric Company, Racine, 
Wis., has introduced a new all a-c. oper- 
ated theatre amplifier in two models. 
These units are characterized by simplicity 
and compactness. With these units there 
is no need of batteries, chargers, elimina- 
tors or pre-amplifiers. The 6048R or 
6049R amplifiers are self-contained — will 
do the whole job — supplying exciter lamp 
current, photocell voltage, exciting current 
for monitor speaker and button current for 
a microphone. 

At a low cost any theatre owner — 
whether without sound equipment at pres- 
ent or with equipment suitable only for 
sound-on-disc — can, with these new Web- 
ster amplifiers provide the theatre with 
superior sound performance — from either 
system. 

The Webster Electric line of amplifiers 
is complete whether the requirements are 
for small installations or the most pow- 
erful "rack and panel" amplifiers. 



RECEIVER AND AMPLIFIER ACCESSORIES 

One of the most useful bulletins pub- 
lished within a year has just been put out 
by Electrad, Inc., 175 Varick St., New 
York City. 

The bulletin gives engineering, manufac- 
turing and service data on volume con- 
trols, voltage dividers, vitreous resistors, 
adjustable resistors, and other devices. 



THEATRE VENTILATION 

The demands of today in theatre ven- 
tilation and cooling are vastly different 
than in the early days. A new organiza- 
tion is announced as a successor to the 
old Typhoon Co., carrying on the old name, 
as the Typhoon Air Conditioning Co., with 
offices at 233 West 42nd Street, New 
York. J. F. Dailey, long associated with 
the old company, will head the new or- 
ganization as president, and E. L. Gar- 
field, chief engineer of the Typhoon Fan 
Co., will be in charge of design of equip- 
ment. As far as possible, the personnel of 
the old company will be retained, and a 
complete stock of parts will be carried, 
insuring owners of Typhoon equipped 
buildings, of prompt service in connection 
with their systems. 



16 MM. SOUND PICTURES 

A comprehensive catalog of 16 mm. 
sound pictures available through the Filmo 
library has just been issued by the library 
division of the Bell & Howell Co. Ap- 
proximately 500 subjects are listed. 

Many persons will be surprised to learn 
that so large a number of such sound 
films are available. The fact that pro- 
ducers have been so prompt in putting so 
great a volume of these sound releases on 
the market in the comparatively short time 
since 16 mm. talkie reproducing equip- 
ment was perfected is an indication of the 



great importance they are attributing to 
the 16 mm. sound field. 

The subjects listed in the catalog cover 
a wide range. Many are strictly of an en- 
tertainment nature, while others are edu- 
cational and informative. The listing will, 
therefore, be of interest not only to the 
users of sound equipment in the home, but 
to many others also, including educators 
everywhere. 

All subjects listed are sound-on-disc. 
A copy of the catalog, consisting of 33 
mimeographed pages bound in an attrac- 
tive cover, will be sent on request to any- 
one who sends eight cents in stamps to 
defray postage charges. Requests should 
be addressed to Library Division, Bell & 
Howell Co., 1801 Larchmont Ave., Chi- 
cago. 



SPEAK-O-PHONE RECORDING UNIT 

The accompanying illustration is of a 
new portable recording unit manufactured 
by the Speak-o-Phone Recording Studios, 
Inc., 201 W. 49th St., New York. 

A feature of this apparatus is that it 
records instantaneously upon aluminum 
discs. This renders recordings permanent. 




RESISTOR INSULATION 

An innovation in the resistor field has 
been developed by the Precision Resistor 
Company of 113-115 Frelinghuysen Ave., 
Newark, N. J. Their new process of mul- 
tiple baked enamel insulation used in their 
Precision type wire-wound, high resist- 
ance and porcelain tube high wattage units 
has overcome faulty insulation heretofore 
common with the average resistor unit. In- 
sulation being the vital factor governing 
the dependability and permanency of re- 




The specially processed metal used in 
these discs is an absolute protection against 
deterioration, breakage, or any harmful ef- 
fects due to climatic conditions. 



sistors, this improved unit, fills a long-felt 
want in the electronic and radio fields by 
its assurance of permanent, trouble-free 
service. It is now possible, with this new 
multiple insulation, to increase the voltage 
rating of these units, and still have a large 
margin of safety. There is a Precision 
unit for every purpose, Standard units in 
1, 2, 5 and 10-unit ratings or to specifica- 
tions. 



'PUBLIC-ADDRESS REPLACEMENTS 

A high-grade line of replacements of all 
parts employed in public-address equip- 
ment is being marketed by the American 
Sales Co., 44 West 18th Street, New York. 
The company has issued a new catalog il- 
lustrating microphones, amplifiers, and 
other units. 



CLAROSTAT AD-A-SWITCH CONTROL 

As a further convenience to jobbers and 
servicemen, the Clarostat Mfg. Co., 258 
N. 6th St., Brooklyn, N. Y., now has avail- 
able a new Ad-A-Switch line of volume 
controls. These versatile controls are 
made up in the general style and design 
of the genuine wire-wound potentiometers, 
and are obtainable in any taper or resist- 
ance up to 50,000 ohms. They have the 
added feature that a switch may be slipped 
on any of them without the use of tools. 

The Ad-A-Switch arrangement enables 
one to simplify lineup of stock on volume 
controls to a point where duplication of 
resistance on controls carried in stock will 
no longer be necessary. Any Ad-A-Switch 
volume control without switch can be con- 
verted at will into a complete unit with 
switch by replacing the usual dust cap 
with the special snap-on switch. 

These switches are the Compact bake- 
lite type, built into the metal cover so as 
to take up very little room. They are Un- 
derwriters' approved for 3 amperes, 110 
volts. The Ad-A-Switch volume controls 
are more completely described on page 7 
of the new 1932 Clarostat control hand- 
book and catalog, which also covers the 
whole line of Clarostat devices for the 
sound and electrical industries. 



FEBRUARY, 1932 



Page 27 





It Takes A 60 Watt Power Amplifier 
To Deliver the Sock! 

Sound installation men are learning from experience that it pays to make original installa- 
tions with amplifiers of ample power to do the work demanded by critical buyers. We 
have anticipated this trend and have specialized in amplifiers of more than ordinary 
power suitable for just that type of work. 

Rauland Model 185 Power Amplifier (illustrated) develops 60 watts of undistorted power 
output; designed to cover large crowds assembled in Stadiums, Athletic Fields, Fair 
Grounds, Parks, etc. Equally efficient for indoor use where great power is required. 

The output stage utilizes two 845 or 545 type tubes in special push pull arrangement with 
two 866 or 566 rectifiers. Individual Grid Bias control to balance plate current of amplifier 
tubes, time delay switch for proper application of plate potentials. The amplifier is 
equipped with proper and ample fuse protection*. Prices moderate. 

Rauland Power Amplifiers and Sound Equipment reflect the highest quality in design and 
manufacture behind which is twelve years of specialization in the science of audio amplifi- 
cation. We welcome the opportunity to supply technical information. Our staff of expert 
engineers are eager to help in any sound problem. Write for information. — Now. 

THE RAULAND CORPORATION 

3341 Belmont Avenue Chicago, Illinois, U. S. A. 



iimiiiiimiiniiiiii 



« A SYNCROFLIM "B" SOUND HEADS 
t*° FOR SIMPLEX or POWERS 

DESIGNED ESPECIALLY FOR SMALL THEATRES 
WHERE LOW PRICE EQUIPMENT IS DESIRABLE 



Compact and sturdy in construction, simple to operate, per- 
fect in efficiency. Smooth, quiet, positive drive assures even 
tone quality without distortion. 

Sound heads for Simplex or Powers projectors are furnished 
complete and include optical systems, photo-cells, exciter 
lamps, adjustable motor mounting brackets, endless woven 
belts, grooved motor pulleys and all necessary attachments 
for projector. 



EASY TO 
INSTALL 



$<£ ID per pair 
complete 

Write for further information 



MONEY-BACK 
GUARANTEE 



WEBER MACHINE CORP. 

59 RUTTER STREET ROCHESTER, N. Y. 

Export Office: 15 Laight St., N. Y. C. 



j £ Mini nun 



iimiii i 1 1 iniiinii i ii 



lllllllllllllllllllhl 



Page 28 



PROJECTION ENGINEERING 



CONDENSER MICROPHONE 

The Shure Brothers Company, 337 West 
Madison St., Chicago, with reference to 
their new condenser microphone, state: 

"This instrument is designed to meet 
the most exacting requirements for high 
quality radio broadcasting, sound record- 
ing, and sound measurement tests. Its out- 
standing characteristic is its relatively uni- 
form response to all frequencies from 40 




to 10,000 cycles. In the special design of 
its amplifier are combined the advantages 
of high output level with extreme wealth 
of richness in tone quality. Its reproduc- 
tion is so realistic as to make it difficult 
for even the trained ear to discern the use 
of the instrument between the original 
source of sound and the listening ear." 



PHOTOCELLS 

Telephoto photoelectric cells for sound 
heads employed in talking pictures are 
manufactured by the Telephoto Corpora- 
tion, 133-135 West 19th St., New York. 
These cells are made in four types to fit 
in all types of equipment. 



FILM SOUND REPRODUCER 

After two years of research work a new 
film reproducer is being announced by 
Acoustic Engineering Company, of Sagi- 
naw, Michigan. This reproducer reflects 
the designer's long experience in electri- 
cal and sound equipment design. 

The drive from the motor is by means 
of dual V belts, which method proved to 
be the most satisfactory after four models 
of direct and worm gear-driven types had 
been given exhaustive tests and proved less 
efficient. The projector drive, film drive 
and holdback sprocket shafts are all ground 
to very close tolerances and run in bronze 
bearings which have automatic oiling. 
These shafts are driven from the main 
drive through bronze helical spur gears 
which run in oil, assuring absolute quiet 
and smooth operation and freedom from 
lubrication difficulties. The film sprocket 
drive is filtered from the other shafts to 
prevent possibility of film flutter and a 
holdback sprocket prevents flutter from be- 
ing transmitted from the takeup. The mo- 
tor is optional at slight additional cost and 
is a specially developed slow-starting type 
which prevents jerking of the projector. 

The exciting lamp bracket is designed to 
be interchangeable with ease and can be 
prefocussed to prevent delays in sound 
reproduction in case of a lamp burnout. 
The optical system is a recent develop- 
ment and is capable of giving the same in- 



tensity of light on a .0005-inch slit as is 
usually produced on a .001 -inch slit. The 
sound aperture is of the curved type 
preventing possibility of film buckling and 
giving a perfect focus at all times. Ad- 
justable hardened and ground guide rollers 
of ample physical dimensions are used 
which permits of perfect alignment of 
sound track over aperture. The photo 
cell is of the caesium type and is mounted 
in a totally shielded housing so that no 
stray light or electrical disturbances can 
enter. 

The reproducer is adaptable to Simplex 
and Powers projectors. The overall di- 
mentions of the unit are 6]/ 2 inches high, 
10J4 l on g an< i 10 inches deep, which is 
compact and presents a clean appearance, 
especially so since all moving parts, ex- 
cept the flywheel, which also serves for 
a handwheel in framing, are enclosed. 

This reproducer may be used with any 
standard amplification system, but the 
manufacturers have developed their own 
amplifying unit which is completely a-c. 
operated and supplies P. E. cell voltage 
as well as current for exciting lamp and 
does away with the necessity of head am- 
plifiers, thus giving a complete power 
and control system all in one unit, which 
may be placed on the front wall between 
two projectors. 

Merchandising of the above described 
sound system which is called super sound 
reproducer will be through distributors 
and valuable territory is still available. 



FULTON DIVISION OFFICE TO BE LOCATED 
IN SAN FRANCISCO 

Western Divisional headquarters for the 
E. E. Fulton Co. of Chicago, manufacturers 
and distributors of theatre equipment, under 
a new policy which is now being formu- 
lated by C. H. Fulton, will be located in 
San Francisco. 

Paul Bush will continue as western 
representative, with headquarters in San 
Francisco. 



FILM CLEANER 

_ The importance of keeping all motion 
picture films clean, particularly the sound 
track type, is so well understood by those 
in the business that it is unnecessary to 
advance any reasons for it. 

Frequently films become oily during their 
first run or soon after. Then they quickly 
go from bad to worse. The oil holds the 
dust and grit which grinds into the emul- 
sion and the surface conditions become 
such that both the sound and screen effects 
are damaged. 

The oil and grit should be wiped off 
of the film as soon as it appears and before 
it has time to soak into the emulsion and 
grind into the surface. 

The exchanges frequently have no time 
to do this. It means an extra operation 
and when bookings are close together and 
the films have to be rushed out, not even 
the usual inspection and repair is well done. 

This condition can now be easily cor- 
rected. The Film Inspection Machine Co., 
630 9th Avenue, New York, is marketing 
a theatre model film cleaner. 

It is designed for reels up to 15 inches 
diameter. This is a combination of three 
machines each supreme in its class. It is 
an enclosed, motor-driven rewinder inspec- 
tion machine which detects all breaks, tears 
and open splices, a cleaning machine which 
effectively removes oil and grit from the 
film. 

Each of the above operations can be 
done separately or all three can be done at 



once at the rate of 225 feet per minute. 
Stops at all splices when it is desired that 
it should do so. 

A 

SPACING RINGS FOR CONDENSERS 

The Blue Seal Products Company, 260 
Wyckoff St., Brooklyn, N. Y., has brought 
out a new spacing ring to be used with the 
new type cylindrical condensers. The ring is 
made of asbestos, and is now being used 
by many theatres. The use of these rings 
prevents the chipping and cracking fre- 
quently experienced with this type of con- 
denser. The asbestos product used radiates 
heat as quickly as does the glass. The iron 
rings formerly used retained heat longer 
than glass, causing breakage due to contact 
between the glass and the hot iron ring 
after the arc was cut off. Asbestos rings 
are economical as frequent replacements 
of condensers will be avoided. 

▲ 
ACOUSTICAL MATERIAL 
There has been published a new and 
valuable compilation of coefficients of prac- 
tically all commercial materials used as 
interior surfaces of rooms for acoustical 
correction and noise abatement. More than 
fifty used products are considered, each 
type in various thicknesses. A copy of 
the report will be sent free by requesting 
same from Acoustic, room 1202, 52 Van- 
derbilt Ave., New York City. 
A 
WIDE ANGLE HORN 

The Racon Electric Co., Inc., 18 Wash- 
ington Place, New York City, announces 
the development of a new type No. 6320 
wide angle horn which is particularly 
adapted for sound distribution in theatres 
or auditoriums of extreme width — 50 feet 
or greater. 

Weighing but 60 lbs. this horn has an 
air column in excess of 10 feet. The bell 
is 76 in. by 28 in. and 37 in. deep. The 
throat is cast aluminum, and is self-sup- 
ported on the frame. The speaker is fully 
covered by patents. 

The speaker is made of a patented non- 
vibratory material of sturdy construction, 




and is not affected by atmospheric condi- 
tions, such as heat, cold, moisture or arid- 
ity. Full details concerning this and other 
types of Racon air-column speakers are 
included in the latest Racon catalog, which 
will be sent upon request. 

A 
RECORD PLAYING ATTACHMENT 

A new portable and completely self- 
contained unit for reproducing records 
through radio sets and power amplifiers 
has been announced by the Operadio Manu- 
facturing Co., St. Charles, 111. 

Housed in the leatherette carrying case 
are an electric phonograph motor and 
turntable, and a sensitive electro-magnetic 
pickup. A carrying case in the cover 
provides for storage of several records 
without danger of breakage. 

Available with either high or low im- 
pedance pickup, and with 78 or 33% r.p.m. 
motors, for 25 or 60 cycle, 110 volt power 
supplies. 



FEBRUARY, 1932 



Page 29 



The Higher The Quality Of Your Product 
The More Reason For 

PRECISION RESISTORS 

TO INSURE QUALITY — USE QUALITY 




DELIBERATELY DESIGNED FOR 

GREATER 
PERFORMANCE THAN NEEDED 



ALLOY WIRE WOUND MULTI ENAMELED 

REBAKED INSULATION. EXCLUSIVE 

PRECISION FEATURES. 



DOUBLE PROTECTION. DOUBLE ASSURANCE 
OF PERMANENT TROUBLE FREE SERVICE. 



PRICED IMPRESSIVELY LOW 
WHY PAY MORE FOR LESS 



EVERY TYPE FOR EVERY PURPOSE 
OR TO YOUR SPECIFICATIONS 



BY ALL MEANS INVESTIGATE 
SEND FOR BOOKLET E 



PRECISION RESISTOR CO 

113-115 FRELINGHUYSEN AVENUE 
NEWARK, N. J. 



SURPLUS STOCK 



=Must Sacrifice! 



Film Cement, per gal $2.00 

Spray Perfume, per gal.. . . 1.50 

(20 aromas) 

Gum Remover, per gal.. 2.00 

Screen Cleaning Fluid, per 
gal 2.00 

(For sound or beaded screens) 



Flame-proof 2 in I 
Cement, per gal.. 

Urikalces, per doz. . . 



Fil 



m 



2.75 
1.00 



No Regard to Cost 
! ! Get Our Price ! ! 

GALLON CANS ONLY 

Prices C.O.D., F.O.B. New York City 

BOX 15— PROJECTION ENGINEERING 

52 VANDERBILT AVE., 

NEW YORK CITY 




Portable Type 
Reflector Arc Lamp 

The sensation of the industry — this new lamp designed 
for projection of 35 or 16 mm. film. 

Gives a brilliant picture as large as 8 to 12 feet wide, 
even on porous screens, making it especially valuable with 
sound equipment. 

Operates from any lamp socket with current from 8 to 
16 amps. Weighs less than 25 lbs. Size 18" x 12" x 10". 
Extremely simple in operation. 

A new rectifier unit as companion to this lamp is also 
available. 

For Sale by Independent Supply Dealers 

£>he Strong Electric Corporation 

2501 LAGRANGE STREET TOLEDO, OHIO 

Export Office: 44 Whitehall Street, New York City, N. Y. 



General Radio 
Volume 
Control 

employing an entirely 
new circuit and 
mechanical construction 
at low cost. 






Contacts of Advance metal (using same wire for its resis- 
tance). Noise level is low and may be used in circuits at 
levels as low as 60 to 80 decibels without introducing noise 
in the circuit. 



Type 


Impedance 


Price 


652 M.A. 


50 ohms 


$12.50 


652 M.B. 


200 ohms 


12.50 


652 M. C. 


500 ohms 


12.50 



Let us assist you in your requirements 




JHhoHomeofRADK 

45 VESEY STREET NEW YORK CITY 



Page 30 



PROJECTION ENGINEERING 



Carbon Prices Reduced 



EFFECTIVE January 1, 1932, sub- 
stantial price reductions apply to all 
National Projector Carbons. 

Motion Picture Theatres will save 
from five to twenty-eight per cent on 
their carbon costs at these new prices. 

This announcement is in line with 
National Carbon Company's policy of 
sharing with the industry benefits derived 
from its program of intensive research 
and steady improvement in manufac- 
turing methods. 

Use National Projector Carbons in 
your theatre. 

A sound investment in 1931. 

A better investment in 1932. 



N AT 

P R 



I O N A L 

OJECTOR 



CARBONS 



. . . Sold exclusively through distributors and 
dealers. National Carbon Company will gladly 
cooperate with the producer, exhibitor, machine 
manufacturer or projectionist on any problem 
involving light. 

NATIONAL CARBON COMPANY, INC. 
Carbon Sales Division • Cleveland, Ohio 

Unit of Union Carbide QH3 and Carbon Corporation 

Branch Sales Offices: 

New York Pittsburgh Chicago San Francisco 



COMPLETE STUDIO EQUIPMENT 

engineered to your specific needs. Supplementary elements added 
and matched to your present equipment. Recording or projection 
equipment for sound on disc or film. Complete public address 
systems designed, manufactured, rented for particular occasions. 

HARRY A. SUMMERS, M.E. 

37 Kenilworth Place, Brooklyn, N. Y. 




Where the Ultimate in 
dependability is required! 
MORRILL & MORRILL 

30 CHURCH ST., NEW YORK CITY 
Sole U. S. A. Distributors for the 

SIEMENS & HALSKE 

Condensers and Resistors 

Write for Bulletin P 




DEPENDABLE . . 

Telephoto Caesium Argon 
P.E. cells are Precision 
made : 

THEREFORE you may 
depend on their perform- 
ance at all times. 



QUALITY and PRICE RIGHT 
Telephoto & Television Corp. 

133 West 19th Street 
New York City, New York 



SAPPHIRE POINTS 

for recording and play - back 

standard and special types of jeweled needles avail- 
able, reasonably priced. Sapphire po'ints afford better 
sound. 

MEYER KOULISH CO., Inc. 

64 FULTON ST., N. Y. CITY BEekman 3-6109 




Low Range 



INSTRUMENT 
LITTELiFUSES 

1/100, 1/32, 1/16, Yt, 
Ya, %, H, 1, 2 amps, 
for galvanometers, 
milliammeters, etc. 




RADIO FUSES 

Vs amp. for "B" circuits, 

also 1, 1V4, 2 and 3 amps. 

for radio manufacturing. 

Details by return mail. 



LITTELFUSE LABORATORIES 



For Radio Amplifiers 
and Transmitters 

500, 1,000, 5,000 and 
10,000 volt ranges, in 
1/1/5, Yt, Y*. %, Y>, M, 
1, 1Y, 2 amps. 



1778 Wilson Ave., 
Chicago, 111. 



FILM TO WAX DUBBING MACHINES 

Wax Recording Equipment for sound pictures and 
Commercial Recordings 

R. W. NICHOLLS 

119-28 Twenty-seventh Ave., College Point, L. I*., N. Y. 



Automatic Record Changers 

If continuous automatic record changing is one of your 
problems write for data on our Model "A" chassis. 
Rapid program arrangement, absolutely reliable opera- 
tion. Light, compact and true toned. 



644 Broadway 



HARDRAY, INC. 



New York, N. Y. 



INDEX TO ADVERTISERS 



Ad. Auriema, Inc 



Bell Equipment Corp 

Blue Seal Sound Devices, Inc. 
Brawley Felt Co., Inc., T. R.. 



31 



30 

5 

31 



Cameron Publishing Co 32 

F 
Forest Electric Corp 3 

H 
Hardray, Inc 30 

K 
Koulish Co., Inc., Meyer 30 



Leeds Radio Co. 
Littelfuse Labs. 



29 
30 



M 



Meyer & Company, Hugo 31 

Morrill & Morrill 30 

N 

National Carbon Co., Inc 

National Theatre Supply Co 

Nicholls, K. W 



30 

5 

29 



Pitman & Sons, Isaac 31 

Precision Resistor Co 30 

R 

Racon Electric Co., Inc.... Back Cover 
Rauland Corporation, The 27 



Samson Electric Co Second Cover 

Siemens & Halske 30 

Simplimus, Inc Third Cover 

Sound Equipment Co 30 

Strong Electric Co., The 29 

Summers, Harry A 30 



Telephoto & Television Corp 30 

TJ 

Universal Elec. Welding Co 31 

W 

Weber Machine Corp 27 

Webster Company 6 

Weston Elec. Inst. Corp 3 



FEBRUARY, 1932 



Page 31 



WE 



otter to mannfac- 
tiwers Interested, in. 



EXPORT 

tlxe services of a. dependable organization, 
•well established in tne entire foreign field 

AD. AURIEMA, Inc. 

Manufacturers' Export Managers 
116 Broad Street, New York, N. Y. 





Universal Elec. Welding Co. 

All-Welded and Demountable 

REELS 

16 mm-ll"-14"-15" and Larger 

All Wire Reels Protected By Patent- 

9-10 37th Ave., Long Island City, N. Y. 



Papini "Gearless" professional recorder for 16" records, 33-1/3 
R.P.M. Price including- dynamic cutting head and microscope, 
$1,000. Original cost $3,800. 

Also 3 Jenkins & Adair condenser microphones complete. 
Original cost $225 each. Our price $100 each. 

SOUND EQUIPMENT CO. 

Manufacturers of professional and amateur equipment. 

Ill WEST 48TH STREET NEW YORK CITY 



HOTEL 



MAmUAWAM -IINCilO 



\ii 



ATLANTIC AVE. AND EIGUTU ST. 

VIRGINIA BCACH VA. 



^ Fireproof brick construction. 

li. The coolest spot on the beach. 

J! Invigorating breezes from ocean on East and 

■ Lake Holly on West. 

* Bright, airy outside rooms, parlor suites and 

|i]J||. apartments, private baths, superior cuisine — 

I li [P Surf bathing, riding, fishing, golf, dancing, 

I r Private tennis court and children's play* 

Ip ground. 

K J. WESLEY GARDNER, Manager 



^3 




TALKING PICTURES 

By Bernard Brown 

A detailed discussion of the principles of construction and opera- 
tion of sound film apparatus, including a complete history of its 
development. Of great importance is the full account of R.C.A. 
power system and the Western Electric speaker unit. Specially 
valuable for technicians and ..also the general reader. Many illus- 
trations and charts. $3.00 



TELEVISION: 

TODAY AND TOMORROW 

By Sydney A. Moseley and 
H. J. Barton-Chappie 

The development of television, early experiments, and its present 
and probable commercial use. Well illustrated. $2.50 



PHOTOELECTRIC 
CELLS 

By Dr. Norman A. Campbell and 
Dorothy Ritchie 

Comprehensive presentation of the practical application of photo- 
electric cells in television, sound projection, etc. Illustrated. $4.50 



Write for descriptive lists. 

ISAAC PITMAN & SONS 



2 WEST 45th ST. 



NEW YORK 



HUGO MEYER LENSES 

FOR PHOTOGRAPHY AND PROJECTION 

The discriminating user of lenses appre- 
ciates the superb correction, the mathe- 
matically precise formulae and the high 
standards of perfection inherent in 
Hugo Meyer photographic and projec- 
tion lenses. 

SPECIAL OPTICAL SYSTEMS CONSTRUCTED 
TO INDIVIDUAL REQUIREMENTS 

HUGO MEYER & COMPANY 

245 West 55th St. New York 

Works: Goerlitz, Germany 



Investigate this New 
Sound Absorber! 

Brawley Felt Feet are designed to meet the 
especial needs of the Sound and Light In- 
dustries. For some time progressive manu- 
facturers have successfully used Brawley Felt 
Feet to deaden sound from shocks. Let us 
send details. 

Machine screw, nail, 

rivet and reverse 

rivet types. 



S)j£> n/ 



m 



Free sample of any 
type you want. 




T. R. BRAWLEY FELT COMPANY, INC.| 

279— 20th Street, Brooklyn, N. Y. 



Page 32 



PROJECTION ENGINEERING 



A New Book by Cameron 

Now on thePress 



EXAMINATION 



QUESTIONS & ANSWERS 

SOUND MOTION PICTURES 

THE SUBJECT OF RECORDING AND REPRODUCING OF SOUND MOTION PICTURES COVERED IN 

QUESTION AND ANSWER FORM 

HERE ARE 35 OF THE 542 QUESTIONS THAT CANADIAN PROJECTIONISTS 
MUST BE ABLE TO ANSWER CORRECTLY TO OBTAIN A GRADE "A" CARD 



v HOW MANY OF THESE CAN YOU ANSWER CORRECTLY"? 



If you develop excessive plate current what 

would you do? 
How is amplification accomplished? 
Would any kind of synchronized motor or 
constant speed motor do for sound projec- 
tion? 
Why are all the wires carrying sound or 

speech lead covered and again enclosed 

in conduit? 
What is the "gain" control, and what are 

its functions? 
What would a low plate reading on the 

panel indicate? 
How many tubes in a D.C. and A.C. motor 

control cabinet? 
The photo-electric cell has a silvered lining; 

one wire is connected to the lining. Is 

this wire positive or negative? 
Does the voltage to the photo-electric cell 

cause a steady current flow? 
What and where is the grid leak in the 

amplifier? 
What is the function of the exciting lamp? 
What is the action of a, the plate; b, the 

grid; c, the filament in a vacuum tube? 



What might result from placing motor gen- 
erator sets and batteries in the same room? 

Explain what a rectifying tube does? 

What is "specific gravity"? 

What are the causes of motor-boating? 

Why does the needle on the disc travel from 
the centre of the disc to the outside? 

On Vitaphone disc is the sound recorded on 
the bottom of the track or groove or is it 
cut into the walls of the groove? 

What apparatus do the "H" batteries sup- 
ply with current on W.E. or N.E. equip- 
ment? 

Should all motor generator sets be grounded; 
if so, state why? 

What is a prismatic condenser? 

When using a prismatic condenser, will the 
condenser be closer to the aperture than 
if you used a piano condenser? 

Can a prismatic condenser be used when 
showing slides? 

When using a cinephor condenser system, is 
accuracy in the focal distance of much 
importance, and why? 



Can a cracked mirror or condenser be used 
with mazda projection? What will be the 
result on the screen? 

What is the average amperage on a high 
intensity; b, reflector arc; c, hi-low arc? 

If the voltage drops, what effect will the 
cutting out of resistance have? 

In an electric arc circuit, what various things 
offer resistance to the flow of current? 

What is the standard aperture size? 

Why does a cracked condenser show up when 
projecting slides and not when projecting 
film? 

Define the following: Collector lens, piano 
lens, menicus lens, converging lens, con- 
densing lens? 

What is absorption of light? 

What is the optical axis? 

What causes film to buckle; what effect has 
this on the screen? 

Which make of projector has an actual faster 
movement, that is the movement of the 
intermittent from full rest to full rest? 



All of the 542 Canadian examination questions, with several hundreds of others, are answered for 
you in this new book. The subject of Sound Motion Pictures fully explained in an easy as 
A-B-C manner. 



THE BOOK WILL BE PUBLISHED AT 3.50, BUT YOU CAN SAVE A DOLLAR BY TAKING 
ADVANTAGE OF THE SPECIAL PRE-PUBLICATION OFFER 

FILL IN THE COUPON NOW 



CAMERON PUBLISHING COMPANY 

Woodmont, Conn., U.S.A. 

Here is the special pre-publication price of 2.50. Send me a copy of QUESTIONS AND ANSWERS as soon as ready to the address 
below. I understand that I save a dollar by ordering now. 



Name. 



Addr 



THIS COUPON WILL BE HONORED UNTIL DAY OF PUBLICATION ONLY, WHEN PRICE BECOMES 3.50 

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Attention! 



Sound Engineers 

Sound Equipment Dealers 

Theatre Owners 




Here is something NEW 

SAF all A.C. 
ADAPTER 



offers an economical way of equipping 
theatres for all A.C. Sound-on-Film op- 
eration. It is not necessary to discard 
the present amplification system. 

The SAF ALL A.C. ADAPTER protects the 
theatre owner's investment in his present ampli- 
fication system. It eliminates all batteries, 
chargers, generators, etc. It gives enough vol- 
ume for the theatres up to 1000 seating capacity. 

The SAF ALL A.C. ADAPTER fills a long felt 
want in the talking equipment field. The im- 
provement is startling — for its elimination of 
hum — its sweetness of tone — its adaptability to 
all theatre amplifiers. Just think of it — by plug- 
ging into the output stage of any theatre am- 
plifier, you convert the present equipment into 
the latest ALL A.C. set. With a built-in tone 
control, you get fidelity of tone and a fre- 
quency response up to 10,000 cycles. 

The SAF ALL A.C. ADAPTER can be attached 
to all amplifiers used either on disc or film 
equipment. And it is not necessary to match 
impedances. Why? It plugs into a tube socket. 
Simply remove the tube preceding the output 
stage of the theatre amplifier. And insert the 
ADAPTER plug into the tube socket. See illus- 
tration. 

The SAF ALL A.C. ADAPTER is a three stage 
high gain amplifier. It is designed to work into 
the power output stage of any make amplifier. 
It also contains the necessary controls for volume 
and voltage. And it supplies exciter lamp and 
photo cell current. 



SPECIFICATIONS AND FEATURES OF THE SAF ALL A.C. ADAPTER 



All A.C. operation 

Can be used with any type Sound Head 

2 shielded five foot photo cell leads 

Disc or Non-Sync input jack 

Exciter lamp supply 

Photo cell supply for any type Caesium 

cell 
Frequency response up to 10,000 cycles 
Junction box outlets 
Silent change-over switch 
Photo cell balancers 
Built-in volume control 
Mounts on booth wall between projectors 



Tubes: One -24, two -27, one -80 and one 
Amperite automatic voltage control 
tube 
Automatic voltage control of exciters, 

photo cells and tubes 
Tone control to compensate for acousti- 
cal conditions 
Dimensions: l5'/4 inches high by 8% 

inches wide by 6/4 inches deep 
Can be used for Portable Equipment 
Power supply I 10 volts, 50-60 cycles 
Price: List $150.00, Less Tubes 
Set of Tubes, including Amperite: $5.00 



$150 oo 

Discounts to Dealers and Agents 



LIST 
PRICE 



LESS 
TUBES 



Fully Guaranteed - Write for Details 

SDlFUiyS, MC. 

67 CHURCH ST. BOSTON, MASS. 

Telephone Cable Address 

DEVONSHIRE 6542 "SIMPLIMUS BOSTON" 



for every type of 
sound installation 




RACON HORNS AND UNITS 
ARE COVERED BY U. S. PAT- 
ENTS NOS. 1,507.711 1,501,032 
,577.270 73,217 73,218 1,722.448 
1.711,514 1,781,489 1,832,608 
1,834,327 1,835,739 



horn speakers and dyn- 
amic units are better!! 



RACON Horns are constructed of an ex- 
clusive patented *non-vibratory material 
that positively eliminates resonance, so 
common in other type horns. 
RACON Horns are superior in reproducing 
high frequencies, especially at high volume. 
Distortion is impossible, tone quality ap- 
proaching that of the human voice is as- 
sured. 

RACON "all-weather" Horns are uncon- 
ditionally guaranteed against climatic con- 
ditions, rain, heat, snow, aridity, — nothing 
can affect RACON Horns. 



RACON 

ELECTRIC CO., Inc. 

18 Washington PL, N. Y. C. 
London, England Toronto, Canada 



Write for Racon's Cata- 
logue P. E. 1 and price 
list they will be sent 
upon request. 




"i i i i ' i ' i ' 1 1 II 1 1 Hi II 1 1 i ll ii lltf il li'i i ll M III II l i l ll HWII IIII III III III' i l l Hi 



IN THIS ISSUE 



ENS FOR SOUND PICTURES 
By Gordon S. Mitchell 

MICROPHONE IN PUBLIC- 
ADDRESS SYSTEMS 

By Charles Felstead 

JND TRANSMISSION FOR THE 
HARD OF HEARING 

By Henry L. Williams 

;ational and commercial 
lms with sound-on-disc 

By Roger W. Fenimore 



.D'S LARGEST PUBLIC-ADDRESS 
JD PROGRAM DISTRIBUTING 
SYSTEM 

By J. J. Kuhn 



Fourth Year 
Of Service 



# \aj? \sjll \ ILs** 



VI/UAL 






■ 



Photo, Courtesy RCA Institutes, Inc., 
New York 



View of Screen and Large Horn used in Sound 
Amplification Course. 



■■H 



ssvSfii 
5M24 

EE9_ 




I 






journal of the Sound and Lignt Projection Industries 



APRIL, 193' 



ARCTURU 

ANNOUNCES 




a line of 

TRANSMITTING TUBES, 

POWER AMPLIFIERS 

and MERCURY VAPOR 

RECTIFIERS 

Arcturus has built into these new 
products the same superior qualities 
of construction and performance 
which have established Arcturus as 
the name for dependability and qual- 
ity in the receiving tube field. 

The two tubes of the series now 
ready for distribution are Mercury 
Vapor Rectifier No. E-766 and the 
heavy duty type Mercury Vapor Rec- 
tifier No. E-772. 

IMPORTANT POINTS 
OF SUPERIORITY 



1. Rugged construc- 
tion. 

3. Special oxide 
coated filament — 
emission is distrib- 
uted evenly over 
entire length of 
filament. 



3. Uniform output 
voltage variation 
over wide range 
of current drain. 

4. Constant output 
for hundreds of 
hours on inter- 
mittent life tests. 



Write for details of the new Arcturus 
Mercury Vapor Rectifier Tubes Nos. 
E-766 and E-772. Arcturus Radio 
Tube Company, Newark, New Jersey. 




*E-766 (Upper) 

Filament Voltage 2}/ t Volts 

Filament Current ..... 5 Amperes 
Maximum Peak Inverse Voltage 7500 Volts 
Maximum Peak Plate Current 0. 6 Amperes 
Approximate Tube Voltage Drop 12 Volts 
* Interchangeable with *66 types 



**E-772 (Lower) 

Filament Voltage 5 Volts 

Filament Current .... 10 Amperes 
Maximum Peak Inverse Voltage 7500 Volts 
Maximum Peak Plate Current 2y% Amperes 
Approximate Tube Voltage Drop 10 Volts 
**lnterchangeable ujith '72 types 



ARCTURUS 

Quality Tubes for Transmitting, 
Receiving and Industrial Uses 



s 



APRIL, 1932 



Page 



When sound must fill 
the spaces of a theater 

Recommend the Completely A. C. Operated 
Webster Electric Theater Amplifier 

. . . it has many new features! 



wK '.. " ® ; yy 'wm 



mm -l' mm 



TheTone Compensator ill ustrated below 
is another new Webster Electric product 
which is highly desirable in any Theater 
or other Sound installation. It is particu- 
larly advantageous in reducing the bass 
response, reducing hum, needle scratch, 
carbon hiss, etc. It permits reduction of 
high or low frequency response to the 
desired level. 




IN this theater amplifier Webster Electric engineers have embod- 
ied the very latest developments. It incorporates many new 
features ... It is characteristically Webster Electric in design, con- 
struction and performance ... It meets the exacting requirements 
of Sound-On-Film and Sound-On-Disc reproduction equally well. 
Its simplified operation — with only one main control — provides 
Superior Sound performance at lower cost than ever before . . . 
In Webster Electric high quality you are assured the utmost value 

for the price you are asked to pay . . . 
Bulletin RC 118 which describes it in detail 
will be sent upon request. 



ill 

'Zeat SP dCCS 

SPECIFY 



WEBSTER ELECTRIC COMPANY 

ESTABLISHED 1909 

Racine, Wisconsin, U. S. A. 



Webster Electric 
Sound Amplifica- 
tion Equipment 
Includes: 

A complete line of Head 
Amplifiers, Power Supply 
Units; Faders;Tone Com- 
pensators; Microphone 
Coupling, Matching and 
Output transformers for 
theaterinstallation. Power 
Amplifier and Power Sup- 
ply Panels in 15, 25, 50, 
100, 150 watts or larger; 
15 watt Output Stage 
Panels; T.R.F. or Super- 
heterodyne radio panels; 
Microphone amplifiers 
and mixer panels, either 
battery or A. C. operated 
for one or more micro- 
phones; Phonograph or 
Turntable attachments 
for 78 or 33 Vy R.P- M. 
operation; a complete line 
of standardized Panels foe 
"Rack and Panel" Ampli- 
fiers to fully meet require- 
ments for general Sound 
Distribution Systems. 



WBSTER ELECTRIC 



Projection 

Engineering 




Sound Pictures 

Visual Projection 

Sound Recording 

Audio Amplifiers 

Public-Address Systems 

Photography 

Facsimile Recording 

Television 

Photo-Voltaic Cells 

Circuit Measurements 

Automatic Music 

Acoustic Engineering 

Radiant Energy Devices 

Electric Recording 

Phototubes 

Home Talkies 

Theatre Engineering 

Amplifier Tubes 

Sound Reproducers 

Screen Engineering 

Electric Power for Projec- 
tion 

Recording Studio Engi- 
neering 

Location Sound Equipment 

Rectifier Tubes 

Industrial Tube Applica- 
tions 



Donald McNicol 
Editor 

Jas. R. Cameron 
Associate Editor 

Ulmer G. Turner 
Western Editor 

F. Walen 
Managing Editor 



Vol. IV 



APRIL 
1932 



Number 1 



Contents 



PAGE 
4 



Editorial 

Screens for Sound Pictures By Gordon S. Mitchell 7 

The Microphone in Public-Address Systems 

By Charles Felstead 9 

The Screen Problem . , By Sylvan Harris 1 3 

A Re-Recording Machine for Sound Films By J. J. Kuhn 14 

Sound Picture Lectures Expansion 17 

Sound Transmission for the Hard of Hearing 

By Henry L. Williams 1 8 

Thermionic Switchboard Controls Theatre Light 20 

Educational and Commercial Films with Sound-on-Disc 

By Roger W. Fenimore 21 

World's Largest Public-Address and Program Dis- 
tributing System By J. J. Kuhn 22 



Departments 



New Developments of the Month and News of the 
Industry 



24 



Index of Advertisers 30 



Bryan S. Davis 
President 

James A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

19 East 42nd Street 

New York City 



E. M. Bacon 
Advertising Manager 

J. E. Nielson 

Circulation Manager 



Chicago Office— 333 N. Michigan Ave.— Charles H. Farrell, Mgr. 

St. Louis Office- 505 Star Bldg.— F. J. Wright. 

Kansas City Office— 306 Coca Cola Bldg.— R. W. Mitchell- 



San Francisco Office— 155 Sansome St.— R. J. Birch. 
Los Angeles Office— 846 S. Broadway— R. J. Birch. 
New Zealand— Tearo Book Depot— Wellington. 
Australia— McGill's Agency— Melbourne. 



Entered as second class matter August 15, 1931, at the post office at New York, N. Y„ under Act of March 3, 
1879. Yearly subscription rate $2.00 in U. S. Yearly subscription rate $3.00 in Canada and foreign countries. 



APRIL, 1932 



Page 3 



A message to the 

Motion Picture 
Theatre Owners 

of America 



A most important announcement was deliv- 
ered at the Allied States Convention in 
Detroit, and the M. P. T. O. A Convention 
in Washington by the Photophone Division 
of the RCA Victor Company. 

It was at the same time the most impor- 
tant announcement exhibitors have heard 
since sound became the screen's most domi- 
nating factor. 



Cut to the bone and right down to the solid 
facts, it is herewith transmitted to motion 
picture theatre owners of America, large and 
small, from the largest circuit to the indi- 
vidual exhibitor. 

Before one or the other contemplates the 
installation or replacement of sound repro- 
ducing equipment, investigation of the fol- 
lowing information is respectfully suggested: 



The Photophone Division 
of the RCA Victor Company announces 



The introduction of two new all AC 
operated sound reproducing equip- 
ments, the Standard Super, designed 
for theatres from 2,500 to 4,000 seat- 
ing capacity at $5,000 and Standard 
Large, for theatres between 1,400 and 
2,500 seating capacity at $3,750. 

Reduction in the price of the Special 
Size equipment from $1,600 to $1,450. 



Other material reductions including 
contract service charges, ail made pos- 
sible by the recent merger of the RCA 
Photophone Co. with RCA Victor Co., 
Inc. Increases in capacity limitations 
of all A C operated Special Size equip- 
ment from 500 to 600 seats and all 
AC operated Standard Small Size 
equipment from 1,200 to 1,400 seats. 



For further information communicate with 

Photophone Division 

RCA Victor Co., Inc. 

Camden, N. J.— branch offices in principal cities 




PHOTOPHONE 



SYSTEM 



TRADE MARKS REG. U. S. TAT. OFF 



E d 



Hitiiiiniiuiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiuiiiiiiiiiiiiiiiiiiiiiiiuiiiiiiiiiiiiiiiii 



i t o r i 

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIUIIII 

APRIL, 1932 



a 



THE TIME ELEMENT 
IN THE NEWS 



IT required an event of 
■ worldwide news import- 
ance, the Lindbergh kid- 
naping case, to mark the 
decline of the "extra" newspaper as a pur- 
veyor of the news — not of the day, but of 
the hour. Throughout the days while the 
crime had initial news value, radio broad- 
casting served the people of the world to 
an extent comparable to that which was 
accomplished by the "extra" newspaper, 
now seldom hawked throughout residential 
sections during the night hours. It is but 
a few years since vendors of newspapers did 
a thriving business (at "extra" prices) by 
getting out late editions of daily papers, 
recording late developments in events of 
major news importance. 

The illustrated weekly publication also 
appears to have come upon days when what 
it prints is largely second-hand as news. 
The newsreel of the "movie" houses improv- 
ing, and spreading in its coverage of events 
which have locale importance, now daily 
and nightly brings to the screen in thou- 
sands of theatres, views of all of the details 
of scenery, of principals, of participants, of 
the minions of the law — even of the chalked 
mark "spot." 

We live in a world of continuous change. 
Being aware of important changes as and 
when they take place serves somewhat as 
a cushion against the shock of change. 

Some twelve million homes in the country 
are equipped with ears which may be tuned 
in on the world at any time day or night. In 
the United States there is one picture the- 
atre to each six thousand persons: that is, 
20,000 theatres. 

Should the ultimate in television some 
day arrive what agency will send the daily 
newsreel into the homes equipped to repro- 
duce the scenes? 

Time will have the answer. 



THWART OF T^F talk i n ? P * C Vi r . e 

DOUGLAS Around the World in 

FAIRBANKS Eighty Minutes" which 

Douglas Fairbanks, Sr., 

recently presented pointed the way toward 



many adaptations of the method of sound 
recording therein employed. 

As a record of an adventurous and 
romantic visit to far places the picture was 
an outstanding success. The pictures were 
excellent. There was evidence of instruc- 
tion not to cut off the camera too soon after 
a particular scene was focused, which too 
often is done in haste to move on to other 
shots. Even when the innovation was not 
sensed clearly by all who viewed the pic- 
tures, audiences appreciated the opportun- 
ity to make lasting mental impressions of 
what was photographed. 

Although few theatre patrons who saw 
the picture and listened to the sound effects 
noted that much of the dialog and pictures 
were not synchronized, those who for pro- 
fessional reasons observed the technique 
were aware that a considerable amount of 
the sound recording could have been done 
after the return from Asia to Hollywood. 

There is in this much of suggestion as to 
what may be done by resourceful producers 
in the way of adding sound to pictures — 
taken perhaps with no idea of incorporating 
sound effects, or under conditions where 
simultaneous sound recording was out of 
the question or should have been too costly. 

There is opportunity in this for ingenuity 
and for the introduction of economies, while 
at the same time producing sound-pictures 
having a high value of entertainment. 



CANADIAN 
TALKIES 



f HE first all-Canadian 
sound-picture, "The 
Bells" was shown in To- 
ronto recently. Reports 
indicate, that the production was favorably 
received. E. Wyly Grier, Canadian artist 
and painter, who was present at the 
premiere, said this picture was the forerun- 
ner of an established Canadian film indus- 
try. It was produced in Toronto by 
George T. Booth, and plans are under way 
to follow it with a series of two-reelers. 



o3 



Ondc^WHtic 



<rL 



Editor 



APRIL, 1932 



Page 5 



Ordered Today 

^DelhweiL Today/ 

That's 

NATIONAL'S WAY 

Just what you need is always in stock at National — 
ready to go the moment the order arrives. Excuses 
don't happen. Alibis are out! Every order is a 
RUSHED ORDER at National, where everybody 
knows "the show must go on," and they're on their 
toes to help you keep it going. Carrying full stocks 
of Genuine Repair Parts and a complete line of Ac- 
cessories and Supplies of every kind at every film 
exchange center in the United States, National is 
organized for speedy service. Projectionists every- 
where have found that it pays to order their needs 
from .... 



TRADE 
where you're 
always treated 

RIGHT! 




NATIONAL THEATRE SUPPLY COMPANY 



YOUR LOGICAL 




I SUPPLY SOURCE 



TAKE THE 



Eye Way 

TO 

Greater Profits 




ACTION . . . Thrill . . . Pleasure . . . 
the real enjoyment of the show comes 
to your patrons through their eyes. 
Put it on with Super Cinephors . . . the 
lens that gives your audience sharp, clear, 
easy-to-watch pictures. Let them settle 
back in complete enjoyment when they 
come to your theatre. 

Super Cinephors can be used with either 
regular or wide screens with equal effective- 
ness . . . they project with the same clear- 
cut definition to either size. Used with the 



new Patented B&L Condensing System 
they transmit to the screen 50 to 100% more 
light. You get high screen brilliance even 
with the perforated screen. Correction is 
complete for both spherical and chromatic 
aberration. Strong contrast, maximum de- 
tail and exceptional flatness of field is 
assured. 

Beat your competition. Install Super 
Cinephors. Ask your National Theatre 
Supply man. And 



SEND 

THE 

COUPON 



BAUSCH & LOME OPTICAL CO. 

681 ST. PAUL STREET, ROCHESTER, N. Y. 

Please send me right away all the information on the new Super Cinephors and 
the patented Condenser System. 

Name 

Address 

City State 



Page 6 



PROJECTION ENGINEERING 



NEW Samson CINE-PAN 



Tubes 
can be 
exposed 
for re- 
placement 
by remov- 
ing 4 thumb 
screws. 

There are 2- 

224's, one 280, 2- 
281's, one 245, and 
2-250's. 




HAS SURPRISING 
FEATURES 

For use as portable or permanent booth 
installation of sound-on-film talking pic- 
ture equipment. 

It is highly prized by those connected 
with theatre management. It is only 
28% inches long by 20 Va inches high 
and 10'/4 inches deep, weighs but 
104 lbs. 

Any panel can be removed by 
taking out 4 screws without 
breaking a soldered connection 
as all connections are made 
with flexible wire and plugs. 

2 15-ft. lengths of shielded 
cable from foto cell in the 
sound head to the Cine- 
Pam are provided and 
can be increased to 25' 
lengths without any 
noticeable loss in 
high frequencies. 

Your biggest sur 
prise will be the re- 
markable crisp- 
ness of dialogue 
—heretofore 
sadly lacking 
in most 
sound-on 
film am- 
plifiers. 



Variable output im- 
pedance allows use 
of any speakers you 
already have in your 
theatre. 

Visual volume indicator 
gives operator more ac- 
curate volume control 
than aural indication. Field 
current and voice energy 
are also provided for moni- 
tor speaker if wanted. 

The Cine-Pam is entirely AC 
operated and supplies photo-cell 
voltage and exciter lamp current. 
No batteries of any kind are re- 
quired. 

Sold only through manufacturers 

or jobbers of talking motion picture 

equipment. Ask them for literature 

on the Cine-Pam — or write us for 

Folder No. PE16. 



Manufacturers Since 1882 
Main Office: ■*■=»*„„ ^ Factories: 

Canton, \&£*£?L& Canton and Water- 

Mass. Jife^-^ ""» tQwn Masg 



Projection Engineering 



APRIL, 1932 



Screens for sound 
pictures 



By Gordon S. Mitchell 



In this timely article Mr. Mitchell presents technical 

information of direct use to projectionists and to theatre 

managers, dealing with screen structure, mounting and 

maintenance 



ONE of the perplexing prob- 
lems connected with the ex- 
hibition of motion pictures is 
the selection of a proper 
screen. Into this there enter several 
considerations, among which might be 
enumerated the matters of sound trans- 
mission, most suitable image area, and 
optimum position with reference to both 
front and rear seats. So many factors 
enter into the final considerations that 
an arbitrary statement of recommenda- 
tion cannot be made. Each individual 
exhibitor is forced to take into account 
the conditions under which he is to op- 
erate, and arrive at a conclusion which 
will be satisfactory in his case. 

Theatre characteristics vary and 
there is no one screen which will prove 
to be suitable for all. A theatre may 
range in width from 25 to 125 feet, and 
in length from 50 to 250 feet. There 
may be no balcony or there may be as 




Fig. 1. Showing magnified section of 
screen surface. 



!■!!!:! 



many as three, and the projection an- 
gle may lie at any value between zero 
and 35 degrees. The screen position 
may be anywhere from 10 to 30 feet 
in front of the first row of seats. 

There are in general three types of 
screens which may be used today : the 
diffusive or matte, the reflective or me- 
tallic, or the directive or beaded. All 
three of these type screens are prepared 
for sound transmission; that is, have 
small openings designed to allow sound 
waves *to pass through the screen from 
horns placed behind. 

Diffusive Screens 

The diffusive screen is usually made 
of rubberized or cellulose coated mate- 
rial, which may or may not be covered 
by an additional coating of tiny glass 
or metallic particles. This type screen 
is very efficient, and re-directs a large 
amount of light. It gives good results 
with color pictures due to the fact that 
it is not color selective. Because it re- 
directs the light through wide angles, 
this type is satisfactory for wide the- 
atres and theatres having a steep pro- 
jection angle. Rich photographic detail 
is obtained without an excessive current 
consumption. 

Reflective Screens 

Reflective screens are made of alumi- 
num or other polished, coated metals 
and have varying degrees of diffusive- 
ness. Their particular advantage is that 
they build up the intensity of the re- 
flected light so that under certain con- 



ditions the apparent brilliancy of the 
picture is increased as viewed from the 
rear seats. Their use results in econo- 
my of projection in theatres which are 
long compared to their width. In the- 
atres which operate at an angle of pro- 
jection over 10 degrees such a screen 
is unsatisfactory, and is found in a rela- 
tively small number of houses. They 
are color selective, consequently can- 
not be used for color pictures. 

Directive Screens 

The directive screen is a diffusive 
screen upon which there is placed a 
coating of glass globules. It builds up 
the intensity of,the reflected light, mak- 
ing observation of the picture from the 
rear seats more satisfactory, at the same 
time reducing the glare from the seats 
in the front of the house. Because of 
its apparent brightness, this type screen 
adds brilliancy to color pictures project- 
ed upon it. It is unsatisfactory for the- 
atres with steep projection angles, and 
undesirable for wide theatres because 
of its directive qualities. 

Plaster Wall Screen 

A contemporary writer upon the sub- 
ject is responsible for the statement that 
many of the theatres in Great Britain 
use a common plaster and wall for 
screen, but in his opinion this is usually 
a source of disappointment and trouble 
to the exhibitor because of the bugbear 
of condensation, unless the ventilation 
of the theatre is perfect. While a screen 
of this type might prove satisfactory 
for small theatres, the problem is con- 
siderably more complicated than would 
be indicated by so simple a solution. 

It is almost universal opinion that 
optimum illusion of reality is obtained 
when the projection horns are placed 
behind the screen ; obviously an impos- 
sibility when using the theatre end wall. 
Sound is transmitted through small in- 
terstices in the fabric, these openings 
covering only from four to eight per 
cent of the screen area. This was found 
to be sufficient provided the holes were 
cleanly cut. When audible pictures first 
became universal, sound considerations 
were tho_ught to be of major import- 
ance, and the quality of the projected 
picture suffered somewhat. An equita- 
ble adjustment has been arrived at since 
that time, and an arbitrary loss of ap- 
proximately three decibels has been set 



Page 8 



PROJECTION ENGINEERING 



up as standard by one equipment manu- 
facturer for theatres using their sound 
system. In some quarters this is thought 
lo be rather severe, but fortunately a 
well projected picture is possible with 
a screen meeting these requirements. 
Another company has allowed a slightly 
greater tolerance. 

Sound screen surfaces vary consid- 
erably ; some are hard, some sticky, 
some rough and some smooth. The per- 
forations increase dirt collecting char- 
acteristics, not only from their physical 
presence, but due to the fact that air 
circulates through the openings. Me- 
tallic screens not only collect dirt and 
dust, but become tarnished, which tar- 
nish lowers their light reflecting quali- 
ties considerably. 

The actual amount of dirt which col- 
lects upon any given screen depends 
upon characteristics of the theatre, and 
the care which is taken to protect the 
screen. Certain common sense precau- 
tions should be taken which will de- 
crease the importance of this item of 
theatre maintenance. Curtains, dra- 
peries and travelers accumulate dirt 
which gets on to the screen. These ar- 
ticles should be kept scrupulously clean. 
Drafts should be prevented which would 
carry dirt and dust to the screen sur- 
face, and when not in use the screen 
should be covered in order that the dirt 
stirred up by the house cleaning will 
not settle upon the screen surface. 

The maintenance of screens resolves 
itself into four definite divisions — pre- 
vention of dirt upon the surface, free- 
ing the surface of dirt which does col- 
lect there, thorough and complete pe- 
riodic cleaning, and a periodic renewal 
of the screen surface. 




Fig. 3. Projector type television screen. 



Even with the best of precaution, it 
will be impossible to maintain an abso- 
lutely clean screen surface. Inspection 
will show whether what dirt has col- 
lected upon the screen is dry or greasy. 
Dry dirt obviously can be brushed off 
with a long-handle brush, and it is good 
practice to clean the rear screen sur- 
face weekly or semi-monthly with a 
vacuum cleaner. There is no entirely 
satisfactory way to clean greasy accu- 
mulations from screen surfaces. If such 
cleaning becomes necessary, clean soapy 
water applied by sponge probably does 
the least harm to the surface. 

Renewal of screen surface by spray- 
ing has come in for considerable atten- 
tion of late, and when carefully done 
with good material a fairly satisfactory 
job may be obtained. The material used 
should be highly reflective. 

Installation problems connected with 
the motion picture screen are magnified 
somewhat by the lack of authentic data 
available on the subject. To date there 
is little information available upon the 
subject of keystoning, side distortion, 
optimum projection angle for various 
size theatres, and the relations between 
these various factors as concerned with 
theatres of any given characteristics. 
The screen itself, as a particular sub- 
ject for engineering investigation, has 
to date not received consideration in 
keeping with its importance to the fin- 
ished motion picture. There have been 
investigations made by various agencies, 
but in so far as a general investigation 
of the whole subject is concerned, 
taking advantage of the various items 
of knowledge available, I know of none. 

Installation problems connected with 
the screen increase in proportion to the 
size of the theatre. Certain funda- 
mental considerations enter into the 
final solution. In the first place, the 
human eye is unable to accommodate 
itself to an angle over 45 or SO degrees, 
hence the distance of the front row 
of seats from the screen should be at 
least fifteen inches for each foot of 
screen width. The size of the pic- 
ture is also determined by the dis- 
tance from the rear seats, and for 
this consideration a screen in width ap- 
proximately one-sixth of the distance 
from the screen to the last row of seats 
should be provided. As screen size in- 
creases, imperfections in the projected 
picture become more apparent. Graini- 
ness in the film shows up on a large 
screen, and small faults which might 
otherwise be unnoticeable in the print 
become obvious. On account of these 
considerations, a screen greater than 
18 by 24 feet should never be used. 

Larger Picture Area 

In this connection, the recent craze 
for large pictures might receive some 
small attention here. A large picture 
was practically obtained by merely 




Fig. 2. Showing method of screen 
mounting. 

changing the physical set-up of pro- 
jector and screen assembly, resulting in 
a projected image which was very un- 
satisfactory from a technical stand- 
point. The tendency towards large pic- 
tures has been somewhat discarded, and 
exhibitors are returning to a picture 
size which allows them to obtain some 
measure of technical perfection upon 
the screen. 

In a consideration of the actual prob- 
lem of installation of the screen, it 
might be well to point out that illusion 
is best maintained if the screen be 
placed as near to the stage floor as pos- 
sible. The floor of the stage in front 
of the screen should be painted with a 
non-reflecting, dull dark paint. A black 
frame around the screen decreases the 
jumping effect due to poor film or poor 
projection equipment, and should al- 
ways be installed. 

In certain cases, improved projection 
will result from a tilting of the screen, 
due to a decrease in the keystone ef- 
fect or to a re-distribution of the light 
throughout the auditorium. Tilting in 
general introduces complications of pro- 
jection which are not present when the 
screen is upright.- A tilted screen col- 
lects dirt much more readily than an 
upright. 

In conclusion, a word upon the rela- 
tive importance of the screen to the fin- 
ished motion picture might not be 
amiss. Large amounts of money are 
spent upon the production of a motion 
picture, as well as considerable effort 
on the part of a great number of peo- 
ple. Much effort in the theatre may be 
bent towards the perfection of projec- 
tion. All of this will be wasted if the 
screen does not measure up to the 
standards which have been set in the 
other branches. 

There may be possible important ad- 
vances in screen design which would im- 
prove the reproduction of projected 
pictures. The subject is one worthy of 
the attention of cinema engineers who 
are ever on the alert for points of at- 
tack in forwarding the art of the talking 
picture. 

In short, the screen is the final link 
in the motion picture chain from stu- 
dio to patron, and as such deserves 
more attention than has been given it 
in the past. 







APRIL, 1932 



The microphone in 
public-address systems 



By Charles Felstead* 



In this instructive article Mr. Felstead goes thoroughly 
into the subject of single and double button, and con- 
denser microphone construction and operation 



THE sound pickup device that func- 
tions to transform energy from 
acoustical to electrical form is one 
of the most important instruments 
in any electrical system that transmits, 
records, or amplifies sound. The de- 
vices now available for this purpose are 
not very efficient in operation, nor is 
their fidelity of transformation uniform 
at all audible frequencies. It is neces- 
sary for the engineer in the field of 
sound amplification and transmission to 
have a sound pickup device that will 
produce an electric current having prac- 
tically the same waveform and propor- 
tionate amplitudes as the sound-pres- 
sure waves that are to be amplified and 
supplied to the apparatus that will re- 
cord or reproduce the effect of these 
waves, and so it is his duty to select the 
type of sound pickup device that is most 
suitable for the work to be done. The 
more nearly perfect the electrical copy 
of the sound wave, the better will be 
the quality of the recorded or repro- 
duced sound. 

The Types of Microphones 

There are two main forms of this 
pickup device, which is known as a mi- 
crophone, or transmitter, in general use 
at the present time. The original type 
of microphone is the solid-back carbon 
transmitter, and is of the carbon gran- 
ule type; while the newer form of mi- 
crophone that is superseding the car- 
bon transmitter for all fine sound re- 
cording and reproducing work is called 
the condenser microphone because of 
its peculiar construction. The types of 
carbon microphones can be further sub- 
divided into those having single and 
double cells of carbon granules, and 
known as single-button and double-but- 
ton transmitters. The transmitters used 
in telephones, and in other places, where 
a microphone having great fidelity in 
the transformation of energy from 
acoustical to electrical form is not 
needed, are of the single-button carbon 
granule type ; while the double-button 



carbon transmitter is employed as the 
pickup device in radio broadcast sta- 
tions, public-address systems, and in 
conjunction with other equipment re- 
quiring a high-quality microphone. 
However, chiefly because of the fact 
that it has less inherent "ground" noise, 
the condenser microphone has lately 
been coming into quite wide use in place 
of the two-button carbon microphone 
in radio broadcast stations, and it is 
now used almost exclusively as the 
pickup device in sound motion picture 
recording installations. 

The Simple Carbon Microphone 

The single-button, or single-cell, car- 
bon transmitter was the first form of 
microphone to be employed for com- 
mercial purposes, and it is still used in 
telephones and intercommunicating tel- 
ephone systems in the sound recording 
studios and in large public-address sys- 
tems, so it will be well to describe it 
briefly before going on to a discussion 
of the two types of high-quality micro- 
phones. This simple transmitter con- 



Page 9 

sists of an elastic metal diaphragm 
mounted on a rubber ring that is held 
tightly against the frame of the trans- 
mitter. A carbon block is attached to 
the center of the diaphragm, and di- 
rectly opposite it another similar car- 
bon block is fastened to the frame. A 
band-shaped mica washer is wrapped 
around these two blocks, and the cham- 
ber thus formed between the blocks is 
filled with many small, polished carbon 
granules. This construction will be evi- 
dent from an examination of Fig. 1. 
The carbon blocks form the two termi- 
nals of the transmitter, and a battery or 
other source of e.m.f. is connected in 
series with the microphone and the out- 
going circuit. For some particular types 
of work, the microphone and battery 
are connected in series with the pri- 
mary of a microphone transformer, as 
may be seen in Fig. 2. When 
the alternate rarefactions and compres- 
sions of the air that constitute a sound 
wave encounter the flexible diaphragm 
of the transmitter, they cause it alter- 
nately to be sucked forward by a low 
pressure area in front of it and then 
forced backward by the following com- 
pression of the air. The vibration of 
the diaphragm in tune to the frequency 
of the sound wave varies the physical 
pressure on the packed carbon gran- 
ules. This changes the resistance of the 
transmitter — the greater the pressure on 
the carbon granules, the lower the re- 
sistance — and so varies the amount of 
current flowing in the circuit in which 
the microphone and battery are con- 
nected, for the amount of current that 
flows varies inversely as the resistance 
of the circuit. As we have said, this 
single-button carbon transmitter is of 
the low-quality type, and therefore the 
current variation that is created in it 
by a sound-pressure wave striking the 




*Sound Engineer, Universal Pictures Corp. 



Fig. 1. 



Courtesy Bell Telephone Labs 
Cross-sectional view of the 387 type double-button carbon microphone. 



Page 10 



PROJECTION ENGINEERING 



CARBON 



XJ p 1 

IJJ p V ° — WWV 

RHEOSTAT 




TO AMPLIFIER . 



Fig. 2. Microphone circuit. 

diaphragm may not be a faithful copy of 
the sound wave. 

It is plainly evident that too great a 
movement of the diaphragm in this type 
of microphone will cause a non-linear 
resistance variation. That is, if the to- 
and-fro movement of the diaphragm is 
of greater amplitude than a certain 
maximal value, which is given by More- 
croft as 0.0001 inch for an ordinary car- 
bon microphone, the current in the mi- 
crophone circuit will be an even less 
faithful copy of the sound-pressure 
waves producing the vibration of the 
diaphragm than is normally the case, as 
both odd and even harmonics will be 
present in the electric wave created. 
This type of single-button carbon mi- 
crophone usually employs a mouthpiece, 
and its sensitivity is high, although its 
fidelity of reproduction is poor. It is 
still used in wire telephony because it 
operates efficiently in transforming to 
reasonably faithful speech current just 
enough of the speech frequency band to 
make possible intelligible conversation 
between persons. 

The High-Quality Carbon Microphone 

The double-button carbon transmitter 
is of the stretched-diaphragm, carbon- 
granular type, and because of its con- 
struction it is often termed the push- 
pull transmitter. The sensitiveness of 
this type of microphone is extremely low 
■ — about one- 100th that of the common 
single-buttqn transmitter, but the qual- 
ity of its output is very high, compar- 
ing favorably with that of the con- 
denser transmitter. This double-cell 
carbon microphone is less bulky and 
less troublesome than the condenser mi- 
crophone, and it requires a smaller 
amount of amplification to bring the 
speech current up to a useful value; 
but the carbon hiss that is inherent in 
this type of transmitter somewhat limits 
its use, because the presence of the hiss 
brings the ground noise in the circuit 
up to such a high level as to cause it 
to interfere with the quality of the 
speech. 

This two-button microphone is widely 
used in public-address systems, where 
its many advantages for this type of 
work outweigh the annoying effect of 
the carbon hiss. Sometimes a filter is 
used with the two-button microphone 
to reduce the amount of hiss. The filter 



is formed of series resistances in each 
of the three leads from the buttons and 
small condensers shunted across the 
buttons. Up to the time of the devel- 
opment of the condenser transmitter to 
its present high standard of excellence, 
double-button carbon microphones were 
used exclusively in radio broadcast sta- 
tions ; but, as has been mentioned, they 
are being replaced by condenser micro- 
phones. They are generally employed 
in public-address work, however, and 
in the motion picture sound recording 
installation, this type of microphone is 
still used with the small public-address 
system that permits the monitor man to 
address the actors on the stage. 

Construction of the Double-Button 
Microphone 

In construction, the double-button 
transmitter is flat and circular and ap- 
proximately the size of a doughnut 
(about one inch by three inches). To 
overcome the effect of resonance and 
the resultant distortion in output that 
would be introduced by a mouthpiece or 
other form of collecting horn, this mi- 
crophone is used without such an at- 




Courtcsy Universal Microphone Co. 

Fig. 3. View of two-button carbon micro- 
phone without suspension. 



tachment. It is quite sensitive to me- 
chanical shocks, and so a simple form 
of spring suspension is used to insulate 
it from ' building vibrations and jars. 
The whole assembly is enclosed by two 
metal covers that each have several 
large circular holes cut in them. These 
openings are covered by a fine mesh 
metal screen that serves to protect the 
delicate diaphragms from injury by 
pencils, the ends of wires, or other 
objects. The microphone in its frame 
can be fitted with a base and used on 
a desk ; or the high stand type of mount- 
ing can be employed when the micro- 
phone is to be used by a speaker who 
is standing. 

The stretched diaphragm of this type 
of transmitter is made of a metal called 
duralumin, and it has a thickness of 
0.0017 inch. A spacing washer one mil 
(0.001 inch) in thickness separates the 
diaphragm on one side from a flat metal 
plate called the damping plate. This 



construction can be seen in an accom- 
panying photograph. The diaphragm is 
tightly clamped between stretching 
rings that are screwed up after assem- 
bly until the diaphragm is drawn so 
tightly that its resonant frequency is 
in the neighborhood of 5,700 cycles per 
second (c.p.s. ). This places the nat- 
ural period of the diaphragm safely out 
of the normal frequency range of the 
human voice, although from a sound 
transmission standpoint it would proba- 
bly be better to have the resonant point 
well above 8,000 c.p.s. The diaphragm 
being mounted so close to the back 
plate provides a high damping effect 
and tends to reduce the sensitiveness of 
the transmitter, but these two features 
help to reduce the effect of diaphragm 
resonance and improve the fidelity of 
reproduction obtained through the mi- 
crophone. 

On each side frame opposite the cen- 
ter of -the diaphragm are mounted car- 
bon electrodes similar to the ones em- 
ployed in the single-button carbon mi- 
crophone. Opposite these electrodes are 
24-karat gold-plated areas on the dia- 
phragm, and the two chambers formed 
between the carbon electrodes and the 
diaphragm are filled with polished car- 
bon granules. These cells are each de- 
signed to have a resistance of 100 ohms, 
as measured from the carbon electrode 
to the diaphragm, thus providing an 
overall resistance of 200 ohms from 
one carbon electrode to the other. This 
overall value is said to be the operat- 
ing resistance of the microphone, and 
the microphone will work most effi- 
ciently into a circuit having an impe- 
dance of 200 ohms. 

The arrangement of the carbon cells 
and the associated circuit may be seen 
schematically in Fig. 2. In this dia- 
gram, the transmitter is connected to 
a standard microphone transformer that 
has a primary with a resistance of 200 
ohms and a secondary that is of the 
proper impedance to work into the grid- 
filament circuit of a vacuum tube. A 
rheostat for regulating the amount of 
current supplied to the buttons of the 
transmitter by the battery, and jacks 
to permit the plugging in of a milliam- 
meter to read the current drawn by each 
of the buttons, are also required. This is 
the standard arrangement used with the 




Courtesy Universal Microphone Co. 

Fig. 4. Type of plug used on condenser 
microphone cables. 



APRIL, 1932 



Page II 



microphone in public-address systems 
and in radio broadcast installations. 

Operation of the Double-Button 
Microphone 

The diaphragm is always connected 
to a tap brought out in the exact elec- 
trical center of the primary winding of 
the microphone transformer in the man- 
ner shown, and the carbon electrodes 
are connected to the two ends of the 
winding. This places the resistance of 
each button across one-half of the trans- 
former winding, and thereby creates a 
balanced circuit that helps greatly to 
reduce the distortion produced by even 
harmonics. A sound wave will cause the 
microphone diaphragm to move back- 
ward and forward, thus alternately de- 
creasing the pressure on the carbon 
granules in one chamber while increas- 
ing the pressure on the granules in the 
other chamber. Due to the variations 
in the resistance of the chambers, this 
causes the current through one side of 
the transmitter and one side of the split 
winding of the transformer to decrease 
and the current through the other side 
of the transmitter and the other side 
of the transformer winding to increase, 
and vice versa. These current changes 
do not oppose, but aid each other and 
add together in the transformer, in- 
ducing a voltage in the secondary wind- 
ing that is twice as great as it would 
be if only one cell of the transmitter 
were used. 

So long as the resistance of each 
side of the microphone diaphragm re- 
mains constant, the steady battery cur- 
rent, and any fluctuations in that steady 
current, will not induce a voltage in 
the secondary of the transformer be- 
cause it will not produce a magnetic 
flux in the transformer core, due to the 
fact that the currents flowing through 
the two halves of the primary winding 
are in opposition and balance each 
other. This prevents saturation of the 
core by the steady d-c. current, which 
could readily happen in the microphone 
circuit shown in Fig. 2 if the trans- 
former is not properly designed. The 
value of this steady current flowing 
through the transmitter at all times is 
regulated by means of the series rheo- 
stat or potentiometer in the center lead 
of the transformer circuit. Usually this 
current is adjusted to a value of about 
twenty-five milliamperes per button, but 
often satisfactory results can be ob- 
tained with currents as low as ten or 
fifteen milliamperes, depending on the 
microphone used. A lower current is 
preferable because it is less likely to 
cause burning or arcing of the carbon 
granules and it is better for the deli- 
cate contact surfaces. As the micro- 
phone ages from steady use, its resist- 
ance increases with a resultant loss of 



COMPENSATING 

DIAPHDA-v 



DIAPHRAGM 



Fig. 5. Cross- 
sectional view of 
the 394 type con- 
denser micro - 
phone. 




DAMPING 
PLATE GROOVE 



Courtesy Bell Telephone Labs. 



sensitiveness. As we have seen, the 
double-button transmitter is much less 
sensitive than the single-button trans- 
mitter, due mainly to the stretching of 
the diaphragm, and so a certain amount 
of audio-frequency amplification is nec- 
essary to bring the speech current pro- 
duced by a double-button transmitter up 
to a useful value. 

The Condenser Microphone 

The condenser microphone, which is 
composed of a sound pickup device 
called a condenser transmitter and an 
amplifier, is a later evolution. It was 
first described by E. C. Wente, who 
developed it. It produces speech of high 
quality and is the most perfect micro- 
phone in use at the present time. The 
condenser microphone has several dis- 
advantages, though, for it is more com- 
plicated in construction than the car- 
bon transmitter and more difficult to 
maintain. Its sensitiveness is so much 
lower than even the double-button car- 
bon transmitter that it is necessary to 
use at least one stage of audio ampli- 
fication to bring it up to an approxi- 
mation of the same level of energy out- 
put, and even then its output is about 
six decibels lower than that of the two- 
button carbon microphone, being about 
minus thirty to forty db. 

It is true that there is a slight tube 
hiss from a condenser microphone, but 
that is not so annoying as the carbon 
hiss from a carbon microphone, and so, 
on the whole, there is far less back- 
ground noise present in the condenser 
microphone than in the carbon micro- 
phone. The two-button microphone is 
still used widely, nevertheless, because 
it is more rugged and compact and that 
less batteries and associated equipment 
are needed with it. However, the con- 
denser microphone is very durable and 
is not so easily affected by sudden tem- 
perature changes or mechanical shocks 
as the carbon microphone. It can be 
moved about while in operation with- 
out creating noise. Also, there is no 
danger of "blasting," and it can be op- 



erated in any position, while the car- 
bon microphone should be used only in 
an upright position. 

The condenser transmitter operates 
on a principle that is entirely different 
from that of the carbon microphone. 
Instead of varying its resistance and 
thereby altering the flow of current in 
the circuit in which it is connected, the 
condenser transmitter changes its ca- 
pacity under the influence of the sound 
waves and in that way varies the flow 
of current into it from a source of 
steady e.m.f. in the circuit in which it 
is operating. This change in current 
in the condenser circuit is so very min- 
ute that the only satisfactory way it 
can be used is by causing it to produce 
a change in potential in the grid circuit 
of a vacuum tube. 

Without its associated amplifier, the 
condenser transmitter could not be used, 
because the impedance of the condenser 
transmitter would not match the im- 
pedance of the speech input equipment, 
and so they are always to be found to- 
gether. The amplifier serves to couple 
the condenser transmitter, which oper- 
ates most efficiently into a circuit hav- 
ing an impedance in the neighborhood 
of fifty million ohms, to a 200-ohni 
transmission line. Actually, if only a 
single-stage amplifier is employed, the 
electrical level at the condenser trans- 
mitter is approximately six db. higher 
than the level at the output of the con- 
denser transmitter amplifier, despite the 
gain at the amplifier, due to the extreme 
difference in impedance of the two cir- 
cuits. 

The condenser-like pickup device — 
the condenser transmitter — is sometimes 
known as the "head" ; and the associated 
amplifier is called the condenser trans- 
mitter amplifier. The titles for these 
two parts of the microphone are abbre- 
viated CT and CTA in general prac- 
tice. In the second article of this series, 
the internal construction of the con- 
denser microphone and the theory of its 
operation will be discussed, but before 
closing this article, it might be well to 



Page 12 

describe briefly the external appearance 
of the various types of condenser micro- 
phones in use at the present time and 
the general details of their mechanical 
construction. 

The Associated Equipment 

For reasons that have already been 
mentioned and that will be explained 
more fully in the second article, it is 
necessary that the head of the condenser 
microphone be located close to its am- 
plifier. The nearer they are together 
the better, and at the very most they 
should not be separated by a distance 
greater than twenty-five feet. The types 
of condenser microphones differ mainly 
in the number of stages of audio ampli- 
fication employed in the amplifier. 
There are microphones one-, two-, and 
three-stage CTAs. The output level of 
a condenser microphone with a two- 
stage CTA is usually eighteen to twenty 
db. higher than the output level of a 
single-stage microphone, but otherwise 
there is little difference in them. All 
else being equal, a two-stage or three- 
stage microphone is undoubtedly the 
best to use because the more amplifica- 
tion in the condenser microphone the 
higher the electrical level of the speech 
current passing through the microphone 
cable. Then if there are any electrical 
disturbances picked up by the cable, the 
ratio of speech current to noise will be 
high, and since less amplification will 
be needed in the main line amplifier to 
obtain the necessary electrical level, the 
disturbance will not be as much ampli- 
fied as it would if a single-stage micro- 
phone were employed. 

In all three types of microphones, the 
head is usually held in a metal hous- 
ing that is attached directly to the 
cylindrical or cubical heavy metal case 
which contains the amplifier. If the 
microphone is of the suspension type, 
this amplifier case is equipped with 
a bail on the end farthest from 
the head for the purpose of attach- 
ing it to a microphone boom or 
other support. The housing in which 
the condenser transmitter is supported 
is pivoted so that it can be tipped to 
change the angle which it forms with 
the amplifier case, and a short length 
of shielded conductor connects it with 
the terminal plate on the amplifier. In 
the older type of condenser microphone, 
a length of shielded cable ending in a 



PROJECTION ENGINEERING 



special locking plug was attached to the 
microphone, but in the newer micro- 
phones the special plug is built right 
into the amplifier case on the end to 
which the bail is fastened. A similar 
but longer cable having a braided metal 
shield over the conductors and an out- 
side covering of rubber, equipped with 
plugs on both ends, and known as a 
microphone cable, connects the micro- 
phone to a junction box built into the 
wall of the sound stage. This junction 
box is usually constructed to accommo- 
date the cables from six microphones, 
and it is equipped with fuses in the fila- 
ment and plate battery leads to the mi- 
crophone amplifiers. The plate batteries 
are placed in a metal B battery case 
near the junction box and connected 
directly to it. 

The suspension type of condenser mi- 
crophone that has just been described 
is employed mostly for motion picture 
Sound recording work and is usually 
supported on a microphone boom, while 
the other two forms of the microphone, 
the desk and floor types, are used prin- 
cipally in radio broadcast and public 
address work. The desk-type condenser 
microphone usually has the amplifier 
built in a square box with the trans- 
mitter housing supported solidly on top 
of it in a special frame or set into the 
face of the box. In the floor type of 
microphone the condenser head is fast- 
ened to the top of a slender vertical 
pillar. The height of this stand is ad- 
justable from four to six feet, permit- 
ting the transmitter to be raised or low- 
ered to accommodate the height of the 
speaker. The amplifier is contained in 
a box in the base of the stand. These 
various types of condenser microphones 
all operate on the same principle and 
are identical in internal construction — 
the only variation in them being in the 
mechanical features. 

Fig. 2 illustrates the input circuit 
wiring of a carbon microphone. It will 
be understood that as the diaphragm 
moves in either direction the current 
through one side of the transformer will 
increase while current through the op- 
position side will decrease. This effect 
contributes to the reduction of micro- 
phone hiss caused by the normal cur- 
rent flowing through the carbon gran- 
ules; also reduces distortion due to even 
harmonics. The battery current flowing 
through the microphone transformer 





Fig. 7. Condenser microphone complete. 



Courtesy Jenkins & Adair, Inc. 

Fig. 6. The floor-type of. condenser microphone. 
Illustrating mounting pillar construction. 



creates opposing magnetic fields and is 
therefore balanced. 

The microphone shown in Fig. 7 is 
of the condenser type, widely used in 
sound-picture work. The mounting is 
practical as the suspension allows the 
microphone to be adjusted outside the 
focus of the cameras without difficulty. 



SCREENS FOR TELEVISION 

THE screen upon which the projected 
television image is thrown is second 
only in importance to the scanning 
system used, according to William Hoyt 
Peck, inventor, whose new television 
receiver is now being demonstrated. 

Peck tested numerous types of screens 
during his work with color motion pic- 
tures for many years. For projecting 
pictures from behind the screen, he 
found waxed cloth superior to the 
various glass screens which had for- 
merly been used. He therefore used 
that type of screen for his television 
projector during early experiments. 

Later, however, he determined to try 
glass with a specially ground back, and 
found this to give about twice as bril- 
liant an image, though it had not worked 
nearly so well for motion pictures. He 
further found that the image was much 
clearer when projected against the shiny 
surface of the glass, the ground side 
being toward the audience. 

The system which Mr. Peck is dem- 
onstrating utilizes a novel method of 
scanning, in which fully corrected re- 
flecting lenses transmit all the light 
from the crater tube to the screen with- 
out distortion. 



APRIL, 1932 



The screen 
problem 

By Sylvan Harris* 



Studies are being made of 
the properties of theatre 
screens, from which it is 
believed important picture 
betterments will follow 



THE problem of properly refinish- 
ing motion picture projection 
screens, a matter of great import- 
ance to theatres, is a subject which 
is being given very careful considera- 
tion by the S.M.P.E. projection screens 
committee, headed by S. K. Wolf, 
chairman. It is the opinion of some 
members of the committee that screens 
can not be sprayed or painted uniformly 
while they are in the erected position 
in the theatre, and that screens so 
treated showed noticeable variation in 
reflecting power when illuminated by 
a bare light. Such variations will not 
be detected by laboratory measurements 
of the properties ' of small samples of 
screen for they occur from point to 
point on the screen, and can be appre- 
ciated only by making measurements at 
many points on the screen. Some of 
these variations, of course, are small, 
and may not be noticeable when a pic- 
ture is projected upon the screen, but 
others, it is stated, are quite noticeable, 
especially when views of a clear sky or 
other similar scene are projected upon 
the screen. The committee has already 
collected some material for this study, 
and is proposing to study the matter 
carefully. 

The visibility of seams in the screens 
to those in the audience is a very im- 
portant matter, the committee feels. It 
is stated that some screens now in use 
are actually unfit for use, because of the 
obviousness of the seams, even when 
pictures are projected upon them. This 
fact, and the one referred to above, re- 
lating to large variations of reflectivity 
that may occur from point to point of 
the screen, indicate that laboratory tests 
made on samples are inconclusive for 
determining the fitness of a screen for 
use in the theatre. Another factor to 
be noted is the lack of uniformity of the 
manufactured product, as regards re- 



*Editor-Manager, S.M.P.E. 



fleeting power. Tests made on one 
screen may not, to any great extent, 
be considered as indicative of the qual- 
ity of another similar screen made by 
the same manufacturer. 

The susceptibility of screens to 
gather dust and dirt, and for that reason 
losing a great deal of their reflecting 
power, is a matter of great importance, 
and although the committee has, during 
the past year studied the problem to 
some extent, much yet remains to be 
done. It is of interest to note that, for 
16 mm. projection, an aluminum screen 
is now available which may be sand- 
blasted in order to renovate the surface. 
The committee has accumulated a great 
deal of data later to be presented, and 
which shows the loss o f reflectivity 
which occurs with age and with condi- 
tions of use of screens. 

Although very little has been known 
at least by those engaged in the motion 
picture industry, of the effects of age 
on the pigments, and the vehicles used 
to carry the pigments, with which 
screen surfaces are coated, it is a fact 
that these vehicles or carriers become 
yellow with age, and that it is possible 
that the pigments themselves may suffer 
a change of color. It has been discov- 
ered that this change of color may, 
among other things, be due to the ac- 
tion of actinic light upon the vehicle, 
as samples which have been kept in the 
dark for a long period of time did not 
show the tendency to become discolored. 
Much is to be learned in this matter, 
following which the committee plans to 
consult the manufacturers of the pig- 
ments and to enlist their cooperation in 
the study. 

With regard to the determination of 
the various optical properties of screens, 
the projection screens committee is con- 
cerned primarily with the relation be- 
tween the quality and structure of the 
screen and the brightness of the re- 
sulting image projected upon it. They 
are also concerned with the measure- 
ments of screens and with the speci- 
fication of optically satisfactory screens. 
In the latter connection, the projection 
screens committee is cooperating with 
the S.M.P.E. projection theory and 
projection practice committees in order 
to determine, not only the best prac- 
tices to recommend, but to determine 
as well the values of the various optical 
quantities that exist in practice. 

The projection screens committee is 
investigating the range of applicability 
of several instruments now available to 
theatre operators for the purpose of 
making optical measurements of screens, 
and the best and simplest methods of 
using these instruments. At the same 
time, the committee purposes to define 
the more commonly used units of bright- 
ness and illumination, and to make 
available the proper conversion factors 



Page 13 

so as to simplify the procedure used by 
the theatre operators for making check 
tests of their screens for determining 
the need of renovating or replacing 
them. 

It appears that at the present time ' 
some confusion exists in the "trade" 
concerning the meanings of the adjec- 
tives "specular," "reflective" and "direc- 
tive," as applied to the several types 
oi screen. It is common practice to 
specify the beaded type of screen as 
"reflective," but this acceptation ignores 
the fact that all screens are reflective, 
and, in fact, are motion picture screens 
in virtue of that fact. The standards 
committee of the S.M.P.E. has been 
asked to define these adjectives prop- 
erly, so as to obviate the ambiguity that 
now exists. It has been suggested by 
the projection screens committee that 
the beaded type of screen be known as 
the "directive" type, as it is a property 
peculiar to the beaded screen to direct 
a large portion of the light incident 
upon it, back into the source of light. 



NUMBER OF FILM AND NUMBER 
OF DISC INSTALLATIONS 

Approximately 1,400 theaters in this 
country discarded disc equipment in 
favor of sound-on-film devices during 
the past year, it is indicated by a na- 
tional survey. A total of 3,542 houses 
now are using disc apparatus only the 
checkup shows. Theaters using tracks 
only aggregate 6,360, and houses with 
dual equipments number 4,836. 



MORE QUESTIONS FOR 
PROJECTIONISTS 

Herewith are submitted nine addi- 
tional technical questions — Nos. 49 to 
57 of the series — to be studied and 
answered by projectionists : 

49. What care should be taken of 
storage batteries so that they will not 
become a means of introducing foreign 
noises into the circuit? 

50. What is meant by the term 
"cycle?" 

51. Are the photoelectric cells used in 
the RCA and WE systems the same ? 

52. Does the RCA Photophone em- 
ploy a pickup amplifier ? 

53. What is a fader, and what does 
it do? 

54. What is the impedance in ohms 
of the WE pickup used in sound-on- 
disc? 

55. What is intermediate frequency? 

56. Give a description of the RCA 
voltage amplifier panel type "A,". state 
how the signal passes through this, and 
what type tubes are used. 

57. State what a mechanical filter is 
used for. 



Page 14 



PROJECTION ENGINEERING 



A re-recording 
machine for 



sou 



nd fi 



ms 



By J. J. Kuhn : 



A MODERN sound-picture film 
as "released" usually bears 
little resemblance to the films 
initially taken of the produc- 
tion. It is rather a modified composite 
built from sections of the original films 
with the addition of various accom- 
panying sounds such as rain, thunder, 
trains, revolver shots, or orchestral ac- 
companiments. Not only are these 
other effects added, but the volume 
levels of the various sections are ad- 
justed to make the whole fit properly 
together. The building up of a com- 
plete sound picture for release is thus an 
art in itself, and requires apparatus 
and a technique distinct from those of 
the original taking. 

In the construction of the final 
"released" picture, sections of the 
sound tracks of preliminary films, cor- 
rected for level, are transferred elec- 
trically and in the desired order onto a 
new film. This requires a machine to 
convert the variations of the sound 
track of a film into equivalent electri- 




jBell Laboratories Record, March, 1932. 
*Special Products Engineer, Bell Telephone 
Labs., Inc. 




Fig. 1. On the rear of the new re-recorder are the photoelectric cell 

cabinet, the gear box, and the spring-damped flywheel of the sound 

sprocket. 



cal currents to be used not by loud- 
speakers but for the recording of a new 
sound track. The machine that does 
this, known as a re-recorder, thus plays 
an essential part in the making of the 
final form of the picture. 

Such a piece of apparatus, embody- 
ing all the refinements and improve- 
ments that a wide but rapidly acquired 
experience has made possible, has re- 
cently been developed by the Bell Labo- 
ratories and is being offered to the in- 
dustry by the Electrical Research Pro- 
ducts, Inc. Requirements placed on 
it are more severe than those demanded 
of a reproducer since in the process of 
re-recording, of which there may be 
several successive steps, the variations 
introduced by -the apparatus are cumu- 
lative. The reproduction must be as 
nearly perfect as is commercially pos- 
sible. 

Front and rear views of the new 
machine are shown at the head of this 
article and in 
Fig. 1. Mechan- 
ically there are 
three major sec- 
t i o n s — a film 
magazine above, a 
sound reproduc- 
ing head beneath 
it. and a driving 
motor at one end, 
all mounted on a 
substantial cast 
iron base. The 
film magazine 
compartment has 
space for two 
reels of either one 
or two thousand 
feet capacity. One 
is the supply reel 
and the other the 
takeup reel. Be- 
neath it is the re- 



producing head which includes a sound 
lamp with the necessary optical sys- 
tem for focusing the light on the 
sound track, and a photoelectric cell 
for receiving the modulated light beam. 
To the left of the reproducing head, 
when viewed from the front, is the 
driving motor which is arranged to be 
synchronized with the recording ma- 
chine with which the re-recorder is be- 
ing used. 

Details of the reproducing head are 
shown in Fig. 3. The drive shaft from 
the motor enters a gear box, which is 
integral with the head but faces the 
opposite direction, and through suitable 
gears drives two sprockets within the 
head. One, in the upper left-hand 
corner, is a combination pull down and 
hold back, and the other is the sound 
sprocket, which draws the film across 
the light beam. These are the only 
driven sprockets in the compartment. 

The film, coming from the supply 
reel of the film magazine, is held 
against the pull down sprocket by a 
double pressure . roller, then passes 
around an idler roller directly beneath 
it, and then around a drag roller which 
maintains a constant tension on the 
film as it passes up through the sound 
aperture. From here it passes over 
the sound sprocket, by the other side 
of the pull down sprocket, and then be- 
fore passing back to the film magazine 
runs over the roller of the signalling 
device. This device, evident in both 
Figs. 3 and 4, gives an alarm if the film 
should break. Like most of the other 
rollers in the compartment, the drag 
roller is of stainless steel and accurate- 
ly made to insure that it runs true and 
with constant tension. Flanges on each 
side guide the film along the proper 
path, and tension is maintained by 
friction discs bearing against the sides. 
Tension may be controlled by adjust- 



APRIL, 1932 



'age 






ing a compression spring on the outer 
face of the drag roller. The film is 
held close to this drag by a roll of im- 
pregnated fabric tensioned by a flat 
steel spring. 

The sound aperture is of the double 
roller type which insures a smooth, 
steady movement of the film past the 
scanning beam, and a minimum likeli- 
hood of its moving out of the focal 
plane. These rollers, also of stainless 
steel, are very accurately ground and 
rotate in jewel bearings. They are rig- 
idly mounted and doweled in place so 
that they may be removed for inspec- 
tion or cleaning. The position of the 
two rollers on opposite sides of the film 
gives a pivoting action of the film 
around a point midway between the 
two rollers. This tends to maintain the 
scanning point on the focal plane while 
if both rollers were on the same side 
of the film, changes in the stiffness of 
the film due to variations in thickness, 
temperature, or age would throw it out 
of the focal plane. 

The optical system is shown in the 
photograph of Fig. 2 and diagram- 
matically in Fig. 4. It is mounted on 
a separate base which is secured to the 
casting of the head. It has three major 
elements. On the left is a collimator 
lens for focusing the light passing 
through the film onto the sensitive part 
of the photoelectric cell. In the middle 
is the reproducing lens unit for pro- 
jecting the reduced image of the narrow 
illuminated slit on to the sound track, 
and at the right a lens used for adjust- 
ing lamps in the field. The reproduc- 
ing lens unit consists of an objective 
lens, at the left a slit, and at the right 
a condensing lens. The slit is on the 
optical axis and midway between the 



two lenses. Its 
opening is held 
accurately to the 
proper width and 
its edges are 
selected for 
smoothness and 
parallelism 
throughout their 
entire length. 

A s i x - v o 1 1 , 
nine-ampere rib- 
bon-filament lamp 
is employed, and 
the condensing 
lens, with a mag- 
nification of uni- 
ty, focuses an im- 
age of the fila- 
ment on the slit, 
gives a \ l / 2 to 1 
suits in an image 




Fig. 2. The three lens units of the optical system are mounted on 
common support which also carries the double-roller sound aperture. 



The objective lens 
reduction which re- 
in the plane of the 
film .085 inch long and .001 wide. 
Special care is taken to insure an im- 
age evenly illuminated throughout its 
length and with clearly defined edges. 

Two bearings support the lens unit, 
one of them being slotted to permit 
clamping the unit in place. Between 
them is a collar which, by an adjusting 
screw, allows the unit to be rotated 
sufficiently to permit obtaining the cor- 
rect azimuth adjustment. Focusing may 
be done in the field by a knurled head 
on the objective lens mounting which 
is then held in place by a lock nut. 

When first set up the various units 
are accurately adjusted with the aid of 
single-frequency films. When this has 
been done, the lamp adjusting lens is 
focused so that a sharp image of the 
lamp filament is projected on a ground 
glass screen at the rear of the lamp 
housing:. This screen carries cross lines 




Fig. 3. A double-roller sound aperture in the re 

the 



producing head maintains the film at the focal plane of 
lens unit. 



and is adjusted so that the lines cor- 
respond with the center of the projected 
image. To adjust subsequent lamps it 
is necessary only to center the filament 
image on these cross lines. This ar- 
rangement also makes it possible to 
tell when the filament sags and thus 
when the lamp needs replacement. 

The sound lamp is adjustable in all 
directions as indicated on Fig. 2. Con- 
trary to normal expectation, adjust- 
ment of the lamp is not very critical. 
An out-of-focus condition in the hori- 
zontal position by as much as 2> l / 2 turns 
of the adjusting screw results in only a 
half decibel loss in volume. Although 
the range is not so great for the other 
directions, adjustment of the lamp is 
possible in a comparatively short period 
of time since the width of the lamp fila- 
ment is 30 times that of the slit. 

Projecting through the rear wall of 
the sound head, the photoelectric cell 
has its terminals adjacent to those of its 
coupling transformer which is mounted 
on springs in a separate housing 
as shown in Fig. 5. The spring 
suspension insures that extrane- 
ous vibrations will not be picked 
up by the unit. 

One of the prime requisites 
for high quality reproduction is 
a steady motion of the film 
through the light aperture. As 
an aid in securing this the sound 
sprocket has on its outer end a 
flywheel driven by a damped 
spring as shown in the illustra- 
tions. The motor, rated at Y\ 
h.p. and running at 1200 r.p.m. 
also carries a flywheel on the 
outer end of its shaft. The uni- 
formity of rotation of the sound 
sprocket may be checked strobo- 
scopically by a shutter with 36 
slots mounted on the motor 
drive shaft, and 120 lines equally 
spaced around the rim of the 
flywheel. Both the slots and 
lines are accurately spaced by 
microscopic measuring devices at 
the factory. The combined er- 



Page 16 



PROJECTION ENGINEERING 



ror in location of the 36 slots is held to 
a thousandth of an inch. 

The motor is mounted on a plate 
dovetailed to the base of the machine, 
so as to permit its being withdrawn 
endwise without necessitating readjust- 
ment. Flexible couplings are employed 
which are rigid torsionally but allow 
a certain amount of end play of the 
armature without transmitting it to the 
head. A switch is located in the base 
so that the motor may be shut off in- 
dependently of the system when the film 
in the magazine has been completely 
reproduced. 

The extraordinary efforts to obtain 
accuracy, although costly, insure that 
all machines sent to the field will pro- 
vide the high grade of service expected 
of them. Excluding the scanning loss, 
the frequency response characteristic 
of the reproducing system — from a 
modulated light beam falling on the 
photoelectric cell to the output term- 
inals — does not vary more than one 
decibel for a frequency range of from 
SO to 7,000 cycles. Even at 10,000 cycles 
the loss is only 2 decibels. In addi- 
tion the machine has a volume range of 
57 decibels, which is greatly in excess 
of present day practice. 

In the entire assembly it will be 
realized that exactness and accuracy 
have been requirements of design. The 




DAMPED SPRING 
FILTER 



-FLYWHEEL 






DRAG _ 
ROLLER 



or- 



DAMPED 
SPRINGS 



TRANS- 
FORMER 



-TERMINALS 



Fig. 5. The coupling transformer for the photoelectric cell is carried on 
a spring support to decrease the likelihood of outside interference. 



uniform motion of the film through the the measures taken to insure this are 
light aperture being of first importance, understandable. 



I 1 

INTERLOCK 
MOTOR 

'sTATOR ROTOR ! 




"I C ~\ y OI-KL 



6 6pO 

III fit. 



SWITCH 



TO INTERLOCK 
MOTOR SYSTEM 



SOUND 
SPROCKET 

' EM S%!'° N /HOUSING 

L j 



Ulu." 

ceo 

Q 



COLLIMATOR 



! LENS TUBE. E *^TER 



PHOTO- , 
EL C E E C L^'5W 

FILM DRIVE 
HOUSING 

-IDLER 



- L ^i \ k r >- s - s - E - M - B --^ 7v Vf l 



LAMP 

ADJUSTING 

ENS 





+ LAMP 



TRANSFORMER J o 
COUPLING UNIT I 



[p-JAIij— -r 

ROLLER ^SLIT ii 
APERTURE 



BATT 



'DRAG 
-ROLLER! 



[~ 



+ 6 6 



spring! 

TERM 



PEC NO.IO. 



KEYKIo- 



+90 -90 -B GND OUTPUT 
<? o 

__l 



-j\= 



F3 



ICROSSLINE 
DISC 



F2 

15-A 

> 

- —i • 



15-A 



I FUSE 
BOX 



I 



TO 90-VOLT TO 

"B" BATTERY AMPLIFIER 



Fig. 4. A lamp adjusting 
lens and a cross-line disc 
in the end of the projector 
head permit easy adjust- 
ment of the sound lamp. 



APRIL, 1932 



Sound picture 
ectures expansion 



BURTON HOLMES LECTURES, 
Inc., the internationally known 
motion picture lecture bureau and 
the foremost producer of the so- 
called travelogue type of screen subjects 
in the world, has contracted for the in- 
stallation of RCA Victor Photophone 
recording equipment, according to an 
announcement made by E. A. Nicholas, 
vice-president and general sales man- 
ager of the RCA Victor Company at 
Camden, N. J. Under the provisions of 
the contract entered into between the 
two companies, Burton Holmes Lec- 
tures, Inc., becomes an RCA Victor 
Company licensee and hereafter will 
record its sound motion picture product 
by the Photophone system. For many 
years the Burton Holmes silent product 
was released through Paramount. At 
present and until next September, the 
current releases of twelve sound pic- 
ture programmes are distributed by the 
Metro-Goldwyn-Mayer Pictures Corpo- 
ration. Future releases will be deter- 
mined prior to the expiration of the 
existing contract. 

In addition to maintaining a complete 
recording studio and laboratories for 



the production of standard size 35 milli- 
meter sound motion pictures at its head- 
quarters in Chicago, Burton Holmes 
Lectures, Inc. immediately will begin 
the production of 16 millimeter sound 
pictures for non-theatrical exhibition 
through the medium of the recently in- 
troduced RCA Victor Photophone port- 
able sound-on-film reproducing equip- 
ment. Having upwards of 7,000,000 
feet of standard size 35 millimeter nega- 
tive in its vaults, among which are more 
than 2,000,000 feet that have never been 
publicly distributed, a vast library of 
subjects of inestimable value to schools, 
churches and other non-theatrical in- 
stitutions is made available. From both 
the historical and geographical point of 
view, the Burton Holmes library is said 
to be the most complete collection of its 
kind in the world. Thousands of feet 
of exclusive material have been filmed 
during the past year and a large staff 
of cameramen, located in various parts 
of the world, are constantly shipping 
new subjects to the Chicago studios. 
"We are exceedingly well pleased 
over our new affiliation with the RCA 
Victor Company," said Hilles V. Mont- 



Page 17 

gomery, of Burton Holmes, Lectures, 
Inc. "With the introduction of the new 
RCA Victor Photophone 16 millimeter 
sound - on - film portable reproducing 
equipment, the reproduction of hundreds 
of subjects of particular interest to 
schools, churches and many other non- 
theatrical institutions is made immedi- 
ately possible. The field for the dis- 
tribution of such subjects is almost 
boundless, and our facilities, combined 
with those of the RCA Victor Com- 
pany, will soon bring about the produc- 
tion of hundreds of subjects and make 
them available for early distribution. 
We have more geographical negatives 
than any other organization in the 
world, and when it comes to subjects 
of historical importance, we probably 
can go further back than any motion 
picture producing company. We can 
cover practically every event of out- 
standing significance as far back as the 
days when the late Czar of Russia's 
reign was brought to its sudden end. 
One of the principal activities upon 
which we will embark without delay 
will be the reduction of many existing 
35 millimeter subjects to 16 millimeter 
with accompanying sound. Before the end 
of the current year a large and impres- 
sive library will have been produced." 
W. A. Graham, assistant manager, in 
charge of recording operations of the 
Photophone Division of the RCA Vic- 
tor Company, conducted the negotia- 
tions with Burton Holmes Lectures, Inc. 



ROXY TO ADDRESS S. M. P. E. 
SPRING MEETING 

S. L. Rothafel ("Roxy") has ac- 
cepted an invitation to address the 
spring meeting of the Society of Motion 
Picture Engineers to be held in Wash- 
ington, D. C, May 9 to 12, according 
to O. M. Glunt, chairman of the papers 
committee. 

Mr. Rothafel will talk on "The Ideal 
Theatre" and is expected to describe 
some of the outstanding features to be 
incorporated in the theatres of Radio 
City. It is expected that this paper 
will be one of the outstanding features 
of the spring meeting. 
▲ 

SIDNEY R. KENT ELECTED VICE- 
PRESIDENT OF FOX FILM 

DIRECTORS of the Fox Film Cor- 
poration, on March 22, elected Sid- 
ney R. Kent as executive vice-president 
in charge of operations, and Leonard A. 
Woolams as vice-president. 

Edward R. Tinker, president, in mak- 
ing the announcement said: 

"I have realized since assuming the 
duties of my office that what Fox Film 
Corporation most needed was a general 
executive of outstanding experience in 



the motion picture industry. For some 
time I have been hoping Mr. Kent 
would be available. I consider it most 
fortunate for the corporation that at 
last a mutually satisfactory arrangement 
has been made whereby Mr. Kent takes 
up his duties beginning April 4. 

"The last two years have been trying 
times for all business. This industry 
has learned that it has no immunity 
from those influences which swing the 
tide of business. It is beginning to ap- 
ply to its affairs those rules of sound 
management, without which no industry 
ever prospered long. It is developing a 
consciousness of its responsibilities to 
the public and to its stockholders. Mr. 
Kent's record is in complete accord with 
this philosophy of business manage- 
ment." 

A 

BUREAU OF STANDARDS TO BE 
HOST TO S.M.P.E. AT WASH'GTON 

THE Bureau of Standards will play 
host to the members of the Society 
of Motion Picture Engineers, Tuesday 
evening, May 10, during the spring 
meeting of the society in Washington, 
D. C. 

At this meeting, Dr. L. J. Briggs, 



acting director of the bureau, will de- 
scribe work carried on by the bureau 
of interest to the motion picture indus- 
try. Dr. I. G. Gardner will deliver a 
demonstration and talk on optical phe- 
nomena. 

A 

WESTERN ELECTRIC COMPANY 
REPORTS 

Net profit of Western Electric, in- 
cluding all activities of the company, 
for the year ended Dec. 31, 1931, 
amounted to $10,816,387. Total sales 
were $228,956,000, against $361,478,000 
in 1930, and net profit rate on sales was 
4 per cent against 2.4 per cent in 1930. 

A 

TRI-ERGON PATENT SUIT NOT DUE 

TO COME UP BEFORE FALL 

THE suits which William Fox, 
through Tri-Ergon, has brought 
against Erpi and others with respect to 
infringement of patents on sound repro- 
duction apparatus, are not expected to 
reach the trial stage until next fall, at 
the earliest, according to the belief of 
the Erpi people. The pressing of the 
suits, however, depends entirely upon 
the plaintiffs in the actions. 



Page 18 



Sound transmission 
the hard-of-hearing 



f 



or 



By Henry L. Williams 



llililllilllllll 



Herein, Mr. Williams clearly outlines the requirements 

in a large engineering and sales field, offering an outlet 

for sound amplification equipment 



WITH the beginning of 1932, 
two large national organiza- 
tions are inaugurating an 
intensive campaign which 
has for its purpose the installation of 
hearing devices in churches, theatres, 
auditoriums and other public meeting 
places. Back of this drive is a recog- 
nition of the fact that better than 8 per 
cent of the adult population of the 
United States have some hearing defect 
which makes it impossible for them to 
hear distinctly, normal speech. 

This drive, by its very nature, is also 
serving to call attention to the problem 
of educating hard-of-hearing children 
by means of speech amplifying equip- 
ment — a field which is at the moment 
somewhat of a monopoly in so far as 
the manufacture of teaching equipment 
is concerned. Why this should be so it 
is impossible to surmise, unless it be 
that the opportunity is not realized nor 
the potential value of the market appre- 
ciated. However, although the deaf 
schools form a large and attractive 
market in this respect, the equipment 
they require is highly specialized and 
demands an individual brand of sales- 
manship involving considerable study 
of the characteristics of the defective 
ear and the psychology of the deaf child. 
On the other hand, the picking up of 
speech from short distances and bring- 
ing it, free of extraneous noise and un- 
distorted, to an earphone presents com- 
paratively few difficulties when once a 
few simple factors are known. The 
problem is of course a little more in- 
volved when it is desired to cover an 
entire theatre stage, but a 30-foot stage 
can be taken care of by a single micro- 
phone if the apparatus is carefully de- 
signed and engineered. 

First, let us consider the character- 
istics of the defective ear. In practically 
all cases of partially lost hearing the 
greatest loss is in the higher sound 
frequencies. This means that in repro- 



duction these frequencies should be ac- 
centuated. In other words, the ampli- 
fier, if such is used, should have a 
rising characteristic. It also means that 
there is little need to reproduce fre- 
quencies below 200 cycles, which is a 
big help as we shall see. It has been 
found that for all practical purposes a 
range of 200 to 5,000 cycles for music 
and 200 to 3,500 cycles for speech is 
sufficient. 

Seat Telephones in Theatres 

We need only consider the talking 
picture theatre here briefly. These in- 
stallations often consist of phones wired 
into the loudspeaker circuit, or may 
utilize a telephone type transmitter hung 
in front of the horns. The only objec- 
tion to these arrangements is that there 
is no frequency discriminating compen- 
sation, and all that is done is to bridge 
the distance between the listener and 
the loudspeakers, or, in other words, to 
give them extra volume. In all such 
cases it is necessary to have individual 
volume controls at the seat, and it is 
preferable to use the stick or lorgnette 
type of phone because many deafened 
people are sensitive and do not care 
to be seen with the very obvious head- 
band. 

A third method which gives far more 
desirable results is to use a high grade 
microphone for the pickup, coupled to 
an amplifier having the characteristics 
already mentioned. This is the type of 
equipment which has been used with 
great success for the speaking stage. 
For this work the writer has used con- 
denser microphones exclusively, and 
such microphones have been entirely 
a-c. operated. It is this a-c. operation of 
the condenser microphone which has 
opened up the whole field of amplifica- 
tion for the deafened and makes it now 
possible for any competent engineering 
firm to cater to this valuable market. 



PROJECTION ENGINEERING 

Amplifiers 

By careful design of the amplifier, 
using ordinary radio tubes, including 
the power pentodes, it is possible with 
double filtering, and careful selection of 
values, to produce an amplifier which 
will reproduce all frequencies between 
200 and 5,000 without a trace of hum 
or distortion that is apparent to the nor- 
mal ear, when used with a condenser 
microphone. The use of a-c. also has 
the advantage of economizing space and 
rendering the equipment extremely port- 
able, which is a vital factor in teaching 
units. In the theatre, then, the con- 
denser head with its single or two- 
stage amplifier is built into the "foots," 
and carefully insulated with sponge rub- 
ber or felt against stage vibration. This 
insulation is important since otherwise 
footfalls will come through like thunder. 

The main amplifier can of course be 
stowed away below stage and a single 
pair of wires run to each row of seats 
where the phones are connected in par- 
allel. It is good practice to put one pair 
of phones to each two seats, and to dis- 
tribute them throughout the house. 

With a good condenser head it will 
be found that speech is picked up at 
good volume from all parts of the stage, 
even when an actor commits the unpar- 
donable sin of turning away from the 
audience. For stages of more than 30- 
feet width it may be necessary to use 
two microphones and incorporate an 
efficient mixer, care being taken not to 
separate microphones by more than ten 
or fifteen feet; otherwise the difference 
in pickup will result in a slight echo 
effect. 

As regards phone impedance, it is 
usual to employ receivers of around 
100-ohms, putting, say, 12 in parallel 
and using an 8-ohm line. With this ar- 
rangement it will be found that ordi- 
nary potentiometer type volume con- 
trols can be used, and the variation in 
impedances which results will not have 
any appreciable effect on the quality or 
volume of any one phone. 

Seat Fixtures 

Undoubtedly the best arrangement is 
to have a jack box fastened under the 
arm of the seat, so that the customer 
can procure the phone at the box-office, 
usually leaving a $2 deposit, and plug 
it in. It is a matter of choice more or 
less as to whether the volume control 
is attached to the arm of the seat or 
built in the lorgnette handle; the latter, 
however, is generally the most conveni- 
ent for the user, while the seat position 
helps the impedance problem somewhat. 

To turn now to the more intricate 
design of teaching equipment, there is 
one feature alone which will determine 
the success or failure of the instrument. 
That is the capability of the microphone 
to pick up speech with clarity from a 



APRIL, 1932 



Page 19 






distance of 20-30 feet and return it at 
such volume that the hard-of-hearing 
person can hear his own voice in the 
phones. This is a prime necessity in 
teaching speech, since the pupil must 
hear his own voice as well as that of 
the instructor in order to be certain 
that he has imitated the sounds cor- 
rectly. This necessity imposes a certain 
restriction on the sensitivity of the mi- 
crophone, which must not have a ten- 
dency to feed back from the phones, 
even though the phones are within ten 
feet of it. 

Teaching Equipment 

The most useful general design of 
teaching equipment employs a flat- 
topped desk of the kneehole type. Into 
the center of the forward edge of the 
desk is built the microphone head, with 
the diaphragm upwards in a horizontal 
position. Carbon microphones positively 
can not be used for this work, as with 
the high amplification necessary it is im- 
possible to get rid of hiss and distortion. 
Immediately under the head, and inside 
the desk is the amplifier, with a grid 
lead from the head of the microphone 
well shielded and not more than five or 
six inches long. 

Another necessity in this equipment 
is the incorporation of a phonograph 
for the purposes of ear stimulation. This 
can very well be arranged in a drawer 
to the right of the kneehole, with a 
drawer for records underneath it. It is 
a peculiar fact that a deafened child will 
often pretend to hear when it can not. 
For this reason it is as well to incor- 
porate a cutoff switch which can be 
operated by the knee of the teacher. A 
visible switch can not be used since the 
child will see it operated and act ac- 
cordingly. Similarly the operation of 
the switch must be perfectly silent so 
that there is no indication of when it is 
used. 

The controls on this instrument can 
conveniently be mounted close together 
on a panel on the front of the phono- 
graph drawer. They should consist of 
an on-off switch, phono-mike switch, 



Fig. 1. Teaching set 
for the hard of. hear- 
ing. 



PHONE PLUG 
. HERE 



MICROPHONE 
POSITION 




PHONO. 
DRAWER 



THE following are the answers to 
technical questions for projection- 
ists, Nos. 39 to 48 of the series, 
which were presented in the 
March issue of Projection Engineer- 
ing: 

39. .00075 inch high, .070 of an inch 
wide. 

40. The one on the left, facing fader, 
is for use in event the fader becomes 
inoperative, when this switch is thrown 
either to the left or right to close these 
respective circuits it introduces resist- 
ance, which is equal to the number nine 
fader setting. 

The switch on the right hand side of 



phono volume control — the phonograph 
being cut into the last two stages of the 
amplifier — and some designers prefer 
to incorporate an amplifier volume con- 
trol, although, as each phone has to be 
controlled separately at the students' 
desks, this hardly seems necessary. As 
it is sometimes necessary for the teacher 
to examine a child's hearing separately, 
it is advisable to incorporate a phone 
plug at the end of the desk, and mount 
the volume control for this on the panel. 
It is rather important that the volume 
controls on the students' desks be 
matched as closely as possible so that 
comparisons can be made in the im- 
provement of the hearing. It is also an 
advantage to have the calibrated knobs 
securely attached to the spindles so that 
the children can not twist them on their 
shafts and so confuse the readings. Sin- 
gle headphones are always used for this 
work. 

In Private Clubs 

Any one producing equipment such 
as this will also find a ready market in 
private clubs having a number of hard- 
of-hearing members. In such cases the 
equipment can be mounted in a smaller 
reading desk such as used by lecturers, 
and the floors of one or more rooms 
wired for easy installation by the build- 
ing electrician. 

Finally, a word about costs. In the- 

A A A 

Answers to Technical Questions 

the fader, is for use when three pro- 
jectors are installed. 

41. A storage battery neither stores 
nor generates electricity, what is done 
is to start a chemical action. 

42. Amplification and volume are not 
the same thing. Amplification is the in- 
crease of signal amperage or voltage or 
both. Volume is the result in power re- 
ceived through the amplifier. 

43. The fader in the RCA circuit is 
used to switch sound from one projector 
to the other, while the fader in the WE 
circuit besides being used for this pur- 
pose also within certain limits controls 
the volume. 



(Designed by Henry L. Williams) 

atre installations it is usual to supply 
only six or seven phones for each twelve 
wired positions. A prominent manufac- 
turer of motion picture equipment sup- 
plies seven phones and 12 positions 
wired into the projection amplifier, in- 
stalled for $250. A manufacturer of the 
telephone type units supplies the same 
quantity of apparatus for $195 and 
leaves the installation to the theatre 
electricians. The writer has built and 
installed condenser microphones in "le- 
gitimate" theatres with seven phones and 
12 positions for a net cost of $150 for 
which the usual list price is $500. A simi- 
lar price can be obtained very easily for 
club installations and the net costs are 
about the same. The usual price for 
single phones with the plug boxes is 
$15 each, although one maker asks $20. 
The actual net costs for good quality 
instruments is around $3.40, without 
volume controls. The actual cost for 
the desk teaching equipment should not 
exceed $170 plus the phones. The sell- 
ing prices of this equipment have al- 
ways been high due to lack of competi- 
tion, the desks selling for around $900 
upwards. A list price of around $500, 
however, allows a fair profit, taking into 
consideration the amount of attention 
and instruction in use necessary. It will 
therefore be seen that the market for 
these types of equipment offers far 
greater possibilities than the attention 
it has received would indicate. 



44. Yes. The RCA employ such a 
motor on some of their installations. 
These motors are 220 volt 60 cycle 3 
phase. 

45. Both systems can be used on RCA 
Photophone without any changes in the 
equipment. In fact, all 35 mm. film 
carrying sound may be used. 

46. To hold the speed of the projec- 
tion motor to as near a uniform speed 
as possible. 

47. This is an attachment used to 
"filter" out the scratch noises in the 
reproduction of sound. 

48. The speed is decreased when the 
field current is strengthened and in- 
creased as the field current is weakened. 



Page 20 



Thermionic switch^ 
board controls 
theatre light 



ELABORATE theatre lighting sys- 
tems are now manipulated with 
the same ease and precision as a 
radio receiving set. Color effects 
are selected more easily than broadcast- 
ing stations are tuned in, and light in- 
tensities are controlled just as the vol- 
ume is regulated. 

Great saving in space has been ef- 
fected by the use of thermionic tubes 
similar to those used in radio sets, ac- 
cording to engineers of the Westing- 
house Electric and Manufacturing Com- 
pany, who designed the switchboard 
now being installed in the new munici- 
pal auditorium at Long Beach, Califor- 
nia. 

Stage managers say there must be 
flexibility in the selection of circuits and 
in the control of light intensities. Prog- 
ress in this direction has been constant 
for the past 15 years and the thermi- 
onic tube brought the ultimate solution. 

While the new type of switchboard 
provides greater flexibility than previ- 
ous designs of circuits and dimmers and 
thus much more elaborate and better 
coordination of lighting effects, its con- 
trol is quite simple. The board for the 
two auditoriums has 72 controlled cir- 



cuits for stage and house lighting and 
30 switch circuits for miscellaneous 
lighting. Colors are in combination of 
white, blue and red, and the stage light- 
ing is controlled from a portable switch- 
board mounted on wheels. This porta- 
ble board is connected to the tube units 
by a flexible cord and all lighting is 
controlled by reactors through these 
thermionic tubes. 

One Control 

This installation is one of the largest 
of its type and the only switchboard 
which enables the operator to set up 
lighting combinations at predetermined 
intensities for ten scenes in advance of 
a performance. With this arrangement 
it is necessary to operate only one sim- 
ple control when it is desired to change 
from one lighting effect to the next. 

Each circuit has a scene-fader which 
makes it possible to blend one scene into 
the next with a gradual transition. If 
it is desired to flash suddenly from one 
scene to another this may be accom- 
plished merely by pushing a button. Im- 
mediately the lighting changes from one 
preset to the combination of colors 
chosen for the next, and the circuits re- 

A A ▲ 



PROJECTION ENGINEERING 

spond with the required -intensity. ,., 
Fading is proportional to the amount 
of voltage passing into the electrical 
color master, and this is regulated by 
means of a sliding arm that moves over 
a series of potentiometers. Propor- 
tional changes in. voltages impressed on 
the sliding arm produce corresponding 
changes in the lighting intensities of 
the circuits connected to these controls. 
For example, one of the circuits con- 
nected to this color master is at full 
brilliancy, a second at three-fourths 
brilliancy, and a third at one-half bril- 
liancy. When they are dimmed out by 
the color master, they will all start 
dimming at the same time proportion- 
ally so they will reach the blackout po- 
sition at the same time. 

This gives a much more pleasing ef- 
fect than the interlock type of control, 
which dims the circuit of full brilliancy 
until it reaches three-fourths brilliancy 
when the second circuit is interlocked. 
Both continue to dim until half bril- 
ancy is reached, when the third joins, 
and they all travel to the blackout to- 
gether. Engineers say this method 
gives a spotty effect that is undesira- 
ble. It has been overcome by ganging 
the faders together and giving them a 
common drive. 

The stage being located between the 
concert hall and the main auditorium 
necessitates the movable switchboard so 
that the stage lights can be controlled 
from either side. Westinghouse engi- 
neers say the lighting facilities are so 
flexible that any intensity of any color- 
ing may be obtained for any kind of a 
production on either side of the stage 
or for a performance requiring the 
the stage to be thrown open in both 
directions. 






Mal-exploitation of pictures 



AT the Washington convention of 
the M.P.T.O.A in March there 
were many interesting talks of 
constructive import to the mov- 
picture industry. Among these one that 
reflected the thoughts of many persons 
present was that of Edward Kuyken- 
dahl in his address on unfair legislation 
and admission taxes. It is Mr. Kuy- 
kendahl's view that exhibitors exag- 
gerate costs to the public, and producers 
do the same to exhibitors, thereby get- 
ting the film industry into ill repute and 
inducing legislation. "We need more 
business ethics and less politics in the 
motion picture industry," he said. 

"Directors in Hollywood, by inject- 
ing obscene, indecent scenes into what 
would be clean entertainment, are more 
responsible than any one unit in this 
industry for discriminatory legislation. 
But part of this blame goes to the 



executive head, who, in his mad scram- 
ble for increased box-office results, 
overlooks the necessity for favorable 
public sentiment. 

"A good picture will get money 
without obscenity, and by the same 
token a poor picture cannot be put 
over by obscene injections, though some 
producers seem to think so. 

"Producers and directors do not have 
proper understanding of public senti- 
ment as to this industry, or as to kind 
of pictures most popular. Only the ex- 
hibitors really know this. 

"It is our four-flushing, our parading, 
our utter disregard for the fundamen- 
tals of common decency that is now 
bringing, and will continue to bring, 
discriminatory legislation and unfair 
admission taxes down upon us. 

"It is beyond my understanding how 
some exhibitors and producers can by 



indecent advertising and obscene pic- 
tures hope to ever get the sympathetic 
understanding of decent-thinking men 
and women. 

"We create sentiment for censorship 
of our own free will and accord, then 
spend thousands fighting censorship. 
This same thing applies to admission 
taxes. 

"We spend too little time and money 
in educating lawmakers and the public 
in our real problems. There are many 
exhibitors who have no understanding 
of how to encourage and develop the 
friendship of those elected to public 
office. Sincerity and actual facts will 
work wonders. 

"Too little is known about our real 
problems, and too much about fabulous 
salaries, most of which is more four- 
flushing." 



APRIL, 1932 



Page 21 






Educational and 
commercial films 
with sound-on-disc 1 



Roger W. Fenimore* 



THE application of sound-on-disc to 
educational and commercial motion 
pictures requires the work to be 
considered under the following 
classifications : 

A. Synchronizing sound to old silent 
films. 

B. Synchronizing sound and adding 
talking sequences to old silent films. 

C. Producing new films with sound- 
on-disc. 

Classes A and B contain films respon- 
sible for the original and perhaps the 
greatest present demand for sound on 
disc in the non-theatrical field. These 
films were made with no idea of any 
sound accompanying their showing 
(other than the possible racket of a 
''silent" projector). 

A. The most simple form of sound- 
on-disc is a musical accompaniment 
which is easily timed and requires lit- 
tle or no change in the film. Wherever 
the substitution of an off-stage voice 
for a title will enhance the presentation 
of the subject, remove the title. Spoken 
titles should not be removed because 
dialogue cannot be successfully synchro- 
nized to lip movement without remaking 
the scenes. 

After removal of titles and final ar- 
rangement of all the scenes in the pic- 
ture, the entire film is measured to de- 
termine the exact screen time at 90 feet 
per minute. In arranging the sound 
script the screen time of each separate 
scene must be considered if the voice 
or other sound is intended to coincide 
with some, certain action on the screen. 

Sound effects require even more ac- 
curate timing. The person creating the 
sounds must see the screen all the time 
and have some specific action to watch 
for as a cue. Sometimes punch marks 
in the film will serve as an accurate cue 
and make it possible to create a sound 
perfectly synchronized with very quick 
action. 

A recording may be arranged with 
utmost care and after making the re- 
cording it is evident that a certain sec- 
tion of sound was made just a second 



t Abstracted from paper presented before Chicago 
Section meeting, S.M.P.E., Thursday, January 
7, 1932. 

* Cameraman, Chicago Film Laboratory, Inc., 
Chicago, Illinois. 



or so too late or just a little too soon. 
Rather than go through the recording 
several times, just think of the sound 
as a sliding scale upon which that par- 
ticular scene may be moved a little for- 
ward or backward. This, of course, 
must be done without disturbing the re- 
lation of the sound to the adjoining 
scenes. 

When the script is complete and all 
sound effects and music arranged and 
cued, the next step is a rehearsal of the 
actual recording. The film is projected 
at 90 feet per minute on a projector lo- 
cated outside the recording studio. The 
picture is focused' on a screen within the 
recording studio in view of the speaker, 
musicians, and every one taking part in 
the recording. One or two rehearsals 
will usually correct the slight errors in 
timing which are bound to occur in 
spite of the careful use of a measuring 
machine and a stop watch. 

B. Before discussing the recording 
of this A class, or old silent films, let 
us consider the B class, or the silent 
films to which talking sequences are to 
be added. 

The most simple form of talking se- 
quences added to silent films is an in- 
troductory scene and perhaps occasional 
insert scenes of the speaker, whose off- 
stage voice gives the description of the 
silent scenes. It is necessary to write 
the talking sequences into the script and 
to locate them in the film by splicing in 
blank leaders long enough to allow for 
stopping and starting of the projector. 
The camera must be of a type or located 
in such a manner that the sound of its 
operation does not interfere with the re- 
cording. It must also be driven at ex- 
actly 90 feet per minute. The lighting 
necessary to photograph the speaker 
naturally makes it necessary to arrange 
a shadow box around the screen on 
which the picture is shown. 

For the sake of discussion, let us sup- 
pose that the picture starts out with the 
usual main title and that immediately 
after this title there is to be a talking 
introduction by the speaker, after which 
the story continues in silent scenes ac- 
companied by the speaker's voice off- 
stage. The director signals for "quiet" 
and every one on the stage gets ready 



for the recording. On the "begin" sig- 
nal, the projector starts and the main 
title fades in on the screen. On the same 
cue the musicians play the background 
for the main title. At a cue mark in the 
film a few seconds before the leader on 
which the operator will stop the pro- 
jector, the cameraman starts the cam- 
era. When the leader appears on the 
screen it is the operator's cue to begin 
the talking introduction. The last word 
of this talking introduction is the cue 
upon which the director signals the op- 
erator to again start the projector, and 
with the appearance of the picture on 
the screen the cameraman stops the 
camera and the recording continues 
with the off-stage voice and sound ef- 
fects accompanying the picture on the 
screen. Thus we have the camera start- 
ing before the projector stops and the 
projector starting before the camera 
stops, giving a short overlap necessary 
when conforming the silent print to the 
disc. 

We now have the A and B types of 
pictures ready for recording. 

C. The third, or C class, is a picture 
photographed with sound-on-disc, or 
made with the idea of synchronizing 
sound-on-disc. This class of picture 
may be further divided into three more 
classes, two of which are similar to the 
A and B classes already discussed. That 
is, new films may be made with the idea 
of synchronizing sound such as off-stage 
voice, music and sound effects, but with 
no actual talking scenes, or they may 
be made with the idea of interspersing 
talking scenes with synchronized scenes. 
Or they may be "all talkie," as the ex- 
pression is used. 

If a picture is to be produced for 
synchronizing only, its arrangement 
will be handled in much the same way 
as the arrangement of an old silent film, 
except that the pictures will be photo- 
graphed at approximately 90 feet per 
minute so that the action on the screen 
will be normal. 

In considering an all talkie subject 
to be recorded on disc, we can of 
course forget the silent scenes and the 
projector, but remember that all our 
editing must be done with the camera, 
so to speak. 

We arrange two or more cameras 
with lenses of various focal length and 
photograph the act all the way through 
with the camera containing the lens of 
the shortest focal length. The other 
lenses of longer focal length pick out 
the various high spots in the course of 
the act, and in the completed film these 
medium closeups and closeups will be 
substituted for their corresponding ac- 
tion in the long shot, thereby maintain- 
ing the same entire footage of the re- 
cording, but varying the angle and dis- 
tance of the scene. 



Page 22 



World's largest public 
address and program 
distributing system 



By J. J. Kuhn : 



In the January issue of PROJECTION ENGINEER- 
ING some of the engineering details of the radio and 
program distributing system now in service in the Wal- 
dorf-Astoria Hotel, New York, were presented. In the 
following article additional information is given out. 



AMPLIFYING and distributing 
equipment permits an instant 
choice of six programs to 
• guests in each of the hotel's 
1,940 guest rooms. The same equipment 
provides programs and reenforcement 
in the hotel's many public rooms. In- 
dependently, two radio-frequency dis- 
tributing systems afford the residents 
in each of 138 tower apartments access 
to all radio programs which their own 
receivers can detect. 

The system for distribution to the 
hotel's guest rooms and public rooms 
comprises equipment for pickup, and for 
amplification and distribution over six 
channels. For any of these channels the 
programs may be picked up in any of 
the public rooms, may be reproduced 
from records or may come from dis- 
tant sources by wire or through the aid 
«of radio receivers. 

A program taking place in one of the 
IhotePs public rooms is picked up by 
^portable condenser-transmitters appro- 
priately located and connected through 
flexible shielded cords to plugs in the 
".baseboard of the room. These outlets 
.have been provided in considerable 
mumber, so that microphones can be lo- 

• cated anywhere in a room without the 
mse of unduly long cords. 

Shielded cable connects the speech 

• circuits from all the base plugs to a 
connection box in the control room on 

ithe sixth floor. The filament and plate 
i circuits of the amplifiers directly asso- 

• ciated with the microphones also receive 
; their power over this cable. Each 
: speech input circuit terminates in a 

jack in a switching panel, whence it 
■ can be connected by a patching cord to 

•Special Products Dept., Am. Tel. & Tel. Co. 



the input of any of the six main chan- 
nels. 

Radio programs to be placed on the 
channels are picked up by an antenna 
hung between the hotel's two towers, 
and thence are led down to the control 
room. There the antenna circuit is mul- 
tipled to six Western 10-A radio re- 
ceivers, one associated with each main 
channel. The input circuits of the re- 
ceivers are so arranged that the opera- 
tion of each receiver is independent of 
the operation of the others. Thus they 
can be used without mutual interference 
to detect different programs for their 
respective channels. 

The control rack for each main 
channel contains mixing equipment per- 
mitting the inputs from as many as 
three microphones to be blended, and a 
preliminary amplifier to raise the level 
of the microphone currents. The rack 
also contains a main channel amplifier 
of the Western Electric 59-B type, 
whose input may come from the pre- 
liminary amplifier, the radio receiver, 
a wire line, or a reproducer. Each 
channel is provided with a volume in- 
dicator, and the necessary controls; 
monitoring can be accomplished either 
by headphones or by the monitoring 
loudspeaker in the control room. Com- 
munication with observers in the public 
rooms over separate communication 
circuits is also provided. 

Power amplification is finally accom- 
plished by Western Electric 57-A ampli- 
fiers, of which thirty-one are available. 
Twenty-four of these are normally as- 
sociated with guest-room circuits, six 
with public-room circuits, and one with 
the outgoing wire-line circuits over 
which events of public interest can be 
transmitted to distant broadcast sta- 
tions. Thus, normally each of the six 



PROJECTION ENGINEERING 

main channels has four power amplifiers 
associated with it for guest-room am- 
plification, and one for public-room 
amplification. 

For distribution to guest rooms, the 
output of each power-amplifier is con- 
nected through matching and switching 
apparatus to a strip of jacks from each 
of which a conducting pair passes 
through lead-covered cable up a riser 
in the building to an electrical closet 
serving the rooms in its neighborhood 
on its floor. Here the pair is cross-con- 
nected to four terminal strips from 
which several circuits run, each to 
about twenty guest rooms. To bring 
to each guest room a pair representative 
of each channel requires three 152-pair 
cables and one 101-pair cable. The use 
of terminal strips of a sealing-chamber 
type prevents the moisture prevalent in 
closed shafts and cabinets from reach- 
ing the conductors. 

Low Cost Maintenance 

The system is designed so as to re- 
duce maintenance to a minimum. Two 
brief testing operations will segregate 
trouble to a group of twenty guest 
rooms. To locate the particular guest 
room in which the trouble exists, a 
maximum of only half the group need 
be disturbed. Furthermore, the major 
items of equipment in the control room 
are interchangeable, and can be patched 
from channel to channel to meet any 
unusual need. 

Six pairs of wires are connected to 
a base plug in each guest room and sev- 
eral rooms in each apartment of the 
hotel. To avail himself of the progress 
they offer, a guest requests that a loud- 
speaker be brought him, and the page 
who delivers it inserts the twelve-con- 
ductor plug at the end of its cord into 
the base outlet. By rotating to the 
proper position the knob of a six-posi- 
tion switch in the loudspeaker, any of 
the six programs available can be se- 
lected. The volume of the program can 
be adjusted by a control knob on the 
speaker. The master volume control in 
the control room is so set that no guest 
can raise the volume to a point where 
it would annoy the occwpants of an ad- 
joining room. 

To the public rooms the sound cur- 
rents pass over cable from the power 
amplifiers in the control room. The 
sounds are reproduced by loudspeakers, 
the type and location of which are 
chosen to suit the rooms which they 
serve. In most of the public rooms 
loudspeakers are permanently installed 
behind concealing grilles, chosen to suit 
the decorative schemes of the rooms. 
Both in these rooms and in the public 
rooms not so equipped, portable loud- 
speakers can be connected to base out- 
lets when speech reenforcement is re- 
quired. 



APRIL, 1932 



Page 23 



7 


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The public-address system in the Waldorf-Astoria has been provided with a maximum of flexibility by patching equipment. 



15 KW. Alternator Supplies Power 

Since the hotel is supplied only with 
direct current, and the radio receivers 
and the preliminary, main-channel and 
power amplifiers are designed to oper- 
ate on alternating current, it was neces- 
sary to provide converter equipment. 
Located in a power room on the seventh 
floor, a 240-volt motor operates on 
direct current to drive a 60-cycle alter- 
nator producing 15 kilowatts of power 
at 115 volts. To guard against inter- 
ruption of programs, a duplicate set is 
provided and duplicate control and 
regulating equipment is associated with 
each set. For convenience of operation 
the control facilities located in the 
power room are extended to a remote- 
control panel in the control room. 

Apart entirely from the system dis- 
tributing to guest and public rooms is 
the antenna service for residents of the 
tower apartments. It was thought that 
these residents might wish to use their 



own radio sets as well as the hotel's 
loudspeaker service. For their accom- 
modation two additional antennas have 
been hung between the towers, one to 
serve each. Each antenna is coupled to 
a radio-frequency transmission line of 
low impedance through a protector, a 
wave trap for suppressing strong local 
stations which might overload the sys- 
tem, and a repeating coil. On reaching 
the highest floor on which apartments 
are located, the line is coupled to a 
loaded line of high impedance. To this 
line in turn are coupled low-impedance 
lines, sometimes as long as 250 feet, 
running to the individual apartments, 
where the impedance is again finally 
stepped up. 

The coupling of the individual lines 
is accomplished through single-stage 
amplifiers, balanced and neutralized. 
These insure against the feedback of 
energy from improperly designed re- 
ceivers, and against the modulation of 
one frequency in the signal by another. 



The filament of each amplifier burns 
only when it is needed; its 110-volt 
supply is trunked through the outlet 
in its apartment, and current flows 
only when the set is operating. 

The system forms an unparalleled 
example of what can be accomplished 
when the problem is understood and 
in designing and installing public- 
address equipment when owners, archi- 
tects and builders cooperate with the 
communication engineers from the time 
when the first plans are drawn. To 
adapt standard methods to particular 
needs, to provide many convenient mi- 
crophone outlets, to fit loudspeakers into 
decorative schemes and retain acoustic 
effectiveness, to bring cable for the re- 
quired number of channels to each of 
several hundred rooms and suites, can 
only be efficiently done by carefully 
planning the electrical installation in 
advance. — Bell Laboratories Record, 
January, 1932. 



The monthly examinations 

The progressive projectionists who are studying the questions submitted each month in PROJEC- 
TION ENGINEERING, continue to show improvement in the quality of their answers as sent in to 
the editor. 

Several men have written that, although they have not forwarded answers, they are working out 
the problems, and then when the answers are published are enabled to check accuracy. 

Among those who continue to gain high marks are: Robert A. Passmore, Valdosta, Ga.; W. Hoy, 
Calgary, Alberta; C. L. Merrell, Selmer, Tenn. 



Page 24 



PROJECTION ENGINEERING 



New Developments 



n d 



News of the Industry 



THE POSTOSCOPE 

The Postoscope Company, Beatrice, 
Neb., is marketing the Postoscope pro- 
jector, which is finding use in theatres. 

Any "copy" or design can be projected 
enlarged to the size desired, onto the poster 
board, traced and colored. 

The "copy" may be pictures from press 
sheets, photographs, original sketches or 
designs or advertisements. It is reflected, 
enlarged to any size desired directly onto 
the poster board, compo board or other 
surface, in the original colors and in cor- 
rect proportions. 

Through an arrangement of mirror, re- 
flectors and lenses, the image is projected 
"right-side-to." Lettering does not appear 
backward. 

"Reversed" images can be produced 
easily. 

The sign man can trace this to make an 
exact copy or he can omit details not de- 
sired. He can copy the original coloring 
exactly or change it to produce striking 
poster effects. 

Small black and white copy may be 
colored before projecting or the color 
scheme can be worked out right on the 
poster. 

Will project copy 5x6 inches, but larger 
copy can be projected in sections. 

Any desired magnification can be had by 
moving the Postoscope nearer to or 
farther away from the work. The enlarge- 
ment depends upon the distance of the 
apparatus from the surface upon which it 
is projected. 



PICKUP MICROPHONE CONTROL UNIT 
MODEL PC-713 

The PC-713 — pickup and microphone 
control unit, manufactured by the Webster 
Electric Company, Racine, Wis.; can be 
mounted on top of the amplifier case. This 
unit makes possible the use of the Webster 
6048 R amplifier where sound-on-disc is 
already in use. Two pickups of 200 ohms 
impedance can readily be connected direct- 




ly to the amplifier through this unit. A 
control is provided to switch from one 
turntable to the other. A convenient plug- 
in arrangement connects to the amplifier. 

For announcements and special features 
it is possible to operate a standard two 
button microphone through the PC-713 
unit. The jarnplifier supplies necessary 
button current. 



A NEW SMALL CONDENSER 

A new octave tone condenser of the 
tapped, sliding contact type is offered by 
the Filtermatic Mfg. Co., 4458 Frankford 
Ave., Philadelphia, Pa. 

This is a well made, neat unit which 
should have many applications in radio and 
sound work. 



S. O. S. EXPANDS 

The entire stock, plant and fixtures of 
the Royal Amplitone Corp., 109 W. 64th 
St., New York, has been bought by the 
S. O. S. Corp., 1600 Broadway, New 
York. 

At one time the Royal Amplitone Corp. 
was among the leaders of the independent 
sound field. Thousands of their disc and 
film systems were sold throughout the 
world. Among their larger users was the 
Publix Theatres Corp., while many other 
circuits had adopted the Royal sound sys- 
tems in the early days of the talkies. 

Users of Royal amplitone equipment will 
be glad to know that a complete stock of 
parts and replacements is being carried 
by the S. O. S. Corp., and will be avail- 
able as long as there is any demand. The 
S. O. S. salvage department has been ex- 
tending a helping hand to many of the 
independents who have for one reason or 
another been unable to maintain their 
plants, and thus properly serve their users. 
By absorbing stocks, sorting and classify- 
ing the different items, S. O. S. has made 
themselves a valuable adjunct to the indus- 
try. Exhibitors are now able to secure 
whatever they need for such makes as 
Sterling, Tone-O-Graph, Melotone, Ker- 
sten, Supertone, Biophone, Bristolphone, 
Gennett, Moviephone, Gries, Kinemaphone, 
Orchestraphone, Orotone, Radiotone, Stan- 
aphone and several others. 



PRICES ON THREE TYPES OF EQUIPMENT 
REDUCED 

A further reduction in service charges, a 
substantial reduction in the prices of three 
types of apparatus, introduction of two 
new all a-c. operated models designed for 
houses up to 4,000 seating capacity, and an 
entirely new merchandising policy have 
been announced by E. O. Heyl, manager of 
the Photophone division of the RCA- Vic- 
tor Co. Mr. Heyl said this move was the 
first fruit of the economies resulting from 
the recent consolidation of Photophone 
with Victor. 

Service charge reductions from $32.50 to 
$25 a month on the special size equipment ; 
from $65 to $32.50 oh the standard small 
size equipment and a reduction from $130 
for four contract calls to $65 for two calls 
monthly on the standard super size equip- 
ment, as well as a reduction in the financ- 
ing, interest and collection charges, were 
announced. 

The two new all a.-c. operated sound 



reproducing units, which Mr. Heyl re- 
ferred to as the standard large, for theatres 
having from 1,400 to 2,500 seating capacity 
and the standard super, for theatres having 
from 2,500 to 4,000 seating capacity, are 
said to be the only standard equipments 
operated by a-c. power supply that have 
been designed for theatres of the capaci- 
ties mentioned. In addition to the conveni- 
ence provided by the elimination of 
batteries and motor generators and the 
resultant saving in upkeep and installation 
cost, the prices of these two equipments 
have been materially reduced. Heretofore 
the so-called super size equipment's lease 
price has been $8,000. The new price of 
the standard super all a-c. operated ap- 
paratus is $5,000. The former price of the 
large size equipment was $6,000. The new 
price of the standard large size equipment 
is $3,750. 

Mr. Heyl also announced that the seat- 
ing capacity limitations of the new all a-c. 
operated special size equipment had been 
increased to 600 seats; the standard small 
size to 1,400 seats and the standard large 
size to 2,500 seats. 

A 

NO. 3320-N HORN 

The No. 3320-N folded air-column horn 
has been particularly designed for outdoor 
public-address installations where it is de- 
sired to mount the horns on a pedestal or 
tower to cover large areas. Due to its 




compact size, a number of these horns can 
be easily mounted, and the wide bell angle 
assures adequate distribution of the sound. 
The No. 3320-N horn has been termed 
"the tower type horn." It is manufactured 
by the Racon Electric Company, 18 Wash- 
ington Place, New York. 



UNIVERSAL MICROPHONE COMPANY 
MOVES 

The Universal Microphone Co., Ltd., for- 
merly of 1163 Hyde Park Boulevard, Ingle- 
wood, California, has moved to its new 
building also in Inglewood, at Centinela 
and Warren Lane. This change was made 
because of the need for greatly increased 
space to take care of additional business. 

The new home of the Universal Micro- 
phone Company is located in a modern, 
three-story, fire-proof concrete building, 
with sunlight on all four sides. 



APRIL, 1932 



Page 25 




a 



real 
SOUND 
Amplifier 




Sound, a. Founded in truth; substantial; right; valid. 
— Funk & Wagnalls Standard Dictionary. 

SOUND — a word well applied to WEBSTER- 
CHICAGO Amplifiers and Accessories — sound 
in engineering, sound in principle, sound in con- 
struction and performance. You will be proud to 
own and use such equipment as this. 

Take our new 3-stage Amplifier NC-72 (illus- 
trated above). It includes features you've always 
wanted. It's all-electric, of course. It's equally 
well adapted for radio, phonograph or micro- 
phone. An integral control panel (something 
new!) includes program selector switch, micro- 
phone current control and meter, master volume 
control and power switch. Output is 13.7 watts 
through two 250 tubes in push pull. 

It's a thoroughly dependable amplifier, and when 
you learn the price it'll be the best news you've 
heard in a long time. 

Have You Our Catalog? 

Webster builds all kinds of amplifiers — large and 
small, standard and special. It will pay you to 
consult the Webster Catalog when designing in- 
stallations and ordering equipment. You'll be sure 
of dependable apparatus, and you'll probably save 
money. 

WEBSTER - 
CHICAGO 

The WEBSTER Company 

Sound Amplifiers for Every Purpose 

854 Blackhawk St. * Chicago, III. 



TRADE 




Now — a complete, practical sound-system test set! The new 
Weston Model 595 Test Set gives every test required to 
properly service sound projection equipment. It simplifies 
maintenance! Assures better quality sound reproduction! 
Prevents costly failures! 

The only instrument especially designed for projection 
servicing, Model 595 meets the demand for a reliable, accurate 
instrument, complete in servicing scope, which projectionists 
and service men can use in maintaining sound equipment. 

Engineered by the foremost maker of radio and industrial 
test sets, the new Weston Model 595 has the approval of the 
leading equipment manufacturers and theatre operators. 
Get the details today. Use the coupon below! 

TESTS WITH MODEL 595 

CHECKS ALL TUBES (independent of amplifier)- A. C.-D. C. Fila- 
ment Voltages, Grid Voltages, Plate Voltages, Grid Currents, Cath- 
ode Voltages, Screen Voltages, Rectifier Plate Currents (both plates), 
Screen Grid Currents, Grid Currents, Space Charge Grid Voltages. 
Detects gassy or oscillating tubes. 

CONTINUITY AND RESISTANCE MEASUREMENTS-1 00,000/ 
10,000/1 ,000 ohms. 

CONDENSER TESTS-0.005 to 2 microfarads. 

POWER LEVEL IN DECIBELS 27 to + 39 decibels in steps of 

3 D. B. — for use on 500 ohm line. 

MISCELLANEOUS TESTS-1, 500/750/300/1 50/75/30/1 5 volts 
D.C./ 150/30/3 milliamperesD. C; 2,000/1,000/200 16/8/4 volts 
A.C.; 100/20 milliamperes A.C.; 8/4 amperes D.C. and A. C. 
Higher A.C. and D.C. current ranges may be obtained. 

Model 595 supplied complete with test plug, adapters, test cables with spike 
terminals, test cables with clips, battery and spares fuses. 

LYJSHSH 



ELECTRICAL INSTRUMENT CORP. 



608 FRELINGHUYSEN AVENUE . . . NEWARK, N. J. 

Please send descriptive literature on the new Model 595 Sound 
Equipment Tester. 

Name 



Address. 
City 



_State_ 



Company. 



Page 26 



PROJECTION ENGINEERING 



TYPE A PORTABLE MICROPHONE BOOM 

The Jenkins & Adair type A portable 
microphone boom is designed to supply 
owners of newsreel and similar talking pic- 
ture recording equipment with an ex- 
tremely light and truly portable boom for 
use in the field or in studios. It is also 
useful in broadcasting studios, in orchestral 
broadcasts and public-address work in gen- 
eral. 

The illustration indicates that the boom 
arm and saddle may be removed from the 




vertical mast, leaving a strong and rigid 
tripod which may be extended from 2 feet 
up to 8 feet. A hangar for Jenkins & 
Adair condenser microphones, supplied at 
extra cost, suspends the microphone from 
the end of the boom or supports it on top 
of the tripod. 

The principal feature of the boom is 
that no counter-weight has to be carried. 
The welded steel container becomes the 
counter-weight as soon as it is filled with 
water, sand, gravel or similar material 
which may be readily obtained under any 
conditions. The angle of the boom is held 
fixed by means of a short section of tele- 
scopic tubing, designed with a friction fit. 
The legs of the tripod are equipped with 
1 foot telescopic extensions and all con- 
ceivable adjustments of the tripod are pos- 
sible. The company's address is 3333 Bel- 
mont Ave., Chicago, 111. 



THEATRE AND PUBLIC-ADDRESS 
EOUIPMENT 

The Webster Electric Company, Racine, 
Wis., is introducing a new and improved 
line of faders, tone compensators, power 
amplifiers, microphone coupling units, 
pick-ups, head amplifiers and power supply 
units for theatre and other sound installa- 
tions, new or to add sound-on-film to 
sound-on-disc installations, as well as for 
replacements of existing equipment. 



EXPERIMENTERS NOW WORK PROFITABLY 
WITH PHOTOCELLS AND RELAYS 

Engineers and experimenters have be- 
come interested in a new departure: the 
construction of automatic control devices 
using photoelectric cells. Keen interest 
in this novel avocation is creating a host 
of new fans and home constructors, many 
of them being former radio fans and set 
builders. Although most persons start 
experimenting with photocells for amuse- 
ment, practically all of them find a ready 
and profitable market for the automatic 
control devices which they construct. 

The photocell, popularly known as the 
"electric eye," is one of the most interest- 



ing developments of modern science. This 
cell, in its most efficient form, employs a 
highly sensitive disc, which transforms 
light energy into electrical energy without 
the use of auxiliary voltage. Response to 
light variations is instantaneous and suffi- 
cient current is developed to operate suit- 
able relays directly, without requiring 
auxiliary apparatus or battery. 

Although thousands of applications of 
the photocell have already been invented, 
the surface has merely been scratched. 
For this reason, experimental work is 
certain to bring many useful new inven- 
tions. 

Recently a powerful and highly efficient 
photoelectric cell, known as the Weston 
photronic cell, has been perfected, which 
combines good qualities of existing cells, 
with none of their limitations. Notwith- 
standing the superiority of this cell, it is 
low in cost and moreover, its auxiliary 
apparatus is equally inexpensive. Hence, 
the invention of this device has finally 
placed photocell equipment within the 
means of every experimenter. The pho- 
tronic cell, together with its auxiliary ap- 
paratus, is known as the Weston photronic 
relay. 

In order to encourage originality in the 
application of photronic relays, the Weston 
Electrical Instrument Corporation is offer- 
ing a prize of $10 in cash for each new 
suggested application of this device. For 
those who are becoming acquainted with 
this hobby, a booklet has been published, 
describing a number of interesting ex- 
perimental control devices which can be 
constructed with the photronic relay. 

This pamphlet may be obtained free by- 
writing to the Allied Engineering Insti- 
tute. Suite 541, 98 Park Place, New York, 
N. Y., enclosing 5 cents to cover mailing 
costs. 



HI-POWER OPTICAL SYSTEM DOUBLES 
ILLUMINATION OF 16 MM. PROJECTORS 

The Victor Animatograph Corporation, 
Davenport, Iowa, announces that, after sev- 
eral months of research and experimenta- 
tion, it has developed a new optical system 
of exceptional efficiency which sets ar. en- 
tirely new standard for brilliancy in 16 
mm. projection. It is claimed that this new 
hi^h power system gives twice the illu- 
mination of the regular Victor optical sys- 
tems when the same projection lamps are 
used. 

The constantly growing popularity of 16 
mm. films and projectors among educa- 
tional, religious, and industrial users of 
motion pictures has resulted in demands 
for more and more light to meet the needs 
for large, brilliant images and for projec- 
tion throws of one hundred feet or more. 

Remarkable progress has been made by 
the lamp manufacturers in developing high 
intensity lamps of unusual power. It is evi- 
dent, however, that the size and heat limi- 
tations imposed on the lamp manufacturers 
by the size and design of 16 mm. projec- 
tors has so restricted them that there is no 
great possibility of their being able to add 
annreciably to present lamp efficiencies. 

The new Victor Hi-Power optical system 
is, therefore, an important step forward, in 
that it literally doubles the power of all 
pre-ent 16 mm. projection lamps. It ac- 
complishes this by gathering and transmit- 
ting to the screen twice as much of the 
light from the lamp as is transmitted by 
the regular Victor optical system. It is 
said that the conseauent increase in illu- 
mination will more than satisfy present and 
prospective users of 16 mm. projectors 
who have been demanding greater illu- 



mination to meet daylight projection and 
auditorium requirements. 

The Victor Animatograph Corporation 
had already been successful in mastering 
projection throws of more than one hun- 
dred feet with its regular optical system 
when using 375 watt-75 volt or 165 watt-30 
volt lamps. With the Hi-Power optical 
system capable of doubling the amount of 
light utilized from these lamps, it is evi- 
dent that the illumination it makes possible 
is sufficient to meet every reasonable de- 
mand of non-theatrical users. 

The new Victor Hi-Power optical sys- 
tem consists of a super reflector adjustably 
mounted in a special lamp house extension, 
a set of precision ground bull's eye con- 
densers and a more powerful projection 
lens. These parts may be easily installed 
in a few moments by any Victor owner 
and are available at reasonable cost. 

The Hi-Power optical system will not 
replace the regular Victor optical system 
in all models, due to the fact that it pro- 
vides greater illumination than is required 
for home use or where large pictures and 
long projection throws are not required. 
Therefore, the Hi-Power system will be 
provided in new Victor equipments only on 
order and at a slight extra cost. 



THREE HORNS FROM ONE SPEAKER UNIT 

The Racon Electric .Company, Inc., 18 
Washington Place, New York, is now in 
a position to supply both double and triple 
connectors for enabling the use of two 
or three 39-inch trumpets from a single 
unit. These connectors, which are sold 
in combination with the trumpets, enable 
the public-address installer to get exact 




coverage at a very economical first cost. 
This method of using multiple horns also 
improves the frequency response through 
the greater bell area served from a com- 
mon throat. 



METAL FOR RECORDING PURPOSES 

The Illinois Zinc Company, 332 So. 
Michigan Avenue, Chicago, Ills., announce 
that their metal product Eraydo is a su- 
perior medium for sound records. 

Aluminum has been used for this purpose 
and the patents on recording cover what 
is known as lubricating, which really 
.neans the immersing of the aluminum discs 
in paraffin and buffing the paraffin into the 
surface to reduce friction. 

Eraydo does not have to be so lubricated 
because of its low coefficient of friction and 
its recording properties seem to be superior 
to other metals according to the reports of 
recording laboratories from Boston, New 
York, Los Angeles and Chicago. Right 
now there seems to be a demand for Eraydo 
for this purpose. The appearance is that 
this will ultimately develop into a sub- 
stantial business. 



APRIL, 1932 



Page 27 



^4dd Perfect Sound: 



t 



To your favorite 35 M/M port- 
able projector. No need to scrap 
good portable projectors. Easy 
to set up and operate. No 
changes necessary to projector 
mechanisms. Smooth running 
drive, within sound head, in- 
sures true reproduction without 
waver or other distortion. 
Highest grade materials and 
workmanship insures depend- 
ability and long service. The 
low cost will surprise you. 



WW&A 



f Dealers and Servicemen ! Write for <g 
_ Full Particulars Now! ! 



Manufactured by 

Weber Machine Corporation 



59 RUTTER STREET 



ROCHESTER, NEW YORK 





Po^VK 



The sensation of the in- 
dustry — this new lamp de- 
signed for projection of 35 
or 16 mm. film. 

Gives a brilliant picture as 
large as 8 to 12 feet wide, 
even on porous screens, mak- 
ing it especially valuable 
with sound equipment. 

Operates from any lamp 
socket with current from 8 
to 16 amps. Weighs less 
than 25 lbs. Size 18"xl2"10". 
Extremely simple in opera- 
tion. 

A new rectifier unit as 
companion to this lamp is 
also available. 



For Sale by Independent Supply Dealers 

£he Strong Electric Corporation 

2501 LAGRANGE STREET, TOLEDO, OHIO 

Export Office: 44 Whitehall Street, New York City, N. Y. 



Announcing 
85 Ampere 9 * 20 



MPROVEMENTS in the 9 mm 



Low" White Flame Projector 
Carbon permit operation at 
arc currents up to 85 amperes. 

LONG LIFE 

STEADY BURNING 

EVEN CRATERS 




Page 28 



PROJECTION ENGINEERING 




Pats. 
Pending 



List Price, 



$49.50 

A New Tone Quality 
in Heavy Duty Units 

Accuracy, realism and brilliancy, without dis- 
tortion even under extremes of pressure and 
range. High factor of sensitivity, and very ex- 
ceptional tone balance. Diaphragms and voice 
coils unaffected by moisture or atmospheric 
conditions. Performance of every Fox Unit 
guaranteed. Full information, literature, trade 
discount, etc., on request. No obligation. 

Original and Genuine Fox Equipment 
Manufactured by 

FOX 

The Fox Electric & Mfg. Company 
3118 Monroe St. Toledo, Ohio 



I 



CONFIDENCE 

(ENGLISH READING) 

RADIO TUBE 

MERCHANDISING 

INTERPRETER 
BAD-GOOD-GAS 

The Confidence English 
Reading Tube Tester is not 
just a tube tester — It is a 
selling, merchandising inter- 
preter—It is the most effi- 
cient and appealing medium 
for quick and intensive tube 
sales. More tubes can be 
sold by application of the 
„_„ „.. , ,. T , Confidence to sale than bv 

LUTELY FOOL PROOF- V aS app *. eal ; -V* 5 " IT -" Sim P le: ABS 0- 

Tl.1,1 jv ? : „ Evei 7 &hort '"dicated automatically. 

The actual condition of all tubes is told immediately in English to 
complete satisfaction of all customers J^ngiisn to 

Alter 30 minutes use of a Confidence you would not part with it Trv 
that 30 minute test. In fact we will give vou thro* a\Z t . . • 7 
(See coupon.) We will ship the Confidence to jobbers on "two to three 
reaches the 7W TUbr" me . rchandisi " ff by us ' n * the ConnZce wh ch 
rX^ S o\ h ake 7S t?a 0f st?r U e b, for W test. Calm0t """"^ the tubes from ^ir 

Jobbers take advantage of our trial offer. Comnare th P r^fi^»^„ -*i 
any other device. See its wonderful internTconstrlcti™ 
Dealers— buy through your Jobber or use coupon. 

APPARATUS T D R E , S A 1 L GN° F C F E M R pA A N N Y D -D D ept FE g RED PAY ™"" P 7an _ 
Little Rock, Arkansas 

Gentlemen: 

Please ship immediately one Confidence Tube Tester fnr nM.t. i •„ . , 
559.50 with the express aeent or deposit $16 5 1 cash fl™? LL"' 1 ' 6It i ler deposlt 
nonthly installment notes of $10.00 eart I (»'*,,, ™ ent ™ d s ^" fi"e 
want the Confidence Tester I may return it to the Vw P « \ , th - ree days J do no ' 
and receive my money back. I 'wlflTay"^ s^irtrrnUSon^h^es? "'" 10 "' 




.50 Net 



NAME 



4.DDHESS 



(Please attach three trade references if installment purchase-lst anr i 9** 
credit ratings shipped open ) " UItnase — ^t and 2nd 



T 

J_ HE Group Subscription 
Plan for Projection Engi- 
neering enables a group of 
engineers, executives, projec- 
tionists or technicians to sub- 
scribe at one-half the yearly 
rate. 

The regular individual rate 
is $2.00 a year. In groups of 
4 or more the subscription 
rate is $1.00 a year. (In 
Canada and foreign countries 
$2.00.) 

The engineering depart- 
ments of hundreds of manu- 
facturers and scores of the 
M. P. M. O. U. locals in the 
projection and allied indus- 
tries have used this Group 
Plan extensively, in renew- 
ing their subscriptions to 
Projection Engineering. 



Each subscriber should print 
his name and address clearly 
and state his occupation — 
whether an executive, engi- 
neer, department head, con- 
tractor, installation man, pro- 
jectionist or technician, etc. 



Remember this Group 
Plan when Your 
Subscription Expires 



( Projection Engineering ) 

Bryan Davis Publishing Co., Inc. 

19 East 47th Street 

N. Y., N. Y. 

Los Angeles Chicago Cleveland 



APRIL, 1932 



Page 29 




NO MOKE 

CELL 

WORRIES 



TELEPHOTO 

PHOTOELECTRIC CELLS 

A high degree of sensitivity coupled with long 
life distinguishes Telephoto (Caesium Argon) 
cells. The increased sensitivity reduces the 
amount of amplification required for tonal 
reproduction, obviating to a remarkable ex- 
tent the possibility of distortion. An ultimate 
present day perfection in this ubiquitous neces- 
sity is assured by the painstaking supervision 
these cells are subject to in each detail of their 
manufacture. 

Literature on Request 

TELEPHOTO & TELEVISION CORP. 

133-135 WEST 19TH STREET - NEW YORK 



HOTEL 



MAPIUAWASU INdK) 

1 ATLANTIC AVE. ANP> ClfiUTU *T. ■ 



ATLANTIC AVE. AND EIOHTM ST. 

VIRGINIA BETACI4 VA. 

Fireproof brick construction. 
The coolest spot on the beach. 
Invigorating breezes from ocean on East and 
Lake Holly on West. 

Bright, airy outside rooms, parlor suites and 
apartments, private baths, superior cuisine — iflilSSK 
Surf bathing, riding, fishing, golf, dancing, MP™ 
private tennis court and children's play- 
ground. 

J. WESLEY GARDNER, Manager 




Blue Seal Sound Devices, Inc. 

CINEGLOW SOUND 
SYSTEMS 

Quality sound-on-film, recording 
systems priced within the reach 
of all. 



Single systems for Bell & Howell 
or Alceley Audio Cameras. 

Double systems — battery operated 
portable — for any camera with 
Bell & Howell motor adaptor. 

Double systems — studio 
production type. 

Manufacturers of the famous 

CINEGLOW 
THREE ELEMENT RECORDING LAMP 



1 



H 



;o ♦ 




(Patent Pending) 
Suitable for any glow lamp recording system. 



THERE CAN BE NO COMPROMISE 
WITH QUALITY! 



Write or wire your requirements for specifica- 
tions and prices — fares to New York de- 
cineglow ductible from purchase price of a system. 

BLUE SEAL SOUND DEVICES, INC. 

1 30 W. 46th Street New York, N. Y. 

Cable Address: SOUNDFILM, New York 




One-tenth actual size 




Carbon and Condenser 

Microphones for every 

need 




Lapel 
lapel 



Mike worn 
of speaker 
singer 



The R.T. I.C 

DYNAMIC 
MICROPHONE 

To our complete line of carbon, con- 
denser, lapel and other types, there 
is now added the new R. T. I. C. 
Dynamic Microphone featuring — 

SIMPLICITY: Ribbon diaphragm driving 
magnetic pickup, with two-stage audio am- 
plifier, mounted in compact 5x9 inch case. 

FIDELITY: Perfectly flat curve from 80 to 
8000 cycles. While microphone can respond 
to frequencies even higher or lower, broad- 
cast transmission does not require them. 

NON-MICROPHONIC: Specially designed 
spring mounting renders instrument posi- 
tively non-microphonic. 

ADAPTABILITY: Designed to connect with 
average input circuit without additional 
apparatus or circuit changes. 

WRITE for technical data on this latest 
development in the microphone art, as 
well as other types including the in- 
genious lapel mike. 



RADIO TELEVISION INDUSTRIES CORP. 



Dept. AP-2 



130 West 42nd Street 



New York City 




Page 30 



PROJECTION ENGINEERING 



ANNOUNCING 

A LINE OF HIGH GRADE 



^-r^MICROPHONE STANDS 



1 



Suitable for broadcast and public 
address use. 

Special stands (or Condenser 
Microphones, made to your specifi- 
cations. 

Write for circular and prices on our line. 

EASTERN MIKE-STAND CO. 

168 CENTER ST. NEW YORK CITY 



HUGO MEYER LENSES 

FOR PHOTOGRAPHY AND PROJECTION 

The discriminating user of lenses appre- 
ciates the superb correction, the mathe- 
matically precise formulae and the high 
standards of perfection inherent in 
Hugo Meyer photographic and projec- 
tion lenses. 

SPECIAL OPTICAL SYSTEMS CONSTRUCTED 
TO INDIVIDUAL REQUIREMENTS 

HUGO MEYER & COMPANY 

245 West 55th St. New York 

Works: Goerlitz, Germany 



COMPLETE STUDIO EQUIPMENT 

engineered to your specific needs. Supplementary elements added 
and_ matched to your present equipment. Recording or projection 
equipment for sound on disc or film. Complete public address 
systems designed, manufactured, rented for particular occasions. 

HARRY A. SUMMERS, M.E. 

37 Kenilworth Place, Brooklyn, N. Y. 




Universal Elec. Welding Co. 

All-Welded and Demountable 

REELS 

16 mm. 7" 

35 mm. 11"-14"-15" and larger 

All Wire Reels Protected By Patents 

9-18 37th Ave., Long Island City, N. Y. 



CORRECTION 

Due to a typographical error, 
the wrong illustration of our 
New "Super Giant Dynamic 
Unit" appeared in our adver- 
tisement in the March issue 
of Projection Engineering. . . 
This is the correct illustration 
of the New "Super Giant 
Dynamic Unit." 

RACON ELECTRIC CO., INC. 

18 Washington PI. New York City 




w 



£ offer t© manufac- 
turers interested in 



EXPORT 

tne services of a dependable organization, 
well established in tne entire foreign field 

AD. AUMEMA, Inc. 

Manufacturers' Export Managers 

116 Broad Street, New York, N. Y. 



For Powers, Simplex and all other sound projectors 



CLAYTON 



Even 
Tension 



TAKE-UP 



Assures absolute freedom from flutter. Takes up any amount of film evenly 
with any size reel hubs. Prevents excessive wear on the lower take-up 
sprocket and shaft. Stops the opening of film splices and prevents excessive 
wear on the film. Write for price and details. 



CLAYTON 

9430 Forty-sixth Ave. 



PRODUCTS CO. 

Elmhurst, L. I., N. Y. 



FILM TO WAX DUBBING MACHINES 

Wax Recording Equipment for sound pictures and 
Commercial Recordings 

R. W. NICHOLLS 

119-28 Twenty-seventh Ave., College Point, L. Is., N. Y. 



INDEX TO ADVERTISERS 



Ad. Auriema, Inc 30 

American Sales Company 31 

Apparatus Design Co., Inc 28 

Arcturus Radio Tube Co.. Second Cover 



Bausch & Lomb Optical Co 5 



Inc. 



29 



Blue Seal Sound Devices 

C 

Cameron Publishing Co 32 

Clayton Products Co 30 

E 
Eastern Mike-Stand Co 30 

F 

Forest Electric Corp Third Cover 

Fox Electric & Mfg. Co 28 



H 

Hardray, Inc 31 

K 
Koulish Co.. Inc., Meyer 31 

L 
I-ittelfuse Laboratories 31 

M 

Meyer & Co., Hugo 30 

Morrill & Morrill 31 

N 

National Carbon Co., Inc 27 

National Theatre Supply Co 5 

Nicholls, R. W 30 

R 

RCA Victor Co., Inc 3 

Racon Electric Co.. Inc Back Cover 

Radio Television Instr. Co 29 



Samson Electric Co 6 

Siemens & Halske 31 

Strong Electric Co.. The 27 

Summers, Harry A 30 

T 

Telephoto & Television Corp 29 

U 

Universal Elec. Winding Co 30 

W 

Weber Machine Corp 27 

Webster Company 25 

Webster Elec. Co l 

Weston Elec. Instr. Corp ... 25 

Z 

Zierick Mfg. Works. F. R 31 



APRIL, 1932 



Page 31 



IN CHICAGO 



World's 

Tallest Hotel 

46 Stories High 




LEONARD HICKS 
anaging Director 



The extra attention given to the needs of guests will 
favorably impress you. Nearest to stores, offices, thea- 
tres and railroad stations. A special floor is reserved 
for ladies. Each guest room is outside with bath, cir- 
culating ice water, bed-head reading lamp and Ser- 
vidor. Housekeeper on each floor. Garage facilities. 

2500 ROOMS $3.00 UP 

MORRISON HOTEL 



Madison and Clark Streets 



CHICAGO 



STATEMENT OF THE OWNERSHIP, MANAGEMENT, CIRCULA- 
TION, ETC., REQUIRED BY THE ACT OF CONGRESS 
OF AUGUST 24, 1912, OF PROJECTION ENGINEERING 
Published monthly at New York, N. Y., for April 1, 1932 

State of New York ) ss 
County of New York j 

Before me, a Notary Public in and for the State and county afore- 
said, personally appeared B. S. Davis, who, having been duly sworn 
according to law, deposes and says that he is the Business Manager of 
PROJECTION ENGINEERING, and that the following is, to the best 
of his knowledge and belief, a true statement of the ownership, manage- 
ment, etc., of the aforesaid publication for the date shown in the above 
caption, required by the Act of August 24th, 1912, embodied itr section 
411, Postal "Laws and Regulations, to wit: 1. That the names and 
addresses of the publisher, editor, managing editor, and business manager 
are: Publisher, Bryan Davis Publishing Co., Inc., 19 East 47th Street. 
New York; Editor, Donald McNicol, Roselle Park, N. J.; Managing 
Editor, F. Walerr, Union City, N. J.; Business Manager, B. S. Davis. 
Scarsdale, N. Y. 2. That the owners are: Bryan Davis Pub. Co., Inc.; 
B. S. Davis, Scarsdale, N. Y. ; Roy T. Atwood, Albany, N. Y.; G. R. 
Bacon, Dougleston, N. Y. ; J. C. Munn, Union City, Pa.; J. A. Walker. 
Richmond Hill, N. Y.; A. B. Goodenough, New Roche'lle, N. Y. 3. That 
the known bondholders, mortgagees, and other security holders owtf- 
ing or holding 1% or more of the total amount of bonds, mortgages, 
or other securities are: None. 4. That the two paragraphs next above 
giving the names of the owners, stockholders, and security holders, if 
any, contain 1 not only the list of stockholders and security holders as 
they appear upon the books of the company but also, in cases where a 
stockholder or security holder appears upon the books of the company 
as trustee or in any other fiduciary relation, the name of the person or 
corporation for whom such trustee is acting, is given; also, that the said 
two paragraphs contain' statements embracing affiant's full knowledge 
and belief as to the circumstances and conditions under which stock- 
holders and security holders who do not appear upon the books of the 
company as trustees, hold stock and securities in capacity other than 
that of a bona fide, owner; artd this affiant has no reason to believe 
that any other person, association, or corporation has any interest direct 
or indirect in the said stock, bonds or other securities than as so stated 
by him. 

(Signed) B. S. DAVIS, Business Manager. 
Sworn to artd subscribed before me this 22nd day of March, 1932. 
(Seal) M. S. OELSNER, Notary Public. 

N. Y. County. 

New York Co., Clerk's No. 27. 
New York Co., Register's No. 3-0-10. 
Commission expires March 30, 1933. 



FREE 



WHOLESALE RADIO CATALOGUE 

The Big Book (136 pages) 

Thousands of radio items at 
real bargain prices. Featuring 
Public Address Equipment, 
Microphones, Amplifiers, Rec- 
ording Equipment, etc. Send 
for your copy today. 

Ammratt ^alrs (Enrnpang 

P-44 W. 18th St., N. Y. C. 




For Your Experimental Department 



A tube of 500 as- 
sorted lugs and 
terminals — hot 
tinned for easy 
soldering. 

Price $1.00 




We are also pre- 
pared to handle 
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ings. 

Write Us for 
Quotations 



F. R. ZIERICK MFG. COMPANY 

70 E. 131st ST., NEW YORK CITY 



AUTOMATIC RECORD CHANGERS 

Our full automatic chassis (continuously operating type) 
is reliable, compact and low in price. Will not jam, 
break or warp records. Now giving reliable daily 
service in P. A. Systems, coin phonographs, store 
demonstrators and fortune telling machines. Plays any 
make of 10" records. 



644 BROADWAY 



H ARDR AY, 



INC. 

NEW YORK, N. 



PROTECT Those INSTRUMENTS 



fc Littelfuses afford complete protec- 
V tion for voltmeters, milliammeters, 
tube testers, etc. Range in size 
_ from 1/100 to 2 amps, capacity. 

Write for instructive catalog 



Also Radio Receiver and Amplifier 
Littelfuses, and High Voltage Lit- 
telfuses for transmitting tubes, 
rectifiers, oscillators, etc. 



LITTELFUSE 

1778 WILSON AVE. 



LABORATORIES 

CHICAGO, U. 



Quicker 
than a 
Short circuit* 



LITTELFUSES 




Where the Ultimate in 
dependability is required! 
MORRILL & MORRILL 

30 CHURCH ST., NEW YORK CITY 
Sole U. S. A. Distributors for the 

SIEMENS & HALSKE 

Condensers and Resistors 

Wrj'fe far Bulletin P 



GENUINE SAPPHIRE 

Points — Needles — Styluses — Shavers 

Type "A" — for cutting and recording on aluminum. 

Type "B" — tor recording and play - back on Victor type prc- 

grooved black composition, home recording discs. 
Type "C" — for play-back on all commercial records and elec- 
trical transcriptions. 
Sapphire points afford better sound. 
We will meet your specifications. 

MEYER KOULISH CO., Inc. 




64 FULTON ST.. N. Y. CITY 



BEekman 3-6109 



Page 32 



PROJECTION ENGINEERING 



CONFIDENCE 



In response to our advertising announcing a new book by James R. Cameron 
OVER 3,860 [ U P to the ti me of going to press with this copy] members of 
the Motion Picture industry had sent in their order with cash for a copy of the 
new book — notwithstanding the fact that the book would not be published for 
several weeks. 
This proves the confidence the Motion Picture industry has in the Cameron books. 

AUTHENTIC — UNDERSTANDABLE — COMPREHENSIVE 



NOW READY 



QUESTIONS & ANSWERS 

Sound Motion Pictures 



By James R. Cameron 



50 
100 



PAGES — PRICE 3 

The subject of Sound Motion Pictures covered in 
simple question and answers form — Examination 
questions gathered from every State in the 
Union and Canada will be found in this book. 

OVER 1,000 EXAMINATION QUESTIONS WITH ANSWERS 



SOUND PICTURES 

Trouble Shooters' Manual 

By J. R. Cameron J. F. Rider 
1180 Pages 560 Diagrams Etc. 

"The best book written on the subject." 

— American Projection Society 
Explains in detail the construction, operation and care of 
Sound Picture equipment. 

A COMPLETE TROUBLE TRACER 
Price $7.50 



MOTION PICTURE PROJECTION 

By James R. Cameron 

Introduction by S. L. ROTHAFEL ("ROXY") 

1240 Pages 500 Illustrations 

Used throughout the world as a standard authority on the subject 
"A notable publication, covers the subject of Projection Engi- 
neering in a very thorough manner." 

— Society of Motion Picture Engineers 

Price $6.00 



League of Nations (Cinematograph Bureau): 

"Mr. Cameron is one of the limited number of technical 
writers on Cinematography really worth reading" — "has 
made important contribution to the literature of sound 
picture." 



4 



Dept. of Commerce, Motion Picture Section, 
Washington, D. C: 

"These books should be in the possession of every pro- 
jectionist, theatre manager and everyone interested in 
receiving first-hand authentic information regarding the 
application of sound to motion pictures. Cameron's 
books are a very worth-while contribution to the motion 
picture industry." 



IN PREPARATION 

PROJECTIONIST'S YEARLY 
GUIDE AND REFERENCE BOOK 

PUBLISHERS OF MOTION PICTURE BOOKS SINCE 1915 



f 



CAMERON PUBLISHING COMPANY, WOODMONT, CONN., U. S. A. 



AT LAST! 




AMPERES 

from a rectifier!! 
with 

GREATER ECONOMY 

LESS ATTENTION 

NO NOISE 



2 lamps at up to 1 lamp at up to 

45 amperes each 90 amperes 



For the first time in projection history! The advantages of 
the TUBE Rectifier at HIGH power!! 

The FOREST three-phase rectifier for HIGH INTENSITY 
PROJECTORS gives a perfectly smooth direct current 
without fluctuation. 

# FULL DESCRIPTION AND TECHNICAL DATA WILL BE SENT # 

UPON REQUEST 

Forest Electric Corp., Newark, N. J. 

• FOREST • RECTIFIERS • FOR • BETTER • PROJECTION 



Insist 



on 



aeons 



R 

Excell 



xceuence 



RACON AIR COLUMN HORNS AND 
ELECTRO DYNAMIC UNITS set the 
standard by which others are judged. 

In planning your 1932 activities, look to 
RACON, the pioneer air column manufac- 
turer for the latest and greatest loud 
speaker developments. 

As typical examples, here are illustrations 
of the new type RACON FLARED BAFFLE 
HORN for dynamic speakers, AIR COL- 
UMN HORN and ELECTRO DYNAMIC 
UNITS. There is a RACON HORN for 
every purpose. Racon's catalog P. E. 4 and 
price list will be sent upon request. 



RACON Horns are constructed of an exclusive 
patented *non-vibratory material without resonance, 
so common in other type horns. 

RACON Horns are superior in reproducing high fre- 
quencies, especially at high volume. Distortion is im- 
possible, tone quality approaching that of the human 
voice is assured. 

RACON "all-weather" Horns are unconditionally 
guaranteed against climatic conditions, rain, heat, 
snow, aridity — nothing can affect RACON Horns. 



[( ava/M El^vtkiv Ya, iNv. 

18 Washington Place, New York City 
London, England Toronto, Canada 




New Type 
Square Baffle 
Horn 




New Type Small Theatre 
Horn No. 2115 




New MASTER 
Dynamic Unit 




New SUPER GIANT Dynamic Unit 



*Racon Horns and Units are Covered 
by U. S. Patents Nos. 1,507,711; 
1,501,032; 1,577,270; 73,217; 73,218; 
1,722,448; 1,711,514; 1,781,489; 
(,832,608; 1,834,327; 1,835,739: 
1,845,210 




UBLIC- ADDRESS SYSTEMS FOR 
1,000, 2,000 AND UP TO 5,000 
SEAT INTERIORS 
By Gordon S. Mitche 

UND FILM EDITING 
By Maurice Pivar 

THE TALKING BOOK 
By Dr. Irving J. Saxl 

RECORDING FOR INDUSTRIAL 
AND EDUCATIONAL MOTION 

t PICTURES 

By L. D. Minkler 
EMOTE LEVEL INDICATOR 




Fourth Year 
Of Service 




journal of me Sound ana Light Prqjecf ion Indusi ries 

mm 

MAY, 1932 




0> 






c 




QJ 


03 
t-1 




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— — +? 

a 


«J 4> 


« Rectifier Blvd. », 


ffl *g 


a> o* 


be _ 




- H 


o 







ARE 

YOUR 

BATTERIES 
Wearing Out? 



Well put you on the right road 

to better operation at less expense 

with a FOREST RECTIFIER 



Regarding your power supply, you must make one of 3 choices. 
I. Replace worn out, troublesome storage batteries. 2. Buy new equip- 
ment. 3. Modernize your present apparatus by installing all A.C. 
Forest Rectifiers, inexpensive and practical. Before making a decision, 
consider this fact: Forest rectifiers save current, are efficient, supply 
unfailing non-fluctuating current, require no attention or attendance, 
and^ are always ready for service. They eliminate all "A," "B" and 
"C" batteries. 

Model 77 supplies 7'/ 2 amperes to exciter lamp and I ampere to 
amplifier filaments. We make a rectifier for every direct current 
requirement on sound equipment. 

AND NOW 

A BRAND NEW FOREST RECTIFIER 
for Good Projection Everywhere 

A greatly improved rectifier — the result of years of experience and 
research is now ready. These new Forest Rectifiers will absolutely out- 
perform anything ever offered before. Inexpensive to own, economical 
to operate, easy to install and positively quiet in operation. 

Available in Model No. 30 up to 30 ampere capacity for one pro- 
jector. Model 25-25, up to 25 amperes to one projector and an 
additional 25 amperes to second projector during change over. Model 
No. 45, up to 45 amperes to one projector available for either single 
or three phase A.C. current. 

Model No. 6, up to 65 amperes, and Model No. 10, up to 100 amperes, 
both for one projector, are now available in three phase A.C. cur- 
rent only. 

Model No. 15 is portable, 15 ampere capacity. 

Model No. 20 is stationary, 20 ampere capacity. 

Write for bulletins 

FOREST ELECTRIC CORP. 

Newark New Jersey 




Front View, Model 25-25 



MAY, 1932 



Page 



Blue Seal Sound Devices, Inc. 



anno**^ 



A NEW SALES POLICY-and 
A COMPLETE REVISION of PRICES 



For the CINECLOW SOUND SYSTEMS 

made possible by our rapidly increasing volume 
of business and quantity production methods! 

1. Complete portable double systems for new Akeley, Bell 
Howell or Mitchell Camera (illustrated) $3288 

2. Complete portable single system for new Akeley Audio 
Camera $2092 

3. Complete portable combination single and double system 
for new Akeley Camera $2687 

4. Complete portable single system for Bell & Howell 
Silenced Camera $2992 

5. Complete portable combination single and double system 
for Bell & Howell Silenced Camera $3388 

6. Complete portable combination single and double sys- 
tem for Mitchell Silenced Camera $3388 

7. Complete semi-portable studio double system with spares 
and extras $4502 




Cineglow Microphone 
Hanging 






Cineglow Microphone on 
Table or Stand 




Blue Seal As Usual Is A Step or Two Ahead! 

Note items 3, 5 and 6. COMBINATION SETS FOR 
EITHER SINGLE OR DOUBLE SYSTEM RECORDING 

Item 5 will not be in production for 30 days, but 
orders are now being taken. 




Cineglow 3 Element 
Glow Lamp 



v-— 



w -1§ d 



Cineglow Newsreel Amplifier 



& s-y^ ,o'">. 



Cineglow Studio Amplifier 




Cineglow Film Recorder 



Take A Tip From Those Who Know! Here are a few promi- 
nent current releases on CINEGLOW SOUND SYSTEMS: 

1. Paul Terry Toons (Series) Educational Release 

2. Brown-Nagel Romantic Journeys (Series) Educationa Re ease 

3. Bill Cunningham Sport Series Educational Re ease 

4. Lyman H. Howe Series Educational Re ease 

5. Memories (Series) Educational Re ease 

6. "C6ngorilla" Martin Johnsons Feature Fox Release 

7. "Explorers of the World" Raspin Productions 

8. Manchuria Talking Pictures Epics Release 

9. Land of Shalimar C?"' 1 ? 1 f llms 

10. Tragedy Book of Knowledge (Series) Film Exchange 

11. Beauty Spots of Germany .' Ideal Pictures 

12. "Hell Below Zero" Talking Pictures Epics Release 

13. "Land of Enchantment" Bray Productions Columbia Release 

14. Supreme Screen Service Trailers 

15. Universal Pictures' East Coast tests 



o Write, Wire or Cable for itemized list of goods. 

Each Unit Can Now Be Purchased 
Independently 

BLUE SEAL SOUND DEVICES, INC 



I 30 West 46th Street 



New York, N. Y. 



Cable Address "SOUNDFILM" 



Projection 

Engineering 




Sound Pictures 

Visual Projection 

Sound Recording 

Audio Amplifiers 

Public-Address Systems ' 

Photography 

Facsimile Recording 

Television 

Photo-Voltaic Cells 

Circuit Measurements 

Automatic Music 

Acoustic Engineering 

Radiant Energy Devices 

Electric Recording 

Phototubes 

Home Talkies 

Theatre Engineering 

Amplifier Tubes 

Sound Reproducers 

Screen Engineering 

Electric Power for Projec- 
tion 

Recording Studio Engi- 
neering 

Location Sound Equipment 

Rectifier Tubes 

Industrial Tube Applica- 
tions 



Vol. IV 



MAY 
1932 



Donald McNicol 
Editor 

Jas. R. Cameron 
Associate Editor 

Ulmer G. Turner 
Western Editor 

F. Walen 
Managing Editor 



Number 5 



Contents 



Editorial 



Public-Address Systems for 1,000, 1,200 and Up to 15,000 
Seat Interiors By Gordon S. Mitchell 

Cooling for Comfort By Samuel R. Lewis 

A Decade of Progress in the Recording and Reproducing 
OF SOUND By J. E. Otterson 

Sound Film Editing By Maurice Pivar 

The Talking Book By Dr. Irving J. Saxl 

Disc Recording for Industrial and Educational Motion 
Pictures • By L. D. Minkler 

RCA Photophone Remote Level Indicator 

This Thing Called "Perfect Sound" . By Julius Weinberger 

Rockefeller Center Theatres 



page 

2 

7 
10 

12 
14 

17 

18 

20 
22 
25 



Departments 



New Developments of the Month and News of the 
Industry 26 



Index of Advertisers 



30 



Bryan S. Davis 
President 

James A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

19 East 47th Street 

New York City 



E. M. Bacon 
Advertising Manager 

J. E. Nielson 
Circulation Manager 



Chicago Office— 333 N. Michigan Ave.— Charles H. Farrell, Mgr. 

St. Louis Office- 505 Star Bldg.— F. J. Wright. 

Kansas City Office— 306 Coca Cola Bldg— R. W. Mitchell. 



San Francisco Office— 155 Sansome St. — R. J. Birch. 
Los Angeles Office — 846 S. Broadway— R. J. Birch. 
New Zealand— Tearo Book Depot— Wellington. 
Australia — McGill's Agency — Melbourne. 



Entered as second class matter August 15, 1931, at the post office at New York, N. Y., under Act of March 3, 
1879. Yearly subscription rate $2.00 in U. S. Yearly subscription rate $3.00 in Canada and foreign countries. 



MAY, 1932 



Page 3 



l£ 



CHICAGO 



Official Hotels— 

• • • 

Stevens Hotel 
Blackstone Hotel 



MAY23-26 
19 3 2 



inqs are in store 

. . . for all who attend 



SIXTH ANNUAL 

TRADE SHOW 

EIGHTH ANNUAL 

CONVENTION 



STEVE N S H OTE L 



RADIO'S BIG ANNUAL CONCLAVE 



EXHIBITING ALL NEW LINES AND 
THE LATEST RADIO AND TELEVI- 
SION PRODUCTS. 

ELECTRICAL PRODUCTS ALSO IN 
TRADE SHOW AND MANUFACTUR- 
ERS' DEMONSTRATION ROOMS. 

EVERYBODY IN RADIO (NEARLY 
25,000 RADIO TRADESMEN LAST 
YEAR) ATTENDS THIS ANNUAL NA- 
TIONAL RADIO GATHERING, THE 
BIG INDUSTRY MEETING EACH 
YEAR. 

Better business early in 1932 

The RMA event this year is advanced to 
start sales early. In June, a few weeks after 
the RMA exhibits of manufacturers' latest 
products, there will come the big Republican 
and Democratic national conventions in 
Chicago to nominate presidential candi- 
dates. In June also another heavyweight 
championship match between Schmeling 
and Sharkey is scheduled. 

GO TO CHICAGO MAY 23, SEE THE 
LATEST RADIO AND ALSO ELEC- 



TRICAL PRODUCTS OF RMA MANU- 
FACTURERS, AND GET IN EARLY ON 
THE 1932 TRADE. 

This is the big and only national indus- 
try radio show, sponsored by the RMA and 
under its management, for RMA members, 
jobbers and dealers. 

All exhibitors required to show current 
merchandise — no vacant booths. 

Electrical products also displayed. 

Thirty thousand (30,000) square feet of 
radio and electrical exhibits in the official 
hotels — the Stevens and Blackstone. 

ADMISSION TO THE TRADE ONLY. 
PUBLIC NOT ADMITTED. 

Reduced railroad rates — special trains — 
one and one-half fare for round trip to 
Chicago from everywhere. 

Official hotels — Stevens and Blackstone 
— together on Michigan Avenue. Regular 
rates. Make your reservations early. 

Important and interesting business meet- 
ings of industry and allied organizations. 

Invitation credentials for the trade 
show will be mailed about April 15th. 



REMEMBER THE DATE— MAY 23— AT CHICAGO. 



Radio Manufacturers Association 

H-WEST 42nd ST.N.Y.CITY • 32 W.RANDOLPH ST. CHICAGO 



E d 



i t o r i 

lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll! 

MAY, 1932 



a 



:iiiiiiiiiiiiii'iiiiiiiiiiiir!iiiiiiiiiiiiiii!iiiiniiii!iiiMii 



HOME 
RECORDING 



THE making of reproduc- 
' ible records in the home, 
permanently storing voice 
, and sound impressions, will 
no doubt in time take on the magnitude 
reached by the camera in stocking family 
albums with: collections of individual and 
group photographs, pictures of special 
events and occasions. 

The low state of buying power prevailing 
at the time home recording became a simple 
operation has constituted the main sales 
resistance to recording equipment. 

It may be said also that little sales in- 
genuity has been exercised by manufacturers 
in marketing home recording apparatus as 
a unit separate from radio. 

These factors together with the fact that 
there is yet room for betterment of record 
quality are due for consideration by manu- 
facturers who desire to participate in the 
rewards of industry in the days to come. 

A reasonable degree of perfection of 
recording requires that microphones should 
function equally faithfully at all frequencies 
employed. Microphones' which now so per- 
form are somewhat costly. 

By getting away from the 100-5000 cycle 
range of the average a-f. end of radio receiv- 
ers, the designer of a recording unit should 
have no difficulty in making an a-f. amplifier 
in the 20-10,000 cycle range. 

Cutter design also should have in view 
accurate recording at 20-8,000 cycles. There 
may be serious difficulties in recording on 
pre-grooved celluloid, or aluminum discs at 
these frequencies, but this is an objective 
to keep in mind. 

Being informed is to be prepared. Being 
prepared for opportunity is a responsibility. 



features are delivered directly in the homes, 
but in such variety simultaneously that 
there is usually a choice of program. 

The modern picture and sound presenta- 
tion in theatres, as an offset to the conveni- 
ence of radio has the advantages of pictured 
action, view and scene. I 

According to the findings of the American 
Farm Bureau about 7,300 of the moving 
picture houses are, due to automobile trans- 
portation, accessible to persons who live on 
farms — about one half of the total popula- 
tion. 

A reported falling off in attendance at 
picture shows on the part of farmer citizens 
may be due in some measure to the con- 
venience of radio. But, such questionnaires 
as have been circulated bring out the infor- 
mation that the folks now on the farms dis- 
approve of the salacious pictures, the ad- 
venturous lives of gunmen, and all produc- 
tions which purport to mirror (even as in 
real life) the daily or nightly activities of 
men and women who appear never to have 
a hand in doing' the world's work. 

It may be that the managers of picture 
houses catering to a farm patronage are 
guided, in selecting films, by the box office 
returns in large urban centers, reasoning 
that what pulls big" in the Loop District 
should score also at Painted Post or Wat- 
son's Corners. 

The markedly higher tone of radio pre- 
sentations thus far has brought to radio a 
vast following of loyal fans. 

With Mr. Aylesworth at the head both 
of N.B.C. and R.K.O. we look forward to 
an attempt at acceptable differentiation of 
the two forms of entertainment, or to a 
complementary, cooperative policy. 



FROM all accounts it 
appears that the radio 
AND THE broadcast stations and 

PICTURE SHOWS chains have succeeded bet- 
ter in presenting- enter- 
tainment features which have won the favor 
of folks on the farms than have the moving 
picture producers. 

In the case of radio the entertainment 



J) 



^nJcL^mHUc 



<rL 



Editor 



MAY, 1932 



Page 5 




Come In ♦ ♦ ♦ 

and bring along your troubles! 

This is a standing invitation to all Projectionists and 
Projection Engineers. Gome in and get better acquaint- 
ed with National Service. If you have troubles, bring 
them along for discussion. Discuss the latest mechani- 
cal developments for perfect sight and sound reproduc- 
tion, while you inspect them first hand in our display 
rooms. Verify your impressions by a close-up exami 
nation of what you have been reading about. There's 
always something new to see and talk about at National 
— and you're always welcome. 

National Service meets 
every mechanical prob* 
lem of theatre operation 

NATIONAL THEATRE SUPPLY COMPANY 





YOUR LOGICAL 




SUPPLY STORE 



THEY KEEP PAC E 



The developments of the past year show that NATIONAL 
PROJECTOR CARBONS constantly keep pace with the 
progress of the MOTION PICTURE INDUSTRY. 

Pre-Cratered 
High Intensity Carbons. 

New National SRA Carbons. 

13.6mm x 22 inch 
High Intensity Projector 
Carbons. 



85 Ampere 9 x 20 

"High-Low" White Flame 
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Carbon Prices Reduced. 



NATIONAL 



PROJECTOR CARBONS 

y/ y / // I V^\> NATIONAL CARBON COMPANY, INC. 
// I I \\\\ Carbon Sales Division • Cleveland, Ohio 



and Carbon Corporation 



Branch Sales Offi< 
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Dependable 1 

Why, many exhibitors wouldn't think 
of running their theatres without 

HIGH INTENSITY 

AUTOMATIC REFLECTOR 

ARC LAMPS 

They deliver an abundance of light . . . silently . . . 
automatically . . . assuring full, even screen brilliance. 

For Sale by Independent Supply Dealers. 

Uhe Strong Electric Corporation 

250] LAGRANGE STREET TOLEDO. OHIO 

Export Office: 44 Whitehall Street. New York City. N. Y. 




fMMMMMMSMMM^ \ 



Page 6 



PROJECTION ENGINEERING 



NEW Samson CINE-PAN 



Tubes 
can be 
exposed 
for re- 
placement 
by remov- 
ing 4 thumb 
screws. 

There are 2- 

224's, one 280, 2- 
281's, one 245, and 
2-250's. 




HAS SURPRISING 
FEATURES 

For use as portable or permanent booth 
installation of sound -on -film talking pic- 
ture equipment. 

It is highly prized by those connected 
with theatre management. It is only 
28% inches long by 20 '4 inches high 
and 10 Y 4 inches deep, weighs but 
104 lbs. 

Any panel can be removed by 
taking out 4 screws without 
breaking a soldered connection 
as all connections are made 
with flexible wire and plugs 

2 15-ft. lengths of shielded 
cable from f oto cell in the 
sound head to the Cine 
Pam are provided and 
can be increased to 25' 
lengths without any 
noticeable loss in 
high frequencies. 

Your biggest sur 
prise will be the re- 
markable crisp 
ness of dialogue 
—heretofore 
sadly lacking 
in most 
sound-on- 
film am 
Plifiers. 



Variable output im- 
pedance allows use 
of any speakers you 
already have in your 
theatre. 

Visual volume indicator 
gives operator more ac- 
curate volume control 
than aural indication. Field 
current and voice energy 
are also provided for moni- 
tor speaker if wanted. 

The Cine-Pam is entirely AC 
operated and supplies photo-cell 
voltage and exciter lamp current. 
No batteries of any kind are re- 
quired. 

Sold only through manufacturers 

or jobbers of talking motion picture 

equipment. Ask them for literature 

on the Cine-Pam — or write us for 

Folder No. PE19. 



amso/ii 



Manufacturers Since 1882 



Main Office: 

Canton, 

Mass. 



Factories : 
Canton and Water- 
town, Mass. 



Projection Engineering 



MAY, 1932 



Public-address systems 

for 1,000, 1,200 and 
up to 15,000 seat 



interiors 



By Gordon S. Mitchell 



THE past six months have seen 
many noteworthy advances in the 
design of public-address and sound 
systems, not only in individual 
units, but in many cases in the entire 
system. Extremely portable and efficient 
address systems have been placed on the 
market, systems which may be easily 
carried in a satchel-size case and which 
will give ample coverage to an audi- 
ence space of up to six hundred per- 
sons. New amplifiers have been devel- 
oped which faithfully cover a greatly 
increased frequency range, new speakers 
and reproducer units have been brought 
out. In short, the sound industry is well 
prepared for the increased business 
which is bound to come with improved 
economic conditions. 

While there has been considerable 
technical matter printed in past issues 
of Projection Engineering dealing 
with the installation of various systems, 
these articles have in the main been of 
a general nature. It will be the pur- 
pose of this article to take up the in- 
stallation of specific equipment in (1) 
a sound amplification and distribution 
system such as might be installed in a 
1,000-1,200 seat auditorium, and (2) the 
installation of a sound system in a large 
hall seating upwards of 15,000 persons. 
As a first consideration in the plan- 
ning of a sound system, the necessary 
amplifier power should be determined. 
While arbitrary recommendations as to 



Important principles of 
public-address engineering 
and of radio program aux- 
iliaries are here described 



power requirements will not, as a rule, 
be entirely correct, a chart such as Fig. 
1 may be used to obtain a general esti- 
mate. (The data for this chart has been 
gathered from the recommendations of 
various sound engineers, amplifier and 
equipment manufacturers, and is em- 
piric. A tolerance of at least plus or 
minus five per cent in the power recom- 
mended for any given seating capacity 
is allowed). From this chart it may be 
seen that an amplifier output of be- 
tween ten and fifteen watts is needed to 
properly cover such a space. 

At this point it might be well to bring 
out the fact that the library of every 
well equipped and well informed engi- 
neer should include the catalogs and 
pamphlets issued by the various manu- 
facturing companies in his line. (These 
may be obtained from the advertising 
pages of this journal.) Thus, sound en- 
gineers would do well to watch the ad- 
vertisements carried by the various 
sound projection periodicals and to send 
for such catalogs and printed material 
as is offered from time to time by these 
companies. They are at all times happy 
to cooperate with service and installa- 
tion engineers in solving problems 
which arise incident to the installation 
and operation of sound equipment, fur- 
nishing the benefit of their experience 
and knowledge to those in the field, in 
most cases without charge. 

Selection of a specific amplifier for 
any given sound system is of course a 
matter into which many factors enter. 
An amplification system for use by a 
roadside merchant in crying his wares 
need not have nearly the frequency re- 
sponse which would be considered neces- 
sary in a system installed in the ball- 



room of a large hotel and over which 
fine singing or instrumental music might 
be broadcast. This is an important fac- 
tor which must be considered. Another 
important point which must be taken 
into account is volume required. All in 
all, the selection of an amplifier for use 
with the public-address system is a mat- 
ter which must be given careful thought. 
Consider that the Silver Marshall SM- 
692 auditorium amplifier is the one 
which most closely fulfills the needs, and 
is the one selected for use. 

The Amplifier 

Either from experience or from data 
furnished by the company suppose that 
we have considered the characteristics 
of this amplifier and decided that it is 
the one which from all standpoints will 
give the best return, in service and in 
usefulness, for the money. The 692 is 
an all-electric, 105-120 volt, 50-60 cycle 
a-c. operated amplifier, drawing ap- 
proximately 150 watts and having an 
undistorted power output of 15-16 watts. 
The amplifier is built for use in installa- 
tions where perfect fidelity of reproduc- 
tion is desired, the characteristic curve 
(frequency response) being flat to well 
above ten thousand cycles. There is no 
peak in the region from 60-300 cycles, 
and hence no barrel-like quality in the 
reproduced sound. With a good speaker 
this amplifier will give perfect transmis" 
sion to below 30 cycles. The voltage 
amplification is 4,000 (72 db.), which 
is quite a bit above the amplification of 
the usual amplifier. This increased 
amplification comes from the use of an 
a-c. '24 screen-grid tube in the first 
stage. 

Panel Racks 

With the development of sound ap- 
paratus it has become standard practice 
to assemble public-address equipment 











































































































y 


















































































. 






























/ 




























■ 


/ 




























/ 




























/ 






























/ 




























i 






























1 






























1 





























































Fig. 



»oo iacoo 

SEATING CAPACITY 
1. Relation of watts output and 
seating space. 



Page 8 




Fig. 2. Connection of two pickups to 
692 amplifier. 



upon panel racks, for a variety of rea- 
sons, not the least of which is uniform- 
ity of appearance and ease of operation 
and assembly. Consider that for the sys- 
tem under discussion the SM-692 ampli- 
fier has been obtained assembled for 
panel mounting. 

Depending of course upon the future 
uses of the system will be the extent of 
the input equipment incorporated in the 
system. A complete system equipped for 
all types of broadcast would include not 
only microphone input facilities, but also 
radio tuner, and one or two phonograph 
pickups. However, where initial ex- 
pense is one of the major considera- 
tions, one or more of these facilities may 
be left out of the initial installation and 
added at a later date. This of course is 
one of the major advantages of the rack 
and panel type of installation, for addi- 
tional equipment may be included in 
the system at any time without sacrific- 
ing appearance or without introducing 
any serious problems of mounting or 
connection. 

One of the characteristics of the 
SM-692 amplifier is that it may be op- 
erated either with or without an ex- 
ternal matching transformer. In gen- 
eral the use of a transformer will in- 
troduce some distortion, but this disad- 
vantage is oftentimes offset by the ad- 
ditional amplification which may be ob- 
tained by the use of the transformer. 
Whether or not a matching transformer 
is needed will depend upon the output 
requirements, but for a hall such as the 
one under consideration here, one will 
not be needed. 

Where two pickups are needed — 
which is oftentimes the case when it is 
desired to fade music or other recorded 
sound from one record to another — a 
center tapped potentiometer should be 
connected. See Fig. 2. Potentiometer 
resistance of course depends upon the 
pickup used, but in general, for a high 
impedance pickup a potentiometer of 
approximately 25,000 ohms and for a 
low impedance unit a potentiometer of 
from 3,000 to 5,000 ohms should be used. 

The prevailing method of assembling 
public-address equipment is in rack and 
panel units, which gives maximum flexi- 
bility and uniformity of appearance. In 
the usual system installation, any radio 



tuners or associated apparatus will be 
installed on the amplifier rack in the 
operating room, and connections will 
be essentially as shown in the accom- 
panying Fig. 3. If it should be neces- 
sary to install the radio tuner at some 
distance from the rest of the apparatus, 
a matching transformer connected as 
shown in Fig. 4 should be used. All 
connecting wire should be placed in 
shielded conduit. (A specific case 
wherein it would be necessary to place 
the radio tuner at a distance from the 
operating equipment would be in a 
building in which there is a broadcast- 
ing station. It might then be necessary 
to install the tuner equipment farther 
away from the broadcasting transmitter 
than the public-address operating room 
in order to obtain best results.) 

Location of Rack 

Actual location of the amplifier 
rack and panel equipment within the 
operating room itself will depend upon 
individual arrangements. A conveni- 
ence worth many times its cost will be 




692 

INPUT 



B+ 

DET. PLATE 
SUPPLY 



B- 



Fig. 3. Showing resistance coupling of 
radio tuner to 692 amplifier. 



a window between the operating room 
and stage or auditorium proper, pro- 
viding architectural features of the 
building allowed. If such a window be 
installed, the amplifier rack should be 
so set within the room that all operat- 
ing may be attended to from a position 
convenient to the window. Of course 
it will be necessary to install a double 
plate glass window, the two plates sepa- 
rated by a layer of air which will in- 
sulate each of the rooms from sounds 
originating in the other. 

For a system of the scope of the one 
under consideration, a Silver Marshall 
PA-2A amplifier rack will be large 
enough. This rack gives sufficient space 
for the mounting of six eight-inch 
panels or their equivalent, and requires 
a floor space 22y 2 by 15 inches. See 
Fig. 5. 

Auxiliary apparatus which will in- 
crease the usefulness of the system, but 
which is only more or less necessary ac- 
cording to the financial considerations 
which might enter into the problem, in- 
clude a meter panel (S-M PA 12-A). 
an input control panel (S-M PA 53-A) 
and a volume indicator (PA-60-A). 



PROJECTION ENGINEERING 

A practical point which enters into 
the final assembly of the apparatus upon 
the panel is that certain of this equip- 
ment requires a manual manipulation 
during actual broadcast. For this rea- 
son, some care should be exercised to 
see that this equipment is mounted so as 
to be as conveniently operated as possi- 
ble. 

Loudspeakers 

For use with their public-address sys- 
tem, the Silver-Marshall company man- 
ufactures a dynamic speaker, code num- 
ber 852, which is designed for a-c. oper- 
ation and especially for use with the 692 
amplifier. This speaker is unique in 
that it operates without an input trans- 
former, it thus being possible to connect 
it directly to the output of the 692 am- 
plifier. (This amplifier in turn has been 
designed to work directly into the voice 
coil of the speaker.) By working di- 
rectly into the voice coil of the speaker, 
the cost, power loss and distortion of the 
speaker input transformer is eliminated. 
When the speaker is more than a few 
feet from the amplifier, the low impe- 
dance output circuit also eliminates the 
capacity loading effect present in long, 
high impedance lines, which would re- 
sult in an attenuation of the high fre- 
quencies. 

The power rating of the 852 is ap- 
proximately three watts. Inasmuch as 
the rating of the 692 amplifier is fifteen 
watts, it would be possible to operate as 
many as five of these speakers from the 
one amplifier. However, inasmuch as 
we have determined from previous ob- 
servations of the system under discus- 
sion that a power output of between 
ten and fifteen watts is ample for cover- 
age of the space, consequently four 
speakers should be sufficient. This will 
allow the amplifier to be operated at a 
level considerably below full load, which 
is in general good operating practice 
and tends to keep frequency character- 
istics at an optimum. 

Architectural Features 

Consider the architectural features of 
the auditorium under consideration as 
extremely ornate, and acoustics in the 
space as bad. Efforts should always be 



255 R 




L 



6 

B + 

DET. PLATE 
SUPPLY 



Fig. 4. Connection of radio tuner 
operated some distance from amplifier. 



MAY, 1932 



Page 9 



made in installing a sound system to see 
that architectural features are not 
marred. Ornamental ceilings, an elabo- 
rate proscenium arch, elegant lighting 
fixtures, and decorations about the audi- 
torium will oftentimes prove to be a 
distinct advantage to a sound engineer 
who is called upon to install a public ad- 
dress system in such an auditorium. 
These features may be used to conceal 
loudspeakers which might otherwise be 
difficult to install without marring the 
beauty of the room. Of course, no arbi- 
trary recommendation can be made as 
to speaker placement, inasmuch as so 
many factors of individual arrangement 
enter, but in general we might say that 
two or three of the speakers for the sys- 
tem under discussion would no doubt be 
placed about the proscenium arch of the 
auditorium stage while the remaining 
one or two would be used for reinforc- 
ing the sound part of the way back in 
the hall. 

If there be a large ornamental light- 
ing fixture hanging from the ceiling, a 
speaker might be placed within the fix- 
ture, pointed towards the rear of the 
auditorium. Individual ingenuity must 
be used in solving the problem of 
speaker placement. 

A monitor speaker, which may be of 
the less expensive magnetic type, should 
be connected into the speaker circuit and 
mounted in the operating room for the 
use of the operator during transmission. 

Wiring 

All wiring from the operating room 
to loudspeakers should be of twisted 
No. 18 rubber-covered cable placed in 
rigid metal conduit, to eliminate the 
possibility of inductive interference 
(cross talk). An article appeared in a 
recent issue of Projection Engineer- 
ing dealing with the actual wiring and 
installation of sound systems. The points 
which were brought out in that article 
should be followed in the installation of 
all sound equipment. Careful workman- 
ship should be maintained at all times, 
and is probably the greatest single fac- 
tor in the ultimate success or failure of 
the system. 

Certain precautions have been laid 
down governing the installation of 
sound equipment — a brief review of 
which will be included at this point. 
Regulations regarding the installation of 
radio antennas are no doubt familiar to 
most readers, but for those who are not 
it might be stated that an approved 
lightning arrestor should be included in 
the antenna circuit, set to operate at 500 
volts. The lead-in from the point where 
it enters the building must be insulated 
to withstand a voltage of 600, and the 
connector from lightning arrestor to set 
must be of copper (No. 14) or bronze 
(No. 17). Gas pipe should not under 
any circumstances be used for a ground, 




Courtesy, Silver-Marshall, Inc. 
Fig. S. PA-2 amplifier rack and panel. 



and no ground wire inside the building 
should come closer than two inches to 
any power line not in conduit. No flexi- 
ble hookup wire should be used to carry 
power, and under no circumstances 
should a connection to the power outlet 
be over seven feet in length. This last is 
an extremely important Fire Under- 
writers regulation, and applies equally 
to all light connections in the operating 
room as well as amplifier and other 
equipment power. 

After the speakers have been in- 
stalled and the operating and amplifier 
equipment mounted on the racks in the 
operating room, the system is ready for 
routine inspection and testing prepara- 
tory to being placed in service. Trans- 
mission tests should be conducted in or- 
der to be certain that the system as a 
whole is operating satisfactorily. These 
tests should consist of both microphone 
and pickup transmission, as well as ra- 
dio broadcast pickup, with observers 
stationed throughout the audience space. 
At this time loudspeaker placement may 
be checked, and if there are any dead 
spots or regions of weak volume these 
may be corrected. Repointing of the 
speakers will in almost all cases correct 
difficulties of this kind. In case time of 
reverberation is either too short or too 
long, measures must be taken to correct 
the difficulty. It should be remembered, 
however, that acoustic conditions differ 
depending upon the presence or absence 
of an audience, due to the sound absorp- 
tive properties of the bodies, clothing, 
etc., of the persons within the space. If 
the reverberant time is incorrect, means 
should be taken to correct the difficulty 
in line with principles laid down in the 
several articles which have appeared 
from time to time in Projection Engi- 
neering. 

After the system has been adjusted to 



operate satisfactorily it will be turned 
over to whoever is to be responsible for 
its operation. 

Inspection 

As a concluding thought it might be 
brought out that a periodic inspection of 
the system will do much to maintain 
that satisfaction which is so necessary 
for the commercial success of any in- 
stallation organization. After the equip- 
ment has been installed, the sound engi- 
neer should not feel that his work has 
been completed, but, on the contrary, 
should maintain an active interest in the 
installation throughout its operating 
life. An interest in the customer's wel- 
fare might be considered especially nec- 
essary on account of the newness of the 
"sound idea" and the absolute unfa- 
miliarity of the average person with this 
type equipment. From all standpoints, 
however, this interest will be well worth 
while. 

■ ▲ 

TOTAL WATTS RATING OF RE- 
SISTORS OF EQUAL RESIST- 
ANCE AND RATING 

The total watts rating of resistors of 
equal resistance and watts rating con- 
nected in series or parallel is equal to 
the watt rating of one multiplied by the 
number connected in series or parallel. 



TABLE SHOWING THE EXACT RELATION- 
SHIP BETWEEN THE DB. OUTPUT OF 
AN AMPLIFIER AND WATTS OUTPUT 

db Watts 

31 7.5900 

32 9.4875 

33 11.8594 

34 15.1800 

35 18.9750 

36 23.7188 

37 30.3600 

38 37.9500 

39 47.4375 

40 60.0000 

41 75.9000 

42 94.8750 

43 1 18.5938 

44 151.8000 

45 189.7500 

46 237.1875 

47 303.6000 

48 379.5000 

49 474.3750 

50 600.0000 

51 759.0000 

52 948.7500 

53 1185.9375 

54 1518.0000 

55 1S97.5000 

56 2371.8750 

57 3036.0000 

58 3795.0000 

59 4743.7500 

60 6000.0000 



db 



Watts 
0.0060 


1 


0.0076 


2 


0.0095 


3 


0.0119 


4 


0.0152 


5 


0.0190 


6 


0.0237 


7 


0.0304 


8 


0.0380 


9 


0.0474 


10 


0.0600 


11 


0.0759 


12 


0.0949 


13 


0.1186 


14 


0.1518 


15 


0.1898 


16 


0.2372 


17 


0.3036 


18 


0.3795 


19 


0.4744 


20 


. . 0.6000 


21 


0.7590 


22 


0.9488 


23 


..1.1859 


24 


1.5180 


25 


1.8975 


26 


2.3719 


27 


3.0360 


28. . . . 


..3.7950 


29 


4.7438 


30 6.0000 



Note: The above figures refer only to 
the output of an amplifier and have no 
connection whatsoever with the db gain 

of an amplifier. 

The foregoing technical data wove 
compiled by the engineers of the Amer- 
ican Transformer Co., 178 Knimett St.. 
Newark, X. J. 



Page 10 



Cooling 
for 
fort 



com 



By Samuel R. Lewis,* 



THE following paper on air condi- 
tioning of interiors is abstracted 
from a paper presented by Mr. 
Lewis at a meeting of the Western 
Society of Engineers. Projection En- 
gineering asked Mr. Lewis to suggest 
what bearing the general subject mat- 
ter of his paper might have on theatre 
work. He answered : 

"Emphasis should be made of 
the importance when considering 
theatre heating, also of consider- 
ing theatre cooling. If when the 
heating system is designed, con- 
sideration shall be given also to 
cooling, it will be found, just as 
was discovered in the case of this 
office building, that the number 
of hours per season during which 
refrigeration will be required can 
be shortened materially. In some 
cases the too hot hours can be re- 
duced to such an extent as to per- 
mit use of ice, with the attendant 
great reduction in investment cost. 

"Judicious location of the cold 
air intake in a shady, normally 
cool spot and operation of the sup- 
ply fan taking outside air during 
the cool hours of each night will, 
in many cases, be found eminently 
to be justified. 

"Insulation of the roof against 
the sun, and white-washing the 
surface of the roof to reflect the 
sunshine have been proved to be 
justifiable. Sprinkling the sun- 
heated roof of a theatre and 
thereby reducing the temperature 
by evaporation, has possibilities. 

"There is little intelligence dis- 
played in the design or operation 
of a theatre if there is no insula- 
tion or other provision to keep out 
the potent sun-heat, and if there 
is no effort made to use the cool 
toward-morning air from outside 
to carry off the hang-over stored- 
up heat of the auditorium. 

"The lobbies and auxiliary 
rooms should not usually be venti- 
lated or cooled by the same fan 



equipment which serves the audi- 
torium, since these rooms should 
not require anything like the same 
heat removal. 

"By careful selection of the type 
of heating, having in mind always 
that cooling will be needed, the 
owner can make great savings in 
the investment cost and in the op- 
erating cost. 

"The savings in investment may 
be due to the use of the same heat 
transfer elements for cooling as 
for heating, and the savings in op- 
eration may be due to reduced 
time during which refrigeration is 
needed. The reduced refrigeration 
time will be due to improved build- 
ing construction, and more ef- 
ficient ventilation when using nor- 
mal outside air." 

There isn't very much experience 
covering this subject. Much of that ex- 
perience is negative ; that is, it has 
shown us what not to do. 

Before we start to discuss this mat- 
ter let us be sure that we understand 
what is meant by the term "air condi- 
tioning." The warm air furnace manu- 
facturer thinks it means what will be 
accomplished by a fan added to the or- 
dinary stove in a box placed in the base- 
ment, with a tank of water in the box 
above the stove. The manufacturers of 
devices which circulate some of the air 
of the room through a water spray think 
that air conditioning means the process 
of adding moisture to the air. The 
manufacturers of devices which filter 
out of the air some of the dust think that 
air conditioning means what their equip- 
ment does to the air. The manufacturers 
of compounds which remove moisture 
from air and which probably do nothing 
else to the air, think that their equip- 
ment is an air conditioner. The people 
who build water-spray air washers, 
whether or not the water in the sprays 
shall be heated by fire or cooled by re- 
frigeration, think that they build air 
conditioning apparatus. The people who 
make air washers with built-in direct- 



A Successful Air Dis- 
tribution Circuit for 
an Office Building. 
The incoming air, 
whether warm or cool, 
is delivered at high 
velocity in a horizon- 
tal direction. The ex- 
haust air is taken 
through an upward- 
looking grille behind 
the long, narrow inlet 
grille. 



^Consulting Engineer, Chicago, III. 



Lzms 



V 



PROJECTION ENGINEERING 

expansion coils served by a refrigerat- 
ing plant are sure that they build air 
conditioning apparatus. 

The dictionary believes that "condi- 
tioning" is "limiting or modifying the 
existence or character of something." I 
myself believe that the term is clumsy 
and unfortunate. Since engineering is 
supposed to deal with exact facts the 
term is, I maintain, poor engineering. 
Apparently all of these manufacturers 
may be correct in claiming that they 
condition the air. 

Feeling as I do about this, I began 
some time ago to call the process of 
air conditioning which uses refrigera- 
tion, "cooling-for-comfort." 

Generally speaking, when engineers 
use the term "air conditioning" they 
mean that while air cleaning, heating, 
cooling, moistening, and drying shall be 
applied to the air, any plant which truly 
is air conditioned must have cold water 
from a deep well or from a refrigerated 
source in order to bring the air or a 
good share of it below the dewpoint, so 
that dehumidification may take place. 

Ventilation is another misused term. 
Fundamentally it comes from the Latin 
and means to fan or to winnow. An ac- 
cepted definition of ventilation is that it 
is the act of causing air to circulate 
through a room. It also means "to 
make public," or to open up to scrutiny. 

A few office buildings have been ven- 
tilated. Usually the ventilation has been 
confined to the spaces below grade level 
which could not be provided with win- 
dows. A very limited number of office 
buildings have been cooled-for-comfort. 
Usually this work has been confined to 
the private office buildings of great cor- 
porations ; since owners of public office 
buildings were afraid to face the chances 
of unappreciative tenants refusing to 
pay the increased costs therefor. The 
office buildings which had ventilating 
systems without cooling-for-comfort 
were not, and are not, particularly sat- 
isfactory, especially if the ventilated 
spaces do not have a very evenly bal- 
anced heat loss or gain. 




MAY, 1932 



Page 



This point merits painstaking expla- 
nation and elaboration. 

The ventilated spaces in a school 
building are the separate classrooms. 
Each classroom has about the same 
amount of outside wall and the same 
amount of glass and the same number 
of heat-radiating pupils and electric 
lights. Schools are not occupied in hot 
weather. Air, all at about the same 
temperature, can be delivered to all 
rooms at the same time in a school 
building without serious complaint, be- 
cause the heat transfer is balanced. 
Theatre Auditoriums 
The only ventilated space in a the- 
atre which is of great consequence is 
the auditorium. Since it is but one 
room, the air can be arranged at the 
optimum temperature or volume for 
each zone and can be varied with the 
weather, and the plant may operate 
without serious complaint. 

The ventilated spaces in commercial 
buildings, such as hotels, and depart- 
ment stores, usually are the spaces be- 
low ground, which have no windows or 
outside walls and which therefore 
lose no heat. Air from a ventilating sys- 
tem can be at the same temperature for 
many compartments at the same time if 
their heat transfer is balanced, and, 
while temperature control may be far 
from perfect, it will be so much better 
than if no ventilation is provided that 
complaints will come if the fans are 
stopped. 

Human beings have no sense which 
indicates fresh air or foul air. They 
can feel heat, or coolness, and can de- 
tect odors for a short time after odors 
exist, but human beings do not know 
whether air is new or old, breathed or 
unbreathed, after they have been shut 
up for a short time inside buildings. 

The ventilation code of the health de- 
partment demands that for each square 
foot of floor area there shall be pro- 
vided, where the window area is less 
than 10 per cent of the floor area, 1.2 
cubic feet of outside air per minute. 
This is a reasonable volume of air, and 
I do not know of any way to make a 
code demand more clean cut and cohe- 
rent. 

In a cooling-for-comfort system the 
supply fan and dust filter are in the 
basement 200 feet away. We must in- 
stall a 50-ton refrigerating plant. About 
half of the work of this plant will be 
in bringing a part of the air below its 
dewpoint and in condensing out of it the 
moisture and about half of the effort 
will be in cooling all the air delivered 
to a delivery temperature somewhere 
around 10 degrees below the outside 
temperature. 

We install cross connections from the 
exhaust systems of the office space, so 
that we may recirculate all of the air 
or any part of it except that from the 
separate toilet and dining room systems. 



1 his is so that we may cool things 
down most efficiently during the hours 
when the occupants are not present, and 
so that we may regulate the delivery 
temperature by a judicious admixture of 
recirculated and outside air. 

The entire duct system must be in- 
sulated, since even the return air ducts 
are cooler than the surrounding ducts 
and pipes and we expect to pay well for 
the heat which has been extracted from 
the contents of these ducts. 

We install heat-transferring water 
sprays at the supply fan inlet or a com- 
bination of these with direct-expansion 
heat-absorbing surfaces over which the 
water may fall ; all in the air stream. 
Thus, in the conventional air-condition- 
ing system we are able to cause the sup- 
ply fan to deliver air in large volumes 
which may be held at any reasonable 
temperature and relative humidity. 

It is clear that if we are to use ven- 
tilation air at the same temperature at 
the same time to all of the spaces, we 
must build office buildings with all com- 
partments having very nearly the same 
heat gain in summer and the same heat 
loss in winter. 

It ought to be clear that we cannot 
hope to build office buildings with all 
compartments having anywhere near 
the same heat gain in summer and the 
same heat loss in winter. We have 
recognized this fact in heating, by 
providing valved radiators, mixing 
dampers, registers, etc., and by de- 
signing the ducts and radiators and 
pipes to suit the individual heat loss 
of each compartment. 

A rather large surface of low temper- 
ature radiation gives higher efficiency 
and more comfort in heating than does 
a small surface of very high tempera- 
ture. 

The water in the heater-coolers need 
not be cold enough at any time to bring 
about condensation on the radiator of 
dew out of the room air. The actual 
cooling of each room will be done by 
pure recirculation without the heavy in- 
vestment otherwise required for large 
and complicated duct systems with their 
costly insulation. 

The volume of dried cool air deliv- 
ered may be reduced to the minimum 
necessary for chemical air change. No 
one knows what this minimum is, but 
there is evidence that no observable ob- 
jections are present to cutting this as 
low as eight cubic feet per person per 
minute. Several installations in large 
office buildings of this combination of 
hot water heating, cool water cooling, 
and dried cooled reduced air supply 
have been made and at least one of them 
in a large private office building has 
been in successful operation in both 
warm weather and cool weather. 

Considering the inlets and the outlets 
to the rooms, the inlet of warm or cool 
air to an office compartment, if placed 



anywhere near the floor, usually gets us 
into trouble. We cannot foretell where 
the human occupants of the office will 
dispose themselves. It certainly will not 
be satisfactory if the entering warm air 
in winter strikes directly on a person's 
body. If the entering cool air in sum- 
mer strikes the shoulders or the back 
of the neck, colds and lameness surely 
will be complained of by most people. 
Anyway, if the inlets are anywhere in 
the floor or in the side walls near the 
floor some one will place a filing cabi- 
net or a desk in front of them and will 
thus shut them off. 

The same difficulties attend the floor 
or low-down side-wall location of the 
outlets for air from the rooms. If the 
inlets, and outlets are on or near the 
floor when the entering air is cooler 
than the air already in the room, the 
entering air will never rise up, but the 
room-occupants will have hot heads 
and cold feet. If the inlets and outlets 
are on opposite sides of the room, both 
high up, when the air is warm there 
will be short-circuiting of the entering 
air directly across from inlet to outlet 
and the lower-down zone will be too 
cold and will be smelly. 

The conventional air circuit in a the- 
atre which is cooled for comfort is from 
mechanically diffused high velocity in- 
lets high overhead in a downward direc- 
tion to well distributed mushroom pro- 
tected exhaust openings in the floor. 

A 
NEW ADMISSION TAXES AN- 
NOUNCED BY ONTARIO 

Hon. E. A. Dunlop, Provincial Treas- 
urer of Ontario, announces theatre 
taxes in Ontario will be as follows : 

Tickets up to 25 cents, exempt ; 25 to 
32 cents, 2 cents ; 33 to 37 cents, 3 cents : 
37 to 46 cents, 4 cents; 46 to 55 cents, 
5 cents; 55 to 64 cents, 6 cents; 64 to 
73 cents, 7 cents ; 73 to 82 cents, 8 cents ; 
82 to 91 cents, 9 cents; 91 to $1, 10 
cents; $1 to 1.50, 15 cents; 1.50 to $2, 
20 cents ; $2 to $2.50, 25 cents ; $2.50 to 
$3, 30 cents; $3 to $3.50, 35 cents; $3.50 
to $4, 40 cents ; over $4, 50 cents. 
A 

WOW-WOWS 

A type of pulsation of intensity in re- 
produced sound, due fundamentally to 
change of speed of the sound track dur- 
ing either recording or reproduction. 
While this change of speed produces a 
change of pitch, the latter, when the 
fluctuation is rapid is generally not per- 
ceptible but the phenomena of interfer- 
ence of sound waves in the theatre cause 
this change of pitch to produce a rapid 
periodic change of intensity. \\ ow- 
wows correspond to a variation in speed 
of, say. up to six cycles per second : 
FLUTTER, to a variation of about six 
to thirty cycles; G \RGLE. 30 to 200 
cycles; and WHISKERS, over 200 
cvcles. 



Page 12 



A decade of progress 
in the recording 
and reproducing 
of sound 



By J. E. Otterson* 



Wherein are reviewed various adaptations of the de- 
velopments in telephone communication as related to 
the newer arts of sound amplification, recording and 
transmission. 



FIFTY odd years ago it was possible 
to hear only that speech which was 
uttered in an audible tone in the 
immediate vicinity of the listener. 
Today it is possible to speak in a nor- 
mal, conversational tone in Australia 
and be heard in New York. It is also 
possible to speak in a normal, conversa- 
tional tone in Australia and hear one's 
own voice three-tenths of a second later 
after it has traveled around the world. 

It is possible to speak to ships at sea 
and to ships in the air. It is possible to 
speak to passengers on moving trains. 

A doctor in Chicago has listened to 
the heart beat of a patient in a hospital 
in Baltimore and diagnosed his heart 
malady. 

A short time ago one of the motion 
picture executives informed us that they 
had been directed to put on a command 
performance of their motion picture 
production of "Private Lives" in a Lon- 
don theatre at midnight of a day in 
February. He desired to arrange for 
Miss Norma Shearer, who is the star in 
this production, to speak from Holly- 
wood to the theatre in London by tele- 
phone and to have her voice amplified 
so that she could extend greetings to 
the King and Queen and the audience. 

To accomplish this Miss Shearer 
would speak into a microphone in a 
sound treated room in Hollywood and 
her voice transmitted by wire telephony 
to New York — a distance of three thou- 
sand miles — and then by radio telephony 
across the Atlantic — another three thou- 
sand miles — and by telephony from the 
receiving studio in England to the the- 
atre, where her voice would be ampli- 



fy k address delivered before the Electrical 
Association of New York. 

^President, Electrical Research Products, Inc. 



fied and delivered to the audience 
through loudspeakers. 

The telephone company was prepared 
to do this as a matter of telephone ser- 
vice. 

Let us imagine Miss Shearer in the 
theatre in London in place of in the 
studio in Hollywood, speaking into a 
microphone and having her voice ampli- 
fied and delivered to the audience by 
means of loudspeakers. We would then 
have what is known as a "public-ad- 
dress system," that is, the instrumental- 
ity commonly used where a speaker is 
called upon to address an audience too 
large to be reached by his normal voice 
through direct speech. 

Assume, then, that in place of Miss 
Shearer being in the theatre in London, 
we have there a record of her voice so 
that in place of speaking into the micro- 
phone her voice is picked up from the 
record, transmitted to the amplifier and 
then through the loudspeakers to the 
audience. This arrangement would con- 
stitute an electrical phonograph. 

Synchronize this sound record of Miss 
Shearer's voice with a motion picture 
of Miss Shearer speaking, and we have 
a talking motion picture. 

Return for a moment to the radio 
telephone circuit across the Atlantic. If 
in place of throwing Miss Shearer's 
voice on to the telephone wires upon its 
reception in England we had directed 
it into a radio broadcasting station, we 
would then have made use of telephone 
facilities and instrumentalities for com- 
mercial radio broadcasting purposes. 

In fact, it would have been readily 
possible to broadcast Miss Shearer's 
voice throughout the world at the same 
time that it was being transmitted to the 
assembled audience in a London theatre. 



PROJECTION ENGINEERING 

Telephone Line Broadcasting 

Then again, we might have connected 
every telephone subscriber in the United 
States with the wire telephone circuit 
over which Miss Shearer was talking, 
and by placing a loudspeaker at the sub- 
scriber end of the wire, have developed 
a system of wire broadcasting not yet 
commercially exploited but susceptible 
of commercial development in the fu- 
ture. 

These things have been made possible 
by the development of the science of 
telephony. The word "telephony" is de- 
rived from certain Greek words mean- 
ing "distant sound." The characteristic 
of telephony is a separation in space be- 
tween the speaker and the listener. The 
scientific problems presented to the tele- 
phone engineer are those relating to the 
transmission and amplification of sound, 
and the solution of these problems in- 
volves comprehensive research in the 
fields of electricity and acoustics. 

In pursuing this research a new sci- 
ence, a new art, was evolved. I refer to 
the electrical recording and reproduc- 
tion of sound. This new science is de- 
pendent upon the same laws as the sci- 
ence of telephony and to a large extent 
makes use of the same facilities. In op- 
eration, however, it differs very funda- 
mentally from telephony. Since, where- 
as in telephony there is a separation in 
space between speaker and listener, in 
this new science there is a separation 
in time, and the recorded voice may be 
heard at any time after the original 
speech. 

Postephony 

If I may be permitted to coin a word, 
I would like to refer to this recording 
and subsequent reproduction of sound as 
the science of "postephony," which I 
think may be freely translated as mean- 
ing "later sound" or "sound after." 

The combined science of telephony 
and "postephony" is the basis of one of 
the four or five largest businesses in the 
world, involving as it does transmis- 
sion, recording, amplification, reproduc- 
tion and reception of sound, and em- 
bracing the telephone business, the ra- 
dio business, the phonograph business 
and the talking motion picture business. 

In addressing you in this room four 
years ago I referred to the application 
of the results of the research carried on 
by telephone engineers in the field of 
postephony, and I referred particularly 
to the applications in the phonograph 
and talking motion picture fields. The 
progress that has been made since re- 
lates primarily to the quality of record- 
ed and reproduced sound. 

The term "canned music" was ap- 
propriate to describe the early efforts 
to record sound, since it carried with it 
not only the suggestion of stored-up 
sound, but a certain tinny quality that 
was characteristic of these early efforts. 



MAY, 1932 



Page 13 



Our efforts since may be said to have 
been directed toward getting rid of the 
can, and this effort has been successful 
in large measure not only in a physical 
sense, but in a psychological sense as 
well, since with the improvement in 
quality that has resulted- the public 
prejudice against canned music has for 
the most part disappeared. 

In order to understand why present- 
day sound records are better than the 
early records it is necessary to be a 
bit technical. The human ear can hear 
sounds having a frequency range from 
fifty cycles per second to ten thousand 
cycles per second. The old-fashioned 
phonograph produced only the middle 
band of these frequencies and eliminated 
the high notes and the low notes. In 
these circumstances all voices sounded 
more or less alike and all had that qual- 
ity of tinniness associated with the can- 
ning process. 

Our present-day instruments are per- 
fect enough to record and reproduce all 
of the frequencies which the human ear 
can hear, with a resulting improvement 
in naturalness. 

Noise 

We think of noise as unpleasant 
sound. In the struggle toward perfec- 
tion in this art it has been necessary 
to give study to the suppression of noise. 
When sound is amplified to fill a large 
theatre or auditorium, noises which 
were not noticeable at lower levels be- 
came objectionable. When I say that 
it has been possible in large measure to 
eliminate the noises or unpleasant 
sounds while amplifying the unpleasant 
sounds, it would appear that I am indi- 
cating that the instruments of modern 
postephony have the quality of good 
taste. This, of course, could not be true, 
but they do have the scientific property 
of dealing to some extent sufficient for 
practical purposes in a selective man- 
ner with sounds of different character. 

This is the basis of what is known as 
Western Electric noiseless recording de- 
veloped during the past two years. You 
may have noticed that present-day talk- 
ing motion pictures are more noiseless 
than those of four years ago in that they 
are comparatively free of extraneous, 
unpleasant sounds suggestive of me- 
chanical instrumentalities. 

When listening directly to sound, the 
ear unconsciously rejects those noises 
which permeate the atmosphere in which 
we live. This selective process is made 
possible in part by the separation of the 
source of the noise from the source of 
the sound to which we are listening. 

In the case of postephony, the micro- 
phone is not so discriminating and picks 
up the noise as well as the desirable 
sound, and furthermore, when a record 
is reproduced the sound and the noise 
must emanate from the source — namely, 
the loudspeaker. This is exactly as 



though all of the noise which is pies- 
ent in this room came to you as though 
uttered by me while speaking to you. 
In this way you will see that the in- 
strumental process of postephony is at 
some disadvantage compared with the 
natural process of direct hearing. 

Study of the problem of eliminating 
noises has drawn into a new field of 
acoustic engineering, which has to do 
with the treatment of rooms and public 
places for the purpose of suppressing 
noises on the one hand, and making 
them properly receptive and responsive 
to the sounds that are desired. 

A few examples may serve to illus- 
trate the scope of this field. You have 
perhaps read of the study on subway 
noises for the noise abatement commis- 
sion in New York City ; and, as a cor- 
ollary to that, one for a milk company 




J. E. OTTERSON 
President, ERPI. 

here in an effort to suppress the noises 
connected with the delivery of milk so 
familiarly objectionable in the early 
hours of the morning. Churches, too, 
are seeking ways of making the spoken 
word more audible to congregations 
whose hearing appears peculiarly defi- 
cient as related to words of grace. 

The results of similar studies made 
for the architects of the new Philadel- 
phia opera house have led to some 
fundamental features of design and 
treatment that will insure pleasing 
acoustics. Many public buildings have 
been constructed in the past with unsat- 
isfactory acoustic qualities which might 
have been avoided with the application 
of present-day knowledge. 

We rank as one of our most inter- 
esting projects the recent acoustical 
treatment of Madison Square Garden, 
which made it possible for the great 
Paderewski to give a piano recital there 
in February. His music was heard per- 
fectly in every part of that vast audi- 
torium, which was acclaimed by musical 
critics as an outstanding achievement. 



Four years ago I ventured to 
prophesy that talking pictures would be 
applied to the fields of advertising, poli- 
tics, education and religious teaching. 
Progress in these fields has been steady, 
but somewhat slowed down by the busi- 
ness conditions of the past two years. 
If time permitted, I could present to 
you a comprehensive program of pic- 
tures that have been made in these vari- 
ous fields. 

Talking Pictures in Education 

As was to be expected, the value of 
the talking picture for instructional pur- 
poses has been most quickly seized upon 
and widely used in the field of com- 
merce and industry. Many of the great 
corporations are using talking pictures 
today for the training and instruction 
of their personnel and for conveying the 
personal messages of their executives 
to outlying offices and branches of their 
organizations throughout the world. The 
epic story of many industries is being 
recorded and portrayed. Through these 
we may attain to an understanding of 
how these great industries came into be- 
ing and why they exist, and to under- 
stand these things is to interpret the 
forces that underlie our modern life and 
civilization. 

Already talking pictures have been 
made to advertise commodities of every- 
day life. The cough that is never pres- 
ent in a carload can be recorded in talk- 
ing pictures. The man who owns one 
can tell of his satisfaction with his mo- 
tor car. Railroads, airlines, trade asso- 
ciations, insurance companies, newspa- 
pers and public service companies have 
used this medium to advertise their ser- 
vices and to create public understand- 
ing and good-will. 

Manufacturers, department stores, 
banks, hotels, theatres and other indus- 
trial and business organizations are 
using talking pictures to train their em- 
ployees — churches to train their minis- 
ters and schools to train their teachers; 
athletic coaches to teach games ; Bobby 
Jones to teach golf; Bill Tilden to teach 
tennis. 

In closing I may say that I regard 
talking pictures as, in reality, a means 
of communication, whereby the art and 
inspiration of great actors, teachers, 
preachers, and statesmen may be car- 
ried from the sphere in which they 
move, to the ever widening sphere of 
world interest from the metropolis to 
the hamlet, from the great university 
to the country school-house, from the 
cathedral to the parish church, from this 
generation to future generations who 
may find in the better understanding of 
our lives, our achievements, and our 
dreams, of our personalities and char- 
acters the inspiration and example that 
will lead them to a still higher civiliza- 
tion in the days to come. 



Page 14 



Sound 
film 
editing * 

By Maurice Pivar' 



PERHAPS the least heralded of 
all occupations in the motion pic- 
ture industry is that of the film 
editor, commonly known as the 
''cutter." Unlike most of the technical 
branches of the business, film editing- 
does not follow any set routine but each 
picture and even each sequence in a pic- 
ture presents a different problem to the 
editor. This is especially true today 
when situations are tied up and involved 
with the sound element. 

The film editor must not only know 
how to "cut" and assemble a picture, 
but he must apply intelligence and in- 
genuity to his work. He must not only 
know the routine of editing but he must 
thoroughly understand and know screen 
values — dramatic, comic, and photo- 
graphic, and take full advantage of the 
film he has in hand so that it will ap- 
pear to the audience to the best advan- 
tage. A cutter devoid of the ability to 
feel dramatic and comic impulse would 
be of little assistance to the director 
even though he might be fully versed 
in the mechanics of his work. 

Those who are familiar with produc- 
tions, are aware that the average fea- 
ture picture involves anywhere from 
thirty thousand to sometimes three hun- 
dred thousand feet of film, and it re- 
quires efficiency and system for an 
editor to be able to place his hands on 
any particular scene at any time, with- 
out having to wade through thousands 
and thousands of feet of film. 

The systems used for keeping track 
of this excess film vary in the different 
studios. At Universal, through the co- 
operation ofj the laboratory and the pro- 
duction department, we have simplified 
this phase of cutting to a great extent. 
After each day's work on the set, the 
script girl sends to the cutter a copy of 
the record of the day's work. This 

fA paper presented at a meeting at Fox Hills 
Studio, of the technicians' branch, Academy of 
Motion Picture Arts and Sciences. 

"Supervising film editor, Universal Studios. 



record states clearly the number, the 
length and the dialog of each scene. 
This is kept on file from day to day by 
the cutter. Time and again during the 
course of editing a picture, a director 
will prefer a scene changed from one 
angle to another and, sometimes, there 
is a question as to whether such a scene 
may have been shot and to avoid wading 
through the film to verify it, the cutter 
instead refers to the script girl's notes. 
In addition to the script girl's record, 
a laboratory record is also kept by each 
cutter. This record is sent through 
with the film, commonly termed "dail- 
ies," which is printed up each day by 
the laboratory. The edge numbers and 
scene numbers of each scene printed are 
marked on the record. Quite often dur- 
ing the editing of a picture a scene is 
either damaged, or more often cut up 
by the changing of cuts to the extent 
that a reprint is necessary for practical 
handling. The use of the laboratory 
records and the script girl's daily record 
facilitates the ordering of reprints and 
the checking of various scenes in the 
picture. 

Preliminary Routine 

The routine involved in the prelimi- 
naries of editing a picture vary some- 
what in the different studios. The 
majority, however, favor the use of 
separate sound track and separate action 
during the process of editing. There 
are several studios which use movietone 
prints or, in other words, prints which 
have the sound already printed on to 
the action. This method may be more 
economical from a standpoint of saving 
of film, but the ^writer is in sympathy 
with the use of separate sound track for 
the reason that it offers a greater lati- 
tude in the editing of a picture. 

The first step in connection with edit- 
ing is, as a rule, to synchronize the 
sound track with the action. This is 
accomplished by the use of a specific 
mark or punch at the beginning of each 
scene. This punch or mark is made on 
both the action and the respective sound 
track and it is necessary, therefore, to 
see that both punch marks start at the 
.same point. 

To simplify the handling of separate 
sound track and separate action, the use 
of numbers on the edge of the film, 
spaced one foot apart is necessary. 
These numbers are made in duplicate 
and the same number that appears on 
the edge of the sound track film also 
appears on the edge of the action film — 
both numbers being in the same rela- 
tive position from the start mark. 

With the "dailies" synchronized and 



The art and technique of the film editor largely deter- 
mine the success of the finished sound picture. 



PROJECTION ENGINEERING 

properly numbered, they are then shown 
to the director or any other executive 
interested in the production. Where 
there are more than two takes to a par- 
ticular scene, the director, as a rule, 
selects the one he prefers and this is 
the one which is set aside for use in the 
picture, the others being kept on file. 

The efficient editor as a rule starts to 
edit his picture with the completion of 
the first sequence. All of the film of 
this sequence when completed is as- 
sembled in continuity order. This 
gives the editor an opportunity to 
familiarize himself thoroughly with the 
film on hand and enables him to visual- 
ize the cutting possibilities of the se- 
quence. The editor's objective, then, is 
to cut this sequence to the best advan- 
tage, utilizing such angles as he feels 
will present the sequence in the most 
effective manner on the screen. 

This procedure is continued as the 
director shoots his picture, so that when 
within a few days after the director has 
completed his picture it is practically 
ready for him to see in what is termed 
"first" or "rough" cut. Most directors 
are thoroughly familiar with cutting 
and at times are of great help to both 
the picture and the editor. The director 
having made the picture naturally may 
have his own ideas with regard to the 
way certain angles should be used to 
portray certain scenes. In shooting the 
sequence he may have been striving for 
a certain dramatic or comic value in 
the situation. Then oftentimes, the editor 
may cut it from his own point of view. 
This, naturally, brings about discussion 
and, with an intelligent editor, the di- 
rector at times may find that the editor 
has already gotten the most out of the 
situation with the film in hand. 

The best results are generally ob- 
tained when both the director and the 
editor work in harmony and are open- 
minded as to suggestions. 

First Showing 

The picture in first cut naturally runs 
considerably over the general releasing 
length, and before any final eliminations 
are made the picture is presented to the 
public for its reactions ; all further cuts 
or eliminations being determined by the 
results obtained when shown to an audi- 
ence. Quite often certain situations 
which look very appealing during the 
process of cutting, fail to impress the 
audience and, likewise, certain situations 
which apparently do not seem to carry 
much weight in the studio projection 
rooms, bring a strong reaction from the 
audience. In this way, the director and 
everyone else concerned with the pic- 
ture is enabled to judge, through the 
audience reaction, the screen values of 
all the situations in the picture, later 
removing such situations which prove 
unessential. 



MAY, 1932 



Page 15 



Before a preview is held, however, 
there is a considerable amount of me- 
chanical work that the picture must go 
through. First, there is the work of 
embellishing and refining the various 
cuts. Then the matter of adding sound 
effects and music and also the injection 
of certain photographic effects in the 
shape of lap dissolves and other effects 
to which the picture may lend itself. 
Today, with the perfection of what is 
called the "optical printer," these 
effects, such as lap dissolves, etc., which 
ordinarily were made on the sets by the 
director and which proved very costly 
because of the loss of time involved, are 
made on these optical printers after the 
picture has been completed. 

Some studios have a special depart- 
ment which handles the injection of 
sound effects and music into the picture. 
At this studio, we find it more desirable 
to have the editor himself supervise this 
phase of the work, for the reason that 
he is thoroughly familiar with the film 
and also with the particular desires of 
the director and the manner in which 
they are to be placed. Our sound de- 
partment concentrates on the making of 
the effects desired and, also in the 
handling of the necessary music. There 
is also a close cooperation between the 
sound department and the sound library. 
When the editor is in need of certain 
sound effects or music for his picture, 
this particular track is ordered through 
the sound department. This depart- 
ment first refers to their files in the 
sound library and if the track is not al- 
ready in the library, one is made. How- 
ever, when a picture calls for consider- 
able music or some special type of music, 
the sound department of course places 
this in the hands of a specially assigned 
musical director. 

Dubbing 

After both sound effects and music 
have been supplied the editor he super- 
vises the lining up of these particular 
sound tracks and both the effect tracks 
and the dialog tracks go through the 
process of what is called "'dubbing," 
which is also handled through the sound 
department by special operators for this 
purpose. 

The work of dubbing presents quite 
an interesting phase of motion picture 
production today. Dubbing has sim- 
plified to a great extent the making of 
sound pictures. Where originally 
sound effects were recorded at the time 
the scenes were taken, today all sound 
effects are placed in the picture after 
the scenes are taken — in fact, after the 
picture has been otherwise completely 
edited. 

The disadvantage of trying to shoot 
a scene which carries a decided musi- 
cal background is that the cutting of 
this particular sequence is confined to 



the continuity of the muscial score and 
eliminations cannot be made without 
causing a noticeable break in the music. 
The disadvantage of recording sound 
effects at the same time dialog is being 
recorded is twofold ; it interferes at 
times with the coherence of the dialog 
and results in a changing volume of the 
various effects when the scenes which 
comprise the sequence are placed to- 
gether. In fact, each cut is noticeable 
by the change in volume of this back- 
ground noise. Once a scene has been 
recorded with sound effects in the back- 
ground there is nothing which can be 
done mechanically to change the balance 
of sound effect and dialog should the 
dialog be crowded out by the effect. 




F 'ai amount picture by Don English 
Marion Shilling, Paramount player, watches 
a film editor at work. 

When dialog and sound effects are 
recorded on separate tracks the promi- 
nence of the dialog may be emphasized 
to whatever degree desired in the dub- 
bing. The balance between the two 
may be varied at will, making the sound 
absolutely flexible in the hands of the 
dubber, and enabling him to at all times 
keep the dialog intelligible above the 
general noise level. 

Preparation in Advance 

It might not be amiss at this point 
to emphasize the importance of prepa- 
ration before actual production of the 
picture. With the advent of recorded 
sound to the motion picture the latitude 
of the editorial department has been 
minimized to the extent that where 
originally the possibilities of realigning 
and recutting silent scenes were un- 
limited, we are now confined within the 
limits of the dialog. Today a script be- 
fore it is put into production should be 
letter perfect because once the dialog 
has been put upon the film there is no 
other recourse than to make retakes 
should this dialog show up poorly on 
the screen. 

The question of preparation also ap- 
plies to the timing of scenes. In the 



"silent" days, all a director had to watch 
for was the position of the actors when 
changing from one angle to another. 
He had to make certain that he picked 
up the actors in the same position when 
changing the camera angle. Today, he 
must not only watch the positions of his 
actors but also the dialog that is being 
spoken while the actor is in a certain 
particular position. One of the editor's 
greatest trials is the carelessness of 
some directors who overlook this very 
vital point. 

To illustrate more clearly ; assume 
that the director is shooting a scene 
where an actor is seated at a desk, and 
the actor during the scene arises and 
crosses the room. During this business 
the actor has spoken certain definite 
lines while he was arising, and certain 
others while he was walking across the 
room. Let us further assume that this 
scene is a long shot. The director then 
wishes to shoot the same scene from a 
closer angle. Quite often, we will find 
that in shooting this closer angle, the 
actor did not repeat the lines simul- 
taneously with the action in the long 
shot. We will probably find that he did 
not say the first line as he arose from 
the desk, but as he walks across the 
room, with the result that the editor is 
compelled to play the scene in one angle 
and, even though there may be a decided 
advantage in going to a closer angle, 
this cannot be done without showing a 
break in either the action or the dialog. 
This of course would be bad from an 
editorial standpoint and could not be 
allowed. 

Limitations of Cutting 

The practical director today is one 
who appreciates thoroughly the limita- 
tions of cutting. Directors, however, 
differ considerably in their methods of 
footing. Some directors safeguard 
themselves by overshooting the picture. 
That is, they will shoot a scene from 
many different angles for protection 
purposes. Other directors, being per- 
haps more familiar with the cutting of 
pictures, cut most of their scenes in the 
camera. Both have advantages and dis- 
advantages. From the producer's stand- 
point, overshooting a picture is very ex- 
pensive — and from the editor's stand- 
point undershooting a picture involves 
untold grief. 

A great many obstacles arise as a re- 
sult of a director trying to cut his pic- 
ture in the camera. In his effort to 
economize the editor finds himself in the 
position at times of being limited in the 
cutting of the picture to the manner in 
which the scenes were actually shot by 
the director and unless he is absolutely 
perfect in timing, we find that in trying 
to connect certain scenes either the 
action or the sound does not touch. It 
is always a good expedient for an 



Page 16 



PROJECTION ENGINEERING 



economical director, in attempting to 
cut scenes, to overlap at least part of 
the dialog and action when progressing 
the scene through various angles, and 
to particularly watch that the dialog is 
timed perfectly with the action in each 
angle that he shoots. 

The actual mechanical features in- 
volved in the editing of sound pictures 
are relatively simple. They involve the 
use of the synchronizing machine, the 
moviola, the splices and the rewind. All 
of these devices are easy to operate and 
require only a minimum amount of ex- 
perience to attain more or less perfec- 
tion in their handling. 

Synchronizing 

The synchronizing of film by edge 
numbers has been explained previously. 
In additon, each editor is supplied with 
a synchronizing machine, the purpose 
of which is to enable him to keep the 
film in synchronization as he handles it. 
This device can best be described as a 
machine which carries anywhere from 
two to four sets of sprockets. The 
editor, while handling the film, places 
both the sound track and the picture film 
over these sprockets, keeping the film 
in synchronization at all times while he 
is passing it from one reel to another 
during its handling. Should the film 
by any chance slip over the sprockets, 
the editor has the edge numbers as a 
guide, thus avoiding the necessity of 
going back to the original start mark 
to check the sound track with the action. 
Most editors, however, do not use the 
synchronizing machine but prefer the 
moviola (film viewing and checking 
device). The practice is to place the 
sound track underneath the action, both 
passing over the same sprocket wheel. 



Inasmuch as the greater part of the 
sound film is clear, the light passes 
through and the cutter is able to handle 
both films without interfering with ob- 
servation of the picture. 

Experienced editors require the syn- 
chronizing machine mostly for lining 
up sound effect and musical tracks after 
the picture has been cut, enabling them 
to run the action on one set of sprockets ; 
the dialog on the second, the sound 
effects on the third, and musical or 
other background noises on the fourth 
set. In this manner, the editor can run 
all of the film through the synchronizing 
machine at one time, matching in every- 
thing in the one operation. 

Patching 

There are two different type patches 
used in the cutting room, one which 
covers the full sprocket and the other 
covering only the half sprocket. At 
Universal we find the half sprocket 
satisfactory, because that type seems to 
pass through the projection machine 
more readily, not tearing apart after 
repeated use as does the full sprocket 
patch. 

Each editor is of course assigned one 
or two assistants, each of whom should 
have speed, care and system in the 
handling of film. System in the cutting 
room naturally results in cleanliness. 
Film at all times should be kept on file 
in cans and in fire protection cabinets. 
Fire is a hazard in any part of an or- 
ganization where film is being handled 
and the less film that is exposed, the less 
the hazard. Particular care should be 
taken to expose as little film as possible 
and the efficient editor, with the assist- 
ance of an efficient assistant, will have 
very little film about his room at any 

AAA 



one time. 

The following mechanical devices 
really comprise the fittings of a cutting 
room: metal re-winding tables, each 
table with one set of re-winders and 
racks for the filing of small rolls of 
film, with either artificial or natural 
light in the background, facing the 
rack. Steel cabinets for the filing of 
excess film ; combination sound and 
silent moviolas ; film bins and clips for 
the clipping together of film preli- 
minary to splicing and also the necessary 
reels required in the handling of the 
film. 

It may be added that editing involves 
a great deal of careful and intelligent 
work. Give an efficient editor the above 
mentioned equipment, plus one pair of 
scissors, and no picture is too great a 
task for him. 

I have found it a great advantage to 
surround myself with men who have a 
number of years' experience. In gen- 
eral the longer the experience the 
greater the proficiency. An editor with 
the handling of each picture learns and 
experiences situations which perhaps 
have not confronted him before and in 
time becomes thoroughly familiar with 
dramatic, comic and fast tempo situ- 
ations. Often he is able to create situ- 
ations in the picture which, from all 
appearances, the film would not permit. 

Summing up, I might suggest that a 
thorough knowledge of film editing is 
perhaps the best requisite for success in 
almost any branch of the production end 
of this business. Directors who have 
risen from the ranks of editors are the 
ace directors of the business, the knowl- 
edge which they gained as cutters being 
of untold value to them in their sub- 
sequent work. 



Fabric for light reflecting screens t 



AMR. WILCZEK, in the screen- 
importing business, testified 
that to March, 1930, he was in 
the motion-picture-screen man- 
ufacturing business, and that he bought 
material like that in question from the 
Western Commercial Company, the 
plaintiff herein, about January, 1929, of 
a width of from thirteen to sixteen feet, 
for use in making moving-picture pro- 
jection screens; that after being cut to 
size the cloth is covered in front with 
a spray of two or three layers of white 
paint, and then with a layer of white 
enamel in which are embedded glass 
beads; that the paint seeps through the 
back of the cloth and is brushed in back 
and in front to make an even surface, 
and that the surface in back, which is 
white, is then usually covered with a 



fFrom a recent decision of the V. S. 
toms Court. 



Cus- 



black paint ; that it is left for a week 
to dry, and then rolled up and packed 
. in boxes for shipment to the theatre for 
the projection of pictures thereon; has 
furnished these screens to the Roxy 
Theatre, New York City; to Loew's 
and Proctor's theatres, also to Keith's, 
Fox's and Moss & Brill's theatres — 
altogether to about 500 or 600 theatres 
throughout the United States — and that 
sound pictures are made from the same 
material, except that the screens are 
perforated where the sound comes 
through. 

Another of plaintiff's witnesses, Na- 
thaniel Schneider of the Schneider 
Scenic Studio, New York City, manu- 
facturers of scenery and draperies for 
the stage, states that his concern bought 
cloth like that under consideration from 
the plaintiff, which in that particular 



case was used for making mural panels 
for a church affair, for which cotton 
cloth without seams was necessary. 

For these mural paintings the cloth 
is first sized with a liquid solution of 
starch, water and a little glue to fill in 
the pores and give a solid surface so 
that the water color will stick to the 
painting. The design is sketched on the 
cloth, and then filled in with water color 
by spray or hand. He further stated 
that he used material like. Exhibit 1 for 
these murals ; that he never used water- 
proof materials for mural paintings, as 
water colors could not very well be ap- 
plied to a greasy substance ; that you 
could not apply paint to the raw cloth, 
although water colors could be applied 
to this kind of cloth without putting 
anything else on it, and that it would 
stick. 



MAY, 1932 



Page 17 



The talking 
book 

By Dr. Irving J. Saxl* 



THE phonograph industry has 
suffered severe losses in compe- 
tition with the radio industry. The 
development of radio improve- 
ments has made the present-day radio 
apparatus more preferable to the aver- 
age customer than the old-time phono- 
graph. Now the sciences have added 
new features to the performance of the 
record reproducing equipment which 
could not be obtained with the old ap- 
paratus. In addition, the added im- 
provements make this new apparatus 
valuable and independent of the com- 
petition of radio. Science which, by 
bringing radio into the market made 
serious competition to the phonograph 
industry, has now, with the very tools 
of the radio sciences, improved the 
phonograph so that it is not only useful 
again but its range of application is 
greatly widened into a field where there 
is no competition from radio. 

Phonograph Difficulties 

The phonograph was handicapped by 
two important elements. They were, 
the minor quality of sound recording 
and reproduction and the limited length 
of one sound track that could be re- 
corded upon a single record plate. In 
addition, the record was heavy and sub- 
jected to breakage generally and an 
editing of the record was impossible. 
Although today new records have been 
made available which can play for al- 
most twenty minutes, this type of re- 
cording has some disadvantages. 

The grooves of these vertically cut 
record plates can be more easily filled 
with dust than the horizontal Berliner 
cut, which was considered for a length 
of time superior to the vertical Edison 
cut. Therefore they will probably lose 
their quality of sound reproduction 
sooner than the horizontal cut. Only 
practical experience would make it pos- 
sible to say definitely. 

The second point seems more import- 
ant at present. If sound is to be made 
on these plates then, even if a single 
mistake is made, the whole plate is 
worthless, thus creating difficulty in 
making a record with such plates, and, 
naturally, adding to the expense of re- 
production. 



*Consulting Physicist. 



In the present competition with radio, 
only a machine with excellent sound 
quality will be able to stand up. Audio 
amplification, naturally, is the proper 
means for doing this. In addition, if 
long records are supposed to be played, 
proper means have to be found to make 
possible an editing of the records so 
that if a mistake occurs somewhere in 
the middle of the performance, the en- 
tire recording procedure does not have 
to be begun all over again. A proper 
way of doing this has been found in a 
new machine, Fig. 1. A narrow strip 
of film about one-quarter of an inch 
wide travels from the coil at the right 
side over a guiding mechanism and is 
recoiled again by the other coil. 

In this case an opaque film is used, 
which is strongly illuminated from two 
sides, the center of the film by means of 
the focusing equipment, being centered 
upon a pholo-sensitive cell. A slip of 
proper width provides that the right 
part of the film is reproduced. By this 
way of projection the reproduction takes 
place by diffused and reflected light. If 
transparent film is used, naturally, a 
light source has to be placed at the op- 
posite side of the film so that the light 
passes through the transparent film. 
Six mm. film is used, each side of which 
carries a separate sound track. 

The entire apparatus is driven by a 
small electric motor. The light sen- 
sitive device — in this case a selenium 
cell — is used making possible a greater 
level of initial amplification and reduc- 
ing the noise-level. 

This selenium cell controls amplifi- 
cation equipment of the usual type 
which works either into headphones or 
into a loudspeaker. 

What is the advantage of this type of 
equipment over the old-fashioned phono- 
graph and what can make it a new and 
valuable factor in merchandising elec- 
tronic equipment? Primarily, vacuum 
tube audio reproduction is well known 
as giving better quality of sound than 
mechanical reproduction. Practically a 
greatly increased length of speech or 
music can be recorded, say, for about 
twenty to twenty-five minutes. In addi- 
tion, in the negative of this speech, those 
parts in which a mistake has been made 
can be taken out and corrected so that 
the recording procedure is simplified 
and its expense reduced considerably. 
Editing and cutting of these records is 
practical. 

This increased length and quality of 
sound reproduction makes possible the 
recording of performances and actions 
which heretofore have been impossible. 
For instance, the whole act of an opera, 
or a whole suite of a concert can be 
recorded at one time and it is not neces- 
sary to turn over record plates and in- 



troduce undesirable pauses. A con- 
tinuous reproduction can be made also 
of lengthy works. Should, however, 
any mistakes be made in the recording 
of this performance, they can easily be 
eliminated by simply pasting in, in the 
desired length, a new record of the piece 
where the corrections were made. 

There is at the present time one more 
important outlet for this type of appa- 
ratus which seems to be promising from 
two different angles. One, that it will 
provide work for a number of indus- 
tries and employees, and second, that it 
will amount to a considerable saving for 
the state. At present the law in differ- 
ent states provides from $125.00 to 
$300.00 for each blind pupil per year, 
for this amount the pupil is supposed to 
have somebody who will read scientific 
works to him, or works which will in- 
crease his further study and earning 
capacity. This service of a reader is 
provided for pupils with high school 
background so that they can make their 
college courses or their technical or pro- 
fessional education complete. 

Libraries for the Blind 

It is now much easier and consider- 
ably less expensive to have important 
w'orks in the education of the blind re- 
corded, and one may have as many 
copies made of the sound film as de- 
sired. In libraries for the blind an 
acoustical library would include a much 
greater variety of books than is pos- 
sible with the present method of Braille 
writing or any other method, and it 
would make, in a great many instances, 
the special service of a reader unneces- 
sary. The state department of educa- 
tion could make savings in this line and 
at the same time intensify this important 
service for blind pupils. Incidentally, it 
would be easier to assemble this acous- 
tic library in the form of a few light 
rolls which also can be fitted more easily 
into the limited space of libraries than 
books, heavy and large in Braille 
writing. 

Thus, the introduction of this '"Talk- 
ing Book" may soon become a valuable 
tool in the furtherance of human wel- 
fare and civilization. 




Fig. 1. 



Close-up of the film-playing 
phonograph. 



Page 18 



Disc recording for 
industrial and educa- 



tional motion pictures 



By L. D. Minkler* 



IN this paper I shall attempt a brief 
sketch of the entire art of recording 
sound-on-disc and then to describe 
in detail that part of the work which 
involves the actual practice used in 
transcribing the sound originating in 
the studio on to the wax master. 

First, let us trace the sound in its 
course from the studio to the wax. 

The voices, music, and other sounds 
occurring in the studio are picked up 
by the microphone, which converts the 
audible vibrations to a corresponding 
electrical current. This current passes 
into the transmitter amplifier, thence 
through the intermediate amplifier to 
the mixer and gain control. The mixer 
brings the current from individual mi- 
crophones together into one circuit and 
the overall volume of all the micro- 
phones is regulated by the gain con- 
trol. From the gain control the current 
passes through the input amplifier to a 
recording bus and from there is fed 
into separate amplifiers for each wax 
cutter used. From the recording bus 
the current is also fed into the monitor 
amplifiers, which operate the monitor 
loudspeaker. Usually two wax cutters 
and two monitor speakers are in oper- 
ation simultaneously. 

The wax cutter consists of a perma- 
nent magnet and pole-pieces suitably 
arranged to create a magnetic field 
around a voice coil, and a pivoted arm- 
ature. This armature is mounted ver- 
tically above the wax, the lower end 
carrying a sapphire cutting stylus. The 
armature and stylus vibrating in exact 
accordance with the electrical impulses 
received by the coil, cuts the groove in 
the wax with minute variations, which 
are, it might be said, the actual "sound 
wave" engraved in wax. 

The wax master, itself, is about eigh- 
teen inches in diameter and approxi- 



mate presented at the January 7, 1932, 
Meeting, Chicago Section, S. M. P. E. 

"Recording Engineer, Brunswick Recording 
Laboratories, Chicago. 



An understandable article 
describing the making of 
disc records for education- 
al and industrial purposes 



mately two inches thick, and is com- 
posed of a combination of animal fats 
and other materials, the compounding 
of which is considered a trade secret 
known only to the recording com- 
panies. 

After the wax has been cut, it must 
then be processed to obtain a metal 
stamper from which the required num- 
ber of pressings, or prints, can be 
quickly made. Briefly, this "processing" 
is as follows : 

The wax master is treated to make 
it conductive to electricity. This is done 
by either dusting it with fine graphite, 
or by a treatment of silver nitrate. The 
silver method is preferred. The wax 
is now suspended in an electric plating 
bath in such a way as to be kept in 
continuous motion, and a deposit of cop- 
per is built up on the wax, forming a 
shell which is called the "copper mas- 
ter." This takes about thirty-six hours, 
after which time the shell is removed 
from the wax, the rough edges cut off 
and the master trimmed down to size. 

In "rush" cases where pressings must 
be obtained in minimum time, the shell 
may be taken off sooner and discs 
pressed directly from this master. How- 
ever, to preserve the master from pos- 
sible damage by accident, the usual 
practice is to plate a second shell on 
this master, first treating the master 
with a potassium solution, called the 
"strike" solution, to prevent the second 
shell from sticking to it. This second 
copper shell is known as the "matrix" 
or "mother" and is a positive. That is, 
the grooves are exactly like the original 
wax, whereas the copper master is the 
reverse, having ridges in place of 
grooves. Obviously, records cannot be 
processed from the "matrix," so a third 
copper must be plated on to the "ma- 
trix," first using the "strike" solution, 
to get a negative plate for stamping 
records. 

This third copper plate thus obtained 
is known as the "stamper" and after 
being nickel-plated and cut to size is 
ready to be fitted to a record press. 
The press itself might be compared to 
a printing press where the printing type 
becomes the "stamper" and the paper 
becomes the record material. 

The record material, or stock, is pre- 



PROJECTION ENGINEERING 

viously prepared in slabs of just the 
right weight to contain enough mate- 
rial for one record. These slabs are 
then heated on a steam table next to the 
press, as rapidly as they are used. When 
hot. the stock is folded into a ball by 
hand and placed in the press under the 
center of the "stamper." As the press 
closes, with a pressure of several thou- 
sands pounds per square inch, the 
"stamper" and backing plate are heated 
by steam from behind them, and the hot 
stock is forced out to the form of the 
finished record. At this point the steam 
is cut off and cold water placed around 
the "stamper" so the record is hardened 
almost instantaneously. Then the press 
opens and the record is removed. The 
entire operation of the record press is 
automatic and one good operator can 
turn out about one thousand records a 
day. 

In its application to sound motion 
pictures a number of changes and re- 
finements in the technique of recording 
became necessary. First, a method of 
interlocking the motors driving the cam- 
eras and the wax recording machine 
was needed. This problem has been 
completely solved, through the use of 
the interlock system which holds all the 
motors in exact step at all times. 

Electrically driven wax recording 
machines have been highly developed 
for phonograph recording during the 
past few years, so that speed change or 
variation in disc recording is almost 
unknown in a modern recording system. 
Refinements in wax cutters and ma- 
chines, and a greater accuracy in re- 
cording technique have made possible 
the use of a finer feed, or pitch, of the 
recorded groove, permitting a longer 
playing time, without approaching too 
closely the center of the disc, where, as 
it is well known, the quality of the 
sound falls off very rapidly. 

The cutter, moving across the wax 
at a pitch of around 96 lines per inch 
has been considered the maximum for a 
record having good volume and long 
wearing qualities, but it is now practi- 
cal to use as high as 120 lines per inch, 
without sacrificing anything in the qual- 
ity of sound, volume, and long wear. 
No special needles are needed for re- 






Wax recording machine showing suction pump, 

recording cutter and microscope. Playback pickup 

seen in rear of microscope. 



MAY, 1932 



Page 19 



producing- these 120 line-per-inch discs. 

Through the elimination of resonant 
frequencies from the entire electrical 
system from microphone to wax cutter, 
and through the use of properly de- 
signed studios, or sound stages, it is 
comparatively a simple matter to hold 
a very high level of sound on disc, with- 
out cross-overs or break-downs, in the 
recorded groove. This is the first step 
in the practical elimination of surface 
noise. Of course, the entire electrical 
system must be free from any extrane- 
ous noises, due to faulty design, or con- 
struction. In this connection it might 
be well to mention here that a great 
improvement has recently been made in 
recording with the introduction of a 
new type of magnetic microphone. This 
type of microphone is remarkably free 
from noise even when a high gain is 
used. 

Other points which assist in over- 
coming the surface noise are : 

1. A recording wax which cuts 
smoothly at room temperature and 
which will not absorb chemicals from 
the plating- solution. 

2. Proper preparation of the wax for 
electro plating. 

3. A perfected system of plating to 
build up in succession a "master," "ma- 
trix" and "stamper," which involves the 
depositing of microscopically grainless 
copper to build up shells having perfect 
surfaces. 

4. The record material, itself, must 
be of such a composition that it will 
not create undue surface noise in the 
playing of the record. 

All of these processes have reached a 
high state of development through 
many years of experiment by the vari- 
ous phonograph record companies, dat- 
ing back long before the advent of the 
electrical amplification system, when the 
voice to be recorded was shouted into 
a horn, the actual air vibrations being 
at once impressed on a diaphragm, 
which was mechanically connected to 
the cutting stylus. 

We may now outline the actual pro- 
cedure followed in adding sound to a 
picture which has already been photo- 
graphed. Also, added to the picture 
which we shall discuss is a talking se- 
quence introducing the picture. 

It might be well to mention here that 
in view of the fact that once a record- 
ing is started it must be continued with- 
out interruption clear through to the 
end, it sometimes becomes necessary to 
resort to dubbing for re-recording. This 
permits short sequences to be recorded 
and when the finished records of these 
are obtained can be played back through 
the recording equipment and then re- 
recorded, all on one disc. By this 
method the different shots can be edited 
and arranged almost as easily as though 
the sound had been recorded on film. 




Corner of control room showing mixing panel 

and dubbing machines. Window looks out on 

sound stage. Microphone is used for talking to 

sound stage during rehearsals. 



Take, for example, a one-reel subject 
showing a type of tractor being used 
in farm operation. Here we have a 
number of shots of the tractor perform- 
ing definite tasks in the course of its 
work, which requires a running descrip- 
tion talk to give the necessary educa- 
tional value to the picture. For an ef- 
fective presentation the picture opens 
with appropriate music during the titles, 
followed by the speaker making an in- 
troductory talk, then the shots of the 
tractor at work, with the descriptive 
talk, and ending with a few bars of 
music. A camera, and a projector, both 
synchronized, or interlocked with the 
wax recording machine are in a sound- 
proof projection room. The silent film 
is loaded and ready to project on to a 
small screen in the studio. At a con- 
venient point in front of the screen are 
the microphones, one for the musicians 
and one for the speaker. It is best that 
the speaker be seated comfortably as he 
must watch the picture and time his 
talk to correspond. The monitor, or 
mixer, is located in a sound-proof booth 
at a point where the monitor man can 
watch the speaker, the orchestra, and 
the screen. He hears the sound exactly 
as it will be heard in the finished talk- 
ing picture. In another room are lo- 
cated the wax recording machines and 
associated amplifier equipment. Tele- 
phones connect the recording room, pro- 
jection room, and monitor booth. After 
rehearsals and timing, when everything 
is ready to be recorded, a signal is 
flashed in the studio that everything is 
"ready." 

Following the "ready" signal are the 
"quiet" and "begin" signals, which are 
operated by the wax machine operator. 
These electric signals must be located 
where they are visible to the camera- 
man, the projector operator, the moni- 
tor man, and those in the studio. 

At the "begin" signal both the wax 
machines and camera start turning. 
After a five-second interval allowed for 
the motors to get up to speed, the musi- 
cal director starts the orchestra. 

At a predetermined point, just before 
the speaker starts his talk, the music 
is faded down and remains very soft, or 
it is faded clear out until the speaker 



has finished, when the musical accom- 
paniment is again brought up to a cli- 
max at the end of the reel. 

Most directors prefer to have the 
first wax master played back so that 
errors can be corrected and the record- 
ing made over. At times several play- 
backs are necessary before every detail 
has been made perfect. 

Two waxes are always cut simulta- 
neously so that in case of breakage or 
damage to one there is still one to 
process without having to remake the 
recording. 

After recording, waxes are carefully 
examined with a microscope for flaws, 
and an experienced operator can tell at 
once whether or not the recording is 
good or bad, just how loud it is and 
whether the tone quality is all that it 
should be. When the recording is de- 
clared satisfactory by the monitor man, 
the musical director and the wax oper- 
ator it is safe to assume that the fin- 
ished record will be 100 per cent per- 
fect. 

A 

DR. PETER A. SNELL RECEIVES 
S. M. P. E. FELLOWSHIP 

DR. PETER A. SNELL of the Uni- 
versity of Rochester has been 
awarded the Society of Motion Picture 
Engineers' Fellowship according to an 
announcement made by the Society. The 
fellowship was made possible through a 
donation of $1,500 by the late George 
Eastman to the S. M. P. E. for estab- 
lishment and administration of the fel- 
lowship. 

Dr. Snell prepared for college at the 
Hill School, Pottstown, Pa., graduated 
from Princeton University in 1928 and 
served as assistant in biochemistry at 
Princeton University during 1929 and 
1930. He received his degree of Master 
of Arts in 1930 from Princeton Uni- 
versity and since then has continued the 
medical curriculum at the University of 
Rochester School of Medicine. In 1932 
he received his degree of Doctor of 
Philosophy from Princeton University. 
He is the author of several scientific 
papers, two of which were written in 
collaboration with Dr. E. Newton Har- 
vey. 

Dr. Snell will, within a short time, 
begin active work along lines which it 
is believed will be constructively useful 
to the motion picture field. In particu- 
lar, investigation will be made into some 
phases of production and measurement 
of the physiological processes involved 
in visual fatigue. 

"I am much impressed with the quali- 
fications of Dr. Peter Snell and feel 
that his selection for the Society of 
Motion Picture Engineers' Fellowship 
will result in valuable contribution to 
the science of motion picture engineer- 
ing," stated Dr. Alfred N. Goldsmith, 
president of the S. M. P. E. 



Page 20 



RCA Photophone 

remote 

level indicator 



THE Type PB-30 remote level in- 
dicator is a device used in conjunc- 
tion with a sound-on-film recorder 
for the purpose of visually indi- 
cating, at some point remote from the 
recorder, the volume level of sounds be- 
ing recorded. It consists essentially of 
a small recording optical system mount- 
ed in a small case of rectangular shape. 
Basically, the unit operates as does any 
photophone sound-on-film recorder ex- 
cept that the light beam is finally di- 
rected against a white screen for visual 
monitoring instead of being directed 
through an optical lens barrel assembly 
to a film. 

This remote level indicator consists of 
a lamp and socket, a condenser lens, an 
aperture plate, a "dry" galvanometer, 
two mirrors, an adjustable mirror 
mounting, a fixed mirror mounting, a 
white screen, a fixed resistor, a variable 
resistor, a base casting, a terminal block 
and a removable cover. 

The rating of the lamp is 4 volts, ^4 
ampere. The fixed resistor mentioned 
is connected in series with the lamp, and 
is of such a value that the lamp will 
draw its rated current when the termi- 
nals are connected to a 6 volt source. 
The lamp socket is adjustable so that 
the lamp filament may be readily cen- 
tered upon the optical axis of the con- 
densing lens. 

The condensing lens is located in a 
brass tube mounted between the lamp 
socket and the galvanometer, and serves 
to focus the image of the lamp filament 
upon the galvanometer mirror. In the 
brass tube with the condensing lens is 
the aperture plate, the aperture being 
rectangular in shape. 

The galvanometer is much smaller 
than the galvanometers standard with 
Types PR-3 and PR-4 recorders, and 
is similar in general construction to the 
galvanometer used in the Type PR-7 
recorder (Types PM-15 and PM-19 
newsreel equipment). The galvanome- 
ter is air damped, no oil chamber being 
used as is the case in the Types PR-3 
and PR-4 recorders. The galvanometer 
is totally inclosed in a dust-proof case. 
The light beam from the lamp reaches 
the galvanometer mirror through a 
small window containing a lens. The 
light reflected by the galvanometer mir- 
ror emerges through the same lens, but 



at an angle from the incident beam, 
and strikes the adjustable mirror. From 
the adjustable mirror the light beam 
passes to the fixed mirror and is re- 
flected to the viewing screen, upon 
which the image of the aperture is fo- 
cussed by the galvanometer lens. 

The two mirrors are used to obtain a 
long throw from the galvanometer in a 
small space, since the longer this throw 
the greater is the apparent sensitivity 
of the device due to the resulting mag- 
nification of the galvanometer deflection 
as it appears on the screen. 

The mirror is adjusted in angular 
setting by means of a worm-gear to pro- 
vide the necessary centering of the aper- 
ture image on the viewing screen. 

A hole (one inch by one-half inch) in 
the front of the cover permits observa- 
tion of the viewing screen during nor- 
mal operation. The cover also contains 
a partition which surrounds the lamp 
(except for the space between the lamp 
and the condensing lens) and prevents 
reflected light from interfering with the 
sharpness of the aperture image on the 
screen. The cover is clamped to the 
base casting by two thumb-nuts which 
must be unscrewed to permit its re- 
moval. 

A variable resistor is connected in 
series with the galvanometer coil to pro- 
vide a sensitivity or calibrating control. 
This resistor is located under the base 
casting and its shaft appears in front of 
the galvanometer in Fig. 1. 

Four terminals are provided on the 
rear of the base casting for the connec- 
tion of the lamp filament current sup- 
ply and the sound current input to the 
galvanometer. 

The overall length of the remote level 
indicator with the cover in place is 6}4 
inches, and the width and height are 
both 3^2 inches. 



PROJECTION ENGINEERING 

Electrical Connections 

The filament current supply for the 
lamp may be obtained from any source 
of 6 volts, direct current, or from any 
other direct current supply provided 
suitable resistors are connected in series 
with the line to maintain a potential of 
6 volts across the lamp terminals of the 
remote level indicator at a current of 
0.75 ampere. 

For use with the Type PA-30 ampli- 
fier the galvanometer terminals will be 
connected to the low impedance wind- 
ing of a line coupling transformer, the 
other winding of which will be connect- 
ed in parallel with the recorder across 
the 500-ohm sound output line from the 
main recording amplifier. 

For use with the Type PA-47 am- 
plifier, the same coupling transformer 
will be used, but its high impedance 
winding must be connected across the 
output of the power amplifier unit 
which supplies the sound currents to 
the monitor speaker. 

For use with the Type PA-2 ampli- 
fier and the Type PR-1 recorder no 
coupling transformer is required, the 
galvanometer of the remote level indi- 
cator will be wired in series with the 
recorder galvanometer, and the thermo- 
galvanometer volume indicator on the 
amplifier must be disconnected. In this 
case the sensitivity control is connected 
in parallel with the galvanometer in- 
stead of being in series as shown in 
Fig. 2. 

Adjustments 

Only three adjustments are required 
to place the remote level indicator in the 
proper operating condition. These ad- 
justments are very simple and once 
made require no repetition except when 
it is necessary to replace the lamp or, 
possibly, the galvanometer. Tne adjust- 
ments are : the adjustment of the lamp 
and socket, the adjustment for zero 
modulation, and the adjustment for full 
modulation of the light beam. 

Characteristics 

The resistance and frequency response 
characteristics of the galvanometer are 
very closely similar to the galvanome- 
ters used in all RCA Photophone sound- 
on-film recorders. The long throw of 
the light beam, resulting from the use 






Fig. 1. The Type 
PB-30 remote level 
indicator. Center — 
Front view with cover 
removed to show lo- 
cation of parts. Right 
— Cover of the unit 
shown in the center 
view. Left — Rear 
view showing location 
of terminals. 



GALVANOMETER 




MAY, 1932 



Page 21 



of the two mirrors and the placement of 
the viewing screen, makes it possible to 
obtain a total deflection of 0.75 inch on 
the screen with considerably less power 
than is normally required by the oil- 
damped type of recorder galvanometer 
to produce 100 per cent modulation. 

Advantages 

The Type PB-30 remote level indica- 
tor makes practicable remote monitoring 
and mixing. Its use eliminates the ne- 
cessity for the placement of the re- 
corders on the set, and they may be 
grouped and located in any convenient 
space available in the studio. This brings 
the amount of equipment required on the 
stage to the minimum of a mixing 
panel, a remote level indicator and a 
sound monitor. The remote level indi- 
cator may be mounted on the top of the 
mixer panel or in any other convenient 
location for observation. With a mixer 
panel, a remote level indicator, and a 
monitor loudspeaker only on the stage, 
a very much smaller booth may be used 
with a resulting increase in mobility and 
ease of placement. If headphone moni- 
toring is used in place of the monitor 
loudspeaker, the booth may be dispensed 
with entirely, the space on the set oc- 
cupied by the operator and equipment 
is reduced to a minimum, and the fa- 
cilities for operating under adverse con- 
ditions are greatly increased. 

Other volume indicating devices hith- 
erto used will not serve the same pur- 
pose since they indicate average values, 
rather than the instantaneous peak 
values of volume as does the Type 
PB-30 amplifier. If other devices are 
used considerable over-shooting on the 
film may result, which will not be in- 
dicated by the meter. On the other 
hand, the exact and instantaneous du- 
plication by the remote level indicator 



CONDENSING LENS- 



GALVANOMETER 



Fig. 2. Line diagram 
illustrating principle 
of operation and elec- 
trical connections of 
the Type PB-30 re- 
mote level indicator. 




QGALVQ 



LINE COUPLING 
/TRANSFORMERS-^ 



P 



'RECORDER 
GALVANOMETER 

t " 
TO LINE 

of the action of the recording gal- 
vanometer provides an accurate indica- 
tion of the volume of recorded sound at 
all times. 

(a) The recorder lamp should be ad- 
justed vertically and laterally until the 
light beam falls centrally upon the mir- 
ror of the galvanometer. The lamp may 
be adjusted vertically by loosening the 
clamping screws holding it in the socket. 
The lamp may be adjusted horizontally 
by loosening the two screws holding the 
socket to the base casting, which will 
permit the socket to be pivoted about the 
screw nearer the condensing lens sup- 
port. 

(b) The adjustment for zero modula- 
tion is made by means of the mirror ad- 
justment screw. With no sound current 
input to the galvanometer the adjustable 
mirror should be set so that the left- 



N0TE> 

WITH TYPE ?k-l AMPLIFIER RACKS 
AND TYPE PR-I RECORDERS THE 
SEN5ITIVITY CONTROL WILL 3E 
CONNECTED IN PARALLEL WITH 
THE GALVANOMETER 



II 



J 



LOCAL BATTERY 



hand margin of the aperture image will 
coincide with the center line on the 
viewing screen. 

(c) The adjustment for full modula- 
tion is made by means of the sensitivity 
control (the variable resistor). With a 
sound current input at 1,000 cycles, reg- 
ulate the volume at the amplifier to pro- 
duce full modulation of the recorder 
light beam. The aperture image on the 
viewing screen will appear to expand. 
Now adjust the sensitivity control on 
the remote level indicator until the left- 
hand margin of the aperture's vibrating 
image coincides with the left-hand mar- 
gin line on the viewing screen. 

When the above adjustments have 
been made, the remote level indi- 
cator will simultaneously duplicate the 
performance of the recording gal- 
vanometer. 



AAA 



Unif 



orm image rrame 



h 



GENERAL adoption by theatres 
throughout the United States 
and Canada during April and 
May of the new uniform image 
frame size for' motion picture projection 
machines, established by the Academy 
of Motion Picture Arts and Sciences, 
will mark one of the final steps in the 
technical transition from the silent mo- 
tion picture to the talking film. 

Improvements in the photographic 
appearance of the picture on the screen 
will result from the recommendations, 
made by the motion picture production 
industry's cooperative organization after 
two years of surveys and researches. 

Hollywood studios benefit by a simi- 
lar Academy uniform image frame size 
in use since February 15, which per- 
mits speedier cinematography and more 



flexible technique in talking picture 
making. 

Theatre managers and projectionists 
will receive through their exchanges 
detailed instruction leaflets covering the 
changeover to the new system. The 
leaflets will accompany the new picture 
releases, many of which already have 
been photographed through the new 
Academy uniform camera aperture. 

Uniformity in the size and shape of 
pictures as photographed in Hollywood 
and projected in theatres is attained by 
adoption of a uniform size for camera 
apertures and one for projectors. 

The aperture is the camera's "eye," 
its size and shape limiting the area on 
the motion picture film, which will be 
affected by light rays during the pho- 
tographing of a motion picture. Simi- 
larly the aperture in the projection ma- 



chine limits the size and shape of the 
area of the film, which is to be projected 
in greatly magnified form upon the the- 
atre screen. 

The adoption of a uniform image 
frame size will result in a closer co- 
ordination between the cameras of Hol- 
lywood and the projection equipment of 
the theatres, eliminating at one stroke 
expensive and troublesome variances in 
photographic and projection practices, 
which followed upon the coming of the 
sound device to motion pictures. 

Production and theatre companies 
adopting the Academy uniform image 
size, are : Columbia, Darmour, Educa- 
tional, Fox, Hal Roach, Metro-Gold- 
wyn-Mayer, Paramount-Publix, RKO- 
Radio, Mack Sennett, Tiffany. United 
Artists, Universal and Warner Bros.- 
First National. 



Page 22 



This thing called 
"perfect sound" f 



By Julius Weinberger^ 



\\ 



P 



ERFECT SOUND" may be 
defined : It is a natural re- 
production of the original 
speaker's or singer's voice, 
or of noises, or of orchestral music. 
If upon closing your eyes you do not 
know whether you are listening to a 
mechanical device or to the original 
rendition, that is perfect sound repro- 
duction. 

A good many persons regard mechan- 
ical sound reproducing equipment frank- 
ly as a mechanical device, and therefore 
do not expect it to simulate reality. 
The consequence of this point of view 
is that they accept distorted sound and 
sell it to themselves (and their cus- 
tomers) on the basis of artificially cre- 
ated virtues. The author has a vivid 
recollection of some of the alibis which 
were used in the early days of radio to 
excuse poor sound reproduction. When- 
ever a new line of radio sets was placed 
on the market, a lot of us would sit 
around listening to the various sets or 
loudspeakers and switch from one to 
another. None of them would be even 
approximately realistic, and then ad- 
jectives would begin to issue from the 
audience. One set was called "mel- 
low," another "brilliant," a third "soft" 
:>r "bright." All of these words merely 
meant that the sets in question were not 
reproducing naturally, and so .we ap- 
plied euphemisms to them that would 
disguise the mechanical character of the 
reproduction. 

Striving to Create Illusion 

Today we are striving to create the 
illusion of reality, and if the sound isn't 
natural, it cannot create such an illu- 
sion. The purpose of all entertainment 
is to help the auditor to forget himself 
for the moment, and to enter mentally 
into another world — the world of the 
characters of the stage or screen. The 
more perfectly we create the feeling 
that he is looking at and listening to 
real people, the better is the chance that 
Tie will lose himself in the story which 
is being played out before him, and will 
leave the theatre with the feeling that 
he has derived real enjoyment from the 

'[From the International Review of Cinema- 
tography, February, 1932. 

*En<iincer in charge of research, RCA Photo- 
phone, Inc. 



sliow. What then, are some of the ele- 
ments which are necessary in order to 
achieve this illusion in a sound picture 
presentation ? 

First, in speech reproduction the 
words should be understandable, one 
from another, and they should all sound 
like human beings. There are very 
few people whose voices sound exactly 
alike, and it is often the case that cer- 
tain types of sound apparatus may 
render the speech of the various char- 
acters in a talking picture quite intel- 
ligibly, yet with little difference between 
the voices of the various men or women 
in a picture and with voice quality that 
no human being ever possessed. This 
sort of reproduction is acceptable, but 
it is not realistic. It is also well to 
be critical in listening to speech repro- 
duction and to listen not only to the 
quality of the vowel sounds, but to 
consonants — which are the sounds that 
generally show up the defects of the 
equipment more clearly than the vowels 
and affect intelligibility to a greater 
extent. 

Music's Distinguishing Feature 

In music, the distinguishing feature of 
natural sound reproduction is the fact 
that all of the instruments in a full 
orchestra can be clearly distinguished 
one from another. In addition, there is 
a great width of tonal range, so that 
the lowest bass notes and drum beats 
can be heard as clearly and loudly as 
the highest tones of the violins. Fur- 
ther and even more important, is uni- 
formity and evenness of reproduction. 
By this is meant equal loudness of the 
various tones of the musical scale. 
Poorly designed equipments (particular- 
ly loudspeakers) are frequently marked 
by the fact that as the music goes up 
or down in pitch, certain tones will 
stand forth violently while others can 
scarcely be heard. This difficulty is due 
to what are called "resonance peaks" 
in the loudspeakers. 

In addition to the general character- 
istics outlined there is a characteristic 
which is common to both speech and 
music, and that is smoothness of in- 
dividual speech sounds or musical tones. 
By this is meant freedom from tremolos 
or additional fuzzy, raspy or other types 



PROJECTION ENGINEERING 

of harsh noises, accompanying the words 
or music. 

In attempting to attain the type of re- 
production referred to, RCA Photo- 
phone engineers have used a number of 
expedients in reproducing and recording 
apparatus which are given here : 

Complete naturalness of reproduction 
requires that all equipment be capable of 
recording and reproducing a very con- 
siderable percentage of all sounds which 
the human ear can hear from the low- 
est to the highest tones. The extent to 
which this is done is called the fre- 
quency range of the equipment. It is 
not particularly easy to accomplish this 
and it is especially difficult in the case 
of the microphones used in picking up 
sound on the motion picture stage and 
the loudspeakers used in the theatre. 

Sound Vibrations 

Theoretically the human ear can hear 
sounds having a pitch from about 32 
to 20,000 vibrations per second. How- 
ever, it has been found by experience 
that sound apparatus which covers the 
range from about 60 to 8,000 vibrations 
per second will deliver a very acceptable 
and almost natural result. Certain types 
of equipment reproduce practically noth- 
ing below 300 or above 4,500 vibrations 
per second. When reproduction from 
such equipment is compared with that 
from one which transmits the range 60- 
8,000 (such as the RCA Photophone 
Type PG-30 equipment, used with the 
50-inch directional baffle), there is a 
startling difference in naturalness and 
clarity. Other limited range equipment 
may reproduce speech intelligibly, but 
it does not sound natural. On music, it 
sounds like a phonograph. When repro- 
ducing a full orchestra, it is clearly 
mechanical reproduction instead of nat- 
ural reproduction. 

In RCA Photophone recording equip- 
ment, wide frequency range is secured 
by using the newly developed ribbon 
microphone, carefully designed ampli- 
fiers, and recorders capable of making 
accurate records up to 10,000 vibrations 
per second. 

In RCA Photophone reproducing 
equipment, wide frequency range is se- 
cured by carefully designed optical sys- 
tems in the sound head, amplifiers which 
are practically the last word in ampli- 
fier design, and loudspeakers which rep- 
resent several years of intensive re- 
search effort. In connection with the 
last named, it may be said that they 
reproduce the widest and most uniform 
frequency range that has been obtained 
by a mechanical device. 

The second important element in 
sound reproduction, namely, smooth- 
ness, is obtained largely by careful at- 
tention to the devices which move the 
film in the recorder or reproducer. If 
the film travels with perfectly uniform 



MAY, 1932 

speed, there will be no gurgles, wows, 
fuzz or rasp in the sound reproduction. 
However, to attain this uniformity of 
speed, careful attention to details is nec- 
essary. 

No Speed Fluctuations 

In the RCA Photophone system, the 
sound is recorded on the film as it 
travels across a rotating drum. This 
drum is driven by means of a magnetic 
system and rotates with such extreme 
constancy that no speed fluctuation can 
be observed by the most searching in- 
spection of the original records. Usually 
if there is any speed fluctuation, it oc- 
curs in the reproducing apparatus. 
Here, sound is reproduced by pulling 
the sound track on the film past an op- 
tical system which throws a thin beam 
of light on the film. Film must neces- 
sarily be pulled by means of a sprocket 
as is common in all motion picture ap- 
paratus and the sprocket itself must be 
driven at a very constant speed. In the 
most recent types of RCA Photophone 
equipment, this result is attained by 
placing an extremely heavy flywheel 
on the film pulling sprocket shaft and 
driving this flywheel by means of three 
belts from a large and powerful motor. 
Small speed irregularities due to the 
belts or other causes tend to be smoothed 
out by the heavy flywheel. However, 
a_ sprocket will not pull film with ab- 
solute uniformity sinch as each sprocket 
tooth enters the sprocket holes on the 
film it gives the film a minute jerk. In 
RCA Photophone equipment these jerks 
are ironed out by passing the film over 
an auxiliary roller (known as the impe- 
dance roller) which has a small flywheel 
on its shaft, and which is placed be- 
tween the film pulling sprocket and 
sound gate. This roller tends to smooth 
out the impulses which the sprocket 
would otherwise impart to the film. 

The capabilities of sound reproduc- 
ing equipment may be judged by these 
qualities ; 

On speech reproduction, intelligi- 
bility of the words spoken by the char- 
acters and ability to distinguish one 
character from another with the eyes 
closed. In addition, the illusion of lis- 
tening to an actual person speaking 
from the position of the screen, should 
be present. There should be complete 
freedom from boomy quality in the male 
voices, and harshness or stridency in 
the women's voices, and there should 
be no gurgles, wows, rasp or fuzziness 
accompanying any of the voices. 

In musical reproduction, the follow- 
ing should be observed : 

The ability of the equipment to re- 
produce various musical instruments so 
that they sound like the original to a 
trained musician. In orchestral repro- 
duction, it should be possible to pick out 
individual instruments readily when the 
entire orchestra is playing and there 



should be equal and uniform loudness of 
the bass as well as the higher pitched 
instruments. In other words, the repro- 
duction should sound like an orchestra 
and not like canned music. Further- 
more, solo instruments or the voices of 
singers when traversing a series of 
notes, should sound equally loud on all 
tones. There should be no wide fluctua- 
tions in loudness or tone quality from 
one note to the next. 

Obviously, the last word has not been 
said in the creation of sound reproduc- 
tion which fulfills completely the re- 
quirement of perfect illusion. There are 
still many elements in the situation 
which require research on the part of 
engineers and education on the part of 
exhibitors. 



RESISTANCE IN SERIES 

Rt = R! + R2 + R3 etc. 

If the resistances are all of the same 
value, the total resistance will be equal 
to the resistance of one multiplied by 
the number connected in series. 



ADDITIONAL TECHNICAL EXAMI- 
NATION QUESTIONS FOR 
PROJECTIONISTS 

Herewith are presented eleven addi- 
tional technical questions for ambitious 
projectionists to study. These are ques- 
tions Nos. 58 to 68 of the series being 
presented monthly in Projection En- 
gineering. 

58. What would happen if vibrations 
from a projector were passed to the 
photoelectric cell? 

59. If the filament in an exciter lamp 
sags what would be the result ? 

60. How would you find a burned out 
tube if a number of them were con- 
nected in series ? 

61. Are amplifying tubes connected in 
parallel or in series ? 

62. How many voltages are supplied 
to the grid of the amplifying tube? 

63. What would happen if the open- 
ing in the photoelectric cell was out of 
line with the opening leading to the film 
compartment ? What would you do to 
rectify this ? 

64. In connecting amplifying tubes in 
series, where would the wire from the 
plate output of the first tube be con- 
nected ? 

65. What might happen if the photo- 
electric cell becomes turned in its hold- 
er so that half the window or opening 
in the cell is covered ? 

66. What type of photoelectric cell 
is used in RCA Photophone ? 

67. What would be the effect should 
the photoelectric cell not receive a suffi- 
cient potential ? 

68. What would be the effect on the 
cell if it were supplied with an excessive 
voltage ? 



Page 23 

MICROPHONE CIRCUITS 

IN Fig. 1, herewith is shown in detail 
the makeup of a carbon microphone 
(transmitter), and its associated 
wiring. The circuit principles here 
presented are easy to understand. 
In Fig. 2, the circuit extensions in- 



CARBON GRANULES 



DIAPHRAGM 




CONNECTING 
WIRES 



MICROPHONE 
TRANSFORMER 



II- 



• BATTERY 



TRANSMITTER 



Fig. 1. Simple sketch of a single-button carbon 
microphone and schematic of connections. 

eluding transmitter, its battery, trans- 
former and output to an amplifier tube, 
are shown as actually employed in pub- 
lic-address work. 



TRANSMITTER 



POTENTIOMETER 




MICROPHONE 
TRANSFORMER"' 



Fig. 



2. Schematic of. double-button 
carbon microphone. 



NEW VARIABLE FOCUS LENS 

A paper presented at the Washington 
meeting of the S.M.P.E., May 10. by 
A. Warmisham and R. F. Mitchell, of 
the Bell and Howell Company, des- 
cribes a variable magnification lens of 
new and outstanding design. The Yarn 
is a "zoom" type lens introducing the 
conception of a variable three-element 
system in place of the two-element vari- 
able telephoto system previously used 
for this type of work. 

A summary of the optical problem in- 
volved is presented and a description ot 
the lens showing how the mechanical 
design has been fitted to the optical 
specifications is given. 

A discussion of the relation of the 
rate of "zoom" to the loss in definition 
is also given. 



Page 24 



Answers to 
technical questions 

T 



HE following are the answers 
to technical questions Nos. 49 to 
57, published in the April is- 
sue of Projection Engineering : 



49. These batteries should not be con- 
nected into the circuit, just after receiv- 
ing a charge, or while gassing. They 
should be left for at least thirty minutes 
after taking off the charging table be- 
fore being connected into the circuit. 
The battery terminals should be kept 
clean and greased with a little vaseline. 
Connections should be tight and clean. 
The tops of batteries should be kept dry 
and clean. 

50. One complete set of the changes 
of a wave (or other periodic phenome- 
non), as from crest to trough and back 
to crest again, may ±eter to waves of 
sound, or alternating current, or any 
other waves or vibrations. Always 
relative to a second of time ; thu? 
"cycles" means 60 cycles per second. 

51. No, while all photoelectric cells 
operate practically the same, the cells 
used by each system are of different 
construction and have different ratings. 

52. No. In this respect it differs 
from the WE system. 

53. A potentiometer connected be- 
tween the photoelectric cells of two pro- 
jectors and the vacuum tube amplifiers 
employed to change over from one 
machine to the other at the end of a 
reel. It is sometimes connected as an 
interstage coupling within the ampli- 
fier systems, and in some cases it is 
also used as a volume control. A vari- 
able resistor. 

54. 500 ohms. 



55. This is a frequency higher in 
number of oscillations than audio fre- 
quency but lower than radio frequency. 
It is generally around 30,000 cycles 
or 10,000 meters wavelength. In the 
superheterodyne the incoming signal 
is converted from the broadcast fre- 
quency to the so-called intermediate fre- 
quency at which it can be amplified by 
means of fixed winding transformers to 
alm-vst any extent desired. The method 
of converting the incoming signal in a 
superheterodyne from radio frequency 
to intermediate frequency is by the beat 
method. In this case an oscillating cir- 
cuit controlled by means of a variable 
condenser so as to obtain any desired 
frequency, is brought into interference 
with the first detector and produces a 
beat note for the intermediate frequency 
which has all the characteristics of the 
original signal. In this way, no matter 
what the frequency of the intercepted 
signal may be, the intermediate fre- 
quency amplification is always carried 
on at a fixed wavelength, thus making 
for high efficiency. 

56. After passing through the input 
panel the signal enters the voltage am- 
plifier and passes through three stages 
of amplification. The signal from the 
projector first passes through a trans- 
former similar to that in the projector 
itself and this transformer applies the 
signal to the grid of the first tube. This 
tube is coupled to the second tube by a 
step-up transformer. The first and third 
stages use UX-210 Radiotrons and the 
second stage uses a UX-841 Radiotron. 
Grid bias voltage is supplied by dry bat- 
teries and plate voltage is supplied by 



PROJECTION ENGINEERING 

a 500-volt tap on the 1,000-volt genera- 
tor. The plate circuit of each tube is 
designed with a filter arrangement 
which prevents objectionable hum from 
the generator being heard in the loud- 
speakers. Jacks are provided for read- 
ing the plate current of each tube and 
for reading the bias voltage. The gain 
control mentioned above regulates the 
volume to any desired level. 

57. A mechanical impedance or a 
combination of mechanical impedances 
so designed as to pass or suppress 
mechanical vibrations of certain fre- 
quencies. 

When projecting a motion picture the 
film is advanced intermittently at the 
rate of sixteen frames per second, each 
frame being stationary for the brief in- 
stant during which light is passing 
through it to the screen. Obviously, 
then, the synchronized picture and sound 
record can not be adjacent on the film. 
In practice they are spaced about fif- 
teen inches apart along the film, there- 
by allowing for a "loop" to take up the 
intermittent slack between them. Me- 
chanical filters are used in the drive 
to insure an extreme uniformity of mo- 
tion past the photoelectric cell slit. 

The electrical impulses obtained from 
the photoelectric cell are extremely 
small in amplitude. A two-stage resist- 
ance-coupled amplifier is ordinarily 
necessary to bring them up to an en- 
ergy level comparable with that ob- 
tained directly from the electromag- 
netic pickup used in the disc method 
of reproducing. On account of the 
high impedance of the photoelectric 
cell circuit, it is desirable to build this 
amplifier into the same container which 
holds the photoelectric cell. The output 
of the amplifier, at low impedance, is 
then carried to the fader and, from this 
point on, the same speech amplifying 
system used with the disc method is em- 
ployed. Likewise, the same technique 
of fader operation monitoring, and con- 
trol of the output panel. 



FOX ELECTS KENT AS PRESIDENT 

SIDNEY R. KENT, executive vice- 
president of Fox Film and until 
two months ago holder of the same of- 
fice with the Paramount Publix Cor- 
poration, was elected president of Fox 
Film Corporation at a meeting of di- 
rectors on April 19. Edward R. Tin- 
ker, president of Interstate Equities 
Corporation and hitherto president of 
Fox Film Corporation, was made chair- 
man of the board. 

Harley L. Clarke, head of the Utili- 
ties Power and Light Corporation of 
Chicago and of General Theatres 
Equipment, Inc., was re-elected a di- 
rector but was not re-elected to the of- 



fice of chairman of the board, which, 
with the presidency, he has held since 
he took control of Fox Film. Because 
of his dominating influence in General 
Theatres, Mr. Clarke has been regard- 
ed as the controlling personality in Fox 
Film since William Fox sold out his 
interest in the company. 
▲ 
AYLESWORTH TO R.K.O. 

M. H. Aylesworth, for the past five 
years president of the National Broad- 
casting Company, is reported to have 
been appointed president of RKO, suc- 
ceeding Hiram S. Brown. For the pres- 
ent also Mr. Aylesworth will continue 
as president of N. B. C. Prior to be- 



coming president of N.B.C. Mr. Ayles- 
worth was for several years an official 
of the National Electric Light Associa- 
tion. 

▲ 
UNIVERSAL PICTURES REPORT 

Universal Pictures and subsidiaries 
report net profit of $181,557 after all 
charges for the three months ended Jan- 
uary 30, the first quarter of the fiscal 
year. Had inventories of released films 
at the beginning of the first quarter of 
1931 been valued on the same basis as 
were the released inventories at the be- 
ginning and end of this first quarter 
profit ior the first quarter of 1931 
would have been $90,432. 



MAY, 1932 



Page 25 



Rockefeller Center 
theatres 



THE most complete system of sound 
reproducing and amplifying equip- 
ment ever designed for a theatre 
will be installed in the new Sound 
Motion Picture Theatre, between 48th 
and 49th Streets, in Rockefeller Center, 
New York, according to an announce- 
ment by Metropolitan Square Corpora- 
tion, holding company for John D. 
Rockefeller, Jr. The contract for this 
equipment has been awarded to the 
Photophone Division of the R. C. A. 
Victor Company, according to the an- 
nouncement. 

The steel work for this new theatre, 
which will seat 3,500 persons, is now 
being erected. The theatre will open 
next autumn. It will be operated by 
the Radio-Keith-Orpheum Corporation 
under the direction of S. L. Rothafel 
("Roxy"), as will the International 
Music Hall, in the north block. 

Four standard size Photophone re- 
producing units, an 80-watt double 
channel amplifier in the projection 
booth, and four 50-inch loudspeakers on 
the stage will be used in connection with 
the reproduction of sound motion pic- 
tures in this theatre. In addition, there 
will be a public-address system with 
twenty-five microphones, to reinforce 
the stage productions. 

Unusual features of the installation 
include a rehearsal system for use in 
connection with the direction of pro- 
ductions; a stage manager's call system 
and fifty-two "Acousticon" seat phones, 
attached to selected seats for the bene- 
fit of the hard of hearing. Complete 
radio and phonograph equipment in the 



projection booth will make it possible to 
transmit radio or phonograph programs 
to the audience at any time. 

The rehearsal system is said to be the 
latest development of its kind. With it, 
the stage director, carrying a micro- 
phone, may conduct his rehearsals from 
any position in the auditorium of the 
theatre, through the medium of loud- 
speakers on the stage. 

The stage manager's call system is 
another innovation. It enables the stage 
manager to communicate with any part 
of the theatre through a microphone on 
his desk. 

The "Acousticon" seat phones should 
prove a great boon to theatre patrons 
who through partial loss of hearing have 
been unable, heretofore, to fully enjoy 
the sound motion pictures. 

Air Conditioning 

Each patron of the two theatres un- 
der construction in Rockefeller Center 
will be allotted 40 cubic feet of condi- 
tioned air a minute. Contracts for air 
conditioning systems in both buildings 
have just been awarded to the Carrier 
Engineering Corporation of Newark, 
New Jersey. 

On the hottest day in summer, the 
theatre temperature will be reduced suf- 
ficiently below the temperature out of 
doors to promote comfort without over- 
refrigeration, and the humidity will be 
maintained within a range of from 40 to 
55 per cent. 

Throughout the year, the "weather" 
in the theatres will be made to order and 
will conform with the ideal climatic con- 
ditions as established by the Harvard 
▲ ▲ A 



School of Public Health and the Ameri- 
can Society of Heating and Ventilating 
Engineers. Thermostatic and hygro- 
static controls will operate automatically 
to maintain atmospheric conditions 
within the so-called "comfort zone." 
Every cubic foot of air going into the 
theatres will first be filtered and washed. 
The air conditioning engineers state 
that it will attain better than 96 per cent, 
freedom from dust, ' dirt and other 
molecular organisms. 

The larger of the theatres, known as 
the International Music Hall, will seat 
more than 6,000 persons and will use 
nine tons of conditioned air per minute. 
This is equivalent to 241,890 cubic feet, 
or 40 cubic feet of air a person. Nor- 
mal requirements are 30 cubic feet a 
person. Three huge centrifugal refrig- 
erating machines — the latest scientific 
development in refrigeration — with a 
capacity of 600 tons of melting ice per 
24 hours, will form the basis of the 
weather-making system. In terms of ice 
poundage, they represent the summer 
day requirements of a city of 150,000 
people. Other equipment includes three 
huge air conditioning machines in which 
the air is washed and its temperature 
and humidity fixed. 

The Sound Motion Picture Theatre 
in the south block will have seating ca- 
pacity of 3,500, and will be supplied 
with five tons of conditioned air per 
minute. It also will be equipped with 
three air conditioning and three cen- 
trifugal refrigerating machines, with a 
capacity of 325 tons of melting ice a 
day. 

An ingenious method of distributing 
the air evenly throughout the audience 
has been worked out by the engineers. 
The inlets are to be in the dome and 
ceilings, and the volume of each so con- 
trolled that an "ethereal climatic blan- 
ket" will be falling uniformly over the 
audience. After performing its service 
it is withdrawn through floor outlets. 



Paramount and Block Booking 



THE Court of Appeals for the 
Second Circuit, on April 4, de- 
nied the Federal Trade Com- 
mission's application for en- 
forcement of Paragraph 2 of its order, 
relating to the practice of "block-book- 
ing." In its opinion, the Court (speak- 
ing through Judge Manton), said: 

"There is free competition among 
producers and distributors for the dis- 
tribution and marketing of their pic- 
tures. There is a lack of monopoliza- 
tion by the respondent and, in fact, lack 
of ability to achieve a monopoly and, 
therefore, not a business operation 
which would unduly hinder competitors. 
*****The respondent's sales methods 



have not been shown to have any effect 
upon its competitors — the small produc- 
ers — when the whole field is surveyed, 
and it is impossible to say on the evi- 
dence that the effect of block-booking 
as practiced by the respondent, or its 
accumulative effect as practiced inde- 
pendently by the respondent and others, 
has unfairly affected competition. On 
the other hand, it may fairly be said 
that all persons engaged in the produc- 
tion of pictures have been able success- 
fully to distribute their product. This 
has permitted fair competition in the 
industry.****The respondent has law- 
fully exercised its right to sell its prod- 
uct to the best advantages and in such 
quantities and to such persons as it 



chooses. ****The means and methods 
employed in marketing its leases of films 
to prospective customers are matters 
within the business judgment of a pri- 
vate producer of films and carries with 
it the legal right to bargain and nego- 
tiate as the respondent did. The 
method of negotiation which has been 
condemned by the Commission, does not 
disclose a dangerous tendency unlaw- 
fully to hinder competition, nor does 
it create a monopoly. The findings are 
insufficient in law to support the con- 
clusions of fact reached and therefore 
the petition to enforce Paragraph 2 
of the order to cease and desist must 
be denied." 

The case was argued March 9 last. 



Page 26 



PROJECTION ENGINEERING 



New Developments 



nd 



News of the Industry 



NEW RECTIFIER SUPPLIES CURRENT FOR 
2 MACHINES 

A current rectifier known as the M.P. 
25-25 model that is said to meet the de- 
mand for a single unit in supplying direct 
current for two projectors, and which 
furnishes 15 to 25 amperes to either pro- 
jector continuously, is being marketed by 
the Forest Electric Corp. of Newark, N. J. 

The device, it is declared, embodies the 
use of four rectifier tubes which are con- 
nected to supply current to two direct- 
current circuits independently of each 
other, thus preventing loss of current at 
the first arc when the second arc is struck. 

Both arcs can be operated at the same 
time during the change-over period and 
there will be no diminishing of the light 
from one projector while lighting up the 
second, the company claims. 

A model M.P., 15 for use with one 
projector in smaller houses, schools, 
churches, and small auditoriums where a 
maximum current of 15 amperes is suf- 
ficient, is also being offered by the com- 
pany. 

TYPE 96A MIXER 

Type 96A mixer is designed primarily 
for a 19-inch relay rack. It is nineteen 
by twelve by six inches in size and fin- 
ished in satin. It uses a standard four 
channel parallel mixing circuit incorporat- 
ing modified "T" mixing controls, micro- 
phone current control for carbon type 
microphones, carbon microphone test jacks 
and current switch, as well as individual 
channel selector. 

The entire assembly is standardized at a 




200 ohm input and output impedance and 
is designed for operation with broadcast 
station, public-address and recording am- 
plifying systems. This unit is manufac- 
tured by the Gates Radio & Supply Com- 
pany, Quincy, Illinois. 



THEATRE APPARATUS 

What is considered to be one of the 
most comprehensive, and yet most con- 
densed catalogues which has been pub- 
lished to the trade, is now being distrib- 
uted by the S. O. S. Corp., 1600 Broadway, 
New York City. This is the new catalogue 
No. 10. 

This catalogue is somewhat unique, as 
considerable space has been given to de- 
scriptions of rebuilt and reconditioned ap- 



paratus, which is dealt in almost exclu- 
sively by the salvage department of this 
company. In their own words, "In these 
troubled times, with wholesale theatre clos- 
ings, many splendid values have been made 
available, which at a mere fraction of the 
original cost, have years of trouble-free 
service left. Among these are amplifiers, 
automatic arc lamps, chairs, lenses, motor 
generators, rectifiers, recording systems, 
projectors, ticket registers, portable sound 
systems, etc." 

Every page is illustrated, with highly 
descriptive text, separate sections being 
devoted to sound equipment, projection 
machines, lighting apparatus, lobby dis- 
plays, portable talkie apparatus, 16 mm. 
equipment, and recording systems. 

The catalogue is in colors, and is a dis- 
tinct addition to the many valuable and 
instructive booklets which have been is- 
sued by the trade's leading factors. You 
may secure a copy of Catalogue No. 9 free 
of charge. 



OUTLET PLUGS INDIVIDUALLY FUSED 

The Elmenco fused plug, the newest de- 
velopment in attachment plugs, is an im- 
provement that is so obvious that one 
wonders why it was not made long ago. 

This plug, made in both single attach- 
ment style and three-way multiple style, 
fills the demand for a safe plug. 

Its virtue lies in the fact that it is self- 
fused. Two small fuses are inserted in 
the plug and these fuses prevent any wire 
trouble getting beyond its point of origin. 

It localizes trouble, removes fire hazard 
and avoids the possibility of all lights out. 
When trouble develops, the fuse in the 
plug will blow, affecting the individual 
lamp or accessory only. The main fuses 
are unaffected, protected by the fused plug. 

Fuse elements which have blown are 
easily removed— simply by pushing them 
out with a match. 

These modern plugs are being marketed 
by the Electro-Motive Engineering Cor- 
poration, 797 East 140th St., New York 
City. 

A 

PORTABLE ARC LAMP 

Proof that there is a ready market and 
quick sale today for any product which 
fills a definite need is to be had in the 
instant acceptance by the industry of the 
new Strong portable type reflector arc 
lamp, produced by the Strong Electric 
Corporation, of Toledo, Ohio. 

Designed for the projection of 35 or 16 
mm. film, the lamp was highlv appre- 
ciated by those using pictures, " and es- 
pecially talking pictures, in sales and ad- 
vertising programs and demonstrations in 
schools, colleges, public auditoriums, and 
similar places. 

It produces a brilliantly illuminated pic- 
ture as large as 8 to 12 feet wide, even 
on porous screens. This permits more de- 
sirable sized screens and the proper plac- 
ing of the reproducing equipment. 

It is easily operated from any lamp 



socket with current from 8 to 16 amps. 
The weight is less than 25 pounds, with 
overall size 18 inches by 12 inches by 
10 inches. 



A PUBLIC-ADDRESS MIKE 

The Mayo Instrument Corporation, 281 
East 137th St., New York, announces a 
new microphone for public-address work. 
This mike uses the new ground center, 




heat treated, duraluminum diaphragm for 

sensitivity. 

A 

SUPER-INTENSITY LAMP 
The new H.C. 10 super-intensity lamp, 
introduced by Hall and Connolly, combines 
maximum efficiency with ease and conveni- 
ence of operation for the projectionist. 

Salient features of this new H. C. 10 
lamp are : 

1. A lamphouse shape which provides a 
special compartment for the arc, from 
which all gases are exhausted directly. The 
entire burner and controller is combined in 
one unit that slides easily in and out of 
the lamphouse on tracks. This feature 
facilitates inspection and cleaning. 

2. An effective air-cooling system which 
insures a supply of air which is blown 
from the back of the lamp by a special 
propeller-type fan. 

3. The H. C. 10 takes a full 22-inch car- 
bon trim at one setting with a very mini- 
mum wastage of carbon. 

5. An automatic arc striker, or "self- 
starting" arc, with positive assurance of 
not breaking the positive crater. 
_ 6. Automatic focusing system that posi- 
tively maintains the distance from the posi- 
tive crater to the face of the rear con- 
denser within 1 /64th of an inch at all times. 
This result is attained through a unique 
method whereby an image of the arc con- 
trols the feeding of the positive carbon. 

7. Extreme simplicity in design and 
operation of the mechanism. No lubrication 
is required. The mechanism is equipped 
throughout with ball and roller bearings 
and self-lubricating bushings. 

8. Up-to-the-minute indicators : a Wes- 
ton ammeter is standard equipment on the 
back of the lamphouse. A unique carbon 
trim indicator which tells the projectionist 
at a glance just how many inches of trim 
are left in the lamp. 

9. A neutralized arc : a device for 
neutralizing the stray fields around the arc, 
thus steadying the arc and insuring a 
cleaner, clearer field at all times. 

10. Any standard condensers can be 
used with this lamp, in addition to the 
new Bausch & Lomb parabolic cylindrical 
set-up in both the 6-inch and 7-inch sizes. 



MAY, 1932 



Page 27 



BLOCK UT SO UND FILM SPLICES 
THIS EASY, EFFECTIVE WAY 

PLACE the film on a special registration block. Coat the film ends, 
and an Eastman Sound Film Patch, with cement. Apply the patch 
to the joint. Then pull off the finger tab by which you have been 
handling the patch . . . and the job is done. 

Eastman Sound Film Patches, specially designed and made of opaque 
film, are simple and clean to apply. They obscure a minimum of the 
sound track and are practically inaudible in projection. Together with 
the registration block, they constitute a valuable and unique feature 
of Eastman service. 

Eastman Sound Film Patches, per thousand $S.OO 

Eastman Sound Film Patcher (registration block) 4.25 

Eastman Kodak Company 

J. E. Brulatour, Inc., Distributors 
New York Chicago Hollywood 



NO MORE 

CELL 

WORRIES 




/ 

tele'photo 

PHOTOELECTRIC CELLS 



A high degree of sensitivity coupled with long life 
distinguishes Telephoto (Caesium Argon) cells. The 
increased sensitivity reduces the amount of ampli- 
fication required for tonal reproduction, obviating 
to a remarkable extent the possibility of distortion. 
An ultimate present-day perfection is assured by the 
painstaking supervision these cells are subject to in 
each detail of their manufacture. 

PAMPHLET ON REQUEST 

TELEPHOTO & TELEVISION CORP. 

1 33-1 35 West 1 9th Street New York 




RTIC 

CONDENSER 
MICROPHONE 



The RTIC Condenser Microphone incorporates all the 
advantages of this type without the usual drawbacks. 

1. Dessicator makes the microphone impervious 
to humidity. 

2. Acoustic valve eliminates all effect from 
temperature and pressure. 

3. Only Condenser Microphone on the market 
interchangeable with usual two-button carbon 
mike. 

4. Globular housing of mike and amplifier acous- 
tically streamlined with parts easily accessible. 

WRITE for descriptive bulletin giving full details of this 
and other RTIC Microphones. 

RADIO TELEVISION INDUSTRIES CORP. 

Dept. AP-3 
1 30 West 42nd Street New York City 




Page 28 

MAZDA PHOTOFLOOD LAMP 

The Westinghouse Lamp Company, 150 
Broadway, New York City, announces a 
Mazda photoflood lamp. It has an A-21 
inside frosted bulb, an overall length of 
9 15/16 inches, a medium screw base, and 
is designed for 105 to 125 volt service. 

The Mazda photoflood lamp is particu- 
larly suited as a companion lamp to the 
photoflash lamp for taking still pictures 
and is a convenient and powerful light 
source for taking home movies. It can 
be placed in any house lighting socket or 
fixture, the lamp shades acting as re- 
flectors, but for best results photographic 
reflector equipment is recommended. 

Due to a high operating temperature 
of the filament, the Mazda photoflood lamp 
has a short life, averaging 120 minutes 
at 115 volts. But since it is needed for 
only a minute or two on each subject, it 
can be used for many pictures. Approxi- 
mately 3,000 feet of 16 mm. motion pic- 
tures at normal speed can be made, dur- 
ing the life of one lamp. 



SELLING ON SOUND 

"Sells on Sight." The glowing testimo- 
nial of the enthusiastic salesman has not 
always been without merit. 

"Sells on Sound" has actually been 
demonstrated in exploiting the new Ford 
by sound. Recently a portable Mellaphone 
sound outfit was installed in the show- 
rooms of the Genesee Motor Co., at 
Rochester, N. Y., to announce the outstand- 
ing features of this new car. Over 3,000 
interested prospects who inspected this new 
car the first day listened to the "sales 
talk" simultaneously. Sound seemed to come, 
clearly and distinctly, from an invisible 
salesman. 

Numbers of inquiries were made re- 
garding the promotion stunt. Eleven Mel- 
laphone outfits were ordered by Ford and 
competing dealers the first day. A num- 
ber of dealers featured music reproduc- 
tion by record, at intermittent periods. 

Exhibitors were first to demonstrate the 
possibilities of exploiting by sound. 



MOVIES TEACH GOLF COURSE 
MAINTENANCE 

According to Golfdom Magazine, the 
Midwest Greenkeepers' Association has 
produced a two-reel motion picture on 
golf course maintenance methods . which 
will be loaned to other organizations of 
greenkeepers or to golf clubs, without 
charge, as part of the Midwest's educa- 
tional program. 

The film, which was made with a Filmo 
movie camera, is called "Divots from a 
Greenkeeper's Day" and shows the extent 
and character of work carried on in main- 
taining a metropolitan district golf course. 
We understand that greenkeepers' organ- 
izations or golf clubs can secure prints 
of the film by presenting requests to R. N. 
Johnson, President, Midwest Greenkeepers' 
Association, Medinah Country Club, Me- 
dinah, Illinois. 




ing this unit, special care was taken to 
make it simple to operate. 

In recording, all that is necessary is to 
move the arm to the center of the record 
and throw the lifting lever to the down 
position. This immediately starts the 
recorder, which evenly grooves the record. 
The number of 96 grooves per inch has 




been accomplished in this outfit and the 
recording plays as long as a standard 
phonograph record. 

This recorder does not require a power- 
ful set or power amplifier for recording, 
as normal, small room volume is all that 
is necessary. The recorder grooves its own 
records as blank records remove all sem- 
blance of background noise. 

A diamond needle is used for recording, 
as it is long-lived and the ideal cutting 
needle. 

In utilizing this recorder a good phono- 



PROJECTION ENGINEERING 

graph motor is the only requisite. Records 
from 5 inches to 12 inches may be made 
at either 78 or 33 1/3 r.p.m. A 16 inch 
arm is available at a slightly higher price. 
Recordings are made on aluminum discs. 
A new process is now available which en- 
ables the treating of aluminum discs to be 
used with steel needles : length 9 l / 2 inches, 
height 3Yz inches, depth 5 inches. 



SOUND EQUIPMENT CATALOG 

The Rocke International Electric Corp. 
announces the publication of its new cata- 
logs prepared especially for the export 
trade, which will be classified as follows : 

(A) Sound equipment for theatres. (B) 
Portable sound equipment. 

Items of manufacturers such as the 
Webster Electric Company, of Racine; 
the G-M Laboratories, Inc., of Chicago, 
manufacturers of the famous Visitron 
photoelectric cells ; the Weber Machine 
Corp., of Rochester, manufacturers oi 
Weber sound heads, are featured in the 
theatre sound catalog. 

Copies of the catalog will be forwarded 
to those wr'ting on company letterhead. 
Address Rocke International Electric 
Corpn., 15 Laight St., New York. 



PROTECTION FOR METERS 

Tl:e Littelfuse Laboratories, Wilson St., 
and Ravenswood Ave., Chicago, Ills., have 
published a booklet entitled: "Littelfuse 
Goes To Hollywood." The publication 
describes the utility of fuse protection for 
electric measuring instrument circuits. 



AAA 

50- WATT AMPLIFIER TUBE marketed by the Wakefield Television and 

A new 50-watt tube for service as oscil- Radio Corpn., 27 Hoyt St., Newark, N. J. 
lator amplifier and modulator is being Its characteristics are: 

Filament voltage 10 volts 

Filament current 3.25 amperes 

*Plate current 72 milliamperes 

*Plate resistance 3400 ohms 

*Transconductance 3530 micromhos 

Amplification factor 12 

Plate to grid capacitance 15 mmfd. 

Input capacitance 8 mmfd. 

Output capacitance 7 mmfd. 



Maximum operating plate voltage (d.-c.) . . 

Modulated d.-c. plate voltage 

Non-modulated d.-c. plate voltage 

A.-C. plate voltage (r.m.s.) 

Plate current (d.-c.) 

Maximum plate dissipation 

Plate dissipation 

Maximum r.-f. grid current 

Peak grid swing 

Load impedance 

Undistorted power output 

Modulation factor 

Oscillator input watts per modulator tube. 



Oscillator 


A.-F. Power 


Modulator 


and R.-F. 


Amplifier 




Power Amp. 








1250 volts 


1250 volts 


1000 volts 






1250 volts 






1500 volts 






175 m.a. (max 


) *72 m.a. 


**20 m.a. 


100 watts 


75 watts 


75 watts 




*72 watts 


**20 watts 


7.5 amps. 








*55 volts 


**70 volts 




*6000 ohms 






*10 watts 


**.6 
**4S . 






A NEW DISC RECORDER 

Federated Purchaser, 23-25 Park Place, 
New York, announce a practical home 
recording device. 

The unit is being used at present for 
the recording of auditions made by com- 
ing _ radio stars in a number of the 
nation's most popular broadcasting sta- 
tions. The outfit is low priced and well 
within the range of everyone. In develop- 



*At 1000 volts plate potential and — 55 volts grid bias. 
**At 1000 volts plate potential and —70 volts grid bias. 

Note : The values of grid voltage given above refer to the midpoint of the filament. 

The Type 211 is equivalent to and interchangeable with Navy Type 1818-A, Army 
Type VTA, and Type 511. 

The Type 211-E is equivalent to and interchangeable -with WE-211-E and should 
be only used as an audio-frequency amplifier. 



MAY, 1932 



Page 29 



Logical . Simple . Low Priced . As Good as 

the Best. It's HERE TO STAY! 

ICED/WRE 

SYSTEM OF REFRIGERATING 
AND AIR CONDITIONING 

Use Ice From Your Neighborhood Dealer! 

TYPHOON AIR CONDITIONING CO., INC. m Vwyork eet 




IN CHICAGO 



World's 

Tallest Hotel 

46 Stories High 




LEONARD HICKS 
Managing Director 



"11 1 1 1 riFimfiTmffliTTTn itTTTTTin 



The extra attention given to the needs of guests will 
favorably impress you. Nearest to stores, offices, thea- 
tres and railroad stations. A special floor is reserved 
for ladies. Each guest room is outside with bath, cir- 
culating ice water, bed-head reading lamp and Ser- 
vidor. Housekeeper on each floor. Garage facilities. 

2500 ROOMS $3.00 UP 

MORRISON HOTEL 



Madison and Clark Streets 



CHICAGO 



Presenting a Full Line o£ 
Microphones 

The microphone illustrated offers to public 
address personnel a high quality double 
button all-purpose microphone at a price 
in keeping with the times. 

It uses the new ground center, heat 
treated, duraluminum diaphragm which in- 
sures sensitivity, absence of hiss, and a 
frequency response equal to microphones 
listing up to $75.00. This new and improved 
microphone is a precision instrument built 
to rigid specifications and is broadcast size, 
measuring "&Y&" diameter by 2" thick, 200 
ohms per button and finished in highly 
polished chrome. 

GUARANTEE — We unconditionally guarantee all 
MAYO microphones for a period of one year and 
will repair or replace free of charge any micro- 
phone becoming defective through normal use in 
that time. 




New List Price 

$20.00 



Liberal 
to P. E. 



Discount 
Readers 



MAYO INSTRUMENT CORPORATION 



281 EAST 137th STREET 



NEW YORK, N. Y. 




pfcsi 



MAKING 

PHONOGRAPHp 

RECORDS 



. . . requires the absolute j 
freedom from "hiss" or 1 
"rush" which is guaran- 1 
teed by the condenser | 
microphone. 

SHURE, Model 44, is 
the lowest priced, high 
quality, nationally known 
2-stage Condenser Mi- 
crophone available. Fre- 
quency response remark- 
ably uniform, combined 
with high output level 
and extreme wealth of 
richness in tone quality. 

Write for full particulars today. 
P. S.: Recording is a profitable busi- 
ness. Is it established in your town or 
neighborhood? If not, we can help 
you. 



SHURE BROTHERS COMPANY 

Manufacturers -Engineers 
S. N. SHURE. Pres. 

337 WEST MADISON ST CHICAGO. ILLINOIS 




For Your Experimental Department 



A tube of 500 as- 
sorted lugs and 
terminals — hot 
tinned for easy 
soldering. 

Price 



We are also pre- 
pared to handle 
production stamp- 
ings. 

Write Vs for 

Quotations 




F. R. ZIERICK MFG. COMPANY 

70 E. 131st ST., NEW YORK CITY 



Page 30 



PROJECTION ENGINEERING 



ELMENCO 



QUALITY PARTS FOR 
QUALITY PRODUCTS 




RESISTORS 

CARBON 

WIRE WOUND 

VITREOUS 

ENAMEL 

STRIP AND 

FLEXIBLE 



P" 



Condensers 

BAKELITE 

MICA 

PAPER 

CARTRIDGE 



ASK FOR SAMPLES 

Our years of experience, combined with best 
of engineering and manufacturing facilities 
have made us the leader in this field, and the 
choice of the most prominent Radio Manu- 
facturers. 

Our Quality and Service are the Best 
Our Prices Will Satisfy You 

ELECTRO -MOTIVE ENC. CORP. 



797 E. 140 St. 




NEW YORK 



PROTECT Those INSTRUMENTS 



Littelfuses afford complete pro- 
tection for voltmeters, milliam- 
meters, tube testers, etc. Range 
in size from 1/100 to 2 amps, 
capacity. 



Also Radio Receiver and Am- 
plifier Littelfuses, and High 
Voltage Littelfuses for trans- 
mitting tubes, rectifiers, oscilla- 
tors, etc. 



Write for instructive catalog. 

LITTELFUSE LABORATORIES 

177ft WILSON AVE. CHICAGO. U. S. 



LITTELFUSES 



GENUINE SAPPHIRE 

Points — Needles — Styluses — Shavers 

Type "A" — for cutting and recording on aluminum. 

Type "B" — tor recording and play - back on Victor type pre- 

grooved black composition, home recording discs. 
Type "C" — for play-back on all commercial records and elec- 
trical transcriptions. 
Sapphire points afford better sound. 
We will meet your specifications. 

MEYER KOULISH CO., Inc. 

64 FULTON ST., N. Y. CITY BEekman 3-6109 




HOTEL 



MAPIUAWASUINCK) 




ATLANTIC AVE. AND EIGUTM ST. 

VIRGINIA BETACM VA. 

Fireproof brick construction. 
The coolest spot on the beach. 
Invigorating breezes from ocean on East and 
Lake Holly on West. 

Bright, airy outside rooms, parlor suites and 
apartments, private baths, superior cuisine — 
Surf bathing, riding, fishing, golf, dancing, 
private tennis court and children's play, 
ground. 

J. "WESLEY GARDNER, Manager 




For Powers, Simplex 


and all other sound pro 


ectors 


CLAYTON 


Even j a ix r 
Tension 1 /"\ l\ L 


-UP 


Assures absolute freedom from flutter. Takes up any amount of film evenly 
with any size reel hubs. Prevents excessive wear on the lower take-up 
sprocket and shaft. Stops the opening of film splices and prevents excessive 
wear on the film. Write for price and details. 


CLAYTON 


PRODUCTS 


CO. 


9430 Forty-sixth Ave. 


Elmhurst, L 


. 1., N. Y. 



Will pay cash for 24" Western Electric 
Speakers. Give full details in letter to 
A. Richter, 4633 Wilcox Ave., St. 
Louis, Mo. 



INDEX TO ADVERTISERS 



B 



Inc. 



Blue Seal Sound Devices, 

C 

Cameron Publishing Co 32 

Clayton Products Co 30 

E 

Eastman Kodak Co 27 

Electro-Motive Eng. Corp 30 

F 

Federated. Purchaser 31 

Forest Electric Corp Second. Cover 

K 
Koulish Co., Inc., Meyer 30 



Littelt'use Laboratories 30 

M 

Mayo Instrument Corp 29 

Midwest Broadcast Equip. Co 31 

N 

National Carbon Co., Inc 5 

National Theatre Supply Co 5 

R 

Bacon Electric Co., Inc Back Cover 

Radio Manufacturers Ass'n 3 

Radio Television Instr. Co 27 

Richter, A 30 



Samson Electric Co . . . . : 6 

Shure Brothers Co 29 

Strong Electric Co., The : 5 



Telephoto & Television Corp 27 

Typhoon Air Conditioning Co., Inc. 29 

W 

Webster Company Third Cover 



Zieriek Mfg 



Z 

Co.. F. R. 



29 



MAY, 1932 



Page 31 



T 

X HE Group Subscription 
Plan for Projection Engi- 
neering enables a group of 
engineers, executives, projec- 
tionists or technicians to sub- 
scribe at one-half the yearly 
rate. ^ 

The regular individual rate 
is $2.00 a year. In groups of 
4 or more the subscription 
rate is $1.00 a year. (In 
Canada and foreign countries 
$2.00.) 

The engineering depart- 
ments of hundreds of manu- 
facturers and scores of the 
M. P. M. O. U. locals in the 
projection and allied indus- 
tries have used this Group 
Plan extensively, in renew- 
ing their subscriptions to 
Projection Engineering. 



Each subscriber should print 
his name and address clearly 
and state his occupation — 
whether an executive, engi- 
neer, department head, con- 
tractor, installation man, pro- 
jectionist or technician, etc. 



Remember this Group 
Plan when Your 
Subscription Expires 



( Projection Engineering ) 

Bryan Davis Publishing Co., Inc. 

19 East 47th Street 

N. Y., N. Y. 

Los Angeles Chicago Cleveland 



The NEW 
Acratone 
Recorder 

An Immediate Hit with Engineers 

of Broadcasting Stations and 

Recording Laboratories 





All that is necessary is to move the 
arm to the center of the record and 
throw the lifting lever to the down 
position. This immediately starts the 
recorder on its way of evenly groov- 
ing the remarkable number of 96 
grooves per inch. 

Recordings of from 5" to 12" may be 
made at either 78 or 33 1/3 r.p.m. 



Diamond Cutting 
Needles, $6.00 ea. 

Above price includes 
cutting head, swivel 
arm, threader, center 
spindle and hard- 
ware. 



Federated Purchaser, Inc. 

25 Park Place Dept. P, New York, N. Y. 

Every sound engineer should have the 
complete details of this job, as well as a 
copy of "RADIO BARGAIN NEWS"— our 
100-page catalogue containing over 3,000 
radio items. Write for free copy. 



Aluminum Blanks 


Cat. No. 


Dia. 


Price 


5070 


5" 


13c 


5071 


7>/ 2 " 


20c 


5072 


12" 


50c 


5073 


10" 


33c 




MIDWEST CONDENSER 
MICROPHONES 

Specifications of suspension model No. 150: 
TUBES— 2 type 864 
OUTPUT LEVEL— Minus 25db. 
OUTPUT IMPEDANCE— 200 or 50 ohms 
UNIFORM RESPONSE— 30 to 10,000 cycles 
PHYSICAL DIMENSIONS— V/ 4 " in diameter 
II" in height 

REVOLVING SWIVEL HEAD 

Remarkably low price. 



MIDWEST BROADCAST EQUIPMENT COMPANY 

6007 Diversey Avenue Chicago, III. 



Page 32 a 

LEADERSHIP 



PROJECTION ENGINEERING 



ONE DA Y'S MAIL 



The Cameron Publishing Company have been publishing 
books dealing with the making and showing of motion pictures 
for over 16 years. 

Each new Cameron book has outsold the previous one. 

A pre-publication announcement sent out recently on Cam- 
eron's new book, QUESTIONS AND ANSWERS ON 
SOUND PICTURES, sold 4,841 copies of the book BEFORE 
THE BOOK WAS PRINTED. 

The new book although off the press less than three weeks 
can now be found in (or is on the way to) practically every 
civilized country on the face of the globe. 

Out of a total of 478 Motion Picture Operators Locals in 
this country and Canada, the new book (Questions and 
Answers) has already within three weeks of publication date, 
been ordered by projectionists representing 411 of these locals. 

From Letters Received This Week: 

"The Cameron book is the Projectionist's 
Bible." Henry J. Schmieder, Easton, Pa. 

"They get the best when they buy a Cameron 
book. I have them all." 

J. H. Harrison, Collingwood, Ont., Can. 



Questions and Answers 

Sound Motion Pictures 

JAMES R. CAMERON 

The subject of making and showing motion pictures 
with sound covered in simple question and answer 
form. 

Over 1,000 examination questions with answers. 

240 Pages— Price, $3.50 
JUST PUBLISHED 



Sound Pictures 

Trouble Shooters Manual 

CAMERON & RIDER 

Explains in detail the construction, operation and 
care of sound recording and reproducing equipment. 
Every known trouble to sound recording and reproduc- 
ing equipment is listed in this book — with full ex- 
planation as to its cause and remedy. 

A Complete Guide for TBOTJBLE TRACING 

1180 Pages— 500 Illustrations 
Price, $7.50 



Motion Picture 
Projection 

JAMES R. CAMERON 

Introduction by S. L. ROTHAFEL "ROXY" 

This book is used by the motion picture industry 
throughout the world as the standard authority on the 
subject. 

1204 Pages— Fourth Edition 
500 Diagrams— Price $6.00 



AMERICAN PROJECTION SOCIETY: 

Sound Pictures and Trouble Shooters Manual 
is the best book on the subject — and likely to 
be for some time to come. 



"I'm a booster for the Cameron books." 

George Alhberg, Local 358, Ogden, Utah. 
"Have all your books and I'm well satisfied. 1 
E. H. Witt, Cleveland Heights, Ohio. 



LEAGUE OF NATIONS (Cinematograph 
Bureau) : 
Mr. Cameron is one of the limited number of 
technical writers on Cinematography really worth 
reading" — "has made important contribution to 
the literature of the sound picture." 



"Cameron books are a worthy addition to any 
projectionist's library. 

Louis Oberman, Winnipeg, Canada. 
"Can hardly wait for your new book. Have 
all Cameron's books and they're dandy." 

R. J. Mellien, Lake Geneva, Wise. 



DEPT. OF COMMERCE, Motion Picture Sec- 
tion. Washington, D. C. : 
"These books should be in the possession ol 
every projectionist, theatre manager and every- 
one interested in receiving first hand authentic 
information regarding the application of sound 
to motion pictures Cameron's books are a very 
worth-while contribution to the motion picture 
industry." 



"We thank you for the many fine contribu- 
tions you have made to the projectionist's 
library." 

S. T. Clarke, Sec'y, Local 223, 
Providence, R. I. 

The Cameron books are endorsed or used by-The U. S. Government, the 
Canadian Government Motion Picture Dept., 78 State and City Governments, 
American Projection Society, Society of Motion Picture Engineers, practically 
every motion picture trade journal published in this country and abroad^ 
American Library Association. ' 

AUTHENTIC-COMPREHENSIVE-UP-TO-THE-MINUTE 

DEMAND A CAMERON BOOK 



brought us orders to- 
taling 1786 copies of 
QUESTIONS AND 
ANSWERS ON 
SOUND PICTURES 
from members of the 
following 52 Projec- 
tionists' local Unions: 
Local 550 Norfolk, Va. 

" 355 Sioux City, Iowa 
" 262 Montreal, Canada 
" 488 Harrisburg, Pa. 
" 690 Iowa City, Iowa 
" 466 Fort Wayne, Ind. 
" 568 Columbus, Ga. 
" 360 Edmonton, Canada 
" 223 Providence, R. I. 
" 173 Toronto, Canada 
" 382 Holyoke, Mass. 
" 519 Mobile, Ala. 

64 Wheeling, W. Va. 
" 94 Butte, Mont. 
" 469 Amarillo, Texas 
" 230 Denver, Colo. 
" 434 Peoria, 111. 
" 177 Bridgeport, Conn. 
" 538 Westerly, R. I. 
" 338 Ogden, Utah 
" 303 Hamilton, Ont., 

Canada 
" 367 Evansville, Ind. 
" 278 Asheville, N. C. 
" 524 Victoria, B. C, 

Canada 
" 492 Battle Creek, 

Mich. 
" 615 Hattiesburg, Miss. 
" 337 Utica, N. Y. 
" 182 Boston, Mass. 
" 611 Watsonville, Cal. 
" 437 Brockton, Mass. 
" 343 Omaha, Nebr. 
" 79 Massillion, Ohio 
" 656 El Centro, Cal. 
" 361 Kenosha, Wis. 
" 189 Alliance, Ohio 
" 410 Manitowoc, Wis. 
" 697 Greenville, S. C. 
" 688 Harlington, Texas 
" 390 Lynchburg, Va. 
" 647 Cheyenne, Wyo. 
" 547 Florence, Ala. 
" 556 Sioux Falls, S. D. 
" 530 Bristol, Tenn. 
415 Tuscon, Ariz. 
" 630 Peru, Ind. 

321 Tampa, Fla. 
" 301 New Britain, 

Conn. 
" 302 Calgary, Aha., 

Canada 
" 160 Cleveland, Ohio 
'" 171 Pittsburgh, Pa. 

Simcoe, Ont., Can. 



CAMERON PUBLISHING CO., Woodmont, Conn., U.S.A. 



Here is PROFIT for YOU 

This SUMMER 




The new Webster A-66 com- 
pact 50-watt Amplifier for 
permanent or portable use. 
Adaptable for microphone, 
radio or phonograph input. 
Microphone power supply in- 
cluded — no batteries needed. 



I' 



WITH WEBSTER-CHICAGO Amplifiers and acces- 
sories you can go ahead and make money this 
summer while the other fellow worries. Important 
public events creating big demand. Exclusive features 
of this equipment make it easy to sell or to rent out ! 

High Power Amplifier of Surprising Compactness 

As much volume as you'll ever need, yet so compact that 
it occupies only a cubic foot of space. The Webster A-66, 
a 3-stage amplifier, produces 50 watts output (enough for 
10 good sized speakers), utilizing 845 tubes in push-pull. 
All power is derived from 110-volt A.C. supply, including 
field excitation for 2 dynamic speakers. Time element 
switch allows tube filaments to heat before plate current 
is applied. A safety switch cuts off all power when the 
cover of the amplifier is removed. Simple — anyone can 
operate the unit— moderately priced. 

And you can depend on Webster-Chicago Amplifiers. 
None shipped until thoroughly inspected and tried. 

Adapted to Truck or Outdoor Use — Portable 

While the A-66 may be used for permanent installations, 
its design is so compact and construction so rugged that 
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truck use. The amplifier is easily portable — weighs only 
85 lbs. Operates from light socket or A.C. generator, 
consumes only 320 watts. 

The WEBSTER Company 

854 Blackhawk St. Chicago, III. 



WHERE and HOW 

You Can Earn Money with 

WEBS TER-CHICA GO 

Sound Amplifiers 

The next few months will be profitable 
for the man who is on the job with 
WEBSTER -CHICAGO Amplifiers and 
Public Address Systems. A continuous 
chain of important events will command 
intense public interest. 

G.O.P. and Democratic Conventions. Loca! news- 
papers, party committees and merchants will want 
to relay these events through outdoor amplifiers 
to attract crowds. 

Olympic Games. Here again newspapers and 
merchants will use amplifiers to their advantage 

and yours. 
Political Speeches. Campaigns will be hard fought 
from now till November. Every candidate is a 
prospect for public address equipment or truck 
amplifiers on a rental basis. 

Summer Resorts, Tourist Camps, Parks, Dance 
Pavilions, Refreshment Stands are all good pros- 
pects for radio, music and voice amplifier systems. 
Baseball. Local merchants will use indoor and 
outdoor amplifiers to attract fans to their stores. 
Pays them, pays you. 

And next fall, the World's Series, football games. 
political campaigns and election returns will keep 
your market for amplifiers alive until snow flies. 
Never before has there been such a combination 
of opportunities. Somebody in vour citv is going 
to make good money leasing and selling WEBSTER- 
CHICAGO Equipment for all this. Why don't 
YOU get in on it and kiss the depression good-bye. 



Send for Our Catalog TODAY 

Shows wide range of Amplifiers, Public Address Systems and 
Accessory Equipment, built to perform, priced to sell. We have an 
especially attractive proposition for Special Representatives. Ask us 
about it. 




2-UNIT 6-FT. TRUMPET 




Unconditionally 
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NEW MASTER DYNAMIC 
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An unconditional guarantee is carried by all RACON STORM- 
PROOF HORNS. RACON STORMPROOF HORNS are 
guaranteed against all conditions of weather, direct contact with 
rain, snow, sleet or complete immersion in water and all degrees 
of humidity. 

This is a triumph of RACON ELECTRIC COMPANY inas- 
much as the material which is acknowledged the most perfect 
acoustically, has now the waterproof properties of materials 
which are ordinarily accepted as able to withstand severe climatic 
conditions. 

RACON Horns are constructed ot an exclusive 
patented non-vibratory material without resonance, so 
common in other type horns. 

RACON Horns and Electro Dynamic Units are su- 
perior in reproducing high frequencies, especially at 
high volume. Distortion is impossible, tone quality 
approaching that of the human voice is assured. 

RACON HORNS AND UNITS ARE 

# COVERED BY U. S. PATENTS NOS. A 
1,507,711 1,501,032 1,577,270 73,217 73,218 W 
1,722,448 1,711,514 1,781,489 1,832,608 1,845,210 
1,835,739 1,834,327 

RACON'S Catalog P.E. 5 will be sent on request if 
you use your business letterhead or card. 



foVA/M El^VTKIV Va. IAK 



18 Washington Place, New York City 
London, England Toronto, Canada 




NEW SUPER GIANT 
DYNAMIC UNIT 




fcMwummn i i 'iwii ii i ii i uam'HtwawffiBBi 












IN THIS ISSUE 



EVELOPMENT IN A SINGLE 
SOUND-ON-FILM RECORD- 

KING SYSTEM 



By Leon Morgan 

ID AND LIGHT PROJECTION 
HE UNITED STATES NAVY 

By Daniel Buckley 



ID OF DEVELOPMENT IN 
EQUIPMENT FOR SCHOOLS 

SOUND SYSTEMS IN ROCKEFELLER 
■ CENTER, NEW YORK 

I By James Frank, Jr. 
tLD'S BIGGEST SOUND AMPLI- 
R BROADCASTS CHICAGO 
MUSIC FESTIVAL 



Fourth Year 
Of Service 





IHtftl 

ittttS 


faflii 


* V** xj 1 ll %Jf 


VI/UAL 




HI 



journal of the Sound and Lignt Prqjeciion Industries 



► 
► 
► 
► 
► 
► 




ORTABLE 
AM-O-GRAPH 



THE NEW RECORDING PHONOGRAPH BY SAMSON 



Apparatus is 
Installed 
Inside Two 
Attractive 
Cases Covered 
With Artificial 
Walrus Hide. 
Combined 
Weight is 
70 lbs. 
Size of 
Each Case 
15"xI7"xlO" 




Phonograph 
turntable in 
one case. 
Amplifier, 
visual monitor, 
loudspeaker, 
selector switch, 
head phones 
and cables 
in other case. 



Developed to a high degree of efficiency as a unit that makes it easy to record all kinds of activities 
on blank discs of various, standard sizes with results being on a par with those obtained in studios 
. . . the Samson Pam-o-graph then plays back these or any other records so amplified as to reach an 
audience up to 500. 

The Pamo-o-graph operates from 110 volt, 60 cycle, a-c wall or lamp socket . . . microphone picks 
up voice or music and transmits it through amplifier to recording stylus which cuts sound track in the 
record. By shifting from recording stylus arm to playing needle arm, records are played back immedi- 
ately through loud-speaker. All Pam-o-graphs are equipped with a special Samson visual monitor 
(neon light bulb device) which clearly indicates to operator the proper sound level in making 
records. 

Aside from recording such items as listed below, Samson Pam-o-graphs can be used as regular high 
quality, electric phonographs. 

Zi'JJ- ^Z 0r + d J?l-„ C ° n f eSSi0nS: k T e talent ' children '* ™nss and talks: incoming radio entertainment- school or colleae lec- 

itjJz TT e f pZZTuse d ;: mati "- etc - ; recording auditions - f « r ^ -»*«««•■ — <-* *$&^£%#Jz ; 

S£,S W ^ -„tab,e); Standard Cabinet Mode.; D U a. 



CANTON 




we>io 

MEMBER R. M. A. 



MASS 



NOVEMBER, 1932 



Page I 



A NEW HANDBOOK 




on 




NATIONAL 

PROJECTOR CARBONS 



96 

Pages 



58 
Illustrations 



FREE-TO EVERY PROJECTIONIST 

rWlHE new and completely revised edition of the 
-■- National Projector Carbon Handbook is now 
ready for distribution. 

This book discusses, in detail, the application of 
the carbon arc to all types of projection lamps. 

It contains the practical information needed to 
secure maximum volume of screen illumination, 
freedom from trouble and most efficient operation 
of projection lamp equipment. 

SEND FOR YOUR COPY TODAY 
Use the coupon at the bottom of this page. 

NATIONAL CARBON COMPANY, INC. 

Carbon Sales Division . Cleveland, Ohio 

Unit of Union Carbide |l| ^^ and Carbon Corporation 

Branch Sales Offices: 

New York Pittsburgh Chicago San Francisco 



PROJECTOR CARBONS 




NATIONAL CARBON COMPANY, INC. 
Post Office Box 400 
Cleveland, Ohio 

Gentlemen: Please send me complimentary copy of the New 
Handbook on National Projector Carbons. 



Na 



Title 



Theatre 



Mail to 
City 



Street 



State. 



P.E. 11 



Projection 

Engi neering 




Sound Pictures 

Visual Projection 

Sound Recording 

Audio Amplifiers 

Public-Address Systems 

Photography 

Facsimile Recording 

Television 

Photo-Voltaic Cells 

Circuit Measurements 

Automatic Music 

Acoustic Engineering 

Radiant Energy Devices 

Electric Recording 

Phototubes 

Home Talkies 

Theatre Engineering 

Amplifier Tubes 

Sound Reproducers 

Screen Engineering 

Electric Power for Projec- 
tion 

Recording Studio Engi- 
neering 

Location Sound Equipment 

Rectifier Tubes 

Industrial Tube Applica- 
tions 



Donald McNicol 
Editor 

Jas. R. Cameron 
Associate Editor 

Ulmer G. Turner 
Western Editor 

F. Walen 
Managing Editor 



Vol. IV 



NOVEMBER 
1932 



Number 11 



Contents 

Page 
Editorial 4 

New Development in a Single Sound-on-Film Record- 
ing System .By Leon Morgan 7 

Research in Hollywood 9 

Sound and Light Projection in the United States 
Navy By Daniel Buckley 10 

Lenses With Variable Focal Length 12 

Engineers Want National Technical Standards for 
Motion Picture Industry 13 

Microphones Speed Up Service and Save Space in New 
York Soda Store By H. G. Cisin 14 

Trend of Development in Equipment for Schools. ... 15 

Sound Systems in Rockefeller Center, New York 

By James Frank, Jr. 17 

World's Biggest Sound Amplifier Broadcasts Chicago 
Music Festival 20 

Glossary of Technical Terms for the Projectionist. . 23 



Departments 



New Developments of the Month and News of the 
Industry 24 



Index of Advertisers. 



26 



Bryan S. Davis 
President 

Jas. A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

19 East 47th Street 

New York City 



Sanford R. Cowan 
Advertising Manager 

J. E. Nielsen 
Circulation Manager 



Chicago Office — 1221 Rosemont Ave.— Charles H. Farrell, Mgr. 
St. Louis Office— 505 Star BIdg.— F. J. Wright. 
Kansas City (Mo.) Office— 306 Coca Cola BIdg.— R. W. Mitchell. 
Cleveland Office — 416 National Building— Millard H. Newton. 



San Francisco Office— 155 Sansome St.— R. J. Birch. 
Los Angeles Office— 846 S. Broadway— R. J. Birch. 
New Zealand— Tearo Book Depot— Wellington. 
Australia— McGilT s Agency— Melbourne. 



Entered as second class matter August 15, 1931, at the post office at New York, N. Y., under Act of March 3, 
1879. Yearly subscription rate $2.00 in U. S. Yearly subscription rate $3.00 in Canada and foreign countries. 



NOVEMBER, 1932 



Page 3 



The RCA Victor Company 

ANNOUNCES 

HIGHEST FIDELITY SOUND 

The supreme achievement in the field of sound reproducing equipment 

for theatres of all sizes 

Assuring accurate reproduction of the widest ranges in sound recording 
attained in the production of any sound-on-film motion picture at any studio 



NOW AVAILABLE IN FOUR TYPES: 



STANDARD SUPER SIZE 

For Theatres having 2,500 to 
4,000 seats. 

STANDARD SMALL SIZE 

For Theatres having 600 to 
1,400 seats. 



STANDARD LARGE SIZE 

For Theatres having 1,400 to 
2,500 seats. 

SPECIAL SIZE 

For Theatres up to 600 
seats. 



LEASE FOR CASH or DEFERRED PAYMENTS 

The only all AC Operated Equipment for both large and small theatres. 



NEW FEATURES OF STANDARD SUPER, LARGE and SMALL SIZES 

I New "rotary stabilizer" soundheads— no sound gate— no flutter— no "wow" — free running drum. 

2 Direct drive soundheads— no chains— no belts— few parts requiring replacement — simplest possible design. 

3 Improved AC operated amplifier— extended frequency — richer tone — more natural sound. 

4 Remote Volume Control at projector station and auditorium on larger equipments. 

5 Ten-foot loudspeakers for De Luxe theatres to give reproduction of maximum frequency range — particularly low frequencies. 



SPECIAL SIZE 

1 Greatly improved AC operated amplifier— highest fidelity sound— flat characteristics — greater power. 

2 DC exciter lamp— more low frequencies. 

3 New monitor amplifier speaker— no power diverted from main amplifier. 

4 Belt drive soundheads — no noise— smooth operation. 

5 Separate fader switch for wall mounting. 

Orders now being accepted for December delivery. 

For detailed information concerning this new equipment or the modernizing of yourpresent apparatus, communicatewith 

PHOTOPHONE DIVISION 



RCA Victor Company, Inc. 



Camden, N. J. 




Branches Principal Cities of the World 



E d 



i t o 



i a 



NOVEMBER, 1932 



"YES" 
MEN 



THE other day we had a 
' pleasant and illuminat- 
ing- two hours discussion 
with a high executive in 
the moving picture industry. He told us of 
his problems from the standpoint of his 
office. He particularized successes and fail- 
ures in producing filmed pictures. He told 
us of external and internal influences which 
in large part determine successes and fail- 
ures. He discussed production staffs, man- 
agement staffs and sales staffs. 

It was a temperate recital of conditions — 
conditions which no doubt obtain in many 
other industries, and certainly in govern- 
ment. 

Afterward, reflecting, we reached the en- 
gaging conclusion that the moving picture 
industry, in common with other undertak- 
ings, needs more, not less, "Yes" men. 

Mentally digesting what the film execu- 
tive passed on to us, the thought came that 
the often announced: "I stand on my own 
two feet: I'm independent: I'm no 'Yes' 
man" may now be in the category of the 
bullet which served its purpose by hitting 
the bulls-eye, but then passed through the 
target, killing a man a half mile beyond. 

There may be too many men devoting too 
much of their thought and energies to living 
up to the boast that they are not "Yes" men. 
In a successful enterprise there must be lead- 
ers. But, if you can figure out what use 
leaders are unless they have others to lead, 
you will come close to a pre-run viewing 
of what some executives have to contend 
with. It would appear that there was little 
less misunderstanding at the Tower of 
Babel; that there was no more agreement in 
the Lincoln-Douglas debate, nor in the 
"descent of Man" discussion at Dayton, 
Tenn. than in the average industrial organ- 
ization. When instruction, suggestion, ad- 
vice or definite orders from responsible di- 
rection continually encounter the rejoinder: 
"I'm no 'Yes' man" what in the name of 
Davy Crockett can be accomplished? 



The question arises: can there not be de- 
veloped a type of constructive discipline in 
industry which might serve the interests of 
industry and all of those persons engaged in 
it, in an agreeable sense related to the sort 
of discipline which alone makes the winning 
of battles possible. 

The subject is one which includes socio- 
logical, human, and industrial aspects 
worthy of serious consideration and sane 
analvsis. 



CROM information in 
EXTENSIONS OF r hand it is clear that the 
PUBLIC ADDRESS use of public-address 
equipment has been given 
wide extension during the past two months. 
The political campaigns of the year called 
into service in all sections of the country 
microphones, amplifiers, and loudspeakers 
in number far exceeding units employed in 
previous years. 

Hardly a spot among the seventy-five 
thousand communities in the United States 
but that now has in service or available at 
least one "sound truck" ready to circulate 
through the streets and roadways as Stentor 
of old, announcing to the populace the last 
minute utterances of those who desire to 
reach every pair of ears. 

The advertisement thus given the various 
address systems is sure to result in wider 
applications of the equipment in industry, 
in interiors of all sorts and in many outdoor 
situations. It has been made plain to a host 
of persons that here is a new facility which 
has many useful and economical applica- 
tions. 



Ji 



*nJj^m*iUc 



o\> 



Editor 



NOVEMBER, 1932 



Page 5 




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Inquiries Invited. 



Th( 



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for sharp, full- 
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free from back- 
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distinct advance in this 
particular field. 

<J A special glass is used 
which permits the passage 
of violet and ultra-violet 
rays with a minimum 
amount of loss. 

€][ Every effort has been 
exerted to make this lamp 
as rugged as possible in 
order to withstand shocks 
and abuse incident to ship- 
ping and "field" conditions. 
The Zetka lamp under ordi- 
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more of sound track. A 
number of lamps have re- 
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feet. 




PHYSICAL 
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• A technical bulletin is furnished with lamp • 

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Cable Address 

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Bentley's Code 



Page 6 



PROJECTION ENGINEERING 



Today, more than ever before, 
it is necessary to be posted 
thoroughly on the develop- 
ments taking place within this 
industry of ours. It is only 
the alert, well informed in- 
dividual or organization that 
is today making headway. It 
is essential to know what is go- 
ing on, why and how. 






Projection Engineering 
answers the "what, why and 
how" of the thousands of tech- 
nical men in the fields of sound 
and visual projection and re- 
cording. 

Every contractor, installation 
man and technician who is en- 
gaged in sound work or who 
installs P. A. systems, should 
receive Projection Engi- 
neering every month. 

Enter Your Subscription Now! 
1 year $2.00 — 2 years $3.00 

( Projection Engineering ) 

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19 East 47th Street 

N. Y., N. Y. 

Los Angeles Chicago St. Louis 




Projection Engineering 



Vol. IV 



NOVEMBER, 1932 



No. II 



New development in a 
single sound-on-film 
recording system 



By Leon Morgan 



SINCE talking motion pictures 
swept the country the silent pic- 
ture today is practically out- 
moded, and even in industrial use 
few new productions are made without 
sound. Elaborate and more elaborate 
equipment has been developed for studio 
use, but during all this time little atten- 
tion has been paid to the requirements of 
the commercial photographer who, with 
an extremely limited budget is compelled 
to produce motion pictures of high 
quality for commercial use. Simple 
double recording systems for studio use 
have been developed that will answer 
satisfactorily, but out on location where 
by far the biggest percentage of in- 
dustrial pictures are made, this equip- 
ment is of little value. 

It has been evident that commercial 
motion picture studios as well as news- 
reel men required a simple, portable 
single system sound-on-film camera de- 
signed to stand up under the extremes 
of service which such usage requires. 
The single system eliminates much 
costly wastage of film, it simplifies to 
a considerable extent the laboratory 
work involved, and above all it assures 
light weight and extreme portability of 
the equipment so essential where the 
cameraman is forced to set up almost at 
a moment's notice ; make his shot and 
get on to the next scene or get it back 
to the studio for immediate development. 
To fill this need there has been pro- 
duced a simple, single-system recorder 
which consists of a newly developed 
DeVry sound camera using a glow 
lamp, a portable amplifier complete in 
a single case, a two-stage condenser 
microphone and tripod, two battery 
boxes and a small case containing all 
necessary cables, head phones, etc. With 
this equipment it is possible for a 
cameraman and an assistant to set up 
for a shot in a few minutes and, once 
the shot is made, it is a simple matter 



to jerk out the connecting cables, close 
the cases and be under way. 

The Camera 

The sound recording camera is of the 
single system type, using a standard 
glow lamp. The housing is of aluminum 
to assure extreme rigidity coupled with 
light weight, and all of the parts are 
carefully finished with micrometer pre- 
cision to assure perfect operation. The 
mechanism is of the standard two-claw 
type of highly refined design. An inno- 
vation in this camera is the sound 
sprocket filter. This is a mechanical 
fly-wheel consisting of a modification 
of the Robertson patent — a scientific 
and practical method of filtering. The 
whole system is mounted on ball bear- 
ings. 

The camera is of the removable maga- 
zine type and will accommodate either 
400 or 1,000 ft. magazines as desired. 
Detached from the tripod, the camera is 
a simple metal box equipped with a 
handle, which makes it as easy to carry 
as a light grip. It is furnished com- 
plete with jack for monitoring purposes, 
which makes it possible to determine 
exactly what is being recorded. A 
tachometer at the rear shows the oper- 
ator at all times at what speed the film 
is traveling and two switches are fur- 
nished, one for the motor and one for 
the lamp. Gears are of steel and 
micarta throughout to assure long life, 
and a footage indicator is provided to 
enable accurate measurement of either 
400 or 1,000 ft. reels. 

The camera has been completely 
silenced throughout and may be used in 
a studio without "blimping " 

Lens Equipment 

Any standard lenses may be used in 
connection with the camera as the lens 
mount is of the bayonet type and lenses 



are instantly interchangeable. A stand- 
ard F 3.5 two-inch focusing lens is fur- 
nished with the camera. 

Two systems of focusing are provided, 
one of which consists of a view finder 
which swings down from the lens 
mount, and the other a direct-on-film 
prism type of finder located at the side 
of the camera. The prism type view 
finder is equipped with a magnifying 
lens for easy focusing. 

Sound Recording 

The variable density system of record- 
ing with a glow lamp previously men- 
tioned was chosen because of the con- 
sistency in results both in recording and 
reproducing. This method of light 
modulation for variable density type of 
sound track gives extremely high-fre- 
quency response and requires no me- 
chanical adjustment. The quality and 
volume of the recording is practically 
independent of the average time of ex- 
posure or per cent of gamma develop- 
ment. These glow lamps have high 
actinic and long life characteristics. 
Either a two-element or three-element 
recording lamp may be used with the 
equipment. 

Optical System of Recording 

The light from the glow lamp is pro- 
jected through a lens against the film. 




Fig. I. Recording camera showing construction 
and threading. 



Page 8 



PROJECTION ENGINEERING 



As the microphone picks up the sound 
impulses these are transmitted through 
the amplifier to the glow lamp, the light 
of which varies in intensity and regis- 
ters on the film. 

This system is extremely sturdy as 
there are no moving parts to get out of 
order. The simplicity is, of course, 
ideally suited for newsreel or commer- 
cial work. The direct projection of 
light from the glow lamp through the 
lens assures a parallel line through the 
film emulsion. The contact slit with 
its disadvantages of loss of high fre- 
quencies due to reflection, divergence 
and diffusion of light at the slit is elim- 
inated. The contact slit also causes 
accumulation of dirt and scratches on 
the film, owing to the close contact to 
the film required with the prism or 
slit. 

Operation 

The operation of the recording 
camera is extremely simple. The film 
is first threaded as indicated in Fig. 1. 
Coming from the upper feed magazine 
it passes over the large feed sprocket, 
through the gate in front of the lens, 
back over the takeup sprocket, over the 
sound aperture to the sound sprocket, 
over the takeup sprocket and back into 
the takeup magazine. 

Two switches on the side of the 
camera control the motor and the glow 
lamp. With the camera in operation 
the scene may be followed by the view 
finder and a calibrated volume indicator 
in the amplifier assures control of the 
sound at all times. A headset also per- 
mits of careful check on the sound 
while it is being recorded. 

The whole system consists of a 
camera and tripod, two battery boxes, 
one amplifier and one box holding the 
condenser microphone, cable, head 
phones, etc. 

Amplifier 

The recording amplifier is self-con- 
tained in a compact case. The extreme 
care in its manufacture and the skilled 
engineering back of its design assure 
this amplifier of very little attenuation 
to frequencies within the recording 
range required, and it obtains full ad- 
vantage of the wide band of frequencies 
that can be recorded with the glow 
lamp. Study and investigation showed 
that a considerable loss of frequencies 
occurred during the processing of the 
film, and in order to secure the utmost 
fidelity from the positive print it be- 
came evident that the frequency re- 
sponse of the amplifier must compen- 
sate for this loss. Proper equalization 
is, therefore, included in the amplifier 
to compensate for these losses. In addi- 
tion to the wide frequency response the 



recording amplifier possesses non- 
microphonic tubes, wire wound resist- 
ances, non-inductive condensers, filter- 
ing in all grid and plate circuits, and 
it is completely provided with meters 
so that all circuits may be checked at 
a glance. The volume control oper- 
ates silently and smoothly. 

The sound recording amplifier is bat- 
tery operated. All batteries are fur- 
nished with the equipment. 

In studios where it is desired, a 
special power panel makes it possible 
to operate this equipment from 110 
volt a-c. 

The recording amplifier has a gain 
of 85 decibels and possesses a plug in- 
put for one condenser microphone. Any 
number of microphones or head ampli- 
fiers can be coupled to it with one cable 
from a mixing panel which can be sup- 
plied if desired. This is recommended 
for studio recording or dubbing. 

A calibrated volume indicator is built 
into the amplifier and coupled to the 
output, and indicates actual decibel level 




Fig. 2. Recording amplifier for use with the 
single recording system. 

into recording lamp. Filament and 
plate current on all tubes, current on 
recording lamp and output level can be 
instantly checked by means of two 
meters and two key switches. These 
are connected in the circuit so that 
failure on the part of either meter or 
key switch will not affect the operation 
of the amplifier. External and contact 
noise is entirely eliminated by the use 
of wire-wound resistances and by-pass 
condensers and filters in all tube cir- 
cuits. All amplifier parts are fastened 
to a heavy brass panel which is covered 
with a front panel of polished, engraved 
Bakelite. The amplifier measures 16 
inches long, 9 inches wide and %y 2 
inches deep, and is self-contained. 
While portability, simplicity and light 
weight have been taken into considera- 
tion, quality has come first, and there 
has been no sacrifice in amplification 



to achieve portability. The cover of the 
case is removable. A headset jack is 
provided for monitoring purposes. This 
amplifier will operate on any type of 
recording lamp, either two or three ele- 
ment. The frequency range that can be 
recorded on any type of film stock with 
a proper lamp and lens system, is from 
20 to 12,000 cycles. 

Condenser Microphone 

The microphone furnished with the 
recording camera is of the condenser 
type with two stages of amplification, 
and is contained in a cylindrical case. 
The microphone has an output of ap- 
proximately minus 30 decibels. It is 
extremely light in weight so that it can 
be used conveniently with a microphone 
boom. 

Motor 

A motor can be furnished to operate 
110 volt a-c, 110 volt d-c, or 12 
volt d-c. 

Battery Box and Cables 

The battery boxes furnished with the 
recording camera hold the batteries and 
a Bakelite panel on top provides sockets 
for plugging in the amplifier and 
camera. Interconnecting cables between 
microphone, battery box and cam- 
era are all eight-wire, shielded and 
interchangeable, necessitating only one 
spare cable. The receptacles are wired 
so that nothing can be damaged by 
error in plugging in the wrong one. 
Motor supply to the camera connects 
through the battery box requiring only 
one cable to the camera for both motor 
and lamp. Filament rheostat controls 
current on all tubes, including those in 
the microphone, thus eliminating guess 
work on battery supply. 

The recording system herein de- 
scribed is a product of Herman A. 
DeVry, Inc., Chicago, 111. 



NEW AGREEMENT IS BEING MADE 
FOR FUTURE USE OF MUSIC 

IT is announced, according to Film 
Daily, that a $825,000 settlement was 
made recently in the controversies aris- 
ing out of the domestic copyright 
music agreement between John G. 
Paine, acting as agent and trustee for 
the music publishers, and Electrical Re- 
search Products, acting for its pro- 
ducer-licensees. 

This means the withdrawal of the suit 
instituted by Paine some time ago on 
behalf of music publishers. A tempo- 
rary agreement is to be entered into at 
once to permit use of the music of 
Paine's publisher-principals by Erpi's 
producer-licensees pending the negotia- 
tion of a new long-term agreement to 
replace that which expired on Sept. 4. 



NOVEMBER, 1932 



Page 9 



Resea rch 



in 



Hollywood 



REPRESENTATIVES of the ma- 
jor motion picture studios and 
of the various branches of the 
film industry met recently under 
the chairmanship of Darryl Zanuck, 
Warner Brothers-First National pro- 
duction executive, in the first gathering 
of the research council of the Academy 
of Motion Picture Arts and Sciences. 

Formed to coordinate motion picture 
research and standardization efforts and 
to function as a central bureau for the 
exchange of technical and artistic infor- 
mation, the research council consoli- 
dates the work of the film Academy's 
technical bureau, producers-technicians 
committee and art and technique com- 
mittee. 

The council will hold quarterly meet- 
ings to review technical and artistic 
problems confronting the motion pic- 
ture industry, and will act as a gov- 
erning body to determine policies and 
institute projects. Under the council's 
plan of operation, specific projects in 
research and standardization will be as- 
signed to sub-committees to be chosen 
from the outstanding leaders in the mo- 
tion picture professions. 

Irving G. Thalberg, Metro-Goldwyn- 
Mayer executive, who inaugurated the 
Academy's technical program and has 
directed it during the past three years, 



MILITARY DRILL TO BE TAUGHT BY 
TALKING PICTURES 

A REPORT from Washington states 
that the United States Army is 
going in for talking pictures. The 
rookie of the future will learn squads 
right not only under the personal 
supervision of a hard-boiled sergeant or 
corporal, but he also will be permitted 
to see that elementary military move- 
ment executed with machinelike pre- 
cision on the screen, to the accompani- 
ment of staccato barks proceeding ap- 
parently from the rear of the picture. 
Likewise, budding artillerymen will be 
able to view batteries of artillery going 
into action, the positions and technique 
of gun crews, commands and all other 
details. In the beginning of the use of 
sound films instruction will be directed 



is an ex-officio member of the council, 
as is the chairman of the Academy pro- 
ducers' branch, B. P. Schulberg. 

Adolphe Menjou represents the 
actors' branch, E. H. Griffith the di- 
rectors' branch, Charles E. Sullivan the 
producers' branch and Carey Wilson 
the writers. The Academy technicians' 
branch is represented by the chairmen 
of its three sections : Art directors, Max 
Ree; sound, Virgil Miller; and photo- 
graphic, Wesley Miller. 

Representatives of the studio techni- 
cal departments on the council include : 
Columbia studios, William Holman ; 
Educational studios, H. A. McDonnell ; 
Fox Films, E. H. Hansen; Metro- 
Goldwyn-Mayer, Douglas Shearer ; 
Paramount-Publix, Franklin Hansen ; 
RKO-Radio, Carl Dreher; Tiffany stu- 
dios, Hans Weeren ; United Artists stu- 
dios, A. M. Brentinger ; Universal stu- 
dios, C. Roy Hunter; Warner Brothers- 
First National, Nathan Levinson. 

Among the immediate technical pro- 
jects to be discussed by the council are: 
the investigation of exchange and the- 
atre projection practices to eliminate 
the present mutilation of release prints ; 
research toward the development of a 
practical silent camera so that the cum- 
bersome so-called "blimps" in which 
the cameras are now housed for sound 
synchronization, may be eliminated ; co- 
ordination of research in the new tech- 
nique of "split film" recording; stand- 
ardization of pastel tints for costumes 
and settings to avoid halation in pho- 
tography; and study of the factors en- 
tering into the brightness of the pic- 
tures on theatre screens to determine 
a uniformly pleasing standard. 

Since the advent of recorded sound 
to motion pictures the Academy through 
its technical bureau and producers- 
technicians' committee has taken an 
active part in the technical advancement 
made by Hollywood's producers. 

AAA 

primarily to officers, but later the films 
are expected to be used in the training 
of men as well. 



TAX ON ELECTRIC CURRENT FOR 
THEATRES 

ELECTRICAL energy used by mo- 
tion picture theaters in the projec- 
tion of pictures, lighting of signs and 
display boards, and in the lighting of 
the building, etc., is subject to the 3 per 
cent electric tax, under a ruling just 
issued by the tax department, according 
to J. S. Seidman, tax expert of Seidman 
& Seidman, New York, certified public 
accountants. 

"The law," Mr. Seidman explained, 
"provides for a 3 per cent tax on the 
amount paid for electrical energy used 



A continuous program of industrial 
education has been carried on to facili- 
tate adjustment to the changed tech- 
nique required for sound pictures and 
to keep abreast of the constant improve- 
ments in equipment and methods. The 
Academy school in fundamentals of 
sound recording and reproduction func- 
tioned during the first year of sound. 
From the lectures given in the school 
was evolved the publication, "Record- 
ing Sound for Motion Pictures," one 
of the most authoritative volumes pub- 
lished on the subject to date. 

Under the direction of the producers- 
technicians' committee, chairmaned by 
Irving G, Thalberg, technical projects 
of general industry importance were 
carried out, including adoption of a 
standard release print, research toward 
the elimination of the "ice-box" booths 
for sound cameras, an extensive survey 
which resulted in the silencing of di- 
rect current, "arc-hum," and acoustical 
testing of set materials. 

Establishment of a uniform frame size 
for motion picture cameras and theater 
projection machines was completed by 
the Academy in May, 1932, after two 
years of research during which tempo- 
rary standards were set up. The aper- 
ture practice recommended by the 
Academy is now in effect in all Ameri- 
can studios and in a majority of the 
theaters in the United States and 
Canada. 

The Academy art and technique com- 
mittee will continue to supervise ar- 
rangements for general meetings of the 
Academy's members and inter-branch 
discussions, but the committee's func- 
tion of selecting subjects for discussion 
and stimulating the exchange of profes- 
sional information between branches 
will be taken over by the research coun- 
cil, and considerably expanded to em- 
brace cooperative study of non-techni- 
cal phases of the industry. 



for domestic or commercial consump- 
tion. Electricity used for industrial con- 
sumption is not subject to tax. The 
question arose whether electricity em- 
ployed in the operation of the motion 
picture business is commercial in its 
scope or industrial. The decision of the 
tax department is that it is commercial 
and therefore subject to tax. 

"Another ruling that will be of in- 
terest to the motion picture industry." 
Mr. Seidman added, "has to do with the 
tax on radios and phonograph records. 
It is held that photophone sound systems 
for recording and reproducing sound in 
connection with motion pictures are not 
taxable as such. However, if electrical 
transcription records or phonograph 
records are used in such sound systems, 
they are subject to tax." 



10 



PROJECTION ENGINEERING 



Sound and light projection 
in the United States Navy 



By Daniel Buckley* 



Officers and enlisted men in Navy service make prac- 
tical use of modern projection equipment. Films em- 
ployed for instructional purposes and for entertainment. 



PRIMARILY the U. S. Navy mo- 
tion picture service is provided 
for the recreation of enlisted men. 
It is classed by the producers as 
"non-theatrical." Considering the num- 
ber of men in this military organization 
and the temperamental characteristics 
of the individual something must be 
done to break up the monotony of daily 
routine aboard a "man-of-war." A 
"man-of-warsman" is on duty twenty- 
four hours every day, in each week, 
month, year, and enlistment period, re- 
gardless of whether he happens to be 
ashore, on liberty or aboard ship. In 
order to break up this monotonous rou- 
tine while aboardship there must be 
recreation, in the form of education 
and entertainment. Motion picture pro- 
jection accomplishes a great deal to- 
ward relieving the tension and the re- 
quirement, that a "man-of-warsman" 
answer a call to quarters at a moment's 
notice. 

When sight alone was used for con- 
veying a projected image from the 
screen to the person in the audience 
many different conceptions were formed 
while viewing the projected scenes. 
With the advent of sound in the mo- 
tion picture field only one thought at a 
time can be transmitted to the audi- 
ence and that the correct one. Every 
one attending the performance receives 
the same impression because of the 
scene projected and the sound accom- 
panying it. No opportunity is left for 
the individual to exercise imagination. 
This proves the advantage of the sound 
motion picture in contrast to the silent 
especially where educational films are 
concerned, where the same thought 
must be conveyed to all persons attend- 
ing the exhibition. In the navy we are 
taking the opportunity of showing edu- 
cational films which improve the abil- 
ity of the sailor with his required duty 
and aid him toward attaining a higher 



*C. E M. U. S. Navy {Instructor). 



battle efficiency rating for the ship upon 
which he is serving. These films are 
shown usually at times during the day 
to prevent interference with the regu- 
lar performance each evening given the 
crews for entertainment purposes. Dur- 
ing the entertainment performances a 
well-balanced program is given which 
may consist of a news reel, comedy, and 
feature picture. 

In the navy there are men holding 
special professional ratings such as ra- 
diomen and electricians' mates. Due to 
the necessity of using (amplifiers in 
sound motion pictures, it seemed that 
the most logical profession to take up 
this study would be the radio man. Such 
was the case in the civilian field, but 
foresight used by the navy department 
allotted this study to the electrician's 
mates, which has proven beneficial to 
the service. The radio man has to con- 
fine his activities to communications, 
qualifying himself in procedure and 
operating his set as specified by the 
Bureau of Engineering instructions. 
That field alone for the radioman covers 
quite a range in naval operations. The 
electricians' mates, however, have now 
introduced in their work various other 
equipments and instruments using 
vacuum tube amplifiers, in addition to 
motion picture equipment, which do not 
pertain to communications. Since 
vacuum tube amplifiers are being in- 
troduced into various electrical systems, 
naturally the most logical workers to 
take up the study of sound motion pic- 
tures are the electricians' mates. It is 
the men following the electrical profes- 
sion in the navy to whom instructions 
are given at the navy sound motion 
picture technicians' schools. 

A school is being maintained at the 
navy yard, Brooklyn, N. Y., for men 
located aboard ships and stations doing 
duty in the vicinity of the east coast. 
Another school is maintained at the 
naval training station, San Diego, Cali- 
fornia, to accommodate the men of the 



west coast doing duty aboard ships and 
stations there, including men from the 
Hawaiian Islands and Guam. A tem- 
porary school is located at Cavite, Phil- 
ippine Islands, for the men doing duty 
in the vicinity of Asiatic countries. 

Proficiency Required 

Not only is it necessary for the man 
operating a sound motion picture equip- 
ment to be qualified in maintaining am- 
plifiers, projectors and sound attach- 
ments, at a high standard of efficiency 
at all times, but he must also be pro- 
ficient in the projection of pictures. He 
is taught in the navy schools all the re- 
quirements in the projection of a good 
picture and as far as his equipment is 
concerned to reproduce the sound as 
faithfully as possible with the apparatus 
at his command. 

A great deal depends upon the sound 
film. He is taught to preserve the film 
in order to obtain its maximum effi- 
ciency as regards definition of picture 
and sound track. To maintain the film 
(care and handling) so as to obtain as 
great a length of life as possible dur- 
ing its rounds of travel from one ship 
to another. The films on some ships 
may be shown as many as three times 
during a night. One performance may 
be given to the crew in general, then a 
performance for the chief petty officers 
and again may be exhibited to the com- 
missioned officers; setting up portable 
equipments, exhibiting to the two latter 
classes of men, in their quarters. 

The subjects necessary for students at 
the schools to comprehend are : The 
physics of sound, light, lenses, acous- 
tics, and mathematical problems pertain- 
ing to acoustical conditions of certain 
enclosures. The electron theory is gone 
into as far as necessary to understand 
intelligently the operation of that magic 
bottle of electricity known as the 
vacuum tube. Also the physical con- 
struction of a vacuum tube, during the 
process of manufacture, the principles 
and properties of vacuum tubes and 
the accompanying amplifier, including 
photoelectric effects, and photoelectric 
cells, as used in sound motion picture 
work. The Simplex projector (standard 
theater type) is studied thoroughly, then 
each man individually disassembles and 
assembles the projector head and makes 
all proper adjustments to parts in con- 
tact with the film proper. This being 
part of the student's practical work 
during the course. The R. C. A. Photo- 
phone sound attachment likewise under- 
goes the same process of dissection as 
the projector head. Loudspeakers of the 
dynamic cone type are disassembled, 
and each man required to know how to 
make the required adjustments of the 
individual parts of the speakers to elimi- 
nate defects due to "buzz," and matter 



NOVEMBER, 1932 



II 



collecting between operating parts of 
the speakers. Also the pointing and 
phasing to obtain equal distribution of 
sound in all parts of the audience. Con- 
tinuity tests are given amplifier racks, 
every man being taught to locate trou- 
ble in the amplifier by means of sys- 
tematic tests. Tubes are checked with 
reliable tube-checkers, and character- 
istic curves compared with noted read- 
ings. The standard change-over sys- 
tem of cueing reels to obtain continuity 
of sound and picture aid the men in 
giving an uninterrupted performance 
and enable them to give an exhibition 
which should equal that in any de 
luxe theater so far as continuity is 
concerned. Carbon arc and incandes- 
cent lamp projection is studied, taking 
in various types of projection lamps; 
carbon trims, faults, and remedies of 
improper settings, manipulating by hand 
the carbon arc, and actually showing 
bad effects of carbon trims upon the 
screen, due to improper projection and 
other causes. 

Standard Test Film 

Sound is then studied practically, and 
by ear detection, locating troubles 
caused by improper adjustments of the 
equipment, which includes projector 
sound head, amplifiers and loudspeakers. 
A standard navy-test film is run through 
a projector and the men trained to lis- 
ten critically to the record. On this 
test reel are recorded speech sounds of 
the male and female voice frequencies, 
musical scores by various musical in- 
struments, and various prolonged fre- 
quency sounds. The latter to acquaint 
the students with certain frequencies 
and to enable them to distinguish be- 
tween low, intermediate and high fre- 
quency sounds. 

The equipment then is placed in vari- 
ous states of mal-adjustment to pur- 
posely introduce such defects as to cause 
wows, bow-wows, fuzzy, crackle, whis- 
kers, barrel noise, rasps, motor-boating, 
hum, buzz, etc. The students learning 
to differentiate one sound from an- 
other, and to find the part in the equip- 
ment that would cause such a defective 
sound, then immediately to effect a 
remedy to obtain normal performance 
once more. 

Recording of sound on film also is 
given, employing the three principal 
types of present-day recording appara- 
tus as used in studios. This furthers 
the technician's knowledge, and may 
help him solve some of his difficulties, 
especially should he come in contact 
with old sound films. Special input de- 
vices that can be used with the attend- 
ant amplifier are brought to the atten- 
tion of the men and these devices 
studied to further their knowledge of 
the uses to which amplifiers can be put. 



Such devices as microphones, the non- 
synchronous phonograph, using electro- 
magnetic pick-ups, and radio reception 
which further improves an evening per- 
formance introducing a record or radio 
program of special interest. 

The navy uses exclusively Simplex 
projectors and R. C. A. Photophone 
sound systems. The battleships are 
equipped almost on a par with a de luxe 
theater installation consisting of a Sim- 
plex (standard theater size) projector 
and R. C. A. sound attachment. Cruisers 
and auxiliary surface vessels use a semi- 
portable type equipment which is wholly 
an R. C. A. Photophone product similar 
to the Type PP 6B portable projector 
used commercially, excepting the port- 
able loudspeaker and amplifier. The 
navy uses a standard navy type speaker 
for all types of installations, limiting 
the number of speakers used to the area 
necessary to cover with sound areas 
on the various types of vessels. Aboard 
destroyers and large types of submarines 
the Acme-Simplex R. C. A. portables 
are used similar to those available to 
the commercial field. 

Duplex Operation 

Battleships are equipped for duplex 
operation, likewise the cruisers and 
auxiliary surface vessels. Destroyers 
and large type submarines use single 
equipment, necessitating the loss of con- 
tinuity of sound and picture between 
reels. This condition can not be avoided 
due to insufficient space available 
aboard these smaller vessels. The bat- 
tleship equipments are designated as 
Type I, Class A. Cruisers and auxiliary 
surface vessels as Type I, Class B, and 
destroyers and large submarines as 
Type Il-portable. 



iiiii i I ii iliinmiiri 

One group of Navy 
service projectionists, 



The Type I, Class A, installation con- 
sists of an amplifier rack capable of an 
80-watt undistorted power output, com- 
prising three stages of voltage amplifi- 
cation and two stages of power ampli- 
fication, the two power amplifiers each 
supplying two loudspeakers and con- 
nected by an automatic relay enabling 
two speakers to be placed in parallel 
with the others, in the event one power 
unit should become defective during 
operation. 

The Type I, Class B, installation con- 
tains the identical amplifier as the equip- 
ment described excepting one power 
amplifier unit, giving an undistorted 
power output of 40 watts and using two 
speakers. The Type I amplifiers are 
permanently installed. 

The Type II portable installation is 
completely portable and includes a port- 
able amplifier, comprised of the same 
voltage amplification stages as used in 
the foregoing equipments, differing only 
in the power amplifier consisting of two 
UX 250 power tubes connected in push- 
pull, supplying 10 watts undistorted 
power to one loudspeaker. 

Screens Used 

All sound screens used in the navy 
have been constructed to meet naval 
specifications. They are constructed to 
meet requirements as to size, depending 
upon the type of equipment used (focal 
length effect of projection lenses, and 
distance from the screen being con- 
stant). Ruggedness is very essential 
in order to withstand wind conditions 
existing when the screens are rigged 
on the decks of the vessels. The screens 
are made of light canvas or heavy duck 
perforated for sound and reinforced on 
the rear side with strips of black can- 
vas sewn lattice fashion about four 
inches apart. Black canvas ribbing was 
necessary to obtain an equalization of 
light upon the screen, the black por- 
tion used to absorb, and thus compen- 



SOUNDhotiwPICU 
[TECHNICIANS Si-HOI 



?1 ?f '* ! 



At 



12 



PROJECTION ENGINEERING 



sate for the penetrating light rays 
passed through the white perforated 
portions. These screens can easily be 
washed. All that is necessary is a good 
grade of soap, and water, and a thor- 
ough rinsing. The screen is lashed to 
a frame and the speakers are mounted 
upon a rack directly in back of the 
screen. These parts are portable and 
can be removed from the deck hurriedly 
after each performance, clearing the 
deck for routine purposes. 

Not only does the navy handle per- 
sonnel of its own organization in this 
school, but has accommodated men from 
other military organizations such as the 
U. S. coast guard, U. S. marine corps, 
U. S. army transport service and the 
U. S. army. 

Film circulation throughout the naval 
service is accomplished by means of the 
naval film exchanges. These exchanges 
are divided into units such as main and 
sub-exchanges, thus allowing a circula- 
tion of film throughout the navy in an 
orderly and systematic manner, and at 
times designated ships, acting as main 
fleet and sub-exchanges. The exchanges 



further maintain film in a high degree 
of efficiency as to care and repair, 
noting and checking comments from 
ships' technicians ; the conditions before 
and after the technicians handled same. 

The advantages for a man in the 
navy to benefit by these instructions are 
manifold. He may specialize in many 
professions. He gains a knowledge of 
projection, a knowledge of sound engi- 
neering; touches on radio material, 
public address installations, and tele- 
vision. Of course, much depends upon 
the individual, his initiative and interest. 

How the navy gains by the man's 
knowledge of battle efficiency is not due 
to sound motion picture projection di- 
rectly (although the morale is kept 
higher by giving clean entertainment), 
but the knowledge gained in studying 
amplifiers and loudspeakers. In battle, 
word may be passed by means of am- 
plifier systems. Telephones may be used 
as a secondary device where previously 
it was used primarily. A loudspeaker 
may be placed in each compartment 
aboard ship. If a man is needed in a 
certain part of the ship his name is 

AAA 



called through a microphone and am- 
plifier. No matter where the man may 
be he can be reached almost instantly 
and will respond more readily when he 
hears his name called through the ap- 
paratus. Whereas when a telephone 
rings he may figure it not very impor- 
tant and delay answering. This slight 
delay may prove to be a fatal factor 
in routine. A telephone in each com- 
partment must be connected individually 
and the messages transmitted on inde- 
pendent lines, necessitating calling in- 
dividually each compartment until the 
man is located. There is no doubt that 
efficiency in carrying out orders and 
the haste accompanied with the order 
plus the haste in complying is equal to 
saving of time and therefore means 
greater efficiency. 

Since vacuum tubes are used in other 
mechanical apparatus apart from motion 
picture equipment the men have the 
fundamental principles of tube action 
and amplifier operation, and are able 
to maintain any such apparatus at the 
highest degree of efficiency, no matter 
for what purpose used. 



Lenses with variable focal length* 



THE problem of constructing lenses 
with variable focal lengths has for 
some time been the subject of 
study by the makers of optical 
material. The principal object aimed 
at with such lenses is twofold, 1, the 
possibility of obtaining pictures of vari- 
ous sizes at the same distance without 
changing the lens ; 2, the possibility of 
obtaining a longitudinal carriage (bring- 
ing the subject closer or making it fur- 
ther away) without moving the camera 
itself. 

Two such types of lenses have been 
recently constructed; one by Bell and 
Howell and the other by Otto Durholz 
of Paterson. The "Varo" lens of Bell 
& Howell, which is really a special 
device, is enclosed in a rectangular box 
almost as large as the camera itself, and 
is applied to the anterior part of it. The 
focal length of the optical system may 
be varied continuously from 40 to 120 
mm., and the variation can be made dur- 
ing the actual photographing. Natural- 
ly, during such operation the various 
parts of the lens move in such a manner 
that the subject is continually kept 
under its eye. The dimensions of the 
pictures vary in the proportion of one 
to three, that is naturally when the 
whole field of variation of focal length 
is used. The maximum relative aper- 
tures do not, however, remain constant 
for all the focal lengths. At between 40 



tFrow International Review of Educational 
Cinematography, June, 1932. 



and 50 mm. such maximum aperture is 
F :3,5. For the intermediate zones, up 
to 85 mm. the aperture is diminished to 
F :4,5, while for the other variations 
from 40 to 120 mm. the maximum aper- 
tures are from F :5,6 to F :8. 

With regard to the focusing, it must 
be observed that this does not take place, 
as with ordinary lenses, by means of 
varying the distance of the plane of the 
image, but by a focusing system that is 
calculated from 150 feet to infinity. This 
really means that with the lens in ques- 



THE FIELD FOR PUBLIC-ADDRESS 
EQUIPMENT 

Auditoriums 

Parks 

Sound trucks 

Colleges 

Schools 

Clubs 

Churches 

Ball parks 

Airports 

Industrial instruction 

Railroad stations 

Railroad yards 

Traffic direction 

Funeral parlors 

Ships 

Show rooms 

Call systems 

Race tracks 

Bell towers 



tion the position is less favorable than 
with ordinary lenses, for the hyperfocal 
distances for 40 mm. and F :3,5 is about 
14 meters; for 50 mm. and F:3,5 it is 
about 21 meters; for 85 mm. and F:4,5 
it is about 48 meters, and for 120 mm. 
and F:5,6, it is 77 meters. When it is 
necessary to photograph at a distance, 
additional lenses must be employed, 
which are attached to the front section 
of the device. 

The variation of the focal length is 
obtained by means of a handle placed 
at the side, which gives a synchronized 
movement of the various parts of the 
device, each part moving according to 
its own laws. 

The solution of the problem offered 
by the firm of Durholz seems simpler. 
The optical system has in this case the 
appearance of a telephoto lens, easily 
mountable in the place of one of the 
normal lenses, and with a revolver- 
shaped head. Its weight is about 2200 
kilograms. 

According to the instructions issued, 
the focussing is very easy, and can be 
made from a distance of one meter with- 
out any need of adding additional lenses. 
The focal length may be changed con- 
tinuously between 40 and 160 mm. In 
fact, when it is necessary to cover the 
reduced superfices of the sound film, the 
minimum focal length can be reduced to 
37 mm. In this case, as in the foregoing, 
the maximum aperture varies with the 
focal length. 









NOVEMBER, 1932 



Engineers want nationa 
technical standards for 



motion picture industry 



NATIONAL standards for all phases 
of the technical equipment and 
operation of the motion picture indus- 
try, from the lighting and acoustics of 
studios to the projectors and screens 
of picture houses, have been requested 
by the Society of Motion Picture 
Engineers. In a letter to the Ameri- 
can Standards Association by Dr. 
P. G. Agnew, secretary of the Associa- 
tion, Alfred N. Goldsmith, vice presi- 
dent of the Radio Corporation of 
America and president of the Society 
of Motion Picture Engineers, asks for 
the development of uniform national 
standards to avoid the danger of con- 
fusion and waste resulting from the 
establishment of conflicting standards 
by different groups within the industry. 
If the request of the Society is ap- 
proved, a technical committee represent- 
ing all branches of the industry will 
be organized under the procedure of 
the American Standards Association. 
Topics outlined by Dr. Goldsmith for 
consideration are included in his com- 
munication, which follows : 

Some Topics Suitable for Consideration 
for Standardization 

Standardization projects, such as 
this proposed project on motion pic- 
ture standards, grow logically step by 
step. Topics which initially seem of 
importance turn out to be not particu- 
larly susceptible to constructive and 
useful standardization ; other topics 
which would not be considered as suit- 
able for standardization on preliminary 
consideration afterward develop into 
topics of major importance. In the fol- 
lowing it is therefore possible only to 
consider the general field of motion pic- 
ture activities (so far as they are of 
technological character) and to mention 
some of the topics which might be suit- 
able for standardization. The list must 
be regarded as entirely tentative. 

Definitions 

The terminology of the motion pic- 
ture field is confused at present. Such 
terms as "blimp," "zoom," "pan," "tilt," 



"projection angle," "wow," or "flutter," 
and the like, are used without any of- 
ficial recognition. This situation re- 
quires correction so far as is feasible. 

Film 

Measurement of characteristics of the 
base of the film, dimensions of the film 
and of its perforations, study of film 
shrinkage and permissible maximum 
shrinkage, photographic sensitometric 
tests, measurement and specifications of 
"safety film," standard width of film of 
various types, standard containers for 
film for storage and for transportation, 
together with methods of preservation 
of films (for archives, etc.) 

Studio 

The acoustic treatment and illuminat- 
ing methods for studios doubtless would 
permit of a considerable degree of 
standardization, both as to nomencla- 
ture, measurement, and specifications. 
Great varieties of lamps are used 
which are designated, for example, as 
"spots," "baby spots," "rifle spots," 
and so on. Light-diffusing media are 
used which are known by a variety of 
colloquial terms but are not definitely 
specified, for example, in what is 
known as "oil diffusion," and presum- 
ably a wide variety of characteristics 
can be obtained under the same name. 
The acoustic characteristics of studios 
have not as yet been specified in any 
precise form in many instances, nor 
has measuring equipment for the pur- 
pose been adequately considered. Pass- 
ing on to studio equipment, we find : 

Cameras 

The amount of significant noise pro- 
duced in these devices at certain def- 
inite distances and in certain definite 
directions (in free space), the toler- 
ances in the dimensions of the various 
working parts, the tensions and pres- 
sures in various parts of the mechan- 
ism, the dimensions of the magazines 
and of the magazine hubs, the take up 
tension, and numerous other charac- 
teristics of cameras require study for 



Seek Standard Definitions for "Blimp," "Zoom," 
and Other Terms 



'Wo 



w 



13 



possible standardization. The mode of 
mounting the lenses, the possibility of 
standardizing focal lengths and aper- 
tures of lenses for motion picture prac- 
tice, standardization of shutter aper- 
ture, definition of tripod arrangements 
and nomenclature for devices permit- 
ing moving shots (traveling trains, and 
the like), require consideration. Meas- 
urement of the effectiveness of camera- 
silencing inclosures is required. 

Recording Equipment 

Microphones, amplifiers, acoustic re- 
flectors, recording equipment, and sound 
track measuring equipment fall under 
this heading. Numerous characteristics 
of these devices are measurable, might 
be specified to advantage, and may 
ultimately be suitable for standardiza- 
tion. 

Re-recorders 

These are used for the introduction 
of modification of sound effects, and 
are rapidly becoming an important part 
of the studio technic. They are used 
for recording from 35 mm. film to 35 
mm. film ; and are now being produced 
as well for re-recording from 35 mm. 
film to 16 mm. film. The over-all fre- 
quency and volume characteristics of 
these devices, the amount of acoustic 
distortion that they produce, and cer- 
tain other factors are of major im- 
portance. 

Photographic Printing Equipment 

Classification of types of equipment 
of this sort (continuous and step print- 
ers, optical reduction printers, contact 
printers). Permissible speed variation. 
Definition of maximum desirable 
operating speed. Specification of il- 
lumination of the printing surface. 

Laboratory Processes 

The development of film is now car- 
ried out in various ways by automatic 
machinery. The terminology requires 
study, and certain of the processes re- 
quire precision measurement and defini- 
tion. For example, methods of measur- 
ing developer concentration or speed, 
measurements of the effectiveness of 
processes for "hardening," or other- 
wise preserving film, and the like. 

Exchange Equipment 

Films, after being returned from the 
theater, pass to the exchange where 
they are inspected. Inspection methods 
have never been definitely specified or 
defined. Dimensions and mechanical 
specifications, as well as strength tests 
of reels and containers used by ex- 
changes require consideration, both for 
nitrate and safety stock. 

(Concluded on page 16) 



14 



PROJECTION ENGINEERING 



Microphones speed up service and save space in 
New York soda store 



By H. G. Cisin 



BECAUSE of a modern invention, 
the old-fashioned "soda-jerker" 
is apparently doomed to disappear 
from public view. He will be 
relegated to the basement, merely to 
concoct sodas and sundaes, while his 
place will be taken behind the counter 
by an attractive waitress, who will re- 
peat the customer's order into a con- 
venient microphone. 

This is not an idle dream, but is the 
description of an actual installation in 
the Loft candy store at 251 West 42nd 
Street, New York City. In this store, 
two long counters occupy the center of 
the store. Numerous pretty waitresses 
stand behind the counters. There are no 
soda fountains, drink mixers, ice-cream 
refrigerators in evidence. These are 
all located far below in the basement. 
Instead, there is a shining chrome- 
plated microphone in front of each 
maiden. As the customer gives his or- 
der, the girl presses a switch and re- 
peats it into the "mike." It is heard in- 



stantaneously by the soda clerk in the 
basement. He fills the order immedi- 
ately, sending it up to the waitress by 
means of a high-speed dumbwaiter di- 
rectly alongside of his fountain. 

The effect of this is very pleasing to 
the customer. The service is remarkably 
rapid and the customer deals only with 
the cool, neatly-attired young woman 
behind the counter. From the stand- 
point of the store operator, the micro- 
phone installation is also a decided suc- 
cess. For one thing, it saves valuable 
space, since the removal of the bulky 
fountains and refrigerators leaves a 
great deal more room for customers and 
for counter displays. Furthermore, the 
service is speeded up so that more cus- 
tomers can be served in a given time. 
Last, but not least, the customers like 
this modern innovation and show their 
approval by increased patronage. 

Technically, the installation is quite 
simple. Six Universal model "X" two- 
button microphones are used. These are 



spaced at equal intervals along the 
counter so that a microphone is availa- 
ble within convenient reach of each 
waitress. The microphones are mounted 
on banquet stands, fastened to the coun- 
ters. The stands may be raised or low- 
ered. 

In the basement, there are three audio 
amplifiers, each feeding into a separate 
Wright-DeCoster dynamic reproducer. 
Two microphones are connected to each 
amplifier input. The amplifiers employ 
a 120 screen-grid tube in the first stage 
and a 150 power tube in the output 
stage. Each amplifier and speaker is 
contained within a metal case and the 
three metal cases are fastened to posts 
at suitable intervals along the soda 
fountain. 

Each amplifier is permanently con- 
nected to a 110-volt outlet alongside of 
it, but the "on-off" switch is located on 
the floor above, so that the current is 
consumed only when an order is being 
transmitted over the sound system. 



AAA 



British quota films to be made in Ontario 



ACCORDING to Film Daily, 
New York, Canada Produc- 
tions, Ltd., a million-dollar 
motion picture production com- 
pany, is being organized for the pur- 
pose of buying and operating the pres- 
ent Ontario Government studios at 
Trenton, Ont. The plan is to have the 
large American companies produce 
their British quota films at the Trenton 
studios thus solving this growing prob- 
lem for them. Production of enough 
good pictures in England to fill the 
quota, which jumps to 15 per cent next 
year, \7 l / 2 per cent in 1934-35, and 20 
per cent in 1935-36, is already being 
found extremely difficult, and it is be- 
lieved that a studio in Canada, accessi- 
ble to Hollywood, would simplify the 
situation. Two Canadian provinces, 
Ontario and British Columbia, also 
have film quota laws, though not as yet 
put into force. 

The plan proposed by Canada Pro- 
ductions, Ltd., is to have the American 
companies send their stars and directors 
of British citizenship to the Trenton, 
Ont., studios to make a number of fea- 



tures annually to fill the English quotas. 
In this way, the company having its 
distributing organization in Canada, the 
United States and Britain, and employ- 
ing the services of screen stars and di- 
rectors well and favorably known in the 
American theater, will be assured of 
release for its film productions. 

The actors, and directors, now in 
Hollywood, who are British subjects 
and who are available for motion pic- 
ture production in Canada under the 
British quota regulations, include: 

Actresses : Lilliam Rich, Elsie Fergu- 
son, Alice White, Polly Moran, Doro- 
thy Mackaill, Fay Wray, Doris Lloyd, 
Barbara Kent, Daphne Pollard, Beryl 
Mercer, Aileen Pringle and Marie Pre- 
vost. 

Actors : Clive Brook, Reginald Den- 
ny, Montagu Love, Tom Moore, Owen 
Moore, Matt Moore, Ivor Novello, Wal- 
ter Pidgeon, Jameson Thomas, Alan 
Mowbray, Walter Huston, David Man- 
ners, Ralph Forbes, John Loder and 
Harold Neison. 

Directors : Donald Crisp, Rupert Ju- 
lian, Mai St. Clair, Alan Dwan, Em- 



mett Flynn, George Melford, Sidney 
Olcott, James Whale, John Robertson, 
Leslie Pearce and Nick Carter. 

There is a report that those interest- 
ing themselves in this new Canadian 
film venture include Sir Herbert Holt, 
president of the Bank of Montreal, and 
E. W. Beatty, president of the Canadian 
Pacific Railway. 



REGAL WILL DISTRIBUTE MONO- 
GRAM IN CANADA 

NEGOTIATIONS have been com- 
pleted between Regal Films, Ltd., 
of Toronto and Monogram Pictures, 
whereby Regal has obtained the Mono- 
gram franchise for the Dominion of 
Canada. Pictures in the deal include 24 
features and 16 westerns. Regal dis- 
tributes through branches in Toronto, 
Vancouver, Winnipeg, Calgary, Mon- 
treal and St. John. According to W. 
Ray Johnston, president of Monogram, 
the tie-up gives his company the widest 
distribution of any independent organ- 
ization. 



NOVEMBER, 1932 



Trend of developement 
in equipment for 
schools* 



PRIOR to the advent of 16 mm. 
film, much of the schools' projec- 
tion equipment had been bought 
up "second-hand" from theatrical 
equipment exchanges. It was compara- 
tively heavy and cumbersome, and the 
more earnest the attempt to introduce a 
safety factor against fire hazard, the 
heavier the projectors became. This 
equipment, like its film material, was 
the natural child of the theatre. 

Quite otherwise is the situation with 
the 16 mm. projector. It is not a mere 
adaptation or reduced version of the 
theatrical projector, it is a fundament- 
ally new machine, having many points 
not at all in common with its prede- 
cessor. For instance, it needs to make 
no provision whatever against fire haz- 
ard, because it is automatically confined 
to the use of non-inflammable film. In 
order to raise their effectiveness as a 
teaching tool, a factor that never en- 
tered into the design of a theatrical ma- 
chine, the better 16 mm. projectors pro- 
vide for stopping the film on a single 
frame for the showing of a "still," and 
the reversing of the direction of the 
film to facilitate ready comparison and 
review. 

Just because 16 mm. film is referred 
to as "amateur" film, it does not mean 
that the 16 mm. projector can be made 
with any less care and precision. To 
demand that a school projector be above 
all things "cheap" is to lose sight of 
the fact that exact registration and rock- 
like steadiness are more essential where 
the eyes of young pupils are involved 
than under any other conditions. An 
error of registration of even only one- 
thousandth part of an inch at the aper- 
ture means the quivering of the screen 
image by about one-half inch at ordi- 
nary distance. That thousandth part of 
an inch play in a poorly made projector 
may wreck the eyes of a thousand chil- 
dren. 

American schools have found that it 
is not even good account-book economy 
to place heaviest emphasis on first cost. 
There are many cases where schools 
that bought the best 16 mm. equipment 
obtainable eight years ago are still get- 
ting perfect service from it every day 

Wy William F. Kruse, in The International 
Review of Educational Cinematography, August, 
1932. 



in the school year, whereas "economy" 
purchases proved unsatisfactory from 
the start and had to be quickly replaced. 
The careful school administrator buys 
a projector for the long years of quality 
service obtainable from the instrument, 
rather than for its first cost. 

As a matter of fact the better modern 
16 mm. projectors are at least as finely 
built as the best of their theatrical pre- 
decessors. Tolerances held to within 
one-half of one-thousandth part of an 
inch assure absolute steadiness; a nine- 
to-one ratio on occultation is used on 
at least one 16 mm. projector, in com- 
parison to the four-to-one customarily 
found in large machines. 

The modern 16 mm. projector weighs 
but from 10 to 20 pounds. Its direct il- 
lumination, from 300 to 500 watt Mazda 
bulbs, is equal to every demand, includ- 
ing that of the large school auditorium. 
Projection distances of over 100 feet 
and pictures 12 feet wide are not all 
uncommon with the best type of 16 mm. 
projectors. For example, Northwestern 
University has reported the showing of 
16 mm. football films at 160 feet dis- 
tance. The 16 mm. projector is adapta- 
ble for color and sound. It has already 
solved all the more serious difficulties 
that stood in the way of the general use 
of film in the school. 

Progressive Improvement 

This does not mean that every prob- 
lem of projector construction has al- 
ready been solved once and for all. Pres- 
ent projector development is a response 
to school requirements worked out by 
visual instructionists on the basis of 
their experience, and as these require- 
ments change or clarify, projector de- 
velopment keeps pace. There are two 
principal trends of school demand to- 
day with respect to projector specifica- 
tions. The first is for a machine just as 
fine, as powerful, as versatile as is pos- 
sible to be made. The other is a demand 
for most extreme simplicity coupled 
with lower costs. 

This latter demand was formulated 
most commendably, for example, by 
Dr. Ernst Ruest in Kinotechnik, Janu- 
ary, 1931. His specifications were in the 
main echoed from an entirely unre- 
lated source, viz., by Paul G. Edwards, 



15 



head of the visual instruction depart- 
ment of the Chicago Schools. In the 
main We can subscribe whole-heartedly 
to Dr. Ruest's specifications, although 
on minor points we may disagree. For 
example, there is opposition to the 
"still" feature because it is believed that 
it cannot be efficiently cooled. But it 
is properly cooled on a properly de- 
signed 16 mm. projector. No one would 
dispute that a glass stereopticon slide 
affords a superior projected still pic- 
ture, but when the "still" is held wher- 
ever desired in a reel of film it instantly 
relates dynamic to static concepts in a 
way that can hardly be duplicated in 
any other manner. If the laboratory, 
when making the print, exercises ordi- 
nary care, then framing on 16 mm. film 
is fully automatic and a framing device 
unnecessary. The limiting of projection 
lenses to a maximum of F 1.9 leaves out 
of consideration the improvements in- 
troduced, for example, with the new 
2-inch Cooke F 1.65. And the need for 
a splicing outfit should be apparent only 
where a film is taken constantly from 
school to school, instead of following 
the usual practice of going back to the 
center, unrewound, for inspection. 
However, in the main, Dr. Ruest's spe- 
cifications are entirely acceptable and 
indicative of serious and well-informed 
consideration. 

Preferred Types 

The comparative strength of the two 
tendencies, of versatility against sim- 
plicity, power against cost, was tested 
at the recent meeting of the National 
Education Association. Visiting super- 
intendents, principals and visual instruc- 
tionists were asked to express prefer- 
ence as between two projector models, 
designated JL and M respectively each 
worked out in direct response to educa- 
tional demand. The Model JL was the 
latest all-gear-driven machine, eliminat- 
ing belts entirely, powered with 400 
watt 100 volt biplane filament lamp, 
Cooke F 1.65 oversize 2-inch projection 
lens, micrometer focus mirror, auto- 
matic rewind, reverse and still features, 
integral pilot light, radio interference 
eliminator and other advanced features. 
The Model M was a single-control 
classroom machine, with excellent illu- 
mination from a 300-watt 115-volt lamp 
film movement and cooling system iden- 
tical to other Bell & Howell models, but 
without reverse or "still" features, and 
priced at one-half the Model JL. 

The test was purposely designed to 
be between extremes. When the results 
were tabulated, they showed that two 
out of every three preferred the more 
versatile, more expensive machine. 
Some of the reasons assigned are in- 
teresting as showing the trend of 



16 



PROJECTION ENGINEERING 



thought among American schoolmen on 
projector design. About the Model JL 
the comments included : "Can get larger 
pictures," "Will not have to darken the 
classroom complete," "Can use it in 
auditorium," "One machine for every 
school purpose," "Really need the still 
feature." About the Model M the com- 
ments included: "The simpler the bet- 
ter," "We can equip twice as many 
schools," "Just the thing for the un- 
trained teacher ; all she does is press 
the switch." It was to be observed that 
those selecting a machine for their own 
use, or for a single machine to be per- 
manently placed in a single school, or 
for an auditorium situation, invariably 
chose the heavier machine. Those buy- 
ing for large school systems with hun- 
dreds of untrained elementary teachers, 
or those influenced by financial strin- 
gency, cast their votes for the lower 
priced model. A personal survey among 
members of the National Academy 
present at the Washington meeting dis- 
closed substantially the same ratio of 
preference. 

Film Material for School Projectors 

When the school had to depend on 
the theatre almost entirely for its film 
material, it was to be expected that 
much of the use to which film was put 
in the school bore a distinct theatrical 
"tinge." A considerable part of the 
"work" with motion pictures consisted 
of "shows" given in the auditorium, and 
the strictly educational benefits derived 
were limited and difficult to measure. 

Today, thanks to the availability of 
16 mm. projectors, there is unanimous 
recognition that the place where the 
film contributes the most to the school 
is in the classroom. And the bulk of 
the films now available to schools are 
made with the requirements of the class- 
room distinctly in mind. These class- 
room films bear an increasingly close 
relationship to the textbook and the 
study outline. More and more the edu- 
cator is demanding factual film mate- 
rial that will fit his courses, not in a 
highly edited or pre-digested form, but 
in short lengths of authentic "docu- 
mentary" topical material that shows 
actual pictures of the thing studied in 
natural motion and in relationship to 
its milieu. 

Where sound is essential to a com- 
plete understanding there is no doubt 
but a similar demand will develop for 
authentic sound film of the same char- 
acter. Most educators are not yet ready 
to grant that the sound film will sub- 
stitute an entirely new technique and 
methodology. One hears much sus- 
picion directed against "canned lec- 
tures" as a step backward toward a 
revival of methods banned by the more 



progressive schools of pedagogy. On 
the other hand, one of our most noted 
authorities on visual education, Dr. Jo- 
seph J. Weber, of Valparaiso Univer- 
sity, suggested, already in 1929, that 
the "talkie" might very well check the 
rising cost of formal education, by syn- 
dicating master teachers, to instruct pu- 
pils more quickly and interestingly. Dr. 
Weber pointed out specifically, how- 
ever, that this would not eliminate the 
human teacher, but, on the contrary, by 
freeing her from the task of cramming 
facts into her pupils, and by giving her 
master teachers of the screen as models, 
she would be better able to exercise 
personal direction of the class. 

Every reason that led to the adoption 
of the 16 mm. standard for silent film 
in the school applies with equal force 
to the talkie. Theatrical producers who 
enter the talkie school field find them- 
selves practically forced to furnish 16 
mm. films, and all but one of these pro- 
ducers now offer 16 mm. as well as 35 
mm. prints. 

The argument that only sound-on-disc 
is available for 16 mm. prints, while in 
addition sound-on-film can be had for 
35 mm. subjects, is not of basic impor- 
tance, and indications are that the ar- 
gument itself will be eliminated shortly. 

The sharp divorce between school 
films and those designed for theatrical 
exploitation does not mean that the edu- 
cator now turns his back entirely on 
the theatre. It merely means that the 
entertainment film is recognized as such 
and its qualities appraised accordingly. 
Quite a number of feature productions 
are looked upon as having distinct his- 
torical and literary background values 
for school children. Attendance at such 
pictures is encouraged. Public libraries 
distribute bookmarkers which give dates 
when such approved pictures are played 
at local theatres, and also include book- 
lists dealing with subject matter re- 
lated to the pictures. Sometimes these 
pictures are discussed in the classroom, 
and occasionally they are run in the 
school auditorium. Periodicals devoted 
to the special interests of teachers, of 
parents, of visual instructionists, etc., 
publish motion picture reviews, and 
treat the screen as a powerful educa- 
tional force, helpful or harmful as the 
case may be. Notable are the "Film 
Estimates" of Nelson L. Greene, editor 
of "Educational Screen," and the bul- 
letins of the National Committee for 
Better Films. 

Recent experiments at the University 
of Chicago indicate that motion pic- 
tures have a direct and lasting effect 
upon social attitudes, according to Ruth 
Peterson, in a report to the Chicago As- 
sociation for Child Study and Parent 
Education. "All's Quiet on the West- 
ern Front" was found to exert a dis- 



tinct anti-war effect, while two widely 
different films dealing with China, 
shown in two different towns, were 
found to arouse favor in one case and 
antipathy in the other. The importance 
of the theatrical screen as a propaganda 
force cannot be overestimated. Teachers' 
organizations, parents' organizations, 
and similar bodies with enrolled mem- 
berships running into the millions are 
directing more and more searching at- 
tention toward the theatrical screen. At 
the same time, such organizations are 
awakening to the tremendous possibili- 
ties of the classroom screen as a teach- 
ing tool. Producers of films, and of 
equipment for talking and showing film, 
now pay serious heed to these tenden- 
cies, because there is a promise here of 
a vast market at present almost un- 
touched. 

Interest in the educational possibili- 
ties of the motion picture film tran- 
scends all national borders. 



ENGINEERS WANT NATIONAL 

TECHNICAL STANDARDS FOR 

MOTION PICTURE INDUSTRY 

(Concluded from page 13) 

Theater Equipment 

Projectors have numerous dimensions 
requiring standardization. The tension 
and pressure at various points of the 
mechanism, magazine dimensions, safe- 
ty devices, contrivances to protect the 
projectionists' eyes from undue glare, 
take-up tension, and the like, may all be 
considered for standardization. Screens 
(both of the continuous type and of the 
perforated "sound-transmitting" type 
merit study for standardization of their 
reflection characteristics and specifica- 
tions thereof. The re-surfacing of 
screens as they become warped brings 
up a similar series of problems. The 
amplifying and loud-speaking equip- 
ment gives rise to the usual series of 
electro-acoustic standardization prob- 
lems ending with the frequency charac- 
teristic, distortion characteristic, and 
space distribution of the output of the 
loudspeaker system. 

Miscellaneous 

Such fields as color photography re- 
quire study. The various processes have 
never been satisfactorily defined nor 
have the various forms of cameras, 
lenses, processing equipment, and pro- 
jectors been put on a suitably precise 
basis. Three-dimensional pictures re- 
quire definition. Frequency systems 
which give perspective impressions are 
classified as three-dimensional or 
"pseudo-stereoscopic." A considerable 
amount of confusion exists here on 
terminology. 



1 



NOVEMBER, 1932 



Sound systems in 
Rockefeller Center, 
New York 



By James Frank, Jr.* 



THE city in a city now rapidly 
nearing completion in New York 
and to be known as Rockefeller 
_ Center is to include two theatres, 
the larger to be known as the "Inter- 
national Music Hall" with a seating 
capacity of 6,300 seats, the smaller to 
be called the "RKO Photoplay Thea- 
tre" and having a seating capacity of 
3,000 seats. 

The installation for the "International 
Music Hall" is the larger and covers a 
wider scope. It has a total undistorted 
output of 510 watts. 

The RCA Victor sound systems to 
be installed in the larger theatre are di- 
vided into eight units, as follows : 



Sound reinforcing system. 
Rehearsal address system. 
Stage manager's call system. 
Main sound projection system. 
Rear stage sound projection sys- 




1. 
2. 
3. 
4. 
5. 
tem. 

6. Deaf headphone system. 

7. Preview sound projection systems. 

8. Radio and monitoring system. 
The installation of these systems is 

to be so arranged that through physical 
location and electrical connection cer- 
tain of the equipments may be intercon- 
nected. Fig. 1 shows the equipment lay- 
out on the projection room level. From 
the diagram the various amplifiers and 
sound reproducers may be easily located. 
It is important to note that the am- 
plifiers and loudspeakers used on the 
various systems are essentially alike, al- 
though various assemblies of apparatus 
are employed. 

Sound Reinforcing System 

The purpose of this system is to re- 
inforce the stage presentations and or- 
chestra music to suitable levels in order 
that the desired aesthetic effects and 
clear intelligibility may be obtained at 
all points in the auditorium. This sys- 
tem consists essentially of a number of 
microphones, amplifier equipment, and 
loudspeakers, together with necessary 
control apparatus. The microphone 
transmitters located around the stage 
and orchestra pit pick up the voices or 

*Phctofihoiw Division, RCA-Victor Company. 



music, change the sound waves to elec- 
trical waves, which are fed into the 
microphone amplifiers. After the level 
has been raised by these units the elec- 
trical waves are fed into the mixers in 
the control console where they are prop- 
erly mixed and then fed into a "booster 
amplifier." At this point the level is 
sufficiently raised to feed into the main 
amplifiers. From the main amplifier the 
electrical waves, now at any desired 
level, are fed into the auditorium loud- 
speakers where they are converted into 
sound waves again which are directed 
to all points in the auditorium. 

A. Fifty type PB-31 velocity micro- 
phones of the type used for sound re- 
cording will be furnished, mounted on 
swivel bases in order that they may be 
"aimed" in any desired direction. These 
microphones will be located as follows : 

Eight in traps in the floor of the or- 
chestra elevator. 

Eight on program stands on band 
wagon. '; 

Eight suspended from light bridges. 

Eleven in footlights approximately on 
seven-foot centers. 

Nine on stage connected to traps on 
the stage floor. 

Six (3 on each side) on choral stairs. 

The velocity microphone contains a 
thin metallic ribbon suspended between 
the poles of a permanent magnet in 
place of a diaphragm. Sound waves 
reaching the ribbon vibrate it within the 
magnetic field set up by the magnet. 

The microphone responds faithfully 
to all sound vibration over the range of 
audible frequencies from 30 to above 
10,000 cycles. 

The most important characteristic of 
the velocity microphone is its direc- 



Page 17 

tional property. Since the ribbon is sus- 
pended in free space, sound waves ap- 
proaching the microphone from a di- 
rection on the same plane as the ribbon 
have no effect upon it. but sound waves 
from either direction along an axis 
perpendicular to the plane of the ribbon 
have a maximum effect. For equal dis- 
tances from the transmitter, sound origi- 
nating 70° or 80° off the axis perpen- 
dicular to the ribbon will have prac- 
tically no effect, whereas at 45° off this 
perpendicular the sensitivity is approxi- 
mately 70% of the maximum. This char- 
acteristic is of great value in the solu- 
tion of some of the difficulties usually 
encountered in reverberant locations by 
the reduction of the effect of undesired 
sound reflections, and in the increased 
possibilities of obtaining better balance 
and selectivity in sound pickup. In ad- 
dition, this characteristic is likewise 
outstanding in that this is the only type 
of microphone that responds uniformly 
to all audible frequencies over the en- 
tire 45° angle. This permits placing 
microphones in the footlights on ap- 
proximately seven-foot centers with the 
result that uniform pickup of all fre- 
quencies is accomplished across the 
front of the stage. 

B. Fifty type PA-82 microphone am- 
plifiers will be furnished. These ampli- 
fiers will be located on a specially con- 
structed rack located in an amplifier 
room in the basement under the stage. 
The amplifier is carefully shielded to 
render it free from external interfer- 
ence and undesired pickup. The entire 
unit is enclosed in a cylindrical metal 
case particularly designed for wood rack 
mounting, and is mounted vertically 
with connections made through plugs 
at the top and bottom. Power supply 
to operate the unit is made available 
from the amplifier room on the projec- 
tion room level. 

C. A type PB-78 control console as 
illustrated in Fig. 2 is furnished for 
controlling the individual microphone 
amplifier outputs and mixing them prop- 
erly for amplification. It is located in 
the control room as shown in Fig. 1. 
The console is of the mahogany desk 
type with metal top on which all the 
controls are located. 

At the front right side of the control 
console is located an 80-jack panel at 



Fig. 1. Appa- 
ratus layout on 
projection room 
level 




Page 18 



PROJECTION ENGINEERING 



which point the outputs from the fifty 
microphone amplifiers terminate. The 
additional jacks are for expansion. Di- 
rectly in front of the jack panel are 38 
cords and single plugs with weights and 
rollers divided into four groups, two of 
eleven each and two of eight each, each 
group with a distinctive color. The 
cords are arranged in four rows. 

At the back right and left side of the 
control console are located four mixers, 
two eleven-position mixers and two 
eight-position mixers, each with its dis- 
tinctive color on the mixer knob and 
wired to its respective cords mentioned. 
On the console top a four-position 
mixer is located, one position for each 
of the mentioned mixers, which controls 
the level of its respective group. By 
plugging into the jacks any combina- 
tion of microphone, with a maximum of 
thirty-eight, in groups of eight or eleven 
may be selected and mixed in the four 
mixers. After this position the output 
of each of these four mixers is fed into 
the four-position mixer. A master mixer 
is located on the console top which con- 
trols the mixed output of the four- 
position mixer. 

At the front left side of the console 
top a "booster amplifier" is located 
which compensates for the loss in the 
control console. The output from the 
master mixer is fed into this amplifier 
and the level is raised to such an extent 
that the output can be coupled to the 
main amplifier. 

A volume indicator is mounted on 
the console top at the rear in a vertical 
position. An adjustment is supplied so 
that a predetermined reading on the 
meter may be made to represent any 
output level of the amplifier. 

At the front left side of the console 
is located a jack panel for changing 
normal connections of the outputs of 
the eight position and the eleven posi- 
tion mixers into the four position 
mixers to prevent the failure of one 
unit of the four position mixer from 
interfering with the operation of the 
system. In case of emergency it is also 
possible to circumvent the four position 
mixer and /or the "booster amplifier" 
to feed directly into the main amplifier 
at a reduced output. 

The separate control units of the 
mixers can be removed for repair at a 
moment's notice, such removal not af- 
fecting the operation of the remaining 
units. 

D. The main amplifier equipment 
consists of two duplicate eighty watt 
amplifier channels, Type PB-84. These 
amplifiers are primarily arranged for 
operating in duplicate ; that is, one at 
a time, the other being held in reserve 
for emergency use. However, pro- 
vision has been made so that one chan- 
nel may be used on the regular sound 
reinforcing system and the second chan- 



Fig. 2. Control 
Console (PB-78) 




nel used at the same time to operate 
the effect loudspeakers. These ampli- 
fiers consist of units mounted on stand- 
ard channel-iron racks and are located 
in the amplifier room as shown in Fig. 1. 

Each of the channels include neces- 
sary terminal strips, main power line 
switch, a Type PB-23 voltage amplifier 
unit, two Type PB-45, power amplifier 
units (40 watts each) and a Type 
PB-24 power amplifier unit (10 watts). 

All amplifier units are complete in 
themselves in that they contain their 
own a-c. operated power supply appa- 
ratus. 

Headphone System 

The 10-watt power amplifier unit is 
used for the deaf headphone system. 
The output impedance is such that a 
variable number of headphones may be 
installed. All headphones are connected 
across the output of the amplifier in 
series with an adjustable resistor of suf- 
ficiently high value that all headsets 
may be removed from their jacks with- 
out affecting the frequency character- 
istics of the system. 

E. The Type PB-50 miscellaneous 
equipment rack which is located with 
the main amplifier includes an audio 
relay panel, two jack panels, a Type 
PB-51 tube testing panel, a Type PB-5S 
radio receiver, a Type PB-75 photo- 
graph turntable, a Type PA-80 ampli- 
fier unit. 

The audio relay panel includes the 
relays required to switch the deaf hear- 
ing system amplifier to either the sound 
reinforcing system or the main sound 
projection system, to switch either of 
the sound reinforcing system amplifier 
channels into the circuit, and to con- 
nect the stage manager's call system to 
the sound reinforcing system when de- 
sired. 

The two jack panels are used for 
"patching" or "interconnecting." The 
input and output circuits of all ampli- 
fiers on the sound reinforcing system, 
rehearsal address system and stage man- 
ager's call system are brought out to 
these panels as well as the outputs of 
all special apparatus including radio 



receiver, phonograph turntable, and the 
like. For normal operation no cords are 
required, but for special interconnec- 
tions or for use of special apparatus 
cords tying the desired circuits are used 
in these jack panels. 

The radio receiver is a nine-tube su- 
perheterodyne providing excellent per- 
formance in all the features incorporated 
in modern radio broadcast receivers. 
Automatic volume control, push-pull 
pentode output stage, tone control, cali- 
brated kilocycle dial and the inherent 
sensitivity, selectivity, and tone quality 
of the superheterodyne circuit are some 
of the features of this receiver. This 
unit will work in conjunction with any 
of the power amplifier units in the sys- 
tem. 

The phonograph turntable consists of 
a single turntable designed to operate 
at 78 revolutions per minute. A volume 
control is mounted on the base board 
adjoining the table. The whole unit is 
mounted on a panel which is hinged to 
the rack so that when it is not in use 
it is in a vertical position with the 
panel screwed to the rack channel. 
When in use it is lowered from the top 
and held rigid in front of the rack. 

The amplifier unit included in this 
rack is used for monitoring purposes. 
This unit may be connected across the 
output of the power amplifier unit of 
either the sound reinforcing system, ef- 
fect system ( one channel of sound rein- 
forcing system ) , stage manager's call 
system or the rehearsal address system 
and will operate the monitor loud- 
speaker on the Type PB-60 power con- 
trol rack, in the amplifier room, in the 
spot cove, or at the chief electrician's 
position. 

F. The Type PB-60 power control 
rack is located adjacent to the control 
console in the control room as shown in 
Fig. 1. This rack includes a micro- 
phone power control panel, an amplifier 
power control panel, a rehearsal micro- 
phone mixer, an audio control panel, a 
monitoring loudspeaker panel, and a 
chief electrician's microphone control 
panel. 

The microphone power control panel 



NOVEMBER, 1932 



Page 19 



included switches which through the 
use of relays turn on the power to all 
microphone transmitters and micro- 
phone amplifiers. 

The amplifier power control panel in- 
cludes switches which through the use 
of relays turn on the power to all the 
amplifiers used in the sound reinforc- 
ing system and rehearsal address sys- 
tem. 

The rehearsal microphone mixer in- 
cludes mixer units for controlling the 
output of each of the four microphones 
used on the system with a master mixer 
to control the group. 

Audio Control Panel 

The audio control panel includes two 
key switches, one to select, through the 
use of relays, amplifier channels for this 
system and the other to connect, through 
the use of relays, the deaf hearing sys- 
tem amplifier to either the sound rein- 
forcing system or the main sound pro- 
jection system. In addition, four remote 
volume control push button stations are 
included, controlling the volume on each 
of the amplifier channels of the sound 
reinforcing system, and of the rehearsal 
address system. 

The monitoring loudspeaker panel in- 
cludes a panel mounted electro-dynamic 
loudspeaker unit with volume control. 

The chief electrician's microphone 
control panel consists of a control unit 
to equalize the output of the carbon 
microphone used by the chief electrician 
on the rehearsal address system to the 
three velocity microphones used on the 
same system. 

G. The Type PB-76 loudspeaker con- 
trol rack is located also adjacent to the 
control console in the control room as 
shown in Fig. 1. 

H. The Type PB-56 power supply 
rack which is located in the motor gen- 
erator set room as shown in Fig. 1 in- 
cludes an a-c. relay panel, two d-c. 
relay panels, and two plate and bias 
supply units. 

The a-c. relay panel includes a num- 
ber of relays to connect the a-c. supply 
to the rectifier tubes. The two d-c. re- 
lay panels include a number of relays 
to connect the power supply to the mi- 
crophones of both the sound reinforc- 
ing system and the rehearsal address 
system. 

The two plate and bias supply units 
are connected in duplicate, one being 
used regularly and the other as emer- 
gency, and are used to supply plate and 
bias power to the microphone amplifiers 
and the "booster amplifier." The unit 
is designed to operate from a 205-220 
volt, three phase, 60 cycle a-c. supply. 
It is essentially a three phase-six phase 
rectifier. This type of unit by virtue 
of its fundamental principle of operation 
reduces the percentage of a-c. ripple 
voltage in the d-c. output voltage of the 



rectifier tubes. This is a distinct advan- 
tage over the common one and two 
phase rectifiers in that less filtering is 
required at 360 cycles to reduce the 
percentage of ripple voltage to any pre- 
determined level than at 120 cycles. 
This reduction in required filtering im- 
proves the regulation of the rectifier in 
that the series resistance factor of filter 
inductances is reduced to a minimum. 
The regulation of the rectifier is further 
improved by the use of the mercury 
vapor (Radiotron UX-866) rectifier be- 
cause the voltage drop in this tube is 
practically constant for any load within 
the tube rating. These factors are very 
important because of the fact that this 
rectifier supplies plate power to several 
microphone amplifiers. 

J. The Type PB-79 power supply 
rack is located adjacent to the PB-36 
power supply rack and includes an a-c. 
relay panel, two Type PK-15 loud- 
speaker field supply panels and two 
Type PK-20 loudspeaker field supply 
panels. 

The a-c. relay panel includes a num- 
ber of relavs to connect the power to 
the amplifier of the sound reinforcing 
system, effect system and rehearsal ad- 
dress system. 

The two Type PK-15 loudspeaker 
field supply panels are used to supply 
power to the loudspeaker fields of the 
radio and monitoring system No. 8. 
Each panel delivers 0.5 ampere at 103 
volts. 

The two Type PK-20 loudspeaker 
field supply panels are connected in 
duplicate, one being used regularly and 
the other for emergency, and are used 
to supply power to the fields of the 
sound reinforcing system and rehearsal 
address system loudspeakers. Each panel 
delivers 4.0 a^mperes at 100 volts. 

K. The battery power supply equip- 
ment is all located in the battery room 
as shown in Fig. 1. This equipment in- 
cludes four sets of glass jar storage bat- 
teries together with charging equipment. 

A duplicate set of storage battery cells 
with a capacity of 1,040 ampere hours- 
is furnished to supply filament current 




Fig. 3. Directional baffle loudspeaker (PL-35). 



to all microphone amplifiers and field 
supply to all velocity microphone trans- 
mitters of the sound reinforcing system 
and rehearsal address system. 

Relay Excitation 

A duplicate set of storage battery 
cells with a capacity of 186 ampere 
hours is furnished to supply excitation 
to all relays used with these systems. 
The cells are all mounted in racks 
against the wall. 

A battery charging motor-generator 
set together with control panel, starter, 
and necessary switches, and conduit 
boxes is also furnished. The sets of 
storage battery cells are so connected 
that one set of each type is in use when 
the duplicate sets are being charged. 

L. Six loudspeakers are furnished 
for use on the sound reinforcing system 
in the auditorium, four Model 4 PL35A1 
loudspeakers and two Model 4 PL35B1 
loudspeakers. These loudspeakers con- 
sist of a directional baffle of the expo- 
nential type coupled to a six-inch cone 
driver of rugged construction. This 
type of loudspeaker combines the ad- 
vantage of a flat frequency characteris- 
tic with high efficiency, uniformity of 
response over the entire angle of dis- 
tribution and high power handling ca- 
pacity. Fig. 3 shows a view of one of 
these loudspeakers. 

The four Model 4 PL35A1 loud- 
speakers employing 60-inch directional 
baffles are to be mounted behind a grill 
above the proscenium arch. 

The two Model 4 PL35B1 loudspeak- 
ers employing 37-inch directional baffles 
are to be mounted in the wall, one on 
each side of the proscenium arch. 

M. For effect purposes two Type 
PL-64 loudspeakers employing 17-foot 
directional baffles will be furnished for 
mounting at the rear of the stage over 
the rear stage projection room. These 
speakers may be connected to the sec- 
ond amplifier channel of the sound rein- 
forcing system for simultaneous or sep- 
arate operation when back-stage sound 
effects are desired. Each directional 
baffle employs four of the six-inch cone 
units. 

N. For monitoring purposes three 
Model AF6179 loudspeakers will be fur- 
nished, one to be located in the spot 
cove, one at the chief electrician's posi- 
tion, and one in the amnlifier room. 
These loudspeakers consist of a standard 
magnetic speaker • mechanism mounted 
in the rear of a specially designed wood 
plaque faced with three-ply veneer and 
the center of matched oriental walnut. 

The overall frequency characteristic 
of the sound reinforcing system is such 
as to give faithful uniform reproduction 
over the entire range of 50 to 10.000 
cycles. 

(To be concluded) 



Page 20 



World's biggest sound 
amplifier broadcasts 
Chicago music festiva 



/ J ^^^^ NE of the important things 
# * g^\ that the Chicagoland Mu- 
l J sic Festival has done is 

^^^r to solve the problem of 
electrical amplification. For the first 
time since musical programs have been 
put on in so huge an enclosure as Sol- 
dier's Field, musical tones came across 
the great arena in a thoroughly satis- 
factory manner. It has been possible 
in the past to project spoken words: 
This time it was possible to understand 
the words in song." 

So writes Edward Moore, musical 
critic of the Chicago Tribune, which 
for the past three years has sponsored 
music festivals featuring choruses, solo 
voices, bands, drum and bugle corps 
from the entire middle west. Mr. 
Moore writes further : 

"In fact, the transmission was almost 
too good. Words and tone came to the 
ears almost too plainly. But speaking 
as one who has great respect for the 
English language as a medium of song 
as well as speech, it was a comfort to 
hear words without straining the at- 
tention." 

Mr. Moore does not measure amplifier 
and public-address performance in 
terms of watts and decibels. He leaves 
to the engineers frequency characteris- 
tics and output impedance. He listens 
with a trained musical ear and criticizes 
without fear or favor. But any tech- 
nically trained listener who heard this 
excellent music pageant will agree that 
magnificent progress in sound repro- 
duction has been made in the past year. 
And, if he be fair minded, will join in 
awarding unstinted praise to the men 
who engineered, built and operated the 
public-address system which brought 
every note of the festival to the 250,000 
ears present. 

For the benefit of those unfamiliar 
with it, Soldier's Field in Chicago is 
a huge outdoor amphitheatre, with seat- 
ing capacity for 100,000 persons. On 
the occasion of the Chicagoland Music 
festival, every seat was taken and 25,- 
000 more persons crowded every avail- 
able bit of standing room. At the north 
end of the oval bowl was constructed a 
gigantic stage to hold 10,000 per- 
formers — bands and choruses. The back 
row of the south tier of seats was per- 
haps a quarter mile from the stage. 



Seventy Loudspeakers Used 

Nearly a week was spent in installing 
the public-address equipment. Seventy 
speakers were installed just forward of 
the stage in two banks of 35 each. Both 
horn and cone speakers were used, to 
bring out both high and low frequencies. 
Twenty-four microphones were in- 
stalled on and around the stage, and as 
many as ten were used simultaneously 
in picking up the program. This does 
not include the additional microphones 
used by radio station WGN and the 
Columbia Broadcasting System, which 
had no connection with the public- 
address system. 

The amplifier system was placed in 
a room under the stadium seats, and the 
microphone mixing panel near the 
front of the platform where the opera- 
tor could view the proceedings and com- 
municate by a private telephone line 
to the amplifier operator. 

Nearly six miles (30,000 feet) of 
microphone cable were used. In all 
there were seven stages of amplifica- 
tion between the microphones and the 
speakers. Approximately $20,000 worth 
of sound equipment was used in the 
installation, which figure does not in- 
clude wire or labor. In addition to sev- 
eral preliminary amplifiers, there was 
the large 400-watt output amplifier 
using four type 203A tubes, a mixing 
input panel for the 24 microphones, and 
an output impedance matching panel 
for the 70 speakers. Two spare 100- 
watt amplifiers were held in reserve for 
use in case of trouble. Much ingenuity 
was necessary to accomplish correct 



PROJECTION ENGINEERING 

phasing in the speakers and to eliminate 
reverberation and echo. 

The success of the installation is even 
more remarkable when it is realized 
that there was no opportunity for a real 
test. Speaking tests were made, of 
course, with listeners in various parts 
of the arena, but this could give no 
accurate indication of tonal effects with 
the auditorium full and with ten micro- 
phones working in unison on a massed 
chorus of 5,000 voices. 

Amplifiers of 400 watts rated output 
have been made before, of course, but 
the design of an amplifier of this size 
with the exceptionally flat frequency 
characteristics necessary to produce 
such accurate musical tone under out- 
door conditions necessitated consider- 
able research. Transformers were de- 
signed especially for this installation, 
based on curves of the 203A tubes. 
Power supply was another problem 
which eventually was solved by using 
110-volt alternating current, rectified 
by mercury vapor tubes, for the ampli- 
fier and microphone current. The field 
supply for the speakers came from a 
motor-generator set. 

As a precaution in case of commercial 
power line failure, a gasoline-driven 
alternating-current generator, mounted 
in a motor truck, was kept ready just 
outside the field. There was also a 
spare direct-current generator for the 
speaker field supply. 

The exceptionally faithful tone of the 
system was noticeable on every type of 
music presented in the program. The 
booming bass of John Burdette, sing- 
ing "Old Man River," thrilled every 
listener. Female solo voices, choruses, 
bands and chimes came through true to 
life. The chimes, by the way, were lo- 
cated in the tower of the World's Fair 
Hall of Science Building, nearly a half 
mile away. This was the first time these 
chimes had been picked up by micro- 
phone. 

The Tribune's music festival, which 
promises to be an annual affair, was a 
thorough success both from an artistic 
(Continued on page 22) 



Location of 
loudspeakers and 
control equipment. 





EflERGEiMO"* C GCneR«TO«-*~ 




SEATS 




SEATS 








5 EAT 5 




EQUlPriETiT 






























]o£T^T«| 




Z+ Ml 




35 




2ROPHO 

STAGE 


r*ES 






35 

SPEAKERS 














— » SEATS 













NOVEMBER, 1932 



Page 21 



India as an outlet for low 
priced sound sets 



MANY cinema operators and 
most of the motion picture 
distributors believe the motion 
picture houses of India could 
buy at least 150 reproducing sets, if low 
priced equipment could be had on lenient 
credit terms. 

Lists culled from diverse sources and 
reasonably well verified give 530 off 
houses in India, Burma, and Ceylon, 
where motion pictures are shown, vary- 
ing from large corrugated iron "sheds" 
and traveling "bioscopes" exhibiting at 
fairs and carnivals to up-to-date thea- 
ters, having most of the appointments 
common to "movie" houses in Europe 
and America. 

Practically all of the best Indian 
houses in the ports and large inland 
towns have been wired for sound. 
Latest estimates place their number at 
180, of which more than 85 per cent 
have equipment of American manufac- 
ture. 

Competition Mostly Dutch and British 

Competition for American sound 
equipment is now principally from 
Dutch and British manufacturers, al- 
though German sets, particularly "Zeiss- 
Ikon" are beginning to make their way 
into the market. The "Philisonor," a 
product of the Philips Electrical Co. in 
the Netherlands and distributed by their 
highly competent subsidiary, Philips 
Electrical Co. (India) (Ltd.), seems to 
be gaining ground rapidly. B. T. H., 
the best known British set, apparently 
lacks enterprising representation. 

Accurate information concerning 
ownership, financial standing, and gen- 
eral reliability of the remaining 350- 
odd houses is not available. 

Certain it is that few of these smaller 
houses can afford the more expensive 
American sound equipment. If they are 
to wire, and the scarcity of suitable 
silent films, European and Indian, leaves 
them no option if they are to continue 
in business, they must obtain a sound 
set at a satisfactory price. 

Field Representation Essential 

It is highly desirable that any Ameri- 
can manufacturers of reproducing 
equipment seriously contemplating busi- 
ness in this territory have field repre- 
sentatives in India to assist the agents 
to train salesmen, propagandize the 
trade, and maintain an efficient service 



organization. An American firm and 
Philips make service obligatory to pur- 
chasers of their sound sets, charging 375 
rupees and 300 rupees respectively per 
month. It is hardly possible to obtain 
efficient service for any of the other re- 
producing equipment now in use as the 
agents usually show small concern for 
proper maintenance once the purchase 
is completed. It is said that competent 
Indian technical assistants can be had 
for 200 to 300 rupees monthly, exclusive 
of expenses. European engineers com- 
mand 500 to 1,500 rupees a month. 

Set Should Sell for Approximately 
12,500 Rupees 

According to those conversant with 
the exhibition of motion picture films 
and the sale of cinema apparatus in In- 
dia a reproducing set, to be within reach 
of those houses yet unwired, should sell 
for not more than 12,500 rupees fully 
installed. This would allow approxi- 
mately the following over and above the 
c. i. f. price Bombay or Calcutta. Duty, 
25 per cent; clearing, 2j^ per cent on 
invoice value ; and installation. 

Installation of the expensive sets, in- 
cluding inland freight, usually costs 
from 1,000 to 2,500 rupees, depending 
upon the location of the theater. On the 
average a European engineer and In- 
dian assistant can complete an installa- 
tion in two weeks, although failure of 
the theater operator to have effected all 
preparations incident to the wiring fre- 
quently causes further delay. Indian 
representatives of sound equipment are 
known to contract for installation as 
low as 500 rupees and, though theater 
owners may realize that purchases of 
sets from Indian firms are likely to 
prove unsatisfactory, they gamble, 
hoping for the best, believing their busi- 
ness would be ruined if they do not 
wire, but knowing they can not possibly 
afford a high-priced sound set. 

Equipment Should be Easy to Set Up 
and Simple to Operate 

Obviously a set of simple construc- 
tion, each unit complete within itself, 
which could be installed in a week, or 
less, without the services of a trained 
engineer, would materially lower in- 
stallation charges. The equipment 
should be simple in operation, practi- 
cally foolproof and especially impreg- 
nated to withstand tropical climate. The 



electric current varies from district to 
district in India, but 220 d-c. or a-c. 
is usually available. If the American 
set is 110 volts a-c. a converter must be 
included within the 2,500 rupees as price 
installed. 

Credit Terms Vary 

Credit will vary according to the 
reputation of the concern, but it is 
thought that 25 per cent with order, 15 
per cent against inland railway receipts 
and balance in 12 monthly installments 
is sufficiently lenient. Approximate ad- 
herence to these terms would enable the 
American manufacturer to compete with 
most equipments handled by substantial 
European firms. There is no way of as- 
certaining in advance the degree of 
credit leniency which will be granted 
by Indian agents as they are inclined to 
gamble on each individual customer. It 
is reported that they occasionally accept 
down payments, after installation, as 
low as 1,000 rupees and that the re- 
mainder is paid on a percentage of 
gross receipts running through two 
years or more. A "babu" (Indian clerk) 
in the agent's employ is frequently as- 
signed to the box office of the theater 
of the equipment purchaser to insure 
the agent his just share of the money 

is received. Trade Commissioner 

Paul L. Hopper, Calcutta. 



NAMES OF SOME MOTION PICTURE 
PRODUCING COMPANIES 

ALLIED Pictures Corpn., Ltd., Big 
Four Film Corpn., Trem Carr 
Pictures, Ltd., Columbia Pictures 
Corpn,. James Cruse Productions, Dar- 
mour Productions, Douglas Fairbanks 
Productions, Feature Picture Produc- 
tions, Inc., Ltd., First National Pictures, 
Inc., Fox Film Corporation, Samuel 
Goldwyn, Inc., Ltd., D. W. Griffith, Inc., 
KBS Productions, Willis Kent Produc- 
tions, Burton King Productions, Ma- 
jestic Pictures, Mayfair Pictures Corpn., 
Metro-Goldwyn-Mayer Corpn., Mono- 
gram Pictures Corpn., Principal Dis- 
tributing Corpn., Quadruple Produc- 
tions, RKO-Pathe Studios, RKO Radio 
Pictures, Inc., Sono-Art World Wide 
Pictures, Inc., Television Productions, 
Tiffany Productions, Inc., Universal 
Pictures Corporation, Warner Brothers 
Picture Corpn. 

Foreign companies : Amkino Corpo- 
ration, British and Dominion Film 
Corp., Ltd., British International Pro- 
ductions, Rene Clair Productions. 
Gainsborough Pictures, Ltd., Gaumont 
Productions, Richard Oswald Produc- 
tions, Sonor Film Company. Super Film 
Productions, Twickenham Film Studios, 
Ltd., Ufa Productions. 



Page 22 

COMMERCIAL USER OF MOTION 
PICTURES 

WHAT company is the largest 
user of motion pictures for 
business purposes? The cur- 
rent issue of Filmo Topics 
magazine carries a particularly interest- 
ing article tending to show that Cater- 
pillar Tractor Co., which has increased 
its motion picture sales promotion ac- 
tivities during the depression, is a 
strong contender for the title. 
The article is substantially as follows : 
"The Caterpillar Tractor Co., a pio- 
neer in the use of motion pictures for 
sales purposes, has for years been a most 
extensive and intensive employer of this 
sales method. In view of the recent 
statement, by Caterpillar's O. L. Snider, 
that during the depression his company 
has increased the use of motion picture 
films as a method of presenting its story 
to prospects, possibly this manufacturer 
is now the largest commercial user of 
motion pictures. And possibly Caterpil- 
lar warranted that title even before its 
recent extension of film use. 

"In Caterpillar files, many records 
give proof to the effectiveness of movie 
selling. A Michigan dealer's salesman, 
going from farm to farm with his pro- 
jector, sold eight tractors last winter 
in a region where they had never been 
sold before. A representative sold eight 
tractors, a grader, and a snow plow to 
the government of Afghanistan after in- 
teresting the officials with motion pic- 
tures and then defeating the royal ele- 
phants in competitive demonstrations. 
Another representative showed pictures 
before the Emperor of Ethiopia, who 
became interested, requested a demon- 
stration, and ordered three complete 
Caterpillar road building units. There 
are innumerable instances where all in- 
terest was denied by a prospect, only to 
have the most keen interest expressed 
following a motion picture showing of 
Caterpillar performance — and specific 
sales follow such showings. • Several 
hundred Bell & Howell Filmo projec- 
tors are engaged in this work by the 
firm's representatives and dealers in the 
United States and abroad." 



RECORDING IN INDIA 

The East India Film Company, of 
which B. Khemka is the head, has ac- 
quired a complete RCA Photophone 
studio and location recording unit for 
the production of sound motion pictures 
and upon its arrival from the United 
States, will immediately begin opera- 
tions in a new studio under course of 
construction in Calcutta. Richard C. 
Willman, Photophone recording engi- 
neer, who supervised the installation of 
similar equipment in studios in Eng- 
land, France and Italy, has been en- 



gaged to serve in like capacity for the 
East Indian Company. An ambitious 
program will be undertaken for the 
production of talking pictures in all of 
the principal Indian vernaculars, in- 
cluding Hindi, Urdu, Bengalee, Telugu 
and Tamil. The equipment acquired 
comprises the latest type R-5 recorders, 
ground noise reduction equipment, rib- 
bon microphones on one truck; com- 
plete self-contained power generating 
unit mounted in a second truck and a 
Mitchell sound camera. The East India 
Company's studio will be located at 
Tollygunge, which has been designated 
as the "Hollywood" of the Far East. 
▲ 

MRS. ROOSEVELT ON PICTURE 
PRODUCT 

Mrs. Franklin D. Roosevelt, wife of 
the Democratic nominee for President, 
discusses criticisms aimed at the motion 
picture industry in a signed article ap- 
pearing this month in Modern Screen 
Magazine. 

"Much has been said and written," 
she states, "on the harm which movies 
have done in glorifying the crook and 
gangster and giving oftentimes a 
glamor to a certain type of degenerate 
existence which does exist in some 
place, but which is hardly typical of the 
normal life of the greater part of our 
country. 

"There is, of course, justification for 
these criticisms, and one which is even 
more valid is that the movie, in pic- 
turing every-day life in so-called high 
society, falsely teaches bad taste, bad 
manners, not to say bad morals !" 

However, Mrs. Roosevelt goes on to 
say: 

"There are many signs today pointing 
to the fact that in the movie industry 
itself there is a realization of possibili- 
ties for education along many lines for 
service to the community in this com- 
paratively new art. With that growing 
power goes, of course, a great responsi- 
bility. 

"The educational value of the movies 
seems to me quite limitless if the men 
at the head of the industry have suf- 
ficient imagination to see what possibili- 
ties lie before them. ... To me it seems 
more and more that we are getting 
things in the movies which are of real 
value to many people." 
A 

UNITED AIR LINES SHOW FILMS 
TO PROMOTE TRAVEL 

UNITED AIR LINES are using mo- 
tion pictures for promoting interest 
in air travel. A 16 mm. 800-foot film, 
"Across America in Twenty-seven 
Hours," is being shown by the Air 
Lines' traffic representatives before 
luncheon clubs, business men's organ- 
izations, women's clubs, colleges, and 
high schools. Ten Bell & Howell Filmo 



PROJECTION ENGINEERING 

projectors are being used for present- 
ing the movies in various parts of the 
country. 

The film consists of a pictorial nar- 
rative of a flight from California to 
New York and includes many remarka- 
ble views of planes flying over scenic 
and historic country, particularly the 
western mountain areas. There are 
splendid shots of the big Boeing 14- 
passenger-mail tri-motored transport 
with a background of the Rockies and 
the Sierras, and fine aerial views of 
fourteen cities flown over on this 2,700- 
mile flight from the Golden Gate to the 
Statue of Liberty. 

Interior scenes of the plane in flight, 
including the serving of lunches by uni- 
formed stewardesses, give the public a 
new appreciation of the comforts now 
available in the modern multi-motored 
transport. 

An interesting part of the film is the 
depiction of the many new aerial navi- 
gation aids, such as the two-way radio 
telephone whereby pilots talk to ground 
stations and to pilots of other planes 
hundreds of miles away, and the di- 
rective radio beam, whose dots and 
dashes hold the pilot on his true course 
even if the landmarks of the course are 
not visible. There are interesting views 
of the cockpit and its instrument board 
with ninety instruments and controls. 

The modern air transport system is 
now much more than merely a plane in 
the sky, and sections of the film have 
to do with the servicing and prepara- 
tion of airplanes for flights at division 
points. The audience gets a new in- 
sight into the extremely careful man- 
ner in which responsible air transport 
companies care for their equipment. 

"We know of no more effective sales 
solicitation method than the showing of 
such films," said a United Air Lines 
official. 

A 
WORLD'S BIGGEST SOUND AMPLI- 
FIER BROADCASTS CHICAGO 
MUSIC FESTIVAL 
(Concluded from page 20) 
and a scientific viewpoint. Not includ- 
ing millions who listened by radio, 125,- 
000 persons who personally attended 
heard every note of the program clearly, 
distinctly, without distortion, without 
the "mechanical" feeling common to 
reproduced sound. It was in reality a 
notable advance in sound transmission. 

The public-address system was engi- 
neered and designed by Thomas B. 
Gibbs of the Thos. B. Gibbs Co., Chi- 
cago. The big 400-watt output ampli- 
fier and the 24 position microphone mix- 
ing panel were built by the Webster 
Company, Chicago. Installation and 
wiring were supervised by Milton A. 
Boom, who operated the system jointly 
with Mr. Gibbs. 



NOVEMBER, 1932 



Glossary of technica 
terms for the 
projectionist 1 



(Continued from October issue) 



Dynamic Cone. Type of loudspeaker 
in which the modulated electric current 
passes through a coil placed in a mag- 
netic field. The coil and an attached 
paper cone vibrate and thus generate 
sound in accordance with the modula- 
tions of the current. 

Dynamite. An open connection box 
dangerous if stepped on, into which the 
studio lamps are plugged. 

Dynamo. Machine to convert me- 
chanical into electrical energy. 

Dynamotor. Type of converter (2). 

Dyne. Unit of force in the metric sys- 
tem. Approximately 450,000 dynes equal 
one pound of force. 68,944 dynes per 
square centimeter equal one pound per 
square inch. 

Eagle. (1) An insect that flies across 
the set while the camera is operating, 
usually requiring that the scene must be 
done over again. (2) A perfect photo- 
graphic take. 

Ear Muffs. Rubber cushions attached 
to the monitoring ear phones ("cans") 
to shut out extraneous noises. 

Economizer. Step-down transformer. 

Efficiency, Photographic, of a light 
source, is the ratio of that part of the 
light flux which the photographic emul- 
sion will record, to the total light flux 
emitted. 

Electrode. Terminal of an electric de- 
vice such as a cell or vacuum tube. 

Electrolyte. Liquid conductor of elec- 
tricity, as in a battery. 

Electron. Unit of negative electricity, 
and smallest particle of matter, next to 
the proton. Radius, about 2x10- 13 cm. 
(i. e., 0.000.000.000.000,2 cm.). Mass, 
9xl0'~ 28 gram Negative charge, 1.6x 
10 - 19 coulomb. 

Electron Tube. Generally, same as 
vacuum tube, thermionic. May also re- 
fer to photoelectric cell. 

Electroplating. Process of depositing 
a metal on another metal by making the 
latter the cathode of a suitable solution 
through which an electric current is 
sent. The solution must contain a salt 
of the metal to be deposited. 

Electrostatic. Pertaining to electric 
charges at rest. 

Elephant Ears. Small gobos. 
Emulsion. The light-sensitive sub- 



tX/m condensed glossary of terms is taken 
from the technical digest service of the Academy 
of Motion Picture Arts and Sciences. 



stance on a photographic film or plate, 
consisting of a gelatine containing a 
silver halide or nitrate. For its action, 
see exposure and development and fix- 
ing. 

Energy Density. Quantity of energy 
contained in a given volume, divided by 
the volume. 

Erg. Unit of work or energy in the 
metric system. Approximately 13,560,- 
000 ergs equal one foot-pound of work. 

Exciter Lamp. Light source used in 
reproducing sound from film. 

Exposure. The placing of a photo- 
graph emulsion under the action of light. 
Quantity of exposure varies very nearly 
as the product of time and light inten- 
sity. The quantity of exposure deter- 
mines the amount by which the silver 
halide or nitrate in the emulsion will be 
chemically changed ("reduced") to sil- 
ver when the emulsion is developed. 

Extension. Stage cable with lugs on 
both ends. 

Extinction Coefficient. Same as den- 
sity. 

Eye-piece. Lens to which the eye is 
applied in any optical instrument such 
as a telescope or microscope. 

"F" System. System of marking lens 
diaphram stops in terms of the focal 
length. Thus, an F:6.3 stop has a diam- 
eter equal to 1/6.3 of the lens focal 
length.. 

Fader. Potentiometer used to control 
volume of sound in reproduction, also 
that used to control intensity of the 
printer light. 

Farad. Unit of capacitance. Capaci- 
tance of a condenser in which one cou- 
lomb will be stored by one volt. (The 
microfarad is the unit commonly em- 
ployed in practice.) 

Fast. Cf. Speed. 

Fast Feed. Mechanism used on a disc- 
recording machine to produce the start- 
ing spiral. 

Fear Process. Method of recording 
and projecting wide pictures, by photo- 
graphing on standard film through an 
optical system that turns the image 
through a right angle, so that the image 
on each frame lies along the length of 
the film instead of across the film. The 
frames can be longer than standard, thus 
permitting a width and height of pic- 
ture greater than standard. In projec- 
tion, another optical system is used to 
reverse 90° rotation. 



Page 23 

Feed ReeL Reel of film which has 
not yet passed the aperture. 

Filament. Heated wire from which 
electrons are emitted in a vacuum tube. 

Filament Battery. Same as "A" bat- 
tery. 

Filament Resistance. Rheostat con- 
trolling current through the filament of 
a vacuum tube. 

Film (noun). A celluloid strip coated 
with a light-sensitive photographic emul- 
sion. 

Film (verb). To reproduce a scene or 
series of scenes on film. 

Film Gate. Movable element which 
when in operating position, holds the 
film in proper position against the aper- 
ture plate. 

Filter. An apparatus or instrument 
to remove or weaken certain frequen- 
cies in a beam of sound, light, radio, 
or alternating-current waves, or mechan- 
ical vibrations. Particularly (1) colored 
glass or celluloid used in photography 
to filter out certain rays of light; or (2) 
a selective circuit network, designed to 
pass currents within a continuous band 
or bands of frequencies or direct cur- 
rent, and substantially reduce the ampli- 
tude of currents of undesired fre- 
quencies. 

Filter, Band-Pass. A filter designed 
to pass currents of frequencies within a 
continuous band limited by an upper 
and a lower critical or cut-off frequency 
and substantially reduce the amplitude 
of currents of all frequencies outside of 
that band. 

Filter, High-Pass. A filter designed 
to pass currents of all frequencies above 
a critical or cutoff frequency and sub- 
stantially reduce the amplitude of cur- 
rents of all frequencies below this criti- 
cal frequency. 

Filter, Low-Pass. A filter designed to 
pass currents of all frequencies below a 
critical or cutoff frequency and substan- 
tially reduce the amplitude of currents 
of all frequencies below this critical fre- 
quency. 

First Phase. Initial interlocking of all 
recording machine and camera motors, 
so that they will be synchronized. 

Fixing. After development of a pho- 
tographic emulsion, it is fixed, i. e., 
immersed in a solution (generally hypo) 
to remove the unreduced silver salt, thus 
making the emulsion immune to further 
effect from light. See exposure and de- 
velopment. 

Flat. Same as tormentor. 

Flicker occurs when the number of 
pictures shown on the screen per unit 
time is not sufficient to insure complete 
persistence of vision. 

Flutter. A type of pulsation of inten- 
sity in reproduced sound. See wow- 
wows for explanation. 

Focal Length. Distance from the cen- 
ter of a lens to the focal point. 

Focal Length, Equivalent. Calculated 
focal length of a combination of lenses 
or of a thick lens. Equals the focal 
length of such a simple thin lens as 
would give an image (of a distant ob- 
ject) the same size as the combination 
or thick lens gives. 

Focal Plane. The plane perpendicular 
to the optical axis of the lens at the 
focus. 

( To be continued) 



Page 24 



PROJECTION ENGINEERING 



New Developments 

and 

News of the Industry 



RECORDS FOR THEATRES 

The American Record Company, 1776 
Broadway, New York, announces a list of 
about one hundred records for theatre and 
dance hall use. The theatre records may be 
played with silent trailers on the screen 
during intermission and as exit marches, 
or anywhere motion pictures are projected. 

A 
NEW CONTROL UNITS 

The Electrad Company, 173 Varick St., 
New York, announces new L and T pad 
attenuators and a snap-on control switch 
assembly. 

Electrad constant impedance T pad con- 
trols are useful for the volume control of 
microphones, electrical phonographs, talk- 
ing picture amplifiers and other sound am- 
plifying and distribution systems. Con- 
stant impedance is maintained throughout 
the adjustment of knob. 

The new snap-on volume control switch 
assembly will be standard for all Electrad 
replacement volume controls. By simply 
removing the standard cover which is in- 
corporated in each standard control and 
snapping in place the switch assembly a 
standard switch type control is available. 
All standard controls without switch will 
incorporate the necessary switch arm throw 
lever when shipped. In this way the neces- 
sity for carrying a separate stock of switch 
controls is eliminated for the distributor 
and his investment in merchandise is ma- 
terially reduced. 

▲ 

DEBRIE'S SERVICE DEPARTMENT BUSY 

A number of the special cameras made 
by Andre Debrie for the United States 
Government and used by naval aviators, 
have been sent to New York Debrie ser- 
vice station for their first examination. 
These cameras include the ultra speed GV 
and have been in use by the Government 
for several years. 

▲ 

INTERNATIONAL PROJECTOR CORP. 
S. R. Burns, president of the Interna- 
tional Projector Corp. recently underwent 
a serious operation at the Price Hospital, 
Jersey City, N. J. It is reported that he 
is improving, but his return to duty is 
still several weeks off. 

A 

CARBONS FOR THE PROJECTIONIST 

National Carbon Company, Inc., has just 
announced the issue of a new edition of its 
National Projector Carbon Handbook. 
This new handbook is up to date in every 
respect and contains information of par- 
ticular interest to all projectionists as well 
as to manufacturers and users of carbon 
arc projection equipment. It covers in 
detail the various types and sizes of carbons 
for projection with complete instructions 
for their proper use. Important operating 
precautions are discussed in the text with 
illustrations showing the difficulties en- 
countered when carbons are not used prop- 



erly accompanied by a clear explanation 
of what to do to overcome these difficul- 
ties. The book also contains a very in- 
teresting chapter on carbon brushes and 
their application to the various types of 
motors, generators, and converters used 
in connection with projection equipment. 

A copy of this new book may be ob- 
tained by addressing National Carbon 
Company, Inc., Carbon Sales Division, P. 
O. Box 400, Cleveland, Ohio. Projection- 
ists should name the theatre in which they 
are employed. 

A 

CARBON PRODUCTS 

The Noris Carbon Company, Inc., has 
been organized in New York with head- 
quarters in the Mohawk Building, 160 Fifth 
Avenue. The firm has taken over the ex- 
clusive sales agency for C. Conradty, Niirn- 
berg, Germany, manufacturers of carbons 




ERIC W. SCHUMACHER 



and carbon goods. This concern, estab- 
lished in 1855, is known as one of the 
world's largest manufacturers of carbons 
and carbon products. Eric W. Schumacher 
has been elected president and managing 
director. Mr. Schumacher has returned a 
short while ago from a prolonged stay in 
Niirnberg, where he made a thorough study 
of the Noris products. He believes that 
the American market is still an open field 
for quality products, and a well organized 
sales staff will assist him in his business. 
A 
FRACTIONAL HORSEPOWER MOTORS 
Literature describing a new line of frac- 
tional horsepower motors adapted to vari- 
ous styles of mounting and cushioning, is 
available from the Howell Electric Mo- 
tors, Inc., Howell, Mich. Sizes are from 
1/3 to 1/8 h.p. 



SOUND JOBS COMPLETED 

An increasing trend has been noticed 
recently for non-theatrical institutions in- 
stalling sound-on-film equipment, according 
to the S. O. S. Corp., 1600 Broadway, New 
York. 

Many of these institutions have been on 
the charity lists of the film boards in the 
various key cities, and owing to lack of 
product, both silent and disc, these institu- 
tions have been forced to install sound 
track equipment, or do without. Among 
the recent installations by S. O. S. have 
been the following : 

Young Men's Hebrew Ass'n., Philadel- 
phia, Pa. ; New York Catholic Protectory, 
Bronx, N. Y. ; St. Camillus Hall, Rocka- 
way Beach, N. Y. ; U. S. District Training 
School, Laurel, Md. ; Federal Industrial 
Institution for Women, Alderson, W. Va. ; 
Long Meadow Community House, Long 
Meadow, Mass.; D. C. Penal Institutions, 
Lorton, Fairfax County, Va. ; Carpenter's 
Home, Lakeland, Fla. ; So. Carolina State 
Hospital, Columbia, S. C. ; North Da- 
kota State Penitentiary, Bismarck, N. 
D. ; Olivet Community House, Springfield, 
Mass. ; Starr Institute, Rhinebeck, N. Y. ; 
Ohio State Sanitarium, Mt. Vernon, Ohio ; 
Ensley High School, Birmingham, Ala. ; 
St. Ancolm's College, Manchester, N. H. 



IMPROVED PROJECTORS 

The Victor Animatograph Corpn., Dav- 
enport, la., has available circulars describ- 
ing the company's new line of improved 
projectors: Models 10, 10 FH, and 10 RH. 



PORTABLE PROJECTOR 

The Weber Machine Corpn., 59 Rutter 
St., New York, is distributing literature 
describing a portable sound and picture 
Synchrofilm projector for 35 mm. film, 
complete with amplifier and loudspeaker, 
for professional and non-professional use. 
Copies may be had upon request. 



16 MM. PRINTER 

Illustrated literature describing a 16 
mm. sound-on-film printer so designed as 
to compensate automatically for shrinkage 
by bending the shrunken negative so that 
its emulsion surface temporarily regains 
the exact length that matches the positive, 
may be obtained from H. T. Cowling, 6 
Sibley Place, Rochester, N. Y. 



CONDENSORS AND RESISTORS 

Morrill and Morrill, 30 Church St., New 
York, are marketing a dependable line of 
condensers and resistors manufactured by 
Siemens and Halske. 



NOVEMBER, 1932 



Page 25 



DON'T 



SPLICE FILMS THE 
OLD, MESSY WAY . . . 

EASTMAN Sound Film Patches do the job more 
quickly, neatly, and dependably. Because of their de- 
sign, they are practically inaudible in projection. At 
the same time they obscure a minimum of the sound 
track, and assure fast, accurate, and clean treatment of 
all splices. Together with their precise registration block 
they represent a valuable yet inexpensive feature of East- 
man service to the motion picture industry. Eastman 
Kodak Company. (J. E. Brulatour, Inc., Distributors, 
New York, Chicago, Hollywood.) 



USE 



EASTMAN 



SOUND FILM PATCHES 



, ^ NOT ONE IN 10,000 

\J) I Not one patron in ten thousand knows an anastigmat from an 

aperture . . . but when the picture he sees on the screen is 
strong, clear and sharp . . . when there are no smudgy edges to 
distract him, he gets a lot more satisfaction from the show. He 
likes the house. He'll come again. 

The shows you take today have got to be good. They deserve and 
require the best projection. Show them with the new Super 
Cinephor . . . and treat yourself to the added good- 
~vS) I will of increased patron pleasure. 

*£-' ' -^"* Here are the highlights of its superiority. I. First true 

anastigmat, fully corrected for spherical and chromatic 
aberration. 2. Available in focal lengths down to 2 
inches. 3. Gives full detail right to the edge. 4. With 
new B&L Condensing System transmits 50 to 100% 
more light to the screen . . . insures high screen 
brilliance. 

Ask your National Theatre Supply man about 

Super Cinephor and write direct, today, for com- | BAUSCH & LOMB OPTICAL CO. 

plete details. You'll like the sound of the price. 681 ST. PAUL ST., ROCHESTER, N. Y. 

It will prove its value on the first job. i c , . . 

I send me complete details on the new Super Cinephor. 

SEND THE COUPON TODAY Name 

The catalog contains valuable information for pro- Address i 

jection men. r-i. r- I 

1 City State v 

I 1 




Page 26 



PROJECTION ENGINEERING 



Two stage ampli- 
fier. 864 tubes. 
New acoustic 
equalizer. Floor 
type list $1 25 



REMLER 

CONDENSER 
MICROPHONE 






Used ind endorsed by radio stations throughout the 
country. WFAS says: "Beautiful visually and from 
engineering standpoint." Harington, engineer, says: "Un- 
believable that you can sell such a high grade product 
at so low a price." 

Features: Precision machined sensitive head free from 
noise. Moisture proof. Special alloy diaphragm. Shock 
proof; mica insulated. Non-resonant grill. Copper 
shielded housing. Audio filters eliminate oscillation. 
50-200 or 200-500 ohm output. Essentially flat response 
40 to 10,000 c.p.s. Statuary bronze finish. 



Send for folder show- 
ing four types with 
prices. 



Rentier Company, Ltd. 

2101 Bryant St., San Francisco 



REMLER-THE RADIO FIRM AS OLD At RADIO 



WAX RECORDING EQUIPMENT 

MUST SACRIFICE FOLLOWING SLIGHTLY USED EQUIPMENT: 
2 Jenkins &. Adair condenser microphones; I J. & A.. Transmitter; J. & A. 
Amplifier panels complete with V. I and 3 place Mixer mounted on racks. 
2 Studio Mike Stands; 24 crates of Philco Diamond grid Type UX-5I-I Bat- 
teries: I 33 1/3 wax recorder fitted with microscope and W. E. type c"" e J 
holder; 2 wax recording cutters fitted with advance base; I G. E. Tungar tun 
wave charger. 
R. W. NICHOLLS 119-35 27th AVE.. COLLEGE PT.. LONG IS.. N. Y. 




NOW . . we serve 
you in America 



CAMERAS • PRINTERS • DEVELOPING 
MACHINES • LABORATORY EQUIPMENT 
PORTA B LE SOUND PROJECTORS • • ; 



EDITING MACHINES 

Andre Debrie inc. 

M5 WEST 45* STREET • • NEW YORK 



FREE 



13th ANNIVERSARY RADIO CATALOGUE 

124 pages containing thou- 
I sands of the greatest radio 

and electrical values at real 
(bargain prices. 

Send for your copy now! 

j American Sales Company 

Wholesale Radio Distributors 

RE-44 West 18th Street 

New York City 



<^^= 


I3"»NNIVERSAHY 


^ 


RADIO 1 


L 


CATALOG 






■NEW! 



2 MFD — 600 Volt. 
Size: 2" x 1%" x %". 



MORRILL 

Uncased Condensers 

Especially compact. A prod- 
uct of outstanding quality. 
The ultimate in reliability. 
Send for circular E-l. 



MORRILL & MORRILL 

30 CHURCH STREET NEW YORK CITY 

Sole U. S. A. Distributors of the Siemens & Halske 

Condensers and Resistors. 



PROTECT Those INSTRUMENTS 



Littelfuses afford complete pro- 
tection for voltmeters, milliam- 
meters, tube testers, etc. Range 
in size from 1/100 to 2 amps, 
capacity. 



Also Radio Receiver and Am- 
plifier Littelfuses, and High 
Voltage Littelluses for trans- 
mitting tubes, rectifiers, oscilla- 
tors, etc. 
Write for instructive catalog. 

LITTELFUSE LABORATORIES 

1778 WILSON AVE. CHICAQO. U. S. A. 



LITTELFUSES 



For Powers, Simplex and all other sound projectors 



CLAYTON 



Even 
Tension 



TAKE-UP 



Assures absolute freedom from flutter. Takes up any amount of film evenly 
with any size reel hubs. Prevents excessive wear on the lower take-up 
sprocket and shaft. Stops the opening of film splices and prevents excessive 
wear on the film. Write for price and details. 



CLAYTON 

9430 Forty-sixth Ave. 



PRODUCTS CO. 

Elmhurst, L I., N. Y. 



Tungsten Rod and Wire 

for Cathodes, Supports and Welds 
A Special Tungsten Filament Coils 
Tungsten Contacts for Special Purposes 

CALLITE PRODUCTS CO., INC. 
UNION CITY NEW JERSEY 



When You Renew Your Subscription to 
PROJECTION ENGINEERING 

Remember the Group Rate — $1.00 a year for 
four or more subscriptions 

Regular Rate — $2.00 a year in U. S. A. — $3.00 in foreign countries 



INDEX TO ADVERTISERS 



American Sales Co. 



B 



26 



25 



Bausch & Lomb Optical Co 

C 

Callite Products Co 26 

Canady Sound Appliance Co., The. 5, 27 
Clayton Products Co 26 



Debrie, Inc., Andre. 



26 



Eastman Kodak Co 25 

P 

Federated Purchaser, Inc 27 

Forest Electric Corp Third Cover 



N 
National Carbon Co.. Inc. 

Nicholls. E. W 

Xoris Carbon Co., Inc 



1 
26 



R 



K 
Koulish Co., Inc., Meyer 28 

L 
Littelfuse Laboratories 26 

M 
Morrill & Morrill 26 Zierick Mf 



RCA Victor Photophone Corp 3 

Racon Electric Co., Inc Back Cover 

Remler Co., Ltd 26 



SOS Corporation 28 

Samson Electric Co Second. Cover 

Shure Electric Co 27,28 

Strong Electric Co.. The 5 



z 

Works, F. R. 



28 



NOVEMBER, 1932 



Page 27 










NOW! PROFESSIONAL 
SOUND RECORDING 
APPARATUS AT 
POPULAR PRICES 

It is no longer necessary to purchase 

high priced recording devices to ^ t^ attached ^ any 

produce good records. record radio programs and 

The New ACRATONE RECORDER cuts Stained E «ilHn.uiiZd 
and records on aluminum instantaneously (,y anyone. 
96 grooves per inch at either 78 or 33-1/3 
r.p.m. 

RECORDING OUTFIT 

Consisting of: Center Spindle, Cut- 
ting Head, Threader, Hardware, 
Swivel Arm. 




19 



5© 



Impedance 
Cat. No. of cutter 

70 IS ohms 

71 500 ohms COMPLETELY 

72 4000 ohms ASSEMBLED 
In ordering mention type required 

Carbon Steel Recording Needles. 
Cat. No. 6975— 25c per pkge. of 15. 

Fibre Reproducing Needles. 

Cat. No. 6929— 25c per pkge. of 50. 



Acratone 3 Stage 250 Am- 
plifier for Microphone, radio 
and phonograph recordings. 
Power output 11 Watts. Cat. 
No. 101— $24.50 




Special 2 speed Recording 
and Playback Motor. 78 and 
33-1/3 r.p.m. Cat. No. 274 
—$12.50. 



tederate dPurchaser inc . 

25 Park PL, Dept. S, New York, N. Y. 

Every sound engineer should have the complete details of this job, 
as well as a copy of "RADIO BARGAIN NEWS"— our 108 page 
catalogue containing over 3,000 radio items. Write for free copy. 




MAKING 

PHONOGRAPH 

RECORDS 

. . . requires the absolute 
freedom from "hiss" or 
"rush" which is guaran- 
teed by the condenser 
microphone. 

SHURE, Model 44, is 
the lowest priced, high 
quality, nationally known 
2-stage Condenser Mi- 
crophone available. Fre- 
quency response remark- 
ably uniform, combined 
with high output level 
and extreme wealth of 
richness in tone quality. 

Write for full particulars today. 
P. S.: Recording is a profitable busi- 
ness. Is it established in your town or 
neighborhood? If not, we can help 
you. 



SHURE BROTHERS COMPANY 

Manufacturers-Enjjineers 
S.N. SHURE. Pres. 

337 WEST MADISON ST CHICAGO, ILLINOIS 





The New 

CAN All ¥ 

precision built 35 mm sound-on-film 

.RECORDER 



Comparison will prove that Canady Recording 
systems are the best value available. For over 
two and a half years they have fulfilled every 
requirement encountered in commercial record- 
ing. Takes standard B & H magazine. Suitable 
for Studio or Sound Truck operation. An im- 
proved filter system eliminates flutter, while a 
footage counter indicates used footage at all 
times. Canady-Zetka glow lamps assure full range 
recording. I 10 volt 60 cycle Synchronous motors 
are furnished as standard equipment unless other- 
wise specified. Any type motor can be furnished 
for special applications. 

SPECIFICATIONS 

Weight — Complete without magazine. .40 pounds 

Length of base 20 inches 

Height without magazine 14 inches 

Casting Aluminum 

Shafts Extra heavy. Hardened and Ground 

Bearings Bronze and Ballbearing 

Sears Steel, Bronze and Formica 

Finish Enamel 

We manufacture a complete line of equipment 

• for Recording and Reproduction of Sound # 

Pictures. Camera Motors, Microphones, High 

Quality Amplifiers, Cable, etc. 

CANADY SOUND APPLIANCE CO. 

1776 BROADWAY NEW YORK CITY 



: Cable Address: 

iCANRECORDj 

Bentley's Code: 



Page 28 



PROJECTION ENGINEERING 



Final Forms Close 

the First of 

Each Month 



CLASSIFIED 
ADVERTISING 

Ten cents per word, cash with copy, $2.50 minimum advertisement accepted. Contract rates on 
application. No borders or cuts. Publisher reserves right to reject any copy. Address copy and 
checks to PROJECTION ENGINEERING, Classified Dept., 19 East 47th Street, New York City. 



NEW EQUIPMENT 

BUSIEK I'HAN KVER SUPPLYING THE DE- 
MAND— HEKE' S WHY:— Bectifler Bulbs. 6 ampere, 
$4.44; 15 ampere. $8.68; Typewriter Slides. 98c box; 
Sprockets for Simplex, $1.95; 11" Sound Keels, 89c; 
Film Splicers, $5.25; Double Bearing Intermittents. 
$78.47; Stock Tickets, roll 33-l/3c; Genuine KCA 
Professional Projectors, $395.00; 15" Wire Sound 
Beels, $1.75; Acoustical Felt, per yd.. 27V4c; Lobby 
Frames, one sheet, $5.60 up; Acoustical Carpet. 69y2C 
yd; Superior Projector Mechanisms, $244.00; Genuine 
RCA TJX868 or W.E. Photocells, $4.95; Beaded Sound- 
screens, 29c ft.; Kollmorgen Special Lenses. $11.95; 
Rear Shutters for Simplex, $49.50; Newsreel Cameras, 
35 mm.. $66.60; Exciter Lamps, any voltage, 90c; 
Catalog mailed*. DEALERS PROTECTED. S. O. S. 
Corp., Deot. PE, 1600 Broadway, New York. 

RELAMP YOUB MARQUEES AND DISPLAYS- 
LOWEST PRTCES EVER. All sizes G. E. Licensed 
Bulbs, including new 6 watt lamps, any standard 
color (saves almost half current), 30% discount, addi- 
tional 10% ten cases or more. International Theatre 
Accessories Corp.. 730 Seventh Ave.. New York. 

BRAND NEW MOTOR GENERATORS FACTORY 
STOCK— ORIGINAL CRATES— BELOW COST. All 
60 cycle 220 volt, multiple type. 20/40 Three Phase, 
$225.00; 20/40 Single Phase, $265.00; 30/60 Three 
Phase, $305.00; 125/250 Three Phase, $675.00; 200/400 
Three Phase. $880.00. Standard make with control 
panels, subject prior sale. Box 4A, Projection Engi- 
neering. 

REPAIR SERVICE" 

Amplifiers, Generators, Lamphouses, Projectors, 
Rectifiers, Soundheads, Speakers, Sound or Booth 
Equipment, all makes; reasonable prices. Parts and 
material guaranteed. Dealers Radio Laboratories, 
1600 Broadway. New York. 



GENERAL 
EQUIPMENT 



RESURFACE YOUR SCREEN— DO IT YOUR- 
SELF—EXPERIENCE UNNECESSARY. Permanent 
color, for Silver, Gold Fibre, all makes diffusive or 
metallic screens. Easily applied, no unpleasant odor, 
economical, quick drying. Gallon covers 300 square 
feet. Write S. O. S. Corp., 1600 Broadway, New 
York. 



SOUND EQUIPMENT 



IT'S A LANDSLIDE— THE ELECTRICAL TRUSTS 
ARE IN RETREAT— EXHIBITORS ASSERT YOUR- 
SELVES—QUALITY PRICES WERE NEVER 
LOWER. Famous S. O. S. Sound Track. $179.70; 
Convert your old" Disc Equipment oi trade in for All 
AC job. Tachometers free with each outfit. TJ. S. 
Government Specifications. Make your own installa- 
tion. S. O. S. Corp., 1600 Broadway, New York. 



Two Weber Syncrofilm DeLuxe Soundheads, never 
used", complete, $120.00 each. Box 25. Projection Engi- 
neering. 19 E. 47th St.. New York. 



CLOSE-OUT SALE ON SAMSON PAM AMPLI- 
FIERS— PAM 2, 3, 8, 45, 47M, 59, 16, and 17, 
each $17.50; Pam 100 (with built-in Speaker in 
carrying case), $29.75; Pam 19, $37.50; Pam 29, 
$90.00. Sparton 15 Record Automatic Turntables, 
$29.75. THESE ARE LESS THAN ONE-FOURTH 
PRICE. Dealers Radio Lab., 1600 Broadway, New 
York. 



ACCESSORIES 



PUBLISHERS OVERSTOCK — WHAT YOU'VE 
ALWAYS WANTED— THREE INDISPENSABLE 
BOOKS: — "Sound Projection," "Servicing Projection 
Equipment," "Trouble Shooting in Sound Equipment"; 
last two just off press. ALL THREE. $15.00 value, 
$3.95. Individually, $1.50. S. O. S. Corp.. Dept. 
1>E, 1600 Broadway, New York. 



WANTED TO BUY 



SOUND EQUIPMENT — New or reconditioned, at a 
bargain tor cash. Box 13, Projection Engineering. 



CASH for Simplex Machines or Heads. Box 23, 
Projection Engineering. 



USED EQUIPMENT 



Six NEW R. C. A. I'holophone Amplifiers For 
Sale Suitable for threatre or Public Address work. 
15 watts output. Price each $90. Box 17, Proj. Eng. 

HUGE SAVTNGS IN USED PUBLIC ADDRESS 
EQUIPMENT. Send for Bargain List. S. O. S. 
Corp., Dept. PE, 1600 Broadway, New York. 

12,000 CHAIRS OF ALL DESCRIPTIONS — DE- 
PRESSION PRICES — Write us your requirements 
giving floor space, pitch, and types desired — we have 
what you want at 50c up. We will buy your old 
chairs. Independent Seating Co.. 1600 Broadway, 
New York. 



FREE OFFER 

mtroduarzq SHUREmodel5I 

. ADJUSTABLE DESK STAND 

in the. nccui chrome- japan ccrmbiaaticm 



With all orders received for Model 22N (List 
Price $25.00 — usual discounts apply) or Model 33N 
(List Price $50.00) before December 30, 1932, men- 
tioning PROJECTION ENGINEERING we will 
include one new $10.00 Adjustable Desk Stand ab- 
solutely FREE, and — your money back if not 
satisfied. Write for full details at once. 



SHURE BROTHERS COMPANY 

Manufacturers-Engineers 
S.N.SHURE. Pres. 
337 WEST MADISON ST. CHICAGO, ILLINOIS 



Sapphire Recording 
Needles 

Styluses — Shavers, standard and special 

Type AW, for cutting and recording on ALUMINUM 
" BW, for recording and playback on all types of 

PREGROOVED DISCS 
" CW, for playback on REGULAR COMMERCIAL 

RECORDS 
" DW, for cutting and recording on CELLULOID 
SPECIAL. Type DD, DIAMOND NEEDLE for cutting 
out a thread and recording on CELLULOID. 



Type "A" 
Needle 



MEYER KOULISH CO., Inc. 

64 Fulfon Street, New York City. Phone BEekman 3-6109 



For Your Experimental Department 



A Tube of 500 
Assorted Lugs 
and Terminals — 
Hot Tinned for 
Easy Soldering 
Price $1.00 



We are also 

Prepared to Handle 

Production 

Stampings. 

Write us for 
quotations. 




F. R. ZIERICK MANUFACTURING CO. 

68-72 E. 131st ST., NEW YORK, N. Y. 



HOTEL HENRY 



ON 5th AVENUE 

Near Smithfield — one of the most conveniently 

situated hotels in town — with easy access to all the 

main points of interest. 

RATES 

Single $2 00 and up Double $3-00 and up 

EXCELLENT RESTAURANT 

POPULAR PRICED COFFEE SHOP 



PITTSBURGH 




ARE 

YOUR 

BATTERIES 
Wearing Out? 



Well put you on the right road 
to better operation at less expense 

with a FOREST RECTIFIER 



Regarding your power supply, you must make one of 3 choices. 
I. Replace worn out, troublesome storage batteries. 2. Buy new equip- 
ment. 3. Modernize your present apparatus by installing all A.C. 
Forest Rectifiers, inexpensive and practical. Before making a decision, 
consider this fact: Forest rectifiers save current, are efficient, supply 
unfailing non-fluctuating current, require no attention or attendance, 
and are always ready for service. They eliminate all "A," "B" and 
"C" batteries. 

Model 77 supplies 7 , / 2 amperes to exciter lamp and I ampere to 
amplifier filaments. We make a rectifier for every direct current 
requirement on sound equipment. 

AND NOW 

A BRAND NEW FOREST RECTIFIER 
for Good Projection Everywhere 

A greatly improved rectifier — the result of years of experience and 
research is now ready. These new Forest Rectifiers will absolutely out- 
perform anything ever offered before. Inexpensive to own, economical 
to operate, easy to install and positively quiet in operation. 

Available in Model No. 30 up to 30 ampere capacity for one pro- 
jector. Model 25-25, up to 25 amperes to one projector and an 
additional 25 amperes to second projector during change over. Model 
No. 45, up to 45 amperes to one projector available for either single 
or three phase A.C. current. 

Model No. 6, up to 65 amperes, and Model No. 10, up to 100 amperes, 
both for one projector, are now available in three phase A.C. cur- 
rent only. 

Model No. 15 is portable, 15 ampere capacity. 

Model No. 20 is stationary, 20 ampere capacity. 

Write for bulletins 

FOREST ELECTRIC CORP. 

Newark New Jersey 




Inside View 
Model 77 



5 




Front View, Model 25-25 



S $ YOUR DOLLAR BUYS MORE S $ 
$ ... IN RACON EQUIPMENT . . . $ 

Today, when economy is the watchword and value is 
paramount you get more than ever before for your Racon 
dollar— more value than you could possibly get in any other 
line. 




SUPER GIANT "B" UNIT 




MASTER "B" UNIT 




JUNIOR "B M UNIT 




BABY "B" UNIT 



Compare these values in the new Type B Units. 

H PEAK POWER ratings as high as 60 watts. 

|f CONTINUOUS POWER ratings as high as 30 watts. 

|[ FIVE different sizes from which to select the unit that fits the 
requirements and fits your pocketbook. 

|[ NON-RUSTING cadmium-plated metal parts — waterproof assem- 
bly — and the finest workmanship you've ever seen. 

U QUALITY, unapproachable in naturalness, realism and wide range. 

There is added economy, too, in the higher acoustic efficiency of the 
new Type B. That means more units per amplifier, more acoustic 
power output per electrical watt input, more coverage, more profit 
on each p. a. job. 

The four sizes illustrated meet every loudspeaker requirement from 
the small trumpet p.a. rental to the magnificent far-reaching 
chime-carillon system. Call on our Engineering Department for 
the full benefit of a nation-wide field experience. 

Every Racon product is guaranteed by the largest independent 
manufacturer of air-column speakers, having adequate financial 
resources to substantiate every claim and a wide field organization 
to meet every service demand. 

Note: Old-style Racon Units can be rebuilt to the 
Type B head at a nominal charge. Write us. 



For valuable information 
RACON'S Catalog P.E. 1 1 
will be sent on request it 
you use your business 
letterhead or card. 



RACON Horns and Units are 




Covered by U. S. Patents Nos. 




1,507,711; 1,501,032; 1,577,270; 




73,217; 73,218; 1,722,448; 1,711,- 




514; 1,781.489; 1,832,608: 1,834,- 




327; 1,835,739; 1,845,210; 1,878.- 




1 360. 






TTCrrYATiN^. "East 19th Street, New York Ci 

— London, bngland Toronto, Canada 



iTiTI 1 I ' l H ' i 'i' I iN' MI I'lll II l i llllll i I I li iliJ i in ■■.■■■i.. m . m -, 





■f 


IN THIS ISSUE 


w 


• 




ELECTRO - ACOUSTIC 
ENGINEERING 




By R. H. Herrick 




THE ABSOLUTE MEASUREMENT 
OF THE INTENSITY OF SOUND 




By Arthur Gordon Webster 




A NEW DOUBLE SYSTEM OF 
FILM RECORDING 


"j 


By John Dunsheath 


A 


SOUND SYSTEMS IN ROCKE- 1 
FELLER CENTER, NEW YORK 




By James Frank, Jr. ' 





Fourth Year 
Of Service 









\ 1 1 f 1 I A I 

%# 1 J 1 I II 



m 




16 W •) 



Courtesy Fox Film Studio 
A set from "Transatlantic" which won an 
Academy nomination for Gordon Wiles. 



<£/r--.,- 







journal of me Sound ana Light Prqjecf ion Indus! rieis 




DECEMBER, 1932 



An A-C Operated Three Microphone 
Mixer, Button Current Supply and 
Amplifier Unit . . . 




MIK-2— Mixer Amplifier 



MIK-2— Power Supply 



The Samson Mik-2 Mixer Amplifier 

Is a new unit which supersedes the MIK-1 (the first and original all a-c 
operated microphone amplifier), of which there are thousands in use in 
broadcast stations as remote pick-up amplifiers, in public address sys- 
tems, and in centralized radio systems. 

The MIK-2 may be operated as a source of power amplifier input; or as a line amplifier 
for broadcast pick-up work. 

Two output levels — 5000 ohms and 500 ohms. The 5000 ohm terminals may be operated 
into any terminating load of that value or greater. 

The Samson MIK-2 Mixer Amplifier is furnished in two units — the Mixer Amplifier unit 
and a separate power supply: Results . . . 

1. Less Cumbersome 

2. Marked Reduction of Hum Level 

A button current of 10 milliamperes per button (20 milliamperes per microphone) is fur- 
nished, free from hum, and limited so that microphones cannot easily be damaged, exces- 
sive currents being an impossibility. 

The volume of each microphone position is independently variable and is absolutely free 
from "interlock." In addition there is a master gain control. 

Send 5 cents in stamps for Bulletin No. P. E. 27, descriptive of this unit to 

R. W. COTTON, Sales Manager 

SAMSON ELECTRIC COMPANY 

Member R.M.A. 

CANTON MASS. 



l! 



DECEMBER, 1932 



Page I 



NATIONAL HIGH INTENSITY 
PROJECTOR CARBONS . . . 
WIN COMPETITIVE TESTS 




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COMPETITIVE tests of three makes of 
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superiority of National High Intensity Pro- 
jector Carbons. 

Tests were made with both condenser and 
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Every Projectionist should have a copy of the recent- 
ly published handbook on National Projector Car- 
bons. If you have not received your copy, fill out 
and mail this coupon. 



NATIONAL CARBON COMPANY, INC. 
Post Office Box 400 
Cleveland, Ohio 




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Gentlemen: Please 
Handbook on National 


send me complimentary 
Projector Carbons. 


copy 


of the New 


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Projection 

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Sound Pictures 

Visual Projection 

Sound Recording 

Audio Amplifiers 

Public-Address Systems 

Photography 

Facsimile Recording 

Television 

Photo-Voltaic Cells 

Circuit Measurements 

Automatic Music 

Acoustic Engineering 

Radiant Energy Devices 

Electric Recording 

Phototubes 

Home Talkies 

Theatre Engineering 

Amplifier Tubes 

Sound Reproducers 

Screen Engineering 

Electric Power for Projec- 
tion 

Recording Studio Engi- 
neering 

Location Sound Equipment 

Rectifier Tubes 

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tions 



Donald McNicol 
Editor 

Jas. R. Cameron 
Associate Editor 

Ulmer G. Turner 
Western Editor 

F. Walen 
Managing Editor 



Vol. IV 



DECEMBER 
1932 



Number 12 



Contents 

Page 
Editorial 4 

Electro-Acoustic Engineering By R. H. Herrick 7 

The Absolute Measurement of the Intensity of Sound 

By Arthur Gordon Webster 10 

New High Fidelity Sound System Employs New Sound 
Head 14 

A New Double System of Film Recording 

By John Dunshcath 16 

Sound Systems in Rockefeller Center, New York 

By James Frank, Jr. 18 

Glossary of Technical Terms for the Projectionist. . 20 



Departments 



New Developments of the Month and News of the 
Industry 22 

Index of Advertisers 23 



Bryan S. Davis 
President 

Jas. A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

19 East 47th Street 

New York City 



Sanford R. Cowan 
Advertising Manager 

J. E. Nielsen 
Circulation Manager 



Chicago Office — 1221 Rosemont Ave. — Charles H. Farrell, Mgr. 
St. Louis Office- 303 Star Bldg.— F. J. Wright. 
Kansas City (Mo.) Office — 306 Coca Cola Bldg.— R. W. Mitchell. 
Cleveland Office— 416 National Building— Millard H. Newton. 



San Francisco Office — 153 Sansome St. — R. J. Birch. 
Los Angeles Office — 846 S. Broadway— R J. Birch. 
New Zealand— Tearo Book Depot — Wellington. 
Australia — McGill's Agency — Melbourne. 



Entered as second class matter August 13, 1931, at the post office at New York, N. Y., under Act of March 3, 
1879. Yearly subscription rate $2.00 in U. S. Yearly subscription rate $3.00 in Canada and foreign countries. 



DECEMBER, 1932 



Page 3 





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consider this fact: Forest rectifiers save current, are efficient, supply 
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additional 25 amperes to second projector during change over. Model 
No. 45, up to 45 amperes to one projector available for either single 
or three phase A.C. current. 

Model No. 6, up to 65 amperes, and Model No. 10, up to 100 amperes, 
both for one projector, are now available in three phase A.C. cur- 
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DECEMBER, 1932 



i a 



I F there is to be a feature 
GIVE THE FEATURE ' picture sandwiched in 
A BREAK among a couple of shorts 

and a newsreel why should 
the featuring cease, for the theatre patron, 
after he has deposited his ticket in the hop- 
per? 

A feature picture may be exploited, ad- 
vertised, and emblazoned above the mar- 
quee, but thereafter, screen-ward, the fea- 
ture has to make its own way unheralded 
as, likewise, the shorts and fillers. 

Showmanship should suggest that there 
should be a "sound" rather than a "silent"* 
beginning to the feature. The opportunity- 
is there for the herald; for the sound effects 
i-serving the same ends as the alarums arid 
•excursions of stage presentations. A~s~ a. 
short comic fades out the audience is in the 
middle of a laugh, when, immediately (too 
soon) on comes the feature, silently and 
inadequately announced. Even after the 
silent introduction has passed one hears 
from neighboring seats the whispered ques- 
tion: "Is this the feature?" or "Is this the 
main picture?" 

Clearly, preceding the main picture there 
is a hiatus which should be filled with some 
of the "promotion" hung outside of and be- 
yond the box office. 

If producers cannot think of the sound 
effects which would adequately serve the 
purpose, which could be placed on the film 
ahead of the picture, theatre managers 
might capitalize the opportunity to read 
from the stage, or through the sound dis- 
tribution system, a brief, prepared introduc- 
tion, thus giving the "feature" a break. 



CHRISTMAS, 
1932 



J~HE greatest salesman 

who ever lived was 

Charles Dickens. Dickens 

sold Christmas. He sold 

Christmas to the peoples of the world — the 

peoples of his own time and of succeeding 

generations. 

Dickens, of course, knew that the signifi- 
cance of Christmas Day had been known to 



the civilized world since the beginning of 
the Christian era, but he was not satisfied 
with the way the day was annually being 
observed. 

For the purpose of selling his own idea of 
how Christmas should be observed Dickens 
created a fictitious character whom he called 
Scrooge — fictitious in name only, but true 
to type. 

Scrooge typified those who in large num- 
bers thought only of themselves and their 
own welfare. He was a miser. He was a 
skinflint. In the language of our times he 
"was a iiard : boiled tightwad. — 

But Dickens in story led Scrooge through 
a series of harrowing experiences which in 
time caused him to see a light. The light 
shone brightly upon the good deeds of 
others who were far less selfish than he. It 
illumined for his view a pathway of good 
cheer, of friendship, of keen satisfaction and 
of happiness, along which he might travel. 

To travel this path it was necessary for 
Scrooge to buy Christmas. The price was 
that he must give up selfishness; that he 
must rid his nature of avarice and greed. 

And so Dickens, through his stories sold 
Christmas. 

In our day it is difficult to imagine that 
there ever was a time when the Christmas 
season was not availed of to exchange kindly 
greetings, to send gifts to loved ones and 
friends, and to offer thanks for blessings 
received. 

We can not (any longer, now, or, as yet) 
legally invite our friends to gather around 
the festive Wassail Bowl, but we can, and 
we do, here, extend to everyone we know 
and who knows us the sincere wish for a 
high old time on Christmas and a New Year 
freighted with happiness, success and per- 
sonal achievement. 



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Editor 



DECEMBER. 1932 



Page 5 



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Page 6 



PROJECTION ENGINEERING 



Today, more than ever before, 
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is today making headway. It 
is essential to know what is go- 
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DECEMBER, 1932 



The acoustic characteris- 
tics of a given interior are 
determining factors in de-t 
signing sound transmission 
and distribution systems. 




Ferris Russell residence, 
Mill Meek, L. I., N. Y. 
equipped with sound dis- 
tribution system. Sound 
projectors in ceiling. 



Electro-acoustic engineering 



FEW persons can visit that magnif- 
icent building, the Riverside 
church in New York, without 
some curiosity as to how a speak- 
er at the rostrum can be heard and un- 
derstood throughout such a vast space. 
Undoubtedly, a public-address system 
plays its part. 

In the first place, electro-acoustics is 
an art rather than a science. That is, 
unlike most branches of engineering, it 
is not subject to exact mathematical 
treatment. 

The average public-address installa- 
tion employs standardized equipment — 
amplifiers, loudspeaker units, horns, and 
accessories. From a cost standpoint this 
is, of course, highly desirable, but un- 



By R. H. Herrick 

fortunately each location presents such 
special problems that satisfactory re- 
sults cannot always be obtained without 
special design. Electro-acoustics enters 
the picture at this point. 

The method often used in engineer- 
ing a public-address system is to em- 
ploy standard amplifiers and sound-pro- 
jectors, and to install the projectors 
at the point or points which will give 
the least acoustic feedback to the mi- 
crophone with the greatest possible 
coverage. Some attempt may or may 
not be made to give the impression that 
the sound is coming from the rostrum. 
Contrast this with the attack of the 
electro-acoustic engineer. An experi- 
enced engineer starts with no fixed 



ideas as to the equipment to be used. 
He knows that every auditorium has a 
"voice" or "voices" which are the result 
of resonance, and inasmuch as many 
of the difficulties will be traceable to 
these, he starts with a consideration of 
them. 

Resonance 
What is resonance as applied to 
acoustics? It is. briefly, a reinforce- 
ment of certain tones. The sound we 
hear at any point is the combination of 
the direct and reflected or refracted 
waves simultaneosuly reaching that 
point. Thus, if the components are at 
a maximum when they arrive, the sound 
heard is louder than any of them alone 
and we have, then, a condition of em- 



Page 8 



PROJECTION ENGINEERING 




phasis or resonance. Inasmuch as the 
condensations and rarefactions occur at 
different times for different frequen- 
cies, resonance will normally occur at 
only one frequency or possibly a few, 
and never at all of them. 

This condition of resonance may not 
be serious for music and yet may give 
considerable trouble for speech. A 
speaker unconsciously pitches his voice 
to one of the "voices" of the hall in 
order to reduce the amount of energy 
required for coverage. But mere cov- 
erage is not all there is to the problem 
or there would be no need for the elec- 
tro-acoustic engineer in the field. By 
pitching his voice to the auditorium 
the speaker permits many of his speech 
frequencies to be unduly emphasized. 
The remaining sounds are lost by com- 
parison, and intelligibility to the listen- 
er suffers correspondingly. 

IIW • II 

Voices 

The most obvious solution to such a 
problem is, of course, to eliminate the 
reflections and refractions which give 
the hall its voices, but the difficulty 
and cost of this method usually prohib- 
its its application while the accompany- 
ing additions or other changes in the 
appearance of the hall will often in 
themselves halt such an attack. In lieu 
of this, the electro-acoustic engineer 
may employ as much acoustic treatment 
as practicable and supplement it with 
the proper use of projectors, or he may 
be forced to depend entirely upon the 
electro-acoustic system. In either case 
the problem, so far as it affects the 
speaker, is to so minimize the hall's 
resonances at the rostrum as to give its 
occupant no voice to which he can pitch 
his speech. This may usually be done 
either by directing one or more projec- 
tors to give him a strong direct beam 
which will mask the hall's reflections, 
or, strange as it may seem, by main- 
taining a low sound level from some or 
all of the projectors. 



Athletic stadium, Duke 

University, Durham, N. C. 

Projectors over score 

board at far end. 



The reason for the latter may become 
apparent when it is realized that the 
sound absorbing materials in the room 
will become saturated when the sound 
has reached a sufficient intensity. If 
an energy-level greater than this trig- 
ger point is provided, the excess sound 
will be returned to the hall in the form 
of reflections or refractions which 
markedly increase the intensity of the 
resonances. And thus is introduced a 
major difference between specific design 
and that found with standardized equip- 
ment, namely, rigid control of sound 
level from the projectors. The engi- 
neer ascertains the maximum permis- 
sible level and his amplifiers and mix- 



Sound control cabinet, 
Church of St. Andrew and 
St. Paul, Montreal, Canada. 



ing equipment should be so designed 
that this cannot be exceeded. 

Thus far we have considered only the 
talker and his effect on the overall per- 
formance of the system. Yet he may 
avoid pitching his voice to the audi- 
torium and still be unsatisfactorily 
heard by his listeners. The auditorium 
and its acoustic conditions affect the 
auditor to an even greater extent than 
the speaker. 

Let us consider the hall itself. We 
have stated that resonances which are 
likely to make speech unintelligible are 
not necessarily undesirable for music. 
This statement needs some amplifica- 
tion. The "voices" of a hall may be 
either harmonious or otherwise ; that is, 
their frequencies may or may not be of 
the proper ratios to form a pleasant 
combination to the ear if heard simul- 
taneously (like a chord struck on the 
piano). If they are not harmonious 
their effect upon speech is less than if 
they are, both because the speaker him- 
self is less likely to select one of them 
upon which to pitch his voice, and be- 
cause the discordant resonances are not 
apt to distract the attention of the lis- 
tener. If, on the other hand, the 
"voices" of the auditorium are har- 
monious, the resonances appear to blend 
with the music itself, giving, with echo 
or reverberation effects, an acoustic 
quality often described as "live." 

Design 

It is a strange fact that an auditorium 
design which is pleasing to the eye is 
likely to be acoustically satisfactory as 
well, principally for music. This does 
not mean that the hall will not have its 
"voices" which must be considered, but 
rather that these resonances will be har- 
monious and not so pronounced as to be 
serious. This explains, perhaps, why 
so many of the famous European cathe- 
drals are also noted for their acoustical 
perfection to music, although but very 
few may be considered satisfactory for 
speech. Unfortunately, however, there 




DECEMBER, 1932 



Page 9 



are exceptions which must be made 
usable by the electro-acoustic engineer, 
as must also many auditoriums not com- 
ing under either the visual or acousti- 
cal category "good." 

In such cases the sources of reflec- 
tion or refraction causing the undesir- 
able characteristics are located and 
studied. In their treatment it is often 
possible to so direct the projectors as 
to isolate such points acoustically, thus 
removing their effects upon the balance 
of the room. If the offending locations 
form a part of the audience space, it 
is frequently possible to effect a suffi- 
cient reduction in reflections or re- 
fractions by treatment with materials 
of the proper acoustic characteristics. 
In other cases special projectors must 
be installed to feed this space alone, 
or possibly a combination of electro- 
acoustic and acoustic treatment may be 
required. 

Electro-acoustic consideration is now 
recognized as an important part of the 
modern auditorium design. Many build- 
ings, notably the Riverside Church in 
New York, were planned in consulta- 
tion with T. F. Bludworth of New 
York. Many other edifices now equipped 
were built without benefit of such ad- 
vice. Of the latter, Trinity Church* 
in New York, was constructed long be- 
fore the advent of the electro-acoustical 
art, while the Church of St. John the 
Divine*, also in New York, is repre- 
sentative of those which were contem- 
porary but did not avail themselves of 
this utility until construction was well 
under way. 

Sound Absorbing Materials 

Trinity Church has an auditorium 
which is an example of one having poor 
acoustics for speech, in which the addi- 
tion of sound-absorbing materials would 
have required such radical changes in 
the architecture as to affect the his- 
toric value. This forced the employ- 
ment of electro-acoustics entirely, with 

*Engineered and installed by Bludworth, Inc., 
New York. 





final results which one must hear to 
appreciate. The Church of St. John 
the Divine, also with poor acoustics 
for speech, was on the other hand, made 
entirely satisfactory by a combination 
of acoustical and electro-acoustical 
treatment. 

It is necessary to go further afield 
for an illustration of another type of 
installation — Duke University Stadium 
at Durham, N. G, which comfortably 
seats 35,000. This is an example of 
the necessity which mothered the pub- 
lic-address system. Obviously the hu- 
man voice alone would be inadequate 
for coverage of such an immense out- 
door space. One could logically expect 
that here would be the ideal application 
of a standardized public-address sys- 
tem. Not so. With the projectors placed 
in the usual location within the horse- 
shoe it was found that echoes were so 
pronounced as to seriously affect in- 
telligibility. Mr. Bludworth solved the 
problem simply, however, by placing the 
projectors outside of the horseshoe, 



Typical remote control box. 
Bludworth, Inc., sound dis- 
tribution system provides 
for remote tuning and 
volume control of radio, 
phonograph and program 
sources. 



Portion of interior, River- 
side Church, New York. 
Speech projectors in 
canopy over pulpit on left 
and in end of wall, left 
aisle. Music reinforcement 
projector in recess over 
center arch. 



carefully directing them to cover the en- 
tire space. 

It is generally recognized that the 
horn or baffle of a projector is the 
coupling device between the diaphragm 
of the unit and the air, but the engi- 
neer goes further in his conception of 
this important element. He feels that 
not merely the column of air in the 
horn, but the entire room with its re- 
verberations must be coupled to the 
unit, implying a special impedance and 
a particular design of acoustic coupler 
or baffle for each space to be covered 
by a projector. The architecture of 
a building determines to a large extent 
the form of the coupler, from which a 
design is derived and the corresponding 
electrical impedance obtained. The pro- 
jector employs a baffle deviating from 
the usual "flat" type in that it is given 
dimension along the third axis as well, 
(Concluded on page 19) 



Page 10 



The absolute 
measurement of the 
intensity of sound 



By Arthur Gordon Webster 



Third, a step in the process remains 
which is perhaps equally as important 
as the first and second. Given the in- 
vention of the proper source of sound, 
which I have denoted a phone, because 
it is a sound and nothing- else, and a 
proper measuring instrument, which I 
call a phonometer, there still remains 
the question of the propagation and the 
distribution of sound in space between 
the phone and the phonometer. Any 



This paper by the late Professor Webster describes his 
fundamental researches extending over a period of 
twenty-eight years, dealing with the properties of 
vibrating bodies and elastic hysteresis. 
The paper was presented at the Boston meeting of the 
A.I.E.E., March 14, 1919. 



THE profession of acoustical engi- 
neering is a new one that has 
arisen during the last few years. 
The late Professor Wallace C. Sa- 
bine, of Harvard University, attracted 
the attention of the public to the very 
great importance of physical measure- 
ment and thoroughly scientific design in 
the construction of auditoriums which 
until his time had remained an entire 
mystery to architects. 

The writer has been interested for 
many years in the problem of the meas- 
urement of sound in absolute units, in- 
volving the design of an instrument 
which is capable of determining, at any 
point in space, the pressure in the air 
wave as a function of the time. In order 
to carry out this object three things are 
necessary. 

First, the construction of a standard 
of sound which will enable a given 
sound of the simplest possible charac- 
ter, namely, that in which the pressure 
varies as a simple harmonic function of 
the time, to be reproduced at any time, 
and which permits an output of sound to 
be measured in watts of energy. This 
problem has been solved by a number 
of persons, including Professor Ernst 
Mach and Dr. A. Zernov of Petrograd. 
Second, the invention of an instru- 
ment capable of measuring a sound of 
the simple harmonic character de- 
scribed, also in absolute measure ; that is 
to say, in such a way that the amplitude 
of pressure variation may be measured 
in absolute measure, as dynes per square 
centimeter, or in millionths of an at- 
mosphere. This problem has also been 
successfully treated by a number of in- 
vestigators, among whom may be men- 
tioned Professor Max Wein, Lord Ray- 
leigh and Lebedeff. 



PROJECTION ENGINEERING 

measurements made in an enclosed space 
will be influenced by the reflection from 
the walls, and even if we had a room 
of perfectly simple geometrical form and 
were able to make the instruments of 
emission and reception work automat- 
ically without the disturbing presence 
of an observer, it would still be impos- 
sible to specify the reflecting power of 
the walls without a very great amount 
of experimentation and complicated the- 
ory. Nevertheless, this is exactly what 
Sabine did. He did it, however, by em- 
ploying as a receiving instrument the 
human ear. Those who have made ex- 
periments upon the sensitiveness of the 
human ear for a standard sound will 
immediately doubt the possibility of 
making precise measurements by the 
same ear at different times, and par- 
ticularly of comparing the measure- 
ments made by one ear with those made 
by another. Nevertheless, Sabine at- 
tained wonderful success and was able 
to impart his method to pupils and col- 
leagues who carried on his methods 
successfully. 

To proceed with the question of dis- 
turbing objects, one should take his 
phone and his phonometer to an infinite 
distance from all objects, which is mani- 
festly impossible. The plan which I fol- 
lowed was to attempt to get rid of all 
objects except an infinite space covered 
with a surface the reflecting coefficient 
of which could be measured. I found 







A. Phonometer. B. Phonometer interior. C. Phonometer front view. 



DECEMBER, 1932 



Page 



the proper weather and the proper space 
on the golf links of a country club 
where conditions appeared to be favor- 
able. Several days were spent in deter- 
mining the reflection coefficient. This 
was done about ten years ago, whereas 
with the instrument available today it 
could be done in a very few minutes. 

First Steps 

The history of my investigations is 
briefly as follows: In 1890 I proposed 
to use a diaphragm made of paper or 
some similar substance which should be 
placed, shielded on one side, at the spot 
where the sound was to be measured. 
Upon the center of the diaphragm was 
cemented a small plane mirror. In close 
juxtaposition and parallel with this was 
the plane side of a plano-convex lens 
which viewed in the light from a sodium 
flame was to give Newton's rings, or as 
we now call them, interference fringes. 
Of course, when the sound falls upon 
the diaphragm, the fringes vibrate rap- 
idly and disappear from sight. I then 
■determined to use the stroboscopic ar- 
rangement which would permit the 
viewing of the fringes as they slowly 
shifted their position. All sorts of dif- 
ficulties occurred. The light from the 
sodium flame was not strong enough to 
permit the fringes to be seen through 
the stroboscopic device. It was not 
at that time easy or perhaps possible 
to make an electric motor that would 
drive a stroboscopic disk at a constant 
speed. One of the first difficulties was 
to devise a method of controlling a syn- 
chronous motor. This was accom- 
plished by means of interrupting the 
current by a tuning fork. 

Later I made the acquaintance of 
Professor A. A. Michelson and of his 
remarkable optical interferometer, and 
I immediately saw that one of the dif- 
ficulties that I had met, namely, the dif- 
ficulty of adjustment of the lens so that 
it should not strike the vibrating 
plate, could be overcome at once, as 
the two mirrors in the Michelson inter- 
ferometer could be any distance apart. 
Also the trouble due to the faintness of 
the light disappeared, for in Michel- 
son's instrument white light could be 
used, and it was possible to use gas, 
incandescent or arc light with good 
effect. 

In 1896 I put the subject in the hands 
of a student who produced an instru- 
ment which was successful. The ex- 
amination of the substance suitable for 
a membrane or a diaphragm consumed 
much time, and all organic substances 
such as parchment, paper or anything 
of that sort had to be discarded be- 
cause it was impossible to keep the ten- 
sion constant under the changes of 
moisture in the air. Metal was found 



to be quite out of the question on ac- 
count of the difficulties due to thermal 
expansion. We next decided upon thin 
glass diaphragms which we afterward 
found were used by phonograph com- 
panies. A slight change of temperature, 
however, such as was made by breathing 
upon the diaphragm, would sometimes 
produce a change of pitch of several 
tones, so I next decided to clamp the 
glass diaphragm upon a ring sawed out 
of plate glass and cement it on with sili- 
cate of soda. I finally found that it was 
possible to get mica so flat that it was 
superior to the best glass, and this gave 
me the best results up to that time. 

Diaphragm Qualities 

Let me now state briefly the quali- 
ties which the diaphragm must have in 
order to be successful. It is well known 
to physicists that a flat diaphragm can 
vibrate in an infinite number of modes 
which the physicist calls normal vibra- 
tions. In the simplest mode the dia- 
phragm vibrates so that every point 
moves in the same direction. The nat- 
ural period of this vibration is the low- 
est that the diaphragm can have. Next 
is a mode in which the central portions 
of the membranes move in one direction 
while all those outside of a certain cir- 
cle, which we call a nodal line, move 
in the opposite direction. Other vibra- 
tions have radial, as well as circular, 
nodal lines on the opposite sides of 
which the diaphragm is moving in op- 
posite directions. When a mass is 
screwed to any point of the diaphragm 
its motion is entirely changed. And any 
apparatus that may be attached to the 
diaphragm and required to do work, 
such as the carbon button of the tele- 
phone, or anything that interferes with 
the free response of the diaphragm to 
the variations of the air pressure will 
alter the action in such a way as to 
make it extremely difficult of interpre- 
tation. My idea, then, was to make a 
diaphragm which did not do any work 
at all, but merely carried the mirror 
which moved practically by itself. 

Now in spite of the great variety of 
forms and vibrations, it can easily be 
shown that under proper circumstances 
the diaphragm will move essentially as 
a whole, and may, therefore, be com- 
pared to a single body which has three 
characteristic constants : First, its mass ; 
second, its stiffness, defined as the force 
required to produce a unit deflection of 
its nodal point ; and third, and most dif- 
ficult to control, the coefficient of damp- 
ing, which is defined as the force 
of resistance that will be exerted from 
any cause when the velocity of the body 
or the nodal point of the diaphragm is 
unity. This damping must be due to a 
large number of causes. In the first 



place, the resistance of the air will 
cause damping. In the second place, the 
energy of the sound waves that are ra- 
diated from the vibrating diaphragm 
will cause damping. In the third place, 
and by far the most important, the bend- 
ing of any body is resisted by elastic 
forces and we therefore have the phe- 
nomenon of elastic fatigue. In order to 
settle the question "what is the best 
material from which to make tuning 
forks," which has been variously an- 
swered as tool steel, bronze, bell metal, 
quartz, etc., I perceived that it was nec- 
essary to have an exact method of ex- 
perimentation. 

In striking a steel bar supported by 
a string at two points it will be observed 
that the high overtones emitted by the 
bar rapidly die away, and it occurred 
to me that if the bar was thrown into 
one normal vibration there would be 
a bar rate of damping for every nor- 
mal vibration, and that by stating the 
rate of natural damping a natural hys- 
teresis could be studied. This was dem- 
onstrated experimentally by my assist- 
ant, James L. Porter, with very suc- 
cessful results as far as the experiment 
went. The mathematical theory has been 
lacking up to the present time. Two 
theories are possible, first the theory of 
solid viscosity, and second the theory 
of heredity, or elastic hysteresis. The 
attempts to compute the results of our 
experimental measurements are now ap- 
proaching completion, and we soon shall 
be able to give a theory of elastic hys- 
teresis. My conclusion is that quartz 
is the best substance from which to 
make tuning forks. 

This digression from the investiga- 
tion is told in order to show the very 
great difficulties that this subject pre- 
sented. 

The illustrations herewith show the 
apparatus as it was built several years 
ago. It was mounted upon a heavy 
stand made of bronze, covered in at the 
back by a heavy bronze cover, through 
which protruded through air-tight fit- 
tings the shafts turning the screws of 
the interferometer adjustments, three in 
number. Upon the front of the instru- 
ment was attached a resonator properly 
tuned and at the side was a small in- 
candescent lamp with a straight fila- 
ment arranged horizontally, an image 
of which was projected by a lens upon 
the first mirror of the interferometer. 
A telescope was focused upon this im- 
age, giving an image in the reticle of 
the horizontal straight filament. This 
was crossed by the vertical interference 
fringes. The objective of the telescope 
was carried by one prong of a tuning 
fork which oscillated vertically and this, 
combined with the horizontal oscillation 
of the fringes due to the vibration of 
the diaphragm, resulted in a figure in 



Page 12 



PROJECTION ENGINEERING 



the form of an ellipse. On tuning the 
two sounds together this ellipse could 
be caused to go through its various 
phases as slowly as desired. At the mo- 
ment when the ellipse degenerated into 
an inclined straight line the reticle, 
which was tilted by an observer, was 
brought into line with the interference 
lamp and the tangent of the angle was 
read off on a tangent scale. The pres- 
sure on the sound wave was then pro- 
portional to the number read off on the 
tangent scale. The apparatus was used 
in this form for a good many years, a 
precursor of it being shown at the Con- 
gress of Physics at Paris in 1900. 

Professor D. C. Miller's phonodeik, 
which is a very beautiful instrument, 
was designed for quite other purposes 
than the phonometer of the writer. It 
was intended to photograph sound 
curves of any sort and by means of it 
Professor Miller has obtained most 
beautiful reproductions of speech, and 
sounds of musical instruments. Unfor- 
tunately, this instrument does not adapt 
itself in the least to absolute measure- 
ments. One objection to Professor Mil- 
ler's instrument is that it employs a 
spring made of rubber material. This 
spring has to be calibrated whenever 
measurements are taken, and it is well 
known that the properties of soft rub- 
ber are far from constant. 

Diaphragm Vibrations 

The speaker next undertook to devise 
a better mode of reading the amplitude 
of vibrations of his diaphragm. In the 
first place, the mirror which was car- 
ried by the diaphragm in Professor Mil- 
ler's apparatus, instead of being carried 
on an axis in jewels was placed on a 
thin steel torsion strip which could be 
made at far less expense and could be 
rapidly adjusted. The straight filament 
lamp was now viewed through a tele- 
scope into which the mirror focused the 
filament in the reticle of the eyepiece. 
A magnification of about 1,200 to 1,500 
is used. The instrument was also used 
photographically just as the old instru- 
ment had been used to photograph the 
motion of the interference fringes. Pho- 
tographing moving interference fringes, 
however, was attended by many experi- 
mental difficulties. 

A new instrument in the form de- 
scribed was made for Professor Louis 
Vessot King, of McGill University, 
who had a commission from the Cana- 
dian Government to make experiments 
upon fog signals and had secured per- 
mission to investigate the great siren at 
Father Point on the St. Lawrence. Pro- 
fessor King spent the whole summer at 
Father Point in making the first survey 
of an acoustical field ever made. The 
Canadian Government had furnished 







D. Quartz tuning-fork E. Damping of quartz tube. F. Damping of 
phonometer. G. Phonotrope. H. Phonotrope tuning device. 



him a large steamer with which he went 
out every day, blew the "criard" as the 
natives call it, the very perfect siren 
which can be heard thirty miles away 
in good weather, and explored the gra- 
dient of sound under all meterological 
conditions, studying the wind, the tem- 
perature, and the temperature of the 
water, etc. This spurred the writer 
on to undertaking the same thing in this 
country. It was impossible to get from 
the lighthouse board the loan of a 
steamer, but permission was given to 
go on any lighthouse steamer going 
along the coast of Maine. The first step 
was to tune the phonometer for the dif- 
ferent pitches, and at that time the only 
method of tuning the diaphragm was 
to load upon it small pieces of wax. 
This, although it worked perfectly, 
seemed very clumsy, and not an engi- 
neering method. It was therefore de- 
cided to redesign the whole instrument 
so that it could be tuned continuously. 
It occurred to me that this could be 
accomplished by furnishing potential 
energy to the diaphragm by means of a 
spring parallel to it, and bearing against 
it by means of a bridge, and tunable like 
a violin string. The very first attempt 
showed this to be entirely successful. 
Then the idea immediately presented it- 
self that if a string could be tuned con- 
tinuously why use the energy of bend- 
ing at all and why not get entirely rid 
of all difficulties of elastic fatigue. Since 
that time the diaphragm has been en- 
tirely discarded and replaced by a stiff 
disk supported upon three strings in ten- 
sion. The disk is made of aluminum 
or mica and is carried by a little spider 
made of aluminum containing three 
clamps to hold the wire. The wire is 



made of steel and is under tension about 
steel pegs, two of which are turned 
roughly by means of a screw driver, the 
other by means of a lever actuated by a 
micrometer screw. We have now a very 
perfect instrument at least ten times as 
good as the one Professor King had. 

Reduction of Damping 

A few figures will show the advan- 
tages in the reduction of the damping. 
In a system of one degree of freedom 
the amplitude of the vibration for the 
most perfect tuning is inversely propor- 
tional to the quotient of the damping co- 
efficient k divided by the mass m. When 
we began with the good glass diaphragm 
we had a value of k something like 150. 
In 1913 the mica diaphragm lent to 
King had reduced this to 30. With the 
phonometer as built now we have re- 
duced this to 1.34. In all these cases 
the mass was about the same so that 
so far as the sensitiveness goes, the in- 
strument is more than one hundred 
times as good as it was ten years ago. 
The instrument now competes in sensi- 
tiveness with the human ear and may 
be tuned to pitches varying by perhaps 
two octaves. If I strike a tuning fork 
and allow its amplitude to die away, a 
person looking into the eye-piece of the 
instrument cannot say with certainty 
whether he can see the sound or hear it 
the longest. Unfortunately, however, 
this very great sensitiveness obtained 
by a small damping is attended with a 
very great disadvantage. The instru- 
ment is extremely selective and if the 
tuning varies by a very small amount 
the amplitude falls off very greatly. 

Within the last three months I have 



DECEMBER, 1932 



Page 13 



devised a plan of doing away with this, 
and making an artificial ear. For, as 
you know, the human ear has a wonder- 
ful sensitiveness, not for all sounds, but 
to sounds of a frequency of perhaps 30 
per second up to perhaps 30,000 per sec- 
ond, attaining a maximum sensitiveness 
for frequencies of from 1,000 to 1,500. 
We know how this affects the telephone 
and how the damping of the telephone 
and microphone disks enables the re- 
sponse to be carried over a large range, 
so that they answer very well for the 
frequencies involved in speech. Never- 
theless, the sounds of s, f, t, and certain 
others, on account of the very high har- 
monics involved, are most difficult to 
transmit telephonically. 

Theory of Device 

Having described the construction of 
the diaphragm, the new piston with 
wires, and the method of reading the 
vibration by means of the inclined mir- 
ror which is also reduced to absolute 
measure by means of the interferometer 
temporarily attached, or more simply 
by displacing the diaphragm by a mi- 
crometer screw, I come to the theory 
of the instrument. The resonator into 
which the air enters, and the hole which 
is now constituted by an angular open- 
ing around the disk, furnishes through 
the movement of the air in and out an 
additional degree of freedom. We are 
then in the possession of a system with 
two degrees of freedom, statically 
coupled by means of the increased pres- 
sure in the resonator when the piston 
is forced in. The theory of such a sys- 
tem under the action of the periodic 
force is well known and has been treated 
by Professor Max Wien in great detail. 
If the frequency in 2 % seconds be n 
and if the mass be m, I shall call the 
stiffness minus the product of the mass 
and square of the frequency the uncom- 
pensated stiffness or mistuning. If this 
were equal to zero for a system of one 
degree of freedom we should have reso- 
nance. In the case of two degrees of 
freedom I plot the mistunings horizon- 
tally and vertically, and the amplitude 
of response as a third co-ordinate. I 
thus get a surface that may be described 
as two mountain peaks with a pass be- 
tween them, the summit of the pass be- 
ing when both mistunings are zero ; but 
this is by no means the highest point 
of the region. To attain either summit 
we must mistune both systems by a cer- 
tain amount which is proportional to 
their two dampings. The addition of 
the resonator to this instrument may 
produce an increase of sensitiveness of 
fifty times. You now see, I hope, how 
we have obtained an engineering in- 
strument, everything in which is meas- 
urable in absolute measure. It is ob- 
vious that the piston may be made the 



diaphragm of the telephone, that the in- 
strument may be used by the psycholo- 
gist, the engineer, the physiologist, for 
instance in a stethoscope, and in many 
other applications. 

I turn now to the source of the 
sound, the phone. With the advent of 
the tuneable diaphragm came the new 
phone. It is very light. The amplitude 
of the diaphragm is measured by a 
microscope. I use a hot wire vacuum 
tube as a source of alternating current, 
tuneable at will, and tune the phone to 
it. We thus have in small compass a 
very perfect set of acoustical instru- 
ments. 

] DR. GOLDSMITH OFFERS 

S.M.P.E. COOPERATION § 

PRESENTING constructive f 

argument to the film indus- | 

I try for extended use of what I 

I the Society of Motion Picture | 

Engineers offers, Dr. Alfred N. | 

I Goldsmith, president, told sev- | 

! eral hundred film technicians { 

| and engineers at a recent meet- | 

I ing that the Society is gaining | 
1 steadily in recognition. 

He stated that the Society is } 

beginning to feel it is steadily 1 

1 coming to be regarded as the | 

| major exponent of organization i 

I and of systematic analytical en- | 

| deavor in the field of motion | 

1 pictures by all of the important 1 

1 manufacturing and production 1 
| interests. 

Some of the important pro- § 

1 ducing and manufacturing inter- | 

| ests "have, unfortunately, been | 

I slow to recognize fully how im- 1 

1 portant the S.M.P.E. could be [ 

| to the industry," said Dr. Gold- 1 

1 smith, and "some of them have | 

| developed their own individual | 

1 organizations within their own | 

1 companies, to a very high de- 1 

I gree; but they failed to under- f 

I stand that this is not sufficient. | 

| It is necessary also to organize \ 

| the entire industry. | 

The third portion of my investiga- 
tions involved a determination of the 
coefficient of reflection of the ground. 
In order to accomplish this the phone 
is set at a convenient height and the 
phonometer at a convenient distance. 
The latter is then moved back and forth 
at the same height, when it is immedi- 
ately found that interference between 
the phone and its image in the ground 
sets in, producing a variation of the 
intensity of the sound. Different curves 
have been plotted for different coeffi- 
cients of reflection. When the reflection 
is zero or the ground is acoustically 
perfectly black we have a rectangular 
hyperbola. The existence of the mini- 



mum is obvious to the most unskilled 
observer. We found the coefficient of 
reflection of grass, or gravel surface, 
to be about 95 per cent. I may say that 
the whole measurement of the instru- 
ments of the two ends and the transmis- 
sion between checks up with an ac- 
curacy of probably better than two 
per cent. With this apparatus all 
sorts of experiments have been per- 
formed. By attaching to the phono- 
meter a long glass tube or antenna it 
has been made possible to explore all 
sorts of places, such as the field within 
a horn or a tube lined with absorbent 
substance. The theory has been always 
completely verified. In order to ex- 
amine the transmission of sound a piece 
of substance is clamped between two 
heavy cast iron rings cemented against 
a hole in a brick wall which will ex- 
clude all sound except that which comes 
through the fabric. The transmission 
through doors, windows, walls, and 
telephone booths may be carried out 
very quickly, and the coefficients of ab- 
sorption and reflection determined. 

The Phonotrope 

Finally, there has resulted an instru- 
ment for determining the direction of 
a fog signal blowing in the fog which 
I call a phonotrope ; since the heliotrope 
turns toward the sun, the radiant of 
heat, so the phonotrope turns toward 
the radiant of sound. This instrument 
consists of two equal horns bringing 
the sound to the opposite side of the 
same disk. It is arranged to be rapidly 
tuned to the whistle, and when the 
whistle blows the band of light spreads 
out; the whole instrument is then re- 
volved until the band reduces its width 
to zero when the whistle is directly 
ahead. This instrument was taken to 
Pensacola to see whether it would de- 
termine the direction of an aeroplane 
in the night. It was found to be as 
sensitive as the ear, but owing to Dop- 
pler's principle, the continual coming 
and going of the aeroplane changed the 
pitch so as to put it out of tune. A new 
modification that I have devised will 
obviate this I hope. 

I have now given you briefly and 
without any mathematics an account of 
the principles which I think must al- 
ways be involved in any measurements 
of sound. I have always been very 
anxious to join forces with Professor 
Miller and to calibrate his instruments 
so as to render his wonderful results of 
serious interest to the physicist. I am 
also glad to co-operate with all my col- 
leagues whether engineers, physicists, 
physiologists or physicians. It will be a 
great pleasure to me to know that this 
apparatus may be of use in solving any 
of the multitude of questions that con- 
front us. 

(Concluded on page 17) 



Page 14 



PROJECTION ENGINEERING 



New high fidelity sound 
system employs new 
sound head 



WITH the development of an 
entirely new sound head 
that utilizes a rotating 
drum instead of a gate for 
sound takeoff and with the existing 
highly successful all-a-c. operated 
equipment as a basis for design and 
performance, the RCA Victor Com- 
pany announces the introduction of 
what is referred to as highest fidelity 
Photophone sound reproducing equip- 
ment for theatres and auditoriums of 
all sizes. It is claimed that this new 
apparatus will reproduce the widest 
ranges in recording that have been at- 
tained in the production of any sound 
picture at any studio. Recent demon- 
strations of this apparatus, employing 
the new high fidelity system of record- 
ing, reproduced sound frequencies 
ranging from 40 to 9,500 cycles with a 
richness and clarity of tone and speech 
said never before to have been attained. 
Four types of this equipment have 
been designed — the standard super size, 
for theatres having from 2,500 to 4,000 
seats; the standard large size, for the- 
atres having from 1,400 to 2,500 seats; 
the standard small size, for theatres 
having from 600 to 1,400 seats, and the 
special size, for theatres having up to 
600 seats. All types are a-c. operated, 
with newly developed and designed 
voltage amplifiers that are identical for 
each type. The first major installations of 
this new equipment are now being made 



in the new RKO Roxy theatre and the 
Radio City music hall at Rockefeller 
Center, New York. Obviously, because 
of the magnitude of the Rockefeller 
Center building enterprise as a whole 
and particularly with respect to these 
two magnificent palaces of amusement, 
the sound reproducing equipment instal- 
lations will be the most complete ever 
undertaken in connection with the build- 
ing of any theatre in the world. Al- 
ready, in addition to the new RKO 
Roxy and the Radio City music hall, 
contracts have been accepted for instal- 
lations in a number of other theatres. 

Outstanding features in the new ap- 
paratus include the improved sound 
head of the drum type, quieter a-c. am- 
plifiers and extended frequency range, 
directional baffle and improved cone 
speaker. Of interest to exhibitors whose 
theatres have recently been equipped 
with Photophone apparatus is the fact 
that at moderate cost the equipment can 
be modernized. 

Amplifiers 

The amplifiers for the standard series 
are mounted on standard channel iron 
racks, the height of which has been in- 
creased to 82ji inches. The voltage am- 
plifiers on the three types are identical. 

The power amplifiers vary, the stand- 
ard small size using one 10-watt unit, 
the standard large size two 10-watt 
units, and the standard super size one 



EXCITER LAMP 
SWITCH 




Enlarged view of 
sound head for 
Photophone fidel- 
ity sound repro- 
ducing equip- 
ment. 



^ ■ 


m|p ii 




Kj^i 


\ * ■■• 'ia& FTP 








I 



Sound head for RCA Victor Photophone 
standard series sound reproducing equipment 
mounted on rack beneath Simplex projector. 



40- watt unit. The voltage amplifier unit 
has been slightly modified to give im- 
proved response. 

The fader relay switches are mounted 
on a box with a relay and remote vol- 
ume control button, if used, together 
with a photocell voltage control for 
mounting at each projector station. 

The 50-inch directional baffle loud- 
speaker is furnished regularly with the 
standard series equipments. The best 
results are obtained from a 10-foot 
directional baffle loudspeaker which can 
be furnished at an additional charge. 
The larger baffle reproduces low fre- 
quencies with about the same output as 
the higher frequencies and is more 
directional than the shorter baffles for 
low frequencies. Since this results in 
the reproduction being more independ- 
ent of the acoustical characteristics of 
the auditorium, the 10-foot directional 
baffle loudspeaker should be installed 
in de luxe theatres wherever possible. 

300 Cycles 

A loudspeaker filter is provided to 
compensate for the response at 300 
cycles,^ thereby providing the smoothest 
and widest frequency range of any loud- 
speaker yet produced, eliminating the 
necessity for using a low- and high- 
frequency unit to cover the frequency 
band. 

A loudspeaker coupling transformer 
is furnished with the two larger equip- 
ments to make possible the relative ad- 
justment of the power supplied to the 
speakers. 

The monitor loudspeaker furnished 



DECEMBER, 1932 



Page 15 



includes a 16-inch metal directional baf- 
fle with volume control and speaker 
unit, providing an efficient unit. 

The special size equipment (PG-59) 
has been revised to have approximately 
the same fidelity of reproduction as the 
larger equipments. The frequency char- 
acteristic has been increased consider- 
ably in range. 

The new amplifier for the special 
size equipment is mounted on standard 
channel iron rack 38>4 inches high. 
It includes a single amplifier unit with 
a power output of 6 watts and employs 
an RCA-57, an RCA-56, four UX-245 
and two UX-280 Radiotrons. It uses a 
double push-pull power stage. Two 
exciter lamp supply units are included. 
Loudspeaker field supply is provided 
from the amplifier unit. 

The sound head attachments, for 
Simplex and for Powers 6B, are the 
same as the belt-drive attachment for- 
merly used with this type of equipment 
except that the a-c. exciter lamp trans- 




Directional baffle loudspeaker (PL-35). 

former is not required. A fader switch 
for wall mounting between the projec- 
tors is furnished. The 37-inch direc- 
tional baffle loudspeaker is furnished 
regularly with this equipment. 

A monitor amplifier loudspeaker con- 

A ▲ A 



sisting of a speaker unit and amplifier 
unit mounted in a metal box is included 
with the special size equipment. This 
amplifier unit consists of a simple push- 
pull power stage using two UX-245 
and one UX-280 tubes. Through the 
use of a separate amplifier no power is 
directed from the stage loudspeakers 
for monitoring purposes. No additional 
amplifier is required with this new 
equipment for theatres up to 600 seats. 
In addition to the permanent types of 
equipment designed for the reproduc- 
tion of high fidelity sound, the RCA 
Victor Company manufactures 35 mm. 
portable apparatus and only recently in- 
troduced a new 16 mm. 400 watt sound- 
on-film portable and an automatic con- 
tinuous projector that have begun to 
attract widespread attention. Facilities 
for the recording, re-recording, syn- 
chronizing and reduction from 35 mm. 
to 16 mm. sound-on-film subjects are 
maintained at the Company's studios in 
Camden, N. J., and New York City. 



Bureau of Standards Activity 



THE annual report of the director 
of the Bureau of Standards, 
Washington, for the past year, 
lists the following projects as 
having had the attention of the 
Bureau : 

Investigation of Optical and Other 
Types of Glass 

Thirty-two pots of optical glass, em- 
bracing five different kinds, were 
melted. From a part of these melts 
36,787 blanks for optical elements, 
weighing 3,627 pounds, were made for 
the Navy Department. The time re- 
quired for melting borosilicate crown 
glass has been reduced about 45 per 
cent, or from 24 to 13 hours. 

The tensile strength of six types of 
glasses was determined. It has been 
found that borosilicate, medium-flint, 
barium-flint, and dense-flint glasses 
have approximately the same maximum 
tensile strength, namely, 11 kilograms 
per square millimeter, and the strength 
of light barium crown and light crown 
(ordinary plate) glass is approximately 
15 kilograms per square millimeter. 

The thermal expansion of a number 
of soda-lime-silica glasses has been de- 
termined from room temperature to the 
initial softening point, and equations 
derived for computing the expansion of 
any glass in the range of compositions 
studied. 

In attempting to determine definitely 
why some glasses transmit only a few 
per cent of the therapeutic rays (ultra- 
violet) in sunlight while others may 
transmit as much as 60 per cent, small 



samples of soda-lime glasses were made 
which would transmit as much as 85 
per cent, which is only exceeded by 
fused quartz. Apparently iron in the 
glass has a very large effect on the 
ultra-violet transmission. 

A method for the direct determina- 
tion of soda in commercial glasses was 
developed, and is now being used by 
glass chemists with very satisfactory 
results. 

Standard Glass Filters 

These are intended for checking 
spectro-photometric transmission as de- 
termined by various instruments and 
different laboratories. Filters of five 
different kinds of glass have been 
selected, and measurements of the spec- 
tral transmission of four have been 
made. In accordance with a plan agreed 
upon by the national laboratories of 
Great Britain, Germany, and the United 
States, one set of these glasses, meas- 
ured with great care, is to be sent in 
turn to the National Physical Labora- 
tory of Great Britain and the Reichs- 
anstalt of Germany to serve in an 
international comparison of measure- 
ments of spectral transmission. 
Photographic Emulsions 

In the bureau's studies to improve 
photographic emulsions, it has been 
found that gelatin forms a nonionized 
compound with the silver, in appreci- 
able quantity, under emulsion condi- 
tions ; that sensitivity of emulsions, free 
of dyes, is little affected by large 
changes in silver-ion concentrations ; 
that the desensitizing action of soluble 



bromides increases with the acidity of 
the emulsion; and that bathing with 
ammonia leaves the emulsion with an 
excess of silver over halogen. 

Sound Investigation 

Sound absorption measurements have 
been made on 97 different samples of 
material submitted by manufacturers. 
It is worthy of note that this work is 
associated with the development of a 
new business in the country, and that 
fully three-quarters of this development 
has taken place in the last three years. 
In this the bureau has taken an active 
part. The materials are used in the 
interior finish of auditoriums to produce 
good acoustic qualities. 

Thirteen panels of various construc- 
tions submitted by different manufac- 
turers were measured for sound trans- 
mission, and improved methods and 
instruments were developed for this 
work. The public demand for sound- 
proof walls and floors in apartment and 
2-family houses is steadily increasing. 

An investigation of the speed of 
travel of ultrasonic waves in various 
organic liquids has been completed and 
published. This work supplements in- 
vestigations in other sections of the 
bureau on the mechanical and electrical 
properties of electrical insulating ma- 
terials. 

This includes such routine testing as 
the bureau is called upon to make, 
chiefly the rating of tuning-forks, oscil- 
lograph records of vocal and instru- 
mental sounds, and their subsequent 
harmonic analysis. 



Page 16 



PROJECTION ENGINEERING 




Left: Fig. I. Front 
view of recorder. 



Right: Fig. 2. Rear 
view of recorder. 




A new double system 
of film recording + 



SINCE the introduction of silent 
recording the shortcomings of 
| the single system method have 
been evident. This is due to the 
grain in the picture negative, part of 
which is inherent and part due to im- 
proper processing. The frequency range 
is being widened both in recording and 
reproduction. The fact that regular 
negative must be used in the single sys- 
tem method precludes the possibility of 
recording the higher frequencies so es- 
sential to high quality sound. 

It is evident that in order to keep 
pace with the producers the double sys- 
tem Of recording holds out advantages. 
The latest contribution to the industry 
is shown in Fig. 1. This is a sound 
recording camera possessing many un- 
usual features, one of which is the high 
degree of filtering obtained. 

This was necessary in order to faith- 
fully record frequencies from 5,000 
cycles up. Anyone who has actually 
tried to record frequencies from 6,000 
to 8,000 cycles will appreciate the prob- 
lems involved. Another important fea- 
ture is a new type of "glow" lamp. 
Unlike other glow lamps in use today, 
this lamp faithfully reproduces fre- 
quencies up to 30,000 which is much 
higher than we are interested in for 
sound picture work. 

There is no mechanical slit or optical 
system necessary, requiring large ex- 
penditures, plus unsatisfactory results. 
The lens on the Q lamp does this with 
100 per cent efficiency. The loss of 
light in optical systems is fully 40 per 
cent of the lamp value depending on 

^Produced by The Canady Sound Appliance 
Co., 1776 Broadway, New York. 



By John Dunsheath 

the type of glass used, i. e., lead glass 
will pass approximately 20 per cent of 
actinic rays desired for variable density 
recording; lime glass approximately 26 
per cent, Nonex 38 per cent, E. J. 
Pyrex 40 to 46 per cent, Corex 68 per 
cent, Quartz 88 per cent. Therefore 
it will be readily seen that all lamps 
made of lead or lime glass are ineffi- 
cient, especially where it is necessary 
to interpose additional glass regardless 
of its nature between the source of 
light and the film to be exposed. 

The Q lamp is made of Corex. This 
type of glass has been found to per- 
form satisfactorily when the lens is in- 
corporated in the lamp itself. This 
means that no compensation is neces- 
sary in the amplifier to faithfully record 
frequencies up to where the grain in 
the film begins to manifest itself. 

In order to record the higher fre- 
quencies with the glow lamps available 



today, "compensation" or distortion is 
resorted to in the amplifier. That is, 
the amplifier favors the high frequen- 
cies more than the lows. At first glance 
this should be an ideal method. In fact, 
it would if the input to the amplifier 
contained no harmonics. If the output 
of the microphone contains harmonics, 
these are amplified out of proportion to 
the original signal, resulting in raspy, 
blurred, high-frequency response. This 
same result will be obtained if com- 
pensation is incorporated in the early 
stages of the recording amplifier. 

The main frame of the unit is cast 
in one piece from aluminum. It is accu- 
rately machined within close limits. 
The door is also cast of aluminum and 
accurately machined to fit into the 
frame, flush with the outside of the 
main casting. It is continuously hinged 
at the base and swings downward to a 
horizontal position when fully opened. 



Fig. 3. I nterior of 
recorder, threaded 
ready for operation. 




DECEMBER, 1932 



Page 17 



Footage Counter 

The door is provided with an im- 
proved type locking arrangement. A 
half turn of the large knob at the top 
of the door securely locks the door 
and at the same time opens the valves 
in the film magazine. The action is 
quick and positive. Mounted on the 
door, below the knob, is the footage 
counter. This is at all times visible to 
the recordist. 

On the right side of the recorder, 
directly under the film magazine, is a 
film punch. A slight tap on the knob 
produces a smooth notch on the edge 
of the film of approximately jM$ inch 
radius which is easily found in the dark 
room. 

On the left side of the recorder is 
shown the casting entirely enclosing 
the glow lamp assembly. There are no 
delicate glass tubes exposed with wires 
dangling on the end. This very impor- 
tant part of the recorder is fully pro- 
tected both mechanically and electric- 
ally. 

Several improvements have been 
added to the film moving mechanism. 
Labor and time-saving devices that will 
allow the recordist to devote more time 
to the recording of better sound. The 
film has free travel from the magazine 
through the recorder and back to the 
magazine. No friction or tension is 
applied at any point. 

The motor and silent coupling are 
totally enclosed by a well ventilated 
aluminum housing. Looking at the 
back, Fig. 2, we see the necessary 
socket connections mounted in the base. 
An unusual arrangement permits in- 
stant replacement of takeup belt. A 
carefully designed spring idler keeps 
the proper tension on the takeup belt 
at all times. 

Synchronizing or "Bloop" Light 

An unusual feature of the type "B" 
recorder is the synchronizing light. 
This is a radical departure from sys- 
tems now in use. The "sync" light is 
sharply focused on the edge of the film 
on the side opposite to the sound track, 
but directly in line with the light beam 
of the glow lamp. 

Instead of a "smudge" of light all 
over the film a small intense beam of 
actinic light is sharply focused on the 
film. During a recent test the sound 
engineer, a former telegraph operator, 
telegraphed information on the edge of 
the film while recording was in prog- 
ress. When the film was developed it 
resembled ticker tape on one side. 
Needless to say the applications are un- 
limited. 

Glow-Lamp Holder 

The glow lamp holder assembly rep- 
resents several new and exclusive fea- 
tures. The glow lamp is inserted at F 




(Fig. 4) and locked in place by 
knurled ring H. The entire assembly 
is moved back and forth by rack and 
pinion movement. Fig. 4 shows the 
assembly racked out for threading or 
inspection. The micrometer adjusting 
rings M and N rest against the face 
E when the assembly is in recording 
position and are used for adjusting 
clearance between assembly and film. 
In and out movement is performed by 
turning knob U right or left, which- 



Fig. 4 — Glow-lamp 
holder. 



ever the case may be. 

Looking at Fig. 3 we see the interior 
of the recorder threaded ready for op- 
eration. 

A half turn of the knurled knob T 
removes the four idler rollers from the 
sprocket G and at the same time lifts 
idler roller J from drum R. A slight 
turn of knob Y removes idler roller Z 
from sprocket K. Turning knob U to 
the left moves glow lamp assembly 
away from film drum R. These three 
operations performed, the recorder is 
instantly ready for threading. A few 
turns of knob L permits the removal 
of the aluminum housing enclosing the 
glow lamp assembly. This is necessary 
only when inserting a new glow tube. 
The "sink" or "bloop" light "X" is 
permanently installed as it needs no 
adjustment and is out of the way for 
threading. 

The horizontal adjustment of the 
light beam is effected by the two screws 
S. All idler rollers are self-locking in 
the open or closed positions. Provision 
is made for positive oiling of all rotat- 
ing parts. 



THE ABSOLUTE MEASUREMENT OF THE INTENSITY OF SOUND 

(Concluded from page 13) 



PAPERS ON SOUND 

1. B. A. A. S. Toronto, Aug., 1897. "A 
New Instrument for Measuring the Inten- 
sity of Sound." 

2. A. A. A. S. Boston, Aug., 1898. "A 
New Instrument for the Measurement of 
the Intensity of Sound." 

3. A. A. A. S. Washington, Jan., 1903. 
"A Portable Apparatus for the Measure- 
ment of Sound." 

4. American Phys. Soc., New York, 
April, 1902, "An Apparatus for the Quan- 
titive Study of Sound." 

5. Am. Phys. Soc, New York, April, 
1902. "Vibrations of Rotating Wires, 
Spindles and Shafting." 

6. Nat. Acad. Sciences, Boston, Nov., 

1906. "Acoustic Measurements." 

7. Nat. Acad. Sci., New York, Nov., 

1907. "Rayleigh's Disc as an Absolute 
Measure of Sound." 

8. Am. Acad. Arts & Sci., Boston, May, 

1908. "Absolute Measurements of Sound." 

9. Am. Phys. Soc, New York, Oct., 
1908. "Distribution of Sound from the 
Megaphone." 

10. National Acad. Sci., Washington. 
April, 1910. "On the Distribution of 
Sound from the Megaphone or Speaking 
Trumpet." 

11. Nat. Acad. Sci., Washington, April, 

1910. "A New Method for the Study of 
Elastic Hysteresis." 

12. B. A. A. S., Sheffield, Aug., 1910. 
"A complete Apparatus for the Measure- 
ment of Sound." 

13. Am. Phys. Soc, Washington, Dec, 

1911. "Elastic Hysteresis in Metal Bars." 

14. Am. Phys. Soc, Washington, Dec, 
1911. "Another Instrument for Photo- 
graphing Sound." 

15. Am. Acad. Arts & Sciences. Dec, 
1910. "The Wave Potential of a Circular 
Line of Sources." 



16. Am. Math. Soc, Poughkeepsie, Sept., 
1911. "The Wave Potential of a Circular 
Line of Sources." 

17. Am. Phys. Soc, Cleveland, Jan., 
1913. "Some Points Concerning Absolute 
Measurements in Sound." 

18. Am. Phys. Soc, New Haven, March, 
1913. "Forced Vibration of a Circular 
Plate." 

19. Nat. Acad. Sci., Baltimore, Nov., 
1913. "A New Portable Phonometer." 

20. Nat. Acad. Sci., Baltimore, Nov., 
1913. "The Transmission of Sound 
Through Porous Materials." 

21. Am. Phil. Soc, Philadelphia, April, 

1913. "Some Observations of the Trans- 
mission of Sound Through Walls." 

22. Am. Physical Soc, Washington, 
April, 1914. "A New Phonometer." 

23. Am. Phys. Soc, Philadelphia, Dec, 

1914. "A New Standard Phone and 
Phonometer for any Pitch." 

24. Nat. Acad. Sci., New York, Nov., 

1915. "Experiments and Theory of Coni- 
cal Horns." 

25. Nat. Acad. Sci., New York. Nov., 
1915. "Instruments for the Measurement 
of Sound." 

26. Nat. Acad. Sci., New York, Nov., 
1915. "An Instrument for Finding the 
Direction of a Fog-Signal." 

27. Am. Phys. Soc. Columbus, Dec, 
1915. "Mechanical and Acoustical Impe- 
dance, and the Theory of the Phonograph." 

28. Am. Phys. Soc. Columbus. 1915. 
"Impedance of Conical Horns." 

29. Am. Phys. Soc. Columbus, Dec, 

1915. "The Phonotrope, a New Instru- 
ment for Finding the Direction of an 
Acoustical Ray." 

30. Am. Math. Soc. Cambridge. Sept., 

1916. "On Acoustical Impedance, and a 
Theorv of Horns." 



Page 18 



Sound systems in 
Rockefeller Center, 
New York 



By James Frank, Jr.* 



(Concluded from November Issue) 
Rehearsal Address System 

THIS system is to be used in 
connection with the execution 
of rehearsals of stage and or- 
chestra presentations. It con- 
sists essentially of microphones located 
at definite positions feeding through 
amplifiers to a number of loudspeakers 
located to cover the stage, auditorium 
and various booths. 

Three velocity microphone transmit- 
ters will be furnished mounted on 
stands, two of telescope stand type, and 
one of the desk stand type. One of these 
will be located on a desk which will be 
placed in the twelfth row of the or- 
chestra floor during rehearsals. An- 
other will be located in the director's 
private box located at the rear of the 
auditorium. The third is to be located 
in the control room. 

In addition, a carbon microphone an- 
nouncing station including necessary 
switches and pilot lamps is to be lo- 
cated at the chief electrician's position. 
Three velocity microphone amplifiers 
will be furnished, one for each of the 
above mentioned velocity microphone 
transmitters. The amplifier for the 
transmitter located at the twelfth row 
of the orchestra floor will be located 
in the amplifier room in the basement 
under the stage where the amplifiers 
for the sound reinforcing system are 
located. The amplifier for the trans- 
mitter located in the director's private 
box is to be located on the wall of the 
adjacent "spot booth" while the ampli- 
fier for the transmitter in the control 
room is to be located on the wall of 
that room. 

The main amplifier used for this sys- 
tem is similar to one of the ampli- 
fier channels used on the sound rein- 
forcing system. The equipment in- 
cludes necessary terminal strips, main 
power line switch, a voltage amplifier 
unit, and two power amplifier units (40 
watts). The rack is located adjacent 
to the main amplifiers of the sound re- 
inforcing system in the amplifier room. 

*Photophone Division, RCA-Victor Company. 



A large number of loudspeakers are 
used with this system to cover the audi- 
torium, entire stage including light tow- 
ers, light control stations, and various 
spot and equipment booths. This 
equipment includes twenty-five loud- 
speakers employing 37-inch directional 
baffles, seven loudspeakers employing 
magnetic units on flat wood baffles. 

Through the use of these loudspeak- 
ers the director or anyone else at a mi- 
crophone location may communicate 
with anyone in the theatre concerned 
with the rehearsal. This system may be 
used during regular performances op- 
erating certain of the loudspeakers at 
low level. 

Main Sound Projection System 

This system consists of a duplicate 
channel 80 watt a-c. operated system 
employing four soundhead attachments. 
This equipment is similar in every de- 
tail to the "standard" series of RCA 
Photophone sound reproducing equip- 
ment. The entire projection room 
equipment is finished in a specially se- 
lected green to match the balance of 
the projection room equipment. 

Four Simplex soundhead attachments 
are furnished with this system for 
mounting in the projection room. These 
attachments are to be mounted on Chi- 
cago cinema bases with Super-Simplex 
mechanisms. The soundhead attachment 
is illustrated in Fig. 4. The attachment 
is the same as supplied with "stand- 
ard" series RCA equipment except that 
three phase a-c. motors are employed. 

A duplicate channel 80 watt main am- 
plifier is to be furnished with this sys- 
tem. The voltage and power amplifier 
units are the same as those used on the 
sound reinforcing system. These racks 
are located in the rear wall of the pro- 
jection room. These racks are particu- 
larly adapted for flush mounting in the 



Fig. 4. Simplex sound 
head attachment. 



PROJECTION ENGINEERING 

wall because all servicing is done from 
the front. 

The Type PA-88 amplifier includes 
necessary terminal strips, main line 
power switch, a voltage amplifier unit, 
two power amplifier units (40 watts 
each), a jack panel, a dual channel 
switching panel, a projector changeover 
panel and a loudspeaker field supply 
panel. The jack panel is to be used for 
"patching. By this means the main sound 
projection system may be intercon- 
nected with any of the other systems. 
The rear stage projection system is ter- 
minated at this panel and may be con- 
nected to the main sound projection sys- 
tem by the use of patching cords. For 
normal operation, no cords are required. 
The dual channel switching panel in- 
cludes a switch with a knob mounted 
on it for switching from one amplifier 
channel to the other. The projector 
changeover panel includes a number of 
relays and pilot lamps to connect the 
output of any of the four projectors 
to the input of the correct amplifier 
channel. The loudspeaker field supply 
panel is of sufficient size to produce 
0.8 ampere at 100 volts. 

The amplifier includes necessary ter- 
minal strips, main line power switch, 
a voltage amplifier unit, two power 
amplifier panels (40 watts each), a 
loudspeaker field supply panel, and a 
tube testing panel. 

Located alongside the duplicate am- 
plifier channels a power supply rack is 
to be located. This rack includes four 
exciter lamp panels and a monitoring 
amplifier unit. Each panel delivers 5.0 
amperes at 10.0 volts. One exciter lamp 
panel is supplied for each soundhead 
attachment. 

Four fader and volume control sta- 
tions are to be furnished for wall mount- 
ing, one in front of each projector, for 
fading the amplifier input to the prop- 
er sound head attachment and for con- 
trolling the volume of sound emitted 
by the loudspeakers. A remote volume 
control indicator consisting of twenty 
indicator lamps which indicate the am- 
plifier volume control setting is to be 
furnished for wall mounting in the pro- 
jection room. Five remote volume key 
control stations for mounting at vari- 
ous points in the auditorium are to be 
furnished. 

The stage loudspeaker equipment to 




DECEMBER, 1932 



Page 19 






1 




/&/¥• Z&a/y/tB ^£/?e&/rer J**c/**otsr>p ^/>&er/tc 




ZbAto. 




2?a 

1 


M. 











be used with this system consists of 
three loudspeakers (10-inch baffles) and 
three loudspeakers (60-inch baffles). A 
loudspeaker (37-inch baffle) with metal 
frame and mesh covering is to be 
mounted in the rear wall of the projec- 
tion room for monitoring purposes. 

This sound system comprises the lat- 
est and most modern sound reproduc- 
ing equipment available for theatres. It 
is all a-c. operated, simple in design, 
compact for easy installation ; easy to 
operate; and requires a low mainte- 
nance cost. The over-all characteris- 



Fig. 5. Overall frequency 
response curve of main 
sound projection system. 



tic of the system is such as to provide 
for faithful reproduction of all the au- 
dible frequencies from 50 to 10,000 
cycles. A curve indicating this response 
is shown in Fig. 5. 

Deaf Headphone System 

Provision has been made for the in- 
stallation of twenty-six outlets located 



under the arms of alternative seats in 
the thirty-third and thirty-fourth rows 
of the orchestra floor into which Acous- 
ticon seatphone instruments may be 
plugged in order that those people who 
are hard of hearing may more clearly 
and intelligibly hear the sound motion 
picture and stage presentations. Each 
jack-box mounted under the arm of the 
chair includes two jacks, for permitting 
the use of two instruments, one with 
each of the two adjoining seats. The 
amplifier for this equipment is located 
on the main amplifier racks of the 
sound reinforcing systems. 

It is intended that individuals can 
obtain instruments at the box office up- 
on request. Anyone who owns a pri- 
vate instrument designed for this par- 
ticular use will be permitted to use same 
if he so desires. 

Radio and Monitoring System 

The purpose of this equipment is to 
furnish to the private studios on the 
studio floor radio pickup of a predeter- 
mined number of radio stations and to 
permit the monitoring of the various 
sound systems in the theatre and for out- 
side lines terminating within the theatre. 



ELECTRO-ACOUSTIC 
ENGINEERING 

{Concluded from page 9) 

to provide somewhat of a directive ef- 
fect. This is termed an "expanding 
baffle." 

Amplifiers and accessory equipment 
are important components of any electro- 
acoustic system. The public-address 
organization finds it highly desirable to 
design the equipment for each job, not 
only because of special requirements 
such, for example, as the need for trans- 
mission of both speech and music to 
overflow halls, or the use of remote con- 
trol of the equipment, but also to ob- 
tain special frequency characteristics 
when needed. The equipment is rack- 
mounted for convenience in mainte- 
nance and for appearance as well, with 
the reference meters and the controls 
which are subject to frequent adjust- 
ment placed on inclined shelves to make 
their settings readily visible to the op- 
erator. 

Servicing 

Servicing of equipment is an import- 
ant part of the work. In addition to the 
usual test routine to locate "weak" or 
defective equipment before failure, an- 
other and greater problem, that of 
maintaining the original performance 
presents itself. An installation is sub- 

*Bludworth, Inc., New York. 



AAA 

ject to innumerable changes due to mis- 
handling, deterioration, humidity ef- 
fects, or accidental damage by building 
service personnel, all of which may af- 
fect fidelity or reliability of operation. 
For example, even as simple a change 
as an increase in level from a single 
projector may not only seriously affect 
intelligibility in its own coverage space, 
but may change that in other spaces as 
well. As a check on such changes, the 
service department of one electro- 
acoustic organization* makes routine 
performance measurements on each in- 
stallation, the data so obtained being 
compared with similar measurements 
made at the time of installation. These 
comparisons, properly interpreted, indi- 
cate minor as well as major changes 
which have occurred in equipment or 
even in the hall itself. 

It is recognized that routine tests 
made frequently without sign of trouble 
are apt to degenerate, with even the best 
of workmen, into hit-and-miss affairs. 
To reduce the chance of this occurring, 
all performance comparisons are made 
in the office. The service organization 
never sees the original data. 



J. GARRICK EISENBERG IN CHINA 
J GARRICK EISENBERG for sev- 
"'■ eral years identified with the engi- 
neering departments of picture produc- 
ing companies in Hollywood, is now 
vice-president in charge of plant and op- 



erations for the Electric Service Cor- 
poration, Shanghai, China, at 1667 
North Kiangse Road. The president of 
the company, Roy E. DeLay, who has 
been in China for many years, was for- 
merly in the communication engineer- 
ing field in the United States. 



AN ITALIAN WORK ON THE 
SOUND FILM 

An excellent 440-page work in the 
Italian language dealing with the en- 
gineering of sound films has been writ- 
ten by Enrico Costa and published by 
Ulrico Hoepli, Milan, Italy. The title 
of the textbook is "II Proiezionista Di 
Film Sonori." 



DUBBING ABROAD 

WVITH two dubbing studios now 
" operating at The Hague and Lon- 
don, World Industrial Co., formed by 
Jack and Loet Barnstyn, plans to open 
two more plants in Paris and Berlin, 
said the former recently upon his return 
to New York. 

Jack Barnstyn also stated that he has 
acquired the American rights to the 
Erikson superimposing process. While 
abroad he sold 12 principal features and 
40 shorts to B.I. P. He also arranged 
for distribution of "The Divorce 
Racket," made by Paradise Pictures. 



Page 20 



Glossary of technica 
terms for the 
projectionist 1 

(Continued from November issue) 



Focal Point. Point at which a lens 
forms the sharpest image of a very dis- 
tant object. 

Focus (noun). The point at which a 
lens produces the smallest image of a 
point object at a given distance. Also 
used for focal point or for focal length. 

Focus (verb). To adjust the position 
of a lens so as to secure the sharpest 
possible image of an object. 

Focus, Out Of. Of a camera lens: 
not properly focused, producing a dis- 
torted image. 

Focus, Principal. The focus for an 
object at an infinite or very great dis- 
tance. 

Focus, Soft. Device to obtain an 
image not sharply defined, by (1) plac- 
ing gauze on the camera lens, (2) use 
of a specially ground lens. 

Fog. Darkening of photographic film 
due to its exposure to undesirable light, 
or due to poor emulsion or to improper 
development. 

Footage. Film length measured in 
feet. 

Foot-Candle. Unit of illumination of 
surface. The average illumination of a 
surface measured in foot-candles, equals 
the luminous flux (expressed in lumens) 
falling on the surface, divided by the 
area of the surface in square feet. 

Frame (noun). A single rectangle of 
the series on a motion picture film. 

Frame (verb). To bring a frame into 
register with the aperture during the 
period of rest in recording, printing, or 
projection. 

Frame Line. Dividing line between 
two frames. 

Frame Line Noise. Noise in repro- 
duction, due to the displacement of the 
film to the right in the projection ma- 
chine, so that the beam of light for the 
sound track shines through part of the 
picture area as well, and cuts the frame 
lines. This noise is a type of motor- 
boating. 

Framing Device. An attachment on 
the projector which allows the operator 
to frame the picture properly. 

Freak. Slang for frequency. 

Frequency. Number of cycles (com- 
plete vibrations) per second in a wave 
or other regular recurring phenomena. 

Frilling. Separation of the emulsion 
from the base at the edges. 

Fringe. Refers to overlapping of 
colors in color photography. 

Frozen. Of carbon electrodes, means 
fused together so that lifting mechanism 
cannot pull them apart and so strike the 
arc. 

Fryer. A large electric lamp, usually 
employed in connection with color pho- 
tography. 

Wilis condensed glossary of terms is taken 
from the technical digest service of the Academy 
of Motion Picture Arts and Sciences. 



Fundamental. Lowest natural fre- 
quency of oscillation for a sounding 
body or for an electric circuit. 

Fuzzy. (1) Of sound track on visual 
inspection; lack of sharpness. (2) Ot 
reproduced sound; characterized by dis- 
tortion, particularly of high frequencies. 
The distortion may have been intro- 
duced in recording, processing or repro- 
duction. 

Gaffer. Electrician in charge of a 
group of electrical workers. 

Gain. Gain of energy in an apparatus 
is ratio of output to input energy. 

Gain Amplifier. Any amplifier which 
handles comparatively small amounts of 
energy, as in the initial stages of a sound 
recording system. Specifically, the first 
amplifier used in disc reproduction for 
amplifying the varying current from the 
magnetic pickup or the first amplifier 
after the photoelectric cell amplifier, for 
the purpose of further amplifying the 
varying currents, in sound-on-film re- 
production. 

Gain Control. Device for varying 
the gain of an amplifier. 

Galvanometer. An instrument for 
measuring electric current strength (or 
for detecting a small current, and deter- 
mining its direction), generally by the 
deflection of a needle due to the mag- 
netic field caused by the current. 

Galvanometer, String. Utilizes a con- 
ducting wire or ribbon vibrating in a 
strong magnetic field according to the 
variations of the conducted current. 

Gamma. Slope of the straight portion 
of the characteristic curve of a photo- 
graphic emulsion; measure of the con- 
trast of the emulsion. 

Gargle. A type of pulsation of inten- 
sity in reproduced sound. 

Geneva Movement. Intermittent 
movement (produced by a cam-and-star 
wheel) used in most projection ma- 
chines. 

G. E's. (Colloq.) Generally, same as 
inkies. 

Give 'Em A C! To start synchroniza- 
tion of camera and recording motors. 

Glass Work. Trick photography in 
which pictures on glass are used to 
replace parts of the setting. 

Glow Lamp. Lamp containing gas 
which, when the voltage across the lamp 
reaches a certain ("critical") value, con- 
ducts an electric current and in doing so 
emits light. 

Gobo. Portable wall covered with 
sound-absorbing material. Not intended 
to be photographed. 

Goesover. A shield for a camera lens 
to protect against top light. 

Governor Movement. Mechanism 
which^ controls the automatic shutter. 

Grains. Refers to the tiny clusters of 
silver grains on a developed photo- 
graphic film. See DEVELOPMENT. 

Gram. Metric unit of mass. Approxi- 
mately 454 grams equals one avoirdu- 
pois pound. 



PROJECTION ENGINEERING 

Granularity. Coarseness in the silver 
grains in a developed photographic 
image. 

Graphite (noun). Soft form of car- 
bon. Used as a lubricant. 

Graphite (verb). To cover a surface 
uniformly with graphite (which is a con- 
ductor) so that the surface can be elec- 
troplated. 

Green Light. In certain studios, sig- 
nal that stage is ready for a sound take. 

Grid. In a vacuum tube, the frame of 
wire gauze between the filament and 
plate. Small changes in the electric 
potential of the grid circuit produce far 
greater changes in the electron flow 
from filament to plate. 

Grid Battery. Same as "C" battery. 

Grid Leak. Very high, non-inductive 
resistance, usually connected across a 
condenser in the grid circuit of a three- 
electrode vacuum tube, to stabilize the 
action of the condenser (in making the 
tube more efficient) by permitting ex- 
cess charge to leak off. 

Ground Glass. Glass ground or sand- 
blasted on one side, so that it is no 
longer transparent, although still trans- 
lucent (i. e., transmitting light diffusely) ; 
used for a focusing screen. 

Ground Noise. Undesirable noise ap- 
pearing in reproduced sound, due to 
film grain, amplifier noises, etc. 

Halation. Blurring about a brightly- 
lit part of the picture, due to the lateral 
spreading of light in the film, or to re- 
flection, or to improper development. 

Halide. May mean bromide, chloride 
iodide, or (though not generally) flu- 
oride. 

H and D Curve. The characteristic 
curve of a photographic emulsion. 
(Hurter and Driffield curve.) 

Hard. Of a vacuum tube, thoroughly 
evacuated. 

Hard Lights. (1) Arc lights. (2) Illu- 
mination from arcs, in general. Refers 
to the sharp shadows cast. 

Hardener. Solution used to harden 
photographic emulsion. 

Harmonic. Same as partial. 

Harmonic Cam Movement. Common 
type of intermittent movement for mo- 
tion picture cameras. 

Harvey Meter. Mechanical calculator 
designed to give the correct exposure 
when set for the various conditions 
which effect the quantity and quality of 
light. 

Heyde Meter. Light meter for deter- 
mining desirable exposure. 

High Hat. A very low camera stand. 

High Light. Object, scene, or picture 
having low color saturation, that is, con- 
taining a large proportion of white. 

Hook-Up. Diagram of an electrical 
circuit; or, the construction of such a 
circuit. 

Horn. Loudspeaker of either horn or 
cone type. 

Horn, Click Your! Tickle the play- 
back needle (before starting a playback; 
to produce clicks in the horn as a test 
of whether or not the circuit is com- 
plete). 

Horn, Exponential. Type of loud- 
speaker horn in which the cross-section 
area increases exponentially with the 
axial distance from the diaphragm, so 
that cross-section areas, taken at equal 
intervals along the axis, have a constant 
ratio each to the next. 

Hot. Electrically charged, particu- 
larly when dangerous. 

Hurter and Driffield Curve (Hurter 
and Driffield Curve). Characteristic 
curve of a photographic emulsion. 

Hypo. Sodium Thiosulphate, used 
for fixing photographic emulsion. 



DECEMBER, 1932 



Page 21 



Wise Projectionists 

change to 




The Standard of 

Quality for over 

75 years. 



"NORIS-HS M 

"NORIS-SCH" 

'NORISCHROMO 

HI-LOand 

HI-INTENSITY" 



in all 

standard 

sizes 



NOBIS 
CARBONS 

*— > because ^ 

1. NORIS CARBONS produce 
unvarying brilliancy, im- 
proving projection. 

2. NORIS CARBONS operate 
on lower amperage. 

3. NORIS CARBONS burn 
longer, effecting greater 
economy. 

4. NORIS CARBONS too, are 
lower in price. 

Inquiries Invited. 



NORIS CARBON COMPANY, Inc. 

NEW YORK, N. Y. 160 FIFTH AVENUE MOHAWK BUILDING 
Sole Distributor for C. CONRADTY, Nuernberg, Germany 



llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllli 

Daven High Sensitivity Volume Indicators 

These instruments are 
specially designed for 
the broadcasting field 
but may be used for a 
great many other meas- 
urements in telephone, 
radio and acoustic en- 
gineering. . . . Made for 
standard rack or box 
mounting. . . . Accuracy 
±0.1 db. or better. 
Flat frequency charac- 
teristics up to 50,000 
cycles. . . . Also output 
meters with scale in 
volts. 

DAVEN ATTENUATORS 
have become the stand- 
ard where high quality 
is required. Lower noise 
level than any other 
make! Excellent fre- 
quency characteristics. 
Light, sturdy, compact 
design. Available as bal. 
"H", •T", mod. "T", 
"L" and Potentiometers. 

Quick delivery, standard 

units in stock. Special units built to order. Satisfaction guaranteed. 

Everything in the resistance line: Decade boxes, Line Equalizers, 
Attenuators (variable and fixed), heavy duty and precision re- 
sistors. 

Write for Catalogue 531 

THE DAVEN COMPANY 

158- 160 SUMMIT STREET NEWARK, N. J. 

miiiiiiiiiiimiimiimimiiiiimiiiiiinimiiiiiiiiiiiimiiiiiiiiiiMiiii 




Type A- 185 Volume Indicator 




CINCH 
ANNOUNCE 
A NEW 
PRODUCT! 



the New Cinch 

Radio Plug 



Another addition to the line of Cinch 
quality products. Positive, depend- 
able contact is provided in both male 
and female plugs. Available in 4, 5, 
and 6-prong types. Neat, positive 
locking cap of moulded bakelite al- 
lows for easy, simple assembling. 
More room is provided for soldering. 
Female plugs have standard Cinch 
"Floating Contacts." 

The new Cinch Radio Plugs are 
strong, durable, compact. Cinch 
Quality throughout — yet priced eco- 
nomically ! Write at once for sam- 
ples and prices. A Cinch Plug can 
be designed to suit your requirements. 

CINCH PRODUCTS: 

Standard and Midget Size Radio Sockets 
with "floating contacts" — Binding Posts — 
Soldering Lugs — Insulated Mounting 
Strips — Tip Jacks — Small Intricate Metal 
Stampings. 



CINCH MANUFACTURING CORP. 

2335 W. Van Buren St. Chicago, III. 

SUBSIDIARY OF 
UNITED-CARR FASTENER CORP. 

31 Ames St. Cambridge, Mais. 



Page 22 



PROJECTION ENGINEERING 



New Developments 

and 

News of the Industry 



S 



PHOTOELECTRIC CELLS FOR THEATRE 
APPLICATIONS 

The Continental Electric Company of 
St. Charles, Illinois, has just announced the 
completion of their full line of photoelec- 
tric cells. The Cetron is offered in all 
standard types, with and without bases. 
These are available for immediate delivery, 
while any special type may be quickly fur- 
nished. 

The Mcllvaine patented process of 




cathode coating plus a number of import- 
ant mechanical improvements employed 
in the construction of these cells, make 
possible extremely stable operation and 
long life at high efficiency. 



ANIMATION STAND 

The Bell & Howell Company has de- 
veloped an animation stand which provides 
a complete, efficient, easily used unit for 
making, on 35 mm. film, animated draw- 
ings, maps, mechanigraphs, etc.; producing 
film slide negatives ; photographing titles ; 
also copying documents, books and records 
of any kind — document copying being a 
new field for the motion picture camera 
with single exposure device. 

This stand will be particularly worth 
while for industrial film laboratories, for 
it will facilitate their title work and en- 
able them to cut costs while getting excel- 
lent results. Moreover, at a comparatively 
slight cost, it equips them ideally to handle 
other classes of work which, though in 
good demand, are not done in many studios 
and hence offer a new source of profitable 
business. 



MARBLE-CARD ELECTRIC COMPANY TO 
EXPAND ACTIVITIES 

R. H. Garrison, former general sales 
manager, for the Universal Motor Co., 
Oshkosh, Wisconsin, has become asso- 
ciated with the Marble-Card Electric Co., 
Gladstone, Mich., manufacturers of elec- 
trical machinery, as vice-president in 
charge of merchandise. 

According to Mr. Garrison, Marble- 
Card have catered to a limited select cli- 
entele which has kept the factory busy 
during good times. The company took 
advantage of the depression period to re- 
tool for larger production, and with the 
greater facilities now available, wider dis- 
tribution will be sought. 

The company is a member of the Na- 



tional Electric Manufacturers' Associa- 
tion, and manufactures a complete line of 
a-c. motors up to 100 hp. and d-c. motors 
up to 75 hp. 



NEW AUTOMATIC SAFETY LOCK 
FLOOR STAND 

The new microphone floor stand manu- 
factured by the Shure Brothers Company, 
337 West Madison Street, Chicago, offers 
many new and unusual features. 

Many a microphone operator has felt his 
heart thump when he turned the wing 
nut or set screw of a floor stand, and the 
microphone suddenly slipped down with a 
bang. In the new Shure floor stand the 
extention tubing is merely moved up or 
down or around to the position wanted. 
In this way it can be adjusted to any 
height or face any direction. Sufficient 
friction is furnished within the mechanism 
of the tubings to support the weight of 
even the heaviest condenser microphone ; 
and yet very little effort is required to 
move the extension ; but no wing nuts or 
set screws are used in any part of the 
stand. 

Another feature of the new stand is that 
it is silent in operation. In no part of 
the stand is there any rattling due to rub- 




bing of metal against metal. Specially 
designed leather cups and springs of the 
proper tension eliminate the noise, and 
provide the proper friction. Full allowance 
is made to compensate for wear and use, 
and the mechanism is guaranteed indefi- 
nitely. 



NEW PRE-VIEW FILM SAVING EOUIPMENT 

Electrical Research Products has recently 
developed and made available for use a 
new pre-view attachment which, it is stated, 
is being utilized by West Coast producers 
at a considerable saving in pre-viewing 
talking pictures in theatres in California. 
The attachment's advantage is that it en- 
ables the sound track and the picture to be 
run on separate films through the same 
machine, obviating the expense and time 
involved in processing a composite print 
which would be otherwise worthless for 
subsequent cutting and editing.' 

While the process is subject to modifi- 



cation according to the type of projector 
in the theatre, the usual procedure is to 
remove the front plate of the projector 
head and mount in its place the attachment 
which is driven from the main drive 
sprocket by a series of gears and silent 
chains. The attachments, which are adapt- 
able for the use of "split" film (sound 
track on 17^2 mm.), necessitate the re- 
placement of the regular optical assem- 
blies and of the gates with a new type 
carrying an extra guide for the narrow 
film. The standard film guide roller is also 
replaced by one which is adjustable either 
for standard or split film. 

During the past few weeks the western 
division operating department of Electrical 
Research Products has effected the instal- 
lation of these attachments in theatres 
chosen by the studios for pre-view on no- 
tice sometimes as brief as a last-minute 
telephone request. 



CONSTANT SPEED GENERATOR WITH 
GOVERNING SWITCH 

This machine will operate at constant 
speed, and when furnished as a self-excited 
a-c. generator, will deliver constant out- 
put voltage and frequency, when driven 
from a source of power, the speed of which 
is varying. It is particularly applicable to 
a-c. generators supplying power to sound 
amplifiers or talking moving picture equip- 
ment mounted on motor trucks. The gen- 
erators may be driven from the automo- 
bile or truck engine, and will then pro- 
vide a constant and reliable source of 
power. 

The generator consists in a self-excited 




alternator, with d-c. windings for field ex- 
citation, which may also be used for charg- 
ing the storage battery, if desired, and with 
a-c. windings delivering 60 cycles, a-c. A 
special centrifugal clutch has been devel- 
oped for driving these generators. The 
working faces of the clutch are covered 
with a special lining which has a constant 
coefficient of friction throughout a very 
wide range of activity. The entire ma- 
chine is furnished totally enclosed, with 
ribs on the clutch housing to dissipate the 
heat, and non-corrodible parts are used 
throughout. As a result a very constant 
output voltage and frequency is obtained. 
The generator is being marketed by the 
Electric Specialty Company, Stamford, 
Conn. 



DECEMBER, 1932 



Page 23 



REMLER 

CONDENSER 
MICROPHONE 




Two stage ampli- 
fier. 864 tubes. 
New acoustic 
equalizer. Floor 
type list $125 

Used and endorsed by radio stations throughout the 
country. WFAS says: "Beautiful visually and from 
engineering standpoint." Harington, engineer, says: "Un- 
believable that you can sell such a high grade product 
at so low a price." 

Features: Precision machined sensitive head free from 
noise. Moisture proof. Special alloy diaphragm. Shock 
proof; mica insulated. Non-resonant grill. Copper 
shielded housing. Audio niters eliminate oscillation. 
50-200 or 200-500 ohm output. Essentially flat response 
40 to 10,000 c.p.s. Statuary bronze finish. 



Send for folder show- 
ing four types with 
prices. 



Rentier Company, Ltd. 
2101 Bryant St., San Francisco 



REMLER-THE RADIO FIRM AS OLD AS RADIO 



Sapphire Recording 
Needles 

Styluses — Shavers, standard and special 

Type AW, for cutting and recording on ALUMINUM 
" BW, for recording and playback on all types of 

PREGROOVED DISCS 
" CW, for playback on REGULAR COMMERCIAL 

RECORDS 
" DW, for cutting and recording on CELLULOID 
SPECIAL. Type DD, DIAMOND NEEDLE for cutting 
out a thread and recording on CELLULOID. 



Type "A" 
Needle 



MEYER KOULISH CO., Inc. 



64 Fulton Street, New York City. 



Phone BEekman 3-6109 




^^Buustf^ 



CAMERAS .. PRINTERS . . . 
DEVELOPING MACHINES . . 
LABORATORY EOUIPMENT . 
PORTABLE SOUND PROJECTORS 
EDITING MACHINES. . . . 

Andre Debute,. 



M5 WEST 455 STREET 



NEW YORK 



For Powers, Simplex and all other sound projectors 



CLAYTON 



Even 
Tension 



TAKE-UP 



Assures absolute freedom from flutter. Takes up any amount of film evenly 
with any size reel hubs. Prevents exeesalve wear on the lower take-up 
sprocket and shaft. Stops the opening of film splices and prevents excessive 
wear on the film. Write for prlee and details. 

CLAYTON PRODUCTS CO. 



9430 Forty-sixth Ave. 



Elmhurst, L. I.. N. Y. 




NEW! 



2 MFD — 600 Volt. 
Size: 2" x 1%" x %". 



MORRILL 

Uncased Condensers 

Especially compact. A prod- 
uct of outstanding quality. 
The ultimate in reliability. 
Send for circular E-l. 



MORRILL & MORRILL 

M CHURCH STREET NEW YORK CITY 

Sole U. S. A. Distributors of the Siemens & Habke 

Condensers and Resistors. 



FREE 



13th ANNIVERSARY RADIO CATALOGUE 

124 pages containing thou- 
I sands of the greatest radio 
and electrical values at real 
(bargain prices. 

Send for your copy now! 

j American Sales Company 

Wholesale Radio Distributors 

PE-44 West 18th Street 
New York City 




PROTECT Those INSTRUMENTS 

II Littelfuses afford complete pro- Also Radio Receiver and Am 
|j:|| tection for voltmeters, milliam- plifier Littelfuses, and Hifl 
; Jill meters, tube testers, etc. Range Voltage Littelfuses for trans 
'j II in size from 1/100 to 2 amps. mining tubes, rectifiers, oscilla 
j || capacity. tors, etc. 
Write for instructive catalog. 

LITTELFUSE LABORATORIES 

Hill 1778 WILSON AVE. CHICAGO. U. S. A. 


1 


ISt LITTELFUSES 









Tungsten Rod and Wire 

for Cathodes, Supports and Welds 
A Special Tungsten Filament Coils 
Tungsten Contacts for Special Purposes 

CALLITE PRODUCTS CO., INC. 
UNION CITY NEW JERSEY 



INDEX TO ADVERTISERS 



Ad. Auriema, Inc 24 Federated Purchaser. Inc. 

American Sales Co 23 Forest Electric Corp 



B 

Bausch & Lomb Optical Co. 



K 



Koulish Co.. Inc.. Meyer. 
L 



Callite Products Co 23 

Canady Sound Appliance Co.. The. 

Back Cover 

Cinch Mfff. Co..... 21 Littelfuse Laboratorie: 

Clayton Products Co 23 



5 National Carbon Co.. Inc 1 

3 Noris Carbon Co.. Inc 21 



Racon Electric Co.. Inc.... Third Cover 
28 Remler Co.. Ltd 23 



SOS Corporation 24 

Samson Electric Co Second. Cover 

23 Shure Bros. Co 24 

Strons Electric Co.. The 6 



D 

Daven Co.. The 

Debrie, Inc., Andre. 



M 



21 

23 Morrill & Morrill 23 Zierick Mfsr. Works. F. R. 



Page 24 



PROJECTION ENGINEERING 



Final Forms Close 

the First of 

Each Month 



CLASSIFIED 
ADVERTISING 

Ten cents per word, cash with copy, $2.50 minimum advertisement accepted. Contract rates on 
application. No borders or cuts. Publisher reserves right to reject any copy. Address copy and 
checks to PROJECTION ENGINEERING, Classified Dept., 19 East 47th Street, New York City. 



NEW EQUIPMENT 

HEBE'S MAS CHEEK FOB. HARASSED SHOW- 
MEN—BUY THESE— SPEND THE DIFFERENCE: 
— Imported Carbons 8/12, 100 sets, $6.75; Synchronous 
Motors, $12.95; Stabilarc Multiple Generators. $229.00; 
Slide Mats, 98c; Bacon Giant Horns, $49.50; Projec- 
tionists Filmscales, S9c; Operadio Soundfilm Ampli- 
fiers. $59.50 up; 6 amp. Bectifier Bulbs, $4.44; 
Acoustical Felt, 22%c sq. yd.; BCA Professional 
Projectors, $395.00; Lobby Display Frames, $5.60 up; 
Genuine Western Electric or BCA Photocells, $4.95; 
Portable Soundfilm Projectors complete, $295.00; 
Beaded Soundscreens, 29c ft. Catalog mailed. 
DEALERS PROTECTED. S.O.S. COBP., 1600 
Broadway, New York. 

BELAMP YOUR MARQUEES AND DISPLAYS- 
LOWEST PRICES EVER. All sizes G. E. Licensed 
Bulbs, including new 6 watt lamps, any standard 
color (saves almost half current), 30% discount, addi- 
tional 10% ten cases or more. International Theatre 
Accessories Corp., 730 Seventh Ave.. New York. 

REPAIR SERVICE" 

Amplifiers, Generators, Lamphouses, Projectors, 
Rectifiers, Soundheads, Speakers, Sound or Booth 
Equipment, all makes; reasonable prices. Parts and 
material guaranteed. Dealers Radio Laboratories, 
1600 Broadway, New York. 



EQUIPMENT 



RESURFACE YOUR SCREEN— DO IT YOUR- 
SELF—EXPERIENCE UNNECESSARY. Permanent 
color, for Silver, Gold Fibre, all makes diffusive or 
metallic screens. Easily applied, no unpleasant odor, 
economical, quick drying. Gallon covers 300 square 
feet. Write S. O. S. Corp., 1600 Broadway, New 
York. 



SOUND EQUIPMENT 



$179.70 NOW CONVERTS YOUR DISC TO 
SOUNDTRACK— DON'T WAIT ANY LONGER- 
FAMOUS S.O.S. SOUND SYSTEMS AGAIN RE- 
DUCED. Trade your old equipment for new. Sound- 
heads, Amplifiers, Speakers. Tachometers free with 
each complete outfit. U. S. Government specifications. 
Make your own installation. DEALERS PRO- 
TECTED. S.O.S. Corp., 1600 Broadway, New York. 

Weber Syncrofilm or Mellaphone Soundheads, com- 
plete $60.00 each. Box No. 5, Projection Engineer- 
ing, 19 E. 47th St.. New York City. 

SALE ON GENUINE SIMPLEX LENSES— PBAC- 
TICALLY ALL BRAND NEW— Standard focal lengths 
from 3" to 8", only $0.75 each. Now's the time 
to change — give us size of picture, throw and 
whether using new apertures. International Theatre 
Accessories Corp., 1600 Broadway, New York. 



HELP WANTED 



Thoroughly high class experienced salesmen to 
handle New Nationally Advertised attractive line 
involving amplification, on liberal commission basis. 
Address J. C. Deagan, Inc.. Deagan Bldg.. Chicago. 



ACCESSORIES 



ANOTHER LOT OF THESE WORLD-FAMOUS 
BOOKS— WAY BELOW MARKET PRICE:— "Sound 
Projection," "Servicing Projection Equipment," 
"Simplified Servicing of Sound Equipment"; last 
two just off press. ALL THREE. $15.00 value. 
$3.95. Individually, $1.50. S.O.S. CORP., 1600 
Broadway. New York. 



WANTED TO BUY 



SOUND EQUIPMENT — New or reconditioned, at a 
bargain for cash. Box 13, Projection Engineering. 



CASH for Simplex Machines, National Ticket 
Registers, Powers bases. Box 23, Projection 
Engineering. 

USED EQUIPMENT 



WORLDS LARGEST CLEARING HOUSE AN- 
NOUNCES ST'l'KR-SUPER VALUES:— Optical Sys- 
tems, $10.00; Reflector Arcs, $35.00; Mellaphone 
Soundheads, $19.75; Pacent Soundheads, $100.00; 
Weber Soundheads, $69.75; Samson Amplifiers, $17.50 
up; Simplex Projectors, complete, $129.75; Simplex 
Heads, $96.60; Powers Projectors, complete, $57.60; 
Powers Mechanisms. $25.00; Hertner Transverters, 
$74.75 up; Forest Rectifiers, $49.50 up; Peerless 
or Strong Reflector Arcs, $110.00. S.O.S. CORP.. 
1600 Broadway, New York. 



Six NEW R C. A. Photophone Amplifiers For 
Sale Suitable for threatre or Public Address work. 
15 watts output. Price each $90. Box 17. Proj. Eng. 



HUGE SAVINGS IN USED PUBLIC ADDRESS 
EQUIPMENT. Send for Bargain List. 8. O. S. 
Corp., Dept. PE, 1600 Broadway, New York. 

12,000 CHAIRS OF ALL DESCRIPTIONS — DE- 
PRESSION PRICES — Write us your requirements 
giving floor space, pitch, and types desired — we have 
what you want at 50c up. We will buy your old 
chairs. Independent Seating Co.. 1600 Broadway. 
New York. 



5HURE AUTOMATIC 
MICROPHONE 

FLOOR STAND 



At Last! A real Floor Stand that is Silent and 
Automatic! No Thumb Screws! No Wing-Nuts! 
No Rattling! Lots ot Tension Prevents Sudden 
Dropping! Raise, Lower, or Turn in any direction 
without adjustments. Special Mechanism (patent 
pending). Guaranteed Indefinitely. 

g^^Q Wfite f0r De+ailSH 



SHLRE BROTHERS COMPANY 




S N SHURE. P. 
337 WEST MADISON ST C 



CHICAGO. ILLINOIS 



w 



E, after to manufac- 
turers interested in. 



EXPORT 

the services of a dependable organization, 
well established in the entire foreign field 

AD. AURIEMA, Inc. 

Manufacturers' Export Managers 

116 Broad Street, New York, N. Y. 



For Your Experimental Department 



A Tube of 500 
Assorted Lugs 
and Terminals — 
Hot Tinned for 
Easy Soldering 
Price $1.00 



We are also 

Prepared to Handle 

Production 

Stampings. 

Write us for 
quotations. 




F. R. ZIERICK MANUFACTURING CO. 



6S-72 E. 131st ST., NEW YORK, N. Y. 



HOTEL HENRY 



ON 5th AVENUE 

Near Smithfield — one of the most conveniently 

situated hotels in town — with easy access to all the 

main points of interest. 

RATES 



Single 



$ 2 



.00 



nd up Double $3 -00 and up 

EXCELLENT RESTAURANT 
POPULAR PRICED COFFEE SHOP 



PITTSBURGH 



$ 



$ 



YOUR DOLLAR BUYS MORE 



$ 



$ 



S ...IN RACON EQUIPMENT... $ 



Today, when economy is the watchword and value is 
paramount you get more than ever before for your Racon 
dollar— more value than you could possibly get in any other 
line. 




SUPER GIANT "B" UNIT 




MASTER "B" UNIT 




JUNIOR "B" UNIT 




BABY "B" UNIT 



Compare these values in the new Type B Units. 

|[ PEAK POWER ratings as high as 60 watts. 

|f CONTINUOUS POWER ratings as high as 30 watts. 

|f FIVE different sizes from which to select the unit that fits the 
requirements and fits your pocketbook. 

|f NON-RUSTING cadmium-plated metal parts — waterproof assem- 
bly — and the finest workmanship you've ever seen. 

|f QUALITY, unapproachable in naturalness, realism and wide range. 

There is added economy, too, in the higher acoustic efficiency of the 
new Type B. That means more units per amplifier, more acoustic 
power output per electrical watt input, more coverage, more profit 
on each p. a. job. 

The four sizes illustrated meet every loudspeaker requirement from 
the small trumpet p.a. rental to the magnificent far-reaching 
chime-carillon system. Call on our Engineering Department for 
the full benefit of a nation-wide field experience. 

Every Racon product is guaranteed by the largest independent 
manufacturer of air-column speakers, having adequate financial 
resources to substantiate every claim and a wide field organization 
to meet every service demand. 

Note: Old-style Racon Units can be rebuilt to the 
Type B head at a nominal charge. Write us. 



For valuable information 
RACON'S Cataolg P.E. 12 
will be sent on request H 
you use your business 
letterhead or card. 



RACON Horns and Units are 
Covered by U. S. Patents Nos. 
1.507.71 1: 1.501.032: 1.577.270: 



73.217: 73.218 
514: 1.781.489 
327: 1.835.739 
360. 



1.722.448: 1.71 1. - 
1.832.608: 1.834.- 
1.845.210: 1.878,- 



13 



r AVAfl~ELEV TKIY VA. IN X. "East 19th Street. New York City 

London, England Toronto, Canada 



THE 



1933 CANADY 

RECORDER IS HERE! 
STUDY ITS 9 

EXCLUSIVE FEATURES 





The Canady Reel- End Alarm 

Consists of aluminum casting "A" which houses a small 
light and condensing lens. A narrow beam of light is 
focused upon an aperature in casting "B" containing a 
light sensitive cell. This cell is connected to the neces- 
sary vacuum tubes or relays which in turn control the 
operation of an electric bell or other signalling means. 
The operation is simple. When the film unwinds to a 
predetermined point, the light beam from "A" is allowed 
to pass "B." The light sensitive cell in "B" actuates the 
alarm indicating the approach of the end. Positive in 
action. No arms or levers to set every ,time the pro- 
jector is threaded. Nothing to forget. Will' not scratch or 
mutilate film like present mechanical devices. No more 
white screens. Removes the human, element. Inexpensive 
in upkeep. Another step forward to better projection. 



This new Compact, precision built 35 m.m. 
sound' on 'film recorder surpasses all others 
—in both Studio and Sound Truck work. 



• MICROMETER GLOW LAMP ADJUSTMENT. Made by 2 
counter locking hand screws, once set, no further adjustment is 
necessary during the life of the glow lamp. Knob U controls 
glow lamp focus. 

• SIMPLIFIED THREADING. A turn of knob T (see arrow) 
actuates 5 locking rollers denoted I and J. Knob Y sets roller Z. 
This is the most improved simplified and positive threading and 
locking assembly ever built. 

• HERMETICALLY SEALED CASE. A worm gear screw, oper- 
ated by a half turn locks the case closed and automatically sets 
a pin releasing the film in the feeder magazine. A real time 
saver! Protects the recorder from being opened by vibration 
or accident. 

• INSTANTANEOUS "SYNC" LIGHT. An ingenious patented 
method automatically checks start point of recorder with start 
frame of camera (arrow X). 

• REPLACEABLE MAIN DRIVE PULLEY. A simple time saving 
arrangement ! Must be seen to be appreciated. It includes an 
automatic even-tension take-up. 

• EXTERNAL (FOOTAGE PUNCH. Conveniently placed, any de- 
sired footage may be cut. Footage meter on recorder is positive 
gear driven. 

• HORIZONTAL LIGHT BEAM ADJUSTMENT. The glow 
lamp's beam may be kept positively horizontal by a double 
screw-locked aperture (arrows S.) 

« CANADY ZETKA GLOW LAMP. Affords full range, noiseless 

recordings of 25,000 to 60,000 feet. Special glass envelope passes 
violet and ultra violet rays with but minimum loss. 

• WORKMANSHIP — DESIGN — MATERIAL. Although Canady 
Recorders are priced exceptionally low — no expense has been 
spared in making them the finest precision recorders available. 
Ball bearings used thru-out, moving parts of cadmium plated 
nickle, solid bronze bushings, heavy aluminum castings, full 
enclosed trouble-proof motor, shielded glow lamp and micrometer 
setting — all in all the finest that money can buy and experience 
construct. 



write for catalog today 



THE CANADY SOUND APPLIANCE CO. 



1776 BROADWAY 



NEW YORK CITY, N. Y. 



rJIQi ' < »! )l l LLIHI l l i1 l l iMJtii.lUi h' l ' UUHJ 



nnrwiwvr' ■"' |M " *■«■■■■—— • — 






IN THIS ISSUE 



FOR INDUS- 
AND SOCIAL USES 

By S. Young White 

>UND ABSORPTION AND 
MATERIALS 

)e W. Baker 

H AND PREPARATION 
MOTION PICTURES 

}y Tarbotton Armstrong 

1PLIFIF.D METHOD FOR THE 
TERMINATION OF HAR- 
lONICS IN VACUUM 
TUBE CIRCUITS 

B r Gilbr-H Si 



Fifth Year 
Of Servi 



■ 



•V* 



H 



■ 



Photo Courtesy RCA-Photoplu 

Sound reinforcing amplifier, rehearsal 
address amplifier equipment, Rocke- 
feller Center, New York. 



«-. Ji 




journal of the Sound ana Ugnt Prqjedion Industries 



JANUARY, 1933 






An A-C Operated Three Microphone 
Mixer, Button Current Supply and 
Amplifier Unit . . . 




MIK-2— Mixer Amplifier 



MIK-2— Power Supply 



The Samson Mik-2 Mixer Amplifier 

Is a new unit which supersedes the MIK-1 (the first and original all a-c 
operated microphone amplifier), of which there are thousands in use in 
broadcast stations as remote pick-up amplifiers, in public address sys- 
tems, and in centralized radio systems. 

The MIK-2 may be operated as a source of power amplifier input; or as a line amplifier 
for broadcast pick-up work. 

Two output levels — 5000 ohms and 500 ohms. The 5000 ohm terminals may be operated 
into any terminating load of that value or greater. 

The Samson MIK-2 Mixer Amplifier is furnished in two units — the Mixer Amplifier unit 
and a separate power supply: Results . . . 

1. Less Cumbersome 

2. Marked Reduction of Hum Level 

A button current of 10 milliamperes per button (20 milliamperes per microphone) is fur- 
nished, free from hum, and limited so that microphones cannot easily be damaged, exces- 
sive currents being an impossibility. 

The volume of each microphone position is independently variable and is absolutely free 
from "interlock." In addition there is a master gain control. 

Send 5 cents in stamps for Bulletin No. P. E. 27, descriptive of this unit to 

R. W. COTTON, Sales Manager 

SAMSON ELECTRIC COMPANY 






CANTON 



Member R.M.A. 



MASS. 



JANUARY, 1933 Page I 

It Pays to be Critical 




IN the manufacture of National Projec- 
tor Carbons we are as exacting in our 
demands for QUALITY as the most crit- 
ical exhibitor can be about the quality 
of his projection. 

That is why you will always find it 
safer, more economical and more satis- 
factory to insist on National Projector 
Carbons. 

There is a National Projector Carbon 
for every type of projection lamp. 

Old Type, Low Intensity, D.C. Arcs 

Low Intensity, White Flame, A.C. Arcs 

Low Intensity, Reflector D.C. Arcs 

High Intensity, Condenser Type, D.C. Arcs 

"High-Low" Reflector Arcs 

Effect Machines. 



PROJECTOR CARBONS 




. . . Sold exclusively through distributors and 
dealers. National Carbon Company icill gladly co- 
operate with the producer, exhibitor machine 
manufacturer or projectionist on any problem 
involving light. 

NATIONAL CARBON COMPANY, INC. 

Carbon Sales Division . Cleveland, Ohio 

Unit of Union Carbide |l| 3 3 and Carbon Corporation 

Branch Sales Offices: 

New York Pittsburgh Chicago San Francisco 



Projection 

Engineering 




Sound Pictures 

Visual Projection 

Sound Recording 

Audio Amplifiers 

Public-Address Systems 

Photography 

Facsimile Recording 

Television 

Photo-Voltaic Cells 

Circuit Measurements 

Automatic Music 

Acoustic Engineering 

Radiant Energy Devices 

Electric Recording 

Phototubes 

Home Talkies 

Theatre Engineering 

Amplifier Tubes 

Sound Reproducers 

Screen Engineering 

Electric Power for Projec- 
tion 

Recording Studio Engi- 
neering 

Location Sound Equipment 

Rectifier Tubes 

Industrial Tube Applica- 
tions 



Donald McNicol 
Editor 

Jas. R. Cameron 
Associate Editor 

Ulmer G. Turner 
Western Editor 

F. Walen 
Managing Editor 



Vol. V 



JANUARY 
1933 



Number 1 



Contents 

Page 

Editorial ' 4 

Voice Recordings for Industrial and Social Uses 

By S. Young White 7 

Sound Absorption and Materials. . .By George W. Baker 11 

New Film Recording System Announced 13 

Dubbing By Eva Elie 14 

Research and Preparation in Motion Pictures 

By Tarbotton Armstrong 15 

A Simplified Method for the Determination of 
Harmonics in Vacuum Tube Circuits 

By Gilbert Smiley 16 

The Closeup By C. H. Barnick 18 

Some Projection Observations By William H. Reasin 19 

Modern Ideas in Public- Address Work 19 

Glossary of Technical Terms for the Projectionist. . 21 



Departments 



New Developments and News of the Industry 20 

Index of Advertisers 23 



Bryan S. Davis 
President 

Jas. A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

19 East 47th Street 

New York City 



Sanford R. Cowan 
Advertising Manager 

J. E. Nielsen 
Circulation Manager 



Chicago Office— 1221 Rosemont Ave.— Charles H. Farrell, MgT. 
St. Louis Office- 505 Star Bldg.— F. J. Wright. 
Kansas City (Mo.) Office — 306 Coca Cola Bldg.— R. W. Mitchell. 
Cleveland Office — 416 National Building— Millard H. Newton. 



San Francisco Office— 155 Sansome St.— R. J. Birch. 
Los Angeles Office— 846 S. Broadway— R. J. Birch. 
New Zealand— Tearo Book Depot— Wellington. 
Australia— McGUl's Agency— Melbourne. 



Entered as second class matter August 15, 1931, at the post office at New York, N. Y., under Act of March 3, 
1879. Yearly subscription rate $2.00 in U. S. Yearly subscription rate $3.00 in Canada and foreign countries. 



JANUARY, 1933 



Page 3 









FOR BETTER, 
QUICKER SPLICES 

• • • Use Eastman Sound Film Patches, together with the simple, precise 
registration block specially designed for them. 

Here are the advantages of this combination: (1) It gives clean, 
uniform splices ... in record time; (2) it removes the necessity of 
painting out joints; (3) the splices obscure a minimum of the sound 
track; (4) they are practically inaudible in projection. 

The adoption of this system represents an extremely profitable in- 
vestment, especially since it involves only these nominal costs: Eastman 
Sound Film Patches (per thousand), $5.00; Eastman Sound Film 
Patcher (registration block), $4.25. Eastman Kodak Company (J. E. 
Brulatour, Inc., Distributors, New York, Chicago, Hollywood) . 



EASTMAN 



SOUND FILM PATCHES 







Amplifier 

economy 



fk% ■ 







30 WATTS 
from 2-250 tubes 

with the 
, ACRATONE 
MODEL 125. 



Wise Projectionists 

change to 



The plate efficiency of 250 
power tubes is normally ex- 
tremely small. Class "A" 
Prime in a special circuit 
enables this amplifier to use 
this wasted energy in greater 
output production. Over 3 
times the normal output of 
2-250 tubes is obtained. 



FREE 

108 page Cata- 
log of public 
address equip- 
ment — radio 
parts — sets — 
tubes — etc. 

WRITE TODAY 



tederate dPurchaser inc . "BSttf " 




The Standard of 

Quality for over 

75 years. 



"NORIS-HS" 

"NORIS-SCH" 

'NORISCHROMO 

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HI-INTENSITY" 



in all 

standard 

sizes 



NORIS 
CARBONS 

^ because -^ 

1. NORIS CARBONS produce 
unvarying brilliancy, im- 
proving projection. 

2. NORIS CARBONS operate 
on lower amperage. 

3. NORIS CARBONS burn 
longer, effecting greater 
economy. 

4. NORIS CARBONS too, are 
lower in price. 

Inquiries Invited. 



NORIS CARBON COMPANY, Inc. 

NEW YORK, N. Y. 160 FIFTH AVENUE MOHAWK BUILDING 
Sole Distributor for C. CONRADTY, Nuernberg, Germany 



E d 



i t 



JANUARY, 1933 



i a 



ru^T^MM^crc DESOURCEFUL- 
SHORT FOCUS LENSES K NFSS in ma kine 
WITH TRANSLUCENT lN-h^b in maKmg 

SCREENS moving picture thea- 

tres pay in dull times 
brings to the surface methods and practices 
which in prosperous times have little appeal. 

In this connection it appears that projec- 
tion from behind a translucent screen has 
distinct advantages in small theatres where 
for space requirements there are possibili- 
ties of low rental and minimum operating 
staff. Indeed, with such practice it is in 
various instances practicable to operate 
theatres which otherwise would not be in 
service. 

Naturally, unless the projection distance 
can be made very short for a given size of 
picture the method loses its advantages. 

Some months ago Mr. W. B. Rayton 
pointed out in a S. M. P. E. paper that for 
this purpose lenses have been developed 
with a focal length as short as one inch that 
will project 35 mm. film. Some patents have 
been granted disclosing that all of these 
make use of the diverging power of a nega- 
tive lens in order to cover a larg-e field of 
view. 

In projection lens practice, simple menis- 
cus, compound meniscus, and negative 
lenses with compound curves have been dis- 
closed in the patents issued. 

There is another construction in which 
the distortion introduced by the usual nega- 
tive element is compensated by an addition- 
al positive element, the two elements being- 
used in conjunction with any standard pro- 
jection lens to give the effect of a lens of 
shorter equivalent focal length, high aper- 
ture, and freedom from distortion. 



R. K. O. 
MUSIC HALL 



THE opening of the 
1 Radio City Music Hall, 
New York, on the evening 
of December 27, disclosed 
that man's mechanical triumphs continue to 
run ahead of man. Adjectives of helpful use 
in describing show places heretofore opened 
are not adequately suggestive when employ- 
ed verbally to paint a true picture of the 
mechanics of the new house of entertain- 
ment. It was however clear to observers 



at the premiere that pretty much the same 
types of talent, of "stuff," of "stunt," of act, 
with which playgoers are familiar, are what 
the showman has to draw upon, even if new 
accomplishments in bigness and of spectacle 
serve as settings. 

If new ideas of stage magnitude, of stage 
splendor and of lighting effects can add en- 
tertainment value to the efforts of present 
day entertainers, in the new Music Hall 
these men and women will have such ad- 
vantages. If new values of individual per- 
formance can be worked out which will en- 
able individual and group performers to act 
up to the environment of the new hall, there 
should be novelty on a new scale and of a 
new order. 

From the staff viewpoint, it is of interest 
to note that the new Music Hall started off 
with 748 employees, including 350 perform- 
ers. Manipulation of the stage settings and 
effects requires the attention of nearly one 
hundred electricians, property men and 
carpenters. 

In the operating organization Eugene 
Braun is chief engineer; Harry Hiller, chief 
sound engineer, and Arthur Smith, chief 
projectionist. 



A HEALTHY 
BASIS 



JESSE L. LASKY is 
-'sound when he says 
"motion pictures must be 
cut from the cloth the 
times provide. Cost must be revised down- 
ward throughout the entire production, dis- 
tribution, and exhibitor scheme without one 
iota of sacrifice of either originality or 
quality. 

"The dollar of today, the public's dollar, 
is spent only when it will buy a dollar and 
a half's worth of goods." 

For a year past all business managers 
have been streaking headlong back to sure 
anchorages from which new, onward prog- 
ress and success may be organized. Soon 
the tide will swing. 



J> 



^jck^w^nxc 



i 



Editor 



JANUARY, 1933 



Page 5 



Good News 



High fidelity all AC operated 

equipment available for theatres of 

all sizes on three year deferred 

payment plan, with small down 

payment and weekly payments, as 

follows: 

Standard Super Size, 

$46.67 per week 
(2500 to 4000 seats) 

Standard Large Size, 

$3 5.72 per week 
(1400 to 2500 seats) 

Standard Small Size, 

$24.10 per week 
(600 to 1400 seats) 

Special Size, 

$15.02 per week 
(Up to 600 seats) 
Trade-in allowance on old equip- 
ment will further reduce above 
weekly payments! 

Above payments include cost of 
periodical scheduled service. 




THAT HAS SCOOPED THE NATION 

NOW . . . you can buy outright 
the world's best sound equipment! 

No more leasing — no more prolonged contract service! 



It's the sensation of the industry — 
the RCA Victor Company's revo- 
lutionary new policy which provides 
for outright sale, on liberal terms, of 
the new Photophone High Fidelity 
sound-reproducing apparatus. At 
one stroke we have eliminated for 
motion picture exhibitors the out- 
moded leasing system and prolonged 
contract service. We have provided 
for minimum contract service on de- 
ferred payments, and a liberal trade- 



in allowance on old equipment. . . . 
No wonder exhibitors from all parts 
of the country have been vastly in- 
terested . . . have sent eagerly to 
the company's home office and to its 
sales representatives for further de- 
tails. We'll be glad to send you full 
facts on this new plan — study the 
deferred payment listings given at 
left — then get in touch with us or 
our representatives! 



PHOTOPHONE DIVISION 



RCA Victor Co., Inc. 

CAMDEN, N. J. 

Branches in Principal Cities of the World 



RECORDING STUDIOS 



MAKING 

PHONOGRAPH 

RECORDS 

. . . requires the absolute 
freedom from "hiss" or 
"rush" which is guaran- 
teed by the condenser 
microphone. 

SHURE, Model 44, is 
the lowest priced, high 
quality, nationally known 
2-stage Condenser Mi- 
crophone available. Fre- 
quency response remark- 
ably uniform, combined 
with high output level 
and extreme wealth of 
richness in tone quality. 

Write for full particulars today. 
P. S.: Recording is a profitable busi- 
ness. Is it established in your town or 
neighborhood? If not, we can help 
you. 



SHURE BROTHERS COMPANY 

Manufacturers -Engineers 
S.N. SHURE. Pre*. 

337 WEST MADISON ST CHICAGO, ILLINOIS 




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Daven High Sensitivity Volume Indicators 

These instruments are 
specially designed for 
the broadcasting field 
but may be used for a 
great many other meas- 
urements in telephone, 
radio and acoustic en- 
gineering. . . . Made for 
standard rack or box 
mounting. . . . Accuracy 
±0.1 db. or better. 
Flat frequency charac- 
teristics up to 50,000 
cycles. . . . Also output 
meters with scale in 
volts. 

DAVEN ATTENUATORS 
have become the stand- 
ard where high quality 
is required. Lower noise 
level than any other 
make! Excellent fre- 
quency characteristics. 
Light, sturdy, compact 
design. Available as bal. 
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"L" and Potentiometers. 

Quick delivery, standard 

units in stock. Special units built to order. Satisfaction guaranteed. 

Everything in the resistance line: Decade boxes, Line Equalizers, 
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sistors. 

Write for Catalogue 531 

THE DAVEN COMPANY 

158- 160 SUMMIT STREET NEWARK, N. J. 

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Type A- 185 Volume Indicator 



Page 6 



PROJECTION ENGINEERING 



Today, more than ever before, 
it is necessary to be posted 
thoroughly on the develop- 
ments taking place within this 
industry of ours. It is only 
the alert, well informed in- 
dividual or organization that 
is today making headway. It 
is essential to know what is go- 
ing on, why and how. 

Projection Engineering 
answers the "what, why and 
how" of the thousands of tech- 
nical men in the fields of sound 
and visual projection and re- 
cording. 

Every contractor, installation 
man and technician who is en- 
gaged in sound work or who 
installs P. A. systems, should 
receive Projection Engi- 
neering every month. 

Enter Your Subscription Now! 
1 year $2.00 — 2 years $3.00 

(Projection Engineering) 

Bryan Davis Publishing Co., Inc. 

19 East 47th Street 

N. Y., N. Y. 

Los Angeles Chicago St. Louis 






***** 







SJhj')';',;^-.-ry?-!-...i|.u,i 1 i .u.Luiu . 



PROJECTION ENGINEERING 



for 
JANUARY, 1933 



Voice recordings for 
industrial and social uses* 



THE voice carries thoughts only 
partly within the machinery of 
words, grammar, and the parts of 
speech. The color and flavor are 
carried by countless inflections and 
tones which express meanings familiar- 
ly and thoroughly. The communicating 
of what we call personality is far bet- 
ter managed by the straight voice than 
by print. Sentiment, which is a big ele- 
ment in speech, is difficult of handling 
in writing, requiring more learning 
than we realize it does, a lot of prac- 
tice, and a baggage of culture not pos- 
sessed by most beings. 

The purpose of this paper is to dis- 
cuss the mechanical technique that can 
be developed for the average person, 
of average monetary means, so that he 
may fully use voice communication. If 
he can use voice communication he will 
get ease of understanding because that 
advantage flows automatically from 
ease of expression. 

There are three means of conveying 
spoken intelligence, which means are 
direct talk, the telephoned conversation, 
and the recorded or frozen speech. We 
propose here to go into the recorded 
form of sound. 

Several methods of recording, each 
advantageous in its special way, exist. 
All of them come under the general 
heading of a relatively fine-grained ma- 
terial moving under a point of some 
kind. Recording may be done opti- 
cally, on film or on paper, as on the 
sound track of talking moving pictures, 
a medium which varies in its ability to 
pass light and thus causes the desired 
fluctuations of sound to register on a 
light-sensitive device. This method is 
obviously unsuited to individual use. 
Another means of considerably more 
promise in this field is recording upon 
an iron wire by variably magnetizing it 
in limited areas. Reproduction is ac- 
complished by simple reversal. This sys- 



tPresented before the Radio Club of America. 
September 14, 1932. 



By S. Young White 

tern does not necessitate any physical 
contact with the wire, and in the nu- 
merous classes of service where the re- 
cording would be played only once or 
twice the system has the marked ad- 
vantage that the wire can be easily 
wiped clean of recording, and hence 
used indefinitely. However, the appa- 
ratus of this system is not as yet in 
general distribution. 

Availability 

The field thus narrows itself to the 
use of phonograph records because peo- 
ple are familiar with them and since 
machines capable of playing them are 
universally available. Because this 
type of apparatus is almost univer- 
sally adapted to play the laterally re- 
corded disc record we shall confine our 
discussion to this form of disc. 

We find no literature generally avail- 
able on the subject of recording as prac- 
ticed before the advent of the electric 
amplifier, so our history is made up 
of such glimpses as the Patent Office 
affords. Originally, good recording was 
apparently confined to waxes and soaps. 
That was because of lack of power in 
the voice itself to actuate a diaphragm 
strongly enough to drive a heavily 
loaded cutting or pressing tool ; one 
capable of recording satisfactorily upon 
the more difficult sorts of materials. 
About the only patent that shows a 
clear grasp of the problem was one filed 
by George K. Chaney, of the Victor 
Company, in 1902, which describes the 
most practicable method of attack. 

Since our choice is narrowed to the 
laterally cut phonograph disc, we shall 
examine here the two fundamentally 
different methods of forming the groove, 
the first by cutting, a process which 
actually removes material in the form 
of shavings, the second a pressing 
method, which is altogether analogous 
to drawing one's finger over the top 
of a tub of butter, leaving a groove, 
although no material (butter) will have 



been removed from the tub. 

We must reject the cutting method, 
despite the fact that it is standard in 
wax recording because it requires too 
fragile a tool for general use. The dif- 
ficulties connected with removing or 
disposing of the shavings is another 
reason for not taking on this method 
for universal application. 

Since we are obliged to use the press- 
ing method, we must examine its phe- 
nomena with considerable care. Fig. I 
shows the profile of a groove made by 
this process. It will be noticed that the 
material piles up in front of the travel- 
ing stylus under what must be enormous 
pressure, pressure which is, in fact, 
usually far beyond the tensile strength 
of the material itself. These pressures 
sometimes approach 200,000 lbs. to the 
square inch and very high temperatures 
are developed. This piled up material 
then splits and flows to either side of 
the stylus precisely like the formation 
of the bow wave in front of a boat. 
At either side it freezes into permanent 
shoulders. Fig. 2 is the cross-section 
of an ordinary phonograph groove of a 
wax record with the material removed 
leaving a shallow trench approximately 
as shown. Fig. 3 shows the type of 
groove under discussion, with the usual 
below-the-surface portion and the above- 
the-surface shoulders. Fig. 4 shows the 
laminated type, in which a surface ma- 
terial is superimposed upon the main 
body. These illustrations suggest the 
division of records into several clearly 
defined classifications. 




Fig. l. 



Page 8 

Class I record is homogeneous 
throughout. Class II record is a two- 
ply laminated record, as shown in Fig. 
4. The top material is usually chosen 
for low noise level and attractive sur- 
face while the body of the record is 
usually composed of a cheaper mate- 
rial. There are three different methods 
of forming Class II records. What we 
will call II A Class has a top coating 
with a thickness of the order of the 
depth of the groove. Class I B record 
has a surface material of a greater 
thickness than the groove's depth. Class 
II C has a soft top which is graded in 
hardness down to the hard base within 
depths of the order of the groove itself. 

Class III record has a cheap base sup- 
porting a Class II record. Between its 
base and its top there is usually a 
layer of adhesive stuff which is, of 
course, itself protected from needle- 
wear by that top layer. Consequently, 
the top layer being a thin one, the ad- 
hesive material itself can be given re- 
cording properties. 

Returning to Fig. 1, we observe that 
the stylus has a smoothly rounded point. 
An infinite variety of styles are prac- 
ticable, from the pointed, through the 
truncated cone, to the ball point, in all 
angles and of all radii of curvature. 
Various materials may also be used, 
from chromium plated steel to the dia- 
mond. 

The Stylus 

We must first design a desirable 
groove profile from the known char- 
acteristics of the record material, hav- 
ing due regard for the number of 
grooves per inch, for a useable play- 
back needle, and for the class of service 
desired. It will then be found that the 
most important factor in the design of 
the stylus is the rate at which the work 
is done. From its first point of influ- 
ence, which is ahead of its path through 
the material to its last point of contact 
the stylus must cause the material to 
flow as rapidly as possible without ex- 
ceeding at any point a certain critical 
rate of doing work. 

From a recording viewpoint the 
weight on the point of the stylus should 
be as light as is practicable and we de- 
sire the stylus to be as nearly vertical 
as possible to the record surface. Under 
these conditions high frequencies are 
impressed upon the record more easily, 
the weight on the stylus can be a mini- 
mum, and the load on the motor is light. 
In general, it will be found that due 
to the small area of such a stylus, which 
is actually employed in forming this 
groove, the rate of doing work is ex- 
tremely high, and the record material 
no longer flows like a liquid under these 
enormous pressures, but begins to tear, 
resulting in a very rough lining of the 
groove with the side wall thrown out 




Fig. la. 

in chunks, which causes a very high 
noise level. It will be found that this 
rate of doing work can be decreased by 
using a stylus having a minimum co- 
efficient of friction to the record mate- 
rial, having a relatively blunt point that 
is highly polished and which rests upon 
the record with a considerable trailing 
angle. These considerations seriously 
curtail our ability to put on really high 
frequencies with readily available re- 
cording materials, but it is altogether 
necessary to minimize the all-important 
noise level. 

The stylus is the middle link of a 
three-element chain, the other two be- 
ing the cutting head and the record. 
Before further detailed study of the 
stylus we should observe some of the 
actions of the cutting head. In Fig. 
5 we see a skeleton diagram which will 
aid us in discussing the main elements 
of cutting head design. The portion 
above the bearing represents the mov- 
ing armature, its driving force fur- 
nished by a simple magnetic iron sys- 
tem, or by a moving coil, or by a Ro- 
chelle salts crystal. Since we are ask- 
ing this device to move at least 5,000 
times a second it must usually be de- 
signed to be relatively small, the entire 
series of elements not exceeding one 
inch in length. As this tiny moving ele- 
ment is to be pressed into the record 
with a weight of the order of twenty 
ounces, it will readily be seen that the 
most difficult point of design is the 
bearing which must withstand this 
weight plus the great drag on the record 
with no sidewise play whatsoever. To 
faithfully record faint breathing sounds, 
the bearing must transmit without loss 
armature motions of from 20 to 50 mil- 
lionths of an inch. With the best de- 
sign at present practicable it will gen- 
erally be found that at some frequency 
in excess of 2,000 cycles it will be the 
bearing and not the stylus point that 
will move. 

Because the actuating force and the 
damping are at some distance from the 
bearing, we can, obviously, allow no 
bending of the armature. 

In commercial wax recording one of 
the most serious points of design is 
avoiding a resonance spot due to the 
armature mass and elasticity. In direct 
recording, however, the load is so great 
that resonance phenomena, due to any 
cause, are almost entirely absent, but in 
return for this blessing many difficul- 



PROJECTION ENGINEERING 

ties are found in recording the higher 
frequencies. The function of damping 
is confined to centering the armature, 
avoiding hysteresis and cooperating in 
limiting the motion to prevent one 
groove from crossing over into an- 
other. This latter function will be dis- 
cussed further under remarks on moni- 
toring. 

Bearings 

The most immediately practicable 
form of actuating means was found to 
be the balance armature, magnetic- 
drive type, with rubber wrapped bear- 
ings. The design of dynamic units met 
great difficulties in the bearing. Among 
bearings tried for this type of head were 
knife-edge, torsion, pivot, ball and plain 
metallic sleeve. Results were indifferent 
throughout the list. The Rochelle salts 
head had the marked advantage of be- 
ing its own bearing, but difficulties were 
encountered in impressing smooth low 
frequencies, as well as with the fra- 
gility of the element. But this type has 
considerable promise, nevertheless. 

The rubber wrapped sleeve bearing 
has a certain lack of permanence, but 
will pass the highest frequency for the 
longest period of service of any type 
tried. This is due to the fact that rub- 
ber can be considered as a liquid, with 
considerable inertia, and while at very 
low frequencies movement is general 
throughout the mass, when the fre- 
quency is increased it tends to localize 
itself on the surface, until at extreme 
high frequencies it becomes remarkably 
solid. We have recorded 8,000 cycles 
with medium success through this type 
of bearing. 

Since resonant peaks are not appar- 
ent, damping can be obtained by metallic 
springs or by rubber, in its forty odd 
varieties. If rubber is used it may be of 
considerable thickness in the direction 
of compression with a consequent uni- 
form reaction through the ordinary dis- 
tances of travel of the armature; or it 
may be quite thin with exponentially 
increasing reaction through relatively 
short distances. The rubber may be in 
a state of high initial compression, or 
in no state of compression at all, when 
the armature is at rest, a major factor 
in determining hysteresis. 

This brief review of some cutting 
head and stylus limitations will allow 
us to more intelligently choose a re- 
cording material. Such a material must 
above all be inexpensive, attractive in 
appearance, light in weight, capable of 
being mailed at an ordinary post box, 
of relatively low noise level, of at least 
fair quality, and resistant to wear. 

The surface must obviously be of a 
fine grained, homogeneous material with 
very small crystals. It must smoothly 
flow under proper stylus conditions and 
must nave a minimum of resiliency. 



JANUARY, 1933 



Page 9 



Record Materials 

Materials for Class I (homogeneous) 
records are rather limited in number. 
Among the metals, brass, copper, zinc, 
cadmium, lead, tin, and steel are ruled 
out by several factors, such as weight, 
noise level, too easy bending, or other 
defects, leaving only aluminum and 
magnesium. Aluminum has most of the 
desired qualities, but its cost is exces- 
sive, it cannot be played with a steel 
needle, and its noise level is rather high. 
Of the non-metallic substances suitable 
for Class I records, there are practi- 
cally none available at a reasonable 
price, and we are forced to conclude 
that the universal direct recorded rec- 
ord of the future will be a laminated 
article. Normally we associate quali- 
ties of fineness of texture, toughness, 
and attractive appearance with rather 
expensive materials, so it is logical to 
use such materials for the recording 
surface because recording never de- 
scends more than two one thousandths 
of an inch below the surface, allowing, 
of course, the body of the record to be 
made of a far less expensive material. 
Although it has been determined that 
for wide commercial use the manufac- 
turing cost of a six-inch disc must not 
exceed a fraction of a cent, neverthe- 
less one may find a wide variety of sur- 
faces at this economic level. 

Metal rolled to a few mils in thick- 
ness has had its crystalline structure 
broken down somewhat and is an excel- 
lent recording material because of its 
resultant low noise level. The greatest 
difficulty is to find a method of forc- 
ing the metal to closely adhere to the 
base without piling up and wrinkling 
in front of the moving stylus, especially 
in the Class II A record, where the top 
layer is of a thickness of the order 
of the depth of the groove. The most 
practical form seems to be the Class III 
record, consisting of a metal foil top, 
a rather thick layer of adhesive, and 
a base that merely forms the physical 
body of the record. Some success has 
been achieved in recording on pulp pa- 
per, suitably protected by metal foil, 
where actual compression of the paper 
takes place, resulting in great density 
at the bottom of the groove. A large 
choice is available among these ductile 
foils because the method of forming the 
groove is radically different from those 
of the homogeneous Class I record, and 
many materials will meet these condi- 
tions. 

Approximately 150 non-metals have 




Fig. 2. 



been experimented with for recording. 
A familiar substance is cellulose acetate 
which has low noise level, attractive ap- 
pearance, moderate cost, but which has 
too great elasticity ; that is, if one 
pushes it ten units it bounces back one, 
and if it is displaced only one unit it 
bounces back practically the full unit. 
In recording the low frequencies we 
do displace ten units, and the loss of 
this single unit due to resiliency is rela- 
tively insignificant. The high fre- 
quencies, however, displace the mate- 
rial only one unit, which promptly dis- 
appears after the stylus has passed, 
resulting in a very serious high fre- 
quency cutoff. Hard rubber shows some- 
what the same phenomena, whereas an- 
other large class of non-metals tends to 
crack before recording stresses are 
reached. Materials employed as fillers, 
such as wood-flour, chalk, or fibres, 
generally display too high a noise level 
to be practicable. Some artificial waxes 
show promise where a limited number 
of record playings is enough. 

Cellophane belongs to a class of ma- 
terials which shows excellent promise. 
Some difficulty has appeared in develop- 
ing here an adhesive of desirable char- 
acteristics. We will dismiss all other 
non-metals as being still in the experi- 
mental stage. 

Monitoring 

In most classes of general service no 
monitoring is possible, microphones 
used must be non-blasting, the amplifier 
of limited power, the cutting head in- 
capable of cutting over to the next 
groove. The serious monitoring is that 
below 200 cycles, and the system must 
have a response characteristic such that 
the weak signals are handled in a linear 
manner built up above the noise level 
on the record, but stronger signals 
asymptotically approach the high inten- 
sity limit imposed by the proximity of 
the next groove. 

To prevent an irregular rate of ro- 
tation of the turntable during record- 
ing (wows), it will be found best to 
place the motor in a shock-absorbing 
cradle coupled to a heavy flywheel type 
turntable through a flexible means, such 
as a rubber belt or the equivalent. This 
has proven more effective than precision 
machine work where the motor was 
coupled by stiffer means. 

Average values of recording elements 
for metal are: stylus 50 per cent, to 100 
degrees ; cones with ball points 1 to 3 
mils in radius and operated at angles 
in the neighborhood of 25 degrees. 
Weights on stylus are from 6 to 25 
ounces. Amplifiers are of 1 to 5 watts 
output. Cutting head impedance may 
be any convenient value. Grooves per 
inch may be 80 to 150. Actual cutting 
load as reflected into turntable motor 



is one to three watts if the record is 
lubricated, more if it is not. Any lu- 
bricant will do, although paraffin oil 
seems to be most practical. 

The quality of the recording is de- 
termined by a rather large number of 
factors. The main ones to keep in mind 
are background noise level, hysteresis 
in the head, high and low frequency re- 
sponse. Noise has been discussed. Hys- 
teresis is quite common in cutting heads 
under these heavy loads and results in 
"mushy" recordings. It is quite difficult 
to add a strong restoring force to the 
armature and still allow large low fre- 
quency swings. There is considerable 
difficulty in impressing high frequencies 
due to inefficiency, heavy load on the 
head, large stylus point, record elas- 
ticity, bearing losses, inability of the 
needle to take them off and numerous 
other factors. 

Needle Design 

Assuming that a record has been 




Fig. 3. 

made, we must of course use a needle 
of some sort to play it back. The chief 
point in needle design is to achieve 
maximum permanence without appre 
ciable wear on the record. The needle 
must be of a material that is not costly 
and which is easily worked into shape. 
It must have considerable longitudinal 
strength and must successfully resist 
bending. The needle's point should fit 
the groove to provide maximum coup- 
ling and must have a low coefficient of 
friction. 

Both metal and non-metal needles were 
tried. Of all familiar metals chromium 
plated steel was moderately success- 
ful upon non-metal records, but a needle 
of any metal upon a metal record de- 
veloped too high pressures, tending to 
re-record and to straighten out the 
groove. This erosion effect is confined 
to the smaller deflections, as in general 
there is no wear on the large low fre- 
quency swings. Of the more practica- 
ble non-metals suitable for needle use 
on metallic records a bakelite-impreg- 
nated birch wood needle has been most 
successful of the commercially produce- 
able forms. Moulded bakelite needles 
have been tried, as well as wooden 
bamboo needles impregnated with a 
number of grades of bakelite. and beetle- 
ware, as well as those hardened by 
chromic acid and by other means. Vari- 
ous shapes have been tried, but the 



Page 10 




Fig. 4. 

only departure from the conventional 
that seemed worth while was a bent 
needle of the shape of the tail-skid of 
an airplane, to reduce the drag, but, as 
with all asymmetrical needles, the pub- 
lic would never learn to insert it prop- 
erly. A well polished sapphire needle 
with a two-ounce Rochelle salts pick-up 
is the best permanent play-back arrange- 
ment that we have developed. 

The Amplifier 

Little need be said concerning the 
characteristics of the amplifier. A grad- 
ual cutoff below 200 cycles will tend 
to prevent overload and a considerable 
rise from 1,000 to 6,000 cycles will tend 
to compensate for the numerous fac- 
tors which tend to prevent satisfactorily 
recording the higher frequencies. 

It is quite difficult to couple an am- 
plifier to a magnetic type head because 
it requires a large amount of power and 
has approximately the frequency — impe- 
dance characteristic — of an air-core 
coil, which it is difficult to compensate 
in such manner as will allow the output 
tube to work into an optimum load. If 
the tube impedance is matched by the 
head at high frequencies, it will tend to 
compensate for the numerous other fac- 
tors which militate against the highs, 
and since it will be a serious mismatch 
at the lower frequencies it will tend to 
break them up into harmonics, which is 
a very desirable form of distortion, in- 
asmuch as it is not practicable to put 
true lows on a laterally recorded phono- 
graph disc. 

The actual amount of power required 
to record a good standard intensity note 
is only five milliwatts or so, but be- 
cause, as is the case with all electro- 
mechanical translators of sound, the 
less efficient the head the better the re- 
cording, it is not practicable to design 
a magnetic head of greater than one per 
cent, efficiency. Consequently, several 
watts must be available from the am- 
plifier. The Rochelle salts head, being 
an electrostatic device, is voltage op- 
erated, and requires from 100 to 200 
volts across it for satisfactory low fre- 
quency response. 

Uses for Recordings 

A few years ago it would not have 
been practicable to introduce this art to 
the public in the many forms of its use- 
ful destiny because the essential electric 



elements had not descended to their low 
price and had not reached their rugged- 
ness of today. But with contemporary 
technical background it should be fairly 
simple to introduce equipment suitable 
for these wide uses. 

The three main uses of personal re- 
cording are communication, delayed 
transmission and storage of speech. To 
obtain immediate wide recognition of 
this art the first requirement would 
seem to be the offering of facilities to 
the average person to make his first 
record for amusement or communica- 
tion use. A machine providing this 
facility was developed and placed in 
contact with the public. Several ex- 
perimental types of this machine were 
actually put out over a period of almost 
one year in these times of money strin- 
gency and they were used to the extent 
of several hundred records at 25 cents 
apiece per day over the entire period. 
These results would seem to indicate 
that the larger public will use record- 
ing facilities if they are presented under 
proper psychological conditions, at rea- 
sonable price, and of easy access and 
use. The average person's first record- 

- dampina 
-aelualiru} force 
-armature 
-bearing 

-stylus -point 
Fig. 5. 

ing was just to find out how he really 
sounded to others while the second 
record was usually mailed to some- 
body. The recipient was usually so 
pleased at such a faithful expression of 
the personality of the sender that re- 
quests came back from relatives or 
friends to carry on future correspond- 
ence by this means. Because the sen- 
timental value was prized, the sender 
was glad to comply, and he was also 
pleased because the horrible ordeal of 
writing home regularly was done away 
with, to the saving of much mental 
anguish. The medium was also used to 
find out whether one had a foreigner's 
accent or other eccentricity of speech. 
Mothers fetched their babies to squall 
for posterity, or for their own mature 
embarrassment. Very old folks dic- 
tated moral maxims and ethical counsel 
to be played yearly on anniversaries of 
their deaths. Many illiterate foreigners 
used it for correspondence. In fact, 
about 60 per cent, of the records made 
were posted in the mails. These simple 
statistics rather strongly indicate that if 
engineers extend this service of record- 
ing in the direction of the public, which 
has its mind already educated to the 
talkie and the radio, the medium will 



PROJECTION ENGINEERING 

be rather generally adopted into daily 
life. 

The most obvious use of delayed 
transmission is in connection with the 
telephone message, which may take sev- 
eral forms. Most important would 
seem to be the telephone answering 
machine. This is being developed in 
a form that does not cut in to the 
telephone line or interfere with the 
service in any way and that can still 
take a number of messages when no- 
body is at the 'phone. To be practical 
this requires the utmost simplification 
of equipment, such as motors, lead- 
screws, means of suppressing wows, 
and the numerous checks against im- 
perfect operation of the nachine. 

A talking night-letter service would 
be practical with a message 'phoned to 
a central office, there recorded for re- 
transmission when the wires are less 
busy, for re-recording at the other end 
on a small record to be delivered to 
the addressee or on a very large rec- 
ord, individual message being played 
over the telephone for delivery. The 
advantages over a written night letter 
are, again, ease of composition, full 
understandability when received, plus 
the sentimental value of hearing the 
voice of somebody which one can play 
over and over again when one is lonely. 

The Telecheck machine that has been 
developed records both sides of a tele- 
phone conversation. The importance 
of this can be realized when one thinks 
of the enormous amount of business 
done over the 'phone, the orders given 
and taken, with all the opportunities 
of lapsus linguae, mistaken meanings, 
and forgetfulness. The recording is 
done with no connection to the 'phone 
at all. There is only a small button 
near the telephone which is held down 
as long as one wishes to record. 

The same checking idea can easily 
be extended to recording meetings, 
taking testimony, or to any situation 
where a dispute is likely to occur. The 
full grasp of any proceedings depends 
not only on what is said, as reflected 
in a stenographic report, but on how 
it was said, which can only be done 
through a record. 

The list of uses of direct recording 
can be extended indefinitely, but we 
hope enough has been shown to allow 
realization of the opportunities the en- 
gineering profession has to develop the 
new art of direct recording to the point 
of use in everyday life. 




Fig. 6. 



Wff? Htfc.t.u tt r i« i * w w 



JANUARY, 1933 






Sound absorption and 
materials' 



By George W. Baker* 



IN the discussion of sound absorp- 
tion and its relation to theaters I 
have limited myself to the con- 
cepts and materials in commercial 
use today. 

When absorption is spoken of we 
mean the change of sound energy into 
other less objectional forms. This 
change of energy might be into the form 
of heat or mechanical work but which- 
ever it is we are rid of the annoyance 
caused by the sound energy that is ex- 
cessive reverberation, troublesome re- 
flections, etc. Sound impinging on a 
diaphragm of a microphone is trans- 
formed into mechanical work while 
sound impinging on a finely porous ma- 
terial is transformed largely into heat 
by friction. The use of these acoustical 
facts, especially the latter, enable us to 
correct and to build acoustically cor- 
rect rooms in which all the auditors can 
hear to perfection. Having a trans- 
formation of energy it is only natural 
that the scientific mind should turn to 
a means of measurement and expres- 
sion so that the engineer and acousti- 
cians can use it in their work. Wal- 
lace Sabine, one of the pioneers in the 
study of acoustics, devised a unit in 
which absorption could be expressed. 
He compared all absorbing materials 
to an open window, since all the sound 
impinging on an open window passed 
through. He gave the open window a 
coefficient of one or one hundred per 
cent absorption, based on an area of 
one square foot. Now anything which 
absorbs only part of the incident sound 
energy will have a coefficient less than 
unity and will mean that per cent ab- 
sorption as compared to a square foot 
of open window. 

Coefficient of Absorption 

There are several methods of meas- 
uring the coefficient of absorbing ma- 
terials. The reverberation method in 
which the reverberation time of the bare 
room is obtained, the material to be 
tested is then placed in the room and 
the reverberation time is again ob- 
tained. From the two time values one 
can calculate the value of the absorp- 
tion. This is the method used at the 

fPaper presented before Chicago Section, So' 
tiety of Motion Picture Engineers. 

*U. S. Gypsum Company, Chicago, Illinois. 



various laboratories throughout the 
country. It has several disadvantages 
in that it requires a very large sample 
of the material and a considerable num- 
ber of measurements. Another method 
makes use of the well known law of 
optics, in which the angle of reflection 
equals the angle of incidence. Sound 
is allowed to impinge, from an angle, 
on the material to be tested. The ratio 
of the reflected intensity of the material 
to the reflected intensity of a non-ab- 
sorbing blank, is considered a measure 
of the absorption of the material. The 
apparatus must be calibrated against 
samples of known coefficients. This 
method requires small samples conse- 
quently it can be used to study the vari- 
ation of absorption coefficient between 
individual small tile. 

Another method is known as the tube 
measurement in which the sample is 
placed at one end of a small diameter 
tube and a source at the other end. 
Standing waves are set up in the tube 
and the points of maximum and mini- 
mum pressure are found by means of 
an exploring microphone. From the 
two pressure values and their respec- 
tive distances from some known point 
on the tube, one can get the absorption 
cofficient. This apparatus must be cali- 
brated by samples of known coefficients. 
This method is not very favorable be- 
cause of mechanical difficulties which 
present themselves to the technician. 
The mineral wood sample, manufactured 
from a slag blown into cold water, has 
a high coefficient of absorption, i. e., 
about .82. Due to its dustiness it must 
be enclosed in a cloth sack. However, 
this sack does not have an appreciable 
effect on the coefficient since the sound 
pulse passes through the cloth, as if it 
were not there. The pad formed is 
placed behind a perforated metal pan 
and the whole suspended from the ceil- 
ing. 

The sample of acoustone is made 
from mineral wool and other substances 
mixed with a binder and cast into molds. 
The material can be made into various 
shapes and by the addition of various 
dyes which can be made into a very 
decoratve product. The absorpton co- 
efficent is about .61. Due to its sur- 
face and the various shapes and colors 



Page I I 

into which the tile can be made, it is 
used as a ceiling as well as a wall deco- 
ration for sound treatment. The mate- 
rial may be spray painted, several times 
before the absorption coefficient begins 
to decrease appreciably. 

There are many forms of sound ab- 
sorbing products such as hairfelt, flax- 
olinum, cork board, masonite, insulite, 
pyrocell, celotex, etc. Celotex is a 
shredded wood product drilled with 
holes at a definite spacing. These holes 
form an access into the interior of the 
material more readily and thus the high- 
er value of sound absorption is ob- 
tained, (coefficient between .63 and .70). 
The material has the advantage in that 
it can be brush painted as many times 
as necessary without suffering a de- 
crease in absorbing power. The holes 
must not be filled with paint. Weath- 
erwood, masonite and presswood come 
under this form of absorbing mate- 
rial. The coefficient of the undrilled 
material ranges from .18 to .80 depend- 
ing upon the porosity and thickness of 
the material. 

Sound Absorbing Materials 

I have been talking about absorbing 
material and the various coefficients ; but 
what about how to use them and what 
are the most efficient uses for them ? If 
we take a medium untreated room (vol- 
ume about 10,000 cubic feet) with hard- 
wood floors, plaster walls and ceiling, 
we will find that when we speak or 
play music, the various individual syl- 
lables or notes can be heard for sev- 
eral seconds after the sound has 
stopped. There will be interference be- 
tween the notes as they follow one an- 
other. In talking to another person in 
this room we will find that we have 
difficulty in being clearly understood. 
This is due to the various reflections 
from the walls, floors and ceiling ; in 
other words when the path of the direct 
sound from the source is considerably 
shorter than the path of the reflected 
ray, we hear the note as many times as 
it is reflected. Since the difference in 
path is related to time we have only to 
find the ideal hearing time as it were 
and use this time in the construction of 
further rooms. Again we are interested 
in the time necessary for the sound of 
an initial intensity of 60 db. to decay to 
inaudibility. This time is known as the 
reverberation time of the room. When 
this time and the time difference in 
paths are correct in a room, ideal hear- 
ing is assured. Wallace Sabine has 
given a formula which is almost univer- 
sally used in the calculation of rever- 
beration time, but it does not apply to 
dead rooms, i.e., highly treated rooms. 
For our purpose Sabine's formula 
t — 05Y will suffice for the room we 



Page 12 



PROJECTION ENGINEERING 



have under consideration. Through a 
great many observations on various in- 
dividuals it has been found that if the 
time difference in paths of the direct 
and reflected sound is less, than about 
.06 second, we will be unable to notice 
the phase difference between the two 
rays. By the same process of experi- 
mentation on rooms of various volumes 
it was found that an optimum curve 
or reverberation time could be drawn 
and from this curve the time for any 
room could be found. 

Reverberation Time 

In the room we have under consider- 
ation the optimum reverberation time is 
about 1 second. Substituting this time 
and the volume of 10,000 cubic feet in 
the formula we can solve for the amount 
of absorption. This absorption con- 
sists of the product of various areas 
and their corresponding coefficients. In 
order to get the amount of absorption 
we need to have the room corrected, 
we must subtract the absorption of the 
walls, ceiling and floors, from the total 
amount and what remains is the amount 
that must be added to the room to get 
the reverberation time of one second. 
In dealing with openings in the room 
such as open doors into rooms we 
treat them as a positive or negative ab- 
sorption. If the room on the other side 
of the opening is highly absorbent we 
estimate a coefficient for it and multi- 
ply this by the area of the door. The 
absorption which we obtain is then sub- 
tracted from the total necessary to cor- 
rect the room. If the room is highly 
alive we will have to estimate a low 
coefficient for the opening. 

After we have determined the amount 
of absorption that we need to correct 
our room we must select the material. 
In selecting the material we ought to 
bear in mind that if we have a large 
amount of reflecting surface we ought 
to get a material with a low coefficient 
so that we have enough of it to cover 
all of the objectional reflecting sur- 
faces. If we do not have objectional 
reflecting surfaces we may select a ma- 
terial with a high coefficient and con- 
centrate it in one place. Suppose for 
example, that in our room we have some 
reflecting surfaces which give us the 
trouble I mentioned in the beginning of 
having the reflected path greater than 
the direct path. To overcome this diffi- 
culty we will have to place some ab- 
sorbing material on this surface so that 
the reflected ray will be of considerably 
less intensity than the direct ray and 
as a result the objectional reflection 
will not be so noticeable. If the sur- 
face is too large for our absorbing ma- 
terial we will have to resort to coffer- 
ing so as to break up the reflected ray 
into different length paths. 



Curved Surfaces 

In treating curved surfaces for echo, 
coffering is about the only absolute cure 
but there is another idea of changing 
the phase relation of parts of the re- 
flected ray so that most of it is elimi- 
nated by phase opposition. This is ac- 
complished by placing material of high 
reactance in strips mounted away from 
the curved wall. Incident sound then 
suffers a change of phase and a direct 
reflection from the wall between the ma- 
terial. This method is not as satisfac- 
tory as it might be because of the nec- 
essity of covering the whole set-up with 
a cloth and then decorating the cloth. 

This same analysis of an acoustically 
incorrect room is applied to a theater 
in which the acoustics are very bad. If 
the house is to be used for rehearsals, 
reverberation time should be adjusted 
so that it will be approximately the 
same as when the house is filled with 
auditors. This can be done in several 
ways, i. e., by having high absorbing 
material which can be covered as the 
house fills up. Again the stage should 
not be made highly absorbent since it 
is highly desirable that the speaker 
should have all the reinforcement he 
can get. 

▲ 

SOUND RECORDING 
EXHIBITION 

ACTING as a critical jury to pass 
judgment on the results of their 
skill in handling the complex machinery 
which gives a voice to the screen, lead- 
ing sound engineers recently staged an 
annual exhibition of the best sound re- 
cording done by various studios during 
the year as a preliminary to the awards 
of merit voting in the Academy of Mo- 
tion Picture Arts and Sciences. 

In the preliminary exhibition this 
year the current vogue for courtroom 
pictures was strongly reflected, dra- 
matic scenes from "The Mouthpiece," 
"States Attorney," "An American 
Tragedy," "The Champ," and "Two 
Seconds" being among those presented 
to demonstrate the maximum effective- 
ness of the combination of sound and 
picture. 

The achievements of four sound de- 
partments, those of Metro-Goldwyn- 
Mayer, Paramount Publix, RKO- 
Radio and Warner Brothers-First Na- 
tional Studios were selected by the 
technicians for comparison in the final 
voting. 

Contrasted to the awards the Acad- 
emy gives for other achievements the 
award for best sound recording is not 
given for any one picture or example, 
but is awarded for the best overall per- 
formance by a studio sound department 
during the year. 

At the preliminary showing each stu- 
dio is allowed to submit five scenes from 



separate pictures, which will give a 
representation of the best work of the 
studio's technicians for the year. These 
scenes are exhibited to the sound tech- 
nicians section of the Academy, each 
member judging such technical point- 
as correct volume, frequency charac- 
teristics, and freedom from all noises 
which do not belong to the picture. The 
engineers are particularly concerned 
with naturalness and realty in the dia- 
logue and music. 



RCA PHOTOPHONE NOW 
SELLS OUTRIGHT 

INSTEAD of licensing for a ten-year 
period — the practice heretofore 
maintained by the leading manufac- 
turers of sound reproducing equip- 
ment — outright sale, the elimination of 
contract service as soon as apparatus is 
fully paid for and further reduction of 
contract service in cases of deferred 
payments, has been decided upon by the 
RCA Victor Company. 

Ever since sound pictures replaced 
the silent screen, manufacturers of re- 
producing apparatus have leased their 
equipment to exhibitors for a period 
of ten years. Some companies also re- 
quired the exhibitor to accept periodical 
service at specified rates for the entire 
term of the contract. In 1929, RCA 
Photophone revised its service policy so 
that in no case was an exhibitor re- 
quired to accept service for more than 
three years, and last year, in addition to 
making a marked reduction in contract 
service charge, made the maximum 
period two years on the larger sizes 
and one year on the smallest. 

"It is the company's conviction that 
this new policy will be highly acceptable 
to all exhibitors," the announcement 
stated. "Under its provisions, once the 
terms of the contract are met, whether 
they provide for cash or deferred pay- 
ments, the equipment belongs to its 
purchaser. Service will be optional 
with him. Our experience leads us to 
believe, at our reasonable rates, he will 
want regular service, but he does not 
have to take it. In this connection, to 
protect and supervise our property, we 
make one necessary reservation, namely, 
under the deferred payment plan. When 
deferred payments cover a one-year pe- 
riod, six months service is required. 
Under the two-year plan, one year serv- 
ice, and under the three-year plan, 
eighteen months service. We specify 
periodical scheduled calls, averaging 
from one to two calls per month, de- 
pendent upon the type of equipment. Of 
course, we always stand ready to render 
emergency service at rates currently 
maintained by our installation and serv- 
ice department which has stations in 
various parts of the country." 



JANUARY, 1933 



Page 13 



New film recording 
system announced 



ANEW "high fidelity" system of 
sound-on-film motion picture 
recording which promises to 
revolutionize previous concep- 
tions of realism in sound motion pic- 
ture reproduction was demonstrated in 
November in the offices of the RCA 
Victor Company, at 411 Fifth Avenue, 
New York. 

A greatly increased range of tonal re- 
production ; an increased dynamic range 
with the ability to reproduce sound 
shadings from the merest whisper to the 
full ensemble effects of the symphony 
orchestra ; and virtual elimination of 
extraneous "ground" noises by a new 
system of masking off the spaces on 
the sound track not actually utilized by 
the sound wave itself, are the principal 
features of the new RCA Victor record- 
ing system. 

By way of contrast, the demonstra- 
tion was begun with the showing of a 
reel of film representative of the best 
reproduction of the early days of sound 
pictures. This was followed by a reel 
from a picture representing high present- 
day standards. Next, a Van Beuren 
cartoon subject recorded with the new 
"High Fidelity" system was run off. 
The demonstration concluded with a 
sound recording alone, of the stirring 
Ravel "Bolero." 

With the playing of the first few bars 
of music recorded by the new process, 
there was a perceptible "lift" to the 
sound. Instruments in the orchestra took 




\i 



1 






Left: R.C.A. Photophone new process 
high fidelity (variable area) re- 
corded sound track. Right: Normal 
(variable area) recorded sound track. 



on new life and a delineation rivaling an 
actual performance. Spoken dialogue 
lost the usual metallic quality and took 
on an intimate, human timbre. The 
usual background noises and hissing 
sounds during the extremely soft pas- 
sages seemed absent and the whole ef- 
fect was a revelation of recreated sound. 
According to RCA Victor officials, 
film recorded with the new high fidelity 
system can be used in all types of pro- 
jectors without any adjustments or 
changes, and can be counted upon to 
effect a great improvement in reproduc- 
tion on even the oldest types of equip- 
ment. 

Symmetrical Sound Track 

The high fidelity recording system 
employs a variable area, "symmetrical" 
sound track. Instead of the familiar 
"saw-toothed" effect along one side of 
the sound track, the new recording pro- 
duces a double-edged, symmetrical pat- 
tern, with both edges of the sound wave 
identical in every respect. This is ac- 
complished by the development of a new 
optical system in which a triangular 
beam of light is focused on a horizontal 
opening leading to the sensitized film; 
so that, as the triangular beam vibrates 
in accordance with the incoming sound, 
small and larger portions of its light 
expose the film as it moves past the 
horizontal opening, producing the 
double-edged effect. 

The sound wave image on the de- 
veloped film is clear and transparent, 
while the unused portion of the sound 
track film is left black and opaque. In 
this way, background noises formerly 
caused by shadows of grain in the film 
and minute dirt particles are minimized. 

Reproducing speech and music in a 
frequency range of from 40 to 10,000 
cycles, the new high fidelity system, it 
is stated, provides the widest range of 
reproduction available to the motion pic- 
ture producer. Some idea of the extent 
of this range may be had when it is 
considered that the first sound film did 
not reproduce many frequencies clearly 
above 4000 cycles, and that sound 
systems now in use do not provide re- 
production above 8000 cycles. In terms 
of audible sound this means that the 
subtle overtones, reaching up to 10,000 
cycles, which give vitality and realistic 
timbre to speech and music are now 
faithfully reproduced. 

An important adjunct to the high 
fidelity system is the new "velocity" 




High fidelity recorder. 

ribbon microphone. This new micro- 
phone differs radically from ordinary 
microphones in that instead of the usual 
diaphragm it utilizes a thin strip of 
metallic ribbon which vibrates exactly 
to the velocity of air particles set in 
motion by the sound. It is considerably 
more sensitive than other microphones 
and responds uniformly to the full range 
of frequencies from 40 to 10,000 cycles. 
▲ 

SOCIETY OF MOTION PIC- 
TURE ENGINEERS MEET- 
ING IN APRIL 

THE regular semi-annual Spring 
meeting of the Society of Motion 
Picture Engineers will be held at the 
Pennsylvania Hotel, New York, April 
24 to 28, according to an announcement 
made by the Board of Governors of the 
Society. The semi-annual banquet is 
planned for Wednesday night during 
the meeting. 

W. C. Kunzman, of Cleveland, chair- 
man of the convention committee, has 
appointed Herbert Griffin, of the Inter- 
national Projector Company, chairman 
of the local arrangements committee, 
and plans are already under way for the 
meeting. The meeting will cover five 
full days, due to the abbreviated con- 
vention held last fall and the mass of 
valuable material that has accumulated 
as a result. 

O. M. Glunt, chairman of the papers 
committee, has begun the preparation 
of the program and promises a meeting 
of unusual interest. The number of pa- 
pers will be limited to what can be ac- 
commodated in the allotted time with- 
out haste or crowding. The exhibition 
of newly developed equipment is ex- 
pected to be of particular interest and 
magnitude since an entire year has 
elapsed since the last exhibition was 
held. 

A 

CANADIAN THEATRES 

THERE are at the present time 695 
theatres in Canada, a reduction of 

32 from the figure of a year ago. Of 
these 262 are in Ontario and 112 in the 
province of Quebec. Toronto has 91 
houses. 



Page 14 



Dubbing 



By Eva Elie 

THE problem of dubbing or dupli- 
cating a film, which it is useless 
to set forth in this note, continues 
to arouse everywhere the liveli- 
est controversies. It is a most admi- 
rable subject for dissipating apathy, 
reanimating discussion and proving to 
the readers of newspapers or cinema 
reviews that criticism is never asleep. 

What is it that its enemies charge 
against dubbing ? 

A serious accusation ; that the listen- 
ers hear certain words, while the lips 
of the actors seen on the screen are 
engaged in pronouncing others. 

This is true, but it is becoming less 
and less true. The progress of the 
sound film, due to the union of the 
cinema and the theatre, is continuous. 
There have already been screened films 
which satisfy all the demands of both 
sight and hearing from every point of 
view. The German version of a Metro 
Goldwyn Mayer film "Die Freunde 
Mutter," played by American artists, 
is an example, Wallace Beery and 
Marie Dressier play the leading parts, 
which, when dubbed, give, as far as 
the speech goes, the exact impression 
of listening to any Hamburg sailor or 
any German woman of the people. 
However the actors are seen, whether 
in closeups or long shots, the words 
pronounced in German by their doubles 
correspond perfectly to the lip move- 
ments of the personage on the screen 
talking in English. The difficult mo- 
ments have been overcome by showing 
the actors in profile or making them 
speak from a distance. 

In his paper, "Informations Cine- 
graphiques," Jean Pascal speaks of an- 
other dubbed film which has succeeded 
perfectly, namely, "The Brothers Kara- 
mazoff," adding, however, that the 
dubbed film must always be considered 
an expedient to help out the momentary 
deficiencies of the French production. 

This point of view, though casting 
disapproval on the dubbed film, placing 
it on the level of a tolerable substitute, 
is more to the point than all the accu- 
sations and noisy protests used against 
dubbing which charge it with being a 
brain-muddling, incomprehensible mix- 
ture, a device insulting to the public, 
and so on. At any rate, I propose to 
plead the cause of at least one section 
of the public which desires that dub- 
bing should continue. There comes to 
mind the case of that charming Ameri- 
can actress with the sweet, gazelle-like 
eyes, who, through the sound film, in- 



stead of allowing us to hear a musical 
voice such as her appearance would 
lead us to expect, startled us with a 
rough, rusty, almost timberless voice. 
The result was a martrydom even for 
the most indulgent section of the pub- 
lic, while for the artist, it was suicide, 
or at least moral suicide and as far as 
Europe is concerned for the actress's 
fame as a star. In this case, would it 
not have been much better to perform 
a work of charity for both listeners 
and artist, since, after all, art is a mix- 
ture of illusion and lies, and to dub 
her voice, lending her one such as the 
public wants to hear, and one suitable 
to her appearance and part? 

The process of dubbing, as I under- 
stand it, requires fine taste and an acute 
sense of physical and vocal accords. It 
requires great skill, also, because the 
public ought to be kept in ignorance of 
the subterfuge as it is of other film de- 
vices, and rightly so, since the purpose 
of them is merely to add to the attract- 
iveness of the picture. It would now 
seem that anonymous dubbing is no 
longer possible, because the French 
Superior Cinema Council has decided 
that "no dubbed film can be allowed un- 
less the work of post-synchronization 
has been carried out in a studio or 
studios situated in French territory and 
unless it is shown to the public "with- 
out any attempt to disguise the fact that 
it is a dubbed film, carrying the indica- 
tion of the country where it was origin- 
ally made, the names of the artists who 
acted originally in the picture and the 
names of those who dubbed the parts." 

In this fashion, the problem seems 
definitely settled, but not in the best 
way possible. 

Sub-Titles 

There is also the question of the sub- 
titles or running comment printed at 
the bottom of the picture as was done, 
for instance, in "Sonny Boy," and as is 
still done with success in some modern 
films as "Girls in Uniform." I recog- 
nize that this method seems right when 
we are dealing with dramas or comedies 
of a typically national character, which 
cannot, without becoming ridiculous be 
taken out of their natural living frame- 
work. We cannot, for instance, imagine 
a Bancroft, in "Chicago Nights" speak- 
ing French, or any other language save 
the slang of Chicago bandits. Nor can 
we imagine a Napoleon speaking with 
the accents of a dweller in Whitechapel. 

A third system is to substitute some 
artists by others, and to make as many 
versions of the picture as it is desired to 
issue editions of the same. This method 
places in relief the various character- 
istics of the races, unless there is an at- 
tempt to secure a uniformity of style 
and a modeling of the successive artists 
on the actors who make the first ver- 



PROJECTION ENGINEERING 

sion. The contrasts thus obtained are 
not without interest. 

In the film "L'Opera de Quat 
'Sous." it is easy to define the points 
which divide two mentalities and two 
diverse methods of feeling and reveal- 
ing such feelings. Charles de St. Cyr 
in "Semaine a Paris" — though we no 
longer see his name in connection with 
the piece — wrote a careful study on this 
film which went to show that while in 
the French version of Pabst's picture 
the two principal actors Prejan and 
Florelle accentuated the satirical side 
of the film, illustrating it in a French 
spirit, in the German version, the act- 
ors, taking their roles more seriously, 
gave a certain dramatic heaviness to 
the piece, which was much appreciated 
beyond the Rhine. 

We may classify with this type of film 
the "Arianne, Russian Girl," with 
Elizabeth Bergner in the German ver- 
sion, and Gaby Morlay in the French 
edition. The plot here could develop 
in any country, seeing that the little 
Russian student might go to any foreign 
university, and as a consequence, speak 
the language of the country where she 
was residing. It would have been a 
good plan to choose for the part of 
Arianne a real Russian girl, since it 
could not be supposed that either a 
French or a German actress could find 
in their spirits that indefinable sense of 
life of the Russian soul, which is gen- 
erally referred to as Slav charm. 

Summing the matter up, if we cannot 
condemn outright the methods of dub- 
bing at present in use, which after all 
permit us to see and hear foreign works 
of art which is an international thing 
itself and only capable of improvement 
by contrasts, we must at least exhibit 
great prudence in choosing the persons 
to carry out the dubbing. We should 
safeguard the national character of the 
films as far as possible, because it is 
one thing to translate a book, and a 
very different thing to present a film in 
a language different from the original 
language of its makers, when such a 
film has about it all the evidences of its 
originating country. 

Film adaptors ought to have much 
tact and a wide knowledge of ethno- 
graphy and psychology. {Translated 

from the French.) International 

Review of Educational Cinematography. 

EXPORTS 

A STATEMENT from the Bureau 
of Foreign and Domestic Com- 
merce, Washington, shows that exports 
of American made projectors and 
sound equipment for November, 1932, 
continued in some volume to Belgium, 
France, Italy, Portugal, Spain, Great 
Britain, Canada, Mexico, Colombia, 
Ecuador, India, China and South 
Africa. 



JANUARY. 1933 



Page 15 



Research and preparation 
in motion pictures 



w 



ITH the progress of civili- 
zation, research has become 
an essential part of modern 
life. Comparatively few 
persons engage in research activities, 
but the influence of these few is bound- 
less, even if the personal rewards re- 
ceived are sometimes negligible. 

To research and experiment the mo- 
tion picture owes its existence. The 
drama of the legitimate stage existed 
before the invention of machinery, light- 
ing, artificial scenery, or anything else. 
The only requirements for a play are 
actors and audience — and some outline 
of a play. In the case of the Commedia 
dell'Arte, even written plays were not 
used. 

The case of the motion picture is en- 
tirely different. It was only after con- 
siderable research that cameras and, 
later, moving picture cameras were de- 
veloped. Likewise, about a quarter of 
a century elapsed between the discovery 
of motion pictures and the perfecting 
of accompanying sound recording ma- 
chinery. 

In the mechanical development of the 
motion picture, the value of research 
work has generally been fully appre- 
ciated. However, one of the great needs 
of the film industry at present is a mu- 
seum adequately equipped to store and 
exhibit old forms of motion picture 
equipment, and to have it available for 
study with full descriptions of what is 
often obsolete material. 

A museum of this type has been 
started at the University of Southern 
California, but at present it has neither 
the space nor the endowment to do any- 
thing like what might be done on these 
lines. The project should receive fuller 
co-operation. 

While the main value of the motion 
picture is entertainment value, there is 
also the educational feature and the 
fact that, regardless of what may be the 
true facts, the impressions given by the 
motion picture are liable to remain. 

The motion picture has a distinct 
advantage over the spoken legitimate 
theatre in that spectacular scenes are 
far more within its financial possibili- 
ties. A scene is done only once, and 
that for an audience of millions. Con- 
sequently, it is possible to do things 
upon a much larger scale. 



^Director, University of Southern California 
Kinematographic and Art Museum. 



By Tarbotton Armstrong* 



Many of the inconsistencies of motion 
pictures are due, not to the expense of 
eliminating them, but to the carelessness 
and lack of thought often exhibited by 
both writers and directors. What is 
really missing, incongruous as the 
statement may seem, is a proper com- 
bination of science and art. 

The motion picture industry is over- 
burdened with systems and technicians. 
Every attempt is made to get something 
done that will please the general public, 
and to get it done as quickly as pos- 
sible. Of course, it is true that the big 
companies have their own theatres to 
keep supplied with pictures, but better 
pictures mean longer runs. 

The motion picture offers a great 
field for educated men and women — if 
they are given a chance to break in. 
Eventually, the motion picture field 
will be taken over by college graduates, 
or others especially trained. Many of 
the professions into which the colleges 
are sending their graduates are over- 
crowded — so the field of the motion 
picture will become a desirable one. 

Speed is one of the greatest evils of 
the motion picture industry today. Some 
companies rush through a programme, 
and then close down for several months. 

The great interest in stories is the 
unusual. Creating this by continually 
bringing in ridiculous coincidences will 
end by irritating the cinema public. 

Veterans of the World War are often 
extremely critical as to proper depict- 
ing of conditions during the great strug- 
gle — often to the point of wishing to 
sacrifice the story to some minor point 
of realistic presentation. 

The World War as a theme has been 
widely used, in fact over-used. Some 
of the pictures and pathetic incidents 
have been so badly overdone as to be- 
come almost comedy. But there are no 
doubt hundreds of angles to the World 
War which have never even been 
touched upon. 

Of themes of the past, there is only 
one which has been overdone and that 
is the "Wild West." The unfortunate 
part of it is that many of these 'West- 
erns" have been of inferior grade, while 
the best ones have often copied from 



each other. There is a succession of 
type sheriffs, outlaws, Indians, cov- 
ered wagon caravans, with accompany- 
ing Indian attacks, etc. Yet there have 
been very few motion pictures dealing 
with the pioneer days before the gold 
rush times. This is partly due to the 
character of the country adjoining Hol- 
lywood, but it should be possible to find 
some places giving the right atmos- 
phere of the Eastern coast. 

Included in research, must be a great 
deal of experiment. Let stars be per- 
mitted some of their high-salaried time 
for trying out new characterizations, 
even though nothing be done with them. 
Let the directors of period stories know 
thoroughly the history of the times the 
story depicts — for that matter the actors 
might also be given some study of his- 
tory as a side-line. 

The motion pictures have been so 
popular that the public has seemed to 
take anything that was given it. But 
lately there has been a great deal of 
discontent with the "talkies." The 
talking films demand a higher standard 
of production than the silent pictures. 
The reason is that sound effects serve 
to distract the attention of the audience 
from the general theme of the picture. 
Another reason is that the talking pic- 
ture must become far more closely 
allied to the stage play than previously. 
— International Review of Educational 
Cinematography. 



AVERAGE THEATRE SHOW 
HOURS 52.8 WEEKLY 

THE average theatre is open to the 
public 52.8 hours per week and the 
lost playing time per theatre, due to 
emergencies, is .088 minute per week. 

The above averages are the result of 
a survey made by the Operating Plan- 
ning Division of Electrical Research 
Products in the course of weekly duties 
and covers almost 5,000 theatres or, ap- 
proximately, 90 per cent of the theatre- 
using Western Electric equipment. 

Both the highest and the lowest aver- 
ages of show hours occur within the 
northeastern division, varying from a 
high of 81.9 show hours per week among 
129 theatres in Manhattan to a low of 
40.6 hours in 122 theatre- of the Scran- 
ton, Pa., district. 



Page 16 



A simplified method for 
the determination of 
harmonics in vacuum 
tube circuits 



By Gilbert Smiley 5 



Foreword 



IN the design of audio-frequency am- 
plifying equipment it is desirable to 
know in advance as many of the 
factors determining the ultimate 
performance of the equipment as can 
readily be predicted. Increasingly im- 
portant among these factors, in view of 
the rapid progress in electro-mechanical 
audio-frequency technique, is that of 
fidelity. Fidelity is, of course, a matter 
determined by two factors in amplify- 
ing equipment, the response character- 
istic and harmonic distortion. The re- 
sponse characteristic may pretty well 
be predetermined by ordinary consider- 
ations of transformer design plus con- 
siderations of the other involved power 
supply and transmission networks, as- 
suming sufficiently accurate data, and 
a modicum of experience and theoretical 
background. Harmonic distortion, how- 
ever, does not so readily lend itself to 
predetermination, involving, as it does, 
not only the computation of distortion 
due to such iron-cored coupling devices 
as may be interposed in the network or 
to regulation of power supply devices, 
but of the distortion introduced by the 
vacuum tube repeater devices that form 
the essential working parts of the 
system. 

It is true that any steady state wave- 
form may be analyzed in terms of a 
fundamental and harmonics, but the 
procedure is relatively laborious, re- 
quiring the use of complex sched- 
ules and considerable time. For these 
reasons, the general procedure has been 
to let the subject of harmonic distor- 
tion more or less take care of itself 
until after an experimental model has 
been constructed, at which time meas- 
urements may be made, sometimes 
rather sketchily, to determine the har- 
monic content of the output wave. 

Such a procedure, naturally, mili- 
tates against the achievement of a bal- 
anced design, for, of what use is it to 
design coupling devices for given har- 

*Chief Engineer, Samson Electric Company 
Canton, Mass. 



monic limits without a rational con- 
sideration of the harmonic content un- 
avoidably introduced by the vacuum 
tubes? To avoid this particular design 
dilemma, the author has developed a 
method of harmonic determination 
which seems to meet commercial re- 
quirements closely enough to be of real 
value in pre-analysis of a given design, 
without involving any particularly la- 
borious technique. Such a method 
should permit the designer of audio- 
frequency amplifying systems to hit 
more closely than previously the desired 
design limitations without necessitating 
any computations not justifiable in view 
of the results. 

Distortion in Vacuum Tubes 

Distortion in vacuum tube repeaters 
arises through non-linearity in the 
transfer characteristic between input 
and output waves. Using data which is 
made available by tube manufacturers, 
the design engineer can readily deter- 
mine the transfer characteristic for any 
type of tube or combination of tubes. 
For purposes of harmonic determina- 
tion, such a plot is most conveniently 
made with cartesian co-ordinates, plac- 
ing instantaneous input signal volts 
along the X axis and instantaneous load 
volts along the Y axis. If this be done, 
the curve represents an operator, which 
when applied to the input wave will 
yield the output wave. As an operator, 
the transfer characteristic must contain 
within itself the elements that will in- 
troduce ultimate distortion, and the 
problem becomes one of devising a 
method of analysis applicable to the 
transfer characteristic which will yield 
the desired result, i. e., the per cent 
harmonic content in the output wave. 

Single Class A Repeaters 

The distortion introduced by a prop- 
erly operated class A repeater consists 
mainly of second harmonic. Owing to 
the resemblance of the transfer charac- 
teristic to a quadratic, it is entirely 



PROJECTION ENGINEERING 

reasonable for purposes of pre-analysis 
to assume that the class A characteristic 
is, in fact, quadratic in nature. This 
assumption, of course, must except cer- 
tain pentode and tetrode repeaters, 
whose characteristics are somewhat 
more complex. However, it is, for ex- 
ample, entirely applicable to triode 
stages used as voltage amplifiers or 
power stage drivers, or even to power 
triodes. 

The Quadratic Transfer Characteristic 

Fig. 1 illustrates a typical transfer 
characteristic expressed in terms of in- 
stantaneous signal and load volts. The 
construction is extended to include a 
sinusoidal input wave of peak ampli- 
tude, K, and the resulting output wave 
with its components individually plotted. 
If the assumption be made that the 
characteristic is approximately a quad- 
ratic, its equation will be as follows : 

y = ax 2 + bx (1) 

where y == instantaneous load volts 
x = instantaneous signal volts 
a and b are unknown constants. 

The choice of origin is such that the 
constant term of the quadratic is zero, 
and thus may be omitted. 

If the equation of x is given by 

x = K sin wt (2) 

then y, from equations 1 and 2 becomes 

y = aK 2 sin 2 «n + bK sin ">t (3) 

aK 2 aK 2 

= cos 2&>t + bK sin ">t. . (4) 

2 2 

where the first, second and third terms 
are the rectified, second harmonic and 
fundamental components respectively. 
Since the coefficients of the second and 
third terms represent the peak ampli- 
tudes of the second harmonic and fun- 
damental, the harmonic voltage, in per 
cent of fundamental, may be expressed 
as follows : 



% H 



aK 2 
100 — h- bK 
2 



aK 
100 — ....(5) 
2b 




JANUARY, 1933 



Page 17 



and the problem becomes merely one of 
evaluating this expression. To do this, 
it is necessary to find the value of con- 
stants, a and b, in terms of x and y. 
Since the curve is not necessarily a true 
quadratic, the points investigated should 
be chosen with an eye towards selecting 
the quadratic which most nearly repre- 
sents the actual curve. For this reason, 
the points + K / 2 and — K / 2 on the 
X axis are used, since they, with the 
origin, divide the active portion of the 
curve from — K to + K into four 
approximately equal intervals. Substi- 
tuting the values + K / 2 and — K / 2 
into equation (1), yields equations (6), 
and (7). 

aK 2 bK 
Yi = — + — (6) 

4 2 

aK 2 bK 
Y a = (7) 

4 2 

Adding equations (6) and (7) yields 

aK 3 
Yl + Y 2 = — (8) 

2 

from which 

Y, + Y 2 

a = 2 (9) 

K 2 

Subtracting equation (7) from equation 

(6) yields 

Yi — Y 2 = bK (10) 

from which 

Yi — Y» 

b = (11) 

K 

Substituting the values of a and b from 
equations (9) and (11) into equation 
(5) gives the desired result. 

Yi + Y 2 

% H. = 100 (12) 

Yi — Y 2 

and it should be noted that Y 2 is a nega- 
tive quantity, so the algebraic sum is an 
arithmetic difference, and the algebraic 
difference is an arithmetic sum. 

Checking the Quadratic 

If there be a doubt that the result is 
incorrect, it may readily be allayed or 
justified by superimposing the curve of 
equation (1) with the a and b values 
yielded by equations (9) and (11) upon 
the transfer characteristic in question. 
The author has examined several tubes 
in this way, and, for class A triodes 
has found concurrence to lie within the 
limits of plotting accuracy in some in- 
stances, and always within limits suf- 
ficiently approximate to determine the 
suitability or non-suitability of the de- 
sign. ..-.,-: 
Symmetrical Repeaters 

If two class A or class B repeaters be 
symmetrically disposed in a circuit so 
that their grid voltage is changed 
equally and oppositely by impressed 



signal voltages, and the repeaters are 
so nearly alike as to be considered iden- 
tical, then even harmonics are, in ef- 
fect, suppressed, either entirely or suf- 
ficiently to be considered quite negligi- 
ble. In such cases, the harmonic distor- 
tion will be odd in nature, and, for tri- 
odes operated with a negative grid bias 
at such signal amplitudes that the grids 
never go positive, will consist mainly 
of third harmonic. Quite generally, 
class A repeaters so operated will have 
a negligible harmonic content, again ex- 
cepting "trick" tubes of the pentode or 
tetrode type. 

The Cubic Transfer Characteristic 

Fig. 2 illustrates a typical symmetri- 
cally disposed transfer characteristic, 
with the same choice of axes and origin 
as in Fig. 1. As in Fig. 1, the con- 
struction includes source and output 
waves and components. This character- 
istic is closely approximate to a cubic, 
so, as before, the assumption that it is 
a cubic is made. 

y = ax 3 + bx (13) 

where x, y, a and b as are in equation 
(1) and there are no other terms be- 
cause of proper choice of origin. 

The equation of X is as in equation 
(2), so 
y = aK'sinV + bK sin <"t (14) 

3aK 3 aK 3 

= ■ sin w t + bK sin <»t 

4 4 
sin 3«t (15) 

where the first and second terms to- 
gether form the fundamental and the 
third term is the third harmonic. 
When the input wave is such that 

sin «t = 1 (16) 

then 

sin 3<»t = —1 (17) 

at which point equation (15) may be 
rewritten 

3aK 3 aK 3 

Yi = + bK + — (18) 

4 4 

= aK 3 + bK (19) 

Furthermore, at the origin, the cubic 
terms are of negligible magnitude and 
the slope of the curve is determined by 
the constant, b, so that the line termi- 
nating in the value of 

Y 2 = bK (20) 

is tangent to the curve at the origin. 

As in the earlier case, the per cent 
harmonic may be expressed in terms of 
peak amplitudes of fundamental and 
harmonic, so 

aK 3 3aK 3 \ 

% H. = 100 — -M bK H .... (21) 

4 \ 4 / 

aK 2 

= 100 (22) 

4b + 3aK a 







Ttou^e 2 



From equations (19) and ( 20; may be 
derived 

Yi — Y 2 = aK 3 (23) 

from which 

Yx — Y 2 

a = (24) 

K° 

and, from (20) 

Y 2 

b = — (25) 

K 

Substituting the values of a and b from 
equations (24) and (25) into equation 
(22), yields the result 

Yi — Y 2 

% H. = 100 (26) 

3Yi + Y 2 

Checking the Cubic 

The result may be checked, as in the 
quadratic solution, by superimposing the 
cubic having the equation (13) with con- 
stants, a and b, from equations (24) 
and (25). If the deviation is negligible, 
the error in the result is likewise. The 
author has used this method with grati- 
fying results on class B 245's, the grids 
of which were not driven positive, and 
believes it applicable to other triodes 
so operated. 

Some Results of the Application of 
This Method 

It has been most interesting to check 
up on certain designs by the applica- 
tion of this method of analysis. Know- 
ing the tube, operating voltages and 
loads, it becomes apparent that most 
designs make the serious mistake of 
generating a large per cent of the total 
harmonic voltage in stages earlier than 
the output. Often the class A tube im- 
mediately preceding the power stage 
will introduce five per cent second har- 
monic while the power stage, push-pull 
class A triodes, will be practically dis- 
tortionless except for the effects of 
coupling units. Certainly, if the method 
proves useful, more balanced designs 
should result. 



Page 18 



PROJECTION ENGINEERING 



The closeup 

By C. H. Barnick 

A 

One of the greatest tech- 
nical and artistic advances 
made by the film 



ONE of the most important ad- 
vances in the development of 
the film occurred on the day 
when, for the first time, a 
cinema camera, furnished with a Jupi- 
ter lamp, was brought close up to the 
face of a cinema actor, and the "close- 
up" picture was made. This event 
marked an important line of differ- 
entiation between the cinema and the 
stage. The advent of the closeup 
marked out an individual path for the 
film, and made it what it is today : an 
artistic microscopy of acting. 

If we watch an actor on the stage, we 
can only see him in the whole. If he 
laughs or weeps, if he speaks a mono- 
logue in angry mood, it is always the 
whole man who laughs or weeps, the 
whole of an angry person that we see. 
Thus, the actor forms in a certain 
sense a convention apart. He is an in- 
divisible being, a unit that cannot be 
destroyed, or resolved into various 
parts. 

This was originally the case with the 
film. Formerly the film was merely 
the transposition from the plastic stage 



to the two dimensional screen, with, 
additionally, the surrounding setting or 
landscape. 

Then came the closeup, and suddenly 
the actor, till then indivisible, was split 
into a thousand separate fractions of 
the event in course of being acted. 
With the closeup, it is possible to dif- 
ferentiate fractions of a smile, the twist 
of the mouth, or an eyebrow raised in 
wonder, and keep the pose for a whole 
scene. 

Complete dramas or entire comedies 
can be revealed by the closeup in an 
actor's or actress's face, but who would 
have thought it possible before the in- 
troduction of the closeup? The finest 
of opera glasses will not, even in the 
best circumstances, allow a spectator 
at a theatre to see the actor's face torn 
with anguish, save in natural size. But 
the face does not live a life of its own. 
It is only the mimic accompaniment of 
the text, and joins this in an indivisible 
unity. 

This is the reason why certain little 
peculiarities and mannerisims of cele- 
brated cinematographic actors have a 
very great importance, and have be- 
come identification signals for the en- 
thusiastic public. Chaplin's mous- 
taches, Douglas Fairbanks' luminous 
mouth, Harold Lloyd's eyes, with their 
half ironic, half stupid expression would 
never have reached world-wide fame 
had their owners been stage actors in- 
stead of film stars. Charlie Chaplin's 



down at heel boots, or the good- 
natured childish face of Jannings, or 
the coquettish laugh of Lya de Putti 
would never have obtained on the stage 
the effect they make in the film with the 
closeup. 

Long before closeup was thought out, 
Urban Gade wrote that the film was not 
for psychological dramas, that it ought 
not to represent scenes limited to the- 
atrical literature, but, on the contrary, 
as an exponent of animated pictures, it 
should simply transport the spectator 
into a fantastic world of fables. Such 
a statement from one of the most theo- 
retical of stage managers would per- 
haps have been accepted if the closeup 
had not opened a new path for the film 
namely, that of the interior dramas re- 
flected in psychological details rendered 
visible. 

Once a film was made in which noth- 
ing but hands was shown. Imagine a 
stage play where such a thing hap- 
pened ! Why should we not have in a 
near future the possibility of seeing 
films showing us only the tragedy of a 
pair of eyes, or the ironic play of the 
mouth? Films which would be all 
closeups and advertised as such. 

With the possibilities given by the 
slow motion projector and the speeded- 
up film, the closeup is, so far, the big- 
gest artistic advance made in the film 
world. — (Translated from the German.) 
— International Review of Educational 
Cinematography. 



Trinidad market for motion picture sound reproducing apparatus of 

American manufacture 



DISCUSSIONS as to the possi- 
bilities for the sale of American 
talking picture equipment in 
Trinidad, British West Indies, 
to small theaters with the leading film 
exchange in Trinidad and the two firms 
who are interested and in a position to 
assume the responsibilities of installing 
such equipment, led to the conclusion 
that, for the present, there is no pros- 
pect for the sale of such equipment here. 
Small outlying theaters are entirely 
dependent for their patronage on labor- 
ing classes, largely employed by cocoa 
estates and other producers of agricul- 
tural products. Severe retrenchment in 
all Trinidad's agricultural industries 
has necessitated lower wages and a ra- 
tioning of work among laborers on es- 
tates, usually amounting to two or three 
days. 

Reduced purchasing power is felt 
much more keenly in the country dis- 



tricts than in the cities, and the attend- 
ance at country theaters has fallen off 
considerably. Small theater owners find 
themselves in a very unfavorable 
financial position, with little prospect 
of material improvement in view. 

Obviously these small theater owners 
are not in a position to purchase sound 
reproducing equipment outright and 
financing would be necessary. As Trini- 
dad banks apparently refuse to consider 
such propositions, the normal course 
would be for one of the two firms 
equipped to handle such apparatus to 
install the equipment on a time-payment 
basis. Both these firms have concluded 
that they would not be adequately pro- 
tected in financing the installation of 
the equipment and have deferred such 
a venture until patrons in those areas 
are in a position to patronize the thea- 
ters and until exchange and trade con- 
ditions become more normal. 



Sound reproducing apparatus of 
American manufacture is being in- 
stalled in the two new theaters under 
construction in Trinidad, and will be 
installed in the theater that is being 
remodeled, with the lifting of a court 
injunction restraining the remodeling 
operations. 

Attempts made to install sound repro- 
ducing equipment of British manufac- 
ture in various Trinidad theaters have 
been unsuccessful. American equipment 
is greatly preferred by film distributors 
and theater owners for its quality, even 
though in view of a depreciated cur- 
rency British equipment can be pur- 
chased much more cheaply. It is be- 
lieved that when general economic con- 
ditions in Trinidad improve, American 
equipment will be purchased. — Vice 
Consul Obert Ronald Nelson, Jr., Trini- 
dad, B. W. I. 



JANUARY, 1933 



Page 19 



Some projection observations 



IN observing the projection in a 
number of large and small theatres 
1 noted a number of faults that a' 
little care and thought would have 
easily prevented. I am passing my 
observations on to my fellow projec- 
tionists in the hope that they will derive 
some benefit from them. 

In both large and small houses the 
patrons sitting near the booth are often 
annoyed by the "clack" of the change- 
over apparatus. This can be easily 
prevented by the judicious use of small 
felt or asbestos fiber strips. The use 
of glass in the ports to reduce booth 
noise may be eliminated if the inside 
of the port is lined with "Ozite" or 
some other sound absorbing material. 
If glass is used it must be kept in mind 
that the glass in the projection ports 
must be kept just as clean and free from 
dust as the projection lens. Care should 



By William H. Reasin 

be taken that glass used in the ports 
fits tightly enough to prevent rattling 
under the force of the ventilating sys- 
tem. Where there are large ports, such 
as spot ports, it is a good idea to have 
shutters made that can be closed over 
that port when it is not in use. The 
"snap" of the projector gate and rollers 
can be heard outside the booth unless 
care is used in releasing these parts. 
It should be kept in mind that the 
patrons sitting directly beneath or in 
front of the booth are entitled to as 
much consideration as those farther 
from the booth. 

A clean cut frame for the picture may 
be obtained if the aperture is cleaned 
with a soft lintless cloth after each reel. 
All the screen not covered by the picture 
proper should be covered with scrim. 
The use of a vacuum cleaner on the 
horn side of the screen will do much 

AAA 



toward insuring sharp sound. The 
booth should be cleaned with a vacuum 
cleaner, as it is a sure way to prevent 
the raising of dust harmful to both 
sound and projection equipment. If 
the booth has an uncovered cement floor 
it is imperative that it be given a good 
coat of cement paint. 

Particularly in some of the smaller 
houses there was noted a series of very 
disconcerting white flashes near the 
reel ends, made as cues by some mis- 
guided projectionist. The projectionist 
getting a print in this condition may 
help the situation with the use of black 
India ink and a fine brush. Using the 
brush and ink, paint out all marks on 
the non-emulsion side of the film, being 
careful to keep the sound track clear. 
This treatment will reduce the sudden 
flashes and make them unnoticeable to 
the audience. 



Modem ideas in public-address work 

Submitted by winners in contest 
conducted by S. N. Shure 



THE contest conducted by S. N. 
Shure, president of Shure Broth- 
ers Company, Chicago, through 
the columns of Projection En- 
gineering, brought to the surface 
many money making ideas. The best of 
the suggestions are to be tabulated and 
passed along to all of the individuals 
and companies participating in the big 
drive for sound equipment promotion. 

Herewith we present the names of the 
nineteen winners — those whose entries 
were judged to be the best: 

First Prize Complete portable 

public-address system, donated by 
Silver-Marshall, Inc. won by Rob- 
ert H. Lehfeldt, in care of Flagler 
Radio Company, 1068 W. Flagler St., 
Miami, Fla. 

Second Prize Microphone mix- 
ing panel, mixing control and pre- 
amplifier, donated by The Webster 
Company won by Paul L. Thorn- 
burg, in care of Foster-Thornburg 
Hdwe. Co., 851 Jefferson St., Hunt- 
ington, W. Va. 

Third Prize Combined voltage 

and power amplifier, "The Universal 
Amplifier," donated by Samson Elec- 
tric Co. won by George Gimera, 

Bradford, Penn. 

Fourth Prize 
microphone amplifier, 




Single position 
donated by 



S. N. SHURE 

Webster Electric Company won 

by Nathan D. Reiss, in care of Public 
Address Systems, 340 E. Grand Blvd., 
Detroit, Mich. 

Fifth Prize Two-button micro- 
phone, floor stand, 25-ft. shielded 
cable, donated by Shure Brothers 

Company won by B. C. Burden, 

in care of Lincoln Telephone & Tele- 
graph Co., Lincoln, Nebr. 

Sixth Pr