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Full text of "Projection Engineering (Jan-Dec 1931)"




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AUDIO-VISUAL CONSERVATION 
at The LIBRARY jf CONGRESS 





4fe $M* 






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 



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ENGINEERING 

Television - Sound and Light Projection - Theatrical Engineering 




Airplane View of Kodak Park 

(Eastman Kodak Company, Rochester, N. Y.) 



JANUARY 
1931 



THE JOURNAL OF THE SOUND AND LIGHT PROJECTION INDUSTRIES 



A 




THEATRES-AIRPORTS 
CONVENTION HALLS 
AMUSEMENT PARKS 

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RACON'S LATEST TYPE 
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Portable Horn 
Model 3320A 



New type portable horn num- 
ber 3320A air column length 
slightly less than 7 feet. Oval 
bell 27" x 35", depth 28" 

Can be separated in two halves 

for portability. Excellent for 

speech as well as music. 



Air Column slightly less than 10 

feet. Depth 30 inches. Bell 30x40 

Inches. Weight 30 pounds. 



Improve your Sound Equipment with RACON Speakers and Watch Results! 

Our Latest Catalogue Is Yours Upon the Asking 



RACON HORN 5325 

Especially Appealing Where There 
Is Very Little Space Between the 
Screen and Wall 



Amplifies as perfectly as the 

parent horn, No. 4320, on both 

speech and music 

Patented non-vibratory, non-porous 
material and construction, plus 
light weight, which makes for per- 
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These outstanding features of 
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x4 

r$ JANUARY, 193! Page I 

INew Liffht Exceeds 






. . . Sun's Brilliancy 



M, 



.ODERN projection calls for a light source equaling 
and in some cases exceeding the brilliancy of the sun itself. 

Sound, color, and wide films, with long throws on porous 
screens now demanded by the modern theatre, have called 
for a most intense and active program of research and 
development to keep National Projector Carbons ahead of 
the requirements of modern projection. 

The concentration of large quantities of electrical energy 
in slender carbons, while keeping the light confined to a 
point source, represents a most remarkable advance in 
lighting practice. 

The results of this development program have been the 
production of National Projector Carbons of the highest 
quality with economies which make carbon cost* extremely 
low in comparison with other important items needed for 
the successful operation of the theatre. 

NATIONAL 

PROJECTOR CARBONS 

National Carbon Company will gladly cooperate ivith 
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 I I I ■ ■ and Carbon Corporation 

Branch Sales Offices: New York Pittsburgh Chicago San Francisco 




2>„li\\^ 








Projection 



Engineering 



Applicant, 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. Ill 



JANUARY 
1931 



Number 1 



Contents 



Editorial 4 

Motion Pictures in Color By Gordon S. Mitchell 7 

Line Voltage Problems and Solutions . By J. W. Harmon 1 

Monitoring Sound Motion Pictures, Part III 

By Charles Felstead 12 

Radio Television is Really Here . . By Austin C. Lescarboura 1 6 

A Three-Element Glow Lamp for Sound Recording 

By Verne T. Braman 19 

Wide Film and Third Dimension . . . .By James R. Cameron 2 1 

Microscopic Photography 22 

A Revolutionary Advance in Sound Recording 

By Charles Fels f ead 23 

Projectionists' Routine Tests , By D. C. McGalliard 24 

What is the Decibel? By Gordon S. Mitchell 26 



Departments 



News of the Industry and New Developments 28 

Index of Advertisers .30 



Bryan S. Davis 

President 

James A. Walker 
Secretary 



Entered as Second Class Matter 

at the Post Office at Albany, 

N. Y., October 9, 1929, under 

the act of March 3, 1879. 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 
52 Vanderbilt Ave., New York City 

Publication Office — North Broadway, Albany, N. Y. 

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

Cleveland Office — 10515 Wilbur Ave. — James C. Munn Mgr 

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

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

San Francisco Office — 318 Kohl Bldg. — R. J. Birch. 

Los Angeles Office — 846 S. Broadway — R. J. Birch! 

New Zealand — Tearo Book Depot — Wellington. 



Sanford R. Cowan 
Advertising Manager 

]. E. Nielson 
Circulation Manager 



Yearly subscription rate $2.00 
in U. S. and Canada. 

Yearly subscription rate $3.00 
in foreign countries 



JANUARY, 193! 



Page 3 



KLZ 
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WPCH 
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WHBC 
WAAT 
WBRE 
KTSL 
KVOS 

WDGY 
WEBR 
WGBB 
WHBV 
WJBO 
WOR 
KGKY 
KFVS 
KGIR 
KWCR 
KWKH 
Etc., Etc. 



The Standard By Which 

Others Are Judged 

And Valued 




% t • Professional 

llicho-Chmmalir pick ui' 



RADIO 

BROADCAST STATIONS 

Must Use The Best! 

In scores of leading broadcasting stations far too numerous to 
get them all on this page .... after strenuous tests where 
PRECISION and QUALITY counted most .... the ELEC- 
TRO-CHROMATIC Pick-Up has been adopted as standard 
equipment. What is the moral for YOU? That you COULDN'T 
INSTALL A BETTER PICK-UP IN YOUR THEATRE AT 
ANY PRICE! Think it over. Here is science's ultimate 
development in electrical reproduction .... a broad line, 
priced to suit every purse and purpose . . . with POLYPHASE 
(Tone Controlled) PICK-UP to furnish absolute control of 
bass and brilliancy . . . accommodating the music to the 
tempo of the scene being shown on the screen! Why in the 
name of common sense should any projectionist take a chance 
with equipment of sub-AUDAK CO. standard! 



KOL 
KPCB 
KSCJ 
WBZA 
WCOA 
KWKC 
WDSU 
KGCX 
WGBI 
WHDI 
WJBW 
WHBU 
WOL 
KFYO 
KGRS 
CFBO 

WHBY 
KYW 
WPAD 
WAGM 
KTK \ 
WCCO 
WCX 
WEAN 
WFBE 
WHAP 
WIXA 
WJAG 
WEBC 
KFQW 
KFYP 
KJR 
CKCK 
KDFN 
Etc., Etc. 



Let your Jobber Demonstrate Our Latest Models . . . Particularly the POLYPHASE Development 
Which Gives You REMOTE CONTROL From The Pick-up! 

The AUDAK COMPANY 

565 Fifth Ave. New York, N. Y. 

"Creators of High Grade Electrical and Acoustical Apparatus Since 1915" 



E d i t o 



i a 



January, 1931 



THROUGHOUT the 
I United States and Can- 
ada there are thousands of 
young men who have before 
them opportunities for per- 
sonal advancement, in but 
We refer to sound-picture pro- 



OPPORTUNITIES 

FOR 

PROJECTIONISTS 

few cases sensed, 
jectionists. 

Within two or three years past a new art has 
come into use — the art of sound amplification. It 
requires some degree of imagination to visualize 
the possible practical applications of the new 
science. Of course, talking pictures are giving 
theatres added earning power and, as reproduction 
is improved all along the line, mechanized enter- 
tainment will gain new artistic placement in the 
amusement field. 

In addition to> the theatre field there are devel- 
oping many commercial applications for the equip- 
ment and instruments now in the hands of theatre 
projectionists. Reference here is to audio amplify- 
ing equipment and to uses of the phototube. 

Ordinarily a projectionist if he makes a success 
of his theatre work finds it necessary to devote 
time to the job in addition to that put in in the pro- 
jection room. But, being first on the ground in 
thousands of communities, in knowledge of and 
experience with these new tools, the projectionist 
with a business head will overlook opportunity if 
he does not capitalize his advantage. 

The limitations of the natural range of voice 
and other sounds have been removed. Audio 
amplifying systems are made by many dependable 
manufacturers. A hundred industries have uses 
for phototube operated systems, and a question 
here presented is: who will show these industries 
how they may use these new gifts of science to 
advantage and profit? 

Nine of every ten fire alarm superintendents 
and about the same proportion of police signal 
superintendents in ten thousand communities were 
ex-telegraph employees. These men were on the 
ground and were familiar with the required instru- 
ments when the need arose. They capitalized 
their opportunities. 

The daily mail reaching Projection Engi- 
neering discloses that demand is growing for 
information about these new developments and 
for men who have a working knowledge of the 
devices used. 

A word to the wise .....! 



TELEVISION 

IN 

1930 

large scale. 



THERE are eight companies 
now engaged in designing 
equipment for television trans- 
mission and reception. A tele- 
vision parts merchandizing idea 
is to be launched soon on a 



Occasionally there is published a story purport- 
ing to record that the large radio manufacturing 
companies are not interested in television. The 
following is from the annual review of the Gen- 
eral Electric Company: 

"Television was employed for the first time as 
part of a regular performance in a theatre, the 
television images being transmitted by radio from 
a studio located about one mile from the theatre. 

"The active images of the performers were 
reproduced upon a screen 6 by 7I/0 feet, and were 
readily visible to those seated in the back rows of 
the balcony. The light impulses were transmitted 
on a wavelength of 140 meters, and were accom- 
panied by voice and sound effects. 

"This increase in area of the projected image 
from the previous maximum size of about 14 
inches square to an area equivalent to about one- 
fourth that of the standard motion-picture screen 
was rendered possible by the introduction in the 
projection optical train of a light valve operating 
on the principle of altering the direction of polar- 
ization of a beam of polarized light by passing the 
beam through an electrostatic field. This light 
valve thus renders possible the use of more power- 
ful rays of light than have heretofore been prac- 
ticable in television projection. 

"A television picture which had traveled 
approximately 20,000 miles through space was 
received with a fair degree of accuracy, thereby 
establishing a distance record for television recep- 
tion. The picture, a rectangular design in black 
on a white card, was transmitted by the short- 
wave station, W2XAF (31.48 meters) at Sche- 
nectady, N. Y., received in Sydney, Australia, by 
station VK2ME, rebroadcast by that station 
(28.8 meters), and received back in Schenectady 
in about an eighth of a second." 




*nJck^mm.i 



1 



Edit 



or. 



JANUARY, 1931 



Page 5 



METALLIZED 
RESISTORS 



n .Sound pictures 




AMONG the many scientific contributions which have 
-^A made talking pictures possible, none is more im- 
portant than the use of amplifiers with our resistors. 

This scene illustrates the use of our Metallized Resistors 
by Universal Sound Pictures. 

An industry which cannot profit by the use of electron 
tubes is indeed rare, and an electron tube circuit which 
cannot employ resistors to improve its performance and 
at the same time reduce its first cost, is equally rare. 
Whenever resistors are used, leading engineers find 
there is no substitute for the International Resistance 
Company's resistors. 

-Warfc by the MuIhts of 
DURHAM # # . 




INTERNATIONAL RESISTANCE CO. 

2006 CHESTNUT ST. PHILADELPHIA, PA. 



H 




Blue Seal Heat Resisting Improved Film Traps 

FOR SIMPLEX PROJECTORS 

MADE OF AN IRON ALLOY 

Guaranteed not to Warp under the intense 

heat of the Arc Spot. A necessity for the 

Perfect Projection of "Sound" Pictures 

B-16 Film Traps with Sliding 
Double Round Corner Aper- 
tures, one Aperture for Disc 
and Silent Film and one cut 
Proportional for Movietone 
Film to be used with our 
Adaptors $30.00 

B-17 Sliding Double Aperture 

Plate 6.00 

B-24 Film Trap with individual 
mats for silent, movietone 
and magnascope effect. Traps 
complete with all mats 30.00 

B-20 Master Plate to hold mats 
stationary 1 . 50 

B-21 Standard Aperture with 

Square Corners 1.50 

B-22 Proportional Movietone 
Aperture with Square Cor- 
ners 1 .50 

B-23 Blank Mat (CAN BE 
CUT ANY SIZE APER- 
TURE) 1.50 

Manufactured by 

RLXJE SEAL PRODUCTS CO., Inc., BROOKLYN, N. Y. 

260 WYCKOFF ST. 
Manufacturers of Motion Picture Accessories Since 1913 




Page 6 



PROJECTION ENGINEERING 




«J Light beam less than .0005 
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Projection Engineering 



JANUARY, 1931 



Motion Pictures 



in 



Col 



or 



By Gordon S. Mitchell* 



WHILE motion pictures in 
color have been a labora- 
tory possibility since 1902, 
it was not until Warner 
Brothers released their production "On 
With the Show" that an all-color mo- 
tion picture was a commercial possi- 
bility. This production served to 
arouse the public interest in color and 
was followed shortly after by the 
"Hollywood Revue" and several short 
subject releases. Since that time there 
have been many all-color productions 
photographed, some of which, of 
course, have been more successful than 
others. Within the last half year, the 
box office appeal of color has seemed 
to be on the wane — for which fact 
various reasons have been assigned. 
However, as the art of color cinema- 
tography advances and the pictures be- 
come more perfect, the public interest 
will again become manifest in color. 

There are two possible methods of 
producing color motion pictures today ; 
— the additive, in which certain colors 
are added to white in the process of 
photography and development of the 
film, and the subtractive, in which cer- 
tain colors are subtracted from the 
colors left upon the film during these 
processes. Color filters are passed be- 
tween the lens and film in such a way 
that only certain rays of light are 
allowed to register upon the film at 
any given instant. Both of the two 
main commercial processes operating 
in Hollywood at the present time are 
subtractive. 

If we accept the wave theory of 
light transmission — that is, that light, 



like sound, is a wave motion — we can 
readily explain the separation of white 
light into its component colors. At 
the red end lie the long wavelengths 
and at the violet end the short. Inter- 
mediate lengths make up the color 
which lies in between these two ex- 
treme colors, such as yellow, orange, 
green and blue. Ordinary white light 
is composed of a combination of all 
wavelengths. If white light, such as 
sunlight, be passed through a crystal 
prism, it will be broken up into its 
component colors, due to the difference 



An Informative Semi-Tech- 
nical Account of the Vari- 
ous Processes of Producing 
Color Films 



"Sound Department, Universal Pictures Corpn. 



in the degree of bend experienced by 
the different wavelengths. Thus, the 
red end of the spectrum (as the light 
which is broken up into its fundamental 
colors is called) will be refracted, or 
bent the least, while the violet end will 
be bent the most. The light waves of 
different lengths, when they impinge 
upon the eye result in the various color 
sensations in the brain. The basic 
problem of color cinematography is to 
separate all of the light into its funda- 
mental colors, procure a record of 
these colors upon the film, fix that 
record permanently, and at any desired 



time in the future project the picture 
which has been put onto the film upon 
a screen in such a manner that the 
record will again combine into the 
original colors. 

The Spectrum 

While there are only seven pure 
colors in the spectrum of white light, 
there are over two hundred and thirty 
colors which may be encountered in 
color photography. However, these 
colors are all derived from the funda- 
mental colors. If the spectrum be 
thought of as a circle, it is a fact that 
there are four principal points upon 
this circle occupied by the red, yellow, 
green and blue. Each of these four 
colors blends into the two adjacent 
colors, forming the intermediate colors 
which lie between the principal points, 
such as orange, blue, green, violet, etc. 
Any three of these colors, combining 
in certain given ways, may be made to 
produce any one of the more than two 
hundred and thirty color combinations 
of human experience. Why this is true 
has not yet been determined, yet it is 
a fact which has been scientifically 
proven. One of the most common com- 
binations used in color work is that of 
red (or orange red), green and blue. 
These three colors, if combined in equal 
quantities will give white light, while 
if they be combined in unequal quanti- 
ties will give some one of many colors. 
Ey a proper combination of these base 
colors, any desired color may be 
procured. 

Color History of An Object 

The photography of motion pictures 
in color at the present time depends 
upon the fact that if we first make a 
record of all of the red rays which are 
reflected by the object being photo- 
graphed, then of all of the green, then 
of all of the blue, we will have a com- 
plete color history of that object. Then 
in order to reproduce our record, we 
must recombine these three separate 
records simultaneously upon the screen 
in the same proportions in which they 
existed in the object. The first color 
photography did just exactly this, — 



Page 8 



PROJECTION ENGINEERING 



three photos were taken in quick suc- 
cession, each obtaining- one color 
record. The red, the green and the 
blue were separately photographed by- 
passing color filters in the correct suc- 
cession before the lens. The film and 
filters were synchronized in such a way 
that every third frame passed before 
the lens at the time that the correspond- 
ing filter was in position. This re- 
quired the photographing of three pic- 
tures where before in ordinary black 
and white photography it was only 
necessary to take one. The film and 
shutter had to move three times as fast 
as formerly. In projecting, an identical 
set of filters revolved before the lens, 
so synchronized that the red filter 
passed before the projector at the in- 
stant that the red picture was in place, 
the green filter before the green pic- 
ture, and the blue filter before the blue 
picture. 

Persistence of Vision 
The photographing and projecting of 
motion pictures depends fundamentally 
upon the physiological law which is 
known as the Persistence of Vision 
principle. It will be recalled that this 
principle states that the eye will con- 
tinue to retain any impression which 
actuates it for a period of time approxi- 
mately equal to one eighth of a second 
after the impressing object has been 
removed. This phenomenon, which 
might be called the inertia principle of 
vision, applies to color impressions as 
well. If the eye be activated by a 
colored object, it will continue to see 
the color for the same period of time 
after the removal of the object — one 
eighth of a second. If another color 
be put into the field of vision before 
the expiration of this period of time, 
the second color will be superimposed 
upon the first, and both will register 
upon the brain. Were it not for this 
fact color pictures, as well as the ordi- 
nary black and white motion pictures, 
would be an impossibility. The audi- 
ence will see the frame which contains 
the record of all of the red rays, con- 
tinuing for one eighth of a second 
after removal, then all of the green, 
then all of the blue. The eye itself will 
blend these color records into a single 
unit of color which, if the photography 
has been faithful, will exactly corre- 
spond to the original. 

Cause of Color Fringe Around Picture 

For several reasons this type of 
cinematography has never been particu- 
larly successful. There was a pulsation 
of the picture, explained by some au- 
thorities as being due to eye fatigue. 
The eye was compelled to work hard 
and fast in order to register the many 
individual pictures upon the brain. At- 
tempts were made at a later date to 
eliminate this fatigue by running still 
faster, thus making a slighter differ- 
ence between pictures, but due to the 



extreme speed the wear upon the film 
was excessive. Flicker; that is, a pulsa- 
tion due to the change of intensity of 
light upon the screen was another ob- 
jectionable feature of this type of color 
projection. Fringing, a streaking of 
the various component colors especially 
noticeable after a rapid movement, was 
a factor which has not been, and in 
all probability never will be, entirely 
eliminated from this type of color pho- 
tography. No matter how fast the indi- 
vidual color records were taken, in the 
case of rapid movement of the object, 
motion between the three separate color 
pictures would be shown. The three 
pictures would appear at slightly differ- 
ent positions upon the film. The red 
would not be exactly covered by the 



In Exports Sound Leads Silents | 

| TiyfOTION picture exports dur- j 

1 IVL i n g the 1930 period increased j 

1 over those of the corresponding § 
period of 1929. 

Europe leads in importing the § 

largest proportion of sound pic- § 

tures of American films sent | 

abroad. The Far East ranks | 

second, while Latin America, al- j 

though using almost as many | 

I talking pictures as silent films, j 

ranks last in utilisation of sound i 

films as compared to silent pic- § 

I tures exported by the United | 

I States. 

American talking pictures are I 

going to foreign countries in 1 

nearly double the quantity of | 

silent films, according to prelimin- j 

ary figures for the first nine 1 

months of 1930, compiled by the j 

Commerce Department's Motion 1 
Picture Division. 

The total of all United States 1 

I motion picture exports during the § 

1930 period was 210,037,969 linear j 

I feet as compared with 201,137,429 | 

feet in the corresponding period j 

of last year. Of this amount 1 

137,448,391 feet were sound syn- § 

chronized and 72,589,578 were I 

silent, thus showing a percentage | 

figure of 65.4 for the former and j 
34.6 for the latter. 



green, nor the green by the blue. This 
results in a fringe of the individual 
component colors showing around the 
edge of any rapidly moving object. 

Panchromatic Film 

The film itself which carries this type 
of color record is black and white, the 
color value being latent in the film and 
appearing only when combined with the 
proper filter. The only difference ap- 
pearing to the eye is in shading. A 
red automobile in the red frame would 
appear very light, in the green frame 
it would appear darker, while the green 
tree beside the road would appear very 
light in the green frame. The film used 
in this kind of work is known as 
"panchromatic film." Theoretically, 



panchromatic film and this type color 
photography have many advantages. 
The film may be developed in any 
laboratory without the use of special 
processes, while if the film itself is 
colored, additional dye processes are 
necessary, — which means extra time and 
expense. However, in spite of theoreti- 
cal disadvantages, all of the operating 
commercial color methods in the motion 
picture industry today are of the type 
which uses a film containing the actual 
color values present upon the film. 

There have been several methods of 
photographing motion pictures in color 
which for one reason or another have 
not been successful commercially, yet 
are of interest when considering the 
subject of color. A multiple film process 
which may at some time in the future 
develop into a commercial success has 
been the object of research, and works 
in this way. Instead of taking three 
pictures at minutely separated instants, 
this method proposes to take three in- 
dividual pictures upon separate films at 
the same time. If three separate 
cameras are used, or three separate lens 
assemblies in the same camera, each 
lens with its appropriate filter, the pic- 
ture would be taken with each from a 
slightly different angle, and so would 
not project correctly. However, if the 
same lens assembly be used, and the 
separate films be exposed to the correct 
color rays by means of prisms and 
filters, this fault will be eliminated. The 
same assembly in its entirety may be 
used in projecting — the three films each 
running behind its appropriate prism 
and filter. While the results achieved 
by this method are extremely beautiful, 
the synchronizing of the three films in 
order to place the correct picture of 
each color upon the screen exactly over 
the corresponding two pictures of the 
other colors is perhaps a commercial 
impossibility. It might be noted that 
this method gives the only absolutely 
true color representation. A short 
amount of film may be projected and 
kept in synchronism if under perfect 
laboratory conditions, but under the 
usual theatre conditions, this method is 
out of the question. The slightest lack 
of synchronism produces a blur. The 
shrinkage of one film a bit more than 
the other due to a slightly different 
temperature, or the smallest incorrect 
prism adjustment will be enough to 
completely spoil the effect. 

Another method which resembles the 
foregoing in many details, yet which 
lacks many of the difficulties utilizes a 
set of prisms and reducing lens to take 
three tiny pictures upon one frame. 
These three pictures, each of one- 
fourth the usual height and regular 
width, lack much of the definition and 
detail of the larger picture. Each has 
its own color value latent in itself, and 
if the prism adjustment is correct for 
projection, will fit one upon the other 



JANUARY, 1931 



Page 9 



with no fringe. The same number of 
frames as in the ordinary black and 
white photography, and the same speed 
of projection are two obvious advan- 
tages claimed by the proponents of this 
method. However, complications pre- 
sent themselves which may or may not 
be worked out at some time in the fu- 
ture allowing this method to take its 
place with — or even replace — the 
commercial processes now in use. 

These additive processes have been 
attempted at their best; that is, in using 
three colors. If only two colors are 
used nearly all of the two hundred and 
thirty colors may be recorded, and the 
complications are fewer. If the spec- 
trum be roughly divided there will be a 
light and a dark region. The light re- 
gion begins at the red and ends at the 
green, while the dark region begins at 
the green and ends at the violet beyond 
the blue. In the two color process of 
the additive method, one color which 
lies near the beginning of each region 
is selected. Bright red may be selected 
to represent the light region, while a 
green may represent the dark. How- 
ever, certain natural colors may never 
be obtained by this method. If red and 
green be the base colors, yellow, blue 
or violet will not register as such. 
If blue be the base color of the dark 
region, green will not record upon the 
film as green. If orange be the base 
color for the light region, bright red 
will not photograph as red. While less 
complicated, limitations are imposed 
when the two color method is used. 
The speed, both of photography and 
projection is appreciably reduced by 
this method. 

Multicolor and Technicolor 
The two principal color methods in 
Hollywood which are operating com- 
mercially today, Multicolor and Techni- 
color, are both subtractive two-color 
processes. The Multicolor base colors 
are orange-red and blue. In contrast 
to the Technicolor method, Multicolor 
uses the standard motion picture camera 
without the addition of any filters or 
prisms. The company furnishes an at- 
tachment which is reasonably inexpen- 
sive, and a special magazine threaded 
with two films. These two films are 
placed emulsion to emulsion, so that the 
light shining through the lens strikes 
the celluloid side of the first film. The 
front film is so treated in the emulsion 
that it records only the dark end of the 
spectrum. A blue green picture of the 
object is impressed upon the first film. 
The emulsion of the front film is sur- 
face dyed red, so that in addition to 
recording the dark end of the spectrum 
it also acts as a color filter for the rear 
film. A red-orange color picture ap- 
pears upon the back film. The two films 
are separated, developed, and a print 
made upon a film coated upon both 
sides. The record now consists of a 



film which contains a latent blue-green 
image upon one side, and a latent 
orange-red image upon the other. This 
film then goes through a chemical 
process in which the pictures upon one 
side of the film turn red, and those 
upon the other side turn blue-green. 
Contrasted with the dye process of 
Technicolor, this is a chemical conver- 
sion process. The actual chemicals 
which comprise the picture record are 
converted into other chemicals to make 
up the desired color photo. Many 
practical objections arose to this double 
coated film. It was claimed, and the 
claims upheld by practice that the film 
would scratch easily, break and crack, 
and quickly wear out. The Multicolor 
Corporation developed a special shellac 
with which the film was treated and 
which overcame the objections noted. 
With the Multicolor process it is im- 
possible to obtain a bright red or yel- 
low, but a very beautiful gold is ob- 
tained which closely approaches yellow. 
It might be noted in passing that if 
lighting conditions be perfect, it is pos- 
sible to obtain a yellow, but under or- 
dinary studio conditions, it is not prac- 
ticable. The same difficulty is present 
in obtaining violet and purple. The 
green has a slight bluish tinge. Out- 
door scenes when photographed in 
Multicolor are exceptionally beautiful. 
The blue of sea or sky seems to impress 
itself particularly well in this method, 
which is a distinct advantage and does 
much to recommend the method for out- 
door work. One of the most beautiful 
motion picture shots which it has been 
my pleasure ever to witness was a 
Multicolor shot of a lake over which 
was thrown a gorgeous streak of golden 
moonlight. The combination of the 
dark of the lake and the gold of the 
moonlight was one which will always 
remain in memory as a vivid example 
of what is possible with color 
photography. 

The Technicolor method uses a spe- 
cially built camera, equipped with a 
special single lens and a set of prisms 
arranged so that the separate and indi- 
vidual color pictures are thrown upon 
successive frames of the same film. A 
revolving color filter is placed so that 
the one red and one green picture are 
photographed simultaneously. Thus, 
when the film is developed, there are 
two color sequences present upon the 
same film. Each set of color records 
is printed upon a separate positive — 
the red upon one and the green upon 
another. These prints are developed 
and fixed in the regular way. Each is 
then treated so that the silver images 
are concerted into mordanted images — 
that is, images which have the prop- 
erty of absorbing certain dyes. The 
positive having the red record is dyed 
green, while the print having the green 
record is dyed red. Then, a fresh film 
which is coated with a specially pre- 



pared gelatine is pressed successfully 
against the two prints. This gelatine 
absorbs the dye from the prints in the 
same manner that newsprint paper ab- 
sorbs ink. The process of transfer of the 
image to the single gelatine coated film 
is called imbibition — referring to the 
property of the gelatine to imbibe the 
dye from the dyed film. Ordinary 
lithographing embraces the same 
process. The two color records, having 
now been transferred to the same side 
of one film, are ready for projection. 
A tremendous advantage of the Techni- 
color process is that no new attach- 
ments are necessary for the projection 
machine. The prints contain their own 
color and may be projected upon any 
ordinary machine. 

There are certain outstanding disad- 
vantages to this process. The dye tends 
to spread in the imbibition operation, 
much as ink spreads on the cheaper 
grades of newsprint paper, tending to 
make a hazy outline ; each print will 
vary from another due to a slight dif- 
ference in time it is allowed to remain 
in the bath, and there are certain 
natural colors which may never be ob- 
tained with this process. Red and green 
being the base colors of the Technicolor 
process, it is impossible to obtain a true 
blue, yellow or violet. Yellow will ap- 
pear orange upon the screen. The final 
print contains the actual color upon the 
film and the combination of red and 
green will give a very close approxima- 
tion to the natural color of the object. 
However, the two color process can 
never give as true a representation as 
the three, and the development of a 
commercially possible three color 
process is the aim of those connected 
with the color companies. 

Summary 

In conclusion, a brief comparison of 
these two methods, Multicolor and 
Technicolor, may be of interest. A 
great advantage of the chemical con- 
version method is that it is a process 
which goes to completion and stops. 
The amount of color does not vary from 
print to print, while in the dye process 
the amount of dye and the length of 
time the print remains in the dye bath 
determine the shadings and the amount 
of color which will be present in that 
individual print. Due to lack of imbibi- 
tion, there is more definition to a 
chemical conversion print than there is 
to a dye process print. The dye process, 
however, has the advantage that it is 
able to register reds, which contributes 
much to scenes often encountered in 
motion picture photography. 

Many studios, as well as companies 
formed for the express purpose, are at 
this time at work upon individual meth- 
ods of color photography, and the fu- 
ture promises to bring out many inter- 
esting developments in this field of the 
motion picture industry. 



Page 10 



PROJECTION ENGINEERING 



Line Voltage Problems 
and Solutions 



By J. W. Harmon* 



In Sound Amplifying Systems Such Troubles as 

Short Life of Tubes, Tone Distortion and Blasting 

May Be Avoided by Employing Line Voltage 

Regulating Units 



THE part played by line voltage in 
the operation of sound reproduc- 
ing systems is not generally ap- 
preciated by the average engineer, 
installation man, or projectionist. Just 
because the term "no volts" is univers- 
ally and rather loosely used, it is taken 
for granted that line voltage must be 
definitely set at no volts at all times. 
This assumption is far from true. 
Readings taken in different sections of 
the country with recording voltmeters 
indicate a wide range of line voltages 
throughout the twenty-four hours of 
the average day. The fluctuations may 
be gradual during certain times of the 
day, due to definite load changes, or 
rapid and unexpected variations 
throughout the day, due to unexpected 
load conditions. 

In the average sound installation, 
little or no attention is paid to line volt- 
age fluctuations. At most, there are 
taps or switches to provide a choice of 
mean or average input voltages with 
given line voltages, but no provision is 
made for handling rapidly fluctuating 
line voltages which constitute the real 
problem. In other words, it is not so 
much a question as to whether the line 
voltage averages 105 or 125 volts, as it 
is a matter of following the rapid 
changes in line voltage from 105 to 135 
volts throughout the entire day. 

In the sound system installation, good 
tone quality and uniformly sustained 
volume are a far greater importance 



*Amperite Corporation 



than in the home radio set. The listen- 
ers expect and demand maximum real- 
ism with minimum nervous strain. 
Because of the extreme volume required 
to fill a theatre, auditorium, church, or 
hall, differences in volume and tone are 
readily detected by critical listeners. 
Therefore, it is essential to maintain 
both factors of a uniform level. 

Compensating for Voltage Variations 

Fortunately, while nothing can be 
done about fluctuating line voltage in a 
preventive way, much can be done by 
way of compensating for line voltage 
fluctuations. It is possible to employ 
self-adjusting line voltage controls 
which maintain a given input voltage 
by automatically changing in resistance 
as the line fluctuates up and down. 
Such units must not only protect equip- 
ment and tubes against excessive volt- 
age by introducing the proper amount 
of voltage drop, but must also reduce 
the voltage drop as the line voltage de- 
creases, so as to strike the desired uni- 
form input voltage at all times. 

It is generally assumed that the gen- 
eral problem of fluctuating line voltage 
is one of abnormal line voltage, result- 
ing in excessive wear and tear on tubes 
and on power packs. While excessive 
voltages generally work the greatest 
havoc, it is nevertheless true that sub- 
normal line voltages are almost equally 
troublesome. Not only are tone quality 
and volume greatly hampered by sub- 
normal voltages, but power tubes and 



rectifiers break down when filament 
supply voltages are reduced below sate 
limits. Such tubes either have a tend- 
ency to arc when operating on in- 
sufficient filament voltage, or the fila- 
ments crystallize and become brittle, in 
either event calling for premature re- 
placement. 

The ideal method of compensating 
for fluctuating line voltages is the use 
of a reduced voltage primary for the 
power transformer, together with a 
self-adjusting balancing resistance in 
the primary or supply circuit. In the 
case of the usual no-volt supply, the 
primary is wound for 90 volts, while 
the self-adjusting line voltage control 
inserted in one leg of the primary cir- 
cuit serves to reduce the line voltage 
to the 90-volt input. In such an ar- 
rangement it is possible to regulate line 
voltages anywhere from 95 to 135 volts, 
maintaining the primary voltage within 
the 5 per cent plus or minus specified 
by tube manufacturers. Already, many 
radio set manufacturers have realized 
the necessity for line voltage com- 
pensation, and have built this feature 
into their radio assemblies. This 
practice is bound to become common- 
place in radio broadcast reception, and 
is of even greater importance in sound 
reproducing systems. 

In the absence of low primary fea- 
ture, however, it is still possible to in- 
troduce line voltage compensating 
means in the sound reproducing system. 
This may be done externally, and 
without any changes in the equipment 
itself. It is simply a matter of plac- 
ing one or more mounting sockets in 
series with the primary or supply cir- 
cuits, inserting the necessary type and 
number of control devices, so as to in- 
troduce the current carrying capacity 
corresponding to the requirements of 
the apparatus used. The control unit, 
through its automatically variable re- 
sistance, supplies the necessary voltage 
drop so as to maintain a uniform input 
voltage at all times, despite wide line- 
voltage fluctuations between 100 and 
140 volts. 

The Symptoms 

There are several symptoms that 
positively indicate line voltage fluctua- 
tions exceeding the safe limits. When 
tubes burn out prematurely, for in- 
stance, it is usually an indication of ex- 
cessive line voltage, Tube life may be 
reduced 50 per cent or more when line 
voltage fluctuates above the rated tube 
requirements. Tone distortion and 
blasting are also caused by excessive 
line voltage. Power-pack breakdowns 
are by no means rare when operating 
on excessive line voltages. Tube noises 
are usually an indication of excessive 
line voltage. 

Subnormal line voltages, while per- 
haps not as costly as abnormal line 



JANUARY, 1931 



Page II 



voltages, are even more troublesome. 
Diminished volume, even with the 
volume control turned on full, is usu- 
ally an indication of subnormal line 
voltage. Poor tone quality is also a 
symptom of low line voltage. Finally, 
tube failure may frequently be due to 
subnormal line voltage, since filaments 
crystallize when insufficient voltage is 
applied on the filaments. Also, certain 
types of power tubes have a tendency to 
arc when operating at insufficient fila- 
ment temperature. 

With proper line voltage compensa- 
tion, it is possible to maintain the input 
voltage with 5 per cent plus or minus 
the ideal operating voltage, despite 
fluctuations of 15 per cent plus or minus 
the mean line voltage. 

There are various forms of line volt- 
age control, some of them fully auto- 
matic, while others are either fixed or, 
at best, manually operated. The fixed 
resistance units serve to reduce the line 
voltage only, provided the line voltage 
stays reasonably constant at a high 
value. In other words, where line volt- 
age runs uniformly high, it is possible 



to insert a fixed resistance in the or- 
dinary circuit, reducing the applied 
voltage to a safe value. However, such 
a fixed resistor does not take care of 
conditions when the line voltage drops 
to a lower value. The resistance re- 
mains in circuit, consequently dropping 
the applied voltage below the desired 
value, and bringing about the unsatis- 
factory conditions due to subnormal 
voltage. Such devices are frequently 
made in tapped form, so as to provide 
a suitable range of voltage drop, to take 
care of varying conditions, if one 
knows what tap to use — and when. 

For automatic or self-adjusting line 
voltage controls, is the type illustrated 
herewith which can be relied upon to 
control line voltage fluctuations even 
though they may extend up to 140 
volts, which is by no means uncommon. 

The Amperite type of voltage con- 
trol is in the form of a glass bulb, not 
unlike the usual radio tube, containing 
a special wire winding in an atmosphere 
of nitrogen. The bulb is frosted to 
distinguish it from radio tubes and pro- 
vided with a two-prong base, for use 



AMPERITE 



4V 




SET POWER LINE 




in either the standard UX socket or a 
special mounting socket. 

The unit is available in a wide range 
of current capacities. Also, it is pos- 
sible to employ two or more bulbs in 
series parallel, so as to handle any given 
load in the form of the sound repro- 
ducing equipment. 

Not only does line voltage control 
insure a longer life for the costly radio 
tubes employed in the usual sound re- 
producing system, as well as protection 
for the equipment itself, but more uni- 
form results are an absolute certainty 
as the result of properly controlled in- 
put voltage. 






ACADEMY OF MOTION PICTURE 
ARTS AND SCIENCES 

President William C. de Mille, of the 
Academy of Motion Picture Arts and 
Sciences, after consultation with other 
officers, branch executive committees 
and members, has appointed as members 
of the Producers-Technicians Com- 
mittee, administering the Academy 
technical bureau : Irving Thalberg, 
chairman ; M. C. Levee, Fred W. Beet- 
son, Sol Wurtzel, Charles Sullivan, 
Henry Henigson, H. Keith Weeks, 
J. A. Ball, Fred Pelton, J. T. Reed, 
Carl Dreher, Nugent H. Slaughter, 
Frederick M. Sammis, and K. F. 
Morgan. 



METROPOLITAN MAKING A FILM 

FOR AMERICAN TELEPHONE AND 

TELEGRAPH COMPANY 

THE industrial division of Metro- 
politan Sound Studios at Hollywood, 
California, reports that it has been 
awarded the production of an industrial 
picture for the American Telephone and 
Telegraph Company, entitled "Making 
the Grade." The production will be in 
a measure a dramatic one, and will 
visualize the hazards attending the 
duties of linemen. It will be shown 
within the organization, as well as to 
the public, and will display the esprit 
de corps of this group of technical men, 
who know no danger when telephone 
property is in jeopardy. Charley 



Grapewin plays a featured role in this 
production, and will be supported by 
Eddie Baker, F. D. Wilcox, Bob Chap- 
man, Charles Hamilton, and several em- 
ployees of the American Telephone and 
Telegraph Company will also appear in 
the production. The picture is to be 
directed by Charles H. Brownell of 
Metropolitan's industrial department, 
and Jerry M. Hamilton, of New York 
City, representing the Telephone Com- 
pany. 

A 

17,500,000 LUMENS OF LIGHT — 
AND ARRESTED MOTION 

A FLASHLIGHT battery is 
powerful enough to release a 
flash of 17,500,000 lumens of 
light — or even more — in a re- 
flector designed by the General Electric 
Company for use of photographers at 
its Schenectady plant. The reflector, 
which employs the new Photoflash lamp 
recently announced by the company, 
contains seven standard sockets placed 
at various angles within a dull alumi- 
num reflector. The sockets are so ar- 
ranged that the bulbs themselves are 
uniformly spaced within the reflector to 
supply an intense, momentary light for 
the making of photographs of larger in- 
teriors in spite of adverse natural light 
conditions. The reflector is attached to 
an ordinary flashlight cell container, 
and the bulbs are wired in parallel so 
that all are flashed simultaneously. 
Investigations at the engineering 



laboratory of the incandescent lamp 
department of the company at Cleveland 
show that the new lamp, which replaces 
flashlight powder and makes possible 
pictures hitherto impossible because of 
fire or accident hazard, has an output 
of 200,000 candlepower, or about 2,500,- 
000 lumens, as a bare lamp. The use 
of a reflector will increase this three 
or four fold within a limited angle, so 
that a single lamp in a reflector has an 
output of upwards to 600,000 candle- 
power. 

Further investigations at the labora- 
tory show that the flash of the lamp 
rises very rapidly in intensity, drops 
quickly, and then trails off for a longer 
period. The intensity of the flash 
which is photographically effective lasts 
for about i/50th of a second. This is 
further shown by actual exposures, in 
which it is proved that the flash is suf- 
ficiently fast to stop action that can 
ordinarily be stopped by a camera in 
such a time. 

The Photoflash lamp consists of a 
clear bulb of standard design, with the 
flashlight filament coated with a special 
preparation, and with a quantity of 
very thin aluminum foil in crumpled 
sheet form within the oxygen-filled 
bulb. When the circuit is closed the 
filament is lighted and this, in turn, 
lights the foil, giving a flash of intense 
light. The lamp operates on any 115- 
volt house supply, or with dry, storage 
or flashlight batteries. A new lamp is 
needed for each flash. 



Page 12 



PROJECTION ENGINEERING 



Shooting a scene with portable sound equipment. Cameras 

in sound-proof blimps in center; portable microphone 

boom at right. Picture: "Fingerprints." 



Monitoring 
Sound 
Motion 
Pictures 



PART III 



By Charles Felstead* 



WE will take up the practical 
side of monitoring work in 
this article. It will be neces- 
sary first that we discuss the 
construction of sets having the neces- 
sary acoustic properties for the record- 
ing of sound before discussing the 
types of microphones used and the man- 
ner in which they are arranged for 
recording. 

When sound was first introduced into 
motion picture work, it was found that 
the sets used for the shooting of silent 
pictures were entirely unsuited for use 
in the talkies. Accordingly, engineers 
had to cast about and discover new 
ways to construct sets with the proper 
acoustic properties and which would 
photograph satisfactorily. In the be- 
ginning, many experiments were tried 
in set construction in endeavoring to 
fulfill these two requirements. It was 
necessary that the set have just the 
right amount of reverberation, neither 



* Sound Engineer, Universal Pictures Corpo- 
ration. 




Figure 1. 



too little nor too much ; because too 
little reverberation would cause a set to 
sound "dead", while too much reverber- 
ation would produce a set that was too 
"live." As practically all of these early 
sets were built inside of the sound 
stages, there was little occasion to 
worry about reverberation from sur- 
faces outside of the set proper, because 
the walls of the sound stage were 
covered with sound-absorbing materials 
and so heavily draped that the effect of 
any reverberation coming from them 
could be discarded. It will be interest- 
ing to review here some of these ex- 
periments and the results obtained from 
them. 

Early Sound Sets 

The first sound sets tried out were 
constructed of heavy cloth, such as can- 
vas, covered with paint to make it stiff 
resembling a solid wall. A heavy 
framework was used to hold the cloth 
in much the same manner as the canvas 
of an oil painting is supported. A very 
realistic appearing set could be con- 
structed quite cheaply in this manner. 
These cloth sets were not satisfactory, 
however, because they offered almost 
no opposition to the passage of sounds 



This is the Third and Closing Article in Mr. Felstead's 
Series On the Making of Sound Pictures. These 
Articles Present a First Hand Account of the Present 
Technique of Sound Effects Recording in the Making 
of Moving Pictures 



of a high-frequency, and so practically 
no reverberation was obtained from 
them ; but low-frequency sounds were 
reflected by these walls to such an ex- 
tent that the set sounded very "boomy" 
or "tubby." The effect was more or 
less like shouting into an open barrel. 

The designers went to the other ex- 
treme in the next sets and constructed 
them of Celotex, Flax-li-num, and other 
sound-absorbing materials. This re- 
sulted in a set that was also very 
boomy ; but in this case, the high fre- 
quencies were absorbed by the material 
in the set walls, instead of passing 
through them as in the cloth sets. Both 
of these types of sets lacked sufficient 
reverberation of the "highs" to sound 
natural when recording was done in 
them. Hard materials that would pro- 
duce the proper balance of reverbera- 
tion of all frequencies were almost en- 
tirely absent in these sets. 

It was found that sound-absorbing 
material absorbs high-frequency sounds 
to a much greater extent than it does 
sounds of low-frequency. Hard ma- 
terials, such as wood and metal, present 
a more nearly flat absorption factor 
over the entire audio-frequency band, 
and so the "highs" are reverberated al- 
most equally with the "lows." A set 
that is too completely enclosed by hard 
materials, however, is too reverbera- 
tory : that is, the time of reverberation 
is greater than it should be for the 
size of the set, and the percentage of 
articulation becomes low because of the 
overlapping of spoken words and their 
many reflections from the walls. 

As a compromise the next sets were 
built partly of soft and partly of hard 
materials. This was not the solution of 
the problem, though, because strong 



JANUARY, 1931 



Page 13 



high-frequency reverberation would be 
found to come from certain angles in 
the set and none at all from other 
angles. When considerable recording 
was done in the same set and the mike 
•was moved to several different positions, 
rather peculiar results were often ob- 
tained. In some places, the set would 
be very "boomy," due to the presence of 
considerable sound-absorbing material ; 
and in other spots, the high-frequency 
tones were over-emphasized because of 
reflection from small areas in the walls 
made of hard materials and not solidly 
supported. These small panels reson- 
ated at certain high frequencies and 
threw out extremely strong reverbera- 
tion when tones of those particular fre- 
quencies were sounded. An example of 
this phenomena is seen in the case of 
two violins having strings that are 
tuned exactly alike. If these violins are 
placed several feet apart and the string 
on one is plucked, the corresponding 
string on the other violin will be also 
set into vibration. This is termed 
"sympathetic vibration," and is due to 
the resonance of the two strings. A 
similar effect is encountered in sound 
sets when panels of hard materials are 
not firmly supported. These panels 
have each a natural period of vibration, 
or resonant frequency, which is deter- 
mined by the physical dimensions of the 
panel and other factors, and at which 
frequency they can very easily be set 
into vibration. When the certain tone 
at which a panel resonates is sounded, 
the panel is thrown into sympathetic 
vibration with the tone and greatly aug- 
ments it, producing distorted sound 



quality because of the over-emphasizing 
of this one particular tone. 

Natural Materials 

Finally, it was found that sets con- 
structed of materials as nearly like 
those that would be used if the set were 
real produced the best and most natural 
results from the standpoint of sound. 
Economically, of course, it is impossible 
to use all natural materials in the set; 
and so cheaper substitutes are used 
wherever it is possible to do so without 
impairment to sound quality or photo- 
graphic value. To reduce the weight 
and cost of construction of the walls, 
they are now almost universally made 
out of three-ply veneer, or the equiva- 
lent, strongly supported so that they will 
not be "drummy," or resonant at low 
frequencies. Real doors of light weight 
are used. This provides a set that is 
quite "live," but because two of the 
six sides of the set are open — namely, 
the roof and the front — almost exactly 
the right amount of re/erberation is 
produced to simulate normal sound con- 
ditions. In other words, the reverbera- 
tion produced by a sound in this four- 
walled set (three walls and a floor) 
seems the same to a monaural recording 
system as the reverberation produced by 
the same sound in a six-walled room 
would seem to binaural human hearing. 
The amount of reverberation in the 
sounds recorded must not be too great 
because there is a second, though lesser, 
set of reverberations in the theatres in 
which the sound is later reproduced. 
These two sets of reverberations add 



together and produce a rather bad effect 
if either set is too great. However, 
most theatres are now heavily sound- 
proofed to prevent excessive reverbera- 
tion. 

Sound-Proofing 

Large folding baffles, like Japanese 
screens, made of sound-absorbing 
materials, such as rock wool, are often 
used to reduce the amount of reverbera- 
tion in a set by adding more damping. 
They are placed around the set at the 
different points where they are needed, 
but out of sight of the camera. Some- 
times hard baffles are also used for cer- 
tain purposes. Padding is laid on the 
floor wherever it is possible to use it 
without it being seen, so that the foot- 
steps of the actors will not be disturb- 
ing. Raised floors that are to be walked 
on must be solidly constructed and sup- 
ported in order that they will not sound 
drummy. A wooden floor of double 
thickness with sound-proof material be- 
tween the two layers of boards is often 
used for this purpose. Likewise, large 
parallel hard walls have to be watched 
or they will pick up certain audible 
frequencies and bounce them back and 
forth, producing "standing waves." 
Also, supporting beams must not be 
placed too far apart, or the space be- 
tween them will be such that it will 
resonate at some points within the audio 
range. The incandescent lamps used 
in lighting the set must likewise be 
watched carefully so that they are not 
placed in such positions that their re- 
flectors reflect certain sounds strongly 
against the microphone. There are 











+ -S.S. 




Fig. 2. Shooting a desert scene in "Hell's Angels.' 



Page 14 



PROJECTION ENGINEERING 



many other similar things that experi- 
ence will teach the monitor man to 
watch out for. 

Before we go into a discussion of the 
practical side of monitoring work, it 
might be well to describe briefly the 
monitoring equipment used with the 
portable sound trucks. This equipment 
is mounted in a small trunk. Cables are 
provided so that it can be used in or 
on top of the sound truck, or at a 
reasonable distance from it. It may be 
noted in Fig. 4 that the upper part of 
this trunk contains two, three-position 
mixing panels, the same as those used 
for channel monitoring. Just below 
these panels are six key switches that 
control the filaments of the tubes in the 
condenser microphone amplifiers. Be- 
low them are two meters — the left-hand 
one is the volume indicator extension 
meter, and the one on the right is the 
filament voltmeter for the condenser 
transmitter amplifier tubes. To the 
right of this voltmeter is the filament 
rheostat, and to the left of the other 
meter is the main volume control 
potentiometer. The box between the 
meters contains the fuses for the con- 
denser microphones. Six large jacks 
to the left and below the meters are 
for the microphone cables, one of which 
can be seen plugged in. Two other 
jacks to the right, which also have 
plugs in them, are for the cables that 
connect the monitoring apparatus to the 
amplifying and recording equipment in 
the sound truck and to the truck bat- 
teries. A one-tube booster amplifier is 
mounted inside the monitoring trucks. 
Portable monitoring is done by means 
of special headphones, which have a 
very flat frequency characteristic over 
the entire band of frequencies that is 
normally recorded. An intercommuni- 
cating telephone and hand-set may be 
seen in the foreground Fig. 1. Except 
for the arrangement of the equipment, 
monitoring on a sound truck is practic- 



ally the same as it is in a portable 
monitor booth or permanent monitor 
room. 

Microphones 

Condenser microphones are used ex- 
clusively in sound motion picture work 
as they are more rugged than carbon 
microphones and have not the char- 
acteristic carbon hiss. These con- 
denser microphones are made up of tiny 
condensers, called condenser trans- 
mitters, coupled to suitable one- or two- 
stage amplifiers. The whole assem- 
blage is termed a condenser transmitter 
amplifier, or C. T. A. It has the ad- 
vantage that it puts the gain at the 
point in the recording system where it 
is most valuable. Monitor men use 
whichever type of C. T. A. is better 
suited for the work at hand, and for 
difficult shots they often use both types 
at one time. The two-stage C. T. A. 
is always employed, of course, when ex- 
treme sensitivity is required, particularly 
when whispering or distant conversa- 
tion is to be recorded. Some trouble 
has been encountered from noise in 
these two-stage mikes, due mainly to 
moisture collecting on the resistors, but 
that difficulty is being gradually over- 
come. When in use, the microphone is 
usually hung on a portable, counter- 
balanced boom, called the "mike boom." 

Microphone Placement 

Some monitor men favor but one 
microphone for recording dialogue and 
music. Others are addicted to the use 
of several microphones. There are 
good things to be said for both methods 
— the choice depending on the monitor 
man's preference and experience. It is 
often difficult to handle action that is 
spread out over a large set with one 
microphone. On the other hand it is 
not easy to control several microphones 



HARD - 
BACKING 



•" HARD 
BACKING 



CORNETS, TRUMPETS 
AND TROMBONES. 



BASS 
HORN 




FRENCH 
HORN 



PIANO 



HARP- 



BASS 
VIOL 



> 



BAS5 

POSITIONS OF MICROPHONES—"' 
IF THREE ARE USED 




VIOLA 



POSITION OF MICROPHONE FOR 
SINGLE- MICROPHONE RECORDING " 



Fig. 3. Placement of Instruments and microphones in recording room. 



at the same time, or to fade smoothly 
from one microphone to another when 
following progressive action. If the 
microphone is to be the ears of the 
imaginary person whose eyes are 
formed by the camera lens, it is evident 
that the use of two or three micro- 
phones simultaneously or consecutively 
on a set is not at all desirable because 
that would be disrupting the relation- 
ship between the eyes and ears of this 
fictitious person — and that should be a 
fixed quantity. Without doubt, better 
results are secured as a rule from 
single-mike recording when the micro- 
phone position for each set-up is care- 
fully chosen. There are cases, though, 
where the use of two microphones is 
desirable, such as when a close-up shot 
is made of two persons talking together 
with a noisy crowd for a background. 
In this case one mike is placed in the 
foreground for the close-up conversa- 
tion, and another is hung in the back- 
ground to pick up the crowd noise. 
That makes it possible to get a nice 
balance between the dialogue and the 
crowd noise without much difficulty. 
Where the crowd noise is quite heavy, 
it is often well to use a two-stage mike 
for the dialogue and a single-stage mike 
for the noise. That helps to raise the 
dialogue to the proper level above the 
background noise. A similar setup is 
frequently used when an orchestra or 
band takes the place of the crowd. 

Fundamentals 

The secret of monitoring lies in this : 
maintaining the correct relationship be- 
tween the position of the camera and 
the lens system used on it and the posi- 
tion of the microphone, placing the 
microphone and arranging the baffles on 
the set so that the proper balance of 
direct and indirect sound to create the 
illusion of reality will be obtained, and 
keeping the recorded sound at a con- 
sistent level throughout the picture. 
These are the three commandments of 
the monitor man. 

There is one other point that the 
monitor man must not overlook, and 
that is to watch constantly that the 
microphones do not pick up outside dis- 
turbances ; such as, camera gear noise, 
sputtering from the arcs when "hard" 
lights are used, sounds from off stage 
and from the people working on the 
picture, and a-c. hum from microphone 
cables running parallel to power wir- 
ing. Cameras are now almost always 
enclosed in sound-proof cases, called 
"blimps," which greatly reduce the 
noise coming from that source. On 
location in the open it is necessary also 
to watch for wind noise, noise from the 
portable electric generating plants, and 
for distant sounds such as train whistles 
and airplane motors. Noisy amplifiers 
in the main recording system are an- 
other common source of concern. 



JANUARY, 1931 



Page 15 



There are three main types of "shots" 
used in motion picture photography. 
They are called the "close-up" or "close 
shot," the "medium shot," and the "long 
shot." The close-up usually shows a 
single person from the waist up, or just 
his head. A medium shot generally 
takes in two persons and a portion of 
the set. A long shot reveals the whole 
set and the action taking place in it. 

The usual positions of the camera 
relative to the action for these shots is 
evident from the titles, although even 
that varies with the size of the lens 
used on the camera, as has been ex- 
plained. For a close-up the camera can 
be used near the action with a two- or 
three-inch lens, or at a little distance 
from it with a four-inch lens. The 
photographic result is practically the 
same in both cases. Regardless of that, 
the microphone should be hung close to 
the actor for a close shot, so that the 
sound will be recorded at the proper 
level, and the ratio of direct to indirect 
sound will be high. Usually for a 
medium shot, the microphone is hung 
some five feet in front of the action, 
between the camera and the actors and 
just high enough to be out of range of 
the camera lens. Care must be taken 
that the shadow of the hanging micro- 
phone does not intrude itself into the 
picture. 

If a long shot is being made with a 
thirty-five or forty millimeter lens on 
the camera, the microphone is generally 
hung back near the camera and just a 
few feet in front of it. This position 
allows the microphone to pick up the 
reverberation from the four sides of the 
set, and so more indirect than direct 
sound is received by it. There is no 
fixed rule for the relationship of the 
positions of the camera and microphone 
because of the various sizes of lens used 
at will on the camera. The monitor 
man will have to learn for himself how 
best to obtain the proper relationship 
for each individual set up. 

The placing of the microphone be- 
comes much more difficult when, as is 
often the case, all three shots — the 
close-up, the medium shot, and the long 
shot — are made at the same time. This 
puts the monitor man in a rather trying 
situation, because the director expects 
him to get the proper sound for all 
three shots at one time. Most action is 
photographed twice as a precautionary 
measure. During one take, the micro- 
phone can be hung in the proper place 
for the medium shot. On the next take 
a microphone in position for close dia- 
logue can be used to match the photog- 
raphy of the close-up camera. Then 
the monitor man will have to trust that 
the cutter uses the right sound track 
with the action from each camera. The 
long-shot photography will have to be 
matched with the medium-shot sound 
at a slight loss in realism. It is rather 



hard to hang the microphone in situa- 
tions like this so that it will be out of 
range of all three cameras. 

Occasionally a dummy chandelier is 
suspended in such a position that it 
shields the microphone from view. A 
little ingenuity when three cameras are 
used at one time will often save the 
monitor man worry. 

Following the Sound 

When action on a large set moves 
some distance, there are two usual ways 
of following the sound of the voice, if 
the camera is being "panned" to fol- 
low the action. Of course, if the 
camera is stationary and the action is 
moving away from it, the voice should 
not be followed by the microphone, but 
should be allowed to grow fainter with 
distance. When the camera is being 
actually moved to follow the actor, the 
boom carrying the microphone should 
likewise be moved in harmony with it 
so that the picture-sound relationship 
will remain the same. This is termed 
a "perambulator shot." It is necessary 
that the microphone cable be held up 
off the floor in order that it will not 
make a scraping sound when it is 
moved. Sometimes the microphone is 
hung from a long rope and swung in 
the proper direction by another rope 
tied to it. 

However, when the moving action is 
followed by changing the focus of the 
lens on the camera the sound accomp- 
panying the action must be followed 
and maintained at the same level by 
having several microphones concealed 
along the path the action takes, and 
"fading" by means of the mixer dials 
from one microphone to the next as the 
action progresses. This arrangement 
keeps the direct-indirect sound ratio 
more nearly correct than if one mike 
were used and the sound level raised as 
the action recedes from it. 

Sound Perspective 

Obtaining the proper sound perspec- 
tive is also of the greatest importance 
in monitoring. By that we mean that 
if the action seems to be in the next 
room the sound from it naturally should 
appear to come from that room. If a 
door between the two rooms is then 
opened the sound should become cor- 
respondingly louder. If the action then 
comes in through the door the sound 
should increase proportionately in 
volume. When a "fade in" or "fade 
out" is done by the cameraman, the 
sound should accordingly be faded in or 
out by the monitor man. 

Scenes are rehearsed a number of 
times before being taken. This is to 
enable the actors to learn their roles, to 
permit the cameraman and electricians 
to obtain the proper lighting of the set, 
and for the monitor man to secure the 
most suitable position for the micro- 




(Photo courtesy Universal Pictures Corp.) 
Figure 4. 

phone. Before the take is made, the 
cameraman and monitor man have to 
give their okays to the director. Some- 
times a wax record of the sound is 
made during a rehearsal, and played 
back to the director and monitor man 
so that they can determine how it will 
sound. 

"Play backs" like this are practically 
always made when music is scored, to 
enable the musical director to obtain 
just the right effect. The monitor man 
and director go to one of the studio 
projection theatres each morning to see 
and hear the "dailies," or "rushes," of 
the previous day's shooting. They 
determine then whether or not the 
work has to be done over again. 

Scoring 

The scoring of music, or the making 
of "orchestrations," is one of the most 
delicate operations that the monitor 
man has to perform. As in dialogue 
recording some monitor men prefer 
one-mike, and others prefer three-mike 
recording. The successful recording of 
an orchestra depends upon the proper 
arrangement of the musical instruments 
to secure the most pleasing sound 
balance. Generally the arrangement of 
the orchestra is much the same as it 
would be on the stage, with the micro- 
phone taking the place of the audience. 
The reverberation constant of the stage 
in which the scoring is done can bt 
quite a little higher than that of a stage 
used principally for dialogue recording. 
To secure this effect a backing ~nade up 
of a wall of hard material is usually 
placed behind the orchestra. Some- 
times a heavy rug is placed under the 
microphone, or a cloth curtain is hung 
behind it, to take the place of the damp- 
ing afforded by the missing audience. 
Whether one- or three-microphone re- 
cording is used, the arrangement of th& 
musicians is very much the same. This 
is often varied, of course, to suit the 
musical ear of the individual monitor 
(Concluded on page 18) 



Fage 16 



PROJECTION ENGINEERING 



Radio Television 
is Really Here 

By Austin C. Lescarboura 

Mem. A.I.E.E., Mem. I.R.E. 



If Entertainment Value Is the Criterion of Practical 
Television, the Basis of the Television Industry Is 
Now At Hand, Waiting for the Merchandising 

Touch 



A FEW evenings ago the writer 
sat in the library of Allen B. 
^ DuMont, chief engineer of the 
DeForest Radio Company, in 
his Montclair, N. J., home. Mr. 
DuMont wanted the writer to check 
with him on the entertainment possibili- 
ties of present-day radio television or 
radiovision. 

About a year and a half ago, Mr. 
DuMont built a home-made short-wave 
receiving set, together with a resistance- 
coupled amplifier, as a means of tuning 
in and' i "amplifyi r j the radiovision sig- 
nals. / lso, he secured one of the 
Jenkins radiovisors taken from regular 
production. These two units have 
served to keep him posted as to what 
is going on in radiovision circles. He 
has kept a log of his observations for 
the past two years. The log is really 
a day-to-day history of the progress of 
the struggling art and must eventually 
be an important historical document. 

The pictures were a revelation with 
regard to the entertainment value of 
radiovision. Heretofore, the writer had 
seen the usual demonstration, showing 
a close-up of a human being with 
enough detail to permit of ready recog- 
nition. But the picture seen the other 
evening not only could be recognized 
but possessed real story-telling charac- 
teristics. First of all, there was a syn- 
chronized sight and sound presentation 
of two comedians telling jokes, sing- 



ing songs, and playing an accordion; 
then came a girl singing a television 
song, followed by a man who came to 
help her with the song; a bit later a 
series of prominent personalities was 
thrown on the screen, which could be 
identified for the most part although 
the writer must confess that he missed 
out on the close-up of Orville Wright 
for the reason that he does not know 
that face quite as well as he knows 
Mussolini, Edison, Helen Wills and 
others prominent in the public eye; and 
finally, we had a movie thriller reminis- 
cent of the nickelodeon days of the 
nascent motion picture. All in all, it 
was an enjoyable show, although there 
were certain difficulties at times by way 
of extreme interference of other radio- 
vision stations. During the evening, we 
tuned in the Jenkins television station, 
W2XCR, at Jersey City; the DeForest 
television transmitter, W2XCD, at Pas- 
saic; the Jenkins station, W3XK, out- 
side of Washington, D. C. ; and finally, 
some unknown signals which later 
proved to be those of the NBC 
transmitter in New York City. 

Importance of Picture Detail 

Any discussion of television possi- 
bilities always comes down to a ques- 
tion of definition. The experimenter or 
the engineer may be quite content with 
a flickering silhouette appearing on the 
screen, for the reason that such a mind 



knows the enormous difficulties by way 
of reproducing an image, and therefore 
secures the kick out of the technical 
achievement. On the other hand, the 
lay mind may be little interested in the 
means employed, taking the final results 
on the screen as the sole criterion of 
the worth of radiovision. Consequently, 
the entire matter, as frequently pointed 
out by radio leaders, is a question pure 
and simple of definitions. 

The pictures reproduced under typical 
home conditions in the test just 
described contained a surprising amount 
of detail, even though they are of the 
48-line, 15 pictures-per-second cate- 
gory. We have been led to believe in 
the past that 48-line pictures are com- 
parable to a 48-line half-tone, which is 
even coarser than the usual 65-line 
screen of the newspaper. That is to 
say, if we were to take a ^4-inch 
square of a typical 65-line newspaper 
half-tone picture, we would obtain 
about the amount of detail which is 
present in a 48-line radiovision picture. 
Actually, this is a misconception of the 
entire technique. In the first place, 
while it is true that the pictures are 
being scanned in 48 horizontal strips, 
the fact remains that we are not deal- 
ing with 48 elements from left to right, 
but, rather, we are dealing with deli- 
cately and gradually variable lights and 
shadows across each horizontal strip, 
rather than 48 dots or picture elements. 
Therefore, we are dividing our picture 
only in the vertical plane, and not in 
the horizontal plane. We are securing 
excellent detail with half-tone values 
from high light to shadows, from left 
to right, although our picture may be 
divided into 48 strips from top to 
bottom. 

The Pickup 

The limitations of the 48-line screen 
heretofore criticized seriously, have 
been in large part due to numerous 
interdependent factors rather than to 
the basic principle involved. For one 
thing, pickup apparatus in the past has 
been very much at fault. Even when 
using the film pickup, there was 
failure to scan in a mathematically 
precise manner. Therefore, we have 
not secured the proper pictorial values 
for the 48 strips constituting each pic- 
ture flashed at the rate of 15 pictures- 
per-second. Also, our amplifiers have 
not given us a sufficient range of fre- 
quencies so as to secure proper pictorial 
detail. Again, modulation of the trans- 
mitter has been very much at fault, so 
that whatever may have been picked up 
with a crude pickup and amplifier, has 
not been properly impressed on the 
out-going carrier wave. Then, at the 
receiving end, there have been many 
poor links further to cause loss of de- 
tail in the intercepted pictures. By 
spending many months in checking over 



JANUARY, 1931 



Page 17 



each detail and making it as perfect as 
possible, the engineers have been able 
to obtain a surprising amount of de- 
tail from the 48-line technique. 
Furthermore, the engineers are only 
using about 13 kilocycles of the total 
of 100 kilocycles available in the usual 
broadcast radiovision channel. 

Entertainment Value 

Since any discussion of radiovision 
gets down to a matter of definitions, it 
becomes necessary at this point to 
state a conception of reasonable enter- 
tainment value, so as to provide a 
yardstick whereby to measure the pres- 
ent possibilities of radiovision. By fair 
entertainment, we mean the telling of 
a story of real interest, which can be 
followed without the exercise of ex- 
traordinary imagination. If we must 
turn to a parallel, we might mention the 
motion picture screen. The present- 
day theatre shows the animated cartoon 
on the one hand, which conveys an 
excellent story in a grotesque manner, 
but with very high entertainment 
value. On the other hand, there is 
the highly artistic photoplay with ex- 
cellent photography together with the 
sound accompaniment, telling a story 
with practically complete detail. In the 
case of the present radiovision presen- 
tation, the art is approximately half- 
way between these two extremes of the 
screen. Instead of the simple silhouette 
or again the close-ups of heads to 
which radio television was limited 
some six months ago, we now have 
long shots of complete scenes, includ- 
ing as many as a dozen persons, with 
about the same detail as was available 
in the first home-movie picture presen- 
tations. There is some flicker, due to 
the 15-pictures-per-second rate, as well 
as the 48-line scanning which weaves a 
pattern of coarse and apparently hori- 
zontal strips. If the film at the trans- 
mitting end is not carefully selected, 
there is a considerable loss of detail in 
the case of elaborate scenes with rather 
flat lighting. However, if the film is 
carefully selected, it becomes possible 
to present a really complete picture, 
which causes no strain upon the 
imagination of the lookers-in. 

Standard Film 

Recently, the DeForest engineers 
have been broadcasting standard mo- 
tion picture film without any changes 
whatsoever and without deletion of 
scenes. Consequently there are some 
excellent scenes, while there are other 
scenes not quite so good due to every- 
thing being included in the radio movie 
presentation. For instance, on the oc- 
casion of the writer's visit, a film being 
transmitted included several so-called 



moonlight scenes, blue tinted form on 
the film at the transmitting end. Need- 
less to state, such film is hardly suit- 
able for any kind of presentation, much 
less for radiovision pickup. Otherwise 
the scenes were well detailed, so that 
the action could be readily followed. 
To be more specific, one scene repre- 
sented an auction sale in which various 
articles were put up by the auctioneer. 
Such items as a bottle of liquor, an 
old trunk, clothes, collars, ties and 
other things could be readily identified, 
even when the scene included at least 
a dozen persons. The liquid in the 
bottle could be plainly seen in the 
hands of the auctioneer, in a waist- 
high closeup. Another scene depicted 
three automobiles in a chase, one being 
a taxicab. It was easy to follow 
the chase of the three cars, and to 
identify each as to its particular make, 
which requires a fair amount of detail 
in a long-shot picture including three 
cars. The black-and-white taxi could 
be readily identified, and it was almost 
possible to read the sign on the side. 
To the author's way of looking at the 
situation, the pictures are approxi- 
mately on a par with those of the old 
nine-millimeter film employed for home 
movies several years ago, when magni- 
fied to a considerable degree so as to 
show the imperfections. 

Program Material 

From an entertainment standpoint, it 
is now largely a question of selection 
of suitable program material. The ma- 
terial may take three different forms : 
first, the film, which may be either 
regular theatrical film or special film 
made with the requirements of tele- 
vision foremost in mind; direct pickup 
of subjects in the studio, making use of 
the flying spot illumination of the sub- 
ject and suitable photoelectric cells; 
and lastly, the direct pickup camera, 
which, scanning the subjects in broad 
daylight or artificial illumination, can 
be used practically everywhere, includ- 
ing out in the field. 

Analyzing the three possibilities just 
referred to, we come to the first or 
film pickup, which, for a long while to 
come, will be found to be the back- 
bone of the radiovision program, just 
as the automatic piano and phonograph 
were the foundation of the sound 
broadcast programs in the early days. 
A good deal of old and new film is 
available, so that the radiovision 
broadcaster need not fear a dearth of 
program material. However, unless 
original film is secured, or at least in 
a reasonable proportion to the total 
amount of material presented over the 
air, the lookers-in are not going to be 
satisfied for long, after their first curi- 
osity is satisfied. However, it is rela- 



r j! 


'i 


M 


1 



Complete home radiovision equip- 
ment, comprising special receiver in 
table form, and cabinet radiovisor 



tively inexpensive for the radiovision 
broadcasters to have special film pre- 
pared for their requirements. The 
radiovision presentation of today must 
not be judged strictly from the stand- 
point of entertainment value, for the 
reason that the television broadcasters 
are for the most part experimenting 
with transmitters, receivers, and gen- 
eral atmospheric conditions, without 
particular regard for the entertainment 
end of their work. But there is a great 
danger with film pickup of repeating 
the same subjects over and over again. 

Flying Spot Pickup 

The flying spot studio pickup is an 
ideal method, particularly as a supple- 
ment to the film pickup. Thus the 
Jenkins studio in Je ;ey City 1.^ a -meet- 
ing place for speakers, musicians, 
singers, and others who are willing to 
aid the struggling television art at this 
time. Such talent as can be coaxed 
before the flying spot pickup, is not 
only scanned and sent over the air in 
pictorial form, but the voice or music 
can also be intercepted by a nearby 
microphone, so as to give a complete 
sight and sound presentation. The pic- 
ture signals are sent over the W2XCR 
television channel on 149 meters, 
while the sound is amplified to the 
necessary degree and sent over a direct 
wire to the DeForest telephone trans- 
mitter, W2XCD, at Passaic, N. J. At 
the receiving end the broadcast re- 
ceiver tuned to the lowest point on its 
dial brings in the sound accompani- 
ment, while the television short-wave 



Page 18 



PROJECTION ENGINEERING 



receiver and scanning mechanism 
weaves the accompanying picture. 

Due to certain pickup difficulties by 
way of flying spot scanning and photo- 
cell placement, it is not as yet practical 
to pick up as much detail as can be 
safely handled with the film pickup. 
Consequently, aside from close-ups or 
intimate portraits, the film method is 
more suitable on a strictly pictorial 
basis. On the other hand, in the case 
of prominent speakers, singers or 
artists shown in close-up form together 
with their sound accompaniment, the 
flying spot studio pickup certainly 
freshens up a program and presents 
the real reason for radiovision. It 
must be obvious that the mere repro- 
duction of old film will never put 
radiovision where sound broadcasting 
is today. Just as the phonograph and 
automatic piano passed out of the 
sound broadcast picture some seven 
years ago, so must the old film be dis- 
carded when radiovision gets down to 
genuine entertainment. 

The Camera 

The direct pickup camera, while 
leaving quite a bit to be desired by 
way of detail, possesses perhaps the best 
entertainment value of the three 
methods. With this method it becomes 
possible to stretch the radiovision 
pickup to outside events. Thus in the 
case of the usual broadcast pickup of 
prominent persons, the radiovision 
camera may be moved up close to the 
microphones, picking up the visual 
half of the presentation. This is an 
invaluable feature, inasmuch as it gives 
the radio audience its eyes. It 
completes the job of the news broadcast. 

Due to the use of short waves, the 
direct camera pickup used out in the 
field may perhaps go forth with one- 
quarter kilowatt or a one-half kilowatt 
portable transmitter so as to broadcast 
the programs direct. In fact, the 
Jenkins organization has done some ex- 
cellent work in a half-kilowatt portable 
transmitter in the field. The problem 
of remote-control lines may not prove 
a serious obstacle after all. 

Air Channels for Pictures 

The one great handicap in the im- 
mediate exploitation of radiovision, as 
the writer sees it, is the question of a 
place on the air. The demonstrations 
he has recently seen have frequently 
been marred, particularly at night, by 
conflicting carriers and even conflicting 
modulation or what would be con- 
sidered cross talk if we were dealing 
with sound rather than pictures. So 
far, it appears that the Federal Radio 
Commission has not given radiovision 
broadcasters the necessary wavelengths 
or frequencies with which to carry on 
their experimental work. At the Mont- 
clair demonstration, for instance, three 



distinct carriers were being picked up 
on a given frequency, resulting in the 
marring of the powerful DeForest sig- 
nals from a transmitter only five miles 
away. The interference takes the form 
of horizontal and vertical lines super- 
imposed on the pictures and ruining 
detail. In fact, it was only after ten 
o'clock in the evening that we were 
able to secure satisfactory pictures, 
after the transmitter in Washington 
and that in New York City had gone 
off the air. 

The greatest handicap at the present 
time is the question of radiovision in- 
terference. It is absolutely impossible 
to put on good pictures if they are go- 
ing to be broken up by conflicting car- 
riers or images. Just how the Federal 
Radio Commission will work out this 
detail, is rather difficult to see, inasmuch 
as the ioo- to 150-meter band for 
radiovision transmission carries exceed- 
ingly well, so that interference may 
take place at great distances as com- 
pared with the usual sound transmis- 
sion. Nevertheless, no real progress 
can be made if serious interference 
exists between television transmitters. 
It is to be hoped that the Radio Com- 
mission will set aside the necessary 
frequencies or arrange to have the 
stations divide time so that pictures 
will not be marred. 

System Now Practicable 

In conclusion, the author does not 
agree with the leaders of the radio in- 
dustry who persistently claim that tele- 
vision is five years hence. He firmly 
believes, following the demonstration 
he has seen, that there is real enter- 
tainment value in radiovision technique 
as it exists today, and that it is pos- 
sible to put out suitable receivers and 
radiovisors at a cost within reach of 
the average family. Furthermore, he 
believes that radiovision can be made 
the salvation of the radio industry dur- 
ing the coming year. If a suitable 
radiovision broadcast service is estab- 
lished in various parts of the country, 
on a regular entertainment basis rather 
than the present experimental basis, 
the public will want radiovision equip- 
ment. The new industry is bound to 
follow in the footsteps of sound broad- 
casting, beginning with a great deal of 
home experimentation with many home- 
made outfits, a keen interest in the de- 
sign and engineering end, and a tre- 
mendous amount of curiosity displayed 
in picking up pictures. There will also 
be a large part of the public which will 
want complete equipment, ready for 
use. The second consideration, follow- 
ing the establishment of a satisfactory, 
dependable radiovision broadcast serv- 
ice, is mass production so as to reduce 
the price of equipment to the point 
where it really can be sold. Until now, 
this feature has been most discourag- 



ing, inasmuch as such equipment as 
has appeared on the market, claimed to 
be practicable and was offered at a 
price far beyond what the public is 
willing to pay. It seems to the writer 
that someone must take the initiative. 
Someone must establish a satisfactory 
broadcasting service, placing the neces- 
sary programs on the air so as to cre- 
ate a keen desire for a means of "look- 
ing in." Someone must take a chance 
and place in production a sufficient 
volume of radiovision equipment, 
whether it be complete sets or kits or 
parts, so as to bring the price down to 
within reach of the average family. If 
these two things will be done during 
193 1, which seems quite probable, we 
shall see a revival of the radio industry 
which will surpass our fondest 
expectations. , 

Rather than preach the distant future 
of television, as many of us are con- 
sistently preaching the permanency of 
depression, it would be far better for 
the leaders of the radio industry at 
large to take the radio television situa- 
tion more seriously, endeavoring to 
work out ways and means of getting 
this art on a real merchandising basis, 
thereby bringing real prosperity back 
to the radio industry. 



MONITORING SOUND MOTION 
PICTURES 

(Concluded from page 15) 
man. Naturally somewhat different ar- 
rangements of instruments are used for 
recording jazz orchestras and brass 
bands. Hard and soft baffles are gen- 
erally used with orchestrations as an 
aid to securing just the proper effect. 

When three microphones are used for 
scoring, one is placed for the wood 
winds, another for the violins and a 
third for bass. By controlling the 
three mixer dials connected with these 
microphones the monitor man can quite 
easily get the correct relationship be- 
tween these divisions of the orchestra. 
The overall volume is then regulated by 
the main volume control. When a 
single mike is employed its position and 
the arrangement of the orchestra is 
much more critical, but the results seem 
to be worth the extra work as the effect 
is much more like normal binaural 
hearing. When it is projected, the 
sound from a one-mike job seems to be 
much more unified. However, monitor 
men are obtaining excellent results with 
both systems of scoring, although the 
majority are inclined toward the one- 
microphone method. 

Practically all of the information on 
monitoring contained in the last two 
articles of this series applies to the 
making of phonograph recordings as 
well, particularly the part relating to 
monitoring orchestrations. 



JANUARY, 1931 



Page 19 



A Three-Element 

Glow Lamp 

for Sound Recording 

By Verne T. Braman* 



THE ordinary two-element glow 
lamp (gas discharge tube) con- 
sists of a glass, Pyrex, or quartz 
tube which contains rarified gases, 
and into which are 
sealed two electrodes, 
an anode and a cath- 
ode. If sufficient volt- 
age be applied to the 
two electrodes, t h e 
gas will ionize and 
carry current, at the 
same time becoming 
luminous. 

If now the voltage 
be varied up or down, the current will 
also vary, causing a variation in illumi- 
nation proportionate to the variation in 
current. Thus, if the lamp voltage is 
modulated, its illumination is modulated 
proportionately. 

This lamp may be modulated at 
sound frequencies and photographed 

* Engineer, Blue Seal Sound Equipment Cor- 
poration. 



The Employment of a 
Third Element in Glow 
Lamps Overcomes Cer- 
tain Difficulties Here- 
tofore Experienced in 
Sound Recording 



FIG 1A ORDINARY TWO ELEMENT LAMP. 



DISTORTION 




FIG. IB CINEGLOW THREE ELEMENT LAMP. 




Current curves of two types of glow lamps. 



through a slit onto film to make a 
sound track, such as is done in a num- 
ber of recording systems. 

Objections to the use of the glow 
lamp for sound re- 
cording have been 
given as lack of suffi- 
cient illumination for 
use with positive 
stock, short duration 
of life, lack of uni- 
formity, and "blast- 
ing" when modulated 
at high volume levels. 
This last will be gone 
into more fully later. 

Intense illumination can be gotten 
enly by the proper combination of cer- 
tain gases and vapors, which must be 
extremely pure and at the proper pres- 
sure. If all impurities and gases are 
not completely eliminated from all parts 
of the tube and tube elements, they are 
almost certain to manifest themselves 
later and cause early 
deterioration of the 
lamp. Likewise the 
nature of the gas and 
its pressure, as well as 
the material and pu- 
rity of the electrodes 
determine the amount 
of sputter and the use- 
ful life of the lamp. 
Only by careful con- 
trol of all of these 
factors can lamps be 
made with illumina- 
tion sufficiently i n - 
tense to expose posi- 
tive stock, and with 
reasonably long life 
and uniformity. 

Blasting at Full 
Modulation 

If the voltage ap- 
plied to the tube ter- 
minals be decreased, 
the current will grad- 
ually decrease until a 



4 






iW 



voltage is reached where the current 
drops from a certain value (say L) to 
zero. Let us call this the extinguishing 
voltage. If, after extinguishing, the 
lamp voltage be increased, it will not 
ignite until a voltage somewhat higher 
than the extinguishing voltage is 
reached, which we will call the ignition 
voltage. At this point ionization of the 
gas is affected and the current suddenly 
rises from zero to a value (say L), 
which is greater than L. 

Thus, when the voltage is modulated 
down to the -extinguishing voltage and 
back again, the current will not exactly 
follow the voltage modulation, but will 
remain at zero until the ignition volt- 
age is reached. Thus a hysteresis loop 
is introduced into our modulation curve. 
Fig. I A shows how this can affect the 
current waveform at 
maximum modula- , — -r^ 

tion. L is the mini- 
mum current before 
extinguishing and L 
the current at igni- 
tion. The current re- 
mains at zero over a 
portion of the cycle, 
introducing a wave- 
form which, due to 
the extremely sharp 
wave front or rise in 
current, is very pro- 
ductive of undesir- 
able harmonics and 
distortion, causing 
harsh, raspy quality. 

The Three-Element 
Tube 

Obviously the only 

way to prevent this 
form of distortion is 
to make the ignition 
voltage equal to the 
extinguishing v o 1 t- 
age. This is done by introducing a third 
element into the tube which allows an 
unmodulated ionizing current to flow at 
all times, independent of the modulated 
current flowing between the two normal 
electrodes. This unmodulated current 
from the third electrode keeps the gas 
ionized at all times, so that for the two 
normal electrodes the extinguishing 
voltage and ignition voltage are equal, 
and the hysteresis loop is eliminated. 
The resultant undistorted waveform is 
shown in Fig. iB. • 

The distortion shown in Fig. iA is 
mild compared with that of some tubes 
the author has measured. Certain im- 
purities in the gas and improper spac- 
ing of the electrodes causes L and L to 
be much more widely separated. 

Besides the "lag" in ionization be- 
cause of the time required for the volt- 
age to reach the ionizing voltage, there 
is also a time lag in the ionizing of the 
gas even after the ionizing voltage is 
reached. This effect tends to accentuate 



Fig. 2. 
Three - ele- 
ment glow 
lamp. 



Page 20 



PROJECTION ENGINEERING 



the distortion previously described. By 
causing continuous ionization, the third 
element eliminates this effect also, and 
certain otherwise desirable gases and 
\apors which are sluggish in ioniza- 
tion can be utilized to advantage. 

Fig. 2 shows the appearance and me- 
chanical construction of a Cineglow 
three-element recording lamp. 

The construction of this lamp is sim- 
ple and rugged, and it is made entirely 
by machinery, thus eliminating the hu- 
man equation which is not only costly 
but subject to non-uniformity. 

The circuit for the three-element re- 
cording lamp is extremely simple. The 
two modulated electrodes are connected 
as in the standard two-element lamp cir- 
cuit; i.e., the cathode is connected to 
the negative voltage supply, and the 
anode to the positive voltage supply 
through a transformer or inductance 
and a stabilizing resistance, the modulat- 
ing voltage being introduced by the 
transformer or inductance in the usual 
manner. The third electrode is con- 
nected directly to the positive voltage 
supply through a very high resistance, 
say one or two megohms, which allows 
an unmodulated ionizing current on the 
order of 0.3 milliamperes to flow. This 
simple addition is enough to accomplish 
the desired purpose and eliminates all 



of the undesirable effects previously 
described. 

Effect of Overload 

Since the hysteresis loop has been 
eliminated and the ignition voltage made 
equal to the extinguishing voltage, ob- 
viously any over-modulation of the 
three-element lamp will result in only a 
flattening of the lower peaks of the 
waves, similar to the overloading of a 
vacuum tube, light valve, etc. It has 
been found that a certain amount of dis- 
tortion of this nature is not noticeable 
in most forms of sound work, as prac- 
tically all natural sounds are already 
very rich in the harmonics which are 
introduced, and a slight increase changes 
neither the character nor the quality of 
the tones. In addition to this, most com- 
plex waveforms consist of high frequen- 
cies "riding" on the waveforms of lower 
frequencies, so that the peaks of these 
higher frequencies are the first to be- 
come flattened, and the higher harmon- 
ics introduced are soon lost by being 
above the audible range as well as the 
transmission characteristic of the sound 
system. 

Reason for High Modulation Level 

In sound systems our modulation level 
is limited at the lower end by ground 



noise and at the upper end by over- 
modulation. Since these limits are nar- 
rower than the volume range of sounds 
in nature, we must keep the average 
modulation reasonably high so that the 
weaker sounds are not lost in the ground 
noise. To take full advantage of vol- 
ume range we must record with peaks 
on the verge of over-modulation. With 
the ordinary two-element tube this can- 
not always be done with good results, 
since full modulation results in the in- 
troduction of the previously described 
harsh and raspy quality, the distortion 
introduced bearing no harmonic rela- 
tionship to the original sound. Thus 
the two-element tube must be modulated 
at a lower level, with corresponding loss 
in volume level and range. 

With the three-element tube, how- 
ever, full advantage may be taken of 
the volume range of the system with the 
knowledge that full modulation may be 
utilized, a slight amount of over-modu- 
lation on the extreme peaks being per- 
missible. The use of a lamp capable of 
exposing positive stock also makes pos- 
sible increased volume range and a re- 
duction of ground noise. The net re- 
sult is high quality sound recording with 
a greatly increased volume range and 
volume level. 



RCA PHOTOPHONE GAINS 

W7ITH more than 3,000 installations 
of sound reproducing equipment 
contracted for during 1930, as against 
slightly more than 900 to its credit at 
the beginning of the year, RCA Photo- 




CHARLES J. ROSS 

Executive Vice-President 

RCA Photophone, Inc. 

phone, Inc., has registered more than a 
300 per cent increase in business in its 
domestic and foreign commercial de- 
partments during the last twelve 
months. In addition thereto, RCA Pho- 



tophone recording division in both 
domestic and foreign fields showed by 
far the greatest number of new installa- 
tions of recording apparatus of any 
company engaged in the manufacture 
and distribution of sound equipment. 
In spite of the financial depression that 
affected all lines of business, RCA Pho- 
tophone, Inc., under the leadership of 
Charles J. Ross, executive vice-presi- 
dent, has established a record that has 
been the subject of much favorable 
comment in all branches of the motion 
picture industry. 

In commenting upon the outlook for 
193 1, Mr. Ross made the following 
statement : 

"Continued refinements in recording 
and reproducing apparatus, the simpli- 
fication of operation and the standardi- 
zation of installations to reduce ex- 
penses, will receive primary attention 
during the coming year. Prices of 
equipment will not materially change, 
due to the high cost involved in the 
manufacture of standard equipment. 
Improvements will be made, however, 
and the number of models will be 
reduced. 

"There are at least 10,000 unwired 
theatres of the smaller type in the 
United States and at least 5,000 of these 
will install sound reproducing equip- 
ment, in addition to several thousand 
others that will replace unsatisfactory 
apparatus with dependable equipment." 



S. M. P. E. TO HOLD SPRING 
MEETING IN HOLLYWOOD 

THE Spring meeting of the Society of 
Motion Picture Engineers will be 
held in Hollywood May 25 to 28, 1931, 
according to announcement by W. C. 
Kunzmann following a recent meeting 
of the Board of Governors. 

O. M. Glunt, chairman of the Papers 
Committee, has already begun work in 
securing representative speakers and 
papers for the meeting. 

The last meeting to be held in Holly- 
wood was in the Spring of 1928 and 
with so many new developments 
brought about by sound in the studios 
since then, the coming convention is ex- 
pected to be of great interest and value 
to the members of the Society. 
A 

THEATRE ACOUSTICS 

Kendell & Dasseville, of New York 
have opened a branch office at 1734 
Ridge Avenue, Philadelphia. It is 
staffed with a complete sales, service 
and engineering unit and covers East- 
ern Pennsylvania, New Jersey and 
Delaware. Five houses, The Ridge, 
Grand, Jackson, Diamond and Ritz 
have already been acoustically corrected 
via The Kendell Method. Lewen Pizor, 
chain operator, is having eleven of his 
houses gone over ; George Kline of Na- 
tional-Kline Poster fame, nine of his, 
and Comorford tops the list with 
twentv. 



JANUARY, 1931 



Page 21 



Wide Film 

and 

Third Dimension 

By James R. Cameron 



Mr. Cameron Believes the Present Economic Situa- 
tion Will Delay General Introduction of Wide Film 
Pictures 



ANOTHER of the wide film 
processes reached Broadway 
^ late in December. This time 
it is the Spoor 65 mm. devel- 
oped for R.K.O. The management of 
the Mayfair Theatre advertised the new 
wide film as a "Natural Vision" produc- 
tion and from the advertising copy one 
might expect to see stereoscopic pic- 
tures. 

In doing this, of course, R.K.O. fol- 
lows the lead of the other wide film 
productions already shown. Each of 
these productions has been heralded as 
third dimension pictures. 

It has been the writer's lot to see 
each of the wide film processes already 
shown, and we wish to go on record 
with the statement that to our way of 
thinking these pictures have as much 
third dimension as has Washington's 
picture on a two cent postage stamp. 
We are going to receive mail telling us 
that in certain spots in these wide film 
pictures there is an illusion of depth, 
and with this we agree, but this illusion 
of depth is in no way attributable to the 
wide film. One of the first subjects 
shown by the Fox wide film (Gran- 
deur) was a picture of Niagara Falls, 
and the Spoor R.K.O. process has used 
these same Niagara Falls in the first 
public showing of that company's wide 
film. 

In certain spots in both the Fox and 
the Spoor film a stereoscopic effect is 
obtained, but this same effect has been 
obtained in certain "travel" pictures on 
35 mm. film practically since the incep- 
tion of motion pictures. To the writer's 
way of thinking a much better illusion 



of depth was obtained in a 35 mm. pic- 
ture made by Edwin S. Porter, who will 
be remembered as the director of the 
first motion picture with a story "The 
Great Train Robbery" and later as the 
manufacturer of the Simplex projector. 
The picture we refer to, curiously 
enough, happens to be another picture 
of Niagara Falls and was made, we be- 
lieve, by Porter for Edison in the early 
days of motion pictures. 

It has been claimed for the wide film, 
that due to using a 65 or 70 mm. film 
in place of a 35 mm. film, a wider angle 
camera lens may be used, thus ap- 
proaching more closely the angle of 
human vision. In practice this does 
not work out. Approximately the short- 
est focus lens that can be satisfactorily 
used when using wide film would be a 
three inch, and this would give an angle 
of about 35 degrees, which is practic- 
ally the same angle as that obtained 
when using a i J / 2 inch lens with 35 mm. 
film. 

As we see it the width of the picture 
on the film has little or no bearing on 
the question of stereoscopic pictures. 
If the producers of wide film pictures 
intend marketing their product on a 
basis of stereoscopic films, then sales- 
men are going to have a tough time. 
The wide film has certain advantages 
over the 35 mm. standard in use today, 
but third dimension is not one of them. 

We are ready to admit that certain 
cf the motion picture critics on the 
New York newspapers in reviewing 
these pictures, have referred to certain 
shots having "an illusion of depth." 
One critic tells how the improvement 



in sound reproduction on one of these 
wide film pictures was due to the wider 
sound track, etc. The fact is this sound 
happened to be recorded on disc. 

The picture at the Mayfair is one of 
those railroad dramas, in which the 
Chicago, Milwaukee and St. Paul Rail- 
road gets some advertising. It is entitled 
"Danger Lights" and features Louis 
Wolheim, Robert Armstrong and Jean 
Arthur. The screen on which the pic- 
ture is projected completely covers the 
stage opening, and renders the first ten 
rows of seats useless for perfect view- 
ing of the picture. For a while we sat 
in the fifth row a little to one side, and 
there was both eye strain and distortion. 
We changed our seat repeatedly to try 
end get the "natural vision" but with- 
out result. All through the picture we 
noticed that the characters in the back- 
ground were out of focus when the 
characters in the foreground were in 
sharp focus. 

The scenes showing a locomotive and 
one passenger car making a time record 
run to Chicago were most impressive, 
as were the panoramic scenes taken 
outdoors. 

From what we were able to learn 
during our reecnt stay on the West 
Coast and from recent developments in 
the East, the wide film is probably out, 
;:nd activity on wide film and any other 
radical change is to be dropped for the 
time being. The present economic sit- 
uation is the primary reason for this. 



SMALL THEATRE IN TIMES SQUARE 
SECTION, NEW YORK 

D ROADWAY'S first international 
theatre, to be dedicated to the pre- 
sentation of first run foreign language 
sound motion pictures, in addition to 
the best product of the studios in this 
country, will soon be opened under the 
management of Sigmund Weltner and 
Nicholas Weiss, operating as the Sig- 
nick Corporation. This theatre, the 
President, at 247 West Forty-eight 
Street, between Broadway and Eighth 
Avenue, one of the smallest of Times 
Square's legitimate de luxe playhouses, 
is now in the hands of RCA Photo- 
phone engineers who are installing that 
corporation's small theatre sound re- 
producing equipment, especially de- 
signed for houses having seating 
capacities of 1,000 and under. It will 
be the first small theatre on Broadway 
to have Photophone's new loudspeaker 
and directional baffle, which is said to 
come the nearest to perfect sound re- 
production that has been obtained 
through the medium of a mechanical 
device. 

The President theatre has a seating 
capacity of 300 and engineers in 
charge of the sound equipment installa- 
tion, are said to be impressed with its 
excellent acoustics. 



Page 22 



PROJECTION ENGINEERING 



Microscopic 
Photography 



By Employing the Close- 
to-Visible Ultra- Violet 
Rays, a Gain of Nineteen 
Per Cent Over Visible Ray 
Method Is Obtained 



ANEW microscopic system which, 
using invisible, ultra-violet 
light, is able to reveal the na- 
ture of minute objects with 
theoretically 19 per cent greater de- 
tail than the best visible-light mi- 
croscope can yield has been reported 
to the Optical Society of America by 
A. P. H. Trivelli of the Eastinac 
Kodak Research Laboratories and 
Leon V. Foster of the Bausch & Lomb 
Optical Company, both of Rochester, 
N. Y. The microscope constructed by 
Mr. Trivelli and Mr. Foster is ex- 
pected to be a furtber step in the 
process of permitting clearer pictures 



of microscopic objects to be made by 
biological scientists. 

Photomicrography by ultra-violet 
light is not new, but experimentation 
heretofore has been conducted with 
ultra-violet light from a point in the 
spectrum comparatively remote from 
the visible. The system worked out 
by the Rochester men uses light closer 
to the visible and yet makes the in- 
dicated 19 per cent gain over visible 
microscopic systems. Use of light 
nearer the visible portion of the 
spectrum avoids the expensive neces- 
sity of using quartz instead of glass 
for lenses and in other ways is 
simpler than other ultra-violet micro- 
scopic systems. Also it permits the 
use of ordinary biological microscope 
slides with the object for examination 
mounted in Canada balsam. Previ- 
ous ultra-violet micrography has 
required specially mounted slides be- 
cause light of wavelengths previously 
used was too greatly absorbed by 
balsam. 

Microscopy using visible light, ac- 
cording to Mr. Trivelli, has reached 
such a state of perfection that very 
little more in the way of improve- 
ment can be accomplished. The use 
of ultra-violet light, however, has 
brought forth many surprising results. 

A demonstration of microscopic pic- 
tures obtained by visible light and by 
invisible light with the new micro- 
scope with its subject a grain of 
hollyhock pollen magnified 300 times, 
showed the minute object surrounded 
by nothing more than a vague, grey 
ring under visible light. The ultra- 
violet light picture of the same grains 
showed the ring resolved into a cir- 
cumference of tiny spines previously 
not in evidence. Sharply increased 
detail showed in other ultra-violet 



photomicrographs of shells, leaves, and 
a section of calfskin. 

The light source of the Trivelli- 
Foster microscope has a wavelength 
of about l/70,000th of an inch, which 
is in the ultra-violet portion of the 
spectrum. Since ultra-violet light is 
invisible, the microscope's results are 
recorded on photographic materials. 
The system is so arranged that the 
object to be examined can be focused 
and viewed by visible green light and 
then, by a change of the light filter, 
photographed in greater detail by 
ultra-violet light. 

Quoting Trivelli-Foster on the com- 
parison with visible microscopy: 
"Photomicrography with radiation of 
365 millimicrons (about l/70,000th of 
an inch) makes available a consider- 
able increase of resolving power 
(ability to show detail at high mag- 
nifications), or alternatively, if the 
resolving power obtained with visible 
light is sufficient, the use of the ultra- 
violet enables an increase of depth to 
be obtained by reduction of the 
aperture." 

One phase of experimentation with 
the new microscopic system involved 
the discovery that sandalwood oil, used 
in connection with one element of the 
optical system, improved the resolving 
power because it absorbed much less of 
the particular wavelength of ultra- 
violet light used than did cedar oil, 
ordinarily employed. 

A curious sidelight of the demon- 
stration was a comparison showing 
the microscopic sections of the dis- 
codrellid worm made with visible 
light were clearer than with ultra- 
violet because the worm's surface 
contained a protective layer against 
ultra-violet rays. 



THE SELSYN MOTOR 

SELSYN motors are used for inter- 
locking picture machines and dum- 
mies. As we use them they are three 
phase slip ring motors. The stators 
of all the motors to be interlocked 
are hooked to the supply, just as in 
ordinary practice, the corresponding 
slip rings are then connected to each 
other, that is, the inner slip ring on 
one rotor is connected to the inner 
slip ring on the other rotor, connec- 
tion being made through the brushes, 
of course. The two other slip rings 
are connected in a similar manner. If 
one rotor is turned all the others that 
are hooked to it in this fashion will 
also turn, and in the same direction 
and in the same amount. 

Wired in this manner the motors 
will not run of their own accord, but 
a different motor is used to turn one 
of the Selsyn motors. This one is 
then called the distributor and the 
other motor or motors follow it, or 
are driven by it. 



ERPI is now putting resistances 
across the slip rings. The motors will 
then run by themselves, that is, with- 
out being driven by another motor. 
This is done so that the pickup will 
be better, and a smaller motor can also 
be used to drive the Selsyn motors. 
These resistances are of such a value 
that the Selsyn motors alone will drive 
the machines at about 70 to 80 feet 
per minute, the control motor tak- 
ing the balance of the load and bring- 
ing the speed up to 90 feet. 

These motors are also built to work 
on single phase, but these are not used 
in motion-pictui - e work. The single 
phase motors have only two slip rings 
and the power supply is connected to 
these. The stators are somewhat sim- 
ilar to those of the three phase motors, 
but they form the secondaries in this 
instance, each of the three taps being 
connected to corresponding taps on 
the other motors to be locked together. 
This particular type is being used in 
the remote control of radio sets. 

— The Loudspeaker. 



CRABTREE ANNOUNCES NEW 
COMMITTEES FOR S.M.P.E. 

APPOINTMENTS for the personnel 
of the committees to serve the 
Society of Motion Picture Engineers 
for the following year have been made 
by J. I. Crabtree, president. 

Color, W. V. D. Kelley, DuChrome 
Film Systems, 6723 Santa Monica 
Boulevard, Hollywood, Calif. ; Conven- 
tion, W. C. Kunzmann, National Car- 
bon Co., Cleveland, Ohio ; Membership, 
H. T. Cowling, Eastman Kodak Co., 
Rochester, N. Y. ; Papers, O. M. Glunt, 
Bell Telephone Laboratories, New 
York, N. Y. ; Progress, G. E. Mat- 
thews, Eastman Kodak Co., Rochester, 
N. Y. ; Publicity, W. Whitmore, Elec- 
trical Research Products Inc., New 
York City ; Historical, C. L. Gregory ; 
Sound, H. B. Santee, Electrical Re- 
search Products Inc., New York City; 
Standards, A. C. Hardy, Massachusetts 
Institute of Technology, Cambridge, 
Mass. ; Studio Lighting, M. W. Palmer. 



JANUARY, 1931 



A Revolutionary 
Advance 



in 



Sound Recording 



By Charles Felstead* 



A New Device Which Silences Ground 
Noise Introduced in Sound Recording 



ONE of the great bugaboos of 
motion picture sound record- 
ing has been the presence of 
"ground noise," or "back- 
ground noise," and the difficulty of 
maintaining so low a level of noise that 
it will not interfere with the reproduced 
sound to an extent great enough to 
reduce the intelligibility of recorded 
dialogue and the quality of music. This 
appellation "ground noise" was given 
by sound engineers to the sputtering, 
grinding, gritty noise that has been 
present to a greater or less extent in 
the reproduced sound of all earlier 
sound pictures. It is an interfering 
sound somewhat analogous to the static 
that is encountered in radio reception. 
By taking extreme care in all the steps 
of recording sound, engineers have gen- 
erally kept the ground noise below the 
point where it is annoying during dia- 
logue or music ; but during the portions 
of the picture where there was no 
recorded sound, the noise often became 
very noticeable and prevented the spec- 
tator's full enjoyment of these silent 
sequences. Whether or not the specta- 
tor was consciously aware of this noise 
did not particularly matter. The ever- 
present noise beating on his ear-drums 
served to irritate him and make him 
restless. Even though he was uncon- 
scious of the presence of the noise, he 
was constantly straining his ears to 
hear the voices of the actors and to 
catch the words as they rose out of and 
above this steady blanket of noise. 
Because this ground noise drowned out 
all faint sounds as a low blanket of fog 



* Sound Engineer, Universal Pictures Corpo- 
ration. 



covers up all objects near the surface 
of the earth and leaves only the taller 
objects showing clear, it served to place 
a limit on the lower end of the range 
of sound volume that might be recorded 
safely, reducing the volume range that 
would be possible if ground noise were 
not present. But now, through a clever 
invention, all of that is changed because 
the background noise is reduced to the 
point where it is no longer noticeable. 

Noiseless Recording 

This new device added to the West- 
ern Electric sound recording system 
produces what is to be known as the 
Western Electric new process noiseless 
recording system. The first test of this 
device was made at the Paramount 
Studio in the shooting of the picture, 
"The Right to Love ;" and it proved so 
successful that the device has been 
adopted for use in the filming of all of 
Paramount's present productions. It 
was the thorough test that the device 
underwent in the recording of this pic- 
ture that satisfied the electrical engi- 
neers who spent years in working to 
eliminate ground noise in sound record- 
ing that the device was satisfactory for 
general use. As a result of this the de- 
vice has been made available to other 
studios equipped with Western Electric 
apparatus, and is being installed in their 
recording channels as rapidly as pos- 
sible. 

Previously the volume range of the 
Western Electric recording system was 
estimated to be approximately thirty to 
forty decibels, the exact range depend- 
ing on certain recording conditions ; 
but the addition of this new device has 



Page 23 

extended the range some six to ten db 
downward by almost totally eliminating 
the ground noise. The volume range 
of a sound recording and reproducing 
system is limited on the lower end by 
the point where the dialogue and music 
become so faint that they are covered 
up, or "masked," by the ground noise, 
and the volume range is bounded at the 
upper end by the point at which the 
recording or reproducing system or the 
film overloads. This device acts to in- 
crease the volume range by driving the 
ground noise to a much lower level. 
Even the faintest of recorded whispers 
will now become clearly audible ; and 
directors will be able to obtain sound 
effects that formerly were impossible 
because all faint sounds were blanketed 
by the ever-present ground noise. Now 
when silence is required on the screen, 
the reproducing horns will be truly 
quiet, the attention of the audience will 
not be diverted by the extraneous pop- 
ping and hissing sounds, and the dra- 
matic effect will be accordingly height- 
ened. Greater enjoyment of the picture 
by the audience will also be possible 
because the straining of attention to 
hear sounds that are so faint that the 
ratio of recorded sound to ground noise 
i.i low will no longer be necessary. 

▲ 

PROJECTION COUNCIL TO MEET 

THE annual meeting and election of 
officers of the Projection Advisory 
Council, will be held at 12 noon on 
February 11, at the Astor Hotel, New 
York. 

The meeting will be followed by a 
luncheon at which a number of promi- 
nent motion picture executives will 
speak. 

P. A. JMcGuire, of the International 
Projector Company, New York, has 
charge of the dinner arrangements. 

▲ 

FILM MAKERS' PIONEERING 
SERVICE RECOGNIZED 

ONE of the most important actions 
of the new Board of Directors of 
the Academy of Motion Picture Arts 
and Sciences, at a recent meeting was 
the unanimous election of George East- 
man to become an honorary member of 
the Academy. 

During the entire existence of the 
academy the board has been properly 
conservative in extending honors of this 
character. Only once before has an 
honorary membership been voted by 
the board, when it invited Thomas A. 
Edison to accept this distinction. Mr. 
Edison signified his acceptance at the 
time by wire, but owing to delays in 
arranging a convenient occasion for 
presenting the engraved invitation the 
event did not occur until a recent date. 

The election of Mr. George Eastman 
also has been announced to the 
Academy. 



Page 24 



PROJECTION ENGINEERING 



Projectionists' 
Routine Tests 



By D. C. McGalliard* 



Careful Attention to Detail Will Avoid Service 
Interruption While the Show Is On 



A CAREFUL motorist checks his 
gas and oil, and the mechan- 
ical condition of his car before 
starting on a long trip. It 
is equally important for the projection- 
ist to thoroughly check the sound sys- 
tem daily. Such a practice will do 
much to forestall operating troubles. 
A large proportion of failures do not 
happen suddenly, but develop gradu- 
ally and hence can be detected and 
remedied before they become serious. 
Testing should be started at least . a 
half hour before the house opens so 
that irregularities, if found, may be 
corrected. Although the exact order 
of testing is not important, it is well 
to establish the habit of following the 
same routine daily. The procedure 
which follows is effective for determin- 
ing whether the equipment is in satis- 
factory condition. 

The system should be turned on as 
specified in the operating instruction 
book which is furnished with the 
equipment. If batteries are required 
for the operation of the system, their 
condition should be checked by the 
usual specific gravity tests. 

Before operating the equipment it 
should be carefully oiled. Excessive 
lubrication should be avoided, as well 
as lubrication of parts that do not re- 
quire oil. Excess oil is harmful be- 
cause it runs off, gets on the film and 
spoils the picture and sound. Further- 
more, the rubber insulation of the wir- 
ing deteriorates rapidly upon becoming 
oil soaked, causing noisy operation of 
the system. 



* Director of Instruction Electrical Re- 
search Products, Inc. 



The sound reproducing mechanism 
should be thoroughly inspected and 
cleaned. Use a pipe cleaner, bent 
double, and toothbrush for cleaning 
the sound sprocket, guide rollers, 
sound aperture plates and tension 
pad. Wipe off any dust and oil with 
a dry cloth. Do not scrape the film 
tracks or shoes with a knife or use an 
abrasive in cleaning. The film tracks 
should always feel perfectly smooth 
and polished to the touch. Run the 
finger tips over them to make sure 
that no rough spots are developing, due 
to dirt or hardened emulsion. 

The exciting lamp must be clean and 
correctly focused as directed in the 
operating instruction book. Dirt on 
the exciting lamp, lens system, or in 
the opening in the aperture plate and 
tension pad may cause low volume and 
poor quality. 

Current Values 

Filament and plate current readings 
should be made to see that the values 
are within the specified limits. A tube 
may be defective if its plate current is 
either too high or too low while that of 
the other tubes of the amplifier is nor- 
mal. In order to eliminate the possi- 
bility of failure during the show, any 
tube showing abnormal performance 
should be taken out of service and held 
for testing by the service engineer. 
Abnormal plate current of all tubes 
is indicative of abnormal plate voltage. 
If difficulty is experienced in locating 
or remedying the fault the service 
engineer should be called. 



Sound-on-Film 

In order to check "sound-on-film" 
reproduction, switch one machine to 
"film," open the sound gate, move the 
fader to step 8 or 10 (not higher, as 
damage to the receiver may result) 
then move a card rapidly up and down 
across the light beam in the open 
sound gate. This should result in a 
click being heard from the monitor 
horn every time the light is inter- 
cepted. The theatre horns should be 
turned off during these tests. The 
other machine should be tested in the 
same way. 

Further tests should be made, using 
the theatre horns, at the same time 
checking the operation of the projector 
and reproducer mechanism. This 
should be done with sound film kept 
specially for testing. Piano, speech, 
and orchestra selections are most suit- 
able. Someone qualified to judge whe- 
ther the reproduction through the 
theatre horns is satisfactory, should 
now listen in the theatre. 

Comparison of Units 

When the first projector is started, 
sound should be heard from the moni- 
tor horn. With the theatre observer 
near the stage, each theatre horn 
should be tested individually to make 
sure that the sound is clear, quality 
good, and of full volume. Then stop 
the machine, re-wind the film and re- 
thread it; also thread a duplicate 
print in the other machine and starting 
both projectors simultaneously, com- 
pare their outputs for volume and 
quality by switching from one to the 
other. If the reproduced sound from, 
both machines has been satisfactory, 
the equipment is ready for operation. 
If the tests indicate that the equip- 
ment is not in a satisfactory operating 
condition and the cause of the 
trouble cannot be eliminated then the 
service engineer should be called. 

Disc sound reproduction should alao 
be checked. Make a preliminary check 
of the reproducer and amplifying sys- 
tem by touching the needle with the 
finger. A clicking and grating noise 
should be heard from the monitor horn 
which will indicate that the system is 
operating. Identical test records 
should then be placed on the turn- 
tables, and the outputs compared for 
volume and quality as in film repro- 
duction. 

Strict adherence to this daily test- 
ing routine is fully justified by the 
definite assurance that the equipment 
is in good operating condition before 
the house is opened. 
▲ 
CHICAGO SECTION S.M.P.E. 
ELECTS OFFICERS 

Election of new officers of the Chi- 
cago Section of the Society of Motion 
Picture Engineers has been announced. 
J. Elliott Jenkins is the newly elected' 
chairman; R. Fawn Mitchell is the 
secretary and the Governors are Oscar 
B. Depue and Robert P. Burns. 

Members of this Section now total; 

77- 



JANUARY, 1931 



Page 25 



DIRECT READING 




TYPE 586 Power-Level Indicator 

An open clearly marked decibel scale makes 
the General Radio TYPE 586 Power-Level 
Indicator a truly direct-reading instrument. 
The time saved and the freedom from costly 
mistakes such a scale insures are advantages 
readily appreciated by the monitoring oper- 
ator in the broadcast and recording studio. 

If you are not familiar with this instrument, 
a request on your business letterhead will 
bring you a catalog description. Please ask 
for Bulletin 932-P. 

GENERAL RADIO COMPANY 



Offices 

CAMBRIDGE A, 



Laboratories Factory 

MASSACHUSETTS 



JENKINS & ADAIR 

OUTPUT PANEL 

For recording, sound measurement and similar uses, 
built to match cutter, sound head or other device. 




Type C Output Panel 

The Type C output panels are built to order to meet 
the individual requirements of your problem. The 
price in U. S. A. complete with meters, switching 
facilities and bias control but without tubes is $375.00 
net f. o. b. Chicago. Write for further information 

JENKINS & ADAIR, INC. 

3333 Belmont Avenue 
Chicago, 111., U. S. A. 



Cable Address: 
JENKADAIR 



Phones. Keystone 2130 
3333 Belmont Avenue 



British Offices: 76 Old Hall St,, Liverpool. England ; 

40 Buckingham Gate, London, S. W. 1 England 
French Office: 16 Rue de Chateaudun, Asnieres, France 



FOREST 

RECTIFIERS 




T 




'■J'».U^.^ 





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. 

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. 



Page 26 



PROJECTION ENGINEERING 



What is the Decibel? 



By Gordon S. Mitchell 



ONE of the most used, yet least 
understood terms in sound 
recording and reproduction is 
"decibel." Previous to 1923 
the engineers of the Bell Telephone 
system used the expression "mile 
of standard cable" to designate a 
definite level of sound transmission 
■ — being the amount of sound heard 
in a telephone receiver after the 
actuating currents had passed through 
one mile of standard telephone 
cable. In 1923, the term "trans- 
mission unit" was adopted merely 
as a temporary term until the mat- 
ter had been considered by all who 
had occasion to use a unit of sound 
transmission. For very obvious rea- 
sons, a unit of universal definition was 
desirable, and with this idea in mind, 
the International Advisory Committee 
on Long Distance Telephony in Europe 
was asked to devise such a unit. 

There were two units proposed — one 
based on the decimal logarithm, and 
one based on e 2 , of the Naperian sys- 
tem of logarithms. Certain European 
countries, already using the Naperian 
unit, were reluctant to change. Engi- 
neers of the Bell System, invited to sit 
in on the conferences, made the sug- 
gestion that the basic power ratios of 
the two systems be standardized as 
10 1 and e 2 , and that decimal multiples 



designated by the usual signs be used 
with either base. Numbers of the two 
systems corresponding to a given 
power ratio would differ by fourteen 
per cent. Inasmuch as the conference 
had reached a deadlock, it was finally 
recommended that the telephone sys- 
tems of Europe use one or the other of 
the two approved systems of units, 
designating the one used by the name 
given it by the committee. The unit 
based on the Naperian system was 
given the name Neper, from the in- 
ventor of that system of logarithms, 
and the unit based on the decimal sys- 
tem was given the name Bel, from 
Alexander Graham Bell of telephone 
fame. Within a short time the Bell 
system in the United States adopted a 
unit which they called the decibel — 
this unit being one tenth of a bel and 
named in accordance with standard 
decimal nomenclature. The abbrevia- 
tion db was adopted at the same time. 
The mathematical definition of the 
decibel is given by the following equa- 
tion; 

S 
db = 10 log — 

So 

where S is the loudness of the sound 
under consideration and So is the 
loudness of a sound of identical pitch 
which is barely audible in acoustically 



dead surroundings. The loudness as 
expressed in the above formula is 
measured in any convenient unit of 
energy per cubic centimeter. 

To arrive at a common understand- 
able definition for the decibel let us 
consider a sound of any given pitch 
which is just audible. The loudness of 
sound reproduced in the usual theatre 
is about one million times this just 

S 
audible sound. The ratio — ■ becomes 

So 

1,000,000 

■ . The logarithm of 1,000,000, 

1 
as given by the table of natural logs 
is 6, which makes the loudness level of 
the sound originally under considera- 
tion 6 x 10 or 60 decibels. 

To convert back from the decibel 
level as read from the TU meter, a re- 
verse process is used. Let us consider 
a level of 40 db. Dividing 40 by 10, a 
quotient of 4 is obtained. From the 
table of antilogs, we find that the num- 
ber whose log is 4 is 10,000 — which 
means that the sound which plays on 
a level of 40 db. has ten thousand 
times the energy content that a barely 
audible sound in the same surround- 
ings would have. 

The decibel, as evolved from the 
first "mile of standard cable" of the 
Bell Company, through the "transmis- 
sion unit" as proposed to the Interna- 
tional Advisory Committee, has been 
generally adopted as the standard 
unit of energy content for sound 
waves. The advent of talking pictures 
with recording of all types and varie- 
ties of sound has brought the decibel 
into common use by all connected with 
this kind of work. While originally 
intended for telephone usage, the deci- 
bel has taken its place in sound record- 
ing and talking picture reproduction 
and has become a term of common 
usage in the studio and the theatre. 



TECHNICAL ASSISTANCE CON- 
TRACT FOR THE SOVIET 
CINEMA INDUSTRY 

"THE Amkino Corporation, which 
' represents the Soyuzkino (United 
Motion Picture Industry of the Soviet 
Union), announced recently the con- 
clusion of a contract with Joe W. Coff- 
man, president of Audio-Cinema, Inc., 
whereby the latter will become con- 
sultant in connection with the develop- 
ment of sound films by the Soyuzkino. 
Mr. Coffman left a short time ago for 
the Soviet Union. 

L. Monosson, president of the Am- 
kino Corporation, stated that the pres- 
ent contract is the first providing for 
American technical assistance in the 
Soviet motion picture industry. "The 
possibilities of sound motion pictures 
are keenly realized in the Soviet 
Union," said Mr. Monosson. "The mo- 
tion picture is regarded as one of the 
most important means of educating the 
people of the country. At the same 
time the cinema occupies a high place 



among the arts. In order to further 
general cultural and, particularly, ar- 
tistic development in the country, the 
Soviet authorities are anxious to ap- 
ply the most advanced technical meth- 
ods of sound motion picture produc- 
tion. It is likely that American tech- 
nique may play a role in the Soviet 
motion-picture industry commensurate 
with that which it plays in other fields 
of the economic life of the U. S. S. R." 

The Amkino Corporation sells and 
distributes in the United States films 
produced by Soviet motion-picture com- 
panies. It purchases for shipment to 
the U. S. S. R. studio and theatre 
equipment, raw film, and other motion- 
picture machinery and materials, and 
also American pictures. Copies of 
films purchased here are printed in the 
United States on American or Cana- 
dian raw stock. 

Many of the Soviet films imported 
into the United States have won a dis- 
tinguished place for themselves for ar- 
tistic merit in respect to direction, act- 



ing and photography. Industrial and 
educational pictures of scientific value 
are also imported. A number of Soviet 
directors have been invited by Ameri- 
can producing companies to direct pic- 
tures in this country. One of the best- 
known of these, Sergei Eisenstein, is 
at present connected with the Para- 
mount-Publix Corporation in Holly- 
wood. 

Since its organization in 1926 the 
Amkino Corporation has released forty- 
two feature pictures and a number of 
news reels. Of the feature films one 
each was released in 1926 and 1927, 
eight in 1928, twenty-one last year, and 
this year through July, eleven. 
▲ 
BOOK REVIEW 

PHOTOCELLS, oy V. K. Zworykm 
and E. D. Wilson, John Wiley & Sons, 
New York, 210 pp., illustrated. 

This new book contains much use- 
ful information on the design and 
operation of photocells as used in 
various industries. 



JANUARY, 193 



Page 27 



POLYMET 

SOUND EQUIPMENT 




Main and Head Amplifiers 

Specially designed parts carried 

in stock, including 

Condensers, Transformers 

Chokes, Resistors 

Ask for new Bulletin AMP-1 P 

POLYMET 3IA3nLTACTI.*RIXG CORP. 



SOUND EQUIPMENT DIVISION 



839A East 134th St. 



New York Citv 



LOOK AT THESE BARGAINS!! 

BRISTOL DOUBLE AND SINGLE BUTTON M1CBOPH0NE 
TRANSFORMERS 
Uncased. The first time a well designed mike transformer has been 
offered at this extraordinary price. Order now before thev are 

sold out Special $1.95 

VACUUM SPECIALTY UX 866 TUBES 

First quality. List piice $8.50 Stwcial $7.95 

Selected "seconds" Special 5.50 

GUARANTEED TUBES, 30 day replacement guarantee 
UX '230.. $3. 95. UX 2S1..52.75. UX 215.. SI. 00. UX 280.. $0.85. 
UY 227 $1.10 

WESTERN ELECTRIC 

Regular 3 wire 3 foot mike cords $ .40 

Six wire (double mike) cord,. 8 ft 1. 10 

MIO i wire shielded rubber covered. 100 ft. with plug 8.95 

12 ft. length 2.20 

Huhbell 3 prong receptacle 75 

Five wire shielded condenser mike cable 35 

Two wire and shield, cotton braid covered. 4'/ 2 c ft. $3.75 per 100 ft. 

W. E. hand mike No. CW 930 3.95 

Sprague S Mfd. electrolytic condenser 1.25 

G. E. Induction Phonograph motors with 10" turntable. SO RPM 

Complete special 8.95 

Two-Channel Rack Amplifier SPECIAL PRICE 

THOED ARSON 
245 PP Power Transformer. Gives 750 ct.. 2*4 ct.. 2>i ct.. 5, and 

\Vi vclts. Shielded. 150 watts. 'Ok lbs $3.25 

250 watt. Delivers 1200. 7hi. 7% and 24 volts. All center-tapped. 

Fine for 210 or 250 PP amplifier or transmitter 5.75 

175 watt. 1125. TA. 7%. and 2V4 volts. All center-tapped 4.25 

Power chokes: 20 Henry. 250 milliampeTe. .$3.75. Double 30 H. 

100 -MA.. $2. 25. Double 15 II. 350 MA 6.75 

Jefferson 30 H, 125 MA. neat metal case 1.75 

PARCON FILTER CONDENSERS 
Bigger and better! More conservative ratings. And sold with a guarantee 
that really means something! Neat metal cases with novel standoff insula- 
tors. The best value in condensers today! 
DC Working Voltage I Mfd. 2 Mfd. 4 Mfd. 

2000 Volts $3.95 $6.45 $10.95 

1500 Volts 2.45 3.90 6.95 

1000 Volts 1.50 2.45 3.90 

650 A r olts 1.25 1.80 2.90 

Faradon Block. Contains 2 mfd.. 1000 volt DC working and 2 mfd. 

600 volt $2.20 

Allen Bradley. 500 watt Radiostat. .$5.45. E-210 95 

Universal, Sangarno, Cardwell, 



Lowest prices on Flechtheim. Electxad, 
Jewel, Thordarson, Aerovox and others — 



Send for catalogue 

Deposit required. Postage Extra. Xor orders under $2.50 

EVERYTHING SOLD WITH A MONEY-BACK GUARANTEE 

HARRISON RADIO CO. 

Dept. E New York City 



189 Franklin Street 



SUPER-LITE 

LENSES 



\S isely Chosen By 
America's Best Theatres 

New Bifocal Super-Lite Lens 

An adjustable focus lens with a 
wide range of foci for both silent 
and sound film. 

Series III. Super-Lite Lens 

Standard full Half-Size lens fur- 
nished in short focus as low as 4" 
E. F. and up to 10" E. F. 

Series 1A . Super-Lite Lens 

Full 3" diameter lens to meet the 
demand for more light for longer 
throws. 0" E. F. to 10" E. F. 

Quality Guaranteed 



PROJECTION OPTICS CO.. INC., 

330 LYELL AVE. 
ROCHESTER. N. Y. U. S. A. 





/ THERE 



SSRSK5 




LIGHT 



High Intensity 

Au tomaticR e fl { ' 



Provide 



Arc Lt 



ector 



'Omps 
°N ENI AD ^ OJ ECTJO,V 




, which 
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v AU 

. Minute 

Jrn Prov e - 
nients. 



or S a l e by , _, 

2 *» u/4 e f'f Operation 




Page 28 



PROJECTION ENGINEERING 



M New 


Devel< 

and 

of the 


Dpments M 


News 


Industry 



CONDENSING LENS SYSTEM 

A patent (U. S., 1783481) has been issued 
to Bausch and Lomb Optical Company, 
Rochester, N. Y., covering a condensing 
lens system for projectors. The system is 
the invention of Wilbur B. Rayton, of the 
Bausch and Lomb Company. 



SOUND DISTRIBUTING SYSTEMS 

The Webster Electric Company, Racine, 
Wis., manufacturers of accurate electrical 
apparatus for over twenty years, reports a 
rising demand for their amplification system. 
Two large installations of Webster equip- 
ment have just been completed by their Mil- 
waukee, Wis. representative, the Wirtz 
Company. 

One of these installations indicates the 
trend of educational development, through 
the transmission of important study ma- 
terial and facts to classrooms from a central 
source. The Sheboygan High School, at 
Sheboygan, Wis., is now utilizing this 
method by means of Webster amplification. 



SUCCESSFUL SCREEN MODIFIER 

The Vallen Electrical Co., Inc., Akron, 
Ohio, has developed a successful screen 
modifier. 

The screen modifier is a perfected stage 
appliance, designed specifically, and essential 
to the proper presentation of widescope, 
magnascope, grandeur, and any size film on 
mammoth screens. 

With the Vallen automatic screen modi- 
fier, a program consisting of wide film and 
narrow film presentations can both be pro- 
jected on the screen to the best possible 
advantage, without any attention or manual 
effort to the modifying curtains. Unusual 
and unique close-up and fade-out effects, 
distinctly fitting to sound and scene, can be 
achieved with the screen modifier, and im- 
possible to duplicate with any manually op- 
erated or temporary mechanism or device. 



MERCURY VAPOR RECTIFIER 
TUBES 

Dr. Paul G. Weiller, the well-known 
consulting research engineer, of 28 Clubb 
Street, Bloomfield, N. J., has developed new 
designs of mercury vapor rectifier tubes 
which have many uses. These tubes may be 
used as power supply rectifiers for speech 
amplifiers used in talking picture work ; for 
high voltage supply in broadcasting and for 
automatic devices operated by phototubes. 



SCREEN RENOVATOR 

Benjamin Perse announces that The 
Sound Screen Cleaning & Renovating Co., 
at P-630 Ninth Ave., New York City, has 
developed a process that gives new life to 
faded, discolored and dirty screens of all 
types. 

It is claimed that this process ofttimes 
brings a screen into better reflective condi- 
tion than it was on original installation. 

A very nominal charge is made, and if 
so desired, screens can be fireproofed with- 
out being removed from the theatre. 



POLYMET ENTERS SOUND EQUIP- 
MENT FIELD 

The entry of this firm into the sound 
equipment field has been expected for some 
time. Widely known throughout the elec- 
trical and radio industries,, Polymet products 
are now destined to become important 
factors in the newer field of sound. 

Realizing the need for exceedingly wide 
safety-factors in equipment of this sort, 
Polymet announces its new line of equip- 
ment bearing the descriptive legend Polymet 
"Safety Margin" parts. 

Polymet is well equipped to manufacture 
such parts. Plants of the company, each 
under the exclusive direction of a special- 
ized engineer insuring strict adherence to 
standards, fabricate all the elements enter- 
ing into the construction of these items. 
The Polymet plant at Winsted, Conn., makes 
the copper, enameled and insulated wire. 
The Easton, Pa., plant fabricates the coils, 
solenoids, chokes and transformers. The 
main plant, in New York, is entirely de- 
voted to the manufacture of condensers 
and resistors. 

Besides parts manufacture, Polymet also 
assembles complete amplifiers suitable for 
sound work of every sort. 



CONNECTION LUGS 

Hoffmann-Soons, manufacturers of Per- 
fection Rheostats announce that a newly 
designed series of solderless, adjustable lugs, 
is ready for release. These terminal lugs, 
capable of handling all wire sizes from 
number 4 to 4/0 will be assembled on the 
new Perfection Rheostats at no additional 
cost. 



THE BESTOPTICON 

The Best Devices Company, Cleveland, 
Ohio, is displaying the Bestopticon. 

The Bestopticon has proved itself to 
be the ideal stereopticon for the theatre, 
especially where distance to the screen is 




not over seventy-five feet. And not only for 
the theatre, for it is unusually popular with 
the lecturer for church and classroom use. 
It is high in efficiency. 



VITAGLO SOUND ON FILM 

A. B. Chereton, president of the Vitaglo 
Corporation and designer of the Vitaglo 
light, announces the opening of a com- 



merical sound recording studio at 4942 
Sheridan Road, Chicago, Illinois. 

The Vitaglo light marks a great advance 
in the recording of sound on film, in that it 
utilizes an entirely new principle of sound 
photography. The Vitaglo portable record- 
ing unit is sold outright to commercial 
producers and newsreel cameramen on a 
budget plan which enables the purchaser to 
pay for the unit in ratio to its earning 
capacity. There are no royalty arrange- 
ments to be entered into, the sale being 
made outright. The Vitaglo sound head 
may be attached to any standard camera 
which has been silenced for sound. The 
Vitaglo amplifiers are sturdy and rugged 
and lend themselves very well to the rigors 
of transportation. 

The entire unit, stripped for action in the 
field, weighs only 150 pounds and may be 
carried in the rumble seat of a roadster. 



TYPE T PAD VOLUME CONTROL 

The Central Radio Laboratories, 16 Keefe 
Avenue, Milwaukee, Wis., have available a 
flexible volume control known as the T 
Type Pad. 

The T pad consists of one group of three 
resistances. Two offer constant impedance 
to the input and output circuits. The third 
is a tapered graphite resistance to give 
smooth and linear variation of volume. 

These T pad volume controls are essential 
for efficient operation of a wide variety of 
circuits in the sound projection field. 



HEAD AMPLIFIER 

The G-M Laboratories, Inc., Grace & 
Ravenswood Aves., Chicago, announce the 
development of an improved preliminary 
(head) amplifier for use with sound-on-film 
equipment. This amplifier can be used on 
all makes of sound equipment and because 
of its small size and the simplicity of instal- 
lation can be used with either new or old 
equipment. 

The complete unit is mounted in a steel 
service case, permitting the wiring through 
rigid or flexible armored conduit. The 
chassis proper is white alloy metal, offer- 
ing a very attractive appearance. Electrically, 
the amplifier has a very flat frequency 
response characteristic assuring equal 
volume output at all audio frequencies. 
The tube support is of heavy cast-brass 
supported by four steel springs, eliminating 
the possibility of microphonic noise. Elec- 
trostatic shielding is accomplished by com- 
plete enclosure of all parts including tubes. 

Other features include variable cell 
voltage control, which permits adjustment 
of the photoelectric cell output for best 
quality and minimum background noise ; ad- 
justable interstage gain control ; jacks for 
testing cell voltage and plate current ; on- 
and-off switch which controls all battery 
supply, and low "A" and "B" battery drain. 

The overall gain of this amplifier is rated 
at 40 db. at the 500 ohm output transformer 
which may be connected directly to any 
standard fader. 

Overall dimensions of the service box 
container are height, I2j^ inches; width, 
9 inches; depth, 6 inches. 



JANUARY, 1931 



Page 29 



We Move! Our Prices Hit 

New Lows! 

To save the cost of trucking to our new quarters of 
over 15,000 sq. ft., our new BARGAIN BULLETIN 
No. 66 contains the lowest prices yet! . . . It is on 
the press now! .«pj. 




WRITE! 
A card 
will put you 
on our list! 



sotf%6* *7 b*^\v^ 




^iv^!-;.">: 



s et*> 



a* c 



*fi' 









**NS£S** 



AMERICAN SALES CO. 

R.21 WARREN ST. NEW YORK CITY 



For Powers, i 
all other projector 
equipped for 
sound. 




Used by the 
S. Army Motion 
Picture Service. 



The Clayton Even Tension Take-up 

assures absolute freedom from nutter. It takes up 
any amount of film evenly. It will take up with 
any size reel hubs. It prevents excessive wear on 
the lower take-up sprocket and shaft. It stops the 
opening of film splices and prevents excessive wear 
on the film. 

Write for price and 
further information. 

Joseph Clayton 

9430 Forty-Sixth Ave. 
Elmhurst, L. I., N. Y. 



1 



announcing 

CINEGLOW 

the 3 element 
recording lamp 

(patents pending) 





U OPTICAL RECORDING ON 




POSITIVE FILM. 




H GREATER VOLUME — BET- 




TER SOUND QUALITY. 



BLUE SEAL 

SOUND EQUIPMENT CORP. 

260 WYCKOFF STREET, BROOKLYN, NEW YORK 



L. 



DEPENDABLE PROJECTION—CONTINUOUS SHOWS" 






Fits Motiograph Model 
B, Simplex and Super- 
Simplex, Sure-Fit, 
with or without Rear 
Shutter Mounts. 



Installed at the crucial spot 

. . . where the cross-sec- 
tional area of the light 
beam is smallest — 
where the smallest shut- 
ter, operating through 
the smallest space at a 
minimum current con- 
sumption gives maxi- 
mum speed and effi- 
ciency! Simple for 
mounting and replace- 
ments; every part ma- 
chine tooled and preci- 
sion assembled. Special 
wound coils for D.C., 
any voltage, and for 
A.C., any voltage and 
frequency. 3-wire cir- 
cuit foot switch allows 
synchronization of all 
projectors with effect 
machine. 

AUTOMATIC SHUTTER CONTROL 

with 3-wire circuit foot switch 

HOWSER 



691 LINCOLN PL. MANUFACTURING CORP. BROOKLYN N .Y. 




Rear shutter mounts 
require Model D type. 
Your Model A Change- 
over replaced with 
Model D type. Liberal 
allowance for Model A. 



Page 30 



PROJECTION ENGINEERING 




1 5,000 

GRISWOLD 

FILM 

SPLICERS 



are in constant use, 
daily, in theatres and 
laboratories throughout the world. 



Projectionists and technicians are invited to 
communicate with us. 

GRISWOLD MACHINE WORKS 

PORT JEFFERSON, L. I. NEW YORK 

The Standard Film Splicer for efficiency, economy and durability 



For Perfect Projection 
use 

S.O.G. IGNAL Condensers 

Highly polished, will not discolor. 
Throws an even white light on the screen. 

Full Particulars 

FISH-SCHURMAN CORP. 

45 West 45th St. 6364 Santa Monica Blvd. 

New York City Los Angeles, Calif. 



♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦*>♦<»♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦ 




REDUCE YOUR 
BACKGROUND NOISE 

by using 

Isitron Type U A" 

PHOTOELECTRIC CELLS 

— the cells with the high current output 
that permits reduction of amplification 
and consequent reduction of background 
noise. 

Cells for every type of equipment. 

LABORATORIES |N< 



1802 GRACE ST. CHICAGO, U. S. A. ♦ 

♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦ 



ORDER IT 
NOW 

"Best" Magazine 

Light for Simplex 

Only 

New — Compact 
Light Weight 



Permits projectionist to see amount of film in upper maga- 
zine without opening magazine door. Reel can be ob- 
served from either side of projector. 

Complete with 4 ft. baby BX and lamp. Price $3.50 

BEST DEVICES CO. 

2108 Payne Ave., Cleveland, O. 




w 



E. offer to manufac- 
turers interested in 



EXPORT 

tne services of a dependable organization, 
-well established in the entire foreign field 

AD. AUMEMA, Inc. 

Manufacturers' Export Managers 

116 Broad Street, New York, N. Y. 



D' Arcy Laboratories 

place at your disposal their laboratory facili- 
ties for your assistance in volume controi 
problems. 

Bulletin M. I. is now ready for those who 
inquire for it. 

D'Arcy Laboratories 

160 B. East Illinois Street Chicago, Illinois 



INDEX TO ADVERTISERS 



30 

29 
. Third Cover 
3 



30 



Ad. Auriema, Inc 

American Sales Co 

Amplion Corp. of America 
Audak Company, The 

B 

Bass Camera Co 31 

Best Devices Co 

Blue Seal Products Co., Inc 

Blue Seal Sound Equipment Corp. 

C 

Cameron Publishing Co. , 32 

Chicago Gear Works , 31 

Clayton, Joseph 29 

D 

D'Arcy Laboratories 30 

Dowser Mfg. Corp 29 

E 
Ellis Electrical Laboratory 31 



29 



Fish-Schurman Corp 30 

Forest Electric Corp 25 



G-M Laboratories, Inc 30 

General Radio Co 25 

Griswold Machine Works 30 



Harrison Radio Co 27 

Hoffmann-Soons 6 



International Resistance Co. 



Jenkins & Adair, Inc 25 

N 



National Carbon Co., Inc. 



Polymet Mfg. Corp 27 

Projection Optics Co., Inc 27 

R 
Racon Electrical Co., Inc. . Second Cover 



Samson Electric Co Fourth Cover 

Silman Distributing Co 31 

SOS Corporation 31 

Strong Electric Co., The 27 

U 

Universal Microphone Co 31 

V 

Voice-of-the-Air Co 31 

W 

Weber Machine Corp 6 



JANUARY, 193! 



Page 31 



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 for- 
eign 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 




BASS BARGAINGRAM 

Issue 202 Ready 

FREE! The Classic of Bargain Lists. World's 
largest stock of Motion Picture Cameras and ac- 
cessories. Professional and Amateur. Save real 
money. Send for your copy. Free! 

BASS CAMERA CO. 

179 W Madison St. Chicago, 111. 




Dealers in Al 
New York — Howard F 



MICROPHONES £^5™ 

For Connection to Radio Set S7 50 

For Home Recording $1000 

For Public Address, etc., list ....'.'." S25 

Standard Broadcast Model, list ...'. $75 

Condenser ilodels for Film and Becord Work 
/f list $300.00. $350.00 

Also Desk and Floor Stands. CoTers, Cords, etc. 

EXPERT iXICROPHOXE REPAIRS 

UNIVERSAL MICROPHONE CO., LTD. 

Inglewood, Calif. 

Export Rep. 
Principal Cities Ad. Auriema.Inc.,116 

Smith— 142 Liberty St. Bread St.. N. T. C. 



SILMAN Synchronous Disc POINTS 

The only perfect Point for Sound reproduction 

Eliminates surface scratch. Clears voice articulation. No 
blurry, raspy tone. Let us prove it to you. 

Send for FREE Samples. 

SILMAN DISTRIBUTING COMPANY 

Sound Equipment and Apparatus 
620 Grant Street ... Pittsburgh, Pa. 



THEATRE OWNERS ! LOOK INTO THIS 

New Electrodynamic 
Speaker Unit. 

Improve your sound 
greatly, and improve 
your business. 
Cost very reasonable. 
Write for our free- 
trial proposition. 

VOICE-OF-THE-AIR CO. 

502 S. ST. CLAIR ST., TOLEDO, O. 




Our speaker has a light metal dia- 
phragm which Is far superior to 
other types. 




GEARS 

In Stock — Immediate Delivery 
Gears, speed reducers, sprockets, thrust bearings, 
flexible couplings, pulleys, etc A complete line Is 
carried in our Chicaeo stock. Can also quote on 
special gears of any kind. Send us your blue prints 
and inquiries. 

Write for Catalog No. 60 

CHICAGO GEAR WORKS 

769-773 W. Jackson Blvd., CHICAGO, ILL. 



THEATRE AND SOUND EQUIPMENT AT FACTORY 
PRICES— EVERYTHING BRAND NEW 

Sound-on-Film Heads, $198.50: Photocells, $14.95: G. E. Exciter Lamps. 
98c: Optical Systems, $29.50: Head Amplifiers. $29.60: W. E. and RCA 
Approved Sound Screens, 39c sq. ft.: V* h.p. Synchronous Motors, $29.50: 
Turntables with Re-synchronizer, $49.50: Samson Pam 19 Amplifier, $69.15; 
Audak Pickups, $8.97: Jensen Speakers. $17.85: Racon Exponential Horns, 
$59.90: Powers and Simplex Parts. 20% off: Rear Shutters for Simplex. 
$49.40. Also used Simplex and Powers Projectors. Rectifiers. Reflector 
Arcs, Motor Generators, Sound Heads. Turntables. Many Other Values- 
Address S. 0. S. CORP., Dept. P. E.. 1600 BROADWAY, N. Y. C. 



© 



ELLIS tflCKCPI-ICNES 



A complete line of two-button microphones for Indoor and 
outdoor Public Address systems. Radio Broadcasting, and 
Home Recording, available in several models at $25.00, 
$45.00, and $75.00 list. Also a complete line of stands, 
cables, and other accessories. New two-button Hand-Mike 
now ready. Have you seen our new DEMOUNTABLE? 

ELLIS ELECTRICAL LACCCATCCT 



«4 



337 Vi EST MACISC- ST 



Qic 




Page 32 



PROJECTION ENGINEERING 



CAMERON'S 
ENCYCLOPEDIA 

ON 

SOUND MOTION 
PICTURES 



A List 
of a Few 
of the 2,000 
Subjects 
Contained in 
This Book. 



336 Pages Crammed 

Full of Motion 

Picture Facts. 




PRICE 
THREE 
FIFTY 



Wide Film. — Grandeur Pro- 
jector. — Stereoscopic Motion 

Pictures. Magnascope. 

Intermittent Movements. 

Vitaphone. — Movietone. — 

Phonofilm. Photophone. 

Faders. — Hum from Speakers. 

Frame Line Noise. Instructions 

for Operating R. C. A. Reproducing 
Equipment. — Instructions for Oper- 
ating Western Electric Sound Equipment. 
— Instructions for Operating P a c e n t 

Sound Reproducing Equipment. Control 

Panels. Amplifiers. Photo-electric cells. 

Mechanical Filters. Multicolor. Tech- 
nicolor. Continuous Projectors. Electric 

Service for Theatres. Gas type Photo-cells. 

Exciting Lamps. Film Splicing. Buckling of 

Film. Spotlights. Recording of Sound on 

Discs. Recording of Sound on Film. Effect Pro- 
jectors. Portable Sound Equipment. Projector 

Motors. Remote Control. Rotary Shutters. 

Screen Grid Tubes. Condensers. Theatre Acoustics. 

Background Noise. Care in Handling Sound Film. 

Troubles During Show. Selenium Cells. Resistances. 

- Electro-Dynamic Speakers. Exponential Horns. Faulty 

Synchronization. — Volume Levels. — Charging of Storage Batteries. — 
Baffle Boards. — Stage Lighting. — Automatic Screen Masks. — How to 
Check Sound Equipment. Speed for Sound Pictures. Arc-controls. 

Testing Sound Equipment. Sound Proof Studios. Cutting and 

Editing Sound Film. — Difficulties of Mechanical Recording. — Color 
Photography. — How to Check the Amplifiers. — Amplifier Tubes. — 
Sound Values. — Screens. Troubles in Dynamic Speakers. — 

- Dubbing Sound Pictures. — R. C. A. Sound Recording Equip- 
ment. Western Electric Sound Recording Equipment. How 

Sound Pictures Are Recorded. — Sound Absorption. Some Early 

Attempts at Sound Recording. — Distortion. — Care of Sound Reproduc- 
ing Equipment. — Rotary Shutters. — Principle of Motion Picture Pro- 
jection. — How to Match Loud Speakers to Output of Amplifier. 

Microphone Mixer, etc. 



HARRY RUBIN (Chief of Projection, 
Publix Theatres) : 

The most complete book on the sub- 
ject published — should be in every pro- 
jection room in the country. 



LEWIS M. TOWNSEND, Publix Theatres: 

" — the field is covered in a very thor- 
ough, clear and concise manner — projec- 
tionists would profit both mentally and 
financially by owning and reading your 
books." 



Motion Pictures 
With Sound 

By James R. Cameron 
Introduction by William Fox 

Motion Pictures With Sound 
covers the subject from A to 
Z in such a manner that the 
subject is easily understood. 
The book measures 7% X 5 
inches — Contains 400 pages 
and over 150 photographs 
and diagrams. 

Price Five Dollars 



Motion Picture 
Projection 

By James R. Cameron 
Introduction by S. L. Rothafel 

(Roxy) 
Fourth Edition — 1280 Pages 
500 Illustrations — Price $6.00 

Sound Pictures 
Trouble Shooters 



Manual 



By Cameron & Rider 
Introduction by William F. 
Canavan, International Presi- 
dent I.A.T.S.E. & M.P.M.O. 

OVER 1,100 PAGES 
500 ILLUSTRATIONS 
The whole question of Sound 
Motion Pictures treated from 
a new angle, explains in de- 
tail the construction, opera- 
tion and care of sound re- 
cording and reproducing 
equipment. 

Every known trouble to sound 
recording and reproducing 
equipment is listed in this 
book — with full explanation as 
to its cause and remedy. 

Price Seven-Fifty 



Cinematograph 
Annual 



675 Pages — 300 Diagrams 
48-Page Pictorial Art Section 

A book covering the making 
and showing of motion pic- 
tures with sound. Written by 
40 of the country's sound ex- 
perts. Will be found of great 
value to the Studio worker, 
Projectionists and Managers. 

Price Five Dollars 



Amateur Movie 
Craft 



By James R. Cameron 
A book dealing with the tak- 
ing and showing of 16 m/m. 
pictures and equipment nec- 
essary for same. 

Price One Dollar 



We shall be glad to send you full information on any motion picture book published — 
CAMERON PUBLISHING COMPANY, Manhattan Beach, Brooklyn, New York 



New Series 




of 

Transverse 
s^ Current 

>*. Microphones 











rype II. M. 

S25.00 



Type C. M. 

$65.00 

Less Stand 



Type I. M. 
In keeping with $25.00 

the Amplion policy | ,. ss >,, ;lM( | 

of supplying the engineer 
with every instrument re- 
quired in any Group Address In- 
stallation, instruments not only with 
impedances so carefully matched that wide 
range frequency response is attainable, but with 
frequency characteristics carefully combined to com 
pliment each other thus permitting the preservation of 
those delicate overtones so essential to high quality, we an- 
nounce herewith a new series of microphones priced from S25.00 to 
$65.00. These microphones are of the Amplion Transverse Current 
Type. They contain no metal diaphragm, no carbon buttons, no metal levers 
or moving parts. Carbon hiss is entirely eliminated and they do not pack. The] 
may be used in the conventional manner with a matching transformer and the applica- 
tion of 12 to 32 volts, or with the Amplion Microphone Amplifier. 

Write for 20-page catalogue and price list describing 
microphones, microphone amplifiers, 50-watt power 
amplifiers, giant dynamic air column units, exponen- 
tial horns, synchronous and non-synchronous turn- 
tables, and complete panel mounted equipment for 
schools, hotels, hospitals, dancehalls. parks, football 
stadiums, baseball fields, polo grounds, skating rinks, 
golf links, steam-ships, clubs, restaurants, airplanes, 
airports, sound truck-. auditoriums. churches, 
theatres, etc. 

CENTRALIZE RESPONSIBILITY FOR THE SUCCESS OF YOUR INSTALLATIONS 
BY PURCHASING ALL THE PARTS FROM ONE SOURCE. 





AMPLION 



Amplion Corporation of America 

New York Citv 133-W. 21st St. 









\ 




quickly 

Pays for Itself 

Schools, churches, clubs, hotels need the portable PAM Address 
system. With it, a speaker addresses 500 people as easily as 
half a dozen. Speech and music, both vocal and instrumental, 
are amplified with excellent quality. 

The units in this system are completely matched and designed 
to operate together. Naturally the results obtained are superior 
to a combination of units procured from different sources which 
were not designed to operate together. 

The two units that are required (MIK 100 and PAM 100) to- 
gether weigh less than 75 pounds, and the system can be set 
up ready for use in less than five minutes. No batteries are 
required . . . and the price complete with tubes, microphone, etc., 
and nothing left to buy, is $343.00. 

Send for twin folders PEl; one descriptive of the PAM-100 and 
the other of the MIK-100. 



SELL 

Portable PAM Address system to 
institutions that hold regular meet- 
ings and need the equipment per- 
manently. This price is reasonable 
and the profits are large. 




RENT 

Portable PAM Address systems for 
special occasions. One man can 
transport the entire system and set 
it up in five minutes. After a few 
rentals the cost is recovered and 
future income is all profit. 



Factories: Canton and 
Watertown, Mass. 



PROJECTION 




Television - Sound and Light Projection - Theatrical Engineering 




Outdoor Sound Installation in Colombia, 
So. America. 

Courtesy M. Simons & Son Co., Exporters, 
New York, N. Y. 



FEBRUARY, 
1931 




THE JOURNAL OF THE SOUND AND LIGHT PROJECTION INDUSTRIES 



■** 



ii iiimiiiiMir — = "" — »*-*~-~~~~~~>~>-'*> 



BMH _ | ^ ^jjUjg-^ 



New Series 




of 

Transverse 
••s. Current 

>^_ Microphones 





Type H. M. 

$25.00 



Type C. M. 

$65.00 

Less Stand 



Type J. M. 
In keeping with $25.00 

the Amplion policy Less stan( , 

of supplying the engineer 
with every instrument re- 
quired in any Group Address In- 
stallation, instruments not only with 
impedances so carefully matched that wide 
range frequency response is attainable, but with 
frequency characteristics carefully combined to com- 
pliment each other thus permitting the preservation of 
those delicate overtones so essential to high quality, we an- 
nounce herewith a new series of microphones priced from $25.00 to 
$65.00. These microphones are of the Amplion Transverse Current 
Type. They contain no metal diaphragm, no carbon buttons, no metal levers 
or moving parts. Carbon hiss is entirely eliminated and they do not pack. They 
may be used in the conventional manner with a matching transformer and the applica- 
tion of 12 to 32 volts, or with the Amplion Microphone Amplifier. 

Write for 20-page catalogue and price list describing 
microphones, microphone amplifiers, 50-watt power 
amplifiers, giant dynamic air column units, exponen- 
tial horns, synchronous and non-synchronous turn- 
tables, and complete panel mounted equipment for 
schools, hotels, hospitals, dancehalls, parks, football 
stadiums, baseball fields, polo grounds, skating rinks, 
golf links, steam-ships, clubs, restaurants, airplanes, 
airports, sound trucks, auditoriums, churches, 
theatres, etc. 

CENTRALIZE RESPONSIBILITY FOR THE SUCCESS OF YOUR INSTALLATIONS 
BY PURCHASING ALL THE PARTS FROM ONE SOURCE. 




aMPLIOn 






Amplion Corporation of America 

New York City 38 W. 21st St. 



FEBRUARY, 1931 Page I 



Two Patrons 



Buy Your Carbons 




T 



HE modern theatre and its furnishings represent 
the acme of splendor. The staff is thoroughly trained. 
Managers carefully select pictures in accord with popular 
taste. This lavish expenditure to attract patronage. ^ et, 
if the screen is dim or the light unsteady, valuable pat- 
ronage wdl be lost and two empty seats cost 

more than your carbons. 

Light is the most important factor in the operation of a 
motion picture theatre. That is why National Projector 
Carbons are preferred by tbe projectionist. They are depend- 
able. And the manager knows that, with good projection, 
patrons will return and bring their friends. 

National Projector Carbons give the steady, brilliant white 
light necessary for the quality of projection demanded by 
theatre-goers today. Their uniform quality is assured by 
the experienced organization behind them. Two satisfied 
patrons will buy them. 



NATIONAL 

PROJECTOR CARBONS 



/, 



y/,,,uw$> 





National Carbon Company will gladly cooperate ivith 
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 I I I ■ ■ 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. Ill 



FEBRUARY 
1931 



Number 2 



Contents 



Editorial 



page 
4 



Extending the Range of Pickup in Sound Picture Work 

By J. Garrick Eisenberg 

Testing Equipment for Sound Projection 

By E. W. D'Atcy 1 1 

The Camera Crane Used in Making Intricate Shots 

By Gordon S. Mitchell 1 3 

Study Conducted on Use of Films for Advertising 14 

Radiovision Programs in the Making 

By Austin C. Lescarboura 15 

Amplification in Sound Motion Picture Work, Part I 

By Charles Felstead 17 

New Motion Picture Projection Optics . By W. B. Rayton 20 

An Examination for Projectionists . . By James R. Cameron 23 

Departments 

News of the Industry and New Developments 26 

Index of Advertisers 30 



Bryan S. Davis 
President 

James A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

52 Vanderbilt Ave. 

New York City 



Sanford R. Cowan 
Advertising Manager 

J. E. Nielson 
Circulation Manager 



Publication Office— North Broadway, Albany, N. Y. 

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 Offic 
Los Angeles Office- 
New Zealand — Tearo Book Depot- 



318 Kohl Bldg.— R. T. Birch. 
846 S. ^Broadway — R. J. Birch. 
-Wellington. 



Entered as Second Class Matter at the Post Office at Albany, N. Y., October 9, 1929, under the act of March 3, 1879. Yearly subscription 
rate $2.00 in U. S. and Canada. Yearly subscription rate $3.00 in foreign countries. 



FEBRUARY, 1931 



Page 3 



FOREST 

RECTIFIERS 




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. 

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. 




Read 



how many 
ways THIS TEST SET 
CAN HELP YOU 



;t> 



SEND for your Copy of Instructions on how to use 
Weston Model 566 — the new test set that every 
projectionist needs to properly take care of his Sound 
Equipment. Amplifier tubes, speaker-coils, batteries 
and the vast number of electrical circuits in Sound 
Equipment must be checked at regular intervals to 
assure continuous and satisfactory performance. 

Weston Model 566 is a compact, light, relatively in- 
expensive test set, designed to help you keep a reli- 
able and accurate check on your Sound Apparatus. 

Model 566 is typically Weston. It possesses the re- 
finements in design, ruggedness in construction, and 
reliability in operation that has made Weston instru- 
ments the world's highest standard of quality elec- 
trical testing instruments. 

Write for your Copy of Ijistructions today ! 




INSTRUMENTS 



WESTON ELECTRICAL INSTRUMENT CORP. 

608 Frelinghuysen Avenue Newark, N. J. 



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February, 1931 



COMMERCIAL | T is an impressive tribute to 

TELEVISION engineers and to science 

laboratories that commercial 

projects for exploiting and 

marketing television are in the 

making. Television as a commercial enterprise 

does not exist as yet, but engineers are at work 

on it and that seems to be sufficient to convince 

promoters that commercial systems will emerge 

from the laboratories in due time. 

The many who for twenty years did the invent- 
ing and the pioneer development work in radio 
have, since the events of 192 1, had time to sense 
the advantages of coordinating inventive ability 
with business ability. In 1921, interests previ- 
ously somewhat contemptuous of radio gathered 
up the scattered elements of the art, capitalized 
them, and put them to work to produce revenue. 

Much of the jockeying with television as it 
progresses toward success is based upon the ex- 
periences of individuals, years ago, with radio. 
It would be a great thing if the hundreds of engi- 
neers who are now and who have been for the 
past few years struggling to wrest this new art 
from the stores of darkness, should be permitted 
to participate in the fruits' thereof — -with the 
Roxys and the Rudy Vallees. 

At the moment there is much afoot which 
reflects keen interest in the possibilities of com- 
mercial television. The National Broadcasting 
Company, of RCA, and the Columbia-Paramount 
organization have been granted experimental 
permits by the Federal Radio Commission, and 
with 25,000 television receivers of miscellaneous 
makeup already in the hands of persons interested 
throughout the country, it is possible that tele- 
vision is about where radio was in the period 
1915-1920. 



INDEPENDENTS 
INCREASE 



OLD Man Economics has 
a way of shouldering in 
when an industry finds itself 
in that perplexing condition 
where enormous gross receipts 
do not automatically signify satisfactory net 
revenue. 

In the moving picture industry with several 
producing major groups individually depending 
for success upon originality of product, ingenuity 
in presentation, aggressiveness and boldness in 
exploitation, it is natural that a time arrives when 
Dad Economics with his balance sheet in hand 
has a word or two to say. 

One natural consideration has been the possi- 
bilities in the way of applying the chain store 
idea to theatres. Obviously, the tremendous 
costs of originality of product, scale of produc- 



tion and of exploitation may in some degree be 
circumvented where the producer controls the 
theatres. Control of zones of sales outlets per- 
mits of regulating various items of marketing 
costs, to the advantage of net receipts. At least 
this is the way it works out with chain stores. 

In the entertainment industry, however, there 
appears to be an intangible element which, when 
some day minutely dissected may be discovered 
to be peculiarly a personal relation between the 
individual theatre patron and the ensemble which 
is the theme of the story, the art of the performer 
and the subtle environment of the theatre itself. 
The hero or the heroine of the story always does 
what the onlooker would do if he or she had the 
same opportunity. There is in this a spiritual 
experience in self-expression which perhaps may 
be chain-stored only with the most intelligent 
care, and with a never overlooked consideration 
for the personal, individual intellectual needs of 
the theatre patron. 

During the eighteen months prior to October 
last, producer controlled theatres increased in 
numbers. Then, a recession set in. No doubt 
there were various factors which had a bearing 
on this recession. 

As a sign of the times it may be stated that in 
the Philadelphia, Penna., territory there are at 
present 630 independent theatres compared with 
590 in September, 1930, while producer-owned 
theatres now total 200 compared with 250 in 
September, last. 

The economics of canned goods merchandising 
may not with equivalent revenue gain apply to 
the entertainment industry. 



MR. LASKY 
TELLS THEM 



H 



IOLLYWOOD makes too 
many pictures," Jesse 



Lasky, producer, told members 
of the Academy recently. "So 
many theatres have to be kept 
supplied with changing programs that the total 
income isn't large enough to stand the costs of 
the individual pictures." There aren't enough 
good stories in the world to supply the annual 
demand, he asserted, declaring that whereas a 
stage producer need only present one to five plays 
a year, the motion picture producer must meet 
release dates with a production a week. "Holly- 
wood has too many 'yes' men, but not enough 
creative artists who can do worthwhile work and 
meet the producer half way . . . ."' 




^Jc^^m^ru 



arL 



Editor. 



FEBRUARY, 1931 



Page 5 




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Projection Room of Roxy 

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Page 6 



PROJECTION ENGINEERING 



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The three element principle 
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The Cineglow modulates very 

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with positive stock. 

The Cineglow will record on 
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The Cineglow illumination is 
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The Cineglow can be used in 

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Instructions and special circuits supplied 
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PRICES 
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Special discounts in quantities. 

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Cineglow — the Standard of Quality. 



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SOUND DEVICES, INC. 

130 W. 46th STREET, NEW YORK 



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N. Y. C. 



Projection Engineering 



FEBRUARY, 1931 



Extending 

the Range of Pickup 




Photo courtesy RKO Radio Pictures Studios 

Fig. 1. Pickup 42 feet away 

obtained across the top of a 

salmon trap in Alaska. 



in Sound Picture Wxk 



By J. Garrick Eisenberg 



HERETOFORE one of the es- 
sentials for high quality 
microphone pickup in the re- 
cording of sound pictures has 
been that the pickup device be located 
relatively close to the source of 
sound, so that it will be within the 
beam of the higher speech frequencies 
upon which intelligibility so largely 
depends. Because of this well known 
"beam effect" the distance at which 
high quality dialogue may be obtained 
with an unaided microphone is limited 
roughly to within four feet from the 
source of sound. At greater distances 
quality falls off rapidly, due to the 
spreading of the upper frequency band 
with a subsequent attenuation of sound 
pressures at the microphone. Also, 
factors such as reverberation from 
walls, the acoustic properties of set 
and stage, etc., become more serious in 
proportion as the microphone is moved 
away from the source of sound. Ac- 
cordingly, microphone placement in 
sound picture work has been held 
within narrow limits whenever high 



A Discussion on Micro- 
phone Concentrator De- 
vices 



quality pickup was essential to the 
action. 

This limitation imposes serious diffi- 
culties upon the process of motion pic- 
ture production. Quite often the most 
desirable position for the microphone 
lies well within the field of the cam- 
eras, which of course is not permissi- 
ble when photographing the action. A 
conflict between best camera setup and 
best microphone setup continually 
takes place, and in the nature of 
things, compromises must be made so as 
to satisfy, as far as possible, the legit- 
imate demands of both. In this respect 
the camera possesses a very important 
production advantage in that while the 
unaided microphone can secure good 
quality of pickup corresponding to the 
close-up picture only when it is near 
the speaker, the cameras, by the use of 
suitable lenses, can photograph close- 
up and medium-long shots from the 
same setup without much difficulty. 
Placing the microphone outside the 
long shot camera lines in a setup of 
this sort results in an inadequate qual- 
ity of sound pickup for the close 
views of the picture. In order to 
secure pickup sufficiently close to the 
action to obtain the proper perspective, 
it usually becomes necessary to move 
the cameras in for the close-up shot, 
the limited camera field permitting the 
microphone to be placed nearer to the 
action. It has long been recognized 



that a pickup device which would make 
it possible to obtain high quality sound 
at a distance corresponding, say, to a 
medium length camera shot, would be 
of considerable value to the industry 
by eliminating the necessity of making 
takes for close-up sound only, with a 
consequent saving of time and cost of 
production. Devices of this nature, 
whose function it is to concentrate the 
sound within a definite plane or beam 
and thus increase the range of high 
quality pickup of the microphone, have 
been developed for talking picture 
work at the RKO Radio Pictures 
Studios in Hollywood. Not only has 
the desired economic objective been 
attained by their judicious use, but in 
addition, an all around improvement 
in artistry of performance has been 
made possible, by virtue of the fact 
that the area of movement of the 
actors has been extended, resulting in 
a much more natural performance on 
their part. 

Microphone Range Extended 

Two types of microphone concen- 
trators have been developed for this 
work, favorable results being obtained 
with both at distances of the order of 
20 feet from the source of sound. 
Under exceptional conditions this dis- 
tance has been increased to as much as 
40 feet, and more, from the speakers. 
Advantages of such long range pickup 



Page 8 



PROJECTION ENGINEERING 




Photo courtesy RKO Radio Pictures Studios 
Fig. 2. Rehearsing an outdoor "dolly" shot. 



are at once obvious, particularly in the 
photographing of outdoor scenes of 
large scope where characteristic noises 
other than speech are to be recorded. 
These concentrators take the form 
of open bowls mounted on suitable 
supports, their fundamental purpose 
being to act as collectors of sound 
waves. The concave surface of the 
bowl, which is of sheet metal, is de- 
signed so as to reflect all of the sound 
picked up to a focal region at or near 
which point of concentration the 
microphone is placed. The micro- 
phone transmitter is turned away 'from 
the source of sound and faced toward 
the reflecting surface of the bowl ; 
sound issuing from the source strikes 
the reflector at various angles and is 
turned back towards the transmitter. 
An additive effect is thus secured, 
which is maximum at a certain point 
in relation to the reflector surface. One 
type of concentrator utilizes an open 
reflector curve corresponding roughly 
to a parabola of the equation 
y 2 =i2x. A second type makes use of 
the principle of an ellipsoidal reflector 
and utilizes a softer focus than the 
parabolic form. The diameter of the 
bowls varies between 40 and 60 
inches. Means are provided for accu- 
rately sighting and orienting them in 
the lateral and vertical planes, and the 
devices are extremely flexible in oper- 
ation. Sound originating outside the 
beam of the reflectors is sharply dis- 
criminated against. The bowl thus 
serves to shield the microphone from 



sounds occurring in a direction away 
from the scene of action, a useful 
property in limiting camera motor and 
other undesirable noises. A number 
of different mountings developed for 
use with the concentrators are shown 
in the accompanying photographs. 

Mike Need Not Be Close-up 

In one of these, Fig. 1, is indicated 
the setup for a scene made during the 
filming of RKO's "Silver Horde," the 
greater part of which was photo- 
graphed in Alaska. The action takes 
place on top of a salmon trap, a struc- 
ture of piling built out into deep water. 
These traps are designed simply to 
catch salmon, and without regard to 
their possible value as location atmos- 
phere in motion picture production. 
Despite the apparent nonchalance of 
the crew in this photograph, it is a 
risky business juggling the necessary 
equipment atop the narrow ledge. 
Sufficient planking was laid along one 
side of the trap, however, to provide a 
working platform for the cameras, 
etc. Important dialogue occurs during 
the action which takes place in one 
corner of the trap at the extreme right 
of the photograph shown here ; both 
close-up and medium-long shots of the 
action were required. In this case, 
cameras could not very conveniently be 
moved in for the close-up action. A 
parabolic type of microphone concen- 
trator was mounted on the camera plat- 
form and centered on the action. Good 
pickup was obtained in this way over 



a distance of 42 feet, a rather excep- 
tional instance made possible by the 
favorable conditions over water. The 
cameramen were thus enabled to make 
their various shots from the same 
setup, obviating the possibility of hav- 
ing to duplicate the setup in the studio 
later for the close-up action. 

Unwanted Sounds Excluded 

An example of the value of the con- 
centrators in discriminating against 
interfering noises originating outside 
their beam is afforded in another RKO 
picture "Danger Lights," during which 
it was necessary to shoot some scenes 
in a railroad roundhouse. With open 
microphone pickup it was impossible to 
obtain intelligible dialogue at a dis- 
tance of three feet from the speaker. 
By utilizing the directional properties 
of the concentrator, satisfactory dia- 
logue pickup was made possible at 
much greater distances, the attendant 
noises being reduced to a realistic back- 
ground. Fig. 2 shows a rehearsal for 
a scene in this production, cameras and 
microphone being dollied up on the 
actors to achieve a smooth fade into a 
bit of intimate dialogue. The noises 
incident to the movement of the hand- 
car, etc., are effectively shielded from 
the microphone by the concentrator 
bowl. A fine sense of fluidity of 
movement is secured when camera and 
microphone can be mounted in this 
manner ; an ideal perspective is af- 
forded, the photographic eye and ear 
being in proper juxtaposition at all 
times. While it is possible to make a 
shot of this type with open microphone 
pickup also, two separate setups would 
be required for the medium and close- 
up views, and a great many more pre- 
cautions for limiting extraneous sounds 
would be necessitated with a subse- 
quent waste of valuable production 
time. 

Dubbing Not Always Successful 

Crowd scenes, where it is desired to 
pick up the lines of one or two speak- 
ers clearly, at some distance, and other 
outdoor shots entailing considerable 
movement over a large area, have in 
the past depended upon the "dubbing 
in" of sound after the action had been 
photographed. This artifice is at best 
a compromise, and not always a suc- 
cessful one. Good pickup can be 
achieved during the action in shots of 
this type by the use of microphone 
concentrators. Another valuable prop- 
erty of the device in outdoor work is 
its effectiveness as a break against 
wind interference. When the concen- 
trator bowl can be turned with its re- 
flecting surface away from the wind 
somewhat, so as to place the micro- 
phone transmitter in its lee, it acts as 
a shield against direct wind pressures. 
Wind interference is a frequent cause 



FEBRUARY, 1931 



Page 9 



of delay in outdoor shooting with open 
microphone pickup, sometimes holding 
up tire production schedule several 
days. 

Useful Also for Indoor Pickup 

The use of microphone concentrat- 
ors is not limited to outdoor work. 
Promising results have also been se- 
cured with the device indoors. Cer- 
tain precautions are necessary when 
they are so used. Set construction 
must be of a "soft'' nature acousti- 
cally and, also, care must be taken that 
the device is not pointed directly 
toward any large wall surfaces' which 
may act as reflecting mediums. Re- 
verberation and reflection of sound 
occurring within the beam of the con- 
centrators are, by the very nature of 
its design, exaggerated in effect. 
These secondary sound waves are 
picked up and added to the original 
sound, the net result being similar to 
that obtained with open microphone 
pickup located a considerable distance 
from the source of sound in an 
extremely hard set. Observing the 
precautions mentioned, however, the 
device can be of considerable value for 
certain types of interior shots. For 
example, in covering a wide angle of 
pickup, as when two speakers are sta- 
tioned approximately i8o° apart and 
the action calls for considerable move- 
ment, two concentrator pickups can be 
used, each being focused so as to cover 
one speaker. In this way a number of 
cameras can be set up at the same time 
to obtain the various angles necessary 
for picture cutting purposes, and good 
pickup can be obtained from both 
speakers with due regard to the 
proper camera angle. The area of 
movement permitted the actors is also 
extended appreciably. With open mi- 
crophone pickup at least two different 
setups would be required to obtain 
proper sound values for a shot of this 
type. Otherwise some sacrifice of 
pickup quality would have to be made 
for one of the speakers, since it would 
not be possible to cover both ade- 
quately, even with a microphone boom 
of the following-crane type. 

Another case where such devices are 
of value for use indoors is in the fol- 
lowing of continuous action moving 
through several rooms, the concen- 
trator being mounted upon the camera 
dolly and moving along with it to cover 
a close-up of the dialogue ensuing. 
Numerous problems of a similar 
nature occur during production in 
interiors. The increased flexibility of 
pickup afforded by the concentrators 
offers useful assistance in their solu- 
tion. 

Size of Bowl 

A definite relationship exists between 
size of collector bowl and its efficiency 
at different wavelengths. The lower 



speech frequencies, being made up of 
sound waves of considerable length, 
require a device of large diameter if 
any appreciable portion of their wave- 
fronts is to be utilized. Beyond cer- 
tain reasonable dimensions, however, 
such a device becomes unwieldy^ in pro- 
duction. It may throw long shadows 
across the area of action, interfere 
with the proper setting up of lights 
and cameras because of the large 
amount of space occupied, and in gen- 
eral, be difficult to handle. These 
reasons necessitate that some compro- 
mise be made with the most effective 
sizes possible. Concentrators having 
diameters between 40 and 60 inches 
are considered to be desirable commer- 
cial sizes. 

Some loss of response at frequencies 
below 500 cycles occurs with these ; a 
loss made more obvious by the inten- 
sification of sound pressures occurring 
at frequencies above about 2000 
cycles. This increase amounts to an 
approximate ratio of 6:1 as compared 
to open microphone pickup at these 
frequencies. The exaggerated rein- 
forcement of the highs may be modi- 
fied, however, by altering the shape of 
the concentrator curve somewhat, and 
also, by throwing the microphone 
slightly out of focus with the reflector, 
thus sacrificing maximum sharpness of 
focus and obtaining a "softer" pickup 



effect. In practice, the microphone is 
placed about one-third off the true 
focal distance from its reflector. As 
may be surmised from these remarks. 
the pickup technique involved in the 
use of the concentrators is a rather 
special one. A discriminating ear is 
sometimes required to fit the concen- 
trator characteristics to the type of 
pickup being handled. On a properly 
constructed set indoors, however, or in 
outdoor work an experienced recordist 
often can obtain a quality of pickup 
with the concentrators at a distance of 
twenty feet, which is difficult to dis- 
tinguish by ear from open microphone 
pickup three feet from the speaker. It 
is usually desirable to place the con- 
centrators at a point not further back 
from the action than the camera 
position. 

Focusing the Microphone 
The devices are focused accurately 
upon the source of sound by means of 
the sighting arrangements previously 
mentioned, the source of sound being 
considered as a target. For lateral 
focusing, a pair of sights quite similar 
to those of a long range gun are made 
use of. One of these is stationary 
and is used as a reference sight. The 
other is mounted upon the movable 
head of the concentrator frame which 
can be swun? in a wide arc. These 




Photo courtesy RKO Radio Pictures Stu 

Fig. 3. A double concentrator pickup covering a wide angle of action. Note 
the mike man in foreground sighting his concentrator through center 

peephole. 



Page 10 



PROJECTION ENGINEERING 



sights afford a means of quickly lining 
up the concentrator in the lateral plane, 
with reference to the pickup source. 
The concentrator bowl is also adjust- 
able in a vertical direction through a 
cam lever arrangement. A peep hole 
is provided in the approximate centre 
of the bowl through which the mike 
man sights on the speaker, tilting the 
bowl up or down as required so as to 
just cover the action with the beam. 
It is somewhat ambiguous to speak of 
focusing these devices upon the source 
of sound, since they cannot strictly be 
considered to have a definite focal 
depth, certainly not in the degree that 
obtains with photographic lenses. 
Pickup is not limited to one certain 
distance within their beam, with sound 
originating ahead of or behind this dis- 
tance being blurred out. With a true 
ellipsoid reflector, having two conju- 
gate foci, it would be possible to focus 
sharply upon the source of sound at a 
definite distance, excluding other 
sounds from the pickup. This would 
require two reflecting surfaces of el- 
lipsoidal shape. Sound occurring at a 
certain distance with reference to one 
of these would then be reflected back 
to an opposite point of focus equi-dis- 
tant from the second reflector, the 
distance between the two surfaces 
being determined by the dimensions, 
angles of curvature, etc, of the re- 
flectors. 

Fig. 4 illustrates the theory of pick- 
up with such a device. Naturally it is 
impossible to construct a movie set in 
an ellipsoidal form (to afford the 
opposite half of the reflector) and still 
obtain satisfactory photographic re- 
sults. Accordingly, it is only possible 
in practice to realize a partial ellipsoid, 
the main effect of which is to soften 
the focus preventing undue emphasis 
on the treble range. Some degree of 
discrimination probably does obtain 
against sounds originating at a dis- 
tance considerably removed from that 
for which the reflectors are theoreti- 
cally designed. Both types of con- 
centrators may be made to discriminate 
further against undesirable background 
sound by tilting their planes as sharply 
downward as possible, thus limiting the 
angle of pickup. 

It is general practice when utilizing 
these devices for pickup to shoot close- 
up quality of sound only, modifying 
the quality in re-recording when nec- 
essary to stimulate more distant pickup 
for the long shot picture. It is also 
possible, however, to utilize a com- 
bined concentrator and open micro- 
phone pickup, to secure close-up and 
long shot perspective at the same time 
at an additional saving in production 
time. Such an arrangement requires 
the use of two separate recording chan- 
nels, of course. 

The use of microphone concentrat- 



ors in sound pickup work is in a broad 
sense a recent development. Early day 
broadcast engineers used a common 
wooden chopping bowl to intensify the 
pickup of the quite insensitive micro- 
phones then available. A patent cov- 
ering the use of parabolic reflectors in 
broadcast work was applied for in 1924 
by C. W. Horn, then superintendent 
of radio operations of the Westing- 
house Electric and Manufacturing 
Company, a patent being granted in 
October, 1929. The application of 
such devices to sound picture record- 



MIC. LOCATION 
WHEN LONG SHOT 
CAMERA IS USED 

LONG SHOT 
CAMERA 



MIC. LOCATION 

WHEN CLOSE 

CAMERA IS USED 

*1Z 




MICROPHONE AT 
POINT OF FOCUS 



SOUND OUTSIDE DOTTED 

LINES AND BEHIND BOWL 

HAS LITTLE EFFECT 

ON MICROPHONE 




MIC. AT 2~P 
POINT OF FOCUS 



SOURCE OF SOUND 
AT ONE POINT 
OF FOCUS 



Fig. 4. — A. Showing how combined 
long shot and close-up camera set- 
up affects relative placement of 
microphone with regard to action. 
B. Pickup with portable concen- 
trator. C. Theoretical assumption of 
reflection using ellipsoid reflectors. 
Such a reflection has two focat 
points, equidistant from either re- 
flector. Sound originating at any 
other point is not sharply focused on 
concentrated back reflector (set 
walls, etc.). 



ing, however, has until recently been 
neglected. Experimental work carried 
out by staff engineers under the direc- 
tion of Carl Dreher, director of sound 
at PvKO Radio Pictures Studios in 
Hollywood, at once demonstrated their 
value in this new field. They have 
now been in use for nearly a year, and 
while by no means considered as a 
panacea for all problems of pickup en- 
countered, they constitute a very inter- 
esting step in the right direction. By 
the judicious use of such devices in 
combination with open microphone 
pickup, a considerable increase in speed 
of production and facility in photo- 
graphing is effected ; in some cases a 



reduction in overall production cost as 
high as 15 per cent has been obtained. 
This is an important saving when one 
considers the cost of large outdoor 
types of productions. The use of con- 
centrators also makes possible the re- 
cording of difficult outdoor shots which 
might otherwise have to be sacrificed. 
Coupled with the added flexibility of 
movement permitted the actors, which 
the extended area of pickup affords, it 
does not seem too optimistic therefore 
to assert that the introduction of these 
microphone concentrators in motion 
picture work marks one of the most 
important developments since the in- 
ception of sound picture recording. 

In addition to a paper on the sub- 
ject, "Microphone Concentrator in Pic- 
ture Production," delivered by Mr. 
Dreher at the October, 1930 convention 
of the Society of Motion Picture 
Engineers in New York, and which 
appears in the January, 1931, issue of 
the Society's Journal, the writer is in- 
debted to Ralph K. Spotts and Philip 
J. Faulkner, Jr., RKO Radio Pictures' 
technical staff, for much of the informa- 
tion on these devices contained herein. 



SELSYN MOTORS FOR SYNCHRO- 
NOUS SYSTEMS 

SELSYN is the name of a make of 
self-synchronous motor. These 
motors are similar to three-phase induc- 
tion motors, but have shuttle wound 
rotors with definite poles, the windings 
of which are connected through col- 
lector rings to a single-phase, alternat- 
ing-current source of excitation. Two 
of these motors are used in a Selsyn 
system, one operated at the sending 
point as generator, and called the 
transmitter, and the other at the 
receiving point as a motor, and 
called the indicator. The stator wind- 
ings of the transmitter are connected to 
those of the indicator. When the rotor- 
excitation circuit is closed, an alternat- 
ing current voltage is impressed on the 
rotors of both the transmitter and the 
indicator. Since the indicator rotor is 
free to turn, it assumes a position 
similar to that of the transmitter rotor, 
as the transmitter rotor is turned, the 
indicator rotor follows at the same 
speed and in the same direction. It will 
thus be seen that as the transmitter 
rotor is moved, whether mechanically 
by gears or a float in a liquid, or manu- 
ally for signaling or control operation, 
the indicator immediately follows and 
assumes the desired position. A pointer 
attached to the rotor shaft will then 
indicate exactly as at the transmitter, 
and further for continuous indicating 
this motion can be transmitted to a re- 
cording instrument. 



FEBRUARY, 1931 



Testing Equipment 

for 

Sound Projection 

By E. W. D'Arcy* 



CONSIDERABLE interest has 
been evidenced by the sound in- 
dustry in a practical means of 
locating trouble quickly with a 
minimum loss of time. 

A tester has been designed for this 
purpose, making possible a complete 
checking of theatre sound systems 
rapidly and with unfailing accuracy. 

Incorporated in this equipment are 
facilities to measure vacuum tube 
characteristics, continuity of circuits, 
photoelectric cell operation, phasing of 
loudspeakers where multi-speaker in- 
stallations are made, and testing the 
frequency response characteristics of 
the entire sound system. A great deal 
of attention has been paid, in the de- 
sign of the equipment, to the condi- 
tions encountered when used with vari- 
ous types of theatre equipment. As 
will readily be realized the establish- 
ment of known standards of perform- 
ance when testing the same kind of 
equipment repeatedly is rather easy, but 
where application of a tester is used in 
the field with several types of equip- 
ment, facilities must be incorporated 
within to allow reliable data to be item- 
ized quickly. The detailed description 
of the test facilities incorporated in 
this instrument will undoubtedly be 
highly informative to individuals and 
firms with testing problems. 

Vacuum Tube Characteristics 

This tester, being primarily a piece 
of field equipment, uses the power sup- 
ply furnished by the sound installation 
for measurements of vacuum tube 
characteristics. Plugs are used to ob- 
tain power for tube measurement 

* Chief Engineer, D'Arcy Labs. 



direct from the socket in which the 
type of tube to be measured is oper- 
ated normally. Adapters are supplied, 
allowing measurements of any type of 
tube. 

Continuity of Circuits 

For testing circuit continuity, the 
master selector switch is set for the 
continuity test. When in this position, 
a direct short circuit will give a meter 
deflection of four and one-half volts. 
This provides a speedy means of test 
setup for checking circuits for opens 
or shorts. 

Photoelectric Cell Operation 

The accurate determination of pho- 
toelectric cell and associated optical 
system performance can best be deter- 
mined by tests made with the equip- 
ment in normal operation. It is under- 
stood that different values of exciter 
lamp brilliancy are used with various 
makes of projection equipment. The 
establishment, therefore, of previously 
determined photoelectric cell current is 
somewhat complicated by reason of this 
variance in operational characteristics. 

Successful operation of any sound 
device using a slit and photoelectric 
cell is dependent upon variance of light 
intensity above and below a previously 
determined light standard, this varia- 
tion in normal operation being sup- 
plied by the sound track on the film. 
A photoelectric cell operating properly 
does not depend for its successful 
operation on any one specific light 
value, but rather upon light varia- 
tion, for its performance. In this 
respect a photoelectric cell is somewhat 
similar to a vacuum tube, illumination 
being considered as the variable grid 



Page 1 1 

potential. To carry the analogy a little 
further, possibly a better way of grad- 
ing photoelectric cells would be in a 
term corresponding to the mutual con- 
ductance of the vacuum tube. 

Determination of photoelectric cell 
performance can best be made, due to 
the factors previously mentioned, if a 
standard light source is used and the 
light reaching the photoelectric cell 
from this source varied in its value in 
a normal manner by. for instance, the 
insertion of test film whose develop- 
ment and exposure have been accurately 
determined. An innovation is, there- 
fore, presented in modes of testing by 
the use of film which has been exposed 
to four different known light intensities 
and, when measurement of photoelec- 
tric cell current is made with this film, 
the result is directly transposable into 
decibels which accurately determine 
the performance of the sound track 
system under test. 

In operation, the microammeter sup- 
plied with this instrument is connected 
in series with the photoelectric cell and 
exciting power supplied. Measurements 




Description of What May be Accomplished in Pro- 
jection and Recording by Testing and Checking 
Electrical Equipment 



Fig. 1. Response curve, theatre am- 
plifier. 



may then be made of the current flow- 
ing through the cell with different 
values of light as supplied from the 
light source through the standard film. 
This information is then plotted on 
standard graph paper. The results are 
then compared with the characteristics 
plotted by the manufacturer of the 
photoelectric cell. The procedure seems 
rather difficult, but is really no more 
so than that of testing a vacuum tube 
wherein the grid voltage (the amount 
of light varied and determination of 
tube excellence obtained by the noted 
corresponding variation of plate cur- 
rent) which compares with photoelec- 
tic cell current variance. It is fairly 
obvious from the foregoing statement 
that the unmodulated current of a 
photoelectric cell is not an accurate 
way of determining whether a photo- 
electric cell is defective or not. This 
test procedure, when applied to equip- 



Page 12 



PROJECTION ENGINEERING 



ment in operation, allows speedy deter- 
mination of defects in the optical and 
photoelectric cell systems. 

Phasing of Loudspeakers 

Unless all of the speakers in multi- 
speaker sound installations are so con- 
nected as to be in phase, difficulty in 
sound distribution will be encountered. 
The test procedure for checking this 
condition speedily is quite ' simple, it 
merely being necessary to connect a 
source* of direct-control to the voice 
coils of the speakers and note the direc- 
tion of movement of the voice coil. As 
an example, all coils should move for- 
ward simultaneously upon application 
of a direct-current, dependent upon the 
polarity of current. 

Frequency Response Measurements 

It is often desirable to determine 
with reasonable accuracy the frequency 
response characteristics of the ampli- 
fier system from the pickup device to 
a known terminating load. A thermo- 



10 
in 
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u 
a 

I 8 

o 
a 
o 

1 6 

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Z 
u 

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•05 .10 .(5 .20 .25 
LIGHT FLUX - LUMENS 



Fig. 2. Photoelectric cell character- 
istics. 



galvanometer with a multiplier is sup- 
plied for this purpose. 

Standard test procedure for these 
measurements is given herein. Resist- 
ance units of the correct value to re- 
place the existing speaker bank are 
connected across the output of the 
amplifier under test. The output ter- 
minals on the testing panel are con- 
nected in series with this resistor bank. 
Frequency test records or film is then 
set for a standard frequency of, say, 
i,ooo cycles. The multiplier supplied 
with this device is then so adjusted as 
to bring the meter deflection on the 
thermogalvanometer to a previously 
determined center scale reading. Loga- 
rithmic cross-section paper is used 
in plotting the graph. Since the read- 
ings are taken from a thermocouple 
galvanometer and then plotted on log 
paper, the curve will be immediately 
translatable into decibel units. A curve 
made on a representative amplifier is 
shown, Fig. i, to illustrate the ease 




Fig. 3. A typical test set for sound 
circuits. 



with which the graph may be plotted. 

It is highly desirable, in making 
these tests, that the speaker bank be 
replaced by non-inductive resistors of 
known value. It is suggested that the 
replacement resistances be matched to 
the impedance of the speakers at ioo 
cycles. 

More accurate determination of the 
frequency response of an amplifier can 
be had if an oscillator be used in place 
of the pickup device. It is then merely 
necessary to hold the input to the am- 
plifier at a uniform level and make 
notations of the variations in current 
as shown by the thermogalvanometer. 

Testing Versatility 

Any piece of testing apparatus must 
of necessity be versatile and facilities 
incorporated to allow any component 
part to be used individually in cases 
where the necessity arises for such use. 

A suitable instrument is exceedingly 
versatile in that respect as each meter 
is equipped with multipliers which 
permit a wide extension of their range 
of measurement. 

It is possible, with this equipment, 
to measure input and output voltages 
of the power supply transformer as 
well as current flowing through any 
part of the circuit. The- continuity 
test can also be used for the measure- 
ment of resistance as a calibration is 
supplied with each tester, showing the 
resistance per unit scale of variation 
occurring in the voltmeter. 



TALKING PICTURES IN SCHOOLS 

HARRY D. KITSON, of Columbia 
University, New York, thus sum- 
marizes the present value of modern 
sound projection to education in 
schools : 

( i ) It will prove a useful supplement 
alike to textbook and to teacher. 

It will not wholly take the place of 
either. It can, however, bring the text- 
book to life, and it can relieve the 
teacher from the merchandising of in- 
formation, leaving his energies free for 
the higher role of guide in the learning 
process and giving him more time for 
attention to individual pupils. 

(2) It will improve the quality of 
instruction. 

At every point where the talking 



film proves at all usable, it can present 
instruction by the masters instead of by 
the mediocre u,pon which we must all 
too often lean. 

(3) It will make possible frequent 
repetition of materials, where desirable, 
without consuming the teacher's time 
for such repetition, and insuring that 
the repetition shall be exactly the same. 

(4) It will make possible a widening 
of the curriculum that might not be 
possible if teachers had to be hired and 
expensive equipment bought. 

(5) It will enable pupils to learn 
through the eye as well as through the 
ear — two senses that are not always 
adequately employed in learning. 

(6) It will enable us to standardize 
the content and quality of all instruc- 
tion that should be standardized 
throughout a State or Nation. 

(7) It will make possible many 
economies. 

▲ 

R-K-O GETS PATHE EXCHANGE 

CONSUMMATION of the sale of 
assets of Pathe Exchange, Inc., to 
Radio-Keith-Orpheum Corporation was 
announced on February 2, by Hiram S. 
Brown, president of the latter company. 

The deal previously was approved 
by a majority of Pathe stockholders, 
but various suits had been brought to 
halt the transfer. These legal actions, 
it is reported, were withdrawn follow- 
ing a long conference on February 1. 

Pathe Exchange, Inc., retains its 49 
per cent, interest in Du Pont Pathe 
Film Manufacturing Company, but sells 
its studios and other principal assets to 
R-K-0 for $4,630,789, payable in notes 
maturing over a period of about five 
years. 

Mr. Brown issued the following 
statement concerning plans for opera- 
tion of Pathe properties : 

"It is intended to operate two distinct 
and separate motion picture producing 
and distributing organizations — one the 
present R-K-0 Radio Pictures Cor- 
poration and the other a separate com- 
pany to continue the operations of the 
present Pathe studio and Pathe branch 
offices in this country and abroad. 

"A separate production organization 
will be maintained in the Pathe studio 
in Culver City, Cal., which will func- 
tion independently of the Radio Pic- 
tures studio. 

"In the sale and distribution of Pathe 
pictures the present Pathe branch of- 
fices, manned by the Pathe personnel, 
will continue to function as a separate 
selling and distributing organization. 
There will be an independent home 
office for the new company in New 
York city at its present headquarters 
on Forty-fifth street., While the full 
name of the new operating company has 
not been definitely determined, the 
word Pathe will be maintained in its 
corporate title." 



FEBRUARY, 1931 



Page 13 



The taking of a well remem- 
bered scene in "All Quiet on 
the Western Front" 



Th 



C 



amera 



Cran 




Used in Making Intricate Shots 



By Gordon S. Mitchell* 



WHENEVER an especially 
involved camera shot is de- 
sired, the great camera crane 
is called into service. This 
crane can, in the language of its 
operator, "do anything but talk." 

The crane itself is electrically oper- 
ated, controlled by the operator who 
rides in the cage on the end of the 
boom at all times. Large electric 
motors, properly geared, enable the 
crane to be moved up and down, for- 
ward and back, and from side to side, 
at any speed. Mounted as it is upon 
rubber tired wheels, the entire assem- 
bly may be made to crawl forward or 
back at the same time that the crane 
proper is moving in any other direc- 
tion. The cage may be placed at any 
point within a sphere whose center is 
at the base of the boom and of a radius 
of approximately sixty feet. The cage 



Sound department Universal Pictures Corp. 



may be set down upon the floor or sta- 
tioned sixty feet in the air, straight 
overhead. As may be seen in the pho- 
tograph, the cage floor remains level 
in any position. Due to the extreme 
versatility of the crane, it is possible 
to achieve any desired camera effect. 

A Dramatic Episode in "All Quiet" 

The crane was used extensively dur- 
ing the filming of Universal's "All 
Quiet on the Western Front," from 
which the scene herewith presented is 
taken. Many of the particularly strik- 
ing photographic effects in this picture 
were shot with the aid of this crane. 
Being built and mounted as it is, the 
crane may be taken inside of any sound 
stage for interiors, or to any location 
for exteriors. An impressive shot, 
which was much enhanced by the use 
of the crane, comes to mind. The set- 
ting was a diplomatic ball — with all of 



Ingenuity Provides Photographing and Sound Recording 
Device for use in Difficult Positions 



the pomp and splendor usually associ- 
ated with such affairs. The orchestra 
played at the far end of the room, from 
their place on a platform raised a foot 
or so above the general floor level. 
Hundreds of dancers, the men in bril- 
liantly decorated uniforms and the 
ladies in long evening gowns, filled the 
hall. While the director wished to lose 
none of the brilliance and color of the 
background, he also wished to pick up 
and fasten attention upon his main 
characters, in order to carry the action 
and plot along. 

A Difficult Set 

The set was probably two hundred 
feet in length and sixty or seventy feet 
wide. A wall, with offset boxes in 
which sat the dowagers and their es- 
corts, ran the length of one side. The 
star and his lady were to slowly walk 
along the edge of the dance floor, close 
to the wall below the boxes. While 
there are several ways in which this 
shot could be obtained, the crane pre- 
sented the simplest solution to the 
problem. It might have been taken by 
mounting the camera above, and from 
a stationary position following the 
action with the lens, or the camera 



Page 14 



PROJECTION ENGINEERING 



might have been mounted upon a small 
perambulator which could have been 
rolled along among the dancers imme- 
diately in front of the principal char- 
acters. 

This last type of shot, in which the 
action follows the camera which moves 
about the set always focused upon that 
action, is very common in motion pic- 
ture photography. However, by using 
the crane a commonplace piece of pho- 
tography was turned into an impres- 
sive and extraordinary example of the 
camera-man's art. The crane was 
tracked along the far side of the set, 
the boom arm reaching out over the 
heads of the dancers. The cage imme- 
diately preceded the principal charac- 
ters, placed so that the camera shot at 
an angle down upon them. Keeping pace 
with them throughout their walk along 
the dance floor, attention was focused 
upon them until they reached the end 
of the hall, at which spot the crane be- 
gan to rise, and from a height of 
forty-five feet, the camera in one 



grand sweep took in the entire colorful 
scene. Such photography, interspersed 
throughout the more commonplace 
scenes, does much to determine the 
success or failure of any motion pic- 
ture. The problem of keeping the plot 
moving along and at the same time im- 
pressing the beauty and color of set- 
ting upon the spectator is solved in 
many instances by the camera crane. 

Camera Mounting 

The camera is mounted upon a regu- 
lar tripod set upon the floor of the 
cage, and the microphone may or may 
not accompany the camera upon the 
crane depending upon the type of shot 
desired. The cables, which in the 
accompanying picture may be seen en- 
tering the cage through the hub of the 
large wheel, are power lines which 
carry the current for the camera 
motors. The smaller cable at the floor 
level is the microphone cable, which 
connects the mike to the sound re- 
corder. A cue box, which enables the 



operator to be kept in contact with the 
director is mounted in front of the 
assistant's post at the left. Various 
colored lights, one of which means 
"up," another "down," another "for- 
ward," and so forth, each separately 
controlled from a switch in this cue 
box keep the operator informed at all 
times as to what type of motion the 
director desires. 

This cue box is made necessary due 
to the need for absolute quiet while 
actual photography is going on. All 
of the director's commands must be 
made noiselessly. The large hooded 
object on the cage is the camera, so 
covered in order that camera noise will 
not be picked up by the microphone, 
seen directly over the players in the 
illustration. 

This crane is only one of the many 
mechanical devices which have been 
developed in the studio shops to add to 
the spectacular quality of present-day 
motion pictures. 



Study Conducted on Use 
of Films for Advertising 



EXPLOITATION of the motion 
picture by American industry, now 
rapidly reaching into the field of 
advertising films for theatre ex- 
hibition, is being surveyed by the De- 
partment of Commerce, according to 
an oral statement January 6 by 
Eugene I. Way, of the Motion Picture 
Division, in charge of the survey. 

The Department's survey will seek 
to determine the many uses to which 
the motion picture is being put in busi- 
ness and the value attending its em- 
ployment. The incorporation of sound 
in the industrial film will be investi- 
gated and this phase of motion picture 
development may be the object of a 
separate study following the general 
survey, he stated. 

Films Widely Used 

The use of the motion picture in 
business has been established for some 
time, Mr. Way explained, and today 
its services extend into practically 
every channel of trade. It is being 



Commerce Department Expects 

to Determine Results Obtained 

from Business Pictures 



employed by almost every large manu- 
facturing concern and by many mer- 
chandising establishments and its uses 
range from factory operation instruc- 
tion to sales promotion demonstrations. 
The development of this field of mo- 
tion pictures, he said, has stimulated 
the establishment of numerous inde- 
pendent industrial film companies 
which produce for this market and has 
attracted the attention of the big fea- 
ture studios, some of which are enter- 
ing the field. 

In conjunction with the expansion 
of the industrial film used for interor- 
ganization purposes, the business mo- 
tion picture is now being advanced for 
theatre exhibition. This development, 
Mr. Way explained, is being promoted 
on the assumption that "romance in in- 
dustry," affords a rich field for motion 
picture exploitation, especially now that 
sound has been incorporated into the 
film. This type of film is being pro- 
duced for theatre presentation by large 
picture producers at the instance of 
business organizations. Recently, one 
such film, employing a well known 
comedian, was produced for a large in- 
surance Company which plans to dis- 
tribute the film in various theatres. 
These films follow two general trends ; 
those which are shown "by courtesy 
of" the advertiser and have no direct 



advertising in the run of the film, and 
those which embody advertising in the 
film proper. The "courtesy" films are 
analogous to radio programs presented 
by business firms which are without 
reference to the company during the 
course of the entertainment, it was 
explained. 

According to the division's informa- 
tion, Mr. Way said, there are approxi- 
mately 5,000 theatres, with a seating 
capacity of 18,000,000 persons, which 
have been made available for the dis- 
tribution of entertainment films distrib- 
uted by business concerns. Efforts are 
being made to enlist additional theatres 
as outlets for these films, he said. 

The activities of industry in this field 
of motion pictures will be included in 
the division's survey of business pic- 
tures, the questionnaire sent out for the 
survey listing inquiries on the various 
uses of films in industry by those con- 
cerns which have included motion pic- 
tures in their advertising expenditures. 
A statement by the Department regard- 
ing the survey follows in full text: 

To what extent the American movie 
has "gone into business" as an aid in 
promoting operating efficiency, and the 
degree of success attending the use of 
such methods by industry, form the 
subject of a special study now being 
made by the Motion Picture Division 
of the Bureau of Foreign and Domes- 
tic Commerce. 

At least 2,000 concerns in the United 
States, it is known, have used the mo- 
tion picture for some business purpose. 
In other cases the ends sought are crea- 
tion of good will through illustration 
{Concluded on page 22) 



FEBRUARY, 1931 



Page 15 



Radiovision Programs 
in the Making 



By Austin C. Lescarboura 

Mem. I.R.E. Mem. A.I.E.E. 



In Which We Study the Program Possibilities of 

Radio Television Broadcasters in Creating Public 

Acceptance 



THE American public is ever 
ready to invest in sound enter- 
tainment. Be it theatre, movies, 
talkies, circus, broadcasting and 
even television, the average family will 
dig down into its pocket and salvage 
enough loose change to pay for that 
which makes it forget its troubles and 
cares. And thereby hangs the follow- 
ing discussion of just what can be 
done by radiovision workers in gaining 
public acceptance for the radio tele- 
vision idea preliminary to building up 
a large and profitable industry. 

Until now, the greater part of tele- 
vision broadcasting has been of an ex- 
perimental nature. In fact, the tele- 
vision broadcasters have made no spe- 
cial attempt to interest the average 
layman beyond the mere curiosity 
stage. Television broadcasters have 
been experimenters first of all, and 
showmen last of all. Most transmit- 
ters have been of a haywire nature, 
subject to changes every fifteen min- 
utes by the clock. If television has 
been made the joke of hard-boiled 
journalists, it is because of changes in 
the usual equipment on the very eve of 
an important broadcast demonstration, 
resulting in a grand flop to the disgust 
of all concerned. Until now, television 
experimentation and television entertain- 
ment have been wrapped in a single 
package, with the same facilities used 
in catering to the extremes of experi- 
menter and layman. 

To those closely identified with 
radiovision development, it has been a 
source of consternation to note how 
slowly radiovision equipment has sold 
to the public at large. Even before the 
Wall Street crash, which is as conven- 



ient an alibi for television's slow prog- 
ress as it is for any other line, the 
public did not rush in to buy a com- 
plete radiovision receiver for a mere 
$'400 list. That $200 list is as much 
as the public will spend for some- 
thing that is certain to become obso- 
lete in a year, and that the public in- 
sists on tuning in to something worth 
seeing on definite schedule, are points 
heretofore not mentioned in reports to 
the Board of Directors or to others 
interested in radiovision's welfare. 

Reasonable Progress Made 

From an engineering standpoint, 
radiovision has made rapid and satis- 
factory progress during the past six 
months. Today it is possible to trans- 
mit and to receive scenes with as many 
as half a dozen persons, and with 
some background. Standard motion 
picture film may be broadcast, al- 
though all scenes are not equally suit- 
able for this purpose. It is possible to 
broadcast excellent closeups of living 
persons. With silhouettes, fair enter- 
tainment possibilities are now at hand. 
And of course, the synchronized sound 
accompaniment greatly enhances the 
radiovision presentation. Indeed, al- 
most unlimited entertainment value is 
available if sound accompaniment is 
employed. 

Just now. the engineers engaged in 
radiovision work may well rest on their 
laurels for a few moments and allow 
the merchandising brains to catch up 
with them. The engineers have given 
us a practical experiment. It now re- 
mains for merchandisers to convert 
that practical experiment into a self- 



supporting and even profitable in- 
dustry. 

Just what can be done to make 
radiovision interesting to the average 
American family? That question is 
now in order, and here is our answer 
based on recent observations. 

There are four forms of radiovision 
presentation available today, with the 
existing engineering status of the art: 
(1) the film pickup, with or without 
sound accompaniment; (2) the flying 
spot pickup for personality close-ups, 
with or without sound accompaniment; 
(3) the camera pickup in the studio, 
with or without sound accompaniment; 
and (4) the outdoor camera pickup in 
conjunction with the portable trans- 
mitter, with or without sound accom- 
paniment. Analyzing these in due 
turn, here is what we have by way 
of an entertainment inventory: 

The film pickup is the favorite with 
most radiovision broadcasters, for the 
reason that heretofore this method has 
provided the least troublesome pro- 
gram. It has been unnecessary to 
have persons stand and act before the 
radiovision pickup. Instead, the same 
film has been ground through the 
pickup, hour after hour, until much of 
it has gained the appearance of a scene 
taken during the Deluge, due to the 
"rain" on the wornout film. 

Until quite recently, the usual 48- 
line or 60-line scanning system has 
not permitted of really fine detail. In 
fact, C. Francis Jenkins, a pioneer 
radiovision broadcaster, made all his 
films until recently, in silhouette or 
black-and-white form. Within the past 
three months, however, radiovision 
workers such as the Jenkins Tele- 
vision Corporation and the DeForest 
Radio Company, have found it entirely 
feasible to handle standard motion pic- 
ture films, including backgrounds and 
several persons. 

Film Pickup 

Just as the automatic piano and the 
phonograph played a major role in 
early sound broadcasting, so must the 
film pickup serve as the backbone of 




Side view of Jenkins television camera with 
amplifier case opened to show tubes. 



Page 16 



PROJECTION ENGINEERING 




The television cameraman focusing and 

checking up on his pickup by means of the 

monitoring view-finder. 



the radiovision program. It is bound 
to work hour after hour in supporting 
a daily schedule, but this is no reason 
why it should not prove attractive to 
the lookers-in. To this end, some of 
our more advanced broadcasters have 
arranged for regular film rentals so as 
to have a steady supply of fresh film. 
The only point which we hope they 
will observe in presenting such film is 
to preview each film under typical 
radiovision conditions, editing the film 
accordingly so as to present over the 
air only those scenes which are really 
meaningful. Too often an otherwise 
convincing demonstration of radio- 
vision entertainment is ruined by in- 
cluding a moonlight scene or an out- 
of-focus scene which means little or 
nothing to the chap a hundred miles 
away, peering anxiously into the 
radiovisor and wondering why his re- 
sults have suddenly gone haywire. 

Sound Accompaniment 

Sound accompaniment is invaluable 
to radiovision entertainment at the 
present stage of the art. Some of the 
broadcasters are equipped with com- 
bination film and disc pickups, so that 
sound-on-disc films may be employed, 
although such films must be made to 
order since television pictures are run 
at 15 pictures per second instead of the 
higher speeds for theatre work. For 
this reason too the sound-on-film sub- 
jects are not suitable today, although 
the radio television engineers are 
working out a means of utilizing 
standard sound films. 

The sound accompaniment is, of 



course, handled through a second radio 
channel. Several radio television sta- 
tions have suitable tieups with sound 
broadcast stations, so as to provide a 
sound accompaniment. It is well to 
note that the sound accompaniment 
may be on the usual broadcast frequen- 
cies, thus being tuned in by the usual 
broadcast receiver, or slightly below 
the usual broadcast frequencies but 
still tuned in by the average broadcast 
receiver at its lowest dial setting. 
Again, the sound accompaniment may 
be on a short-wave frequency- Also, 
the sound accompaniment may be noth- 
ing more than the standard broadcast 
entertainment feature as now pre- 
sented, with radiovision as an optional 
feature. Some programs have already 
gone on the air in this manner, with 
the announcer stating that a radio- 
vision presentation of the program 
was available on such-and-such a 
wavelength for those provided with 
the necessary equipment. Indeed, it is 
our personal belief that radiovision 
will fit in best by being a supplement 
to the usual and established broadcast 
features, purely as an optional consid- 
eration, rather than as a prime enter- 
tainment factor, for a long while to 
come. It is simple enough to include 
a radiovision pickup in the broadcast- 
ing studio, so as to have this optional 
feature. Or it may be possible to have 
a film pickup handling some suitable 
visual accompaniment to the musical 
program. Let us make no mistake 
aoout it, the aural entertainment will 
always be more interesting - to the pub- 
lic than the visual. It should, there- 
fore, be the main feature at all times. 

Flying Spot Pickup 

The flying spot pickup has made 
notable progress in the past few 
months. Prior to this period of rapid 
development, this technique consisted 
of a tiny spot of light flashed line by 
line horizontally across the subject 
pressed up against a frame carrying 
photoelectric cells, behind which was 
the revolving disc and light source. 
Recently, the engineers have evolved 
ingenious photoelectric cell units, com- 
prising cell, reflector and amplifier, 
mounted in suitable camera-like units 
on fully adjustable stands. Thus the 
photoelectric cells may be placed at 
any distance and any angle with rela- 
tion to the subject, obtaining the re- 
flected light from any angle, thereby 
obtaining interesting lighting effects 
not unlike those with photography. 
The flying spot is an ideal pickup 
means for personalities, but unless the 
microphone for the sound accompani- 
ment is at hand, the entertainment pos- 
sibilities are of a very low order. Just 
merely to watch a person speak with- 
out hearing what that person says, or 
to watch a musician play without 



hearing anything, is decidedly dull. 
After the first thrill of seeing a picture 
flashed through space, there is little 
left to do but to yawn and fall asleep. 

Camera Pickup 

The camera pickup takes the sub- 
jects out of the darkened room, made 
necessary by the flying spot technique, 
and into the fully ilmminated studio or 
even outdoors. Recently some really 
practical radiovision cameras have 
been developed, with interesting fea- 
tures and possibilities. The usual 
camera comprises an exceedingly fast 
lens, an enclosed scanning disc, a 
photoelectric cell, and an amplifier, 
suitably housed. One of the latest 
cameras includes a direction finder and 
focusing feature whereby the operator 
sees in televised form precisely what 
he is picking up. This feature is 
really a visual monitoring check on 
what is being sent over the line to the 
transmitter. The operator usually 
wears a pair of headphones, so as to be 
sure of his signals by the characteris- 
tic sounds while the camera is in 
operation. 

The beauty of the camera pickup is 
that larger groups can be handled 
than in the case of the flying spot, and 
also that the actors have full freedom 
of action within the field of the camera 
lens. Greater amplification is neces- 
( Concluded on page 24) 




Adjustable photoelectric cell unit employed 
for direct flying spot pickup. 



FEBRUARY, 1931 



Amplification 



in 



Sound Motion Picture 
Work 



Part I 

By Charles Felstead* 



Page 17 

LEGEND FOR DIAGRAMS 

Ei = grid voltage (the C bat- | 

tery) 
E 2 = filament voltage (the A j 

battery) 
E 3 = plate voltage (the B bat- \ 
tery) 
| G = grid of tube 

F = filament of tube 
P = plate of tube 
R p = plate resistance 
| I p = plate impedance 
CC = coupling condenser 
GL = grid leak 
Vj = first amplifier tube 
V 2 = second amplifier tube 
P' = primary of coupling trans- j 

former 
S' = secondary of coupling 
transformer 



The Projectionist and the Engi- 
neer Will Find Here a Detailed 
Description of the Equipment 
in Present-Day Sound Amplify- 
ing Systems 



A SOUND recording channel 
for motion picture work can 
be roughly divided into three 
main departments ; pickup and 
monitoring, amplifying, and recording. 
There are, of course, a number of 
other departments in the sound record- 
ing studio which are more or less inti- 
mately connected with these three de- 
partments that are directly associated 
with the actual recording work. By a 
curious analogy, a sound recording 
channel can be compared to a human 
being — the microphone being the ears 
of the sound system, the monitor man 
and his controls representing the brain, 
the main amplifying equipment being 
the heart that supplies the energy to 
the recording system, and- the hands 
the recording device that makes a per- 
manent record on a suitable sensitive 
medium of the sounds picked up by the 
microphones. A thorough discussion 
of the monitoring equipment and of 
the art of monitoring, and some de- 
scription of the pickup equipment, or 
microphones, was contained in the 
series of articles on monitoring that 
has been appearing in Projection 
Engineering. 

Reviewing briefly the material lead- 
ing up to this article, we see that a 
sound originating within range of a 
condenser microphone in the sound 
stage sets up a series of condensations 
and rarefactions in the air, which 

" Suund Engineer, Universal Pictures Corp. 



strike the diaphragm of the micro- 
phone, causing it to vibrate in tune to 
the frequency of vibration of the 
sound source. This movement of the 
microphone diaphragm, which forms 
one plate of a small condenser, pro- 
duces a minute alternating voltage on 
the grid of the vacuum tube in the am- 
plifier that forms a part of the micro- 
phone. This alternating voltage like- 
wise has a frequency that corresponds 
exactly with the frequency of the 
sound. This minute voltage is ampli- 
fied by the one- or two-tube amplifier 
mounted within the microphone assem- 
bly, and then transmitted along the 



microphone cable and line to the moni- 
toring apparatus in the monitor room. 
There, each microphone is connected to 
a special potentiometer on the mixer 
control panel, which permits the pro- 
portionate amount of energy fed to the 
recording system by the individual 
microphones to be regulated. The 
speech current is at a very low electri- 
cal level in this part of the recording 
circuit, and it is necessary that it be 
amplified to a suitable value by a two- 
or three-stage "booster'' amplifier. 
The output of the amplifier connects 
to another special potentiometer which 
is for the purpose of controlling the 
overall amount of sound current that 
is delivered to the main recording am- 
plifier- Erom the several microphones. 
The output of this potentiometer is 




Fig. 1. Amplifier bays of two-channel recording installation. 



Page 18 



PROJECTION ENGINEERING 



carried by a transmission line to the 
main amplifiers in the amplifier roof. 
It is at that point that the discussion 
in this article begins. 

Amplifier Bays 

In the accompanying photograph, 
Fig. i, may be seen the amplifier bays 
of a two-channel installation of the 
Western Electric sound recording sys- 
tem. A channel includes all of the 
equipment that is directly connected 
with a single recording unit, from the 
microphones on the stage to the two or 
four recording machines in the record- 
ing room. There must be a separate 
channel for each sound stage that is in 
operation at any one time, although the 
recording channels are arranged so that 
they can be switched from one stage to 
another at will. Separate crews of 
men are required for each channel, the 
man in charge of the amplifying 
equipment being the only one who can 
double up in his work. The several 
permanent recording channels in a 
studio are installed in a building called 
the sound studio, which adjoins the 
sound stages. The main amplifying 
equipment for all the channels is situ- 
ated in the amplifier room, which is 
generally located near the center of the 
sound studio. The main distributing 
frame, or MDF, at which most of the 
wires in the installation are brought to 
connection blocks and strapped to- 
gether, and the switchboards carrying 
the switches for charging and dis- 
charging the batteries that supply 
power to the amplifiers are also located 
in this room. 

As may be seen in the photograph, 
the amplifiers are mounted in vertical 
frameworks, which are called "bays ;" 
and there are seven of these bays in a 
two-channel recording installation. 
Three bays are required for each 
channel, and the seventh bay — the cen- 
ter one — carries the jacks that are used 




^2 



Fig. 2. Transformer coupled vacuum 
tube circuits. 



for swinging the recording channels to 
different sound stages. Of the three 
bays that constitute one channel, the 
left-hand bay carries the amplifiers for 
monitoring, the center bay is for the 
volume indicator and auxiliary equip- 
ment, and the right-hand bay carries 
the amplifiers employed in the direct 
recording circuit. The frameworks 
that form the support for the ampli- 
fiers are rectangular in shape and are 
constructed of steel I-beams. Each 
framework is approximately seven feet 
high and twenty inches wide. These 
are mounted on a special concrete and 
cork foundation that is separate from 
the rest of the floor, in order that 
heavy vibrations will not be so readily 
transmitted to the sensitive tubes in the 
amplifiers. 

The Amplifiers 

The amplifiers are built on iron 
panels nineteen inches wide, and have 
removable metal box covers on the 
back that serve as electrostatic shields 
and prevent dust from accumulating 
on the apparatus and in the wiring. 
The metal panels and covers are 
grounded through the framework. 
Blank iron panels are used to fill in 
the spaces between the amplifiers. 
Shielded leads connect the amplifiers 
to terminal blocks at the bottoms of 




cc 



Rp 



GL 



11 




CC 



v 2 




GL 




-RESISTANCE COUPLING- 



-IMPEDANCE COUPLING- 



V ( 



COUPLING 
TRANSFORMER 



COUPLING 
TRANSFORMER 






Vi 




x p: 




-TRANSFORMER COUPLING- 



IMPEDANCE -TRANSF 
COUPLING 



Fig. 3. Types of amplifier tube coupling. 



each of the amplifier bays. Panels 
carrying fuses for all of the battery 
circuits in the amplifiers are also lo- 
cated at the rear of the bays. A 
heavy copper bar that serves as a com- 
mon ground for all of the amplifiers 
runs across the bottoms of the seven 
bays in the installation. It is con- 
nected to a number of large copper 
plates that are buried in the earth 
directly beneath the amplifier room. 

Before going into a description of 
the amplifiers and their arrangement in 
a sound recording installation, it might 
be well to examine in as concise a 
manner as possible the elementary prin- 
ciples of audio-frequency amplification 
and vacuum tube operation. An audio 
amplifier is a device for increasing the 
amplitude of any small alternating cur- 
rent having a frequency that falls 
within the audio-frequency band, 
which extends roughly from about 
twenty to twenty-thousand cycles a 
second. This small alternating cur- 
rent is applied to the primary of an 
audio transformer, or other suitable 
coupling device, the output of which 
is connected so that it produces a 
small alternating voltage between the 
grid and filament of a three-element 
(grid, filament, and plate) vacuum 
tube. The circuit of a simple form of 
transformer-coupled vacuum-tube am- 
plifier may be seen in Fig. 2. 

Now the characteristic of a vacuum 
tube when connected in this regular 
manner in an audio amplifier is such 
that a small change in the potential on 
the grid of the tube will produce a cor- 
responding but larger change in the 
flow of current in the plate circuit. 
The grid of the tube is kept at a cer- 
tain negative d-c. potential at all times 
by means of a C battery — or by bring- 
ing out a tap at a predetermined point 
in the filament circuit, thereby taking 
advantage of the voltage drop across a 
resistor in the negative lead of the fila- 
ment. The alternating voltage applied 
to the grid in addition to this fixed 
negative voltage adds to the negative 
grid potential when the a-c. voltage is 
on the negative half of the cycle, and 
subtracts from the d-c' bias voltage 
when it is on the positive half of the 
cycle. Negative electrons are drawn 
from the heated filament in the tube to 
the plate by the positive plate poten- 
tial furnished by the plate battery, and 
this flow of electrons to the plate con- 
stitutes the plate current. The plate 
current flow has a certain value when 
there is only the fixed d-c. bias voltage 
on the grid; but when an alternating 
voltage alternately adds to and sub- 
tracts from this steady voltage, the 
plate current is correspondingly de- 
creased and increased. 

The grid functions in a manner 
analogous to the action of a small 
valve that regulates the flow of a large 



FEBRUARY, 1931 



Page 19 



volume of water. An increase in the 
negative potential on the grid reduces 
the flow of electrons from the filament 
to the plate, because the negative grid 
repels the negative electrons to a 
greater extent than it did when it was 
at a lower negative potential and will 
not permit so many of them to pass 
through it. For the same reason, a 
decrease in the negative potential of 
the grid in relation to the filament 
allows more electrons to pass, and so 
increases the plate current. So long 
as the tube is operated on the straight 
portion of its characteristic curve, the 
relationship between the grid voltage 
change and the plate current change 
will be a linear function. Otherwise, 
if it is operated on the toe or the knee 
of the curve, distortion in the output of 
the tube will be the result. The value 
of the fixed negative bias on the grid 
of the tube is the main factor in deter- 
mining the portion of the characteristic 
curve on which the tube will operate. 
The operation of four-element and 
other types of tubes in audio ampli- 
fiers will not be described here because 
they are not used at the present time in 
sound recording work. 

Coupling Amplifiers Together 

There are three commonly em- 
ployed methods of coupling the output 
of an amplifier tube to the grid circuit 
of the next amplifier tube, or to the 
device that is to be supplied with 
power. These three types of amplifier 
coupling devices are known as resist- 
ance coupling, impedance coupling, 
and transformer coupling, and they are 
diagrammed in simplified form in Fig. 
3. There is also an alternative form 
of transformer coupling, called imped- 
ance-transformer coupling, that is like- 
wise shown. These types of tube 
couplings all act in more or less the 
same manner; but with proper design, 
transformer or impedance-transformer 
coupling provides a step-up ratio that 
gives greater overall amplification. 

These coupling devices function in 
the following manner : The plate cur- 
rent flowing through the plate resist- 
ance, Rp, in the case of resistance- 
coupled amplification, produces a drop 
in voltage across the resistance. Any 
variation in the grid potential of tube 
V a causes a change in the plate current 
flowing through R p , which results in a 
variation in the voltage drop across it. 
Actually, under average conditions, 
this change in the voltage drop across 
R p is equal to the change in grid vol- 
tage multiplied by about two-thirds 
the mu (a), or amplification con- 
stant, of the tube. That is, if the mu 
of the tube is nine, this voltage change 
in the grid circuit of tube V 2 will be 
approximately six times the voltage 
change in the grid circuit of tube V a . 
The value of the plate resistance, R p , 




Fig. 4. Schematic of layout of a single recording channel. 



in relation to the a-c. plate resistance 
of the tube — together with the u. — de- 
termines the amount of amplification 
that will be obtained. 

As in the grid circuit, there are two 
current components in the plate circuit 
of a vacuum tube: the steady d-c. cur- 
rent component from the plate battery, 
E 3 , and the a-c. current component that 
is produced by an a-c. voltage applied 
between the filament and grid of the 
tube. The a-c. current component in the 
plate circuit of V, is passed almost 
without hindrance by the coupling con- 
denser, CC, to the grid circuit of tube 
V 2 ; but the direct current from the 
plate battery is effectually blocked by 
this condenser. Thus there are sepa- 
rate paths for the a-c. and d-c. current 
components to follow. In the resist- 
ance-coupled and impedance-coupled 
circuits shown in Fig. 3, the a-c. vol- 
tage on the grid of the second tube is 
higher than the a-c. voltage on the grid 
of the first tube, as was explained; but 
that is not due to the coupling devices, 
which have a one-to-one input to out- 
put ratio, the only amplification ob- 
tained being within the tubes them- 
selves. 

A transformer-coupled amplifier, 
however, provides an additional source 
of amplification in the coupling trans- 
former used between the tubes. When 
properly designed, the transformer has 
a step-up ratio of primary to secondary 
that serves to increase the voltage 
change on the grid of the second tube, 
V 2 , over the voltage change in the 



plate circuit of the first tube by a value 
depending on the step-up ratio of the 
transformer. With transformer coup- 
ling, less stages of amplification are 
needed to obtain the same amount of 
amplifier gain; but a transformer- 
coupled amplifier is liable to give a less 
uniform amplification at all audio fre- 
quencies than is an amplifier that uses 
either of the other two forms of tube 
coupling. Also, if the plate current 
flowing through the primary winding 
of the transformer is rather high and 
the transformer is poorly designed, the 
core will become saturated with the 
magnetic flux produced by the d-c. 
current and distorted amplification will 
be the result. To prevent that occur- 
rence, impedance-transformer coup- 
ling, which provides separate paths for 
the a-c. and d-c. components, is com- 
monly used in the amplifiers employed 
for sound recording. 

This form of tube coupling is partic- 
ularly desirable for these amplifiers 
because cores made of permalloy, or of 
similar core material of high permea- 
bility, are used in most of the trans- 
formers in them. The use of this core 
material provides an audio transformer 
having greatly improved characteris- 
tics ; but there is the advantage that 
even a relatively small amount of 
direct current flowing through the pri- 
mary of a permalloy-core trans- 
former will ruin it for use in an am- 
plifier. It is for that reason that 
impedance-transformer or resistance- 
(Continued on page 24) 



Page 20 



New Motion Picture 
Projection Optics 



By W. B. Rayton* 



The Addition of Sound Effects to the Moving 

Picture Called for Improved Light Projection 

Systems 



THE improvements to be described 
were developed to meet the con- 
ditions which resulted from the 
addition of sound to the moving 
picture. Shortly after the installation 
of the earliest sound systems, com- 
plaints began to be heard as to the de- 
crease in brightness of the projected 
picture. For two reasons this was not 
so high as these theatres had been get- 
ting from their old equipment. One 
of these reasons was the fact that it 
was found desirable to use a screen 
more transparent to sound than the old 
types of screen and this sound trans- 
parency was gained at the expense of 
the reflecting power of the screen. In 
the second place, in the sound-on- film 
processes, the picture area was re- 
stricted and required greater magnifi- 
cations to restore the projected picture 
to the size which had become estab- 
lished for a given house. This in- 
creased magnification also resulted in 
a reduction in the brightness of the 
picture. The decrease was sufficient to 
be disturbing and from all the inter- 
ested sources came a request for more 
illumination. 

It is an important condition, also, 
that the advent of sound has stimulated 
interest in the apparatus and the tech- 
nique of the projection room and sim- 
ultaneously in the quality of the pro- 
jected picture. Furthermore, the cost 
of sound equipment is so large that 
the question of a few dollars more for 
condensers and projection lenses does 
not look so formidable as it once did, 
Improved optical systems are the logi- 
cal outcome of such conditions. 

Work on both of these problems, 
projection lenses and condensers, has 
been under way in the scientific bureau 
of the Bausch and Lomb Optical Com- 



*Director of the Scientific Bureau, Bausch and 
Lomb Optical Company. 



pany for several years. Experimen- 
tally satisfactory results had been 
reached and plans were being made for 
production of these new optical sys- 
tems when the wide film activities be- 
gan. The experimental projection 
lenses developed were found to yield a 
quality of performance absolutely un- 
approachable by anything else avail- 
able. The condenser lenses on which 
we had been working were modified in 
a manner to be described presently and 
they were found to provide by far the 
best illumination obtainable for these 
huge pictures. Later, the same con- 
densers were tried for the projection 
of 35 mm. film and were found to ex- 
ceed by from 50 to 100 per cent the 
illumination obtainable with the con- 
densers in current use. 

Anistigmat Lenses 

The projection lenses are sold under 
the name Super-Cinephors. They are 
true anastigmats, the first anastigmatic 
projection lenses which have been of- 
fered the motion picture projectionist. 
Projection lenses hitherto offered have 
been either of the type developed by 
Petzval nearly a century ago for use 
as a portrait lens or of a type which 
amounts essentially to a telescope ob- 
jective with an achromatic condenser 
mounted a short distance ahead of the 
film which functions simultaneously as 
part of the illuminating system and as 
part of the projection objective. Pro- 
jection lenses of the latter class have 
no distinguishing class name but are 
sometimes referred to as lenses with 
a short back focus. Both of these 
types are characterized by more or less 
the same type of performance, viz., 
very sharp central definition and a 
very small field of view which can be 
called flat. The latter type suffers 
somewhat more than the Petzval this 



PROJECTION ENGINEERING 

limitation as to field of view. Fig. 1 
is a reproduction of curves showing 
the curvature of field and astigmatism 
of these three classes of lenses. 

Some explanation may be necessary 
to make the significance of these curves 
apparent to those who have not had the 
opportunity for much study of geo- 
metrical optics. It is an unfortunate 
provision of nature that a single lens, 
applied to the task of forming an 
image, gives an image about as far 
from the quality wanted as could well 
be and still have it recognizable as an 
image. The ideal image is the true 
projection of the object spaces onto a 
plane, such a projection as might be 
constructed by drawing a single line 
from every point in the object space 
through a pinhole and continuing 
them until they intersect the desired 
plane of projection. The image 
formed by a lens differs from this 
ideal in many respects. In the case of 
the pinhole, the image is equally sharp 
no matter at what distance from it lies 
the plane of projection, for it is as- 
sumed to be so small that only a single 
ray of light from any one object point 
can pass through it. The lens, how- 
ever, is of finite size and many rays 
from any one object point are received 
by the lens. 

For perfect performance all these 
rays coming from any one object point 
should be re-united by the lens in an- 
other point on the desired plane of pro- 
jection (the focal plane of the lens). 
It happens otherwise, however, as il- 
lustrated in Fig. 2. Here there is rep- 
resented an object point O lying in the 
margin of the field. Instead of the 
lens forming a point image of O, it 
forms as the nearest approach to it an 
elliptical spot of light as O'. If we 
explore the cone of light in the neigh- 




Fig. 1. (At top). Showing correc- 
tions for astigmatism and curvature 
of field for: A, Super Cinephor lens; 
B, Cinephor lens; C, Lens of short 
back focus. Fig. 2. (Below). Illus- 
trating astigmatism and curvature 
of field. 



FEBRUARY, 1931 



Page 21 



borhood of O', we will find that it no- 
where comes to a point focus. At the 
place marked T in the diagram the 
light seems to be concentrated in a 
short line as indicated and at another 
place such as S it again seems to be 
concentrated into another line at right 
angles to the line at T. T is the focus 
for the meridian of the lens marked T, 
and S is the focus for the correspond- 
ing meridian of the lens. 

The phenomenon of the representa- 
tion by the lens of object point O as a 
pair of perpendicular lines is called 
astigmatism. The distance from O' to 
the center of the distance between T 
and S is the curvature of field for the 
lens for this angle. The astigmatic 
difference (distance between T and S) 
and the curvature 6i field will vary 
from point to point over the field de- 
pending on the angle of the field of 
view. The focus of all points T and 
S is a pair of curved surfaces which 
constitutes the image of the object 
plane. These surfaces are indicated 
by the dotted curves connecting T and 
S in the figure with the center of the 
image. 

Correction of Curvature 

By using more than a single lens, 
compounding, diverging and converg- 
ing elements and choosing glass and 
curvatures of surfaces to the best ad- 
vantage it is possible to overcome or 
"correct" astigmatism and curvature 
of field. Different lens constructions 
lead to different degrees of correction. 

Fig. i shows the condition of cor- 
rection of astigmatism and curvature 
of field of the Super-Cinephor lens in 
comparison with two other types of 
projection lenses now in general use. 
The curves represent the positions of 
the focal points T and S with respect 
to the ideal focal plane (the straight 
vertical line) for fields of view up to 
14J/2 . Lens B, the Cinephor is chosen 
as representing the Petzval type of 
lens. Lens C was bought on the open 
market as a representative of that class 
of lenses described above as character- 
ized by a short back focus. It is 
peculiar in that the amount of astig- 
matism it exhibits is practically nil but 
such advantage as this would indicate 
is more than neutralized by the exces- 
sive curvature of field. While the T 
and S sections come to the same focus, 
that focus is farther from the image 
plane than either and considerably far- 
ther than the average of T and S in 
the Cinephor. The advantage of the 
latter over both the other lenses is 
manifest. The superior correction of 
the Cinephor with respect to astigma- 
tism and curvature of field are the 
characteristics which entitle it to the 
rating of an anastigmat. 

To add to the significance of the 
curves it is well to take into consider- 







1 


[ 






' . 






























A 


8 


c 




Fig. 3 (at top). Spherical aberration 
for: A. Super Cinephor lens; B, Cine- 
phor lens; C, Lens of short back 
focus. Fig. 4 (below). Illustrating 
spherical aberration and a method of 
plotting it in curve form. 



ation that for standard film the angu- 
lar field of view of a 5" focus lens is 
about 14 and for a 4" lens about 18 . 
For wide film the corresponding values 
are 23 and 29 . Since the curves in 
Fig. 1 are plotted for distance from 
the center of the field (half the total 
field) the above figures should be 
divided by two for reference to the 
curves. 

Sacrifice of Definition Avoided 

The reason that anastigmats have 
not hitherto found favor for projec- 
tion lies in the fact that for large rela- 
tive apertures, the correction for as- 
tigmatism and curvature of field has 
been obtained at the sacrifice of defini- 
tion in the center of the field. The 
construction used in the Super-Cine- 
phor, however, permits central defini- 
tion equal to that afforded by the pre- 
vailing types of lenses in addition to 
the excellent flatness of field. This is 
shown in Fig. 2 which contains curves 
representing the spherical aberration 
for the three types of lenses described 
above. 

To comprehend the significance of 
spherical aberration it will suffice to 
consider briefly Fig. 4 in which i^ 
shown a bundle of rays of light com- 
ing from a distant object point at tin- 
left and falling on a simple lens. 
After passing through the lens they 
fail to unite in a common image point. 
All rays, however, which strike the 
lens equidistant from its axis ; that is 
to say, in a zone of a given radius 
come to a common focus, but the focus 
for each zone differs from the focus 
for every other zone, the focal points 
for zones farther out from the center 
of the lens lying closer to the lens than 
the focus for the central zone. If we 
plot the radius of the zone on a verti- 
cal axis and the distance of the focus 
of the zone from the focus for the cen- 
ter of the lens on a horizontal axi« and 
connect the corresponding points with 
a curve we arrive at a curve such as 
is shown at the right of Fig. 4 which 



is a complete representation of the 
condition of spherical aberration in 
the lens. 

The result of spherical aberration in 
a lens is to prevent it from forming a 
sharp image of the object. The out- 
lines of the details in the field will be 
blurred and black areas will be more 
or less gray instead of black. From 
Fig. 2 it will be evident at a glance 
that there is practically no difference 
between these three kinds of lenses in 
this respect and that the superior per- 
formance of the Super-Cinephor in re- 
spect of astigmatism and flatness of 
field has not been gained at the ex- 
pense of image quality in the center of 
the field. 

The quality of the performance of 
these lenses has never been equalled 
hitherto in projection lenses. It is a 
revelation to see the quality of perform- 
ance given by a 2-inch focal length 
working at a speed of f :2, and cover- 
ing standard motion picture film. The 
focal lengths from 3^ inches up will 
cover the 23 x 46 picture of wide film 
with complete satisfaction when em- 
ployed with suitable condensers. 

Super-Cinephors are made in focal 
lengths from 2 inches to 2~y+ inches in 
the speed of f :2, and from 3 inches to 
5^2 inches in the speed of f :2.3. Focal 
lengths longer than ~, l /> inches are not 
yet available. 

The general appearance of some of 




FOR WIDE FILM 

FOR STANDARD FILM 3 [ \ 

Fig. 5. Improved condenser for both 
standard and wide film. 



the mounted lenses is shown in Fig. 5. 
This figure also shows the appearance 
of the condenser lenses described. 

Experimental work was begun by 
this company in 1925 on improvements 
in condensers. The results of those 
experiments were reported by Town- 
send and Stark in the Transactions of 
the Society of Motion Picture Engi- 
neers. This work was made the 
basis of further study beginning about 
the first of 1929 and led to a condenser 
combination illustrated in Fig. 5 in 
which the rear surface is cylindrical 
and the front surface paraboloidal. 

Others Make Use of the Invention 

This combination has been so well 
received that it has been reproduced in 
Europe. The fact that the Bausch and 
Lomb Optical Company had sold con- 



Page 22 



PROJECTION ENGINEERING 



densers of this type a year before the 
appearance of the foreign duplicates, 
that they were referred to in a paper 
presented by the writer at the S. M. 
P. E. meeting in Toronto in October, 
1929, on the "Optical Problems of 
Wide Film Motion Pictures," and that 
letters patent have been granted to him 
on the construction (U. S. P. No. 
1,783,481) would seem to dispose of 
the question of priority. 

The Condenser System 

The condenser system in question 
consists of a rear lens five and a half 
inches in diameter with a rear surface 
which is a convex cylinder and a front 
surface which is spherical, also con- 
vex. The front lens of six inches 
diameter is meniscus in shape with a 
rear concave spherical surface and a 
front surface which is parabolic. 

The axis of the cylinder of the rear 
condenser is indicated on the rear sur- 
face and should be set horizontally- 
The combination yields an oval spot of 
light on the aperture plate which in 
wide film projection permits illumina- 
tion of the whole area and in the pro- 
jection of 35 mm. film permits some- 
what more freedom for horizontal 
movements of the arc than spherical 
condensers. The peculiar combination 
of powers makes it possible to illumi- 
nate a spot, let us say, in the center of 
the field with a cone of light of suffici- 
ent angle to completely fill, in the ver- 
tical meridian, the aperture of a projec- 
tion lens of f :2.3 relative aperture and 
to nearly fill the aperture in the horizon- 
tal meridian when used with a high 
intensity arc with 13.6 mm. carbons. 

In order to obtain the maximum 
illumination with a given projection 
lens and light source it is necessary to 
design a condenser which will illumi- 
nate any point within the film aperture 
with a cone of light whose angle of 
convergence is equal to the angular 
aperture of the projection lens and at 
the same time, form an image, in the 
film plane, of the light source as large 
as the area to be projected. In order 
to secure a cone of light of the re- 
quired angle and of reasonably even 
light distribution, condensers corrected 
for spherical aberration are necessary, 
hence the use of the parabolic surface. 
The size of the illuminated area de- 
pends on the size of the light source 
and magnification of the condenser. 
By suitable adjustment, sufficiently high 
magnifications of the light source can 
be obtained with small condensers but 
not in conjunction with high angles of 
convergence. Without going through 
all of the reasoning necessary to estab- 
lish the fact, it can be stated that in 
order to meet the two conditions men- 
tioned above with condensers of the 
old four and a half or five inches in 
diameter was an impossibility. It can 



be done with symmetrical condensers 
giving a round spot of light if made 
sufficiently large in diameter but not 
with lenses of six inches diameter. 
The use of the cylindrical surface per- 
mits the conditions to be met, however, 
for the vertical meridian with only a 
slight failure to meet them in the hori- 
zontal meridian using condensers of a 
maximum diameter of six inches and 
at the same time preserving a safe dis- 
tance from arc to condenser, i. e., safe 
with respect to breakage of the latter. 

These condensers are made of a heat 
resisting glass. It is remarkably free 
from the green color of some con- 
denser glass and is next to fused 
quartz in its freedom from breakage. 
They are standard equipment with one 
prominent lamp manufacturer; a larger 
size, seven and a quarter inches in 
diameter, is standard equipment with 
another lamp maker, and a third is put- 
ting out lamps which are especially de- 
signed to accommodate the 6-inch size 
although he does not equip the lamp 
with any condensers. 

Projection lenses and condensers, to- 
gether provide for the projectionist 
optical equipment which marks a dis- 
tinct advance over the lenses available 
five years ago for the projection of 
standard film. The purchaser of this 
equipment can, however, derive added 
satisfaction from the fact that with it 
he can project equally well from 70 
mm. film when the time comes for this 
next advance in motion picture prac- 
tice. 



GENERAL ELECTRIC IN MOVIE 
PRODUCTION 

A SERIES of twelve short subjects 
produced by General Electric and 
titled "The House of Magic" have 
been offered to RKO by John Klenke, 
G. E.'s motion picture manager, to be 
sold to exhibitors under the same 
terms as regular theatrical shorts. 
According to Klenke, the subjects 
have been made so that they will 
classify with the non-advertising 
shorts of other producers. 



TALKIES FOR PENITENTIARY 

PRISON reform through the medium 
of sound motion pictures, based upon 
a comprehensive plan conceived by 
Warden Preston E. Thomas, of the 
Ohio State Penitentiary, is to be placed 
in operation as soon as the installation 
of equipment is completed. Contracts 
have been closed with RCA Photophone 
for.the installation of sound apparatus 
in the Protestant Episcopal Chapel at 
the penitentiary and it is expected the 
work will be finished within thirty days. 



The Ohio State Penitentiary, the first 
major penal institution to adopt this 
revolutionary method of moral reform, 
will be remembered -as the scene of the 
disastrous conflagration in which nearly 
300 convicts lost their lives. Warden 
Thomas believes that a great construc- 
tive work can be accomplished by the 
introduction of sound motion pictures 
into prison life and it is his present in- 
tention to present varied programs of 
instructive and educational value in ad- 
dition to specially selected entertain- 
ment features. Photophone engineers 
will instruct one or more "trusties" in 
the operation of the sound equipment. 



STUDY CONDUCTED ON USE OF 
FILMS FOR ADVERTISING 

(Concluded from page 14) 

of the firm's products or services. 
Safety and efficiency of plant opera- 
tion are being promoted and better per- 
sonnel relations secured by many firms 
through exhibition of educational films 
within the organization itself. 

The Commerce Department through 
a questionnaire addressed to these 2,000 
concerns is seeking to determine how 
extensively the films are being em- 
ployed for these various purposes and 
how efficient in point of results they 
are found to be. With regard to the 
public use of business movies in par- 
ticular, the Commerce Department 
wants to know from each firm the 
number of people viewing its films in 
the course of a year in schools, thea- 
tres, trade meetings, etc., how difficult 
it is to arrange for showings, and the 
places in which the showings are found 
to be most profitable. 

The planning and control of motion 
picture campaigns for business pur- 
poses, technical problems of production 
and distribution, and methods of mea- 
suring the efficiency of the use of films 
in the different branches of business 
are also dealt with in the Commerce 
Department's questionnaire. 

What the Department finds out is 
expected to shed much light on the use 
and value of motion pictures in busi- 
ness, and help formulate plans for the 
most effective use of films. The ex- 
perience record of past users of films 
in business will be of assistance, it is 
believed, not only in suggesting suc- 
cessful methods of procedure in secur- 
ing best results with new productions, 
but also in helping to obtain a more 
extensive and productive use of films 
which may be already in use. A com- 
bined experience record in this field 
will also offer a standard by which the 
success of motion picture activities in 
general may be gauged. — The United 
States Daily, January 7, ipji. 



FEBRUARY, 1931 



Page 23 



An Examination 
for Projectionists 



By James R. Cameron 



In the Province of Ontario, Canada, Projectionists 
are to be Re-examined 



IN Ontario it has been decreed that 
all projectionists holding operating 
cards are to be re-examined. This is 

being done, they claim, due to the 
increase in the number of fires in the 
motion picture theatres throughout the 
Province. 

R. C. Buckley, chief of theatres for 
the Provincial Government, has issued 
a booklet containing 542 questions per- 
taining to the showing of motion pic- 
tures and sound motion pictures. The 
first page of this booklet carries the fol- 
lowing statement : 

"We are submitting herewith, for 
your guidance and instruction, a list of 
questions which every projectionist de- 
siring a grade 'A' projectionist license 
should be able to answer correctly. 
Please note, however, that this list is 
not being forwarded to you as an ex- 
amination paper, though you may be 
called upon to answer any questions on 
this form or any other questions hav- 
ing a bearing on the requirements to 
be met by motion picture projectionists. 
If there are any questions that you can- 
not answer correctly we would suggest 
that you ascertain from your instruction 
and text books the correct answers, so 
that your knowledge of motion picture 
projection and the reproduction of syn- 
chronous sound with motion pictures 
will be improved." 

The following are a few of the ques- 
tions contained in the booklet : What 
would cause poor quality or noisy out- 
put? What are the primary causes of 
noise in sound on film attachments ? 
What general wiring precautions should 
be observed to minimize the possibility 



of external , electrical disturbances? 
How is current obtained for disc 
method? How is the small electric cur- 
rent from the reproducer or the photo- 
electric cell amplified? How is current 
converted into sound? When a battery 
runs down or is permitted to discharge, 
what happens? How is amplification 
accomplished? Is it necessary for am- 
plifier tubes to be matched; if so, why? 
What does a vacuum tube do when 
used as an amplifying tube? What is 
the "gain control" and what is its func- 
tion? 

What is a "flutter"? What would a 
low plate reading on the panel indicate? 
Describe the course of the sound from 
the pick-up until it reaches the horns. 
What could be done with a microphonic 
tube? What is the film attenuater? 
What is the photoelectric cell voltage 
on R.C.A. ? Why are all wires carry- 
ing sound or speech, lead covered and 
again enclosed in conduit? If there 
was a difference of three points on the 
fader between two projectors, what 
might cause the trouble ? Name thy 
three essential elements that make up a 
reproducing system and their various 
functions. Which wire connects to the 
grid of the first tube from the photo- 
electric cell ? What is the best method 
in cleaning dirty battery tops? What 
are the various elements in a vacuum 
tube? What is the function of the ex- 
citing lamp? What is "electrolyte" in 
batteries? Does a storage battery gen- 
erate power? Why does the needle on 
a disc record travel from the center of 
the disc to the outside? On the Vita- 
phone disc is the sound record on the 



bottom of the track or groove, or is it 
cut into the walls of the groove? What 
is the mechanical "filter" on sound 
equipment? Which of the lines, the 
white or dark ones, make the actual 
sound from the film? What density 
does R.C.A. use in their recording? 
How can "motor-boating" be overcome ? 
What is "specific gravity"? 

Give two or more reasons why 
brushes on a motor-generator set will 
spark. What is a prismatic condenser? 
Show how you would adjust the lamp 
and mirror when using Mazda equip- 
ment to get a correct focus. Give 
approximate distances between: a, Cen- 
tre of mirror and filament ; b, filament 
and condenser ; c, condenser and aper- 
ture; d, lens and rotating shutter. Give 
some of the advantages of Madza equip- 
ment. What is a "grid type" rheostat? 
What prevents the burning away of 
the lamp metal due to excessive heat 
from the high intensity arc ? If a rheo- 
stat coil burns out, how would you make 
an emergency repair? Why are some 
starting switches on motor-generators 
and larger equipment enclosed in oil? 
Show by diagram the wiring in a cir- 
cuit of a polarity reversing switch ? 
What is a Hi-low lamp? What is the 
average amperage used on a, old style 
arc lamp, b, high intensity, c, reflector 
arc. d. Hi-low lamp? 

Show by diagram balanced load of 
two arcs, two motors, and two rheostats 
on a three wire no- and 220-volt circuit. 
What is meant by the safe carrying ca- 
pacity of a wire? 

Define the following: Flicker, con- 
densing lens, collector lens, converging 
lens, piano lens, plano-convex lens, men- 
iscus lens, a volt, an ampere, an ohm, a 
watt, a kilowatt, a horsepower, direct 
current, alternating current, a cycle, a 
megohm, a ground, an electric arc, a 
short circuit. 

What advantage is there to gears that 
are spiral cut? Why should aperture 
tension be varied when using new and 
old film? What is the standard aper- 
ture size? Which make of projector 
has an actual faster movement? What 
is chromatic aberration? What is 
spherical aberration? What is meant 
by the optical axis ? What is absorption 
of light? 

These are some of the more import- 
ant of the 542 listed in the new book- 
let and whoever drew them up certainly 
covered the whole question of projection 
in a very thorough manner. 



FRED NIBLO, SECRETARY OF 
ACADEMY 

FRED NIBLO has been elected Sec- 
retary of the Academy of Motion 
Picture Arts and Sciences, succeeding 
Frank Woods, resigned. Mr. Woods 
has been awarded a life membership in 
the Academy. 



Page 24 



PROJECTION ENGINEERING 



OPTICS OF SPECTACLE LENSES 

THE image on the retina is upside 
down and it would seem that we 
should see everything upside 
down. 
This idea comes from the conception 
that the brain is something which looks 
at the image on the retina from behind, 
whereas the light which falls upon the 
retina simply stimulates the optic 
nerve, and this stimulation when car- 
ried to the brain produces certain 
changes which give us the sensation of 
light. It is not known what changes 
are produced in the brain by the stimu- 
lus from the optic nerve, nor how these 




From ''Everyday Physics" (Macmillan) 

How the Spectacles Work 

changes produce the sensation of light. 

There is one striking difference be- 
tween the eye and the camera, and that 
is in the method of focusing. 

The camera is focused by moving 
the lens back and forth, but the eye is 
focused by changing the shape of the 
lens. When the eye is viewing an ob- 
ject near at hand, the muscles of the 
eye contract the lens so that it is more 
convex. When it is viewing a distant 
object, the muscles extend the lens so 
that it is less convex. That is, when 
we look at an object near at hand, the 
lens of the eye is smaller and thicker; 
and when we look at a distant object 
it is larger and thinner. 

Many people can see things at a dis- 
tance, but not those close at hand. In 
such cases the eyes are far-sighted. 

The eye lens can not be made thick 
enough to focus, on the retina, light 
from objects near at hand, and the 
image would be formed behind the 
retina, as shown in B, Fig. I. To 
overcome this difficulty spectacles 
with converging lenses are used, and 
the proper lens is one which will pro- 
duce just enough convergence to en- 
able the eye to focus the image on the 
retina. 

Some people can see things near at 
band, but not those at a distance. In 
such cases the eyes are near-sighted. 

The eye lens can not be made thin 
enough to focus, on the retina, light 
from a distant object, and the image is 
formed in front of the retina, see A. 
To overcome this difficulty, spectacles 



proper lens is one which will cause the 
light to diverge to such an extent that 
the eye can focus the image on the 
retina. 

If, instead of ordinary near- or far- 
sightedness, there are other defects in 
the lenses of the eye, distorting the 
image, these can often be corrected by 
a compensating distortion of the spec- 
tacle-lens. After the eyes have been 
carefully tested by an oculist, he gives 
directions that enable the optician to 
grind a lens of exactly the proper 
shape to correct these eccentricities of 
vision. 

The foregoing is abstracted from the 
book Everyday Physics by Carlton J. 
Lynde (MacMillan Company). 

A 
PICKUPS 

In the March issue of Projection 
Engineering will appear a complete 
technical article describing and illus- 
trating pickups as used in theatre repro- 
duction, and for recording. 



RADIOVISION PROGRAMS IN THE 
MAKING 

(Concluded from page 16) 

sary, which has heretofore constituted 
a serious drawback, but today the am- 
plification problem is solved. 

The outdoor camera pickup is hardly 
a separate classification, since it is lit- 
tle more than taking the camera out- 
doors so as to pick up news features 
and personalities in the public eye. 
However, in view of the fact that the 
average telephone line of today cannot 
handle the necessary wide range of 
frequencies called for by television 
images, it is necessary to use a port- 
able transmitter as part of the equip- 
ment. Excellent results have been ob- 
tained by means of % kw. and J4 kw. 
transmitters out in the field, side by 
side with the camera. Here again, the 
usual broadcast feature of a prominent 
person or news event may be handled 
as at present, while the radiovision ac- 
companiment may be picked up along- 
side the microphones. 

It's the showman's turn next. The 
engineer has done an excellent job so 
far, in bringing radiovision up to the 
commercial point. The showman must 
take the radiovision technique, with its 
four pickup methods, and endeavor to 
build up regular programs of real en- 
tertainment value. Once the programs 
are on the air on a schedule basis, with 
something of interest to the average 
family, the production man can come 
along with a production sufficiently 
great to bring costs down to within 
reason. The merchandiser can com- 
plete the picture by selling radiovision 
equipment to most of the homes now 



equipped with sound broadcast re- 
ceivers. 

Just as Station KDKA of the West- 
inghouse organization took radio tele- 
phone experiment and made of it the 
broadcasting institution, laying the 
foundation for the vast radio industry 
that followed, so proper showmanship 
must convert the radiovision experi- 
ment into the organized radiovision 
entertainment, paving the way for a 
much needed industry. 

Will history repeat itself? That's 
the question which awaits an answer 
in the form of prompt and capable 
action. 



AMPLIFICATION IN SOUND 
MOTION PICTURE WORK 

(Continued from page 19) 

transformer coupling is nearly always 
used with these transformers. All of 
the types of tube couplings described 
here are employed in the various am- 
plifiers used for sound recording. 

A Single Recording Channel 

In Fig. 4 is shown a block sche- 
matic layout of a single recording 
channel. This type of diagram is 
given the name "block schematic" be- 
cause simple squares are employed to 
represent the various pieces of equip- 
ment, and the groups of connecting 
wires between them are shown as sin- 
gle lines. The special double-hole 
jacks that are connected in the input 
and output circuits of all of the main 
pieces of apparatus in the installation 
are not represented in this diagram be- 
cause they would only serve to compli- 
cate it and make it confusing. How- 
ever, it should be remembered that they 
are there and that they permit any part 
of the equipment to be patched in or 
out of the circuit at will. By means 
of multiple jacks connected to the ends 
of lines that terminate in the center 
bays of both channels, amplifiers in 
one channel can be patched in circuit 
in the other channel in place of the 
equivalent amplifiers that may be giv- 
ing trouble. This is done by means of 
special "patch cords," which are short 
lengths of two-wire conductor with 
plugs on each end having two pins 
that fit into the two-hole jacks in the 
jack fields of the amplifier bays. This 
arrangement provides an extremely 
flexible amplifier system that is very 
convenient to operate. 

(To be continued) 



MIKES AND BLIMPS 

The Versatile Crane Microphone and 
the subject of Camera blimps will be 
taken up in special, illustrated articles 
in the March issue of Projection 
Engineering. 



FEBRUARY, 1931 



25 




GORDON S. MITCHELL 

We present herewith a likeness of 
Gordon S. Mitchell, Sound Engineer 
with Universal Pictures Corpn., Uni- 
versal City, Cal. 

Mr. Mitchell received his technical 
training at the California Institute of 
Technology and the University of Cali- 
fornia. He is a Lieutenant in the 
975th., Coast Artillery, Fort McArthur, 
Calif. Several of the excellent technical 
stories dealing with sound engineering 
which have appeared in Projection 
Engineering during the past year were 
prepared by Mr. Mitchell. 

▲ 
GENERAL ELECTRIC PRODUCTION 

"QTEPPING Ahead," the first all- 
O color, all-talking, professionally 
directed industrial motion picture film, 
has been produced by the Motion Pic- 
ture Section of the General Electric 
Company, Schenectady, for the use of 
the National Lamp Works of the com- 
pany at Cleveland. The speed with 
which the production was effected also 
sets a record — the idea was conceived 
December 1, the scenario was started 
December 8, and the photograph}' was 
started December 1 1 in New York, 
Chicago and Schenectady. Tn one week 
from then the picture was complete. 
On January 10 the film was given its 
premiere showing at Cleveland, and on 
January 15 the production was routed 
for showing to more than 3500 lamp 
' distributors. 

The two reel's (2000 feet) of film 
include a night view of New York's 
gaily illuminated Broadway, the in- 
terior of the National Broadcasting 
Company's studios in Chicago where 
sun-lamps are employed as ceiling fix- 
tures, and numerous etudio scenes made 
in Schenectady to portray the progress 
of light, including floodlighting, 
Colorama, street lighting, and in- 
candescent lighting in general. 

For the General Electric Company 
the work was under the supervision of 
John Klenke. Alvin WyckofF, formerly 



associated with Cecil DeMille in the 
production of "Hell's Angels," cared 
for the direction and supervision of the 
picture for Multicolor, Ltd. James 
Williamson, cameraman, and Earl 
Pearsall, technician, both of Hollywood, 
assisted Mr. WyckorY. 
A 
A NEW TYPE OF FILM 

ANEW type of motion picture film, 
about three times as "fast" as that 
previously in use, was announced on 
February 5, by the Eastman Kodak 
Company to a group of leading camera- 
men and laboratory technicians. The 
new -film is expected to work marked 
changes in studio technique, by per- 
mitting greater freedom in making 
sound pictures and by cutting down the 
necessary amount of lighting, thus 
reducing heat, glare, and cost. 

The faster film is described by motion 
picture engineers as the greatest 
advance in motion picture materials 
since the introduction of panchromatic 
film eighteen years ago. The motion 
picture industry, subsequent to that 
development, went over almost entirely 
to panchromatic film, which, in mono- 
chrome, portrays colors in their proper 
tonal relation to each other instead of 
with distorted values. 

The new type of film was announced 
as possessing increased panchromatic 
qualities in addition to its greatly 
increased ''speed." Increased speed, in 
cinematographic terminology, means 
simply the ability to expose a photo- 
graphic image with lcs< light. 

Since the advent of sound in motion 
pictures three years ago, the Eastman 
Kodak Research Laboratories have 
experimented in the direction of de- 
veloping a film to meet present condi- 
tions in the sound studios, where the 
substitution of incandescent lighting 
electric arcs presented a new photo- 
chemical problem. 

The Arrival of Incandescents 
The panchromatic film heretofore in 
use was developed for exposure with arc 
lighting. When the change to incandes- 
cent illumination swept over Holly- 
wood, the film was adapted to the new 
conditions so far as that was then 
possible. The new type of film, on the 
other hand, was specially made for use 
with the "inkies," as Hollywood calls 
incandescent lights, and has a sensitivity 
to red and green hitherto undreamed of. 
Incandescent light contains a higher 
proportion of red than does the light 
from arcs. 

The increased speed and extraordi- 
nary color sensitivity of the new film 
are expected to be of particular use- 
fulness in natural color photography, 
where the great concentration of light 
hitherto necessary has been a drawback. 
Another practical advantage claimed 
for the supersensitive film by Eastman 
representatives here is an increase in 



the possible "depth of focus" in sound 
film photography. The use of incandes- 
cent lighting made desirable the wider 
opening of lens diaphragms to let addi- 
tional light into the cameras. This, in 
turn, by a law of optics, greatly 
diminished the range within which the 
actors could move and yet remain in 
focus. When sound came to the 
movies, depth of focus became of 
increasing importance because it is irri- 
tating to audiences to hear a clear voice 
coming from an out-of-focus actor. 

Greater Latitude in Focusing 

With the greatly increased speed of 
the new film, it will henceforth be pos- 
sible to "stop down" lenses, increasing 
the depth of focus and thus permitting 
greater latitude to directors in moving 
their actors about before the camera. 
The characters will no longer have to 
remain in a narrow plane at a fixed 
distance from the lens under penalty of 
blurring into the background or becom- 
ing fuzzy in the foreground. 

An alternative advantage of the new 
type of film is the possibility of reduc- 
ing the amount of light to one-half or 
one-third the present quantity necessary 
for sound picture cinematography. In 
practice, it is expected that the studio- 
will compromise between the maximum 
reduction of lighting and the maximum 
gain in depth of focus, taking partial 
advantage of both benefits offered by 
the new type of material. 




Headquarters of the International 
Projector Corpn., 90 Gold Street, 
New York, on the right, and National 
Theatre Supply Co., 92 Gold Street, 
on the left. 



Page 26 



PROJECTION ENGINEERING 



New Developments 

and 

News of the Industry 



THE RIBBON MICROPHONE 

By Lowell V. Calvert* 

A new type of microphone, in process of 
development for the past_ several months 
and successfully operated in studios which 
employ the RCA Photophone system of re- 
cording, has been perfected. The new de- 
vice, which marks a revolutionary step in 
the transference of sound to film and which 
is known as the "Ribbon Microphone," was 
developed by Dr. Harry F. Olson, research 
engineer, who specializes in loudspeaker 
and microphone operations. 

Many difficulties heretofore experienced 
in the recording of sound motion pictures 
have been solved by the use of the "Ribbon 
Microphone." Among other revolutionary 
virtues, it has what are known as "direc- 
tional sound pickup" characteristics, by vir- 
tue of which sounds coming only from cer- 
tain directions are picked up, and sounds 
coming from other directions are completely 
ignored. This enables the microphone to be 
used in reverberant sets, in such a way as to 
pick up the voices of the actors and at the 
same time considerably reduce the amount of 
reverberation picked up. Another way in 
which it can be used is to pick up an actor's 
voice and at the same time ignore the noise 
of the camera. Up to the present, bulky and 
inconvenient hoods or "blimps" have been 
used over cameras, in order to reduce the 
noise picked up by the microphones. These 
clumsy encumbrances are now obsolete. 

The principle on which the "ribbon micro- 
phone" operates is that of induction of 
electric current in an extremely thin and 
light corrugated aluminum ribbon, placed 




between the poles of an electric magnet. 
This aluminum ribbon is only one ten thou- 
sandth of an inch thick, 3/16 inch wide and 
2 inches long. The minute changes in air 
pressure occasioned by sound waves cause 
this ribbon to flutter or vibrate between the 
magnet poles, and electric currents are 
thereby set up in it. These currents are led 
to a transformer, which is connected to a 
vacuum tube amplifier of the conventional 
type. 

The "ribbon microphone" proper is con- 
tained in a perforated box. The output of 
the microphone is fed to an amplifier. A 
plug and cable located at the top of the 
amplifier runs to a standard recording am- 
plifier. The accompanying illustration shows 
the microphone tilted at an angle to pick 
up action located below the microphone. Its 
efficiency of pickup is the greatest in the 
direction normal to the face of the micro- 
phone. Its reception in the plane of the 
face of the microphone is zero. Thus if 
objectionable noises such as a camera are 
placed in this plane this noise will not be 
picked up by the microphone. 

^Manager of Recording Operations, RCA Photo- 
phone. 



COMMERCIAL FILMS 

The use of talking motion pictures as a 
medium of public education in the invest- 
ment _ field was demonstrated for the first 
time in December before a group of invest- 
ment bankers at a private film showing held 
at the Tavern Club in Chicago. 

The film is the work of the Burton 
Holmes Studios, and was developed through 
the cooperation of the Administrative and 
Research Corporation of New York, 
sponsors of Corporate Trust Shares, a fixed 
investment trust. The picture, which is 
titled "An Investment in American Prosper- 
ity," depicts in story form the size, strength 
and broad scope of activity of twenty-eight 
of America's leading corporations — such 
companies as United States Steel, New 
York Central, Standard Oils, General Elec- 
tric, American Telephone & Telegraph, 
International Harvester, duPont and others. 

The picture, believed to be the first of 
its kind ever produced, will be placed at 
the disposal of a group of more than 800 
investment houses and banking institutions 
throughout the country, who will join in the 
educational program by arranging com- 
plimentary local showings of the film. 



HEAT RESISTING CONDENSERS 

The Fish-Schurman Corporation, 45 West 
45th Street, N. Y. C, after extensive 
laboratory tests, produced a condenser of 
heat resisting Ignal glass combining superior 
optical qualities. Ignal glass is a specially 
tempered glass and can withstand extreme 
changes of temperature with no danger of 
cracking and will outlast condensers made 
of ordinary optical or other glass. The 
following table points to the technical phases 
of Ignal glass, which make it adaptable for 
the purpose to which it has been adopted. 
Cooefficient of Expansion : 

25- 75 degrees C — 399 x 10 — 8 

175-225 degrees C — 430 x 10 — 8 

Softening Point : 

630° at 1 mm. thickness 

640 ° at 2 mm. thickness 

675° at 5 mm. thickness 
N. D. 1.496. 
Hydroscopic glass I. 



RADIOVISION EQUIPMENT PRICES 
REDUCED 

Radio television is going to make a strong 
bid for public support during 1931, accord- 
ing to the statement of D. E. Replogle, 
assistant to the president of the Jenkins 
Television Corporation. 

"Coincident with the unusual activity of 
the press with regard to television develop- 
ments and possibilities, together with greatly 
increased production facilities at our new 
plant in Passaic, N. J., we find it possible 
to reduce the list prices on our home tele- 
vision equipment," states Mr. Replogle. 
"Dealers can now afford to stock television 
equipment and to demonstrate radio tele- 
vision possibilities to their clientele, there- 
by expediting the public acceptance of this 
form of home entertainment. 

"The Jenkins 1931 line will definitely 
appeal to two classes of buyers : first, kits 
will readily interest home set builders and 
tinkers who were the mainstay of the radio 



industry in its early years ; secondly, com- 
pletely manufactured units are priced right 
to appeal to the middle class man who 
desires television in an immediately usable 
and living room form. 

"Meanwhile, television broadcasting sta- 
tions are consistently reaching out with 
good picture detail, and most of the tele- 
vision broadcasters are contemplating in- 
creases in power, ranging up to five times 
their present output. Therefore, buyers of 
home television equipment are assured the 
proper signals and entertainment. 

"We anticipate an immediate reaction on 
our_ price reductions. It is our belief that 
radio television is here. The engineering 
work has been done to the point where the 
commercial stage is at hand. The job 
from now on is one of merchandising as 
well as engineering," concludes Mr. Replogle. 



MICROPHONE STANDS 

Jerome A. Schwartz, 246 5th Avenue, 
New York, has entered the field with a line 
of microphone stands, special boxes and 
incidental steel work including relay racks. 
Steel work to specifications is being fea- 
tured. 

Some of the talking points in favor of the 
microphone stands are; concealed wiring 
on all models, table and desk models have 
felt-lined bases, while the floor type has 
been designed to minimize the toppling-over 
hazard. All models are beautifully plated 
with a rich brown English bronze finish 
which matches with walnut. 



SPRAGUE TO ENTER FIELD OF 
HOME TALKING MOVIES 

R. C. Sprague, president of the Sprague 
Specialties Company, Quincy and North 
Adams, Mass., announces : 

"After a careful survey into the manu- 
facture and merchandising possibilities of a 
home talking moving picture machine, we 
have contracted for the exclusive manufac- 
turing and sales rights for a unit that can 
be produced at an attractively low list price. 

"It is our purpose to manufacture two 
models for sale to distributors and dealers 
throughout the United States and Canada. 
Model A will consist of a talking picture 
unit to plug into a radio set using the 
amplifier and speaker of the radio. Model 
B — a talking picture unit incorporating an 
amplifier and speaker to operate inde- 
pendently of a radio set. This unit, will 
be attractively priced, simple in construc- 
tion, and easy to operate. 

"Merchandising authorities consulted to 
date are enthusiastic, and we see no reason 
why the demand for this unit will not 
closely parallel that of the early days of 
radio receivers. 

"We also intend to make available for 
radio set manufacturers a compact unit 
consisting of the turntable and projector 
mechanism, so that manufacturers can 
produce for -their trade a complete talking 
picture machine, together with a complete 
radio set at a reasonable price. 

"Agreements have been made with some 
of the leading film producing companies 
whereby one, two and six reel feature talk- 
ing pictures released by them will be avail- 
able to all dealers of Sprague machines." 



FEBRUARY, 1931 



Page 27 



DEPENDABLE PROJECTION—CONTINUOUS SHOWS- 



Standard 



It works... 



Fits Motlograph 
Model F, Simplex and 
Super-Simplex, Sure- 
Fit, with or without 
Rear Shutter Mounts. 




Rear Shutter Mounts 
require Model D 
type. Your Model A 
Changeover replaced 
with Model D type. 
Liberal allowance for 
Model A. 



Our sales argument? — A 
revolutionary theory in 
changeover successfully 
applied — that's all! But 
applied so well that al- 
ready 3000 Dowser Auto- 
matic Shutter Controls 
have been installed 
throughout the country. 

The theory? — The small- 
est shutter operating 
through the smallest 
space at a minimum 
current consumption 

yields maximum effi- 
ciency. And that logi- 
cal place for the change- 
over is the smallest cross 
sectional area of the 
light beam. 

Send for literature. 



AUTOMATIC SHUTTER CONTROL 

with 3-wire circuit foot switch 

iDOWSFRs 



691 LINCOLN PL. MANUFACTURING CORP. BROOKLYN N.Y. 



SUPER-LITE 
LENSES 



Wisely Chosen By 
America's Best Theatres 

New Bifocal Super-Lite Lens 

An adjustable focus lens with a 
wide range of foci for both silent 
and sound Sim. 

Series III. Super-Lite Lens 

Standard full Half-Size lens fur- 
nished in short focus as low as 4" 
K. F. and up to 10" E. F. 

Series IV. Super-Lite Lens 

Full 3" diameter lens to meet the 
demand for more light for longer 
throws. 6" E. F. to 10" E. F. 




Quality Guaranteed 



INC., 



PROJECTION OPTICS CO. 

330 LYELL AVE. 
ROCHESTER, N. Y. U. S. A. 




DIRECT READING 



^1 . W • • • 



TYPE 586 Power-Level Indicator 

An open clearly marked decibel scale makes 
the General Radio TYPE 586 Power-Level 
Indicator a truly direct-reading instrument. 
The time saved and the freedom from costly 
mistakes such a scale insures are advantages 
readily appreciated by the monitoring oper- 
ator in the broadcast and recording studio. 

If you are not familiar with this instrument, 
a request on your business letterhead will 
bring you a catalog description. Please ask 
for Bulletin 932-P. 

GENERAL RADIO COMPANY 



Offices 

CAMBRIDGE A, 



Laboratories Factory 

MASSACHUSETTS 



BLUE SEAL HEAT RESISTING 
IMPROVED FILM TRAPS 

FOR SIMPLEX PROJECTORS 

MADE OF AN IRON ALLOY. Guaranteed not to Warp under the intense 

heat of the Arc Spot. A necessity for the Perfect Projection 

of "Sound" Pictures 




B-16 Film Traps with Sliding Double Round Corner Apertures, one 
Aperture lor Disc and Silent Film and one cut Proportional for 

Movietone Film to be used with our Adaptors $30.00 

B-17 Sliding Double Aperture Plate 6.00 

B-24 Film Trap with individual mats for silent, movietone and 

magnascope effect. Traps complete with all mats 30.00 

B-20 Master Plate to hold mats stationary 1 . 50 

B-21 Standard Aperture with Square Corners | . 50 

B-22 Proportional Movietone Aperture with Square Comers I 50 

B-23 Blank Mat (CAN BE CUT ANY SIZE APEBTUBE) 1.50 

Manufactured by 

BLUE SEAL PRODUCTS CO., Inc., BROOKLYN, N. Y. 

260 WYCKOFF ST. 

Manufacturers of Motion Picture Accessories Since 1913 



Page 28 



PROJECTION ENGINEERING 



BABY SPOTLIGHT 

The Best Devices Company, Cleveland, 
Ohio, has in stock a new spot light. 

"Best" Baby Spotlights are extensively 
used for commercial lighting effects in dis- 
play windows, in banks, office buildings and 
factories ; used in theatre work for foot- 
lights, border lights and lobby display board" 
illumination ; and used in any other places 
where individual lighting is required. Photo- 
graphers have found "Best" Baby Spotlights 
unusually effective for background and high- 
lighting illumination. 



AN ADVERTISING PROJECTOR 

As an inevitable result of the progressive 
change that revolutionized the motion pic- 
ture industry when audibility supplanted the 
printed title in screen entertainment, a novel 
automatic advertising projector, designed to 
accommodate standard-sized sound motion 
picture film, has been perfected and will 
soon be introduced to the public. The new 
device is the product of RCA Photophone, 
Inc., in collaboration with the Auto Cinema 
Corporation, which has had a silent motion 
picture advertising projector on the market 
for several months. The machine itself, a 
compact piece of engineering workmanship, 
operates within a neatly modeled metal 
housing occupying a space less than two 
feet square. The projector is motor-driven 
with power supplied from an ordinary lamp 
socket. Projector, amplifier, motor and six- 
inch speakers are collocated within an at- 
tractively designed cabinet, similar in ap- 
pearance to a radio console, which stands 
about five feet six inches high. The picture 
is thrown upon a transparent screen, eigh- 
teen by twenty-two inches in dimension 
near the top of the cabinet and in the line 
of vision of the average-sized person when 
standing. The entire equipment, including 
cabinet, weighs less than one hundred 
pounds. When placed in operation, the film 
is endless self-rewinding, permitting repeti- 
tion of the subject indefinitely. The sound 
amplification can be controlled to any 
desired volume. 



WEBSTER ELECTRIC COMPANY 

To supply a direct sales and service 
contact in a rapidly developing market for 
its products, the Webster Electric Company 
has opened a New York office at 15 Laight 
Street. This office will be in charge of 
Arthur Rocke, manager, and T. H. John- 
ston, sales engineer. 

The Webster Electric Company, with main 
offices and factory at Racine, Wis., has been 
developing and producing precision elec- 
trical devices for over twenty years. 
Webster electric pickups and Webster 
amplifying equipment, are said to have 
natural, life-like sound-reproducing qualities. 



SET OWNERS ARE SHOWN 
CAUSES OF INTERFERENCE 

In the interests of improved radio recep- 
tion through a clearer understanding,- by the 
broadcast listener, of the causes, manner of 
distribution and methods of suppressing 
radio interference, a motion picture has 
been prepared by the Radio Interference 
Committee of Southern California and is 
being made available to radio clubs, Cham- 
bers of Commerce, trade associations and 
service clubs by the Tobe Deutschmann 
Corporation, Filterette Division, of Canton, 
Massachusetts. 

The first scene of the film is of a modern 
receiver being installed in a home. The 
installers provide a short inside antenna, 
instruct "Mrs. Prospect" in the operation 
of the receiver and leave her enjoying a 
good program. 

The action of the second scene takes place 
in the evening, showing the arrival of the 
salesman to close the sale, and indicating 
his discomfiture when radio interference 
causes the listeners to fear that an ex- 
plosion has occurred within the receiver. 
Just as all salesmen have done since the 



advent of the a-c. operated receiver, this 
salesman hurriedly tries to adjust the sta- 
tion selector and volume control to obtain 
clear reception, but with no success. He 
then tries to explain the interference situ- 
ation, but is obliged to leave most of this 
for the interference investigator, who ap- 
pears in the next scene. 

Because "Mrs. Prospect" is convinced that 
the receiver is responsible for the unpleasant 
sounds introduced in her home, the inves- 
tigator shows, by removing the antenna 
connection from the receiver, that the dis- 
turbance originates outside the receiver. He 
then explains the many causes of radio 
interference. The receiver fades out and 
the electric refrigerator appears. An ani- 
mated wiring diagram shows the interference 
at the starting or stopping of the compressor 
motor, and the investigator explains just 
when interference may be expected from an 
electric refrigerator. 

Next, in rapid succession, are shown a 
heating pad, bottle warmer, sewing machine, 
vacuum cleaner, adding machine, dictating 
machine, fan, drink mixer, fruit juice ex- 
tractor, vibrator charger, bulb charger, motor 
generator set, cash register, violet ray and 
diathermy. The correct manner of filter- 
izing home and office appliances is shown 
both in picture and in animated wiring dia- 
gram. The direct radiation of high fre- 
quency energy from a diathermy machine 
is shown, in animated diagram, and the 
type of shielding required for the suppres- 
sion of this interference is explained. 

The inductive transfer of interference 
from one circuit to another is shown, and 
the importance of erecting the antenna out 
of the field of interference is stressed. With 
further animated diagram, the manner in 
which interference enters the receiver, 
through antenna, power line, a ground wire 
is depicted. The procedure to be followed 
by the set owner to make his receiver as 
little as possible subject to interference is 
explained in detail. 

After so complete a discussion of the 
interference question, and after the sub- 
stitution of a properly erected outside 
antenna for the makeshift indoor antenna 
first installed, "Mrs. Prospect" is better 
satisfied with her receiver, and in the clos- 
ing scene the salesman receives his check 
from another satisfied customer. 

To provide moments of relaxation for the 
layman who may not be able rapidly to 
absorb the semi-technical subject matter of 
the film, a number of shots of a battle be- 
tween a mongoose and a cobra are intro- 
duced. As these scenes are being shown 
the interference investigator shows the simi- 
larity of interference to the deadly cobra, 
and of the mongoose, which kills the cobra, 
to the Filterette which kills radio inter- 
ference. 

The picture is printed on standard' 16 mm. 
film for use in home projectors. 



COIL WINDERS 

Edward Spiegler, General Radio Winding 
Company, 214 Fulton Street, New York, 
announces his entry into the field of produc- 
ing high grade coils. Mr. Spiegler is in 
the market for additional coil winding 
machines. 



AMPLION MOVES 

On February 1 the Amplion Company, 
Inc., moved to 38 West 21st Street, New 
York. 



SCHOONMAKER MOVES 

The Schoonmaker Equipment Corpn., 
manufacturers of Raytone sound screens 
has moved to larger quarters, at 276 Ninth 
Avenue, New York. 



AMERICAN SALES COMPANY 
MOVES 

The American Sales Company, formerly 
at 21 Warren Street, New York, has moved 
to 44 West 1 8th Street. 



CONDENSER TRANSMITTERS 

In order to meet requirements of certain 
new mixing equipment in which a 50 ohm 
input is used, the Jenkins and Adair Com- 
pany, Chicago, have brought out the Type 
D-6 and D-12 condenser transmitters, and 
are prepared to change Type C instruments 
to 50 ohm output. 

No change is made in the transmitter 
unit or the amplifier housing. A new 
amplifier chassis is substituted, which is the 
same in general construction as the type C 
except that the output transformer has four 
secondary terminals, numbered 1, 2, 3 and 
4. These represent two windings, which in 
series give 200 ohms, and in parallel, 50 
ohms output impedance. The 90 volt lead 
is not used, and a series resistance is 
inserted in the plate circuit of the tube so 
that all high voltage service comes from the 
180 volt connection. 



PORTABLE SOUND ON DISC 
TURNTABLE 

All parts of the Mellaphone portable are 
cast aluminum, insuring lightness and 
portability with exception of the turntable 
disc, which is cast steel plate insuring 
smooth quality of reproduction of voice and 
music. 

Mellaphone portable uses special gears. 
Together with these gears are embodied an 
ingenious spring suspended filter which also 
tends to guarantee excellent tonal quality. 
Audak pickups are furnished and may be 
had in either high or low impedance and 
tuned models. An especially designed fader 
is included. The Mellaphone portable motor 
drive is easily attached. No drilling or 
altering of the projector is necessary. It 
is not necessary to send the projector to the 
factory. 

Mellaphone portable may be attached to 
either DeVry, Acme, or Holmes or any 
projector on the market. The complete 
turntable is furnished with a compact carry- 
ing case. Portable amplifier and speakers 
are also supplied. 

M 

ROTH ELECTRIC SUPPLY 

Sound projection of the highest quality is 
possible through the use of Roth multiple 
arc type Actodectors. There is no electrical 
interference, no background noise or vibra- 
tion. Roth Actodectors are furnished in 2 
and 4 bearing types. The 2-bearing Acto- 
dector delivers 20/40 to 100/200 amperes. 

Many houses are now installing the new 
Roth emergency lighting plants, assuring 
positive current supply to the projectors 
and exit lights in event of a break in the 
main current supply. 



PETER CLARK MAGNASCOPE 
FRAME 

Nearly 200 installations have been made, 
60 in Paramount-Publix, and in many deluxe 
houses owned by Warner Bros., Fox Corpo- 
ration, Loew's and R. K. O. 

The Peter Clark Co., was the first to 
manufacture a screen enlarging device, and 
during the past six years many progressive 
improvements have been added. 

Rigidly constructed of steel trusses, 
provision having been made for .lacing the 
screen to the inside ot the frarfie. The 
masking curtains are of black, flame-proofed 
velour. These masking curtains are attached 
to moveable trusses insuring true vertical 
and horizontal edges of the picture on the 
screen. 

The maskings move simultaneously for 
opening and closing the curtain ; in and 
downward to close-out and up to open ; 
being controlled by an electric button. These 
control buttons are located on the stage and 
in the projection booth. 

The Masking Machine has adjustable, 
automatic stops, assuring the correct size of 
the picture and limiting the size of both 
large and small pictures. The motor and 
mechanism are mounted on the frame. 
Provision is made for hanging speakers on 
the frame directly behind the screen. 

The whole frame is fast working and is 
slung on Peter Clark heavy duty counter 
weight sets. 



FEBRUARY, 193 



Page 29 



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 $r.oo a year. (In for- 
eign 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 




For Sound Equipment, 
Radio, Television, 
Laboratory 

and 

Industrial 

Uses 



SUPER-DAVOHM 

Wire Wound Precision Resistors 



Engineers and 
manufactur- 
ers are invited to 
bring their resistor 
problems to Daven. 
We manufacture a com- 
plete line of resistors 
ranging from 0.1 ohms to 
30 megohms or more. Volt- 
age dividers and heavy duty 
resistors a specialty. 



mvm 



Type BWE 




(^9 



Type BLT 



THE DAVEN COMPANY 

RESISTOR SPECIALISTS 

General Office and Factory 
158—160 Summit Street. Newark, N. J. 



For Powers. Simplex and 
all other projectors 
equipped for 
sound. 




Used by the 
S. Army Motion 
Picture Service. 



The Clayton Even Tension Take-up 

assures absolute freedom from flutter. It takes up 
any amount of film evsnly. It will take up with 
any size reel hubs. It prevents excessive wear on 
the lower take-up sprocket and shaft. It stops the 
opening of film splices and prevents excessive wear 
on the film. 

Write for price and 
further information. 

Joseph Clayton 

9430 Forty-Sixth Ave. 
Elmhurst, L. I., N. Y. 



Page 30 



PROJECTION ENGINEERING 




REDUCE YOUR 
BACKGROUND NOISE 

by using 

Visitron Type "A 

PHOTOELECTRIC CELLS 

— the cells with the high current output 
that permits reduction of amplification 
and consequent reduction of background 
noise. 

Cells for every type of equipment. 

LABORATORIES I 



« 



Write for 
Bulletin 119 1802 GRACE ST. CHICAGO, U. S. 

♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦< 



♦ 
♦ 
♦ 
♦ 
♦ 
♦ 
♦ 
♦ 
♦ 
♦ 
♦ 
♦ 
♦ 

♦ 
♦ 

♦ 



♦ 

id 

A. ♦ 



for SO UND on WIDE or 
STANDARD FILM 



F> GRISWOLD 
ILM SPLICER 

Dependable, durable splicers 
built to your specifications 
for any size film. Our 35mm 
splicers are in daily use in 
thousands of theatres and 
exchanges throughout the 
world. 

Send for Literature 

GRISWOLD 

MACHINE WORKS 
PORT JEFFERSON, N. Y. 












,-..—„, JU1 .f^rrr^^msa 




mkmi^^m^mM^mmtS 


BEST CARBON SAVER 

for Low Intensity Arcs 

Permits projectionist to get at least one more 

reel from each set of stubs. Made in 7, 8, 9, 

10, 12 and 13 mm. sizes. 

$2.50 each at your dealer. 

BEST DEVICES CO. 

2108 PAYNE AVE. CLEVELAND, OHIO 



For Perfect Projection 

use 

S. O. G. IGNAL Condensers 

Highly polished, will not discolor. 
Throw an even, white light on the screen. 

Full Particulars 

FISH-SCHURMAN CORP. 



45 West 45th St. 
New York City 



6364 Santa Monica Blvd. 
Los Angeles, Calif. 




BASS BARGAINGRAM 

Issue 202 Ready 
FREE! The Classic of Bargain Lists. World's 
largest stock of Motion Picture Cameras and ac- 
cessories. Professional and Amateur. Save real 
money. Send for your copy. Free! 

BASS CAMERA CO. 

179 W. Madison St. Chicago, III. 



S1LMAN Synchronous Disc POINTS 

The only perfect Point for Sound reproduction 

Eliminates surface scratch. Clears voice articulation. No 
blurry, raspy tone. Let us prove it to you. 

Send for FREE Samples. 

SILMAN DISTRIBUTING COMPANY 

Sound Equipment and Apparatus 
620 Grant Street ... Pittsburgh, Pa. 




GEARS 

In Stock — Immediate Delivery 

Gears, speed reducers, sprockets, thrust bearings, 
flexible couplings, pulleys, etc A complete line Is 
carried in our Chicago stock. Can also quote on 
special gears of any kind. Send us your blue prints 
and inquiries. 

Write for Catalog No. 60 

CHICAGO GEAR WORKS 

769-773 W. Jackson Blvd., CHICAGO, ILL. 



Tin lieu) Ellis 2<Buttoa HAND HIKE, 

ELLIS Model 12N Hand Microphone employs the same 

patented buttons used in our most expensive broadcast models. 

Diaphragm is a special corrugated, gold plated metal. 

Write for specifications. List price without cord, $25.00. 

Export "Simons," 25 Warren St., New York. 

ELLI§ ELECTRICAL LACCRATCCY 

337 WEST MADISOM ST S °'" C ""''" CUcqo, lll.no.s 



M 



«J 



INDEX TO ADVERTISERS 



Ad. Auriema, Inc. 31 

American Sales Co 31 

Amplion Corp. of America . . Second Cover 



B 



Bass Camera Co. 

Bauseh & Lomb Optical Co. . . 

Best Devices Co 

Blue Seal Products Co., Inc. . . 
Blue Seal Sound Devices, Inc. 



30 



30 

27 



Cameron Publishing Co 32 

Chicago Gear Works 30 

Clayton, Joseph 29 

D 

Daven Company, The 29 

Dowser Mfg. Corp 27 



E 

Ellis Electrical Laboratory 30 

P 

Fish-Sehurman Corp 30 

Fogelberg Engineering Co 5 

Forest Electric Corp 3 

G 

G-M Laboratories, Inc 30 

General Radio Co 27 

Griswold Machine Works 30 



Hoffmann-Soons 



II 



N 



National Carbon Co., Inc. 



Pitman & Sons, Isaac 31 

Projection Optics Co., Inc 27 



R 



Racon Electrical Co., Inc. .Fourth Cover 



Samson Electric Co Third Cover 

Silman Distributing Co 30 

SOS Corporation 31 



Typhoon Pan Co., Inc 6 

U 

Universal Microphone Co 31 

Voice-of-the-Air Co 31 



W 



Weber Machine Corp. 
Weston Elec. Inst. Corp. 



FEBRUARY, 1931 



Page 31 




THEATRE OWNERS! LOOK INTO THIS 

New Electrodynamic 
Speaker Unit. 

Improve your sound 
greatly, and improve 
your business. 
Cost very reasonable. 
Write for our free- 

Our tpeaker hat a light metal dia- . • 1 ■ .• 

phragm which la far superior to trial proposition, 
other types. 

VOICE-OF-THE-AIR CO. 

502 S. ST. CLAIR ST., TOLEDO, O. 




OK£> 



See Page 29 



<r+o 



MICROPHONES A " Kinds ,rom 

«£Vk ""^"yrnuiiLO S750 t0 $3500o 

'*Ml For Connection to Radio Set $750 

For Home Recording $10 00 

For Public Address, etc.. list $25 

Standard Broadcast Model, list ,| $75 

Condenser Models for Film and Record Work 
S# BT_ f list $300.00, $350.00 

Also Desk and Floor Stands. Covers, Cords, etc. 

EXPEKT MICUOPHONE REPAIRS 

UNIVERSAL MICROPHONE CO., LTD. 

Inglewood, Calif. 

Export Rep. 

Dealers in All Principal Cities Ad. Auriema.Inc.,118 

New York— Howard F. Smith— 142 Liberty St. Broad St. N. T. C. 




Our new address is 

44 West 18th St., New York 

where we are equipped to give you even better service than 
before. In over 15,000 square ft. our shipping facilities have 
been tripled. We have made a move — a move to serve you 
better. 




WRITE! 
A card 
will put you 
on our list! 



r\c£ 




^V^ 



J*** ^o. bb ;^e^ s ' 









a V* 






SlS^ 




Mr 



(*$$£&** 



AMERICAN SALES CO. 



44 West 18th St. 



(Dept. P) 



New York City 



w 



E offer 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. 



LATEST THEATRE and SOUND EQUIPMENT— BRAND 
NEW— FACTORY DIRECT 

Sound-on-Film Heads, standard makes. $198.50: PhotoceUs, $14.95; G. E. 
Exciter lamps. 98c; Optical Systems, $29.50: Head Amplifiers. $29.60; W. E. 
and It. ('. A. Approved Sound Screens. 39c so., ft.: Acoustical Felt. 27V4c 
su. yd.; Samson Pam 19 Amplifiers. $69.15: Silver-Marshall G92 Amplifiers. 
$89.75; Itacon Giant 10' Exponential Horns, $87.50; Genuine Audak Pick- 
ui>s, SS.97; Jensen Auditorium Speakers. $14.85; Aperture Masks. $2.90; 
Automatic Changeovers, $39.85; Battery Eliminators for Sound-on-Film. 
$39.95; Many Other New Items. Write S. O. S. Corp.. Dept. P. E„ 1600 
Broadway. New York City. 



V 



HOTOELECTRIC CELLS 

By Dr. Norman K. Campbell and Dorothy Ritchie 

Research Staff, General Electric Co., Wembley, England. 
A complete, practical treatise. Illustrated $4.50 

TELEVISION ^T^rd 

By Sydney A. Moseley and H. J. Barton Chappie 

History, latest theories and developments. Illus- 
trated $2.50 

ISAAC PITMAN & SONS, 2 West 45th Street, New York 



Page 32 



PROJECTION ENGINEERING 



Section 



ES RCAMER0 



W? 



CAMERON'S BOOKS GOOD ENOUGH FOR UNCLE SAM 



The DEPARTMENT OF PUBLIC IN- 
STRUCTION, Washington, D. C, in a 
letter dated December 20th, 1930, says — 



(Note. — All Unsolicited) 



"The U. S. Army, Navy, Marines, the Bureau of 
Standards, the United States Veterans Bureau, 
and practically every other Government Depart- 
ment using motion pictures like ourselves, rely on 
the CAMERON TECHNICAL BOOKS for our 
knowledge of the motion picture industry." 



The DEPARTMENT OF COMMERCE. Motion Picture Section. U. S. Government. Washington, D. C. 
UNITED STATES "These books should be in the possession of every projectionist, 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." 

CANADIAN GOVERNMENT MOTION PICTURE BUREAU. 



CANADA 



THE "CINEMA," London. 

ENGLAND 



"Your books have proven a very valuable addition to our Bureau technical library." 
"Motion Picture Projection is a most excellent work, we have found it a great help in 
our work here." 

"Cameron's book is a remarkably comprehensive and authoritative text book, surveys 
the whole field of modern equipment and modern day practice — is as lucid as it is prac- 
tical it would be a gilt edged investment to theatre owner, manager or projectionist at 

ten times its cost." 



AFRICAN THEATERS LIMITED 

SOUTH AFRICA 



Krugersdorp, South Africa. George E. Smith, Chief Sound Electrician. Vaudette. 
— "personally have your four latest books, and I'd sooner loose a week's meals than 
part with any one of them, if they could not be replaced. Your books have been wbrth 
a million dollars to the sound men in South Africa." 

ELECTRICAL TIMES. Australia's Pioneer All-Electrical Monthly, Melbourne. 
AUSTRALIA "CAMERON'S new book MOTION PICTURES WITH SOUND has just reached this coun- 

try, and after reading it through, we can predict a large sale in Australia and New 

Zealand. The new book is on the same high standard as Cameron's earlier works 

a new treat for Cameron's Australian readers." 

RANJIT FILM COMPANY LIMITED. Motion Picture Producers, DADAR, BOMBAY. 



INDIA 

LIGHTBILD-BUHNE 
GERMANY 



your fine publications have always been a source of inspiration to our technicians and 
hope you may constantly add more to motion picture literature." 



Berlin 



"a series of four books all written by James R. Cameron of New York U. S. A. will be 
found of great value to those interested in motion pictures." "Cameron's method of pre- 
senting technical data is most interesting and instructive." "We recommend these books 
very highly." 

La CINEMATOGRAHPHIE FRANCAISE. Paris. 

FRANCE "Motion Pictures With Sound is the title of the first book to be published dealing with 

sound pictures, a book of 400 pages containing a complete history of the 'talkies' and 
instructions for the making and projecting of motion pictures accompanied with sound. 
The author is James R. Cameron of Manhattan Beach, New York U. S. A., whose books 
are favorably known in this country." 
FILMOVY KURYR. Czechoslovakia leading Motion Picture Paper. Wein. 

CZECHOSLOVAKIA "another of Cameron's books on motion pictures is available 

under the title of Cameron's Encyclopedia on Sound Pictures." 
" the book is practically a history of the motion picture indus- 
try and a complete text book on studio and theatre work. Get 
a copy and read it." 
MESHDUNARODNAYA KNIGA. Moscow. 

RUSSIA "Your books have been of great assistance to us in our work. 

Your new publications have been ordered through Amkino 
Corp. of New York." 



PICTURE 



INTERNATIONAL EDUCATIONAL CINEMATOGRAPH INSTITUTE OF LEAGUE OF NATIONS. 
Rome. 



ITALY 



" we are most grateful for your interesting and instructive 
books, all of which have been listed in our review." 

J. FEDERICO MEJIA. A.R.R.L. & A.I.E.E. Western Electric Sound Engineer, San Salvador. Republica 
de El Salvador. 

CENTRAL AMERICA — " am very much satisfied with your books, the information 

therein is invaluable for all those, who, like myself, are con- 
nected with sound pictures." 

Cameron Books Again This Year Are The Only Books on The Subject of 
Motion Pictures Selected by the American Library Association 

PUBLISHERS OF RELIABLE TECHNICAL BOOKS SINCE 1916 

CAMERON PUBLISHING COMPANY INC., MANHATTAN BEACH, NEW YORK 



tCE7t 



*930 





Schools, churches, clubs, hotels need the portable PAM Address 
system. With it, a speaker addresses 500 people as easily as 
half a dozen. Speech and music, both vocal and instrumental, 
are amplified with excellent quality. 

The units in this system are completely matched and designed 
to operate together. Naturally the results obtained are superior 
to a combination of units procured from different sources which 
were not designed to operate together. 

The two units that are required (MIK 100 and PAM 100) to- 
gether weigh less than 75 pounds, and the system can be set 
up ready for use in less than five minutes. No batteries are 
required . . . and the price complete with tubes, microphone, etc., 
and nothing left to buy, is $343.00. 

Send for twin folders PEl; one descriptive of the PAM-100 and 
the other of the MIK-100. 



Portable PAM Address system to 
institutions that hold regular meet- 
ings and need the equipment per- 
manently. This price is reasonable 
and the profits are large. 



Portable PAM Address systems for 
special occasions. One man can 
transport the entire system and set 
it up in five minutes. After a few 
rentals the cost is recovered and 
future income is all profit. 



Factories: Canton and 
Watertown, Mass. 






! 


The 


Leaders 


in 


Sound Reproduction 


in 


Every 


Field 




J J 






- - 






1 



THEATRES- AIRPORTS 
CONVENTION HALLS 
AMUSEMENT PARKS 

"There Is A RACON For Every Purpose" 

Racon Horn No. 5325 is especially appealing where there is 
very little space between screen and wall. Amplifies as per- 
fectly as the Parent Horn No. 4320 for Speech and Music. 

Patented non-vibratory, non-porous material and construction, plus 

light weight, which makes for perfect results and maximum convenience. 

These outstanding features of RACON products have made imitation 

and competition impossible. 

RACON'S L ™ PORTABLE HORN 

New type portable horn number 

3320A air column length slightly 

less than 7 feet. Oval bell 27" x 

35", depth 28" 

Can be separated in two halves for 

portability. Excellent for speech 

as well as music. 

Newest Storm-proof Horn 




Air Column slightly less than 10 

feet. Depth 30 inches. Bell 30x40 

Inches. Weight 30 pounds. 





Portable Horn 
Model 3320A 



Improve Your Sound Equip- 
ment with RACON Speakers 
and WATCH RESULTS! 



. Our Latest Catalog is 
Yours Upon the Asking 



TRUMPET <^Mf 
HORN W 

Bell 22 inches round, length 40 
inches. Equipped with cast alumi- 
num ferrule and suspension ring. 

For Public Address and all Out- 
door use. This horn has been per- 
fected after years of exhaustive re- 
search in Racon Laboratories. Will 
withstand all weather conditions. 
Requires no replacements or servic- 
ing after heavy rainstorms. . . . 
Guaranteed for one year. Prices 
slightly higher than regular horns. 



GIANT 




ELECTRO 

DYNAMIC 
HORN 
UNIT 

Weight 20 lbs. 
Field consump- 
tion approx. 1 
amp. at 6 volts. 
Eating 30 watts, 
continuous ope- 
rating load 10 
watts. 



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 



RACON ELECTRIC CO., Inc. 

17 Ar^XODICTQ. 18 to 24 WASHINGTON PLACE, NEW YORK 

rrtL 1 WrXlILk-}. SLOUGH, BUCKS, ENGLAND AND 3 MUTUAL ST., TORONTO, CAN. 



mmfmKRmmSnBamWMf*\ r ' 



APRIL, 1931 



PROJECTION 
ENGINEERING 



SOUND » VISUAL 







and Reproducing Sound 
(See page 26) 



& 









THE JOURNAL OF THE SOUND AND LIGHT PROJECTION INDUSTRIES 



$1,000 for Junior Talkie Portable Projector 





$1,150 for junior, with amplifier and speaker. 

$2,150 for two projectors, with amplifier and speakers. 



F.O.B. Derby, Conn. 



Announcing the 

BELL PORTABLE TALKIE 

The Latest Achievement of Sound Equipment Based on Compactness and Quality 

B 



The sound and projection heads 
are built in one unit. The Photo 
Electric Cell assembly oh the out- 
side of the case conveys the im- 
pulse to the amplifier circuit. 

Film running over an idler con- 
nected to a circuit breaker keeps 
the circuit open ... a film break 
releases and shuts off the entire 
unit. 

An ingenious rear shutter is built 
in, while the aperture is constant- 
ly cooled by forced draft. Entirely 
assembled in double sheet steel, 
asbestos lined, fireproof and 
noiseless operation is assured 
besides eliminating the use of a 
fireproof booth. 

All moving parts arz ball bearing, 
hermetically sealed in grease. 
Special condensers handle the 
intense light from the 1000 watt 
projection lamp and throw a full 
theatre size picture on a screen 
100 to 125 feet distant. 

Bell Equipment is sold complete 
in every detail. 




VERY salesroom, advertis- 
ing agency, church, school, hotel, hospital, auditorium 
and community center can now have perfect sound 
and visual projection. With this added educational 
and amusement attraction, you have revenue produc- 
ing facilities which will spell profits, we introduce 
this most modern series of talkie projectors in response 
to popular demand. Learn more about Bell Equipment! 
You will profit from the introduction. 

In construction, every engineering problem has been sur- 
mounted — from the very portability of the apparatus to the 
prevention of fire hazard. Perfection in sound AND visual 
projection was our aim — price, the secondary consideration. 

We believe that the many features incorporated in both the 
Junior and De Luxe models, made possible by years of actual 
working experience, will convince you that the ultimate of 
perfection has been achieved. 

Now is the time to see and hear the portable talkie equip- 
ment by which others will be judged and valued. 

REPRESENTATIVES WANTED FOR FOREIGN AND STATE RIGHTS 



BELL EQUIPMENT CORPORATION 

Tortable Talkie Equipments 



Suite 605 



729 SEVENTH AVENUE 



NEW YORK 



Telephone BRyant 9-9890 



Telegram WESENOJ 



APRIL 1931 



Page 



Sixteen Million 

to One . . . m 



NATIONAL 

PROJECT 



OTION picture projection 
today demands a source of light sixteen million 
times as brilliant as the screen. 

Due to losses through aperture, shutter, film, 
optical system and screen absorption, only a 
small percentage of the light from the source is 
reflected from the screen. This is spread over a 
picture a half million times the area of the arc 
crater from which it comes. That is why the 
crater brilliancy must be sixteen million times 
the brilliancy of the screen. 

National Projector Carbons hold their leader- 
ship in the motion picture theatre because they 
provide a source of steady, white light surpassing 
the sun in intrinsic brilliancy. 

Over fifty years of experience, constant research 
and the most modern manufacturing facilities 
assure their uniformity. Yet they are paid for, at 
each performance, by two satisfied patrons. 

OR CARBONS 

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

NATIONAL CARBON COMPANY, INC. 

Carbon Sales Division » Cleveland, Ohio 

Unit of Union Carbide I jlHIl 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. Ill 



APRIL 

1931 



Number 4 



Contents 



Editorial 



page 
4 



Typical Public-Address Installations 

By Henry L. Williams 9 

Sound Disc Synchronization By B. Brown 1 1 

Talking Picture Equipment for Portable Use 

By John Dunsheath 14 

Film for Home Record Reproduction . . . . By A. L. Walker 1 6 

The Romance of Television By L. C. Vipond 1 7 

Amplification in Sound Motion Picture Work, Part III . 

By Charles Felstead 19 

Advances in Science By Dr. C. Kenneth Mees 21 



Departments 

News of the Industry and New Developments 



26 



Bryan S. Davis 

President 

James A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

52 Vanderbilt Ave. 

New York City 



Sanford R. Cowan 
Advertising Manager 

J. E. NlELSON 

Circulation Manager 



Publication Office — North Broadway, Albany, N. Y. 
Chicago Office-333 N. Michigan Ave.— Charles H. Farrell, Mgr. San Francisco Office-155 Sansome St.-R. J. Birch. 

St. Louis Office— 505 Star Bldg.— F. J. Wright. Los Angele^ Office— 846 S. Bjoadway— R._J._ Birch. 



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



New Zealand — Tearo Book Depot — Wellington. 



Entered as Second Class Matter at the Post Office at Albany, N. Y., October 9, 1929, under the act of March 3, 1879. Yearly subscription 
rate $2.00 in U. S. and Canada. Yearly subscription rate $3.00 in foreign countries. 



APRIL, 1931 



Page 3 



RACON'S LEADERSHIP AGAIN DEMONSTRATED 

Racon Portable Horns Used 

at Times Square, New York, in 
2-Way Communication with U. S. Navy Blimp 




Racon Products Have 

Proven Their Superiority 

Patented non-vibratory, non-porous material and 
construction, plus light weight, which makes for 
perfect results and maximum convenience. These 
outstanding features of RACON products have 
made imitation and competition impossible. 



f 



or 



THEATRES — AIRPORTS 

CONVENTION HALLS 

SOUND TRUCKS — PARKS, etc. 



Racon Portable Trumpet 




is demountable into 3 sections. 
Designed for easy assembly and 
small space storage. Unique iu 
tone reproduction over wide area. 
Acoustically perfect for speech 
and music under all weather con- 
ditions. 



Racon Portable Horn 

New type number 3320A Air column length slightly 
under 7 feet. Oval bell 27 inches by 35 Inches, 
depth 28 inches. Demountable into 2 sections. 
Ideal in small space and portability. 



RACON 

HORNS & 

UNITS 

Are covered by U. S. 
Patents Nos. 

1,507,713 
L,501,032 

1. 577. 270 
73,217 
73,218 
1. 722,448 
1.711,514 
1,781,480 



Racon Theatre Horn 



BACON HORN" No. . r >32.j — For small 
space between the screen and wall. 
Air Column slightly less than 10 feet. 
Di pth 30 inches. Bell :50x40 indies. 
Weight 30 pounds. 



Racon Giant Unit 



Weight 20 lbs. Field con- 
sumption approx. 1 amp. at 6 
volts. Rating 30 watts, con- 
tinuous operating load 10 

watts. 




E d 



i t o 



i a 



THE MARKET 
FOR SOUND 
EQUIPMENT IN 
THEATRES 



ACCORDING to the latest 
1 authoritative statistics 
there are 18,000 moving pic- 
ture theatres in operation in 
the United States. This is aside 
from an additional 11,000 
theatres which are either tem- 
porarily, or permanently closed. Of the theatres 
in operation 64.9 per cent are equipped for sound 
projection. That is, 11,560 are so equipped. 

Of the theatres having sound facilities a total 
of 5,619 are equipped with ERPI or RCA 
Photophone Systems. This leaves 5,941 theatres 
which have in service sound systems manufactured 
by a score or more of independent manufacturers 
of sound amplifying apparatus. 

Of the existing 18,000 theatres operating, less 
than one third are equipped with sound systems 
manufactured by the two largest companies. There 
remain 12,381 theatres which constitute the mar- 
ket for both the independent manufacturers and 
the two large companies. 

The present aggressive sales projects on the 
part of all manufacturers of sound equipment 
are understandable when one considers the magni- 
tude of the business yet to be procured 



THE STANDARD 

RELEASE 

PRINT 



EVERY projectionist who has 
not already received a copy 
of the questionnaire entitled, 
"Survey on How to Improve 
the Release Print Standard," 
should procure a copy from 
Lester Cowan, manager of the Academy Tech- 
nical Bureau, 7046 Roosevelt Blvd., Hollywood, 
Calif. 

A primary aim of the Standard is to keep the 
print in better condition for subsequent runs. The 
conscientious projectionist who endeavors to put 
on the best possible sound presentation at every 
showing of a given picture, under difficulties 
experienced with the prints he receives, is the man 
to be considered in any contemplated technical 
betterment. 

The technical bureau of the Academy is desir- 
ous of receiving the information called for in the 
questionnaire referred to and all projectionists 
should avail themselves of this opportunity to air 
their views. 



THE Spring meeting of the 
Society of Motion Picture 
Engineers will be held at 
Hollywood, Cal., May 25 to 
29, inclusive. The technical 
sessions at this meeting will be 
highly important and instructive. There are to 
be papers on color photography, studio practices, 



THE 

S.M.P.E. 

CONVENTION 



April, 1931 



film characteristics and processing, and sound 
recording. There will be several papers on each 
of these timely subjects, each paper prepared by 
engineers closely in contact with the details of 
theatre projection work. 

Every one identified with the technical side of 
the theatre who can make the trip should go to 
Hollywood for this convention. 



SOUND 
AMPLIFIERS 



WITH the astonishing 
growth of the sound am- 
plifier business in recent 
months it is interesting to 
speculate upon the greater ex- 
tensions of the service which would be under way 
if business conditions were normal. There seems 
no end to the situations into which modern sound 
amplifying systems fit economically and profitably. 
A noteworthy development is that a very con- 
siderable number of the applications of sound 
reproduction and amplification now being engi- 
neered were sold by local electrical contractors, 
radio service managers, and theatre projectionists. 
There are upward of thirty thousand communi- 
ties in the country where one or more sound instal- 
lations are almost certain to be placed in service 
within the next year or two, for commercial 
industrial, auditorium, sports, and outdoor amuse- 
ment purposes. 

These installations are in addition to sound- 
picture theatre requirements, and aside from the 
hundreds of installations made and to be made 
in hundreds of cities and large towns. 

The requirements of the smaller communities 
offer opportunity for many of the smaller manu- 
facturers of sound equipment. Although the 
points of sale are widely scattered, in the aggre- 
gate the business is sure to be of gratifying 
proportions. 



$8,000,000 
FOR FILMS 



SEVERAL foreign countries 
whose film needs are meas- 
ured in millions of feet a year 
bought from America in 1930 
more than in 1929. The rec- 
ord of sound film shipments to the leading 
markets in 1930 discloses some encouraging signs 
of improvement in this trade. 

Commerce Reports says the total value of all 
film exports in i93 1 o exceeded $8,100,000. 




+nJjLsff?*iUc 



crL 



Editor. 



APRIL, 1931 



'age 




quickly 

Pays for Itself 

Schools, churches, clubs, hotels need the portable PAM Address 
system. With it, a speaker addresses 500 people as easily as 
half a dozen. Speech and music, both vocal and instrumental, 
are amplified with excellent quality. 

The units in this system are completely matched and designed 
to operate together. Naturally the results obtained are superior 
to a combination of units procured from different sources which 
were not designed to operate together. 

The two units that are required (MIK 100 and PAM 100) to- 
gether weigh less than 75 pounds, and the system can be set 
up ready for use in less than five minutes. No batteries are 
required . . . and the price complete with tubes, microphone, etc., 
and nothing left to buy, is $343.00. 

Send for twin folders PE4; one descriptive of the PAM-100 and 
the other of the MIK-100. 



SELL 

Portable PAM Address system to 
institutions that hold regular meet- 
ings and need the equipment per- 
manently. This price is reasonable 
and the profits are large. 



RENT 

Portable PAM Address systems for 
special occasions. One man can 
transport the entire system and set 
it up in five minutes. After a few 
rentals the cost is recovered and 
future income is all profit. 



Main Office: 
( jruiin. Mass. 



\a/mo/7i 



r ieelfI(?(of. 



Factories: Canton and 
Watertown, Mass. 



MANUFACTURERS SINCE 1382 





Page 6 



PROJECTION ENGINEERING 



AMPL10N PUBLIC ADDRESS 
SYSTEMS- 



UNIVERSALLY APPROVED 




AMPLION 
DYNAMIC 



GIANT 
UNITS 



600% more efficient 
8000 cycle range 



TRANSVERSE 

CURRENT 

MICROPHONES 




USE AMPLION 
WOOD HORNS 



WL-6 




WL-12 



AT 



BASEBALL PARKS important announce- 
ments and league results are announced 
thru Amplion equipment. An Amplion Public Address 
System is operated at the Polo Grounds in New York City. 



AT 



FYLING FIELDS, above the noise of motors 
and expectant passengers, flying schedules, 
aviation news and last minute words of instruction are in- 
stantaneously announced through the powerful trumpet 
horns. 



IN 



SCHOOLS AND CHURCHES Amplion's 
public address system has had widespread 
acceptance. For amusement and educational diversions 
phonograph records may be played on the electric 
turntable. 



FOP PORTABLE TRUCKS, many of which 
• V^l\ are now being equipped. This form 

of public address system is meeting with great success as 

an advertising medium. 



MICROPHONES, 



Amplion transverse current microphones are available 
in every type and capacity and for every requirement. 
Amplion hand and stand microphones of the very latest type are approved by record- 
ing laboratories and home talkie apparatus manufacturers. 



HORKI^ acoustically correct and not affected by any climatic condition, are 
nvyi\INJ| ava iiable in every size and shape— from the narrow air column to be 
used in the narrow space behind sound theatre screens to the six foot bell mouth 
trumpets which are portable and can be set up in a few seconds for outdoor and 
amusement park gatherings. 



WRITE FOR 20 PAGE CATALOGUE AND PRICE LIST 
ON SOUND SYSTEM APPARATUS FOR EVERY PURPOSE. 



dSBb 



Amplion Corporation of America 

38 W. 21st Street New York City 



APRIL, 1931 



Page 7 





NO BATTERIES! 
NO MOTOR GENERATORS! 
EASY TO OPERATE! 

FOR FURTHER INFORMATION SEE OUR LOCAL 
DISTRIRUTOR OR USE COUPON RELOW. 



GRIES REPRODUCER CORPORATION, 

465 E. 133rd ST., BRONX, NEW YORK. 

GENTLEMEN: Please send me particulars on your 
A.C. operated Portable Sound Picture Equipment. 



Name. 



Address 

Type Equipment 

now using 

Power Supply 

available 

What purpose do you 
intend using Sound 
Picture Equipment. . . . 



Page 8 PROJECTION ENGINEERING 

Better Projection Pays 

Three Projectors 

or 
Emergency Equipment 
Kept in A1 Condition 

» 

Is a Sure Indication 

oF 

Practical-Progressive 
Showmanship 

GENUINE SIMPLEX PARTS 

FOR 

SIMPLEX PROJECTORS 

GIVE MOST SATISFACTORY RESULTS 

Send for Booklets Giving Full Particulars 
Rear Shutter Attachment 

Lens Aligning Device 

Lens Focusing Assembly 

Triple Lens Turret 

International Projector Corporation 

90 GOLD STREET NEW YORK 



Projection Engineering 



APRIL, 1931 



Typical 

Public- Ad dress 
Installations 

By Henry L. Williams 



Although the Requirements for Each Installation 

Are Special, There Are Various Fundamentals 

Common to All. 



W 



HEN municipalities or pub- 
ic authorities want a public- 
address or centralized radio 
system installed they usually 
retain an engineer to draw up definite 
specifications. Private concerns, on 
the other hand, generally leave the lay- 
out to the individual contractor, so that 
each sound engineer designs his own 
system and the resulting estimates 
may vary as much as ioo per cent. 

This is one of the reasons why the 
sound installation concerns should have 
a really competent engineer on the staff, 
even though they specialize in the use of 
factory-built equipment. On the sound- 
producing capacity of the equipment 
depends the price, and efficiency often 
governs the capacity of any unit. An 
inefficient layout therefore usually costs 
more than it should — if the contractor is 
fortunate enough to get the job. 

The necessity for careful planning of 
an installation is well illustrated in the 
following example. 

The requirements under this contract 
were a p-a. system to cover a new ball- 
park seating 35,000 people. As the park 
was also to be used as a football field, 
a second position was designated for the 
microphone, which therefore had to be 
movable. Both radio and phonograph 



had to be provided so that they could 
readily be controlled by the announcer. 

The real problems of this installation 
were introduced by the fact that the 
speaker assembly had to be mounted at 
a considerable distance from the an- 
nouncing points — raising questions of 
voltage drop and efficient impedance 
relations. 

As the sketch-plan, Fig. 1, shows, the 
speakers were to be mounted on the 120- 
foot lighting tower. As it was pro- 
posed to use a certain make of horns, 
these were drawn to scale on the park 



elevation and plan blueprints. Accurate 
projection of the sound beams, both 
horizontally and vertically, showed that 
the most efficient height for these horns 
was a little over 65-feet, and that six 
of them would be required to give the 
necessary spread. 

The next problem was to decide on 
the most efficient arrangement of the 
amplifiers. It was determined that the 
utmost in flexibility could be secured — 
allowing for future expansion — by using 
one PAM-5a voltage amplifier (consist- 
ing of a type -27 tube working into a 
pair of -45's) feeding three PAM-25a 
power amplifiers (two -27's and two 
-50's, both push-pull). These three out- 
put stages would each work into two 
dynamic speakers, allowing about 75 
watts undistorted output per speaker. 

A controlling factor, however, was 
the long run of the voice lines from the 
microphone. Naturally, the two-stage 
microphone amplifier had to be located 
close to the microphone, as the distance 
from the mike to the speakers was 
either 800 or 1100 feet, dependent on 
whether the game was baseball or foot- 
ball. After due consideration, it was 
decided to use a 60-ohm line between 
the mike amplifier and the voltage am- 
plifier, and to locate the latter as near 
the speakers as possible. Low capacity 
lead-sheathed twin cable was adopted 
throughout, having a d-c. resistance of 
about 5 ohms per 1000 ft. The final 
arrangement therefore was to house the 
main amplifiers in the base of the light- 
ing tower — for which purpose a room 
was built — and to work direct from the 
amplifiers into the speaker voice coils. 
This of course necessitated using out- 



RADIO 



BELL TRANSr 

» a.c. o / , , !r 




Fig. 3. Amplifier layout. 



Page 10 



PROJECTION ENGINEERING 



put transformers having two 15-ohm 
winding's, or rather, less. 

This arrangement resulted in the use 
of six separate pairs from the ampli- 
fiers to the speakers. This was con- 
sidered a better arrangement than 
putting the voice coils in series, as in 
case of breakdown each line could then 
be checked separately. 

A refinement introduced here was 
the installation of an impedance plug 
panel which enabled each voice coil 
circuit to be opened and an impedance 
of equal value substituted ' in the feed 
line, by means of an ordinary plug. 
Thus, should a voice coil burn out, it 
could readily be detected and the im- 
pedance substituted. The length of 
the 15-ohm lines, it will be noted was 
but 60-feet. 

In order to minimize the possibility 
of having to service the speakers on the 
mast, the standard dry rectifiers were 
removed and the fields supplied from 
a tube-type rectifier assembly in the 
amplifier room, using pairs of type -81 
tubes for full-wave rectification. 

Announcing Equipment 

As the microphone assembly had to 
be portable, it was necessary to house 
the mike amplifier in a suitable carry- 
ing box, with plug receptacles for the 
phonograph and radio, and a simple 
switching arrangement. All that the 
announcer had to do then was to detach 
his a-c. and line cords. A special small 
bakelite panel was built into the end of 
this box to carry the switches, and in- 
dicator lights were provided to show 
what was "on" and what was "off." 
A switch on the plug panel in the press 
box where the announcing was done, 
cut out the dead end of the line when 
the remote position was not in use. 

On the same panel was incorporated 



a momentary-contact switch which 
operated a relay in the amplifier room 
and threw the a-c. "on" or "off." With 
this arrangement, the announcer could 
operate the entire system from the press 
box or the football announcing booth, 
and it was unnecessary to enter the 
amplifier hut. 

In distinct contrast to this job as to 
the problems involved, was a small ship 
installation. This installation, which 
was duplicated on another boat, con- 
sisted of four dynamic speakers built 
into the panelling of three public 
rooms — the smoke-room, observation 
room, and dining saloon. Music is 
provided by a phonograph and radio 
receiver, with centralized control of 
volume. The receiver used is the latest 
type superheterodyne having a pair of 
— 45 tubes in the output stage. This, 
of course, was not quite sufficient out- 
put for the four speakers, giving but 
a little over 1 watt per speaker. A 
separate output stage of push-pull — 50's 
therefore was built up in this installa- 
tion from AmerTran parts, with its 
own power supply. It was considered 
quite unnecessary to go to the trouble 
of altering the — 45 stage to — 27's as 
there was ample gain in the — 45 stage 
to produce maximum grid swing on the 
—50's. 

As the ship's supply was 115-v. d-c, a 
converter was supplied to transform 
this into Iio-v. a-c. Some temporary 
difficulty was experienced with this 350- 
watt converter due to the hum of the 
armature. The converter was installed 
in the engine room, yet the faint whine 
was audible two decks above at the 
radio input. Mounting the converter 
on springs eliminated this, while the 
abolition of the frame ground also 
helped. 

All speaker fields, which were de- 
signed for ioo-v. d-c, were fed from 
the distribution box at the radio so that 




6 HORNS 
S 65 FT. UP 




Fig. 2. 



Fig. 1. 



they were automatically switched off 
with the radio. 

Multiple Speakers 

Another minor problem that prom- 
ised to give trouble was the method of 
splitting the output among the three 
speaker circuits, each being handled by 
a separate volume control. The first 
method tried was to insert an output 
amplifier having a separate secondary 
winding for each speaker circuit. This 
however did not give the quality desired. 
The arrangement finally adopted con- 
sisted of using the original speaker 
input transformers removed from the 
speakers and mounted on the amplifier. 
The quality was then excellent, regard- 
less of the position of the various vol- 
ume controls. Packard No. JJ cable 
was used for voice lines throughout. 



CAMERA SILENCING SUBCOM- 
MITTEE PLANS FOR 1931 

AS a first step in the renewed 
investigation of the problem of 
silencing the camera, the committee is 
conducting a survey of the experiences 
and opinions of all first cameramen in 
Hollywood studios with regard to 
camera covers (blimps, bags, etc.). In 
this survey the committee is receiving 
the cooperation of officials of Local No. 
659 (International Photographers of 
the Motion Picture Industries), of the 
I.A.T.S.E. and M.P.M.O. Leaders of 
the American Society of Cinema- 
tographers have also expressed approval 
of the survey. 

The questions call particular atten- 
tion to the effects of new developments 
in noiseless recording and directional 
microphone devices. 

This survey is intended to keep the 
Producers-Technicians Committee of 
the Academy of Motion Picture Arts 
and Sciences, abreast of current de- 
velopments and needs in camera silenc- 
ing. In 1930 this subcommittee con- 
ducted a thorough survey of the prob- 
lem followed by scientific noise tests 
of all varieties of camera covers and of 
the cameras themselves. It was found 
that the silencing efficiency of the device 
varied over a wide range, and that the 
range in noise from the uncovered 
camera was a very considerable factor 
in the problem. The published report 
of the subcommittee established stand- 
ards for desired camera silence, listed 
fundamental requirements and recom- 
mended materials for camera covers. 
It is planned to bring this report up to 
date after the present investigation. 

The camera silencing subcommittee 
consists of Kenneth F. Morgan, Fred- 
erick M. Sammis, and Lester Cowan, 
manager of the Academy Technical 
Bureau. 



APRIL, 1931 



Page 



Sound Di 



ISC 



Synchronization 



By B. Brown, B. Sc. 



IllllllllllllI 

Practical methods of quickly reestablishing synchronous 
operation of sound and picture in projection equipment 



THE greatest disadvantage associ- 
ated with the use of the disc rec- 
ord is undoubtedly the possibility 
of losing synchronism between the 
picture and sound. Even the most 
hardened projectionist feels a shudder 
go down his spine when picture and 
voice by some means or other manage 
to get out of phase. 

Some of the smaller types of sound 
equipment were so designed that it was 
possible to regain synchronism once lost 
by speeding up either the head me- 
chanism or the turntable drive. In 
the larger and more popular systems, 
however, no such mechanism exists 
probably because it would be capable 
of abuse. As a matter of fact the idea 
of regaining lost synchronism is one of 
the oldest associated with talkie picture 
science. Gaumont in some of his early 
experiments incorporated a sort of 
differential drive by means of which the 
projector could be brought into line 
with the turntable by means of an extra 
electric motor which, as soon as it had 
accomplished its object, was cut out of 
circuit. 

What is to be done if synchronism is 
lost on one of the inflexible types of 
mechanism? We refer of course to 
those cases where either the needle 
jumps a number of grooves or the film 
breaks above the intermittent sprocket. 
A breakage below the sprocket is of 
course of no importance since the rela- 
tionship between picture and portion of 
sound groove still remains the same. 

In most of the instruction books on 
the subject it is stated more or less defi- 
nitely that when synchronism is lost as 
described above it is useless to endeavor 
tc regain it. In practice, however, this 
is by no means true as we shall en- 
deavor to show in the following notes. 



Let us first examine the different 
means by which we may lose syn- 
chronism : 

(i) The needle may jump a groove 
due to an excessively recorded passage 
which usually occurs in the lower fre- 
quencies. 

(2) The needle may jump from the 
start mark to the first groove if the 
projectionist has not gone to the trouble 
of pulling the machine round for the 
better part of a revolution prior to 
switching on the motor. 

(3) Either the pickup or turntable 
may have been jogged causing the 
needle to jump. 

(4) A needle not properly clamped 
in its holder may vibrate strongly caus- 
ing a jump. 

(5) A worn or low grade needle may 
have the same effect. 

(6) A warped disc acts much after 
the same style as the previous causes. 

(7) A film may break above the in- 
termittent sprocket — this is by far the 
worst case. 

Recording on disc is a well-estab- 
lished art and is probably Hearing the 
limit of its efficiency. With the advent 
of talking pictures, however, fresh fac- 
tors added themselves to its limitation. 
In ordinary commercial recording of 
the domestic phonograph record one of 
the prime considerations is to make 
sure that the record will have a suffi- 
ciently long life. It is more or less 
essential for a disc to withstand at least 
one hundred playings without deteri- 
orating to such an extent that the repro- 
duction becomes poor. 

For sound motion pictures, this con- 
sideration did not weigh greatly since 
the life of twenty playings was all that 
was required for the standard running 
theatres. This gave greater latitude to 



the recording engineers who, we fear, 
allowed the amplitude of the grooves 
sometimes to exceed the danger point. 

Needle Pressure 

Projectionists will have often noted 
that in heavy base passages the repro- 
ducer or pickup is seen visibly to quiver 
and careful men often place a finger on 
the arm to reduce the chances of jump- 
ing a groove. It does not appear to 
have been fully appreciated by manu- 
facturers of disc equipment that needle 
point pressure might have been in- 
creased to an extent at least 30 per cent 
greater than is the rule at the present 
time. This would undoubtedly tend to 
reduce the life of the disc itself, but as 
we have just mentioned, most discs are 
scrapped long before they show marked 
signs of deterioration. 

The second cause of losing synchron- 
ism is really inexcusable. The rapid 
lead out spiral is sufficiently acute to 
apply enough momentum to the pickup 
to cause it to over-shoot the standard 
spiral grooves when it blends in with 
them. Always it should be taken as a 
rule that the turntable should be pulled 
round for at least half a revolution 
after the needle has been set to start 
mark with the initial film rack in the 
gate. Naturally some systems are more 
lie to give trouble in this direction 
than others. The repulsion type motor 
with electrical speed control rarely 
gives cause for trouble in this respect 
even when abused. Nevertheless even 
with such a smooth and slow takeup it 
is quite possible to have needle jump- 
ing especially if the head is a free run- 
ning one and the weather warm when 
the bearing lubricants are lowest in 
viscosity. 

Turntable Protection 

( Ireat care should always be exer- 
cised when passing round or near the 
turntable and reproducer arm. Most 
systems are fitted with guard rails or 
sunken turntables to act as a protec- 
tion against jogging of any description. 
Nevertheless one cannot help but think- 
that there is much room for improve- 
ment in this matter. A guard rail at 
the best of times is a poor way out of 
the difficulty and gives one the impres- 
sion of being an afterthought rather than 
a definitely designed piece of mechan- 
ism. One of the best examples of 
turntable protection is to be seen in the 
Motiograph de Luxe Sound Projector 
of the Enterprise Optical Manufactur- 
ing Company. The turntable besides 
being sunk is given a further protection 
by being drawn partly beneath the lamp 
house carrying bracket which rapidly 
reminds the unwary one that he is near- 
ing the clanger zone. 

That a loose needle should cause loss 
of synchronism appears a somewhat 
fatuous remark. This is not the case, 



Page 12 



PROJECTION ENGINEERING 



however, since as projectionists have 
found to their sorrow too strenuous ap- 
plication on the needle clamping screw 
is capable of throwing- a pickup out of 
adjustment. This applies particularly 
to the rubber damped armature types 
although if too great force be expended 
on the disc diaphragm of the 4a repro- 
ducer the diagonal bar may easily be 
loosened causing a fall off in reproduc- 
tion quality quite as bad as that of an 
out-of-tune armature pattern. 

Clamping a needle in a holder suffi- 
ciently tight to give maximum repro- 
duction and yet refraining from over- 
straining the pickup mechanism is 
something of an art in itself especially 
as no two projectionists have fingers 
equally sensitive. It is well worthwhile 
making an experiment on needle tight- 
ness. Take one of the ordinary loud 
tone type of "talkie needles" and clamp 
it in the holder just sufficiently tight to 
prevent its moving. Now try out a disc 
with which you are familiar noting at 
the same time the fader or potentiometer 
setting to give a certain degree of vol- 
ume. Next, lift the pickup from the 
disc, tighten the screw hard down and 
play over again. It will usually be 
found that an increase in loudness cor- 
responding to two fader steps will have 
been achieved. 

Poor Quality Needles 

The use of a poor quality needle is 
to be condemned from every aspect 
since it gives neither reasonable repro- 
duction nor saves any money in the 
long run. The manufacture of phono- 
graph needles has been delevoped by 
many years of experience and scientific 
research. As is commonly known the 
point pressure is exceedingly high espe- 
cially at the start when it is sometimes 
well over two tons to the square inch. 
If the steel be not exactly to specifica- 
tion or the heat treatment wide of the 
mark the three thousandths diameter 
point will break down under its load 
giving a somewhat hooked form which 
besides carrying away the tiny har- 
monic curves tends to slide from one 
groove to another over the dividing 
wall. 

When 16 inch discs were first re- 
leased they possessed considerable bulk 
and carried recording on one side only. 
Nowadays, however, economy has be- 
come essential and thus the thickness of 
the disc has been cut down and one 
finds recording on both sides. While 
from the point of view of keeping costs 
within reasonable limits this is much to 
be admired, yet at the same time there 
is an increased tendency to warping 
especially during the hot weather. The 
backstock from which most records are 
moulded becomes slightly plastic at the 
temperature of a hot day and thus if 
the disc itself be stored in an upright 
position warping is almost certain to 



occur. For this the pressing firm is 
usually blamed but their task is by no 
means an easy one. Generally speak- 
ing, it is wrong handling of records 
which causes warping rather than im- 
perfections in manufacturing processes. 
Always discs should be stored ab- 
solutely flat and in a cool place. 

While in only very bad cases is warp- 
ing sufficient to cause actual needle 
damage, yet even the slightest amount 
out of true will tend to mar reproduc- 
tion by varying the effective pressure 
between needle point and bottom of the 
recording groove. 

Another fault which may be safely 
laid at the door of the pressing com- 
panies is the eccentricity of the record- 
ing circle to the hole in the middle. A 
little consideration will show that a 
very few thousandths of an inch out 
of center will produce quite a high 
force causing the needle to be thrown 
strongly against the outer wall once per 



TABLE I 

Revolutions of 

Turntable Film Footage 

{pitch = 100 grooves per inch) 

10 27 

20 54 

30 81 

40 108 

50 135 

60 162 

70 189 

80 216 

9° 2 43 

100 270 

And so on in steps of 27 film feet 

250 675 

260 702 

270 729 



revolution. It has been suggested that 
some sort of taper device should be em- 
ployed for locating the disc exactly 
upon the center spiggot. This would, 
however, be likely to induce consider- 
able manufacturing difficulty and at the 
same time increase the possibility of 
disc fracture. A far more important 
point would be for pressing companies 
to devote more care to centering the 
hole in relation to the recording circles. 

Film Breakage 

Film breakage is nothing like so 
prevalent nowadays as it was, say four 
years back. However, statistics of this 
nature do not help a projectionist when 
he finds that the key reel has broken 
off above the intermittent. It is all 
very well tabulating the various direc- 
tions which should be taken to avoid 
trouble of this nature, but the fact re- 
mains that it does occur on occasion 
even in the best of projection rooms. 

When a needle jumps the dividing 



walls between the grooves acting on its 
volition rather than the combination of 
circumstances which go to make up this 
action, in nine cases out of ten it jumps 
one dividing wall only and thus is 
either one revolution in front or behind 
the corresponding picture. Further 
consideration of this makes it evident 
that when synchronism is lost in this 
manner it is lost by one or more com- 
plete revolutions of the turntable. Since 
most reproducers are set with a slight 
outward drift the probability is that the 
needle will jump from an inner groove 
to an outer rather than vice-versa al- 
though this is not always the case. 

Sound in Advance 

Supposing the sound suddenly be- 
comes slightly in advance of the picture 
then an attempt at remedy may be made 
by stopping the projector after bringing 
the fader to zero and carefully lifting 
the needle point from the groove in 
which it rests to the next one inwards. 
In most cases of loss of synchronism 
this will be found effective and the only 
query in the mind of the projectionist 
is his ability to lift the needle from one 
small groove to another without missing 
one or two in the process. The ap- 
proximate pitch of grooves is ten thou- 
sandths of an inch. It is quite possible 
with a little care and proper illumina- 
tion to remove a needle from one 
groove to another or for that matter to 
any predetermined number. The writer 
knows of one projectionist who has 
fitted a small lens to a hand flashlamp 
which he uses for this purpose. 

The same object may be accomplished 
in a different manner by stopping the 
machine and gently turning the disc 
backwards for one complete revolution 
while the turntable itself remains sta- 
tionary. The little cam trigger on the 
center spindle may be turned round so 
that it points directly to start mark and 
this serves as an efficient indicator. 
While it is quite an easy matter to turn 
the disc an extra revolution round in 
the correct manner it requires much 
more gentle operation to rotate it in the 
reverse direction since this is against 
the 6o° slope of the needle. Neverthe- 
less it presents no practical difficulties 
tc a careful hand. 

Regaining Synchronism 

The most drastic method of regaining 
synchronism after the style mentioned 
above is to make the alteration while 
the projector is running at full pace. 
Thus, if the sound gets in advance of 
the picture the clamping cap of the 
turntable is first raised and twisted so 
that the trigger points to start mark. 
The thumb is then applied to the edge 
of this disc just as start mark passes 
the hand. This stops the rotation of 
the disc entirely and when the turntable 



APRIL, 1931 



Page 13 



has completed another revolution as in- 
dicated by the trigger, the pressure is 
released thus allowing disc and turn- 
table again to rotate as a whole. Na- 
turally the sound in the auditorium is 
affected but since the whole operation 
takes place in two seconds there is 
nothing very much to worry about. 

When for some unknown reason 
sound gets behind picture the problem 
is distinctly more difficult. It is neces- 
sary to pull round the disc for one 
revolution in advance of the turntable 
while the latter is revolving at its 
normal pace. It will be found that 
simple thumb-pressure on the edge, 
while sufficient to move the disc, is not 
a convenient method of drawing it 
round quickly into the desired position. 
The best way is to moisten the fingers 
and draw them quickly and firmly 
across the top surface of the disc thus 
pulling it round as required. Before 
doing this a certain amount of drag 
should be applied to the edge of the 
turntable so as to draw the damping 
mechanism taut which otherwise would 
produce a bad wobble of the reproducer 
while this was taking place. The whole 
of the operation is of a distinctly finicky 
nature and requires skill and steady 
nerve but if carried out well is prob- 
ably better than stopping the show for 
a minute or so while the needle is lifted 
from one groove to another. 

If the Needle Jumps 
The above notes cater for reasons 
given under numbers (i) (2), (5), and 
(6) providing the needle has jumped 
only a single groove. If the removal 
from one groove to the next does not 
effect complete synchronization another 
move to the next groove should be car- 
ried out in the same manner. It takes 
a long while to describe but the expert 
projectionist will not occupy more than 
thirty seconds in the action, from start 
to finish. Film breakage, jogging the 
reproducer arm, and a loose needle may 
be classed within the same category 
since that usually means that the needle 
finds a resting place in any but the 
correct spot. Can synchronism once 
lost in this manner be regained? The 
mathematical problem of locating any 
one particular place on a very long 
spiral together with a corresponding 
spot on an equally long film appears a 
very difficult one. As a matter of fact, 
however, it is considerably simpler than 
would be supposed from first considera- 
tions. We do not definitely require to 
locate any point of disc with its cor- 
responding point of film. All we wish 
to do is to be able to re-synchronize 
both elements at any known place on 
the one or the other and reasonably 
close to the place where trouble oc- 
curred. While positions on the disc are 
not located by any numerical values, 
each foot of synchronized film is given 
a number starting at the beginning-. 



Thus, if the film breaks off say at 50 
feet and 3 inches it would be quite satis- 
factory to regain synchronism at say 
60 feet. The 10 feet of film lost would 
naturally not be serious since it rep- 
resents something less than 7 seconds 
of entertainment. 

Pitch Must Be Known 

It is actually possible to regain 
synchronism at any part of a properly 
made film providing the pitch of the 
record grooves is definitely known. We 
used to believe that disc recording was 
carried out at a uniform pitch of 100 



EXHIBIT OF NEW APPARATUS 

TO FEATURE S.M.P.E. SPRING 

MEETING 

One of the features of the 
spring meeting of the SMPE to 
be held in Los Angeles, May 25- 
28, will be an exhibit of new 
motion picture equipment devel- 
oped within the last year, accord- 
ing to announcements by the pro- 
gram committee. The board of 
governors has also announced 
that the convention will be ex- 
tended over a period .of five days 
to permit ample time to visit 
studios and all other points of 
interest. 

The equipment exhibit will not 
be in the nature of a trade exhibit 
since there will be no booths for 
exhibits, although definite free 
space will be allotted to each ex- 
hibitor. Rides regulating the ex- 
hibits require that the equipment 
be new or developed within the 
last twelve months; no pamphlets 
or advertising literature will be 
permitted. Each exhibitor will 
be permitted to display one small 
card giving the name of the 
manufacturing concern and each 
equipment shall be labeled with a 
plain label free from the name of 
the manufacturer. A technical 
expert capable \of explaining the 
technical features of the ap- 
paratus will be required to be 
present during the exhibition. 
All exhibition space will be fur- 
nished gratis and the apparatus to 
be exhibited will be censored by 
the apparatus exhibits committee. 



grooves to the inch. Now, however, 
we are wiser and find that they may 
vary from round about 80 to no. The 
standard pitches adopted by the West- 
ern Electric Company are 86, 92, and 
98 grooves per inch. These rather 
"odd" numbers are not adopted through 
sheer "cussedness" but owing to the 
most convenient gear ratios employed 
between turntable drive and cross-feed. 
While it is doubtful whether the fol- 
lowing method is sufficiently practicable 
to be adopted in every day use, never- 
theless it is of some interest and has 



been carried out satisfactorily in quite a 
number of cases known to the writer. 

Briefly the idea is as follows: Since 
the turntable rotates at 2>iVz revolutions 
per minute its value corresponds to 
1^ feet of film per second, and the 
first problem is to find the highest com- 
mon factor of these two quantities 
which works out to be 90 feet. Thus 
one revolution of the turntable cor- 
responds to 2.7 feet of film, two revolu- 
tions to 5.4 feet and so on. It is thus 
possible to correlate each revolution of 
the turntable with a definite position on 
the film which may be determined by 
reference to the marking numbers on 
the edge. Table I provides the film 
numbering which corresponds to com- 
plete revolutions of the turntable. Now 
suppose the film broke at 680 footage 
then referring to the table the next high- 
est number about this is 702 feet which 
would then be set in the film gate as 
the new start mark. Referring again 
to the table we find that this value cor- 
responds to 260 revolutions of the turn- 
table which if the pitch were the nor- 
mal 100 to the inch would be equivalent 
to 2.600 inches. A needle pointed ver- 
nier would then be set to this value 
less .09 inches which corresponds to the 
distance between the start mark and the 
first groove. Applying one end of the 
needle point to the sound groove oppo- 
site the start mark and the other end 
diagonally across the record the new 
position for the reproducer needle can 
be found. 

Standardized Grooves 

As a matter of fact although the 
method appears complicated it can be 
reduced to reasonable simplicity by a 
specially calibrated vernier which might 
well have found a place on the market 
if pitch grooves were standardized. 
However, the present regime of vary- 
ing pitches renders it a problem 
scarcely worth the trouble involved 
which may be remedied when the new 
type of 12 inch disc becomes the rule 
with its lower recording amplitude. 

In conclusion, a few words may be 
said as to the best procedure to adopt 
when synchronism has been lost and 
cannot be regained by any quick 
method. The alternatives are of course 
to run on silent, to cut the particular 
reel, or stop the programme, mend and 
re-wind. As to which is the best to 
adopt depends entirely upon circum- 
stances, although the worst possible 
thing is to run a sound picture without 
its sound. If the reel is unimportant 
and may be cut out this method involves 
the least trouble and probably the great- 
est satisfaction to all concerned. A 
vital reel, however, containing the key- 
note of the story cannot be scrapped 
without annoyance to the audience. 
Splicing synchronized disc film is by 
no means a pleasant task even at the 
(Concluded on page 18) 



Page 14 



PROJECTION ENGINEERING 




Projector with screen and loudspeaker. 



Talking Picture Equipment for 

Portable Use 



Description of a Practical 
and Simple Portable Projec- 
tion Equipment for Portable 
Service 



THE success of and public demand 
for the talkie screen is today 
attracting the attention of every 
type of industry. Steamship 
companies find it necessary to entertain 
their passengers at sea with talking 
pictures. Colleges, schools, clinics and 
other educational institutions find a 
great asset in the talkies for their edu- 
cational value. State hospitals, sani- 
tariums and even penal institutions find 
much good use in this new industry. 
Clubs and other fraternal organizations 
are feeling the necessity of talking pic- 
tures to complete their amusement 
facilities. Many hotels are finding an 
asset in providing talkie equipment in 
one of their show or sample rooms. 
Some have already gone so far as to 
provide complete projection rooms for 
the showing of advertising films, etc. 
Large automobile and other manufac- 
turers are producing talkie film adver- 
tising and sales campaigns. A hotel 
having the equipment can accommodate 
the officials of such firms and provide 
a means of showing films at the same 
time. Local clubs and orders may rent 
the rooms having such equipment at an 
attractive non-competitive price. 

But what are the requirements for 
this field? 



By John Dunsheath 



This equipment must be : ( I ) Very 
dependable and give a high quality of 
reproduction; (2) as fire-proof and as 
safe as human ingenuity can make it ; 
(3) the price must be within the range 
of the field; (4) the equipment must 
not require too much space and must be 
readily portable; and, (5) the operation 
of the equipment must be simple and 
fool-proof, the construction rugged to 
withstand being transported. 

After a thorough analysis of the field 
and as a result of much research, the 
equipment described in this article was 
designed to meet the requirements set 
forth above. This equipment passed 
severe tests covering a period of eigh- 
teen months before it was released to 
the public. 

To make the equipment of extraordi- 
nary safety to the audience and the 
property, this projector is provided 
with several novel and simple automatic 
devices. 

The film runs over an idler roller 
which is connected to an automatic cir- 
cuit-breaker. Under normal operating 
conditions, with the film in the projector, 
this idler holds the motor and lamp cir- 
cuit "closed." The automatic dowser, 
or fire-shutter, is also connected to a 
circuit-breaker which controls only the 
lamp circuit by means of a governor. 

If film is in the machine and the lamp 
switch is turned to the "on" position, 
the lamp will not light until the pro- 
jector has attained full speed, at which 
time the governor moves the dowser out 
of the path of the light and turns the 
switch' to the "on" position. With this 
arrangement if the film runs out or 



breaks, the lamp and motor circuits are 
instantly broken and the entire unit is 
stopped. This eliminates fire hazards 
due to film breakage. 

Air Cooled 

In addition to the foregoing feature, 
a rear projection shutter is used and 
reduces the heat on the film by 40 per 
cent. The aperture and heat plate 
assembly is air-cooled by forced draft 
and is kept at a very low temperature — 
never being more than lukewarm. This 
reduces damage to film from over-heat- 
ing and drying out. This item is of 
great importance in the non-theatrical 
field because in many cases valuable 
scientific or educational subjects are 
shown, and the wear and tear is an item 
of much concern. In the theatrical field 
wear and tear is ignored almost com- 
pletely because the subjects lose their 
box-office attraction before the films are 
worn out. Educational subjects never 
lose their value and are preserved for 
indefinite use. 

With the foregoing in mind a search 
was made for a smooth, easy movement 
— one that would be wear-proof and 
easy on the film. 

The continuous rotary movement 
which is described herein was selected 
for this purpose, after many exhaustive 
tests and a great deal of research work. 
It is the only movement yet designed 
which is of the continuous rotary type 
with all the advantages of the star and 
cam intermittent without its disadvan- 
tages of short life and delicate adjust- 
ment. 

To be assured of perfect performance 



APRIL, 1931 



Page 15 



these machines are designed with steel 
to micarta gears which are enclosed in 
a housing and run in a bath of oil — the 
practice used in the automobile indus- 
try today. This construction takes the 
lubricating problems out of the hands 
of the operator and provides sufficient 
lubrication for a period of four or five 
years. No other lubrication is required 
except for lubricating the motor which 
should be done once a year. 

Fire Hazard Reduced 

In order to further reduce fire haz- 
ards, the projector and film magazine 
have doors and the film is enclosed in 
that particular part of the device. The 
projector case is lined with asbestos and 
sheet steel to assure quiet operation and 
still further reduce fire hazards. 

The lens is of very large diameter, 
2 9/16 inches, giving a maximum of 
brilliance and definition to the screen. 
A triple belt drive is used as a quiet 
but positive power transmission, and all 
belts are adjusted by turning a screw 
on the exterior front of the projector. 
There are no idlers and the belts may 
be tightened while the projector is in 
operation. Any one belt will operate 
the machine ; hence, the show will never 
be paralyzed by belt breakage. Only 
endless belts are used. 

In the amateur field the operators 
need know very little of talkie prin- 
ciples to successfully operate this 
machine. To further facilitate this, the 
amplification was developed entirely 
separate from the projector — not a 
single sound or speech wire is con- 



nected to the machine. The photo- 
electric cell and amplifier are con- 
tained in a separate case which is 
placed in a position adjacent to the 
projector. 

The amplifier case is placed so 
that the light from the sound image 
on the film, and which comes from 
an opening in the side of the pro- 
jector case, will fall upon the 
photocell. This amplifier is de- 
signed to accommodate two pro- 
jectors, and, under these conditions, 
is located between them. This 
arrangement is shown in the illus- 
tration showing the tandem setup. 

One of the purposes of this de- 
sign is to occupy a minimum of 
floor space so that a very small 
booth can be used with comfort to 
the operator. This is accom- 
plished by the use of a right and 
left projector designed especially to 
meet these requirements. In many 
places, such as on ocean liners, in 
schools, and clubs, a permanent or 
large unsightly booth is very unde- 
sirable, and in some cases practi- 
cally impossible. This feature 
eliminates the necessity of a per- 
manent booth. Another very im- 
portant advantage of this design is 
that it permits of the use of very 
short leads from the photocell to the 
amplifier. This tends to increase the 
quality of the reproduction because 
the quality decreases in direct propor- 
tion to the increase of the length of 
these leads. 





_ 



The projector 



Mod 



els 




The tandem setup. 



This equipment is available in two 
standard models: The DeLuxe and 
the Junior models. The DeLuxe model 
is designed for daily and heavy-duty 
work. Every shaft is of ^ inch diam- 
eter and is mounted on precision ball 
bearings. These are packed in grease 
and sealed. The main castings are of 
aluminum. The sound-head and the 
projection head are built into one unit, 
especially for sound-on-film repro- 
duction. 

By using special condensers and the 
unusually large lens the 1000-watt pro- 
jection lamp is made a close competitor 
of the arc lamp and a clear picture can 
be had on a standard theatre-size 
screen at a distance of from 100 to 125 
feet from the projector to the screen. 
The amplification can be used with reg- 
ular theatre speakers to accommodate 
a large audience. 

This model, complete with two pro- 
jectors, rewind, cables, carrying-cases, 
accessories and all extra tubes, lenses, 
etc., weighs just 510 pounds. The 
heaviest case (the projector) weighs 
113 pounds.- All cases can be carried 
in the tonneau of a five-passenger 
automobile. 

The Junior model is of the same 
rugged design and construction as the 
DeLuxe model and differs only in that 
plain bunting bronze bearings are used 
in lieu of ball bearings. The same gear 
construction and automatic lubrication 
is prevalent in the Junior, and a bath of 
(Continued on page 20) 



Page 16 



PROJECTION ENGINEERING 



m ror 



Film f 
H 



ome 



Record 



Reproduction 



By A. L. Walker 



SINCE the commercial adoption of 
film recording for sound picture 
work there have been many at- 
tempts at utilizing the device in 
place of phonograph discs for ordinary 
sound reproduction. It now appears 
that these attempts have taken practi- 
cable form. The Austrian Selenophone 
Company well known for their full-size 
sound projection system which has at- 
tained a degree of popularity in Europe 
are now in process of manufacture of a 
home reproducing equipment which em- 
bodies sound-on-film recording. 

For a long time the exponents of the 
disc have maintained that the high price 
of celluloid and the expense of photo- 
sound printing rendered popularity of 
this type of apparatus out of the ques- 
tion for many years to come. There 
was much to back this opinion and it 
seemed that the disc even while losing 
strength in the sound picture field would 
retain its position as a home entertainer. 

The Selenophone Company, however, 
has proceeded along lines which are 
practical. They have abandoned the use 
of celluloid and instead print the sound 
tracks on a strip of paper, some y 2 inch 
wide and cut to standard lengths of 300 
meters. Another argument against the 
use of the sound track was that the size 
of a roll of film corresponded more or 
less to that of a disc record since the 
thickness of the film was roughly equal 
to the pitch of the sound grooves. 

To combat this the Selenophone Com- 
pany prints four sound tracks side by 
side on a single paper band thus quad- 
rupling the time of play. On the stand- 
ard projection speed a single 300 meter 
drum gives some 70 minutes perform- 
ance, equivalent to about 10 double 
sided records. 

▲ 

In Europe the Selenophone 
makes a bid to displace 
disc records. 



Ink Printing 

The expense of photo-printing has to 
a large extent been eliminated by an 
especially developed method of ink 
printing. The photographic impression 
of the original photographed sound 
track is first transferred to a metal 
plate and then to a "rubber blanket" 
which is used as a printing roll much 
after the style of the machinery used 
in turning out daily newspapers. 

When one considers the difficulties 
which occur even in producing a good 
sound track the technical development 
necessary for placing ink printing on a 
commercial basis will be appreciated. 
Nevertheless there is positive evidence 
that sound reproduction from the Selen- 
ophone already reaches a quality not 
far less than the commercial disc with 
its many years of service. High fre- 
quencies are naturally the most difficult 
to reproduce since blurring during 
printing is bound to occur to a greater 
or lesser extent. It is stated, however, 
that this droop in the response curve 
may be adequately compensated for by 
the introduction of a response capacity 
input filter. 

Variable Width Track 

A preliminary consideration of the 
principles involved in this method indi- 
cates immediately that the variable 
width sound track must be adopted since 
it would be scarcely possible to repro- 
duce variable density with its multi- 
tude of graduations. 

Modulation of the photocell unit takes 
place by reflected light instead of trans- 
mitted, as in the case of the normal 
theatre projector. This involves a 
number of difficulties owing to straight 
light reflections but for the major part 
these have been overcome. 

An interesting feature of the appara- 
tus is that it employs a selenium cell of 
the well-known Thirring type. It would 
appear that the employment of this type 



of unit would be liable to accentuate 
the fall off in response at high fre- 
quencies. Nevertheless it will be fully 
appreciated that in view of recent de- 
velopments the selenium cell is by no 
means dead even in the talking picture 
world and may easily find a new source 
of outlet in this rival of the electric 
phonograph. 

The instrument itself already made 
into marketable form is not dissimilar 
in appearance to the ordinary phono- 
graph although it incorporates two 
turntables or drums. 

As soon as one length of sound track 
has been reproduced the relative posi- 
tions of the light focus and tape are 
changed automatically and the drums 
are reversed in direction of rotation. 
This cycle is continued until four sound 
tracks have been completed. 

Both Sides of Track May Be Used 

A further advantage 01 tne reflection 
method of modulation is that both sides 
of the track carrier may be employed 
if necessary. It is probable, however, 
that this last step on the path of econ- 
omy would not be necessary owing to 
the cheapness of paper as a medium and 
the probability that extra expense 
would be involved in storage between 
the two printing processes. 

While the fate of the Selenophone is 
still in the balance it seems a certainty 
that before much time has elapsed the 
disc record will have to suffer some 
radical if not revolutionary changes if 
it is to maintain its present popularity. 
After all, this is as it should be, for the 
disc has suffered very little advance for 
six years since the introduction of the 
electrical methods of recording. 



SPEECH AND MUSIC TRANSMITTED 
ON BEAM OF LIGHT 

RADIO and recorded music from a 
standard radio-phonograph instru- 
ment was transformed into a beam of 
light, transmitted to another radio 
receiver at the other end of the 
auditorium and converted back into its 
original form, at a demonstration 
staged recently by Dr. V. K. Zwory- 
kin, research engineer of the RCA- 
Victor Company. 

Following his lecture. Dr. Zwory- 
kin demonstrated the transmission of 
sound with a beam of light. Two 
standard Victor phonograph-radio 
instruments were used as the trans- 
mitting and receiving points, respec- 
tively. At the transmitting end, the 
radio was tuned in to a local radio 
station. The electrical impulses were 
passed through a transformer and con- 
verted into light by a neon lamp. The 
light from this lamp, focused by a lens, 
was then projected across the entire 
length of the auditorium to a mirror, 
which, in turn, reflected the light back 
across the room to the receiving end. 



APRIL, 1931 



Page 17 



Th. 



R 



omance 



of 



Televisi 



evision 



By L. C. Vipond 



WHEN I began research on 
television I was considerably 
surprised at two things : 
The first was that the princi- 
ples underlying seeing at a distance by 
electricity were known as far back as 
the early days of wireless telegraphy 
when radio telephony and radio broad- 
casting were unknown. The second 
was the eagerness with which experi- 
menters and certain large corporations 
had taken up this new art in an effort 
to hurry it on to its ultimate practical 
success. 

Now, two years later, it is more sur- 
prising to see the comparatively small 
progress that television has made when 
one considers the fanciful predictions 
that were made by the press and a 
number of scientists a few years back. 
However, there are various causes that 
are retarding television's progress. 

Jules Verne, French author of many 
scientific romances, accurately pre- 
dicted television as far back as 1870 in 
his famous "Twenty Thousand 
Leagues Under the Sea" which was 
written in that year. In that book he 
told how Captain Nemo, the mysteri- 
ous owner of the great submarine, had 
worked out the scientific application of 
seeing at a distance. 

Many decades have passed since 
the novelist's prophecy and during the 
intervening years, ambitious scientists 
and eager inventors have been striving 
to make television practicable. We 
realize now that radio television is an 
accomplished fact; from a dream it 
has become a reality. Television, like 
flying, had long been an enchanting 
hall in the dream-palaces of experi- 
menters and inventors and it is difficult 
yet to realize the importance and full 
significance of such an epochal 
achievement. 

In considering briefly the history of 
television it would be well to state that 
although its underlying principles were 



known to scientists many years ago, 
they were not applicable with the appa- 
ratus heretofore available. The main 
event leading to actual television was, 
of course, the transmission of photo- 
graphs by telegraph and later by radio. 

In 1925, there were several pioneers 
at work on the fascinating problem of 
transmitting photographs by wire and 
by radio. Of these pioneers, C. Fran- 
cis Jenkins in Washington, D. C, was 
perhaps the most successful. Although 
demonstrated long before this as en- 
tirely possible, it remained for Jenkins 
to show that television could also be 
made commercially profitable. 

It took five minutes or more to send 
one picture with Jenkins' early machine 
and in television at least eight or more 
images a second must be sent and 
received. 

While radio-photography was being 
developed to a fairly high degree of 
perfection several other developments 
took place in 1926 that were to prove 
even greater strides toward useful tele- 
vision, the goal that all were seeking 
to attain. 

The Photocell 

One of the most difficult problems 
heretofore had been to produce a de- 
vice that was sensitive enough to react 
to a shadow as the modern microphone 
responds to a whisper. The simple 
photoelectric cell had been in use for 
some time for the purpose of convert- 



Brief Review of the Begin- 
ning and of the Present 
Status of Television Engi- 
neering 



*Paper presented before the A. I. E. E. Branch, 
Louisville, Ky. 



ing variations of light into variations 
of electric current. The cell used up 
to this time had proved too weak and 
its response to light changes too slow. 
V. K. Zworykin, a physicist of the 
Westinghouse laboratory, succeeded in 
combining the ordinary photoelectric 
cell with a special form of radio 
vacuum tube amplifier in a single in- 
strument, producing an extremely sen- 
sitive "radio eye." This "eye" re- 
sponded to light variations with the 
astonishing rapidity of over one hun- 
dred thousand times each second. 

A short time after this, Jenkins 
demonstrated a machine for success- 
fully sending faint silhouettes of mov- 
ing objects by radio. This was made 
possible by using the newly perfected 
photoelectric cell in converting the 
highlights and shadows of objects into 
corresponding intensities of electric 
currents. 



In December 1926, Dr. E. F. W. 
Alexanderson, consulting engineer of 
the General Electric Company and of 
the Radio Corporation of America pub- 
licly announced that he had accom- 
plished the feat of seeing at a distance 
through the medium of electricity. 
However, the apparatus he used was 
somewhat unstable and also expensive. 

In spite of the attempts made and 
partial successes attained, television, at 
the beginning of 1927, was still re- 
garded as lacking in commercial possi- 
bilities. True it had been proved the- 
oretically promising, but all of the sys- 
tems that had been devised necessitated 
a costly outlay of apparatus and were 
also impractically delicate, compli- 
cated and in other respects unsatisfac- 
tory. 

Telephone Engineers Contribute 

Engineers in the Bell Telephone 
Laboratories have done much toward 
placing television on the plane it occu- 
pies today. It is stated that they were 
the first to make use of the neon glow 
tube and the scanning disc. This 
scanning disc is still the essential ele- 
ment in modern television transmitters 
and receivers and will continue to be 
until a better device is invented to take 
its place. Also, the Bell Laboratories' 
engineers discovered that a whole bat- 
tery of large photoelectric cells could 
be used to pick up the light variations 
instead of depending upon one small 
cell. The resulting increase in re- 
sponse was tremendous as compared 
with any method previously used. 

With the advent of the scanning 
disc and the neon tube a number of 
stations in the east began broadcasting 
television programs and hundreds of 
amateur experimenters began building 
receivers. All of this gave the new 
art the impetus it needed and at pres- 
ent several manufacturing companies 
have television receivers on the market. 

Breaking up the Image 

The underlying principles involved 
in television are comparatively simple 
and no doubt many students are fa- 
miliar with them. The first essential 
of this remarkable development is the 
division of the image to be transmitted 
into a large number of separate units. 
No one has yet found a means for 
transmitting a picture as an entity. 
Sound is a linear quantity, having only 
length, and only linear quantities can 
as yet be transmitted. A picture has 
length and breadth so it is obvious that 
it must be broken up into successive 
sections before it can be transmitted." 

The breaking-up process is accom- 
plished by passing a powerful beam of 
light through a spiral of tiny holes per- 
forated in a round disc. The rapidly 
turning disc is the scanning disc re- 
ferred to and it guides the tiny shaft 



Page 18 



PROJECTION ENGINEERING 



of light across the subject to be trans- 
mitted in a number of separate paths 
until the whole subject has been 
scanned. The spiral of holes is usu- 
ally arranged so that the subject to be 
televised is scanned once with each 
revolution of the scanning disc. The 
swift, sweeping pencil of light casts 
reflections of varying intensities that 
are caught by sensitive photoelectric 
cells placed in front of the image, 
which change into electrical impulses 
whose strengths vary in exact accord- 
ance with the amount of light received. 
The principle of the photoelectric cell, 
of the "electric eye," is known to most 
students of electricity and with this 
knowledge the principles underlying 
television should prove surprisingly 
simple. It should be sufficient to say 
that after the light variations have 
been changed into electrical impulses, 
these impulses are amplified and trans- 
mitted by means of the conventional 
radio transmitter. 

Of course the breaking-up process 
must be repeated a sufficient number 
of times each second to create the illu- 
sion of smooth action, just as in mo- 
tion picture projection a certain num- 
ber of images must be set up succes- 
sively on the screen each second. In 
both cases the appearance of smooth 
action is obtained through that peculi- 
arity of the human eye known as per- 
sistence of vision. In television the 
number of images sent each second de- 
pends upon the speed of the transmit- 
ter's scanning disc which, in most of 
the stations sending out television sig- 
nals at present, is fixed at 900 revolu- 
tions per minute. This is 15 images 
each second. 

The Neon Tube 

At the receiving station the televi- 
sion signals are picked up by means of 
the the conventional radio tuner and 
after being greatly amplified the sig- 
nals are translated back into light by a 
special lamp containing the rare gas 
neon. This lamp glows brightly or 
dimly in response to the varying in- 
coming signals. The glow of the neon 
tube has no lag such as is found in 
filament lamps. The response of the 
neon tube is practically instantaneous. 

After the signals have been received 
and changed back into light, the next 
step is to resolve these light variations 
into their proper positions in order to 
re-form the image, as presented before 
the transmitter. The scanning disc is 
again made use of and in this case it 
must have exactly the same number of 
holes around its outer rim as the disc 
used at the transmitting station. 

It is obvious that to obtain any re- 
sults at all the receiving disc must be 
rotated at exactly the same speed as 
the scanning disc at the transmitter. 
But even this synchronism of speed is 



not sufficient, the two discs must be ro- 
tating in exact step, or isochronism. 
This means that at the instant the shaft 
of light is passing through, say the 
twenty-fifth hole of the scanning disc 
at the transmitter, the light from the 
neon lamp at the receiver must also be 
shining through the twenty-fifth hole 
of its scanning disc. 

It has been found a very difficult 
problem to obtain exact synchronism 
and isochronism in television, but re- 
cent developments and refinements have 
greatly helped along this line. 

Increased Light for Scanning 

In connection with television re- 
ceivers there has been recently devel- 
oped and demonstrated by the General 
Electric Company at Schenectady a re- 
ceiver that does not make use of the 
neon tube to change the electrical im- 
pulses into variations of light. In a 
demonstration, this company made use 
of a projector having a high-frequency 
light valve controlling a local source 
of light. With this apparatus the engi- 
neers were able to use the incoming 
television signals to control the inten- 
sity of a powerful beam of light and 
thus project the images on a small 
screen. It had been impossible to pro- 
ject the images on a screen until then 
because the glow from a neon tube is 
comparatively weak. 

This is admittedly a big step forward 
in advancing television from the "peep 
hole," limited to a single observer, to 
the screen, which a number of persons 
may view simultaneously, as in motion 
pictures. But the detail of the images 
sent and received in this demonstration 
remained unimproved and as a result 
of having been so greatly enlarged the 
images appearing on the screen were 
somewhat coarse and subject to the 
same limitations as before. 

Evolution in any art is a slow 
process and the miraculous art of tele- 
vision, like the automobile and radio 
broadcasting, will gradually evolve into 
the perfected, product. Television is 
in its infancy. Its present stage of de- 
velopment is comparable to broadcast- 
ing in 1920 and 1921, before the boom 
in radio. While it may yet take many 
more years, television will be gradually 
simplified and improved until it will be 
universally adopted by the general pub- 
lic, to supplement radio receivers. 

Television offers an interesting field 
for the experimenter and engineer. It 
is possible now for anyone with fair 
mechanical and electrical ability to fit 
a television receiver together. Into this 
fascinating art enters not only elec- 
tricity, but much more in the realm of 
physics, as it deals with mechanical 
and optical, as well as with intricate 
electrical problems. 

Leading scientists and engineers all 
over the world in most of the great 



laboratories have been working for 
many years on the problem of televi- 
sion and although progress does seem 
slow it is probable that we, who are 
accustomed to miracles, are too im- 
patient. 

Given sufficient time, I am convinced 
that civilization is about to reap the 
fruit of this latest achievement of sci- 
ence and this world of ours will shrink 
again. Not only will television enter- 
tain and be of service to the public, but 
in warfare it will be an invaluable in- 
strument of offense and defense. Man 
in his onward progress has again 
reached out ond conquered, and his 
pace does not slacken as he passes on 
in search of new worlds to conquer. 



SOUND DISC SYNCHRONISM 

(Concluded from page 13) 
best of times and with the audience and 
the management waiting becomes some- 
thing of an ordeal. It can, however, be 
carried out fairly quickly by an experi- 
enced man. When the joint has been 
made it will not be necessary to re- 
project the whole of the picture prior 
to the break. Probably the best way 
out of the difficulty is to run the 
machine on fast variable with arc light 
doused and stage horns cut off until the 
breakage point is neared. The speed is 
then reduced to regular and at the criti- 
cal moment, the stage horn cut in and 
the douser opened. 
A 

SMPE MAKES SPECIAL STUDIES 
OF PROJECTION PROBLEMS 

THE Society of Motion Picture 
Engineers has begun a specialized 
study in all phases of motion picture 
projection and has appointed three sep- 
arate committees to carry out the work. 
The committees consist of the Pro- 
jection Practice Committee, the Pro- 
jection Theory Committee and the Pro- 
jection Screens Committee, with H. 
Rubin, W. B. Rayton and S. K. Wolf 
acting as chairmen of each committee 
respectively. 

The Projection Practice Committee 
is dealing with problems such as the 
ideal layout of the projection room and 
is collaborating with theatre architects 
to insure the most satisfactory location 
of the projection room. Other pro- 
blems under investigation are projec- 
tion room routine and maintenance, 
monitoring and control of sound in the 
theatre, improvements in projector 
design and accessories, film buckle, pre- 
vention of film mutilation, and fire pre- 
vention. The committee is composed 
of H. Rubin, chairman ; T. Barrows, 
S. Glauber, J. H. Goldberg, C. Green, 
H. Griffin, J. Hopkins, R. H. McCul- 
lough, R. Miehling, M. Ruben, F. H. 
Richardson, H. B. Santee and P. A. 
McGuire. 



APRIL, 1931 



Page 19 



Amplification in 
Sound Motion Picture 
Work 



Part 



By Charles Felstead* 



The Projectionist and the Engineer Will Find Here a 

Detailed Description of the Equipment Used in Present- 

Day Sound Amplifying Systems 



CONTINUING the article on amp- 
lification begun in the February 
issue of Projection Engineer- 
ing we may now consider the 
photoelectric cell. 

The Photoelectric Cell 

Inside of each film recording ma- 
chine a photoelectric cell is mounted 
behind the moving film in line with 
the light beam that shines through the 
"light valve" and forms a narrow strip 
of varying exposure (the sound track) 
on the film. Through the action of this 
light valve, the beam of light is modu- 
lated by the amplified speech current 
produced in the microphone by sounds 
on the stage. After exposing a strip' 
near the edge of the film in a degree 
directly proportional to the frequency 
and volume of the sound being picked 
up by the microphone, a portion of the 
light passes through the film and 
impinges on the sensitive surface of 
the photoelectric cell. Negative elec- 
trons are thrown out by the part of the 
sensitive photoelectric surface that is 
affected by the light, and the polarizing 
voltage that is applied to the PE cell 
causes these electrons to be drawn to 
the anode, thereby setting up a minute 
current flow in the PE cell circuit. This 
current flow is proportional to the 
quantity and intensity of the light fall- 
ing on the photoelectric surface. Since 
the light is from an incandescent lamp 

* Sound Engineer, Universal Pictures Corpn. 



of constant intensity, the current varies 
directly as the changes in the quantity 
of light that the moving ribbons of the 
light valve permit to pass. 

The Photoelectric Cell Amplifier 

This photoelectric cell is connected 
to the input of a special three-stage 
amplifier known as the PEC amplifier, 
that is mounted in a metal box just be- 
low the recording machine. The ampli- 
fier uses three small tubes of the "pea- 
nut" variety that are held in spring- 



suspended sockets, and has its own in- 
dividual plate battery, which also sup- 
plies the polarizing voltage to the pho- 
toelectric cell. The variable rheostat 
filament switch, and filament ammeter 
are mounted on the panel that carries 
the controls for the recording machine. 
The outputs of the two PEC amplifiers 
in each recording channel are connected 
to the contacts of the PEC relay. 

The monitor man normally leaves the 
two keys that control the relays in the 
off positions, and so he is monitoring 
directly from the bridging bus. How- 
ever, it is compulsory that at least once 
during each "take" he turn on the key 
that causes the springs of the monitor- 
ing relay to be thrown from the direct 
to the PEC side, and then by means of 
the other relay alternately listen 
through the monitoring horns to the 
outputs of the two PEC amplifiers. That 
will assure him that the sound is ac- 
tually being recorded on the film, and 
that no trouble has developed in the film 
recording circuit, such as a tube burn- 
ing out or the strings of a light valve 
breaking. 

There is a very considerable loss in 
electrical level from the bridging bus 
to the output of a PEC amplifier, and 
so, if there was no attenuation in the 
direct monitoring circuit, the output 
speech current from the PEC ampli- 
fiers, being of such a low electrical 
level, would not produce audible sounds 
in the monitor horns when the monitor- 
ing amplifier was adjusted to have the 
right amount of gain to operate from 
the bridging bus. The attenuator, 
which is similar to the ones used in 
the output circuits of the bridging 
amplifiers but which has a greater loss, 
is adjusted so that the speech current 
in its output is of the same level as the 
speech current in the outputs of the 
PEC amplifiers. It is only necessary 
then to raise the gain in the monitor- 
ing amplifier until the sounds created 




Fig. 1. Battery and generator sw 
recording i 



Courtesy Universal Pictures Corpn. 



itchboard for a two-channel sound 
retaliation. 



Page 20 



PROJECTION ENGINEERING 




lllllllllllllllllllll! Illlllllllllllllllllll 

Fig. 2. Inter- 

con nection 

panels. 



Courtesy Universal Pictures Corpn. 



by the horns are of a volume that is 
satisfactory to the monitor man. When 
the levels are properly adjusted the 
only noticeable change in sound when 
the relay keys are turned to the on po- 
sition is the addition of the "rush" 
noise produced in the PEC monitoring 
circuit by the passage of the film be- 
tween the light source and the PE cell 
and the slight hiss that is inherent in 
these cells. 

The Meters 

In the center bay of each amplifier 
channel there is mounted a meter panel 
containing three meters for reading the 
filament and plate currents of the tubes 
in the amplifiers. Two of the meters 
are for checking plate currents ; and the 
other is a filament ammeter. The high- 
range plate current meter is normally 
in circuit, but by means of a push-but- 
ton, the low-reading meter can be con- 
nected in circuit when a tube drawing 
a low plate current is to be checked. 
Two-wire conductors connect the me- 
ters with special plugs that fit the fila- 
ment and plate jacks in the amplifiers. 
The plugs are of two sizes so that there 
is no possibility that a plate meter will 
be plugged in the filament circuit of a 
tube and be burned out. 

There is a complicated jack field in 
the center bay of each two channel in- 
stallation, and there are also smaller 
jack fields in each amplifier bay. Prac- 
tically every piece of apparatus in the 
recording installation has jacks con- 
nected in its input and output circuits. 
The jacks are hooked together through 
the terminal blocks in such a manner 
that the channel is in normal operating 
condition when there are no plugs in the 
jacks. When testing is being carried 
on or when unusual combinations of 
amplifiers are desired for special work, 
"patch cords" which are short lengths 
of two-conductor cord ending in plugs, 
are used for making connection between 
the jacks. The main jack field in the 
center bay is for the purpose of con- 
necting the recording channels to sound 
stages other than the ones to which they 
are "normalled," — each channel being 



normally connected to a certain sound 
stage when no plugs are in the jacks. 
This arrangement permits four record- 
ing channels to take care of as many as 
eight sound stages, because it is not 
usual that all of the stages would be 
needed for recording at any one time. 
Another advantage of this arrangement 
is that if a channel that is in use breaks 
down, another one can be substituted 
for it in a few seconds, thereby avoid- 
ing the expensive process of holding up 
a production company. 

Distributing Frames 

The main distributing frame, or 
MDF, which was mentioned in the first 
article, is composed of a metal frame- 
work on which are mounted a large 
number of terminal blocks. Interme- 
diate distributing frames are installed 
in the monitor rooms and at strategic 
points in the recording building. Other 
terminal blocks are mounted at the bot- 
toms of the amplifier bays and when- 
ever bays and wherever several pieces 
of equipment are grouped together. All 
of the recording apparatus and the 
jacks are connected to terminals on these 
blocks, as are all incoming and outgo- 
ing circuits, and the circuits and ap- 
paratus are connected together in the 
proper manner by means of "cross con- 
nects," which are wire straps run be- 
tween the terminals on the blocks. This 
arrangement makes it an easy matter 
to change the permanent connections of 
the apparatus when the necessity arises. 
An elaborate intercommunicating tele- 
phone and signal light system is also 
connected to these terminal blocks. The 
signal lights are arranged so that they 
indicate when channels and stages are 
busy, when multiple jacks are in use, 
and other things. 

Battery Rack 

Across one side of the amplifier room 
is a six-foot high battery switchboard. 
A multiplicity of fused knife switches, 
which are connected in each of the bat- 
tery circuits in the installation, are 
mounted on this switchboard. There are 



also other switches for throwing the 
several sets of batteries from charge 
to discharge. Ammeters that read both 
charge and discharge are connected in 
all of the main battery circuits. High 
and low reading voltmeters are also 
mounted on the switchboard, as are the 
buttons that operate the starting relays 
for the battery charging generators. 
The batteries controlled by the switch- 
board are mounted in wooden racks in 
a battery room adjoining the amplifier 
room. Duplicate sets of all batteries 
are provided so that one set can be 
charging while the other set is in use. 
The batteries are of the storage type 
and are built in glass containers to per- 
mit the conditions of the plates and the 
amount of sediment in the bottom of the 
cells to be observed. The batteries that 
supply plate current to the tubes are 
about the size of the storage batteries 
used in automobiles ; while the filament 
batteries and the batteries that supply 
current to the exciting lamps on the 
recording machines are much larger. 
Considerable care must be exercised to 
keep the batteries properly charged and 
to see that they are always clean and in 
proper operating condition. The super- 
vision of the men who care for the bat- 
teries is one of the important duties of 
the engineer in charge of the ampli- 
fying equipment. 



TALKING PICTURE EQUIPMENT 
FOR PORTABLE USE 

{Concluded from page 15) 

oil is pouring over the bearings as long 
as the machine is in operation. 

This model is especially useful for 
colleges and institutions where light 
weight is required and the duty is not 
of the "all day" kind. It is very con- 
venient where it is desirable to give 
showings in different rooms ,or build- 
ings or for the industrial advertising 
field. 

Both of these models are of the 
overhead-loop or straight feed design. 
The overhead-loop machine has both 
reels on one common shaft in one maga- 
zine located within the projector case, 
while the straight feed design has both 
reels located in separate exterior maga- 
zines — one on top and one in front of 
the projector case. 

Four-roller fire traps are used and all 
other possible requirements are incorpo- 
rated in the design of both of these 
models for the purpose of meeting the 
laws of any state or country. 

Filtered, oil-damped flywheeled sound 
shafts are used and each has a separate 
takeup sprocket to' assure quality of 
reproduction of the most difficult num- 
bers. 

This equipment has been developed 
for and is sold exclusively by Bell 
Equipment Corporation, Suite 605, 729 
Seventh Avenue, New York City. 



APRIL, 1931 



Page 21 



Advances 
in Science 



By Dr. C. E. Kenneth Mees 



The Opportunities for Engineers, Physicists and 
Inventors Are Unlimited 



THE fact that the world in which 
we live is changing at a very 
high rate is, I think, obvious and 
undisputed. Within our own 
lifetimes we have seen changes in 
method and technique which will affect 
the economic and social organization 
of society to as great an extent per- 
haps as the whole of the changes made 
from the Neolithic period to the begin- 
ning of the Twentieth Century. 

At the present time, the rate of 
change is greater than any in the pre- 
vious experience of man, and it ap- 
pears to be still accelerating. The 
origin of this change is, of course, the 
development of our knowledge of 
nature, that knowledge which we clas- 
sify under the general heading of 
"science." As long as our increase in 
the knowledge of science continues to 
accelerate, the resulting change in 
social and economic conditions will 
also accelerate. 

At the present time, the proportion 
of human effort devoted to the acqui- 
sition of new scientific knowledge is 
increasing each year, but it is still only 
an infinitesimal part of the activities of 
mankind and only a very small part of 
the amount of energy which might be 
expended upon the development of sci- 
ence if that were generally thought to 
be worth while. 

It has recently been estimated, for 
instance, that the industrial research 
laboratories in the United States are 
spending a sum of the order of $100,- 
000,000 a year upon scientific research. 
It is certain that the universities are 
not spending as much ; but if we in- 
clude all available agencies, we might 

t Talk before the City Club, Rochester, N. Y., 
January 17, 1931. 

* Director of Research, Eastman Kodak Com- 
pany. 



perhaps reach a total expenditure of 
$200,000,000 a year on the development 
of scientific knowledge and its direct 
applications. 

Value of Research 

It is estimated that during the last 
ten years the developments due to sci- 
entific research have increased the 
wealth of every family in the United 
States by more than 25 per cent ot 
their income, while the cost of research 
has been less than $10 per family per 
annum. It would, therefore, clearly 
not be impossible to increase our ex- 
penditure on research if it were neces- 
sary or desirable to do so. 

A more immediate limitation to the 
development of science probably lies in 
the availability of men suitable for 
carrying on the work ; but although 
the number of such men is certainly 
limited, and it would be difficult to in- 
crease the number very rapidly or to 
an extent comparable with, the rate at 
which expenditure could be increased, 
there is still a very large number of 
men and women suitable for scientific 
work who for some reason or other are 
not engaged in it, so that the increase 
in the production of scientific knowl- 
edge is not likely to come to an end in 
the near future either for lack of 
funds or for lack of workers. 

The production of scientific knowl- 
edge produces changes of great impor- 
tance in our economic and social life, 
and the changes lag very much behind 
the production of science, so that as a 
general rule the science which is being 
applied today is not the science which 
is produced today but the science of 
which the fundamentals were discov- 
ered a number of years ago. As the 
rate of progress increases the period 



between a scientific discovery and its 
application diminishes, and, whereas it 
took us fifty years to apply Faraday's 
discovery of electromagnetic induc- 
tion, such discoveries as the amplifier 
tube have been applied on a world-wide 
scale within two decades, and at the 
present time we may perhaps be con- 
sidered as applying general and scien- 
tific discoveries of only ten years ago. 

The much greater production of sci- 
entific knowledge at the present time, 
however, means that the application of 
science to industry and still more its 
effects on our economic and social life 
will continue to increase even if the 
amount of scientific discovery does not 
increase in the near future and there 
is every probability that that also will 
continue to increase. 

No system which is changing at an 
increasing rate, and especially no sys- 
tem in which the product of the reac- 
tion increases the rate of change, can 
be stable. It is probably by analogy 
although it is not certain, that our 
present social system is in a completely 
unstable stage and that, after a period 
of violent change, it will settle into a 
new and stable phase which will endure 
until some new cause provokes another 
period of change. 

This is what has happened in history 
before. After the great changes of 
the Twelfth Century B. C, the eastern 
world stabilized for a long period. 
After the fall of the Roman Empire, 
the world settled into the stagnation of 
the Middle Ages. After the changes 
of the Fifteenth Century, a new and 
comparatively stable system was devel- 
oped throughout Europe, to be de- 
stroyed in its turn by the industrial 
revolution and the growth of modern 
science. What that stable system may 
be and how it can be stabilized, since 
we must assume that scientific discov- 
ery will continue, it is impossible for 
us to foresee, but it is certain that 
change can not continue at an ever in- 
creasing rate and that the end of revo- 
lution in any form is stability. 

Energy of the Sun 

The advance in our knowledge of 
the structure of matter has been of 
greatest value in connection with the 
light which it has thrown upon the 
production of energy by the sun and 
stars. It is generally held now that 
the source of the energy of the stars 
is the matter which they contain and 
that, either because of the form of 
that matter or because of the conditions 
in which it exists in the interior of the 
stars, it is being transformed into radi- 
ation, so that the sun is actually radiat- 
ing its own substance out into space 
and is losing weight at the rate of four 
million tons per second — this prodigi- 
ous amount, however, only reducing 
the weight of the sun by 1 per cent 



Page 22 



PROJECTION ENGINEERING 



in a hundred billion years. This has a 
direct relation to the future life of 
man, since it opens up vistas of new 
sources of power. 

At the present time, engineering-, 
which deals with the production and 
application of power, is utilizing the 
science of a hundred years ago. Most 
of our power comes from the burning 
of coal, the utilization of which in 
steam engines was related to the phys- 
ics of the seventeenth and eighteenth 
centuries. The electrical engineer is 
utilizing the discoveries of Faraday 
and his fellow physicists of the early 
nineteenth century, and so far the dis- 
coveries of physics which correspond 
to what has been termed the "new 
era," the era of "atomic physics," have 
found very little utilization by the 
engineer. The airplane and the auto- 
mobile depend upon the gas engine, 
and the general principles of the gas 
engine were well understood fifty years 
ago. 

The Electron Tube 

What are we likely to do when the 
new physics is applied? I doubt if 
any scientific man will dare prophesy 
in this field. The only thing that is 
certain is that there will be applica- 
tions of the new physics in engineering 
and that these applications will open 
up entirely new vistas and be radically 
different from all previous experience. 
In one narrow field some of the work 
of the new physics has been applied. 

The fact that a hot body gives off 
particles of electricity or that these 
electric units can be driven out of 
materials by the impact of light has 
produced the valve tubes and photo- 
electric cells which have enabled us to 
amplify electric currents and to trans- 
form light into electricity, so that there 
has been developed from these discov- 
eries the great modern amusement in- 
dustries depending on the production 
and amplification of sound. The radio 
and the talkies are a first earnest of 
what we may expect when the engineer 
is able to apply the physics of the 
twentieth century. 

The greatest revolution which sci- 
ence could produce in human affairs 
would of course come from an entirely 
new source of power. At the present 
time man-produced power is very 
costly and we have to economize it to 
the greatest possible extent. We can 
not transmit it to long distances be- 
cause to do so involves waste, and the 
natural order of things is that man 
always finds it necessary to avoid 
waste because his reserves are so lim- 
ited, whereas in nature the waste is 
prodigious and the resources are un- 
limited. 

In nature there are no efficiency 
engineers. If a factory were to start 
to produce fish, they would make tre- 
mendous efforts to ensure that a large 



proportion of all the fish started 
reached the eventual market. A loss 
of 20 per cent in the process of produc- 
tion would certainly grieve the engi- 
neers of the factory, but when nature 
produces fish, millions of eggs are laid, 
only a few thousand of which develop 
into fish at all, and only a few units 
into mature fish that can reproduce 
their kind. 

Again, if an engineer had organized 
the solar system, he would presumably 
have tried to get a sun so arranged 



| AUDIO FREQUENCIES IN C.P.S. | 



Cycles 

per 
Second 



32.7°8 
16,384 
10,000 



8,192 
5.000 



4,096 
2,560 

3.072 
3,000 



2,048 
2,000 
1.500 

850 
800 

600 

426.66 

256 

200 



128 
100 



80 

64 
60 
32 



27 
25 
16 



Beyond limit of audibility for g 

average person. 
Telephone silent with 40 volts on g 

receiver terminals. 
Considered ideal upper limit for g 

perfect transmission of speech = 

and music. 
Highest note on fifteenth stop. g 

Considered as satisfactory upper = 

limit for high quality trarsmis- || 

sion of speech and music. 
Highest note on pianoforte. 
Approximate resonant point of = 

ear cavity. 

Considered as satisfactory upper g 
limit for good quality transmis- g 
sion of speech. 

Maximum sensitivity of ear. 
Mean speech frequency from g 
articulation standpoint. 

Representative frequency tele- g 
phone currents. 

Orchestra tuning. 

Considered as satisfactory lower g 
limit for good quality transmis- g 
sion of speech. 

Considered as satisfactory lower g 

limit of high quality trarsmis- g 

sion of speech and music. ; g 

Lower note of average mar s g 
voice. 

Lowest note of cello. 

Lowest note of average church = 

organ. _ _ § 

Considered ideal lower limit for = 

perfect transmission of speech § 
and music. 

Lowest note of pianoforte. 

Lowest audible sound. Longest g 
pipe in largest organ. 



■B. S. Cohen, Proc, I. R. E., March, 1928. g 



that its radiation was directed towards 
those of the planets that it was consid- 
ered necessary to warm and that the 
remainder of its radiation would be 
conserved; but the actual sun which 
warms us so efficiently radiates its 
energy in every direction and wastes, 
if we may use the word, 2.y 2 million 
times as much energy as falls on the 
planets. 

The whole of nature is made on this 
plan. Almost all the matter in the 
universe is at a temperature quite un- 
suitable for life: probably nearly all 
the matter is far too hot, and practi- 
cally all the rest is far too cold. The 
amount of matter in the whole universe 
which is at a temperature between the 
freezing and boiling points of water, 



in which range alone life as we know 
it is conceivable, is probably less com- 
pared with the matter in the universe 
than a single speck of dust compared 
with the earth. 

Now, if we can tap the sources of 
power which are available in the stars 
and change the sun that warms us, 
then we can change our policy. If we 
could, for instance, break down matter 
and turn it into radiation, power would 
be available in limitless quantities, and 
we could afford to waste it as nature 
does. We could warm our homes and 
propel our vehicles and run our ma- 
chinery by radiation of which only a 
small proportion achieves the end that 
we desire and most of which was 
thrown away as far as actual utiliza- 
tion is concerned. 

At the present time the physicists 
give us very little encouragement in hop- 
ing for new sources of power. Never- 
theless, it is incredible to me that 
sooner or later we shall not find some 
method of tapping the sources of 
power which are the ultimate sources 
of the universe. All the power we 
have comes eventually from the sun 
and must come from the breakdown of 
the atoms. It is incredible that we 
shall not sooner or later be able to 
produce that breakdown. 

Turning from physics to chemistry, 
it seems certain that we can build up 
the whole reality of the carbon com- 
pound, starting with water, air and 
coal. The future supply of chemical 
materials for the human race, there- 
fore, depends primarily upon the sup- 
ply of coal, and while the quantity of 
those which can be used is limited, 
since the size of the earth itself is lim- 
ited, it is very large. Nobody can 
make any accurate estimate of the 
time for which the coal supplies will 
last us, but it must be measured in 
hundreds of years if not in thousands, 
and to be concerned about the future 
supply of a material available for so 
long calls to one's mind the concern 
of the British people a little more than 
a hundred years ago when they were 
afraid that the oak necessary for the 
building of battleships would be ex- 
hausted. Until the exhaustion of a 
material is within one hundred years, 
it is unnecessary and often undesirable 
to be concerned about it. The prob- 
ability is that, by the time the world is 
running out of its coal supply, some 
other source of power will have been 
found. 



Adding Loudspeakers and 
Film Sound Recording Systems 
are the titles of two of the 
technical articles to appear in 
the May issue of PROJECTION 
ENGINEERING. 



APRIL, 1931 



Page 23 



BLUE SEAL HEAT RESISTING 
IMPROVED FILM TRAPS 

FOR SIMPLEX PROJECTORS 



MADE OF AN IRON ALLOY 

Guaranteed not to Warp under the intense heat 

of the Arc Spot. A necessity for the Perfect 

Projection of "Sound Pictures" 

B-16 Film Traps with Sliding Double 
Round Corner Apertures, One 
Aperture for Disc and Silent Film 
and one cut Proportional for 
Movietone Film to be used with 
our Adaptors $24.00 

B-17 Sliding Double Aperture Plate. 6.00 

B-24 Film Trap with individual mats 
for silent, movietone, and magna- 
scope effect. Traps complete with 
all mats 24.00 

B-20 Master Plate to hold mats sta- 
tionary 1.50 

B-21 Standard Aperture with Square 

Corners 1.50 

B-22 Proportional Movietone Aper- 
ture with Square Corners. 1 .50 

B-23 Blank Mat (CAN BE CUT ANY 

SIZE APERTURE) 1.50 



Dl 




BI7 



j;f 


[ 

J 








[ 




• 


— 










I 


J J 


! 



BI6 



B23 




PORTABLE 

AND 

PERMANENT 

FIRE -PROOF 
PROJECTION ROOMS 



Bot.h portable and 
permanent type 



STANDARD SIZES 



4 ft. 
6 ft. 

5 ft. 
9 ft. 
9 ft. 



x 6 ft. 
x S ft. 
x 9 ft. 
x 12 ft. 
x 14 ft. 



x. 7 ft, 
x 7 ft. 
x 7 ft. 
x 7 ft. 



iy 2 
iy 2 
iy 2 
1% 



x 7 ft. iy 2 



in. high 

in. high 

in. high 

in. high 

in. high 



THESE booths are made of 1/^" thick transite with angle iron I'/j" x 
I'/t" x 3/16". The panels are interchangeable and bolted together 
with stove bolts. The seams are filled with transite cement. The floor 
sheets are %" thick asbestos. The Underwriters throughout the country 
have approved these booths, as well as the fire and building departments 
of all cities. Special booths built to conform with the Rules and Regula- 
tions of the Steamship Inspection Service on United States Shipping Lines. 



RLUE SEAL PRODUCTS CO.. Inc. 



260 WYCKOFF ST. 



Distributor for Johns-Mansville Asbestos Products. Also Manu- 
facturer of Motion Picture Accessories since 1913 

WRITE FOR CATALOG OF BLUE SEAL PRODUCTS 



BROOKLYN, N. Y. 



Page 24 



PROJECTION ENGINEERING 



New Developments 

and 

News of the Industry 



FILM REELS 

A new series of sound film reels is being 
marketed by the Universal Electric Welding 
Co. 

These reels are spot welded, have no 
brazing screws, clamps or paint. Sizes vary 
from 1 6mm. to 70mm. in 1,000 and 2,000 
foot capacities. 

Aside from their rugged construction and 
light weight, the reels are designed to offer 
the least film friction, thus adding long life 
to the print by eliminating possibility of 
film damage. 

A 

PRESTO RECORD MAKER 

An entirely new conception of home en- 
tertainment, Presto Record Maker, makes 
records instantly, right in the home or office. 

Attaches to any radio _ receiving set, 
thereby forming a combination for playing 
the record back as on a radio phonograph 
combination. One of the many features of 
this device is that it cuts and grooves its 
own records. It does not use pregrooved 
records. 

With Presto, homes are transformed into 
recording studios. Permanent records can 
be made of baby's voice, personal expres- 
sions or musical and other offerings. 
Records can also be made direct from 
broadcast reception. 

Presto uses smooth discs, 6 inch, 7H 
inch, 10 inch and 12 inch in diameter. 
Records are made of aluminum alloy and 
are unbreakable. 



SYNCHROFILM IN PRINCESS 
THEATRE 

Weber Syncrofilm sound-on-film equip- 
ment was chosen by the management of the 
Princess Theatre, 39th St., and Broadway, 
New York, after a thorough investigation 
of the independent field, and the results are 
up to standard in every respect. The job 
was done in record time, as the house 
closed its stage runs, with the picture 
booked less than a week later. The instal- 
lation was supervised by J. A. Tannenbaum, 
Inc., eastern sales representatives for 
Weber Machine Corp. 




Lens turret 



A TRIPLE LENS TURRET 

For Film, Disc and Magnascope 

A new triple lens turret for motion pic- 
ture projectors has been placed on the 
market. 

This turret may be easily and quickly 
assembled to any Simplex projector me- 
chanism. It will at once be apparent that 
by the use of this turret all projection prob- 
lems affecting lens changes are eliminated. 
Each of the three lens mounts may be 
separately adjusted both vertically and 
laterally and each may be separately 
focused ; also, these lens mounts accommo- 
date all makes and focal lengths of lenses 
either half or quarter size. It is only 
necessary to insert, adjust and focus three 
lenses of the desired focal lengths after 
which any one of the three may be instantly 
swung onto the optical axis. One lens of 
the proper focal length may be used for 
silent or sound-on-disc prints, the second 
for sound-on-film, and the third for Mag- 
nascope or other types of effects. Where 
sound-on-disc is not in use, one of the lens 
mounts may be equipped for Magnascope, 
and another for some other particular ef- 
fect, while the third remains for sound-on- 
film projection. It is obvious that any 
number of combinations of lenses may be 
used for different purposes and it becomes 
unnecessary to slilp lenses in and out of the 
mounts during an entire performance. 

The turret proper is mounted in a sub- 
stantial frame on four 90 degree V grooved 
rollers with provision for taking up all end 
and radial play in rollers, thereby provid- 
ing a free-turning turret which is rigidly 
supported and free from shake and vibra- 
tion. Positive audible stops have been pro- 
vided for each projection position by means 
of index pins and a tapered lock so that 
normally but one lens at a time may be 
swung into position. 

Due to the design of this unit none of 
the fire prevention devices have been re- 
moved from the mechanism and the fire- 
proof properties of the projector have, 
therefore, in no way been impaired. 

With the turret a new film protector 
and gate latch assembly 
are furnished, the use of 
which eliminates the neces- 
sity for the projectionist to 
place his hand within the 
mechanism when closing the 
gate while threading. The 
new lever release comes 
through the film protector and 
is very handily located. A 
slight pressure on the release 
button immediately closes the 
gate. A mirror arrangement 
is also provided on the rear 
of each lens chamber by means 
of which the aperture may be 
observed for checking up on 
framing after film is threaded 
in place. 

No difficulty will be experi- 
enced in attaching it to the 
mechanism, and it is not nec- 
essary to cut away any part 
of the mechanism whatsoever. 
As stated, all half size 
lenses of standard dimensions 
may be readily inserted and 
clamped by the entire inside 
diameter of the mount. Where 
quarter size lenses are used it 
is necessary to use quarter 
size adapters. 



CUTLER HAMMER DIMMERS 

The illustration herewith is of the Sim- 
plicity dimmer manufactured by the Cutler- 
Hammer Company, Milwaukee, Wis. The 
plates used in dimmer equipment may be 
arranged with the operating levers assem- 
bled either above the plates or below them. 




In many installations the plates are located 
behind or away from the switch-board. The 
methods of mounting vary. 



OPERADIO MANUFACTURING 
COMPANY 

The Operadio Manufacturing Company 
of St. Charles, Illinois, has opened offices 
and display rooms at 116 West 65th Street, 
New York City. This location is temporary 
until permanent location can be obtained. 

Paul R. Fernald has been appointed 
manager of the New York office. He will 
have full charge of the sales for the New 
England territory as well as that of the New 
York. Mr. Fernald has been connected with 
the radio industry since its infancy, and is 
well known in the New York territory. 

The Operadio Manufacturing Company, 
manufactures a comprehensive line of ma- 
terial for sound projection and speakers in 
all their branches, and is well equipped to 
supply the needs of the trade using these 
materials. 



RACON SUES MACY 

The Racon Electric Company, Inc., has 
instituted suit in the U. S. District Court, 
Eastern District, against the Macy Manu- 
facturing Company for manufacturing horns 
infringing on U. S. Patent No. 1,781,489, 
and has also instituted a separate suit 
against one of the latter Company's custom- 
ers for using these infringing horns. 

The Racon Electric Company, Inc., states 
that it intends to protect its patent rights, 
and will hold all infringers responsible for 
the use of infringing horns, whether they 
be manufacturers, jobbers, dealers, or users, 
such as individual theatres and dance halls. 



MAGNAVOX COMPANY 

The Magnavox Company of Chicago ad- 
vises that the settlement of the suit of 
that company against Frederick H. Thomp- 
son Company of San Francisco and the 
Grigsby-Grunow Company of Chicago. 

The settlement made by the Grigsby- 
Grunow Company involves a substantial 
down payment, and a royalty on each and 
every dynamic loud speaker manufactured 
in future. 

The company will shortly announce a 
new and improved loudspeaker for which 
patent applications have been filed. 



APRIL, 1931 



Page 25 



FOREST 

RECTIFIERS 




/ 


FOR 






- 


Hjgj 


- - ■- 


''?•' ' 



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. 
/ \. 

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

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 M Newark, N. J. 




CHECKS 

OUTPUT 

of SOUND APPARATUS 

WESTON model 

571 



The portable Model 571 OUTPUT METER is an in- 
valuable instrument to projectionists for checking 
sound apparatus. 

It measures directly the voltage output of the sound 
apparatus at speakers or at any other point in the cir- 
cuit. It is exceptionally useful for checking the relative 
volume of speakers: for determining the relative gain 
of tubes and for determining fader settings. 

The Weston OUTPUT Meter, when used in the pro- 
jection room, provides a visual indication of the sound 
level in the auditorium. In this way. the correct vol- 
ume of sound can be dependably predetermined for 
different capacity audiences from previous meter read- 
ings taken with audiences of various sizes. 

This method eliminates guess work and furnishes im- 
mediate indication of the least perceptible variation of 
the output of the sound apparatus. Thus the change 
over to the reserve circuit may be made without annoy- 
ance to the audience. 

These uses alone make Weston Model 571 OUTPUT 
METER invaluable to modern high-quality sound pro- 
jection. This instrument is moderately priced and will 
. pay for itself in a short time. 

Model 571 consists of the Weston Model 301 A.C. 
^ oltmeter of the Rectifier type with a constant imped- 
ance of 4,000 ohms. Its five ranges, 1.5/6/15/60/150 
volts, selected by means of a dial switch, are brought 
out to two binding posts. The instrument is enclosed 
in a sturdy, black bakelite case. Size: 5% x 3% x 2 l / s 
inches. Weight: 1 pound, 10 ounces. 

-:>| Write for Circular RR |> 

WESTON ELECTRICAL INSTRUMENT CORP. 

608 Frelinghuysen Avenue Newark, N. J. 



Page 26 



PROJECTION ENGINEERING 



THE RECORDOGRAPH SOUND, 
DIRECTLY RECORDED 

Important advance has been made in re- 
cent months in the development of sim- 
plified equipment for the direct recording 
of sounds for immediate reproduction. 

Originally, tin foil was employed to re- 
ceive the sound wave voice impressions. 
This was followed by wax cylinders. In 
recent months the process of recording has 
been improved so that now celluloid, gelatin 
and aluminum and its alloys serve this 
purpose to better advantage. 

In playing back the record (reproducing 
the impressions) there is used a needle 
softer than the material of the record. This 
is so that the bulk of the wearing away 
will be on the replaceable needle. At 
present cactus fibre and bamboo are favored 
for needles. 

In the process of recording a turntable 
is operated by a powerful motor, a feeding 
device to guide the cutting head in the 
conventional spiral form, an amplifier and 
associated speed and volume control. A. 
playback arrangement can be mounted in 
the same cabinet, using the same turntable 
and motor for reproduction. The same 
amplifier is used. For the cutting head a 
loudspeaker is substituted, and for the 
pickup, a microphone. By the movement of 
a small switch an instantaneous change- 
over is effected from recording to play- 
back. 

These outfits are available _ in portable 
form and one model has associated with it 
a camera for making moving pictures simul- 
taneously with the sound recordings. 

An excellent type of recording and repro- 
ducing machine is the Recordograph manu- 
factured by G. J. Badgley, 106 West 46th 
St., New York. 



AMERTRAN ANNOUNCES NEW 
SOUND SYSTEM PANELS 

A new and complete line of AmerTran 
sound system panels has just been an- 
nounced by the American Transformer 
Company, 178 Emmet Street, Newark, N. J. 
These panels are made for fourteen dif- 
ferent applications and may be assembled 
in various combinations on standard mount- 
ing racks to make up complete sound sys- 
tems for every conceivable requirement. 
The panels have been designed to permit 
extreme flexibility so that standard apparatus 
may be supplied promptly for every pur- 
pose and so that the equipment may be en- 
larged or reduced whenever new conditions 
make a change advisable, the latter being 
possible without loss of time and at a mini- 
mum of expense. 

AmerTran panels are of rugged construc- 
tion and have been designed to meet the 
most exacting requirements. In all cases 
the apparatus is mounted on solid aluminum 
panels of standard (19 inches) width but 
varying in height in 1 54 inch multiples, the 
edges being notched to facilitate assembly 
in the most convenient position on standard 
mounting racks. The fronts of the panels 
are scratched-brushed and clear lacquered, 
and dust covers are provided on the rear 
to protect apparatus and for the safety of 
the operator. Knockout boxes for BX wir- 
ing are also included on all dust covers to 
comply with Fire Underwriters' regulations. 



BEST CARBON SAVER 

The Best Devices Co., 200 Film Building, 
Cleveland, Ohio, manufactures the carbon 
saver herewith illustrated. This permits the 
projectionist to get at least one more reel 
from each set of stubs. Made in 7, 8, 9, 
10, 12 and 13 mm. sizes. 



ADVERTISING PROJECTOR 

The new Auto Cinema sound-on-film 
advertising projector, product of the Auto 
Cinema Corporation in collaboration with 
RCA Photophone, Inc., was demonstrated 
before a group of representatives of motion 
picture trade and technical publications at 
the former corporation's offices in the Gen- 
eral Motors building, No. 1775 Broadway 
on March 11, last. 

Enclosed within an attractive cabinet 
which stands about five feet six inches high 
and which is approximately three feet 
square, the sound reproducing equipment, 
comprising the projector, amplifier, motor 
and six-inch loudspeaker, operates as a unit 
from power supplied from a lamp socket. 
The picture is projected upon a transparent 
screen eighteen by twenty-two inches in 
dimensions which is located at the top of 
the cabinet. 

An outstanding feature of the apparatus 
is that the film may be projected indefi- 
nitely. This is made possible by means of 
an endless re-winding device upon which 
the Auto Cinema Corporation has been 
granted patent rights in the United States 
and Canada. At the demonstration a num- 
ber of sound trailers and what might be 
classified as "short short" subjects were 
projected expressly for the purpose of em- 
phasizing the importance of this feature in 
connection with the reproduction of trail- 
ers for current and forthcoming attractions 
in the lobbies of theatres or advertising 
subjects in hotels, railroad stations or other 
public places. 

The sound attachment was developed in 
the engineering laboratories of RCA Pho- 
tophone, Inc., to which the Auto Cinema 
Corporation had taken a model of a silent 
projector into which the endless rewinding 
feature had been fabricated. With the only 
difference being in the size of the objects 
upon the screen, both projection and sound 
compared favorably with the sound and 
projection obtained on standard size RCA 
Photophone reproducing equipment. 



VALLEN AUTOMATIC SCREEN 
MODIFIER 

As its name implies, the modifier is used 
in connection with wide size films. E. J. 
Vallen devoted more than three years time 
to its perfection before announcing the 
device to the trade. 

In construction it is extremely simple and 
exceptionally rigid. The steel framework is 
built like a skyscraper and is positively safe. 
This framework supports and contains all 
modifying apparatus. 

The entire unit is electric motor driven, 
simply operated by a single button, push- 
button station, which provides instantaneous 
starting, stopping and reversing, and because 
of the remote control switch, can be con- 
trolled from the projection room. Quiet 
operating electric motors were specially 
designed for this application. Positive 
chain drive provides perfect synchronism 
and noiseless operation. The flameproof 
velour curtains move smoothly and evenly 
from the sides and top, contracting or 
expanding the screening surface at the will 
of the operator. A truss at the top and 
battons on either side, to which velour is 
securely fastened, assure an absolutely 
straight modifying edge line. 

Vallen automatic screen modifier can be 
easily installed without changes or altera- 
tions to the stage and occupies no space 
beyond the screen frame it embodies. The 
curtains are accommodated at either side on 
rollers and brailled at the top, making the 
unit unusually compact. 

Vallen automatic screen modifiers have 
been installed in many theatres throughout 
the country. Complete description of equip- 
ment and prices may be had from Vallen 
Electrical Co. Inc., Akron, Ohio. 





Best carbon saver. 



UNDIRECTIONAL SPEAKERS 

The loudspeaker herewith illustrated is 
manufactured by The Operadio Manufac- 
turing Company, St. Charles, 111. This is 
an electrodynamic air column speaker, fur- 
nished both in outdoor and indoor types 
for all public address purposes. 



375 WATT-75 VOLT 16 MM. 
PROJECTION LAMP 

The Victor Animatograph Corporation, 
Davenport, Iowa, announces that the new 
375 watt-75 volt lamp can be used in any 
Model 3 Victor cine'-projector that is 
equipped with the No. 10 Victor lamp rheo- 
stat, by having a slight change made in the 
rheostat resistance. 

It is only necessary to return the rheo- 
stat to the factory as no change is required 
in the projector. A charge of $5 is made 
for changing the resistance in the rheostat. 

After the revision is made, the rheostat 
can be operated with 250 watt-50 volt, 165 
watt-30 volt and 375 watt-75 volt lamps. 
Also, the rheostat can be disconnected to 
permit the use of 200 watt-100 to 120 volt 
lamps in the same projector. Victor thus 
offers the widest range of lamp inter- 
changeability of any manufacturer in the 
field. 



PHOTOCELLS 

The G-M Laboratories, Inc., announce 
three new sizes of Visitron type "A" pho- 
toelectric cells. These additions bring the 
number of sizes and shapes of standard 
Visitron type "A" cells to a total of seven, 
which constitutes the most complete line of 
(photoelectric cells manufactured in the 
United States. 

There is a G-M Visitron suitable for use 
in every type of sound equipment manufac- 
tured in America. Their high sensitivity, 
low operating voltage, stability, and long 
life make Visitrons a valuable component 
of all sound systems and industrial appli- 
ances of every kind in which light sensi- 
tive cells are used. 



THE CUE-METER 

A versatile and indispensible accessory of 
prolperly equipped projection rooms is the 
cue-meter manufactured by the Theatre 
Engineering Service Company, 1442 Beach- 
wood Drive, Hollywood, Cal. This device 
indicates the correct time to start the motor 
and make changeover, and gives cue indi- 
cations of all other operating essentials. 



A GOOD AMPLIFIER 

The Model RV amplifier of the General 
Amplifier Co., 27 Commercial Ave., Cam- 
bridge, Mass., is a two stage a-c. operated 
voltage amplifier employing one -27 tube 
and two -45 tubes connected in push-pull. 
Due to the fact that it employs -45 tubes in 
the output, it may be used as an output 
stage where the power output requirements 
are of a low value, delivering in this respect 
approximately 4 watts of energy. 



APRIL, 1931 



Page 27 



The PAST, The PRESENT, The FUTURE ! 

» having been tried it cannot be denied » 



Light beam less 
than .0005. 



H. A. impedance 
output will be 
matched to your 
present main am- 
plifier. 

Disc to film change- 
over. 

Shielded P. E. Cell. 

Special super-con- 
densed optical sys- 
tem (fully covered 
by patents) repro- 
duces variable area, 
density or squeeze 
track. 



Wearing surfaces 
chromium plated, 
chain driven. 




Syncrofilm may be obtained for any 
make and style projector. Write 
for prices. 



SYNCROFILM 

SOUND-ON-FILM reproduction is second 
to NONE. 

Designed and engineered by men who 
have studied every intricate problem . . . 
built of the finest materials obtainable, 
easy to operate and service, that is 
the reason for SYNCROFILM'S supe- 
riority. It is up-to-the-minute in every 
detail. 



Export Dept., 
15 Laight St., N. Y. C. 



WEBER MACHINE CORP. 

59 Rutter Street 
Rochester, N. Y. 



Cable Address 
"ARLAB," New York 



The Most Famous 

PROJECTION BOOKS 

In The World 



« 



Handbook of Projection" 

(5th edition) 

By F. H. Richardson 

In 1910 Mr. Richardson wrote the 1st Handbook 
a a of Projection. It was a sell out. 2nd, 3rd and 
4th editions, each bigger and more successful 
have followed. The present 5th edition in three 
• separate volumes is the culmination of years of 

intensive effort. 

These books are being used by projectionists and theatre 
managers all over the world to secure improved results. 

Richardson knows the problems of the field — meets the 
men on their own ground. His books reflect a practical 
knowledge of Just what information is needed. Recently 
he completed a 17,000 mile trip through the U. S. and 
Canada in the interests of projection. 

CONTENTS 
Volumes I and II are devoted entirely to the general sub- 
ject of projection and everything related to it. Volume III 
deals exclusively with sound projection. All are profusely 
illustrated and contain over 1,400 pages of projection 
information written so you can understand it clearly. 
Each volume contains Richardson's famous question and 
answer index giving immediate information to hundreds of 
different problems. 

Send for this finest of projection libraries today. 
USE COUPON TO ORDER 

CHALMERS PUB. CO., 516 Fifth Avenue, New York, N. Y. 

Enclosed find (check) (money order) for $10.25. Send Richardson's 3 
volume Handbook of Projection to 



Name 



25 years of actual 

EXPERIENCE 

THAT'S WHAT COUNTS ! 

DESIGNING 
PLANNING 
BUILDING 

No Matter What 
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either visual or 
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. . . home record- 
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eras, etc., our 25 
years of successful experience assures you of 
the finest engineering skill from the incep- 
tion of an idea to the delivery of the finished 
product. 

Let Us Solve Your Designing or Manufacturing Problem! 

G. J. BADGLEY 

106 West 46th St. New York, N. Y. 

Phone Bryant 9 — 4351 




I 



The Recordagraph, Home 
Recorder, designed and 
manufactured by 6. J. 
Badgley. 



] 



Page 28 



PROJECTION ENGINEERING 



CINEGLOW 

the 3 element 
recording lamp 

(patents pending) 



y£-'^~ 



ACKNOWLEDGED THE BEST! 

For Optical or Contact Slit. 
For Positive or Negative Film. 
For Any Standard Glow Lamp 
Circuit. 



CONSISTENT 



RELIABLE 




Maximum Volume — Abundant 
Exposure — Without Distortion 



PRICES 

Type T9 — 6 inches long — $50 each 
Type T8 — 4 inches long — $40 each 
Special discounts in quantities. 



BLUE SEAL 
SOUND DEVICES, 



Inc. 



130 W. 46th STREET. NEW YORK 



MEYER 

LENSES 



The discriminating cinematographer, 
interested in accurate color rendi- 
tion, appreciates the superb correc- 
tion of the Hugo Meyer Plasmat 
. he appreciates the deep, 
pictures on the screen 
wherein each object stands out in 
stereoscopic relief — natural and 
lifelike ... In the calculation of the 
Plasmat Lenses, a fuller correction 
of the primary colors of the spec- 
trum has been attained. This ac- 
counts for the greater efficiency of 
the Plasmats in photographing red. 



series 
plastic 



Kino Plasmat f:1.5 (focal lengths to 3y 2 ") 
The new Alakro Plasmat f:2.7 and f:2.9 

We welcome inquiries from manufac- 
turers of cameras and designers of ap- 
paratus on standard or special optical 
equipment. 

HUGO MEYER & CO. 

245 West 55th St., New York 

Works: Goerlitz, Germany 



BOOKS PERTAINING TO 
SOUND MOTION PICTURES 

SOUND PICTURES 

By CAMERON and RIDER 

The Latest, Largest and Most Comprehensive Book on the Subject 
Published. Introduction by WILLIAM F. CANAVAN, International 
Pres. I.A.T.S.E. M.P.M.O. 1,100 PAGES - - - 500 ILLUSTRATIONS 

Explains in detail the construction, operation and care of 

sound recording and reproducing equipment. A complete 

Guide for "Trouble Shooting." 

PRICE $y.50 

MOTION PICTURES WITH SOUND 

By JAMES R. CAMERON 
Introduction by WILLIAM FOX 

The book covers the subject from A to Z in such a manner 

that the subject is easily understood. Contains over 400 

pages and 150 diagrams and photographs. 

PRICE $g.00 

ENCYCLOPEDIA ON SOUND PICTURES 

By JAMES R. CAMERON 

Here's a book that will answer all your sound motion picture 
questions. 336 pages with over 2,000 subjects. 

PRICE $0.50 

MOTION PICTURE PROJECTION 

By JAMES R. CAMERON 
Introduction by S. L. ROTHAFEL "ROXY" 

A book of 1204 pages now in its fourth edition, fully illus- 
trated with over 500 diagrams and photographs. Covers the 
subject of motion picture projection and equipment neces- 
sary for same. Used for the past 1 4 years throughout the 

world as "The Standard Authority." 

PRICE $g.00 

CINEMATOGRAPH ANNUAL 

675 pages 300 diagrams 48 page pictorial section. 

Written by forty of the country's greatest sound experts. 

PRICE $g.00 

TALKING MOVIES 

By JAMES R. CAMERON 

A history of the "Talkies" since 1900. 

PRICE $1.50 

AMATEUR MOVIE CRAFT 

By JAMES R. CAMERON 

A book dealing with the making and projecting of 16' m/m 

motion pictures. 

PRICE $1.00 

You Can't Go Wrong With a Cameron Book 
CAMERON PUBLISHING COMPANY 

Manhattan Beach, Brooklyn, N. Y. 



APRIL, 1931 



Page 29 



Hoffmann - Soons 




The Only Union Made Rheostat 



We Build 


Rheo- 


stats for 


Special 


KfQiiirf ments. 


C o m m u n icate 


With 


Us Di- 


\ rect. 


There 


\ Is 


No Ob- 


\N ""•'• 



Every known quality necessary in producing perfect projec- 
tion is embodied in perfection rheostats. 



PERrKTION 



Recognized as the highest standard everywhere 

[Sold by all branches of the National Theatre "71 
Supply Co., Sam Kaplan, New York, and by your 
dealer. JJ 



R 



Now equipped with 
solderless adjustable 
lugs to take wire size 
from No. 4 to 4/0 

without additional ELECTRICAL & ENGINEERING CORPORATION 



HOFFMANN - SOONS 



387 FIRST AVE., NEW YORK 



HEOSTATS 



DIRECT READING 




TYPE 586 Power-Level Indicator 

An open clearly marked decibel scale makes 
the General Radio TYPE 586 Power-Level 
Indicator a truly direct-reading instrument. 
The time saved and the freedom from costly 
mistakes such a scale insures are advantages 
readily appreciated by the monitoring oper- 
ator in the broadcast and recording studio. 

If you are not familiar with this instrument, 
a request on your business letterhead will 
bring you a catalog description. Please ask 
for Bulletin 932-P. 

GENERAL RADIO COMPANY 



Offices 

CAMBRIDGE A, 



Laboratories Factory 

MASSACHUSETTS 



o hum, noise 




FOREST 
RECTIFIER 



Leading Sound Recording Studios, Theatres, 
and Laboratories where unfaltering current 
supply is required use FOREST — because 
it is superior. 

Adaptable to all sound equipment — inter- 
changeable with your present storage bat- 
tery — several types. 




Just tarn the switch to con- 
vert a 110 or 220 v. a-c. 
into fully filtered d-c. 



FOREST ELECTRIC 
CORP. 

New and Wilsey Steets 
Newark, N. J. 



Page 30 



PROJECTION ENGINEERING 



F. S. C. 

GENUINE OPTICAL CROWN 

GLASS PLATES 

Enclose all Portholes for Sound Films and 

Shut Out the Disturbing Noise of the 

Projection Booth. 



No Distortion 



No Loss of Light 



FISH-SCHURMAN CORPORATION 

45 West 45th Street NEW YORK CITY 




BEST CARBON SAVER 

for Low Intensity Arcs 

Permits projectionist to get at least one more 

reel from each set of stubs. Made in 7, 8, 9, 

10, 12 and 13 mm. sizes. 

$2.50 each at your dealer. 

BEST DEVICES CO. 



2108 PAYNE AVE. 



CLEVELAND, OHIO 



BUILT 

for SOUND 



FLAT RESPONSE CURVES 

for Exacting Requirements 

Ferranti Audio Frequency and Spe- 
cial Impedance Matching Trans- 
formers give the Flat Response 
Curves required by Broadcast Sta- 
tions and Laboratories, and in Speech 
Transmission. 

Special Transformers, made in the 
TJ. S. A., can be shipped within 48 
hours from receipt of order. 
BETTER AMPLIFICATION ... for 
Educational and particular commer- 
cial requirements, is furnished by 
Ferranti Amplifiers. 

Write for quotations and 
complete particulars. 



... _ ; ,:-j;..,. „i.:_.Jk 



'..-. .all 



Typical Curve of 600 Ohm line 
to line transformers 



FERRANTI, Inc. 



130 West 42nd Street 
New York 




We build splicers to 
your specified require- 
ments — for sound film, 
wide film, 35mm or 
16mm film. Our splic- 
ers, both standard and 
custom-made, are giving 
sturdy, dependable serv- 
ice in theatres and ex- 
changes throughout the 
world. 

Send for literature 

GRISWOLD 

MACHINE WORKS 
Port Jefferson New York 



w 



E, offer to manufac- 
turers interested in. 



EXPORT 

the services of a dependable organization, 
well established in the entire foreign field 

AD. AXJMEMA, Inc. 

Manufacturers' Export Managers 

116 Broad Street, New York, N.Y. 




%JV» " HAN Dl- MIKE" a, ** 

X* MOST EFFICIENT GENERAL flL^. 



No. 1275 
Transformer 

Input transformer 
designed for any 
single button mi- 
crophone. 200 ohm 
Primary, 100 000 
ohm on secondary 
side. List price $o. 



UTILITY MICROPHONE KNOWN 

List I O Complete 
The truly perfected single button 
hand microphone. Two models, "Reg- 
ular" and "Special Home Recording." 
Scientifically damped diaphragm, gold 
plated button, toggle switch, 15-foot 
cord. Finished bronze or gunmetal. 
Dealers, write for our "direct deal." 
Get our complete catalog. 

UNIVERSAL 
MICROPHONE CO., Ltd. 

1163 Hyde Park Blvd. 
INGLEWOOD, CALIF. 

Microphones $5 to $350. Also cabl 
ers, mountings, stands, etc. Experi 




INDEX TO ADVERTISERS 



Ad. Auriema, Inc 30 

American Radio Hardware Co 31 

Amplion Corp. of America 6 

B 

Badgley, G. J 27 

Bass Camera Co . 31 

Bell Equipment Corp Second Cover 

Best Devices Co 30 

Blue Se.al Products Co., Inc 23 

Blue Seal Sound Devices, Inc 28 

C 

Cameron Publishing Co 28 

Central Radio Corp Fourth Cover 

Chalmers Pub. Co 27 

Chicago Gear Works 31 

E 

Ellis Electrical Laboratory 31 



F 

Fish-Schurman Corp 30 

Ferranti, Inc 30 

Forest Electric Corp 25, 29 

G 

General Radio Co 29 

Gries Reproducer Corp 7 

Griswold Machine Works 30 

H 

Hoffman'-Soons 29 



Int'l Broadcasting Equipment Co. 
Int'l. Projector Corp 



32 



Leeds Radio Co 31 

M 



Meyer & Co., Hugo. 



28 



N 



National Carbon Co., Inc. 



Pacific Research Labs 31 

R 
Racon Electrical Co., Inc 3 

S 

Samson Electric Co 5 

SOS Corporation 31 

TJ 

Universal Microphone Co., Ltd.... 30 

V 
Vitaglo Corp., The Third Cover 

W 

Weber Machine Corp 27 

Weston Elec. Inst. Corp 25 



APRIL, 1931 



Page 31 




BASS BARGAINGRAM 

Issue 202 Ready 
FREE! The Classic of Bargain Lists. World's 
largest stock of Motion Picture Cameras and ac- 
cessories. Professional and Amateur. Save real 
money. Send for your copy. Free! 

BASS CAMERA CO. 



179 W. Madison St. 



Chicago, 111. 




GEARS 

In Stock — Immediate Delivery 

Gears, speed reducers, sprockets, thrust bearings, 
flexible couplings, pulleys, etc. A complete line is 
carried in our Chicago stock. Can also quote on 
special gears of any kind. Send us your blue prints 
and inquiries. 

Write for Catalog No. 200 

CHICAGO GEAR WORKS 

769-773 W. Jackson Blvd., CHICAGO, ILL. 



STATEMENT OF THE OWNERSHIP, MANAGEMENT, CIRCULA- 
TION, ETC., REQUIRED BY THE ACT OF CONGRESS 
OF AUGUST 24, 1912, OF PROJECTION ENGINEERING. 

Published monthly at Albany, N. Y., for April 1, 1931. 

State of New York ) __ 
County of New York J ss 

Before me, a Notary Public in and for the State and county 
aforesaid, 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, management, etc., of the aforesaid publication for the 
date shown in the above caption, required by the Act of August 
24th, 1912, embodied in section 411, Postal Laws and Regulations, 
to wit: 1. That the names and addresses of the publisher, editor, 
managing editor, and business managers are : Publisher. Bryan 
Davis Publishing Co., Inc., 52 Vanderbilt Avenue, New York; 
Editor, Donald McNicol, Roselle Park, N. J. ; Managing Editor, F. 
Walen, Union City, N. J. ; Business Manager, B. S. Davis, Scars- 
dale, N. Y. 2 That the owners are : Bryan Davis Public Co., Inc. ; 
B. S. Davis, Scarsdale. N. Y. ; Roy T. Atwood, Albany, N. Y. ; G. R. 
Bacon, Douglaston, N. Y. ; J. C. Munn, Union City, Pa. ; J. A. Walker, 
Richmond Hill, N. Y. ; A. B. Goodenough, New RocheJle, N. Y. 3. That 
the known bondholders, mortgagees, and other security holders own- 
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 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 trustees 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 stockholders 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 ; and 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 and subscribed before me this 27th day of March, 1931. 
(Seal) J. A. WALKER, Notary Public. 
Kings Countv. 
Kings Co., Clerk's No. 363. 
Kings Co., Register's No. 1062. 
New York Co., Clerk's No. 167. 
New York Co., Register's No. 1W177. 
Commission expires March 30, 1931. 




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IN CIRCLES ! ! ! ! ! 

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Problems. Send a Sample or Blue-print 

and Compare Our Quotations! ! 

Write for our catalogue of stock items. 

AMERICAN RADIO HARDWARE CO. 

137 Grand St., New York, N. Y. 



FILM CEMENT— SCREEN CLEANING FLUID 
GUM REMOVER— SPRAY PERFUMES 

Nationally known brands must be closed out far below 

cost. Gallon cans only. Write for price and quantities. 

Dealers can make a real buy. 

"Hewes" — Projection Engineering, 52 Vanderbilt Ave. 
New York City. 



FOR SOUND-ON-FILM 

THE X-CELL 

HAS FIVE DISTINCT ADVANTAGES 

1. High Sensitivity, 900 Microamps Per Lumen. 

2. High Frequency Response, up to 10,000 C.P.S. 

3. No Background Noise, Perfectly Quiet. 

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5. Long Life, One Year Guarantee. 

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Are you troubled with room noises, 

studio noises, motor noises or ' ' feed 

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If any of these noises are present i n the 

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know about a special feature of Ellis 

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Write for details on how Model 20N can 

be used to Cut Out The Noise. 

Export "Simons," 25 Warren St., New 

York. Cable: " Simontrice." 



ELLIS ELECTRICAL LABORATORY 



337 WEST MADISON ST. 



Sales Corporation 



CHICAGO, ILLINOIS 




CORPORATION 

S.O.S. IS UNDISPUTED LEADER — LOOK AT THESE 
VALUES WHILE THEY LAST ! — Tone-O-Graph Sound-on- 
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conditioned Simplex Projectors, $195.00; Acme SVE Portable 
Projectors, $75.00; Powers Projectors complete with lamps, 
$75.00; Synchronous Turntables, $49.50; Sterling Faders, $12.75; 
Ward-Leonard Faders with dummy, $39.75 ; Racon 6' exponential 
Horn with Jr. Unit, $29.75 ; Standard Microphone, $13.75 ; Dou- 
ble Turntable non-sync steel case, $44.00; Powers Inductors, 
$17.50; AC Speedometers, $8.00; 54 h.p. Constant Speed Motors, 
$11.47; Giant 10' Macy Exponential Horns, $57.75; Samson Pam 
19 Amplifiers, $69.15; Silver-Marshall 690 Amplifiers, $110.75; 
1,000 Watt G.E. Mazda Lamps, $5.35; 10 Volt G.E. Exciter 
Lamps, $1.12; Powers Aperture Masks, $1.90; Simplex Aperture 
Masks, 98c ; Da-Tone Sound Screens, 39c sq. ft. ; Genuine Audak 
Pickups, $8.97; Automatic Changeovers, $39.85 pr. ; BEWARE 
OF FLY-BY-NIGHTS— DEAL WITH ESTABLISHED COM- 
PANIES. Write S.O.S. Corp.. Dept. P.E., 1600 Broadway, New 
York City. Cable Address, ''SOSOUND," New York. 



HEADQUARTERS for the hard to get 
parts or material. Complete stock of 
shielded and plain covered wire on hand at 
all times. Full line of Weston and Jewell 
meters in stock for immediate delivery. All 
standard microphones in stock. 




45 VESEY STREET, NEW YORK CITY 



Page 32 



PROJECTION ENGINEERING 



ASSURED 




PERFORMANCE 




PRICES 

Complete $110.00 

Type "B* $75.00 

Transmitter only 

Type "3B" $35.00 

Amplifier only 

Net, F.O.B. Chicago. 

(Prices quoted include 

25 foot cord, plugs 

and wall plate.) 



Type "B" Condenser Transmitter 
Type "3B" Microphone Amplifier 



In introducing the "INTERNATIONAL" 
Type 44 B" Condenser transmitter with the 
Type "3-B" Amplifier, we are offering a 
piece of apparatus which is the result of 
three years' research combined with mechan- 
ical and engineering experience. This Com- 
pany has, in the past, maintained a reserved 
policy in the sale of Condenser Transmitters, 
inasmuch as freedom from trouble in cli- 
mates subject to wide variations of tempera- 
ture and humidity, was to be proven. 

It has never been the policy of this Company 
to allow the purchaser to perform the experi- 
mental work for the manufacturer. Several 
Condenser Transmitters of this type have 
been in active, every day operation for the 
past two years, and from the data obtained 
on their performance, a Transmitter prac- 
tically free from trouble or servicing has 
been developed. Transmitters are tested in 
actual operation for several weeks before 
shipment. 

The Unit is of sturdy construction and is un- 
conditionally guaranteed for one year against 
any mechanical or electrical failure. 

Folder "3-B" describes the Unit in detail. 

WRITE FOR IT! 



International Siroafccasttng Sqnipm^nt Ca. 



3112 West 51st St. 


Manufacturers of 


Chicago, 111. 


Public address ~ Broadcasting 
systems equipment 


_ Centralized Radio 
systems 


_ Complete Recording 
systems 




THE finest qualities of much higher priced recording 
units are incorporated in the Vitaglo Portable 
Sound on Film Recording Unit. 

The Vitaglo system is designed for direct recording in 
any standard Bell & Howell camera which has been 
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silence it and install a special sprocket, motor, ta- 
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The Vitaglo light is guaranteed to have a life sufficient 
to properly expose 50,000 feet of negative or positive 
film. These lights are extremely stable and consume little 
current. Exhaustive laboratory tests have proven this 
lamp to have a flat response from 30 to 7,000 cycles. 

Due to increased production facilities, the Vitaglo Lamp, 
heretofore available only when incorporated in the complete 
unit, may now be obtained by experimenters in sound and 
television, at an extremely low cost. 

Folder "B" describes the unit and lamp in detail. Write 
for it. 



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0WI?& 




4942 Sheridan Road .. CHICAGO 



No essentials necessary for durability and proper recording 

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ARE BVILT TO STAND 



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They are more Rugged than 
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The Tempered Steel Springs 

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Full insulation of high quality 
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They have sufficient clearance 

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•••• 

Submit your socket problems to 

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CENTRAL RADIO CORPORATIO 

156 Roosevelt Avenue Beloit, Wisconsi 




' ■— 



■ 



MAY, 1931 




SOUND 'VISUAL 



V 




Tanforan Race Track, San Francisco, Cali- 
fornia. Samson Electric Company Amplifiers 
Used for Loudspeaker Service From Judge's 
Stand. 



■ 



THE JOURNAL OF THE SOUND AND LIGHT PROJECTION INDUSTRIES 



$1,000 for Junior Talkie Portable Projector 




$1,150 for junior, with amplifier and speaker. 

$2,150 for two projectors, with amplifier and speakers. 




F.O.B. Derby, Conn. 



Announcing the 

BELL PORTABLE TALKIE 

The Latest Achievement of Sound Equipment Based on Compactness and Quality 



The sound and projection heads 
are built in one unit. The Photo 
Electric Cell assembly on the out- 
side of the case conveys the im- 
pulse to the amplifier circuit. 

Film running over an idler con- 
nected to a circuit breaker keeps 
the circuit open ... a film break 
releases and shuts off the entire 
unit. 



An ingenious rear shutter is built 
in, while the aperture is constant- 
ly cooled byforced draft. Entirely 
assembled in double sheet steel, 
asbestos lined, fireproof and 
noiseless operation is assured 
besides eliminating the use of a 
fireproof booth. 

All moving parts are ball bearing, 
hermetically sealed in grease. 
Special condensers handle the 
intense light from the 1000 watt 
projection lamp and throw a full 
theatre size picture on a screen 
100 to 125 feet distant. 



Bell Equipment is sold complete 
in every detail. 




I — VERY salesroom/ advertis- 
ing agency/ church/ school/ hotel/ hospital/ auditorium 
and community center can now have perfect sound 
and visual projection. With this added educational 
and amusement attraction/ you have revenue produc- 
ing facilities which will spell profits. We introduce 
this most modern series of talkie projectors in response 
to popular demand. Learn more about Bell Equipment! 
You will profit from the introduction. 

In construction/ every engineering problem has been sur- 
mounted — from the very portability of the apparatus to the 
prevention of fire hazard. Perfection in sound AND visual 
projection was our aim — price, the secondary consideration. 

We believe that the many features incorporated in both the 
Junior and De Luxe models, made possible by years of actual 
working experience/ will convince you that the ultimate of 
perfection has been achieved. 

Now is the time to see and hear the portable talkie equip- 
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REPRESENTATIVES WANTED FOR FOREIGN AND STATE RIGHTS 



BELL EQUIPMENT CORPORATION 

^Portable Talkie Equipments 
Suite 605 .. . 729 SEVENTH AVENUE . . . NEW YORK 

Telephone BRyant 9-9890 Telegram WESENOJ 



MAY, 1931 Page I 

Announcing - 

Pre-Cratered 9 mm x 20 
High Intensity Projector Carbons 



ANOTHER achievement of National Carbon research. 

The history of National Projector Carbons is one of con- 
stant improvement. But the merit of each new idea is 
definitely proved, by exacting laboratory and service tests, 
before it is applied to the product. 

The latest improvement is the pre-cratering of 9 mm 
x 20" National High Intensity Projector Carbons. 

Exhaustive tests, both in the laboratory and in actual 
theatre projection, have shown that pre-cratering achieves 
two highly important results. It enables the arc to "burn 
in" much more quickly and smoothly. It results in clean 
burning when the arc is struck on a new carbon. The 
Projectionist will recognize the value of these features. 

All 9 mm x 20" High Intensity Carbons now leaving our 
factory are pre-cratered. Also, the holder end of each 
carbon is beveled for easy insertion in the holder jaws. 
There is no extra charge. 



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 I jjjljjj and Carbon Corporation 

Branch Sales Offices: New York Pittsburgh Chicago San Francisco 



Projection 



Engineering 



Donald McNicol 
Editor 

Jas. R. Cameron 
Associate Editor 

Ulmer G. Turner 
Western Editor 



Member, Audit Bureau of Circulations 



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. Ill 



MAY 
1931 



Number 5 



Contents 

PAGE 

Editorial 4 

Public-Address and Sound Engineering Problems 

By Ralph P. Glover 7 

The Unsound Sound Business By Henry L. Williams 9 

Loudspeakers Added to Existing Public- Address or Radio 
Installations By D. B. Looney 10 

Film Recording in Sound Motion Pictures, Part I 

By Charles Felstead 1 1 

The High Intensity Arc in Projection. . . By E. R. Geib 14 

S. M. P. E. Convention 16 

Apartment House Antenna Distribution System 

By E. V. Amy, J. C. Aceves and F. King 17 

Departments 

News of the Industry and New Developments 26 

Index of Advertisers . . 30 



Bryan S. Davis 
President 

James A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

52 Vanderbilt Ave. 

New York City 



Sanford R. Cowan 
Advertising Manager 

J. E. NlELSON 

Circulation Manager 



Chicago Office— 333 N. Michigan Ave. — Charles ] 
St. Louis Office— 505 Star Bldg.— F. J. Wright 
Kansas City Offici 



Publication Office — North Broadway, Albany, N. Y. 
n Ave. — Charles H. Farrell, Mgr. San Francisco Office^-1 5 5 Sansorne St.— R._J._ Birch. 



-306 Coca Cola Bldg.— R. W. Mitchell. 



Los Angeles Office — 846 S. Broadway — R. J. Birch. 
New Zealand — Tearo Book Depot — Wellington. 



Entered as Second Class Matter at the Post Office at Albany, N. Y., October 9, 1929, under.the act of March 3, 
1879. Yearly subscription rate $2.00 in U. S. and Canada. Yearly subscription rate $3.00 in foreign countries. 



MAY, 1931 



International Products 



mean 



Assured Performance 



Page 3 




The Engineering Experience which is built into 
International products is your guarantee of 
uninterrupted performance and minimum ser- 
vicing. 



Revolutionary manufacturing methods make it 
possible to quote prices in keeping with 
present day budgets. 





Type I3F. Speech Input Panel. 
Gain range — 24 to 88 decibels. 
Maximum deviation over range of 30 c.p.s. 
to 5000 c.p.s. is two decibels at full gain. 
Price $350.00. (Less tubes) 



Type B. Condenser Transmitter. 
Type 3B. Microphone Amplifier. 
Complete $110.00. 
Type B. (transmitter only) $75.00 
Type 3B. (amplifier only) $35.00 

(including 25ft. cord, plugs and wall plate.) 
All prices quoted are net f.o.b. Chicago. 




Type 26C. Volume Indicator Panel. 

Range minus 10 decibels to plus 40 

decibels. 

Galvanometer reads in half decibel 

steps. 

Price $198.00. (Less tube) 



International SSroafc tasting Ejqnipm^nt 6to. 



3112 West 51st St. 



Chicago, 111. 



Public address 
systems 



Manufacturers of 

Broadcasting Centralized Radio 

equipment systems 



Complete Recording 
systems 



E d 



i t 



i a 



MAY, 1931 



SUBJECTS FOR 
HOME MOVIES 



ONE of the largest dealers 
in New York, retailing 
home movie-talkers, tells us 
that considering the times the 
demand for these instruments 
has during the past year been healthy. At pres- 
ent, with a slightly improved buying power the 
demand has sloped off noticeably. The reason 
advanced is that there is a paucity of new subjects. 

In this situation there is opportunity. _ With a 
considerable number of the machines in homes 
throughout the country it would seem that manu- 
facturers would sense the demand and take steps 
to meet it. If the rental and sales prices hereto- 
fore charged for films and discs, or duo-films, 
have not been high enough to make manufacture 
profitable perhaps the products, if of improved 
grade, would stand an increase in list. 



THE THIRST IN the February, 193 1 issue 

I of Projection Engineer- 
F™ ing we published some of the 

KNOWLEDGE questions included in An Ex- 

amination for Projectionists. 
The response to this presenta- 
tion was wide and enthusiastic. Scores of projec- 
tionists have written us to publish the complete 
list of examination questions. This we decided to 
do— one-half of the list appearing in this issue of 
Projection Engineering, the remainder to be 
presented in the June issue. 

This demonstration of interest is an encourag- 
ing sign. It is a sure indication of a widespread 
desire on the part of the men in the projection 
rooms throughout the country for knowledge of 
direct use in the daily operations. 

A list of technical questions propounded by 
those in authority does not in itself contain infor- 
mation, but it is of the utmost value in outlining 
and identifying the particular items of knowledge 
of importance to the men engaged in the business. 

When a student (and we are all students) has 
before him a schedule of the things he should 
know he has in hand the first requisite of useful 
education. Forthwith his studies may become 
orderly, organized and purposeful. Sources of 
information are numerous — books, technical peri- 
odicals, and one's own daily experiences are avail- 
able to all who desire to learn and progress. 



SOUND 
SERVICING 



THE inevitable has happened. 
The growth of sound in- 
stallations during the past year 
has been so extensive that 
already a serious situation has 
developed in regard to servicing. 

The two major companies which have sold or 
leased sound equipment to some six thousand 
theatres in the United States have well planned 
maintenance and servicing organizations. The 
sound installations put in by these two companies 
will be properly serviced. 

However, there are about six thousand sound 
installations of various makes and brands which 
have been put in by the smaller, independent 
manufacturers. Also, in addition to the sound 
installations in theatres there are probably 
thousands of other places where sound or public- 
address systems have been put in. 

It is in the case of these numerous miscellaneous 
sound installations that the need has grown for 
expert servicing. In time there may be oppor- 
tunity for a large national servicing organization, 
but in the meantime there is an immediate 
opportunty for state and county units. 

The growing correspondence carried on by 
Projection Engineering with users of sound 
systems indicates that many additional sound 
installations are contemplated for the coming 
year. Also, owners of systems now in service 
appear to be experiencing difficulty in procuring 
dependable replacements of parts. The situation 
throughout the country is such that engineers and 
servicemen competent to repair and maintain 
sound and public-address installations should soon 
sense the increasing opportunities for employment. 
Essentials for success are : knowledge of the 
equipment, industrious activity, and trustworthi- 
ness. 




OnJjL^tn^fUc 



0\s 



Editor. 



MAY, 1931 



age 



AMPLION PUBLIC ADDRESS 
SYSTEMS- 



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DYNAMIC UNITS 

600% more efficient 
8000 cycle range 



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thru Amplion equipment. An Amplion Public Address 
System is operated at the Polo Grounds in New York City. 



AT 



FLYING FIELDS, above the noise of motors 
and expectant passengers, flying schedules, 
aviation news and last minute words of instruction are in- 
stantaneously announced through the powerful trumpet 
horns. 



IN 



acceptance, 
phonograph 
turntable. 



SCHOOLS AND CHURCHES Amplion's 
public address system has had widespread 
For amusement and educational diversions 
records may be played on the electric 



FOR P0RTABLE TRUCKS, many of which 
' ^-'l N are now being equipped. This form 

of public address system is meeting with great success as 

an advertising medium. 



k/| ] f"* R (~) P H O N FS Amplion transverse current microphones are available 
" J ' in every type and capacity and for every requirement. 
Amplion hand and stand microphones of the very latest type are approved by record, 
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WRITE FOR 20 PAGE CATALOGUE AND PRICE LIST 
ON SOUND SYSTEM APPARATUS FOR EVERY PURPOSE. 



iSi 



Amplion Products Corporation 

38 W. 21st Street New York City 



Page 6 PROJECTION ENGINEERING 

Better Projection Pays 

Three Projectors 

or 
Emergency Equipment 
Kept in A1 Condition 
Is a Sure Indication 

of 

Practical-Progressive 

Showmanship 

GENUINE SIMPLEX PARTS 

FOR 

SIMPLEX PROJECTORS 

GIVE MOST SATISFACTORY RESULTS 

Send for Booklets Giving Full Particulars 



Rear Shutter Attachment 

Lens Aligning Device 

Lens Focusing Assembly 

Triple Lens Turret 

International Projector Corporation 

90 GOLD STREET NEW YORK 



Projection Engineering 



MAY, 1931 



Public address and 
sound engineering 
problems 



By Ralph P. Glover 



The Knowledge of Line Impedance Characteristics 

Established by Telephone Engineers May to Advantage 

Be Applied by Sound Engineers 



AUDIO-FREQUENCY trans- 
mission lines, so long utilized 
and exhaustively studied by 
the telephone industry, are 
now important tools of the public- 
address and sound picture engineers. 
In permanent sound installations which 
have been carefully designed and con- 
structed, we find many outstanding ex- 
amples of adequate coverage combined 
with a minimum capital investment. In 
less carefully engineered installations, 
inattention to important details and 
fundamental principles almost invari- 
ably results in enormously reduced effi- 
ciency and a corresponding increase in 
the cost and extent of the required 
apparatus. The transmission line, whe- 
ther long or short, is often the weak 
link in the chain. Some knowledge of 
its properties and characteristics, in 
several instances known to the writer, 
would have saved the difference be- 
tween fifty-watt tubes and "a pair of 
two-fifties," with their respective asso- 
ciated apparatus. 

Transmission lines, whether they be 
open wire, cable or merely twis,ted pair, 
have uniformly distributed constants of 
inductance, resistance, capacitance and 
leakance. The magnitude and propor- 
tion of these constants establish a defi- 



nite set of transmission characteristics 
for each particular line. They affect 
the characteristic impedance of the line, 
the amount of attenuation and phase- 
shift of the signal attributable to the 
line itself, and govern the manner in 
which these effects vary with frequency. 
The distributed constants referred to 
depend mainly on the proximity and 
configuration of the conductors and 
upon the dielectric constant, insulation 
resistance and apportionment of the line 
insulation. 

Fortunately, it is neither necessary 
nor desirable to consider any of the 
properties of transmission lines other 
than characteristic impedance, and to a 
lesser extent, attenuation, in this article. 
The technically-minded reader can draw 
on the excellent standard works on 
transmission theory should he desire to 
pursue the matter further 1 . 

When a generator is required to de- 
liver power to a load, it is commonly 
appreciated that the maximum power 
will be transferred when the load im- 
pedance is the same as the internal out- 
put impedance of the generator. Like- 
wise, when intervening apparatus exists 

1 For instance, K. S. Johnson, "Transmission 
Circuits for Telephonic Transmission," Van No- 
strand. 



between the generator and the ultimate 
load, this same equivalence of imped- 
ance must prevail at the junction points 
if each unit is to transmit the optimum 
amount of power. If the output and 
input impedances between particular 
units are not inherently identical, 
equivalence is obtained through the use 
of the proper impedance-matching 
transformer. 

Value of Line Impedance 

The transmission line is no exception 
to the impedance-matching principle. 
However, unless previous experience is 
available, the value of the line impe- 
dance is all too seldom known. In any 
event, the fact that the impedance of 
both line and terminal apparatus may 
vary considerably with frequency, calls 
for careful consideration. Especially 
under these conditions, does the effi- 
ciency of the system depend on enlight- 
ened technical judgment. 

For an ideal transmission line; that 
is, one having zero conductor resistance 
and leakage conductance, the character- 
istic impedance (the value of imped- 
ance to be considered from the match- 
ing; standpoint) is 

II 

where L and C are the inductance and 
capacitance per unit length. It should 
be noted that the relation is entirely in- 
dependent of the length of line and the 
• frequency of transmission. For the 
more general case of a practical line, 
the expression becomes 



Z„ = 



V! 



(i) 



V 



R + j coL 



lG+j<oC (2) 

where R and G are the conductor resist- 
ance and leakage conductance per unit 



1000 

800 

{/> 

2 600 

I 

o 

2 400 

N 200 




























\ 




























\ 




























\ 


V 




























s 


". 








COMPUTED 


















X 






/ 




















J 






y 


l 




























>J. 
















MEASURED 




^*^^._ 
































^ 


==» 
































































c 


I 8 8 

FREQUENCY -CYCLES PER SEC. 



Fig. 1. Characteristic impedance of 
No. 19 rubber covered twisted pair. 

C=0. 00129 m.f. per 100 feet loop. 

R=1.73 ohms per 100 feet loop. 



Page 8 



PROJECTION ENGINEERING 



28,000 

24.000 

20.000 
2 
O (6.000 

z 

<n 12.000 
8000 
4000 


































| 














































1 










































f 














































II 


i 


























































































J 


/ 






























IMPEDANCE-^ y^~ 


> 


/ 












































V 








































































RESPONSE, 
















sy ' 


i_ 


























rJ 




















\ 


























*\ 












































£U- 




































































l 
















































\ 


























































50 100 1000 (0,000 
FREQUENCY - CYCLES PER SECOND 



Fig. 2. R103 mag- 
netic speaker im- 
pedance and re- 
sponse. 



length, respectively, and u>~2%f. As be- 
fore, the impedance is independent of 
the length but, except in special cases, 
will be a function of frequency. 

When dealing with cables and twisted 
pair, (lamp cord, for instance) the 
most common transmission lines found 
in sound work of all sorts, a simplified 
expression for the characteristic imped- 
ance may be used due to the fact that 
the inductance and leakage conductance 
are generally negligible. The result is 



Z = - 



(3) 



The expression is given in the second 
form because it demonstrates that the 
characteristic impedance of a uniform 
line is also the square root of the prod- 
uct of open-circuit and short-circuit im- 
pedances (in other words, the geomet- 
ric mean of the open-circuit and short- 
circuit impedances). When the line is 
open at the far end, the impedance 
which obtains is the capacity reactance 
of the conductors at the frequency of 
measurement. When short-circuited, 
the impedance will be entirely the re- 
sistance of the "go and return" con- 
ductors. Indeed, this serves to describe 
the usual method of measuring char- 
acteristic impedance. 

An Equivalent Method 

An equivalent method consists of 
measuring the capacity of the open line 
with, for instance, a portable buzzer 
capacity bridge and then measuring the 
resistance with the far ends short-cir- 
cuited by means of a low-reading 
ohmmeter or Wheatstone bridge. The 
impedance at any frequency can then be 
calculated from expression (3). Fig. 
1 was obtained from such measure- 
ments on a length of No. 19 B&S 
gauge, rubber-insulated twisted pair. 
The computed curve was calculated 
from resistance and capacitance data 
while the other curve was the result 
of actual impedance measurements. 
The values of impedance are typical of 
those found in practice for this kind of 
line and vary from about 950 ohms 
at 200 c.p.s. to 250 ohms at, 3,000 c.p.s. 



The technician is now face to face 
with the problem of selecting the proper 
value of impedance from his deter- 
mined data so that an impedance match 
can be made. Impedances are fre- 
quently matched at the conventional 
frequency of 1,000 cycles and although 
this choice is infinitely better than sheer 
guesswork, it is doubtful that this 
method can be used with universal suc- 
cess. Certainly in many cases better re- 
sults are secured by the choice of other 
values of impedance for matching. 

As has been pointed out, matching 
to the source or load can probably be 
obtained at but one frequency and at 
all other frequencies there will be a 
loss of power due to mismatching. 
This mismatching loss, occurring at the 
generator and load junctions of the 
transmission line, is by far the most 
serious loss encountered in this sort of 
transmission and has a marked effect on 
both the quality and power output of 
the system. The actual attenuation for 
the twisted pair of Fig. 1 is only about 
one-half decibel per thousand loop feet 
at 5,000 c.p.s. over the line itself and 
is entirely negligible. 



N2.I9 R.C. 
TWfSTED PAIR 



MAGNETIC SPEAKER. 
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a. 

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FREQUENCY - CYCLES PER SEC. 



Fig. 3. 



Ratio of speaker impedance 
to line impedance. 



A Specific Problem 

A practical method of solving such 
problems is best indicated by the dis- 
cussion of a specific case. Other cases 
involving loads of different character 
may be handled in an analogous man- 
ner. Fig. 2 shows impedance and re- 
sponse curves for a high-impedance 
magnetic speaker which it is desired to 
feed from the transmission line of Fig. 
1. A step-up transformer will of 
course be necessary between the low- 
impedance line and the speaker and our 
problem thus includes the selection of 
the proper turn ratio for this trans- 
former. 

In Fig. 3, the ratio of speaker im- 
pedance to line impedance has been 
plotted for the important frequencies 
within the range of reproduction of 
the speaker. The turns ratio required 
for matching at any frequency is also 
given, calculated from the impedance 
ratio as indicated. 

The rising response tendency (the 
ordinates are proportional to decibels) 
toward the high frequencies in Fig. 2 
leads to the conclusion that some sacri- 
fice of power in this range would not 
be objectionable and might even be de- 
sirable. Remembering that the greater 
part of the power of the human voice 
lies in the frequencies below 1,000 cy- 
cles per second, we might well decide 
to match in the region between 200 and 
1,000 c.p.s. A turns ratio of 1 to 4, 
step-up, for the transformer would be 
convenient and would match imped- 
ances at 500 cycles. 

In case the loudspeaker impedance 
and response data are not available, 
the manufacturers will undoubtedly be 
glad to supply information or suggest 
the proper transformer ratio. Where 
the loudspeaker impedance is known, it 
is advisable to make a preliminary trial 
using a variable ratio impedance-match- 
ing transformer, starting the test with 
the ratio indicated by the impedance re- 
lationships at about 1,000 cycles. The 
ratio can then be varied either way un- 
til the most satisfactory compromise 
between volume and quality is secured. 
A fixed ratio transformer of the in- 
dicated value may then be substituted 
if desired. 

The considerations are somewhat dif- 
ferent at the junction point between the 
line and the power amplifier. Here it 
is necessary to remember that the amp- 
lifier should be terminated by approxi- 
mately twice its plate impedance for 
maximum undistorted power output. 
We are faced with a compromise, 
since we have large variations in load 
impedance to contend with again. A 
good solution, however, would consist 
of a step-down transformer between 
the tube and line which would reflect 

(Concluded on page 22) 



MAY, 1931 



The unsound 
sound business 



By Henry L. Williams 



The Imminent Large Mag- 
nitude of the Sound Am- 
plification Business Calls 
for Organized Merchan- 
dising 



C 



-ONFUSION worse con- 
founded" is the dire fate in 
store for the Sound business 
during 193 1 unless a halt is 
called to the haphazard merchandising 
methods indulged in by ninetey per cent 
of the manufacturers. 

With the decline of the parts busi- 
ness, more and more of these manu- 
facturers have turned their attention to 
public-address equipment. With many 
of them such products are still a side- 
line, which makes matters even worse. 
Practically all of them, whether special- 
ists or not, appear to be satisfied with 
the manufacturing, and leave the dis- 
tribution and merchandising to luck and 
ill-chosen representatives. This year 
finds a rapidly expanding market for 
sound equipment; month by month the 
sound business grows more and more 
attractive, and now is the time for 
manufacturers to bring their scheme 
of distribution into line with the actual 
marketing conditions, and to look ahead 
a little and see" where their present 
policies are leading them. 

At the present time there are about 
a dozen sound equipment manufacturers 
actively engaged. A couple of them 
operate under license, the others claim 
there is no "patent situation," a matter 
that has never been definitely decided 
and operates to the disadvantage of the 
humble salesman. Apparently this state 
of affairs will continue for some time 
to come, as the alleged patent holders 
evidently prefer to postpone the issue 
and content themselves with holding a 
real or imaginary big stick over the 
heads of the sellers and buyers of un- 
licensed equipment, to the detriment of 
both. 



Who Sells Sound Equipment? 

One of the really big and funda- 
mental problems facing the manufac- 
turers concerns who shall sell sound 
equipment and who shall not. As al- 
ready pointed put, a very haphazard 
condition exists in this respect, seri- 
ously retarding the growth of the in- 
dustry and clogging the progress of 
education among the potential users of 
sound equipment. Practically all the 
factories have their local representa- 
tives, who, for the most part, are dis- 
tinctly not sound engineers. These men 
sell to radio jobbers on occasion and 
more often to radio dealers ; to amateur 
sound engineers ; direct to theatres and 
schools ; to broadcasting stations ; to 
municipal authorities ; to anyone who 
has the cash to buy. Discounts for the 
most part are decided by these rep- 
resentatives on the spur of the moment. 
Protection for the legitimate sound con- 
cern is usually a thing unknown. 

An immediate result of this mer- 
chandising chaos is that the sound in- 
stallation people are often in direct 
competition with the people who should 
be their customers, and another is that 
installations are made by people who 
have no idea of what good sound is or 
how to procure it. This is one of the 
reasons why the market for sound 
equipment has been almost killed in 



P^ge 9 

many localities, for the results produced 
have been so atrocious that other pros- 
pects have grown to think that nothing 
better need be expected, or is available. 

The first thing to be done therefore 
is to clean shop by establishing definite 
discounts to specified customers. The 
only true customers of sound equip- 
ment manufacturers should be sound 
installation concerns, and then only 
those of them who conform to certain 
standards. What those standards should 
be is very easily determined by the 
factory, and when such outlets are not 
available it might well be worth the 
while considering the establishment of 
installation units either by direct finan- 
cing or through the local representa- 
tive's organization. 

In any event, it is of paramount 
importance that the factory control, to 
a large degree, the use of the products 
they make. In the sound business as 
in few others, the operation of the 
equipment after installation is of di- 
rect importance to the factory, and it 
is well worth the factory's time to see 
that it is at least given a chance to 
operate as it should. More sales have 
been lost through careless or ignorant 
installation than through any other one 
cause. 

Sound Engineers 

In seeking desirable outlets, the fac- 
tories and their representatives should 
realize that a radio engineer is not 
necessarily a sound engineer, and that 
sound equipment installation is a highly 
technical business in itself. The work 
that the sound engineers do is of value 
because technical knowledge is a vital 
necessity, and there is far more to a 
good sound installation than a collec- 





Which system of merchandising sound will be followed: 



Page 10 



PROJECTION ENGINEERING 



tion of sundry apparatus. That is one 
reason why sound equipment should not 
be sold to radio dealers or jobbers for 
resale to pseudo-installation men who 
work on a cost-plus basis, charging only 
for the time involved. 

It cannot be emphasized too often 
that the salvation of the sound industry 
is in the hands of the sound engineers, 
and the wisest course they can pursue 
is to bend every effort to see that only 
approved sound engineers have the op- 
portunity of handling their equipment. 
Inasmuch as the prosperity of the 
sound industry depends directly upon 
the prosperity of sound engineers, it 
would be good policy to give them 
every financial advantage and minimize 
internal competition through proper 
grading of discounts and protection of 



territory. There is sufficient competi- 
tion abroad without introducing inter- 
necine warfare in the form of rivalry 
between concerns merchandising the 
same factory's equipment. 

As things are, it often happens that 
anyone at all can buy from factory 
representatives at forty off, the same 
discount that is offered to radio dealers. 
Radio jobbers, who are so often also 
retailers can generally command fifty 
and ten, which is the maximum for 
sound engineering concerns. Public 
institutions, such as municipal depart- 
ments, hospitals, etc., can sometimes de- 
mand another ten per cent over what 
the sound engineers get. To all in- 
tents and purposes therefore, the actual 
retail price is forty off list, and the 
extra ten and ten is far too little to 



keep the sound men in business. Cour- 
tesy discounts of all kinds add to the 
already unhealthy state described, and 
only drastic action will put the industry 
on a really stable basis. 

The logical course seems to be to 
appoint only approved engineers, give 
them the maximum discounts, and 
through the local representatives, keep 
a close tab on the work they do. All 
other equipment should be sold through 
the representative only to customers 
who are not likely to injure the repu- 
tation of the merchandise by public 
demonstration of inferior quality due to 
faulty assembly or hookup. 

Only by the assumption of such a 
definite policy will the sound industry 
build a firm foundation for prosperity 
in the davs to come. 



Loudspeakers Added to Existing 
Public-Address or Radio Installations 



By D. B. Looney* 



ONE of the more common prob- 
lems in connection with pub- 
lic-address and centralized 
radio is that of .installing 
additional loudspeakers. In what fol- 
lows some ideas on this subject will be 
presented. 

Men who have had radio servicing 
experience, as well as theatre projec- 
tionists, now have enlarged opportunity 
for personal earnings as the field of 
sound amplification expands. 

In the immediate future real busi- 
ness is in sight in installing additional 
loudspeakers at dance halls, bathing 
beaches, stores or in private homes. 
Many home owners would like an extra 
speaker on their porch, in the garden 
or kitchen. This last appeals strongly 
to the busy housewife and is a good 
selling point. 

Fig. i shows how we may connect as 
many as thirty magnetic speakers to a 
single broadcast receiver (or phono- 
graph amplifier). Connections for an 
additional dynamic speaker are also 
shown. 

The two 2 mfd. blocking condensers 
are to prevent the direct plate current 
from flowing through the speakers 
while at the same time allowing the 
alternating component of the plate cur- 
rent to flow through the magnetic 

*N.R.I. Technical Staff. 



An everyday problem 
answered in an under- 
standable manner. 







II 


2 MFD. 




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' RECE 

LO 

SPE 

C 


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:iver 

UD 

M<ER 

> 


II 


I 

MAGNETIC 
SPEAKER 






TO "B 1 


SUPPLY 



Fig. 2. Adding speaker where no 
push-pull amplification. 



speaker windings. As these speakers 
are connected in parallel, the maximum 
volume from each will be the same. 
The individual volume is controlled by 
the 100,000 ohm resistors. Don't run 
the common lead from the output of the 
receiver in metal covered wire as the 
capacity effect would decrease the vol- 
ume. Good rubber covered wire will 
suffice. There is no fire hazard if the 
2 mfd. condensers are built to withstand 
a potential of 400 volts when using 245 
tubes and 600 volts with 250 tubes. 
However, the leads should' be well 
separated. 

When using extra dynamic speakers, 
connections may be made directly across 
the output of the receiver as shown, al- 
though if the dynamic speaker input 
impedance is like that of a magnetic 
speaker, it may be connected with the 
latter. We must, however, use a sepa- 
rate field excitation for the additional 
speaker. Most dynamic speakers have 
incorporated in them either a dry me- 
tallic rectifier or a vacuum tube recti- 
fier. Suitable speakers can be secured 
from dealers. 



When you wish to add additional 
speakers to a receiver which does not 
use a push-pull output, follow the 
hookup shown in Fig. 2. 

Many manufacturers of broadcast 
receivers have plans and parts al- 
ready assembled for adding additional 
speakers to their sets. On a big job it 
would be a good idea to write to the 
receiver manufacturer stating all the 
facts of the case — the type of receiver 
— the number and type of speakers to 
be added and any constructional details 
which have to be surmounted. Manu- 
facturers are always glad to cooperate 
on matters of this sort and by writing 
to them mistakes may be avoided and 
much time saved. 



OUTPUT OF 
RECEIVER 



DYNAMIC SPEAKER 
OF RECEIVER 



VOICE 
COIL 




I — d o z^^ 

A\\W o tpu 

1 f o Q 2 „ 



ADDITIONAL 

DYNAMIC 
SPEAKER 



^¥ 



SEPARATE 

FIELD 
SUPPLY 



Fig. 



1. Adding speakers with push- 
pull. 



MAY, 1931 



Page I I 



Film recording in 
sound motion pictures 



Part I 

By Charles Felstead* 



Detailed description of procedure in making sound 
records on film, including Fox Movietone and Western 

Electric 



WITH the great advances that 
were made in the develop- 
ment of the microphone and 
of audio amplification, the 
engineers who were working on the 
problem of finding a method of record- 
ing sound to accompany the motion 
picture, were faced only by the diffi- 
culty of creating a device that would 
transform the electrical copy of the 
sound waves into some other form of 
energy that could be easily recorded 
on a suitable sensitive medium. The 
amount of audio amplification that they 
had available assured the engineers 
that the electric current would be of 
sufficient magnitude to operate the 
device after it had been perfected, and 
they knew that the fidelity of the am- 
plification was great enough to produce 
an electric current having practically 
the same wave forms and proportionate 
amplitudes as the sound-pressure waves 
that they wished to record. The devel- 
opment work progressed along several 
lines, as is demonstrated by the fact 
that there are a number of distinctly 
different sound recording systems in 
use in motion picture work at the 
present time. In some of them, the 
electrical energy is caused to operate a 
device that modulates a beam of light, 
either at the source or after the light 
has been generated ; and in another 
recording system, the electrical energy 
is transformed directly into suitable 
mechanical energy. In the first case, 
the modulated beam of light is per- 
mitted to fall on a moving strip of 
unexposed motion picture film, thereby 
creating a photographic image of itself 
as a narrow sound track near one edge 
of the film, and in the other recording 
system the mechanical energy records 
itself as a varying trace on a soft wax 



record. These are rather roundabout 
methods of recording sound, but they 
are the best that is now available. It 
is probable that eventually the speech 
current, as this changing electric cur- 
rent that represents the sound waves is 
called, will be recorded directly on 
some medium without recourse to the 
expedient of first changing it into 
some other form of energy that is 
more easily recorded ; but that develop- 
ment will not come about until some 
method of so recording electrical 
energy has been devised. 

Two Types of Sound Film 

The two general methods of record- 
ing sound on film are known as the 
variable area-fixed density and the 
variable density-fixed area methods. 
Since we have not the space to enter 
into a detailed discussion of these two 
types and systems of film recording, 
we will take up only the variable 
density-fixed area method in the 
present paper. There are two record- 
ing systems that employ this method 
of recording sound on film. In the 
Fox Movietone, this type of sound 
track is produced by the flickering 



light from a lamp that is connected 
directly to the output of the recording 
amplifiers, while in the Western Elec- 
tric system of recording, the modula- 
tion of the light beam is accomplished 
by a device called a "light valve" which 
is interposed between a light source of 
constant intensity and the moving film. 
In order not to make it necessary to 
review the complicated electrical 
equipment that is connected between 
the microphones on the sound stage 
and the recording machine in which 
the film is exposed to the modulated 
light beam, we will assume that we 
have a speech current at the recording 
machine that is of the proper ampli- 
tude and that is a faithful eppy of the 
sound waves which we wish to record. 
In addition to this speech circuit, we 
must take for granted that there are 
the necessary battery and power cir- 
cuits also entering the recording room. 
The machine in which the film is 
exposed to this varying light beam is 
known as the film recording machine 
and is comparable to the motion pic- 
ture camera in which other film is ex- 
posed to the light reflected from a 
scene that is to be photographed. 
Both the film recording machine in the 
recording room and the motion picture 
camera on the sound stage are driven 
by special "interlocked" motors that 
start and stop at exactly the same time 
and run at precisely the same speed. 
The speed of these motors is regu- 
lated so that they never vary by more 
than one-tenth of one per cent from a 
fixed speed of exactly 1200 r.p.m. when 
they are running. The use of inter- 
locked motors makes it possible to 
place start marks on the film in both 
the camera and recording machine, 
and then to print the two pieces of film 
together after they have been exposed, 
with the assurance that they will 
match perfectly. Because the two start 
marks were made at identical places 
on the pieces of film in both machines 
and the machines were run at precisely 
the same speed, the picture and sound 
track on the two pieces of film will 
coincide exactly. Another similarity in 
the camera and recording machine is 
in the light-tight construction of the 



Fig. 1. Schematic 
diagram of bat- 
tery circuits. 



"Sound Engineer, Universal Pictures Corp. 



TO LAMP BATTERY 



TO MAG. 
WINDING BATT. 




V 



HT 



WARNING 
"' LIGHT 
(IF USED) 



MAGNETIZING 
WINDING 



®=Qs 



^m 





©' 


OUTPUT 





OF 




AMPLIFIERS 







° 



SWITCH 



'OBJECTIVE 

LENS 

SYSTEM 



REPEAT 
COIL 



CONDENSING 
LENS SYSTEM 



LIGHT 
VALVE 
STRINGS 



Page 12 



PROJECTION ENGINEERING 



box in which the film is exposed to 
light shining through a lens system 
in one end. However, the two ma- 
chines differ in that the film moves 
uniformly and continuously past the 
lens system in the recording machine, 
whereas in the camera the film is 
drawn down intermittently a frame at 
a time past the lens. The same type 
of film magazine is employed now 
generally on both machines, and they 
are both equipped with footage counters 
that indicate the number of feet of film 
run through the machine. ' 

The mechanical construction of a 
film recording machine is evident from 
the accompanying photograph. The 
rectangular metal box is the chamber 
in which the film is exposed, and the 
two drum-shaped containers are the 
magazines in which the film is held 
before and after exposure. The film 
travels down from the loaded maga- 
zine through the recording machine 
and on into the other magazine. On 
the end of the exposure chamber oppo- 
site the driving motor is the lens sys- 
tem and the light valve assembly. 
Farther out on this same end of the 
machine is the lamp house in which the 
lamp that furnishes the light of con- 
stant intensity is located. The footage 
indicators are the two knob and pointer 
arrangements on the front of the ex- 
posure chamber. The whole recording 
machine and motor assembly is built 
on a special concrete foundation. Just 
beneath the center of the machine is 
suspended a square metal box carrying 
the photoelectric cell amplifier, the 
function of which was discussed in a 
preceding article. The large panel on 
the wall back of each recording ma- 
chine is the control board on which are 




mounted the battery and speech circuit 
controls and meters and the other equip- 
ment that is associated with the 
recording machine. There are usually 
two film recording machines attached to 
each recording channel. The film 
magazines are removable to permit 
loading and unloading the film, and the 
door on the front of the exposure 
chamber is easily opened to allow the 
threading of the machine and the 
punching of the film for the start mark. 
The film magazine from which the film 
is taken is known as the feed maga- 
zine and the other one is termed the 
take-up magazine. 

It is necessary that the angular ve- 
locity with which the film is carried 
past the lens system that focuses the 
image of the light valve onto the film 
be as uniform as it is physically pos- 
sible to make it. In the photograph 
showing a loaded film recording 
machine, it will be observed that there 
are two large wheels around which the 
film is carried inside of the exposure 
chamber. These wheels are known as 
the sprockets. It is while passing over 
the left-hand sprocket, which engages 
just twenty of the sprocket holes in 
the edge of the film, that the film is 
exposed by the light passing through 
the light valve. These sprockets are 
both driven by the motor shaft through 
a worm and worm-wheel, but whereas 
the right-hand sprocket is driven di- 
rectly by the shaft of the worm-wheel, 
the left-hand. sprocket is driven through 
a special mechanical filter. This me- 
chanical filter is a form of heavy fly- 
wheel that is connected directly to the 
sprocket shaft and through a filter 
arrangement of springs to the shaft 
carrying the worm-wheel drive. 



Mechc 



Filt 



er 



Courtesy Hal Roach Studios 
Loaded film recording machine. 



The purpose of this mechanical filter 
is to iron out any variations that may 
occur in the speed of the driving motor 
and to compensate for any imperfec- 
tions in the driving gears. The heavy 
flywheel built directly on the motor 
shaft likewise helps to steady the speed 
of the motor. All of this mechanical 
filtering has for its object the elimi- 
nation of flutter in the sound track, 
which is produced by any intermittent 
variations in the angular velocity of 
the film as it is carried past the point 
of exposure. The speed at which the 
film is pulled through the recording 
machine is precisely ninety feet a 
minute, corresponding to a driving 
motor speed of I2CO r.p.m., and in the 
ideal recording machine, the film would 
pass the exposing light beam at this 
speed with absolute uniformity and 
steadiness in rate of travel. The uni- 
form rotation of the left-hand sprocket 
wheel is not affected by variations in 
the rotation of the right-hand, or feed, 
sprocket, due to the two loops of film 
by which the sprockets are connected, 



because any variations in the rotation 
of the feed sprocket from normal will 
be absorbed by these two film loops 
and have no effect on the angular ve- 
locity of the left-hand sprocket. This 
right-hand feed sprocket draws the 
film out of one magazine and feeds it 
down to the other take-up magazine. 
If a steady sine wave representing any 
audio frequency, such as iooo cycles 
per second, is recorded and there is 
any flutter present in the recording 
machine, the recorded sound when it is 
projected will vary up and down in 
tone. The same thing happens to any 
sound that is recorded in a machine in 
which there is flutter present, but it is 
more noticeable with a steady tone be- 
cause of the pureness of the note. 

The Assembly 

Directly ahead of the lens system 
attached to the front end of the ex- 
posure chamber, and through which the 
modulated light shines on the film and 
exposes it, is the magnetizing winding 
and the light valve assembly. Still 
farther out pn this end of the record- 
ing machine is the metal lamp house 
in which the lamp that provides the 
light for exposing the film is located. 
Between the lamp and the light valve 
is a condensing lens system that serves 
to concentrate the light from the lamp 
onto the opening in the frame of the 
light valve. The mounting of the lamp 
is adjustable so that it can be moved 
around to the position that permits the 
condensing lens to focus the light most 
sharply on the hole in the light valve 
frame. This is one of the adjustments 
that must be made . every morning by 
the men who operate the film record- 
ing machines. An eighteen-ampere pro- 
jection lamp with a heavy flat ribbon 
filament less than an inch long is used. 
It is lighted from a twelve-volt lamp 
battery through an adjustable rheostat. 
The lamp and light valve are so ar- 
ranged that the plane of the ribbon 
filament of the lamp is focused on the 
plane of the ribbons in the light valve. 
The metal housing that may be seen 
over this lamp is for the purpose of 
shielding the recording operator's eyes 
from the very bright light of the lamp. 
Since the speed with which the film 
moves past the lens system in the re- 
cording machine is constant and un- 
alteiable, the degree of exposure of 
the sound track is regulated by varying 
the intensity of the light from this 
lamp. In order that a sound track of 
the correct average density will be 
obtained, it is necessary that just the 
right amount of current be supplied to 
the lamp. There is a vernier rheostat 
on the main rheostat that controls this 
lamp, and the two of them, with the 
ammeter that indicates the amount of 
current drawn by the lamp, are mounted 
on the large control panel on the wall. 
The arrangement of the battery circuits 



MAY, 1931 



Page 13 



is shown schematically in Fig. i. The 
proper lamp current for each lamp is 
given the recording men and it is their 
duty to maintain the current at exactly 
that value at all times during the mak- 
ing of sound takes. 

Modulating Device 

The assembly of electromagnet and 
light valve that constitutes the light 
beam modulating device is mounted 
between the lamp house and the objec- 
tive lens system on the exposure cham- 
ber. The field winding of the electro- 
magnet, which is sometimes known as 
the magnetizing winding, is a large 
multi-layer coil of wire wound around 
the center leg of an E-shaped core, 
with the open part of the E facing the 
lamp house. The end of this center 
leg of the core, which is shorter than 
the other two legs of the core, is wedge- 
shaped, with the long way of the wedge 
on the same plane as the plane of the 
light valve ribbons. There is an open- 
ing in the face of this wedge that is 
eight mils wide by 256 mils long, and 
this opening is part ,of a slot that tapers 
toward the back of the E to form an 
opening 204 mils wide by 256 mils long 



CAMERA SILENCING 

THE producers-Technicians Commit- 
tee of the Academy of Motion 
Picture Arts and Sciences heard re- 
ports recently on camera silencing, the 
standard release print survey, cue 
sheets, film processing, supersensitive 
film, and other technical developments 
in the industry. M. C. Levee presided. 

At the meeting it was reported that 
sixty first cameramen, representing all 
Hollywood studios, had replied to the 
questionnaire sent out in March by the 
camera silencing subcommittee. Ninety- 
one per cent of the replies advocate 
strong efforts toward the development 
of cameras which would not require 
blimps or covers of any sort. Fifty- 
two per cent of these replies urged 
such efforts in strong terms. 

The weight of the blimps in use was 
condemned by 90 per cent of the re- 
plies; the bulk by 87 per cent. Fifty- 
five per cent said the blimps made 
focussing difficult and 73 per cent said 
they crowded the sets uncomfortably 
on close-ups. Practically every type 
of camera cover in use in Hollywood 
was criticized for one or more of these 
reasons. 

At the meeting it was resolved to 
bring this situation to the attention of 
the camera manufacturers and inquire 
what efforts are being made toward 
the production of a silent camera. The 
Committee will offer to have studio 
experts confer with the manufacturers 
in an endeavor to advance such efforts. 



Sound film record- 
ing room, Uni- 
versal Sound 
Laboratory. 




facing the objective lens system in the 
end of the exposure chamber. After 
the elctromagnet assembly has been 
lined up at the factory to exactly the 
right position, it is fastened securely 
in place and the screw heads covered 
with sealing wax. This is to prevent 
any shifting in the alignment of the 
slot through which the light shines. 
There is no control in the magnetizing 
winding circuit other than the key 



The camera silencing subcommittee 
consists of Kenneth F. Morgan, Fred- 
erick M. Sammis, and Lester Cowan, 
manager Academy Technical Bureau. 

▲ 

RICHARD W. COTTON 

Herewith we present a likeness of 
Mr. Richard W. Cotton, Sales Manager 
of the Samson Electric Company, Can- 
ton, Mass. Mr. Cotton is well known 




switch mounted on the panel on the 
wall. The winding operates directly 
from a twelve-volt battery without any 
series resistance. Failure on the part 
of the recording operator to turn on 
the magnetizing winding will result in 
sound not being recorded on the film, 
so it is well to have a signal light in 
this circuit to serve as an indicator 
when the key switch is turned to the 
on position. 



RICHARD W. COTTON 

throughout the sound field as the origi- 
nator of the "PAM" sound amplifier, 
widely used throughout the world. 



GOVERNMENT MAKES TALKIES 

TWO government departments in 
Washington are now engaged in the 
production of sound motion pictures, 
RCA Photophone sound recording and 
reproducing units having been installed 
by the Signal Corps of the United 
States Army and the Department of 
Agriculture. The first subject made by 
the Signal Corps under the direction of 
Major C. W. Lewis, a well-assembled 
picture describing the latest develop- 
ments in anti-aircraft artillery by the 
ordnance department, was presented for 
the first time at the opening of the new 
sound studio and projection room in the 
extension service building of the De- 
partment of Agriculture. 

About seventy high officials and other 
executives of the Department of Agri- 
culture attended the opening of the new 
studio when a special programme was 
presented under the direction of Ray- 
mond Evans, chief of the office of mo- 
tion pictures of the department. Prior 
to the beginning of the programme, 
Clyde W. Warburton, director of ex- 
tension service, gave a brief talk in 
which he told of the department's ac- 
tivities in connection with the distribu- 
tion of silent motion pictures for the 
past several years and the plans now 
being made for similar distribution of 
sound pictures. The pictures produced 
by the Department of Agriculture are 
sent to schools, churches, granges and 
other organizations throughout the 
United States. 



Page 14 



The high intensity 
arc in projection 



By E. R. Geib* 



This article contains directly useful information for pro- 
jectionists on how to obtain the most brilliant light. 



NOT so many years ago, a 50-am- 
pere direct-current straight arc 
was considered a very powerful 
light source. By "straight arc" 
we have reference to the type in which 
both the positive and negative carbons 
were burned in a position shown in Fig. 
1. The carbons were of the grade 
known as neutral cored, i. e., no special 
light producing materials were placed 
in the core. The light came entirely 
from the crater. The intrinsic bril- 
liancy, i. e., the brightness of such an 
arc is 130 candle power per square 
millimeter. 

Gradually, larger theatres were built 
and stronger light sources were re- 
quired. The current was increased to 




Fig. 1. D-C. 
straight arc. 



75-100 and in some few cases to 125-140 
amperes. It was not long before the 
light at even these amperages proved 
inadequate. This condition was met by 
the development of the high intensity 
projector arc. When first introduced 
it was operated at 75 amperes, but 
within a short time most high intensity 
arcs were operated at 100-125 amperes. 
It is this type of arc that we shall dis- 
cuss in this article. The lamps used 
are of the Hall & Connolly (H. & C.) 
Ashcraft, and Brenkert types. 

Sound film with its necessary semi- 
porous screens, color photography, wide 
pictures and larger theatres, now makes 

* National Carbon Co., Cleveland, Ohio. 



necessary the procurement of even more 
light than has been obtainable from the 
high intensity lamp operated at 125 
amperes. In general there are three 
ways in which additional light can be 
obtained : 

First: By the development of higher 
powered light sources. Super high in- 
tensity carbons have been produced 



imiiiiiiiiiiiiiiiiimiiiimiiiiiiiiiiiiiiiiiis 




Fig. 2. High in- 
tensity arc. 

illllUlllillllllllllllllllllllllllllllllllllllllU 



which will operate at 250 amperes. The 
intrinsic brilliancy of these carbons is 
approximately 1200 candle power per 
square millimeter, which is even higher 
than the sun at zenith. These carbons 
are not yet available for the projection 
of motion pictures. 

Second: More efficient high intensity 
projection lamps. The lamp manufac- 
turers are now at work on this problem. 

Third: The procurement of more 
light from present equipment and from 
present high intensity carbon trims. 
There is a way in which this can be 
done and many projectionists have al- 
ready discovered the method. We shall 
attempt to describe it briefly in the hope 
that more projectionists may avail 
themselves of the maximum amount of 
light and steadiness available from the 
present 13.6 mm. H. I. projection 
carbons. 

Let us first study the characteristics 
of high intensity arcs. With the 
straight arc, Fig. 1, the light came only 
from the crater. In the case of the 
high intensity arc, though, the light 




PROJECTION ENGINEERING 

emanates from two distinct sources — the 
crater and the tail flame. (See Fig. 2.) 
The light from the tail flame repre- 
sents about 30 per cent of the total light 
emitted. However, this tail flame can- 
not be utilized for projection purposes 
because practically none of it can be 
focused and thus picked up by the 
optical system. We are interested, 
therefore, only In the crater light. 

Position of Carbon 

The candle power as well as the 
steadiness of operation is affected by 
the angle and relative position of the 
negative carbon with respect to the 
positive crater and by the voltage main- 
tained across the arc. The angle is 
usually fixed by the lamp manufac- 
turers. The position of the positive 
carbon, however, with respect to the 
negative can be changed by moving the 
positive backward or forward. The 
correct position is a matter of great 
importance as we shall see later. From 
Fig. 3-A it is observed that the positive 
carbon burns with a cup-shaped crater 
and that the negative arc stream tends 
to direct the mass of light produced by 
the positive carbon. By some, it is 
claimed that the light in this crater 
takes the form of a gas ball ; others 
term it a mass of vapor. By whatever 
term you choose to call it, the object 
is to keep the hot gases confined in the 
cup-shaped crater. If the negative car- 
bon is too close to the positive (Fig. 
3-B) the negative flame appears to 
impinge on the hot gases in the posi- 
tive crater with such force that they 
actually drive them out of the cup- 
shaped crater with a consequent loss of 
light and steadiness. In other words, 
the light actually spills out of the 
crater. If the negative is too far away 
from the positive (Fig. 3-C) then there 
is apparently not sufficient force to the 
negative flame to confine the gases in 
the positive crater and again there is a 



4 


V 




A 


\ 




vS 


X 


\ 


v 




z 





Fig. 4. 

loss of light. From this, it will be seen 
that the proper arc length or voltage 
is very necessary if the best results are 
to be obtained. 

The 13.6 mm. x 20 national high 
intensity projector carbons are designed 
for 1 10-125 ampere service and when 
operated in this current range, the arc 
voltage should be approximately 67-73 
volts. The 16 mm. national high in- 
tensity projector carbons are designed 
for 140-150 ampere service and in this 
current range the best results are ob- 



MAY, 1931 



Page 15 









Fig. 5. 120-ampere arcs. 

tained when the arc voltage is 73-83 
volts. Although this article is on the 
subject of high amperage high intensity 
carbons, it might be stated in passing 
that a 9 mm. national H. I. reflecting 
arc projector carbon which is designed 
for 60-70 amperes, operates best at 48- 
55 volts across the arc. In general, if 
lower currents are used, the voltage 
should be correspondingly decreased. 
Conversely, if the current is increased 
the arc voltage should likewise be in- 
creased somewhat. 

Arc Voltages 

The question of arc voltages, how- 
ever, is tied in very closely with the 
relative position of the positive and 
negative carbons and this relationship 
is probably more important than the 
arc voltage. In Fig. 4 we have graphic 
representations of three 70-volt arcs, 
but the arc lengths measured as shown 
in the figure vary from 1% to Y% in. 
In X the negative flame does not touch 
the lower part of the positive carbon; 
in Y it just touches it and in Z it over- 
laps it considerably. These arcs give 
entirely different results in quantity 
and quality of crater light and the pro- 
jectionist would only be confused by 
any voltage specifications without quali- 
fication as to the relative position of 
the positive and negative carbons. The 
latter relationship is probably more im- 
portant than the arc voltage. 

In Fig. 5 are shown graphic repre- 
sentations of the arcs obtained at 120 
amperes (13.6 mm. x 20 national high 
intensity positives and % x 9 Orotip 
negative carbons were used) by mov- 
ing the positive carbon successive steps 
of y% inch along its axis. The arc volt- 
age for this particular set varies from 
86 in position A to 55 volts in position 
F. The negative flame in position A, it 
will be observed, is considerably ahead 
of the positive so that the positive flame 
actually rolls out of the bottom of the 
positive crater before the negative flame 
strikes it and diverts it upward. As the 
positive carbon is moved ahead this 
condition is altered, so that at D the 
edge of the negative flame just touches 
the lower edge of the positive carbon 
and practically the whole negative flame 
is sweeping across the crater opening 
as though compressing the positive 



flame. Finally, at F a good portion of 
the negative flame plays against the 
bottom of the positive carbon and again 
only a part sweeps across the positive 
crater. The values of relative light 
and arc voltage for these different arcs 
at 120 amperes are shown in Fig. 6. 
The maximum useful light is obtained 
at position D (as would be expected 
from the above description of the action 
of the negative flame against the posi- 
tive crater opening). The light dimin- 
ishes as the positive is moved in either 
direction from position D. 

Stability 

Unfortunately the position of maxi- 
mum light is not the position of 
maximum steadiness. With the arc in 
position A, the direction of the positive 
flame from the crater is not stable, re- 
sulting in many large flickers in the 
crater or useful light. This condition 
is improved as the positive carbon is 
moved forward so that the large flickers 
decrease and are practically eliminated 
at positions C and D. In these posi- 
tions small flickers of rather short 
duration are evident. The negative 
flame is either just hitting or just clear- 
ing the lower side of the positive carbon 
in these positions and tends to oscillate 
on and off the edge of the positive shell 
in a rapid movement causing medium 
size flickers of short duration. 

When the positive has been advanced 
to position E in Fig. 5 the edge of the 
negative flame is permanently on the 
bottom side of the positive shell and 
the negative flame drives against the 
positive arc stream with a steady force 
of uniform direction and magnitude so 
that there is practically no flicker in 
the useful light from the arc. With 
the arc in this position, a high intensity 
spot lamp has been observed for half 
an hour at a time without detecting any 
noticeable flicker in the spot. 

As shown in Fig. 6 the light is less 
for this position than in position D 
where some flickering is obtained. The 
light is still less in position F without 
any change in steadiness so that the 
position of optimum condition is that 
in which the edge of the negative flame 
impinges on the positive carbon as close 
to the end as possible without noticeable 
flickering on the screen or in the spot- 
light. 

If the positive carbon is moved from 
position C or D to position E without 
changing the position of the negative 
or the ballast resistance and with line 
voltage held constant, as is often done 
in the projection booth, there might be 
an actual increase in light as well as 
the elimination of noticeable flicker. 
This effect would result from increasing 
arc current. Movement of the positive 
carbon in the opposite direction toward 
position A would decrease the light 
much more than is indicated by the solid 



line in Fig. 6. The variation of light 
with position under these conditions is 
indicated for a 115 volt power line by 
the dotted line in Fig. 6. 

The distance from the projected axis 
of the positive carbon to the tip of the 
negative carbon for the arc illustrated 
in Fig. 5 is 5^ inch. Similar experi- 
ments were made with distances of l /2 
in. and 24 m - with exactly the same 
results. Within these limits and with 
the same relative position of the posi- 
tive and negative flames the arc length 
had no noticeable effect on the useful 
light. 

In the high intensity arc burning 
16 mm. positives with an angle of 28 
degrees between the carbon axes, it was 
found similarly that the position of 
maximum light was not that of maxi- 
mum steadiness and that the edge of the 
negative flame definitely bathed the 
lower edge of the positive carbon when 
the light was most free from flickers. 

In the beginning of the article men- 
tion was made that the determination 



-o relative: LIGHT AT 120 amperes 

-X ARC VOLTAGE " •" 

- RELATIVE LIGHT WITH VARYING CURRENT AND ' 
CONSTANT BALLAST RESISTANCE 




Fig. 6. Light intensity graph. 

on the 13.6 mm. carbons were made at 
no to 125 amperes. 125 amperes is 
as high as we recommend that this par- 
ticular size be used although many pro- 
jectionists operate at 130 amperes and 
in some instances at still higher cur- 
rents. 

The carbon manufacturer is always 
glad of the opportunity to co-operate 
with the lamp manufacturer, the theatre 
manager, or projectionist on any prob- 
lem involving the producing or applica- 
tion of light. 

Acknowledgement is given to the 
Journal of the Society of Motion Pic- 
ture Engineers for permission to use 
illustrations and data given in this 
article. 

▲ 

STANDARD RELEASE PRINT 

The establishment of the standard 
release print has made possible the 
abandonment of cue sheets for the pro- 
jection of sound pictures, according to 
announcement of the technical bureau 
of the Academy of Motion Picture Arts 
and Sciences. Studios and exchanges 
have been notified by Lester Cowan. 



Page 16 



PROJECTION ENGINEERING 




S. P. M. E. Convention 




Donald MacKenzie, 
member Board of Gov- 
ernors, S. M. P. E. 



A LIST of the 
papers so far 
scheduled to be 
presented at the 
S. M. P. E. Convention 
follows : 

"Detail in Television," by D. K. 
Gannett, American Telephone & Tele- 
graph Company. 

"Pioneer Experiments in Sound Re- 
cording," by Eugene Lauste. 

"Baron Shiba Films." (These films 
were made in Japan and loaned to the 
Society through the courtesy of the 
Bureau of Standards. The pictures 
are made at a very high rate of speed 
and are projected so as to show in 
slow motion certain very high speed 
phenomena.) 

"The Latin American Audience 
Viewpoint to American Films," by C. 
J. North and N. D. Golden, Motion 
Picture Division, Bureau of Foreign 
and Domestic Commerce. 

"Technicolor," by J. A. Ball, Techni- 
color Motion Picture Corporation. 

"Multicolor Process," by R. M. Otis, 
Hughes Development Co., Ltd. 

"Multicolor Laboratory," by Bruce 
Burns, Hughes Development Co., Ltd. 

"Comparison of the Technique of 
Making Two and Three Color Separa- 
tion Negatives," by P. D. Brewster, 
Brewster Color Film Corporation. 

"M-G-M Color Process," by O. O. 
Ceccarini, Metro - Goldwyn -Mayer 
Studios. 

"Hand Coloring of Motion Picture 
Film," by Gustav Brock. 

"Noiseless Recording," by H. C. 
Silent, Electrical Research Products, 
Inc. 

"A Shutter for Ground Noise Re- 
duction," by E. W. Kellogg and M. C. 
Batsel, RCA- Victor Company. 

"Noise Reduction with Variable 
Area Recording," by B. Kruezer, RCA 
Photophone, Inc. 

"The Ribbon Microphone," by H. F. 
Olson, RCA Photophone, Inc. 

"A Moving Coil Microphone for 
High Quality Sound Reproducing," by 
W. C. Jones and L. W. Giles, Bell 
Telephone Laboratories. 

"A Sound Film Reproducer for Re- 
recording Work," by J. J. Kuhn, Bell 
Telephone Laboratories. 

"Recording, Re-recording and Edit- 



The spring meeting of the Society of Motion 
Picture Engineers at Hollywood, May 25-29 will 
have for presentation a large number of impor- 
tant technical papers, according to O. M. 
Glunt, chairman of the papers committee. 



Peter Mole, Chairman, 

Pacific Coast Section 

S. M. P. E. 



'mg of Sound," by Carl Dreher, RKO 
Studios, Inc. 

"Recording Sound for Split Mat 
Photography," by L. E. Clark, RKO 
Pathe Studio. 

"Sensitometry — Part I," by L. A. 
Jones, Eastman Kodak Company. 

"Characteristics of DuPont Negative 
Film," by B. R. White, DuPont Pathe 
Film Mfg. Co. 

"Characteristics of New Eastman 
Negative Film," by Emery Huse, East- 
man Kodak Co. 

"High Speed Oscillograph," by A. 
M. Curtis and C. H. Rumpel, Bell 
Telephone Laboratories. 

"Improvements in Motion Picture 
Laboratory Apparatus," by C. E. Ives, 
A. J. Miller, and J. I. Crabtree, East- 
man Kodak Company. 

"Recent Developments in Thermionic 
Devices," by M. J. Kelly, Bell Tele- 
phone Laboratories. 

"Sensitometry — Part II," by L. A. 
Jones, Eastman Kodak Company. 

"Miniature Models of Sets," by Hans 
Dreier, Paramount Publix Corp. 

"Use of Dialogue in Sound," by 
Colonel Joy, Motion Picture Producers 
and Distributors Association. 

"The Depth of Field of Camera 
Lenses," by A. C. Hardy, Mass. Insti- 
tute of Technology. 

"Making a Motion Picture," by Paul 
Snell, Paramount Publix Corp. 

"Universal Developing Machine," by 
J. A. Dubray. Bell & Howell Co. 

"M-G-M Developing Machine," by 
J. M. Nickolaus, Metro-Goldwyn- 
Mayer Studios. 

"Variable Area Processing," by D. 
D. Foster, Bell Telephone Laboratories. 

"The Study of Exposure and Film 
Processing for Variable Area Record- 
ing," by E. W. Kellogg and G. L. Dim- 
mick, RCA Victor Company. 

"The Processing of Variable Area 
Sound Records in the Film Labora- 
tory," by W. P. Bielicke, RKO Studios, 
Inc. 

"Processing for Variable Density 
Records," by J. G. Frayne, Electrical 



Research Products, Inc. 

"Analysis of Nega- 
tives," by L. A. Jones and 
C. M. Tuttle, Eastman 
Kodak Company. 

"New Sensitometer," by 

L. A. Jones, Eastman Kodak Company. 

"Two Special sensitometers," by 

B. R. White, Dupont Pathe Film Mfg. 
Co. 

"Sensitometry — Part III," by L. A. 
Jones, Eastman Kodak Company. 

"Directional Effects in Sound Film 
Processing," by J. Crabtree, Bell Tele- 
phone Laboratories, Inc. 

"Straight Line and Toe Records with 
Light Valve," by D. MacKenzie, Elec- 
trical Research Products, Inc. 

"Reducing and Intensifying Solu- 
tions for Motion Picture Film," by J. 
I. Crabtree and L. E. Muehler, East- 
man Kodak Company. 

"Electrolytic Regeneration of Motion 
Picture Fixing Baths," by K. Hickman, 
Eastman Kodak Company. 

"Automatic Control of Electrolytic 
Recovery Apparatus," by K. Hickman, 
Eastman Kodak Company. 

"Some Properties of Two-Bath De- 
velopers for Motion Picture Negative 
Film," by J. I. Crabtree, H. Parker and 
H. D. Russel, Eastman Kodak Com- 
pany. 

"The Dunning Process and Process 
Backgrounds," by C. H. Dunning, 
Hollywood, Cal. 

"An Apertureless Optical System 
for Sound on Film," by R. C. Burt, R. 

C. Burt Scientific Laboratories. 
"Continuous Non-Intermittent Pro- 
jectors," by A. J. Holman. 

"Properties of Low Intensity Reflect- 
ing Arc Projector Carbons," by D. B. 
Joy and A. C. Downes, National Car- 
bon Co. 

"An A-C Operated Sound Motion 
Picture Reproducing Equipment," by 
T. D. Cunningham, RCA Victor Com- 
pany. 

"Motion Pictures Screens," by F. M. 
Falge, Beaded Screen Corp. 

"New Printing Machine," by O. B. 
DePue, DePue & Vance. 

"Air Conditioning By Carrier 
Method," by A. H. Simonds, Carrier 
Engineering Corp. 

"Air Conditioning," by E. C. Holden, 
Silica Gel Corp. 



MAY, 1931 



Apartment house 
antenna distribution 
system 

By E. V. Amy, J. G. Aceves and F. King 



A mulficoupler antenna arrangement which solves the 

problem of antennas for numerous receivers located in 

one building. 



THE growth of the radio receiver 
industry has created an urgent de- 
mand for a radio wave distributing 
system for the operation of the in- 
numerable radio sets in apartment 
houses and other large buildings in the 
great centers of population to supplant 
the individual aerial wires with their 
hideous appearance on the roofs. 

The means of providing every radio 
set in an apartment house with the 
proper signal energy from broadcasting 
stations must be such that: 

(i) It will supply sufficient signal 
strength well above any disturbing 
noises. 

(2) It must permit the use of all 
commercial as well as special types of 
radio receiving sets. 

(3) The operation of one or more 
sets must not affect the performance of 
the other sets connected to the system 
to an extent that may be detected by 
any of the listeners. 

(4) It must be simple and the cost of 
installation and maintenance must be 
low. 

It is the object of this paper to show 
how the Multicoupler Antenna System 
fulfills the above conditions, as well as 



to briefly describe the theory of its 
operation and the practical development 
of the system for commercial installa- 
tions. 

There have been a number of at- 



Page 17 

tempts made to operate a plurality of 
radio receivers from one source of 
signal voltage. As soon as the vacuum 
tube was sufficiently developed as an 
electronic "relay" or repeater, some 
engineers used it as a coupling device 
of very high input impedance to trans- 
fer the signal voltage to the radio re- 
ceiver. It was used also, or at least 
proposed to be used, for the purpose of 
obtaining a voltage amplification be- 
tween the antenna and a two wire 
transmission line that would distribute 
the voltage to the individual coupling 
tubes. In connection with these tubes 
all kinds of selectors were proposed to 
be attached to reinforce weak stations 
and to obtain further selectivity in the 
radio receivers themselves. Such ar- 
rangements are too expensive and com- 
plicated. 

Other attempts were made to operate 
radio receivers by means of conductors 
which existed in the building, such as 
gas and water pipes, heating systems, 
telephone leads and electric light cir- 
cuits. The indoor type antenna became 
quite popular when sensitive sets were 
first developed commercially. Unfor- 
tunately, in all the latter cases there was 
present either one or all of the objec- 
tions resulting from interference, noisy 
operation and generally unsatisfactory 
performance of the sets. To overcome 
all of these difficulties, a great deal of 
experimental and development work 
was undertaken by the writers. The 
idea of a single radio frequency line of 
distribution, without vacuum tubes or 
other apparatus subject to renewal and 
upkeep, was developed after many tests 
both in the laboratory and out-of- 
doors. The Multicoupler Antenna 
System of reception and distribution 
was evolved until it reached a very 



Aerial arrange- 
ment to feed 200 
apartments. 



* Delivered before the Radio Club of America, 
Feb. 16, 1931. 




Page 18 



PROJECTION ENGINEERING 




Fig. 1. Elementary coupler line. 

satisfactory commercial stage, the 
theory of which will be given very 
briefly, as this paper aims particularly 
at the practical end and at the results 
of commercial operation for a period 
of about three years. 

Theory of the Mul+icoupler Antenna 
System 

It will be seen that the Multicoupler 
Antenna System consists essentially of 
a uniform attenuation line connecting a 
good antenna to a number of radio re- 
ceivers, the line being connected to a 
terminal resistance at the other end. 
The signal voltage is supplied to the 
various radio receivers by means of 
multicouplers. The most elementary 
representation of a multicoupler line 
consists of a generator G, Fig. i, which 
impresses an e.m.f. through an artificial 
line containing inductances L and con- 
densers C to a resistance (R ). The 
inductances and condensers have small 



losses and are such that R„=VL/C. 
At all frequencies from o to w=2/VLC, 
the voltage will reach R with very 
small attenuation. The multicoupler, 
however, is not a filter section per se 
and does not act as such. 

If, the resistances in series with the 
coils and in shunt with the condensers 
are of appreciable magnitude, the 
propagation constant per section will be 



Art W 




Fig. 2. Generator replaced by an 
antenna. 



P=V(R+jcoL) (G+jwC) and the 
terminal impedance will be 

Z=V(R+ja)L)/(G+jo)C). 

This line may attenuate the higher fre- 
quencies more than the lower ones un- 
less o)L is large in comparison with R, 
and coC with respect to G. Let us now 
replace the generator G by an antenna, 
and the line by a riser, Fig. 2, then the 
losses in the line may be considered 
as made of two components; one due 
to the series resistance of the conduct- 
ors R', and the other due to shunting 
conductances G representing dielectric 
losses and the energy consumed by the 
radio receivers R'. 

This schematic representation is 
only a first approximation. The ca- 
pacities C represent a combination of 



distributed capacity along the downlead 
and the coupling condensers. The con- 
ductance G also represents at the same 
time the losses due to the dielectric, 
leakage, etc., along the line, as well as 
the effect of the radio sets. If we make 
G small compared to wC, and R small 
compared to wL, the line will transmit 
the e.m.f. without appreciable attenua- 
tion, as previously stated, and the ter- 
minating impedance will be sensibly 



equal to 



V 



An approxima- 



tion of theoretical conditions may be 
obtained by representing a section of 
the multicoupler line by means of a 




Method of fastening head of 
downlead. 



series inductance L, Fig. 3 ; a series 
resistance R 1 =f(oo), which takes into 
account ohmic losses, eddy currents and 
skin effect; a shunt capacity G with 
leakage resistance R 2 =9(a>), represent- 
ing the dielectric losses and leakage ; 
another resistance R 3 =t|/(w), represent- 
ing a radio set, with the coupling con- 
denser C 2 in series. The three resist- 
ances, which are functions of w, may be 
expressed approximately as follows : 
R 1 =K 1 w, R 2 =K 2 co- 5 and R 3 =K 3 w 1 - 5 . 
There may be some radio sets in which 
R ? . is independent of to and some others 
in which R 3 =Kco 2 with tuned inputs; 
hence, we may assume R 3 =K 3 o) 1 - 5 for 
an approximation. 

The equations for the propagation 
constant per section obtained by intro- 



ducing these functions of w in the ex- 
pression P=V(R+jwL) (G+jwC) 
where P = a+jb, from which the at- 

L, R 




Fig. 3. Section of multicoupler line 
represented by an inductance. 



tenuation a may be obtained are rather 
complicated, and even after making 
the calculations the results would not be 
in close conformity with practice for 
the following reasons : 

In the first place, the radio receivers 
may have any values of resistance and 
reactance, which are variable according 
to the tuning condition. 

Second, the shunt capacity is not uni- 
formly distributed along the line and 
the losses due to eddy current, dielectric 
hysteresis, skin effect, etc., vary accord- 
ing to local conditions. 

Third, it is assumed that the im- 
pressed electromotive force is applied 
to the beginning of the line. In prac- 
tice, however, additional voltages are 
induced by the field of the broadcasting 
stations along the downlead. The man- 
ner in which these extra e.m.fs. are in- 
duced depends upon the surrounding 
medium. As there are so many build- 
ings in the vicinity of the downlead, 
the pickup of both antenna and down- 
lead varies in a very complex way — 
which cannot be predicted. 

All these considerations lead to the 
experimental, rather than to the treat- 
ment a priori of the multicoupler line. 

The most important properties of the 
Multicoupler Antenna System, or, in 
fact, of any common radio signal sys- 
tem of distribution, to be considered, 
are: 

(1) The propagation of the signal 
from one end of the line to the other. 
This means the relative energy level 
at every outlet. 

(2) The lack of interaction, if any, 
between radio receivers connected to 
the system. 

(3) The actual signal strength at any 
outlet in comparison with individual 
signal collectors. 

(4) The terminal impedance of the 
line and the prevention of standing 
waves along the line. 

In connection with the last item, it 
is well to mention here that there are 
two types of multicoupler lines ; the out- 
door type and the conduit system. In 
the latter, additional distributed shunt 
capacity will be found and the terminal 




Fig. 4. Receiving system. 



MAY, 1931 



Page 19 



TABLE 



7S0 kc. 


AU Sets 

Tuned to 

780 kc. 


AU Sets 
Com- 
pletely 
Detuned 




Set No. 


Detuned 
+ 1 —1 




30 
24 
29 
28. 
31 


30.5 










28 31 






s 





Potential distribution along line at input — 30 

1 — 30. S 

2 — 24 

3 — 25 
4—29 

R — 28 

1100 kc. 



Set No. 

1 

2 

3 

4 



35 
36 
37 

34- S 
31 



33 



impedance will be found to be lower 
than in the former, in which case, a 
suitable impedance-matching trans- 
former is found very advantageous to 
connect the line in the conduit to the 
antenna as indicated in Fig. 8. 

Propagation of the Signal 

Two sets of signal strength measure- 
ments will be described : 

(A) In the laboratory with a number 
of multicouplers to which sets are con- 
nected. 

We have seen that one of the im- 
portant requirements of the multicoup- 
ler line is that it should act as a uni- 
form attenuation conductor for all 
broadcast frequencies. In order to ver- 
ify this experimentally, a special receiv- 
ing set was constructed, the schematic 
diagram of which is given in Fig. 4. 
In this set, the volume control VC, 
which is of the inductive (variable 
mutual induction) type, was calibrated 
in dbs. Additional range is obtained by 
means of a switch S permitting the use 
of one or two audio stages, the differ- 
ence amounting to 15 dbs. and the total 
range about 60 dbs. With an "artifi- 
cial" signal source made of an r-f. mod- 
ulated by a single a-f. tone, a meter in 
place of or in addition to the head 
phones will permit a more accurate level 
determination. With actual broadcast 
signals, the meter will keep moving all 
the time and it is better to use the van- 
ishing signal as reference level and note 
how many dbs. are needed to make the 
signal just inaudible. The more deci- 
bels the higher the level, and in the 
table of results the dbs. have this par- 
ticular meaning. 

Before the Multicoupler Antenna 
System was put in operation, in actual 
practice, a number of signal strength 
tests were made at the laboratory. The 
general layout is represented diagram- 
matically in Fig. 5. M, Mi . . . M„ 



represent multicouplers all connected to 
an antenna of about 120 feet in total 
length at one end, and to a 1000-ohm 
terminating resistance. To the coup- 
ling condensers of the multicouplers 
were attached a number of radio sets, 
in many cases just equivalent tuned in- 
put circuits, LC, or mere resistances 
Ro, simulating commercial receivers 
equipped with or without "coupling 
tubes." 

By means of this signal strength 
measuring set, the effects of the various 
radio receivers connected to a multi- 

w nms^—nms^- 

.LC A.L,Cj ]_ j_L n C n 

'/OOOcu 




Multicoupler Multicoupler 

imp — -tirvw -y 




Fig. 5. Laboratory trial of Multi- 
coupler System. 

coupler line upon any particular one of 
them, can be determined experimentally. 
The actual procedure consisted in con- 
necting to one of the multicouplers a 
radio set with a vacuum tube voltmeter 
across the speaker to indicate the vol- 
ume of the signals received, which dur- 
ing the tests were either regular broad- 
cast programs or locally generated 
modulated signals, the voltage of which 
was controlled by means of an attenua- 
tion resistance network calibrated in 
dbs. as shown in Fig. 6. When using 
this source of signal the measurements 



Fig. 6. Signal strength measure- 
ment. 



could be made very accurately and ex- 
pediently. All that was necessary was 
to maintain the reading of the vacuum 
tube meter constant while increasing or 
reducing the signal voltage by a given 
number of decibels. The results of the 
tests made under these conditions are 
given in Table I, where the first column 
gives the position of the set, starting 
from the antenna end. The second col- 
umn gives the levels in dbs. at the vari- 
ous points along the line when the radio 
sets were all short-circuited or badly 
detuned, which has the same effect. The 
third column gives the same data but 
with all sets tuned, while the last two 
columns refer to conditions where the 
sets were very slightly detuned on each 
side. The last set of tests shows the 
effect of tuning at least half of the sets 
to one station. 

The severity of the conditions under 
which the tests were made will never 
be found in practice. First of all, there 
was hardly two feet between outlets ; 
then all sets were of the tuned input 
close coupling type with low-loss coils 
and condensers, and finally, the line 
was practically devoid of distributed 
capacity. 



TABLE II 





Station 


Level for vanishing signal 


Difference 
in level due 
to effect of 

the 
transformer 


Floor 


Without 
transformer 


With 

impedance 

matching 

transformer 


1 5th 


WMCA 


42 dbs. 
38 
45 
37 


58 dbs. 

50 

60 

57 


16 dbs. 




WEAF 


12 




WABC 


15 
20 




WOV 








12th 


WMCA 


46 
40 
44 
34 


55 
48 
63 
54 


9 




WEAF 


8 




WABC 


19 




WOV 


20 








9th 


WMCA 


43 
39 
40 

37 


55 
50 
60 
53 


12 




WEAF 


11 




WABC 


20 




WOV 


16 








6th 


WMCA 


43 
40 

43 
41 


59 
52 
65 
58 


16 




WEAF 


12 




WABC 


22 




WOV 


17 








3rd 


WMCA . . 


38 
39 
45 
39 


55 
45 
60 
52 


17 




WEAF 


6 




WABC 


15 




WOV 


13 









Page 20 



PROJECTION ENGINEERING 



(B) In the field, in a building 
equipped with the Multicoupler An- 
tenna System. 

Similar tests were made later on an 
actual conduit installation at 770 Park 
Avenue, New York City. The portable 
set was carried to the third, sixth, ninth, 
twelfth and fifteenth floors of the seven- 
teen story building and signal strength 
tests were made at four different fre- 
quencies. At the same time, the effect 
of an impedance matching transformer 
was determined upon the signal level at 
the same floors. Using the. best ratio, 
the volume went up by an average of 
15 dbs. Table II gives the results 
obtained. 

These results are given in graphical 
form in Fig. 9. It will be noted how 
uniformly the propagation of the signal 
takes place along the line. The effect 
of the additional capacity due to the 



V 



AT 




^viw- j 



Fig. S. Impedance 
matching with con- 
duit system. 



conduit lowers the impedance of the 
line to such extent that the transformer 
is found to be quite beneficial. 

Interaction With Individual Antennas 

It is very interesting to compare the 
interaction between two sets when con- 
nected to the Multicoupler Antenna 
System or to individual antennas. For 
this purpose, two antennas five feet 
apart were brought down and sets 
connected to each one of them. The 
first set was of the tuned input type 
and the second one had means for 
measuring the volume in dbs. The 
two sets were connected successively 
to the aerial wires 'five feet apart 
and then to two consecutive multi- 
couplers. The effects in the case 
of the multicoupler connection may 



be studied from data such as 
given in Table I under extremely ad- 
verse conditions. However, when the 
two sets were connected to individual 
aerials, the effect of tuning one of 
them to the station being received by the 
other was a level difference of between 
5 and 20 dbs., according to the fre- 
quency and the sharpness of the tuning. 
A signal, the strength of which does 
not vary by more than 1 to 2 dbs., is 
considered to be of constant volume 
from the listeners' standpoint. Five dbs. 
variations are noticeable only in com- 
parative tests. A gradual fading of 5 
dbs. can hardly be detected. With these 
premises in mind, it is possible to judge 
the performance of a multicoupler lay- 
out in the laboratory from tests made 
as described above. It must be remem- 



TABLE III 



Station 



WMCA 
WEAF. 
WOR.. 
WPCH. 
WABC. 
WAAT. 
WOV.. 
1500 kc 

WMCA 
WEAF. 
WOR.. 
WOV.. 
1500 kc. 



Energy Level 



Multi- 
coupler 



Test 

Antenna 



(At the ninth floor) 



60 dbs. 

60 

60 

32 

39 

42 

S3 

13 



30 dbs. 

47 
47 

20 
32 
18 

53 
58 



Gain in 
dbs. Mul- 
ticoupler 
over Test 
Antenna 



(At the fourteenth floor) 



60 
60 
60 
60 
40 



43 

43 
44 
44 
14 



30 
13 
13 
12 

7 
26 


-43 



17 
17 
16 
16 
26 



bered that these tests were made under 
the severe conditions described before. 
In practice, in any of the buildings 
equipped with this system, there has not 
been as yet a single complaint on rec- 
ord of fading due to interference be- 
tween sets, which may be looked upon 
as a favorable confirmation of the 
working theory. How is it then pos- 
sible to reconcile two apparently mutu- 
ally conflicting conditions, namely, suf- 
ficient signal strength, requiring large 
coupling condenser, and independence 
of operation demanding small coupling 
condenser? The results given above 
offer an answer but not an explanation. 
One explanation is as follows : The 
action that takes place with a multi- 
coupler connected to a set is one of 
phase rotation rather than mere magni- 
tudes of voltages. To make this clear, 



60 
SO 


---_ 


_With"T" 


r--'' 






Wrthout-"T' 


t 




40 
30 















Floors 
WMCA 



60 



•= 40 = 



<d 30 



70 



1 


Wiih"T" 












Without"T 


n 












5 


12 9- 


i 


3 



Floors 
WEAF 



50 



E 40 



30 





With"T" 


^,- r ' 


■ — ^ 












H^ou^Y' 














5 12 S 


) 6 3 



Fl o o rs 
WABC 




EFFECT OF IMPEDANCE MATCHING TRANSFORMER 
UPON A CONDUIT MULTICOUPLER LINE 

Fig. 9. 

let us give some numerical values to the 
quantities involved. Let the multicoup- 
ler condenser have a reactance of say 
900 ohms at a frequency close to the 
middle of the broadcast band. Assume 
the radio set to offer a pure resistance 
of 300 ohms when tuned to that fre- 
quency. The e.m.f. available from the 
antenna at the junction of the multi- 
coupler condenser to the line will be 
across both condenser and set in series 
with each other and let it be of, say, 
one millivolt. The current supplied to 
the set would be 



.001 



10" 6 amperes. 



V900 2 + 300= 
If the set were detuned, its effective re- 
sistance and reactance would be very 
small and the current would be practic- 
ally 

.001 
-7== 1.11 X 10" 6 

or only 11 per cent greater. Hence, 



Fig. 7. Bridge 
method of deter- 
mining terminal 
impedance. 




MAY, 1931 



Page 21 



the available voltage will still be sub- 
stantially the same at all the other 
points in the line. The average set will 
offer a higher impedance to the line, so 
its effect on the signal will be less. 

The signal voltage available to the 
set when tuned will be io"° X 300, or 
.3 millivolt which is about one-third 
of the total available potential from 
the riser. Hence, by cutting down 
the available voltage to 30 per cent 
the sets will become independent of 
each other. The phase rotations in 
the vector diagram offer the ex- 
planations of how the two conditions 
of sufficiency of signal voltage 
and freedom from interactions are 
fulfilled to a practical extent, without 
resorting to one-way repeaters, or 
coupling tubes. 

Comparison with Individual Antennas 

In order to find out experimentally 
how the signal strength from the multi- 
coupler system compares with that ob- 
tained from an individual antenna, ex- 
periments were carried out at a 17 story 
apartment house. At the ninth and 
fourteenth floors successively, a stand- 
ard set (Radiola, model 33, a-c.) with 
the volume control previously calibrated 
at the laboratory, was attached by 
means of a s.p.d.t. switch either to the 
multicoupler system or to a 40-foot out- 
door antenna strung over an open court 
at the roof (seventeenth floor). 




Detail of a multicoupler support outside 
rear window. 



The average gain at the ninth floor 
was 14 dbs. ignoring the last reading 
which was no doubt the result of a 
standing wave formed in the individual 
aerial. The average gain at the four- 
teenth floor was 18. dbs. 

These observations are typical of a 
larger number which for the sake of 
brevity, are not given, but they are 
enough to illustrate what has been 
found to be the case in all the Multi- 



coupler Antenna installations — that 
there is plenty of signal voltage avail- 
able at the antenna-ground posts of the 
outlet plates. 

Terminal Impedance Measurements 

In order to determine experimentally 
the terminal impedance of a multi- 
coupler line, measurements were made 
on both laboratory layouts and in actual 
installations. These measurements 
were made by means of a portable 
Wheatstone bridge, the circuit of which 
is given in Fig. 7. The oscillator tube 
VT 2 has a balanced coil L„ so that one 
end is just as high above ground po- 
tential as the other end is below ground 
at the same instant throughout the a-c. 
cycles. The "figure eight" winding 
coils make magnetic induction very 
small. Besides, the aluminum double 
shield arrests the small leakage field 
that may be present. The oscillations 
are modulated by means of the audio 
frequency oscillator tube VT a which 
gives about 700 cycles. To prevent 
serious errors, a "Wagner earth" C B 
is used to prevent capacity coupling in- 
terference in the operation of the 
bridge. 

The bridge is made of four non-re- 
active variable resistances R 1; R 2 , R 3 , and 
Ri from o to 200 ohms. In series with 
one of them there are; a variable con- 
denser d and a multistep inductor L 4 . 
The condenser at the maximum capacity 



Aerial Wire 



Elevator Machinery 
or Tank House \ 



, . Eye Bo If (galv. iron) 
^Insulator 



- Ahtenha 
' 7- #22 Copper or Silicon 
Bronze Wire of least SO-ft. long 



Waterproof 
Fitting 



\ Approved 
Lightning 
Arrester 




Fig. 10. Conduit 
type of installation. 



4 x4 Box with 
.'1 "Cover 



Elevation and Section of Apartment Building 
Showing Typical Conduit Layout 



J /z Conduit 

_*l4Duplei1o 
Lighting 

Standard 2 Gang Outlet "Pj 
Box with Multicoupler 



Page 22 



PROJECTION ENGINEERING 



setting will become short-circuited, and 
the inductor has four taps the first one 
of which puts it out; hence, both L 4 
and C 4 may be put out of the circuit. 

The unknown resistance may be con- 
nected between the resistance R and 
the ground, or between the resistance 
R 4 , condenser and inductor and the 
ground, so that in the first case the re- 
actance will be balanced by means of a 
standard reactance of the same sign in 
the opposite arm, while in the second 
case the unknown reactance is neutral- 
ized by a known reactance, of opposite 
sign in series with it, making the bridge 
non-reactive in all four arms. 

The detector is a regenerative detect- 
ing tube with a tickler and a series re- 
sistance R T in the primary to vary the 
sensitivity and help thereby to find ap- 
proximately the balance settings. Once 
located it is easy to obtain an accurate 
balance by increasing the sensitivity of 
the regenerative detector. It is en- 
closed in its shielded compartment, and 
the tuning condenser has a scale cali- 
brated in megacycles. The measure- 
ments with the bridge above described 
may be relied upon to be within 10 per 
cent or better. 

In Table IV are given the results of 
the terminal resistance and reactance 
measurements at various frequencies of 
a setup of multicouplers with their con- 
densers grounded and the line termi- 
nated by iooo ohms. The same measure- 
ments were made on a conduit line in a 
commercial installation. 

It will be noted that the impedances 
of conduit lines are much lower than 
those of the laboratory setup. There 
are several reasons for this which 
would take too long to enumerate. 
Better still to repeat that an impedance- 
matching transformer can raise the 
energy level by about 15 dbs. as seen 
before. The schematic arrangement is 
shown in, Fig. 8. 

The impedance of the multicoupler 
measured from the antenna and ground 
outlet to the radio set is approximately 
that of a .0003 mf. condenser. Thus it 
is evident that a set which will align 
properly on an antenna of this capacity, 
which is not much greater than that of 
an average antenna, will not be ad- 
versely affected by the impedance of the 
multicoupler. 



The inductance of the multicoupler 
units is small enough so that the ca- 
pacity of the downlead to ground fur- 
nishes enough capacity to make the 
operation satisfactory when only a few 
of the multicouplers in a long down- 
lead are connected to receiving sets 
which are also connected to ground in 
the usual manner. 

Practical Conclusions and Advantages 

A large number of apartment houses 
in New York and other cities have 
already been equipped with the Multi- 
coupler Antenna System and owners 
have been quick to realize that their 
radio antenna problem has been solved 
by this simple and inexpensive system, 
which may be installed by the average 
electrician or radio man. 

The finished installation is neat, in- 
conspicuous and exceedingly convenient 
for the apartment house tenant, as 
shown in the accompanying photo- 
graph of an outside installation in 
buildings already erected. The advant- 
ages extend to the set owner, since there 
are several benefits from this group 
antenna system and the multicoupler. 
First, each multicoupler is so de- 
signed that it serves to pass all the 
broadcast frequencies to reach the 
receiver. All interfering noises, such 
as electric motors, elevator contacts and 
so on, are reduced, resulting in a 
minimum of background noise. This 
arrangement also stands for greater 
selectivity and a much better quality of 
reception. Nevertheless, although ad- 
justed primarily for broadcast fre- 
quencies, short-wave fans and television 
experimenters are not neglected in an 
installation of this sort. By connecting 
a small series condenser .0003 mf. to 
the main downlead, a few inches above 
the multicoupler, each tenant simultane- 
ously secures the benefits of an excellent 
outdoor antenna for short-wave recep- 
tion. 

The multicoupler, with its coils and 
coupling condenser properly protected 
by a weatherproof case, contains noth- 
ing that can wear out. There are no 
tubes or other parts to replace. There 
is no further expense to this system 
once it is installed. 



GAL. PIPE -_„* 



TABLE IV 

Effective resistance of a Multicoupler line containing 10 multicouplers with the 
condensers grounded and terminated by a 600 ohm resistance. 

Frequency in megacycles .6 .7 .8 .9 1 .0 1.1 1 . 2 

Effective resistance in ohms 640 525 453 420 400 385 375 

Effective Reactance Negligible 
Effective Resistance and Reactance of a Conduit Multicoupler Line with 17 outlets. 

Frequency 6 .7 .8 .9 1.0 1.1 1.2 1.3 

Resistance 196 44 36 34 3* 30 26 17 

Reactance —4 8 o — 6 3 —10 5 1 1 



MULTICOUPLER - 



MULT/COUPLEP 




Fig. 11. Outside type of installation 
used on completed buildings. 



The installation of the system in con- 
duit in new buildings has proved 
equally as satisfactory as the outside 
system. Architects and consulting 
engineers are specifying the system as 
a standard feature in plans for new 
apartment buildings, apartment hotels, 
hospitals and dormitories. 



PUBLIC-ADDRESS AND SOUND 
ENGINEERING PROBLEMS 

(Concluded from page 8) 

a load equal to twice the plate imped- 
ance at 500 cycles. Thus if the plate 
impedance is 4,000 ohms, a trans- 
former ratio of 3J4 to 1 would be suit- 
able, since in our problem the line im- 
pedance at 500 cycles is approximately 
630 ohms. Under these conditions, 
there would be little distortion due to 
low plate loading up to at least 1,000 
cycles. The power delivered to the 
line would increase gradually with fre- 
quency to a maximum at about 2,000 
cycles. As before, a variable-ratio 
transformer might well be used until 
the most satisfactory ratio has been 
determined. The methods indicated, 
however, will give very satisfactory 
and economical results at both ends of 
the line. 

It is frequently desirable to parallel 
a number of transmission lines. When 
this is the case, the lines may be 
treated as parallel impedance of the 
ordinary sort. Characteristic imped- 
ance values must be used. 



MAY, 1931 



Page 23 



Examination questions 
for projectionists 



Herewith is presented a list of guiding questions which 

applicants for grade A projectionist licenses in Canada 

are expected to be prepared to answer correctly 



ALL projectionists, no matter 
where located, should study 
these questions. The informa- 
tion necessary to answer the 
questions may be gained from back 
issues of Projection Engineering, 
from instruction books and from J. R. 
Cameron's text books. 

i. What are the requirements regard- 
ing construction of projection rooms? 

2. What dimensions are required? 

3. How must port-hole openings be 
covered or protected? 

4. What area of ventilation is re- 
quired for projection and rewind 
rooms, and where must vent pipes 
lead to? 

5. What entrance and exits are re- 
quired in projection room? 

6. What is the fire fighting equip- 
ment required, and where must the 
units be located? 

7. How often should port-hole shut- 
ters be tested? 

8. What is the maximum footage of 
film permitted to be used on a stand- 
ard 10 inch reel? 

9. Where must all films be rewound? 

10. How large a rewind room is re- 
quired ? 

11. Where must all film not in the 
projector be kept? 

12. What are the toilet requirements? 

13. What effect will the placing of 
the projection room above the center 
of the screen have on the shape of the 
picture? 

14. Is it advisable to place glass in 
observation ports, and if so, why? 

15. How should glass be placed in 
observation port to avoid reflection? 

16. What is meant by overloading a 
reel? 

17. When should film be revised? 

18. Would you use water on a film 
fire? 

19. Should film be stored in projec- 
tion magazine when not in use? 

20. Describe the methods by which 



dry and brittle film may be cleaned and 
re-moistened. 

21. What constitutes one reel of 
film ? 

22. Where should all films be re- 
wound ? 

23. Why should both ends of the re- 
winders be in line with each other? 

24. Where should all film scraps 
from repairs be placed, and give 
reasons ? 

25. What is meant by "pulling down" 
when rewinding? 

26. Give nature of damage to film 
caused by "pulling down" film at re- 
winding ? 

2y. Describe how to make a splice 
in film. 

28. What are some reasons for film 
fires in projectors? 

29. What will cause film to stop or 
pile up at the aperture opening or in 
front of the light beam? 

30. What are the results of large 
film loops? 

31. What damage may result from a 
wide, stiff or out-of-line splice? 

32. What will unequal gate springs 
or traps do to the film? 

2,Z- If sprocket idler rollers are out- 
of-line or binding, what may happen to 
the film? 

34. What happens to the film if the 
top magazine reel shaft is tight? 

35. What film or other damage re- 
sults from dirty magazine rollers? 

36. Why are new prints waxed and 
old prints not? 

37. What effect has overloading a 
reel on the film ? 

38. Why should a blank leader and 
tail piece be attached to each reel of 
film? 

39. What is film buckling? 

40. What will cause film to buckle? 

41. What will the effect be on the 
screen if the film buckles? 

42. What effect will an over scraped 
film splice have? 



43. Name some causes for rain effect 
on film. 

44. What causes corners of sprocket 
holes to become cracked? 

45. Name several faults in a projec- 
tor which will cause damage to a film. 

46. Supposing a fire gets into top 
magazine what would you do? 

47. What may cause film to jump 
sprockets ? 

48. Does the use of bent and broken 
reels damage film, and if so, how? 

49. How is the speed of reels in 
magazines regulated? 

50. What is the cause of flicker? 

51. When the picture size is in- 
creased, without other changes, will 
there be apparent loss of light on the 
screen ? 

52. What harm results from dirty 
sprockets ? 

53. What causes white streaks both 
up and down from letters or titles? 

54. What causes emulsion to collect 
on the aperture shoes and what dam- 
age may it do? 

55. What will cause film to have an 
up and down movement on the screen? 

56. What causes film sprocket holes 
to be pulled or broken out at the sides ? 

57. What is a mis-frame? 

58. What would you do in the event 
of the projector binding up? 

59. Of what use is film gate tension 
and how would you adjust same? 

60. Name the parts and function of 
the intermittent movement. 

61. What is travel ghost? Tell how 
to correct it. 

62. If a decided flicker is noticeable 
at a speed of 90 feet a minute, what 
can be done to lessen the flicker ? 

63. What damage is caused by over- 
tight magazine take-up tension and how 
can it be overcome? 

64. What causes loss of lower loop? 

65. Describe the various parts of the 
projector that are provided for fire 
prevention. 

66. What would cause the intermit- 
tent sprocket to stand still while the 
rest of the projector mechanism is in 
motion ? 

6y. What are the uses of the idler 
rollers and what is their proper adjust- 
ment? 

68. Explain purpose of film gate 
idlers. 

69. What purpose do film gate ten- 
sion springs serve? 

70. What effect on the picture image 
will worn aperture plate tracks have ? 

71. What is the requirement for the 
fire shutter on projectors? 

72. Why is a revolving shutter used 
on a projector? 

73. What will cause hooked sprocket 
teeth ? 

74. What would you use to clean the 
projector after an aperture fire? 

75. Can and should sprockets be re- 
versed when they show wear? 

76. Which make of a projector has 



Page 24 



PROJECTION ENGINEERING 



an actual faster movement, that is, the 
movement of the intermittent from full 
rest to full rest? 
yy. What is the star? 

78. What is the cam? 

79. What is the intermittent sproc- 
ket? 

80. What damage may out-of-line 
sprockets cause? 

81. Why are fibre gears used? 

82. What advantages are there to 
gears that are spiral cut? 

83. What is the aperture plate? 

84. How tight should aperture ten- 
sion be on new film? 

85. Why should aperture tension be 
varied on new and old film ? 

86. Should there be slight end play 
in film idlers? 

87. What is the standard aperture 
size? 

88. What damage will excess oil 
cause? 

89. What factors decide the size of 
lens required? 

90. Name some causes of out of 
focus effect. 

91. How would you adjust the opti- 
cal system to obtain a clear field of 
light on the screen? 

92. How far apart should condensor 
lens surfaces be spaced? 

93. Why are the curved surfaces of 
condensors placed next each other? 

94. Suppose you could not move the 
lamp-house or lamp nearer the aper- 
ture, what can you do to get a clear 
white light on the screen? 

95. What is a light ghost? 

96. What will cause a brown streak 
on one side of the screen? 

gy. How can the spot at the aperture 
be enlarged? 

98. What will be the effect on the 
picture of a badly pitted and dirty con- 
densor ? 

99. Give some causes of condensor 
breakage. 

100. Why does a cracked condensor 
show up when using slides and not 
when using film? 

101. What sizes of condensors are 
generally used? 

102. What is reflection of light? 

103. What is refraction? 

104. What is the optical axis? 

105. What is chromatic aberration? 

106. What is spherical aberration? 

107. What is working distance of a 
lens? 

108. What is lens diameter? 

109. What is keystone effect? 

no. How can keystone be overcome 
to a certain extent? 

in. Knowing size of screen and 
projection distance, how would you 
find size lens necessary to give a re- 
quired size picture? 

112. What is absorption of light? 

113. What is the optical system of 
the projector? 

114. What is meant by the focal 



length of an ordinary projection lens? 

115. What is used to cement lenses 
together ? 

116. Why should the inside of the 
lens barrel be painted flat black? 

117. How should the various ele- 
ments of a projection lens be assem- 
bled? 

118. What effect have dirty projec- 
tion lenses on the screen image? 

119. Should projection lens be held 
tightly in the mount, and if so, for 
what reason? 

120. How would you measure the 
focal length of a condensor lens? 

121. What is meant by equivalent 
focus of a projection lens? 

122. How could you test a lens for 
distortion? (By this is meant, how 
can you prove that your lens will give 
a complete sharply focussed picture?) 

123. How could you measure the 
working distance of any projection 
lens? 

124. In changing from a lens of 
small diameter to one of large diameter, 



I MEMBERSHIP IN THE S.M.P.E. 

SUBSCRIBERS of Projection 
Engineering who desire to 
I apply for membership in the 
Society of Motion Picture Engi- 
1 neerSj may procure application 
I forms by writing to Donald Mc- 
j Nicol, editor of Projection 
Engineering, 52 Vanderbilt aue- 
| nue, New York. Write on your 
own letter head or that of your 
I employing company. 



what change might be necessary in the 
shutter blades ? 

125. What is meant by front and 
back factors of a projector lens? 

126. Why is the diameter of the pro- 
jection lens of great importance? 

127. Define flicker. 

128. Define a condensing lens. 

129. Define collector lens. 

130. Define converging lens. 

131. Define piano lens. 

132. Define piano convex lens. 

133. Define meniscus lens. 

134. Define a volt. 

135. Define an ampere. 

136. Define an ohm. 

137. Define a watt. 

138. Define a kilowatt. 

139. Define a horsepower. 

140. Define ohm's law and state how 
it works. 

141. Define direct current. 

142. Define alternating current. 

143. Define a cycle. 

144. Define an alternation. 

145. Define a megohm. 

146. Define electric current. 

147. Define a short circuit. 



148. Define a ground. 

149. Define an electric arc. 

150. How can the "size" of a wire 
be measured? 

151. What necessary appliances does 
no v. d-c. pass through from the 
main switch until it reaches the arc? 

152. What governs the size of wire 
used on any circuit? 

153. What is a two-wire circuit? 

154. What is a three-wire circuit? 

155. What will cause a wire or ter- 
minal to heat up? 

156. Show by diagram two arcs con- 
nected to a no v. two-wire circuit. 

157. Show by diagram two arcs con- 
nected to a 110-220 v. three-wire circuit. 

158. Show by diagram balanced load 
of two arcs, two motors and two rheo- 
stats on a three-wire no and 220 volt 
line. 

159. Why is the neutral of a three- 
wire system grounded? 

160. Why does the power company 
prohibit fuses on the neutral wire? 

161. What type of covering should 
be used on wires that lead to the arc 
lamp? 

162. What is meant by resistance 
wire? 

163. What is meant by the negative 
wire of a d-c. circuit? 

164. What is meant by the term 
"open circuit?" 

165. What is meant by the term 
"closed circuit?" 

166. What is" the neutral wire of a 
110-220 v. circuit? 

167. What is meant by the safe car- 
rying capacity of a wire? 

168. What does the term electrical 
conductor mean? 

169. With tight connections and good 
insulations, what will cause wires to 
overheat ? 

170. What insulation is used where 
wires pass through the lamp house? 

171. In what position should a 
switch be pulled to open the circuit? 

172. How would you determine the 
voltage on your line? 

173. What protection is required for 
knife-switches? 

174. Should wires have terminal lugs 
where they are connected to switches? 

175. Why should all connections be 
kept clean and tight? 

176. Describe the method of making 
a joint or splice in a wire. 

177. Why are some starting switches 
on motor generators and larger equip- 
ment enclosed in oil? 

178. What is a live wire? 

179. How are tubes used as ampli- 
fiers? 

180. What does polarity mean? 

181. Why is d-c. used more than a-c. 
on projection arcs ? 

182. Why is a-c. used more than 
d-c. in commercial work? 

(To be continued) 



MAY, 1931 



Page 25 




The new catalog is full of informa- 
tion of value to projectionists. You 
are entitled to a copy. Write for it 
today. 



To Tell You About 
Modern Projection 

This catalog gives complete information 
about the new Super Cinephor lenses and condenser 
system. This projection system is one of the most 
important developments in motion pictures. It gives 
better definition than ever before, especially on short 
focal lengths. It supplies more intense illumination and 
better distribution of light, due to the new condenser, 
and therefore gives a more nearly perfect projected 
image. 



BAUSCH & LOMB 

681 St. Paul Street 



OPTICAL CO. 

Rochester, New York 




Makers of Orthogon Eyeglass Lenses for Better Vision 




STANDARD RHEOSTATS 

For lower power re- 
quirements our standard 
line of rheostats pro- 
vides the same satis- 
factory electrical and 
mechanical assurance 
characteristic of our 
heavy duty design. Sup- 
plied as rheostats or po- 
tentiometers for panel 
mounting. 



POWER-DELICATELY CONTROLLED 

Gily&rifcjsco 

Power Rheostats and Potentiometers 

Dejur-Amsco power rheostats and potentiometers are engineered 
mechanically and electrically to provide a consistent and unvarying 
current control and to give an added degree of perfection in the power 
control of circuits and systems to which the wire wound variable 
resistor is adapted. 

Engineers will immediately recognize in 
these Dejur-Amsco variable resistors the 
solution of many problems in Power Cir- 
cuits, Mixing Panels, Spot Welding, Motors 
and in the Photo-Electric field. 

Write us your .requirements. Our engineers are ready 
to assist you in the development of special apparatus 
to fit your particular needs. Literature on request. 

DsJuRL-ff Msco C orp 



Varitors — Variable Condensers — Power Rheostats ■ 
Pilot Lights — Escutcheons 



■ Dials 






95 Morton Street 



New York City 



Page 26 



PROJECTION ENGINEERING 



New Developments 

and 

News of the Industry 



W. H. HUTTER WITH CAPEHART 
CORPORATION 

Of interest to the trade is the announce- 
ment that W. H. Hutter, formerly chief 
engineer of the Webster Electric Company, 
Racine, Wisconsin, has become associated 
with The Capehart Corporation, Fort 
Wayne, Indiana. 

In his new connection with Capehart, Mr. 
Hutter is chief electrical engineer and in 
charge of manufacturer's division sales. He 
brings with him long experience in audio 
and acoustic research, and will concentrate 
on the more intensive development of tone 
quality for the Capehart line. 

For the past twenty-five years, Mr._ Hutter 
has specialized in audio and acoustics and 
during that time has served as consulting 
engineer in an advisory capacity to many 
companies engaged in radio production. _ 

His early training was with the American 
Telephone and Telegraph Company in the 
field of acoustics, audio research and public- 
address work. While with them he con- 
ducted and developed original design in 
electric pickup construction. 



PROJECTOR CARBONS 

Another important improvement in pro- 
jector carbons is announced by National 
Carbon Company, Inc. This is the "pre- 
cratering" of 9 mm. x 20-inch National high 
intensity projector carbons. Pre-cratering, 
as the name implies, consists in forming a 
crater at the burning tip of the carbon 
during the process of manufacture. In ad- 
dition to the pre-cratered tip, the holder 
end of each carbon is beveled to permit 
easy insertion in the holder jaws. All 9 
mm. x 20-inch high intensity carbons now 
leaving the factory embody these improve- 
ments. . • • 1 

Pre-cratering gives better initial per- 
formance of the carbon in two respects. It 
results in clean burning when the arc is 
struck on a new carbon and it reduces the 
time required for the arc to burn in. Every 
projectionist will appreciate the importance 
of these features. 



PANEL MOUNTED AMPLIFIERS 

The General Amplifier Company. 27 Com- 
mercial Avenue, Cambridge, Massachusetts, 
announces a new line of panel amplifiers 
embracing several different types of rack 
mounting. This new line consists of micro- 
phone amplifiers, voltage amplifiers, and sev- 
eral types of output amplifiers, ranging in 
power output from 5 to 50 watts. These 
amplifiers are constructed on a quarter-inch 
steel panel finished in black crackle. They 
are of quality construction throughout, and 
very ruggedly made. They were primarily 
designed for the utmost in sound reproduc- 
tion. 

NON-THEATRE SOUND 
INSTALLATIONS 

In addition to having broken all records 
for the sale of sound apparatus for theatre 
installations during the past sixty days, 
RCA Photophone, Inc., has increased its 
activities in the non-theatrical field to a 
marked degree. The largest single order 
for sound apparatus ever placed by the au- 
thorities of a state was received yesterday 
by Sydney E. Abel, general sales manager 
of RCA Photophone, Inc., from the depart- 



ment of business control of the State of 
Washington. Four complete units of sound 
reproducing apparatus were ordered for the 
Washington State reformatory at Monroe ; 
the Washington State penitentiary at Walla 
Walla ; the Eastern State hospital at Medi- 
cal Lake and the State training school at 
Chehalis. F. W. Normand, district mana- 
ger of RCA Photophone at Seattle, nego- 
tiated the contracts. Mr. Abel said it was 
the intention of the Washington state au- 
thorities to install sound apparatus in every 
large state institution and that the con- 
tracts for the installation in the four insti- 
tutions mentioned came after Messrs. 01- 
sen and McKibben had seen and heard 
various types of apparatus demonstrated. 



LIGHT VALVE CONTROL 

The Enterprise Optical Mfg. Company, 
564 West Randolph Street, Chicago, 111., 
for the Motiograph De Luxe Sound equip- 
ment employs an ingenious light valve con- 
trol for the regulation of sound level. This 
is accomplished by controlling the amount 
of light falling on the light sensitive sur- 
face of the photocell. It is stated that by 
its use the fader device may be eliminated 
from the audio circuit. 



SOUND EQUIPMENT 

Jenkins and Adair, Inc., 3333 Belmont 
Avenue, Chicago, 111., have issued bulletin 
iE, illustrating a line of transformers, 
retards, gain controls, mixing controls and 
amplifier accessories. Bulletin 13 A de- 
scribes a new monitor panel, and bulletin 
14 A, a portable amplifier and portable 
mixer. 



NEW SOUND HEADS 

The Weber Machine Corpn., 59 Rutter 
St., Rochester, N. Y., announces a new 
synchrofilm unit for Motiograph de Luxe 
projectors. The illustration shows the drive. 




HOME TALKING PICTURES 

The Visionola Mfg. Corporation, 60 East 
42d Street, New York, is having outstand- 
ing success in marketing the Visionola, a 
home talking picture outfit. The projection 
equipment, sound reproducer and screen all 
are mounted in one cabinet unit. 



NEW AMPLIFIER EQUIPMENT 

Five items of associated equipment espe- 
cially designed for use with AmerTran 
series 80 power amplifiers have just been 
announced by the American Transformer 
Company, 178 Emmet Street, Newark, N. J. 
The new equipment is also arranged so that 
it may be used with other standard ampli- 
fiers having 500-ohm input circuits. The 
various units available are as follows : 
Master control, Type C-81 ; master control 
with one-stage pre-amplifier, Type A-88 ; 
two-stage, low-level input amplifier, Type 
A-89 ; "A" power supply unit (12-volt), 
Type P-78 ; and dynamic field supply unit, 
Type P-101. 

It is the function of master control Type 
C-81 to control volume, to select signals 
from a 500- or 200-ohm source, and to 
regulate operating current to the 200-ohm 
source. The volume control is a 500-ohm 
constant-impedance, T-pad attenuator and 
the output impedance is 500 ohms. The 
Type A-88 master control with pre-amplifier 
is identical to Type C-81 except a one-stage, 
low-level amplifier is connected in the 200- 
ohm input circuit. 

Input amplifier Type A-89 is _ for raising 
low-level signals to values sufficient for ex- 
citing the main amplifier. It employs two 
transformer-coupled stages utilizing d-c- 
operated 227-type tubes and has an output 
impedance of 500 ohms. It is available with 
a high-impedance or 500-ohm impedance in- 
put and is supplied in a compact metal case 
designed for wall mounting. 

Power supply unit Type P-78 has been 
designed to provide filament current for 
AmerTran d-c.-operated amplifiers, such as 
Type A-89. It has an output of 12 volts 
filtered d-c. at 1.75 amperes and operates 
from no-volt, 60-cycle lighting circuits. 
Power supply Type 101 is of similar design 
but provides an output of 7.5 or 15 volts at 
1.5 amps. It will energize the fields of one 
or two dynamic loudspeakers. 



AMPLIFIER EQUIPMENT 

The Polymet Manufacturing Corpn., 829 
East 134th Street, New York, has issued 
bulletin Amp-i illustrating and describing 
a new and up-to-date line of main and head 
amplifiers for sound installations. 

The company manufactures a standard 
line of condensers, resistors and chokes. 

The eauipment is being marketed in com- 
plete panels and in kits. 



"QUEEN" DIRECT-READING OHM- 
METERS 

An improvement over existing types ohm- 
meters with slide as rheostat of Wheatstqne 
bridge thereby giving uniform scale. Ratios 
0.1, 1, 10, 100, 1000 and 10,000 with ranges 
from fraction of an ohm to 2,700,000 ohms. 
Operation consists only of closing keys and 
rotating scale index for balance. These 
are made by The Gray Instrument Co., 64 
West Johnson St., Philadelphia, Pa. 



MAY, 1931 



Page 27 



DIRECT READING 




TYPE 586 Power-Level Indicator 

An open clearly marked decibel scale makes 
the General Radio TYPE 586 Power-Level 
Indicator a truly direct-reading instrument. 
The time saved and the freedom from costly 
mistakes such a scale insures are advantages 
readily appreciated by the monitoring oper- 
ator in the broadcast and recording studio. 

If you are not familiar with this instrument, 
a request on your business letterhead will 
bring you a catalog description. Please ask 
for Bulletin 932-P. 

GENERAL RADIO COMPANY 



Offices 

CAMBRIDGE A, 



Laboratories Factory 

MASSACHUSETTS 



Hoffmann- Soons 



PERFECTION 
^ 




LAN. NEW YORK, CONTINENTAL 
your dealer. 



ONE OF THE 
PIONEERS 

The motion picture industry 
is a strong chain composed 
of many links. Each link 
represents a branch and is 
the result of years' ex- 
perimental and research 
work put forth by pioneers 
in this great industry. 
HOFFMANN-SOONS is one 
of the links that forms 
this chain and has played 
an important part in the 
building up of this enor- 
mous institution. 

THE OXL? UNION 
MADE RHEOSTAT 

Recognized as the Highest 
Standard everywhere. 

Now equipped with solder- 
less, adjustable lugs to 
take wire sizes from No. 4 
to 4/0 without any addi- 
tional cost. 

We build rheostats for spe- 
cial requirements. Com- 
municate with us Direct. 
There is no obligation. 
Sold by all Branches of 
NATIONAL THEATRE 
SUPPLY CO.. SAM KAP- 
THEATRE ACCESSORIES, and by 



HOFFMANN-SOONS 

Electrical and Engineering Corporation 
387 First Avenue, New York 

Contracting Electrical Engineers — Moving Picture 
Theatre Electrical Specialists 

RHEOSTATS 



FOREST 

RECTIFIERS 




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. 

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. 



Page 28 



PROJECTION ENGINEERING 



FILM MEASURING MACHINE 

Theatre Engineering Service Co., Ltd., of 
Hollywood, Calif., announce their new 
T.E.S. Precision film measuring machine, 
which has many desirable features^ among 
these being a heavy cast-iron base with rub- 
ber feet, allowing the machine to be placed 
on a work-bench and film measured without 
the annoyance of the machine moving dur- 
ing this process. 

This new measuring machine has a large 
64-tooth sprocket constructed of duralumin ; 
and, although this sprocket is twice as large 
as those generally used, the weight has been 
kept to an absolute minimum, making start- 
ing and stopping much easier. The sprocket 
is supported on two bearings, and is directly 
connected to the counter, thus eliminating 
all gears. Frame numbers are engraved on 
the edge of the sprocket. The base and- the 
sprocket are so constructed that when the 




machine is placed over a light on the work- 
bench, it permits of the frame lines being 
distinguished without removing the film 
from the sprocket. The counter is placed 
at a 30-degree angle, making it easier to 
see at all times. 

The base is finished in black crystal-lac 
enamel, while all other parts are nickel- 
plated. 

T.E.S. Precision film measuring machines 
are being distributed throughout the United 
States through the National Theatre Supply 
Co. 

▲ 

HOME TALKIES 

Oroscope is the offering of the Oro- 
Tone Company of Chicago. It is a self 
contained combination radio-phonograph- 
home talkie, projecting either silent or 
sound pictures and adjustable for 78 or 
33% r. p. m. 

AMPRO TALKER 

Ampro, is arranging for a_ New _ York 
demonstration of its new talkie projector, 
which is designed for industrial and educa- 
tional fields. 

▲ 

STEWART WARNER EXPANSION 

Stewart Warner Company of Chicago 
has progressed from speedometer, then 
radio manufacture, and will now follow 
with the production of an amateur movie 
camera with the manufacture of a pro- 
jector. 

TWO PHOTOLYTIC CELLS DEVEL- 
OPED BY ARCTURUS 

Two new Photolytic cells, designated as 
Tvpe P-23 and P-27 and designed especially 
for use in equipment where space is lim- 
ited, yet maintaining the photo-sensitive 
area, have been placed on the market by 
the Arcturus Radio Tube Co. of Newark. 

Because of the ruggedness and principle 
of the photolytic cell, these units are non- 
microphonic and require no polarizing po- 
tential, the company claims. Background 
noise is eliminated and because of the 
extremely low impedance of these cells 
there is no pickup of parasitic noises. The 
high sensitivity of these cells provides an 
exceptional audio frequency response which 
is characteristic of the Photolytic prin- 
ciple, it is said. 

A new folder describing the complete 
line of photolytic cells has just been issued 
by the company. 



EASY WAY TO ADJUST SIMPLEX 
REAR SHUTTER 

A practical and simple method of de- 
termining when the rear shutter on the 
new Simplex machine is in a neutral posi- 
tion, has been worked out by Max Silver- 
man, projectionist. 

Ever since these machines were intro- 
duced, operators have had difficulty in 'plac- 
ing the shutters in the neutral position. It 
has necessitated much trying to get the 
pilot light in just the right position, and 
then experimenting until the neutral posi- 
tion was found. 

• Following is the method which Silver- 
man worked : 

There is a shaft that protrudes from the 
front of the machine where the original 
shutter was held in place. By the easiest 
means practical, place the blades of the rear 
shutter in a neutral position. Then with 
white paint make a little arrow on the hub 
of the shaft in front. This arrow will at 
all times indicate the 'position of the blades 
of the rear shutter, and when the arrow is 
directly in front the blades will be in 
neutral. 

A 

RCA PHOTOPHONE ABROAD 

Patrons of motion picture theatres in 
England, France and Italy are more par- 
ticular about the quality oi sound repro- 
duction than are the patrons of theatres in 
the United States, according to M. C. 
Batsel, chief engineer of RCA Photophone, 
Inc., who has just returned from a five 
weeks' business trip abroad. American 
made pictures are the backbone of the in- 
dustry in each of those countries, although 
local producing corporations are beginning 
to become more active. With one excep- 
tion, seven of the eight large studios in 
England record by the RCA Photophone 
system and the two principal studios in 
both France and Italy employ the Photo- 
phone method. 

"The installation of sound reproducing 
apparatus in the motion picture theatres of 
England, France and Italy is progressing 
rapidly with a definite demand for equip- 
ment that will deliver sound of high 
quality." said Mr. Batsel. "The people 
have become sound conscious and as a 
result inferior sound apparatus is being re- 
placed. Theatres which do not offer good 
sound are empty and those that have good 
sound are enjoying excellent patronage. In 
Italy the demand is for quality musical 
sound reproduction. A well-scored picture 
will play to good business. A poorly 
scored picture will starve." 



VOLUME CONTROLS 

The Clarostat Manufacturing Company, 
Inc., 285 N. 6th Street, Brooklyn, N. Y., 
offers a graphite unit which includes a 
positive rolling contact. A rotating move- 
ment is given to the roller contact (c) by 
means of a small pinion Cp) attached to 
the contact roller, engaging gear track (g) 




NEW PORTABLE RECORDER DEVEL- 
OPED BY RCA PHOTOPHONE 

A new portable sound recording equip- 
ment for use in connection with the 
Mitchell camera, and designed for greater 
efficiency in location and newsreel work, 
has been produced by RCA Photophone in 
collaboration with Westinghouse and Gen- 
eral Electric. Entire equipment weighs less 
than 400 pounds. 

A feature of this apparatus is the adop- 
tion of the single system of recording by 
means of which the sound is recorded upon 
the film 19^2 frames in advance of the 
exposure of the picture, which makes pos- 
sible the immediate reproduction of the 
subject after it has ben developed and 
printed. 

A HORN FOR PUBLIC ADDRESS 

A new two-unit, six foot trumpet is 
announced by the Racon Electric Company, 
18 Washington Place, New York, which will 
find wide application in the public-address 
and sound field. It has a 30-inch bell, 
round, length 54 inches. It has a metal 
beaded edge, cast aluminum throat section, 




moulded in the periphery of resistance ele- 
ment (r). Turning the knob imparts a 
rotary motion to the contact arm. A smooth, 
positive contact is assured over the length 
of the resistance surface. 



loose counlings for units, and is demount- 
able. It is equipped to operate with two 
units. The weight is 22 pounds. 



POTENTIOMETERS 

The Dejur-Amsco Corporation, 95 Morton 
Street, New York, state that the electrical 
features of that company's heavy duty rheo- 
stats and potentiometers are made possible 
by refinements in mechanical structure. 
The resistance wire is wound over three 
layers of .015 inch (per layer) asbestos 
covering on a steel core. The anchorage 
is permanent and of low electrical 
resistance. 

The Alleghany metal arm is of special 
design, providing an unwearing pressure 
upon the resistance wire of ten pounds to 
the square inch. The contact between the 
bushing and the contact arm is under a 
constant pressure of twenty pounds, and the 
current is carried both by the bushing and 
the shorted-out section of the rheostat, with 
the definite elimination of microphonic 
effects associated with resistance variations 
in ordinary rheostats. 



BEACON PROJECTOR 

The Beacon projector, manufactured by 
the Beacon Projector Co., 521 West 57th 
Street, New York, is equipped to take 
standard size 35 mm. film. The Beacon 
standard lighting equipment is a 300 watt 
■ — no volt projection lamp and the motive 
power is a no volt universal motor taking 
either direct or alternating current. Equip- 
ment for use with a 32 volt farm lighting 
circuit or an automobile storage" battery can 
be furnished. The Beacon is also equip- 
ped with a hand drive. 



FILM REELS 

A new series of sound film reels is being 
marketed by the Universal Electric Welding 
Co. 

These reels are spot welded, have no 
brazing screws, clamps or paint. Sizes vary 
from 16mm. to 70mm. in 1,000 and 2,000 
foot capacities. 

Aside from their rugged construction and 
light weight, the reels are designed to offer 
the least film friction, thus adding long life 
to the print by eliminating possibility of 
film damage. 



MAY, 1931 



Page 29 



Noh 



urn, noise 




or moving parts... 

FOREST 

RECTIFIER 



Leading Sound Recording Studios, Theatres, 
and Laboratories where unfaltering current 
supply is required use FOREST — because 
it is superior. 

Adaptable to all sound equipment — inter- 
changeable with your present storage bat- 
tery — several types. 




Just turn the switch to con- 
vert a 110 or 220 V. a-c. 
into fully filtered d-c. 

FOREST ELECTRIC 
CORP. 

New and Wilsey Steets 
Newark, N. J. 



For Powers, S 
all other projectors 
equipped for 
sound. 




Used by the 

U. S. Army Motion 

Picture Service. 



The Clayton Even Tension Take-up 

assures absolute freedom from flutter. It takes up 
any amount of film evenly. It will take up with 
any size reel hubs. It prevents excessive wear on 
the lower take-up sprocket and shaft. It stops the 
opening of film splices and prevents excessive wear 
on the film. 

Write for price and 
further information. 

Joseph Clayton 

9430 Forty-Sixth Ave. 
Elmhurst, L. I., N. Y. 



CTNEGLOW 



the 3 element 
recording lamp 

(patents pending) 

ACKNOWLEDGED THE BEST! 

For Optical or Contact Slit. 
For Positive or Negative Film. 
For Any Standard Glow Lamp 
Circuit. 

CONSISTENT — RELIABLE 

Maximum Volume — Abundant 
Exposure — Without Distortion 

Special circuits supplied with each 
lamp. 




PRICES 
Type T9 — 6 inches long — $50 each 
1 ype T8 — 4 inches long — $40 each 
Special discounts in quantities. 



BLUE SEAL 

SOUND DEVICES, Inc. 

130 W. 46th STREET. NEW YORK 



^ PERFECT^ & gHE R SO ^ 
PRODUCT^ WABL E *» 

SYSTEM Vi 

PRICE 1 1 




No Friction on 
Film; Steady 
Drive; Pat- 
ented Light 
Beam Optical 
System .0005 
Wide. High 
Intensity. 



All Wearing 
S u rfaces 
Chromium 
Plated; Rollers 
Ball Bearing. 



Easy to Install. 
Models for 
Simplex, 
Powers and 
Motiograph. 



Price and Particulars on request. 

WEBER MACHINE CORP. 

59 KUTTER ST., ROCHESTER, N. Y. 

Export Dept., 15 Laight St., N. Y. C. Cable, "Arlab," 
New York 



Page 30 



PROJECTION ENGINEERING 



F. S. C. 

GENUINE OPTICAL CROWN 

GLASS PLATES 

Enclose all Portholes for Sound Films and 

Shut Out the Disturbing Noise of the 

Projection Booth. 



No Distortion 



No Loss of Light 



FISH-SCHURMAN CORPORATION 



45 West 45th Street 



NEW YORK CITY 




Portable Sound Distribution Equipment 

For schools and colleges, churches, 

lodges, parks, airports, etc. Output 

sufficient for two dynamic speakers at 

heavy volume. Completely equipped 

with meters and controls. Padlocked 

against tampering. 

Dealers can rent this equipment 

profitably. 

20" high, \2>Y\" wide, 12J4" deep. Complete 

with microphone and speaker — $350.00. 

Write for illustrated folder. 

FERRANTI, Inc. «*•.«£& 




BUILT 

SOUND 




We build splicers to 
your specified require- 
ments — for sound film, 
wide film, 35mm or 
16mm film. Our splic- 
ers, both standard and 
custom-made, are giving 
sturdy, dependable serv- 
ice in theatres and ex- 
changes throughout the 
world. 

Send for literature 

GRISWOLD 

MACHINE WORKS 

Port Jefferson New York 



%JV» " HAN Dl -MIKE" ,a ** 

X* MOST EFFICIENT GENERAL 1L™. 



single button mi- 
crophone. 200 ohm 
Primary. 100.000 
ohm on secondary 
side. List price $5. 



UTILITY MICROPHONE KNOWN 

List I O Complete 
The truly perfected single button 
hand microphone.Two models, "Reg- 
ular" and "Special Home Recording." 
Scientifically damped diaphragm, gold 
plated button, toggle switch, 15-foot 
cord. Finished bronze or gunmetah 
Dealers, write for our "direct deal." 
Get our complete catalog. 

UNIVERSAL 
MICROPHONE CO., Ltd. 

1163 Hyde Path Blvd. 
INGLEWOOD, CALIF. 

Microphones $5 to $?50. Also cable 
ers, mountings 



transform- 
stands, etc. Expert microphone repairs. 










] 


,»-,, **-~2^*>^»m*m*k 






BEST CARBON SAVER 

for Low Intensity Arcs 

Permits projectionist to get at least one more 
reel from each set of stubs. Made in 7, 8, 9, 

10, 12 and 13 mm. sizes. 

$2.50 each at your dealer. 

BEST DEVICES CO. 

2108 PAYNE AVE. CLEVELAND, OHIO 1 



W* 



offer to manufac* 
turers interested in. 



EXPORT 

the services of a dependable organization, 
well established in the entire foreign field 

AD. AUMEMA, Inc. 

Manufacturers' Export Managers 

116 Broad Street, New York, N. Y. 



INDEX TO ADVERTISERS 



A 



Ad. Auriema, Inc 30 

American Radio Hardware Co.... 31 
Amplion Corp. of America 5 



B 

Bausch & Lomb Optical Co 25 

Bass Camera Co 31 

Bell Equipment Corp Second Cover 

Best Devices Co 30 

Blue Seal Sound Devices, Inc 29 



Cameron Publishing Co 32 

Chicago Gear Works 31 

Joseph Clayton 29 



D 
DeJur-Amsco Corp 25 



Ellis Electrical Laboratory 31 

F 

Fish-Schurman Corp 30 

Ferranti, Inc 30 

Forest Electric Corp 27, 29 

G 

General Radio Co 27 

Griswold Machine Works 30 

H 

Hoffman-Soons 27 



Int'l. Broadcasting Equipment Co.. 3 
Int'l. Projector Corp 6 

N 
National Carbon Co., Inc 1 

R 
Racon Electrical Co., Inc... .Third Cover 

S 

Samson Electric Co Fourth Cover 

SOS Corporation 31 

U 
Universal Microphone Co., Ltd .... 30 

W 

Weber Machine Corp 29 



MAY, 193] 



Page 31 




A Guest at the Morrison 
enjoys all the luxuries 
that only a hotel of premier 
standing can offer. Yet rates 
are remarkably low — $2.50 
up — because sub-rentals pay 
all the ground rent. The sav- 
ing is passed on to guests. 

Every room in the Morrison 
Hotel is an outside room, with 
bath, circulating ice water, bed- 
head reading lamp and Servi- 
dor. A housekeeper is stationed 
on each floor. 




CHI C A G O 



MORRISON HOTEL 




Corner Madison and Clark Streets 

2500 Rooms 
«2.50 Up 




HOTEL 



,PiuAWAsuiN(rm 



ATLANTIC AVE. AND EIGHTH 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 





BASS BARGAINGRAM 

Issue 202 Ready 
FREE! The Classic of Bargain Lists. World's 
largest stock of Motion Picture Cameras and ac- 
cessories. Professional and Amateur. Save real 
money. Send for your copy. Free! 

BASS CAMERA CO. 

179 W. Madison St. Chicago, 111. 



Now . . . SELL Talkie Sound-on-Film 

To Theatres, Schools, Churches, Clubs 

Write for manufacturers' prices on Soundheads, Photocells, 
g Optical Systems, Rectifiers, Amplifiers, Horns, Paders, Syn- 
chronous Motors, Projectors, Lamphouses, Screens, Micro- 
1 phones, etc. 

S.O.S. CORPORATION 

Dept. P.E., 1600 Broadway, New York City 

Cable Address "SOSOUND" 

rillllll!l!IHI!llllllll!!ll]|lllllllllllllllllllli;HIIII!llllllllllll!IIN 




GEARS 

In Stock — Immediate Delivery 

Gears, speed reducers, sprockets, thrust bearings, 
flexible couplings, pulleys, etc. A complete line is 
carried in our Chicago stock. Can also quote on 
special gears of any kind. Send us your blue prints 
and inquiries. 

Write for Catalog No. 60 

CHICAGO GEAR WORKS 

769-773 W. J ack son B lvd., CHICAGO, ILL. 



D'Arcy Laboratories 

place at your disposal their laboratory facili- 
ties for your assistance in volume control 
problems. 

Bulletin M.I. is now ready for those who 
inquire for it. 

D'Arcy Laboratories 

160 A. East Illinois Street Chicago, Illinois 



ELLIS 

MICROPHONES. 

and accessories 
Write for Details 
ellis electrical laborator 

Sales Corporation ' 




337 WEST MADISON ST 



CHICAGO, ILLINOIS 




STOP GOING AROUND 
IN CIRCLES!!!!! 

Come to Us With Your Metal Stamping 

Problems. Send a Sample or Blue-print 

and Compare Our Quotations! ! 

Write for our catalogue of stock items. 

AMERICAN RADIO HARDWARE CO. 

137 Grand St., New York, N. Y. 



FILM CEMENT— SCREEN CLEANING FLUID 
GUM REMOVER— SPRAY PERFUMES 

Nationally known brands must be closed out far below 

cost. Gallon cans only. Write for price and quantities. 

Dealers can make a real buy. 

"Hewes" — Projection Engineering, 52 Vanderbilt Ave. 
New York City. 



Page 32 



PROJECTION ENGINEERING 



Books That Carry the Indorsement of the Entire Industry 

SOUND PICTURES 




HOTlONPICTiniE SOUNDFICTUKES | 

cmmn CAMERON'S 
SOUND ENCYCLOPEDIA 



J AMIS R. CAMERON CAMERON &RIDER 



F °URTH EDITION 



JAMESR.CAMIRON 



ON 
®m MOTION HCI08ES 



PRICE 6^ PRlCE7i¥o PRICE58& PWCE3& 



M»UBL!SHlWJgMF^^ 



You Can't Go Wrong with a 
Cameron Book 

The Department of Public Instruction, Washington, D. C, 
says: 

"The U. S. Army, Navy, Marines, the Bureau of 
Standards, the United States Veterans Bureau, and 
practically every other government department using 
motion pictures like ourselves, rely on the Cameron 
technical books." 

Cinematograph Bureau of League of Nations says: 

"Mr. Cameron is one of the limited number of 
technical writers on Cinematography really worth read- 
ing."' — "Has made important contribution to the liter- 
ature of the sound film." 

The American Projection Society (A.P.S.) says: 

"The best book (Sound Pictures and Trouble Shooters 
Manual) on the subject now available." 

Cameron's Books are endorsed by practically every 
Manufacturer of Motion Picture Equipment in this 
country and abroad. — Every Motion Picture Trade 
Paper throughout the world — 

They are up-to-the-minute — complete and 
understandable — Demand Cameron Books. 



TROUBLE SHOOTERS MANUAL 

By James R. Cameron and John F. Rider 

Introduction by William F. Canavan, International 
President I.A.T.S.E. & M.P.M.D. 

Largest, Latest and Most Comprehen- 
sive Book on the subject published 

Explains in detail the construction, operation 
and care of all Sound Recording and Re- 
producing Equipment. 

1,100 PAGES 500 DIAGRAMS 

PRICE SEVEN-FIFTY 

CAMERON'S 

ENCYCLOPEDIA 

SOUND PICTURES 

An Encyclopedia covering the subject of "Talking 
Pictures" from A to Z — Contains over 2000 subjects. 

PRICE THREE-FIFTY 

MOTION PICTURE PROJECTION 

By JAMES R. CAMERON 

Introduction by S. L. Rothafel (Roxy) 

1200 PAGES 500 ILLUSTRATIONS 

FOURTH EDITION 

Used Throughout the English Speaking World as 
"THE STANDARD AUTHORITY" 

PRICE SIX DOLLARS 

MOTION PICTURES WITH SOUND 

By JAMES R. CAMERON 

Motion Pictures With Sound covers the subject from A 
to Z in such a manner that the subject is easily under- 
stood. The book measures 73/| x 5 inches. 

400 PAGES 150 ILLUSTRATIONS 

PRICE FIVE DOLLARS 



Cameron Books Are Carried in Stock By All Branches of 

National Theatre Supply Company 




Williams Press, Inc., new york — Albany 



RACON'S LEADERSHIP AGAIN DEMONSTRATED 

Racon Portable Horns Used 

at Times Square, New York, in 
Broadcasting directly from Aeroplane on Saturday, April 18 

Racon Products Have 

Proven Their Superiority 

Patented non-vibratory, non-porous material and 
construction, plus light weight, which makes for 
perfect results and maximum convenience. These 
outstanding features of RACON products have 
made imitation and competition impossible. 

for 

THEATRES — AIRPORTS 

CONVENTION HALLS 

SOUND TRUCKS — PARKS, etc. 



Racon 
Portable Trumpet 

is demountable into 3 sections. 
Designed for easy assembly and 
small space storage. Unique in 
tone reproduction over wide area. 
Acoustically perfect for speech 
and music under all weather con- 
ditions. 






RACON 

HORNS & 

UNITS 



Racon 
Portable 
Horn 



New type number 3320A 

Air column length slightly 

under 7 feet. Oval beU 

. 27 inches by 35 inches. 

i3§|\ depth 2S inches. De- 

\m mountable into 2 sec- 

^^l tions. Ideal in small 

<!Z\ space and porta- 




NEW 
MASTER UNIT 
Continuous operating 
capacity 6-8 watts. 
Peak load capacity 
25 watts. 



Racon 
Theatre Horn 

RACON HORN No. 5325— For small 
space between the screen and wall. 
Air Column slightly less than 10 feet. 
Depth 30 inches. Bell 34x44 inches. 
Weight 55 pounds including frame. 



Continuous ojperal 
capacity 7-10 wa... 
Peak load capacity 
25 watts. 




quickly 

■ mJm. y "^ m%*W m HI s^^*/ I I 

Schools, churches, clubs, hotels need the portable PAM Address 
system. With it, a speaker addresses 500 people as easily as 
half a dozen. Speech and music, both vocal and instrumental, 
are amplified with excellent quality. 

The units in this system are completely matched and designed 
to operate together. Naturally the results obtained are superior 
to a combination of units procured from different sources which 
were not designed to operate together. 

The two units that are required (MIK 100 and PAM 100) to- 
gether weigh less than 75 pounds, and the system can be set 
up ready for use in less than five minutes. No batteries are 
required . . . and the price complete with tubes, microphone, etc., 
and nothing left to buy, is $343.00. 

Send for twin folders PE4; one descriptive of the PAM-100 and 
the other of the MIK-100. 



SELL 

Portable PAM Address system to 
institutions that hold regular meet- 
ings and need the equipment per- 
manently. This price is reasonable 
and the profits are large. 



RENT 

Portable PAM Address systems for 
special occasions. One man can 
transport the entire system and set 
it up in five minutes. After a few 
rentals the cost is recovered and 
future income is all profit. 



Main Office: 
Canton, Mass. 




Factories: Canton and 
Watertown, Mass. 



MANUFACTURERS SINCE 10*3 



j£E3fe? 





JUNE. 1931 





(Photograph courtesy Amplioii Corp. of America) 

Showing Loudspeaker Horns of Public- 
Address System, Polo Grounds Baseball 
Park, New York. 







THE JOURNAL OF THE SOUND AND LIGHT PROJECTION INDUSTRIES 



^m-m 




Products Have Proven their Superiority 

THEATRES-AIRPORTS 
* CONVENTION HALLS 

AMUSEMENT PARKS 

"There Is A RACON For Every Purpose" 

Patented non-vibratory, non-porous material and construction, plus light weight, which 
makes for perfect results and maximum convenience. These outstanding features of 
RACON products have made imitation and competition impossible. 




Portable Horn 
Model 3320A 



RACON P Hor„ Ie 

New type number 3320A Air column 
length slightly under 7 feet. Oval bell 
27 inches by 35 inches, depth 28 
inches. Demountable into 2 sections. 
Ideal in small space and portability. 





Racon 2 Unit 6 Ft. Trumpet 

Bell 30 inches round. Length overall 64 inches. 
Storm proofed, metal beaded edge. Cast aluminum 
throat section. Demountable. Loose couplings for 
units. Equipped to operate with 2 giant units. A 
powerful Public Address Horn, where great projec- 
tion is desired. Weight 23 pounds. 

„^*. -". 

Racon 
Portable Trumpet 

is demountable into 3 sections. 
Designed for easy assembly and 
small space storage. Unique in 
tone reproduction over wide area. 
Acoustically perfect for speech 
and music under all weather con- 
ditions. 



^W 




RACON 
THEATRE HORN 

RACON HORN No. 5325 — For 
small space between the screen 
and wall. Air Column slightly 
less than 10 feet. Depth 30 
inches. Bell 34x44 inches. 
Weight 55 pounds including 
frame. 



Racon's New Master 
Unit 




Continuous oper- 
ating capacity 
6-8 watts. Peak 
load capacity 25 
watts. 



Improve Your Sound Equip- 
ment with RACON Speakers 
and WATCH RESULTS! 



GIANT ELECTRO 




DYNAMIC 
HORN 
UNIT 



Continuous oper- 
ating capacity 
7-10 watts. Peak 
load capacity 25 
watts. 



RACON HORNS & 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 

RACON ELECTRIC CO., Inc. 

FAPTORIP^- 18 t° 24 WASHINGTON PLACE, NEW YORK 

1 »»^ * V_Vl\.ll— ikJ . LONDON, ENGLAND TORONTO, CANADA 



JUNE, 1931 Page I 

Fundamentals of Projection 



^^MALL AREA of light source is essential to the projection 
of a clear, sharp image on the screen. The crater of the 
carbon arc, just a few millimeters in diameter, is the ideal 
source of light. 

HIGH INTRINSIC BRILLIANCY is required of this mi- 
nute area of light — sixteen million times the high intensity 
of screen illumination demanded by the critical patron. 
National Projector Carbons afford an intrinsic crater 
brilliancy rivaling that of the sun at zenith. 

STEADY LIGHT is equally essential to satisfying pro- 
jection. Extensive research and years of experience have 
enabled National Projector Carbons to supply the steady, 
white light that is a source of satisfaction to both projec- 
tionist and patron. 

/ 

Two satisfied patrons pay for the 
ISational Projector Carbons 
used at each performance. 

NATIONAL 

PROJECTOR CARBONS 



. Sold exclusively through distributors and dealers. 
National Carbon Company will gladly cooperate uith 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 I IJBJ 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. Ill 



JUNE 
193 1 



Number 6 



Contents 



Editorial 



page 
4 



Notes on Public- Address Installation and Operation 

By Gordon S. Mitchell 

Ground Noise Reduction 

By Ralph H. Townsend and Hugh McDowell, Jr. 10 



"Moving Talkie" Brings Dead Language to Life 



13 



Film Recording in Sound Motion Pictures, Part II 

By Charles Felstead 1 4 

An A-C. Operated Portable Talking Picture Equipment 

By J. DeGiovanni 1 7 

Motion Picture Cost Accounting 18 

Examination Questions for Projectionists 19 

Departments 

News of the Industry and New Developments 24 

Index of Advertisers 30 



Bryan S. Davis 
President 

James A. Walker 
Secretary 



Published Monthly by 

Bryan Davis Publishing Co., Inc. 

52 Vanderbilt Ave. 

New York City 



Sanford R. Cowan 
Advertising Manager 

J. E. Nielson 
Circulation Manager 



Publication Office— North Broadway, Albany, N. Y. 
Chicago Office — 333 N. Michigan Ave. — Charles H. Farrell, Mgr. San Francisco Office — 155 Sansome St. — R. J. Birch. 

St. Louis Office— 505 Star Bldg.— F. J. Wright. Los Angeles Office — 846 S. Broadway— R. J. Birch. 

Kansas City Office — 306 Coca Cola Bldg.— R. W. Mitchell. New Zealand — Tearo Book Depot — Wellington. 

Entered as Second Class Matter at the Post Office at Albany, N. Y., October 9, 1929, under the act of March 3, 
1879. Yearly subscription rate $2.00 in U. S. and Canada. 'Yearly subscription rate $3.00 in foreign countries. 



JUNE, 1931 



Page 3 



Wet 

or 
Dry! 




In his insatiable thirst for Knowledge, 
the Gentleman pictured herewith has 
invaded the Domicile of Mr. and Mrs. 
Carassius Carassius* and has forcibly 
prevailed upon them to accept a Star 
Boarder. 

The International Type "B" Con- 
denser Microphone remained sub- 
merged with its Finny Hosts for 
Three Weeks — in constant operation 
— and at the end of that period was 
Still Going Strong! How many micro- 
phones with which you are familiar 
can withstand such a test? 



We make no Wild Claims that it will 
still be Going Strong in thirty weeks, 
but — we have proven that Interna- 
tional Microphones function per- 
fectly when exposed to dampness, and 
if you don't believe it was damp, ask 
Mr. and Mrs. Carassius Carassius* 

The Standard Type "B" Condenser 
Transmitters will operate under ex- 
treme atmospheric conditions and for 
a small extra charge can be processed 
to make them absolutely waterproof. 



"(Gold Fish to YOU) 



International 2Sraa&casttng lEqnipment Co. 



3112 West 51st St. 



Chicago, 111. 



Manufacturers of 



Public address 
systems 



Broadcasting 
equipment 



Centralized Radio 
systems 



Complete Recording 
systems 



E d i t o 



i a 



JUNE, 1931 



THE 
ART OF 

RECORDING 



IN ANY discussion of features 
of sound effects recording, no 
one else, in our opinion, knows 
more clearly what it is all about 
than does Carl Dreher. 

In Mr. Dreher's paper, 
"Recording, Re-recording and Editing Sound 
Film," presented at the S. M. P. E. convention, at 
Hollywood, in May, there is evidence of an artistic 
conception of the requirements, not common 
among engineers. In this paper Mr. Dreher 
describes how re-recording and editing must be 
coordinated in order to yield the desired emotional 
and artistic effects in the finished picture. 

It is a test of good picturization when the thea- 
tre patron of a critical bent, in absorption of the 
story screened, is lulled away from analysis of 
the mechanics involved. 

As the illusions of projected sound and picture 
approach perfection this condition is realized. It 
is this achievement that marks the best we have 
in the way of coordination such as dealt with in 
Mr. Dreher's paper. 



FIRE 
PROTECTION 



THE projection booth fire 
which occurred recently in 



the Palace Theatre, St. Louis, 
resulted in the death of a pro- 
jectionist. The projectionist, 
William Gibson, was the hero 
of the fire. Gibson alone fought the fire to extinc- 
tion but in doing so his clothes caught fire. 

The first responsibility of all theatre manage- 
ments is to make sure that every possible provision 
is made in their booths and other parts of the 
theatre to instantly combat fire regardless of its 
origin or cause. 



THE 

SPOKEN 

WORD 



THE power for good or ill, 
of the written word was 
realized as early as Omar's 
day, and earlier. It was of the 
written word that Omar wrote : 
"Nor all your piety nor wit will 
lure it back to cancel half a line, nor all your tears 
wash out a word of it." And so, as far back as 
records may be traced the written, intelligible 
word, the symbol and the mark, bridge the present 
with the past. 

The widespread applications of sound record- 
ing now being made promise to revolutionize 
ideas of passing along for present and future 
purposes those impressions of evidential value 
heretofore carried only by the written word. 

The substance of history and the windrowed 
stepping stones of civilization have existence only 



in memory and in the written word. Blessed as 
have been the glory and the uses of written words, 
to understand their message in a large, cultural 
sense, has called for the establishment and main- 
tenance of vast educational systems. 

When one listens to a child haltingly reading 
the lines of Hamlet's soliloquy, and recalls the 
same words recited by a mature, experienced 
actor, there is food for thought in the realization 
that words in written or printed form only are 
but a part, a share of what is intended — a 
deficiency must be made up. 

By means of sight, through reading, we may 
visualize events of the past. By means of sound 
recordings oncoming generations of men will not 
for the truth be entirely dependent upon the 
viewpoints and interpretations of scriveners and 
"historians." 

In this matter we are on the eve of far reach- 
ing advances. 



AUDITORIUM 
ACOUSTICS 



A 
AY 



N APPARATUS is now 
available by means of 
which it is practicable to study 
the acoustical properties of 
auditoriums — the rate of decay 
of sound energy in a room 
may be measured. 

When the sound has reached the steady state 
the loudspeaker circuit is opened and at the same 
time a timer is started. When the sound energy 
has decayed to some definite value the timer is 
automatically stopped. 

The subject of this measuring device is covered 
in a paper presented at the Hollywood conven- 
tion, May 27, of the Society of Motion Picture 
Engineers, prepared by Messrs. V. L. Chrisler 
and W. F. Snyder. 



PUBLIC- 
ADDRESS 



AS Projection Engineer- 
ing has predicted repeat- 
edly during the past two years, 
the extension of sound ampli- 
fying and public-address sys- 
tems is reaching commercial 
proportions. If all of the present business were 
being handled by one or two companies, there 
would be that many manufacturing plants operat- 
ing to capacity. The fact is that the many parts 
which go into the makeup of public-address are 
being made by a score or more manufacturers. 
In time it may be that all of these companies will 
have satisfactory billings. 




cnJjL^tttZiUa 



<rL 



Editor. 



JUNE. 1931 



Page 5 




quickty 

Pays for Itself 

Schools, churches, clubs, hotels need the portable PAM Address 
system. With it, a speaker addresses 500 people as easily as 
half a dozen. Speech and music, both vocal and instrumental, 
are amplified with excellent quality. 

The units in this system are completely matched and designed 
to operate together. Naturally the results obtained are superior 
to a combination of units procured from different sources which 
were not designed to operate together. 

The two units that are required (MIK 100 and PAM 100) to- 
gether weigh less than 75 pounds, and the system can be set 
up ready for use in less than five minutes. No batteries are 
required . . . and the price complete with tubes, microphone, etc., 
and nothing left to buy, is $343.00. 

Send for twin folders RE4; one descriptive of the PAM-100 and 
the other of the MIK-100. 



SELL 

Portable PAM Address system to 
institutions that hold regular meet- 
ings and need the equipment per- 
manently. This price is reasonable 
and the profits are large. 



RENT 

Portable PAM Address systems for 
special occasions. One man can 
transport the entire system and set 
it up in five minutes. After a few 
rentals the cost is recovered and 
future income is all profit. 



Main Office: 
Canton, Mass, 



Factories: Canton and 
Watertown, Mass. 




Page 6 



PROJECTION ENGINEERING 



AMPLION PUBLIC ADDRESS 

SYSTEMS- 



UNIVERSALLY APPROVED 




AMPLION GIANT 
DYNAMIC UNITS 

600% more efficient 
8000 cycle range 



TRANSVERSE 

CURRENT 

MICROPHONES 




TYPE WL-12 



AT 



BASEBALL PARKS important announce- 
ments and league results are announced 
thru Amplion equipment. An Amplion Public Address 
System is operated at the Polo Grounds in New York City. 



AT 



FLYING FIELDS, above the noise of motors 
and expectant passengers, flying schedules, 
aviation news and last minute words of instruction are in- 
stantaneously announced through the powerful trumpet 
horns. 



IN 




SCHOOLS AND CHURCHES Amplion's 
public address system has had widespread 
acceptance. For amusement and educational diversions 
phonograph records may be played on the electric 
turntable. 

FOR PORTABLE TRUCKS, many of which 
' ^-^'N are now being equipped. This form 

of public address system is meeting with great success as 

an advertising medium. 

Vilf % pf*\pLJf"\k|pC Amplion transverse current microphones are available 
^ 'W'tJi j n every ty pe ann - capacity and for every requirement. 

Amplion hand and stand microphones of the very latest type are approved by record- 
ing laboratories and home talkie apparatus manufacturers. 



HORNS Under the paint what? Amplion horns 
1 proof from the surface to the core. Th 



is are weather- 
proof from the surface to the core. They are acoustically 
correct and not affected by any climatic condition, are available in every size and 
shape — from the narrow air column to be used in the narrow space behind sound 
theatre screens to the six foot bell mouth trumpets which are portable and can be 
set up in a few seconds for outdoor and amusement park gatherings. 

Ask about Amplion's two new amplifiers — PA-50 watt 
amplifier for large theatres and outdoor usage, and the 
MP-45 combined microphone and power amplifier for 
small public address systems and recording. 

WRITE FOR 20 PAGE CATALOGUE AND PRICE LIST 
ON SOUND SYSTEM APPARATUS FOR EVERY PURPOSE. 

Ask about the PORTOVOX, a complete portable sound 
system in two pieces for convenient carrying listing at 
only $250. 



dfe 



Amplion Products Corporation 

38 W. 21st Street New York City 



Projection Engineering 



JUNE, 1931 



Notes on public-address 
installation and operation 



By Gordon S. Mitchell* 



ONE of the rapidly increasing 
uses to which sound amplifica- 
tion equipment is being put is 
in increasing the volume level 
of sound as it emanates from a rela- 
tively weak source to such a point that 
it may be heard throughout any size 
space. The public-address field is one 
which embraces the allied radio broad- 
cast, sound motion picture recording 
and sound projection in the theatre, and 
developments in any one of these fields 
may well be applied to the public- 
address. Interrelated as these several 
industries are, their dependence upon 
developments in sound amplification 
for progress mainly means that im- 
provements in one field will advance 
the entire industry step for step. 

In a consideration of the develop- 
ment of the public-address field, some 
thought may well be given to the first 
commercial installation of the kind, 
which was made in the Arlington 
Cemetery for the burial of the 
Unknown Soldier in 1921. This was 
one of the first large installations made, 
and in addition to the amplification of 
sound in the adjacent region, embraced 
a transcontinental transmission of the 
ceremony by long distance telephone 
lines. Throughout, it was a problem in 
acoustics which was faced by the 
engineers responsible for the success or 
failure of the project. 

The very nature of the ceremony and 
the place wherein it was held offered 
many problems from an acoustic stand- 
point. The main amphitheatre, sur- 
rounded by its colonades of marble, was 
the scene of the principal address. A 
large marble arch topped the speakers 
platform. The floor of the audience 
chambers was of concrete, lined with 
long benches of marble. In the midst 
of all this hard surface, the bodies of 

^Reprinted, with permission, from forthcoming 
textbook prepared for National Radio Institute, 
Washington, D. C. 

*Engineer, Universal Sound Labs. 



the listeners and their clothing offered 
the only sound absorptive inside of the 
amphitheatre. 

Such universal interest having been 
manifest in the ceremony beforehand, 
the authorities in charge decided that 
the installation of sound amplification 
equipment was a necessity. Conse- 
quently, large projectors were placed 
in four groups, one group facing in 
each direction from the tops of the 
colonades about the amphitheatre, which 
would serve to increase the sound in- 
tensity to such a degree that it would 
be possible for vast crowds outside the 
arena to hear the ceremony. These 
projectors are numbered from one to 
twenty in Fig. 1. The horns were care- 



Practical problems en- 
countered in designing and 
operating sound project- 
ing equipment. 



fully directed, and provided with 
sufficient power to project the sound 
so as to be intelligible at a distance 
of one thousand feet from the 
amphitheatre. 

The first tryout of the equipment 
showed that the sound from the group 
of projectors mounted over the west 
colonade reached the rear seats inside 
the amphitheatre before the sound com- 
ing from the speaker's stand direct had 
time to reach the same place. The time 
lag between these two identical sounds 
was of such magnitude that it was ob- 
jectionably noticeable. After some 
experimentation, it was found that four 
smaller projectors, mounted directly 
over the speaker's stand and pointed 
towards the rear portion of the audi- 
ence space would overcome the sound 



leaking in from the larger horns and 
correct the difficulty. These horns, 
number 28, 30, 31 and t,^, required just 
the right amount of power to acquire 
a volume level sufficient to overcome 
the leakage from the larger horns, yet 
not enough volume to set up reflections 
inside the amphitheatre. The hardness 
of the entire inside surfaces made this 
a particularly ticklish proposition. 

The smaller projectors number 35 
and 36 were used to overcome the leak- 
age over the western top of the colon- 
ades as were the projectors number 27 
and 34 placed over the eastern colon- 
ades for the same purpose. The pro- 
jectors number 3 to 6 inclusive were 
found to interfere seriously with speech 
originating at the graveside. Conse- 
quently, another set, number 22 to 26 
inclusive was placed in the position 
shown, and the former set switched out 
of the circuit and these substituted 
when the ceremony transferred to the 
graveside. In order that those inside 
the amphitheatre would be able to fol- 
low the ceremony at the grave without 
leaving their seats, the projectors num- 
ber 29 and 32 were placed in the posi- 
tion shown to be used during that part 
of the services. The entire assembly 
of projectors was divided into small 
groups and connected electrically to 
volume control dials in order that the 
volume level in any one portion of the 
audience space could be raised or 
lowered without disturbing the level on 
the remainder of the system. 

Placement of Microphones 

The transmitters were placed in 
order to give complete coverage of the 
ceremony — microphone A being placed 
in front of the box in which sat the 
choir and the band ; microphone B be- 
ing at the speakers stand; while micro- 
phone C was at the graveside. The 
substitution of projector group 22-26 
for group 3-6 eliminated a slight sing- 
ing which was noted when microphone 
C was in the circuit as well as eliminat- 
ing the interference previously men- 
tioned. A fourth microphone, not 
shown, was used by an announcer who 
kept the audience in New York and 
San Francisco informed as to what was 
transpiring between actual spoken 
events. 

The speech currents from the four 
transmitters were amplified by a two 
stage amplifier which brought them up 



Page 8 



PROJECTION ENGINEERING 



to moderate volume. From this ampli- 
fier they were divided into two parts, 
one part of which was additionally 
amplified to supply the projectors of 
the system at Arlington, the other part 
going to an additional amplifier and 
thence to the long distance telephone 
circuit to supply the remote stations. 
The necessary switches were placed at 
the control station at Arlington for 
properly dispatching the impulses to 
their proper destination. Two volume 
indicator meters were placed here also, 
one of which at all times showed the 
amount of power going into the system 
locally and the other to show the 
amount of energy entering the tele- 
phone circuit. Changing conditions at 
the input end necessitated constant 
adjustment of both amplifier circuits. 
Shifting of the audience and changing 
of the wind contributed most of the 
trouble from this score. 

The portion of the power which was 
dispatched to New York City was 
there again divided into two parts, one 
of which served to feed the projectors 
at Madison Square Garden, the other 
being sent on across the continent to 
San Francisco. Projector arrange- 
ments at these points were largely 
similar to those already discussed as 
installed at Arlington. In order to 
insure against failure of any part of 
the system elaborate tests were con- 
ducted previous to the ceremony. In 
order to further guard against failure 
of the system at the last moment, sub- 
stitute circuits were set up and main- 
tained in readiness throughout the 
period of the ceremony. 

With the aid of this equipment, 
twenty thousand persons in San Fran- 
cisco and thirty-five thousand in New 
York City in addition to one hundred 
thousand at Arlington were enabled to 
clearly hear the entire ceremony ex- 
actly as it transpired. 

The success with which this enter- 
prise was carried through is all the 
more notable when it is remembered 
that operating practices, as they have 
been standardized by the experience 
gained in sound recording, public- 
address and radio broadcast, both direct 
and by intercity chains, were then 
entirely a matter of cut and try. The 
successful transmission of this cere- 
mony may well be considered the first 
step in the foundation of the extensive 
public-address field as it is today. 

The public-address system as it was 
then consisted essentially of the same 
pieces of apparatus as at present, 
although vast improvements have been 
made upon individual units during the 
last decade. Fundamentally, it is a col- 
lection of electrical apparatus designed 
and assembled in such a manner that 
it will take in sound at a low volume 
level, amplify this sound and reproduce 
it at such a level that it will be intel- 
ligible to a great number of people. 



The various arrangements and differ- 
entiations between sets depend upon 
several factors, among which might be 
mentioned audience size, location of 
transmitting apparatus, location of pro- 
jection apparatus and the general uses 
to which the system is to be put. 

Degrees of Naturalness 

Present public-address equipment is 
limited in the range over which it may 
be operated successfully. While this 
point is of not so great importance in 
the transmission of speech sounds, it is 
of great importance in the transmis- 
sion of music. The increase in the 
range over which the system will 
operate, both by increasing the high 
frequencies and the low will result in 
increased naturalness where music is 



GOOD THINGS COMING IN 
JULY 

TJOLICE inquiries, examinations 
and investigations heretofore 
have been recorded by means of 
statements copied stenographi- 
cally and typewritten. The recent 
development of sound systems 
and records has given police de- 
partments a new and valuable 
means of direct voice recording. 
This is now being used to advan- 
tage in police work. In the 
July issue of PROJECTION 
ENGINEERING will appear an 
account of the application of 
sound recording as employed by 
the New York Police Department. 
In the July issue will be pub- 
lished also an exclusive story 
describing the Selsyn system of 
lighting effects as used in up to 
date theatres — also directly use- 
ful articles on various topics of 
theatre projection and public 
address installations. 



concerned, and a slight increase in in- 
telligibility where speech sounds are 
concerned. However, public address 
systems as they have been developed 
and improved in the last few years are 
entirely satisfactory as far as intelligi- 
bility characteristics are concerned. As 
amplifiers are improved, the frequency 
range over which the systems will 
operate will increase, for it is amplifier 
equipment in general which limits this 
factor at the present time. 

Acoustic limitations of the equip- 
ment, that is, limitations on the loud- 
ness of the projected sounds which are 
imposed by the equipment are probably 
the more difficult of the two factors to 
improve. Experimental data has shown 
that the variations in loudness between 
two component parts of the same 



orchestral selection may be of a ratio 
as great as fifty thousand to one. 
Present equipment will not operate 
satisfactorily over such a great range 
in loudness level. Due to this fact, it 
is necessary to take care of these varia- 
tions by a manual adjustment of the 
amplifier during the actual rendition of 
the selection. If the gain be varied by 
small enough intervals the change will 
not be noticeable. An increase in the 
loudness range — that is, an increase in 
the range over which the system will 
faithfully reproduce sound without ad- 
justment — would make the reproduction 
an exact and faithful duplicate of the 
sound as originally produced. 

Frequency Range 

The audio spectrum, complete, em- 
braces a frequency range from sixteen 
to about twenty thousand double vibra- 
tions per second, (d. v.). Sounds, or 
more properly, regular disturbances in 
the air strata either above or below 
this frequency limitation cease to be 
audible. Musical sounds which contain 
an abundance of harmonics will often- 
times reach this top frequency figure. 
However, an electrical system which 
will transmit a band of frequencies 
from sixteen to ten thousand d. v. per 
second will fulfill all requirements for 
satisfactory musical reproduction. A 
system which will transmit a band of 
from one hundred twenty-eight to 
eight thousand d. v. per second has 
been deemed satisfactory for speech 
transmission under favorable condi- 
tions, although sounds so cut off will 
sound somewhat unnatural to the ear. 
The more this range is extended at 
both ends the more naturalness will be 
given the transmitted sound. 

Use to Be Made of an Installation 

Arbitrary statements as to frequency 
requirements can never satisfactorily 
be made without consideration of the 
future use to which the system is to be 
put. A single example will illustrate 
this point. A public-address system, 
such as would be used by a city mer- 
chant in advertising his wares through- 
out the streets, (either with a portable 
system mounted on a truck or a perma- 
nent installation in front of his place 
of business) would be entirely satisfac- 
tory if it transmitted a frequency band 
of from one hundred to eight thousand 
d. v. per second. Especially would this 
be true were speech announcements to 
comprise the bulk of the program. 
There would be no need of an abso- 
lutely faithful reproduction of the 
sound embracing all frequencies, be- 
cause the audience for which the pro- 
gram is meant would hear only a small 
portion of it, the audience being con- 
stantly changing and always on the 
move. In addition, the person hearing 
such a program, as he moves down the 



JUNE, 1931 



Page 9 



street would hear it with only a part of 
his attention fixed on what he was 
hearing. Thinking of a myriad of ex- 
traneous things as he would be. he 
would only half consciously hear the 
selection or accompanying announce- 
ments. An exactly faithful reproduc- 
tion in such a case would be wasted. 
On the other hand, if the system is to 
be used by an audience giving its en- 
tire attention to the program, such as 
for instance a concert in a public park 
on a Sunday afternoon, a faithful 
reproduction of the entire audio 
spectrum would be necessary for full 
enjoyment of the program. 

Harmonics Important 

The fundamental tone, that is, the 
fundamental of the melody of vocal 
music and certain instruments can be 
reproduced by a system which cuts off 
at the above mentioned frequencies, 
although music so reproduced will 
sound unnatural. It is the harmonics 
which give life and color to the trans- 
mitted musical tone, hence a system 
which cuts off most of the harmonics 
would be considered unsatisfactory for 
successful music transmission. 

The presence of foreign noise is a 
problem almost exclusively of the out- 
of-door public-address system. Foreign 
noises influence the ability of the 
listener to hear the transmitted sounds, 
and thus lower the general intelligi- 
bility. In addition to this, the constant 
effort necessary to sort out the desired 
from the undesired sounds tends to tire 
the listener. If this strain is to be 
inappreciable, the sound delivered by 
the system should be at a power level 
of at least ten thousand times the power 
level of the extraneous noise. If a 
correct relationship between the trans- 
mitter and projector is not- maintained, 
there will be foreign noise introduced. 
the elimination of which forms one of 
the most troublesome problems of the 
operation of public address equipment. 
When a portion of the sound emitted 
by the projectors feeds back into the 
microphone with sufficient intensity 
that its reproduction is greater, or as 
great, as the sound originally trans- 
mitted by the projectors, and in such 
phase relation that it tends to aid the 
original sound, the system will emit a 
continuous note. This is known as 
"singing." However, the sound may 
not reach the microphones in such 
phase relation that it will aid the 
original, yet may be of such intensity 
that it will seriously distort the trans- 
mitted speech or music. Proper place- 
ment of the microphones with relation 
to the projectors, determined by experi- 
ment, will eliminate the difficulty. In 
addition, the presence of an audience, 
due to damping effect, helps greatly to 
eliminate singing in the svstem. 



Reflection Difficulties 

An interesting point in the considera- 
tion of projector placement is the 
problem introduced by diffraction 
phenomena. Certain systems, notably 
those operating on athletic fields 
encounter distortion due to reflection 
of sound from regularly spaced re- 
flectors such as open board fences. 
The same trouble is encountered when 
the sound is passed through openings 
regularly spaced, the transmitted sound 
being badly distorted in certain portions 
of the audience. 

The public acceptance of the electro- 
mechanical reproduction of sound has 
contributed mightily to the advance of 
this new art. This in turn has been 
made possible by the tremendous ad- 
vance in vacuum tube and amplifier 
performance. The operation of a 



public-address system at the present 
time is mainly a matter of experimen- 
tation — plus individual and personal 
knowledge applied to the problem at 
hand — combined and applied to each 
installation. However, just as radio 
and sound recording practices have 
been more or less standardized with 
the passage of time, so will all of the 
problems of public-address and sound 
amplification be solved and standard 
procedures developed. Until that time, 
the present success of each installation 
lies wholly in the hands of the oper- 
ators of the equipment, who are in 
many cases responsible for its installa- 
tion and often for its design as well. 
Every bit of information which can be 
assembled and placed available for 
their use will hasten the final perfec- 
tion of the art of sound amplification 
and dissemination. 






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Fig. 1. Public-address system, Arlington Cemetery. 



Page 10 



Ground 

Noise 

Reduction 

By Ralph H. Townsend 

PART I 

Hugh McDowell, Jr.* 

PART II 



RCA Photophone 
System 

T 
Part I 



EVER since Thomas A. Edison 
made his first sound recording on 
a piece of tinfoil, reproduced 
sounds have been what we might 
call "victims of circumstances." This 
is true not only of phonograph disc 
reproduction but that from film as well. 
Always has the listener been compelled 
to hear reproduced sounds of speech 
and music accompanied by needle 
scratch or extraneous background 
noises of various sorts. 

In phonography this ever present 
background noise was and still is a 
source of untoward disturbance and 
annoyance. It has been reduced some- 
what by careful attention to the many 
processes involved in record production. 
For instance, the wax on which the 
original recording is made has a 
homogeneity and uniformity undreamed 
of in the early days of the art. Elec- 
trolytic copper anodes, carefully pre- 
pared solutions and accurate timing and 
temperature control now produce from 
the master record a copper plating of 
almost microscopic smoothness. The 
plastic compounds from which commer- 
cial records are pressed have been im- 
proved and refined to a remarkable 
degree. 

But in spite of all this we still have 
needle scratch or surface noise to con- 
tend with. 

With the advent of electrical recording 
the useful frequency range was greatly 
expanded. Electrical reproduction was 
capable of taking off the record all that 



t Two contributions on this Subject, recently 
presented to the Academy of Motion Picture 
Arts and Sciences, Hollywood. 

* Supervising Engineer, RCA Photophone West 
Coast Studios, Author of Part I. 

* RKO Radio Pictures, Author of Part II., 



was on it including surface noise, and 
then what did we do? We found by 
analysis and measurement that a great 
deal, although not all, of the disturbance 
from background noise lay in the fre- 
quency range above 5000 cycles. Elec- 
trical niters being easily constructed we 
then proceeded to cut off by means of 
a low pass filter everything above about 
4500 cycles. The surface noise dis- 
appeared to a considerable degree but 
so did most of the higher frequencies 
we had worked so long and diligently 
to include in our recordings. However, 
the ground noise was reduced and that 
was what we set out to do, hence, the 
experiment was a success. 

The use of film as a medium on 
which to record sounds involved all of 
the trouble heretofore encountered in 
disc recording and reproduction. As 
a matter of fact there is a striking 
similarity between the processes. Instead 
of granular wax we now have to con- 
tend with emulsion grain; instead of 
graphiting, plating and pressing we 
have developing and printing; instead 
of a plastic shellac compound we have 
another piece of positive film stock as 
a final record ; instead of defective 
phonograph needles which do not fit 
the grooves we have light slits which 
get out of focus. 

Most engineers are familiar with the 
reasons why ground noise interferes 
with reproduction and there is no neces- 
sity for a discussion of that particular 
point. If there were no ground noise 
or extraneous sound disturbances speech 
and music would be clearer. The ques- 
tion is how can the ground noise be 
kept out or removed without interfering 
in any way with the wanted sounds or 
frequencies. 

C. R. Hanna of the Westinghouse 
Company and C. W. Hewlett of the 
General Electric Company in the early 
part of 1929 did considerable research 
on this problem and at that time devised 
ways and means of accomplishing such 
an end. So far as we know Hanna's 
method is the basis of all those used 
commercially today. 

Before we go further suppose we 
consider for just a few moments what 
ground noise is. A general definition 
would probably run something like this. 
"Ground noise is all sound evident in 
reproduction which was not present in 
the original sounds." You have all sat 
in theatres and heard this type of dis- 
turbance but probably few have taken 
the trouble to try and analyze this back- 
ground noise. It has been analyzed, 
however, and found to consist of dis- 
turbances from many different sources. 

For instance during a take on a stage 
or set it is almost a physical impossi- 
bility to have perfect quiet. There is 
always a certain amount of set noise 
due to movement on the part of the 



PROJECTION ENGINEERING 

many people who are on the set at the 
time, the cracking of arc lamp housings 
or incandescent lamp housings, noise 
due to the cameras and their driving 
motors, to say nothing of a certain 
amount of noise which is caused by 
traffic outside the studio or extraneous 
disturbances in adjoining studios. 

The next source of noise is located 
in the microphones and their associated 
amplifiers. No matter how carefully an 
amplifier is constructed we always find 
a certain amount of noise due to circuit 
conditions and tube characteristics. 

If we add all of the components of 
noise mentioned above we find that up 
to the film we have a total noise level 
which may, and often does, assume con- 
siderable proportions. In some in- 
stances actual measurements indicate 
that this noise level is as high as 20 db. 
Since all of these disturbances are 
included in the signal fed to the record- 
ing mechanism, whether it be an aeo 
light, light valve, or vibrator, all of 
them make their impression in the re- 
sulting sound track on the film. Every 
film on which recording is made has a 
.certain definite resolving power, that is, 
the ability to respond evenly to ex- 
posure. The emulsion on film which is 
susceptible to the action of light and 
development is a very sensitive medium. 
For this reason it is very desirable that 
it be treated with respect. 

It is not reasonable to suppose that 
we can subject a film to under exposure 
and over development or over exposure 
and under development and get uni- 
formity throughout the resulting opaque 
portions. In other words, unless the 
exposure and development is carried 
out with precision there is the possi- 
bility that the resulting granular struc- 
ture will be a source of disturbance 
later on. 

During the developing, washing, and 
fixing of film there are plenty of oppor- 
tunities, even in a well ordered labora- 
tory, for the film to pick up small 
particles of dirt. By small I do not 
mean particles of a size visible to the 
naked eye. These particles may be, and 
usually are, microscopic in size. Their 
ability to produce noise, however, is 
still considerable. 

The handling of film, that is, of 
negative film and also of the positive 
stock, during the printing operation is 
another potential source of noise. The 
developing and drying of the positive 
print is still another source. 

You may well ask at this point how 
can the disturbance due to a recorded 
sound track combine with dirt and 
make more disturbance. If you will 
consider for a moment the manner in 
which a sound track on film is repro- 
duced as sound the answer will be quite 
evident. 

Most reproduction from film is ac- 
complished by interposing the recorded 



JUNE, 1931 



Page I I 



film between a source of light and a 
photoelectric cell. The intensity and 
amount of light may be considered as 
fixed, consequently any change in the 
opacity or width of the sound track as 
if passes through the light beam will 
cause a variation in the current through 
the photocell. The output of any given 
cell varies directly with the amount of 
light change and is independent of the 
rate of light change. This being true 
it makes no difference whatever to a 
photocell whether the light is cut off 
or varied by means of a sound track 
variation or by specks of dirt or foreign 
matter on the surface of the film. 

In normal variable area recording 
the sound track is always made up of 
equal portions of exposed and clear 
film. 

Any dirt or foreign matter getting 
on the exposed or dark side of the 
track would have no effect whatever but 
should it get on to the clear side its 
presence would be noticed as noise in 
the reproduction. The reason for this 
is evident. Dirt is opaque and the dark 
side of the track is nearly so, but dirt 
on the clear portion would cause a 
change in the amount of light falling 
on the photocell and produce noise. 

At normal gain settings during repro- 
duction, the ease with which wanted 
sounds can be heard depends on the 
ratio of the recorded sounds to the 
ground level. In other words if the 
modulation during recording was low, 
i.e., of the order of say 10 or 15 per 
cent and we accumulated a little noise 
from each of the sources mentioned a 
few minutes ago we would find it diffi- 
cult to distinguish speech or music 
above the noise level. 

The problem then was how to drop 
the level of ground noise to a point 
where it no longer interfered with re- 
corded sounds. Hanna and Hewlett did 
it by making opaque all that portion of 
the track not actually occupied by 
modulation. 

Their method was simple and effec- 
tive. They merely took a little of the 
output of the amplifier just before it 
was fed into the recording mechanism, 
amplified it, rectified it and used the re- 
sulting direct current to furnish what 
may be termed a secondary control 
over the vibrator. 

The output from an audio frequency 
amplifier is in the form of alternating 
current. The wave shape may or may 
not be symmetrical but in all cases the 
current values during any cycle start at 
zero, increase to a positive maximum, 
decrease through zero to a negative 
minimum and then increase again to 
zero. If these values be plotted and a 
straight line be drawn through the zero 
points, this line may be considered as a 
base line above and below which the 
current values rise and fall. In RCA 
Photophone recording this base line 



corresponds to the center line of our 
sound track when the vibrator is at rest 
in its normal position. 

Since the vibrator is designed to 
change its position with respect to this 
base line under the application of cur- 
rent changes, its position at any instant 
is determined by the value of the cur- 
rent at that same instant. As the 
current rises to a positive maximum, 
the vibrator twists to an extreme posi- 
tion in one direction. As the current 
falls through zero and decreases to a 
negative minimum, so the vibrator 
twists back through normal to an ex- 
treme position in the opposite direction. 

Suppose now that some direct current 
were introduced into this circuit. It 
would have the effect of shifting the 
base line about which the vibrations 
took place to a new position and we 
would have a new zero line. Current 
changes and vibrator deflection with 
respect to the base line would remain 
the same as before but neither would 
be the same with respect to the new 
zero line. 

It will be noted that the value of the 
d-c. from the rectifier placed across the 
output of the amplifier is at all times 
proportional to the strength of the a-c. 
signal so we here have an automatic 
and positive control over this d-c. com- 
ponent or "bias" if you will. In other 
words it is necessary only to choose, 
first, the new base line for the vibrator 
setting, and secondly, the proper value 
of the d-c. to return the vibrator to its 
heretofore normal position in the cen- 
ter of the sound track. Both are easily 
obtained and once set the ensuing action 
is simple, positive and automatic. 

Applications of this principle have 
been made during the past year or more 
at RKO Studios and Pathe Studios,' 
where a number of productions have 
been made and released. 



Part II 

DURING the filming of the RKO 
production, "Hit the Deck," in 
September, 1929, musical effects were 
desired that would produce extremes 
in volume beyond the range of the 
normal variable area recording system. 
At this time, Carl Dreher, director of 
sound at RKO Studios, mentioned to 
the writer a system of recording de- 
vised by C. R. Hanna, of the research 
laboratory of the Westinghouse Elec- 
tric & Manufacturing Company, for 
the purpose of eliminating ground noise 
and consequently permitting greater 
volume spread. The writer was much 
impressed by the principle that Mr. 
Hanna had made use of, namely, elimi- 
nating the unused clear portion of the 
sound track in the variable area method 
of recording, and proposed further in- 
vestigation. The objection was raised, 
however, that as this system displaced 
the position of the sound track at mini- 
mum modulation to the edge of the 
film, it was of doubtful utility in com- 
mercial projection machines, as any 
weave in the film in its travel might 
cause it to lose contact with the scan- 
ning beam during intervals of low 
modulation. The writer thereupon set 
about devising a system which would 
retain the advantages of Mr. Hanna's, 
but would keep the sound track at all 
times in the center of the seventy mils 
allotted to it on the film. The writer 
is also indebted to C. W. Hewlett, of 
the General Electric Company, for the 
use of a portion of his system which is 
similar to Mr. Hanna's. 

Natural sound film recording must 
meet two essential requirements, namely, 
good quality of pickup, and range of 
sound from soft to loud with only a 
tolerable amount of noise. In standard 



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Page 12 



PROJECTION ENGINEERING 



methods of recording, the former is ac- 
complished, while the latter is restricted 
to the limiting factor of ground noise 
caused by the unused clear portion of 
the emulsion on the film, admitting un- 
necessary light to the photoelectric cell 
of the reproducing equipment. As the 
light reaching the photocell is in effect 
the carrier of all current within the cell, 
it is evident that unused clear portions 
of the film cause the cell to produce 
energy not required by the legitimate 
sound, thereby producing extraneous 
noise in the output. Noise is also pro- 
duced by the transparent portion of the 
film not being totally clear, but contain- 
ing dirt, scratches, etc., which disturb 
the carrier in such manner as to cause 
additional noise, in effect, reproducing 
the dirt, scratches, etc. It is obvious, 
therefore, that in the standard method 
of recording sound volume reaching the 
film must at all times be adequate to 
overcome the ground noise factor, which 
remains constant. This requirement 
restricts the compass of electrically re- 
produced music and is an obstacle to 
natural and effective reproduction. 

The remedy for this condition in 
variable area recording is found in eli- 
minating the clear portion of the film, 
except at times when the modulation re- 
quires it. With this accomplished, it is 
possible to allow the modulation to fall 
to its natural minimum and rise to its 
natural maximum, for, with the clear 
portion of the film eliminated, ground 
noise no longer remains a constant 
quantity, but changes in proportion to 
the degree of volume. 

Roughly, in standard methods of re- 
cording, the volume range from mini- 
mum to maximum is approximately 20 
db., while with the anti-ground noise 
methods of recording described herein, 
the volume range may be extended to 
approximately 35 db. 

Electrical and Mechanical Design 

The following is a description of the 
device illustrated in Fig. 1 : 

Connected to the output of the re- 
cording amplifier is a two-stage ampli- 
fier of sufficient power to operate a 
rectifier tube following. The d-c. out- 
put from the rectifier is then passed on 
to a direct-current amplifier which 
amplifies the d-c. impulses of the recti- 
fier, increasing their amplitude to any 
desired point, by varying the input volt- 
age on the two-stage amplifier. The 
d-c. impulses are then fed through one- 
half of a voice coil of an electro-dy- 
namic shutter movement to a resistance 
and battery of low voltage which aids 
the flow of current from the plate cir- 
cuit of the d-c. amplifier to ground. 
Across the aiding battery and ground is 
connected the remaining one-half of the 
voice coil which is excited by the aid- 



ing battery when the normal plate cur- 
rent is depressed, due to rectified modu- 
lation. 

It is seen, therefore, that two voice 
coils in series in this manner are ex- 
cited in such a way as to cause one coil 
to exert pressure, when excited, in one 
direction, while the other coil exerts an 
opposite pressure when excited in the 
other direction. This balanced circuit 
of voice coils in the magnetic field 
causes pressure to be exerted equally 
and oppositely in both directions, and in 
opposite phase. To these voice coils is 
directly attached a moving shutter actu- 
ated by the voice coils which is placed 
mechanically in the beam of light re- 
flected by the vibrating element of the 
recording system. The shutter, there- 
fore, moves in proportion to the amount 
of input to the two-stage amplifier, 
moving outward under pressure of the 
rectifier and voice coil to accommodate 
the peaks of the modulation on the film, 
and moving backward when the modula- 
tion decreases, also under pressure of 
the voice coil. It is obvious, then, that 
electromagnetic pressure is exerted in 
both directions in the functioning of 
the shutter. 

The electromagnetic assembly is sup- 
ported mechanically by a lathe carriage 
arrangement so that manual adjust- 
ments may be made to place the shut- 
ter in the proper position with respect 
to the light beam. 

The vibration of the shutter is in 
exact accordance with the d-c. impulses 
of the rectifier, and, therefore, it admits 
light to the extent required by the peak 
modulation reaching the film at any 
given instant. When no modulation oc- 
curs, the shutter is adjusted to admit to 
the film light approximately five thou- 
sandths in width as against thirty-five 
thousandths width for the normal vari- 
able area recording system. It is seen 
by this that there remains about ten per 
cent of the clear portion of the film that 
formerly existed. This factor in turn 
admits only about ten per cent of the 
light formerly reaching the photoelec- 
tric cell in the projector, cuttine down 
overall excitation of the photocell when 
no sound is in evidence, and conse- 
quently reducing extraneous disturb- 
ances in the cell. 

The equipment used in recording 
during; 1930 consisted of a two-stage 
amplifier-rectifier and direct current 
amplifier built in a steel box 18x18x8, 
internally divided, the partition separat- 
ing the d-c. amplifier, from the other 
units. The two-stage amplifier is oper- 
ated from a small B-supply working 
from 50-cycle alternating current and 
supplying 250 volts to these stages. The 
direct current amplifier consisted of 
seven UX-250 tubes in parallel, fed by 
a 180-volt storage battery. A small 
meter control box containing two 
o-to-500 milliammeters is used with a 



switch tor breaking plate current and 
aiding battery current to the voice coils. 
Each voice coil has connected in series 
with it a milliammeter indicating the 
variations of current in each circuit. A 
variable resistance is also used in series 
with the battery to adjust its value so. 
as to make the voice coils balance elec- 
trically, that is to say, when one is at 
maximum current, the other is at zero r 
and vice versa. These meters, there- 
fore, represent the movement of the 
shutter. 

Work on the system described was 
first started in November, 1929. Prac- 
tical results were obtained in Febru- 
ary, 1930, and the device put into pro- 
duction on Radio Pictures' "Dixiana," 
in March, 1930. "Dixiana" was re- 
leased in August, 1930. After further 
development, the system was again used 
on Radio Pictures' production "Half 
Shot at Sunrise," released in Septem- 
ber, 1930. Since this time, develop- 
ment has continued with the aim of 
simplifying and reducing the amount of 
apparatus necessary and to procure 
simpler adjustments in operation. The 
device will continue in use on forth- 
coming RKO productions. 

▲ 

HIGH SPEED PANCHROMATIC 
NEGATIVE FILM 

THE Technicians Branch of the 
Academy of Motion Picture Arts 
and Sciences met on the evening of 
March 31, for a symposium on the new 
high-speed panchromatic negative film 
stocks recently brought out by the East- 
man and Dupont companies. The dis- 
cussion centered around the practical 
use of the new films as compared to 
the old types, without comparison of the 
relative merits of Eastman and Dupont 
stocks. Leading cinematographers, 
film experts, laboratory technicians and 
electrical experts took part in the dis- 
cussion. H. Keith Weeks, executive 
manager of Fox Studios, presided. 

Emery Huse of Eastman, and J. Wes-r 
ley Smith for Dupont, described the 
new stocks and showed demonstration 
reels. J. M. Nickolaus, head of the 
Metro - Goldwyn - Mayer laboratory, 
summarized the effects of the negatives 
on laboratory practice. L. E. Clark of 
Pathe Studios talked on changes in 
lighting equipment and practice being 
brought about by the high-speed film. 
Demonstration film, with talks, were 
shown by Virgil Miller, Karl Struss, 
Ray June, and a number of other lead- 
ing cinematographers who have had ex- 
perience with the new stocks. 

The meeting was arranged by the 
Papers and Programs Committee, of 
which Carl Dreher is chairman. Only 
Academy members, and a few others by 
special invitation, attended the session. 



JUNE, 1931 



Page 13 



"Moving talkie" brings 
dead 



language 



to lif 




Fig. 2. This "moving talkie" shows 
the "high" and "low" spots of Prof. 
H. S. Scribner's voice as he speaks 
into the new device developed by 
W. O. Osbon of the Westinghouse 
Research Laboratories. 



A DEAD language came to life 
recently in a lighted room be- 
fore the Greek class at the 
University of Pittsburgh when 
Prof. H. S. Scribner, head of the Greek 
department, spoke the famous Greek 
word "Eureka" into a new device devel- 
oped in the Westinghouse Research 
Laboratories. 

As the word Eureka entered the de- 
vice, curious lines very much like an 
animated movie wriggled from left to 
right across a screen about the size of 
a large plate. 

These lines showed the "high" and 
"low" spots of the professor's voice. 
They made it possible for observers to 
distinguish the pure from the compound 
notes or tones which are heard by the 
human ear. 

Words of other languages — including 
French, German, Spanish, and English 
■ — were spoken into the device, and 
other curious lines wriggled across the 
screen. For the first time a moving 
talkie of a human voice was shown in 
a lighted room before a large number 
of persons. This device makes "mov- 
ing talkies" of all sounds, as well as 
those of the human voice. When a 
stone is dropped in a pond, this device 
enables one to see the sound waves 
which the splash creates just as the 
eye sees the water waves. It enables 
engineers to examine the high and low 
levels of various sounds, and thus, take 
their first major step in relieving the 
tremendous strain which city noises are 
said to impose upon the human nervous 
system. 

It is entirely possible to dovetail the 
.high and low spots of many noises to 



New method of studying 
the shape of any a-c. volt- 
age or current. 



produce, or approach, silence. For in- 
stance, two tuning forks with equal 
wavelengths or frequencies are set in 
motion. While ■ each produces a note 
which is heard by the human ear, yet 
both together, under certain conditions, 
produce a "silent" note which is not 
heard by the human ear. 

For specific machines, such as air- 
planes, the solution to our present noise 
problem may be in the direction of 
dovetailing the high and low spots of 
the various objectionable noises so that 
Ihey do not fall within the range of the 
human ear. 

Professor Scribner is using this ap- 
paratus for test purposes at the Uni- 
versity of Pittsburgh. 

The application of this device in 
schools and colleges, is not limited to 
reviving and showing students the cor- 
rect pronunciation of dead languages 
such as Greek, Latin, or Sanskrit. 

Language Instruction 

It is expected to be helpful in teach- 
ing the correct pronunciation of Eng- 
lish, French, Spanish, and Italian. With 
a photograph of 
a correctly pro- 
nounced word be- 
fore him, the be- 
ginner is able to 
see just how far 
and in what way 
his pronunciation 
is wrong. Stud- 
ents should be 
able to learn to 
speak a language 
in nearly half the 
time if they can 
see their mistakes 
and correct them 
accordingly. 

The apparatus 
consists essenti- 
ally of an ordin- 
ary microphone 



such as is used in radio broadcasting, 
the new cathode ray oscilloscope and 
some batteries. The whole setup can be 
packed in two large suitcases. 

The heart of this new instrument is 
the cathode ray tube of the oscilloscope. 
It resembles a funnel about the size of 
an old fashioned phonograph horn- 
speaker. The large end of the tube, 
about the size of a dinner plate, fills a 
round opening on the front panel of 
the case. This is the screen upon which 
the moving talkies strut their stuff. 

In the neck of the funnel is an 
"electron gun" that shoots a narrow 
beam of electrons toward the large end, 
or screen. These electrons strike the 
inside surface with a very high velocity 
due to the influence of high voltage im- 
pressed on a coating of silver on the in- 
side surface of the tapered part of the 
tube. The bombardment of any small 
spot on the inside surface by a narrow 
high speed beam of electrons causes the 
spot to glow on the outside with a 
bright green light. 

The bright spot is caused to move 
about on the screen by deflecting the 
beam of electrons as it emerges from 
(Concluded on page 22) 




Fig. 1. A dead language comes to life as Prof. H. S. Scrib- 
ner speaks the famous Greek word "Eureka" into a new 
device developed by W. O. Osbon of the Westinghouse 

Research Laboratories. 

Mr. Osbon is pointing to the curious wriggling lines which 

are "moving talkies" of the word "Eureka." 



Page 14 



PROJECTION ENGINEERING 



Film recording in 
sound motion pictures 



Part 



By Charles Felstead* 



Detailed description of procedure in making sound 
records on film, including Fox Movietone and Western 

Electric 



IN the first article on film recording 
(May, 1931, issue) the general 
methods of recording sound on mo- 
tion picture film were considered, 
and the construction of a film recording 
machine of the type employed in the 
Western Electric system of sound re- 
cording, together with its associated 
apparatus, was studied in detail. The 
discussion is taken up in this second 
article at the point where it was left 
off in the previous article, and we begin 
with an examination of the mechanical 
construction of the light valve, which is 
the light modulating device used in the 
Western Electric recording system. 

The frame of the light valve is 
formed of a flat slab of metal that just 
fits across the two side arms of the 
E-shaped core of the electromagnet. 
Two screws with knurled knobs hold it 
firmly and exactly in position when it 
is placed on the core. This flat piece 
of metal forms the armature of the 
electromagnet, and it is equipped with 
a central projecting wedge of metal 
that is just like the wedge-shaped end 
of the center leg of the electromagnet. 
Likewise, there is a similar slot cut in 
this elevation of metal on the center of 
the armature. On the front face of the 
wedge, the opening is eight mils wide 
by 256 mils long and it tapers out to an 
opening 204 mils wide by 256 mils long- 
in the outside face of the armature, 
which is exactly like the tapered slot in 
the electromagnet core. When the light 
valve is fastened in place on the core, 
the wedge-shaped elevation in the cen- 
ter of the frame of the light valve is 
precisely opposite the similar wedge- 
shaped end of the center leg of the 
core, and the small ends of both slots 
are parallel and facing each other. With 

* Sound Engineer, Universal Pictures Corpora- 
tion. 



the light valve thus in position, the two 
elevations are spaced eight mils apart 
when there is no current flowing 
through the winding on the electromag- 
net, but when the electromagnet is 
energized from the battery, this air gap 
is reduced to seven mils. 

Ribbon Support 

On the face of the light valve frame, 
which is the side that has the central 
elevation, there are two screw-like ar- 
rangements called windlasses mounted 
near one end. These windlasses are 
slotted to hold the two ends of a loop 
of duralumin ribbon, and they fit their 
mountings tightly enough so that they 
will not turn of their own accord and 
permit the ends of the ribbon to come 
loose. One windlass is insulated from 
the light valve frame, but the other one 
is grounded directly to the frame, and 
they connect to the two binding posts 
on the back of the frame that form 
the two terminals of the valve. The 
center of the loop of ribbon is drawn 
tight by a miniature, spring-held pulley 
mounted at the other end of the light 
valve frame. This pulley is insulated, 
and it is constructed so that the spring 
keeps a constant tension on the loop of 
ribbon. The strength of the pull of 
the spring on the ribbon can be regu- 
lated by means of a screw that projects 
through to the back of the metal 
frame. Insulating bridges are mounted 
on each side of the central elevation, 
and the windlasses and the pulley are 
arranged so that the two sides of the 
loop of ribbon are supported by the 
bridges just three mils above the face 
of the projecting metal wedge in the 
center of the frame. These bridges are 
comparable to the bridge that holds the 
strings of a violin, only in this case the 
bridges are smooth and not slotted. 



Four adjustable insulated pincers 
confine the two sides of the loop of 
ribbon to the centers of the insulating 
bridges, which places the two sides of 
the loop directly over the longitudinal 
dimension of the tapered slot in the 
face of the projecting wedge. When 
the two ribbons are properly centered 
over the slot and spaced exactly one mil 
apart by adjusting the four pincers, 
they shut off most of the opening, and 
if the light valve is viewed against a 
light the slot appears to be only one mil 
wide and 256 mils long. The flat side 
of the portion of the ribbon that passes 
over the slot is parallel with the face 
of the light valve frame, but the rest 
of the ribbon is turned so that the flat 
side of the ribbon is perpendicular to 
the frame. When the light valve is 
mounted on the electromagnet core, the 
ribbon is approximately centered in the 
air gap between the wedge-shaped ele- 
vations on the core and on the light 
valve frame ; and, as has been ex- 
plained, the sides of the ribbon loop 
contract the size of the aperture 
through which the light from the lamp 
can pass to a width of just one mil. 

Size of Image 

The objective lens in the end of the 
exposure chamber has a two-to-one 
ratio, and so it reduces the optical 
image of the slit at the point where it 
is focused on the film to one-half the 
actual slit dimensions. This means 
that the image on the film is one-half 
mil wide and 128 mils long when the 
light valve strings are in their normal 
position of rest. In printing the film 
after it has been developed, a part of 
the sound track is matted off in the 
printer, however, leaving a track just 
100 mills wide on the final positive print 
that is released to theatres. 

Stringing the light valve, which is 
the term used for the operation of plac- 
ing the loop of ribbon on the valve 
frame and adjusting it over the slot, is 
a very delicate operation that requires 
extreme care on the part of the record- 
ing operator. The duralumin ribbon is 
purchased in strips of the right length 
fastened to a sheet of metal. The rib- 
bon must be handled very gently with 
tweezers, because any kinks or twists 
in it will make it unsuitable for use. 
It is placed carefully in position on the 
light valve frame with the center of 
the loop over the insulated pulley and 
the two ends put through the slots in 
the windlasses. The windlasses are 
turned slowly then by means of screw- 
drivers. This serves to twist the ends 
of the ribbon around the windlasses and 
secure it in place, and also to draw the 
loop of ribbon tight. After the ribbon 
has been pulled up firmly into position, 
the light valve is placed in a special 
frame under the lens of a microscope 
and the four pincers adjusted until the 



JUNE, 1931 



Page 15 



two sides of the ribbon loop are exactly 
centered over the slot in the projecting 
wedge on the frame and are spaced 
precisely one mil apart over the entire 
length of the slot. 

Tuning the Light Valve 

After stringing, the light valve is 
tuned by means of a light valve tuning 
panel. This tuning panel comprises an 
adjustable audio-frequency oscillator 
that supplies a tone of predetermined 
frequency to the light valve. The light 
valve is mounted on an electromagnet 
on the front of the tuning panel in the 
regular manner and a light directed 
through it onto the sensitive surface of 
a photoelectric cell. There is an am- 
plifier that terminates in a volume in- 
dicator connected to the output of this 
photoelectric cell. With the light valve 
in place on the tuning panel, the ap- 
paratus is turned on and a tone gen- 
erated by the audio oscillator is sent 
through the strings of the valve. The 
frequency of the tone is adjusted to the 
valve to which it is desired to tune the 
natural period of vibration of the valve 
ribbon. A frequency of 8,500 cycles 
per second is usually chosen for this 
valve — although 7,000 c.p.s. used to be 
employed, because it places the reson- 
ant frequency of the light valve strings 
well out of the frequency band that the 
human voice occupies. With the oscil- 
lator in the tuning panel generating a 
frequency of this valve, the tension on 
the loop of ribbon in the light valve is 
slowly increased by turning the screw 
attached to the spring that holds the 
pulley in the center of the ribbon loop. 
When the tension on the ribbon is 
great enough to cause the resonant fre- 
quency of the valve ribbons to reach a 
value that is the same as that generated 



POLES OF 
ELECTROMAGNET 




X- CURRENT FLOWING INTO RIBBON 
• - " OUT OF " 



Fig. 2a. (at top). Current flow on 
one-half cycle causes reaction of 
fields to draw ribbons toward each 
other. Fig. 2b. (below). Current flow 
on other half of cycle causes reac- 
tion of fields to force ribbons away 
from each other. 



by the audio oscillator, the amplitude 
of vibration of the strings will attain 
a maximum value and the meter of the 
volume indicator will indicate highest 
reading at this point. 

The Tuning Panel 

Besides the volume indicator meter 
and the potentiometer that permits the 
grid bias on the volume indicator tube 
to be adjusted to the valve that gives a 
five-division reading on the meter scale 
when there is no a-c. excitation, there 
are a number of other meters and con- 
trols mounted on the light valve tuning 
panel. There are rheostats and am- 
meters in series with the oscillator tube 
filaments, the amplifier tube filaments, 
and the sound lamp that provides the 
light of constant intensity that acts 
through the light valve on the sensitive 
surface of the photoelectric cell. Then 
there are the switches that turn on and 
off the battery circuits and the input to 
the light valve, and a potentiometer that 
controls the a-c. tone input to the light 
valve strings. The dial of the fre- 
quency control is marked directly in 
frequencies, and there is a three-posi- 
tion key switch just below it that pro- 
vides the three frequency ranges which 
carry the range of the oscillator well 
above and below the 8,500-cycle tuning 
point of the light valve. 

After it has been tuned, it is neces- 
sary to examine the ribbons of the light 
valve under the microscope again to 
determine if there has been any varia- 
tion throughout the length of the slot 
in the one mil spacing of the ribbons. 
If there has been any divergence from 
this value, it will be necessary to re- 
adjust the spacing of the ribbons by 
means of the pincers. The light valve 
must be examined under the microscope 
also to make sure that there are no 
nicks or imperfections in the edges of 
the ribbons where they form the sides 
of the slit and that there are no bits 
of fuzz or particles of dirt in the slot, 
for any of those things would cause 
streaks in the sound track produced by 
that valve. Specks of dust and dirt 
can be removed by a fine camel's hair 
brush. The only thing that can be done 
for a valve with nicked or imperfect 
ribbon is to break and re-string it with 
new ribbon. The slot in the core of 
the electromagnet should likewise be 
examined for particles of dirt by plac- 
ing a small light inside of the exposure 
chamber and observing it through the 
slot by means of a powerful magnify- 
ing glass. All of the operations 
described in this paragraph have to be 
carried out each time a light valve is 
to be put in service on a recording 
machine. When a poor grade of rib- 
bon is encountered, it is sometimes 
necessary to re-string and re-tune a 
light valve a half dozen times before it 
is satisfactory. 



Principle of Light Valve 

The principle on which the light 
valve operates is the same principle as 
that which causes an electrodynamic 
loudspeaker to function, but in the 
light valve the duralumin ribbon takes 
the place of the speech coil and the 
diaphragm of the dynamic speaker. 
The speech current from the recording 
amplifiers is fed to the loop of ribbon 
in the light valve through a repeat coil 
that matches the impedance of the 
amplifier output to the impedance of 
the strings in the light valve. With 
the light valve in position on the elec- 
tromagnet core the ribbons are sus- 



Section of film 
showing sound 
track, variable 
density, fixed 
area type. 



r 


m ' 


p 



pended in a plane at right angles to 
the electromagnetic field of force pro- 
duced by the d-c. current flowing 
through the winding of the electro- 
magnet. When sound is not being 
picked up by the microphones there is 
no speech current flowing through the 
loop of ribbon on the light valve, and 
so the ribbon has no field of force of 
its own. When such is the case the 
flux produced by the electromagnet has 
absolutely no effect on the ribbons 
because they are of non-magnetic 
material. But when an a-c. speech 
current flows through the loop of rib- 
bon an alternating field of force is set 
up around the ribbon. On one half of 
the a-c. cycle the field around the rib- 
bons reacts with the field of the elec- 
tromagnet in such a way that it tends 
to cause the two ribbons to be brought 
together, and on the other half of the 
a-c. cycle the two fluxes react to cause 
the two ribbons to be forced apart. 
This action can be made evident by 
applying the law of electromagnetic 
induction to a study of the reaction of 
the fields produced by the current flow- 
ing in the electromagnet winding and 
in the loop of ribbon ; as is illustrated 
in Fig. 2. 

The tendency of the lines of force 
flowing between the two poles of the 
electromagnet is to assume straight 
paths from one pole to the other. Fara- 
day thought of these lines of force as 
acting like stretched rubber bands : that 
is, they can be bent out of their natural 
positions, but when the force that is 
holding them is released they will 



Page 16 



PROJECTION ENGINEERING 



snap back into position again. A 
modification of Lenz's law states that 
a ivire carrying a current in a magnetic 
field tends to move in, a direction at 
right angles both to the direction of 
the field and to the direction of the 
current. This is sometimes known as 
the motor rule, because it is this prin- 
ciple that causes electric motors to 
function. In Fig. 2a, the reaction of 
the fields of the ribbons and of the 
electromagnet causes most of the lines 
of force from the electromagnet to be 
bent around the outsides 'of the two 
ribbons. Now, in this case, the strength 
of the field on the outsides of the rib- 
bons is the sum of the two separate 
fields, while the strength of the field 
between the ribbons is the difference 
of the two fields. If we think of the 
lines of force acting like stretched rub- 
ber bands, as did Faraday, then we will 
see that the energy exerted by these 
lines of force in an effort to take 
straight paths between the poles of the 
electromagnet will tend to bring the 
two ribbons closer together. In Fig. 
2b, which represents the current flow 
on the other half of the a-c. cycle, 
exactly the opposite action takes place 
and the ribbons are forced farther 
apart by the reacting magnetic fields. 
In these illustrations, a cross-section of 
the ribbons is shown; and the X indi- 
cates the current flowing into the page, 
while the dot represents the current 
flowing out of the page. 

Vibration of Ribbon 

So we see that an a-c. speech current 
passing through the ribbon loop causes 
the two sides of the loop to be alter- 
nately drawn toward each other and 
forced apart by the reacting magnetic 
fields. In an ideal recording system, 
this movement of the ribbons is of the 
same frequency as the frequency of 
the a-c. speech current, which in turn 
has the same frequency as the sounds 
producing it; and the amplitude of the 
movement of the ribbons corresponds 
precisely to the amplitude of the speech 
current." This narrowing and widening 
of the light slit by the ribbons alter- 
nately reduces and increases the amount 
of light from the lamp that falls on the 
moving film. This results in narrow 
and wide bands, or striations, of vary- 
ing density running transversely of 
the sound track on the film, as may be 
seen in the photograph (Fig. 3) of a 
strip of sound track of the variable 
density-fixed area type. This sound 
track is of the full 128-mil width. The 
higher the pitch of the sound produc- 
ing the modulation of the light beam, 
the narrower and the closer together 
will be the lines of the sound track; 
and, the louder the sound, the greater 
will be the contrast in density between 
adjacent light and dark lines on the 
film. 



Operation of Recorder 

The operation of a film recording 
machine during the actual making of 
a sound motion picture requires con- 
siderable experience and close atten- 
tion to detail on the part of the recorder 
operator. The various departments in 
the sound studio — stage, monitoring, 
amplifying, and recording — are con- 
nected by a system of colored signal 
lights and intercommunicating tele- 
phones. The recorder operator loads 
his recording machine with a 1000-foot 
roll of film ; punches the start mark in 
it ; numbers it properly ; sets the foot- 
age counters on the recording machine 
at zero, and then writes down all the 
details, such as picture number, di- 
rector, film roll number, and film re- 
corder number on a special form card. 
He turns on the current to the various 
recording circuits and adjusts the 
rheostats to the positions that provide 
the proper meter readings. When the 
director and cast on the stage are ready 
to make a sound "take," the microphone 
man calls the recorder operator on the 
telephone, gives him the scene number 
and calls for "interlock." The record- 
ing technician then throws the first of 
the two motor switches mounted on the 
wall near the recording machine and 



turns on the recording room signal 
light. This motor switch interlocks all 
of the motors and brings them to the 
starting position. The microphone man 
calls out, "Interlock," when he sees the 
recording room light go on, and when 
everything is quiet on the stage, he 
turns on his stage signal light, and 
warns, "We're running." At sight of 
the stage signal light, the recorder 
operator closes the second motor 
switch, which sets all of the interlocked 
motors into rotation. He adjusts the 
motor rheostat that compensates for 
changes in the amount of load on the 
master Selsyn motor in the generator 
room, and watches the extension mil- 
liammeter in the motor control circuit 
until it shows a reading that indicates 
the motors are up to their normal speed 
of 1200 r. p. m. Then, when the motors 
have reached their full speed, he turns 
on the bull's eye running light. At 
this, the microphone man calls out, 
"Speed," the scene is "shot," and the 
stage signal light is switched off. The 
recorder operator then turns off the 
motors ; writes down the scene number, 
whether or not it was ok, and the num- 
ber of feet of film run through the 
machine, and makes the necessary 
preparations for the next take. 



AAA 



Future Developments in Moving Pictures 



jytR. LESLIE ROWSON, of Lon- 
don, England, returned recently to 
that city after an American trip which 
included a visit in Hollywood. 

The following is that portion of Mr. 
Rowson's report of his observations 
which deals with probable future devel- 
opments : 

"Many improvements loom dimly 
ahead — wide film, natural colors, stere- 
oscopy and television. Which one of 
these will come first? Twelve months 
ago wide film in one form or another 
seemed to be a certainty for the imme- 
diate future : the public, however, 
showed no interest in it, and it has been 
quietly shelved, temporarily, at any rate. 

"That a new standard size of picture 
will eventually be adopted seems prob- 
able, but what it will be, one can hardly 
say. Certainly not the wide, flat shape 
which met with so little success last 
year. 

"On the purely photographic side, I 
think we can hope for very much faster 
film. Eastman Kodak have recently 
placed on the market in America a 
new film, three times faster than the 
Type 2 Panchromatic at present in use, 
and I am sure that the limit in this 
direction has by no means been reached. 

"As regards lenses, I do not think we 
can expect any very great advances as 
regards speed, as covering power and 



depth of focus both become very poor 
at apertures larger than f.2. 

"Stereoscopy, I am certain, we will 
have within the next few years, though 
I do not believe there is any optical 
principle at present known by which it 
can be achieved, but I am certain that 
some new principle will be discovered 
which will startle us all by its sim- 
plicity. 

"Television is knocking at the door, 
and the only factor which is preventing 
its immediate entrance is, I understand, 
the purely mechanical difficulty of ob- 
taining a picture of adequate size. 

"Natural color, too, is just around the 
corner ; Eastman Kodak, Multicolor, and 
other important companies arc working 
on it, and the solution cannot be long 
delayed. 

"Anyhow, if I may be allowed tc 
speculate as to the future, I predict 
stereoscopic pictures in color projected 
by television from a single print to a 
whole chain of theatres on to a screen 
whose shape continually changes to suit 
the composition of the scene which is 
being projected. 

"But of one thing I am certain. 
Whatever new forms cinematograph 
entertainment may take, there is one 
man at least who will always find him- 
self striving to improve his knowledge 
and increase his mastery of his medium, 
and that is the cameraman." 



JUNE, 1931 



Page 17 



An a-c. operated 
portable talking 
picture equipment 



By J. deGiovanni 



THE portable equipment described 
in this article was designed to 
meet the requirements demanded 
in this field of highly specialized 
work. Quality of reproduction, porta- 
bility, ease of operation, flexibility to 
meet field conditions ; each were fac- 
tors which required serious considera- 
tion and much technical research was 
expended over a period of two years 
before the present instrument was 
designed. 

What can be more simple than to be 
able to plug into an ordinary a-c. house 
line and in a few minutes give a 
talking picture show equivalent in per- 
formance to the best of theatre instal- 
lations ? Transportation of this unit 
simply resolves itself into a mere trunk 
carrying proposition. 

On the field, the power supply is 
somewhat serious. Because of their 
weight, motor-generators are out of the 
question. For long performances bat- 
teries are not reliable enough and entail 
considerable trouble. 

A system known as the G. R. C. 
portable has been tested and operated 
in the field. This portable sound pic- 
ture equipment has been designed along 
sound engineering principles. All the 
requirements were carefully compiled 
and a unit was designed that not only 
meets the requirements of a portable 
equipment but also that of the semi- 
professional field. This unit can be 
used in small class-rooms as well as 
in large theatres of over iooo seats. 
The only change required is the use 
of two or more exponential horns to 
meet the sound distribution require- 
ments. 

Description of the Apparatus 

Not only is the projector, protected 
and enclosed, but another metal case 
completely encloses the entire unit. 



A Practical Talking Picture 

Outfit Contained in Three 

Medium Size Trunks 



This metal case is lined with sheet rock 
asbestos. Both upper and lower maga- 
zines are totally enclosed. With this 
type of assembly, fire hazards are 
reduced to a minimum, a feature which 
is all important when the equipment is 
being used in class-rooms or other 
places where it is impossible to use a 
booth. 

The projector is powered with a 
constant-speed motor, dynamically bal- 
anced, and the frame filtered from 
vibrations. All driving is done through 
shafts or gears, no belting or chains 
being used. The sound-head is driven 
by a separate shaft other than that used 
to drive the projector mechanism, 
thereby eliminating speed fluctuations 
due to mechanical overloads on the 
projector mechanism. 

To further insure against "gargle" 
and uneven speed, the driving sprocket 
is filtered against gear noises and 
other vibrations that would tend to 
introduce ground noises. The picture 
can be framed while the projector is 
running, and without necessitating 
opening the doors. 

Provisions are made to insure easy 
and free motion of the film, thereby 
contributing an important element to- 




Complete equipment of portable 
movie-talker. 



wards obtaining pure and natural tone. 

The optical system used in the sound 
head is designed along new lines. Its 
construction eliminates the "mechanical 
slit" and allows more freedom in the 
operation of the photocell. The photo- 
electric cell and its circuit do not 
require extreme amplification in order 
to obtain volume with high quality 
reproduction. The lens block has been 
designed so that the optical system may 
be taken out and cleaned without mak- 
ing it necessary to readjust it after it 
has been replaced. 

The lamphouse is enclosed in a sepa- 
rate metal case and lined with asbestos. 
A blast of air is blown upwards 
through the lamphouse expelling the 
heat generated by the projection lamp. 
A iooo-watt projection lamp insures 
brilliant pictures even with throws 
exceeding 80 feet. 

The a-c. operated amplifier and 
power-pack is designed to operate from 
a no-volt 60-cycle a-c. No batteries 
are necessary. The current consump- 
tion is such that it can be plugged into 
an ordinary light socket without special 
precautions. This amplifier includes 
(Concluded on page 22) 



Projector 
unit. 




Page 18 



PROJECTION ENGINEERING 



Motion picture 
cost accounting 



TO the motion-picture corporation 
costs of production correspond to 
cost of sales, and for a true report 
of earnings it is necessary to 
adopt conservative and common-sense 
methods of distributing production costs 
over the period of earning power pi a 
film. 

Since the advent of talking pictures 
there has been a substantial change in 
the rate at which film negative costs 
are charged against rentals. Earnings 
from a picture are garnered now in a 
much shorter period than in the days of 
silent films, and there has been conse- 
quently a shortening of the period in 
which the entire cost of production is 
written off. 

This process of amortization, the 
writing down of cost over a number of 
months, in its simplest form follows a 
schedule that is drawn up readily on 
the basis of experience. The corpora- 
tion totals in one column the production 
cost of a number of films, good and bad 
together ; in other columns it sets up, 
month by month, the revenues from 
those pictures until they reach a level 
approaching the vanishing point. The 
total earnings of each month in the life 
of the group is then calculated as a per- 
centage of the total earnings received 
from the group, and this percentage 
fixes the amount of the production cost 
to be charged against all films of the 
corporation. 

The table shows the actual amortiza- 
tion schedule used by one producer in 
the time of silent pictures. 

Thus it appears that by the end of 
the sixth month the corporation had re- 
ceived 62 per cent, of the revenue to be 
expected from the film ; at the end of a 
year, 90 per cent. ; and in eighteen 
months, 100 per cent. 

Practice among various companies 
differed and still does. Some compan- 
ies might follow the very conservative 
practice of writing off the whole pro- 
duction cost as soon as a picture is re- 
leased. The objection to this is that, 



Practices in amortizing 

film costs differ in motion 

picture industry 



although it gives the same result in the 
long run as a periodic writeoff, it dis- 
torts the earnings for any period in 
which a high cost picture is released. 
If a million-dollar feature were issued 
on December 15, for example, $1,000,- 
000 would be knocked out of earnings 
in the report for the quarter or the year, 
without any corresponding offset in 
revenues from the feature. 

Another variant is to charge a cer- 
tain percentage from revenues to cost 
of production. In the case of a flop, of 
course, earnings would never supply 





Per Cent. 




Month 


of Life 


Cumulative 


After 


Revenue 


Per Cent. 


Released. 


Received 


Received. 


I 


i2y 2 


i2y 2 


2 


14 


26y 2 


3 


12 


38/2 


4 


9^ 


48 


5 


8 


56 


6 


6 


62 


7 


7 


69 


8 


6 


75 


9 


5 


80 


10 


4 


84 


11 


3H 


87/2 


12 


2/ 2 


90 


13 


2/2 


92/2 


14 


2V2 


95 


15 


iy 


9 6y 


16 


i/ 2 


98 


17 


1 


99 


18 


1 


100 



enough to permit writing down the 
whole cost, and inventory would be 
padded by this undepreciated item. Set- 
ting an arbitrary date for completing 
the writeoff, regardless of insufficiency 
of revenues from the film, corrects that 
evil but produces the other one of 
throwing an unexpected and unwar- 
ranted burden of depreciation into the 
month in which the final charge is 
made. 

It is almost universal practice, there- 
fore, to follow a diminishing scale of 
depreciation charges that starts at a 
high rate and rapidly writes off the 
total cost. 

Changes in the industry in the past 
five years have accelerated the rate of 
this depreciation. 



When the large producing companies 
gathered up great chains of theaters as 
distributing outlets, the need for quick 
circulation of new films among the qual- 
ity houses was realized. Prompt dis- 
tribution of new releases also was de- 
manded by the small theaters who had 
invested in equipment for sound. The 
result, facilitated by lower cost of film 
itself, was a great increase in the num- 
ber of prints circulated simultaneously 
and a shortening of the domestic earn- 
ing life of a production. 

Thus it is usual now for producers to 
receive 65 to 70 per cent, of the prob- 
able total domestic earnings of a film 
during the first three months following 
release and 85 to 90 per cent, in the 
first six months. 

The Fox Film Corporation audit pre- 
pared for the purposes of the recent 
financing established a revised amorti- 
zation schedule that writes off 93 y 2 per 
cent, of production cost in the first 
twenty-six weeks of a film's distribu- 
tion, compared with previous rates 
reported to have allowed approximately 
a year. 

The problem of amortization charge- 
able to foreign rentals has many ramifi- 
cations. Probably typical practice is to 
allocate 15 or 20 per cent, of produc- 
tion cost as a charge to be written off 
out of the earnings of prints circulated 
in foreign countries. The rate of this 
amortization might well be slower than 
on domestic distribution because of the 
longer earning life of many American 
films in foreign houses, but there, as at 
home, the introduction of talking pic- 
tures is bringing changes. — New York 
Times, April 19, 1931. 



LIGHT REFLECTION OF ACOUSTI- 
CAL MATERIALS 

TOO often are the purchasers of 
acoustical materials inclined to think 
in terms of sound absorption coefficients 
only. Many other characteristics merit 
consideration. Light reflection is a very 
important factor. This is emphasized 
in a recent article by A. L. Powell and 
C. L. Dows of the Nela Park engineer- 
ing department of the General Electric 
Company published in the December, 
1930, issue of the Transactions of the 
Illuminating Engineering Society. The 
article also reports tests on the light 
reflection of many acoustical materials. 
Some time it is hoped that similar 
tests can be made on material over a 
considerable period of time. Such tests 
would show up another important char- 
acteristic of acoustical materials — 
paintability. The accumulation of dirt 
on the ceilings of offices is unfortun- 
ately a reality and if high light reflec- 
tion is to be maintained painting at fre- 
quent intervals is essential. 



JUNE, 1931 



Examination questions 
for projectionists 



Herewith is presented a list of guiding questions which 

applicants for grade A projectionist licenses in Canada 

are expected to be prepared to answer correctly 



THE first 182 questions appeared 
in the May issue of Projection 
Engineering. 

183. Why must all equipment be 
grounded ? 

184. What is an overloaded circuit? 

185. Why should projectors be 
grounded ? 

186. What is a test lamp? 

187. How would you test fuses ? 

188. Explain how to find the posi- 
tive wire on a d-c. line with a test 
lamp. 

189. How would you find the posi- 
tive wire on a d-c. line if you had no 
test lamp? 

190. What is meant by the term 
e.m.f. ? 

191. What is meant by the primary 
side of a transformer? 

192. What is meant by the secondary 
side of a transformer? 

193. Using 25 cycle, how many alter- 
nations are there per second ? 

194. What is meant when voltage is 
"stepped up"? 

195. What is the first indication of 
a short circuit? 

196. Give types of fuses used in 
motion picture projection. 

197. What is voltage drpp, and what 
effect will it have on a carbon arc? 

198. What advantages has d-c. over 
a-c. on a carbon arc? 

199. How would you test for a 
ground in the arc lamp? 

200. What will cause wires to burn 
off at carbon arms ? 

201. Where does a ground usually 
occur in the lamp? 

202. In an electric arc circuit, what 
various things offer resistance to the 
flow of current? 

203. What advantages are there to 
copper-coated negative carbons ? 

204. Name some types of arc lamps 
in use. 

205. What determines the diameter 
of carbons used? 



206. What is the average amperage 
required on mazda illumination? 

207. What is meant by stealing the 
arc ? 

208. What causes the asbestos cov- 
ering on lamp leads to become cracked 
and broken? 

209. Which gives the best projection 
arc results on a-c? A motor gener- 
ator, transformer, rheostat, mercury 
arc rectifier? 

210. Does the arc -gap offer any re- 
sistance ? 

211. Show by diagram the wiring in 
a circuit of a polarity reversing switch. 

212. Should lamp houses be vented to 
the open air, and if so, why? 

213. What is a reflector lamp? 

214. What is a Hi-low lamp? 

215. What might cause breakage of 
reflector and condensor while arc is 
lit? 

216. How often should carbon jaws 
or clamps be cleaned? 

217. How would you clean carbon 
jaws so as to make good electrical con- 
tact? 

218. What will a coating of carbon 
dust or ash on the lamp insulation 
cause ? 

219. What will be the result of the 
carbon jaws or clamps making loose 
connections with the carbons ? 

220. What will cause pencilling of 
carbons? Give more than one reason. 

221. Should you lubricate the carbon 
clamp screws, and what with? 

222. What would result from one 
carbon making accidental contact with 
the lamp house walls or floor? 

223. What is the positive arm of an 
arc lamp ? 

224. What is the negative arm of an 
arc lamp? 

225. What will be the result of the 
silver backing of the mirror wearing 
out? 

226. Can a cracked mirror be used? 

227. What is the average amperage 
used with old style arc lamp? 

228. What is average amperage on 
high intensity? 



Page 19 

229. What is average amperage on 
reflector arc ? 

230. What is average amperage on 
Hi-low arc? 

231. With a reflector type arc, how 
can the spot at the aperture be en- 
larged? 

232. Why do high intensity arcs 
have the positive carbon revolve ? 

233. What prevents the burning 
away of the lamp metal due to exces- 
sive heat from the high intensity arc? 

234. Is the film fire hazard in a re- 
flector arc lamp with condensor open- 
ing free greater than with any other 
light source? If so, why? 

235. What is the purpose of a fuse? 

236. Should fuses carry more than 
their rated capacity? 

2^7. What is meant by over-fusing, 
and is it permissible? 

238. What happens when a fuse 
blows? 

239. What causes a fuse to blow ? 

240. What is the construction of a 
rheostat? 

241. What is best to use on a-c, an 
economizer or rheostat, and why? 

242. When using 220 v. d-c, how 
many rheostats would you use, and how 
wired? 

243. Show by sketch how to connect 
two rheostats in series. 

244. Show by sketch how to connect 
two rheostats in multiple. 

245. What is a rheostat used for? 

246. What is a coil type rheostat? 

247. What is a grid type rheostat? 

248. When are rheostats used in 
series ? 

249. When are rheostats used in 
multiple? 

250. How would you test a rheostat 
to find out which coil or grid is 
burned out? 

251. What is meant by an adjustable 
rheostat? 

252. What is meant by a fixed rheo- 
stat? 

253. If the voltage drops, what effect 
will the cutting out of resistance have? 

254. If the coil or grids of a rheo- 
stat become bright red, what would 
that indicate, and what would you do? 

255. What precautions must be 
taken in location of rheostats, and how 
would you protect same? 

256. Should rheostats be inspected 
frequently ? 

257. If a coil should burn out, how 
could you make an emergency repair? 

258. Why are rheostats commonly 
used on a no v. d-c. circuit? 

259. Where rheostats are used on 
d-c, what value is there in connecting 
rheostat; (a) on the positive line; (b) 
on the negative line ? 

260. Why are some starting switches 
on motor generators and larger equip- 
ment enclosed in oil? 

261. Should m.g. sets be kept well 
cleaned and lubricated, and why? 



Page 20 



PROJECTION ENGINEERING 



262. Should all m.g. sets be grounded, 
and, if so, why? 

263. How should the commutator be 
kept clean? 

264. How tight should the brush ten- 
sion be on the commutator? 

265. What will cause a bearing to 
run hot? 

266. When would you consider a 
m.g. set to be heating excessively? 

267. How do you replace old brushes 
and fit the new ones to the curvature of 
the commutator? 

268. Give two or more reasons why 
brushes on a m.g. set will spark. 

269. What are the causes for brushes 
sparking, and what are the remedies? 

270. What is a motor generator? 

271. What is meant by the arma- 
ture? 

272. Give the chief causes which 
will make your motor generator vibrate. 

273. What is a transformer? 

274. Give some of the advantages of 
mazda equipment. 

275. What will cause the bulbs to 
blacken, and what is the reason for the 
height of the glass bulb? 

276. What is a prismatic condensor? 

277. When using a prismatic con- 
densor, will the condensor be closer to 
the aperture than if you use a piano 
condensor ? 

278. Using a small diameter projec- 
tion lens, which condensor combination 
(prismatic or piano convex) will al- 
low more light through the lens? 

279. Can a prismatic condensor be 
used when running slides ? 

280. Describe how to start a mazda 
lamp in operation, and tell what hap- 
pens at each step. 

281. How close should revolving 
shutters be to end of lens barrel? 

282. What would you use for a fo- 
cussing card on a projector with a 
rear shutter ? 

283. Show how you would adjust the 
lamp and mirror to get a correct focus. 

284. Give approximate distance be- 
tween (a) center of mirror and fila- 
ment, (b) filament and condensor, (c) 
condensor and aperture, (d) lens and 
revolving shutter. 

285. When using a cinephor con- 
densor system, is accuracy in the focal 
distance of much importance, and why? 

286. What is the mirror image, and 
where should it be focussed? 

287. What is meant by filament 
image ? 

288. How many filament coils has a 
mazda lamp ? 

289. When the mirror image is not 
properly focussed, what will be the 
appearance of the light on the screen? 

290. Can a cracked mirror be used 
pn mazda? What will the effect be 
on the screen? Can a cracked con- 
densor be used? 

291. How can you overload a mazda 
lamp, and will you derive any benefit 
from so doing? 



292. What will usually result from 
overloading a mazda lamp ? 

293. What is meant by the term 
"sound picture" ? 

294. At what speed must a sound 
picture be projected to get correct re- 
production ? 

295. What results are apparent in 
the reproduction when the projector is 
run at a lower speed? 

296. What results are apparent in 
the reproduction when the projector is 
run at a higher speed? 

297. How can the speed of the pro- 
jector be varied on Western Electric 
or Northern Electric equipment? 

298. At what speed does the turn- 
table revolve? 

299. Define a sound track film. 

300. Define a disc film. 

301. Why does the needle on the disc 
record travel from the center of the 
disc to the outside? 

302. On the Vitaphone disc, is the 
actual sound record on the bottom of 
the track or groove, or is it cut into 
the walls of the groove? 

303. What is meant by "drift" of 
the reproducer arm, and why is it 
used? 

304. What might happen if the 
clamping weight is not secured on the 
disc, and the projector is in motion? 

305. What is the "mechanical filter" 
on synchronous sound equipment? 

306. What usually results from 
turntables not being level ? 

307. How often should a disc be 
used? 

308. What is meant by a scratch 
filter? 

309. What is surface noise? 

310. How often should a disc be 
cleaned, and what should be used? 

311. How often should a needle be 
used? 

312. Suppose the needle continually 
jumps out of the groove, and on put- 
ting on a new disc the jumping con- 
tinues, what would cause this, and how 
could you remedy it ? 

313. What effect on reproduction 
may a warped disc have? 

314. How and where should discs be 
stored in the projection room? 

315. How could you test a disc for 
warpage ? 

316. What should you do with a disc 
that is badly scratched? 

317. On disc film, what is the "start 
mark"? 

318. Why is the "start mark" used? 

319. On disc film, why is each foot 
marked on the side of the film? 

320. Define "footage marks". 

321. Of what help to projectionists 
are the "footage marks" ? 

322. Do Technicolor films have foot- 
age marks? 

323. Suppose you were projecting a 
Technicolor print and the film broke, 
piled up at the upper sprocket, and due 
to the brittleness of Technicolor was 



badly broken up, how could you put it 
in synchronism again? 

324. Define synchronism. 

325. What type of film must be used 
to replace any film removed, due to 
breaks, or for any other reason ? 

326. Tell how to splice a sound 
track film. 

327. Which of the lines, the white 
or dark ones, make the actual sound 
from the film ? 

328. What is the difference between 
"variable area" and "variable density"? 

329. What film producers use "vari- 
able density"? 

330. What density does R.C.A. use 
in recording? 

331. What is known as "motor-boat- 
ing" ? 

2,2,2. What is the cause of motor- 
boating ? 

22,3- How can "motor-boating" be 
overcome ? 

334. What effect on reproduction 
may a poorly made sound track splice 
have? 

335- Why should a sound track 
splice be painted out? 

336. What causes surface noises on 
sound track film? 

33J. How should sound track film 
be cleaned? 

338. What effect may a heavy 
scratch on the sound track have on the 
sound reproduction? 

339. What effect may oil on the 
sound track have? 

340. What type of paint should be 
used on sound track splices, and why? 

341. How could you tell if any foot- 
age had been cut from a disc film if it 
suddenly went out of synchronism ? 

342. How would you proceed to 
restore it to sychronism ? 

343. Is the start mark on disc film 
of any importance ? 

344. What are storage batteries used 
for? 

345. What apparatus do the "H" 
batteries supply with current on 
Western Electric or Northern Electric 
equipment? 

346. What tubes do the "F" batteries 
supply ? 

347. What tubes do the dry "B" bat- 
teries supply? 

348. What bad effect will a defective 
"B" battery have on sound reproduc- 
tion? 

349. How often should wet batteries 
be charged? 

350. How can you tell when batteries 
need re-charging? 

351. What is "specific gravity"? 

352. What is the use of a hydrom- 
eter? 

353. What is "electrolyte" in storage 
batteries ? 

354. What may happen if there is 
dirt or water on battery tops ? 

(To be concluded in July issue) 



JUNE, 1931 



Page 21 



FOREST 

RECTIFIERS 



jm^\WVVf r WW ' 





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 
J 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. 

/ 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. 



Adapters 
for 







211-E . . 50 WATT tubes 



for use with 

WESTON SOUND APPARATUS 

TEST SETS . 



MODELS 565 and 566 



• Sound apparatus test sets are vitally necessary in the 
projection booth of the modern theater which features 
quality sound reproduction. Amplifier tubes, speaker- 
coils, batteries and the vast number of electrical circuits 
must be checked at regular intervals to assure continuous 
and satisfactory performance. For this work, the depend- 
able, accurate operation of Weston Test Sets is invaluable. 

• To make Weston Test Sets even more useful to the 
projectionists, Weston has designed an adapter which per- 
mits 50 Watt, type 211-E tubes, to be checked quickly and 
easily. It may be used with either Weston Model 565 or 566. 

• Model 565 is a 
three meter test set. 
It is practically a 
portable testing lab- 
oratory. It makes 
every electrical test 
that might be neces- 
sary in the servicing 
of sound apparatus 
and the attendant 
equipment. It is rec- 
ommended for the 
larger theaters. 

• Model 566 is a compact, light, relatively inexpensive 
two meter test set, designed to give the projectionist the 
necessary readings to intelligently service sound apparatus. 
Model 566 Weston Test Set is considered the standard 
equipment for servicing sound apparatus and public ad- 
dress systems. 




Model 566 



FREE* 

to Projectionists 



A free "Copy of Instructions," 
showing how Weston Model 
566 Test Set can be used, will 
be sent to all projectionists 
who request it on their the- 
ater's letterhead. 



WESTON 

ELECTRICAL INSTRUMENT CORP. 



608 Frelinghuysen Avenue 



Newark, N. J. 



Page 22 



PROJECTION ENGINEERING 



ULTRA-SONIC VIBRATIONS 

IN his recent evening discourse deliv- 
ered at the Royal Institution Profes- 
sor F. L. Hopwood discussed ultra- 
sonics or inaudible sound. Sound is, of 
course, produced whenever a vibrating 
body is placed in a material medium, 
whether the latter is a solid, a liquid or 
a gas. For sounds to be audible the 
vibrations must not only be of sufficient 
amplitude but also their frequencies 
must lie within the range 20-20,000. 
Disturbances of the same type as sound 
waves but having frequencies exceed- 
ing 20,000 vibrations a second are 
termed ultra-sonic. 

Remarkable effects are obtained when 
sound waves of great intensity, and fre- 
quency of about half a million, are gen- 
erated in an oil bath by means of a 
quartz crystal set into resonant vibra- 
tion by a thermionic valve oscillator. 
Acoustic radiation pressure exerted on 
the free surface of the oil may raise in 
it a mound several centimeters or even 
inches in height, and cause it to erupt 
droplets like a miniature fountain. On 
plunging vessels of appropriate form 
into this mound of oil, vibrations of 
great intensity may be communicated to 
the walls of the vessels, or, through the 
walls, to liquids contained in them. 

Following the methods of Langevin, 
Boyle and Wood and Loomis, demon- 
strations were given of reflection, re- 
fraction and interference of sound 
waves of short wave length; the pro- 
duction of bubbles and expulsion of dis- 
solved gases from liquids ; acoustic dis- 
tillation; transverse vibrations in solids 
accompanied by anomalous movements 
of dust particles; flocculation of sus- 
pended matter and production of emul- 
sions; acceleration of chemical action; 
pronounced thermal effects ; remarkable 
effects produced on plants, bacteria, 
muscle nerve preparations, and on liv- 
ing organisms such as planaria and fish. 
, — Nature. 

A 

NEW COLOR FILM 

LEARNED members of the Royal 
Society in London witnessed a de- 
monstration on May 20, of the Spicer- 
Duffy three-color system of motion pic- 
ture photography, for which the claim is 
made that it will revolutionize cinema- 
tography. 

The secret of the new British inven- 
tion, it is said, is that the actual film 
base is painted with a foundation or 
matrix consisting of 500,000 minute red, 
green and blue-violet squares — the three 
primary colors — to every square inch of 
film. Over this foundation is coated a 
highly sensitive emulsion. The film is 
then exposed in an ordinary camera and 
shown by an ordinary projector with- 
out any special attachment. The result 
appears to be a perfect natural color 
film which inventors have been seeking, 



which can be thrown on a screen, it is 
asserted, within an hour of photograph- 
ing. The film, moreover, is non-inflam- 
mable. 

SELSYN-THYRATRON CONTROL 

In the July issue of Projection 
Engineering will appear a complete 
description of the Thyratron rectifier 
tube — Selsyn method of control of stage 
lighting effects. 

MOTION PICTURE INDUSTRY 

Compilation by Association of Motion 
Picture Producers based on figures 
available as of March 1, 1931, shows 
17,097 picture houses in the United 
States, of which 13,515 are wired for 
sound reproduction. There are 28,454 
theatres of all types in Europe, of 
which 7,720 are wired. Capital invested 
in motion picture industry throughout 
the world is placed at $2,500,000,000, of 
which $2,000,000,000 is in the United 
States. Introduction of sound necessi- 
tated an investment of $200,000,000 in 
this country. Motion picture industry 
rates as the fourth largest in this coun- 
try. A 

RECORDING EQUIPMENT IN CRIME 
INQUIRY 

In the July issue of Projection 
Engineering will appear a complete 
description of the latest use of sound re- 
cording—in taking testimony and in 
securing confessions of crimes com- 
mitted. 

PROJECTOR WITH SOUND ON 
DISC 

In adapting a De Vry 35 mm. port- 
able projector for sound on disc, it will 
be found that the normal speed of the 
35 mm. projector is 24 frames per 
second or, in other words, the projector 
runs 1440 r. p. m. and the speed of the 
turntable is 3 3 J/3 r. p. m. The star 
sprocket, however, operates on a one to 
four ratio with the projector or, in other 
words, it is running 360 r. p. m. when 
the projector is running 1440 r. p. m. 

▲ 

"MOVING TALKIE" BRINGS DEAD 
LANGUAGE TO LIFE 

(Concluded from page 13) 
the muzzle of the gun. This is done by 
placing two pairs of magnetic coils at 
right angles on the neck of the tube 
near the muzzle. 

Through one pair of these coils flows 
a current generated by a special vacuum 
tube oscillator located in the lower com- 
partment of the oscilloscope case. The 
magnetic field produced by this current 
causes the bright spot to move back and 
forth across the screen. The motion 
from left to right is linear — that is, at 
a constant velocity — and the return 
from right to left is at about fifty times 
the forward velocity. 



This whole cycle, in a typical case, 
lasts only one-thirtieth of a second and 
is repeated time after time so that the 
path of the bright spot appears as a 
bright, straight, horizontal line across 
the face of the cathode ray tube. 

Now, if alternating current resulting 
from a voice wave striking the micro- 
phone is sent through the second pair 
of coils, the magnetic field produced by 
it will cause the straight line to bend 
itself into the exact shape of the wave 
of the alternating current. 

Thus, the shape of any alternating 
current or voltage can easily be studied 
by connecting the current or voltage to 
the proper terminals of the oscilloscope 
panel. 

A 

AN A-C. OPERATED PORTABLE 
TALKING PICTURE EQUIPMENT 

(Concluded from page 17) 
the power-packs that supply the cur- 
rent for the exciter lamp and the anode 
voltage for the p. e. c. The amplifier 
and air-column speaker are coordinated 
to give linear response over the entire 
frequency range. The safety factor is 
ample, allowing for excessive line volt- 
age and overloads. 

The output wattage is sufficient to 
operate two standard air-column speak- 
ers in an auditorium with a seating 
capacity for 1000 persons. The air- 
column speaker is supplied as a stand- 
ard part of the equipment, although, 
whenever conditions demand it the 
baffle type dynamic cone speaker can 
be used to advantage. 

Turntable Connection 

Connections are provided to facilitate 
connecting a "non-sync" phonograph 
turntable for supplying dance or inci- 
dental music before and after a per- 
formance. A microphone for making 
announcements can be connected in the 
amplifier circuit. 

Due to an unusual safety factor, con- 
tinuous operation in theatres is possible 
without overheating. Two complete 
shows of 12 reels can be given without 
undue strain. 

The portable amplifier is designed to 
operate with either one or two pro- 
jectors. All controls are dual with 
exception of the volume-control. 
Changeover from one projector to an- 
other is accomplished by means of a 
switch. The volume is controlled by a 
balanced network and arranged in con- 
venient steps providing for close con- 
trol of sound. 

All units are interconnected with 
cables which terminate in plugs con- 
veniently marked. 

A single projector unit consisting of 
a projector, an amplifier, a 6 x 8 screen 
and stand, an exponential horn and one 
set of cables, can be packed in three 
small trunks and weighs 350 lbs. A 
double projector unit weighs 450 lbs. 



JUNE, 1931 



Page 23 



= piio ioiom: talkafilm 



Phototone Portable Sound Film 

35 MM Talking Picture Effuipment with Projector 



Complete A. C. operated — nothing 
else to purchase — installed in 15 
minutes time or less. 




For Permanent and Temporary Installation 



BUILT for Discriminating Purchasers 
That Must Have Quality Above Any- 
thing Else Both in Reproduction and 
Construction 




S*«KSfc-»* 



for Phototone Portable Equipments 

For Further Information Write 

The Phototone Equipment Corporation of America 

309 North Illinois Street - Indianapolis, Indiana 





eiUR~MMSCO 



HEAVY DUTY 

RHEOSTATS and 
POTENTIOMETERS 

Mechanical and electrical 
permanence at power ratings 

POWER— DELICATELY CONTROLLED 

Write us your requirements. Our engineers are ready to assist you in the develop- 
ment of special apparatus to fit your particular needs. Literature on request. 

PeTuR-ff Msco Corp 

Varitors — Variable Condensers — Power Rheostats — Dials — Pilot Lights — Escutcheons 
95 Morton Street, New York City 



Page 24 



PROJECTION ENGINEERING 



New Developments 

and 

News of the Industry 



THE VIGILANT SAFETY CONTROL 

The Vigilant automatic safety control, 
manufactured by the Vigilant Safety De- 
vice Co. at Sharon, Pa., seems to be the 
most simple and neatest control on the 
market. Contrary to other makes of safety 
controls, the Vigilant does not use mer- 
cury switches, and operates on an open 
circuit instead of a closed circuit. Its 
operation is extremely simple as well as 
accurate. 

Fig. i shows the automatic motor control 
switch and transformer housing. This 
switch is so arranged that when it is closed 
it latches and is held closed against a 
strong spring pressure. 

Fig. 2 shows the Vigilant dowser arrange- 
ment. When this dowser is raised it also 




Fig. 1. 

latches against spring pressure. One of 
the features of this dowser is that there 
are no electrical parts to it, and only a 
small steel wire running through a flexible 
cable is used to connect it with the rest 
of the control. A small button is ar- 
ranged so that it may be released at will. 
Fig. 3 shows a Vigilant film switch for a 
Simplex projector. This switch is held in 
an open position by the film, and makes 




Fig. 2. 



contact either up or down which takes care 
of the film breakage, or the loop taking up 
at this point, which is directly under the 
intermittent sprocket. 

Fig. 4 shows the lower take-up switch 
for a Simplex machine. This switch is also 




Fig. 3. 



Fig. 4. 



held in an open position, and should the 
film break just before it enters the lower 
magazine, or should the take-up belt break, 
this switch immediately closes. 

The operation of the Vigilant safety con- 
trol is as follows. The machine is threaded 
in the usual manner- When time to start 
the projectionist closes the Vigilant motor 
switch and raises the dowser in the_ usual 
way. In case trouble develops within the 
projector the small film switches close the 
circuit, which causes two magnet coils to re- 
lease the latch holding the motor switch 
closed. This action allows the spring to 
open the motor switch, and at the same 
time pull the small steel wire running up to 
the dowser latch, causing the dowser to 
close. This entire operation is done in an 
instant. 



NEW PHOTOTONE PORTABLE 
REPRODUCER 

A portable sound-on-film reproducing 
equipment, weighing less than 175 pounds 
and said to be the lightest, smallest and 
most compact apparatus so far developed 
for 35 mm. film, has been perfected by 
Laurence M. Corcoran, eastern sales 
manager for Phototone Equipment Corp. 
of Indiana, and will be placed on the market 
soon by this company. The device can be 
set up in 15 minutes by any layman, ac- 
cording to Mr. Corcoran, and packs into 
two small cases that will fit in an ordinary 
pleasure car. To operate the equipment, it 
is only necessary to plug into a light socket 
and turn on the switch. 



VICTOR ANNOUNCES RESULTS OF 

COMPARATIVE TESTS WITH 16 

MM. PROJECTION LAMPS 

The rapidly increasing demand for 16 
mm. projectors capable of serving both 
the auditorium and small room require- 
ments of schools and churches has made 
light a factor of major importance in the 
construction of the better projection equip- 
ments. 

The lamp manufacturers have accom- 
plished remarkable things in developing 
lamps to meet this demand. Due, how- 
ever, to the limitations imposed by the 
small size of the T-io bulb and of the 
optical accessories in the projectors, it ap- 
pears that their creations in the low voltage, 
concentrated-filament type of lamp leave 
little, if any, room for major improvements. 

Of these lamps, there are three that are 
contending for first place as being the best 
general purpose lamp for the majority of 
maximum illumination requirements. 

These are the 165 watt-30 volt Mazda, 
the 250 watt-20 volt Mazda, and the 375 



watt-75 volt which does not carry the 
Mazda stamp. That the watt-volt specifica- 
tions on these lamps are somewhat con- 
fusing to the average layman is evidenced 
by the fact that "165 watts-30 volts" sounds 
like a comparatively low rating, whereas the 
lamp is actually equivalent in power to 605 
watts in a 110 volt lamp. 

The Victor Animatograph Corporation, 
Davenport, Iowa, offers a projector equip- 
ment in which any one or all of these high 
intensity lamps may be used interchangeably. 
The model 3G Victor Cine-Projector has a 
built-in transformer to accommodate the 
250 watt-20 volt lamp. A change-over sys- 
tem of wiring permits the transformer to 
be cut out. By plugging-in with the No. 
11 Victor lamp rheostat, the 250 watt-50 
volt, the 1 65 watt-30 volt and the 375 watt- 
75-volt lamps may all be used in the same 
projector. 



TONE CONTROL 

The Clarostat Manufacturing Company, 
Inc., 285 N. 6th Street, Brooklyn, N. Y., 
is marketing a completely bakelite encased 
tone control for panel mounting. It has an 




extra long threaded bushing with two nuts 
for mounting on any thickness panel or 
cabinet. A 2-jj inch hole is required. The 
unit takes up but one inch space behind the 
panel, and is 2 inches in diameter. 



HOME TALKIES 

The Talkiola Corporation, 1600 Broadway, 
New York, is bringing to the market a 
home talkie equipment which combines a 
talking picture machine, using 16 milli- 
meter film, together with a specially de- 
signed radio and phonograph. The cabinet 
is quite different from the usual radio type. 
It resembles a secretary and can be used as 
a desk when open. 

The manufacturer had to develop and 
design a noiseless projector to take care of 
the increased speed of talking pictures over 
the silent pictures and at the same time 
eliminate noises which would interfere with 
the proper reproduction of talking pictures. 

Talkiola has a radio perfectly matched to 
the pickup, which is specially designed for 
it and produces the rich, natural tone 
which you find only in the best of radios. 
By a quick turn of the dial you switch 
from the radio to the phonograph and can 
then play any record recorded at the speed 
of 78 r.p.m. 

Shifting a lever changes the speed of 
the turntable from 78 to 33-1/3, which is 
the speed used in talking pictures. 

The threading of the film is easily ac- 
complished and the plate is so marked that 
any one can project a picture without 
technical knowledge or training. 



JUNE, 1931 



Page 25 




HOFFMANN-SOONS say 

^^Tfa ^ ve *"* " —^^ ^^^ Making claims is one 

thing — Making good is another! 

Projectionists and theatre owners who have 
installed Perfection Rheostats KNOW our 
guarantee means the best results — clearer 
pictures — longer life. 

SOLD BY ALL BRANCHES OF THE NATIONAL THEATRE SUPPLY CO., 
SAM KAPLAN, NEW YORK, AND BY YOUR DEALER. 

HOFFMANN-SOONS 

Electrical and Engineering Corp., 387 First Avenue, New York City 




THE ONLY UNION MADE RHEOSTAT 



PERFECTION RHEOSTATS 




VACUUM-TUBE VOLTMETER 

Because of its practically infinite input impedance 
and its freedom from frequency errors, the General 
Radio vacuum-tube voltmeter is ideal for develop- 
ment and maintenance work on high-quality sound 
systems. 

The meter illustrated above is the Type 426-A 
Vacuum-Tube Voltmeter, range 0-3 volts. It is of 
the bridge type in which the internal plate resistance 
forms one arm of a resistance bridge, the indicator 
being a calibrated d'Arsonval movement. This con- 
struction makes for accuracy and permanence of 
calibration. 

Price: $160.00 

Bulletin 932-P6 contains a complete 
description. Ask us to send you a copy. 

GENERAL RADIO COMPANY 

Offices Laboratories Factory 

CAMBRIDGE A, MASSACHUSETTS 

Pacific Coast Warehouse: 274 Brannan St., San Francisco 



CINEGLOW 

the 3 element 
_ recording lamp 



(patents pending) 



Y* 



^°.m 




ACKNOWLEDGED THE BEST! 

For Optical or Contact Slit. 
For Positive or Negative Film. 
For Any Standard Glow Lamp 
Circuit. 

CONSISTENT — RELIABLE 

Maximum Volume — Abundant 
Exposure — Without Distortion 

Special circuits supplied with each 
lamp. 

PRICES 

Type T9 — 6 inches long — $50 each 
Type T8 — 4 inches long — $40 each 
Special discounts in quantities. 



BLUE SEAL 

SOUND DEVICES, Inc. 

130 W. 46th STREET, NEW YORK 



Page 26 



PROJECTION ENGINEERING 



SCREEN OF METAL MESH ON 
MARKET 

After several demonstrations with good 
results, a new type metal mesh projection 
screen, under the trade name of "Lustro- 
Pearl" and designed especially for high 
grade theaters, has been 'placed on the 
market by the Mandalian Manufacturing 
Co., North Attleboro, Mass. 

The features claimed for this new screen 
include : A surface treated with the purest 
of known chemicals, entirely free from 
gloss, eliminating distortion common to 
ordinary types. 

Highest reflection factor known to repu- 
table light testing laboratories, effecting a 
considerable saving of electric current. 

Constructed to distribute . sound very 
clearly and uniformly throughout the entire 
theater. 

Can be washed with hot water and soft 
brush without injury to its surface. 

Affords a clear view of any picture from 
any angle of observation, eliminating eye 
strain or discomfort to patrons. 

Its high reflective qualities bring out ob- 
jects in a manner which might be termed 
the nearest approach to three dimensional 
pictures, the company claims. 

RKO Proctor's 58th Street, New York, 
is among the first houses to install this 
new type screen. 

▲ 

ACOUSTICS AND SEATING 
BOOKLET 

A booklet, dealing in acoustics and its 
relation to seating, and containing facts 
about reseating engineering service, is being 
issued by the American Seating Co. 



GENERAL THEATRES EQUIPMENT 
EARNINGS 

Total of $4,454,405, after all charges, in- 
cluding interest, depreciation and taxes, is 
the net income of General Theaters Equip- 
ment, Inc., and its subsidiary companies for 
the year ended Dec. 31, 1930, the company 
stated recently in announcing its annual 
report. This is compared to $2,140,023, in 
1929 had the subsidiaries now embraced by 
the company been operated by it for the full 
year. Portion of earnings accruing to Gen- 
eral Theaters Equipment in the 1929 report 
was $940,296. 

The 1930 earnings are equivalent to $1.57 
per share on the 2,838,913 shares of old com- 
mon stock. Deducting actual dividends on 
the new preferred stock, such earnings are 
equivalent to $2.23 a share on the 1,892,608 
shares of new common. 

Acquisition of controlling interests in Fox 
Film Corp. and Fox Theaters Corp. is re- 
flected in the large increase in assets of 
General Theaters from $55,096,901 on Dec. 
31, 1929, to $129,094,728 at the close of 
1930. Current assets are figured at $9,732,- 
638, and current liabilities at $6,628,109, 
exclusive of a $10,000,000 note on a loan 
obtained for the purpose of paying for 
shares of Class A stock of Fox Film, and 
to provide funds for the acquisition of ad- 
ditional shares of Fox Film Class A stock. 
This loan is secured by 500,000 shares of 
Fox Film Class A stock and was renewed 
from April 10, 1931, the due date, to Sept- 
27, 1931- 



TALKING MOVING PICTURES FOR 
THE HOME AT POPULAR PRICES 

The field of home movies has long been 
well established — and has been emphasized 
by the interest displayed in talking moving 
pictures for the home, which have been a 
reality for several years. 

Much new interest has been created in the 
announcement by the Sprague Specialties 
Company of Quincy, Massachusetts, of the 
Visivox, a home talking moving picture 
machine, priced far below any other item 
previously announced. This field has not 
only been complicated by high prices in the 
past, but also by the inavailability of 16 mm. 
talking moving picture films and records for 
either purchase or rental. There are now, 
however, numerous of such films and rec- 



ords available with regular production estab- 
lished, and the subjects range from a wide 
variety of educational pictures to all sorts of 
comedies, dramas and feature films. 

There are two Sprague models, one port- 
able and one in cabinet form. The portable 
type "Visivox A" lists at $119. This model 
includes the phonograph synchronization 
apparatus, pickup and projector. The user 
plugs a wire into his radio set, another into 
an electric socket, and the apparatus is 
ready to operate. Where no radio set is 
available, another small portable device, list- 
ing at $50, is attached to this model, thus 
providing the audio and loudspeaker. This 
latter instrument is known as Model "B." 

"Visivox C" is a complete machine in a 
walnut cabinet, including projector, syn- 
chronical 'phonograph apparatus, amplifiers 
and loudspeaker. This lists at $189. 

The Sprague Visivox is very simple in its 
mechanical operation and the synchroniza- 
tion is entirely automatic. Both types of 
machines play all sizes of phonograph rec- 
ords, including the 16-inch theatre records, 
and can be used separately as a phonograph 
if the moving picture apparatus is not 
desired. The Visivox may also be used as 
a simple projector of 16 mm. films where 
it is not desired to use it as a talking 
picture- Much significance will be attached 
to the popular prices which open this type 
of machine for a much wider sale than 
hitherto available. 



NATURAL COLOR FILM IS READY 

FOR QUANTITY PRODUCTION IN 

HOLLYWOOD AND NEW YORK 

PLANTS 

Magnacolor, the new natural color film 
perfected and introduced by Consolidated 
Film Industries, Inc., after years of experi- 
menting and consideration of many other 
processes is hailed as a superior and satis- 
factory color process that the industry has 
long been waiting for. It marks progress in 
motion pictures. 

Magnacolor provides color pictures that 
can be produced and processed with the 
same facility, and that are as sharp and 
clear as black and white. 

Magnacolor requires no change in present 
cameras and projectors except the use of 
Magnacolor films and a slight adjustment 
of the camera gate. 



RESISTORS FOR TELEVISION 

The engineers of the International Re- 
sistance Company have been preparing from 
the standpoint of resistors for forthcoming 
television. 

Special types of resistors are required, 
and the demands made upon resistors are in 
some cases more severe than in the con- 
ventional radio receivers because of the 
widespread use of resistance coupling in the 
amplifier portion of the television short-wave 
receiver. 

The International Resistance Company 
Engineering Department is keeping as 
closely abreast of this interesting subject 
as is possible, and is cooperating fre- 
quently with manufacturers who have espe- 
cial problems in this connection. 



VOLUME CONTROLS 

The Central Radio Laboratories, 16 Keefe 
Avenue, Milwaukee, Wis., has issued a new 
bulletin illustrating and describing a line of 
volume controls for sound installations. The 
bulletin contains a considerable amount of 
engineering data valuable to engineers. 



THEATRE EMERGENCY LIGHTING 

Roth Brothers & Co. announce a comlplete 
line of emergency lighting equipment to 
protect patrons from the dangers caused by 
failure of the lighting service. 

The emergency and exit lighting circuits 
in theatres are normally supplied from the 
a-c. lighting service. In the event of a 
power failure, the Roth system automati- 
cally operates by gravity action and trans- 
fers the load to the storage batteries so 



rapidly that, there is only a very slight 
flicker. 

The load is also automatically transferred 
back to the a-c. supply, upon resumption of 
the normal power service. 

The batteries are kept fully charged, ready 
for emergency use by means of electric clock 
control, so that they are always in condi- 
tion to supply the load during emergencies. 
The plant has sufficient capacity to supply 
all exit lights for a period of 3 hours. 



PROJECTOR FOR SCHOOLS 

International Projector Corp., has com- 
pleted a new projector especially suitable 
for schools. The U. S. Navy has ordered 
a "large quantity" of these machines for 
delivery before July 1, this year. 



NEW VOLUME CONTROL WITH 
"DEAD" SHAFT AND BUSHING 

Of especial value in the control of the 
new variable-mu tubes, the new Clarostat 
wire wound volume control with "dead" or 
insulated contact arm and mounting bushing 
has just been announced by the Clarostat 
Mfg. Co., Inc. of 285 North Sixth St., 
Brooklyn, N. Y. 

This improved model 01 the Clarostat 
control makes the use of insulating mount- 
ing bushings unnecessary as all exposed 
parts are out of the electrical circuit. 

It is supplied with a dust cover or not as 
desired and may also be had with no volt 
switch attached. 



GAIN CONTROL 

The Type GL-35 gain control manu- 
factured by Jenkins and Adair, Inc., 3333 
Belmont Ave., Chicago, is of the potentio- 
meter type, built up of nichrome wire 
resistance units of different values, totaling 
350,000 ohms. The steps have a logarithmic 
increase of resistance which gives an equal 
gain in decibels per step. When used in a 
standard amplifier circuit these steps are 
approximately 3 decibels each. 



SILENCE FOR TALKIES 

The variable speed fan drives, manufac- 
tured by the Horton Mfg. Co., 3016 Uni- 
versity Ave., Minneapolis, Minn., make for 
quiet in sound-equip'ped theatres. 

Controlled ventilation for theatres all the 
year through is necessary because the 
health and comfort of patrons require, and 
maximum results from sound reproducing 
equipment demand it. 

It _ is economical because through easy 
starting, it eliminates fuse blowing and 
reduces belt wear. Through speed adjust- 
ments to atmospheric conditions, power bills 
are greatly reduced. 

An average speed reduction of only 25% 
nearly halves the power bill. Records of 
the local power company at Fargo, N. D., 
show that to drive its fan, the Isis Theatre 
used 1975 kwh. electric current during four 
months before and only 1924 kwh. during 
the first full year after installing the Horton 
variable speed drive. 

The owner, Floyd Junkin, advises that 
the variable s'peed drive made it possible 
to operate his fan constantly during every 
performance throughout the winter — a great 
deal of the time at just speed enough to 
prevent air stagnation and sound-defying 
air pockets. 

Through the reduction of electric current 
used, the initial cost is quickly liquidated, 
after which the monthly saving is all profit. 



JENSEN SPEAKERS 

A permanent magnet speaker known as 
Jensen model PM-i, and the first of a new 
line of dynamic speakers designated as 
model J-i were shown and demonstrated at 
the RMA show, Chicago. They are made 
by the Jensen Radio Mfg. Co., Chicago. 
Copies of bulletin will be sent upon request. 



JUNE, 1931 



Page 27 



Put Your Show 



on wi 



ith 



"SYNCROFILM" 



The V Goes On 
">eO 



? er *tor S m ,l 



es 



°P°era n t°on t ' ,er s °«n d systt 

■ no serJZ? te ™ off e 



Sountl-on-fllm, variable, area, density, 
squeeze, are all reproduced to perfec- 
tion . the unique patented super- 
condensed optical system does it. 



No expense has been spared in engi- 
neering: . . or in material. Wearing 
surfaces are chromium plated ; a 
constant chain drive; even tension 
thru aperture; fool proof head 
and matched pre-amplifier; That 
Is Why Syncrofilm Stands Out As 
The Leader. 






"^vicing" 0ffe ^ such ea « 

■ • no trouble f 6 of 



Sine 

there " ,; ■ and 
hea «aches ,u" o 
""'ee a ^ orl "fant 



has i 



"•"eased to s 



R. o 



We invite you to study and consider Syncrofllm from every 
angle, price included. Churches, schools, auditoriums and 
theatres . . there is a model for every purpose . . . and 
for every type projector. 

Price & Particulars On Request 

WEBER MACHINE CORP 

5° RUTTER ST., ROCHESTER, N. Y. 



EXPORT DEPT. 

15 LAIGHT ST., N. V. C. 




CABLE ADDRESS 
"ARLAB" NEW YORK 



Noh 



urn, noise 



or moving parts . . . 



FOREST 
RECTIFIER 



Leading Sound Recording Studios, Theatres, 
and Laboratories where unfaltering current 
supply is required use FOREST — because 
it is superior. 

Adaptable to all sound equipment — inter- 
changeable with your present storage bat- 
tery — several types. 





Just turn the switch to con- 
vert a 110 or 220 V. a-c. 
into fully filtered d-c. 

FOREST ELECTRIC 
CORP. 

New and Wilsey Steets 
Newark, N. J. 




PORTABLE A. C. OPERATED 

SOUND PICTURE 

EQUIPMENT 

No batteries or motor-generators! 

Optical Slit! 
"A truly Portable Sound-on-Rlm. 

Write For Our Descriptive Circular 

List Price $1,685 Complete F. O. B., N. Y 

Manufactured By 

GRIES REPRODUCER CORP. 

485 EAST 133 ST., NEW YORK, N. Y. 



it 



Page 28 



PROJECTION ENGINEERING 



Sound 

Controls 





amaQ 



P?P© 



■Q-ok 



F""©' ■ uif mm O l - J?™"^ 



SPECIFY CLAROSTAT— Whether you need 
simple potentiometer Volume Controls or Dual 
and Triple Units for Constant Impedance work 
— Clarostat makes all types to suit the exacting 
needs of the sound industry. 

Absolutely quiet, long lived units with 
special alloy contactor and windings to avoid 
thermal e.m.f. Insulated or Grounded Shaft and 
Bushing as desired. 

New model Graphite Element Potentio- 
meters for use where extra high resistances are 
required. With the revolutionary, Geared 
Roller Contact for long life and silent operation. 

Rely upon resistor specialists — Specify 
Clarostat ! 

Write for literature — mentioning this magazine 

Clarostat Mfg. Co., Inc. 

285 North 6th St. Brooklyn, N. Y. 







If ♦ ♦ ♦ your apparatus 




(.ACTUAL-SIZE,) 



is built 

for 

quality and 
performance, 
consider .... 




Type BWE 

Accuracy to .1 of 1%. 

Low distributed capacity. 

Non-inductive. JRfcblb H 

Electrically noiseless. All standard values in stock 

Ranges from .1 ohm to f 

100 megohms. 

THE DAVEN COMPANY 

RESISTOR SPECIALISTS 

General Office and Factory 
158-160 Summit Street, Newark, N. J. 



L R. E. 

Convention 
Booth Number 150 



Projection Engineering 



inmiiii 



R. M. A. 

Convention 

Booth Number 121 



JUNE, 1931 



Page 29 



Musi Sacrifice! 



Film Cement 

Spray Perfume 

Gum Remover 

Screen Cleaning Fluid 

Flame-proof 2 in 1 
Film Cement 

No Regard to Cost 
! ! Get Our Price ! ! 

GALLON CANS ONLY 



Boxl5— PROJECTION ENGINEERING 

52 VANDERBILT AVE., 

NEW YORK CITY 




HOTEL 



mUAWAMIINl.TT 



ATLANTIC AVE. AND EIOUTM ST. 

VIRGINIA BEACH 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 



SILENCE 

Hydraulic controlled 
variable speed drive. 
Widely used in sound 
equipped theaters and 
public buildings. Cool 
and quiet at all speeds. 
Power saving quickly 
liquidates cost. 

HORTON MANUFACTURING CO. 

3016 University Avenue, S. E. Minneapolis, Minn. 





Input transformer 
designed for any 
single button mi- 
crophone. 200 ohm 
Primary, 100,000 



side. List pri 



^OPHOAJ^ 

^JV» " HAN Dl -MIKE" ,* ** 

X* MOST EFFICIENT GENERAL jf^g^ 
UTILITY MICROPHONE KNOWN 

List 'IO Complete 

The truly perfected single button 
hand microphone. Two models, "Reg- 
ular" and "Special Home Recording." 
Scientifically damped diaphragm, gold 
plated button, toggle switch, 15-foot 
cord. Finished bronze or gunmetal. 
Dealers, write for our "direct deal." 
Get our complete catalog. 

UNIVERSAL 
MICROPHONE CO., Lid. 

1163 Hyde Port) Blvd. 
IN6LEWOOD, CALIF. 

Microphones $5 to $350. Also cables, plugs, transform- 
ers, mountings, stands, etc. Expert microphone repairs. 





Portable Sound Distribution Equipment 

For schools and colleges, churches, 

lodges, parks, airports, etc. Output 

sufficient for two dynamic speakers at 

heavy volume. Completely equipped 

with meters and controls. Padlocked 

against tampering. 

Dealers can rent this equipment 

profitably. 

20" high, 133,4" wide, 12^" deep. Complete 

with microphone and speaker — $350.00. 

Write for illustrated folder. 

FERRANTI, Inc. %£<■_«$& 




3&£Sj\Jj ®V5vi*3PBS£» 



BEST CARBON SAVER 

for Low Intensity Arcs 

Permits projectionist to get at least one more 

reel from each set of stubs. Made in 7, 8, 9, 

10, 12 and 13 mm. sizes. 

$2.50 each at your dealer. 

BEST DEVICES CO. 



2108 PAYNE AVE. 



CLEVELAND, OHIO 



Page 30 



PROJECTION ENGINEERING 



F. S. C. 
Genuine Opti cal Crown Glass Plates 

Enclose Portholes for Perfect 
Sound Projection 

PRECISION SURFACES NO DISTORTION 

S. O. G. 
"IGNAL" CONDENSERS 



Extra Heatresisting 
Optical Glass 



ALL SIZES 



ALL FOCAL LENGTHS 



FISH-SCHURMAN CORP. 

45 WEST 45TH STREET NEW YORK, N. Y. 



HEADQUARTERS for the hard to get 
parts or material. Complete stock of 
shielded and plain covered wire on hand at 
all times. Full line of Weston and Jewell 
meters in stock for immediate delivery. All 
standard microphones in stock. 




-flhaHome of RADIO. 1 

45 VESEY STREET, NEW YORK CITY 



Now 



SELL Talkie Sound-on-Film 



To Theatres, Schools, Churches, Clubs 

Write for manufacturers' prices on Soundheads, Photocells, 
Optical Systems, Rectifiers, Amplifiers, Horns, Faders, Syn- 
chronous Motors, Projectors, Lamphouses, Screens, Micro- 
phones, etc. 

S.O.S. CORPORATION 

Dept. P.E., 160© Broadway, New York City 

Cable Address "SOSOTJND" 



niCRGPHGNES 

. and accessories 
Write for Details > 



ELLI S ELECTRICAL LABORATORY 



BUILT 
for SOUN 




We build splicers to 
your specified require- 
ments — for sound film, 
wide film, 35mm or 
16mm film. Our splic- 
ers, both standard and 
custom-made, are giving 
sturdy, dependable serv- 
ice in theatres and ex- 
changes throughout the 
world. 

Send for literature 

GRISWOLD 

MACHINE WORKS 
Port Jefferson New York 



w 



E, offer to manu£ac» 
tnrers Interested in. 



EXPORT 

tlte services of a. dependable organization*, 
■well established in the entire foreign field 

AD. AUMEMA, Inc. 

Mantaf acturers' Export Managers 

116 Broad Street, New York, N.Y. 




GEARS 

In Stock — Immediate Delivery- 
Gears, speed reducers, sprockets, thrust bearings, 
flexible couplings, pulleys, etc. A complete line is 
carried in our Chicago stock. Can also quote on 
special gears of any kind. Send us your blue prints 
and inquiries. 

Write for Catalog No. 60 

CHICAGO GEAR WORKS 

769-773 W. Jackson Bivd., CHICAGO, ILL. 




337 WEST MADISON ST. 



CHICAGO. ILLINOIS 




BASS BARGAINGRAM 

Issue 202 Ready 

FREE! The Classic of Bargain Lists. World's 
largest stock of Motion Picture Cameras and ac- 
cessories. Professional and Amateur. Save real 
money. Send for your copy. Free! 

BASS CAMERA CO. 



179 W. Madison St. 



Chicago, III. 



INDEX TO ADVERTISERS 



Ad. Auriema, Inc 

Amplion Corp. of America. 



30 
6 



Bass Camera Co 30 

Bell Equipment Corp Fourth Covet- 
Best Devices Co 29 

Blue Seal Sound Devices, Inc 25 

C 

Cameron Publishing Co 32 

Chicago Gear Works 30 

Clarostat Mfg. Corp 28 

D 

DeJur-Amsco Corp 23 

De Vry, Inc., Herman A.. . .Third Cover 

E 

Ellis Electrical Laboratory 30 



Fish-Sehurman Corp 30 

Ferranti, Inc 29 

Forest Electric Corp 21, 27 

G 

General Radio Co 25 

Gries Reproducer Corp 27 

Griswold Machine Works 30 

H 

Hoffmann-Soons 25 

Horton Mfg. Co 29 



Int'l. Broadcasting Equipment Co.. 3 
L 



N 



National Carbon Co., Inc. 



Leeds Radio Co. 



30 



Phototone Equip. Corp. of America, 
The 23 

R 
Racon Electrical Co., Inc. . Second Cover 

S 

Samson Electric Co. . ., 5 

SOS Corporation 30 

U 
Universal Microphone Co., Ltd... 29 

W 

Weber Machine Corp 27 

Weston Electrical Inst. Corp 21 



JUNE, 1931 



Page 31 




Page 32 



PROJECTION ENGINEERING 




Here is the Best 
Book Published on 

The Subject of Motion 
Pictures With Sound 

AND 

HERE ARE THE PEOPLE WHO 
SAY SO— 



U. S. DEPARTMENT OF COMMERCE, Wash- 
ington, D. C. 

DEPARTMENT OF PUBLIC INSTRUCTION, 
Washington, D. C. 

AMERICAN LIBRARY ASSOCIATION 

AMERICAN PROJECTION SOCIETY 

CINEMATOGRAPHIC BUREAU OF LEAGUE 
OF NATIONS, Rome, Italy 

HARRY SHERMAN, Director of Personnel, 
PUBLIX THEATERS 

HARRY RUBIN, Chief Projectionist, PUBLIX 
THEATERS 

J. DAVIE, Sound Expert, SOUTH AFRICAN 
THEATERS, Ltd., South Africa 

MOTION PICTURE NEWS, N. Y. C, N. Y. 
AMERICAN PROJECTIONIST, N. Y. C, N. Y. 
SOUND WAVES, Hollywood, Cal. 
AMERICAN CINEMATOGRAPHER, Hollywood 
SCIENTIFIC AMERICAN, N. Y. C, N. Y. 
CAMERA CRAFT, San Francisco, Cal. 
AMERICAN PHOTOGRAPHY, Boston, Mass. 
FILM TECHNIK, Berlin, Germany 
THE CINEMA, London, England 
THE NATION, London, England 
LA CINEMATOGRAPHIE FRANCAISE, Paris 
FILMOVY KURYR, Ceskoslovenche 
ELECTRICAL TIMES, Melbourne, Australia 
DER PHOTO MARKT, Wein 

AND THOUSANDS OF OTHERS 



WHY TAKE CHANCES? 
DEMAND CAMERON BOOKS 



THROUGH ALL DEALERS — AND LARGE 

BOOKSTORES — NATIONAL THEATER 

SUPPLY CO. OR DIRECT. 

CAMERON PUBLISHING CO. 
Woodmont, Conn., U.S.A. 




BUT . . . 



THE "CHICAGO" SOUND-ON-FILM PORT- 
ABLE PROJECTOR delivers reproduction 
comparable to that of the most expensive 
and complicated installations. 

A few of its outstanding features are: 

Uses theatre size 35mm. film, with sound track, 
thus giving ample film area for large theatre size 
pictures and sufficient volume for 1000 people. 

Does not employ — synchronous motors — turn tables 
— flexible shafts — discs — needles — tone arms — bat- 
teries — ground wires. 

Automatic speed control. 

Operates on any A.C. circuit range from 90 to 122 
volts. 

Fewer parts — therefore — minimum servicing. 

The DeVry sound head can be installed in DeVry 
Projectors which are not equipped for sound on 
film. The expense is small. 

PRODUCTS BY H. A. DE VRY 

Sound-on-Film Projectors (Portable) 

DeVry Sound Recording Apparatus (Disc) 

DeVry Air Speaker, the new Public Address System with 
more volume 

Battery Eliminators 

Condensers 

Photo Electric Cells 

Vacuum Gauges 

DeVry Radio Beacon Compass 




HERMAN A. DE VRY, INC. Dept. B. 



55 E. Wacker Drive, CHICAGO. 



An Appreciation by 

Bell Equipment Corporation •• • 

— Our Faith is Justified 




lief that a market existed 



ational^emilffiercial and amusement 



The sound and projection heads 
are built in one unit. The Photo 
Electric Cell assembly on the out- 
side of the case conveys the im- 
pulse to the amplifier circuit. 

Film running over an idler con- 
nected to a circuit breaker keeps 
the circuit closed . . a film break 
releases and shuts off the entire 
unit. 

An ingenious rear shutter is built 
in, while the aperture is constant- 
lycooled by forced draft. Entirely 
assembled in double sheet steel, 
asbestos lined, fireproof and 
noiseless operation is assured 
besides eliminating the use of a 
fireproof booth. 

All moving parts are hermetically 
sealed in an oil bath. Special 
condensers handle the intens< 
light from the 1000 watt projec- 
tion lamp and throw a full theatre 
size picture on a screen 100 to 
125 feet distant. \ 

Bell equipment is sold 
in every detail. 



fe TOr4t 'ykjybi^-i^ip ie lr^bi h talkie projector. 



\ We^3|tajr^hat ; an ordi 
Ould defeat its own purpose. We kllev 



rictj consfrjactioh isyjggj 



It 




late 



fa ser^e/oJT 
-to our/initial aniulik 



af y sound movie system 

that, insofar as design 

tk uld be no compromise 



erived from the im- 
ment is the incentive 



gpiirs us on with theoriginal thought intensified. "There is 



m 




ompromise with Quality." Wa 
they be distributors or de 
i^-iheneH^Eflke consuinl 
!-|toK La vyh^i^ilifrF' the sal 
rttration — schools — hospit 
where education and amUsenie 
und Motion Pictures - 
ndardizp on quality tci 




patrons whether 

resent the leader 

iness organiza- 

d demon- 

or clubs 

e use of 

ration will 



TRADE I; I I MARK 

WE AgE ARRAM 11 ^ REPRESENTATION WITH 
t&^MMteiE DISTRIBUTORS FOR 
STATE AND FOREIGN RIGHTS 




BELL EQUIPMENT CORPORATION 

Portahie Talkie Equipaient 



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

Telephone BRyant 9-9890 Telegram WESENOJ 



. 



I • I ] 



AUGUST 1931 



PROJECTION 



SOUND - VISUAL 



W 6 



f}jcA 



«4^6fB0^8^"S6sfS 



bH" 



£ 



V'*-' IF ^JliP *■ .«*>C^ 



m * 



Af> 






lO.- 



^ 



(Photo Courtesy Samson Elec, Co.) 



Rehearsal of "Mikado" directed by 
microphone and loudspeaker 



/ 






THE JOURNAL OE THE SOUND AND LIGHT PROJECTION INDUSTRIES 



Bell 35m.m. Portable 
Sound-on- Film Projector 






Completely Solves the Sound Problem for Smaller Theatres — 
Highest Quality Performance with Economy, Adaptability and Profit Plus 



Primarily designed for portability, Bell equipment is in every respect truly professional in its optical system, sound reproduction and 
mechanism, it is the first equipment of its kind that has been designed to fulfill the requirements of picture projection and sound 
reproduction in a manner equal in every respect to the performance of the best of permanent theatre equipments. 

For owners of smaller theatres seating up to 1,500, it offers the only logical solution to the sound problem, at a price within reason- 
able bounds. An owner equipped with Bell, is not irrevocably tied to his location. The change from semi-permanent installation to 
portable equipment wherewith to fulfill engagements outside the theatre is the work of a few minutes. This opens up a wide field for 
extra profit to theatre owners. The theatre owner who gets into the rental field through Bell equipment, can give the laugh to 
competition. 



Bell equipment is engineered for sound, not adapted to it. The 
Tandem unit, illustrated above, as designed in right and left pro- 
jectors. Can be set up with 18" between lenses or 20 ft. apart. The 
exclusive Bell Uni-remote control provides for smooth "change over," 
and individual operation of each projector from one central point. 

The exclusive safety features incorporated with Bell design, of which 
the automatic "dowser'' which shuts off all current when film has 
run through, or parted, the rear shutter construction, the forced 
draft cooling system and fire proof mounting, are outstanding, 
make Bell the safest of projectors yet designed. 

Film operating- parts are masterpieces of advanced projection engi- 
neering. Drive mechanism consists of a large induction motor 
which assures constant speed under the most adverse power condi- 
tions. Lubrication is rendered automatic by immersing moving parts 
in a bath of oil. 
All steel parts are chromium plated. 



Standard lamp equipment consists of 1000 Watt lamp, but 900 Watt 

may be had if desired, and for semi-permanent installation arc 

lighting may be employed. 

The projection lens mounts will take any type of lens of standard 

dimensions. Standard size theatre screens can be fully covered at 

50 to 100 foot throws. 

Bell sound reproduction is truly superb. 

Bell equipment can be used indoors or out. No special wiring 

necessary. Operates entirely from 110' Volt A.C. house current. 

The Bell Tandem Unit complete consists of two projectors, with 

lenses and lamps, one amplifier and uni-remote control panel, in 

metal case, speaker unit consisting of two synchronized dynamic 

speakers, and baffle board in case, and one film magazine case. 

Weight complete 215 lbs. 

Price of Bell Tandem Unit, complete as above, $2,150. Detailed 

descriptive folder will be mailed upon request. 



Inquiry is solicited regarding our Distributor Plan, from responsible parties in unoccupied territory 

BELL EQUIPMENT CORPORATION Portable Talkie Equipment 

Suite 605 729 SEVENTH AVENUE NEW YORK 

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

Visit us during the Radio World's Fair, New York, Sept. 21-26, Booth 8— Section F. F. 



AUGUST, 1931 Page ! 



Two Patrons 



Buy Your Carbons 




T 

JLh 



HE modern theatre and its furnishings represent 
the acme of splendor. The staff is thoroughly trained. 
Managers carefully select pictures in accord with popular 
taste. This lavish expenditure to attract patronage. Yet, 
if the screen is dim or the light unsteady, valuable pat- 
ronage will be lost and two empty seats cost 

more than your carbons. 

Light is the most important factor in the operation of a 
motion picture theatre. That is why National Projector 
Carbons are preferred by the projectionist. They are depend- 
able. And the manager knows that, with good projection, 
patrons will return and bring their friends. 

National Projector Carbons give the steady, brilliant white 
light necessary for the quality of projection demanded by 
theatre-goers today. Their uniform quality is assured by 
the experienced organization behind them. Two satisfied 
patrons will buy them. 

NATIONAL 

PROJECTOR CARBON 

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 [llllj 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. Ill 



AUGUST 
193 1 



Number 8 



Contents 

PAGE 

Editorial 4 

Applying Public-Address Equipment to Indoor Use 

By Gordon S. Mitchell 7 

The Acoustic Treatment of Auditoriums and Halls 

By E. F. Smith 10 

What Happens Within the Bulb of a Radio Tube? 

By Linwood G. Lessig 13 

Output Matching to Loudspeaker By B. Brown 1 5 

Adolph Zukor and the Early Movies '. 17 

News for Home Movie Makers 18 

Sound Systems in Public Schools By Ralph P. Glover 19 

Measuring Screen Brightness 21 

Don'ts for Theatre Projectionists. By C. B. Gordon-Sale 22 

Portable 16 MM. Camera Used for Slow Action Pictures 23 

The Use of Positive Film in Sound Recording 

By Charles Felstead 24 

Departments 

News of the Industry and New Developments 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 



Sanford R. Cowan 
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 — 155 Sansome St. — R. J. Birch. 
Los Angeles Office— 846 S. Broadway— R. J. Birch. 
New Zealand — Tearo Book Depot — Wellington. 



Application for entry as Second Class Matter at the Post Office at New York, N. Y., under the act ol March 3, 1879, 
pending. Yearly subscription rate $2.00 in U. S. and Canada. Yearly subscription rate $3.00 in foreign countries. 



AUGUST, 1931 



Page 3 




Telling the world with 



* 



the NEW Amplion 
Portable Address Set 

THAN SI VOX 



Not an assembled group of parts, but an engineered whole, Transivox 
meets the demand for a readily portable Public Address System of 
high quality. It can be carried in two small packages and contains a 
genuine Amplion Transverse Current Microphone, a 2-watt amplifier 
and an exponential 4Y 2 feet, collapsible horn with a 22-inch bell. The 
unit is the Amplion Giant Dynamic now used in the best theatres, 
churches and parks throughout the world. It is 600% to 900% more 
efficient than dynamic cones. Covering a range of 8,000 cycles, it is the 
outstanding public address speaker and theatre unit of today. 



The strong wooden horn is made in three sec- 
tions. It is 4'/ 2 feet in length, when extended 
for use, and 19 inches high when closed. The 
bell is 20" x 20" inside measurement. It is well 
braced and stands up under rough handling. 
Its highly polished interior preserves the qual- 
ity and effects a penetration of sound not found 
in ordinary speakers. 



Package No. 1, a fine imitation leather cabinet 8" x 15" x 19", contains 
the microphone, 15-foot microphone cord, tubes and amplifier, weight, 
40 lbs. 



Package No. 2 consists of the bell in which is carried the other two 
sections of the horns, the Giant Dynamic Unit and twenty feet of rub- 
ber-covered, flexible four-conductor cord, weight, 35 lbs. 



The entire equipment can be set up in less than ten minutes. It is 
ideal for lectures, conventions and gatherings of every nature. 



* Next month another important announcement will be made. 

Amplion Products Corporation 

38 W. 21st Street New York City 





Edit 



i a 



ii'iiiiiiiiiNi i iiiiii!iiiiiiiii!iiiiiiii!i!iiiiiiiiiiniii i t i in ran 111 ii i iiiiiiiiiiiii ii iiiiiiiiiinimiii iiiiiiiiiiiiiiiiiiiiiiniiiiini :iiii:iir"iiiiiiHii;;iii!,:::;iiiiii ':i;iii:Hj!irT:Hii'":iiiNi himnii: hi iiii'^ihiii-iiiiimih 



AUGUST, 1931 



RECENT survey in New 
■ Jersey discloses that 



SHOWS 



A RM 

" Jen 

double feature picture pre- 
sentations may very well be 
abandoned to the advantage 
of the exhibitor and with the approval of the 
public. 

It develops that the most desirable patrons 
— those who attend theatres regularly — in 
large number think that a double feature show 
with all the program filler material lasts too 
long. Also, nine times out of ten it is but one 
of the feature pictures announced which 
attracts attendance. 

Further, much of the word of mouth adver- 
tising a good picture should receive is lost when 
two feature pictures are shown, because of the 
confusion of mind natural under the circum- 
stances. 

A single three reel picture would seem to be 
the answer from the exhibitor's and the public's 
viewpoints. 

Two feature pictures mean 104 pictures per 
year where but one change of program per 
week is made. There are not that many 
"feature" pictures produced. 



V\ URING the summer va- 
SENSIBLE cation months a large 

COOPERATION portion of the populace flocks 
to the shore resorts, the 
mountains and the lakes. In many of the va- 
cation centers moving picture theatres are in 
operation during July and August. As these 
houses open up it follows that nearly a like 
number of theatres in cities and towns find it 
necessary to close because of decreased attend- 
ance. 

In the case of the talkie equipped theatres 
there are the contracts for periodical servicing 
to be reckoned with, the charge for which 
ordinarily would continue whether the house 
is in service or dark. 

This year a generous move toward consider- 
able cooperation in this seasonal condition has 
been made by R. C. A. Photophone. Mr. J. H. 
Tingle of that company announces as follows: 

"We are endeavoring to lighten the finan- 
cial burdens of exhibitors who find it necessary 
to close their theatres. Many theatres close 



during the summer months and we have modi- 
fied our previous policy by suspending service 
charges during the period when they are dark. 
Upon receipt of two weeks' written notice of 
intention to close, we shall send engineers to 
the theatre to service the equipment for the 
closed period and upon like notice prior to re- 
opening will place the equipment back in 
service." 

That this action will be duly appreciated by 
the managements of Photophone equipped 
houses may be taken for granted. 



NEW 
THEATRES 



J T is in the architectural de- 
sign of new theatres that 
full advantage may be taken 
of what has been learned 
about the shortcomings of "silent" houses for 
good sound reproduction. It is understood that 
it would not be difficult to design auditoriums 
capable of providing satisfactory sound effects 
in all seat positions if that were the only re- 
quirement, but there are other factors which 
must be given due consideration when theatres 
are planned. 

A theatre is designed to seat a given num- 
ber of persons. It must be adequately venti- 
lated. It must have beauty of decoration and 
appointments. It must be as fireproof as pos- 
sible. Exits must be sufficiently numerous and 
convenient to afford rapid clearing in case of 
fire or alarm. 

During the past two years much has been 
done toward improving the acoustics of many 
theatres and thought also has been given to 
improvement of vision. 

The excellent paper presented at the Holly- 
wood convention of the S. M. P. E. recently 
by Ben Schlanger contains some new and in- 
teresting ideas on this subject. The title of 
the paper was: "Reversing the Form and In- 
clination of the Motion Picture Theatre Floor 
for Improvement of Vision." 



cA 



OndcL^WHlk 



iccrL, 



Editor. 



AUGUST, 1931 



Page 5 




quickty 

Pays for Itself 

Schools, churches, clubs, hotels need the portable PAM Address 
system. With it, a speaker addresses 500 people as easily as 
half a dozen. Speech and music, both vocal and instrumental, 
are amplified with excellent quality. 

The units in this system are completely matched and designed 
to operate together. Naturally the results obtained are superior 
to a combination of units procured from different sources which 
were not designed to operate together. 

The two units that are required (MIK 100 and PAM 100) to- 
gether weigh less than 75 pounds, and the system can be set 
up ready for use in less than five minutes. No batteries are 
required . . . and the price complete with tubes, microphone, etc., 
and nothing left to buy, is $343.00. 

Send for twin folders RE4; one descriptive of the PAM- 100 and 
the other of the MIK-100. 



SELL 

Portable PAM Address system to 
institutions that hold regular meet- 
ings and need the equipment per- 
manently. This price is reasonable 
and the profits are large. 



RENT 

Portable PAM Address systems for 
special occasions. One man can 
transport the entire system and set 
it up in five minutes. After a few 
rentals the cost is recovered and 
future income is all profit. 



Main Office: 
Canton, Mass. 



Factories: Canton and 
Watertown, Mass. 




Page 6 



PROJECTION ENGINEERING 



They must be good to be where they are! 

Today Gates Equipment will be found in over 100 
Radio Broadcasting Stations as well as Theatres, Uni- 
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Projection Engineering 



AUGUST, 1931 



Applying public-address 
equipment to indoor use 



By Gordon S. Mitchell* 



AS sound amplification equipment 
was developed and the industry 
progressed, attention became 
divided naturally along two 
major lines — out-of-door and indoor 
systems. While these two groupings 
of course embody the same principles 
of operation and apparatus, the develop- 
ment along each line has been so in- 
dividual that it has become necessary 
to consider each as a unit. The equip- 
ment as applied to indoor use has by 
its very nature become of wider extent 
than in the related field of activity out 
of doors. Sound amplification equip- 
ment is being put to new uses every day 
— new ways are being found to apply 
the old apparatus, and new apparatus 
is being developed constantly to aug- 
ment the usefulness of that already in 
service. 

It may well be said that the develop- 
ment of the vacuum tube amplifier is 
largely responsible for the present state 
of development of the audible motion 
picture, inasmuch as the "all-talking, all- 
singing, all-dancing" production of the 
present day would still be in the em- 
bryonic state were it not for the high 
state of perfection of the amplifier. The 
development of the talking motion pic- 
ture, in its turn, is in a great way re- 
sponsible for the advancement to its 
present state, of indoor public-address 
equipment. While the modifications of 
such equipment as found today are 

*Electrical Engineer, Sound Department, Uni- 
versal Pictures Corp. 



largely a product of individual ingenu- 
ity, the entire idea of sound amplifica- 
tion was given great impetus by the 
pronounced success of the equipment 
as installed in the theatres for the pro- 
jection of synchronized sound. 

The orthodox public-address system 
as installed for the purpose of raising 
the volume level of sound in hall or 
auditorium may be considered as of first 
importance in any classification of 
equipment according to usage. It might 
be mentioned at this point that the 
operation of such a system indoors is in 
general less complicated than of an 
identical system in the open. The sec- 
ond type of system in any such classi- 
fication is that installed in large build- 
ings for the purpose of providing cen- 
tralized controlled radio or musical 
programs to a multiplicity of outlets. 
These systems may be modified to pro- 
vide facilities for picking up programs 
originating in public rooms in the same 
building or programs originating else- 
where and transmitted to the central 
output station by line wire there to be 
distributed about the building, as de- 
sired. 

As the number of channels increase, 
the complexity of the system, hence 
the difficulties of installation and opera- 
tion, increases in direct proportion. 
These systems range from a single 
channel which makes available one radio 
program to the guest through loud- 



The rapidly increasing opportunities for public-address 
installations make it important that engineers and 
stallation technicians study all of the factors. 



m- 



speaker or headphone, up to the exten- 
sive multichannel system which makes 
available any one of several radio pro- 
grams, a speech in a banquet room 
across the city, or the music of an or- 
chestra playing in the supper room, to 
the guest, chosen at his own desire by 
the twist of a single dial mounted on 
the wall of his room. These systems, 
as installed principally in apartment 
houses and hotels, are rapidly becoming 
one of the marks of modernity by which 
a metropolitan establishment is judged. 

School Room Use 

Public-address systems as designed 
for schoolroom use embody points of 
similarity to the sound distribution 
system as found in hotels and apart- 
ments as well as the orthodox amplifi- 
cation system for hall or auditorium, in 
addition to characteristics of their own 
contributed by the very specialized use 
to which they are put. Due to the fact 
that schoolrooms are in general larger 
than the usual hotel room, the system 
as installed in a school will be operated 
at a higher volume level than would 
the same system applied to hotel and 
apartment usage (a volume which often- 
times approaches public-address level) 
yet the multiplicity of outlets makes 
these systems closely akin in many 
ways. 

Three acoustic phenomena enter into 
consideration when installing an indoor 
public-address system. Of these three, 
reverberation is probably of first im- 
portance. When reverberation time be- 
comes so great that the reflected sound 
embodies two distinct impressions, we 
are conscious of an echo in the hall or 
enclosed space under consideration. 
The time lag between sounds may be 
cut down by drastic acoustic treatment 
of the space, much in the manner of 
lowering the time of reverberation (by 
increasing the number of "absorption 
units" which in turn is increased by 
increasing the area of absorptive ma- 
terial about the space). Blind spots and 
their associated echoes are not often 
encountered in halls or rooms of rec- 
tangular or other regular shape, but are 
found almost entirely in rooms having 
curved or domed ceilings or walls. It 
might be mentioned in passing that 
when such a condition is the result of 
architectural defects — (architectural 
characteristics which would be classed 
as defects when considered from a pure- 
ly acoustic standpoint, such as a domed 



Page 8 



PROJECTION ENGINEERING 



ceiling) the condition can never be 
entirely eliminated but can be improved 
to a great extent by an acoustic treat- 
ment of the space. Experimentation in 
the placement of the loudspeaker can 
also many times do much to minimize 
the effect of domed ceiling or curved 
walls. The microphone should never be 
placed in proximity to regions of local- 
ized echo due to curved walls of ceiling. 
However, it may be advantageous at 
times to place the loudspeaker in such 
a position that the curved surface will 
act as a sounding board, ' tending to 
spread the sound throughout the space. 
However, these are purely local prob- 
lems, peculiar to each individual installa- 
tion and solvable only after a study of 
the particular installation has been 
made. 

Foreign Noise Disturbance 

The problem of foreign noise, as en- 
countered in indoor systems, is mainly 
a matter of microphone placement. The 
microphone should be placed near 
enough to the speaker or other source 
of desired sound to maintain at all 
times sufficient differential between the 
desired and the undesired sounds so 
that the desired sounds will be suitably 
intelligible. Consideration of this factor 
of the public-address problem may best 
be given by an illustration of the dif- 
ficulties encountered and the results 
achieved in a recent installation. The 
function was a dinner, given for the 
purpose of congratulating a political 
candidate on his recent success in elec- 
tion. A hall had been hired, and the 
committee in charge had made their 
preliminary plans as to the location of 
the speakers' table, other tables, space 
for dancing, and so forth. As set up by 
those unfamiliar with the problems of 
sound amplification, the hall embodied 
a very bad feature with regard to 
foreign noise concentration. As planned 
by the committee, the speakers' table 
was to be placed across one end of the 
room, with the remaining tables spread 
about the edge of the space in front 
leaving the center of the room cleared 
for dancing. The doors leading to and 
from the kitchen opened into the hall 
directly in back and to each side of the 
speakers table, while the main entrance 
to the hall from the outside was at the 
far end of the room. It was then planned 
to rent a small public-address system, 
equipped with a microphone pickup for 
increasing the volume of the speaker's 
voice (the hall was rather long and 
narrow and notoriously acoustically 
bad) and a radio pickup for providing 
dance music later in the evening. The 
committee had planned to place the mi- 
crophone on the table before the 
speaker, grouping several loudspeakers 
near the ceiling and at the same end 
of the hall. However, after calling a 
sound engineer into consultation and 



heeding his advice, the setup was en- 
tirely different from that planned pre- 
viously. 

The speakers' table was placed across 
one side of the hall, the remaining tables 
being placed at each end leaving the 
space immediately in front of the 
speakers' table cleared for dancing. Had 
the speaker been placed with his back 
to the kitchen doors, the microphone 
would have faced this definite source of 
foreign noise, and the system would 
have operated very unsatisfactorily. The 
projectors, as installed, were placed in 
three groups, one group being placed 
near the ceiling at each end, consisting 
of three receivers each, while a separate 
small projector was placed high on the 
wall near the kitchen doors for the pur- 
pose of increasing the volume level of 
the desired sound at this point and 
minimizing the effect of the foreign 
noise emanating from the kitchen. This 




{Courtesy, Amplex Instrument 
Laboratories, New York) 

Rack and panel used for school sound 
installation. 



grouping of projectors also eliminated 
the possibility of singing which would 
be present were the projectors placed 
above the speakers' table, due to the 
tendency of any amplifying system to 
howl if the mouths of the loudspeakers 
are placed behind the microphone. The 
system, installed in the recommended 
manner, operated entirely satisfactorily 
throughout the festivities. 

Special Applications 

It might not be amiss to pause at this 
point and consider a very specialized 
type of installation which is often en- 
countered. There are many small res- 
taurants and tea rooms which desire to 
give their patrons music with meals, 
yet are unable to afford the expense of 
an orchestra. The installation of a sound 
amplification system, using as sound 
source either recorded selections or 
radio pickup, solves the problem very 
nicely and at small expense. Because of 
the fact that these places are usually 
small, and acoustically good due to the 
abundance of soft surfaces throughout 
the space (table covers, wall hangings, 
carpets, and clothing of patrons) the 
only factor which enters into consider- 
ation is the matter of foreign noise. 
The level of extraneous noise is usually 
very high in these places, contributed 
by the rattle of dishes, conversation of 
patrons, etc., hence an amplification 
system will have to be operated at a 
higher level than is usually necessary. 
However, to avoid a concentration of 
sound in one portion of the room and 
such low volume that intelligibility is 
bad in another, it is better practice to 
place several smaller loudspeakers about 
the space, operating each at somewhat 
lower volume than would be satisfac- 
tory were one only used. This gives 
even volume distribution throughout the 
entire space. As a practical point, it 
might be brought out that if these 
speakers are placed high up near the 
ceiling, the system can be operated at 
lower volume level than if the projectors 
were situated at table top level, due to 
the fact that absorption is less when so 
located. 

Sound Level 

Best results will be obtained with in- 
door installations if all projectors are 
connected to one volume control dial, 
thus maintaining a level throughout the 
space. Regions of insufficient volume 
should be corrected by the installation 
of small booster horns, or by repointing 
adjacent projectors, but not by raising 
the volume level in nearby horns. This 
is in contrast with the procedure of 
operation of out-of-door systems, which 
by reason of shifting wind, changing 
weather conditions, etc. during actual 
broadcast (broadcast as used herein is 
in connection with the transmission of 
sound by radio, the only difference be- 



AUGUST, 1931 



Page 9 



ing in the vehicle of transfer of energy 
from transmitter to projector) makes 
manipulation of volume level of indivi- 
dual projectors during the broadcast 
necessary. No such factors enter the 
consideration of indoor systems, and it 
is best operating procedure to control 
all projectors from one volume control. 

It has been said that the ultimate suc- 
cess of a public-address system may be 
judged by the degree to which the 
listener is aware of the mechanical- 
electrical aid being given by the system. 
Judging the system by a measure of the 
extent to which the system intrudes 
itself upon the listener's consciousness 
is in general good practice, and may 
well be given as a comparative "yard- 
stick" by which various systems may be 
judged. Consequently, the system should 
always be operated at as low a volume 
level as is consistent with intelligibility. 

Quality in any sound system, whether 
it be radio broadcast, sound recording 
for motion pictures, or phonograph, or 
public-address, may be said to be per- 
fect when the transmitted sound con- 
tains all, and no other, frequencies 
which are contained in the sound as it 
strikes the microphone, and when those 
frequencies contain the same relative in- 
tensities which they had in the original 
before transmission. If a person speaks 
in a normal tone of voice, his voice 
will contain an abundance of the lows, 
but if he raises his voice, these lows 
will be attenuated and his voice will 
seemingly rise in pitch. This may be 
applied to common experience by all — ■ 
when we shout, and the louder we 
shout, our voice appears to rise in pitch 
and becomes unpleasantly shrill. 

Although the average person would 
be unable to explain the effect, the 
phenomena is known by instinct pro- 
vided that person is blessed with normal 
hearing. If any sound system is inter- 
posed between the source of sound and 
the listener which disturbs this balance 
between frequency components and 
volume, the listener will be instantly 
aware of the unnaturalness whether he 
is aware of the psychological reason 
for it or not. If the projector which is 
transmitting the sound be operated at 
such a volume that the listeners in- 
stinct tells him the speaker should be 
shouting although he be actually speak- 
ing in a normal tone of voice, the 
system appears to make the voice seem 
heavy and unnatural due to the apparent 
overabundance of low frequencies. The 
more faithful the reproduction by the 
system, the more noticeable is this 
effect. Consequently it is good operat- 
ing procedure to regulate the volume 
so that the farthest person in the hall 
is enabled to hear comfortably, yet not 
to allow the volume to become any 
greater than necessary. (This effect 
may be further eliminated by group- 
ing the projectors in smaller groups 



about the space instead of in one group 
in a central place). In this connection, 
also, it is well to remember that if the 
volume be of insufficiently high level, 
certain of the weaker speech sounds 
will be lost and the general intelligibility 
lowered. 

Certain buildings have long been fa- 
mous for their architectural beauty, both 
inside and out. However, it is an un- 
fortunate circumstance that it is those 
characteristics which most contribute 
to the interior beauty of an edifice which 
are also responsible for, in great meas- 
ure, the poor acoustic conditions found 
in many beautiful buildings. Suitable 
public-address equipment may be in- 
stalled in these buildings and will im- 
prove hearing in the public rooms to 
such a degree that perfect hearing will 
be possible in the farthermost portion 
of the space. Many large churches and 
cathedrals which have long been fa- 
mous for their beautiful architecture 
have only been slightly less renowned 
for the difficulty experienced in hearing 
services within their auditoriums. 

Church Installations 

The installation of public-address 
equipment in a church will immediate- 
ly fulfill two definite functions. It will 
improve hearing conditions and thus 
lessen the strain upon the collective 
auditory mechanism of the congrega- 
tion, and will improve speaking condi- 
tions for the pastor, allowing full at- 
tention to be placed upon the text of 
the message as well as lessen the vocal 
strain. The installation of sound equip- 
ment is being looked upon with favor 
by many congregations, and a consider- 
able number of churches which are be- 
ing erected are being equipped with am- 
plification systems at the time of their 
construction. 

A rather large and well known church 
in Southern California, confronted with 
the problem of poor acoustics, looked to 
the installation of a sound system for 
relief. Extreme size of the main audi- 
torium coupled with a very high vaulted 
ceiling, was mainly responsible for the 
difficulty experienced in hearing mes- 
sages from seats in the rear portion of 
the hall. A microphone was placed near 
the pulpit, and two small sized booster 
horns installed near the ceiling and ap- 
proximately two-thirds of the way back, 
for the purpose of augmenting the 
sounds as they came from the pulpit 
direct. This setup fulfilled the purpose 
for which it was made. Increasing pop- 
ularity of the services made the provi- 
sion of an overflow hall advisable, so a 
separate transmission line was taken 
from the amplifier to two projectors 
which were placed in a small adjoining 
hall, and those who were unable to find 
accommodations in the main auditorium 
were taken care of in this second room. 
Further increasing the usefulness of the 



system as installed, it was decided at 
the request of one of the elderly mem- 
bers of the congregation to provide ear- 
phone leads from the amplifier to ear- 
phones placed in certain pews, to be des- 
ignated by the ushers as reserved for 
those persons who are hard of hearing 
and who desired artificial aid. This 
system has been operating for a period 
of some twelve months and has proven 
satisfactory in solving the acoustic dif- 
ficulties of the particular church. 

Call Systems 

Another specialized use to which pub- 
lic-address equipment may be put is for 
the purpose of providing a call system 
for large organizations, the personnel 
of which may be scattered over one or 
more large buildings. Such a system, 
consisting of a central microphone, an 
amplifier and loudspeakers placed in the 
designated localities, provides a very 
handy means of calling any desired per- 
son to the central point. Sound equip- 
ment for this purpose has recently been 
installed in one of the large western re- 
search laboratories, consisting of a mi- 
crophone in the central office and a 
loudspeaker outlet in every research tech- 
nician's office or lab. When any one 
of these men is needed in the front 
office, the telephone girl, by throwing 
a switch places the system in use and 
speaks the man's name with the in- 
formation as to where he is wanted, etc. 
into the microphone. This obtains an 
instantaneous response, and is more sat- 
isfactory than the old style method of 
calling by bell or buzzer signal. The 
response to a spoken word, especially 
if that word be a man's own name,' is 
much quicker than is the response to 
a certain number of buzzes coming 
over a signal system. In addition, the 
buzzer necessitates every man stopping 
work while he counts the number of 
buzzes, while the spoken name coming 
over a small loudspeaker commands im- 
mediate attention of the one called, his 
fellows being enabled to continue with 
their work. 

The above are only a few of the speci- 
fic applications of public-address equip- 
ment to indoor use. Sound amplifica- 
tion, as applied to this particular portion 
of the field of public-address, has done 
much to increase the enjoyability of 
modern life and the efficiency of modern 
business. Although progress in the past 
has been marked, greater advances may 
be looked for in the future due to the 
increasing flexibility of equipment as it 
is being developed in the sound labora- 
tories and in the field. Public address 
is the youngest offspring of the Sound 
family, and by some considered as hav- 
ing the best prospects for great future 
advancement. It is certain that great 
steps forward will be made in the mat- 
ter of possible applications of equip- 
ment to new use in the coming months. 



Page 10 



The acoustic treatment 
of auditoriums and hall 



By E. F. Smith* 



ilia 



In this article are discussed the fundamental engineering 

considerations which make possible satisfactory indoor 

sound projection 



IN ORDER properly to understand 
the subject of acoustics it is well 
first to be sure that a fair under- 
standing of sound has been accom- 
plished. Sound is a physical phenome- 
non which is understood by the psy- 
chologist to mean a sensation con- 
ceived within the brain as transmitted 
by way of the organs of hearing. To 
the physicist it is merely an atmos- 
pheric disturbance and is purely me- 
chanical. With this tangible physical 
idea we are mainly concerned. Thus 
sound is caused by a body which is in 
a state of vibration or oscillation. If 
the body vibrates as a unit, all parts 
moving in the same direction and velo- 
city at the same time, it sets up what 
is known as a pure or simple tone. If 
it vibrates in parts, that is, one part 
vibrating independently of the others, 
and the parts not being in synchronism, 
it sets up a complex wave. These 
waves, of course, are in the form or 
compressions and rarefactions of the 
air about the vibrating body. The 
complex consists of a pure wave known 
as the fundamental, and any number 
of superimposed waves known as over- 
tones. These overtones give the vari- 
ous sounds their characteristics of 
timbre, quality, roundness, and other 
distinctive traits recognizable by the 
human mind. 

As stated before, sound is caused by 
a vibrating body, whether it be made 
of iron, wood, glass, human vocal cords, 
or anything else. The sound resulting 
from the compressions and rarefactions 
of the air about the body radiates out 
from it as a center in the form of con- 
centric spheres whose radius is con- 
stantly increasing. The velocity of 
these spheres varies with the medium 
of transmission, but its value lies 
somewhere around 1,075 f eet P er sec_ 
ond in air. This value is determined 
by atmospheric conditions such as tem- 
perature, pressure, humidity and wind. 

* University of Florida. 



The frequency is the number of com- 
plete vibrations the body makes in a 
given time, and the term cycle is used 
to denote such vibrations. Frequency 
of tone or of pitch is designated in 
cycles per second. The human ear can- 
not detect all frequencies. The lower 
limit of ear response varies with the 
individual but lies generally in the 
octave between 16 and 32 cycles per 
second. When the pitch is below the 
response limit of the ear, the brain no 
longer receives the idea of sound but 
witnesses a physical sensation, perhaps 
even pain, if it is heard at all. The 
ear likewise cannot detect sounds hav- 
ing a frequency lying above the octave 
between 16,000 and 32,000 cycles per 
second, this value also depending on the 
individual. 

All Frequencies Needed 

For true reproduction of mechanical 
sound, all frequencies must be present, 
but all frequencies are not entirely nec- 
essary to give intelligibility to speech. 
This 'intelligibility range lies some- 
where between 700 and 1,100 cycles per 
second. In other words, without this 
range being reproduced, it would be 
very difficult or even impossible to 
understand the speech. With only this 
range present the voice would have 
little character — one would be able to 
understand it and that is all. In order 
to be able to distinguish one voice from 
another a wider range of frequencies 
is necessary. The frequencies neces- 
sary for this are those lying between 
200 and 3000 cycles per second. These 
ranges are satisfactory only where un- 
derstanding of the conversation and 
recognition of the voice are necessary, 
but a program of music, for instance, 
having all frequencies below 200 cycles 
cut off and all above 3000 likewise 
eliminated would be very unsatisfactory 
and would be definitely rejected by the 
public. The average person unknow- 
ingly demands every frequency covered 



PROJECTION ENGINEERING 

by his ears to be present in any me- 
chanically produced sound program. 
The frequencies must not only be 
present but also must be reproduced at 
a volume corresponding to that at which 
the other frequencies are produced. If 
certain frequencies are produced at a 
little higher level than the rest the 
whole sound combination assumes an 
artificial aspect, and produces what is 
known as distortion. 

When a sound is produced at some 
particular point we noted before that 
it traveled away from the point in 
ever-enlarging concentric circles. This 
idea only holds true where there is un- 
limited space such as out on a broad 
field in the open. When a surface is 
placed within the range of this emanat- 
ing sound which strikes it, part of the 
sound continues on its way in the new 
medium of the material of construction 
of whatever object was placed in the 
path. However, like light, the sound 
waves enter the medium, at least a part 
of them, and in doing so their speed is 
changed and their angle or direction of 
travel is changed. As the wave pro- 
ceeds through the medium and into 
another, say back into air, a corre- 
sponding change occurs. Furthermore, 
like light, some of the sound wave is 
reflected backward upon the original 
wave. In this case the angle of inci- 
dence is equal to the angle of reflec- 
tion, as in light waves. There is also 
another effect not found in the case of 
light waves, that is, when the sound 
strikes an object on one side, it may 
cause the whole object to vibrate in 
sympathy with the incident sound, and 
the vibrating object may cause a sound 
of its own to be set up on both sides 
of it, that is, on the side toward the 
original vibrating body, which will ap- 
pear like a reflection, and also on the 
opposite side, which will appear like a 
passing through of the original sound 
Obviously, if an attempt is made to 
separate these effects, a very complex 
problem will result. This is unneces- 
sary for our purpose but it is well to 
know that such conditions exist. 

The subject of reflection is the one 
which we are probably most concerned 
with when we consider that the best 
light reflecting surface runs somewhere 
around ninety-five per cent efficient 
while there are sound reflecting sur- 
faces which can reflect more than 
ninety-eight per cent of the incident 
sound. The sound energy which passes 
into and through an object, and that 
which sets the object into vibration is 
considered in this work as being ab- 
sorbed by the material of the object. 

Interference 

Closely interlinked with this subject 
of reflection are those of interference 
and reinforcement. When the sound is 
reflected back upon the original wave 
in such a manner that some of the fre- 



AUGUST, 1931 



Page 11 



quencies fall into step with originals, 
or with others traveling away from 
other reflecting surfaces while some 
meet in such a manner as to cancel 
each other, we have what is called in- 
terference. Interference causes dis- 
torted effects in speech and music. If 
conditions are such that the reflected 
sound is of proper intensity and direc- 
tion we may get an overall effect of 
reinforcement, and even in some occa- 
sional cases we may have almost com- 
plete cancellation. There are on record 
cases of buildings having almost per- 
fect reinforcing properties as in the 
case of the Mormon Tabernacle in 
Salt Lake City, and in the various 
whispering galleries throughout the 
world. There are also cases on record 
where buildings have acoustic proper- 
ties such that a speaker cannot be 
heard although the auditor is standing 
only a few feet from him. Such ex- 
tremes are usually not common but in- 
stead we have a mixture of the two 
effects in the same structure and the 
net effect is troublesome. 

The simplest auditorium is a flat 
field in the open. The speaker is lo- 
cated a little above the audience so 
that auditors near him will not obstruct 
the sound flowing to auditors in the 
rear of the assembly. When this is the 
case, there is no reflection and there- 
fore no reinforcement, no cancellation, 
and consequently no distortion. Every 
sound which must reach the auditors 
must be produced by the vocal chords 
alone and must be of such intensity as 
to provide enough volume to reach each 
and every one of the listeners. If we 
should put a roof above the assembly 
we would find that most of the sound 
which first emanated into space would 
be deflected downward by the ceiling 
and this would help the original voice 
of the speaker so that he would not 
have to talk so loudly. If, however, 
the assembly stretches backward away 
from the speaker to such an extent 
that there is a noticeable difference in 
time between the original voice and the 
reflected voice, the distant auditors will 
have difficulty in distinguishing the 
separate syllables in words and the 



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speech may not be understandable. If 
a back wall is now added, there may 
be more difficulty or there may be still 
better results. When the other three 
walls and floor are added we have a 
common type of auditorium. It is evi- 
dent from the foregoing reasoning that 
reflection is a desirable feature if we 
can control it in such a manner as to 
make it meet the requirements. 

Volume and Reflection 

There is a relationship between the 
volume of the sound and the reflecting 
properties of an auditorium. This is 
best shown by citing a case of a build- 
ing the construction of which was fol- 
lowed rather closely. During construc- 
tion it was not uncommon to witness 
a worker standing on the stage talking 
to another man who was almost at the 
top of the second balcony. His voice 
was understandable though he spoke 
in a moderately loud voice without 
shouting. When this theatre was 
completed it had very heavy sound ab- 
sorbing material covering all the walls 
and ceiling. It also had heavily uphol- 
stered seats and thick carpets with 
lining. It was noted then that a 
speaker standing on the stage and talk- 
ing in a very loud voice could not be 
heard in the second balcony except to 
know that he was speaking. On the 
other hand, when a public-address sys- 
tem was brought into play, the voice 
broadcasted from it could be heard 
almost perfectly in all parts of the 
house. This building had been designed 
to be acoustically correct for the large 
volumes of sound necessary to fill its 
immense cubic volume. A house which 
has too much absorbing material gives 
a "flat" effect and is termed "dead." 
One which has too little absorbing 
material gives a ringing effect and is 
termed "reverberant." Neither type is 
desirable but there must be a combina- 
tion of the two effects to give good 
results. 

Next we may pass to the problem of 
absorption. Everything absorbs a cer- 
tain amount of sound whether it be 
made of iron or of wood, or if it be 
a chair, a table, drapery, carpet, or any 
other object. When we consider the 
acoustic properties of a building with 
a mind toward treatment we must con- 
sider all equipment in place within the 
building, or at least within the acous- 
tic volume. Even the number of per- 
sons that will be present will have to 
be estimated and taken into account to 
obtain anywhere near satisfactory re- 
sults. The unit of absorption has been 
taken as the absorbing power of an 
opening one foot square, such an open- 
ing having ability to absorb nearly all 
incident sound since it merely passes 
through to the opposite side. All other 
materials have coefficients which are 
comparisons between a square foot of 
the material and this standard absorber 



of sound. For instance, celotex has a 
coefficient of .31. This means that it 
would take 31 square feet of celotex 
to absorb as much sound as would pass 
through an opening having an area of 
ten square feet. A person has an ap- 
proximate coefficient of 4.6 units. Seats 
vary in absorption between 1.0 and 3.5 
units depending on the type of uphol- 
stering. Hence, the difference between 
the value for a person and the value 
for the seat he occupies will determine 
the difference in absorbing qualities of 
the building when he is present and 
when he is not. 

Reverberation 

When a steady sound exists in a room 
and is suddenly stopped, the time which 
elapses between the instant the sound 
ceases and the instant the prevailing 
sound can no longer be heard is called 
the "time of reverberation." Sabine, 
the well-known authority on acoustics, 
developed an expression for this time 
of reverberation as follows : 
V 
t = .05 — 
a 
in which t is the time of reverbera- 
tion in seconds, V is the acoustic volume 
in cubic feet, and a is the absorbing 
power per square foot of the exposed 
materials in the room or auditorium. 
This formula is purely empirical and 
was based on observations made in 
many auditoriums. A rather complete 
list of coefficients for materials of 
every type can be obtained from the 
various manufacturers. A few of these 
are listed below : 

Audience, per person 4.6 units 

Wood seats, reg. audit., each .10 " 
Carpet, unlined, per sq. ft. . . .15 

Celotex, per sq. ft 31 

Glass, per sq. ft 03 " 

Concrete, per sq. ft 015 " 

Brick, 18 in. thick, per sq. ft. .032 " 
Wood sheathing, per sq. ft. . .061 " 
Plaster, per sq. ft 034 " 

A very involved mathematical proof 
was then developed to find the ideal 
conditions of reverberation for an audi- 
torium. The necessity of this was, as 
seen before, due to the fact that too 
little reverberation as well as too much 
is detrimental to the results obtained. 
The values thus found were plotted on 
curves as shown in Fig. 1, and then 
these curves were checked by compar- 
ing points thus found with those deter- 
mined from a vast number of audito- 
riums which have been accepted by the 
public as being ideal. 

Acoustic Material 

With this data available it is possible 
to proceed with the designation of 
acoustic material which is to be used 
in any building. It has been found that 
the time of reverberation varies ap- 
proximately as the cube root of the 



Page 12 



PROJECTION ENGINEERING 



acoustic volume and this is the reason 
why the reverberation time, t, was 
plotted against the cube root of the 
volume, V, in the foregoing curve. 
Taking assumed data for an auditorium 
having 120,000 cubic feet of acoustic 
volume we next assume the number of 
square feet of the various materials of 
construction. In the case of an already 
existing auditorium these values would, 
of course, be directly measured and 
the absorption coefficients of each 
material would be determined from 
suitable tables. Shrewd judgment of 
these values will be attained by experi- 
ence in this type of work. Tabulate 
these figures as follows : 
Plaster, 4,000 sq. ft. at .025. 100 units 
Wood, 10,000 sq. ft. at .065. 650 units 
Brick, 4,000 sq. ft. at .032.. 128 units 
Celotex, 3,000 sq. ft. at .31 . . 930 units 
Seats, 500 at .1 50 units 



1,858 units 
If one person has an approximate 
absorption coefficient of 4.6 units, and 
when present this person practically 
covers a seat having a coefficient of 
.1, the net change in the absorption 
makes the apparent value per person 
4. 5 1 units. Hence : 
Absorption, furnished by ma- 
terials, as above 1,858 units 

Audience, 1/3 present at 4.5. 765 units 



2,623 units 
Again : 

Absorption furnished by ma- 
terials, as above 1,858 units 

Audience, all present 2,250 units 



4,108 units 
The cube root of the volume, 120.- 
000, is 49.3. This value corresponds to 
a reverberation time of 2.4 seconds for 
no audience, 1.8 seconds for 1/3 audi- 
ence, and 1.2 for maximum audience, 
as shown by the curve as being ideal. 
Using the above data and substituting 
in the formula, t = .osV/a, we have: 
For no audience 

t — .05 x 120,000 -4- 1858 = 3.2 sees. 
For 1/3 audience 

t = .05 x 120,000 —■ 2623 = 2.2 sees. 
For maximum audience 
t = .05 x 120,000-4-4108 = 1.4 sees. 
Comparing these values with those 
taken from the curve we have: 
For no audience 

3.2 instead of 2.4 for ideal conditions 
For 1/3 audience 
2.2 instead of 1.8 for ideal conditions 
For maximum audience 
1.4 instead of 1.2 for ideal conditions. 
For maximum audience we find that 
the value pretty closely approximates 
that for ideal conditions, but for 1/3 
audience we see that there is a consid- 
erable deviation. Likewise, there is 
also a wide difference between the two 
values for the condition of no audi- 
ence. However, the low percentage of 



audience will be found more often than 
an empty house or than a full house 
so that it is advisable to correct to this 
value rather than for empty house con- 
ditions. Taking the value of 2.2 sec- 
onds as ideal for one-third audience, 
we can substitute in the formula, 
whence we have : 

2.2 = .05 x 120,000 -f- a 
a = 2727 units 
At one-third audience the absorption 
was found to be 2,62^ units, so that an 
addition of about 105 units will have 
to be added to bring the reverberation 
time down to the ideal condition. If 
we assume that celotex or other similar 
material is to be used to supply this 
additional absorption it will have to be 
placed over some other material already 
in place, unless there is some baffle wall 
arrangement. If we assume that celo- 
tex has a coefficient of .31 and that the 
wood which it will replace has a coeffi- 
cient of .065, the net coefficient will be 
.245 units. Therefore, we will have to 
use 105 -r- .245 or approximately 430 
square feet of celotex, which will cover 
over the wood which was included in 
the original calculation. 

Frequently an auditorium will have 
peculiar characteristics such as a bad 
echo in the rear of the upper balcony, 
or a false sound source in the boxes. 
One theatre was noted as having a 
large oval dome in the ceiling about 
in the middle of the orchestra seats 
which were in front of the balcony. 
When a speaker was on the stage and 
a listener is seated within an area 
about ten feet wide and twenty feet 
long just in front of the stage, the 
latter receives the illusion that the 
speaker is located up in the dome in 
the ceiling insofar as the sound is con- 
cerned. The reflected and concentrated 
sound is so much greater than the 
original that the latter is not noticed. 
In a case of this kind it would be best 
to cover the dome with absorbing 
material, or, if architectural beauty 
requires that it remain, its inner sur- 
face could be replastered with special 
acoustic plaster or otherwise covered 
in such a way that the reflection will 
be killed. Many other cases require 
individual treatment such as those ef- 
fects caused by extensive flat walls, 
niches, standing rails, glass panels, 
doors, ventilating grids, etc. The proc- 
ess usually followed is that of breaking 
up the surface or covering it so that 
reflection will be reduced to a minimum. 

Another matter for consideration is 
that of residual noise, that is, noise 
which is normally always present. 
Under this heading comes a variety of 
sounds such as ventilating fans and 
the motors that drive them, the rush of 
ventilating air through the ducts and 
grids, steam heating systems which 
have inherent hissing sounds or those 
emitted from leaking joints or which 



have driving motors whose vibrations 
and rumbling is transmitted to the 
auditorium by way of the piping, noises 
made intermittently by trolley cars, 
automobiles, horns, railroads, or sub- 
ways, and this latter group transmits 
rumbles for many blocks, and other 
similar ones. Under such conditions a 
speaker must talk louder to be heard 
above the noise, or in the case of 
mechanical reproduction the gain of 
the amplifiers must be increased or the 
attenuation decreased. This is known 
as "masking" the noise. 

The audience itself makes much noise 
even when trying to be quiet. This 
noise is caused by breathing, rustling 
of clothing, moving of feet, etc. Such 
noises cannot be eliminated to any 
great extent, though the noises caused 
by moving feet are effectively lessened 
by the installation of carpets in the 
aisles and foyers or in some cases of 
extreme scuffling it has been necessary 
to install cork tile throughout the house. 
A 
E. O. HEYL ADVANCED 

AE. REOCH, executive vice-presi- 
. dent of RCA Photophone, Inc., 
announces the appointment of E. O. 
Heyl, vice-president in charge of foreign 
affairs, to the office of vice-president and 
general sales manager to succeed Syd- 
ney E. Abel, who recently resigned as 
head of the commercial department. 

During the past eighteen months, Mr. 
Heyl's activities have been confined to 
the corporation's interests in foreign 
fields in which he has had a broad ex- 
perience. He became identified with 
RCA Photophone, Inc., in 1928, follow- 
ing extended association with a number 
of the country's leading industrial or- 
ganizations. During the World War he 
was, with Julius Rosenwald, the noted 
Chicago philanthropist, a member of the 
council of national defense and later 
became a division head with Herbert 
Hoover when the latter assumed charge 
of the United States food administra- 
tion. Mr. Heyl brings to his new posi- 
tion a rich background and broad ex- 
perience in merchandising in this coun- 
try and abroad. 

A 

THE DEPTH OF FIELD OF CAMERA 
LENSES 

THE above is the title of a paper pre- 
■ ted by Arthur C. Hardy, at the re- 
cent Hollywood meeting of the S. M. 
P. E. In this paper the usual formulae 
for depth of field are expressed in terms 
of the focal length and relative aperture 
of the camera lens. By expressing the 
depth of field in terms of the magnifica- 
tion between the object plane in sharp 
focus and the film, a very simple and 
rigorous formula results. This makes it 
evident that the depth of field of all 
lenses giving the same magnification is 
the same under comparable conditions. 



AUGUST, 1931 



Page 13 



What happens within the 
bulb of a radio tube? 



By Linwood G. Lessig* 



In this article Mr. Lessig presents an easily understood, 

sound technical explanation of the operation of vacuum 

tubes as used in radio and audio circuits. 



THE most important single device 
known to radio science is the 
thermionic vacuum tube. It con- 
sists of a glass bulb generally 
somewhat similar in appearance to an 
electric light bulb. The bulb contains a 
heated electrode (acting as a source of 
electrons) and additional electrodes, 
such as the grids and plates, which num- 
ber ordinarily from one to four. Spe- 
cial tubes may employ additional elec- 
trodes, depending upon the service for 
which the tube is designed. In general, 
radio tubes are evacuated to a high 
degree, although there are some that 
depend upon a very small amount of gas 
for special characteristics. 

The simplest type of tube is the two- 
electrode type. It contains a filament 
and a plate sealed in an evacuated glass 
bulb. The plate is made electrically 
positive with respect to the filament by 
means of a battery in the plate-to-fila- 
ment circuit. Nearly all modern receiv- 
ers (and transmitters) are designed to 
use two-electrode tubes for the purpose 
of converting alternating current to 

^Commercial Engineering Department, RCA 
Radiotron Co., Inc. 




}2± r\ r\ 

] w vy kj 



COn&NCO RECTIFIED 

voltace 

PL.ATr.S-U2 



SMOOTHED VOLTACE 
.AFTER FIRST SECTION 
OF FILTER • 



DC VOLTAGE 
AVAILABLE FOR 
RADIO RECEIVER 



Fig. 1. Full-wave rectification. 



direct current which is then used for 
the plate, grid and screen supplies of 
three, four and five electrode tubes. 
Sometimes two separate filaments and 
two separate plates are mounted in the 
same bulb. This construction permits 
the rectification of both halves of the 
alternating cycle. Such tubes, which 
are really two tubes in one, are called 
full-wave rectifiers. The effect of rec- 
tifiers on alternating current is shown 
in the waveforms of Fig. i. 

The Operation of a Two-Electrode 
Tube 

When the filament is heated it pro- 
duces a cloud of electrons around it. 
If the temperature of the filament is 
gradually raised by a slowly increasing 
current from the "A" battery (filament 
supply), electronic emission will cor- 
respondingly increase. This action may 
be explained as follows. 

Heat provides the energy to accele- 
rate or stir up electrons. When the 
temperature of a filament is gradually 
raised, then, with each increase of tem- 
perature the electrons gain in velocity, 
and finally, the electrons will have 
acquired sufficient energy to make them- 
selves useful in a radio tube. They are 
projected into the space surrounding the 
wire. This action is known as electron 
emission. 

Since electrons are continuously 
streaming in every direction from the 
filament, it is obvious that there are at 
every instant a number of electrons in 
the space between the filament and the 
plate. They move toward the plate and 
are literally absorbed by it while addi- 
tional electrons are emitted at the same 
rate by the filament. The quantity of 
electrons in the space between the fila- 
ment and plate depends upon the rate 
of absorption by the plate and upon the 
filament emission. An increase of the 
filament temperature increases the elec- 
tron emission from the filament, and, 
therefore, the number of electrons pres- 
ent in the space between the plate and 



the filament. This "cloud" of electrons 
collectively produces a negative charge 
which in itself has a tendency to retard 
new electrons attempting to leave the 
region of the filament. It is known as 
the space charge effect. 

With a fixed filament voltage (which 
produces a definite filament tempera- 
ture) more and more electrons will be 
drawn to the plate as the voltage of the 
latter is increased — up to a certain 
point. Beyond this point additional 
plate voltage has little effect in increas- 
ing the plate current, because all of the 
electrons emitted by the filament at the 
given temperature are being drawn to 
and absorbed by the plate. This maxi- 
mum plate current is called saturation 
current, and because it is an indication 
of the total number of electrons emitted, 
it is also called the emission current, or, 
simply, filament emission. When this 
condition has been reached, however, 
the plate current can again be increased 
by the use of a higher filament temper- 
ature. For any given temperature of 
the filament in a perfect tube, there is 
a corresponding maximum value of 




:=: b 

-=r BATTERY 



A BATTERY 



Fig. 2. Elementary diagram of the cir- 
cuit connections of the two-electrode 
vacuum tube. 



plate current. This maximum value is 
obtained when the electrons are drawn 
over to the plate as rapidly as they are 
emitted from the filament. 

Three-Electrode Tubes 

It has been shown that the plate cur- 
rent may be influenced by changes in 
either filament temperature, plate vol- 
tage, or both. Another factor which 
will influence the flow of plate current 
is the effect of an electric charge on a 
third electrode in the tube. The third 
electrode which is placed between the 
filament and plate is called the control 
grid or merely grid. A diagrammatic 
representation of a three-electrode tube 
is shown in Fig. 3. 

When the grid of a three-electrode 
vacuum tube is made positive, or nega- 
tive, with respect to the filament or 
cathode, the plate current will corre- 
spondingly increase or decrease. The 
grid is located relatively nearer to the 
filament than it is to the plate. Thus, 
a small voltage change on the grid will 
have the same effect on the plate cur- 



Page 14 



PROJECTION ENGINEERING 



rent as a larger voltage change on the 
plate. A grid in performing this func- 
tion requires very little power, serving 
merely as a valve to control the com- 
paratively large amount of power in the 
plate circuit. 

A negatively charged grid tends to 
force the space electrons back toward 
the filament. This effect decreases the 
plate current. Plate current, in fact, 
may be reduced to zero (cutoff) by 
making the negative grid charge suffi- 
ciently large. On the other hand, when 
a positive charge is applied to the grid, 
the electrons are accelerated and in- 
creased plate current results. Radio 
tubes are generally operated with nega- 
tive voltage on the grid. The amount 
of this voltage, called grid bias voltage, 
depends somewhat upon the circuit in 
which the tube is designed to be used. 
The battery used to supply this grid bias 
voltage is called a "C" battery. See 
Fig. 2. 

Interelectrode Capacity 

When a three-electrode radio tube is 
functioning in a circuit its input circuit 
is considered to be from grid to filament 
and its output circuit from plate to fila- 
ment. 

The electrodes of a vacuum tube form 
an electrostatic system, each electrode 
acting as one plate of a small condenser. 
The capacities which exist are the grid- 
to-plate, the grid-to-filament and the 
plate-to-filament. The largest and the 
one most often considered is the capa- 
city which exists between the grid and 
the plate. Its effect tends to produce 
coupling between the input and output 
circuits. Such coupling is often suffi- 
cient to cause undesirable feedback in 
the form of oscillations and general 
instability under conditions of high 
amplification. 

Screen-Grid Tubes 

Several schemes for minimizing this 
effect are offered. The first scheme is 
the use of special circuit arrangements 
to counteract or neutralize the coupling 
due to interelectrode capacitances. The 
second method is to eliminate, or nearly 
eliminate, grid-to-plate capacity in the 
tube itself. This is accomplished by 




OUTPUT 



Fig. 3. Elementary dia- 
gram of the circuit con- 
nections of. the three-elec- 
trode vacuum tube. 




zb B 

21 8ATTER. 



^I'M'Fj.A BATTERY 



employing the screen-grid tube. Intri- 
cate circuits and neutralizing difficulties 
are thus practically eliminated. In gen- 
eral practice the grid-to-plate capacity 
is reduced from approximately 8.0 
micromicrofarads (^fd) in the three- 
electrode tube to o.oi (Ajxfd., or less, in 
the screen-grid tube. This permits stable 
amplification of many times that of 
three-electrode tubes. The screen-grid 



Control 
Connect* 



Plate 



Screen 
Grid 




Cathode 



Control 
Grid 



Fig. 4. 



Screen-grid type drawn to show 
construction. 



Fig. 5. Elementary diagram of the 
four-electrode (screen-grid) connections. 



type consists of the usual electrodes and 
an additional grid called a "screen" 
which is used as a shield around the 
control grid and serves to "screen" it 
from the effect of the plate. The con- 
struction is shown in Fig. 4. 

It is undesirable to completely screen 
the plate from the grid since some elec- 
trons must get to the plate through the 
grid for normal operation. The screen 
is fixed at some positive potential lower 
than that of the plate. The electrons 
from the filament proceed toward the 
screen at considerable speed. Many of 
them go through it and are collected by 
the plate, provided the plate is at a 
higher potential than the screen. Be- 
cause of the interposition of the screen 
between the plate and the grid, the rate 
at which electrons go across the space 
is not controlled so much by the plate 
voltage as it is by the voltage on the 
screen and grid. In other words, 
changes of plate voltage above the 



screen voltage have little effect on plate 
current. 

Secondary Emission 

At plate voltages lower than the 
screen voltage, electrons may come from 
the plate and go to the screen, thereby 
causing the current to the plate to actu- 
ally decrease. This backward-flowing 
current is due to secondary emission. 
That is, an electron from the filament 
may get through the screen, but at the 
plate it dislodges an electron which is 
dragged back to the screen because of 
its greater positive potential. 
A 

ACOUSTICAL SOCIETY MEETS 

MORE than two hundred distin- 
guished engineers, music techni- 
cians, and sound experts from all over 
the country attended the annual meeting 
of the Acoustical Society of America 
recently in Camden, N. J. 

The sessions, in RCA- Victor Audi- 
torium, opened with a symposium on 
musical instruments including papers by 
Dr. William Braid White, American 
Steel and Wire Company; Prof. Otto 
Ortmann, Peabody Conservatory of 
Music; Prof. Dayton C. Miller, Case 
School of Applied Science; and Leslie 
N. Leet, Aeolian Company. A. V. Bed- 
ford of RCA-Victor read a paper on 
"A Planetary Reduction Gear System 
for Turntables." 

The morning sessions of the second 
and last day were taken up with a sym- 
posium on the history, development and 
uses of microphones, including papers 
by H. A. Frederick, Bell Telephone 
Laboratories; Stuart Ballantine, Boon- 
ton Research Corporation ; E. C. Wente 
and A. L. Thuras, Bell Telephone La- 
boratories; Harry F. Olson, RCA-Pho- 
tophone ; O. B. Hanson, National 
Broadcasting Company, Dr. Irving 
Wolff and Frank Massa of RCA-Victor 
and E. W. Kellogg, of RCA-Victor. 

Prof. Dayton C. Miller, of Case 
School of Applied Science, was elected 
president of the society; Dr. C. W. 
Hewlett of General Electric, vice-presi- 
dent ; Wallace Waterfall of Celotex 
Company was re-elected secretary, and 
Dr. E. E. Free was re-elected treasurer. 
E. W. Kellogg of RCA-Victor, was 
elected a member of the executive com- 
mittee. 



AUGUST, 1931 



Output matching 
to loudspeaker 



By B. Brown, B.Sc.Eng. 



Satisfactory sound reproduction in theatres and in other 

auditoriums and halls necessitates correct matching 

of output tubes and loudspeakers 



WHILE in all standard sound 
systems the method of im- 
pedance matching is em- 
ployed throughout design 
and the user has nothing to do with it, 
yet in many cases a knowledge of the 
principles involved is of considerable 
value. This is especially the case 
where additions or modifications to 
existing apparatus have to be carried 
out. In the following short article, 
therefore, some practical notes are given 
on the subject of matching the output 
tube of a low-frequency amplifier to a 
loudspeaker. Although the principles 
remain similar no matter what type of 
speaker movement is employed, we shall 
concern ourselves mainly with the or- 
dinary moving coil or dynamic unit 
employing a paper or buckram cone in 
contradistinction to the small enclosed 
type of receiver where a diaphragm of 
aluminum or similar light alloy is em- 
ployed. 

In the first place it is well known that 
the output tube determines the actual 
power delivered a speaker. Providing 
the tubes are not used in parallel or 
similar arrangement the number of 
them has no effect whatsoever on the 
maximum possible output. Suppose it 
has been decided to fit a low-frequency 
amplification system to a certain room. 
How then is the power required to be 
determined in the first place? It is com- 
mon to express the maximum power of 
an amplifier in undistorted watts output 
and in this connection it may be taken 
that for home use an output of 1^2 
watts is sufficient for a moderate sized 
room. For a cafe of medium size a 
larger output is naturally employed and 
in this case 4 or 5 watts should prove 
ample. For a small cinema, 15 watts 
would be suitable, but here the first 
complication is encountered. A well- 
known theatre sound system has an out- 
put of only 24 watts which is capable 
of filling practically the largest audi- 
torium extant. How is it then, that the 



largest possible cinema requires an out- 
put not more than twice that of smaller 
halls ? The answer is simply that the 
system in mind is an efficient unit cap- 
able of converting approximately 30 
per cent of the electrical output into 
sound energy, but the ordinary type of 
loudspeaker with which we are dealing 
has a much lower efficiency. Care must 
be taken to avoid confusion in this mat- 
ter and using the latter type of loud- 
speaker it may be taken that an output 
of approaching 50 watts would be re- 
quired for a really large auditorium. 

Estimating Wattage 

There is a very simple method by 
means of which the approximate wattage 
output of any output tube may be de- 
termined. In the case of the triode the 
formula is simple : 

Output in milli-watts= 
Anode volts x anode current 

in milliamps. 

5 

For the modern pentode tube a dif- 
ferent constant has to be used and the 
formula then becomes : 

Output in milli-watts= 
Anode volts x anode current 

in milliamps. 



Thus supposing that the anode volts 
were 1,000 and the current 80 milliamps, 
in the case of a triode the output would 
be 16,000 milliwatts which is equivalent 
of course to 16 watts. The greater ef- 
ficiency of the pentode is too well known 
to require discussion here. 

Considering the above formulae it is 
evident that there are two means of 
obtaining greater power. We may use 
either a high anode current, or a high 
voltage. For portable radio sets where 
the weight of high tension batteries is 
of considerable import, output is usual- 
ly determined by a fairly high anode 
current. In the case of fixed amplifiers 



Page 15 

and general sound systems, high voltage 
is usually preferable. 

It must be emphasized, however, that 
this tube output is only obtained when 
the tube itself and the loudspeaker em- 
ployed are correctly matched together. 
Impedance matching is a step of para- 
mount importance to the designer and 
user of amplification, but strangely 
enough although understood in theory 
is not very well appreciated as a def- 
inite practice. Perhaps a simple mechan- 
ical analogy may make things clear. 
Consider the wires running from the 
output tube as pipes supplying a fluid 
and in a similar manner suppose the 
loudspeaker to be a water pump or 
similar device requiring coupling there- 
to. If these two pipes are of different 
size, then at the junction we shall have 
considerable loss of power due to eddy 
motion and to the conversion of poten- 
tial into dynamic energy or vice versa 
as the case may be. Apart from this 
it is evident that unless the two pipes 
are of approximately the same diameter 
or are coupled by some smoothly tapered 
union we shall not get a uniform flow 
of fluid and thus are bound to lose ef- 
ficiency. Such a coupling is in many 
ways analogous to impedance matching. 
When a loudspeaker and output tube 
are properly matched as regards im- 
pedance, it may be considered that there 
is a uniform flow of speech current from 
one to the other resulting only in the 
smallest of losses. Bad matching, how- 
ever, causes considerable loss in power 
and at the same time may greatly mar 
reproduction as we shall show later on. 

Efficiency Rule for Impedance 
Matching 

The conditions for correctly matching 
the impedance of a loudspeaker and out- 
put tube are theoretically quite simple. 
All that is required is for the impedance 
of the loudspeaker to equal double that 
of the output tube. On the face of it 
the proposition seems simple, but actual- 
ly, this is rarely the case. The impe- 
dance of an output tube is a fairly def- 
inite quantity and may be determined 
by reference to the data slip provided 
with it, or by manufacturers' catalogs. 
Loudspeaker impedance, however, is an 
entirely different matter and is not a 
perfectly definite quantity unless the 
particular frequency at which the value 
is taken is also specified. The d-c. re- 
sistance of the speech coil of a loud- 
speaker is practically valueless as a 
guide to its probable impedance and 
should be disregarded. Impedance itself 
depends on so many conditions that it is 
out of the question to attempt to cal- 
culate the values. 

In a table are given the impedance 
values of a small type of moving coil 
speaker in which the diameter of the 
speech coil itself, is approximately 1 
inch and the d-c. resistance 4.41 ohms. 



Page 16 



PROJECTION ENGINEERING 



The diameter of the cone of this speaker 
is only about 8 inches and it happens 
to be of popular American manufac- 
ture. A cursory glance at the figures 
indicates immediately the very large 
variations in impedance according to 
the frequency at which it is taken. 

Speaker Impedance 

Taken with field current on; d.-c. 
resistance = 4.41 ohms. 



Frequency 


Resistance 


100 


4.6 


200 


■4.7 


500 


4.9 


1000 


5.3 


2000 


6.6 


3000 


7.5 


4000 


8.4 


5000 


9.4 


6000 


10.4 


7000 


11.3 



Imagine now the power of the triode 
tube being delivered at a particular im- 
pedance which then is obviously equal 
to a certain frequency. Thus the speech 
output is to a large extent at least con- 
centrated about this particular frequency 
where the maximum volume will occur. 
If we couple a tube to a loudspeaker, 
automatically the output of the former 
is delivered to the latter chiefly round 
'about a frequency corresponding to an 
impedance double that of the tube. It 
is therefore at this point that maximum 
volume occurs tapering off in both other 
directions. It is evident from this that 
improper loudspeaker and tube match- 
ing introduces accentuation of certain 
frequencies which in bad cases can be 
described as nothing less than distor- 
tion. Besides this since the band of 
frequency covered by any amplifier is 
limited, then if the matching is very 
bad this band may be raised or lowered 
in the frequency scale to such an extent 
that actual cutoff occurs and, besides, 
the tone of reproduction being high or 
low, we lose some of the range. This 
latter fact is one which is not always 
appreciated. Very often it is said that 
the matching of tubes and loudspeakers 
is simply a matter of taste. To a cer- 
tain extent this is true but only so long 
as the frequency band of the amplifier 
is low compared to that of the loud- 
speaker. When both amplifier and loud- 
speaker are of good design their fre- 
quency ranges should be approximately 
the same and in this case correct match- 
ing is absolutely essential if no fre- 
quencies are to be lost. 

It is customary to match the impe- 
dance of output tubes and loudspeakers 
at a frequency of approximately 256 
cycles per second which is equivalent 
to Middle C in the pianoforte scale. 
Within limits of say 50 or 60 cycles 
plus or minus, tastes may be exercised 
but if maximum efficiency is to be ob- 



tained greater latitude cannot be per- 
mitted. 

The rule of impedance matching 
therefore may be taken as : 

(Impedance of loudspeaker at 256 
cycles) —2 (impedance of output tube). 
The figures of loudspeaker impedance 
on different frequencies are usually ob- 
tainable from the manufacturers of re- 
putable apparatus and it is certainly not 
advisable to attempt matching without 
this data. 

Neglected matching is not (as might 
be expected) always so evident to the 
human ear. Actually if the loudspeaker 
impedance be too high for the tube, 
then there will be a loss in top 
notes accompanied by an accentuation 
of bass. In a similar manner if the loud- 
speaker impedance is too low the tone 
of the speaker will be shrill and appear 
almost as though a pentode output tube 
was being employed, without the usual 
type of filter circuit to remove its peaki- 
ness. Quite a reasonable degree of effi- 
ciency in matching may be obtained by 
interchanging either tubes or loud- 
speakers until pleasing reproduction is 
heard, but this demands a musical ear 
of the highest quality which very few 
of us possess, and even then cannot 
always make due allowance for the limi- 
tations of mechanical reproduction. 

Two Tubes 

The foregoing remarks have been 
confined to the case of a single output 
tube working direct into a single loud- 
speaker. We have now to consider the 
case where two tubes may work in 
parallel into a loudspeaker. In this in- 
stance the paralleling of the two tubes 
halves their effective impedance and 
allowing for this factor the rule previ- 
ously given may be applied. The addi- 
tion of a tube by lowering the impe- 
dance value at the same time drops what 
we might term "the center of gravity" 
of the music and thereby causes loss in 
top notes. The general tone of the loud- 
speaker will thus be lowered but usually 
it is extremely difficult to judge this 
by the ear since the second tube besides 
making alteration in pitch also doubles 
the output. Projectionists have often 
noted with some surprise that the re- 
moval of a single tube from a parallel 
output makes no apparent difference in 
the volume in the auditorium. Actually, 
of course, it reduces the volume by 10 
per cent but this is not readily discern- 
ible to the ear especially when smaller 
noises are in evidence. Actually, how- 
ever, if one concentrates on the pitch 
of the sound rather than its volume a 
change may usually be perceived. 

Two or More Loudspeakers 

If speakers are placed in parallel their 
impedance is lowered. Thus, if two 
speakers are paralleled the impedance 



is halved while if three be treated in a 
similar manner the effective impedance 
is one-third that of a single speaker, as- 
suming that each one of these devices 
possesses similar characteristics. On 
the other hand, if speakers are placed 
in series their various impedances are 
added. Keeping this fact before us the 
rules given some paragraphs back may 
still be utilized for the purposes of 
matching. It is now possible to make 
due allowance for multiple output tubes 
combined with multiple speakers either 
in parallel or in series circuits. 

Output Transformers and Chokes 

Straightway it may be said that plac- 
ing a 1-1 transformer or non-tapped 
choke between the output tube and the 
loudspeaker makes no difference what- 
soever in impedance matching and for 
this purpose may be completely ignored. 
The only reason for the insertion of 
such a device is to prevent the heavy 
anode current passing through the 
speech coil of the loudspeaker. 

When, however, the transformer ratio 
differs from unity or a tapped type of 
choke is employed the conditions are 
entirely different as also are the reasons 
for the employment of the devices. The 
reason for the use of step-down trans- 
formers or tapped chokes is simply that 
of impedance matching itself. An ex- 
amination of the characteristics of popu- 
lar output tubes and dynamic loud- 
speakers will show immediately that 
these do not fit in with one another. 
If, therefore, we were determined to 
work without any type of coupling be- 
tween them we should have to employ 
possibly loudspeaker units and output 
tubes of indifferent efficiency. In other 
words, we should not be in a position 
to employ the most satisfactory compo- 
nents. 

Generally speaking, when consider- 
ing modern sound systems we have al- 
ready decided upon a suitable output 
tube and type of loudspeaker. The only 
step which requires determination is 
that of selection of a suitable coupling 
device so that the impedance matching 
between the two shall be correct. Step- 
down transformers are practically al- 
ways employed with moving coil loud- 
speakers unless they happen to be of 
the now obsolete high resistance vari- 
ety. By means of output transformer we 
have artificially to raise the impedance 
of the loudspeaker so as to make it 
suitable for matching the tube. The 
output transformers where employed 
for this purpose are always of the step- 
down variety. If we use a 2-1 trans- 
former it raises the impedance of the 
loudspeaker four times. Again, if the 
transformer ratio is 3-1 the speaker im- 
pedance is raised by nine times. Usually 
the ratio employed is about 20-1 when 
(Concluded on page 20) 



AUGUST, 1931 



Adolph Zukor and 
the early movies 



IN 1896, in the Hopkins Theatre, 
Chicago, Adolph Zukor had seen his 
first motion picture, a short flicker- 
ing kissing scene between May 
Irwin and John Rice. The picture was 
used to empty the house after the 
vaudeville performance, to make room 
for the new crowd come to see the 
next show. At the time Zukor was 
impressed with the possibilities of 
Thomas Edison's invention, but awaited 
further development before determining 
his own participation. 

It was on April 23, 1896, at Koster 
& Bial's Music Hall in Herald Square, 
New York, that Edison's Vitascope 
first introduced the "movies" to Broad- 
way. 

Later, about 1904, when he had com- 
mitted himself to the amusement busi- 
ness, Zukor saw his first real movie 
with a plot and some sort of continu- 
ity. This picture was exhibited by 
Harry Davis in the basement of the 
old Grand Opera House in Pittsburgh. 

The day of the Nickelodeon was 
dawning. 

Any old vacant store, a sheet, a pro- 
jection machine, a handful of folding 
chairs (mayhap rented from a conve- 
nient undertaker), or, perhaps, no seats 
at all — just standing room behind a 
railing — some plaster and tinsel and 
lights outside — a Nickelodeon. Uncom- 
fortable, ill-ventilated, ugly. 

Pictures of from 75 to 150 feet, 
flickering, admission 5 cents, "Those 
who have seen the performance please 
pass out." 

But Zukor envisioned the possibili- 
ties. He and his partners, among them 
Marcus Loew, had several vaudeville 
theatres, in Brooklyn, in Newark and 
in New York. In these they began to 
show the novel, but not much liked 
movies. 

Zukor became more and more con- 
vinced that in the motion picture, de- 
veloped properly, lay the great amuse- 
ment of the future. He was alone in 
his belief, the others looking upon the 
lowly flickering movie as a mere ad- 
junct of the more favored and recog- 
nized vaudeville. 

But Zukor saw every picture ex- 
hibited within his reach, he studied 
them and the public's reaction to them. 
He "went crazy" about the movies, in 
the opinions of his associates. 

So much so that in 1908, Marcus 
Loew withdrew from his association 
with Zukor, returned his stock, and 
organized, independently, the Loew 



Arrival and Exit of the 
Nickelodeon 



Consolidated Enterprises, offering 
vaudeville as the piece de resistance 
and movies as the demi tasse, so to 
speak. 

Zukor continued to study the motion 
picture and the public, from 1909 to 
1912. He concluded that the destiny 
of the motion picture could be realized 
only when the pictures themselves were 
made worthy, in subject and execution, 
and when these finer pictures were 
shown in better theatres. The Nickel- 
odeon had an unsavory reputation. Men 
sneaked into them covertly. To Zukor, 
envisioning the future of the motion 
picture, this was a challenge — to win 
for the movie its rightful place as a 
means of entertainment and instruction 
limitless in its possibilities. 

He conceived, then, the project of 
capturing public recognition in one 
great overwhelming assault, risking all, 
to win or lose. 

In that day the picture was regarded 
by professional actors and actresses as 
a mere novelty, unworthy of their art. 
Zukor saw that if he could induce some 
famous player to make a real picture, 
intelligently directed, and then exhibit 
this picture in a real theatre, he could 
wipe away the public's frown and 
create a smile of recognition and 
appreciation. 

In 1912 Zukor organized the Famous 
Players Film Company, including 
among its shareholders the capable 
and respected Daniel Frohman, im- 
pelled by Zukor's sincerity and his pre- 
visioning belief in the motion picture. 

Among the early pictures he had 
seen Zukor was impressed with those 
directed by Edwin S. Porter, then 
producing, for Rex, one one-thousand- 
foot reel per week. Porter stuck to the 
story, had a keen conception of con- 
tinuity, and seemed to have reasoned 
the things he did. Soon Universal ab- 
sorbed Rex, and Zukor invited Porter 
to join him in his undertaking to 
realize the artistic potentialities of the 
motion picture. 

Once organized Zukor made ready 
to unfurl the Famous Players' banner 
emblazoned with the brightest star in 
all the galaxy of the time. Not just a 



Page 17 

famous player, but the most famous 
player of them all ! the "Divine Sarah," 
herself. 

Zukor sent Porter to France where 
Mme. Bernhardt had achieved a stage 
triumph in "Queen Elizabeth." He 
enlisted the assistance of Daniel Froh- 
man. 

Porter cabled finally that the picture 
could be produced and the American 
rights obtained for $35,000. Thirty- 
five thousand dollars I When six to 
eight thousand dollars was considered 
a gambler's, not a business man's, risk 
for a single picture ! 

Zukor cabled back "Go ahead." His 
associates in the Famous Players Film 
Company feared that his enthusiasm 
had swallowed his common sense. 

So Zukor, serene in his faith, paid 
for that first feature film himself, out 
of his own pocket. 

Then in November, 1912, when the 
first negative and print of "Queen 
Elizabeth" were received in America, 
Zukor further amazed his associates 
by insisting that the photoplay be 
shown in a theatre worthy of it. 
Whereupon he leased the Lyceum Thea- 
tre in New York City. 

Instead of the flamboyant lithographs 
of the day, he employed an artist to 
make the first poster ever used to ad- 
vertise a motion picture. 

"Queen Elizabeth," the first drama- 
tic story told in five reels of film, was 
received with acclaim. In one spon- 
taneous burst of enthusiasm the public 
recognized the motion picture as a new 
art, possessing possibilities surpassing 
all prior conceptions. 

Thomas Edison created the motion 
picture, Adolph Zukor had created the 
motion picture art. 

Again, with Daniel Frohman's co- 
operation, he imparted his enthusiasm 
to James K. Hackett, who became the 
first great American actor to add his 
star to the Famous Players' banner. 
And "The Prisoner of Zenda" with 
Hackett in the leading role, was the 
first picture produced by the Famous 
Players Film Company. 

The photoplay, as distinguished from 
the one-reel film, was an established 
fact, endowing a new era in the devel- 
opment of the budding motion picture 
industry. 

During the year that followed, Zukor 
screened the most brilliant stars of the 
day — Mrs. Fiske, Lilly Langtry, Cyril 
Scott, Arnold Daly, Henrietta Cross- 
man, Fritzi Scheff, Lenore Ulric, and 
many others. 

In 1916, in order to expand his pro- 
gram and increase the facilities for the 
production of better and better pictures, 
the Famous Players Film Company and 
the Jesse L. Lasky Feature Play Com- 
pany were combined to form the 
(Concluded on page 23) 



Page 18 



PROJECTION ENGINEERING 



News for home 
movie makers 



THE introduction of Cine-Kodak 
supersensitive panchromatic safe- 
ty film is news to the world of 
home movie making. This re- 
markable new film puts an entirely new 
aspect on the subject of personal movies. 
The extreme speed and high degree of 
color sensitivity of supersensitive film 
batters down many of the photographic 
barriers of the past. Motion pictures 
can now be made of subjects that here- 
tofore could not be photographed satis- 
factorily. 

Pronounced sensitivity at the red end 
of the spectrum makes the emulsion of 
this film particularly efficient when ex- 
posed to rays of artificial light — espe- 
cially light of incandescent lamps. As 
a result, the range of cine activities is 
signally extended. 

With supersensitive panchromatic 
film, it is now possible — in fact, easy — 
for amateurs to photograph subjects 
indoors by the light of ordinary electric 
lights. No longer is it necessary to use 
expensive lighting equipment to obtain 
indoor movies. 

To say the least, the imagination is 
taxed in attempting to conceive of all 
the numerous new channels of interest- 
ing movie making that are now open. 
As a striking example, a living-room 
can be quickly transformed into a tem- 
porary studio simply by placing two or 
more 100-watt bulbs in as many reading 
lamps. With the lens set at f. 1.9, one 
is all ready for first-rate home movie 
portraits ; closeups of the children, or 
numerous interesting subjects that do 
not require the source of illumination 
to be more than a few feet away. 

Lighting effects that are different — 
and beautiful — can easily be obtained by 
placing additional lights at the sides 
of and behind the subject. One lighted 
bridge lamp set behind the subject pro- 
duces a "back lighting" which gives a 
pleasing depth and roundness to the 
picture. See Fig. 1. It should be un- 
derstood that the direct rays of artificial 
lights should not be allowed to enter the 
lens. Lighted floor lamps and table 
lamps can be included in the picture, 
and will not cause fog or halation if the 
bulbs do not show through or under the 
shades. It must be remembered, how- 
ever, that brilliant pictures can only be 



Supersensitive panchro- 
matic safety film for 16 
mm. cameras announced. 



made when there are additional lights 
(out of range of the camera) for direct 
illumination. 

By increasing the number of electric 
bulbs, the camera can be placed farther 
from the subject thereby increasing the 
scope of the picture. 

An exposure table for Cine-Kodak 
supersensitive Panchromatic film when 
it is exposed under artificial light con- 
ditions is given: 

EXPOSURES TABLE 

FOR CINE-KODAK SUPER-SENSITIVE 

PANCHROMATIC FILM 

These exposures are for the Cine- 
Kodak operated at normal speed. Halve 
the illumination at half-speed. 
Distance Total 

from Lamps Diaphragm Wattage 
to Subject Opening of Lamps 

2 feet f.1.9 200 

2 '•< f.2.8 300 

2 " f.3.5 400 



3 " 


f.1.9 


300 


3 " 


f.2.8 


450 


3 " 


f.3.5 


600 


5 " 


f.1.9 


600 


7 " 


f.1.9 


800 


9 " 


f.1.9 


1200 



Best lighting is obtained by arrang- 
ing the lamps on each side of the cam- 
era, so that both sides of the subject are 




Fig. 1. In this picture the diaphragm 

opening was f.1.9, and six 100-watt bulbs 

were supplemented with two 60-watt 

bulbs placed in a reading lamp. 



illuminated. It is advisable to place 
the lights at different distances from the 
subject. For example, the table gives 
an exposure with the lamps 3 feet from 
the subject ; the lamps can be placed 2^2 
and 3^2 feet from the subject. The 
camera must be in a position so that the 
lights used for direct illumination will 



not show in the finder. 

One of the largest fields of picture 
activities opened by the new "pan" film 
is that of indoor sports — basketball 
games played in well lighted gym- 
nasiums, indoor track events. Other 
athletic events taking place on well 
lighted platforms tan be easily photo- 
graphed when stop f.1.9 is used. If the 
illumination is exceptionally good, even 
smaller lens openings can be employed. 

The increased range of picture taking 
provided by the new film actually em- 
braces night scenes on brilliantly lighted 
streets, or theatre districts in large 
cities. For pictures of this kind the 
camera must be fitted with an f.1.9 lens 
and the largest stop (f.1.9) must be 
used. Best results will be obtained 
after a rain. The glazed surfaces of the 
street and the sidewalks will then reflect 




Fig. 2. In well lighted indoor courts, 

excellent pictures can be made on 

supersensitive panchromatic film with 

the lens opening of f.1.9. 

the rays of the hundreds of lights, giv- 
ing added illumination and unusual ef- 
fects. If the lights are very brilliant, 
the camera can be used at normal speed. 
Half-speed gives twice the exposure and 
generally produces more brilliant pic- 
tures. It should be kept in mind, how- 
ever, that the action of moving vehicles 
and people walking on the sidewalks 
will be twice as fast. That is not so 
objectionable in the case of automobiles 
or street cars, because they then only 
appear to move more rapidly, but the 
action of people walking will be jerky. 

Fireworks, flood-lighted buildings, 
camp fire scenes, are all now within the 
scope of night movie making. 

The remarkable qualities of the new 
film are valuable for daylight photog- 
raphy as well as for pictures at night. 
The increased light-sensitivity of the 
film is not confined altogether to the 
red end of the spectrum. It is nearly 
twice as fast to blue and ultra-violet 
light as regular panchromatic film, per- 
mitting successful pictures to be made 
under very adverse weather conditions. 
Unique shots can be made during a 
downpour of rain with supersensitive 
film, and the cine camera becomes an 
efficient instrument during the early 
hours of the morning or in the weak 
light of the afternoon. 



AUGUST, 1931 



Sound 
systems in 
public 
schools 



By Ralph P. Glover 

THE public school systems of this 
country and elsewhere constitute 
a vast potential market for sound 
equipment that is still relatively 
unexplored. However, many manufac- 
turers who confidently expected large 
orders for equipment from the schools 
have been sadly disappointed in the 
volume of this business. The fact that 
all public institutions are practising 
rigid economies due to existing and 
expected reduction in the rate of tax 
receipts, is of course sufficient reason 
for curtailment of expenditures for 
expansion, but there is an additional 
impasse which must be analyzed from 
the educator's point of view. 

Those familiar with the flexibility 
and multitudinous uses of sound service 
may think it strange that considerable 
broad selling remains to be done in this 
field. This is nevertheless true in spite 
of the enthusiasm of prominent educa- 
tors all over the country for what 
promises to be a new method of instruc- 
tion. And naturally, the selling of 
principles must precede the selling of 
particular brands of equipment. 

The educator almost invariably refers 
to sound instruction as "radio" instruc- 
tion. This is the natural mental asso- 
ciation of the loudspeaker with the 
radio receiver, although the significance 
of the microphone and phonograph 
pickup may be known. Additional jus- 
tification for this nomenclature comes 
from the logical plan to utilize radio 
broadcasts as the primary source of this 
type of educational material. This is 
the phase of sound education that 
appears to be uppermost in the minds 
of school authorities at the present 



writing. We find school boards, pro- 
fessional educational societies, colleges 
and government agencies working on 
two main problems ; first, the policies 
involved in the actual broadcasting, 
such as financing, securing appropriate 
speakers and material, and details 
which must be worked out in coopera- 
tion with the stations and networks; 
second, the development of a suitable 
new technique of teaching in the class- 
room with an invisible speaker. To 
summarize : Educators are studying 
formal instruction by means of radio 
broadcasting. They apparently feel that 
sound instruction as a principle must 
stand or fall according to what can be 
done with broadcasting and their in- 
quiries are pointed in this direction. 
The local microphone and phonograph 
pickup are viewed simply as useful 
accessories in a majority of cases. 

If these views are as generally held 
in the educational field as we believe 
them to be, then it is not strange that 
equipment salesmen rarely reach the 
dotted line stage. The large mass of 
educators are not yet ready to lend an 
ear to descriptions of particular makes 
of sound equipment. Of course, a 
great many schools have already pur- 
chased central receiving and distribut- 
ing equipment, and where reliable 
technical guidance has been sought, 
and the situation has been thoroughly 
studied, followed by careful installation 
of suitable reliable equipment, results 
have been most satisfactory. Other 
schools have actually been victimized 
by perhaps well meaning, but obviously 
incompetent or selfish vendors, and it is 
certain that this has reacted to the dis- 
advantage of the sound industry in 
general. The impasse can be broken 
down most rapidly if the problems in- 
volved in sound systems in public schools 
are approached with public service and 
cooperation foremost in mind, relegat- 
ing thoughts of profits, discounts and 
commissions to the background for the 
time being. 

Material From Radio Broadcast 
Sources 

While it is certainly wise and desir- 
able to ultimately divorce educational 
radio programs from commercial spon- 
sorship, there still remain many existing 
programs of various types which ap- 
pear well suitable to school use. With- 
out going into detail, these include 
outstanding musical, dramatic and many 
sustaining program features, eye-wit- 



Sound equipment manufacturers, architects and con- 
tracting company engineers should study the school 
market. There are two services involved: the reception 
of external radio broadcast instructional matter; and, 
the internal use of sound amplifying systems 



Page 19 

ness descriptions of important national 
and world events and addresses by 
prominent individuals. There are a 
number of purely educational programs 
on the air and others are about to be 
inaugurated. Undoubtedly not repre- 
senting the ultimate in desirable educa- 
tional material, we believe that those 
schools which have access to these pro- 
grams at the present time are enabled 
to make good and beneficial use of 
them. 

On the other hand, the justification 
for sound equipment in public schools 
should not be thought of as resting 
entirely on the utility of radio pro- 
grams, and this idea, where held by 
educators, should be dispelled promptly, 
not primarily for the sake of accelerat- 
ing sales and profits, but to insure that 
planning covers the ultimate uses to 
which this equipment is sure to be put. 
The future benefits of a clear under- 
standing of the whole problem to both 
schools and industry, are rather ob- 
vious. 

There are points that the sound 
equipment industry has failed to em- 
phasize sufficiently in dealing with the 
schools. Briefly, they seem to be: 

(i) Sound equipment has many ad- 
ministrative and executive uses, not 
involved in actual teaching, but ex- 
tremely useful in communicating with 
groups of individuals in schools and 
elsewhere. These require no enumera- 
tion — it is simply the case of the tele- 
phone extended within earshot and 
audibility of a group or number of 
groups with evident advantage and con- 
venience. 

(2) The microphone itself is becom- 
ing a familiar sight in broadcasting, 
sound pictures, at meetings, public 
affairs and many group functions. In- 
dividuals are being called upon to face 
the microphone with increasing fre- 
quency. It is probable that the tech- 
nique of public speaking in the future 
will be a microphone technique, requir- 
ing a knowledge # of the correct posi- 
tioning, delivery and enunciation for 
the most effective use of the instru- 
ment, and such instruction may well 
form a part of the school curriculum. 

(3) Complete sound equipment 
makes it possible for students to take 
part in original programs and enter- 
tainments, presented before the whole 
or any selected portion of the school, 
without the necessity for any student 
leaving the home classroom. 

(4) Complete sound equipment offers 
valuable assistance to special teachers 
in music, physical education, etc. It 
enables them to duplicate their efforts, 
to work more rapidly, thoroughly, and 
economically, and widens the possible 
scope of their activities. In many 
applications, no new teaching technique 
is involved. 

(5) The details of the equipment 



Page 20 



PROJECTION ENGINEERING 



itself are educational, particularly for 
science and vocational classwork. 

A properly designed and carefully 
installed sound installation offers the 
advantages enumerated. Whatever the 
situation may be, the equipment should 
be capable of expansion and adaptabil- 
ity to a wide and complete service of 
sound distribution. 

Preliminary Plans 

The preliminary preparations for 
sound facilities in new schools have 
an important bearing on the amount 
and type of equipment that can be sold. 
Many new school buildings are being 
"wired for radio," as the phrase 
goes, since the expense of con- 
duits and cable is a negligible item 
compared with the total building cost. 
Unfortunately, many architects and 
electrical contractors are totally unfa- 
miliar with the special requirements 
and desirable features of audio-fre- 
quency transmission systems. Their 
work is characterized, usually, by lack 
of provision of sufficient radial distri- 
bution lines from the control point, and 
conduit sizes which are too small to 
accommodate shielded cable. Conduit 
facilities for out-of-doors speakers and 
microphones, so desirable for directed 
play and games, and microphone exten- 
sion lines within the building are 
seldom if ever to be found. This, of 
course, imposes immediate limitations 
on the scope of the sound system which 
can be installed without extra wiring, 
and adversely affects the likelihood of 
present and future sales of "extras," 
such as microphones and loudspeakers. 
The moral is evident — sound equipment 
manufacturers and sound engineers 
must encourage school authorities to 
specify complete and proper wiring 



details for all new buildings. Both 
parties will thereby profit in the long 
run. 

Just what amount and type of equip- 
ment should be included in the first 
purchase, is a field problem that must 
be solved on the job. It depends on 
the policy governing sound installa- 
tions and on the amount and source of 
the available funds. In new schools, 
the initial equipment purchase may be 
delayed indefinitely. Where public funds 
are limited, as they often are, financing 
may be undertaken by graduating 
classes, parent-teachers organizations 
or by philanthropic individuals. 

Here again, is an opportunity for 
unselfish public service on the part of 
the sound equipment industry, for it is 
not difficult to sell profitable Dut quite 
unsuitable equipment to such unofficial 
organizations or individuals, particu- 
larly when the school board has adopted 
a "hands off" policy for these cases. 
In one incident which came to the 
writer's attention, a thoroughly reput- 
able maker of so-called "standard 
equipment," either through indifference 
or gross selfishness, sold an expensive 
multiple-channel radio installation to a 
school through a graduating class. Of 
course, the equipment itself was the 
"best" obtainable and beyond reproach 
in that respect, but it is doubtful 
whether a plant of this type will ever 
find wide application in the schools; 
as an initial purchase, it was certainly 
an ill-considered luxury that would 
have been quite in order in the case 
of an apartment house or hotel. 

A genuine public service would have 
been performed if this considerable 
amount of money had been directed 
toward a more balanced sound installa- 
tion, including microphone and phono- 



graph facilities and a wider extension 
of the now limited number of sound 
outlets. Any ethical technical man can 
supply appropriate remarks which can- 
not be included here. 

Although it is manifestly difficult to 
generalize, a few general principles 
appear to have universal application in 
the selection of suitable school instal- 
lations, whether in old or new build- 
ings, and regardless of the s°urce of 
funds. 

( i ) The equipment should be capable 
of high-quality sound reproduction. 

(2) For obvious economic reasons, 
the equipment should be of a type that 
can be expanded or modified as the 
need arises. This requires the least 
initial outlay and only moderate ex- 
pense later on. Obsolescence can be 
made an unimportant factor. Unit 
equipment, rack-mounted seems to offer 
attractive advantages. 

(3) The equipment should be cap- 
able of complete operation by non- 
technical personnel without undue sac- 
rifice of flexibility. 

(4) The purchaser should be pro- 
tected against the possibility of subse- 
quent suits alleging patent infringe- 
ment. 

All of the above points apply with 
more or less force in many cases other 
than school sound installations, but are 
particularly important in this respect. 

It is expected that eventually the 
technical supervision of such work will 
be delegated to qualified experts repre- 
senting school authorities. This step 
should be welcomed by the sound equip- 
ment industry, for it will promote care- 
ful planning in advance of immediate 
requirements and eliminate inferior 
products from the field of acting com- 
petition. 



AAA 



OUTPUT MATCHING 
TO LOUDSPEAKER 

{Concluded from page 16) 

a single output tube and single loud- 
speaker are being considered. A trans- 
former ratio of this latter figure raises 
the effective impedance of the loud- 
speaker 400 times. 

The choice of a coupling transformer 
is now relatively simple. First of all, 
we find the impedance of the output tube 
and then that of the loudspeaker unit at 
a frequency of approximately 256 cycles 
per second. We now double the former 
impedance and if necessary make modi- 
fication of both impedance values de- 
pending on the employment of multiple 
output tubes and loudspeakers. When 
this has been done, we are left with two 
quantities — A, the doubled effective im- 
pedance of the output tube or tubes, and 
B, the effective impedance of the loud- 
speaker or speakers, placed either in 



series or parallel as the case may be. 
In all probability the latter value will be 
smaller and when divided into the other 
approximates a numeral. Whatever this 
may be, its square root is extracted and 
proportioned against 1 gives the trans- 
former ratio required. Thus, if the im- 
pedance of the loudspeaker or speakers 
goes into the effective impedance of 
the output tubes 3.6 times we may take 
this as 4 and extracting the square root 
we find that the ratio of the step-down 
transformer is 2-1. 

Putting this in a nutshell we may say 
that : (the impedance of loudspeaker at 
256 cycles per second) x (Transformer 
ratio ) 2 =2x (impedance of output tube). 
In this due allowance must, of course, 
be made for multiple tubes and loud- 
speakers as previously described. 

The case of the tapped choke is pre- 
cisely similar to that of a transformer 
— in fact a tapped choke when used as a 
coupling between output tubes and loud- 



speakers acts merely as an auto-trans- 
former and possesses in some ways the 
limitations of this type of electrical de- 
vice. Thus a center tapped choke is 
equivalent to a transformer having a 
ratio of 2-1 and if the tapping occurs at 
one-third of the winding the equivalent 
transformer ratio is 3-1 and so on. 



HAND-COLORING OF MOTION 
PICTURE FILM 

A PAPER on the above subject pre- 
sented at the recent S. M. P. E. 
meeting in Hollywood by Gustav Brock 
deals with the advantages of selective 
hand coloring, as distinguished from 
more or less complete coloring which 
is not yet perfected, and covers shortly 
the use of hand-coloring in educational, 
commercial and theatrical pictures. 
Finally, a description is given of the 
equipment used for hand-coloring. 



AUGUST, 1931 



Page 21 



Measuring 

screen 

brightness 



THE appreciation of the vital im- 
portance of the proper degree of 
screen illumination renders the ac- 
companying chart of valuable as- 
sistance to the painstaking projectionist, 
who has substituted mathematical calcu- 
lation for rule of thumb methods in 
solving his problems. 

It is contributed by Hall and Con- 
nolly, Inc., as an aid in ascertaining 
with a more than fair degree of accu- 
racy, the degree of brightness which 
may be obtained on various sizes of 
screen, with any one of the standard 
projection lamps of modern design. 

The chart also pictures the improve- 
ment in projection lamp optics and the 
progress made towards better screen 
illumination by the above named com- 
pany in collaboration with optical manu- 
facturing concerns. 

The chart is based on international 
Lumens, a measure of the quantity of 
light. Lumens being the product of in- 
tensity in foot-candles multiplied by the 
area of the screen in square feet, the 
Lumens, as indicated on the chart, for 
each outfit specified, divided by the 
square-foot area of any individual 
screen, will give the foot-candles bright- 
ness of that screen. 



The chart was based on data ob- 
tained from 240 tests, made at the Hall 
and Connolly laboratory under uniform 
and technically correct operating meth- 
ods during which a mean of the read- 
ings was taken and plotted, with special 
care to avoid abnormal peaks. 

Particular care was taken to tabulate 
only such results as might reasonably 
be duplicated in actual theatre practice. 

With this chart anyone can deter- 



L UM£N5 



mine the intensity of illumination on 
any given size of screen, with any of 
the various types of lamps and optical 
"set ups" — from the 30 ampere low in- 
tensity reflector lamp, to the 120 ampere 
high intensity outfit equipped with lat- 
est large aspheric condensers. 

Condensers indicated on the chart as 
"latest" are the improved types, now 
furnished as standard for all present 
HC lamps. 



9000 



8000 



7000 



€000 



5000 



V-ooo 



3ooo 



2000 




Showing relative light output for various types condensers and reflectors. Note: All 
tests were run under uniform operating conditions — light projected through Cinephor 

Series II objective lens. 



▲ A A 



A SOUND FILM RE-RECORDING MACHINE 

A paper on the above subject was presented by J. J. Kuhn, at the S. M. P. E. meeting 
in Hollywood, recently. 

In sound picture production, the process of making the release print negative for sound 
requires the reproduction of the existing sound record in order that it may be recorded in 
proper continuity and corrected for volume level. The machine used for this purpose is 
called "Re-Recording Machine." 

This paper describes a new re-recording machine recently made available which is suit- 
able for use in studios using either the variable density or variable area method of sound 
recording. The machine described employs a novel type of film aperture and a new method 
of focusing the sound lamp. To insure uniformity of film movement and to eliminate 
unwanted noises in the re-recording process, workmanship must be of the highest order. 
Some of the requirements and testing methods employed in the manufacture of the 
machine are described. 



Page 22 



Dont's for 

Theatre Projectionists 



By C. B. Gordon-Sale 



Here Are 58 "Don'ts" Which, If Properly Observed, 
Will Prevent Expensive Interruptions to Service 



SEVERAL of the other mechanical 
trades have from time to time 
published a series of dont's for 
members of their professions. 
Thus the writer ventures to submit the 
following as applying to sound pro- 
jection. 

1. Don't switch quickly on to "Plate" 
even if tubes seem to stand it. 

2. Don't interchange rectifier and 
amplifier tubes. 

3. Don't use a "recovered" photo- 
cell. 

4. Don't test out horn type receiver 
Jvithout horns. 

5. Don't assume the stage horns are 
O.K. when the monitor is working. 

6. Don't close the motor switch 
before pulling round for one-half 
turntable revolution when on disc. 

7. Don't wear a long trailing over- 
all. 

8. Don't clean contacts with carbon 
tetrachloride — it may eventually cor- 
rode them. 

9. Don't forget to turn down the 
exciter lamps after a show — the bat- 
teries will probably be recharged be- 
tween times. 

to. Don't fix lamps within 4 feet of 
sound unit. 

11. Don't return an exciter lamp 
until it burns out. Renew when it 
starts blackening or the filament sags 
slightly. 

12. Don't alter the position of the 
lens tube in the sound unit. 

13. Don't expect pre-focussed sepa- 
rate exciter lamps to align perfectly 
when they are shot home. Readjust 
after the reel is cleared. 

14. Don't forget a little graphite 
grease often stops a noisy resistance. 

15. Don't forget that any loose metal 
object near the PEC compartment may 
introduce crackle. 



16. Don't, in W.E. equipment, have 
the PEC coil too tight or too slack — 
both conditions are bad. 

17. Don't let oil accumulate in the 
PEC compartment. Swab out with rags 
and be more sparing with the oil can. 

18. Don't try to alter the bill with- 
out unlocking the clamp in a U-Base. 

19. Don't let flexible couplings run 
out of true even if they will stand it. 

20. Don't cuss the second when he's 
late with the dowser. Fit a chain de- 
vice of some sort and let one man do 
the job. 

21. Don't run with a warped disc. 
Use the standby or, if pressed, lay the 
faulty one fiat in the sun or in a hot 
room which should cure it. 

22. Don't try to undo a "buck" hexa- 
gon grub screw with the end of a file. 
Keep the special wrench in your pocket. 

27,. Don't forget that a single uni- 
versal joint can never turn easily. Two 
will if the angles with the main shafts 
are equal. 

24. Don't forget flexible shafts some- 
times require lubrication. 

25. Don't tie a flexible shaft in knots. 
Give it a fair chance. 

26. Don't cut off any wire. Unsolder 
it — you may be glad of a spare inch 
later on. 

27. Don't bare wire ends with cut- 
ting pliers or a pocket knife. Pull off 
the rubber with needle nosed pliers 
which will not damage the wire or 
scrape off the tin. 

28. Don't say resin flux is too slow 
and use spirit. 

29. Don't examine storage cells with 
a lighted match — your eyes are valu- 
able. 

30. Don't forget to clean the solder- 
ing iron after you have used it for 
greasing accumulator lugs. 

31. Don't re-mark a projector with- 



PROJECTION ENGINEERING 

out checking the turntable if your ma- 
chines are U-Base type. 

32. Don't get the picture right and 
let the bed go hang. Level the bed and 
pack the head. 

33. Don't grouse about surface noise 
when there is machine noise. 

34. Don't use cheap needles or try 
experiments with "permanents." "Loud 
tones" are best. 

35. Don't get oil on a disc. 

36. Don't clamp needles too tight or 
you may throw the pickup out of ad- 
justment. 

27- Don't forget that reproducer 
"drift" is almost as important as cor- 
rect tracking. 

38. Don't blame recording for flutter 
before you have checked shaft align- 
ment and damping arrangements. 

39. Don't omit to test the reed type 
pickups for equal tuning. Tap the 
needle both sides and check the "plop" 
for volume and pitch. 

40. Don't forget to replace burned 
out pilot lamps. Some day you may 
have need of them. 

41. Don't expect an amplifier to be 
dead as soon as the mains are pulled. 
Condensers remain charged and a 1,000 
volt kick is painful. 

42. Don't test for a started condenser 
with a 6 volt buzzer. It is useless nine 
times out of ten. 

43. Don't omit to correct output 
levels when replacing a PEC. 

44. Don't smack a dud PEC near 
water — some types explode. 

45. Don't search for echoes in the 
auditorium with the ports open. 

46. Don't forget that heavy drapes 
near the screen will cut off the top and 
leave the boom. 

47. Don't flare a buzzer near the 
sound unit or you may get pickup of 
an unwanted nature. 

48. Don't tighten motor brushes to 
stop sticking before examining the com- 
mutator for dirt. 

49. Don't forget electric motors gen- 
erally want end float. Set couplings to 
allow for this. 

50. Don't test tube emissions before 
everything is properly warmed up. 

51. Don't think a reduced filament 
current is economy. 

52. Don't forget too low value cart- 
ridge fuses sometimes have a higher 
resistance which upsets meter readings. 

53. Don't forget if a grounded wire 
breaks you can always pick up from 
earth. 

54. Don't store "B" batteries. They 
deteriorate with time whether they are 
used or not. 

55. Don't forget an oily lens or 
PEC window cuts off top. 

56. Don't use the scratch filter to the 
sacrifice of clarity. 

57. Don't forget that condensers may 
be shopped out for the time being. 

58. Don't forget there is no such 
thing as a cheap, dependable resistor. 



AUGUST, 1931 



Page 23 



Portable 16mm. 
camera used for 
slow action 
pictures 




Making slow-motion movies of 

with the camera, 



Fhoto by Bell & Howell 
player's golf stroke. Joe Novak 



MANY golfers now-a-days are 
improving their game by the 
motion-picture method. Even 
Bobby Jones, we are told, has 
for some time been accustomed to have 
movies made of his strokes for his per- 
sonal use, and he studies the pictures 
in order to catch possible imperfections. 
When Bobby was in England last year 
the Prince of Wales used his own 
Filmo movie camera to "shoot" the 
Georgian as he played. 

"The point is that a new method of 
teaching and learning the ancient and 
honorable game of golf has arrived — 
the movie method," says a writer in 
June Fikno Topics magazine. "This 
new method, besides winning the com- 
mendation of thousands of players, has 
been unqualifiedly endorsed by the Pro- 
fessional Golfers' Association of 
America, composed of the best golf in- 
structors in this country. The movie 
method aids the tyro and more ad- 
vanced player as well." 

The writer continues : "When golf 
is taught via movies the motion picture 
camera is used to record every detail of 
your play in slow motion. The pictures 
are then studied and suggestions made 
to correct errors and to effect improve- 
ments. The slow-motion feature makes 
it possible to follow every movement. 
Many times you will find that you were 
not playing the way you thought you 
were. The quickness of your play de- 
ceives the human eye but it cannot 
elude the eye of the camera. 

"You can have pictures taken of your 
game and then study the plays yourself, 
or you can have your pro 'diagnose' 
the case and advise what to do. Many 
pros are now equipped with movie 
cameras to take pictures of their pupils 
in action. They throw these pictures 
on the screen and appraise the plays. 
Every single movement can be sub- 
jected to scrutiny, and necessary cura- 
tive methods prescribed. Progress in 
your game can be watched and traced 
in subsequent pictures." 



As a sort of second-line auxiliary in 
the golf-by-movies idea, slow-motion 
film studies of golf stars can be pro- 
jected on a movie screen and studied by 
the aspirant who wants to see how the 
big ones do it. There is available a fine 
selection of 16 mm. golf films, includ- 
ii?._ several "talkies." 

The Professional Golfers' Associa- 
tion, quite generally known as the 
P. G. A., recently sponsored the mak- 
ing of super-slow movies of Jones, 
Joyce Wethered, and Harry Vardon. 
These pictures are rendering a tremend- 
ous service in arousing interest in 
movie golf instruction. Following a 
showing of these movies in Chicago, an 
Associated Press report of the pictures 
was carried in many newspapers 
throughout the country. Arthur Bris- 
bane in his newspaper column "To-Day" 
has raised his voice to comment upon 
golf movies and their objectives, and 
Alex Pirie, the dean of the pros, is of 
the opinion that motion pictures will be 
of extraordinary benefit in teaching. 

Value in Instruction 

Mr. Pirie has been quoted as saying 
that previous instruction has been all 
wrong. "To the contrary," says Herb 
Graffis in Golfdom, "he is of the 
opinion that much of it is far advanced, 
and to make the advance general, the 
P. G. A. pictures were shot. Thor- 
oughly analyzed by competent men, 
the pro pictures, it is hoped, will elimi- 
nate a great deal of debate about what 
is proper instruction. A great simpli- 
fication of golf instruction is one of the 
main objectives of the pictures." One 
noted pro, we might add, is of the 
opinion that golf movies will show that 
all golf instruction can be reduced to 
emphasis on three fundamental points. 

Concrete glimpses of the P. G. A. 
pictures are afforded by Mr. Brisbane 
in his "To-Day" comment. "Slow- 
motion 'movies' of the great Bobby 
Jones and the beautiful Joyce Wethered 
in action show that these great golfers 



do not 'break their wrists on the back 
swing' until very late in the swing," he 
says. "And Jones, the Great, hesitates 
at the top of his swing, shifts his body 
and gets planted before he brings the 
clubhead down." 

For making golf movies the small, 
portable, and relatively inexpensive 16 
mm. camera will fill every ordinary re- 
quirement, provided care is taken to 
select an instrument of reliable make, 
constructed to film pictures at the rate 
of 64 or 128 exposures per second, 
which are the speeds necessary for 
making satisfactory slow-motion golf 
pictures. 

George Sargent, the noted pro of the 
Scioto Country Club, Columbus, Ohio, 
who has been a prime factor in the 
motion-picture golf instruction move- 
ment, uses a Filmo amateur movie 
camera in his golf work, as does also 
Al Lesperance, the well-known pro of 
the Westmoreland Club, in suburban 
Chicago. So do Joe Novak and other 
/eading professional instructors — and 
Bobby Jones has done so for some time. 

Many a player has cut his golf score 
substantially by the movie method and 
is still shaving: it down. 



ADOLPH ZUKOR AND THE 
EARLY MOVIES 

(Concluded from page 17) 

Famous Players-Lasky Corporation. 
Later that year, the Oliver Morosco 
Photoplay Company, Pallas Pictures of 
Bosworth, Inc., and, early in 191 7, the 
Paramount Pictures Corporation, were 
absorbed by the Famous Players-Lasky 
Corporation. 

Though the Paramount Pictures Cor- 
poration was dissolved as a separate 
corporate entity, the appropriate name, 
Paramount, was retained and applied to 
the productions of the Famous Players- 
Lacky Corporation. — From a story pre- 
pared by Esten Boiling for The Carrier 
Engineering Corpn. 



Page 24 



The use of positive film 
in sound recording 



By Charles Felstead* 



CONTRARY to general opinion, 
the film used in film sound record- 
ing machines is not of the same 
type as that employed in motion 
picture cameras. Negative film stock 
is used in the cameras for photograph- 
ing pictures. After exposure this nega- 
time film is developed and printed on 
positive film stock, which is likewise 
developed after being exposed to the 
printing light. But in the film record- 
ing machines employed for recording 
sound in a track near the edge of a 
strip of motion picture film, positive 
film is used. There are two reasons 
for this : positive film has less "grain" 
than negative film, and also it is less 
expensive. A positive print is made 
from the sound track in the same man- 
ner that a positive print is made from 
the negative picture film. Paradoxic- 
ally, to differentiate between the posi- 
tive film stock and the positive print, 
the positive film that is exposed in the 
film recording machines is called the 
"sound negative," because the final 
positive print is printed from it. 

Grain 

A piece of film that is exposed and 
developed has on it an image of the 
objects which reflected light against it 
and exposed it; but that image is not 
smooth and homogeneous ; it is com- 



' Sound Engineer, Universal Pictures Corpora- 



posed of a multitude of minute specks 
that cannot be seen individually under 
even the most powerful magnifying 
glass. These specks constitute what is 
known as the "grain" in film. Although 
they are not large enough in them- 
selves to cause trouble, the specks have 
the odd property of so reflecting light 
that they appear to collect in groups 
and form larger specks. These specks 
are crystals of solid silver formed on 
the celluloid film base, and as such they 
are covered with a multitude of little 
reflecting faces, or facets. 

A light shining on the crystals is re- 
flected from one to another, back and 
forth, and cannot get through the film 
at that point because of the reflection 
and re-reflection of the light beam. 
This multiplies the apparent size of 
each speck many fold, and produces the 
optical illusion of a much larger black 
spot when light is thus directed through 
the film. The effect is really one form 
of what is known as "hallation," and is 
termed "diffusion hallation." 

As far as possible, the grain of the 
developed and fixed emulsion should be 
maintained extremely fine — or rather, 
the reflecting quality of the crystal 
facets should be reduced to the minimal 
amount by treating them chemically in 
the fixing solution to dull them — in or- 
der that the grain will not be evident 
in the film. Naturally, the more homo- 
geneous and smooth the image on the 



An Explanation of What is Meant by "Grain" in Film, 
and Its Effects. 



PROJECTION ENGINEERING 

film, which is to say the finer the 
grain, the better the image will be. 

This is particularly true of a sound 
track of the variable density type, be- 
cause in it the exposure lines represent- 
ing the high frequency sounds are very 
narrow and very close together. If 
these lines are not smoothly and evenly 
recorded by the film, the reproduced 
sound will not be a faithful copy of 
the sound that was recorded, because 
the light beam used in the reproduction 
will not be cleanly interrupted by the 
striations in the sound track. If the 
grain is coarse enough, the reproduced 
sound may even have noise in it from 
that source. Positive film stock is not 
used in motion picture cameras because 
it is treated with a "slow" emulsion, 
made up mostly of silver chloride crys- 
tals with silver bromide crystals some- 
times added carried in suspension in a 
solution of gelatine, which means that 
it requires a much greater exposure 
than the faster negative film emulsions, 
in which silver bromide crystals are 
used entirely in place of the silver 
chloride. From one to ten per cent of 
silver iodide is often included in these 
emulsions. 

This greater exposure can be accom- 
plished by slowing down the rate of 
speed at which the film moves through 
the camera or recording machine, or 
by increasing the brightness of the 
light that causes the exposure of the 
film. The result in either case is prac- 
tically the same. 

Since the speed of movement of the 
film is kept at precisely ninety feet a 
minute in the cameras and recording 
machines in sound picture work, this 
speeding up is not possible. But greater 
exposure of the film is easily accom- 
plished in a film recording machine by 
increasing the intensity of the light 
source producing the exposure. How- 
ever, it is not practicable to increase 
the light causing the exposure of the 
film in motion picture cameras because 
the illumination used on sets is already 
as intense as convenience and economy 
will permit. 



SPLIT MAT SHOTS IN SOUND RECORDING 

A paper on the above subject presented by L. E. Clark, at the recent S. M. P. E. 
meeting at Hollywood, discusses the technical problems which arise in motion picture 
studios and which must be solved quickly, cheaply and with the utmost simplicity. 
All engineering work must be done with an eye to production. As a result, the 
methods and equipment developed in the studios are frequently peculiar and highly 
unorthodox when viewed alongside scientific developments produced in the labora- 
tory. The paper describes the problems which arose in one particular studio, as a 
result of the use of double exposure photography, and the methods, more practical 
than scientific, which were developed to meet these needs. 



AUGUST, 1931 



Page 25 



. •wsrv/N^vwvA/ 



^S5*5«v 



PHOTOTONE 1 II K4I II M 



'^ry-ysAvy^. 



Phototone Portable Sound Film 

35 MM Talhino Picture Equipment *«ith Projector 



Complete A. C. operated — nothing 
else to purchase — installed in 
minutes time or less. 




or Permanent and Temporary Installation 

BUILT for Discriminating Purchasers 
That Must Have Quality Above Any- 
thing Else Both in Reproduction and 
Construction 




•** «BS 25»? » ». 



The Phototome 

309 North Illinois Street 



for Phototone Portable Equipments 

For Further Information Write 

orporation of Amer-ic«fe 

Indianapolis, Indiana 



4 7s/vwsy W^ vs^s/vys/^ 4 



Hoffmann- 




^TK« re 




THE ONLY UNION MADE RHEOSTAT 



ig claims is one 
thing-Making good is another! 

Projectionists and theatre owners who have installed Per- 
fection Rheostats KNOW our guarantee means the best 
results — clearer pictures — longer life. 

Now equipped with solderless, adjustable lugs to take wire sizes from 
No. 4 to 4/0 without any additional cost. 

SOLD BY ALL BRANCHES OF THE NATIONAL THEATRE SUPPLY CO., 
SAM KAPLAN, NEW YORK, AND BY YOUR DEALER. 

HOI I MANN-$OONS 

Electrical and Engineering Corp., 387 First Avenue, New York City 



PERFECTION RHEOSTATS 

<Z> 



Page 26 



PROJECTION ENGINEERING 



New Developments 

and 

News of the Industry 



PHOTOTONE PROJECTOR 

The Phototone projector which is manu- 
factured by the Phototone Equipment Cor- 
poration, 309 N. Illinois Street, Indian- 
apolis, Ind., is a compact and extremely 
sturdy portable talking picture unit. It 
is designed for sound on film recording and 
is capable of reproducing both variable 
density and variable width methods of 
recording. 

The equipment is for use with 110 volt 
50 to 60 cycle a.c. without the use of motor 
converters. The amplifier unit has incor- 
porated in it a rectifier using 281 type 
tubes in a full wave rectification circuit. 
The last stage of amplification is push- 
pull with 250 type tubes. 

The projector head is so designed that 
the wear on films is reduced to a minimum. 
This enables commercial companies which 
use talking films to carry sales messages, 
to use their films repeatedly with little 
wear. 

The operation is simplified so that any 
amateur can operate the projector. It is 
also practical for schools, churches and 
hotels where there is not permanent in- 
stallation. 

The equipment weighs only 195 pounds 
not including the weight of the trunks. 
This weight includes projector, amplifier, 
screen and necessary attachments. The 
trunks bring the weight up to 235 lbs. 
which is light for mechanically strong 
equipment. 

▲ 

A NEW BUG ELIMINATOR 

Bugs, insects, mosquitoes, are the bane 
of all theatres. 

During the hot summer months, these 
pests swarm about lamps, annoying patrons, 
and in general spoiling the effect of re- 
freshment and rest that should accompany 
a good show. Consequently, the news is 
most welcome that a simple and inexpens- 
ive method of eliminating such pests has 
been discovered. 

Reynolds Electric Company have devel- 
oped a special natural colored glass hood 
for placing over white lamps. The Reco 
color hoods in green, canary, or amber 
colors, when placed over white lamps, 
positively repel insects, bugs, etc. 

These hoods are made in sizes to fit 
over white lamps from 10 to 500 w. lamps. 
For floodlights, etc., Reco color plates are 
available. 

Hoods are inexpensive and further in- 
formation will be given by writing direct 
to the manufacturer, Reynolds Electric 
Company, 2650 W. Congress Street, Chi- 
cago, 111. 

▲ 

NEW LAMP FOR PHOTOGRAPHY 

Herbert Conord, president of Blue Seal 
Products Corpn.. 260 Wyckoff Street, 
Brooklyn, N. Y, announces that his com- 
pany has ready for delivery a new lamp 
for shooting both still and silent pictures 
indoors, and outdoors at night. This lamp 
is known as Blue Seal Photo Sun Arc 
Lamp. It gives constant, flickerless light. 



IMPROVED PICKUP FOR ELEC- 
TRICAL TRANSCRIPTIONS 

For the faithful rendition of electrical 
transcriptions at a minimum investment 
the Stevens Manufacturing Corporation of 
Newark, N. J., has developed an ingenious 
turntable and pickup. This equipment is 
suitable for broadcasting, theatre, audito- 
rium, club, demonstration or other pur- 
poses where the superior qualities of 16- 
inch, 33-1/3 r.p.m. recordings are sought. 

The new Stevens product comprises an 
18-inch turntable, a precision electromag- 
netic pickup with balanced tone arm, and 
necessary controls, mounted in a heavy 
wooden case with cover and handles for 
portability. A companion stand is ' pro- 
vided if desired. Instead of an elaborate 
system of driving shafts and gears, the 
turntable is driven by a silent and constant- 
speed motor through a friction drive ap- 
plied directly to the inner face of the turn- 
table rim. The motor is mounted with a 
pivotal spring tension so that the friction 




drive makes positive contact at all times. 
An automatic governor maintains constant 
motor speed despite wide fluctuations in 
line voltage. 

In order to prevent a nautical roll or 
wobble, which is a common cause of tone 
distortion in the handling of large records, 
the turntable is mounted on a ball thrust 
shaft sunk in a deep well. Due to the 
fact that there is no drive or strain of any 
kind on the shaft, the turntable cannot 
become wobbly or go off center. The 
turntable is so accurately balanced and 
mounted on its thrust ball bearings that 
it will rotate for a long period of time 
after the electric power is turned off. 

The Stevens electrical transcription pick- 
up is employed in a steadily increasing 
number of broadcasting stations, as well 
as for theatre, auditorium, club, demonstra- 
tion and other uses. 



SERVICE-ON-SOUND MOVES 

The Service-On-Sound Corporation have 
moved their consolidated offices with J. A. 
Tannenbaum, Inc., into their new head- 
quarters, in Suites 607 and 609 at 1600 
Broadway, New York. The S.O.S. Corp. 
expects to set up a permanent display of 
both portable and stationary sound and 
projection equipment. In addition, there 
are spacious sales rooms, in which out-of- 
town buyers can view the latest in cinema 
and theatre supplies. 

The S.O.S. Corp. is known as the "Mail 
order house of the industry," and its con- 
nections and outlets are far-flung through- 
out the world. 

J. A. Tannenbaum, Inc., have been 
closely associated with the S. O. S. Corp. 
for several years. 

▲ 

CINEGLOW 

The U. S. Navy has purchased a Cine- 
glow Portable Land System with the new 
Akeley Audio Camera for use of the Re- 
cruiting Bureau. 

Dr. Paul L. Hoefler, famous for his 

"Africa Speaks," has also bought a 

Cineglow. He plans another trip to Asia. 

A 

MOTOR SPEED REGULATORS 

Ward Leonard speed regulators are de- 
signed for use with constant torque and 
variable torque a-c. and d-c. fractional 
horsepower motors. They are built to 
conform with N.E.M.A. Classifications 
Numbers 93 and 95 and are listed as 
standard apparatus by Underwriters' 
Laboratories. The Underwriters' listing 
is given under "Industrial Control Equip- 
ment — Motor Controllers — Manual" as 
number 1101. This number appears as the 
first four digits of the identifying number 
on the name plate. 

These regulators can be furnished for 
use with series-wound a-c. motors. When 
so used, the rheostat usually has no "off" 
point or the full speed position is located 
next to the "off" point to assure full 
torque at starting. 

These regulators are furnished with a 
moulded knob designed to indicate the 
position of the contact arm. 

As the current capacity and resistance re- 
quired for proper control of a-c. fans or 
motors varies widely, no rheostats are 
listed for this service, but prices and in- 
formation will be furnished on request. 

These regulators are manufactured by 

the Ward Leonard Electric Company, 

Mount Vernon, N. Y. 

A 

S.M.P.E. MEMBERS VOTE ON NEW 

YORK AND DETROIT FOR 

FALL MEETING 

Ballots have been sent to members of the 
Society of Motion Picture Engineers for 
a vote on the location of the Fall meeting. 
The board of governors have selected New 
York and Detroit for the choice of cities 
and the tentative date for the Fall meeting 
has been set for October 19 to 22 inclusive. 



AUGUST, 1931 



Page 27 



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 foreign 
countries $2.00.) 

The engineering departments 
of hundreds of manufacturers 
in the projection and allied in- 
dustries and scores of the M. P. 
M. O. U. locals have used this 
Group Plan extensively, in re- 
newing their subscriptions to 
Projection Engineering. 



Each subscriber should print his 
name and address clearly and 
state his occupation — whether 
an executive, engineer, depart- 
ment head, contractor, installa- 
tion man, projectionist or tech- 
nician, etc. 



Remember this Group 
Plan when Your 
Subscription Expires 



(Projection Engineering) 

Bryan Davis Publishing Co., Inc. 
52 Vanderbilt Avenue 
New York, N. Y. 

Los Angeles Chicago Cleveland 



Every 



Cineglow Recording 
is noiseless! 



i 



fat's why Uncle 
Sam bought one 
for the 

U. S. NAVY 



Knowing the vast possibilities offered 
in Sound Recording, The Cineglow 
Sound System was designed for per- 
fect, noiseless recording and port- 
ability. The U. S. Navy have awarded 
the contract for a Cineglow System 
on the basis of merit as well as price. 

The world famous Cineglow three 
element recording lamp is employed 
and the many improvements in de- 
sign, such as the Cineglow Optical 
Slit — the Mechanicallv Filtered 
Sound Sprocket— AND A LICENSED 
AMPLIFIER go to make up the finest 
recorder on the market today. 

A live-wire cameraman can make BIG 
MONEY recording local events, tie- 
ing up merchant-theatre campaigns, 
recording Industrial, Advertising, and 
Political campaigns, or Educational 
shorts. In Grantwood, New Jersey, the 
Royal Studios, Inc., is installing a 
double studio type Cineglow System 
and the new management plans a 
series of feature productions. Sim- 
ilarly recordings made in the Atlas 
Soundfilm Studios of New York are 
now enjoying nation-wide release. 

The best is now available at the price of the 

poorest. Write, wire or cable your needs 

for prices. 



Cineglow Sound Systems 

MANUFACTURED BY 

BLUE SEAL SOUND DEVICES, Inc. 




i 



1 30 West 46th St., New York City 

Cable Address: SOUNDFILM, New York 



Page 28 



PROJECTION ENGINEERING 



MOTOR GENERATORS FOR RE- 
PLACING STORAGE BATTERIES 
IN THEATRES 

Motor-generators for replacing storage 
batteries in theatres have been developed 
by the Electric Specialty Company of 
Stamford, Conn. These machines supply 
low voltage direct current for the fields 
of loudspeakers and for the exciter lamps 
of the sound equipment. They are very 
carefully designed so that they do not 
cause any objectionable background hum 
in the loudspeakers. A simple filter sys- 
tem is used when they supply power to the 
exciter lamps, but filters are not used with 
the horn fields. The machines are fur- 
nished complete with filters, when re- 




quired, and they may be readily connected 
in place of the storage batteries. 

These machines are of exceptionally 
rugged construction and are mechanically 
designed for the least possible amount of 
attention and maintenance expense. Wool 
packed sleeve bearings are used, which 
require no attention evcept very infrequent 
lubrication and which run very quietly. 
The machines are semi-enclosed, all live 
parts and rotating members being com- 
pletely protected. Terminal boxes are 
provided for conduit connection. 

These motor-generators provide the most 
reliable source of power obtainable and 
are more economical in the long run than 
other forms of power supply apparatus. 



POWER AMPLIFIER 

Model GA-80 manufactured by the Gen- 
eral Amplifier Co., Cambridge, Mass., is a 
two stage amplifier employing one -24 tube 
in the first stage, followed by four type -47 
pentode tubes in the output stage. The pen- 
todes are connected in a parallel push-pull 
arrangement. 

There is a very logical engineering 
reason for doing this. If a pentode tube is 
used singly and the conventional way is 
employed to obtain the bias voltage by an 
I.R. drop through a resistor, the sensitiv- 
ity of the tube is such that this resistor is 
of a very low value. In order to by-pass 
the audio frequencies successfully, it is 
necessary to employ a very large capacity 
across this resistor. By using the push- 
pull arrangement, the necessity of by-pass- 
ing this resistor is eliminated but the push- 
pull method of connection doubles the plate 
impedance of the tube which is initially 
very high. 

In order to drop the plate impedance to 
a value which will be commercially ac- 
ceptable, two tubes are placed in parallel 
in the push-pull stage, thus reducing the 
impedance value to that of one tube. When 
this arrangement is used it is necessary 
that two -80 type of rectifiers be em- 
ployed in parallel to deliver the necessary 
current for the tubes. 

The Model GA-80 amplifier has an un- 
usually good frequency characteristic and 
will provide approximately 10 to 12 watts 
of undistorted energy to the speaker. The 
input is directly to the grid of the -24 



tube, while the output is from the plates of 
the pentodes and "B" plus. 

The input circuit is practically universal 
and may be used with values of impedance 
from 500 ohms up. When used with a 
microphone it is only necessary to add a 
microphone transformer, the secondary of 
which is connected directly to the input of 
the amplifier. Button current for the mic- 
rophone can be secured by means of dry 
batteries if desired. 



SOUND-ON-FILM 

What may be a life-line to small ex- 
hibitors, is the recent announcement of the 
S.O.S. Corp., 1600 Broadway, New York 
City, of a new a-c. operated sound-on-film 
for two projectors, which is being pro- 
vided at $495.00 complete. 

The S.O.S. eauipment consists of two 
sound heads of standard make complete 
with photoelectric cells ; optical systems ; 
exciter lamps ; lamp mounts ; motor brac- 
kets ; a-c. power supply containing fader 
and photocell balancers. 



TESTS BLOOD ELECTRICALLY 

The accuracy of blood and other 
physiological analyses, which often depends 
upon the accuracy of color observation on 
the part of the analyst, has been enhanced 
by the development of an electric eye 
which can be carefully calibrated in refer- 
ence to sensitivity to different colors. 
George Lewis, vice-president of the Arc- 
turus Radio Tube Company, Newark, 
N. J., manufacturers of the electric eye, 
describes this photoelectric principle as an 
aid in such work. 

"The human eye," declares Mr. Lewis, 
"almost invariably suffers to an extent 
from color blindness. Some persons are 
more color blind than others, and most of 
us will find that one eye sees objects with 
a slightly different shade than the other. 
This can be noticed by looking at a highly 
colored picture first with one eye and then 
with the other. Color blindness, slight or 
even acute, has little effect upon our suc- 
cess in life, if we are lawyers, automobile 
mechanics and about seventy-five per cent 
of all possible trades and professions. But 
when it comes to blood and other physio- 
logical analysis, where color is often a 
determining factor, an electric eye, such 
as the photoelectric cell, which never suf- 
fers from color blindness, or even retinal 
fatigue (which may affect even the normal 
eye) is a considerable contribution to the 
accuracy of results. 

"The photoelectric eye can detect color 
differences beyond the sensitivity of the 
best human eye, and can relay its decision 
to amplifying apparatus that will indicate 
the color or variation from a standard 
color on a printed chart for a permanent 
and accurate record. 

"This scientific development is an in- 
valuable contribution to the medical pro- 
fession and should abet the high peak of 
efficiency for which physicians are striv- 
ing." 

▲ 

NEW BELL & HOWELL STANDARD 

CAMERA SILENT UNIT "I" 

MECHANISM 

All cameramen are familiar with the 
fixed type of registering pilot pin which 
was an exclusive development of the Bell 
& Howell Company for their standard 
cameras. 

Since the inception of sound, there has 
been a need for a mechanism that would 
give the positive and particularly exact 
registration obtained with the familiar B 



& H pilot pin mechanism, but which would 
be silent enough to use on a sound stage. 
The Bell & Howell Company is, therefore, 
particularly pleased to advise that this has 
been accomplished in the new Silent Unit 
"I" pilot pin mechanism. 

The little roller which engages in the 
main cam is now made of fibre, and the 
two slides which engage on the periphery 
of the main cam are equipped with fibre 
inserts. The oscillating rocker arm and 
register leaf parts are cut away and light- 
ened as much as possible without sacrifice 
of rigidity and safety. 

While these silence the mechanism con- 
siderably, two other improvements have 
been developed for further silencing the 
camera equipped with this mechanism. 

First, the camera itself has been equipped 
with a special cam. The stroke of this 
special cam is about one-half of that em- 
ployed in the regular camera. The idea of 
this is that the shortened cam controls the 
stroke of the register leaves exactly to the 
minimum possible limits of movement nec- 
essary to secure perfect results. The cam 
is arranged so as to prevent the register 
leaves from "slapping" against the aper- 
ture, thus eliminating the main source of 
noise. 

The second improvement is the little ball 
bearing roller assemblies, one set of which 
is installed in the camera frame itself, and 
the other set in the angle plate of the 
mechanism. These rollers serve to control 
the loop. 

All in all, this development represents 
a definite improvement. It is attracting 
great attention due to the fact that the 
mechanism can be readily adapted to take 
bi-pack films, thus giving a silent, color 
camera. By merely interchanging mechan- 
isms, regular black and white pictures can 
be obtained without adjustment to the 
focusing ground glass or any other make- 
shift arrangement for compensating for the 
difference in the focal planes of regular 
and bi-pack films. 

A 

ONE-PIECE DIAPHRAGM WITH 
FLEXING ACTION 

Extreme flexing for easy pumping action 
so essential to full scale reproduction of 
music, together with a one-piece con- 
struction for ready assembly at lowest cost, 
is achieved in the latest type Burtex 
diaphragm developed by the Stevens 
Manufacturing Corporation, 42 Spring 
Street, Newark, N. J. 

The new Burtex diaphragm comprises 
cone, voice-coil mounting, flexing member 
and mounting ring, all in a single piece of 
impregnated cloth. The flexing member is 
in the form of several concentric ridges 
made in the cloth which, at that point, is 
treated by a special process to produce the 
desired degree of pliability. Meanwhile, 
cone, voice-coil mounting and mounting 
ring retain the desired stiffness. 

Instead of the usual practice of an as- 
sembled cone with leather flexing, rim and 
cardboard mounting ring, the new Burtex 
diaphragm is a one-piece unit ready to 
receive the voice coil and be mounted in 
the loudspeaker basket. The flexing mem- 
ber has the desired pliability for a free 
motion of the diaphragm, which is imme- 
diately noted in the bass response and 
general richness of the tone. There is no 
danger of losing the tone quality in mount- 
ing this diaphragm, nor is there danger 
of the diaphragm sagging. Doing away 
with the slow and costly assembly of the 
usual leather mounted cone, and insuring 
a uniform product, the new Burtex dia- 
phragm represents a considerable saving 
in loudspeaker production cost while pro- 
viding a new conception of tone quality. 



AUGUST, 1931 



Page 29 




IN THE HEART 
EVERYTHING: 
WORTHWHILE I 



SINGLE ROOM $ 2°° & UP 
DOUBLE ROOM '3 00 &UP 



Sxcellent ^Restaurant 

BREAKFAST 40' U75' LUNCHEON 85' 



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PopularQieed ,oV 

Coffee Jkof> dfW^b. 




HOTEL 



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ATLANTIC AVE. AND CIOWTM 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 




INTERNATIONAL PRODUCTS 

MEAN 

ASSURED PERFORMANCE 

The Engineering Experi- 
ence which is built into 
International Products is 
your guarantee of unin- 
terrupted performance 
and minimum servicing. 
Revolutionary manufac- 
turing methods make it 
possible to quote prices 
in keeping with present 
day budgets. 

Type B. Condenser Transmitter. 

Type 3B. Microphone Amplifier. 

Complete $1 10.00. 

Type B. (transmitter only) 

$75.00. 

Type 3B. (amplifier only) 

$35.00. 

(Including 25 ft. cord, plugs 

and wall plate.) 

All prices quoted arenetf.o.b. 

Chicago. 

international UroanraBttng iEnmnnumt &o. 

31 12 West 51st St., Chicago, III. 

Manufacturers of a complete line of speech input equipment 




A New Volume Contro 




Front View of a TYPE 652 Volume Control 

7/10ths of Full Size 

Development and a rigorous service test have just been 
completed on a radically new type of volume control for 
mixer control work in recording and broadcast studios. 
Compactness, ease of mounting, and freedom from "whip" 
and dirt noises are important features. 

The attenuation is linear between zero and 45 decibels, 
increasing rapidly but gradually to cut-off beyond. Input 
and output impedances remain practically constant. Three 
values are available: 50, 200, and 500 ohms, each priced 
at $12.50. Write for literature. 

GENERAL RADIO COMPANY 

OFFICES - LABORATORIES - FACTORIES 

CAMBRIDGE A - - MASSACHUSETTS 



Page 30 



PROJECTION ENGINEERING 




Input transformer 
designed for any 
single button mi- 
crophone. 200 ohm 
Primary. 100,000 
ohm on secondary 
side.Listpr 



ed single button 
hand microphone. Two models, "Reg- 
ular" and "Special Home Recording." 
Scientifically damped diaphragm, gold 
plated button, toggle switch, 15-foot 
cord. Finished bronze or gunmetal. 
Dealers, write for our "direct deal." 
Get our complete catalog. 

UNIVERSAL 
MICROPHONE CO., Lid. 

, 1163 Hyde Park Blvd. 
INGLEWOOD, CALIF. 

Microphones $5 to $350. Also cables, plugs, transform- 
ers, mountings, stands, etc. Expert microphone repairs. 




WE 



offer to manniac« 
tuxers interested in 



EXPORT 

tne services of a. dependable organization* 
well established in the entire foreign field 

AD, AURIEMA, Inc. 

Manttf acturers' Export Managers 

116 Broad Street, New York, N. Y. 



i Public Address Equipment ► 



< MILES REPRODUCER CO. ► 

Pfi F 9?!10CT UFItf VI\DK rMTV f 



Complete equipment 
for every branch of 
Sound Engineering at 
exceptionally attrac- 
tive prices. Send 
for free catalog B. 
Depl. B. 



26 E.22^ST 



NEW YORK CITY [ 



<w* 



Let's Go! 

THE autumn season will see a 
stepping-up of manufacturing 
and sales activities throughout the 
sound and visual industries. 
Advertising in the September issue 
of Projection Engineering will have 
a great influence in determining 
who will get the major part of the 
Fall business. 

Extra copies of the September 
issue will be distributed from our 
booth at the New York Electrical 
Show. 

Tell the 9,000 paid subscribers to 
Projection Engineering the com- 
plete technical story of your 
products. 



Forms close 
August 25th 




BASS BARGi&NGRAM 

Issue 202 Ready 
FREE! The Classic of Bargain Lists. World's 
largest stock of. Motion Picture Cameras and ac- 
cessories. Professional and Amateur. Save real 
money. Send for your copy. Free! 

BASS CAMERA CO. 

179 W. Madison St. Chicago, 111. 



\0m\ 



INDEX TO ADVERTISERS 



30 



Ad. Auriema, Inc 

Amplion Products Corp 3 

B 

Bass Camera Co 30 

Bell Equipment Corp Second Cover 

Blue Seal Sound Devices, Inc 27 



Cameron Publishing: Co 32 

Claroslat Mfg. Co., Inc Back Cover 



Gates Radio & Supply Co 6 



General Radio Co 29 

H 
Hoffman-Soons 25 



International Broadcasting Equip- 
ment Co 29 



M 
Miles Reproducer Co 

N 
National Carbon Co., Inc. 



30 



Phototone Equip. Corp. of America, 
The 25 

R 

Racon Electric Co., Inc Third Cover 

S 
Samson Electric Co 5 

TJ 
Universal Microphone Co., Ltd 30 

W 
Weber Machine Corp 6 



AUGUST, 1931 



Page 31 




^ 



ROUND ROBIN" 












5^' 



^> 



^-S>" 






• • V V * 




Group 
Subscription 
Rate 

(The subscription rate 
for individual subscrib- 
ers is $2.00 a year.) 






*Will you not co- 
operate with us by 
classifying subscrip 
tions sent in as follows: 

(M) Manufacturer 

(Pleaie check "M" If you are a pur- 
chasing agent, production manager, 
plant superintendent or foreman.) 

(E) Engineer 

(T) Technician 

(D) Distributor, Contractor 

Dealer or Service Man 

(P) Projectionist 

* Note — Please write in your 
occupation if other than 
those listed above. 










5^ ve ' 



**«&&" 



Page 32 PROJECTION ENGINEERING 

AMATEUR M OVIE CRAFT 

A book of 160 pages fully illustrated with photographs and diagrams covering 
the making and showing of motion pictures. 



Selecting a Movie Outfit — Motion Picture Cameras — Motion Picture Projec- 
tors — Suit Case Projectors — Lenses — Condensers — Lighting and the Cam- 
eraman — Backlighting — Filters — Fast Lenses — Interior Lighting Equip- 
ment — Spotlights — Diffusion of Light — Floodlights — Modeling with Light 
— Screens — Reflecting Surfaces — Illumination vs. Distance — Color Filters — 
Motion Picture Film — Titles and Sub-Titles — Cartoon Titles — Trick Cinema- 
tography — ■ Animated Cartoons — Making of Cartoon Pictures — Cutting and 
Editing Film — Putting on a Show — Motion Picture Projection — Making-up for 
Movies — Accessories for Making and Showing of Motion Pictures. 



PRICE ONE DOLLAR 



TALKING MOVIES 



120 pages illustrated with photographs and diagrams. Some Early Efforts of Talk- 
ing Pictures — A History of the "Talkies" Since 1900 — Sound on Film — Sound 
on Wax — Conversion of Sound into Li ght — Reproduction of Sound — Phono 
Film — Movietone — Vitaphone — Use of Photo-Electric Cells — Sound Picture 
Studios — Etc., Etc. 

PRICE ONE DOLLAR 



CAMERON'S ENCYCLOPEDIA 



ON SOUND PICTURES 



Recording Sound on Film — Recording Sound on Wax — Faders — Amplifiers — Photo-Electric 
Cells — Exciting Lamps — Control Panels — Remote Controls — Speakers — Sound Values 

— Sound Absorption — Distortion — Microphones — W. E. Equipment — R. C. A. Equipment 

— Cutting Sound Film — Background Noise — Theatre Acoustics — Mechanical Filters — Ex- 
ponential Horns — Faulty Synchronization — Volume Levels — Baffle Boards — ■ Portable 
Equipment — How to Check Sound Equipment — Etc., Etc. 

33 5 pages crammed full of Sound Picture information that you require daily. 

PRICE THREE DOLLARS FIFTY 

CINEMATOGRAPH ANNUAL 

Technic of Recording Control for Sound Pictures — Non-Theatrical Motion Pictures — Cinema- 
topgraphy Simplified — Studio Lighting — Pictorial Beauty in the Photoplay — Light Filters — 
Optical Science — Evolution of Film — Cinematics — Painting with Light — Motion Picture 
Make-up — Color Rendition — Nature of Sound — Sound Recording — R. C. A., Movietone, 
Western Electric — Reproduction in the Theatre — Dubbing Sound Pictures — Wide Film — 
Etc., Etc. 

675 pages. 48 page Pictorial Section. 

PRICE FIVE DOLLARS 

DEMAND CAMERON BOOKS 

CAMERON PUBLISHING COMPANY, WOODMONT, CONN., U. S. A. 



On Land 
In Air • 



RACON Products 

Have Proven 

Their SUPERIORITY 



Throughout the world leading Sound 
equipment manufacturers have placed all types 
and makes of horns, speakers and units on 
exhaustive laboratory test. Engineers in nearly 
every case have chosen Racon Products as 
being the acoustically perfect, most adaptable 
Sound reproducers for Sound distribution. 

Whether or not you are satisfied with 
your present sound reproduction, Racon assures 
you there is still room for improvement. Let 
us study your problem. 

There is a Racon for every Purpose 

Top illustration shows Racon Horn No. 5325. an 
air column chamber approximating 10 ft. 30 inches 
deep, bell 34 x 44 inches, weight 55 lbs. with frame. 
Ideal for Theatres with small space between screen 
and wall. 

Lower illustration is the new 4 unit aeroplane trum- 
pet. 54 inches long with 30 in. bell, weatherproof, 
demountable — the super Public address horn for 
long range and tremendous volume weighs 30 lbs. 

Racon's Electro Dynamic Horn Units are recognized 

as the finest that money can buy. Natural tone 

volume "with Racon. 





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 



Write for Catalog 



RT7i . • r^ Inc - 
aeon iilectric L^o* 

FACTORIES : 

18 TO 24 WASHINGTON PLACE, NEW YORK 

TORONTO, CANADA 



LONDON, ENGLAND 




HOME, PORTABLE OR THEATER 

TALKIE 
PROJECTORS 

give finest results with 

CLAROSTAT 
CONTROLS 

Speed Controls 

Clarostat Compression 
type Rheostat gives mi- 
crometric control of speed. 
Has been adopted as 
standard equipment by 
some of the largest manu- 
facturers of portable pro- 
jectors. 

Made in various resist- 
ance ranges from 10 ohms 
up to 10 megohms, and in 
five sizes up to 250 watts. 



Volume Controls 

Clarostat Volume Controls are absolutely quiet, 
long lived units, with special alloy contactor and 
windings to avoid thermal e.m.f. Made in simple 
potentiometer or dual and triple units for constant 
impedance work to meet exacting needs of sound 
industry. Insulated or grounded shaft and bushing, 
as desired. 

New model Graphite Element Potentiometers for use 
where extra high resistances are required. These have the 
revolutionary Geared Roller Contact for long life and silent 
operation. 

Clarostat Mfg. Co., Inc. 

285 N. 6th Street, Brooklyn, N. Y. 




SEPTEMBER, 1931 



PROJECTION 




Arlington Race Track, Chicago. 
Insert: Panels of Public-Address System Used. 




THE JOURNAL OF THE SOUND AND LIGHT PROJECTION INDUSTRIES 



BELL 

PORTABLE TALKIE EQUIPMENT 

for 35 M. M. 

SOUND-ON-FILM 



dj gT 



^ 



! i \ w'- 



A PORTABLE SOUND-ON-FILM PROJECTOR that is really portable, in fact as well as in 
name. Designed by acknowledged experts in the projection and electrical fields, who, 
knowing by experience the rigid requirements necessary to meet in the Amusement, 
Industrial and Educational fields have, in designing Bell Equipment, not only met all of these 
requirements, but have anticipated many, by the incorporation of important features that no 
other designers have considered. 

Bell Equipment, in ease and certainty of control, freedom from fire hazards, automatic lubri- 
cation, quality of projection, and in compactness and portability, is far in advance of all 
known development in equipment of this type. 

Bell Equipment is, in short, a real portable adaptable to all portable uses, which in per- 
formance duplicate the results obtained with the most advanced models of de luxe theatre 
equipment. 



THE BELL SINGLE or Industrial Unit is provided with 1000 
ft. or 2000 ft. reels and magazines, and consists of one 
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THE BELL TANDEM UNIT is designed in right and left 
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FACTORY: Hershey Metal Products Co., Derby, Conn. 



SEPTEMBER, 1931 



Page I 



The Show 

. . . . MUST Go On 





F 



ROM the beginning of the motion picture industry, on 
through the many stages of rapid development. National 
Carbon Company research engineers have kept in mind that 
unwritten law of the theatre — the show must go on. That 
is why National Projector Carbons are dependable. 

Larger theatres, longer throw, sound, color and wide film 
have each, in turn, made their demands. Each new devel- 
opment has called for greater volume of illumination, for 
higher current through these slender pencils of carbon, for 
more intense crater brilliancy. 

Extensive research and constant improvement in manu- 
facturing methods have enabled National Projector Carbons 
to meet each new demand. Their brilliant white light pro- 
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that the shoic WILL go on. 



NATIONAL 

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National Carbon Company will gladly cooperate with 
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NATIONAL CARBON COMPANY, INC. 



Carbon Sales Division » Cleveland, Ohio 
j l| 1 and Carbon Corporation 



Unit of Union Carbide 



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. Ill 



SEPTEMBER 
19 3 1 



Number 9 



Contents 



PAGE 

Editorial 4 

Adjustments for Light Valve Recording 

By C. B. Gordon Sale 9 

Increasing the Usefulness of Theatre Sound Equipment 

By Gordon S. Mitchell 1 1 

Splices at Sound Track 13 

Madison Square Garden Takes the Sound Cure 14 

Sound Projection Practice, Part I 15 

Nitrocellulose Motion Picture Film 18 

A New, Dependable, Low Cost Portable Sound Unit. ... 23 

Departments 

News of the Industry and New Developments 24 

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 



Sanford R. Cowan 
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. 



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. and Canada. Yearly subscription rate $3.00 in foreign countries. 



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SEPTEMBER, 193 



A SURVEY stated recently 
WHAT PER CENT ^ t0 have been conducted 
DIALOGUE? among "more than one hun- 

dred" exhibitors, is reported 
to have shown that approximately 25 per cent, 
dialogue is "the right amount." 

The question submitted was: "What do you 
consider the proper amount of dialogue for 
the general run of pictures?" The exhibitors 
interrogated are reported to have indicated 
varying quantities from 20 per cent, and "no 
more than the footage previously used for 
titles," to 7S per cent, "in certain cases, de- 
pending upon the picture," with the average 
working out as 30 per cent. 

The exhibitors queried as to whether their 
patrons would welcome "a return to all si- 
lents," all replied "no," "doubtful," or gave 
similar negative replies. 

It is interesting to learn that numerous ex- 
hibitors recommended that better utilization 
of musical background should be employed 
in film productions. 

From our understanding of the situation 
the percentage reported appears quite low. 
Of course, it is to be recognized that there is 
a difference between per cent, of pictures with 
sound, and per cent, of dialogue per picture. 
It may be that if the questionnaire were sent 
to as many as 1000 managers located in rep- 
resentative districts that the percentage of 
dialogue would be nearer 50 than 30. 



Y ARIOUS well organ- 
SOUND AND ized surveys have been 

PICTURE carried on with the object 

PROJECTION of learning whether advan- 

IN EDUCATION tages may not be gained in 

public and high school in- 
struction by employing the facilities of sound 
and light projection. 

It was necessary only for parents to note 
from time to time the voluminous pronounce- 
ments emanating from church organizations 
to the effect that the modern "movie" is a 
powerful influence for good or for evil. 
Whether in any picturization the influence is 
good or evil, it is realized that the movies are 
attention compelling and effective in transfer- 



ring ideas and knowledge from one person to 
another. 

To utilize to the full these ready facilities 
for formal instruction in schools it will be 
necessary to enlist the interest of educators 
and Boards of Education. Also, some agency 
outside of present educational direction will 
have to work out a new technique of instruc- 
tion which will provide more useful and less 
expensive methods of instruction than those 
now in use. 

The present widespread dissatisfaction of 
educators themselves, and the swelling tide 
of criticism by the public, in regard to the 
present product of American educational in- 
stitutions, presents a situation which is a real 
opportunity for a revolution in instructional 
methods and in educational material. 

Another element, and one which is likely 
to apply expedition to present surveys, is that 
the growing cost of education per year per 
pupil has in recent years added burdens to 
taxpayers which quickly will have to be 
lightened. It is here that modern equipment, 
a new technique of education, and a revision 
of ideas as to what constitutes useful educa- 
tion, enter for serious consideration. 

If those who are giving thought to this 
subject, in a promotional way, recognize that 
the thing they have to sell is more useful edu- 
cation, more thoroughly taught, and at low- 
ered costs, they will succeed in a period of 
time perhaps directly proportional to the 
completeness with which these three require- 
ments are met in what they propose. 

It will not do to try to sell to present school 
officials something to be added to present fa- 
cilities. This would no doubt suit these offi- 
cials best, but would defeat the requirement 
of lower costs. The system that can be sold 
to the people is one that will replace much 
of the antiquated, bureaucratic organization 
now in control, a system that will relieve 
taxpayers of excessive costs and one that 
will make possible a school product better 
equipped for respectable, gainful employ- 



ment. 




onJck^WHlic 



crL 



Editor 



SEPTEMBER, 1931 p age 5 

Department of Public Instruction 

WASHINGTON, D.C. 

« jt \T*y "The U. S. Army, Navy, Marines, The Bureau of 

/Jjf\ JL iS • Standards, The United States Veterans Bureau, and 
practically every other government department using 
motion pictures like ourselves, rely on the Cameron 
technical books for our knowledge of the motion 
picture industry." 

"There are no series of books in the whole Library 
of Congress as much used as those by Cameron." 

THE LEAGUE OF NATIONS 

(CINEMATOGRAPH INSTITUTE) 

sy jt vjrsy "Mr. Cameron is one of the very limited number 

^J^-J X *J / °f technical writers on cinematography really worth 
reading." 

"His books are of particular interest because, al- 
though essentially technical and based upon theoretic 
principles, they are nevertheless within the grasp of 
any reader wishing to acquire a knowledge of the 
sound-film in all its aspects." 

U. S. DEPT. OF COMMERCE 

(MOTION PICTURE SECTION) 

fy jt *tm These books (Cameron's) should be in the posses - 

ljjp% JLiJ / s > on °f every projectionist, theater manager and every- 
one interested in receiving authentic information re- 
garding the application of sound to motion pictures. 
Cameron's books are a worth while contribution to the 
motion picture industry. 

AND — AFTER ALL 

IT'S WHAT THE USERS OF YOUR PRODUCT SAY 

THAT REALLY MATTERS 

The Cameron Publishing Company have been publishing books on motion pictures for the past 
14 years, these books are used throughout the world as the standard works on the subjects. 
They are complete, up-to-the-minute and accurate. The projectionists and theatre managers 
not only of this country and Canada but also of Australia, South Africa, India, England and 
elsewhere depend on these books for their technical knowledge of the motion picture business. 

CAMERON BOOKS ARE KNOWN AND USED THE WORLD OVER-THEY 
CAN BE OBTAINED FROM ALL MOTION PICTURE SUPPLY DEALERS- 
OVER 300 BOOKSTORES CARRY THEM. 

A LIST OF OUR PUBLICATIONS SENT ON REQUEST 

CAMERON PUBLISHING COMPANY, W00DM0NT, CONN., U. S. A. 



Page 6 



PROJECTION ENGINEERING 




a RACON for 

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Page 8 



PROJECTION ENGINEERING 





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Projection Engineering 



SEPTEMBER, 1931 



Adjustments for light 
valve recording 



By C. B. Gordon-Sale 



THE general arrangement and de- 
tails of the light valve and its 
recording machine are fairly well 
appreciated throughout the indus- 
try but there appears to be a certain 
amount of misunderstanding as to its 
usage. In the following brief article, 
therefore, a few notes are given on the 
subject which it is hoped may prove of 
interest to those who, while associated 
with the recording side of the industry, 
are not yet definitely called upon to 
operate the machine themselves. 

In the first place the light valve is 
attached to the base of the recording 
machine between the recorder lamp and 
the film driving mechanism. It is of 
two distinct parts ; first, the field coil, 
and, second, the light valve proper 
which carries the loop of duralumin rib- 
bon which modulates the light beam. 
The mound shaped projection on the 
light valve over which the loop passes 
actually forms one pole of a magnet and 
the magnetic circuit is completed only 
when the light valve is screwed in posi- 
tion. The slit through the centre of this 
projection is continued through the core 
of the electromagnet. In fact, one may 
consider the whole device as a hollow 
electromagnet, the modulating beam 
passing directly through the aperture, 
its path being interrupted in the gap 
by the ribbon. The slit in the central 
pole pieces is .008 inch wide. When 
the light valve is fastened in position 
the gap between the poles of the electro- 
magnet itself and the light valve proper 
is approximately .010 inch and therefore 
the flux density is very high, making for 
the greatest possible efficiency. So im- 
portant is cleanliness to the operation of 



For proper film record- 
ing lamp and ribbon must 
be accurately adjusted. 



the light valve that the yoke when not 
actually being used is removed from the 
machine and kept in a dessicator com- 
pletely free from moisture and dust. 

Stringing the Valve 

The actual stringing of the light valve 
is a delicate operation akin to that of 
fitting cords to a violin or similar type 
of musical instrument. Before a light 
valve is attached to a recording machine 
it has to be examined under a micro- 
scope, preferably calibrated, so that 
gaps and similar dimensions can be 
checked. An essential is that the slit 
through the yoke should be absolutely 
parallel ; unless this be the case there 
is considerable probability of light leak- 
age during heavy modulation. A little 
consideration emphasizes this necessity, 
since the small section of ribbon is only 
just sufficient to enable maximum move- 
ment to take place without the edge of 
the slot being exposed. Maximum 
modulation is in fact reached when the 
two sides of the ribbon are moved £)02 
inch, that is to say .004 apart. Al- 
though naturally all parts have been 
carefully inspected in manufacture and 
after passing from the stores, the limits 
of accuracy demanded are so fine that 
clumsiness in shipment or in handling 
may easily throw the light valve out of 
adjustment. The assembly of the ribbon 
to a light valve yoke is accomplished 
by means of a special jig. First of all 
the tensioning roller is adjusted so that 
it lies at an angle of 45° to a line pass- 
ing through the long dimension of the 
slot. The four spacing rollers are then 
opened out so that they are about one 
eighth inch apart. A strip of ribbon 
just under a foot long is then taken and 
one end inserted in the slot in the cap- 
stan screw. Two or three turns of this 
screw are then given and the ribbon is 
threaded through the jaws over the pole- 
face and around the spring tension 
roller, and, finally, in the same manner 
back to the second capstan screw where 
it is given a couple of turns. Any ex- 



cess ribbon is then cut off. In per- 
forming this operation the greatest care 
must be taken that no twists occur. It 
is not sufficient to ensure that twisting 
is not apparent on the finished job. 
More than this the actual handling must 
be such that not the slightest kink is 
introduced as otherwise it is bound to 
show up in recording even though not 
apparent to the eye. Rough adjustment 
then takes place by means of the capstan 
screws which are rotated until the ten- 
sion arm stands exactly at right angles 
through the line passing through the 
longest dimension of the slit in the pole 
yoke. 

Examination 

When the above operations are com- 
pleted the jig carrying the light valve 
is placed under a microscope and ex- 
amined minutely to see that the edges 
are perfectly straight. At this junction 
it is well to point out that sometimes 
there are inherent faults in ribbons 
which render them unfit for recording 
even though they are treated properly 
in threading. The manufacture of 
duralumin ribbons for light valves is a 
specialized art and, in fact, demon- 
strates forcibly the great improvements 
of recent years in wire drawing. On no 
account should ribbon showing the 
slightest defect be employed as it is 
quite possible for a small piece of ap- 
paratus like this to cost a very large 
sum both as regards spoiled film stock 
and also in time wasted looking for 
trouble. In the writer's experience 
troubles in the first place attributed to 
faulty film have finally been traced down 
to defects of light valve ribbons. This 
might not be the case were the person 
stringing the valve in attendance dur- 
ing recording but this cannot always 
be depended upon. 

The parallelism of the two sides of 
the ribbon is adjusted with the device 
itself still under the microscope, the 
usual set being such that the inner or 
adjacent edges of the ribbon are about 
.002 inch apart and equally spaced on 
both sides of an imaginary centre line 
passing lengthwise through the slot. 

Tuning 

The light valve has to be tuned so 
that it has a natural frequency of ap- 
proximately 7,000 cycles per second. 
The reason for this is that there shall 
be no peak effect within the usual mus- 
ical ranee. Nevertheless, the rising fre- 



Page 10 



PROJECTION ENGINEERING 



quency response makes its presence felt 
somewhat below the actual point of 
tuning, but this is generally to the good 
since the sum total of sound processes 
in the recording chain usually leaves a 
drop off at higher frequencies. Inci- 
dentally it may be mentioned that in the 
oscillator method of recording tuning 
takes place somewhat lower, usually 
round about 6,000 cycles where under 
modern conditions the peak definitely 
makes its presence apparent on the 
sound track. Putting the matter 
briefly : in tuning the light' valve a cir- 
cuit oscillating at 7,000 cycles per sec- 
ond is connected directly to the light 
valve which therefore vibrates at the 
same frequency modulating the beam 
of light from the recorder lamp which 
falls directly upon a photoelectric cell 
included in the body of the recording 
machine. This is connected via a series 
of amplifiers to a film indicator. The 
tension of the ribbon in the light valve 
is then gradually increased and as soon 
as the resonant frequency of 7,000 
cycles is reached the indicator needle 
gives a definite "kick" due to natural, 
and forced vibrations becoming syn- 
chronized. 

Considerable experience is necessary 
before tuning can be carried out with 
accuracy, for, although there is a def- 
inite kick in the reading of the film in- 
dicator, this is usually preceded by a 
gradual rise. If the ribbons are tight- 
ened any further the meter reading be- 
gins to fall. Adjustment of the tension 
should therefore aim to be such that the 
maximum deflection of the meter takes 
place. In practice it is common to 
achieve the greatest accuracy by ac- 
tually passing the 7,000 cycle mark and 
then slightly relieving tension so as to 
return to the actual figure. The reason 
why this is better than straight tuning 
is not always appreciated. 

Careful tests show that the reason for 
higher accuracy is that by de-tuning 
slight frictional effects on the various 
parts of the contacting path of the rib- 
bon are relieved. If, instead, tension- 
ing alone is carried out, friction is 
bound to be developed, and in practice 
it will gradually become relieved, there- 
by resulting in a fall of the point of 
resonance. Of course, when we speak 
of frictional effects in the case of a de- 
vice of this type we are referring to 
quantities entirely microscopic in char- 
acter and discernible only to the most 
sensitive of instruments. 

Sometimes trouble arises because the 
roller on the tension arm is not running 
perfectly free. This causes the two 
sides of the ribbon to be differently 
tensioned, thus producing a double 
resonance point which is highly objec- 
tionable. When tuning the light valve 
a careful check should always be made 
to ensure that such a condition does not 



exist. This test is carried out by vary- 
ing the frequency of the oscillator 
coupled to the light valve from between 
about 3,000 to 8,000 cycles per second in 
operating steps of 200 cycles. If fric- 
tional effects be present, there will be 
two definite peaks to the reading of the 
meter. As a matter of fact it is almost 
a physical impossibility for both sides of 
the ribbon to resonate at exactly the 
same frequency, and tuning is con- 
sidered satisfactory providing the two 
resonant points fall within 100 cycles 
of one another on either side of the 
nominal tuned frequency of 7,000 cycles. 
If this check indicates that there is 
something amiss, it is a good plan to 
slightly decrease the tension of the 
ribbons and at the same time lightly tap 
the tension roller, being careful not to 
touch the ribbon itself. Metal should 
not be employed for this purpose, an 
ordinary lead pencil serving quite well. 
Another method utilizes the fact of the 
existence of two capstan screws. In 
other words, tuning takes place not from 



| QUESTIONS AND ANSWERS 

T n an early issue of Projection j 

| J. Engineering will appear a I 

I new series of technical questions j 

I for projectionists. The correct I 

j answers will be published in 1 
I subsequent issues. 

| It is probable that examina- \ 

= tions will be held which will give j 

j opportunity to students to show | 

I how thoroughly they have studied. 1 



one side of the ribbon alone but from 
both sides. Theoretically, this is the 
best method for tuning, but naturally it 
takes somewhat longer. 

When everything is found satisfactory 
the screws should be carefully locked in 
place with a steady though not violent 
effort. This by the way, is important as 
brute strength is likely to affect the 
resonant frequency. 

When tuning is complete the light 
valve is removed from the field coil and 
the parallelism of both sides of the 
ribbon is again checked by microscope. 
Sometimes the operation of tuning 
affects this other factor and the four 
spacing screws have to be adjusted 
once more. The error, however, is 
likely to be very slight indeed and in 
case of emergency it may not be neces- 
sary to check the resonant point. 
However, wherever possible such 
checking should take place. When 
testing and carrying adjustments on 
the light valve make sure that the speech 
connections to both sides of the ribbon 
are broken prior to the field current 
being turned either on or off. If this 
procedure be not adhered to the sudden 



change of flux may seriously damage 
the ribbon itself even to the extent of 
burning it out. 

The Recorder Lamp 

The adjustment of the recorder lamp 
is another operation requiring more 
than a moderate amount of care. The 
lamp itself is usually of the 6-volt 
variety taking about 14 amperes and is 
fed from a 12-volt storage battery, the 
potential of which is adjusted by means 
of a rheostat and controlled by an 
ammeter. First of all the image of the 
filament has to be focused on the pole- 
face of the field coil. For convenience 
the light valve is usually removed dur- 
ing this operation. By adjustment of 
the rheostat the filament current is 
usually cut down to some 7 or 8 
amperes which sharpens the filament 
image making it easier for focusing. 
First of all the lamp is adjusted ver- 
tically until the strip of light appears 
centrally upon the pole-piece slot. Next 
lateral adjustment takes place by slack- 
ening off the clamping nuts and moving 
the lamp backwards and forward until 
the image on the filament appears 
sharp ; all lock nuts are then tightened. 
As is apparent the procedure is prac- 
tically identical with that employed in 
setting the exciting lamp in projecting 
mechanisms. 

Mean Density 

So that the effect of the unmodulated 
light valve shall produce the mean 
density value of sound track the light 
intensity of the recording lamp has to 
be carefully adjusted by means of the 
rheostat control. To this end each re- 
cording lamp has to be calibrated. First 
of all the lamp is fixed in the manner 
previously described and then a length 
of film is run through the machine at 
recording speed with both field coil and 
light valve on open circuit. The fila- 
ment current of the recording lamp is 
then changed in steps of an ampere 
through a range of 10 to 18 amperes. 
Greater current than this should not be 
passed through the lamps even for the 
shortest of periods as otherwise they 
may suffer damage at least to the extent 
of shortening their service life. The 
density of the resultant unmodulated 
sound tracks can then be measured in 
the usual manner by means of a densito- 
meter after developing to the customary 
gamma value. An exposure of a sensi- 
tometric strip on the test sample of 
film is necessary. The densities of the 
different exposures are then plotted 
against filament current and when 
joined by a curve present the calibration 
data desired. Without going further 
into technical details it will be apparent 
from this curve that the mean un- 
modulated density may be determined 
(Concluded on page 22) 



SEPTEMBER, 193 



Page I I 



Increasing the 
usefulness of 
theatre sound 
equipment 

By Gordon S. Mitchell* 



IN many motion picture theatres it 
has become practice to increase the 
usefulness of the sound amplifica- 
tion and projection equipment. It 
will be the purpose of this paper to 
point out some of the uses, other than 
for audible picture presentation, to 
which this apparatus may be put — to 
show the application of theatre sound 
projection apparatus to more or less 
orthodox public-address use. 

There has been manufactured for use 
with theatre equipment a set which al- 
lows the regular projection equipment 
to be used for paging members of the 
audience or for making announcements 
of coming attractions or other timely 
topics which it might be desired to place 
before the audience. This set com- 
prises a microphone, a control and 
switch panel and associated equipment 
which makes it possible to project the 
microphone output over the regular 
theatre horns. " 

The usual practice is to have the 
announcing equipment placed either in 
the theatre manager's office or in a 
small acoustically treated room adjacent 
to the projection booth. The micro- 
phone is the usual two-button carbon 
microphone with an associated cord and 
plug which fits into a jack on the con- 
trol box. On the control box there are 
two signal lights, which are so con- 
nected that the green light goes on 
when the circuit is cleared from the 
projection booth and signifies to the 



*Electrical Engineer, Sound Department, Uni- 
versal Pictures Corpn. 



Theatre auxiliary sound 
equipment has many uses 
in the modern theatre. 




The Prince of Wales using his Filmo movie camera at Arequipa, Peru. 
His brother, Prince George, is directly behind him. 



announcer that all is ready for him to 
go ahead. The announcer then throws 
the key on his control box, which lights 
the red light and signifies that the sys- 
tem is open throughout and that the 
announcer is "on the air." The booth 
equipment is modified somewhat when 
the system includes announcing facil- 
ities. A switch panel on the amplifying 
rack in the booth contains a key which 
allows the system to be operated on syn- 
chronous or non-synchronous reproduc- 
tion or for announcing through the mi- 
crophone. This panel also contains 
signal lights which visually show which 
type of reproduction the system is set 
for and a light which indicates to the 
projectionist when the announcer is on. 

On this panel also is a repeating coil 
with which are associated the circuits 
for supplying current to the buttons of 
the microphone and the jacks into 
which may be inserted a plug connected 
to a meter for measuring this micro- 
phone current. There is a relay which 
embraces a pair of normally closed con- 
tacts which short circuit the output of 
the repeating coil (also mounted on this 
panel), which is operated by the key 
on the announcer's control panel. Thus 
current is furnished the buttons of the 
microphone only so long as the key on 
the announcer's panel is on the "an- 
nounce" position. This places final con- 
trol of the system in the hands of the 
announcer. 

The setup of equipment allowing au- 
dible announcements to pass through 
the theatre system is simple. At a 
predetermined point in the program — 
rehearsal of this portion is of as great 
importance as rehearsal of the stage or 
picture portion — the announcer inserts 
the plug of the microphone into the 
proper jack and awaits the signal from 
the booth that the system is in readi- 
ness. The projectionist brings his fader 
to zero and simultaneously throws the 



key to the "announce" position on the 
control panel. This lights the green 
light indicating to the announcer that 
it is okay for him to go ahead. He then 
throws his key, thus energizing the 
microphone and placing himself "on 
the air." A rehearsal will have indi- 
cated whether or not it is necessary to 
change the volume setting for the an- 
nouncements depending upon the pecu- 
liarities of the announcer's voice and 
his distance from the microphone. 

For Stage Presentations 

An application of public-address 
principles to theatre use which has be- 
come widespread of late is in reinforc- 
ing the audible portions of stage pre- 
sentations. In the larger de luxe houses 
throughout the country it has become 
usual practice to present a prologue fea- 
turing dancing and singing in conjunc- 
tion with the picture portion of the 
program. These presentations often- 
times may be increased in effectiveness 
by a judicious use of sound amplifica- 
tion equipment. 

The microphones are usually placed 
in the footlight trough, or if special 
conditions necessitate, about the stage 
concealed by vases or other props. The 
control equipment is usually mounted 
on a separate rack, either in the projec- 
tion booth or at some point backstage 
where the operator can see all that 
transpires and regulate his equipment 
accordingly. (The services of an ad- 
ditional operator other than the reg- 
ular projectionist is in general neces- 
sary when using sound equipment in 
this manner). 

On the control equipment rack there 
will be eight panels, including a mis- 
cellaneous equipment panel, two jack 
panels, two volume control panels, a 
volume indicator panel, a rheostat and 
key panel, and a horn control panel. 
The microphone circuits from the stage 



Page 12 



PROJECTION ENGINEERING 



terminate in jacks on one of the jack 
panels, which provides for twenty mi- 
crophone circuits. By means of patch 
cords any one of these microphone cir- 
cuits may be connected to jacks on the 
second jack panel which in their turn 
are connected through an individual 
control channel to the main volume con- 
trol circuit. There are eight individual 
control circuits for supplying current 
to the microphones, with a means for 
measuring and controlling the current 
in each circuit. 

Circuit Control 

The circuits are so arranged that all 
control channels in use are connected 
through a common output circuit which 
leads to the main volume control poten- 
tiometer on the second volume control 
panel. A signal lamp mounted on this 
panel indicates that the amplifiers in 
the projection booth are ready for ser- 
vice. An amplifier is provided at the 
control rack in order that the loss en- 
gendered in the control and switching 
circuits may be compensated for, and 
also that the voice currents may be 
reinforced before being despatched to 
the main amplifiers if necessary. The 
main amplifiers, of course, remain under 
the control of the projectionist in the 
1 booth. 

In order to maintain the illusion of 
reality, the horns should be placed as 
near the stage as possible, although 
care must be exercised in order that 
the microphones are not placed in front 
of the projectors or singing in the sys- 
tem will result. It is of interest to note 
that for this type of work, an ordinary 
horn will give good results. A horn 
which responds to a narrower fre- 
quency band will serve the purposes 
of audible reinforcement, although it 
would prove unsatisfactory for project- 
ing sound for motion pictures. This 
makes it possible to use a folded ex- 
ponential type horn with a six-foot air 
column, which horn may be mounted 
behind the proscenium arch and above 
the stage for the stage presentations 
when it is impossible, due to architec- 
tural features of the building to place 
the regular horns in such a position 
that they will operate satisfactorily in 
this service. It is important that the 
horns projecting this portion of the 
program be carefully placed or unsatis- 
factory results will follow. The entire 
illusion of reality depends upon proper 
placement of the projector horns. If 
it is impossible to place the horns in 
such a position that the sound seems to 
be coming from the stage direct, either 
behind cut out grille work above the 
stage or behind the proscenium arch 
above or at the sides of the stage, it will 
oftentimes be possible to hang a large 
ornamental fixture from the ceiling con- 
taining a projector horn, so decorated 



that it will harmonize with the sur- 
rounding architecture. 

As before mentioned, an operator 
should be at hand who is responsible 
for the operation of the equipment dur- 
ing the stage portion of the show. After 
determining that the microphone cir- 
cuits are clear, the projectionist throws 
a switch which places, control of the 
system in the hands of the operator who 
then becomes the most important sin- 
gle factor in the success or failure of 
the presentation. The operator is able 
to follow proceedings on the stage by 
vision and with the aid of a monitor 
horn and visual volume indicator. 
Equipment is provided with a shelf just 
below the volume control panel upon 
which the operator can rest his arm. 
This is a very desirable feature inas- 
much as it is generally necessary to 
constantly adjust the controls in order 
to follow the changes on the stage. 

A Typical Installation 

The Pantages Theatre in Hollywood 
presents an interesting illustration of 
the use of sound equipment for enhanc- 
ing the beauty and effect of stage pre- 
sentations. This theatre is relatively 
new and embraces all of the innovations 
which are to be found in most up to 
date theatres. The theatre uses ampli- 
fication equipment for reinforcing the 
volume of the audible portion of the 
stage presentations, making the smallest 
voiced performer heard easily through- 
out the auditorium. 

There recently appeared in a stage 
presentation a young lady crooner, who 
is rather noted among her acquain- 
tances for her small voice. This young 
lady had achieved a measure of success 
in singing over the radio, where by 
microphone technique she was enabled 
to retain the low volume characteristics 
of her voice and increase thus the pleas- 
ing qualities for which she is known. 
However, several of her friends were 
rather doubtful of her ability to project 
her voice sufficiently in the theatre. A 
pleasant surprise was at hand for these 
doubters — many of whom, untrained in 
the arts of sound amplification are still 
wondering just how it was done. 

At the rise of the curtain, the young 
lady was seen standing upon a raised 
platform, with what was ostensibly a 
music rack placed slightly to one side 
and a bit in front of her. On this stand, 
concealed from the audience was placed 
a microphone which served to pick up 
the weak voice waves. These waves, 
electrically converted, were passed 
through amplifiers and projectors on to 
an unsuspecting audience. So expertly 
was the presentation handled that the 
performer was able to sing in a very 
low voice, retaining all the intimacy of 
that type singing, and her voice was 
amplified and projected in such a man- 



ner as to leave the audience unaware 
of the electrical aid given. 

In addition to the regular features of 
such an installation, the equipment in 
this theatre is used to bring out and in- 
crease striking orchestral effects during 
the overture which is a weekly feature 
of the program. A microphone is placed 
in the orchestra pit near the instrument 
or group of instruments which it is 
desired to feature. Microphones placed 
on short stands just in front of the 
ornamental railing which surrounds the 
orchestra (out of sight of the audience) 
serve to pick up the remainder of the 
instruments. Thus by a manipulation 
of the mixing control, the music from 
the desired instrument or group is made 
to stand out high above the rest of the 
orchestra. Of course, when such effects 
are attempted extreme care must be ex- 
ercised or the performance will be over- 
done and the effect lost. 

The equipment in this theatre is so 
arranged that in case of a breakdown of 
the regular sound projection equipment, 
the public-address system may be used 
as a substitute. The public-address sys- 
tem comprises separate projectors, am- 
plifiers and controls and in effect places 
an entirely separate substitute sound 
system at the disposal of the manage- 
ment should trouble develop. The con- 
trol equipment is housed in a sound- 
proof booth adjacent to and on a level 
with the projection booth, the two being 
connected by both visual and telephonic 
communication systems. Six large and 
separate projectors are placed around the 
proscenium arch, as well as one extra 
large projector placed directly over the 
center of the auditorium hanging from 
ceiling. Two small horns high up on 
the ceiling and towards the rear of the 
auditorium take care of the balcony 
seats. 

Broadcasting From the Theatre 

The Pantages Theatre is also con- 
nected with one of the chain broadcast- 
ing systems, broadcasting the stage pre- 
sentation direct from the theatre weekly. 
All controls for the broadcast of pro- 
grams from the stage are handled from 
the public-address booth. 

Another use to which sound equip- 
ment installed in the theatre may be 
put is in aiding the director in rehears- 
ing stage presentations. Probably the 
foremost exponent of the use of sound 
amplification equipment in rehearsing 
his shows is S. L. Rothafel. It has 
been well said that a Roxy presentation 
is a combination of the man himself and 
his sound equipment. The perfect co- 
ordination of every presentation at the 
Roxy Theatre is a direct result of the 
use of public-address equipment. 

Loudspeakers are placed throughout 
the theatre at strategic points through 
which Roxy is able to address anyone 



SEPTEMBER, 1931 



Page 13 



in his crew whom he may wish to in- 
struct. Men backstage at the light 
switchboards, the electrician's control 
board, the Kino booth and on the stage 
spot bridges may be addressed direct 
by Roxy who sits far back in the thea- 
tre with a microphone through which 
he issues his orders. The lighting ef- 
fects, for which this theatre is so fa- 
mous are executed with almost light- 
ning like rapidity. The director gives 
an order into the microphone and sees 
it almost instantly carried out ; he can 
change his order immediately if the ef- 
fect achieved does not please him. This 
use of the loudspeaking system direct 
does away with the old method of is- 
suing orders into a telephone to a stage 
manager, with the consequent delay 
necessitated by the relaying of the order 
through a third part}-. 

Even during the first few perform- 



ances of a new presentation, Roxy sits 
in the audience, a small transmitter near 
at hand through which he issues orders 
for any changes he may desire. The 
system is then connected to small loud- 
speakers located backstage near the elec- 
trician's board and the spot bridges. 

The system has been set up so that 
with a small modification of equipment 
a microphone may be connected into the 
circuit and placed backstage, enabling 
the men to answer any question asked 
by the director or call for additional 
instruction if necessary. This modifi- 
cation permits maximum flexibility to 
be achieved by the system as used for 
directing rehearsals. 

The application of sound equipment 
in the theatre to uses other than the 
projection of motion picture sound en- 
genders no new principles of operation. 
As a concluding thought it should be 



borne in mind that with the operator 
of the equipment — (exactly as does the 
success of the sound motion picture ul- 
timately depend upon the projectionist) 
— lies the responsibility for the success 
or failure of the presentation. While 
this responsibility, although present, is 
not of such great importance in uses 
other than for the reinforcement of the 
audible portions of the stage show, it is 
of extreme importance in that partic- 
ular application. The equipment opera- 
tor may nullify the efforts of many per- 
sons in presenting a suitable production 
to the audience by an unsatisfactory 
manipulation of the controls. Hence 
it is of the utmost importance that if 
satisfaction is to be realized from the 
use of the equipment, the operator be 
fully cognizant of his responsibility. 
Upon him rests final responsibility for 
the success of the presentation. 



AAA 



Splices at sound track 




X IMPROVED system of 
treating the sound track at 
splices — a system eliminating 
methods of painting and at the 
same time successfully silencing splice 
noise — has come onto the market. The 
new method was described to the in- 
dustry more than a year ago, but pro- 
duction of the necessary "blooper 
patches" and the simple block for ap- 
plying them has only recently made it 
applicable in processing laboratories 
and projection rooms. 

The introduction of this equipment 
came as a result of many requests that 
followed the announcement of the new 
patching process. The wide interest 
shown indicated that expenditures in- 
volved in acquiring tools to make the 
patchers and the patches would be justi- 
fied. 

The patching system obviates a con- 
dition in which imperfect painting of 
the sound track at splices frequently 
caused noises as objectionable as the 
extraneous sounds made by the repro- 
ducing system when an untreated patch 
went through. The older method caused 
more dissatisfaction in projection rooms 
than in laboratories, where skilled work- 
ers painting the sound track at hundreds 



An Improvement in 
sound track splicing meth- 
ods which results in silenc- 
ing splice noise, is a for- 
ward step which is worth 
noting. 



of splices a day attained proficiency in 
the process. Even in the laboratories, 
however, it is believed that greater 
speed, together with assured accuracy, 
can be gained by the use of the new 
patching process. 

In seeking a solution to the problem, 
the Eastman Kodak Research Labora- 
tories first tried gummed paper, then 
decalcomania transfers, and then an 
opaque film material; but none of these 
materials for patches proved entirely 
satisfactory. 

The material finally adopted was a 
very thin clear film base, coated with an 
emulsion and exposed and developed to 
produce opacity. The patches are five 
perforations long and they are cut in 
a shape designed to cover the sound 
track completely for a distance equal 
to the width of a standard splice, but 
tapering away toward each extremity 
until the sound track is entirely ex- 
posed. When a properly mounted patch 
passes through the reproducer the light 
reaching the photoelectric cell from the 



fiBRraJft&^^A ,^^^^A A 




Fig. 1. Sound track splice. 



Fig. 2. The patcher. 

sound record is reduced gradually to 
an insignificant intensity and so con- 
tinues until the splice has passed, after 
which the light passing through the 
sound record gradually attains its orig- 
inal intensity. The resulting diminu- 
tion of sound lasts not long enough to 
be perceptible. 

Mounting of a patch, after completion 
of a splice, is very similar to the process 
of splicing. Four pins on the patcher 
fit the film perforations so closely that 
pressure clips for holding the film in 
place are unnecessary. A single stroke 
of a camel's hair brush is sufficient to 
apply cement to the shiny side of a 
patch, which comes into contact with 
the shiny side of the film. Five sec- 
onds' pressure with the pressure plate 
of the patcher is sufficient to permit drv- 
ing of the cement. 



Page 14 



Madison Square 
Garden takes the 
Sound Cure 



audience of approximately 18,000 
people. The value of 7.65 seconds was 
obviously much greater than optimum 
or beat reverberation time of 3.0 sec- 
onds, which experience and theory indi- 
cate is most suitable in an enclosure of 
this size. 

Analysis revealed that instead of 
absorbing sound the ceiling reflected it 
into the seating areas. Since the ceil- 
ing is very high, these reflections came 
back to the audience as echoes and con- 
tinued to circulate around the arena as 
reverberation. In addition, the large 



By means of a new, suspended ceiling of sound absorb- 
ing material, the big arena is modernized for sound 
transmission. 



AMERICA'S most famous in- 
door sports auditorium has 
taken the sound cure. The 
official diagnosis called the 
principal trouble excessive reverbera- 
tion. Further analysis revealed the 
presence of too much noise and of 
acoustic reflections from some of the 
surfaces of the auditorium which caused 
echoes. All of these deficiencies com- 
bined to produce low intelligibility, re- 
sulting in complaints from customers 
that they could not understand the 
announcements from the center of the 
huge arena. 

The public-address system assured 
adequate amplification so that the sound 
of the announcer's voice was loud in 
every part of the hall. The volume of 
sound was not enough alone to make 
the speech understandable. The public- 
address system was not at fault and the 
announcer was not at fault. The sound 
rolled around, producing a phenomenon 
called reverberation and echoes to such 
an extent that words could not be 
understood. Even when the hall was 
filled to capacity, the most favorable 
condition for the intelligible transmis- 
sion of sound, the results were unsatis- 
factory. 

The first step taken was to make a 
complete acoustic survey of Madison 
Square Garden. A series of measure- 
ments using the reverberation meter 
and other acoustic measuring apparatus 
revealed a condition of excessive re- 
verberation and the existence of a noise 
level far too high for satisfactory hear- 
ing conditions. Graphic analysis of the 
plans of the arena, in connection with 
the data obtained from measurements, 
revealed the cause of the trouble and 
specifications were prepared covering 
the alterations which would have to be 
made to produce good conditions. 

Reverberation tests showed a vari- 
ation from 7.65 seconds with the audi- 
torium empty to 2.96 seconds with an 



PROJECTION ENGINEERING 

amount of noise which entered the 
arena through the windows and from 
the entrances and lobby space reflected 
around the auditorium so that its 
volume was greatly intensified. 

Two alternates were suggested to 
remedy this condition. First, covering 
the present ceiling with a material hav- 
ing a very high absorbing value, or, 
secondly, constructing a suspended ceil- 
ing beneath the sockets of the existing 
trusses, the suspended ceiling to be 
composed of sound absorbing materials. 

The second course of treatment 
offered a somewhat greater improve- 
ment since in addition to introducing a 
large amount of acoustic absorption of 
the auditorium, it reduced the effected 
volume by several million cubic feet. 
The second alternative was decided 
upon and plans were drawn to erect a 
ceiling framework consisting of struc- 
tural angles, which was hung from the 
trusses. Sections of sound absorbing 
rock wool blanket having an absorption 
of more than 50 percent., and which 
were self-supporting, were made up 
and laid into place on the steel frame- 
work. This makes it possible to re- 
move sections whenever necessary in 
order to replace lights or hang lines for 
special events. 

It took about ten days' time and 

$35,000.00 to give Madison Square 

Garden the sound cure. Alterations 

were all made under the supervision of 

(Concluded on page 22) 



View of new acous- 
tic ceiling installed 
in Madison Square 
Garden to elimi- 
nate excessive rev- 
erberation and im- 
prove acoustic 
conditions. 




SEPTEMBER, 1931 



Sound 
projection 

practice 



Page 15 



Part 



THE Sound Committee, in prepar- 
ing this report, has confined itself 
mainly to a consideration of the 
status of present-day practices in 
sound recording and reproducing. Some 
study has also been given to the possi- 
bilities of standardization as well as to 
those items which might well be investi- 
gated further. 

Good Practices Recommend 

Where a practice has proved itself 
worthy of usage it is the plan of the 
committee to recommend it for stand- 
ardization to the Standards Commit- 
tee of the society. It is recognized that 
in an art so comparatively young as 
sound recording and reproducing, care 
must be taken against premature at- 
tempts at standardization. The progress 
of development is so rapid and the tech- 
nic of recording and reproduction is 
undergoing adjustment so quickly that 
premature attempts at standardization 
might prove a hindrance rather than a 
help. On the other hand, the moment 
any phase of the art becomes stabilized, 
it should be presented at once as a mat- 
ter worthy of standardization through- 
cut the industry. 

In this report the committee intends 
to show a cross-sectional view of the 
newer and more important phases of 
sound recording and reproducing. It is 
not intended that the material presented 
here shall encroach upon the activities 
of the Progress Committee although 
there may unavoidably be some slight 
duplication. 

Suggestions For Betterment 

Neither the Committee nor the So- 



ciety now has facilities to carry on in- 
vestigations, but it can recommend 
what is of importance for further pro- 
gress in the art. The Committee, there- 
fore, feels it may be of considerable 
service in presenting to the Society and 
to the industry matters on which work 
should be done. Some of the items 
which have been suggested to the Com- 
mittee as worthy of consideration have 
already received sufficient study to per- 
mit the formation of definite recom- 
mendations. In these cases, arguments 
for and against are presented and the 
Committee's conclusions submitted. 

Status Report 

Directional Sound Detectors. A di- 
rectional sound detector comprises a de- 
vice in which the efficiency of response 
is a function of the angle between the 
direction of incident sound and a refer- 
ence axis in the system which coincides 
with the direction from which it is de- 
sired to receive the sound. 

In general, there are two principles 
used in directional sound detectors, one 
amplifies the sounds desired by con- 
centrating them and the other avoids or 
suppresses the unwanted sounds. Horn 
and reflector types employ both prin- 
ciples. The ribbon microphone and ab- 
sorptive baffle make use of only the 
second. 

Horns. Horns have been long used in 
conjunction with various types of sound 
reception apparatus, but have not been 
used for high-quality pickup due to the 
difficulty of obtaining a good frequency 
characteristic in spite of the apparent 
efficiency of this type of unit. 

Reflectors. The use of reflectors for 
the reception and focusing of sound is 
well known. In order to receive sound 
pressure variations over a wide fre- 
quency range, it is necessary to use a 
reflector having large dimensions. With- 
in practical limits of size, a reflector is 
likely to have a characteristic which 
will be better at the high end of the 
frequency scale than at the low end, 
although compensation for this effect 
can be applied. 

Combination of Horn and Reflector. 
It is possible to combine the horn and 
reflector principles in a device which 
has a fairly good resultant frequency 
response. The directional properties, 
however, as limited by the design of a 
horn and a reflector, may not be uni- 
form with frequency. 

The directional characteristics of 




Report of the Sound Committee of the Society of 

Motion Picture Engineers, Presented at the Hollywood 

Meeting, June, 1931. H. B. Santee is chairman of 

this committee. 



H. B. SANTEE 
Sound Committee, S. M. P. E. 

these devices have been found useful 
in eliminating undesired sounds and 
noises, particularly where the sound 
which it is desired to pick up is weak. 
The effectiveness has been greater for 
outdoor work where there is no reflected 
sound than for use in studios where 
reverberation is encountered. 

Ribbon Microphone. A properly de- 
signed ribbon microphone may be made 
very directional. Its directional charac- 
teristic is practically independent of 
frequency because of its dimensions, 
and, by virtue of its directional effect, 
increases the distance from which ac- 
ceptable sound may be picked up, in 
spite of the fact that it receives a rela- 
tively small amount of energy due to its 
size. It is also particularly effective in 
reducing unwanted sounds, such as cam- 
era noises and the like. 

Absorptive Baffle. It has been found 
possible to design an absorptive baffle 
for a microphone in such a way that 
any sound coming from a direction not 
included in the throat angle of this ab- 
sorptive structure will reach the dia- 
phragm at a very much reduced in- 
tensity. This structure, while fairly 
large in dimensions in order to obtain 
the necessary absorption, is not depen- 
dent entirely upon the wavelength of 
the lowest frequency for its minimum 
dimension since the wave front remains 
practically undisturbed. This arrange- 
ment, of course, is no more efficient 
than the microphone would be without 
the absorptive device, but its sharp se- 
lectivity of the direction from which it 
effectively receives sound makes it ap- 
pear promising. 

Camera Silencing Devices 

Silencing of cameras became neces- 
sary with the advent of talking pictures. 



Page 16 



PROJECTION ENGINEERING 



While the ideal method would be to use 
a silent camera, until such perfection is 
attained, it is necessary to place the ex- 
isting cameras in some form of silenc- 
ing box. This, in the first place, took 
the form of a camera booth large enough 
to house one or more cameras and the 
cameramen. Being extremely cumber- 
some and heavy, it was in some cases 
very difficult to place on a set and of 
necessity soon gave way to handier 
methods. 

During this preliminary stage, much 
thought and work went into the meth- 
ods of camera maintenance which re ■ 
suited in their being brought to a higher 
state of mechanical perfection than had 
ever before been attempted in the in- 
dustry. It was also found that the com- 
monly used means of interconnecting 
the camera and the camera drive motor 
by a flexible shaft was a great source 
of noise. This camera drive was a de- 
velopment of talking picture equipment 
which the weight of the early motors 
made necessary, as it was not practical 
to hang much weight on the camera 
structure. 

At this period each studio investigated 
camera silencing in its own way. By a 
process of experimentation and elimina- 
tion, the present-day devices were evolv- 
ed. They are by no means ideal and 
are being continually changed and im- 
proved. The generally accepted opinion 
is, of course, that the ultimate solution 
of this problem will depend on the de- 
velopment of a silent camera which it 
will not be necessary to enclose. 

In camera booths, the natural develop- 
ment was along the lines adopted by 
most studios (with a few exceptions), 
that is, an individual camera enclosing 
box which, in its early stages, was 
simply a wooden framework covered 
with various sound insulating materials. 
This did not silence the camera suf- 
ficiently to permit its use within fifteen 
or twenty feet of a microphone and it 
was soon replaced by more efficient de- 
signs. It is unnecessary to follow the 
various stages of this development, but 
from a survey of the present-day equip- 
ment it is easy to see that it is simply 
an elaboration of this silencing box. 

The new camera silencing devices 
became known as "blimps" or "bunga- 
lows." In the majority of cases the 
bungalow was made to contain the drive 
motor as well as the camera. Some of 
the studios adopted a form of drive 
motor which was mounted directly on 
the camera ; others retained the flexible 
shaft but enclosed it inside the bunga- 
low. One or two of the studios made 
separate bungalows for the motor and 
the camera, and covered the flexible 
shaft with heavy layers of sound in- 
sulating material. 

The Fox Movietone Studios adopted 
as standard a camera bag composed of 



rubberized cloth, kapoc floss, and other 
soft insulating materials, fastened by 
means of zippers and snaps. The lens 
and finder protrude through the bag. 

With the adoption of the heavy bun- 
galow covered camera, a very much 
stronger and more rigid camera-tripod 
became necessary. The bungalows used 
by Warner Brothers and United Artists 
are light enough to mount on the stan- 
dard tripod. Most of the other studios 
adopted either a tripod which was de- 
veloped by Metro-Goldwyn-Mayer in 
collaboration with Pathe, or else an 
adaptation of this, used in conjunction 
with a standard tripod for rigidity. 

The Academy of Motion Picture Arts 
and Sciences, under date of May 14, 
1930, published through their Technical 
Digest Service, Report No. 3 of the 
Producers-Technicians Committee re- 
lating to camera silencing. This report 
gives in detail a complete resume of all 
such devices in use at that time. It in- 
cludes information on the insulating 
value in decibels, the methods of con- 
struction, materials used, and the dis- 
tance that a microphone can be used 
from the camera. 

Noiseless Recording Methods 

The noiseless method of recording on 
film, announced at the end of 1930, ap- 
pears to be receiving general accept- 
ance throughout the industry. RCA 
Photophone has described two methods 
of effecting noiseless recording on va- 
riable width track. One of these dis- 
places the zero line on the track in such 
a manner that the clear portion is only 
just wide enough to carry the modula- 
tion. This is subject to the disadvan- 
tage that weaving in the projector may 
cut off some of the weaker sounds. The 
second method uses a movable shutter 
during the recording which causes the 
clear part of the sound track to become 
blackened in those portions which are 
not employed to carry the modulation. 

The Western Electric Company has 
announced a noiseless recording system 
which is applied to their variable den- 
sity method. The density of the sound 
track is increased during the intervals 
in which the sound volume is low, and 
is decreased according to the envelope 
of the sound currents in such a manner 
that the film is always just able to ac- 
commodate the required modulation. 

The Fox organization has devised a 
means for flashing lamp variable den- 
sity recording, in which the intensity of 
the lamp is reduced during the inter- 
vals of low sound amplitude, the inten- 
sity being altered during the process of 
recording. 

A number of independent makers of 
sound equipment, most of whom are 
using the flashing lamp, have announced 
attachments to their equipment which 
produce essentially similar effects. 



The reduction of noise is accomplish- 
ed during the actual recording by an 
attachment to the recording system, 
and, in general, involves no change in 
recording or processing technic. The 
amount of noise reduction which is be- 
ing employed in most studios at ' the 
present time is of the order of 10 db. 

Set and Studio Acoustics — 
Theatre Acoustics 

Extensive investigations have been 
made by many interested in the factors 
concerned in set and studio acoustics 
and theatre acoustics. In some cases 
these studies have been made with re- 
cently developed instruments, permit- 
ting more accurate results than those 
previously obtained by aural methods. 
Several factors have been discovered by 
such means, some of which have con- 
tributed to the development of a more 
general formula for the computation of 
the time of reverberation. The applica- 
tion of this formula, which has been 
published by Dr. C. F. Eyring, of the 
Bell Telephone Laboratories, is of par- 
ticular value in set and studio work, 
where average absorption coefficients 
are comparatively high. Important 
studies of the effect of relative humidity 
on sound absorption are being made. 

The necessity for consideration of the 
reverberation existing throughout the 
frequency spectrum is now well appre- 
ciated. Whereas many enclosures had 
in the past been acoustically treated, 
giving consideration only to the rever- 
beration at 512 cycles, experience -in 
many of these cases indicates the neces- 
sity for obtaining suitable balance be- 
tween the reverberation at the low and 
high ends of the frequency spectrum 
relative to that in the central portions 
of the range. It is becoming the prac- 
tice to adjust theatres and recording 
studios to have times of reverberation 
throughout the frequency spectrum such 
as will give definite rates of decay for 
sounds of equal loudness. With the ap- 
plication of suitable accurate instru- 
ments for the measurement of rever- 
beration times, studies have been made 
of the relative effects of connected vol- 
umes, which have an important bearing 
on complex auditoriums, as well as on 
recording sets on large stages. Further 
study, by instrumental means, has in- 
dicated the effect of direct reflection to 
be of importance and requiring consid- 
eration in the design of auditoriums, in 
addition to the consideration given the 
reverberation time. 

The importance of maintaining a very 
low noise level has been extended to 
cover not only the studio, but the the- 
atre. This has become more necessary 
with the development of recording- 
methods insuring a lower background 
level in the sound picture. Attention 
must be given to the transmission of 



SEPTEMBER, 1931 



Page 17 



noise from the projection room into the 
theatre, from the ventilating systems, 
from sources external to the auditorium, 
and to miscellaneous noise sources 
within the auditorium. 

More information is available upon 
the acoustic power required to provide 
satisfactory sound volume in an audi- 
torium. It is, therefore, possible to pre- 
dict more accurately what effect the in- 
troduction of absorbing material into 
an auditorium will have upon the sound 
volume and, where necessary, upon the 
electrical requirements of the system. 

Many improvements have been noted 
in existing commercial materials and a 
large number of new materials suitable 
for studio and theatre use have been de- 
veloped and introduced in the past year. 
This has considerably widened the field 
for obtaining materials having the de- 
sired acoustic characteristics for the 
particular application and which will be 
more readily acceptable from the stand- 
points of architectural appearance, fire 
hazard, and cost. 

Preservation of Sound Prints 

The Committee has been fortunate in 
receiving from a firm prominent in the 
film industry the results of tests, con- 
ducted over a period of two years, of 
processes which purport to preserve 
motion picture film. The method used 
in these tests was to prepare loops of 
film, half of which were processed and 
half unprocessed, both sections being 
taken from the same reel or roll. These 
loops were projected 300 times, with 
examination at 100, 200, and 300 run- 
nings, on a specially prepared projec- 
tion machine, which caused as little 
wear as possible. 

The processes tested were such as 
lacquer, surface hardening, whole sur- 
face waxing, chemical impregnation, 
liquid edge waxing, etc. 

The noticeable effect of the processes 
investigated was that the film became 
seasoned more quickly, so that during 
the first few times of projection, the 
emulsion did not collect on the shoes 
and tracks of the projection machine as 
is often the case with green emulsion. 
There was also indication' from this 
set of tests that liquid edge . waxing 
provides comparable protection. Once 
past this initial period, however, it was 
not evident that the processes provided 
any material improvement in giving 
greater lasting qualities to the film. 

Talking Motion Picture Equipment 
for Home Use 

In recent years several talking mo- 
tion picture equipments have been de- 
veloped and offered for sale for home 
use. Practically all of these equipments 
use a 16 mm. projector with either a 
flexible shaft or geared connection to a 
synchronous turntable for disc repro- 



duction of sound. All the devices ex- 
amined, except one, project 24 pictures 
per second and employ a turntable driven 
at ZZ l /i r.p.m. This one exception pro- 
jects 16 pictures per second and the 
projector and turntable are driven by 
electrically interlocked motors. In order 
to maintain synchronism with the 2>2> l A 
r.p.m. turntable, every third frame is 
removed in printing from the negative 
to the positive. 

At the present time 16 mm. films syn- 
chronized with sound are difficult to 
obtain and are expensive. If an extend- 
ed library of films were available, it is 
probable that a larger demand would 
appear for home talking movies. To 




GLENN E. MARTIN 
Progress Committee, S. M. P. E. 

date, the supply of films is extremely 
limited and these films are available 
only in the larger centers, requiring 
personal application to obtain them and 
personal return. This mitigates against 
very extended use of these films and is 
a serious detriment toward obtaining a 
large market for the reproducing equip- 
.ment in the home. 

Talking Motion Picture Equipment for 
Non-Theatrical Uses 

Considerable demand is apparent for 
talking motion picture equipment for 
non-theatrical uses, this equipment to 
be used either for advertising purposes, 
instruction work, in schools, churches, 
etc. Equipment for this purpose is built 
by all the leading talking motion picture 
apparatus manufacturers. The trend 
seems to be toward a 35mm, film with 
sound on the film, although some equip- 
ment has been built with the idea of 
using 16 mm. film and a synchronized 
disc, which permits a picture of suf- 
ficient size and brilliance of illumination 
for small audiences. Libraries are be- 



ing developed which will undoubtedly 
stimulate the exploitation of such equip- 
ment. 

Sound Equipment in Theatres 

On January 1, 1931, there were re- 
ported to be in the United States 13,515 
theatres equipped for sound reproduc- 
tion and 8,209 theatres unequipped. It 
might, therefore, appear that during the 
period of sound equipment installations 
only about 63 per cent were completed. 
Many of the theatres now running- 
silent, however, are unprofitable houses 
which may never be able to afford 
sound equipment. With the decreasing 
number of silent picture releases, these 
theatres may be forced to close. It fol- 
lows, then, that the installation period 
is well over 63 per cent completed. Per- 
haps 80 per cent would not be too high 
a figure. 

It may be considered that the indus- 
try is passing out of the installation 
period and is now entering a period of 
stability in operation and of refinement. 
The novelty value of sound has passed 
with every indication that sound has 
become as necessary a factor in the 
theatre as is the picture on the screen. 

The first problem of theatre projec- 
tion is obviously to keep a picture on the 
screen and to maintain sound from the 
horns. It so happens that statistics 
from Electrical Research Products, Inc., 
are available, which show the ratio of 
emergency calls to theatre installations 
in the United States over a period of 
time. In December, 1928, with roughly 
a thousand theatres equipped, the ratio 
of emergency calls per week to theatres 
in service was about 0.185. In Decem- 
ber, 1929, with 3300 theatres equipped, 
the ratio had fallen to about 0.05. In 
December, 1930, when nearly 5,000 the- '. 
atres were equipped, the ratio was as 
low as 0.022. This decrease in emer- 
gency calls is caused by improvements 
in design and manufacture, and to prop- 
er and continued maintenance of the 
equipment. It is logical to believe that 
the operating troubles experienced with 
other reputable systems follow some- 
what the, same general course. It is con- 
sequently obvious that the first require- 
ment of sound projection, namely, con- 
sistent and reliable operation, has been 
achieved. The quality of sound now 
focuses our attention. 

Poor theatre acoustics constitutes one 
of the most serious causes of poor 
sound reproduction in theatres. Acous- 
tic analyses have been made in a large 
number of theatres and corrections of 
the conditions have been made in some 
cases. It often happens that the the- 
atres less able financially to make the 
correction need it most. It has been 
proved in so many cases that improved 
acoustic conditions result in increased 
(Continued on page 22) 



Page 18 



Nitrocellulose 
motion picture film 



The regulations of the National Fire Protection Asso- 
ciation for the handling and storage of motion picture 
film, as here presented, have been voted upon affirma- 
tively by a majority of the association's committee 
covering this subject. 



T 



HE Fire Underwriters' rules and 
their application, follow : 



1. Application of rules. These 
regulations are intended to apply to the 
storage and handling of nitrocellulose 
motion picture film, in all places except 
establishments manufacturing such film 
and storage incident thereto. They are 
not intended to apply to the storage and 
handling of film having a cellulose ace- 
tate or other approved slow-burning 
base nor to photographic and X-ray 
film. ( See separate regulations on Pho- 
tographic and X-ray Film.) 

2. Scope of regulations, (a) These 
regulations are intended to provide 
reasonable provisions for the storage 
and handling of motion picture film, 
based on minimum requirements for 
safety to life and property from fire. 

(b) The intensity of heat and 
rapidity of combustion of burning film 
are such that it is highly preferable that 
occupancies, such as film exchanges, 
laboratories and studios, be permitted 
only in sprinkled buildings of fire- 
resistive construction. In many sections 
of the country buildings of inferior con- 
struction have been adapted to such oc- 
cupancies, under which circumstances 
it is essential that proper consideration 
be given to protective devices, such as 
automatic sprinklers ; and that all verti- 
cal openings, between floors, as elevator 
and stair shafts, be fully enclosed, and 
that adequate exit facilities be provided. 
Such features are most essential from 
the safety to life standpoint. These 
regulations are based on the assumption 
that such features are properly taken 
care of by building ordinances. Suitable 
requirements will be found in the 
Recommended Building Code of the Na- 
tional Board of Fire Underwriters. 



■■Ill 



3. Arrangement of regulations, (a) 
These regulations are divided into two 
parts: Part I gives general provisions 
regarding the storage and handling of 
film; Part II gives special provisions 
for special occupancies as motion pic- 
ture theatres, exchanges, laboratories, 
and studios, which apply in addition to 
any and all of the general provisions 
which may also be applicable. 

(b) The grouping of the special 
provisions under the heading of special 
occupancies is merely for convenience 
in the application of these regulations. 
Any particular process or operation in 
any type of occupancy shall be governed 
by the provisions given for that process 
or operation, whether under the heading 
of that occupancy or any other heading, 
unless otherwise specifically provided 
herein. For example, any process in a 
studio which, from the standpoint of 
the authority enforcing these regula- 
tions, partakes of the same nature as 
some process covered under laboratories, 
shall be governed by the provisions for 
that process given under laboratories. 

4. Approval of plans. Before con- 
structing any building for use as a 
motion picture film occupancy, or re- 
modeling any building for such oc- 
cupancy, or building any film vault, or 
installing any motion picture projection 
booth or screening room, complete plans 
of such proposed construction or in- 
stallation shall be submitted to the in- 
spection department having jurisdiction 
for approval. These plans shall show 
in detail all proposed construction and 
structural changes and the means of 
protection to be provided, the heating 
system with the protection for it, the 
electrical equipment, and the character 
and location of all exposures. 

5. Definitions. Whenever used in 



PROJECTION ENGINEERING 

these regulations the following words 
shall be construed as having the mean- 
ings given below. 

(a) "Film" or "motion picture film," 
motion picture or sound recording film 
having a nitrocellulose base, whether in 
the form of unexposed film, positives, 
negatives, scrap, or used film. 

(b) "Vault," a vault constructed and 
equipped in accordance with the re- 
quirements of Section 17. 

(c) "Cabinet," a cabinet constructed 
and equipped in accordance with the re- 
quirements of Section 16. 

(d) "Standard roll," a roll of film 
\yi inches (35 mm.) wide and 1000 feet 
long, weighing approximately 5 pounds, 
used as a unit in calculating the weight 
of film. 

Note : The weight per 1000 feet, of 
70 mm. and other widths of film will 
vary approximately as the width. 

(c) "Partition," except where some 
other form of construction is specified, 
a partition constructed in accordance 
with the specifications given in sub- 
section 112. 

Part I. General Provisions Regarding 

the Storage and Handling of 

Motion Picture Film. 

Section II. Construction and Arrangement 
of Buildings 

111. Motion picture film should pre- 
ferably be stored or handled only in 
buildings of fire-resistive construction. 

112. Partitions, (a) All rooms in 
which motion picture film is stored or 
handled, except motion picture projec- 
tion booths and film vaults, shall be 
separated from each other and from all 
ether parts of the building by partitions 
of suitable stability and having a fire 
retardant classification of not less than 
1 hour as determined by the Standard 
Fire Test. Partitions constructed as 
follows shall be deemed to have the re- 
quired fire retardant classification: 

(1) Hollow clay tile laid in cement 
mortar, cement lime mortar or gypsum 
mortar, not less than 4 inches thick and 
plastered on both sides with not less 
than y 2 inch of gypsum mortar or 
cement mortar ; 

(2) Gypsum blocks, either solid or 
hollow, laid in gypsum mortar, not less 
than 3 inches thick and plastered on 
both sides with not less than Yi inch of 
gypsum mortar ; 

(3) Metal lath supported by incom- 
bustible studs, plastered on both sides to 
fully cover the metal lath and studs with 
not less than Y\ inch of gypsum mortar 
or cement mortar and having a total 
thickness of not less than 2J^ inches ; 

(4) Wood studs covered both sides 
with metal lath and 24 inch gypsum 
mortar or cement mortar, and having a 
total thickness of not less than 5% 
inches. (This type of construction to 



SEPTEMBER, 1931 



Page 19 



be used only in buildings not of fire- 
resistive construction.) 

(b) Partitions shall be continuous 
from floor to ceiling and securely 
anchored to walls, floor and ceiling. 

(c) Openings in partitions shall be 
protected by approved fire doors of a 
type suitable for use in Class C situa- 
tions as defined in the Regulations for 
the Protection of Openings in Walls and 
Partitions Against Fire. 

113. Exits. It is essential that all 
rooms in which film is handled be pro- 
vided with adequate aisle space and safe 
means of egress. Rooms in which film 
is handled and in which more than two 
persons work shall have two or more 
exits, remote from each other. Every 
exit shall be marked "Exit" in letters 
not less than 6 inches high, or by an 
illuminated sign with letters of the 
same height. 

114. Vents. All new buildings 
erected to be used as, and all existing 
buildings remodelled for film oc- 
cupancies shall be provided in every 
room where film is to be stored or 
handled, with vents which will open 
automatically in case of fire. These 
should be of ample size ; they may be in 
the form of automatic skylights or auto- 
matic-opening window sash. All rooms 
in which film is stored or handled in 
existing buildings shall be provided with 
such vents wherever practicable. 

115. Spacing of workers. A feature 
which often contributes materially to the 
hazard to life in film handling rooms is 
the congestion of workers together with 
large quantities of film. To prevent 
such congestion of workers and the at- 
tendant hazard to life, the number of 
persons working in a room where film 
is handled should never be more than 
will result in a ratio of floor area to 
number of workers, less than 35 square 
feet per person. Not over 15 persons 
shall work at one time in any one room 
(not including the stage of motion pic- 
ture studios) in which film is handled. 

116. Tables arid racks. Tables and 
racks used in connection with the hand- 
ling of film (joining, inspection and as- 
sembling tables for example) shall be 
of metal or other non-combustible ma- 
terial. They should be kept at least 
4 inches away from any radiator or 
heating apparatus. Tables shall not be 
provided with racks or shelves under- 
neath them, which might be used for 
keeping film or other materials. 

Section 12. Electrical Equipment 

121. Artificial illumination in any 
room where film is handled or stored 
shall be restricted to incandescent elec- 
tric lights, except that arc lights or 
other forms of electric lights may be 
used in studios. 

122. All electrical wiring and equip- 
ment shall conform to the National 
Electric Code. Wiring shall be in metal 



conduit, and fuses shall be enclosed. 

123. Light fixtures shall be firmly- 
fixed in place and lights shall be pro- 
tected by vapor-proof globes. All lights 
shall be equipped with keyless sockets 
and operated by wall switches. 

124. Light boxes reading "EXIT" 
in letters not less than six inches in 
height shall be placed at the exits of all 
dark rooms. 

125. Portable electric lights on ex- 
tension cords are prohibited in any room 
(not including the stage of motion pic- 
ture studios) in which film is handled 
or stored. 

126. Motors shall be of the non- 
sparking type, or shall be of an enclosed 
type, so arranged as to minimize the 
danger of sparks. 

127. Motion picture projectors shall 
be of an approved type and safeguarded 
in accordance with the requirements of 
the National Electrical Code, Article 35. 

Section 13. Heating Equipment 

131. Artificial heating in any build- 
ing or room, other than a vault, in 



| I j* ROM the life standpoint a § 

I JT^ fire having only a small | 

| property loss may be as disas- j 

I trous as one involving considera- | 

| ble damage. A gruesome tragedy I 

1 is all too likely to occur when a \ 

I fire breaks out in a theatre during | 

| a performance. Even a small fire, \ 

1 with a crowded auditorium and j 

§ panic, assumes tremendous pro- I 

| portions. j 



which motion picture film is used, 
handled or stored, shall be restricted 
to steam not exceeding 10 pounds pres- 
sure or hot water, provided however, 
that this shall not be construed as pro- 
hibiting the installation of an indirect 
system employing high pressure steam 
when the radiators or heating coils of 
such system are not located in the room 
or rooms to be heated. Heat generating 
apparatus shall be in separate room. 

Note : Ordinary hot air furnaces are 
prohibited. Gas, oil and electric heat- 
ers are prohibited in rooms where film 
is handled or stored. 

132. All steam pipes within 6 feet of 
the floor, and where passing through 
partitions or racks or near woodwork, 
shall be covered with approved pipe 
covering. All radiators, heating coils, 
and pipes and returns that are near the 
floor or are so located as to permit any 
combustible material, waste or dirt to 
come in contact therewith shall be 
guarded and perfected by means of 
j4-inch mesh galvanized steel wire cloth 
No. 20 B. & S. Gauge, or by its equiva- 
lent. The bottom of such guards shall 
be arranged so as to lift up for cleaning 



purposes and the tops to slope so that 
guards cannot be used as shelves. 
Guards shall be so constructed that no 
film can come within 4 inches of the 
heating surface, and shall be made with 
a substantial metal framework which 
will prevent the wire mesh being forced 
against the radiator or pipes. 

Section 14. Sprinklers and Other Fire 
Protection Appliances 

141. Every room in which film is 
stored or handled in quantities greater 
than 50 pounds (10 standard rolls), ex- 
cept in motion picture projection booths 
or rooms and rewinding rooms con- 
nected therewith, shall be equipped with 
an approved system of automatic 
sprinklers. Buildings or sections of 
buildings used as exchanges, laboratories 
or studios shall be equipped with auto- 
matic sprinklers, as provided under sub- 
sections 221, 231 and 241. All build- 
ings used for the storage or handling 
of film should be completely equipped 
with automatic sprinklers. 

142. The spacing of sprinkler heads 
in all sections where film is handled 
shall not exceed one head for each 
64 square feet, with heads and lines 
not over 8 feet apart ; provided that in 
the stage section of motion picture 
studios the spacing of sprinklers shall 
not exceed one head for each 80 square 
feet. In existing buildings where the 
spacing of sprinkler heads exceeds that 
specified above, the inspection depart- 
ment having jurisdiction may require 
the installation of additional heads 
wherever the hazard of some machine, 
process, or accumulation of film war- 
rants such protection. 

143. (a) It is recommended that 
two independent sources of water supply 
be provided, acceptable to the inspec- 
tion department having jurisdiction. 

(b) Water supplies for automatic 
sprinklers shall be based on an estimate 
of 20 gallons a minute per head for 20 
minutes for the total number of heads 
in one vault, plus 25 per cent of the 
number of heads in the largest fire area. 
(A fire area is regarded as an area cut 
off by brick or concrete walls having a 
minimum thickness of 8 inches; each 
opening in these walls to be protected 
by one self closing fire door, Class A 
type.) 

(c) Where gravity tanks form the 
primary source of supply they shall be 
elevated at least fifty feet above top 
sprinklers. Minimum capacity of 
gravity tanks shall be 10,000 gallons. 

(d) Due to alterations and resulting 
impairments customary in plants of this 
type sprinkler equipments shall be so 
arranged by the introduction of floor 
and auxiliary control valves, that maxi- 
mum protection can be maintained at all 
times. 

144. Every room in which film is 



Page 20 



PROJECTION ENGINEERING 



stored or handled except film vaults, 
shall be provided with first aid fire ap- 
pliances of types using water or water 
solutions. 

Note : Small hose equipment is 
recommended, and the following types 
of extinguishers are considered suitable : 
Soda acid, calcium chloride, pump tank, 
water pails and loaded stream. 

Section 15. Storage of Film 

151. The storage of motion picture 
film, having reference to amounts of 
film accumulated or laid by for disposal 
or use at some later time, as a few 
hours or longer, shall be in accordance 
with the following rules : 

(a) Except as hereinafter provided 
in paragraph (b), — 

( 1 ) Amounts in excess of 25 
pounds (5 standard rolls) but not in 
excess of 1000 pounds (200 standard 
rolls) shall be kept in approved cabi- 
nets if not in vaults ; 

(2) Amounts in excess of 1000 
pounds shall be kept in vaults. 

(3) Storage for any considerable 
length of time should be in vaults 
only. 

(b) Unexposed film enclosed in the 
original shipping cases, conforming to 
I.C.C. regulations with each roll in a 
separate container, shall be kept in a 
sprinklered room, and if over 5 cases 
aggregating in excess of 750 lbs. (150 
standard rolls) shall be kept in a 
sprinklered room used for no other 
purpose. 

152. Valuable negatives shall be 
stored in vaults used only for such film, 
in suitable heat-insulating containers de- 
signed to minimize water damage. 

Note : The above paragraph being 
principally concerned with safe-guard- 
ing values would not need to be inserted 
in an ordinance. 

Section 16. Film Cabinets 

161. Construction. (a) Cabinets 
including doors shall be of approved in- 
sulated construction. 

Note : Cabinets may be