History of Sound Motion Pictures by Edward W Kellogg Second

History of Sound Motion Pictures

by Edward W Kellogg

Second Installment

History of Sound Motion Pictures

by Edward W Kellogg

Our thanks to Tom Fine for finding and scanning the Kellogg paper, which we present here as a

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John G. (Jay) McKnight, Chair

AES Historical Committee

2003 Dec 04

June, pp 291...302; July, pp 356...374; and August, pp 422...437.

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SECOND INSTALLMENT

History

of

Sound

Motion Pictures

For

the abstract

of

this paper which was presented on May

5,1954,

at the Society’s

Convention at Washington, D.C., see the first installment published in last month’s

Journal.

The Motion Picture Industry

Adopts

Sound

Many Commercially Unsuccessful Eforts.

The historical outline with which our

story began contains a very incomplete

account of the many efforts to combine

sound and picture, some of which at-

tained a fair degree of technical success,

elicited praise and held public interest

for short periods. We mentioned the

work

of

Edison, Lauste, Rumer, and

de Forest, and might add Path6 Frtres

and Lkon Gaumont* in Fran~e.~ Many

of these were ahead of their time, for

without amplifiers, the production of

adequate and natural sound was prac-

tically impossible. Even after amplifiers

became available the experimenters had

little better success in getting picture

producers seriously interested. The ar-

ticle by Lovette and Watkin~~~ states

that by the end of 1924 practically every

major producer in Hollywood had

re-

jected Western Electric’s sound-picture

system.

Economic Hurdles.

The same authors

give such a convincing statement of the

financial obstacles from the producer’s

standpoint that

I

cannot do better than

quote them:

“The motion picture producers had

large inventories of silent films, which

had cost millions to produce. They

had great numbers of actors and ac-

tresses under long term contracts, most of

whom knew no dramatic technique

except that of pantomime. The industry

was universally equipped with stages and

studios suited only to the silent film

technique.

“Moreover, world-wide foreign mar-

kets had been established for silent

films. To serve these markets, it was

merely necessary to translate the words

printed upon the film from English to

any language desired. Finding stars and

supporting casts who spoke the various

languages of the world, or finding ways

to give the illusion of their speaking

them, appeared to be an insuperable task.

*

Gaumont, in addition to many inventions

and other activities, was a pioneer and successful

leader in the motion-picture business, and prob-

ably came nearer to success with phonograph

sound than others.

See account, and references

given in the Theisen history5 from which ref.

77

is

taken.

“The art of the silent film had at-

tained superb quality and the public

was satisfied. Why then, producers

asked, should Hollywood scrap the

bulk of its assets, undertake staggering

conversion costs, and force upon the

public a new and doubtful experimental

art?

“Nor

were the exhibitors equipped

for sound. Many, it was argued, would

not be able to meet the cost of sound

picture equipment.”

These obstacles would not have pre-

vented the producers from introducing

synchronized sound, had they been con-

vinced that it would give their pictures

greater appeal. A factor which many

developers of sound equipment probably

did not fully recognize, was that to

contribute to the illusion, the sound must

have a degree of naturalness far

sur-

passing that which had sufficed for simply

transmitting information, or making

words understood.

How

It

Looked

in

7926-7.

To many,

the silent motion picture, with its freedom

of action, its settings for much of its

action in natural backgrounds, was

better entertainment than stage drama,

and when one tried to imagine what a

talking motion picture would be like,

one’s thoughts immediately turned to

examples of theater drama.

I

have

already quoted some of Dr. de Forest’s

reflections. The prevailing thought at

the General Electric Co. as our system

began to take shape is probably typical.

Many, even of the most enthusiastic

advocates of the sound-picture develop-

ment were not convinced that the chief

function of the synchronized sound would

be to give speech to the actors in plays.

The art of telling stories with pantomime

only (with the help of occasional titles)

had been

so

highly developed, that

giving the actors voices seemed hardly

necessary, although readily possible.

Such a view was actually a very high

tribute to the movie makers of the silent

era. However, a very large business in

synchronized sound seemed assured (even

without any use of the system for dia-

logue) in furnishing sound effects, back-

ground music, and providing voice for

lectures, speeches and travelogue com-

mentary.

By

EDWARD

W.

KELLOGG

As

one who shared in this misjudg-

ment,

I

would like to suggest to readers

that it is difficult today to divest oneself

of the benefit of hindsight. At that time,

the principal examples of sound pictures

we had seen were demonstration films,

very interesting to

us

sound engineers

working on the project, but scarcely

having entertainment value. None of

us

had seen a talking motion picture with a

good story, and picture and script well

designed for the purpose. When in 1927

such a picture was shown

(The Jazz

Singer)

the story, the music and the

dialogue were splendidly adapted to

produce a fascinating picture with

great emotional appeal, in which no

element could have been spared without

serious loss.

In short, the excellence of

showmanship played no small part in

making it clear to everyone

who saw

it that the day of “Talkies” was here.

The Jazz Singer

and its predecessor

Don

Juan,

it might be noted, had the

benefit of a newly designed lo~dspeaker,~‘

very much superior to those used in the

Western Electric 1924 demonstrations.

Warners

and

Fox

Take the Step.

Warner

Brothers committed themselves to the

adoption of sound pictures in 1926,

license contract being concluded in April,

followed by large investments in sound

stages and equipment. In July of the

same year the Fox Film Corp. became

committed, forming the Fox Case Corp.

which took license for the Case Labora-

tory developments in April, and in

December from Western Electric Co.

for rights to use amplifiers. Both Warners

and Fox operated theater chains. With

two major picture producing and ex-

hibiting organizations definitely launched

on a program of making and showing

pictures, could the other great picture

companies remain on the sidelines?

Large Producers Agree

to

Choose

Same

System.6

Early in 1927 the first Fox

Movietone Newsreel subjects were shown.

The other picture companies must by

this time have become convinced that

ssund pictures were inevitable, for a

part, if not the whole of motion-picture

entertainment. In February 1927, the

“big five”

-

M-G-M, First National,

Paramount, Universal and Producers’

Distributing Corp.

(or

PDC), jointly

asked the Hays organization to study

and make recommendation as to what

system should be adopted. The Movie-

tone and Vitaphone (disk) had already

356

July

1955

Journal

of

the

SMPTE

Volume

64

become commercial systems, Western

Electric was offering a sound-on-film

(light-valve) system, and General Electric

had made a number of demonstrations

of a variable-area system (later offered

to the industry with some modifications

through RCA Photophone). There had

as yet been no formal standardization,

and those participating in the conference

probably felt some uncertainty about

interchangeability of recordings. It is

not strange that the picture companies

thought it would be advantageous for

all to adopt the same system.

By far the most ambitious demonstra-

tion of sound motion pictures that had

as yet (February 1927) been witnessed

was the Warner Vitaphone

Don

Juan

(shown August 1926),l,

4s

with perform-

ances by noted artists and score and back-

ground music for the play by the New

York Philharmonic Orchestra. And the

sound quality was good. But it was

a demonstration of synchronized sound,

and not of sound motion-picture drama.

The producers, still “on the fence,”

continued their “watchful waiting.”

The presentation of

The Jazz Singer

in October 1927 dispelled all doubts.

But whether the future lay with the disk

or the film system was a question not

completely settled for several years.

“Big Fice”

Sign

Contracts with

ERPI.‘j

With such large producers as Warners

making pictures with sound on disk and

Fox

with Movietone releases on film, it

appeared that exhibitors might be

saddled with a dual system. Perhaps it

was the hope that one or the other would

very soon forge ahead in the race that

caused further hesitancy, but in April

and May of 1928 (about six months

after the showing of

The

Jazz

Singer)

Paramount, United Artists, M-G-M,

First National, Universal and several

others signed agreements with Electrical

Research Products Inc. (the commercial

outlet for the Western Electric systems)

for licenses and recording equipment.

Getting Started.’

There followed a period

of feverish activity in erection of sound

stages, and procurement and installation

of recording channels and equipment.

Deliveries of apparatus were far behind

the desires of the customers, and there

was great shortage of engineers and

technicians with sound-picture back-

ground. The manufacturers and asso-

ciated organizations lent or lost many

of their personnel. Intensive training

courses and much instructive literature

alleviated the situation. The Transac-

tions of the SMPE for the fall of

1928 are little short of an encyclopedia

of sound recording and reproduction by

both disk and film. To this body of litera-

ture, the engineers and processing lab-

oratory experts from the producing com-

panies soon began making their contribu-

tions.

Scarcely

a

step behind the building

and equipping of recording studios was

the installation of sound reproducing

systems in theaters. Theater chains con-

trolled by the picture-producing com-

panies which had already signed con-

tracts, used sound systems of the corre-

sponding make, but the business of

furnishing sound equipment to the great

number of independent theaters was com-

petitive between ERPI, RCA Photo-

phone and many other suppliers. An

idea of the rate of growth of the sound

pictures, may be had from the following

figures given in Sponable’s paper.6 At

the end of 1927 there were some 157

theaters in the

U.S.

equipped for sound,

of which 55 were for both disk and

film and 102 for disk only. At the end

of 1928, of the 1046 ERPI theater in-

stallations, 1032 were for disk

and

film.

By the end of 1929 ERPI had equipped

about 4000 theaters in the

U.S.

and 1200

abroad, and RCA Photophone had

equipped some 1200 in the

U.S.

and

600 abroad, most of these being for both

disk and film. The SMPE Progress

Report of February 1930 states that at

the time, Hollywood studios were pro-

ducing only 5% silent pictures. Instal-

lations by other manufacturers brought

the total number

of

theaters equipped

for sound in the

U.S.

to over 8700. There

were at the time 234

diyerent types

of

theater sound equipment including the

large number which were designed for

disk only. At the end of 1930 there were

about 13,500 theaters equipped for sound,

and about 8200 not equipped, according

to the SMPE Progress Report of August

1931.

Contracts

for

Photophone Vuriable-Area

Recording.

In 1928 RCA bought the

theater chain interests of B. F. Keith

and of Orpheum, and the film producing

company Film Booking Office

or

F.B.O.,

and organized Radio Keith Orpheum

or RKO. The new company (RKO),

with Photophone equipment, and draw-

ing heavily on the RCA group for much

of its initial sound personnel, made

many feature and shorter pictures, using

the name Radio Pictures for its product.

RCA Photophone made arrangements

for license and equipment with Path6

Exchange Inc., Mack Sennett, Tiffany

Stahland with Educational Pictures Corp.

One of the first feature pictures made

by Path6 was

King

of

Kings

directed by

Cecil de Mille. The Path6 Newsreels

were an important item, using a number

of RCA mobile recording equipments

or “sound trucks.”

Disney switched to the RCA Photo-

phone system in January 1933. Republic

Pictures Inc. used the RCA system be-

ginning October 1935 and Warner

Brothers in June 1936. Columbia Pic-

tures Inc. began May 1936 to use the

RCA variable-area system for part of

its operations, but continued for several

years to release on variable-density.

Kellogg:

History

of

Sound Motion Pictures

Cinekhone.

The Powers Cinephone

system was developed by R. R. Halpenny

and William Garity for Patrick

A.

Pow-

ers, who financed the project.

It

was

basically similar to the system of de

Forest, with whom Powers had permis-

sive contracts. Cinephone was put on

the market in September 1929 and used

for several years by Walt Disney and

others.

Tyke

of

Contract.

Most of the initial

contracts between the equipment-manu-

facturing companies and the picture

producers were on a lease (rather than

outright sale) basis, for

a

stipulated

term of years, with equipment servicing

and engineering assistance as part of the

suppliers’ obligation, and royalties de-

pending on the film footage recorded.

Evolution

of

a New Art,* Under

Dificul-

ties.

The idea that the silent motion

picture would continue to have its place

in theater entertainment died hard.

What

The Jazz Singer

had proved was

that with

a

suitable story and presenta-

tion, a sound picture could have an ap-

peal far beyond what was possible

without sound. It had not proved that

sound would help in

all

types of presen-

tation. In March 1929, Fox discontinued

making silent pictures. In speaking of

this in his historical paper5 of 1941,

W. E. Theisen calls it a daring decision,

“since a large number of the leaders of

the industry still felt that sound films

were only a passing fad.” In “The

Entertainment Value of the Sound

Movie”

(Trans.

SMPE,

No. 35, 1928),

H. B. Franklin, President of West Coast

Theatres, says: “The silent motion

picture is too well established.

.

.to

vanish because of this new development.”

It

took time, much work and some

mistakes for the industry to learn to use

sound to full advantage, and the great

pressure under which writers and pro-

ducers worked during the years of trans-

ition was not conducive to best results.

Two quotations from 1928 papers are

illuminating. In “The Public and Sound

Pictures”

(Trans.

SMPE,

No.

35) Wm. A.

Johnson, Editor of

Motion Picture News,

speaks of the great demand for sound

pictures, and says: “The present hastily

turned out crop of talkies are for the

most part crude and disappointing.”

In “Reaction of the Public to Motion

Pictures with Sound”

(Trans.

SMPE,

No.

35), Mordaunt Hall, motion-picture

editor of the

New

York

Times,

describes

the shortcomings of many efforts as due

to stories not adapted to talkies, actors

who didn’t articulate,

or

had poor

voices, and misjudgments in production.

*

Many

excellent discussions of the requirements

for the new form

of

entertainment have been

published. One

such

is

Chapter

IX

“Comments

on Production,”

of

H.

B.

Franklin’s

Sound

Motion

Pictures.2

357

viscous

Brake

1

n

Shaf

’t

Opt lGaL

Axis

-Independently-

Journaled Driver

A.

Filtered Sound Sprocket

vi

s

cous

free on Shaft)

C.

Rotary Stabilizer

and Kinetic Scanner

Viscous

or

Coupling

Damper

B.

Magnetic Drive

(or

Fluid

Equivalent)

Flywheel

on

Drum

Shaft

D.

Damped Sprung Idler

on

Drum

Sha

ide

and

Tension

Sprocket free

on

Shaft

and

driven through Spring,

with Damping Pad

E.

Damped

Sprune Sprocket

Fig.

4.

Mechanical filter systems

for

reducing

irregularities

in

film motion.

We tend, fortunately, to forget the

troubles that are past. Still more do we

forget the troubles other people had.

We who took part in the development of

sound equipment may be tempted to

think that we made the talking picture

possible. But if we give the credit they

deserve to the writers, directors, actors

and their bosses, and to the patient

guinea pigs who bought tickets, perhaps

the only bouquet left to hand ourselves

is to say that our stuff was not

so

bad as

to make the talkies impossible.

Mechanical Systems

Of

all the tell-tales that remind the

listener that the sound he hears is from

a

record and not “live pickup,” the

most unmistakable is that due to speed

variations

-

known as “wow” or

“flutter,” and it is probably the most

painful and devastating to realism. The

importance of correct and constant

speed was recognized by Edison and

all his successors in sound recording,

but standards were not very high.

Phonographs sold despite their short-

comings. But sound for pictures could

succeed only by providing better enter-

tainment than silent pictures. In those

systems which gained eventual accept-

ance by the motion picture industry, the

engineers spent much effort on providing

constant speed. In his story of the de-

velopment of the Fox-Case system, for

example, Sponable6 tells of having to

rebuild cameras, and of mounting

a

fly-

wheel on the sprocket shaft and driving

the combination through damped

springs.

The literature dealing with speed

fluctuations has been devoted largely

to discussions of measures for improving

the performance of recorders and re-

producers in this respect.?O Until the re-

cent important contribution by Frank

A.

C~merci,~~” such information as

has been published regarding subjective

thresholds or tolerances has been limited

largely to continuous tones. Further sys-

tematic quantitative studies with typical

program material are very desirable.

There is no question however that all

the present and future improvements

in equipment performance are well justi-

fied in terms of more satisfying sound re-

production. Some of the more general

discussions of the subject will be found

in the literature.

70

3

79

-84a

Wow

Meters.

Of prime importance

toward improving recording and repro-

ducing machines is ability to measure

the departures from uniform speed.

One of the first such meters was built

about

1928

by M.

S.

Meads5 of the

General Engineering Laboratory at Sche-

nectady. It was improved by

H.

E.

Roys

and used extensively at Camden,

N.J.,

being the basis of the flutter-measuring

equipment described by Morgan and

Kelloggs6 This meter made an oscillo-

graphic recording of the fluctuations.

An

extremely simple and light-weight in-

dicating flutter bridge used in RCA

servicing is described in the

Journal.87

Flutter-measuring instruments are de-

scribed by Scoville.8s These are of

the indicating type with band filters, by

which flutter at different rates can be

separated. Another design is described

by Herrnfeld.89

A

widely used wow

meter designed by

U.

R. Furst of Furst

Electronics, Chicago, has been commer-

cially available since

1947

or earlier.g0

Disk

System.

In the disk system the

change from

78

to 33Q rpm increased the

difficulties, for at the low speed even a

very heavy turntable (although very

helpful toward eliminating rapid flutter)

was not a practical answer.

A

flywheel

driven through springs, or what we

call a “mechanical filter,” was a well-

known expedient, but such a system is

oscillatory and will multiply rather

than reduce the speed fluctuations if

the disturbances are

of

a frequency

anywhere near that of the reso-

nance, unless the system is damped

by adequate mechanical resist-

ment that the transient disturbance of

starting shall disappear in not more than

one revolution is more difficult to meet

with extremely large inertia. The ac-

ceptable 334-rpm reproducing turntables

had much more inertia than had been

customary for 78-rpm machines, and

were driven through springs, with enough

damping to reach equilibrium reasonably

quickly, and dependence was not placed

on making the natural frequency low

in comparison with that of the slowest

disturbance (once per revolution). Damp-

ing in some designs was provided by ap-

plying friction to the

spring^,^^^^

and

in others by a viscous drag on the turn-

table. In either case it was essential to

have high indexing accuracy in the low

speed gear or worm-wheel.

For 339-rpm recording turntables,

the Western Electric engineers went

to extraordinary refinement.70sg1 On

the theory that it would not be practically

possible to produce gears with no ec-

centricity or indexing errors, they made

their 33Q-rpm worm-wheel in four lami-

nae, all cut together in one operation.

Then they separated and reassembled

them, each rotated

90”

with respect to

its

neighbor. Each had its own spring

connections to the turntable. Damping

was by means of vanes in oil. Four vanes

ance.

69,70.81,91,94,100,102,104,105

The require-

358

July

1955

Journal

of

the

SMPTE

Volume

64

were rigidly connected to the turntable,

while the pot and four other vanes were

driven from the gears through a system

of equalizing levers (which might be

compared to whiffletrees) which im-

parted to the pot and its vanes a rotation

which was the average of that of the

four gear laminae. The effect of this

was to divide by four the magnitude of

each disturbance due to imperfection in

the cutting of the gear, but to make it

occur four times per revolution instead

of once, and both of these effects are

helpful toward filtering out irregularities.

Filtering Systems

for

Film.

In a very

judicial appraisal of the relative advan-

tages of film and disk,

P.

H. Evansa

speaks of the disk system as giving

better speed constancy. He was of

course referring to the experience up

to the time of writing. There can be no

question that film presents

a

more diffi-

cult problem. Synchronous drive and

the maintenance of free loops require

that it be propelled by sprockets. In the

earlier systems of driving the film, it seems

to have been regarded as sufficient to

provide constant rotational speed for

the sprocket (often called the “sound

sprocket”) which carries the film through

the point of recording

or

reproduction.

To obtain such constant sprocket speed

it was practically necessary to use

mechanical filtering to take out irregu-

larities originating in the gea~-ing.~,’O

But the spring-driven sprocket was very

sensitive to jerks from the film,

so

that it

was necessary to employ extra sprockets

with slack film between to isolate the

filtered sound sprocket. It was also

necessary to have an unusual degree of

precision and concentricity in the sound

sprocket. (Fig. 4A).

But there remained the question of

what imperfections there might be in

the film perforations,

or

how much it

had shrunk since the holes were punched.

Shrinkages up to

1

yo

were not uncommon.

A

sprocket can propel

a

film at uniform

speed only when the pitch of the teeth

and that of the holes match perfectly.*

Otherwise there are continual readjust-

ments of the film on the sprocket, pro-

ducing in general 96-cycle flutter, plus

random small variations. A paper by

Herbert Belar and myselP2 shows

graphically the startling breaking up

of single tones into a multiplicity of

side tones by

a

96-cycle speed change

such as might result from

a

shrinkage of

about

3%.

Recorders, since they are working

with fresh film, may give very little

96-cycle flutter at the sprocket. The

*

Sprocket propulsion of the film through the

light beam has certain advantages for printers,

as will be explained in the section on printer

improvements. This mechanical section, how-

ever, seems the logical place

for

a brief review of

studies by

J.

S.

Chandler and

J.

G.

Streiffert

of the Eastman Co., directed to the reduction of

sprocket-tooth flutter.

Dec.

27,

1932.

E.

W.

KELLOGC

P!WI

SUPPORTING

AND

DRIVING APPARATUS

Filed

July

27.

1928

Fis.

I.

Fis.

2.

1,892,554

Fis.

3.

Film

5.

Schematic representation

of

the magnetic drive for film motion, showing

also

provision for damping

by

use of a movable roller with dashpot.

Western Electric recorders of the earlier

1930’s were designed on this basi~.~~$~

The large sprocket was of precise con-

struction and a nearly perfect fit for

unshrunk film. It was on the shaft with

a flywheel, and driven through damped

springs. Another sprocket (unfiltered)

drew the film from the magazine and

resisted the pulls from the take-up

magazine.

The engineers who designed the re-

corders supplied by

RCA

took no chances

with sprocket teeth. In the first General

Electric recording machines the film

was carried past the recording light on

a

smooth drum (with

a

flywheel on its

shaft) and a soft-tired pressure-roller

prevented

lipp ping.^'

Between the drum

and the sprocket which fed the film

through the machine at synchronous

speed were flexible loops of film which

(so

long as they remained under suffi-

ciently low tension to retain their

flexibility) would not transmit appre-

ciable disturbances from the sprocket to

the drum. Because of uncertain shrinkage

the drum must be free to choose its

own speed. The simplest expedient was

to let the film pull the drum, like

a

belt.

Machines built this way worked

so

well

at times that they delayed the effort to

design something on sounder principles.

My own part in the development of a

better machine lay originally in the

recognition that the stretch of film which

pulled the drum, in combination with

the inertia of the flywheel, constituted

an oscillatory system, although its period

varied

so

greatly that the irregular

action did not look like that of any

oscillator we were accustomed to seeing.

Another trouble was that the film loop

Kellogg: History

of

Sound Motion Pictures

359

Fig.

6.

Original

model

of

magnetic-drive recorder.

was not free enough for isolating the

drum. The cure for the bad effects of

oscillatory action would be to provide

damping. One way to provide this would

be by bending the film around a flexibly

supported idler roller,’05 connected to

a dashpot. Another measure would be

to use eddy-current damping at the fly-

wheel by mounting a copper flange on

the flywheel, spanned by

a

set of mag-

nets. To use stationary magnets would

provide damping but would also produce

a steady drag, making

a

really flexible

film loop impo~sible.’~J~*~ By mount-

ing the magnets

so

that they could be

driven somewhat above flywheel speed,

it became possible to provide a forward

torque as well as damping, thereby

relieving the film of all but a small

part of its tension. (Figs. 4B,

5).94-96

The first magnetic-drive machine (an

experimental model) (Fig. 6) employed

both the damped idler roller and the

rotating magnetic damper, but the latter

was

so

effective that the first was super-

fluous. By adjusting the magnet current

the film loop could be caused to run

anywhere between

a

very slight deflec-

tion and a nearly semicircular bend.

A production model (the R-4) recorder

was designed in 1929 and was in pro-

duction in 1930.94

It

was followed by

other models (PR23 in 19339* and PR-31

in 1 94799) employing the same principle.

The magnetic drive probably carried

the idea of isolation of the film drum

from disturbing forces farther than it

has been carried in any other film-

recording machine. Its extreme effec-

tiveness as a filter system was demon-

strated by Russell

0.

Drew and myself

at the

SMPE’s

1940 spring conventi~n.~~

Although only a few were built,

I

should mention another recorder, the

.R-3,’O designed by

C.

L.

Heisler of the

General Electric Co., which preceded

the magnetic type. This had the smooth

drum with flywheel to carry the film

past the recording point, and the sprocket

drive to hold synchronism. The drum

was driven through a continuously ad-

justable-speed friction drive, which might

be compared to

a

cone pulley, and the

speed adjustment was automatically

controlled by the length of the loop of

film between the sprocket and drum,

which loop was measured by the position

of a movable deflecting roller.

Effect

of

the Tri-Ergon

patent^.^^^"^

Men-

tion has been made of the development,

beginning in 1918, of a sound system

by Vogt, Massole and Engl, to which

the name Tri-Ergon was given. They

obtained very broad patents in Germany

and were allowed some extremely broad

claims in the United States. The patent

which figured most seriously in litiga-

tion was

No.

1,713,726 in which one

claim covered the use of a flywheel on

the shaft of the roller which carried film

past the translation (recording

or

re-

producing) point. Another claim covered

carrying the film on a short roller and

scanning it at the overhanging edge,

and a third (based on a showing of flexi-

bly mounted rollers pressing against and

deflecting the stretches of film on either

side of the drum) called for a spring-

pressed roller engaging the film between

the sprocket and the roller (drum).

Patent attorneys in the RCA group and

Western Electric felt very confident

that the broad flywheel claims could be

safely disregarded because anticipated

in many old sound-recording and re-

producing devices, but the patent de-

partments would not approve construc-

tions using the overhung film for scanning

until after about 1930, when

W.

L.

Douden of the RCA patent department

discovered an older disclosure of the

same idea in a patent application

of

C.

A.

Cawley* (to which RCA obtained

rights).

L

E

I

Film-

Transport System

of

Soundheads.

So

the first reproducing machines to be

marketed avoided the overhanging film

feature, and instead pulled the film

through a sound gate, where the scanning

light passed through it and into the pho-

tocell. Friction in the gate made this

arrangement much less favorable to

constant speed than the use of the over-

hung principle.

For

constancy of film

speed no further measures were used

than to try to provide good sprockets to

pull the film through the gate, and to filter

the motion of the sprocket by use of a

flywheel, and driving through springs.

To

damp this filter, the RCA PS-1

used grease-pads acting on the flywheel

(Fig. 4A) and the Western Electric used

a balanced pair of oil-filled sylphon bel-

lows which acted as a dashpot supple-

menting the driving springs.“ A practical

improvement over filtering the sound

sprocket was to drive

a

heavy flywheel

on the sound-sprocket shaft by multipleV

belts directly from the motor, and then

by gearing take from this shaft whatever

power is needed to drive the projector.

The heavy flywheel and tight coupling

to the motor gave the sound-sprocket

drive such high mechanical impedance

that its speed constancy was not ma-

terially disturbed by the irregularities

of the projector load.

The Rotary Stabilizer.

The discovery of

the Cawley patent application by Douden

made the RCA Patent Department

consider it safe to build machines in

which the reproducing light passed

through the film where its edge over-

hung

a

short roller. With this privilege

the way was open to make the film

motion in reproducing machines com-

parable with that which had been at-

tained in the magnet-drive recorder-

However

a

less expensive construction

was very desirable. The damping in

the recorder was by eddy-current cou-.

pling between the flywheel and a coaxial

magnet running at nearly the same

*

The Cawley application had been filed Jan. 28,

1921, but had been held up on technicalities.

It

was put into suitable shape and issued Sept.

29, 1931 as a parent patent,

No.

1,825,438, and

three divisional patents,

of

which

No.

1,825,441

contained the claims to the overhang feature.

360

July

1955

Journal

of

the

SMPTE

Vulume

64

speed. The functional equivalence of

eddy-current coupling and viscous-fluid

coupling was well recognized.

I

had

tried some experiments with viscous

coupling to a coaxial member which

was not independently driven but was

free to pick up the flywheel speed. The

>

I

inertia of the viscously coupled member

would tend to keep its speed constant

1

so

that a change in flywheel speed would

cause relative movement and hence en-

ergy loss.’O0 But I gave up in view of

the feebleness of the damping

I

obtained.

It remained for C. R. Hanna of West-

inghouse to make an analysis of the sys-

tem. He showed that in order to get

critical damping of the mass which is

rigidly connected to the drum, the vis-

cously coupled mass must have eight

times as much moment of inertia, and

the coupling coefficient must have the

right value.69 In 1932 and 1933 E. W.

Reynolds and F.

J.

Loomis of the RCA

Victor Co. in Camden did the job

right.lol The directly connected mass

was an oil-tight shell of aluminum alloy

inside which was a heavy cast-iron fly-

wheel supported on a ball bearing whose

friction was negligibly small in compari-

.son with the oil coupling. Small clear-

ance between concentric surfaces and

a suitable oil gave the desired coupling.

The inertia ratio was less than 8:1,

but damping somewhat short of critical

is satisfactory. By use of high-grade ball

bearings the drum with attached stabi-

lizer was caused to run with

so

little

tension on the film which pulled it that

the loop had plenty of flexibility for

effective filtering.lo2!

lo20

(See Figs. 4C

and 7.) The rotary stabilizer introduced

in 1933 proved

so

satisfactory that it has

been retained with little change for

twenty years.

A

device on similar prin-

ciples, called the “kinetic scanner” was

used in Western Electric soundheads

early in 1936‘” (Type

209).

In 1941 Alberscheim and MacKenziesl

and Wente and MUllerlo4 described

damped flywheels in which the entire

viscously coupled mass was liquid. In

order that there might be sufficient

viscous resistance to movement of the

liquid with respect to the container,

partial obstructions were placed in the

annular channel. This type of damped

flywheel was used in the recorders and

reproducers of the stereophonic system

developed and demonstrated by the Bell

Telephone Laboratories. Study has been

given to the problem of finding suitable

fluids. A low-temperature coefficient of

viscosity is desirable, and if the entire

coupled mass is liquid, high density is

valuable.

Filters Using Movable Idlcr

Rollers.

The

use of this type of filter was avoided in

this country because of the danger of

infringement suits on the basis of either

the Tri-Ergon patent

(No.

1,713,726)35

or the Poulsen and Peterson patent

(No.

Rotary stabilizer construction

of

F.

J.

Loomis

and

E.

W.

Reynolds.

Fig.

7.

Cross

section, showing construction

of

the “rotary stabilizer.”

1,597,819). Both of these show rollers

elastically pressed against the film to

deflect it from a straight path and

thereby provide flexibility. Neither pat-

ent shows or mentions provision for

damping, and yet the great merit of

such an arrangement is in the simplicity

with which damping can be obtained

and not in the extra flexibility, for plenty

of flexibility can be had by simply freeing

the film of too much ten~ion.~~~J~~~The fly-

wheel may be solid and the arm on which

the film-deflecting roller is mounted

can be connected to a dashpot. (Even

a

cruder frictional device may give good

results, but resistance of the viscous

type is better.)

A

laboratory model of

a

soundhead using this type of filter was

built about 1928 by the writer and

performed very well, but did not receive

patent approval (Fig. 4D).

After the patent obstacle to the use of

the sprung-idler type of filter was

ended, soundheads employing this prin-

ciple were brought out by the Century

Projector Corp. and the Western Electric

C0.105 and

a

recorder by Western

Electric.lo6 RCA adopted this film-

motion system for l6mm machines and

lightweight recorders R-32 and R-33,1°7

but for 35mm soundheads continued to

use the rotary stabilizer, the advantage of

the movable-idler design being not

so

much

a

matter of performance as of

lower manufacturing costs, an item which

is contingent on schedules and tooling

costs. Recently the flexibly mounted

idler filter system has been utilized by

RCAlM and others109J10 in soundheads for

use with multiple magnetic soundtracks.

Kellogg:

History

of

Sound

Motion

Pictures

Filter System With

Drum

and Sprung

Sprocket.

A film-motion system developed

by engineers of M-G-M is described

by Wesley C. Miller.ll1 Recording or

reproduction takes place on a drum with

solid flywheel, and the drum is driven

from

a

sprung sprocket isolated from

other sprockets by loose loops. The film

passes from the sprung sprocket, around

the drum and back to engage the opposite

side of the sprung sprocket, and this

portion of the film is maintained under

tension by

a

roller pressing against a

free span of the film. The tight film

affords the required traction between

film and drum. Adjustable friction pads

between the sprocket and its shaft cause

frictional resistance whenever the deflec-

tion of the sprocket driving springs

changes, thereby damping the system.

Excellent film motion was obtained in

these machines (Fig. 4E).

Minimizing Sprocket- Tooth Flutter.

J.

S.

Chandler, in 1941112 showed it to be

possible to

so

shape sprocket teeth that

the film speed would fluctuate between a

maximum and minimum value which

are the same at perfect fit and spread

progressively with increasing misfit, but

with a net flutter which can for a mod-

erate range of shrinkage be quite small.

However the realization of the calcu-

lated flutter values demands perfect

perforation uniformity and freedom from

any sticking on the teeth as the film is

fed on or stripped

off.

A

further development in improving

sprocket action is described by

J.

G.

Streiffert.ll3 The driving faces of the

361

F

R

1929.

H.

VOGT

ET

AL

1,713,726

DEVICE

FOR

FHONOGRAPHS

WITH

LINEAR PHONOGRAM

CARRIERS

Filed

March

20.

1922

3

Sheets-Sheet

3

..I

7roR.w-s

Fig.

8.

Tri-Ergon showing

(U.

S.

Pat. 1,713,726)

of

flexibly mounted rollers deflecting

the

film

between sprockets and drum.

teeth are radial and the film is sup-

slightly greater than that of the film.

ported on a cylindrical surface which

is slightly eccentric with respect to the

sprocket. The film is fed on at a point

where the teeth project only slightly

above the film support, and as it travels

around its arc of engagement the film

gets closer to the roots of the teeth. The

radius from the sprocket center to the

film thus keeps decreasing, and therefore

the velocity of the tooth face at the plane

of the film decreases. The effect is essen-

tially as though the tooth speed and the

tooth pitch decreased correspondingly.

The design is such that the tooth enters

the hole with

a

margin of clearance and

with the effective velocity (since the

working radius is here near maximum)

The tooth face therefore gains with re-

spect to the film, closing up the clearance,

and as soon as it touches the edge of the

perforation begins propelling the film.

While it is doing

so

the next tooth is

catching up. Each tooth in turn propels

the film from the moment that it reaches

the perforation edge until the next

tooth, which at the instant is moving

slightly faster, touches the edge of its

perforation. Thereafter, the effective

speed of this tooth, which continues to

decrease, is less than that of the film,

so

that a gap or clearance develops

between the tooth and the leading edge

of the perforation. The design is such

that the film is not stripped from the

teeth until, in all cases, sufficient clear-

ance has accumulated to avoid possible

interference during the stripping.

Assuming that the film velocity is

equal to that of the driving-tooth face

at the radius where it touches the film,

the film speed will fluctuate by the

amount by which the effective tooth speed

decreases as it travels one tooth pitch.

This can be a very small change, es-

pecially if there is a large number

of

teeth and the eccentricity no more than

needed to take care of a reasonable

shrinkage range.

The region on the circumference of

the sprocket where the propelling action

takes place varies with the shrinkage

of

the film. Thus with unshrunk film

the propulsion will be relatively near

the place where the tooth enters the per-

foration, while with shrunk film it will

be where the teeth are projecting farther,

so

that the point of contact is nearer the

root of the teeth.

One way

of

describing the action of

the system is to say that a film of any

given shrinkage finds the appropriate

radius where the pitch of the teeth

equals the pitch of the perforations, and

this is the region where propulsion takes

place.

The Eastman Co. has used this system

with excellent results in experimental

printers. The Streiffert paper gives wow-

grams of negative recordings made on

such a sprocket, and also

of

contact prints,

and for comparison wowgram (or flutter

recordings) of prints made in

a

conven-

tional sprocket-type printer, showing

a

major reduction in flutter with the new

sprocket.

Litigation.

Despite the efforts to avoid

infringement of such claims of Tri-Ergon

patent

No.

1,713,726* as appeared to

have any likelihood of being held valid,

the American Tri-Ergon Corp. brought

suit against Altoona Publix Theatres

Inc., who were using an RCA Photo-

phone

(PS-1)

projector attachment

or

soundhead. The case was tried at Scran-

ton, Pa., in the

U.S.

District Court for

the Middle District. The apparatus had

been sold with a guarantee against

patent liability, and the suit was defended

by RCA, Electrical Research Products

Inc. giving technical assistance in the

defense. The court ruled (Feb.

10,

1933) that seven of the claims were valid

and infringed. The case was appealed

and reviewed by the

U.S.

Circuit Court

of Appeals for the third circuit (in

Philadelphia), which affirmed (June

13,

1934) the findings of the lower court.

The defendents then appealed to the

U.S.

Supreme Court, which at first

refused to review the case, but finally

decided to do

so,

and on Mar. 4, 1935,

ruled that the seven claims in the suit

were all invalid (294

US

477).'14

*

This patent, issued May 21, 1929, was filed in

the

U.S.

Mar.

20,

1922,

and had a German

filing date

of

Mar.

24,

1921.

362 July 1955

Journal

of

the SMPTE Volume 64

This removed the threat to the equip-

ment manufacturers of what might have

been almost crippling damages, for

had the findings of the lower courts been

sustained the plaintiffs would have been

in a position to bring suits for damages

for infringement by most of the recording

and reproducing equipment in this

country, and covering a period of over

five years.

The American Tri-Ergon Corp. ap-

plied on Feb. 18, 1937, for a reissue

patent with modified claims, and this

was granted Jan. 11, 1938, as Re.

No.

20,621. On Oct. 25, 1946, RCA reached

an agreement with American Tri-Ergon

Corp. whereby it was granted rights

under both theoriginaland reissuepatents.

Two other patents placed restrictions

on the film-motion systems which Ameri-

can engineers could safely employ,

namely Poulsen and Peterson

No.

1,597,819 (filed July

9,

1924, and

issued Aug. 31, 1926) and Poulsen

No.

2,006,719 (filed Germany Sept. 1, 1930,

and

U.

S.

Aug. 19, 1931, and issued July

2, 1935). These patents to Danish

inventors were owned by British Acoustic

Films Ltd., which brought infringement

suits against RCA Mfg. Co. and against

Electrical Research Products Inc. The

trial (in Wilmington, Del.) was before

the

U.S.

District Court for the District

of Delaware (43 USP-Q69). The ar-

rangement shown in the patent comprised

a

drum propelled by the film, the film

being passed around a flexibly mounted

idler roller. Some of the claims in suit

described the invention as “means con-

tacting the film for increasing its flexi-

bility.” The apparatus in suit was the

RCA PS-24 (rotary stabilizer type),

which has no flexibly mounted roller,

but was alleged to have the equivalent

in that the film loop was

so

formed by

the fixed rollers as to be very flexible.

The court ruled Sept. 22, 1939, that the

claims in suit were not infringed and

not valid (the flexibly mounted idler

having been disclosed in the earlier Tri-

Ergon patent).

Plaintiffs appealed and the case was

reviewed by the Circuit Court of Ap-

peals of the Third Circuit which affirmed

the findings of the lower court (46USP-

4107, June 27, 1940).

To forestall possible future trouble

RCA obtained rights under these pat-

ents by agreement with British Acoustic

Films Ltd., Dec. 21,1944.

Immediate Requirements

for

Sound

Our

historical story thus far has been

confined almost entirely to the three fun-

damental elements, sound pickup

(or

microphone), a recording and reproduc-

ing system and loudspeakers. These

represented the difficult phases of the

problem, but before sound could become

commercial certain items of equipment

had to be made available and techniques

established. Before discussing the ad-

’

vances in the art that followed commer-

cialization, we shall mention some of

these items.

Standard Track Position and Width.l15

Agreement between the makers of vari-

able-width and variable-density systems

was reached in 1928. The reproducing

light spot must cover more than the

extreme width of the clear area of

a

vari-

able-area track, with both ends on black

areas, but should fall entirely within the

width of

a

variable-density track. This

requirement is met with margins of safety,

by recording density tracks 0.100 in.

wide, while the scanning spot is 0.084

in. long. The modulated area of

a

vari-

able-width track is limited to 0.071 in.

with the black parts extending to the

0.100-in. width. The track center line is

to be 0.243 in.

f

0.002 in. from the edge

of the film.

Printers.

Continuous contact printers

previously used for pictures only could

be adapted to sound by providing masks

by which light could be confined to

either the picture

or

the soundtrack area.

Except for certain newsreel negatives,

the sound and picture were on separate

negatives,

so

that the print film had to be

run through the printer twice. Even

when the sound was on the same nega-

tive as the picture, the offset was not

usually the required 14.5-in. and inde-

pendent light controls were needed.

Combination printers were soon devel-

oped which were essentially two printers

in cascade,

so

that the print was com-

plete with one passage through the

machine.116-120

Bloops.

The development engineer can

overlook many defects so long as he

knows their cause and that the apparatus

he is testing is not at fault, but before

sound pictures could be shown the public,

these faults had to be corrected. The

noise which a splice makes as it passes

through the scanning beam can be made

almost inaudible by cutting off the light

gradually instead of suddenly. This was

accomplished at first by painting a black

spot with sloping edges over the splice.

Later, black patches which could be

quickly cemented in place where the

splice crosses the sound track were made

available. These are called “bloops.”

They are of trapezoid shape, masking

off the entire sound track for a distance

sufficient safely to cover the splice and

with end slopes designed to change the

light gradually enough to keep the noise

just below noticeability at normal gain

settings. The design of bloops is dis-

cussed in several To prevent

a

disturbance due to a printed-through

negative splice, SponablelZ4 described

a punch which made a hole in the nega-

tive, resulting in a suitably-shaped black

spot on the print.

Electrical blooping of splices in nega-

tives has come into extensive use. When

a negative splice goes through the printer

an auxiliary light exposes (through

the base) a suitable area of the print

film, an edge notch

or

other means

being employed to control the blooping

light.

Lewin (Apr. 1947)I24a describes a system

of silencing splices in re-recording posi-

tives in which the output is momentarily

suppressed in response to a punched hole.

Blimps.’25

Cameras which were en-

tirely satisfactory for silent pictures were

much too noisy for making sound

pictures. Much quieter cameras were

developed eventually,126-128 but for im-

mediate requirements it was necessary

to reduce the noise radiated by existing

cameras by building shells around them

with thick layers of sound-absorbing

material. These were called “blimps,”

or

sometimes “bungalows.” To smother

the sound and still give access for the

necessary operations was enough to

tax the skill and ingenuity of the de-

signer. Even with the quieter cameras it

is still common to resort to partial

or

complete sound-insulating housing.

Fig.

9.

Tri-Ergon showing

of

filtered sound-sprocket

and overhanging sound-

track.

Kellogg:

History

of

Sound Motion Pictures

363

Sound Stage~.'~~J~~

The requirement of

freedom from noise necessitated the

building of sound stages in which ex-

treme measures were taken to exclude

noise of outside origin. Many of these

had double concrete walls and double

floors, with sound absorbing material

between, the inner walls and floor being

supported on cushion mounts to prevent

transmission of earth tremors. The roof

and ceiling structures were designed on

the same principle.

The high absorption

(or

short reverber-

ation time) desirable for recording pur-

poses helped control noises originating

inside, but

so

far as possible all sources

of noise were eliminated. Noisy arc

lights gave way to incandescent or

other quiet lamps, and all mechanisms

were made to operate as noiselessly as

possible. Ventilating systems required

extreme measures.

In recording dialogue, the better the

suppression of general rcom reverbera-

tion, the farther (within limits) from the

action can the microphone be placed,

thus affording more uniform coverage

and making it easier to keep the micro-

phone out of the field of the camera.

If

some echoes are wanted the "set"

can frequently be designed to produce

enough. Artificial reverberation using

echo chambers in the recording channel

or equivalent devices has many applica-

tions.

In contrast to the requirements for

speech, the recording of music calls in

general for rooms with considerable

re~erberation.'~'-'~~

Theater Acoustical Treatment.134J35

The

acoustical treatment of auditoriums has

probably received more study than any

other phase of architectural acoustics,

perhaps because the desired characteris-

tics are most difficult to attain. The re-

verberation must be sufficient to make

music pleasing and to help equalize

sound intensity in the various parts of the

space, but must be short enough not

appreciably to impair clarity

of

speech.

A high order of directivity in the loud-

speakers plus application of absorbent

materials to any large surfaces toward

which they are directed has helped

with this part of the problem.

In general every theater or auditorium,

many of which were built before the

era of sound pictures, presents its own

problems and calls for individual study.

For

new theaters there is optimum shape

to consider as well as best distribution

of

absorption. The multiple loudspeaker

systems (discussed later) besides making

new effects possible have given the

acoustical designer somewhat more free-

dom.

Booms and Dollies.

In order that micro-

phones might be suspended as near the

action as might be wanted but just above

the field of the camera, and in order

that their positions might be readily

changed, microphone booms of various

types came quickly into use. The more

elaborate of these were much like

derricks on platforms, with rubber-

tired wheels on which they could be

moved quickly and almost noiselessly.

Similarly, rubber-tired, battery-oper-

ated camera dollies enabled the camera-

man rapidly and quietly to change the

position

or

height of his camera.

Equipment of the kind just described

underwent improvements through the

years, but the main features were avail-

able from the start of commercial sound

pictures.

Monitoring and Leuel Contr01.'~~-~~~

An-

other line of equipment the essentials of

which were made available as soon as

recording machines, and which has been

improved from time to time, was that pro-

viding for monitoring and level controls

and (especially in re-recording opera-

tions) for adjusting the relative levels

from several sources, or "mixing." Vol-

ume indicat~rs'~~J~~ of several types

were in use in broadcasting stations, and

the design of mixing controls was well

established.

The man responsible for recording

judged the quality by means of

a

moni-

toring loudspeaker. He could check

quality as represented by the current

supplied to the light modulator,

or

by

means of a photocell, in terms of the

light reaching the film.1964,254 In the case

of the RCA Photophone system there

was a card on which the modulator pro-

jected a light-spot, the movements of

which showed the amplitude being re-

corded on the sound

It was for a time held by some that the

monitoring speaker should be of the same

type as a theater speaker, but high-

quality monitoring speakers of the direct-

radiator type were soon made available,

and these were much better suited to the

small rooms where the controls were

located. In terms

of

frequency range

covered, the cabinet-type monitoring

speakers kept pace with the improve-

ments in theater speakers (see section

on loudspeakers). High-quality head-

phones have also found wide use in moni-

toring.'",

211

Whatever type of listening

device is used, it should obviously be

designed to give the recordist about the

same range and tonal balance that a

theater patron would get.

Screens.

Our sense of the direction

from which sounds come is too keen for

us to be fooled by loudspeakers placed

alongside or above the screen. Sound

must come from directly behind the

screen to give a good illusion. This is

one of the lessons that was learned early.

Screens of the types developed for silent

pictures caused excessive loss and distor-

tion if placed between the loudspeaker

and the audience.

Mention has been made

of

a sound-

transmitting screen developed by E.

I.

Sponable in

1927.6

One

of

the first

papers in the SMPE

Journal

dealing

with screens for sound pictures was that in

1930

by

H.

F.

H0~kins.l~~ His curves of

measured transmission indicate good

results with screens having perforations

whose total area is

4%

or

5%

of the

screen area, and show definite advantage

in a thin (0.013-in.) screen rather than

a thicker (0.030-in.) material. With such

screens the loss of brightness need be

no greater than the proportion of the

area taken out by the holes. Allotment

of about

8%

of the area to holes has been

common, for example about

40

holes

of

0.050-in. diameter per square inch.145

Processing, Variable- Density

.146

In the

story of the work at Western Electric

and Bell Laboratories

I

said that it was

recognized by Wente and by MacKenzie

that for the correct, or linear, relation

between negative exposure and print

transmission, the product of the negative

and print gamma* should equal unity.t

This is in accordance with principles set

forth in early SMPE papers by

L.

A.

Jones62 and by A.

C.

Hardy.61 Since

practice in making pictures had been to

develop the print to a gamma of approxi-

mately two, and both sound and picture

would receive identical development, the

sound negative should be developed to a

gamma of about

0.5

or slightly higher.

Picture-positive film was used for a

number of years for sound negatives.

Developers of the types used for picture

negatives tend to give low contrast and

fine grain, and the use of such develop-

ers helped to give the desired low value

of

gamma for the sound

negative^.'*^*'^*

Ma~Kenzie~~ gives some information

about the harmonic distortion which

results from departures from the unity

product, and thus gives an indication of

tolerances with respect to development.

With the advent of sound, with its

requirement for more strict control of

development, control by use of sensito-

metric test strips, and by specified time,

temperature and developer f0rmulas'~9-'~

supplanted dependence on visual judg-

ments of operators, where that practice

had prevailed.'"J" Maintenance of de-

veloper activity received much atten-

ti or^,'^^-'^^

and stop baths assumed in-

creased importan~e.'~~*'~~ Rack-and-tank

methods, where these had been followed,

*

Gamma is the slope of the straight portion of a

curve plotted withdensity orlogof

as ordinates and log exposure as abscissae. This is

known as the Hurter and Driffield,

or

H

&

D curve. Gamma product is a measure of overall

contrast as compared with that in the original

exposure.

t

In practice, because

of

some

loss

of contrast

due to stray light in optical systems, best results

with pictures had been found with somewhat

higher gamma product.

(

transmission

364

July

1955

Journal of the

SMPTE

Volume

64

gave way to continuous machine proc-

essing.161-163

How generally the distinctions be-

tween specular and diffuse density,164 and

between exposure modulation by varying

time (light valve) and varying intensity

(as by glow lamp)‘65 were understood at

first is a question, but these points were

well covered in the literature. The

Eastman Capstaff Densitometer,166 which

was developed primarily for measuring

picture negatives for contact printing,

reads diffuse densities. This would be

appropriate for measuring the densities

cf sound negatives for use in contact

printers, but not for densities of sound-

track prints, for it is the specularly trans-

mitted light which reaches the photocell

in

a

reproducer.

The widely used EastmanIIb Sensitom-

eter, brought out about 1932,1‘j7 which

gives an accurately standardized series of

test exposures in the form of a step tablet

with exposure time increasing in the

ratio

d?

per step, and ranging from

about

0.004

sec to

4

sec, has been of

utmost vahe in maintaining controls.

However, it does not simulate sound-

track recording conditions, where the

intensity is extremely high and the time

for average exposure was approximately

1/18000 sec (1/36000 sec with a later

light-valve system and in present prac-

tice about 1/90000 sec) and still shorter

for low exposures. The 1934 paper by

Jones and Webb165 gives an indication

of the magnitude of the error. The East-

man Sensitometer on the other hand gives

exposures which approximate sufficiently

well those which

a

print receives, and

are thus suitable for determining gamma

of contact prints. For many purposes it

has been satisfactory to draw conclusions

by applying correction factors, if needed,

to the readings of these instruments.

In the course of a few years densitom-

eters employing photocells were de-

veloped which had the advantages of

greater accuracy and much faster op-

eration than the Capstaff visual-balance

type.168-1i2 For exposing sound negatives

for sensitometry purposes, the light valve

itself, with suitable calibration, can be

used. The subject is again discussed

under “Intermodulation Test.”

While the conditions for low distortion

were to keep both negative and positive

exposures on the straight parts of the

H

&

D characteristics, studies reported

in 1931 by D. MacKenzie17*~ showed that

low distortion was still possible while

using the “toe” range of both films

(“toe recording”) or that of the positive

only (“composite”). Toe recording using

positive stock for the sound negative

might, if the recording-system light was

limited, be preferable to resorting to

faster and coarser-grained recording

stock. In the case of single-film systems

(sound recorded on the picture negative)

where the development of both the nega-

tive and positive soundtracks is fixed

by picture requirements, MacKenzie

found that the composite system offered

best promise of low distortion. Both the

toe and composite systems give higher

output than

a

classical

or

straight-line

system, but poorer signal-to-noise ratios.

It took a number of years to bring

about the full transformation from the

methods (depending much on visual

judgments) which had been employed

for making silent pictures, to the close

controls and scientific precision needed

for satisfactory and consistent sound.

The constant and close checking of

every element exerted

a

pressure for

improvement along the whole front,

including the manufacture of the film,

in which departures from uniformity

were quickly detected. The story is inter-

estingly told by

J.

I.

Crabtree.146 An

early account is given by

J.

W. Coff-

man.153

Processing, Variable-Area.

Since the

ideal variable-area track

is

part clear

and part black with a sharp boundary

between, there is no question of preserv-

ing correct shades of gray, but in general

the higher the contrast (or gamma

product) the better.

As

in the case of

variable-density tracks it must be as-

sumed that the print development will

be that which is wanted for the picture,

and that has been taken in general to

give a gamma of about 2.0. Variable-

area negatives as well as the prints are

processed in high-contrast developers.

The variable-area system is noncritical

with respect to gamma product but, for

a given positive emulsion and processing,

there is for any given negative

a

best

setting of printer light.

A comprehensive study of available

sound-recording films and their process-

ing was published by Jones and Sand-

~ik.’?~ Another study was made by

J.

A.

Ma~rer.’~~ From his curves it ap-

peared that negative densities of 1.3 or

higher were desirable, and the prints

which gave maximum outputs were the

ones having densities (in the dark areas)

about equal to those of the negatives

from which they were made. This held

true for negative densities ranging from

0.6 to

1.3

and higher. The maxima

however were very broad.

In November 1931, Dimmi~kl~~ re-

ported the results of a series of deter-

minations of conditions for maximum

output from a 6000-cycle recording, using

Eastman positive 1301 for negatives and

prints, and

4,

6,

8

and 10 min in D-16

developer. The study covered an ade-

quate range of the four variables

-

nega-

tive (recording) exposure, negative de-

velopment or gamma, printing exposure

and print development. The results

showed that wide ranges in each

of the variables could be used with com-

paratively small loss of output, but for

any negative there was a print density

at which output was greatest.

It

made

Kellogg: History

of

Sound

Motion

Pictures

comparatively small difference (except

near the extremes) whether a given

density of either negative or print was

reached with small exposure and longer

development or more exposure and less

development, but in general the maxima

were broader with the higher values

of gamma, especially that of the print.

The two highest gamma values in the

series, 2 and 2.18 of both negative and

print, in general gave best results, with

negative densities (measured in the black

areas) in the range 1.5

to

2, and print

densities a little less in each case than

that

of

the negative.

While maximum high-frequency out-

put is of less consequence than avoidance

of cross-modulation (which is discussed

in the section on distortion) it is of in-

terest that recommended practices based

on the test just described come very

close to those found to be best in later

experience and after current testing

methods had become established. The

cross-modulation test did not come into

general use until 1938.176

For a number of years a print density

of

1.4

or

slightly higher, with appro-

priate corresponding negative density,

was taken as a practical objective. As

galvanometers and optical systems were

improved and finer grain films came into

use, the tendency was toward higher

densities for both negatives and prints,

especially for the negatives.

Evolution

in

a

Growing Industry

Greatb Expanded Deuelopmental Actiui-

ties.

The development work prior to com-

mercialization of sound was carried

on largely in laboratories supported by

manufacturers of supplies or equipment,

or in independent laboratories, and it

was done on the basis of hope for re-

turns which might be realized either

through patent royalties

or

through

sales of equipment

or

both.

Once sound pictures began to be made

and shown, developmental work was on

a different basis. Research and investiga-

tions of numerous incompletely solved

problems took on rather the character of

plowing in profits, with greatly increased

total expenditures for research and par-

ticipation by all the major picture-pro-

ducing organizations.

Of a11

of

the problems, the most fun-

damental and greatest in magnitude was

learning how to use sound pictures,

or

the evolution of a new art. This is dis-

cussed by

J.

E. Abbott.”? The expres-

sion “growing pains” aptly describes the

less successful phase of this evolution.

Capacity for readjustment is one of the

qualities of greatness in individuals and

in organizations, and the motion-picture

industry came through splendidly.

When any industry becomes large,

and especially if its requirements are as

diverse as those of sound pictures, it

provides a market for numerous special-

365

,,

Fig. 10. Arrangement employed by

6.

L.

Dimmick in 1929 galvanometer, for

multiplying the rotation of the mirror.

ties and services. Many of these require-

ments are met by comparatively small

organizations and others by branches of

companies having many other activities

and products. A few such items will

serve to illustrate

:

special lamps, arc

carbons, screens, cameras, acoustic treat-

ment materials and service, chemicals,

printers, testing equipment and studio

apparatus. Many important improve-

ments and contributions to technical

advances are due to those who develop

and supply such auxiliary equipment.

Mingled with the natural rivalry

between picture producers has been a

spirit

of

cooperation and sharing of ex-

perience and knowledge which has

greatly accelerated progress. In 1930

this society began issuing the monthly

Journal

instead of the quarterly

Trans-

actions,

an appropriate step to accom-

modate the rapidily expanding literature

of sound-picture technology, covering

almost every phase of the making and

showing of motion pictures. The Acad-

emy of Motion Picture Arts and Sciences

also played an important part in pro-

moting interchange of information. En-

gineers and technicians from the sound-

picture laboratories have reported ex-

periences with various problems related to

processing and controls and to sensitom-

etry, while film and photographic sup-

pliers have spared no efforts to enable

those using their product to get the best

possible results.

So

many have been the contributions

to the art and science along these lines,

that

I

find it quite beyond my ability

to do more than pay this general tribute

and to mention a very few developments

which have seemed to me to be of out-

standing importance.

I

trust that

I

may be forgiven for showing partiality

to the types of development with which

I

am most familiar, and also if

I

un-

justly fail to mention many important

advances.

Some of the Improvements After 1930

Galvanometers for Variable-Area Recording.

The galvanometers used in the first

variable-area recorders supplied by RCA

Photophone were practically standard

oscillograph vibrators, as these had been

built at General Electric. They were

oil-immersed and responded well up to

5000

cycles or above. An improved

smaller model was brought out in 1930,178

completely sealed instead of having an

open oil well and with no external ad-

justments. This used molybdenum ribbon

(much stronger than the bronze) and

was tuned to about

6000

cycles.

When recording was started at the

RKO studios in Hollywood, one of the

men from the General Engineering

Laboratory who had had much ex-

perience with oscillographs, F.

B.

Card,

joined the RKO staff. The RKO en-

gineers soon decided that their sound

would be better if the frequency range

were extended. The ribbons of the

os-

cillographs had been of phosphor-bronze.

A small supply

of

duralumin ribbon was

obtained, and with this Card succeeded in

re-stringing the RKO galvanometers,

with sufficient tension to tune them to

nearly 9000 cycles. A thinner damping

fluid was then appropriate,

a

change

almost necessary to realize the benefits

of the higher natural frequency.

G.

L.

Dimmick came to the General

Electric Co. in 1929, and one of his

first projects was the development of a

new galvanometer which was promptly

used in newsreel equipment.178 He used

a magnetic driving system of the balanced

rocking armature type and by an ingeni-

ous

mechanical arrangement, shown in

Fig.

10,

made his mirror rotate through

about ten times the angle of the arma-

ture. The important advantage of this

galvanometer was that the mirror was

about ten times the area of that of the

previous galvanometers. A few years later

Dimmick designed a new galvanometer

on the same principle (Fig.

11)

but

improved in numerous detail~.’~J~~J80

This became the RCA Photophone stand-

ard for all photographic recording.

These galvanometers were tuned to about

9000 cycles. Damping was by means

of

a block of rubber, the action of which

was analogous to that of the rubber line

of

H.

C. but since it

*

See June

Journal,

p.

296,

third col.

‘-DAMPING

LINE

Fig. 12. Construction of RCA record-

ing galvanometer (shown

in

section

in

Fig. 11).

Fig. 11.

Cross

section of improved re-

cording galvanometer,

G.

L.

Dimmick.

A-armature; B,B-pole pieces;

C,C-

working air gaps; D,D-nonmagnetic

spacers; E-tensioned bronze ribbon.

had to work only at high frequency

it

could be of quite small dimensions.

Dimmick found that he could increase

the effectiveness of such damping blocks

by incorporating tungsten powder in

the rubber to increase its density (Fig.

12).

Further improvements in the galva-

nometer were reported by Dimmick in

July 1947.18’ By the substitution of

better magnetic materials he was able to

reduce hysteresis almost to zero, to

increase the sensitivity, and to avoid

a slight saturation effect which had

been present in the previous design.

A

More Eficient and Versatile Optical

System.

In order that the galvanometer

in one of

our

experimental optical systems

might be closer to the slit, and thus

send more light through it,

I

arranged

a

galvanometer

to

work on its side,

so

that it would move the light spot up and

down across, instead of parallel to,

the slit.

I

used a light spot with a sloping

edge at an acute angle such that

the change from zero to full-length slit

illumination was accomplished with a

movement equal to only one-fourth

of

the slit length.

*,la2

Dimmick improved

on this by making the light spot sym-

metrical with respect to middle

of

the

slit, and having two sloping edges (see

Fig.

13,

and in Fig.

14

compare C with

B).

An advantage of the transverse-

movement system was that it became

very simple, by changing the masks

which were imaged on the slit, to pro-

duce a variety of tracks which had their

special

appli~ations.~~2~180~1~3~~~~

The combination of larger mirror

and reduced distance between galvanom-

eter and slit practically eliminated the

diffraction trouble that had, with the

small mirrors, impaired the formation

of clean, sharp, high-contrast images at

the plane

of

the slit.

Ground-Noise Reduction

-

G

NR

.Ia5

Scratches and dirt on film and graininess

of emulsion cause a background noise

*

All galvanometers have practical limits to the

angle through which they can swing the light

beam. And the required light spot movement sets

a minimum to the distance between galvanometer

and slit. The light which a galvanometer can

send through the slit is proportional to the mirror

area and the inverse square

of

its distance from

the slit, up to the point at which the objective

lens is “filled.”

366

July 1955 Journal oft& SMPTE Volume

64

CONDCNSER

LENS

IMRGE

OF

ILLUMINRTED

PORTION

OF

SLIT

IMRGE

OF

WINDOW

WINOOW

LENS

RLVhNOMETER

CONVERGING

LENS

OBJECTIVL

LENS

LRTCNT

IMRGE

/

or

MIRROR

SLIT

IN

SCREEN

Fig.

13.

Variable-area recording optical system.

(Lens

B

images

A

on

slit-plate

D.)

which is particularly conspicuous when

the modulation is low. The noise is

reduced by reducing the transmitted

light. At the same time, for a given modu-

lation level there is no need for the

average transmission to be more than

about half the maximum. The noise

may thus be reduced when the reduction

is

most needed, by decreasing the average

light when the level of the recorded

sound is low. This can be accomplished

by biasing the light modulator toward

zero, and then using a current derived

by rectifying some of the modulation

current to increase the mean light trans-

mission when this is needed. The reduced

transmission when the modulation is

low means a darker track in a variable-

density system, or a narrower clear area

in a variable-area system, and in either

case the noise is reduced. The early

patent on this idea was to

E.

Gerlach.186

This was assigned to Siemens

&

Halske,

but to the best of my knowledge it

occurred independently to L.

T.

Robin-

son in Schenectady and

C.

R.

Hanna

at We~tinghouse,'~' and a system appli-

cable to light valves was developed at

Bell Laboratories.18* The first trials at

Schenectady with variable-area tracks

did not indicate an impressively large

reduction of noise, and there was an

objection (in the case of the earlier,

unilateral, variable-area tracks) in that

the bias threw all of the low-level modu-

lation over to one edge of the track,

where many reproducing light beams

were of reduced intensity. The project

was revived by Hugh McDowell of

RKO

who got around the objection by screen-

ing off the surplus light by means of a

shutter instead of biasing the galvanom-

eter.lsg This method and the results

obtained were reported to the Academy

of Motion Picture Arts and Sciences by

Townsend, McDowell and Clark in

1

930.lg0 Thereafter a commercial form

of shutter was designedxg1 and ground-

noise reduction became standard in the

RCA

system (Fig.

15).

With the introduction slightly later

of

the symmetrical track, the objection

just mentioned to depending on galva-

nometer bias instead of a shutter no

longer applied, but there was still some

danger of saturating the galvanometer.

Therefore

a

double-vane shutter was

developed to mask down the light from

both sides.x92

The Bell Laboratories system is de-

scribed by Silent and Frayne.188 In the

,DIRECTION

OF

MOl

.ION

I

variable-density system there is no ob-

jection to accomplishing the result by

biasing the valve.

In case of a sudden increase in modu-

lation level the rectified current would

change

so

rapidly as to cause an audible

sound. The current for the shutter or for

bias is therefore passed through a filter

which reduces the rate of change.

Limiting the speed with which the

average light can increase means some

clipping of the first few modulation

peaks.

The light valve is a very low imped-

ance device, and since the bias current

may have to be sustained for consider-

--

SCANNING

OR

REPRODUCING

LIGHT]

A

B

C

D

E

F

0

ORIGINAL UNILATERAL PUSH-PULL PUSH-PULL CLASS

B CLASS

B

UNILATERAL VERTICAL CLASS

A

CLASS A

DIRECT

MOTION POSITIVE

Fig.

14.

Variation types of area soundtracks, and light-spot shapes which produce

them.

Fig.

15.

Soundtrack produced by McDowell ground-noise reduction shutter.

Kellogg: History

of

Sound Motion Pictures

367

able periods of time transformers cannot

be used for impedance match coupling

to the output tube of the ground-noise

reduction amplifier. In the system

most widely used with light valves the

modulation current is rectified, passed

through the timing filter, and used to

modulate a 20,000-cycle oscillator, the

output of which is amplified and recti-

fied for supply to the valve. The design

of the timing filter is much simpler when it

can operate at interstage impedance.193

As compared with variable-area, the

variable-density system is characterized

by ground noise which is less in the

nature of “ticks” and “pops” and more a

continuous hiss. Another difference is

that in the density system the noise falls

more rapidly with reduced light trans-

mission,

so

that a given amount of noise

reduction is obtained with a smaller

change in transmission. The con-

tinuous hiss type of noise is especially

noticeable if it comes and goes, which

changing bias causes it to do. This is

often called the “hush-hush” effect, and

becomes noticeable if the valve opening

does not immediately fall when the

modulation drops to a low level. At

the same time the fact that smaller

changes in transmission suffice to control

the ground noise makes it possible to

change transmission

(or

bias) more

quickly without causing “thump.” The

filters for density systems are therefore

designed for much faster timing than

those of area systems, particularly in

closing down when modulation falls.

While clipping of initial modulation

peaks is a less serious problem in density

than in area recording (because of

faster opening and larger margin)

engineers working with both systems

have given much study to minimizing

such clipping. Increased margin will

decrease the frequency of occurrence of

clipping, but this would be at the price

of more noise. In all systems, opening

(increasing light) is about as fast as it

can be made without becoming audible,

while the closing is much slower

so

that

very brief reductions in level will not

produce incessant closing and opening.194

A nonlinear characteristic has been

given to RCA ground-noise reduction

amplifiers, which causes the opening, as

a

function of modulation amplitude, to

rise more steeply at first and then more

Relatively low-level modula-

tion is then sufficient to cause an increase

in margin and thus reduce subsequent

clipping. It is when the modulation

is

nearly zero that close margin is urgent.

Certain characteristics of speech sounds

have an important bearing on the design

of ground-noise reduction systems. The

positive pressure peaks are higher than

the negative, and it is important to

maintain correct polarity from micro-

phone to valve, or to shutter and galva-

n~meter.’~~J~~

R.

0.

Drew and

I

made

an investigation to determine how often

speech sounds build up rapidly.lg6

Instances in which maximum amplitude

was reached in less than three or four

waves (voice fundamental) were sur-

prisingly rare.

The ideal solution to the problem of

avoiding initial clipping would be to

anticipate increases in sound level. This

is discussed by

J.

G. Frayne.197

Anticipation by use of a second

microphone was used experimentally in

the stereophonic system described in the

October 1941

Journal

(p. 351) for

operation of the compre~sor.~~a A system

employing a 14-msec electrical delay

network is described (March 1950)

by Whitney and Thatcher.lg8

When reported it had been in use for

over a year by Sound Services Inc. with

very favorable results. Besides reduced

clipping, advantage was taken of the

system to increase ground-noise reduc-

tion in density recordings by

5

db, and in

area recordings to work with a bias line

only 1 to

1;

mils wide. A low-distortion

network good to

8000

cycles necessarily

employs many sections (several hundred).

Cost is probably the reason that this

expedient has not been widely employed.

A direct-positive variable-area recording

system with the anticipation effect

provided by means of an auxiliary

exposure was designed and demon-

strated by Dimmick and Blaney and

has been used in the Warners’ studios.’Qg

In the re-recording operation anticipa-

tion should be a simple matter, involving

only

a

double reproducing system (with

scanning points a fraction of an inch

apart) with separate amplifiers.

*

Mueller

and Groves (June 1949)200 mention use

of this system at Warners.

I

understand

however that little advantage has been

taken of this possibility, presumably on

account of costs. The explanation is

probably that when initial clipping

occurs in

a

well adjusted re-recording

system, there was probably also some

at the same spots in the original recording

and the possible gain from anticipation

in the re-recording operation is hard to

detect.

If

clipping, in systems using

ground-noise reduction, causes an ap-

preciable impairment to sound quality,

the ideal solution is to use for original

recording

a

system whose ground noise

is inherently

so

low that it needs no such

expedient, and then introduce the

ground-noise reduction when re-record-

ing to the photographic tracks. Similar

considerations apply to the use of com-

pressors. Among the systems which in

more

or

less measure meet this specifi-

cation are Class

B

area recording, wide-

track push-pull (with fine-grain film and

fast-acting noise reduction) direct posi-

tives with the auxiliary exposing light,lQQ

and direct-playback disks. A real answer

*

In a set-up

for

mixing numerous sounds, it

would

for

practical purposes be sufficient to equip

only the dialogue film-phonograph with double

scanner and amplifier.

to this problem seems to have come in

the recent adoption of magnetic record-

ing.

?

200,352

-388

Pre-

and

Post-Equalization.

The prac-

tice of electrically exaggerating the high-

frequency components in recording, as

compared with the low-frequency com-

ponents, in order to compensate for

inevitable losses, began early in the

recording of sound. Studies of the dis-

tribution of energy in program material

had indicated that this could be done

without resulting in overloads in the

high-frequency end of the scale.

A

large amount of high-frequency pre-

emphasis had been employed in cutting

transcription disk records. In film

records as well as disk records, ground

noise can be made less noticeable by

decreasing the gain at high frequency.

Therefore, in addition to such relative

attenuation of high-frequency sounds

as was caused by the imperfections of

reproducing systems and loudspeakers,

the practice became prevalent of produc-

ing a drooping characteristic in the

electrical circuits.

In order that all films might have good

balance in all theaters, a committee of

the Academy of Motion Picture Arts

and Sciences made recommendations for

a standard reproducing characteristic.201

With such a standard adopted, the

producers of sound pictures would have

incentive to use recording characteristics

which would give good balance when

their films were played in a theater with

the typical

or

standard reproducing

characteristic.

The problem is discussed by

J.

K.

Hilliard202,203 and by Morgan and

L0ye.20~

Better

Lumps.

Among the lamps used

in the late 1920’s for recording were some

of the ribbon-filament type. These were

ideal from the standpoint of uniformity,

but required an inconveniently large

current

(18

amp) and did not have as

long life at a given temperature as was

obtainable with lamps of the helical-

filament type. A series of lamps for sound

recording and reproduction was made

available by the lamp companies. The

filaments were close-wound helices, of

relatively heavy tungsten wire, and to

permit operation at high temperatures

with satisfactory life, the pressure of the

inert gas (argon) with which the bulbs

were filled was increased above that

employed in lamps from which less

intensity was required.

In the series of lamps described by

F.

E. Carlson of General Electric in

1939205 the recording lamps were rated

as operating at above 3100

K

(color

temperature) which is several hundred

degrees higher than that of common

t

Some experimenting has been done with a dou-

ble magnetic pickup for anticipation. Cross-tak

between the two heads was a problem. The diffi-

culties will undoubtedly

soon

be worked out.

368

July

1955

Journal

of

the

SMPTE

Volume

64

incandescent lamps. Somewhat later,

krypton-filled lamps were introduced,

permitting still higher temperatures.

The krypton, being heavier, more effec-

tively retards evaporation of tungsten.

(See the section on basic inventions.)

The light from a helical filament

varies somewhat, depending on the angle

from which the lamp is viewed. At the

suggestion of

L.

T.

Sachtleben of

RCA,

the helix of the lamp used in the variable-

area recordings was curved, the convex

side being presented toward the lenses.

The helix with the curved axis gives

definitely better unif~rmity.~~~-~~~~

205a

Improvements in Light-Valves

and

Density

Optical Systems.

In June 1932 Shea,

Herriott and GoehneP5 described the

development of improved duralumin

ribbon (stronger and with straighter

edges) and better methods of adjusting

and anchoring the ribbons at the ends

of

the free span. The new anchoring

system practically eliminated the fric-

tional hysteresis which had been found

in the earlier design, thus reducing

waveform distortion and making for

greater stability. Stability became in-

creasingly important as the mean spacing

between the two ribbons in the valve

was reduced. The ground-noise reduc-

tion system called for reducing the ribbon

spacing when the modulation was low,

and when it was found possible in view

of required exposures to reduce the

unbiased spacing from

0.002

in. to

0.001 in. this was done, while still

keeping the optical reduction from valve

to film at 2:l.

At high frequency and high modula-

tion, the images of the ribbon edges move

with velocities comparable with the speed

of

film travel. This results in a waveshape

distortion which would convert a sine

wave into a saw-tooth wave. Fortu-

nately such

a

combination of high fre-

quency and amplitude is not often en-

countered in program material, and the

harmonics generated would probably not

be

reproduced, nor noticed if they were.

However, it is desirable to minimize

thin

“ribbon-velocity’’ distortion, and

the reduced slit width helps in that

respect and also in giving better resolu-

tion or high-frequency response.

In order that harmful effects (harm

to sound quality if not to the ribbons

themselves) might not result when the

modulation current drives the ribbons

to

the point of touching or hitting each

other (light-valve “clash”) light valves

have been built with the ribbons slightly

offset, or in two planes.207 There appears

to have been difference of opinion about

the necessity of this precaution. It

should be remembered that in a density

system the downward light modulation

ncrmally stops considerably short of

zero, to avoid photographic nonlinearity.

In other words touching of the ribbons

would represent considerable overload.

The two-plane design of valve has be-

come generally standard for variable-

density recording.

The optics of light-valve recording

systems207 have been modified by the

addition of a small horizontal cylindrical

lens close to the film, which results in

greater optical reduction between valve

and film and therefore a narrower image

(0.0002 in.). This makes for improved

high-frequency recording and for further

reduction of ribbon-velocity distortion.

One of the factors which has made the

narrower image possible without sacri-

ficing exposure is that new lamps of

higher intensity have become available.

Light-valve optics have been adapted

to making variable-area tracks, for ex-

ample as used in the stereophonic system

described in 1941

.208

The valve is turned

with the ribbons vertical, or parallel to

direction of film travel. The lens system,

which employs cylinders, magnifies the

ribbon motion ten to one. This means

that the lens must be close to the ribbons,

hence with little depth of focus. There-

fore in this application the ribbons are

in the same plane, and an electrical

current-limiting expedient prevents

clash.20Q

A

strong magnetic field is advan-

tageous for the sake of sensitivity and

damping. In the design described by

Wente and Biddulphm an air gap flux

density of

32,000

gauss is attained, an

achievement which testifies

to

the

excellence of the permanent magnet

materials and the high flux capacity of

the pole-piece material. There is some

further discussion of light valves in the

section on variable density vs. variable

area.

Microphones.

While condenser micro-

phones had excellent characteristics

they were more expensive and required

more servicing than magnetic micro-

phones, and it was practically necessary

to provide a stage of amplification close

to the microphone.

On

the other hand,

the electrical impedance of a magnetic

microphone is such that a transformer

may be used if wanted, and the output

transmitted at

a

convenient impedance.

A

magnetic microphone of the flexibly

mounted rigid-diaphram, moving-coil

type is described by Jones and Giles in

December 1931.210*211 It is

a

pressure-

type (rather than velocity or pressure-

gradient) microphone. Damping is ob-

tained by flow of air when the diaphram

vibrates, back and forth between two

cavities, through passages which are of

such small dimensions as to make air

viscosity effective in dissipating energy.

In June 1931

H.

F.

Olson described

the velocity microphone,212 consisting of

a ribbon of very thin aluminum (0.0001

in.) in a magnetic field between pole

pieces which are adjacent to the edges of

the ribbon,

so

that when the ribbon

moves in a direction normal to its surface

a

voltage is induced in the ribbon.

A

transformer is used to step up this

voltage, which is then applied to the

grid of an amplifier tube. Transverse

corrugations are formed in the ribbon,

which prevent it from curling and give it

lengthwise flexibility. It is mounted under

only such tension as is needed to keep it

between the pole pieces. Olson shows

that theoretically such a microphone

should give uniform frequency response,

and that it should have a polar direc-

tivity curve like

a

figure

8

(cosine law),

the directivity being the same through-

out the frequency range. Experimental

results are also given confirming the

theory. The velocity of movement of

the ribbon is proportional to the velocity

of air movement,

so

that it is often called

a “velocity microphone.”

Since a microphone of this type

responds less and less as the direction of

the sound departs from normal, it picks

up much less reverberation (random

in direction) than

a

nondirectional

microphone having the same sensitivity

for sound of normal incidence. The ratio

of direct to reverberant sound in many

cases sets the limit to how far from the

source the microphone can be placed,

and under such circumstances a ribbon

microphone can get satisfactory pickup

some

70%

farther from the source than

a

nondirectional microphone, such as

one of the pressure t~pe.~l3 Advantage has

been taken of the directional character-

istics of the ribbon microphone to exclude

certain sounds or disturbances (for

example camera noise), for it is deaf to

sounds originating in the plane of the

ribbon.

If the output of a pressure microphone

is combined in correct phase and amount

with that of a velocity microphone, the

combination becomes unidirectional, hav-

ing

a

cardioid-shaped directivity curve.

It

has

a

dead-spot 180’ from the direc-

tion of maximum sensitivity. The forward

directivity is much less sharp than that

of

a

velocity microphone, and such

a

unidirectional microphone

is

better suited

for picking up sound over

a

wide angle,

as for example from a large orchestra.

The cardioid directivity pattern has the

same advantage as the figure

8

pattern

in picking up less noise from random

directions than a nondirectional micro-

phone.

Before making a unidirectional micro-

phone, Olson worked out an arrange-

ment for converting a velocity micro-

phone into a pressure microphone. He

placed close behind the ribbon a com-

bination shield and absorber consisting

of an open-ended tube of the same

cross-sectional area as the active area of

ribbon. He distributed through the tube

tufts of absorbent fiber. The length of the

tube was made sufficient to dissipate

wave energy. The impedance of the

mouth of the tube then becomes equal

to

that of

so

much free air (to plane

369

Kellogg:

History

of Sound

Motion

Pictures

waves) but air in which there is no other

sound to react on the ribbon. The ribbon

is then actuated only by the pressure on

the exposed side.214

Having successfully made this con-

version, Olson applied the same treat-

ment to only one half of the length of the

ribbon, leaving the other half to act as a

bidirectional velocity microphone, and

the combination has the cardioid direc-

tional

characteristic^.^^^

Bell Laboratory engineers also de-

veloped bidirectional or velocity micro-

phones, and unidirectional types, but

differing from the Olson type in employ-

ing a second microphone more nearly

like their standard pressure microphone.

The unit and its applications were dis-

cussed by Marshall and Harry in Sep-

tember

1

939.216

All studios use directional microphones

for situations where the maximum ratio

of direct to random sound is wanted.

loudspeaker^^^^^^^^^^^

Single Range Loudspeakers.

For several

years after the industry had adopted

sound the theater loudspeakers were of the

kinds already mentioned,

(1)

the direc-

tional baffle-type, using a coil-driven

cone, much like those used in direct

radiator speakers, with a short, straight-

axis exponential horn of large throat

area, and (2) those using long exponen-

tial horns217,218 with small throats, and

coil-driven metal diaphragms. In view

of their length the horns were coiled or

otherwise bent to a form which took up

less space.

Multi-Range Loudspeakers and Improved

Single-Range Steakers.

The idea of provid-

ing separate devices to radiate high and

low frequencies is undoubtedly of early

origin. When practically all radiators had

strong fundamental resonances, the

double or triple unit could spread the

range of reasonably high response over a

wider frequency band. With the advent

of coil-driven, untuned diaphragms,

resort to separate radiators was a measure

for improving efficiency, in that the

design did not have to be a compromise

between what was best for low and for

high frequencies.

A

triple-horn speaker

designed with special consideration to

efficiency and load capacity was ad-

vocated and demonstrated by C. R.

Hanna of Westinghouse in 1927.219

However theater speakers of the single-

unit type were

so

far improved (by the

coil-driven unit of Wente and Thuras in

1926,57 and by the adoption of directive

baffles for the GE-RCA cone-type

speakers in 1929) that they handled

quite well the frequency range then

obtainable from film or disk.

As

recording improved, the benefits

from extending the loudspeaker range

became more noticeable. After various

improvements in the recording system

including the new galvanometer, the

symmetrical track, ground-noise reduc-

tion (by galvanometer bias), ribbon

microphone for sound pickup, and a

film-phonograph using the magnetic

drive, Dimmick and Belar gave

a

demonstration of extended frequency

range at the SMPE 1932 Spring Con-

~enti0n.l’~ They did not resort to two-

way (divided-range) speakers, for the

straight-axis, directional baffle units,

which had 6-in. cone diaphragms with

aluminum voice-coils, had good re-

sponse even at

10,000

cycles. The range

was extended downward (to 60 cycles)

by using slow expansion exponential

horns (of the large-throat or directional-

baffle type)

10

ft long, with mouth

openings 75 in. square.

Multi-Range Speakers

of

Bell

Telephone

Laboratories.

A divided-range speaker

system was used by

H.

A.

Frederick in

the demonstrations of vertically cut disk

records in the fall of 1931.220 The high-

frequency units were of the type de-

scribed by Bostwick in the October 1930

Journal

of

the Acoustical Society

of

America,

and in the May 1931

SMPE Journal.n1

These were equipped with small horns

better to load the diaphragms. The low-

frequency units were of the direct-

radiator or flat-baffle type, using (as

I

recall it) approximately 12-in. diameter

dynamic cone units,38 a number of units

being distributed over a large baffle.

A curve indicates a response within

rt

5

db from

50

to

10,000

cycles.

A triple-range system is described by

Flannagan, Wolf and Jones,% whose

review of the development of theater

loudspeakers is comprehensive and of

much interest. The system is also dis-

cussed by Maxfield and Flannagan in the

January 1936

Journa1.222a

The mid-range

units were essentially like the previous

single-range speakers, using the Western

Electric

No.

555

driver units. The

radiators for the high-frequency range

(3,000-13,000) were the same as used

in the Frederick demonstrations. The

authors state that for the range below

300 cycles large coil-driven conical

diaphragms in a large flat baffle gave

better results than designs using horns.

In April 1933 the Bell Telephone

Laboratories gave a demonstration of

reproduction of orchestra music in

“auditory per~pective,”~~~~~

the orchestra

being in Philadelphia and the reproduc-

tion in Constitution Hall in Washington,

D.C. Three microphones picked up the

music at three well-separated positions,

and at the other end the independently

transmitted and amplified currents were

supplied to three correspondingly placed

loudspeakers.

In this demonstration no recording

and reproduction entered to affect

frequency range, and it was essential for

the purpose to provide abundant sound

power and frequency range.

A

dual-

range system was decided on.

The low-frequency unit was designed

to work from

40

to 300 cycles, and con-

sisted in a large-diaphragm, moving-coil

unit, working into the %in. diameter

throat of a horn which expanded expo-

nentially to a mouth 60 in. square in a

total length of approximately

10

ft.

The high-frequency driver unit, which

covers the range

300

to 13,000 cycles is

shown in cross section as Fig.

10

in the

Flannagan, Wolf and Jones paper.n2

Particular attention is given in the

design to the air space and passageways

leading from the diaphragm surface into

the horn or group of horns.

If

a single straight-axis exponential

horn is used, the tones of highest fre-

quency are radiated in

a

direction close

to the axis, while those of lower fre-

quency are spread through much larger

angles. This defect is avoided by dividing

the total cross section of the passage into

a number of smaller passages each of

which is a small exponential horn.

In this case there were sixteen horns for

each driver. These are nested with their

mouths adjacent and with their axes

pointed in different directions to cover a

total angle of about 30’ vertically and

horizontally. Since the horns are of

equal length, the waves, whatever their

frequency, unite at the ends of the horns

to form a practically continuous spherical

front, which is the condition for uniform

distribution throughout the 30’ angle.

Two of these 16-horn nests were placed

side by side to give the desired total of

60’ horizontal coverage.

First Commercial

RCA

Two- Way Theater

Speakers.

In the RCA line of theater

equipment a dual-range loudspeaker

system was briefly described by

J.

Frank, Jr., at the 1935 fall meetingzz5

The speakers demonstrated by Dimmick

and Belar, in 1932, using 6-in. cone

diaphragms with aluminum voice coils,

and 10-ft horns, were not seriously

lacking in frequency range and were

used in a number of deluxe installations,

but they had two drawbacks. There

were many theaters without sufficient

room to install the long straight axis

horns, and in addition, the high-fre-

quency sound components were not well

distributed. When

a

wave front reaches

a point in an exponential horn at which

the dimensions of the passageway are

about a wavelength, its ultimate angle of

spread will not greatly exceed the angle

between the walls at that place. From

this consideration it follows that a rapid

flare horn would distribute the high-

frequency sounds through considerably

larger angles. Moreover with short rapid-

flare horns, it is not impractical to mul-

tiply the number of units and thereby

further control the sound distribution. In

the theater speaker described by Frank,

there were three high-frequency horns di-

verging in direction, the driver units being

6-in. cones with aluminum voice-coils.

370

July

1955

Journal

of

the

SMPTE

Volume

64

r

s

These units were rated to operate effec-

tively from 125 to 8,000 cycles, and a

separate folded horn unit took care of

sounds in the 40 to 125 cycle range.

One of the practical advantages of a

direct-radiator (flat baffle) loudspeaker

is the small space it requires. However a

horn makes it possible to radiate more

sound from a given-sized diaphragm

without increasing the amplitude of

motion, and is therefore desirable for

increasing the sound output capacity.

It

also affords some control of the

direction of radiation. But to radiate low

frequencies the rate of expansion (ratio

of increase in cross section per unit

distance along axis) must be small,

which for a given total ratio of expansion

means length. One way to provide a

long passageway without requiring ex-

cessive depth of space back of the screen

is to coil up the horn. Drawings of coiled

horns are shown in ref.

1,

p. 298, and on

p. 251 of the March 1937

Journal.

The

bending of large sound passageways is

objectionable. Instead of expanding

continuously as in the ideal horn, short

waves suffer repeated reflections by the

walls, causing some irregularities in the

response and making the direction of

radiation of high-frequency sounds rather

unpredictable.* On the other hand if the

horn is to handle only low-frequency

sounds, the shapes of the bends are not at

all critical, and the condition is easily

fulfilled that the difference between the

shortest and longest paths around a

bend is a small fraction of a wavelength.

In a common form of low-frequency

horn (in the sense of an approximately

exponentially expanding passageway) the

driver unit

(or

units) is at the middle of

the back of a box-shaped space, and the

passage is forward for

a

short distance,

dividing and forming two passages which

turn back and then forward and expand

to form a pair of large adjacent rectangu-

lar openings, which together form the

mouth of the horn.

This roughly de-

scribes the low-frequency unit of the

theater speaker system reported by

Frank, the drivers in that case being a

pair of 8-in. coil-driven cones.

Shearer

System.n6 In 1936 Douglas

Shearer, sound director for M-G-M,

gave demonstrations of improved sound,

using loudspeakers described by

J.

K.

Hilliard in the July 1936 Journal.

The high-frequency radiators in this

system were similar in many respects to

those used for the Auditory Perspective

demonstrations (see figure in Hilliard

paper). The frequency range to be

covered was 50 to 8000 cycles, and the

division or cross-over was at 250 cycles.

The low-frequency unit was a folded

horn, with four 15-in. cones in

a

vertical

column. For simplicity of construction

the expansion was all in the horizontal

*

This effect can be largely reduced by careful

design

of

re-entrant (zig-zag passage) horns.

Fig.

16.

Controloffilm speed

by

flexure

(A.

V.

Bedford). Principle later utilized

in

nonslip printer.

plane, accomplished by suitably ar-

ranged vertical partitions. The horn

cross section was divided into two expand-

ing passageways, whose final openings

together form a 68-in. square (Fig. 16).

This was surrounded by a flat baffle 10

X

12 ft, to reduce end reflections and

improve the loading of the units. The

mean length of each passageway was

40

in. (very short as low-frequency horn

designs

go),

nor was the expansion

ratio large, the throat area being

sufficient to accommodate the four 15-in.

cones.

A nest of high-frequency horns, similar

to that used for the Auditory Perspective

demonstrations, three high by six hori-

zontally, covered

a

horizontal angle of

about

looo.

With the lengths of the high-

and low-frequency horns nearly the

same, there would be little time differ-

ence in the arrival of the sounds at the

plane of the mouths, thus simplifying the

avoidance of

a

“phasing” error which

has been found to have detrimental

effects with transients. However, in all

divided-range speaker systems the best

relative positions of the high- and low-

frequency units have been determined

by careful trials. This problem of

“phasing” is discussed by Maxfield and

Flannagan,zza by Hilliardz6 and others.

It

appears to be not wholly

a

question

of minimizing the mean time difference,

although that is a part of it.

In all divided-range speaker systems,

dividing networksn7 have been used to

separate the high- and low-frequency

portions of the amplifier output and

direct each to the appropriate speaker

units. The networks consist in general of

simple filter sections, and their design

has received much study.

Commercial

Two-

Way

Systems. Com-

mercial models of dual-range or “two-

way” theater speakers were brought out

in 1936, employing the multicell high-

frequency horn system, and low-fre-

quency units much like those described

by Hilliard. The high-frequency driver

units of the RCA system differed from

the ERPI and Lansing designs in that

the diaphragms were of molded phenolic

instead of aluminum. This resulted in a

more rugged, if less sensitive, device. The

reduced sensitivity and greater “roll

off,” or falling off at high frequency, can

be readily compensated electrically, and

do not mean any serious increase in

amplifier output power, because the

high-frequency components of the sound

represent only a small part of the total

sound power.

The ERPI “Diphonic” speaker system

Kellogg:

History of Sound Motion Pictures

is described in the Flannagan, Wolf and

Jones paper.2n

The description by Hilliard of the

Shearer low-frequency unit may be

taken as in general typical of the com-

mercial speakers of

1936-7.

Divided channel or “two-way”

speakers came into wide use during the

several years following 1936.

In some later designs of low-frequency

units, the sound passageway was not

folded, and consisted only of

a

short

flaring connection between the driver

units (which presented a large total

radiating surface) and the large opening

in the flat baffle.* It is of interest that

the evolution of low-frequency sound

sources has been toward a closer resem-

blance to the cone and baffle speakers

of

1925, but greatly magnified in size, and

with some “directive baffle” effect better

to

control sound distribution.

Higher crossover frequencies than the

250-cycle point of the Shearer system

have prevailed, 400 cycles being the

choice in many of the postwar units.

In 1948 Hopkins and Keith228 described

the design of a two-way theater speaker

in which the crossover had been raised

to

800

cycles, observations having been

made that the irregularities which are

apt to occur at the crossover frequency

are less prejudicial if the crossover is

above the frequency range of maximum

energy (250 to 500 cycles for orchestra

music).

A photograph of a loudspeaker de-

signed to use with “Cinerama” is shown

in the May 1954 SMPTE ProgressReport,

p. 343.This is more or less typical of recent

practice. The horn (or directive baffle

expansion passage) of the low-frequency

units as well as that of the high-frequency

unit is designed to give exponential ex-

pansion of the total cross section by side

walls which are radial, the floor and ceil-

ing of each passage being curved to com-

pensate. The reflex, phase-inversion

principle (mentioned under “Monitoring

Speakers”) is employed to utilize radia-

tion from the backs

of

the diaphragms,

for the extreme bass. Note in the illus-

tration the outlet slots on either side of

the horn mouth.

Alternatives

to

Multicellular

Horns.

A

somewhat simpler way of achieving the

directive characteristic for which the

multicellular high-frequency horns were

designed has been developed in the post-

war period by RCA and others. Horns

are used with linear expansion in the

horizontal plane (i.e. walls radial with

respect to the throat), while in the

vertical plane the rate of expansion

~

*

This would raise the “cutoff” frequency of the

horn,

but

where the total expansion ratio is

comparatively small that is not necessarily very

significant. Below its “cutoff’ frequency, an

exponential horn does not impede sound trans-

mission. It merely fails to multiply the volume

displacement as

it

does above cutoff.

371

is such as to bring the total expansion of

the cross section to an exponential

relation.

Another expedient for gaining the

desired spread of high-frequency sounds

was described by Frayne and Locanthi

at the May

1954

convention of this

Society.229 If the waves issuing from a

straight-axis exponential horn can be

made to assume a spherical instead of

nearly flat front, they will spread as

desired. An acoustic equivalent of a

concave optical lens is placed in the

mouth of the horn, in order to retard

the off-axis parts of the waves relative to

the central part. The reduced velocity

of propagation is achieved by means of a

series of closely-spaced perforated sheet-

metal baffles, the number of layers

being progressively greater toward the

edges. This system was reported to have

given smoother distribution than the

multicell horns.

Monitoring

Loudspeakers.4,230.231

Wider-

range monitoring speakers kept pace

with theater speakers. While a single

conical diaphragm can be designed

so

that the center portion radiates high

frequencies and the outer area radiates

low frequencies, best results have been

obtained by using separate diaphragms

and separate voice coils,

or

in other

words resorting to the dual-range system.

The upper- and lower-range units may be

adjacent

or

concentric. In the latter case

the low-frequency diaphragm becomes a

directive baffle for the high-frequency

radiator.

Permissible cabinet size tends to set

the lower limit of the frequency range,

air reaction on the back of the diaphragm

creating the problem if the back

is

enclosed,

or

inadequate baffling if an

open-back cabinet is used. In order to

utilize the radiation from the back of the

low-frequency diaphragm, a second

opening is often provided (for example

below the diaphragm) and the space in

the cabinet used to provide a folded

horn between the diaphragm and the

opening, or else to serve as a simple

chamber which acts in conjunction with

the inertia reactance of the air at the

second opening as a phase inverter.

This does not greatly augment the low-

frequency output except near the reso-

nance, set by the elastic reactance of the

cavity and the inertia reactance of the

combination of openings (one with the

diaphram and one without). Sound-

absorbing material is often used in the

cabinet to reduce the magnitude of other

resonances.

If

the horn-type back-wave

system is used, its augmentation of output

is limited at the lower end when the

phase shift through the horn becomes

less

than about a quarter cycle, and at

the upper end by the fact that it

is

deliberately designed to have a low-pass

filter characteristic.

References (Continued)

1.

Lester Cowan,

Recording Sound

for

Motion

Pictures,

McGraw-Hill Book Co., New York,

1931

;

H.

G.

Knox, “Ancestry of sound pic-

tures,’’ Chap. 1.

4.

J.

G. Frayne and H. Wolfe,

Elements

of

Sound Recording,

J.

Wiley

&

Sons,

New York,

1949.

6. E.

I.

Sponable, “Historical development of

sound films,” Pt. 1-2,

Jour. SMPE,

48:

275-303, Apr. 1947; Pt. 3-7, ibid., 407-

422, May 1947.

57. E. C. Wente and A. L. Thuras, “A high

efficiency receiver of large power capacity

for horn type loud speakers,”

Bell

Sys. Tech.

J.,

Jan. 1928, p. 140.

70. E. W. Kellogg, “A review of the quest for

constant speed,”

Jour.

SMPE,

28:

337-376,

Apr. 1937.

The

fioe

references

above,

which

are

referred

to in

the current installment

of

this

paper,

are

reprinted from

the

first

installment

for

the convenience

of

readers.

77.

78.

79.

80.

81.

82.

83.

84.

L‘Industrie

du

Film Parlant,

Conservatoire

des Arts et Metiers, Feb. 17, 1929.

Contains

a

resume cowing the Gaumont and the Gaumont-

Peterson-Poulsen sound systems. (The foregoing

is

from the Theisen

historkal

paper-ref.

5.)

H. E. Roys, “The measurement of trans-

cription-turntable speed variation,”

Proc.

I.R.E.,

31:

52-56, Feb. 1943.

T.

E. Shea, W. A. MacNair and

V.

Suhrizi,

“Flutter in sound records,”

Jour. S.MPE,

E.

G.

Shower and R. Biddulph, “Differen-

tial pitch sensitivity of the ear,”

J.

Acoust.

Sac.

Am.,

3:

215-287, Oct. 1931.

W.

J.

Albersheim and D. MacKenzie,

“Analysis of sound film drives,”

Jour.

SMPE,

37:

452-479, Nov. 1941.

E. W. Kellogg and H. Belar, “Analysis of

the distortion resulting from sprocket hole

modulation,”

Jour. SMPE,

25:

492-502,

Dec. 1935.

SMPE Committee on

Sound,

“Proposed

standard specifications for flutter or

wow

as related to sound records,”

Jour.

SMPE,

E. W. Kellogg, “Proposed standard for

measurement of distortion in sound re-

cording,”

Jour.

SMPE,

51:

449-467, Nov.

1948. Further discussion of the Flutter

Standard by the same author appears in an

editorial in the

Trans. I.R.E.,

July-Aug.,

1954.

25:

403-415, NOV. 1935.

49:

147-159, Aug. 1947.

84a.

Frank A. Comerci, of the Material Labora-

tory, Bureau of Ships New York Naval

Shipyard, Brooklyn, N.

Y.,

“Perceptibility

of flutter in speech and music,”

Jour.

SMPTE,

64:

117-122, Mar. 1955.Discusnion,

318, June 1955.

85. M.

S.

Mead,

U.S.

Pat. 1,854,949.

86. E. W. Kellogg and A. R. Morgan, “Meas-

urement of speed fluctuations in sound

recording and reproducing equipment,”

J. Acoust.

Sac.

Am.,

7:

271-280, Apr. 1936.

87. A. Goodman, R.

J.

Kowalski,

W.

F.

Hardman and W.

F.

Stanko, “Safeguarding

theater sound equipment with modern

test instruments,”

Jour.

SMPE,

34:

409-

423, Apr. 1940.

88. R. R. Scoville, “A portable flutter-measur-

ing instrument,”

Jour. SMPE,

25:

41 6-422,

Nov. 1935 Also: “Laboratory flutter-meas-

uring instrument,”

Jour.

SMPE,

29:

209-

215, Aug. 1937.

89. F. P. Herrnfeld, “Flutter-measuring set,”

90.

U.

R. Furst, “Periodic variations of pitch

in sound reproduction by phonographs,”

91. L. A. Elmer and D.

G.

Blattner, “Machine

for cutting master disc records,”

Trans.

92. P.

H.

Evans, “A comparative study of

sound on disk and film,”

Jour. SMPE,

15:

Jour.

SMPTE,

55:

167-172, Aug. 1950.

Proc.

I.R.E.,

34:

887-895, NOV. 1946.

SMPE,

37:

227-246, 1929.

185-192, Aug. 1930.

93.

94.

95.

96.

97.

98.

99.

100.

101.

102.

H. Pfannenstiehl, “High-precision sound-

film recording machine,”

Jour.

S.I.IPE,

E. W. Kellogg, “A new recorder for variabl:

area recording,”

Jour. SMPE,

15:

653-

670, Nov. 1930.

(The title

of

this

paper

is

misleading,

in

that the main features

of

the

recorder were

in

no

wise related to the type

0,’

sound track to

be

recorded.)

E. W. Kellogg,

U.S.

Pat. 1,892,554,

1,899,571, and Re19,270.

R.

0.

Drew and E. W. Kellogg, “Filtering

factors of the magnetic drive,”

Jou~.

See ref. 94.

A.

G.

Zimmerman, “Film recorders,”

Jour. SMPE,

20:

211-227, Mar. 1933.

M. E. Collins, “A deluxe film recording

machine,”

Jour. SMPE,

48:

148-156,

Feb. 1947.

(Model PR-31)

H.

A. Rowland, an early disclosure (1902)

of the general principle of the damped

flywheel is in

U.S.

Pat. 691,667, 1899,

and 713,497. (See refs. 81 and 104.)

F. J, Loomis and E. W. Reynolds, “New

Apparatus-A new high fidelity sound

head,”

Jour. SMPE,

25:

449-460, Nov.

1935; and “New rotary stabilizer sound

head,”

Jour.

SMPE,

27:

575-581, Nov.

1936.

E. D. Cook, “The technical aspects of

the high-fidelity reproducer,”

Jour. SMPE,

25:

289-313, Oct. 1935.

29:

202-208, Aug. 1937.

SMPE,

35:

138-164, Aug. 1940.

102a.Gerhard Schwesineer. “The compliance

103.

104.

105.

106.

107.

108.

109.

110.

111.

112.

113.

114.

of

film loops,”

Jour-SMPTE,

57:

320-327,

Oct. 1951.

G. Puller, “Sound-picture reproducing

system for small theaters,”

Jour. SMPE,

27:

582-589, Nov. 1936; Report of the

Progress Committee,

Jour. SMPE,

27:

29, July 1936.

E. C. Wente and A. H. Miiller, “Internally

damped rollers,”

Jour. SMPE,

37:

406-417,

Oct. 1941.

C. C. Davis, “An improved film-drive

filter mechanism,”

Jour. SMPE,

46:

454-

464, June 1946.

G.

R.

Crane and H. A. Manley, “A simpli-

fied all-purpose film recording machine,”

Jour. SMPE,

46:

465-474, June 1946.

M. E. Collins, “Lightweight recorders for

35 and 16 mm films,”

Jour. SMPE,

49:

415-424, Nov. 1947.

(Models PR-32 and PR-

J.

D. Phyfe and

C.

E. Hittle, “Film-pulled

theater-type magnetic sound reproducer

for use with multitrack films,”

Jour.

SMPTE,

62:

215-220, Mar. 1954.

C. C. Davis and H. A. Manley, “Auxiliary

multitrack magnetic sound reproducer,”

Jour.

SMPTE,

62:

208-214, Mar. 1954.

S.

W. Athey, W. Borberg, and R. A. White,

“Four-track magnetic theater sound re-

producer for composite films,”

Jour.

SMPTE,

62:

221-227, Mar. 1954.

Wesley C. Miller, “M-G-M recorder and

reproducer equipment units,”

Jour. SMPE,

40:

301, May 1943.

J.

S.

Chandler, “Some theoretical con-

siderations in the design of sprockets for

continuous film movement,”

Jour.

SMPE,

37:

164-176, Aug. 1941.

J.

G. Streiffert, “The radial-tooth, variable-

pitch sprocket,”

Jour. SMPTE,

57:

529-

550, Dec. 1951.

“Rulings of the

U.S.

Supreme Court in

recent patent cases of the American Tri-

Ergon Corp.,”

Jour.

SMPE,

24:

529-550,

June 1935.

33.)

115. Report of Standards and Nomenclature

Committee,

Jour. SMPE,

14:

126, 133,

Jan. 1930.

116. Oscar B. Depue, “A machine for printing

picture and sound simultaneously and

automatically,”

Jour. SMPE,

18:

643-648,

May 1932.

372

July

1955

Journal

of

the

SMPTE

Volume

64

117. A.

S.

Howell, B. E. Steckbart and R. F.

Mitchell, “The Bell

&

Howell fully auto-

matic sound picture production printer,”

Jour.

SMPE,

19:

305-328, Oct. 1932.

118. A.

S.

Howell and R. F. Mitchell, “Recent

improvements in the Bell

&

Howell fully

automatic printer,”

Jour.

SMPE,

22:

115-

126, Feb. 1934.

119. Roscoe C. Hubbard, “Printing motion

picture film,”

Trans.

SMPE,

No. 28, 252,

Feb. 1927.

120.

J.

Crabtree, “Sound film printing-I,”

Jour.

SMPE,

21:

294-322, Oct. 1933;

“Sound film printing-11,”

Jour.

SMPE,

22:

98-114, Feb. 1934.

121.

J.

I. Crabtree and C. E. Ives, “A new

method

of

blocking out splices in sound

film,”

JOU7.

SMPE,

14:

349-356, Mar. 1930.

122. F. D. Williams, “Methods of blooping,”

Jour.

SMPE,

30:

105-106, Jan. 1938.

123. W.

H.

Offenhauser,

Jr.,

“Current prac-

tices in blooping sound-film,”

Jour.

SMPE,

124. E.

I.

Sponable, “Elimination

of

splice

noise in sound film,”

Jour.

SMPE,

26:

136-144, Feb. 1936.

124a.George Lewin, “A new blooping device,”

Jour.

SMPE,

48:

343-347, Apr. 1947.

125.

L.

E. Clark, “Some considerations in the

design of sound-proof camera housings,”

Jour.

SMPE,

15:

165-170, Aug. 1930.

126. Report of Progress Committee,

Jour.

SMPE,

27: 3-44, July 1936. Twentieth

Century-Fox camera, p. 8.

127. H. R. Kossman, “A silent camera,”

Jour.

SMPE,

21:

420-425, Nov. 1933.

128. D. B. Clark and G. Laube, “Twentieth

century camera and accessories,”

Jour.

SMPE,

36:

50-64, Jan. 1941.

129.

J.

P. Maxfield, “Acoustic control of re-

cording for talking motion pictures,”

Jour.

SMPE,

14:

85-95, Jan. 1930.

130. A.

S.

Ringel, “Sound-proofing and acoustic

treatment of RKO stages,”

Jour.

SMPE,

15:

352-369, Sept. 1930.

131. M. C. Batsel, “Recording music for motion

pictures,”

Jour.

SMPE,

25:

103-108,

Aug. 1935.

132. R. H. Townsend, “Some technical aspects

of recording music,’’

Jour.

SMPE,

25:

259-268, Sept. 1935.

133. M. Rettinger, “Scoring-stage design,”

Jour.

SMPE,

30:

519-534, May 1938.

134.

V.

0.

Knudsen, “Hearing of speech in

auditoriums,”

J.

Acoust.

Sac.

Am.,

56,

Oct.

1929.

135. W. A. MacNair, “Optimum reverberation

time for auditoriums,”

J.

Acoust.

Soc.

Am.,

242,

Jan. 1930.

136.

S. S.

A. Watkins and

C.

H. Fetter, “Some

aspects of a Western Electric sound record-

ing system,”

Jour.

SMPE,

14:

520-530,

May 1930.

137. B. Kreuzer, “Recent improvements in the

variable-width recording system,”

Jour.

138. W.

P.

Dutton and

S.

Read,

Jr.,

“Some

new RCA photophone studio recording

equipment,”

Jour.

SMPE,

16:

315-329,

Mar. 1931.

139.

S.

Read,

Jr.,

“RCA Victor high-fidelity

film recording equipment,”

Jour.

SMPE,

20:

396-436, May 1933.

140.

S.

Read,

Jr.,

“Neon type volume indica-

tor,”

Jour.

SMPE,

28:

633-642, June 1937.

141. F.

G.

Albin, “Linear decibel-scale volume

indicator,”

Jour.

SMPE,

29:

489-492, Nov.

1937.

142. L.

T.

Sachtleben, “Characteristics of Photo-

phone light-modulating system,”

Jour.

143.

L.

J.

Anderson, “High fidelity head-

phones,”

Jour.

SMPE,

37:

319-323, Sept.

1941.

144. H.

F.

Hopkins, “Considerations in the

design and testing of motion picture

35:

165-171, Aug. 1940.

SMPE,

27:

562-574, NOV. 1936.

SMPE,

25:

175-191, Aug. 1935.

screens for sound picture work,”

Jour.

SMPE,

15:

320-331, Sept. 1930.

145. Charles R. Underhill,

Jr.,

“Practical

solution to the screen light distribution

problem,”

Jour.

SMPTE,

56:

680-683,

June 1951; Report of Progress Com-

mittee,

Jour.

SMPTE,

56:

575, May

1951.

146.

J.

I.

Crabtree, “The motion picture

laboratory,”

Jour.

SMPTE,

64:

13-34,

Jan. 1955.

147. H. W. Moyse and

D.

R. White, “Borax

developer characteristics,”

Trans.

SMPE,

148. H. C. Carlton and

J.

I.

Crabtree, “Some

properties of fine grain developers for

motion picture film,”

Trans.

SMPE,

No.

38, 406-444,1929.

149.

E.

Huse, “Sensitometric control in the

processing of motion picture film in Holly-

wood,”

Jour.

SMPE,

21:

54-82, July 1933.

150. L. A. Jones, “Photographic sensitometry,”

Jour.

SMPE,

17:

491-535, Oct. 1931;

Part 2, 695-742, Nov. 1931; Part 3,

18:

54-89, Jan. 1932; Part 4, 324-355,

Mar. 1932.

151. A. Kiister and R. Schmidt, “The sensito-

metric control of sound records on film,”

Jour.

SMPE,

79:

539-545, Dec. 1932.

152.

J.

B. Engl, “A new process for developing

and printing photographic sound records,”

Trans.

SMPE,

No. 30, 257-266, 1927.

153. Joe W. Coffman, “Sound film processing,”

Trans.

SMPE,

No. 35, 799-808, 1928.

Also “Art and science in sound film produc-

tion,”

Jour.

SMPE,

14:

172-179, Feb.

1930.

154. W. Leahy, “Time-and-temperature vs. the

test system for development of motion

picture negatives,”

Jour.

SMPE,

18:

649-651, May 1932.

155.

J.

I.

Crabtree and C.

E.

Ives, “A replenish-

ing solution for a motion picture positive

film developer,”

Jour.

SMPE,

15:

627-640,

Nov. 1930.

156. R. M. Evans, “Maintenance of a developer

by continuous replenishment,”

Jour.

SMPE,

31:

273-286, Sept. 1938.

157. H.

L.

Baumbach, “Continuous replenish-

ment and chemical control of motion

picture developing solutions,”

Jour.

SMPE,

158. C. E. Ives and E. W. Jensen, “Effect

of

developer agitation on density uniformity

and rate of development,”

Jour.

SMPE,

40:

107-136, Feb. 1943.

159.

J.

I.

Crabtree and H. D. Russell, “Some

properties of chrome alum stop baths and

fixing baths,”

Jour.

SMPE,

14:

Part 1,

483-512, May 1930; Part 2, 667-700,

June 1930.

160.

J.

I.

Crabtree,

L.

E. Muehler and

H.

D.

Russell, “New stop bath and fixing bath

formulas and methods for their revival,”

Jour.

SMPE,

38:

353-372, Apr. 1942.

161. R. C. Hubbard, “The straight line de-

veloping machine,

Trans.

SMPE,

No.

18,

73-85, May 1924.

162. Alfred B. Hitchins, “Machine development

of negative and positive motion picture

film,”

Trans.

SMPE,

No. 22, 46-53, 1925.

163. H. D. Hineline, “Continuous photographic

processing,”

Jour.

SMPE,

26:

38-53, Jan.

1936.

164. Clifton Tuttle and

J.

W. McFarlane,

“The measurement of density in variable-

density sound-film,”

Jour.

SMPE,

15:

345-351, Sept. 1930.

165. L. A. Jones and

J.

H. Webb, “Reciprocity

law failure in photograph exposures,”

Jour.

SMPE,

23:

142-159, Sept. 1934.

166.

J.

G. Capstaff and R. A. Purdy, “A compact

motion picture densitometer,”

Trans.

SMPE,

NO. 31, 607-612, 1927.

167.

G.

A. Chambers and

I.

D. Wratten,

“The Eastman type IIb densitometer as a

control instrument in the processing of

NO. 38,445-452,1929.

39:

55-66, July 1942.

motion picture film,”

Jour.

SMPE,

21:

218-223, Sept. 1933.

168. F. L. Eich, “A physical densitometer for

sound processing laboratories,”

Jour.

SWPE,

24:

180-183, Feb. 1935.

169.

W.

W. Lindsey,

Jr.

and W. V. Wolfe,

“Wide-range, linear-scale photoelectric

cell densitometer,”

Jour.

SMPE,

28:

622-632, June 1937.

170.

D.

R. White, “Direct-reading photoelectric

densitometer,”

Jour.

SMPE,

33:

403-409,

Oct. 1939.

171.

J.

G.

Frayne and

G.

R. Crane, “Precision

integrating-sphere densitometer,”

Jour.

SMPE,

35:

184-200, Aug. 1940.

172. C.

M.

Tuttle and M. E. Russell, “Note on

the use of an automatic recording densitom-

eter,”

Jour.

SMPE,

28:

99-111, Jan. 1937.

172a.D.

MacKenzie, “Straight-line and

’

toe

records with the light-valve,”

Jour.

SMPE,

77:

172-202, Aug. 1931.

173. L. A. Jones and Otto Sandvik, “Photo-

graphic characteristics of sound recording

film,”

Jour.

SMPE,

14:

180-203, Feb.

1930.

174.

J.

A. Maurer, “The photographic treat-

ment of vririable-area sound-films,”

Jour.

SMPE,

14:

636-649, June 1930.

175.

G.

L. Dimmick, “High-frequency re-

sponse from variable-width records as

affected by exposure and development,”

Jour.

SMPE,

17:

766-777, Nov. 1931.

176.

J.

0.

Baker and D. H. Robinson, “Modu-

lated high-frequency recording as a means

of determining conditions for optimal

processing,”

Jour.

SMPE

30:

3-17, Jan. 1938.

177.

J.

E. Abbott, “Development of the sound

film,”

Jour.

SMPE,

38:

541-545, June

1942.

178.

G.

L.

Dimmick, “Galvanometers for vari-

able-area recording,”

Jour.

SMPE,

15:

179. G. L. Dimmick and H. Belar, “Extension

of the frequency range of film recording and

reproduction,”

Jour.

SMPE,

19:

401-406,

Nov. 1932.

180. M. C. Batsel and E. W. Kellogg, “RCA

sound recording system,”

Jour.

SMPE,

28:

507-533, May 1937.

181.

G.

L. Dimmick, “A newly developed light

modulator for sound recording,”

Jour.

428-438, Oct. 1930.

SMPE,

49:

48-56, July 1947.

182.

E.

W. Kellogg,

U.S.

Pat. 1,740,406.

182a.L.

T.

Sachtleben, “Characteristics of the

Photophone light-modulating system,”

Jour.

SMPE,

25:

175-191, Aug. 1935.

183.

G.

L.

Dimmick, “RCA recording system

and its adaptation to various types of

sound-track,”

Jour.

SMPE,

29:

258-273,

Sept. 1937.

184. E. W. Kellogg, “ABC of photographic

sound recording,”

Jour.

SMPE,

44:

151-

194, Mar. 1945.

185.

E.

W. Kellogg, “Ground-noise reduction

systems,”

Jour.

SMPE,

36:

137-171, Feb.

1941.

186. Siemens and Halske, British Pat. 288,225,

Convention Apr. 9,1927.

187. L.

T.

Robinson,

U.S.

Pat. 1,854,159

and 1,935,417; C. W. Hewlett,

U.S.

Pat. 1,853,812; and C. R. Hanna,

U.S.

Pat. 1,888,724.

188.

H.

C. Silent and

J.

G. Frayne, “Western

Electric noiseless recording,

Jour.

SMPE,

78:

551-570, May 1932.

189.

H.

McDowell,

Jr.,

US.

Pat. 1,855,197.

190.

R.

H. Townsend, H. McDowell,

Jr.

and

L.

E.

Clark, “Ground-noise reduction

RCA Photophone system,” Reprint 26,

Tech.

Bul.

Acad.

Mot. Pict.

Arts

&3

Sci.,

Feb. 1931.

191.

E.

W. Kellogg and C. N. Batsel, “A shutter

for use in reduction of ground-noise,”

Jour.

192. H.

J.

Hasbrouck,

J.

0.

Baker and

C.

N.

Batsel, “Improved noise-reduction system

SMPE,

17:

203-215, Aug. 1931.

Kellogg:

History

of

Sound

Motion

Pictures

373

for high-fidelity recording,”

Jour. SMPE,

29:

310-316,

Sept.

1937.

193.

R. R. Scoville and W. L. Bell, “Design and

use of noise-reduction bias systems,”

Jour. SMPE, 38:

125-147,

Feb.

1942.

194.

B. Kreuzer, “Noise reduction with variable-

area recording,”

Jour. SMPE, 16:

671-

683,

June

1931.

195.

J.

L.

Hathaway, “Microphone polarity and

overmodulation,”

Electronics,

Oct.

1939,

p.

28.

196.

R.

0.

Drew and E. W. Kellogg, “Starting

characteristics of speech sounds,”

Jour.

SMPE, 34:

43-58,

Jan.

1940;

and

J.

Acoust. SOC.

Bm.,

72:

95-103,

July

1940.

197.

J.

G. Frayne, “Noise-reduction anticipa-

tion circuits,”

Jour. SMPE, 43:

313-320,

Nov.

1944.

198.

J.

R. Whitney and

J.

W. Thatcher, “In-

creased noise reduction by delay networks,”

Jour. SMPTE, 54:

295-302,

Mar.

1950.

199.

G. L. Dimmick and A. C. Blaney, “Direct

positive system of sound recording,”

Jour. SMPE, 33:

479-487,

Nov.

1939.

See

also Progress Committee Report,

Jour.

SMPTE,

58:

401,

May

1952.

200.

W. A. Mueller and G.

R.

Groves, “Mag-

netic recording in the motion picture

studio,”

Jour. SMPE, 52:

605-612,

June

1949.

201.

Academy Research Council, “Report of

basic sound committee on pre-and-post-

equalization,”

Jour. SMPE, 42:

187-192,

Mar.

1944.

202.

J.

K. Hilliard, “Projects of the committee on

standardization of theater sound projection

equipment characteristics,”

Jour. SMPE,

30:

81-95,

Jan.

1938.

203.

J.

K. Hilliard, “Variable-density film-

recording system used at MGM studios,”

Jour. SMPE, 40:

143-175,

Mar.

1943.

204.

K.

F. Morgan and D. P. Loye, “Sound

picture recording and reproduction char-

acteristics,”

Jour. SMPE, 32:

631-647,

June

1939;

33:

107-108,

July

1939.

205.

F. E. Carlson, “Properties

of

lamps and

optical systems for sound reproduction,”

Jour. SMPE, 33:

80-96,

July

1939.

205a.L.

T.

Sachtleben,

U.S.

Pat.

2,158,308.

206.

0.

Ceccarini, “Recent contributions to

light-valve Technic,”

Jour. SMPE, 17:

305-325,

Sept.

1931.

207.

W. Herriott and L. V. Foster, “Recent

optical improvements in sound-film record-

ing equipment,”

Jour. SMPE, 23:

167-174,

Sept.

1934.

208.

E. C. Wente and

R.

Biddulph, “Light-

valve for the stereophonic sound-film

system,”

Jour. SMPE, 37:

397-405,

Oct.

1941.

209.

R. R. Scoville, “Overload limiters for the

protection of modulating devices,”

Jour.

SMPE, 31:

93-98,

July

1938.

210.

W. C. Jones and

L.

W. Giles, “A moving-

coil microphone for high-quality sound

reproduction,”

Jour. SMPE, 77:

977-993,

Dec.

1931.

211.

E. C. Wente and A.

L.

Thuras, “Moving

coil telephone receivers and microphones,”

J.

Acoust. Soc. Am., 3:

44-55,

Jan.

1931.

212.

H. F. Olson, “The ribbon microphone,”

Jour. SMPE, 16:

695-708,

June

1931;

and

J. Acoust. Soc. Am., 3:

56,

July

1931.

213.

H.

F. Olson, “Collection of sound in rever-

berant rooms, with special reference to the

application of the ribbon microphone,”

Proc. IRE, 21:

655,

May

1933.

214.

H.

F.

Olson and Frank Massa,

Aflfllicd

Acoustics,

P. Blakiston’s Sons

&

Co.,

Philadelphia,

1934.

215.

H.

F.

Olson, “Unidirectional microphone,”

Jour. SMPE, 27:

284-301,

Sept.

1936.

216.

R. N. Marshall and W. R. Harry, “Cardi-

oid directional microphone,”

Jour. SMPE,

33:

254-277,

Sept.

1939.

217.

A. G. Webster, “Acoustical impedance and

theory of horns and phonograph,”

Proc.

Nat. Acad.

of

Sci.,

6:

275, 1919.

218.

C.

R. Hanna and

J.

Slepian, “The Func-

tion and design of horns for loud speakers,”

Trans. AIEE, 43:

393,

Feb.

1924.

219.

C. R. Hanna, “Loudspeakers of high

efficiency and load capacity,”

Trans.

AIEE, 47:

607,

Apr.

1928.

220.

H. A. Frederick, “Vertical sound records:

recent fundamental advances in mechanical

records on wax,”

Jour.

SMPE,

18:

141-163,

Feb.

1932.

221.

L.

G.

Bostwick, “A loud speaker good to

twelve thousand cycles,”

Jour. SMPE,

16:

529-534,

May

1931.

222.

C.

Flannagan, R. Wolf and W.

C.

Jones,

“Modern theater loud speakers and their

development,”

Jour. SMPE,

28:

246-264,

Mar.

1937.

222a.J.

P. Maxfield and P. Flannagan, “Wide

range reproduction in theaters,”

Jour.

SMPE, 26:

67-78,

Jan.

1936.

223.

Symposium on Auditory Perspective, pub.

in

Elcc. Eng.,

(AIEE),

53:

9,

Jan.

1934;

and

BelI

Sys.

Tech. J., 13:

239,

Apr.

1934.

This equipment is again described in

Jour.

SMPE, 37:

331-417,

Oct.

1941.