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 “searchable image”.

John G. (Jay) McKnight, Chair AES Historical Committee 2003 Dec 04

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History of Sound Motion Pictures By EDWARD W. KELLOGG

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 As one who shared in this misjudg- Journal. 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 Motion Picture Industry “The art of the silent film had at- the principal examples of sound pictures Adopts Sound tained superb quality and the public we had seen were demonstration films, Many Commercially Unsuccessful Eforts. was satisfied. Why then, producers very interesting to us sound engineers The historical outline with which our asked, should Hollywood scrap the working on the project, but scarcely story began contains a very incomplete bulk of its assets, undertake staggering having entertainment value. None of us account of the many efforts to combine conversion costs, and force upon the had seen a talking motion picture with a sound and picture, some of which at- public a new and doubtful experimental good story, and picture and script well tained a fair degree of technical success, art? designed for the purpose. When in 1927 elicited praise and held public interest “Nor were the exhibitors equipped such a picture was shown (The Jazz for short periods. We mentioned the for sound. Many, it was argued, would Singer) the story, the music and the work of Edison, Lauste, Rumer, and not be able to meet the cost of sound dialogue were splendidly adapted to de Forest, and might add Path6 Frtres picture equipment.” produce a fascinating picture with and Lkon Gaumont* in Fran~e.~Many great emotional appeal, in which no of these were ahead of their time, for These obstacles would not have pre- element could have been spared without without amplifiers, the production of vented the producers from introducing serious loss. In short, the excellence of adequate and natural sound was prac- synchronized sound, had they been con- showmanship played no small part in tically impossible. Even after amplifiers vinced that it would give their pictures making it clear to everyone who saw became available the experimenters had greater appeal. A factor which many it that the day of “Talkies” was here. little better success in getting picture developers of sound equipment probably The Jazz Singer and its predecessor producers seriously interested. The ar- did not fully recognize, was that to Don Juan, it might be noted, had the ticle by Lovette and Watkin~~~states contribute to the illusion, the sound must benefit of a newly designed lo~dspeaker,~‘ that by the end of 1924 practically every have a degree of naturalness far sur- very much superior to those used in the major producer in Hollywood had re- passing that which had sufficed for simply Western Electric 1924 demonstrations. jected Western Electric’s sound-picture transmitting information, or making system. words understood. Warners and Fox Take the Step. Warner Brothers committed themselves to the Economic Hurdles. The same authors How It Looked in 7926-7. To many, adoption of sound pictures in 1926, give such a convincing statement of the the silent motion picture, with its freedom license contract being concluded in April, financial obstacles from the producer’s of action, its settings for much of its followed by large investments in sound standpoint that I cannot do better than action in natural backgrounds, was stages and equipment. In July of the quote them: better entertainment than stage drama, same year the Fox Film Corp. became “The motion picture producers had and when one tried to imagine what a committed, forming the Fox Case Corp. large inventories of silent films, which talking motion picture would be like, which took license for the Case Labora- had cost millions to produce. They one’s thoughts immediately turned to tory developments in April, and in had great numbers of actors and ac- examples of theater drama. I have December from Western Electric Co. tresses under long term contracts, most of already quoted some of Dr. de Forest’s for rights to use amplifiers. Both Warners whom knew no dramatic technique reflections. The prevailing thought at and Fox operated theater chains. With except that of pantomime. The industry the General Electric Co. as our system two major picture producing and ex- was universally equipped with stages and began to take shape is probably typical. hibiting organizations definitely launched studios suited only to the silent film Many, even of the most enthusiastic on a program of making and showing technique. advocates of the sound-picture develop- pictures, could the other great picture “Moreover, world-wide foreign mar- ment were not convinced that the chief companies remain on the sidelines? kets had been established for silent function of the synchronized sound would films. To serve these markets, it was be to give speech to the actors in plays. Large Producers Agree to Choose Same merely necessary to translate the words The art of telling stories with pantomime System.6 Early in 1927 the first Fox printed upon the film from English to only (with the help of occasional titles) Movietone Newsreel subjects were shown. any language desired. Finding stars and had been so highly developed, that The other picture companies must by supporting casts who spoke the various giving the actors voices seemed hardly this time have become convinced that languages of the world, or finding ways necessary, although readily possible. ssund pictures were inevitable, for a to give the illusion of their speaking Such a view was actually a very high part, if not the whole of motion-picture them, appeared to be an insuperable task. tribute to the movie makers of the silent entertainment. In February 1927, the era. However, a very large business in “big five” - M-G-M, First National, * Gaumont, in addition to many inventions synchronized sound seemed assured (even Paramount, Universal and Producers’ and other activities, was a pioneer and successful without any use of the system for dia- Distributing Corp. (or PDC), jointly leader in the motion-picture business, and prob- logue) in furnishing sound effects, back- asked the Hays organization to study ably came nearer to success with phonograph ground music, and providing voice for and make recommendation as to what sound than others. See account, and references given in the Theisen history5 from which ref. 77 lectures, speeches and travelogue com- system should be adopted. The Movie- is taken. mentary. tone and Vitaphone (disk) had already

356 July 1955 Journal of the SMPTE Volume 64 become commercial systems, Western and equipping of recording studios was Cinekhone. The Powers Cinephone Electric was offering a sound-on-film the installation of sound reproducing system was developed by R. R. Halpenny (light-valve) system, and General Electric systems in theaters. Theater chains con- and William Garity for Patrick A. Pow- had made a number of demonstrations trolled by the picture-producing com- ers, who financed the project. It was of a variable-area system (later offered panies which had already signed con- basically similar to the system of de to the industry with some modifications tracts, used sound systems of the corre- Forest, with whom Powers had permis- through RCA Photophone). There had sponding make, but the business of sive contracts. Cinephone was put on as yet been no formal standardization, furnishing sound equipment to the great the market in September 1929 and used and those participating in the conference number of independent theaters was com- for several years by Walt Disney and probably felt some uncertainty about petitive between ERPI, RCA Photo- others. interchangeability of recordings. It is phone and many other suppliers. An not strange that the picture companies idea of the rate of growth of the sound Tyke of Contract. Most of the initial thought it would be advantageous for pictures, may be had from the following contracts between the equipment-manu- all to adopt the same system. figures given in Sponable’s paper.6 At facturing companies and the picture By far the most ambitious demonstra- the end of 1927 there were some 157 producers were on a lease (rather than tion of sound motion pictures that had theaters in the U.S. equipped for sound, outright sale) basis, for a stipulated as yet (February 1927) been witnessed of which 55 were for both disk and term of years, with equipment servicing was the Warner Vitaphone Don Juan film and 102 for disk only. At the end and engineering assistance as part of the (shown August 1926),l, 4s with perform- of 1928, of the 1046 ERPI theater in- suppliers’ obligation, and royalties de- ances by noted artists and score and back- stallations, 1032 were for disk and film. pending on the film footage recorded. ground music for the play by the New By the end of 1929 ERPI had equipped York Philharmonic Orchestra. And the about 4000 theaters in the U.S. and 1200 Evolution of a New Art,* Under Dificul- sound quality was good. But it was abroad, and RCA Photophone had ties. The idea that the silent motion a demonstration of synchronized sound, equipped some 1200 in the U.S. and picture would continue to have its place and not of sound motion-picture drama. 600 abroad, most of these being for both in theater entertainment died hard. The producers, still “on the fence,” disk and film. The SMPE Progress What The Jazz Singer had proved was continued their “watchful waiting.” Report of February 1930 states that at that with a suitable story and presenta- The presentation of The Jazz Singer the time, Hollywood studios were pro- tion, a sound picture could have an ap- in October 1927 dispelled all doubts. ducing only 5% silent pictures. Instal- peal far beyond what was possible But whether the future lay with the disk lations by other manufacturers brought without sound. It had not proved that or the film system was a question not the total number of theaters equipped sound would help in all types of presen- completely settled for several years. for sound in the U.S. to over 8700. There tation. In March 1929, Fox discontinued “Big Fice” Sign Contracts with ERPI.‘j were at the time 234 diyerent types of making silent pictures. In speaking of With such large producers as Warners theater sound equipment including the this in his historical paper5 of 1941, making pictures with sound on disk and large number which were designed for W. E. Theisen calls it a daring decision, Fox with Movietone releases on film, it disk only. At the end of 1930 there were “since a large number of the leaders of appeared that exhibitors might be about 13,500 theaters equipped for sound, the industry still felt that sound films saddled with a dual system. Perhaps it and about 8200 not equipped, according were only a passing fad.” In “The was the hope that one or the other would to the SMPE Progress Report of August Entertainment Value of the Sound very soon forge ahead in the race that 1931. Movie” (Trans. SMPE, No. 35, 1928), caused further hesitancy, but in April H. B. Franklin, President of West Coast and May of 1928 (about six months Contracts for Photophone Vuriable-Area Theatres, says: “The silent motion after the showing of The Jazz Singer) Recording. In 1928 RCA bought the picture is too well established. . .to Paramount, United Artists, M-G-M, theater chain interests of B. F. Keith vanish because of this new development.” First National, Universal and several and of Orpheum, and the film producing It took time, much work and some others signed agreements with Electrical company Film Booking Office or F.B.O., mistakes for the industry to learn to use Research Products Inc. (the commercial and organized Radio Keith Orpheum sound to full advantage, and the great outlet for the Western Electric systems) or RKO. The new company (RKO), pressure under which writers and pro- for licenses and recording equipment. with Photophone equipment, and draw- ducers worked during the years of trans- ing heavily on the RCA group for much ition was not conducive to best results. Getting Started.’ There followed a period of its initial sound personnel, made Two quotations from 1928 papers are of feverish activity in erection of sound many feature and shorter pictures, using illuminating. In “The Public and Sound stages, and procurement and installation the name Radio Pictures for its product. Pictures” (Trans. SMPE, No. 35) Wm. A. of recording channels and equipment. RCA Photophone made arrangements Johnson, Editor of Motion Picture News, Deliveries of apparatus were far behind for license and equipment with Path6 speaks of the great demand for sound the desires of the customers, and there Exchange Inc., Mack Sennett, Tiffany pictures, and says: “The present hastily was great shortage of engineers and Stahland with Educational Pictures Corp. turned out crop of talkies are for the technicians with sound-picture back- One of the first feature pictures made most part crude and disappointing.” ground. The manufacturers and asso- by Path6 was King of Kings directed by In “Reaction of the Public to Motion ciated organizations lent or lost many Cecil de Mille. The Path6 Newsreels Pictures with Sound” (Trans. SMPE, of their personnel. Intensive training were an important item, using a number No. 35), Mordaunt Hall, motion-picture courses and much instructive literature of RCA mobile recording equipments alleviated the situation. The Transac- or “sound trucks.” editor of the New York Times, describes tions of the SMPE for the fall of Disney switched to the RCA Photo- the shortcomings of many efforts as due 1928 are little short of an encyclopedia phone system in January 1933. Republic to stories not adapted to talkies, actors of sound recording and reproduction by Pictures Inc. used the RCA system be- who didn’t articulate, or had poor both disk and film. To this body of litera- ginning October 1935 and Warner voices, and misjudgments in production. ture, the engineers and processing lab- Brothers in June 1936. Columbia Pic- oratory experts from the producing com- tures Inc. began May 1936 to use the * Many excellent discussions of the requirements panies soon began making their contribu- RCA variable-area system for part of for the new form of entertainment have been published. One such is Chapter IX “Comments tions. its operations, but continued for several on Production,” of H. B. Franklin’s Sound Motion Scarcely a step behind the building years to release on variable-density. Pictures.2

Kellogg: History of Sound Motion Pictures 357 viscous Viscous or ducing machines is ability to measure Brake 1 the departures from uniform speed. Coupling n One of the first such meters was built Shaf ’t about 1928 by M. S. Meads5 of the Damper General Engineering Laboratory at Sche- nectady. It was improved by H. E. Roys Opt lGaL Axis and used extensively at Camden, N.J., being the basis of the flutter-measuring equipment described by Morgan and -Independently- Kelloggs6 This meter made an oscillo- Journaled Driver graphic recording of the fluctuations. An A. Filtered Sound Sprocket B. Magnetic Drive (or Fluid extremely simple and light-weight in- Equivalent) dicating flutter bridge used in RCA servicing is described in the Journal.87 Flutter-measuring instruments are de- vis cous scribed by Scoville.8s These are of the indicating type with band filters, by free on Shaft) which flutter at different rates can be Flywheel on Drum Shaft separated. Another design is described by Herrnfeld.89 A widely used wow meter designed by U. R. Furst of Furst Electronics, Chicago, has been commercially available since 1947 or earlier.g0

Disk System. In the disk system the C. Rotary Stabilizer D. Damped Sprung Idler change from 78 to 33Q rpm increased the and Kinetic Scanner 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 Sha ide and Tension on Drum driven through springs, or what we call a “mechanical filter,” was a well- Sprocket free on Shaft and driven through Spring, known expedient, but such a system is with Damping Pad oscillatory and will multiply rather than reduce the speed fluctuations if the disturbances are of a frequency E. Damped Sprune Sprocket anywhere near that of the reso- nance, unless the system is damped Fig. 4. Mechanical filter systems for reducing irregularities in film motion. by adequate mechanical resistance. 69,70.81,91,94,100,102,104,105 The requirement that the transient disturbance of We tend, fortunately, to forget the ance by the motion picture industry, the starting shall disappear in not more than troubles that are past. Still more do we engineers spent much effort on providing one revolution is more difficult to meet forget the troubles other people had. constant speed. In his story of the de- with extremely large inertia. The ac- We who took part in the development of velopment of the Fox-Case system, for ceptable 334-rpm reproducing turntables sound equipment may be tempted to example, Sponable6 tells of having to had much more inertia than had been think that we made the talking picture rebuild cameras, and of mounting a fly- customary for 78-rpm machines, and possible. But if we give the credit they wheel on the sprocket shaft and driving were driven through springs, with enough deserve to the writers, directors, actors the combination through damped damping to reach equilibrium reasonably and their bosses, and to the patient springs. quickly, and dependence was not placed guinea pigs who bought tickets, perhaps The literature dealing with speed on making the natural frequency low the only bouquet left to hand ourselves fluctuations has been devoted largely in comparison with that of the slowest is to say that our stuff was not so bad as to discussions of measures for improving disturbance (once per revolution). Damp- to make the talkies impossible. the performance of recorders and re- ing in some designs was provided by ap- producers in this respect.?O Until the re- plying friction to the spring^,^^^^ and Mechanical Systems cent important contribution by Frank in others by a viscous drag on the turn- Of all the tell-tales that remind the A. C~merci,~~”such information as table. In either case it was essential to listener that the sound he hears is from has been published regarding subjective have high indexing accuracy in the low a record and not “live pickup,” the thresholds or tolerances has been limited speed gear or worm-wheel. most unmistakable is that due to speed largely to continuous tones. Further sys- For 339-rpm recording turntables, variations - known as “wow” or tematic quantitative studies with typical the Western Electric engineers went “flutter,” and it is probably the most program material are very desirable. to extraordinary refinement.70sg1 On painful and devastating to realism. The There is no question however that all the theory that it would not be practically importance of correct and constant the present and future improvements possible to produce gears with no ec- speed was recognized by Edison and in equipment performance are well justi- centricity or indexing errors, they made all his successors in sound recording, fied in terms of more satisfying sound re- their 33Q-rpm worm-wheel in four lami- but standards were not very high. production. Some of the more general nae, all cut together in one operation. Phonographs sold despite their short- discussions of the subject will be found Then they separated and reassembled comings. But sound for pictures could in the literature. 70 3 79 -84a them, each rotated 90” with respect to succeed only by providing better enter- its neighbor. Each had its own spring tainment than silent pictures. In those Wow Meters. Of prime importance connections to the turntable. Damping systems which gained eventual accept- toward improving recording and repro- was by means of vanes in oil. Four vanes

358 July 1955 Journal of the SMPTE Volume 64 were rigidly connected to the turntable, Dec. 27, 1932. E. W. KELLOGC 1,892,554 while the pot and four other vanes were driven from the gears through a system P!WI SUPPORTING AND DRIVING APPARATUS of equalizing levers (which might be Filed July 27. 1928 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 Fis. I. Fis. 2. 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 advantages 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 difficult 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 irregularities originating in the gea~-ing.~,’O But the spring-driven sprocket was very Fis. 3. 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. Film 5. Schematic representation of the magnetic drive for film motion, showing A sprocket can propel a film at uniform also provision for damping by use of a movable roller with dashpot. speed only when the pitch of the teeth and that of the holes match perfectly.* Western Electric recorders of the earlier (so long as they remained under suffi- Otherwise there are continual readjust- 1930’s were designed on this basi~.~~$~ciently low tension to retain their ments of the film on the sprocket, pro- The large sprocket was of precise con- flexibility) would not transmit appre- ducing in general 96-cycle flutter, plus struction and a nearly perfect fit for ciable disturbances from the sprocket to random small variations. A paper by unshrunk film. It was on the shaft with the drum. Because of uncertain shrinkage Herbert Belar and myselP2 shows a flywheel, and driven through damped the drum must be free to choose its graphically the startling breaking up springs. Another sprocket (unfiltered) own speed. The simplest expedient was of single tones into a multiplicity of drew the film from the magazine and to let the film pull the drum, like a belt. side tones by a 96-cycle speed change resisted the pulls from the take-up Machines built this way worked so well such as might result from a shrinkage of magazine. at times that they delayed the effort to about 3%. The engineers who designed the re- design something on sounder principles. Recorders, since they are working corders supplied by RCA took no chances My own part in the development of a with fresh film, may give very little with sprocket teeth. In the first General better machine lay originally in the 96-cycle flutter at the sprocket. The Electric recording machines the film recognition that the stretch of film which was carried past the recording light on pulled the drum, in combination with * Sprocket propulsion of the film through the light beam has certain advantages for printers, a smooth drum (with a flywheel on its the inertia of the flywheel, constituted as will be explained in the section on printer shaft) and a soft-tired pressure-roller an oscillatory system, although its period improvements. This mechanical section, how- prevented lipp ping.^' Between the drum varied so greatly that the irregular ever, seems the logical place for a brief review of and the sprocket which fed the film action did not look like that of any studies by J. S. Chandler and J. G. Streiffert of the Eastman Co., directed to the reduction of through the machine at synchronous oscillator we were accustomed to seeing. sprocket-tooth flutter. speed were flexible loops of film which Another trouble was that the film loop

Kellogg: History of Sound Motion Pictures 359 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 reproducing devices, but the patent de- partments would not approve construc- tions using the overhung film for scanning L until after about 1930, when W. L. E 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). I 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 photocell. Friction in the gate made this arrangement much less favorable to constant speed than the use of the overhung 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 Fig. 6. Original model of magnetic-drive recorder. flywheel, and driving through springs. To damp this filter, the RCA PS-1 was not free enough for isolating the strated by Russell 0. Drew and myself used grease-pads acting on the flywheel drum. The cure for the bad effects of at the SMPE’s 1940 spring conventi~n.~~(Fig. 4A) and the Western Electric used oscillatory action would be to provide Although only a few were built, I a balanced pair of oil-filled sylphon bel- damping. One way to provide this would should mention another recorder, the lows which acted as a dashpot supple- be by bending the film around a flexibly .R-3,’O designed by C. L. Heisler of the menting the driving springs.“ A practical supported idler roller,’05 connected to General Electric Co., which preceded improvement over filtering the sound a dashpot. Another measure would be the magnetic type. This had the smooth sprocket was to drive a heavy flywheel to use eddy-current damping at the fly- drum with flywheel to carry the film on the sound-sprocket shaft by multipleV wheel by mounting a copper flange on past the recording point, and the sprocket belts directly from the motor, and then the flywheel, spanned by a set of mag- drive to hold synchronism. The drum by gearing take from this shaft whatever nets. To use stationary magnets would was driven through a continuously ad- power is needed to drive the projector. provide damping but would also produce justable-speed friction drive, which might The heavy flywheel and tight coupling a steady drag, making a really flexible be compared to a cone pulley, and the to the motor gave the sound-sprocket film loop impo~sible.’~J~*~By mount- speed adjustment was automatically drive such high mechanical impedance ing the magnets so that they could be controlled by the length of the loop of that its speed constancy was not ma- driven somewhat above flywheel speed, film between the sprocket and drum, terially disturbed by the irregularities it became possible to provide a forward which loop was measured by the position of the projector load. torque as well as damping, thereby of a movable deflecting roller. relieving the film of all but a small The Rotary Stabilizer. The discovery of part of its tension. (Figs. 4B, 5).94-96 Effect of the Tri-Ergon patent^.^^^"^ Men- the Cawley patent application by Douden The first magnetic-drive machine (an tion has been made of the development, made the RCA Patent Department experimental model) (Fig. 6) employed beginning in 1918, of a sound system consider it safe to build machines in both the damped idler roller and the by Vogt, Massole and Engl, to which which the reproducing light passed rotating magnetic damper, but the latter the name Tri-Ergon was given. They through the film where its edge over- was so effective that the first was super- obtained very broad patents in Germany hung a short roller. With this privilege fluous. By adjusting the magnet current and were allowed some extremely broad the way was open to make the film the film loop could be caused to run claims in the United States. The patent motion in reproducing machines com- anywhere between a very slight deflec- which figured most seriously in litiga- parable with that which had been at- tion and a nearly semicircular bend. tion was No. 1,713,726 in which one tained in the magnet-drive recorder- A production model (the R-4) recorder claim covered the use of a flywheel on However a less expensive construction was designed in 1929 and was in pro- the shaft of the roller which carried film was very desirable. The damping in duction in 1930.94 It was followed by past the translation (recording or re- the recorder was by eddy-current cou-. other models (PR23 in 19339*and PR-31 producing) point. Another claim covered pling between the flywheel and a coaxial in 194799) employing the same principle. carrying the film on a short roller and magnet running at nearly the same The magnetic drive probably carried scanning it at the overhanging edge, the idea of isolation of the film drum and a third (based on a showing of flexi- * The Cawley application had been filed Jan. 28, from disturbing forces farther than it bly mounted rollers pressing against and 1921, but had been held up on technicalities. has been carried in any other film- deflecting the stretches of film on either It was put into suitable shape and issued Sept. 29, 1931 as a parent patent, No. 1,825,438, and recording machine. Its extreme effec- side of the drum) called for a spring- three divisional patents, of which No. 1,825,441 tiveness as a filter system was demon- pressed roller engaging the film between 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 > inertia of the viscously coupled member I would tend to keep its speed constant 1 so that a change in flywheel speed would cause relative movement and hence energy 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 system. He showed that in order to get critical damping of the mass which is rigidly connected to the drum, the viscously 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 flywheel supported on a ball bearing whose friction was negligibly small in compari- .son with the oil coupling. Small clear- Rotary stabilizer construction of F. J. Loomis and E. W. Reynolds. ance between concentric surfaces and Fig. 7. Cross section, showing construction of the “rotary stabilizer.” a suitable oil gave the desired coupling. The inertia ratio was less than 8:1, 1,597,819). Both of these show rollers Filter System With Drum and Sprung but damping somewhat short of critical elastically pressed against the film to Sprocket. A film-motion system developed is satisfactory. By use of high-grade ball deflect it from a straight path and by engineers of M-G-M is described bearings the drum with attached stabi- thereby provide flexibility. Neither pat- by Wesley C. Miller.ll1 Recording or lizer was caused to run with so little ent shows or mentions provision for reproduction takes place on a drum with tension on the film which pulled it that damping, and yet the great merit of solid flywheel, and the drum is driven the loop had plenty of flexibility for such an arrangement is in the simplicity from a sprung sprocket isolated from effective filtering.lo2!lo20 (See Figs. 4C with which damping can be obtained other sprockets by loose loops. The film and 7.) The rotary stabilizer introduced and not in the extra flexibility, for plenty passes from the sprung sprocket, around in 1933 proved so satisfactory that it has of flexibility can be had by simply freeing the drum and back to engage the opposite been retained with little change for the film of too much ten~ion.~~~J~~~Thefly- side of the sprung sprocket, and this twenty years. A device on similar prin- wheel may be solid and the arm on which portion of the film is maintained under ciples, called the “kinetic scanner” was the film-deflecting roller is mounted tension by a roller pressing against a used in Western Electric soundheads can be connected to a dashpot. (Even free span of the film. The tight film early in 1936‘” (Type 209). a cruder frictional device may give good affords the required traction between In 1941 Alberscheim and MacKenziesl results, but resistance of the viscous film and drum. Adjustable friction pads and Wente and MUllerlo4 described type is better.) A laboratory model of a between the sprocket and its shaft cause damped flywheels in which the entire soundhead using this type of filter was frictional resistance whenever the deflec- viscously coupled mass was liquid. In built about 1928 by the writer and tion of the sprocket driving springs order that there might be sufficient performed very well, but did not receive changes, thereby damping the system. viscous resistance to movement of the patent approval (Fig. 4D). Excellent film motion was obtained in liquid with respect to the container, After the patent obstacle to the use of these machines (Fig. 4E). partial obstructions were placed in the the sprung-idler type of filter was annular channel. This type of damped ended, soundheads employing this prin- Minimizing Sprocket- Tooth Flutter. J. S. flywheel was used in the recorders and ciple were brought out by the Century Chandler, in 1941112 showed it to be reproducers of the stereophonic system Projector Corp. and the Western Electric possible to so shape sprocket teeth that developed and demonstrated by the Bell C0.105 and a recorder by Western the film speed would fluctuate between a Telephone Laboratories. Study has been Electric.lo6 RCA adopted this film- maximum and minimum value which given to the problem of finding suitable motion system for l6mm machines and are the same at perfect fit and spread fluids. A low-temperature coefficient of lightweight recorders R-32 and R-33,1°7 progressively with increasing misfit, but viscosity is desirable, and if the entire but for 35mm soundheads continued to with a net flutter which can for a mod- coupled mass is liquid, high density is use the rotary stabilizer, the advantage of erate range of shrinkage be quite small. valuable. the movable-idler design being not so However the realization of the calcu- much a matter of performance as of lated flutter values demands perfect Filters Using Movable Idlcr Rollers. The lower manufacturing costs, an item which perforation uniformity and freedom from use of this type of filter was avoided in is contingent on schedules and tooling any sticking on the teeth as the film is this country because of the danger of costs. Recently the flexibly mounted fed on or stripped off. infringement suits on the basis of either idler filter system has been utilized by A further development in improving the Tri-Ergon patent (No. 1,713,726)35 RCAlM and others109J10in soundheads for sprocket action is described by J. G. or the Poulsen and Peterson patent (No. use with multiple magnetic soundtracks. Streiffert.ll3 The driving faces of the

Kellogg: History of Sound Motion Pictures 361 ance has accumulated to avoid possible 1929. H. VOGT ET AL 1,713,726 interference during the stripping. DEVICE FOR FHONOGRAPHS WITH LINEAR PHONOGRAM CARRIERS Assuming that the film velocity is Filed March 20. 1922 3 Sheets-Sheet 3 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, especially 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 perforation, 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 F recordings) of prints made in a conven- tional sprocket-type printer, showing a R 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 ..I7roR.w-s soundhead. The case was tried at Scran- Fig. 8. Tri-Ergon showing (U. S. Pat. 1,713,726) of flexibly mounted rollers deflecting ton, Pa., in the U.S. District Court for the film between sprockets and drum. the Middle District. The apparatus had been sold with a guarantee against patent liability, and the suit was defended teeth are radial and the film is sup- slightly greater than that of the film. by RCA, Electrical Research Products ported on a cylindrical surface which The tooth face therefore gains with re- Inc. giving technical assistance in the spect to the film, closing up the clearance, is slightly eccentric with respect to the defense. The court ruled (Feb. 10, and as soon as it touches the edge of the sprocket. The film is fed on at a point 1933) that seven of the claims were valid perforation begins propelling the film. where the teeth project only slightly and infringed. The case was appealed While it is doing so the next tooth is above the film support, and as it travels and reviewed by the Circuit Court catching up. Each tooth in turn propels U.S. around its arc of engagement the film of Appeals for the third circuit (in the film from the moment that it reaches gets closer to the roots of the teeth. The the perforation edge until the next Philadelphia), which affirmed (June 13, 1934) the findings of the lower court. radius from the sprocket center to the tooth, which at the instant is moving The defendents then appealed to the film thus keeps decreasing, and therefore slightly faster, touches the edge of its the velocity of the tooth face at the plane perforation. Thereafter, the effective U.S. Supreme Court, which at first of the film decreases. The effect is essen- speed of this tooth, which continues to refused to review the case, but finally tially as though the tooth speed and the decrease, is less than that of the film, decided to do so, and on Mar. 4, 1935, tooth pitch decreased correspondingly. so that a gap or clearance develops ruled that the seven claims in the suit The design is such that the tooth enters between the tooth and the leading edge were all invalid (294 US 477).'14 the hole with a margin of clearance and of the perforation. The design is such * This patent, issued May 21, 1929, was filed in with the effective velocity (since the that the film is not stripped from the the U.S. Mar. 20, 1922, and had a German working radius is here near maximum) teeth until, in all cases, sufficient clear- filing date of Mar. 24, 1921.

362 July 1955 Journal of the SMPTE Volume 64 This removed the threat to the equip- vances in the art that followed commer- gradually instead of suddenly. This was ment manufacturers of what might have cialization, we shall mention some of accomplished at first by painting a black been almost crippling damages, for these items. spot with sloping edges over the splice. had the findings of the lower courts been Later, black patches which could be Standard Track Position and Width.l15 sustained the plaintiffs would have been quickly cemented in place where the Agreement between the makers of vari- in a position to bring suits for damages splice crosses the sound track were made able-width and variable-density systems for infringement by most of the recording available. These are called “bloops.” was reached in 1928. The reproducing and reproducing equipment in this They are of trapezoid shape, masking light spot must cover more than the country, and covering a period of over off the entire sound track for a distance extreme width of the clear area of a vari- five years. sufficient safely to cover the splice and The American Tri-Ergon Corp. ap- able-area track, with both ends on black with end slopes designed to change the areas, but should fall entirely within the plied on Feb. 18, 1937, for a reissue light gradually enough to keep the noise patent with modified claims, and this width of a variable-density track. This just below noticeability at normal gain requirement is met with margins of safety, was granted Jan. 11, 1938, as Re. No. settings. The design of bloops is dis- by recording density tracks 0.100 in. 20,621. On Oct. 25, 1946, RCA reached cussed in several To prevent wide, while the scanning spot is 0.084 an agreement with American Tri-Ergon a disturbance due to a printed-through in. long. The modulated area of a vari- Corp. whereby it was granted rights negative splice, SponablelZ4 described able-width track is limited to 0.071 in. under both theoriginaland reissuepatents. a punch which made a hole in the nega- with the black parts extending to the Two other patents placed restrictions tive, resulting in a suitably-shaped black 0.100-in. width. The track center line is on the film-motion systems which Ameri- spot on the print. to be 0.243 in. 0.002 in. from the edge can engineers could safely employ, f Electrical blooping of splices in nega- namely Poulsen and Peterson No. of the film. tives has come into extensive use. When 1,597,819 (filed July 9, 1924, and Printers. Continuous contact printers a negative splice goes through the printer issued Aug. 31, 1926) and Poulsen No. previously used for pictures only could an auxiliary light exposes (through 2,006,719 (filed Germany Sept. 1, 1930, be adapted to sound by providing masks the base) a suitable area of the print and U. S. Aug. 19, 1931, and issued July by which light could be confined to film, an edge notch or other means 2, 1935). These patents to Danish either the picture or the soundtrack area. being employed to control the blooping inventors were owned by British Acoustic Except for certain newsreel negatives, light. Films Ltd., which brought infringement the sound and picture were on separate Lewin (Apr. 1947)I24adescribes a system suits against RCA Mfg. Co. and against negatives, so that the print film had to be of silencing splices in re-recording posi- Electrical Research Products Inc. The run through the printer twice. Even tives in which the output is momentarily trial (in Wilmington, Del.) was before when the sound was on the same nega- suppressed in response to a punched hole. the U.S. District Court for the District tive as the picture, the offset was not of Delaware (43 USP-Q69). The ar- usually the required 14.5-in. and inde- Blimps.’25 Cameras which were en- rangement shown in the patent comprised pendent light controls were needed. tirely satisfactory for silent pictures were a drum propelled by the film, the film Combination printers were soon devel- much too noisy for making sound being passed around a flexibly mounted oped which were essentially two printers pictures. Much quieter cameras were idler roller. Some of the claims in suit in cascade, so that the print was com- developed eventually,126-128but for im- described the invention as “means con- plete with one passage through the mediate requirements it was necessary ’ tacting the film for increasing its flexi- machine.116-120 to reduce the noise radiated by existing bility.” The apparatus in suit was the cameras by building shells around them RCA PS-24 (rotary stabilizer type), Bloops. The development engineer can with thick layers of sound-absorbing which has no flexibly mounted roller, overlook many defects so long as he material. These were called “blimps,” but was alleged to have the equivalent knows their cause and that the apparatus or sometimes “bungalows.” To smother in that the film loop was so formed by he is testing is not at fault, but before the sound and still give access for the the fixed rollers as to be very flexible. sound pictures could be shown the public, necessary operations was enough to The court ruled Sept. 22, 1939, that the these faults had to be corrected. The tax the skill and ingenuity of the de- claims in suit were not infringed and noise which a splice makes as it passes signer. Even with the quieter cameras it not valid (the flexibly mounted idler through the scanning beam can be made is still common to resort to partial or having been disclosed in the earlier Tri- almost inaudible by cutting off the light complete sound-insulating housing. 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 patents by agreement with British Acoustic Films Ltd., Dec. 21,1944. Fig. 9. Tri-Ergon showing Immediate Requirements for Sound of filtered sound-sprocket and overhanging sound- Our historical story thus far has been track. confined almost entirely to the three fundamental elements, sound pickup (or microphone), a recording and reproducing 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-

Kellogg: History of Sound Motion Pictures 363 Sound Stage~.'~~J~~The requirement of that their positions might be readily Mention has been made of a sound- freedom from noise necessitated the changed, microphone booms of various transmitting screen developed by E. I. building of sound stages in which ex- types came quickly into use. The more Sponable in 1927.6 One of the first treme measures were taken to exclude elaborate of these were much like papers in the SMPE Journal dealing noise of outside origin. Many of these derricks on platforms, with rubber- with screens for sound pictures was that in had double concrete walls and double tired wheels on which they could be 1930 by H. F. H0~kins.l~~His curves of floors, with sound absorbing material moved quickly and almost noiselessly. between, the inner walls and floor being Similarly, rubber-tired, battery-oper- measured transmission indicate good supported on cushion mounts to prevent ated camera dollies enabled the camera- results with screens having perforations transmission of earth tremors. The roof man rapidly and quietly to change the whose total area is 4% or 5% of the and ceiling structures were designed on position or height of his camera. screen area, and show definite advantage the same principle. Equipment of the kind just described in a thin (0.013-in.) screen rather than The high absorption (or short reverber- underwent improvements through the a thicker (0.030-in.) material. With such ation time) desirable for recording pur- years, but the main features were avail- screens the loss of brightness need be poses helped control noises originating able from the start of commercial sound no greater than the proportion of the inside, but so far as possible all sources pictures. area taken out by the holes. Allotment of noise were eliminated. Noisy arc of about 8% of the area to holes has been lights gave way to incandescent or Monitoring and Leuel Contr01.'~~-~~~An- common, for example about 40 holes other quiet lamps, and all mechanisms other line of equipment the essentials of of 0.050-in. diameter per square inch.145 were made to operate as noiselessly as which were made available as soon as possible. Ventilating systems required recording machines, and which has been Processing, Variable-Density .146 In the extreme measures. improved from time to time, was that pro- story of the work at Western Electric In recording dialogue, the better the viding for monitoring and level controls and Bell Laboratories I said that it was suppression of general rcom reverbera- and (especially in re-recording opera- recognized by Wente and by MacKenzie tion, the farther (within limits) from the tions) for adjusting the relative levels that for the correct, or linear, relation action can the microphone be placed, from several sources, or "mixing." Vol- between negative exposure and print thus affording more uniform coverage ume indicat~rs'~~J~~of several types transmission, the product of the negative and making it easier to keep the micro- were in use in broadcasting stations, and and print gamma* should equal unity.t phone out of the field of the camera. the design of mixing controls was well This is in accordance with principles set If some echoes are wanted the "set" established. forth in early SMPE papers by L. A. can frequently be designed to produce The man responsible for recording Jones62 and by A. C. Hardy.61 Since enough. Artificial reverberation using judged the quality by means of a moni- practice in making pictures had been to echo chambers in the recording channel toring loudspeaker. He could check develop the print to a gamma of approxi- or equivalent devices has many applica- quality as represented by the current mately two, and both sound and picture tions. supplied to the light modulator, or by would receive identical development, the In contrast to the requirements for means of a photocell, in terms of the sound negative should be developed to a speech, the recording of music calls in light reaching the film.1964,254In the case gamma of about 0.5 or slightly higher. general for rooms with considerable of the RCA Photophone system there Picture-positive film was used for a re~erberation.'~'-'~~ was a card on which the modulator pro- number of years for sound negatives. jected a light-spot, the movements of Developers of the types used for picture Theater Acoustical Treatment.134J35The which showed the amplitude being re- negatives tend to give low contrast and acoustical treatment of auditoriums has corded on the sound fine grain, and the use of such develop- probably received more study than any It was for a time held by some that the ers helped to give the desired low value other phase of architectural acoustics, monitoring speaker should be of the same of gamma for the sound negative^.'*^*'^* perhaps because the desired characteris- type as a theater speaker, but high- Ma~Kenzie~~gives some information tics are most difficult to attain. The re- quality monitoring speakers of the direct- about the harmonic distortion which verberation must be sufficient to make radiator type were soon made available, results from departures from the unity music pleasing and to help equalize and these were much better suited to the product, and thus gives an indication of sound intensity in the various parts of the small rooms where the controls were tolerances with respect to development. space, but must be short enough not located. In terms of frequency range With the advent of sound, with its appreciably to impair clarity of speech. covered, the cabinet-type monitoring requirement for more strict control of A high order of directivity in the loudspeakers kept pace with the improve- development, control by use of sensito- speakers plus application of absorbent ments in theater speakers (see section metric test strips, and by specified time, materials to any large surfaces toward on loudspeakers). High-quality head- temperature and developer f0rmulas'~9-'~ which they are directed has helped phones have also found wide use in moni- supplanted dependence on visual judg- with this part of the problem. toring.'", 211 Whatever type of listening ments of operators, where that practice In general every theater or auditorium, device is used, it should obviously be had prevailed.'"J" Maintenance of de- many of which were built before the designed to give the recordist about the veloper activity received much atten- era of sound pictures, presents its own same range and tonal balance that a ti or^,'^^-'^^ and stop baths assumed in- problems and calls for individual study. theater patron would get. creased importan~e.'~~*'~~Rack-and-tank For new theaters there is optimum shape methods, where these had been followed, to consider as well as best distribution Screens. Our sense of the direction of absorption. The multiple loudspeaker from which sounds come is too keen for * Gamma is the slope of the straight portion of a systems (discussed later) besides making us to be fooled by loudspeakers placed curve plotted withdensity orlogof ( transmission new effects possible have given the alongside or above the screen. Sound as ordinates and log exposure as abscissae. This is acoustical designer somewhat more free- must come from directly behind the known as the Hurter and Driffield, or H & dom. screen to give a good illusion. This is D curve. Gamma product is a measure of overall one of the lessons that was learned early. contrast as compared with that in the original exposure. Booms and Dollies. In order that micro- Screens of the types developed for silent phones might be suspended as near the pictures caused excessive loss and distor- t In practice, because of some loss of contrast due to stray light in optical systems, best results action as might be wanted but just above tion if placed between the loudspeaker with pictures had been found with somewhat the field of the camera, and in order and the audience. higher gamma product.

364 July 1955 Journal of the SMPTE Volume 64 gave way to continuous machine proc- by picture requirements, MacKenzie comparatively small difference (except essing.161-163 found that the composite system offered near the extremes) whether a given How generally the distinctions be- best promise of low distortion. Both the density of either negative or print was tween specular and diffuse density,164and toe and composite systems give higher reached with small exposure and longer between exposure modulation by varying output than a classical or straight-line development or more exposure and less time (light valve) and varying intensity system, but poorer signal-to-noise ratios. development, but in general the maxima (as by glow lamp)‘65 were understood at It took a number of years to bring were broader with the higher values first is a question, but these points were about the full transformation from the well covered in the literature. The methods (depending much on visual of gamma, especially that of the print. Eastman Capstaff Densitometer,166which judgments) which had been employed The two highest gamma values in the was developed primarily for measuring for making silent pictures, to the close series, 2 and 2.18 of both negative and picture negatives for contact printing, controls and scientific precision needed print, in general gave best results, with reads diffuse densities. This would be for satisfactory and consistent sound. negative densities (measured in the black appropriate for measuring the densities The constant and close checking of areas) in the range 1.5 to 2, and print cf sound negatives for use in contact every element exerted a pressure for densities a little less in each case than printers, but not for densities of sound- improvement along the whole front, that of the negative. track prints, for it is the specularly trans- including the manufacture of the film, While maximum high-frequency out- mitted light which reaches the photocell in which departures from uniformity put is of less consequence than avoidance in a reproducer. were quickly detected. The story is inter- of cross-modulation (which is discussed The widely used EastmanIIb Sensitom- estingly told by J. I. Crabtree.146 An in the section on distortion) it is of in- eter, brought out about 1932,1‘j7 which early account is given by J. W. Coff- terest that recommended practices based gives an accurately standardized series of man.153 on the test just described come very test exposures in the form of a step tablet close to those found to be best in later with exposure time increasing in the Processing, Variable-Area. Since the experience and after current testing ratio d? per step, and ranging from ideal variable-area track is part clear methods had become established. The about 0.004 sec to 4 sec, has been of and part black with a sharp boundary cross-modulation test did not come into utmost vahe in maintaining controls. between, there is no question of preserv- general use until 1938.176 However, it does not simulate sound- ing correct shades of gray, but in general For a number of years a print density track recording conditions, where the the higher the contrast (or gamma of 1.4 or slightly higher, with appro- intensity is extremely high and the time product) the better. As in the case of priate corresponding negative density, for average exposure was approximately variable-density tracks it must be as- was taken as a practical objective. As 1/18000 sec (1/36000 sec with a later sumed that the print development will galvanometers and optical systems were light-valve system and in present prac- be that which is wanted for the picture, improved and finer grain films came into tice about 1/90000 sec) and still shorter and that has been taken in general to use, the tendency was toward higher for low exposures. The 1934 paper by give a gamma of about 2.0. Variable- densities for both negatives and prints, Jones and Webb165gives an indication area negatives as well as the prints are especially for the negatives. of the magnitude of the error. The East- processed in high-contrast developers. man Sensitometer on the other hand gives The variable-area system is noncritical Evolution in a Growing Industry exposures which approximate sufficiently with respect to gamma product but, for Greatb Expanded Deuelopmental Actiui- well those which a print receives, and a given positive emulsion and processing, ties. The development work prior to com- are thus suitable for determining gamma there is for any given negative a best mercialization of sound was carried of contact prints. For many purposes it setting of printer light. on largely in laboratories supported by has been satisfactory to draw conclusions A comprehensive study of available manufacturers of supplies or equipment, by applying correction factors, if needed, sound-recording films and their process- or in independent laboratories, and it to the readings of these instruments. ing was published by Jones and Sand- was done on the basis of hope for re- In the course of a few years densitom- ~ik.’?~Another study was made by turns which might be realized either eters employing photocells were de- J. A. Ma~rer.’~~From his curves it ap- through patent royalties or through veloped which had the advantages of peared that negative densities of 1.3 or sales of equipment or both. greater accuracy and much faster op- higher were desirable, and the prints Once sound pictures began to be made eration than the Capstaff visual-balance which gave maximum outputs were the and shown, developmental work was on type.168-1i2For exposing sound negatives ones having densities (in the dark areas) a different basis. Research and investiga- for sensitometry purposes, the light valve about equal to those of the negatives tions of numerous incompletely solved itself, with suitable calibration, can be from which they were made. This held problems took on rather the character of used. The subject is again discussed true for negative densities ranging from plowing in profits, with greatly increased under “Intermodulation Test.” 0.6 to 1.3 and higher. The maxima total expenditures for research and par- While the conditions for low distortion however were very broad. ticipation by all the major picture-pro- were to keep both negative and positive In November 1931, Dimmi~kl~~reducing organizations. exposures on the straight parts of the ported the results of a series of deter- Of a11 of the problems, the most fun- H & D characteristics, studies reported minations of conditions for maximum damental and greatest in magnitude was in 1931 by D. MacKenzie17*~showed that output from a 6000-cycle recording, using learning how to use sound pictures, or low distortion was still possible while Eastman positive 1301 for negatives and the evolution of a new art. This is dis- using the “toe” range of both films prints, and 4, 6, 8 and 10 min in D-16 cussed by J. E. Abbott.”? The expres- (“toe recording”) or that of the positive developer. The study covered an ade- sion “growing pains” aptly describes the only (“composite”). Toe recording using quate range of the four variables - nega- less successful phase of this evolution. positive stock for the sound negative tive (recording) exposure, negative de- Capacity for readjustment is one of the might, if the recording-system light was velopment or gamma, printing exposure qualities of greatness in individuals and limited, be preferable to resorting to and print development. The results in organizations, and the motion-picture faster and coarser-grained recording showed that wide ranges in each industry came through splendidly. stock. In the case of single-film systems of the variables could be used with com- When any industry becomes large, (sound recorded on the picture negative) paratively small loss of output, but for and especially if its requirements are as where the development of both the nega- any negative there was a print density diverse as those of sound pictures, it tive and positive soundtracks is fixed at which output was greatest. It made provides a market for numerous special-

Kellogg: History of Sound Motion Pictures 365 ,, (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- Fig. 10. Arrangement employed by perience with oscillographs, F. B. Card, 6. L. Dimmick in 1929 galvanometer, for joined the RKO staff. The RKO en- multiplying the rotation of the mirror. gineers soon decided that their sound would be better if the frequency range Fig. 11. Cross section of improved re- ties and services. Many of these require- were extended. The ribbons of the os- cording galvanometer, G. L. Dimmick. ments are met by comparatively small cillographs had been of phosphor-bronze. A-armature; B,B-pole pieces; C,C- organizations and others by branches of A small supply of duralumin ribbon was working air gaps; D,D-nonmagnetic companies having many other activities obtained, and with this Card succeeded in spacers; E-tensioned bronze ribbon. and products. A few such items will re-stringing the RKO galvanometers, had to work only at high frequency it serve to illustrate : special lamps, arc with sufficient tension to tune them to could be of quite small dimensions. carbons, screens, cameras, acoustic treat- nearly 9000 cycles. A thinner damping Dimmick found that he could increase ment materials and service, chemicals, fluid was then appropriate, a change the effectiveness of such damping blocks printers, testing equipment and studio almost necessary to realize the benefits by incorporating tungsten powder in apparatus. Many important improve- of the higher natural frequency. the rubber to increase its density (Fig. 12). ments and contributions to technical G. L. Dimmick came to the General Further improvements in the galva- advances are due to those who develop Electric Co. in 1929, and one of his nometer were reported by Dimmick in and supply such auxiliary equipment. first projects was the development of a July 1947.18’ By the substitution of Mingled with the natural rivalry new galvanometer which was promptly better magnetic materials he was able to between picture producers has been a used in newsreel equipment.178He used reduce hysteresis almost to zero, to spirit of cooperation and sharing of ex- a magnetic driving system of the balanced increase the sensitivity, and to avoid perience and knowledge which has rocking armature type and by an ingeni- a slight saturation effect which had greatly accelerated progress. In 1930 ous mechanical arrangement, shown in been present in the previous design. this society began issuing the monthly Fig. 10, made his mirror rotate through Journal instead of the quarterly Trans- about ten times the angle of the arma- A More Eficient and Versatile Optical actions, an appropriate step to accom- ture. The important advantage of this System. In order that the galvanometer modate the rapidily expanding literature galvanometer was that the mirror was in one of our experimental optical systems of sound-picture technology, covering about ten times the area of that of the might be closer to the slit, and thus almost every phase of the making and previous galvanometers. A few years later send more light through it, I arranged showing of motion pictures. The Acad- Dimmick designed a new galvanometer a galvanometer to work on its side, so emy of Motion Picture Arts and Sciences on the same principle (Fig. 11) but that it would move the light spot up and also played an important part in pro- improved in numerous detail~.’~J~~J80down across, instead of parallel to, moting interchange of information. En- This became the RCA Photophone stand- the slit. I used a light spot with a sloping gineers and technicians from the sound- ard for all photographic recording. edge at an acute angle such that picture laboratories have reported ex- These galvanometers were tuned to about the change from zero to full-length slit periences with various problems related to 9000 cycles. Damping was by means of illumination was accomplished with a processing and controls and to sensitom- a block of rubber, the action of which movement equal to only one-fourth of etry, while film and photographic sup- was analogous to that of the rubber line the slit length. *,la2 Dimmick improved pliers have spared no efforts to enable of H. C. but since it on this by making the light spot sym- those using their product to get the best metrical with respect to middle of the possible results. * See June Journal, p. 296, third col. slit, and having two sloping edges (see So many have been the contributions Fig. 13, and in Fig. 14 compare C with to the art and science along these lines, B). An advantage of the transverse- that I find it quite beyond my ability movement system was that it became to do more than pay this general tribute very simple, by changing the masks and to mention a very few developments which were imaged on the slit, to pro- which have seemed to me to be of out- duce a variety of tracks which had their standing importance. I trust that I special appli~ations.~~2~180~1~3~~~~ may be forgiven for showing partiality The combination of larger mirror to the types of development with which and reduced distance between galvanom- I am most familiar, and also if I un- eter and slit practically eliminated the justly fail to mention many important diffraction trouble that had, with the advances. small mirrors, impaired the formation of clean, sharp, high-contrast images at Some of the Improvements After 1930 the plane of the slit. Galvanometers for Variable-Area Recording. The galvanometers used in the first Ground-Noise Reduction- G NR.Ia5 variable-area recorders supplied by RCA Scratches and dirt on film and graininess Photophone were practically standard of emulsion cause a background noise oscillograph vibrators, as these had been built at General Electric. They were * All galvanometers have practical limits to the angle through which they can swing the light oil-immersed and responded well up to beam. And the required light spot movement sets 5000 cycles or above. An improved a minimum to the distance between galvanometer smaller model was brought out in 1930,178 ‘-DAMPING LINE and slit. The light which a galvanometer can completely sealed instead of having an Fig. 12. Construction of RCA record- send through the slit is proportional to the mirror area and the inverse square of its distance from open oil well and with no external ad- ing galvanometer (shown in section in the slit, up to the point at which the objective justments. This used molybdenum ribbon Fig. 11). 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 SLIT IN SCREEN / or MIRROR

Fig. 13. Variable-area recording optical system. (Lens B images A on slit-plate D.) which is particularly conspicuous when Townsend, McDowell and Clark in variable-density system there is no ob- the modulation is low. The noise is 1930.lg0 Thereafter a commercial form jection to accomplishing the result by reduced by reducing the transmitted of shutter was designedxg1and ground- biasing the valve. light. At the same time, for a given modu- noise reduction became standard in the In case of a sudden increase in modulation level the rectified current would lation level there is no need for the RCA system (Fig. 15). With the introduction slightly later of change so rapidly as to cause an audible average transmission to be more than the symmetrical track, the objection sound. The current for the shutter or for about half the maximum. The noise just mentioned to depending on galva- bias is therefore passed through a filter may thus be reduced when the reduction nometer bias instead of a shutter no which reduces the rate of change. is most needed, by decreasing the average longer applied, but there was still some Limiting the speed with which the light when the level of the recorded danger of saturating the galvanometer. average light can increase means some sound is low. This can be accomplished Therefore a double-vane shutter was clipping of the first few modulation by biasing the light modulator toward developed to mask down the light from peaks. zero, and then using a current derived both sides.x92 The light valve is a very low imped- by rectifying some of the modulation The Bell Laboratories system is de- ance device, and since the bias current current to increase the mean light trans- scribed by Silent and Frayne.188 In the may have to be sustained for consider- mission when this is needed. The reduced transmission when the modulation is ,DIRECTION OF MOl.ION 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- I 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, -- SCANNINGOR REPRODUCING LIGHT] unilateral, variable-area tracks) in that A B C D E F 0 the bias threw all of the low-level modu- ORIGINAL UNILATERAL PUSH-PULL PUSH-PULL CLASS B CLASS B UNILATERAL VERTICAL CLASS A CLASS A DIRECT lation over to one edge of the track, MOTION POSITIVE where many reproducing light beams were of reduced intensity. The project Fig. 14. Variation types of area soundtracks, and light-spot shapes which produce was revived by Hugh McDowell of RKO them. who got around the objection by screen- ing off the surplus light by means of a shutter instead of biasing the galvanometer.lsg This method and the results obtained were reported to the Academy of Motion Picture Arts and Sciences by Fig. 15. Soundtrack produced by McDowell ground-noise reduction shutter.

Kellogg: History of Sound Motion Pictures 367 able periods of time transformers cannot speech sounds build up rapidly.lg6 to this problem seems to have come in be used for impedance match coupling Instances in which maximum amplitude the recent adoption of magnetic record- to the output tube of the ground-noise was reached in less than three or four ing. ? 200,352 -388 reduction amplifier. In the system waves (voice fundamental) were sur- most widely used with light valves the prisingly rare. Pre- and Post-Equalization. The prac- modulation current is rectified, passed The ideal solution to the problem of tice of electrically exaggerating the high- through the timing filter, and used to avoiding initial clipping would be to frequency components in recording, as modulate a 20,000-cycle oscillator, the anticipate increases in sound level. This compared with the low-frequency com- output of which is amplified and recti- is discussed by J. G. Frayne.197 ponents, in order to compensate for fied for supply to the valve. The design Anticipation by use of a second inevitable losses, began early in the of the timing filter is much simpler when it microphone was used experimentally in recording of sound. Studies of the dis- can operate at interstage impedance.193 the stereophonic system described in the tribution of energy in program material As compared with variable-area, the October 1941 Journal (p. 351) for had indicated that this could be done variable-density system is characterized operation of the compre~sor.~~aA system without resulting in overloads in the by ground noise which is less in the employing a 14-msec electrical delay high-frequency end of the scale. A nature of “ticks” and “pops” and more a network is described (March 1950) large amount of high-frequency pre- continuous hiss. Another difference is by Whitney and Thatcher.lg8 emphasis had been employed in cutting that in the density system the noise falls When reported it had been in use for transcription disk records. In film more rapidly with reduced light trans- over a year by Sound Services Inc. with records as well as disk records, ground mission, so that a given amount of noise very favorable results. Besides reduced noise can be made less noticeable by reduction is obtained with a smaller clipping, advantage was taken of the decreasing the gain at high frequency. change in transmission. The con- system to increase ground-noise reduc- Therefore, in addition to such relative tinuous hiss type of noise is especially tion in density recordings by 5 db, and in attenuation of high-frequency sounds noticeable if it comes and goes, which area recordings to work with a bias line as was caused by the imperfections of changing bias causes it to do. This is only 1 to 1; mils wide. A low-distortion reproducing systems and loudspeakers, often called the “hush-hush” effect, and network good to 8000 cycles necessarily the practice became prevalent of produc- becomes noticeable if the valve opening employs many sections (several hundred). ing a drooping characteristic in the does not immediately fall when the Cost is probably the reason that this electrical circuits. modulation drops to a low level. At expedient has not been widely employed. In order that all films might have good the same time the fact that smaller A direct-positive variable-area recording balance in all theaters, a committee of changes in transmission suffice to control system with the anticipation effect the Academy of Motion Picture Arts the ground noise makes it possible to provided by means of an auxiliary and Sciences made recommendations for change transmission (or bias) more exposure was designed and demon- a standard reproducing characteristic.201 quickly without causing “thump.” The strated by Dimmick and Blaney and With such a standard adopted, the filters for density systems are therefore has been used in the Warners’ studios.’Qg producers of sound pictures would have designed for much faster timing than In the re-recording operation anticipa- incentive to use recording characteristics those of area systems, particularly in tion should be a simple matter, involving which would give good balance when closing down when modulation falls. only a double reproducing system (with their films were played in a theater with While clipping of initial modulation scanning points a fraction of an inch the typical or standard reproducing peaks is a less serious problem in density apart) with separate amplifiers. * Mueller characteristic. than in area recording (because of and Groves (June 1949)200mention use The problem is discussed by J. K. faster opening and larger margin) of this system at Warners. I understand Hilliard202,203and by Morgan and engineers working with both systems however that little advantage has been L0ye.20~ have given much study to minimizing taken of this possibility, presumably on Better Lumps. Among the lamps used such clipping. Increased margin will account of costs. The explanation is in the late 1920’s for recording were some decrease the frequency of occurrence of probably that when initial clipping of the ribbon-filament type. These were clipping, but this would be at the price occurs in a well adjusted re-recording ideal from the standpoint of uniformity, of more noise. In all systems, opening system, there was probably also some but required an inconveniently large (increasing light) is about as fast as it at the same spots in the original recording current (18 amp) and did not have as can be made without becoming audible, and the possible gain from anticipation long life at a given temperature as was while the closing is much slower so that in the re-recording operation is hard to obtainable with lamps of the helical- very brief reductions in level will not detect. If clipping, in systems using filament type. A series of lamps for sound produce incessant closing and opening.194 ground-noise reduction, causes an ap- recording and reproduction was made A nonlinear characteristic has been preciable impairment to sound quality, available by the lamp companies. The given to RCA ground-noise reduction the ideal solution is to use for original filaments were close-wound helices, of amplifiers, which causes the opening, as a recording a system whose ground noise relatively heavy tungsten wire, and to function of modulation amplitude, to is inherently so low that it needs no such permit operation at high temperatures rise more steeply at first and then more expedient, and then introduce the with satisfactory life, the pressure of the Relatively low-level modula- ground-noise reduction when re-record- inert gas (argon) with which the bulbs tion is then sufficient to cause an increase ing to the photographic tracks. Similar were filled was increased above that in margin and thus reduce subsequent considerations apply to the use of com- employed in lamps from which less clipping. It is when the modulation is pressors. Among the systems which in intensity was required. nearly zero that close margin is urgent. more or less measure meet this specifi- In the series of lamps described by Certain characteristics of speech sounds cation are Class B area recording, wide- F. E. Carlson of General Electric in have an important bearing on the design track push-pull (with fine-grain film and 1939205the recording lamps were rated of ground-noise reduction systems. The fast-acting noise reduction) direct posi- as operating at above 3100 K (color positive pressure peaks are higher than tives with the auxiliary exposing light,lQQ temperature) which is several hundred the negative, and it is important to and direct-playback disks. A real answer degrees higher than that of common maintain correct polarity from microphone to valve, or to shutter and galva- * In a set-up for mixing numerous sounds, it t Some experimenting has been done with a dou- would for practical purposes be sufficient to equip ble magnetic pickup for anticipation. Cross-tak n~meter.’~~J~~R. 0. Drew and I made only the dialogue film-phonograph with double between the two heads was a problem. The diffi- an investigation to determine how often scanner and amplifier. culties will undoubtedly soon be worked out.

368 July 1955 Journal of the SMPTE Volume 64 incandescent lamps. Somewhat later, The two-plane design of valve has be- a voltage is induced in the ribbon. krypton-filled lamps were introduced, come generally standard for variable- A transformer is used to step up this permitting still higher temperatures. density recording. voltage, which is then applied to the The krypton, being heavier, more effec- The optics of light-valve recording grid of an amplifier tube. Transverse tively retards evaporation of tungsten. systems207 have been modified by the corrugations are formed in the ribbon, (See the section on basic inventions.) addition of a small horizontal cylindrical which prevent it from curling and give it The light from a helical filament lens close to the film, which results in lengthwise flexibility. It is mounted under varies somewhat, depending on the angle greater optical reduction between valve only such tension as is needed to keep it from which the lamp is viewed. At the and film and therefore a narrower image between the pole pieces. Olson shows suggestion of L. T. Sachtleben of RCA, (0.0002 in.). This makes for improved that theoretically such a microphone the helix of the lamp used in the variable- high-frequency recording and for further should give uniform frequency response, area recordings was curved, the convex reduction of ribbon-velocity distortion. and that it should have a polar direc- side being presented toward the lenses. One of the factors which has made the tivity curve like a figure 8 (cosine law), The helix with the curved axis gives narrower image possible without sacri- the directivity being the same through- definitely better unif~rmity.~~~-~~~~205a ficing exposure is that new lamps of out the frequency range. Experimental higher intensity have become available. results are also given confirming the Improvements in Light-Valves and Density Light-valve optics have been adapted theory. The velocity of movement of Optical Systems. In June 1932 Shea, to making variable-area tracks, for ex- the ribbon is proportional to the velocity Herriott and GoehneP5 described the ample as used in the stereophonic system of air movement, so that it is often called development of improved duralumin described in 1941.208 The valve is turned a “velocity microphone.” ribbon (stronger and with straighter with the ribbons vertical, or parallel to Since a microphone of this type edges) and better methods of adjusting direction of film travel. The lens system, responds less and less as the direction of and anchoring the ribbons at the ends which employs cylinders, magnifies the the sound departs from normal, it picks of the free span. The new anchoring ribbon motion ten to one. This means up much less reverberation (random system practically eliminated the fric- that the lens must be close to the ribbons, in direction) than a nondirectional tional hysteresis which had been found hence with little depth of focus. There- microphone having the same sensitivity in the earlier design, thus reducing fore in this application the ribbons are for sound of normal incidence. The ratio waveform distortion and making for in the same plane, and an electrical of direct to reverberant sound in many greater stability. Stability became in- current-limiting expedient prevents cases sets the limit to how far from the creasingly important as the mean spacing clash.20Q source the microphone can be placed, between the two ribbons in the valve A strong magnetic field is advan- and under such circumstances a ribbon was reduced. The ground-noise reduc- tageous for the sake of sensitivity and microphone can get satisfactory pickup tion system called for reducing the ribbon damping. In the design described by some 70% farther from the source than spacing when the modulation was low, Wente and Biddulphm an air gap flux a nondirectional microphone, such as and when it was found possible in view density of 32,000 gauss is attained, an one of the pressure t~pe.~l3Advantage has of required exposures to reduce the achievement which testifies to the been taken of the directional character- unbiased spacing from 0.002 in. to excellence of the permanent magnet istics of the ribbon microphone to exclude 0.001 in. this was done, while still materials and the high flux capacity of certain sounds or disturbances (for keeping the optical reduction from valve the pole-piece material. There is some example camera noise), for it is deaf to to film at 2:l. further discussion of light valves in the sounds originating in the plane of the At high frequency and high modula- section on variable density vs. variable ribbon. tion, the images of the ribbon edges move area. If the output of a pressure microphone with velocities comparable with the speed is combined in correct phase and amount of film travel. This results in a waveshape Microphones. While condenser micro- with that of a velocity microphone, the distortion which would convert a sine phones had excellent characteristics combination becomes unidirectional, hav- wave into a saw-tooth wave. Fortu- they were more expensive and required ing a cardioid-shaped directivity curve. nately such a combination of high fre- more servicing than magnetic micro- It has a dead-spot 180’ from the direc- quency and amplitude is not often en- phones, and it was practically necessary tion of maximum sensitivity. The forward countered in program material, and the to provide a stage of amplification close directivity is much less sharp than that harmonics generated would probably not to the microphone. On the other hand, of a velocity microphone, and such a be reproduced, nor noticed if they were. the electrical impedance of a magnetic unidirectional microphone is better suited However, it is desirable to minimize microphone is such that a transformer for picking up sound over a wide angle, thin “ribbon-velocity’’ distortion, and may be used if wanted, and the output as for example from a large orchestra. the reduced slit width helps in that transmitted at a convenient impedance. The cardioid directivity pattern has the respect and also in giving better resolu- A magnetic microphone of the flexibly same advantage as the figure 8 pattern tion or high-frequency response. mounted rigid-diaphram, moving-coil in picking up less noise from random In order that harmful effects (harm type is described by Jones and Giles in directions than a nondirectional micro- to sound quality if not to the ribbons December 1931.210*211It is a pressure- phone. themselves) might not result when the type (rather than velocity or pressure- Before making a unidirectional micro- modulation current drives the ribbons to gradient) microphone. Damping is ob- phone, Olson worked out an arrange- the point of touching or hitting each tained by flow of air when the diaphram ment for converting a velocity micro- other (light-valve “clash”) light valves vibrates, back and forth between two phone into a pressure microphone. He have been built with the ribbons slightly cavities, through passages which are of placed close behind the ribbon a com- offset, or in two planes.207There appears such small dimensions as to make air bination shield and absorber consisting to have been difference of opinion about viscosity effective in dissipating energy. of an open-ended tube of the same the necessity of this precaution. It In June 1931 H. F. Olson described cross-sectional area as the active area of should be remembered that in a density the velocity microphone,212 consisting of ribbon. He distributed through the tube system the downward light modulation a ribbon of very thin aluminum (0.0001 tufts of absorbent fiber. The length of the ncrmally stops considerably short of in.) in a magnetic field between pole tube was made sufficient to dissipate zero, to avoid photographic nonlinearity. pieces which are adjacent to the edges of wave energy. The impedance of the In other words touching of the ribbons the ribbon, so that when the ribbon mouth of the tube then becomes equal would represent considerable overload. moves in a direction normal to its surface to that of so much free air (to plane

Kellogg: History of Sound Motion Pictures 369 waves) but air in which there is no other symmetrical track, ground-noise reduc- The low-frequency unit was designed sound to react on the ribbon. The ribbon tion (by galvanometer bias), ribbon to work from 40 to 300 cycles, and con- is then actuated only by the pressure on microphone for sound pickup, and a sisted in a large-diaphragm, moving-coil the exposed side.214 film-phonograph using the magnetic unit, working into the %in. diameter Having successfully made this con- drive, Dimmick and Belar gave a throat of a horn which expanded expo- version, Olson applied the same treat- demonstration of extended frequency nentially to a mouth 60 in. square in a ment to only one half of the length of the range at the SMPE 1932 Spring Con- total length of approximately 10 ft. ribbon, leaving the other half to act as a ~enti0n.l’~They did not resort to two- The high-frequency driver unit, which bidirectional velocity microphone, and way (divided-range) speakers, for the covers the range 300 to 13,000 cycles is the combination has the cardioid direc- straight-axis, directional baffle units, shown in cross section as Fig. 10 in the tional characteristic^.^^^ which had 6-in. cone diaphragms with Flannagan, Wolf and Jones paper.n2 Bell Laboratory engineers also de- aluminum voice-coils, had good re- Particular attention is given in the veloped bidirectional or velocity micro- sponse even at 10,000 cycles. The range design to the air space and passageways phones, and unidirectional types, but was extended downward (to 60 cycles) leading from the diaphragm surface into differing from the Olson type in employ- by using slow expansion exponential the horn or group of horns. ing a second microphone more nearly horns (of the large-throat or directional- If a single straight-axis exponential like their standard pressure microphone. baffle type) 10 ft long, with mouth horn is used, the tones of highest fre- The unit and its applications were dis- openings 75 in. square. quency are radiated in a direction close cussed by Marshall and Harry in Sep- to the axis, while those of lower fre- tember 1 939.216 Multi-Range Speakers of Bell Telephone quency are spread through much larger All studios use directional microphones Laboratories. A divided-range speaker angles. This defect is avoided by dividing for situations where the maximum ratio system was used by H. A. Frederick in the total cross section of the passage into of direct to random sound is wanted. the demonstrations of vertically cut disk a number of smaller passages each of records in the fall of 1931.220The high- which is a small exponential horn. loudspeaker^^^^^^^^^^^ frequency units were of the type de- In this case there were sixteen horns for Single Range Loudspeakers. For several scribed by Bostwick in the October 1930 each driver. These are nested with their years after the industry had adopted Journal of the Acoustical Society of America, mouths adjacent and with their axes sound the theater loudspeakers were of the and in the May 1931 SMPE Journal.n1 pointed in different directions to cover a kinds already mentioned, (1) the direc- These were equipped with small horns total angle of about 30’ vertically and tional baffle-type, using a coil-driven better to load the diaphragms. The low- horizontally. Since the horns are of cone, much like those used in direct frequency units were of the direct- equal length, the waves, whatever their radiator speakers, with a short, straight- radiator or flat-baffle type, using (as I frequency, unite at the ends of the horns axis exponential horn of large throat recall it) approximately 12-in. diameter to form a practically continuous spherical area, and (2) those using long exponen- dynamic cone units,38a number of units front, which is the condition for uniform tial horns217,218with small throats, and being distributed over a large baffle. distribution throughout the 30’ angle. coil-driven metal diaphragms. In view A curve indicates a response within Two of these 16-horn nests were placed of their length the horns were coiled or rt 5 db from 50 to 10,000 cycles. side by side to give the desired total of otherwise bent to a form which took up A triple-range system is described by 60’ horizontal coverage. less space. Flannagan, Wolf and Jones,% whose review of the development of theater First Commercial RCA Two- Way Theater Multi-Range Loudspeakers and Improved loudspeakers is comprehensive and of Speakers. In the RCA line of theater Single-Range Steakers. The idea of provid- much interest. The system is also dis- equipment a dual-range loudspeaker ing separate devices to radiate high and cussed by Maxfield and Flannagan in the system was briefly described by J. low frequencies is undoubtedly of early January 1936 Journa1.222aThe mid-range Frank, Jr., at the 1935 fall meetingzz5 origin. When practically all radiators had units were essentially like the previous The speakers demonstrated by Dimmick strong fundamental resonances, the single-range speakers, using the Western and Belar, in 1932, using 6-in. cone double or triple unit could spread the Electric No. 555 driver units. The diaphragms with aluminum voice coils, range of reasonably high response over a radiators for the high-frequency range and 10-ft horns, were not seriously wider frequency band. With the advent (3,000-13,000) were the same as used lacking in frequency range and were of coil-driven, untuned diaphragms, in the Frederick demonstrations. The used in a number of deluxe installations, resort to separate radiators was a measure authors state that for the range below but they had two drawbacks. There for improving efficiency, in that the 300 cycles large coil-driven conical were many theaters without sufficient design did not have to be a compromise diaphragms in a large flat baffle gave room to install the long straight axis between what was best for low and for better results than designs using horns. horns, and in addition, the high-fre- high frequencies. A triple-horn speaker In April 1933 the Bell Telephone quency sound components were not well designed with special consideration to Laboratories gave a demonstration of distributed. When a wave front reaches efficiency and load capacity was ad- reproduction of orchestra music in a point in an exponential horn at which vocated and demonstrated by C. R. “auditory per~pective,”~~~~~the orchestra the dimensions of the passageway are Hanna of Westinghouse in 1927.219 being in Philadelphia and the reproduc- about a wavelength, its ultimate angle of However theater speakers of the single- tion in Constitution Hall in Washington, spread will not greatly exceed the angle unit type were so far improved (by the D.C. Three microphones picked up the between the walls at that place. From coil-driven unit of Wente and Thuras in music at three well-separated positions, this consideration it follows that a rapid 1926,57and by the adoption of directive and at the other end the independently flare horn would distribute the high- baffles for the GE-RCA cone-type transmitted and amplified currents were frequency sounds through considerably speakers in 1929) that they handled supplied to three correspondingly placed larger angles. Moreover with short rapid- quite well the frequency range then loudspeakers. flare horns, it is not impractical to mul- obtainable from film or disk. In this demonstration no recording tiply the number of units and thereby As recording improved, the benefits and reproduction entered to affect further control the sound distribution. In from extending the loudspeaker range frequency range, and it was essential for the theater speaker described by Frank, became more noticeable. After various the purpose to provide abundant sound there were three high-frequency horns di- improvements in the recording system power and frequency range. A dual- verging in direction, the driver units being including the new galvanometer, the range system was decided on. 6-in. cones with aluminum voice-coils.

370 July 1955 Journal of the SMPTE Volume 64 These units were rated to operate effec- is described in the Flannagan, Wolf and tively from 125 to 8,000 cycles, and a Jones paper.2n separate folded horn unit took care of The description by Hilliard of the sounds in the 40 to 125 cycle range. Shearer low-frequency unit may be One of the practical advantages of a Fig. 16. Controloffilm speed by flexure taken as in general typical of the com- direct-radiator (flat baffle) loudspeaker (A. V. Bedford). Principle later utilized mercial speakers of 1936-7. is the small space it requires. However a in nonslip printer. Divided channel or “two-way” horn makes it possible to radiate more speakers came into wide use during the plane, accomplished by suitably ar- r sound from a given-sized diaphragm several years following 1936. s without increasing the amplitude of ranged vertical partitions. The horn In some later designs of low-frequency cross section was divided into two expand- motion, and is therefore desirable for units, the sound passageway was not ing passageways, whose final openings increasing the sound output capacity. folded, and consisted only of a short together form a 68-in. square (Fig. 16). It also affords some control of the flaring connection between the driver This was surrounded by a flat baffle 10 direction of radiation. But to radiate low units (which presented a large total frequencies the rate of expansion (ratio X 12 ft, to reduce end reflections and radiating surface) and the large opening improve the loading of the units. The of increase in cross section per unit in the flat baffle.* It is of interest that mean length of each passageway was distance along axis) must be small, the evolution of low-frequency sound 40 in. (very short as low-frequency horn which for a given total ratio of expansion sources has been toward a closer resem- designs go), nor was the expansion means length. One way to provide a blance to the cone and baffle speakers of ratio large, the throat area being long passageway without requiring ex- 1925, but greatly magnified in size, and sufficient to accommodate the four 15-in. cessive depth of space back of the screen with some “directive baffle” effect better cones. is to coil up the horn. Drawings of coiled to control sound distribution. A nest of high-frequency horns, similar horns are shown in ref. 1, p. 298, and on Higher crossover frequencies than the to that used for the Auditory Perspective p. 251 of the March 1937 Journal. The 250-cycle point of the Shearer system demonstrations, three high by six hori- bending of large sound passageways is have prevailed, 400 cycles being the zontally, covered a horizontal angle of objectionable. Instead of expanding choice in many of the postwar units. about looo. With the lengths of the high- continuously as in the ideal horn, short In 1948 Hopkins and Keith228described and low-frequency horns nearly the waves suffer repeated reflections by the the design of a two-way theater speaker same, there would be little time differ- walls, causing some irregularities in the in which the crossover had been raised ence in the arrival of the sounds at the response and making the direction of to 800 cycles, observations having been plane of the mouths, thus simplifying the radiation of high-frequency sounds rather made that the irregularities which are avoidance of a “phasing” error which unpredictable.* On the other hand if the apt to occur at the crossover frequency has been found to have detrimental horn is to handle only low-frequency are less prejudicial if the crossover is effects with transients. However, in all sounds, the shapes of the bends are not at above the frequency range of maximum divided-range speaker systems the best all critical, and the condition is easily energy (250 to 500 cycles for orchestra relative positions of the high- and low- fulfilled that the difference between the music). frequency units have been determined shortest and longest paths around a A photograph of a loudspeaker de- by careful trials. This problem of bend is a small fraction of a wavelength. signed to use with “Cinerama” is shown “phasing” is discussed by Maxfield and In a common form of low-frequency in the May 1954 SMPTE ProgressReport, Flannagan,zza by Hilliardz6 and others. horn (in the sense of an approximately p. 343.This is more or less typical of recent exponentially expanding passageway) the It appears to be not wholly a question practice. The horn (or directive baffle of minimizing the mean time difference, driver unit (or units) is at the middle of expansion passage) of the low-frequency although that is a part of it. the back of a box-shaped space, and the units as well as that of the high-frequency In all divided-range speaker systems, passage is forward for a short distance, unit is designed to give exponential ex- dividing networksn7 have been used to dividing and forming two passages which pansion of the total cross section by side separate the high- and low-frequency turn back and then forward and expand walls which are radial, the floor and ceil- portions of the amplifier output and to form a pair of large adjacent rectangu- ing of each passage being curved to com- direct each to the appropriate speaker lar openings, which together form the pensate. The reflex, phase-inversion units. The networks consist in general of mouth of the horn. This roughly de- principle (mentioned under “Monitoring simple filter sections, and their design scribes the low-frequency unit of the Speakers”) is employed to utilize radia- has received much study. theater speaker system reported by tion from the backs of the diaphragms, Frank, the drivers in that case being a Commercial Two- Way Systems. Com- for the extreme bass. Note in the illus- pair of 8-in. coil-driven cones. mercial models of dual-range or “two- tration the outlet slots on either side of way” theater speakers were brought out the horn mouth. Shearer System.n6 In 1936 Douglas in 1936, employing the multicell high- Shearer, sound director for M-G-M, frequency horn system, and low-fre- Alternatives to Multicellular Horns. A gave demonstrations of improved sound, quency units much like those described somewhat simpler way of achieving the using loudspeakers described by J. K. by Hilliard. The high-frequency driver directive characteristic for which the Hilliard in the July 1936 Journal. units of the RCA system differed from multicellular high-frequency horns were The high-frequency radiators in this the ERPI and Lansing designs in that system were similar in many respects to designed has been developed in the post- the diaphragms were of molded phenolic war period by RCA and others. Horns those used for the Auditory Perspective instead of aluminum. This resulted in a demonstrations (see figure in Hilliard are used with linear expansion in the more rugged, if less sensitive, device. The horizontal plane (i.e. walls radial with paper). The frequency range to be reduced sensitivity and greater “roll covered was 50 to 8000 cycles, and the respect to the throat), while in the off,” or falling off at high frequency, can vertical plane the rate of expansion division or cross-over was at 250 cycles. be readily compensated electrically, and The low-frequency unit was a folded ~ do not mean any serious increase in * This would raise the “cutoff” frequency of the horn, with four 15-in. cones in a vertical amplifier output power, because the horn, but where the total expansion ratio is column. For simplicity of construction high-frequency components of the sound comparatively small that is not necessarily very the expansion was all in the horizontal represent only a small part of the total significant. Below its “cutoff’ frequency, an exponential horn does not impede sound trans- * This effect can be largely reduced by careful sound power. mission. It merely fails to multiply the volume design of re-entrant (zig-zag passage) horns. The ERPI “Diphonic” speaker system displacement as it does above cutoff.

Kellogg: History of Sound Motion Pictures 371 is such as to bring the total expansion of References (Continued) 93. H. Pfannenstiehl, “High-precision sound- the cross section to an exponential film recording machine,” Jour. S.I.IPE, 1. Lester Cowan, Recording Sound for Motion 29: 202-208, Aug. 1937. Pictures, McGraw-Hill Book Co., New York, relation. 94. E. W. Kellogg, “A new recorder for variabl: Another expedient for gaining the 1931 ; H. G. Knox, “Ancestry of sound pictures,’’ Chap. 1. area recording,” Jour. SMPE, 15: 653- desired spread of high-frequency sounds 4. J. G. Frayne and H. Wolfe, Elements of 670, Nov. 1930. (The title of this paper is was described by Frayne and Locanthi Sound Recording, J. Wiley & Sons, New York, misleading, in that the main features of the at the May 1954 convention of this 1949. recorder were in no wise related to the type 0,’ 6. E. I. Sponable, “Historical development of sound track to be recorded.) Society.229If the waves issuing from a sound films,” Pt. 1-2, Jour. SMPE, 48: 95. E. W. Kellogg, U.S. Pat. 1,892,554, straight-axis exponential horn can be 275-303, Apr. 1947; Pt. 3-7, ibid., 407- 1,899,571, and Re19,270. 422, May 1947. made to assume a spherical instead of 96. R. 0. Drew and E. W. Kellogg, “Filtering 57. E. C. Wente and A. L. Thuras, “A high factors of the magnetic drive,” Jou~. nearly flat front, they will spread as efficiency receiver of large power capacity SMPE, 35: 138-164, Aug. 1940. desired. An acoustic equivalent of a for horn type loud speakers,” Bell Sys. Tech. J., Jan. 1928, p. 140. 97. See ref. 94. concave optical lens is placed in the 70. E. W. Kellogg, “A review of the quest for 98. A. G. Zimmerman, “Film recorders,” mouth of the horn, in order to retard constant speed,” Jour. SMPE, 28: 337-376, Jour. SMPE, 20: 211-227, Mar. 1933. the off-axis parts of the waves relative to Apr. 1937. 99. M. E. Collins, “A deluxe film recording the central part. The reduced velocity machine,” Jour. SMPE, 48: 148-156, The fioe references above, which are referred to in Feb. 1947. (Model PR-31) of propagation is achieved by means of a the current installment of this paper, are reprinted from 100. H. A. Rowland, an early disclosure (1902) series of closely-spaced perforated sheet- the first installment for the convenience of readers. of the general principle of the damped metal baffles, the number of layers 77. L‘Industrie du Film Parlant, Conservatoire flywheel is in U.S. Pat. 691,667, 1899, being progressively greater toward the des Arts et Metiers, Feb. 17, 1929. Contains and 713,497. (See refs. 81 and 104.) edges. This system was reported to have a resume cowing the Gaumont and the Gaumont- 101. F. J, Loomis and E. W. Reynolds, “New Peterson-Poulsen sound systems. (Theforegoing is Apparatus-A new high fidelity sound given smoother distribution than the from the Theisen historkal paper-ref. 5.) head,” Jour. SMPE, 25: 449-460, Nov. multicell horns. 78. H. E. Roys, “The measurement of trans- 1935; and “New rotary stabilizer sound cription-turntable speed variation,” Proc. head,” Jour. SMPE, 27: 575-581, Nov. Monitoring Loudspeakers.4,230.231Wider- I.R.E., 31: 52-56, Feb. 1943. 1936. range monitoring speakers kept pace 79. T. E. Shea, W. A. MacNair and V. Suhrizi, 102. E. D. Cook, “The technical aspects of “Flutter in sound records,” Jour. S.MPE, the high-fidelity reproducer,” Jour. SMPE, with theater speakers. While a single 25: 403-415, NOV. 1935. 25: 289-313, Oct. 1935. conical diaphragm can be designed so 80. E. G. Shower and R. Biddulph, “Differen- 102a.Gerhard Schwesineer. “The compliance that the center portion radiates high tial pitch sensitivity of the ear,” J. Acoust. of film loops,” Jour-SMPTE, 57: 320-327, frequencies and the outer area radiates Sac. Am., 3: 215-287, Oct. 1931. Oct. 1951. low frequencies, best results have been 81. W. J. Albersheim and D. MacKenzie, 103. G. Puller, “Sound-picture reproducing “Analysis of sound film drives,” Jour. system for small theaters,” Jour. SMPE, obtained by using separate diaphragms SMPE, 37: 452-479, Nov. 1941. 27: 582-589, Nov. 1936; Report of the and separate voice coils, or in other 82. E. W. Kellogg and H. Belar, “Analysis of Progress Committee, Jour. SMPE, 27: words resorting to the dual-range system. the distortion resulting from sprocket hole 29, July 1936. The upper- and lower-range units may be modulation,” Jour. SMPE, 25: 492-502, 104. E. C. Wente and A. H. Miiller, “Internally damped rollers,” Jour. SMPE, 37: 406-417, adjacent or concentric. In the latter case Dec. 1935. 83. SMPE Committee on Sound, “Proposed Oct. 1941. the low-frequency diaphragm becomes a standard specifications for flutter or wow 105. C. C. Davis, “An improved film-drive directive baffle for the high-frequency as related to sound records,” Jour. SMPE, filter mechanism,” Jour. SMPE, 46: 454- radiator. 49: 147-159, Aug. 1947. 464, June 1946. Permissible cabinet size tends to set 84. E. W. Kellogg, “Proposed standard for 106. G. R. Crane and H. A. Manley, “A simpli- fied all-purpose film recording machine,” the lower limit of the frequency range, measurement of distortion in sound recording,” Jour. SMPE, 51: 449-467, Nov. Jour. SMPE, 46: 465-474, June 1946. air reaction on the back of the diaphragm 1948. Further discussion of the Flutter 107. M. E. Collins, “Lightweight recorders for creating the problem if the back is Standard by the same author appears in an 35 and 16 mm films,” Jour. SMPE, 49: enclosed, or inadequate baffling if an editorial in the Trans. I.R.E., July-Aug., 415-424, Nov. 1947. (Models PR-32 and PR- open-back cabinet is used. In order to 1954. 33.) 84a. Frank A. Comerci, of the Material Labora- 108. J. D. Phyfe and C. E. Hittle, “Film-pulled utilize the radiation from the back of the tory, Bureau of Ships New York Naval theater-type magnetic sound reproducer low-frequency diaphragm, a second Shipyard, Brooklyn, N. Y., “Perceptibility for use with multitrack films,” Jour. opening is often provided (for example of flutter in speech and music,” Jour. SMPTE, 62: 215-220, Mar. 1954. below the diaphragm) and the space in SMPTE, 64: 117-122, Mar. 1955.Discusnion, 109. C. C. Davis and H. A. Manley, “Auxiliary 318, June 1955. multitrack magnetic sound reproducer,” the cabinet used to provide a folded 85. M. S. Mead, U.S. Pat. 1,854,949. Jour. SMPTE, 62: 208-214, Mar. 1954. horn between the diaphragm and the 86. E. W. Kellogg and A. R. Morgan, “Meas- 110. S. W. Athey, W. Borberg, and R. A. White, opening, or else to serve as a simple urement of speed fluctuations in sound “Four-track magnetic theater sound re- chamber which acts in conjunction with recording and reproducing equipment,” producer for composite films,” Jour. the inertia reactance of the air at the J. Acoust. Sac. Am., 7: 271-280, Apr. 1936. SMPTE, 62: 221-227, Mar. 1954. 87. A. Goodman, R. J. Kowalski, W. F. 111. Wesley C. Miller, “M-G-M recorder and second opening as a phase inverter. Hardman and W. F. Stanko, “Safeguarding reproducer equipment units,” Jour. SMPE, This does not greatly augment the low- theater sound equipment with modern 40: 301, May 1943. frequency output except near the reso- test instruments,” Jour. SMPE, 34: 409- 112. J. S. Chandler, “Some theoretical con- nance, set by the elastic reactance of the 423, Apr. 1940. siderations in the design of sprockets for cavity and the inertia reactance of the 88. R. R. Scoville, “A portable flutter-measur- continuous film movement,” Jour. SMPE, ing instrument,” Jour. SMPE, 25: 41 6-422, 37: 164-176, Aug. 1941. combination of openings (one with the Nov. 1935 Also: “Laboratory flutter-meas- 113. J. G. Streiffert, “The radial-tooth, variable- diaphram and one without). Sound- uring instrument,” Jour. SMPE, 29: 209- pitch sprocket,” Jour. SMPTE, 57: 529- absorbing material is often used in the 215, Aug. 1937. 550, Dec. 1951. cabinet to reduce the magnitude of other 89. F. P. Herrnfeld, “Flutter-measuring set,” 114. “Rulings of the U.S. Supreme Court in resonances. If the horn-type back-wave Jour. SMPTE, 55: 167-172, Aug. 1950. recent patent cases of the American Tri- 90. U. R. Furst, “Periodic variations of pitch Ergon Corp.,” Jour. SMPE, 24: 529-550, system is used, its augmentation of output in sound reproduction by phonographs,” June 1935. is limited at the lower end when the Proc. I.R.E., 34: 887-895, NOV.1946. 115. Report of Standards and Nomenclature phase shift through the horn becomes 91. L. A. Elmer and D. G. Blattner, “Machine Committee, Jour. SMPE, 14: 126, 133, less than about a quarter cycle, and at for cutting master disc records,” Trans. Jan. 1930. the upper end by the fact that it is SMPE, 37: 227-246, 1929. 116. Oscar B. Depue, “A machine for printing 92. P. H. Evans, “A comparative study of picture and sound simultaneously and deliberately designed to have a low-pass sound on disk and film,” Jour. SMPE, 15: automatically,” Jour. SMPE, 18: 643-648, filter characteristic. 185-192, Aug. 1930. May 1932.

372 July 1955 Journal of the SMPTE Volume 64 117. A. S. Howell, B. E. Steckbart and R. F. screens for sound picture work,” Jour. motion picture film,” Jour. SMPE, 21: Mitchell, “The Bell & Howell fully auto- SMPE, 15: 320-331, Sept. 1930. 218-223, Sept. 1933. matic sound picture production printer,” 145. Charles R. Underhill, Jr., “Practical 168. F. L. Eich, “A physical densitometer for Jour. SMPE, 19: 305-328, Oct. 1932. solution to the screen light distribution sound processing laboratories,” Jour. SWPE, 118. A. S. Howell and R. F. Mitchell, “Recent problem,” Jour. SMPTE, 56: 680-683, 24: 180-183, Feb. 1935. improvements in the Bell & Howell fully June 1951; Report of Progress Com- 169. W. W. Lindsey, Jr. and W. V. Wolfe, automatic printer,” Jour. SMPE, 22: 115- mittee, Jour. SMPTE, 56: 575, May “Wide-range, linear-scale photoelectric 126, Feb. 1934. 1951. cell densitometer,” Jour. SMPE, 28: 622-632, June 1937. 119. Roscoe C. Hubbard, “Printing motion 146. J. I. Crabtree, “The motion picture picture film,” Trans. SMPE, No. 28, 252, laboratory,” Jour. SMPTE, 64: 13-34, 170. D. R. White, “Direct-reading photoelectric Feb. 1927. Jan. 1955. densitometer,” Jour. SMPE, 33: 403-409, Oct. 1939. 120. J. Crabtree, “Sound film printing-I,” 147. H. W. Moyse and D. R. White, “Borax Jour. SMPE, 21: 294-322, Oct. 1933; developer characteristics,” Trans. SMPE, 171. J. G. Frayne and G. R. Crane, “Precision “Sound film printing-11,” Jour. SMPE, NO. 38,445-452,1929. integrating-sphere densitometer,” Jour. 22: 98-114, Feb. 1934. 148. H. C. Carlton and J. I. Crabtree, “Some SMPE, 35: 184-200, Aug. 1940. 121. J. I. Crabtree and C. E. Ives, “A new properties of fine grain developers for 172. C. M. Tuttle and M. E. Russell, “Note on method of blocking out splices in sound motion picture film,” Trans. SMPE, No. the use of an automatic recording densitom- 38, 406-444,1929. eter,” Jour. SMPE, 28: 99-111, Jan. 1937. film,” JOU7. SMPE, 14: 349-356, Mar. 1930. 122. F. D. Williams, “Methods of blooping,” 149. E. Huse, “Sensitometric control in the 172a.D. MacKenzie, “Straight-line and ’ toe Jour. SMPE, 30: 105-106, Jan. 1938. processing of motion picture film in Holly- records with the light-valve,” Jour. SMPE, wood,” Jour. SMPE, 21: 54-82, July 1933. 77: 172-202, Aug. 1931. 123. W. H. Offenhauser, Jr., “Current practices in blooping sound-film,” Jour. SMPE, 150. L. A. Jones, “Photographic sensitometry,” 173. L. A. Jones and Otto Sandvik, “Photo- 35: 165-171, Aug. 1940. Jour. SMPE, 17: 491-535, Oct. 1931; graphic characteristics of sound recording Part 2, 695-742, Nov. 1931; Part 3, 124. E. I. Sponable, “Elimination of splice film,” Jour. SMPE, 14: 180-203, Feb. 18: 54-89, Jan. 1932; Part 4, 324-355, noise in sound film,” Jour. SMPE, 26: 1930. Mar. 1932. 136-144, Feb. 1936. 174. J. A. Maurer, “The photographic treat- 151. A. Kiister and R. Schmidt, “The sensito- 124a.George Lewin, “A new blooping device,” ment of vririable-area sound-films,” Jour. metric control of sound records on film,” Jour. SMPE, 48: 343-347, Apr. 1947. Jour. SMPE, 79: 539-545, Dec. 1932. SMPE, 14: 636-649, June 1930. 125. L. E. Clark, “Some considerations in the 152. J. B. Engl, “A new process for developing 175. G. L. Dimmick, “High-frequency re- design of sound-proof camera housings,” and printing photographic sound records,” sponse from variable-width records as Jour. SMPE, 15: 165-170, Aug. 1930. Trans. SMPE, No. 30, 257-266, 1927. affected by exposure and development,” 126. Report of Progress Committee, Jour. Jour. SMPE, 17: 766-777, Nov. 1931. 153. Joe W. Coffman, “Sound film processing,” SMPE, 27: 3-44, July 1936. Twentieth Trans. SMPE, No. 35, 799-808, 1928. 176. J. 0. Baker and D. H. Robinson, “Modu- Century-Fox camera, p. 8. Also “Art and science in sound film produc- lated high-frequency recording as a means 127. H. R. Kossman, “A silent camera,” Jour. tion,” Jour. SMPE, 14: 172-179, Feb. of determining conditions for optimal SMPE, 21: 420-425, Nov. 1933. 1930. processing,” Jour. SMPE 30: 3-17, Jan. 1938. 128. D. B. Clark and G. Laube, “Twentieth 154. W. Leahy, “Time-and-temperature vs. the 177. J. E. Abbott, “Development of the sound century camera and accessories,” Jour. test system for development of motion film,” Jour. SMPE, 38: 541-545, June SMPE, 36: 50-64, Jan. 1941. picture negatives,” Jour. SMPE, 18: 1942. 129. J. P. Maxfield, “Acoustic control of re- 649-651, May 1932. 178. G. L. Dimmick, “Galvanometers for vari- cording for talking motion pictures,” 155. J. I. Crabtree and C. E. Ives, “A replenish- able-area recording,” Jour. SMPE, 15: Jour. SMPE, 14: 85-95, Jan. 1930. ing solution for a motion picture positive 428-438, Oct. 1930. 130. A. S. Ringel, “Sound-proofing and acoustic film developer,” Jour. SMPE, 15: 627-640, 179. G. L. Dimmick and H. Belar, “Extension treatment of RKO stages,” Jour. SMPE, 15: Nov. 1930. of the frequency range of film recording and 352-369, Sept. 1930. 156. R. M. Evans, “Maintenance of a developer reproduction,” Jour. SMPE, 19: 401-406, 131. M. C. Batsel, “Recording music for motion by continuous replenishment,” Jour. SMPE, Nov. 1932. pictures,” Jour. SMPE, 25: 103-108, 31: 273-286, Sept. 1938. 180. M. C. Batsel and E. W. Kellogg, “RCA Aug. 1935. 157. H. L. Baumbach, “Continuous replenish- sound recording system,” Jour. SMPE, 132. R. H. Townsend, “Some technical aspects ment and chemical control of motion 28: 507-533, May 1937. of recording music,’’ Jour. SMPE, 25: picture developing solutions,” Jour. SMPE, 181. G. L. Dimmick, “A newly developed light 259-268, Sept. 1935. 39: 55-66, July 1942. modulator for sound recording,” Jour. 133. M. Rettinger, “Scoring-stage design,” 158. C. E. Ives and E. W. Jensen, “Effect of SMPE, 49: 48-56, July 1947. Jour. SMPE, 30: 519-534, May 1938. developer agitation on density uniformity 182. E. W. Kellogg, U.S. Pat. 1,740,406. 134. V. 0. Knudsen, “Hearing of speech in and rate of development,” Jour. SMPE, 182a.L. T. Sachtleben, “Characteristics of the auditoriums,” J. Acoust. Sac. Am., 56, Oct. 40: 107-136, Feb. 1943. Photophone light-modulating system,” Jour. 1929. 159. J. I. Crabtree and H. D. Russell, “Some SMPE, 25: 175-191, Aug. 1935. 135. W. A. MacNair, “Optimum reverberation properties of chrome alum stop baths and 183. G. L. Dimmick, “RCA recording system time for auditoriums,” J. Acoust. Soc. Am., fixing baths,” Jour. SMPE, 14: Part 1, and its adaptation to various types of 242, Jan. 1930. 483-512, May 1930; Part 2, 667-700, sound-track,” Jour. SMPE, 29: 258-273, 136. S. S. A. Watkins and C. H. Fetter, “Some June 1930. Sept. 1937. aspects of a Western Electric sound record- 160. J. I. Crabtree, L. E. Muehler and H. D. 184. E. W. Kellogg, “ABC of photographic ing system,” Jour. SMPE, 14: 520-530, Russell, “New stop bath and fixing bath sound recording,” Jour. SMPE, 44: 151- May 1930. formulas and methods for their revival,” 194, Mar. 1945. 137. B. Kreuzer, “Recent improvements in the Jour. SMPE, 38: 353-372, Apr. 1942. 185. E. W. Kellogg, “Ground-noise reduction variable-width recording system,” Jour. 161. R. C. Hubbard, “The straight line de- systems,” Jour. SMPE, 36: 137-171, Feb. SMPE, 27: 562-574, NOV.1936. veloping machine, Trans. SMPE, No. 18, 1941. 138. W. P. Dutton and S. Read, Jr., “Some 73-85, May 1924. 186. Siemens and Halske, British Pat. 288,225, new RCA photophone studio recording 162. Alfred B. Hitchins, “Machine development Convention Apr. 9,1927. equipment,” Jour. SMPE, 16: 315-329, of negative and positive motion picture 187. L. T. Robinson, U.S. Pat. 1,854,159 Mar. 1931. film,” Trans. SMPE, No. 22, 46-53, 1925. and 1,935,417; C. W. Hewlett, U.S. 139. S. Read, Jr., “RCA Victor high-fidelity 163. H. D. Hineline, “Continuous photographic Pat. 1,853,812; and C. R. Hanna, U.S. film recording equipment,” Jour. SMPE, processing,” Jour. SMPE, 26: 38-53, Jan. Pat. 1,888,724. 20: 396-436, May 1933. 1936. 188. H. C. Silent and J. G. Frayne, “Western 140. S. Read, Jr., “Neon type volume indica- 164. Clifton Tuttle and J. W. McFarlane, Electric noiseless recording, Jour. SMPE, tor,” Jour. SMPE, 28: 633-642, June 1937. “The measurement of density in variable- 78: 551-570, May 1932. 141. F. G. Albin, “Linear decibel-scale volume density sound-film,” Jour. SMPE, 15: 189. H. McDowell, Jr., US. Pat. 1,855,197. indicator,” Jour. SMPE, 29: 489-492, Nov. 345-351, Sept. 1930. 190. R. H. Townsend, H. McDowell, Jr. and 1937. 165. L. A. Jones and J. H. Webb, “Reciprocity L. E. Clark, “Ground-noise reduction 142. L. T. Sachtleben, “Characteristics of Photo- law failure in photograph exposures,” RCA Photophone system,” Reprint 26, phone light-modulating system,” Jour. Jour. SMPE, 23: 142-159, Sept. 1934. Tech. Bul. Acad. Mot. Pict. Arts &3 Sci., SMPE, 25: 175-191, Aug. 1935. 166. J. G. Capstaff and R. A. Purdy, “A compact Feb. 1931. 143. L. J. Anderson, “High fidelity head- motion picture densitometer,” Trans. 191. E. W. Kellogg and C. N. Batsel, “A shutter phones,” Jour. SMPE, 37: 319-323, Sept. SMPE, NO. 31, 607-612, 1927. for use in reduction of ground-noise,” Jour. 1941. 167. G. A. Chambers and I. D. Wratten, SMPE, 17: 203-215, Aug. 1931. 144. H. F. Hopkins, “Considerations in the “The Eastman type IIb densitometer as a 192. H. J. Hasbrouck, J. 0. Baker and C. N. design and testing of motion picture control instrument in the processing of Batsel, “Improved noise-reduction system

Kellogg: History of Sound Motion Pictures 373 for high-fidelity recording,” Jour. SMPE, 205. F. E. Carlson, “Properties of lamps and 219. C. R. Hanna, “Loudspeakers of high 29: 310-316, Sept. 1937. optical systems for sound reproduction,” efficiency and load capacity,” Trans. 193. R. R. Scoville and W. L. Bell, “Design and Jour. SMPE, 33: 80-96, July 1939. AIEE, 47: 607, Apr. 1928. use of noise-reduction bias systems,” 205a.L. T. Sachtleben, U.S. Pat. 2,158,308. 220. H. A. Frederick, “Vertical sound records: Jour. SMPE, 38: 125-147, Feb. 1942. 206. 0. 0. Ceccarini, “Recent contributions to recent fundamental advances in mechanical records on wax,” Jour. SMPE, 18: 141-163, 194. B. Kreuzer, “Noise reduction with variable- light-valve Technic,” Jour. SMPE, 17: Feb. 1932. area recording,” Jour. SMPE, 16: 671- 305-325, Sept. 1931. 221. L. G. Bostwick, “A loud speaker good to 683, June 1931. 207. W. Herriott and L. V. Foster, “Recent optical improvements in sound-film record- twelve thousand cycles,” Jour. SMPE, 195. J. L. Hathaway, “Microphone polarity and 16: 529-534, May 1931. overmodulation,” Electronics, Oct. 1939, ing equipment,” Jour. SMPE, 23: 167-174, Sept. 1934. 222. C. Flannagan, R. Wolf and W. C. Jones, p. 28. “Modern theater loud speakers and their 208. E. C. Wente and R. Biddulph, “Light- 196. R. 0. Drew and E. W. Kellogg, “Starting development,” Jour. SMPE, 28: 246-264, valve for the stereophonic sound-film characteristics of speech sounds,” Jour. Mar. 1937. system,” Jour. SMPE, 37: 397-405, Oct. SMPE, 34: 43-58, Jan. 1940; and J. 222a.J. P. Maxfield and P. Flannagan, “Wide 1941. Acoust. SOC.Bm., 72: 95-103, July 1940. range reproduction in theaters,” Jour. 209. R. R. Scoville, “Overload limiters for the 197. J. G. Frayne, “Noise-reduction anticipa- SMPE, 26: 67-78, Jan. 1936. protection of modulating devices,” Jour. tion circuits,” Jour. SMPE, 43: 313-320, 223. Symposium on Auditory Perspective, pub. SMPE, 31: 93-98, July 1938. Nov. 1944. in Elcc. Eng., (AIEE), 53: 9, Jan. 1934; 210. W. C. Jones and L. W. Giles, “A moving- 198. J. R. Whitney and J. W. Thatcher, “In- and BelI Sys. Tech. J., 13: 239, Apr. 1934. coil microphone for high-quality sound This equipment is again described in Jour. creased noise reduction by delay networks,” reproduction,” Jour. SMPE, 77: 977-993, SMPE, 37: 331-417, Oct. 1941. See also Jour. SMPTE, 54: 295-302, Mar. 1950. Dec. 1931. refs. 329-332. 199. G. L. Dimmick and A. C. Blaney, “Direct 211. E. C. Wente and A. L. Thuras, “Moving 224. H. Fletcher, “Transmission and reproduc- positive system of sound recording,” coil telephone receivers and microphones,” tion of speech and music in auditory per- Jour. SMPE, 33: 479-487, Nov. 1939. See J. Acoust. Soc. Am., 3: 44-55, Jan. 1931. spective,” Jour. SMPE, 22: 314-329, May 1934. also Progress Committee Report, Jour. 212. H. F. Olson, “The ribbon microphone,” SMPTE, 58: 401, May 1952. 225. J. Frank, Jr., “RCA photophone high- Jour. SMPE, 16: 695-708, June 1931; and fidelity sound reproducing equipment,” 200. W. A. Mueller and G. R. Groves, “Mag- J. Acoust. Soc. Am., 3: 56, July 1931. Jour. SMPE, 27: 99-104, July 1936. netic recording in the motion picture 213. H. F. Olson, “Collection of sound in rever- 226. J. K. Hilliard, “Study of theater loud studio,” Jour. SMPE, 52: 605-612, June berant rooms, with special reference to the speakers and the resultant development of 1949. application of the ribbon microphone,” the Shearer two-way horn system,” Jour. 201. Academy Research Council, “Report of Proc. IRE, 21: 655, May 1933. SMPE, 27: 45-60, July 1936. basic sound committee on pre-and-post- 214. H. F. Olson and Frank Massa, Aflfllicd 227. J. K. Hilliard and H. R. Kimball, “Divid- ing networks for loud speaker systems,” equalization,” Jour. SMPE, 42: 187-192, Acoustics, P. Blakiston’s Sons & Co., Mar. 1944. Jour. SMPE, 27: 61-73, July 1936. Philadelphia, 1934. 228. H. F. Hopkins and C. R. Keith, “New 202. J. K. Hilliard, “Projects of the committee on 215. H. F. Olson, “Unidirectional microphone,” theater loud speaker systems,” Jour. standardization of theater sound projection Jour. SMPE, 27: 284-301, Sept. 1936. SMPE, 57: 385-398, Oct. 1948. equipment characteristics,” Jour. SMPE, 216. R. N. Marshall and W. R. Harry, “Cardi- 229. J. G. Frayne and B. N. Locanthi, “Theater 30: 81-95, Jan. 1938. oid directional microphone,” Jour. SMPE, loudspeaker system incorporating an acous- 203. J. K. Hilliard, “Variable-density film- 33: 254-277, Sept. 1939. tic-lens radiator,” Jour. SMPTE, 63: 82-85, Sept. 1954. recording system used at MGM studios,” 217. A. G. Webster, “Acoustical impedance and 230. H. F. Olson and John Preston, “Wide- Jour. SMPE, 40: 143-175, Mar. 1943. theory of horns and phonograph,” Proc. range loudspeaker developments,” Jour. 204. K. F. Morgan and D. P. Loye, “Sound Nat. Acad. of Sci., 6: 275, 1919. SMPE, 47: 327-352, Oct. 1946. picture recording and reproduction char- 218. C. R. Hanna and J. Slepian, “The Func- 231. James B. Lansing, “New permanent acteristics,” Jour. SMPE, 32: 631-647, tion and design of horns for loud speakers,” magnet public address loudspeaker,” Jour. June 1939; 33: 107-108, July 1939. Trans. AIEE, 43: 393, Feb. 1924. SMPE, 46: 212-219, Mar. 1946.

The third, andjinal, installment of this Paper will be published in the August Journal.

374 July 1955 Journal of the SMPTE Volume 64