Exhibitors Herald and Moving Picture World (Jul-Sep 1928)

August 25, 1928 EXHIBITORS HERALD and MOVING PICTURE WORLD 37 How RCA Photophone Times Synchronism Exact timing of picture and sound is photographed and fixed in the RCA Photophone system, a detailed description of the synchronization device shotvs. While the sound accompaniment may be musical, such as the recording of an orchestra or band, it may also be in the form of incidental sound effects. Four illustrations of the descriptive article appear on this an in the continuation of the article, on Page 54. ^ THE component elements of a Photophone film are shown in Figure 1. Examination will show that this picture has the same proportions of height to width as the standard motion picture. On the right side of this illustration is shown the type of sound record used by RCA Photophone. It will be seen that this is a narrow black band, the inner edge of which (that nearest to the picture) has a wavy outline. This outline constitutes a faithful record of the air vibrations in the original music or speech. Its minute and complex contours are literally the permanent and accurate signature of the original sound waves. The combined picture and sound record shown demonstrates how picture and sound are bound together on every RCA Photophone film. One advantage of the variable width sound track is the comparative independence from extreme precision of exposure during the recording or printing of the film and from exactness in time of development of either the negative or positive. The exact timing of picture and sound is photographed and fixed regardless of any handling of the film or the projector and irrespective of any cutting or splicing of the film. A few frames of film can be lost and the film be spliced without any noticeable effect on either the picture or the sound reproduction. In brief, RCA Photophone films are just as flexibly handled and as simply projected a product as ordinary "silent films." Interchangeability RCA Photophone projectors have the sound head mounted below the picture-projection head and as the sound is twenty frames ahead of the picture it is interchangeable with other synchronous sound-picture systems such as Movietone. The four principal types of RCA Photophone equipment for theatres have the following type designations, and will serve audiences of the following number of persons in any average auditorium or theatre : Type A up to 6,000 persons B up to 3,000 persons C up to 1,500 persons D up to 750 persons The preceding ratings are conservative and may be exceeded in some cases. This equip J V V. W •V.f.'.g'-' k Figure 1. Invents Device to Adjust Synchronism An invention for compensating for any error in synchronization has brought a provisional patent to Charles Goreley of Canterbury. The principle is explained as follows : If the record is, say, a quarter of a turn in advance of the position required for correct synchronization, the arm carrying the sound-box could be moved a quarter of a turn forward by the device, the current being temporarily switched off while the adjustment is being made. Rotating the arm sufficiently often in the required direction would bring adjustment of any degree of error. r ment is designed to give spectacular effects when such are called for, and it therefore has a considerable over-load capacity. The projector is rugged and of the highest grade, and is shown in Figure 2. The sound reproducing head plays all existing types of synchronized sound films. The entire gear system of the projector runs quietly in a forcedfeed oil bath, thereby insuring long life for the gears and quiet operation, together with freedom from the annoyances incident to frequent overhauling of the projector. The film is carefully shielded from oil or dust in this projector. The film path is clearly indicated by conspicuous guide lines within the machine, to facilitate rapid and accurate threading. The optical system is of the highest quality. Through special arrangements of the optical system and position of the shutter, flickerless projection is obtained without overheating of the film. An important advantage claimed for the RCA Photophone projector is that the heating of the film is considerably less than in most other projectors, thereby preventing buckling of the film, lack of registration and blurring of the image on the screen, and injury to the quality of the sound produced. The path of the sound light beam which in the j)rojector, passes through the slit optical system and film sound track, falls on the photo-electric cell. In this cell the varying light gives rise to the electric currents which, after being greatly magiiified by the amplifiers used in this system, operate the loudspeakers that reproduce the original sound on the stage. The action of reproducing the sound is instantaneous, and the sound reproducing system is entirely automatic in operation. The lights which are used to illuminate the sound track are provided in duplicate, and if one burns out during a performance, the touch of a lever brings a second prefocused lamp into position and lights it on automatically without causing interruption in the performance. Amplifiers The initial amplifier is connected to the output of the photo-electric cell, and amplifies this output electrically through a series of vacuum tubes until sufficient power is available to operate the final or power amplifier. The initial amplifier is always placed in the projection room in a convenient location, generally at a porthole, so that the projectiojiisj. at the amplifier control board may view the screen. The placing of the equipment will be different for each installation because of locaB conditions. A typical arrangement of equipment is shown in Figures 3 and 4. (Page 54), The amplifier shown in Figure 3 representsa product developed following extensive experience in the construction of high quality high power amplifiers. In all sizes of RCA Photophone equipment larger than Type D the initial amplifier is provided in duplicate. These initial amplifiers are handled like an ordinary radio receiver, and consequently it takes very little time for the projectionist to master the few adjustments of such equipment. In all forms of the final power amplifier, the equipment is open and accessible, permitting easy replacement of the vacuum tubes when necessary. An important point in these equipments is that by the use of special circuits and grouping of unit parts, the burning out of an individual tube or even the unusual development of a fault in an amplifier unit in general does not stop operation but merely modifies either the quality or the volume of the sound to some extent, thereby directing the attention of the projectionist to the need for a tube replacement or other change in operation without, however, totally interrupting the performance. RCA Radiotrons are used in all Photophone equipment. Loud Speakers The final or power amplifier supplied in the RCA Photophone system may be placed either in the projection room, in a room closely adjacent to the projection room, or back stage, as may prove most convenient and desirable. This feature will be appreciated in the theatres where the projection rooms are of limited dimensions and where "every inch counts." In such cases, the flexible RCA Photophone system permits the separate power amplifier to be installed wherever there is most room for it. The power amplifier is connected to the loudspeakers which it actuates. These consist of electro-dynamic loudspeaker cone units combined in banks, or groups, as required. A bank of four is shown in Figure 4 (Page 54.) Each loudspeaker group produces a wide, smooth fan of sound, instead of a narrow beam. In addition, in larger theatres, several {Continued on page 54) J ^ Figure 2. N r