Sound motion pictures : from the laboratory to their presentation (1929)

ii2 SOUND MOTION PICTURES occur a very large proportion of them can be directly traced to neglect or disregard of this rule. I. General Operation of the Equipment Two methods of recording, let me repeat, are in use. In the one, the record is made on a disk, under the trade name of "Vitaphone." In the other, the record is photographed on the film, under the trade name of "Movietone." Any theatre can be equipped for showing motion pictures by either. The only difference is in the apparatus used at the projector. The film is threaded into the projector in the usual manner, except that great care must be exercised to have the proper sized loop, to avoid disturbing the synchronism, since the sound is registered 14! inches below the aperture, where the sound slit is located. After leaving the lower sprocket of the projector mechanism the sound film enters the reproducing aperture, where it passes over a sprocket that moves it along at a constant speed. The projector driving mechanism consists of a gear box mounted on the same base as the motor. For disk reproduction it is coupled directly to the vertical extensible shaft by means of universal joints and to a second, or upper, gear box. For film there is a train of gears with a chain drive for the lower take-up. By means of these two sets of gears, the speed is reduced from 1,200 R. P. M. (revolutions per minute) at the motor shaft, to 90 R. P. M. at the projector machine drive shaft, which clears to a film speed of 90 per minute. The motor is provided with a flywheel and a guard. The flywheel is directly coupled to the motor shaft by means of set screws. This is a special coupling; the set screws are used also to connect one shaft of the motor with the shaft of the lower gear box. The motor connections are