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REPRODUCTION IN THE THEATRE
S. K. WOLF*
The addition of sound to motion pictures more than doubled the amount of projection equipment necessary in the theatre. The images on the film are after all just translucent miniatures of what is to be shown on the screen. The sound source on the other hand is either a tiny scratch on a wax disc or an odd looking border along the film. In both cases a delicately elaborate arrangement of electrical machinery must intervene before the sound locked in the film or disc by the recording process can be brought to new life.
Three essential elements make up a reproducing system. They are :
(1) A pick up or reproducer.
(2) An amplifier.
(3) A loud speaker or receiver.
The function of the reproducer is to transform the sound record into electrical energy. The function of the amplifier is to magnify the infinitesimal electrical energy to the desired value. The function of the loud speaker is to transform this amplified electrical energy into acoustic energy and to distribute the acoustic energy or sound throughout the theatre or auditorium wherein it is being produced.
At the present time there are two types of sound recording used commercially. These are known as the film and the disc methods. The only essential difference between the systems used for reproducing film and disc records is in the pickup apparatus.
Fig. 1 is a schematic diagram showing the general layout of a sound reproducing system. You will note that provisions are made for reproducing both film and disc records, also that two machines are equipped, making in all. four pickup devices. Obviously two machines are necessary to the continuity of the picture and sound reproduction. Provision is also made for select
*Theatre Acoustics Engineer, Electrical Research Products, Inc.
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