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STANDARD SOUND DEVICES 51
auditorium public speaker invented by Dr. C. W. Hewlett, also of the General Electric Staff. These consist of electrodynamic loudspeaker cone units combined in banks, or groups, as required.
Each loudspeaker group produces a wide, smooth fan of sound instead of a narrow beam. In addition, in larger theatres, several groups of R. C. A.-Photophone loudspeakers can be utilized, thereby to cover the entire theatre with a number of fans of sound.
A group of loudspeakers may be placed on each side of the screen. The groups may, at will, be mounted permanently on the side of the screen and "flyed " with the screen when it is lifted, leaving the stage clear for other performances or presentations.
Or, alternatively, the loudspeaker groups can be mounted on either ornamental, or inconspicuous, towers and wheeled onto the stage from the wings. The complete loudspeaker group is easily handled and practically no more difficult to move than a section of an ordinary stage set. The outside dimensions are 75 inches high, by 21 inches wide, by 21 inches deep, and the weight of a group is 250 pounds.
The ordinary wiring of the arc or incandescent lamp of the motion picture projector is identical with that used in any projector. Only the additional wiring incidental to the sound reproduction in the R. C. A.-Photophone system need be considered. The wiring of the sound-reproducing circuit consists of a continuous connection from the sound head of the projector to the initial amplifier in the projection booth, thence to the final amplifier, and thence to the loudspeaker groups on the stage. The wiring can readily be arranged in cable form, which can be run in existing theatres in almost every instance by a local electrician under the supervision of an R. C. A.-Photophone engineer.