A Shutter for Use in Reduction of Ground Noise

A system for reducing ground noise on variable area records was described by Townsend, McDowell, and Clark in February, 1931. The preferred method employs a shutter mounted on the recorder which intercepts part of the light and reduces the sound track to a width just sufficient at all times to accommodate, the modulation. A commercial design of shutter has been developed for this system. — A motor for actuating the shutter has been designed in which an iron armature moves in a direction parallel to the pole faces so as to change the areas rather than the lengths of the air gaps. Such a motor combines the special advantages of the moving coil type, namely, long throw and stability, permitting the use of a highly flexible spring, and the advantages of the iron armature type, namely, light field structure and large winding space. Electromagnetic damping is provided. The resulting motor gives full deflection on about 20 milliamperes and has the desired speed of action. It can be attached to the optical system of the RCA Photophone type PR-4 Recorder with no operations on the latter except drilling and tapping two screw holes.

Print ISSN

0097-5834

Published

1931-08

Content type

Original Research

DOI

10.5594/J08012