Beam of Silence

The standard way to silence noisy equipment is to enclose it in material that absorbs or reflects sound. This is not easy to do with electrical transformers, which are sometimes unpleasantly noisy and as big as cottages to boot. So General Electric Co.'s laboratory at Pittsfield, Mass, has been looking for a more subtle system. A promising one developed by Engineers W. B. Conover and R. J. Ringlee is to broadcast programs of competing racket.

The noise of a transformer comes from the alternating current that is passing through it, and most of it is in simple harmonics of the current's frequency. Conover and Ringlee constructed a gadget that amplifies the frequencies and broadcasts them through a loudspeaker. The sound matches the transformer's noise, but its phase is opposite. That is, the crest of each synthetic sound wave coincides with a valley of the transformer's waves.

Result: the two trains of waves cancel each other. From the loudspeaker extends a "beam of silence" 30DEG wide. An additional loudspeaker broadens the beam, but even a 30DEG beam is enough in some cases to tranquilize a neighbor who has been protesting about a transformer's noise.

This file is automatically generated by a robot program, so reader's discretion is required.