Noise Destroyer

People bothered by noise may get some relief through electronics. In the Journal of the Acoustical Society of America, Harry F. Olson and Everett G. May of Radio Corporation of America tell about a gadget that reaches out to kill sound waves before they hit the ear.

Olson and May connected an extra-sensitive microphone to an amplifier and a loudspeaker, which they placed directly behind the microphone. When a sound wave hits the microphone, the loudspeaker reacts in such a way that it increases or reduces the air pressure in its vicinity just enough to cancel out the sound wave. The result is a small "quiet zone" near the microphone.

For a distance of two feet, it reduces to one-quarter the loudness of deep-toned noise. The effect is like shutting a door against the noise. Closer to the microphone, the silencing effect is much stronger. Olson believes that a sound killer could be built that would use only one watt of current. It would be small enough to hang over the head of a sleeper to protect him from sleep-destroying noises. Another use: making conversation easy in an airplane. The deep roar of the engines would be reduced, while the higher tones of the human voice would not be affected as much.

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