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From: phil@mips.COM (Phil Arellano)
Newsgroups: sci.physics,sci.math,sci.electronics
Subject: Re: noise cancellation
Message-ID: <15072@electron.mips.COM>
Date: 11 Mar 89 08:03:38 GMT
References: <723@wucs1.wustl.edu> <4225@watvlsi.waterloo.edu> <1989Mar10.173840.732@utzoo.uucp>
Reply-To: phil@mips.COM (Phil Arellano)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 18


A recent "NASA Tech Brief" contained an article on work done on noise
cancellation techniques applied to engine exhuast muffling.  A speaker
enclosure was built around some protion of the exhuast pipe while microphones
were placed around the enclosure.  A feedback/amplifier circuit was used to
drive the speaker such that only a slight exhuast noise was produced.
Engine efficiency was improved, as well as noise reduced.


The point is that cyclical sounds can be easily cancelled out if the
cancellation signal was generated at or around the sound generator, or if the
cancellation signal was generated at the ear.  Noise cancelling headsets are in
use now by pilots.

	phil
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