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From: greg@bilbo (Greg Wageman)
Newsgroups: sci.physics,sci.math,sci.electronics
Subject: Re: noise cancellation
Message-ID: <765@snjsn1.SJ.ATE.SLB.COM>
Date: 22 Mar 89 00:21:21 GMT
References: <723@wucs1.wustl.edu> <7260@fluke.COM> <453@corpane.UUCP>
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Reply-To: greg@sj.ate.slb.com (Greg Wageman)
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In article <453@corpane.UUCP> sparks@corpane.UUCP (John Sparks) writes:
>
>Hmm, In theory you can try taking two speakers from a stereo system and
>wire one of them opposite polarity from the other. Then when one cone
>is extending the other is retracting. The two sound sources will be
>180 degrees out of phase with one another. Make sure you feed the same sound
>into both speakers.
>
>But in reality this won't work. Since each sound source is the center of
>a 3 dimensional spheroid of sound waves, They would have to both be located
>in the exact same space in order to cancel out each other. 

This isn't quite true.  There will be places (nodes) in space where
the waves will cancel each other.  The real trick would be to
guarantee that one of these nodes is where you want it to be.



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