Xref: utzoo sci.physics:6309 sci.math:6047 sci.electronics:5573
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ncar!noao!asuvax!mcdphx!mcdchg!ddsw1!corpane!sparks
From: sparks@corpane.UUCP (John Sparks)
Newsgroups: sci.physics,sci.math,sci.electronics
Subject: Re: noise cancellation
Summary: Try hooking two speakers up opposite polarity
Keywords: anti-noise
Message-ID: <453@corpane.UUCP>
Date: 14 Mar 89 18:38:08 GMT
References: <723@wucs1.wustl.edu> <7260@fluke.COM>
Organization: Corpane Industries, Inc., Louisville Ky
Lines: 36

In article <7260@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes:
] The theory says that the *best* you can hope for is total cancellation of
] the offending noise.
] 
] The idea behind "anti-noise" as you call it is that you generate an exact
] replica of the offending noise, except opposite in polarity. It must be the
] same frequency and the same amplitude, just reversed. As the tops of the
] wave fronts collide, they dissipate each other's energy, and the same thing
] happens all down the trough and up the next wave. The dynamic case would
] monitor the signal and generate it's equal-but-opposite counterpart in
] real-time. It sounds like you are looking for a "static" anti-noise
] generator, so you'll monitor the signal first, and replicate it via some
] kind of noise generator-amplifier arrangement.
] 
] I have never heard either of these in action, so I have no idea what the
] result might sound like, or how successful you are likely to be in blocking
] it out. However, I am really interested in that whole topic, and would
] appreciate it if you post a summary of your responses, and also a
] description of your final setup and the results.

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. 

But it might be fun to experiment with.
-- 
John Sparks      // Amiga  |  {rutgers|uunet}!ukma!corpane!sparks 
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