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From: pfarrell@anselm.UUCP (Gladiator)
Newsgroups: sci.physics,sci.math,sci.electronics
Subject: Re: noise cancellation
Summary: Anti Noise
Keywords: anti-noise
Message-ID: <245@anselm.UUCP>
Date: 10 Mar 89 14:31:45 GMT
References: <723@wucs1.wustl.edu> <4225@watvlsi.waterloo.edu>
Distribution: na
Organization: St. Anselms College, Manchester, NH
Lines: 41

In article <4225@watvlsi.waterloo.edu>, kmheal@watvlsi.waterloo.edu (K. Michael Heal) writes:
> In article <723@wucs1.wustl.edu> kumar@wucs1.wustl.edu (Arun Kumar) writes:
> >For the last few days I have been sharing my room with a very noisy pair
> >of machines -- a Pixar and a Sun -- and I have been thinking about
> >generating some anti-noise....
> >Arun Kumar (kumar@wucs1.wustl.edu)
> 
> Off hand, I doubt that even a theoretical noise reduction is
> possible with your "anti-noise" sources, unless you also fix the
> location of your ears. 
> 
> Anyway, vast reductions could be achieved practically by surrounding
> the machine with surfaces covered with 4 or 6 inch accoustic foam
> (with the wedged surface), especially at or above 1000 Hz. 
> -- 
>                                  Michael.
>                                 ( kmheal@watvlsi.waterloo.edu )
Well if I understand the theory correctly, which I don't. IN order to cancel outa sound. A sound travels in waves. If you have a sound equal in magnitude to
equal in magnitude to the one you are trying to supress that hits it's
peak, at the same moment that the other hits it's low, the waves will cancel
each other out. It is possible in nature, because the waves work like
ocean waves. At rock concerts, they have to spend hours to set up speakers,
because there are places if set up incorrectly that there will be hardly any
sound from the music at all where as in others where the peaks line up,
will be considerably louder than normal so it is possible to last a stereo
and through creative positioning not hear a thing. Unfortunately, I fail
to see how one could plan this without a little super computer help.
Something like a raytracing prog perhaps? That is just to line up
the speakers transmitting the anti noise. Now problem of keeping them
in sync. How are you going to make sure that one is constantly it it's
high when the other is at it's low. If you don't do it right, often
it will be quieter than normal, but often louder as well. Any thoughts
on this? I don't touch this newsgroup for lack of knowledge normaly,
but I have a strong notion of theories. If Someone has a better one, or
wishes to correct any errors I have made (There might be for all I know)
please post em. 
-- 
Patrick Farrell @ St. Anselm's college, Goffstown N.H. 1-603-472-2378
dartvax!anselm!pfarrell

"Laugh and the world ignores you. Crying doesn't help either."