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From: paszkows@prlhp1.prl.philips.co.uk (paszkows)
Newsgroups: sci.physics,sci.math,sci.electronics
Subject: Re: noise cancellation
Keywords: anti-noise
Message-ID: <859@prlhp1.prl.philips.co.uk>
Date: 17 Apr 89 09:01:47 GMT
References: <723@wucs1.wustl.edu> <7260@fluke.COM> <453@corpane.UUCP> <739@wucs1.wustl.edu> <20031@srcsip.UUCP>
Reply-To: paszkows@prlhp1.UUCP ()
Organization: Philips Research Laboratories, Redhill, UK
Lines: 29

In article <20031@srcsip.UUCP> rogers@falcon.UUCP (Brynn Rogers) writes:
>I realize I am a bit late on this thread, but..
>
>Was the active muffler for cars ever discussed?

>basicly trys to cancel loud exhast using anti-noise, with a mike some
>where in the system (near the tailpipe?) and a speaker (heat resistant) inside
>a muffler chamber.  Has been built and tested, but I don't know where it
>is going.

I wish to express my scepticism over the oversimplified solution to the problem.
The fact that sound is being radiated from the exhaust ( muffler in US ) which 
is not a point source and then the wavefronts etc are distorted relflected by
the interior of the car means that the system to cancel the noise will need to
be fairly complex. I can imagine you will need a microphone and a tiny speaker
sited within the ear to be a close to what the individual is hearing. ( I may
of course be wrong )

There was a final year project at my university which was an investigation into
just such a problem, and the conclusion drawn was that an array of speakers
totally enclosing the person was necessary to achieve the noise cancellation. As
you can imagine this is not very practical in a motor vehicle.


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