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From: nelsonaf@thor.acc.stolaf.edu (Andrew F. Nelson)
Newsgroups: sci.physics,sci.electronics
Subject: Re: noise cancellation
Message-ID: <1928@thor.acc.stolaf.edu>
Date: 27 Apr 89 03:26:38 GMT
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In article <17419@cup.portal.com> ISW@cup.portal.com (Isaac S Wingfield) writes:
>Well, there's been a lot of talk about automobile engine noise
>cancellation, using some kind of "active muffler".
>
>The first thing that occurs to me (and I don't know, even
>approximately) is HOW MUCH ACOUSTIC POWER ARE WE TALKING ABOUT?
>Because it'll take pretty much exactly the same amount of "negative
>power" to make it go away.
>
>I bet it's lots of watts, and if you think even *one* acoustic
>watt isn,t that much, then you've never heard that much coming
>from a Hi-Fi (especially at low frequency).
>
>Isaac     isw@cup.portal.com

This sounds vaguely like what in radio controlled aircraft is called
a 'Tuned Pipe'. According to the catalogs I've seen (now around 8-10 years
ago since I haven't been involved in RC since then), these things are actually
mufflers which _increase_ the power output of your engine somehow.  I don't 
have any idea how although I'd hazard a guess that it facilites the removal
of the exhaust gases from the cylinder.  I wonder if this is a similar
thing to what you're talking about with an active car muffler?

This 'Tuned Pipe' thing isn't electronic in nature though.  As I
look back though old articles in this thread I get the sense that most
of the things that have been mentioned are active electronic speakers
and such.


-- 
Andy Nelson                  |Disclaimer: I didn't do it!!  Did I do it??
nelsonaf@thor.acc.stolaf.edu |Well if I did it it was for a good cause.
nelsonaf@stolaf.UUCP         |Are there any good causes out there? I haven't 
                             |found one yet....Help!!!!