On Tue, 14 Dec 2004 07:38:55 -0600, Edward Gisske wrote:

> The out-of-phase audio technique was accomplished by a Ford subsidiary
> called Digisonix in Madison, WI in the late 80's. I believe they closed in
> the mid-90's. I think the technology worked, but was difficult to make live
> in a muffler.

It was used by British Gas to remove the low frequency components from the noise of a stationary jet engine 
(an RR Olympus, as used in Vulcan, Concorde, and Type 42 destroyers, I believe) which drives a gas pump.  They 
found that high frequencies could be filtered out by accoustic muffling, but the low frequencies were hard to 
stop.  The anti-sound system works fine, apparently!

Not sure it would be any good at the scale we're talking about, though.

Cheers,



Howard Winter
St.Albans, England


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