🚀 go-pugleaf

In article <199229.2597.436@dosgate>, "anthony tekatch" <anthony.tekatch@canrem.com> writes:
|> A few weeks ago we had someone here say that dynamic sound/noise
|> reduction required some microphones and a digital signal processor then
|> the signal was inverted 180 degrees to oppose the originating noise.
|> 
|> My question is: why the digital signal processor?

I have heard (a few years ago) of problems with analog components because their
characteristics may vary after some time.

|> 
|> The reason for my question is:
|> 
|> I would like to build a system that would reduce the noise that
|> arrives at my home from a highway that is about 1/2 mile away.
|> 
|> My idea would be to get two microphones one loudspeaker and some
|> circuits.
|> 
|> The first mic (A) would be about 40ft from my house and the second mic
|> (B) would be about 20ft from my house and they would both be in-line
|> from the highway noise.
|> 
|> The first mic's signal would be fed through a delay line of about 40
|> milli seconds (thats the time I figured it would take the sound to get
|> 20ft from mic#1 to mic#2) and produce signal A'.
|> 
|> The loudspeaker would be in the direction of the house and located near
|> mic#2, and connected so that the signal would be 180 degrees from the
|> incoming highway noise.
 [stuff deleted]

First, to get a 'perfect' cancellation over a significant area, you would also need to
recreate the directivity of the noise source with your cancellation signal. Since the
highway is a 1/2 mile away, you are probably hit by something close to a plane wave. I
really doubt that you can recreate one with a single speaker at 20 ft.

Second, have you thought of your neighbours ? The noise that you want to blast in your
speaker may produce a cancellation at a location on your property, but it is likely going to add
to the noise your neighbours get. My guess is that within 24 hours, your going to be explaining
how your system works to a police officer :^) .
 
-- 
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Daniel Ouellet, Research Associate
Pulp and Paper Centre, University of British Columbia
2385 East Mall, Vancouver, BC, Canada V6T 1Z4
Tel:(604)822-8240   Fax:(604)822-8563   Email: daniel@ppc.ubc.ca