🚀 go-pugleaf

In article <453@corpane.UUCP> sparks@corpane.UUCP (John Sparks) writes:
%In article <7260@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes:
%] The idea behind "anti-noise" as you call it is that you generate an exact
%] replica of the offending noise, except opposite in polarity.

%Hmm, In theory you can try taking two speakers from a stereo system and
%wire one of them opposite polarity from the other. Then when one cone
%is extending the other is retracting. The two sound sources will be
%180 degrees out of phase with one another. Make sure you feed the same sound
%into both speakers.

%But in reality this won't work. Since each sound source is the center of
%a 3 dimensional spheroid of sound waves, They would have to both be located
%in the exact same space in order to cancel out each other. 

It depends on how close together you can place the speakers. Far away (as
compared with the distance between the speakers) one would expect the
amplitude field to decrease with the distance r as 1/r^3, whereas one
"undisturbed" speaker alone would have an amplitude field decreasing as
1/r^2. It is assumed that the waves are propagating in all three dimensions.
Cf. electromagnetic theory for dipole (sp?) fields, with two close charges
of opposite polarity, as compared with the field around a single point
charge.

Bjorn Lisper