Re: Generating anti-noise

Adem wrote:

And, now, of course the nezt natural question is: Do you
(or anyone) know of such a sound card?

I'm not sure what you want a sound card for at all. All you should need
is a microphone, and amplifier and a speaker. Normally you would
connect a microphone and speaker to an amplifier so that the amplified
signal is in phase, but if you just switch the signal and ground around
either from microphone to amp or amp to speaker you'll get a signal
that's phase inverted.

That should be enough for you to start experimenting.

What you have to realize tho is that you now have 2 sources of
compression waves (generally refered through as sound) which will
result in some form of interference pattern ( see the picture top right
here : http://en.wikipedia.org/wiki/Interference_pattern )

It gets even more complicated as a) your signal isn't just a simple
sine wave but a full spectrum of different b) the signal for your
speaker is coming from the microphone near the original source, so you
have the original signal traveling at the speed of sound from source to
microphone, from there at (almost) light speed through the cables and
amplifier to your speaker and from there it goes back, phase inverted,
at the speed of sound to the microphone.

You'll have to experiment with the exact position and orientation of
the microphone and speaker and the volume setting. For best possible
effect you would most likely need someone that allows you to adjust the
delay between microphone and speaker but as you are looking at very low
delays here a soundcard isn't an option.

The best you can hope to achieve tho is to get a relatively good
reduction of noise at one specific position, not "everywhere".

Cheers,
Thorsten

--

.

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