🚀 go-pugleaf

In article <zhenya.722059559@ultima>, zhenya@socs.uts.edu.au ( The Firefox.) writes:
> Does anyone have any ideas about the best way to build a device that takes
> an input from an external microphone, shifts the signal 180 degrees out
> of phase, and then re-emits it with little loss of resolution of the
> waveform in the process?
> 
> It would be great if it could also work from frequencies of about 20Hz up...
> 
> Maybe there is a mail-order kit for something similar that someone know...


I assume what you want to do (from your Subject: line) is sound cancellation.
If that is the case, consider that any processing you do on the signal will 
delay its output, so you cannot cancel the sound.  But, the Bose company 
(speakers, etc.) has come up with headphones that cancel much noise, for
helicopter pilots, for example, because the cancellation only has to be done
in the cup of the headphone, and not over a whole room.  (Not only would process-
ing delay the signal, but you'd have to compensate for where the noise was 
coming from -- i.e. worry about room echoes, etc.).

I don't remember where I saw the info about the Bose headphones (Popular Science?)
but do remember that it took much doing to achieve sound cancellation even in
the small, mostly-controllable environment inside the headphone ear cups.



Tom DiGiacomo

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