[Richard Crowley]

Mr.T wrote:
"Richard Crowley" wrote ...
dpierce wrote ...
Irrelevant. Take a signal, run it through ANYTHING
that inverts the phase. A transformer, an inverting
op amp. No discrete sampling, no DSP of ANY
kind required.

But that's not how noise cancellation works. That method
would merely create acoustic feedback.

You do know the difference between positive and negative feedback
right? *Negative* acoustic feedback is actually what they are trying
to achieve. And Dick specifically said to invert the phase, i.e.
negative feedback.

Easy to do electronically, extraordinarily difficult to do accoustically at
short wavelengths. That is why modern consumer noise cancelling products
depend on inexpensive DSP. You cannot just take an acoustic signal from a
microphone "invert" it and try to cancel noise with it. You don't have to
take my word for it. Try it for yourself.