[Richard Crowley]

"Greg Locock" wrote ...
Eeyore wrote :
No. It won't work. You can only ever meaningfully cancel
sound over a tiny area (volume).


Such as the entire cabin of a passenger aircraft,

For low frequencies, perhaps. See the other posting on
first-hand experience with active noise cancellation in his
vehicle.

or in some circumstances even a car park or a harbour-
if you can superimpose the correcting source
and he original.

If you can actively counteract the noise at the source (as
an enclosure around a generator, etc.) perhaps. Only a
very limited cases of effective application, at least at this
stage of development.

If the OP wanted to make a PhD thesis out of the experiment,
it might be interesting, but I wouldn't bet any $$ on it.