The answer here is that if you have a single point where sound is
"tunneled", via a window, a headphone, even a hole in the wall, then you
can work out some noise cancelation technique, but it is very, very hard
to cancel noise in an open environment.   The similarity is that you
could control a "water wave" comming from a hole in the wall, but not
into the ocean.

"James R. Cunningham" wrote:
>
> I don't have any technical info.  I can only say that it works very well indeed
> in reducing the engine and wind noise that get through the headphones of my
> plane.
>
> Jim
>
> Harold Hallikainen wrote:
>
> > I've seen some stuff written
> > about noise cancellation, but don't see how it can work very well.
> >         Anyone have any more info?
> >
> > Harold