Originally Posted by shaddix
It would not have to seal, you can actually do it with two speakers and it is really weird. Point one speaker at the other and invert the sound wave and you hear nothing at all.
Not exactly, you hear nothing at a specific distance (i.e. lambda + 1/2 straight line) AND there is nothing for the sound to reflect off of. Since lambda is different for every frequency, and you have two ears, this becomes extremely complicated quite quickly.
If it was that simple when you wired your stereo speakers backwards you wouldn't hear anything, instead they just sound like crap from all of the destructive interference.
If you can move speakers back and forth and get a sound cancellation effect, but you will only be able to get it to work for a single frequency, and then at low frequencies, when you get into the 18kHZ at 343m/s you don't have a lot of room to create the anti-node with perfect destructive interference.