Three dimensional speaker arrays are definitely possible, a simple one would be a cube, a bit harder would be a cylinder.
Yes, it is extremely hard. The question is though, can it be done? Phased arrays are insanely hard as well, they do work though.
In the 80's there was a free space noise cancelling demonstration on a cross roads in a major city somewhere, I can't seem to dig up any references to it. IIRC that was a completely analog setup, I have no idea how it worked but they had a volume within which background noise was substantially reduced. I can't stand it when I am 100% sure that I read something but I can't find it.
Yes, it is extremely hard. The question is though, can it be done? Phased arrays are insanely hard as well, they do work though.
In the 80's there was a free space noise cancelling demonstration on a cross roads in a major city somewhere, I can't seem to dig up any references to it. IIRC that was a completely analog setup, I have no idea how it worked but they had a volume within which background noise was substantially reduced. I can't stand it when I am 100% sure that I read something but I can't find it.