I never said it would be easy, but you make a good point. Compensating based on other sets of ears would be tough, because their locations are unknown and chang

I never said it would be easy, but you make a good point. Compensating based on other sets of ears would be tough, because their locations are unknown and change fast. Directional sound is possible to an extent, Woody Norris gave a TED talk about it a long while back, it is called hypersonic sound. I think it uses ultrasound to generate compressions and rarefactions far away. I realize it sounds like science fiction, but you could perhaps transduce sound to electricity and again to sound, sending the signal of your voice away from you faster than the speed of sound, in time for a cancellation wave to be generated and have an effect. I suppose the analogy would be quiescing a ripple in a pond.