Ask HN: Is it possible to build generic noise-cancelling speakers?

Although you understood how the technology works, I think you misunderstand the intent . Noise cancellation in headphones exist to cancel out the ambient noise around the cups of the headphones so that effectively only a subset of the total sound waves directed at the ear are in the audible range (everything else is cancelled out to a lower frequency).

Speakers otoh direct sounds outwards in a larger space and do not have the neat separation of the direction where the sound is sent and everything else (the direction where the sound is sent is also the direction of origin of the noise). How will the microphone prevent picking up the sounds coming from the speakers? And even if you do manage to cancel the noise and send it out of the speakers, the listener exists in the same space as the origin of the noise and would still hear the original noise besides the noise cancelled sounds coming from the speakers.

Now all that said there are way for speakers to adapt the sound based on the space that they are placed in. For example

http://worldwide.bose.com/productsupport/en_us/web/article_1...