[kristiandupont]

I once wanted to make something similar, for sound. I wanted to create active noise cancelling "in the room", instead of via headphones. I pictured these devices combining a microphone and a speaker that you could set up in strategic location. After thinking about it for a bit, I realized that inference would cause areas with silence and others where the sound volume would be doubled. Less than ideal but still possibly interesting. But then I thought about it some more and realized that I needed to think in 3D, which makes the setup orders of magnitude more complex.

It seems like that would apply here as well, at least when looking at the effects of refraction?

[withinboredom]

If you had a "sound laser", you could control the waves when entering a column (think a "sound umbrella") to cancel out sounds that enter. However, this only works for "regular sounds" (as in non-directional sound, like sound from distant sources, like speakers). So, it wouldn't cancel out things like people speaking. It would be pretty useful for clubs, where at your table you can have regular speaking conversations.

I hate to mention that this is all currently patented. It's pretty "easy" to build though, but you'll have to wait a bit for all the related patents to expire or pay some licensing fees.

[eurekin]

If that technically worked, I could see that being a next unicorn.

[ahmetrcagil]

It can work (Look up beamforming). However it takes a 3d array of speakers with a lot of elements positioned in specific points in space, as well as very accurate position tracking for both ears. Very very unlikely to ever beat a high end noise cancelling headphone in terms of performance as well.

If the listener can be fixed in space then the problem gets easier but in that case what you have is actually a very large, room sized headphone that you enter and sit down into.

Source: I indirectly consulted a high-end furniture company on this exact project, they decided to pivot after a while.