[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.