[WilliamEdward]

In physics we are learning about sound waves, and how noise cancelling headphones detect noise and produce waves which are destructive to those incoming sound waves, by matching the amplitude and sending them out at a different time interval. I think future noise cancelling materials will make use of some kind of tech like this.

I don't think materials that simply absorb sound are very efficient.

[saagarjha]

This, being an active process, would require energy would it not?