http://www.neomatica.com/2014/08/27/designed-metasurface-thin-near-perfect-acoustic-absorber/
Maybe some of y'all saw this one already. But some scientists at Hong Kong University have created a type of sound absorption technology that relies on a metasurface suspended over a pocket of gas and a small weighted platelet that can be tuned to dampen a particular frequency nearly 100%. It also generates a small amount of energy. The down side is each membrane can only be tuned to absorb one frequency. But there is interesting potential
Tl;dr
Smart people have made super sound blankets