Bah. I thought this was going to be cool passive noise reduction but it’s active.

Back in the 90’s someone figured out these little hollow beads that ate sound. They talked about how we could paint them on walls to dampen whole rooms, or things like airplanes.

Since we never heard from them again, even after the patents would have expired, I suspect that they couldn’t find a binder that adhered to the beads without filling in the holes. Or the paint neutralizes the effect.