Very exciting! My guess is the denser compressed air is reacting to the low frequency sound waves differently than the surrounding air. The "smart" material is holding the wave or oscillation in the compressed air. The overall area covered by the material is then used to absorb the wave. Rather than thinking of it as a thin layer, think of it in the other two dimensions, height and width. The area is immense, even the longest wave length could be handled. It's all in the ability of the "smart" material and the compressed air?
