[JohninCR]

One of the walls in the room I made my office and living room consists of largish lava rocks covering a concrete wall.  It is quite attractive and the acoustical properties of the wall seem to be perfect because unlike my other walls, I can't hear it at all.  It seems to provide just the right combination of diffusion and absorption.

[jermmd]

Pictures?

[JohninCR]

Pictures?

Sure, once my room is finished.  In the meantime, just picture a wall of rocks, not smooth river stones, but rocks, most large enough that you'd have to use both hands to pick them up.