stone wall behind the audio rack and speakers

I built a sandstone wall behind my speakers a few years ago and the sound transformation was absolutely awesome. I suggest it highly. The music just seemed to be more natural and musical. One caveat, you will need to treat the room on the other walls to really take advantage of the stonewall behind the speakers. The sound will be more diffus and energetic, you will notice a more dynamic midrange with lots of energy focused towards all of the walls in front of the speakers.
Ciao,
Audioquest4life