I'm using some ~1/2" thick foam-rubber sheets I found at the dollar store, I think they're for children's playground floors. I use them to support my amp and keep it from sliding around. I don't think it does anything for the sound, but for a dollar, I'm not expecting miracles. I put my CD player on 1/2" thick glass block because it looks kinda cool, again, no effect on sound as far as I can tell.