I made "vibrapods" out of cement blocks from a builder's supply, then glued cork to the reverse side so it won't scratch the rack. also put marble blocks (again, with cork on the underside) on top (got the idea from tntaudio). on some songs the bass drum sounded a little hollow and lacking in punch overall, even when they're being pounded by left and right hands (not pedals), but I can count the CD's where I heard any improvement, and that would be less than 10, at least for audible difference. don't expect the improvement to jump out with every reference disc. if you want to gauge the vibration on the chassis regardless of audible improvement, I touched the chassis with and without the platforms, and without them you can feel the notes being played by the sub. to put that into perspective my rack is 5 inches away from the sub. but hey, when I did this it only cost me less than 300 bucks, cheap enough for what improvements I got out of it.