I have had my REL Storm placed on the (new)carpet w/spikes for several months. The sound has been ok, but a little bit boomy for my taste. As an experiment I obtained a 16" sq. ceramic tile from Home Depot and put it under the sub.
I was thinking that the carpet and pad were adversly affecting the output by absorbing some freqs and trying to compensate, I was over driving the sub.
Well, when I placed the sub on the tile, the bass energy in the room fell of to almost nothing. What a surprise, for me anyway. I removed the tile, changed the sub location by moving it farther away from the wall floor corner, w/o spikes, and now it sounds better than ever.
I was surprised that the tile would suck up the output the way it did.