Under my tower speakers -- Isoacoustics Gaia, other options?

+1 @clearthinker 

Spikes are the best for concrete floors.  If the bass isn't right, then change the listening position of speaker placement.

@rmdmoore 

Pleased to hear you didn't despair over your suspended wooden floor and put the speakers on stone blocks.  Assuming there may be a weight issue, try using a thinner but larger stone block, like a large paving stone.  Spike the speaker to the stone.  If your floor is flat and even, there will be little or no movement in the stone if you shake the speaker.   If there is movement, try putting a thin layer of fabric under the stone, or two layers if the movement remains.

But note: with a concrete floor, nothing stabilises the speakers more than spikes.  Everything else allows movement.  From the listening seat, movement of the speaker chassis means distortion.

As far as I can tell, most of this advice is correct: if you have concrete floors with carpet, as you do, use spikes. Ideally, the cabinet should be completely rigid; all the movement should be in the speaker cones and domes, not reactive movement in the cabinet. Sort of like suspension in a car coupled to a very rigid chassis: the engineers can calculate the dynamics of the suspension, but flex of the chassis is too complex to accurately model and compensate for. If the cabinet can move in reaction to the speaker movement, it will "smear" the sound somewhat.

The exception would be if your speakers stand on a suspended wood floor. In that case, rigid coupling will create a secondary—and uncontrolled—passive radiator in the floor! So, with suspended wood floors, de-coupling is best.

That's what I've done with my 49" tall and 52 lb. Scientific Fidelity Teslas. I tried Gaia, borrowed from a friend, but settled on sorbothane feet attached to a screw threaded to mate with the female threads set into the base of the speaker—where the spikes would go. Eight bucks each on eBay. Significant improvement in imaging, clarity of bass, etc. But the speakers do wobble. Of course, they would on Townshend podiums, too.

+1 kingbr  I have pair of Verity speakers on carpeted concrete.  In theory coupled to floor with spikes seems best, but I went with Herbies Giant Threaded Sliders and haven't looked back.  Makes moving them a breeze, and they sound wonderful.