What should be under my speakers?


I have Sonus Faber Grand Piano Home speakers in a 20' x 17' room with wood floors. The speakers have spike feet, and each one is sitting on a 1 inch thick, 12" x 12" slab of granite. Each piece of granite has a square piece of carpeting under it, as a further buffer. I know I probably could figure this out with a lot of experimentation, but what impact is the carpet likely having on sound quality? Would it be better (Subjective, I know) to have the granite slabs sitting directly on the wood floors? How would the sound change if I ditched BOTH the carpet and the granite? I would like to maximize bass impact, because these speakers are a bit thin in that regard. Thanks.
gipp
Just wanted to give more info on my experience with the Sistrum SP-004 and SP-1 stands.

My Dali Grand speakers were 100lb floor standers with 2 bottom mounted 8" woofers per speaker. Bass was at times heavy and just a tad slow. Very warm and slightly midrange forward tonal character.

The SP004 units delivered a very noticable improvement. In fact, in the order of a very expensive wire or component upgrade.

As TVAD says they are expensive and can be found used if you are patient. They sell used for 1/2 the new price. I purchased Adona floor discs to protect the wood flooring. They cost much less then the Star Sound floor discs.

If you have any components on the floor these do the same magic under those components.

I suppose the improvement will depend on the speaker and room.
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I have owned all of the above solutions… I have had each on wood and carpet… Starting with spikes on Granite or stone block(concrete)… This is probably one of the worst solutions I have heard actually.. And Even have used the same stone block on TOP of the speaker to see what would happen, as it was better than under the speaker, but still took away some integration and warmth of the speaker.

I have also tried MDF blocks like a slab 2" thick on top of carpet… Again not the best results separated the integration and overall impact of bass…

Then going into Sistrum Stands as mentioned on wood, worked well, but Very difficult to do these without damaging your speaker bottom or wood floor, although it can be done.

Then I went to the straight sistrum spikes threaded right into the speaker vs. the stands and with my speakers ended up being slightly better as it brought the sound floor of the size and scope to a more anchored sound, filled the room better. But the stands probably brought out a more Airy presentation.

Spikes or Sistrum stands were far Superior ON CARPET… Over wood.

So in the end with several pairs of speakers later now, I have found the best solution for you on a wood floor is Dump the granite slabs definitely, use the Spikes threaded right to the speaker base plate as they are, buy a couple Really thick carpet squares to put one under each speaker with spikes right into the carpet, hopefully they don't go right thru and stick into your wood floor, first because they can obviously leave a hole in the wood, and also because you will not be able to slide the carpet around to move your speaker back into correct positions or adjust toe in etc…and of course can put some nice gouges in the wood possibly.

You can use the little spike "dimes" under them if you wish to make sure the spikes will not go thru a carpet to your floor, or if you rather skips the carpet square and go directly on your wood floor with the spike protectors.. But I will tell you this, a Good 9 foot or 12 foot wide by like 6 or 8 foot heavy throw rug in front of your speakers (not under but you can use this under) will definitely help your sound as it will absorb your first point reflections out in front of your drivers beaming off the floor into the room, and just sounds better when you have a carpet between your seating area and speakers anyway.

The issue with the "Best" solution is your room frequency responses and other issues will come into play with the interaction of your speaker in the environment as a whole, not just how its coupled or de-coupled to the floor although this is a big part of it. So not sure what kinda room acoustics your getting now if that’s also going to need far more attention to ever get you the results you desire.. Don't believe the hype about a 400 dollar or 4 dollar spike set doing a whole lot if you have other issues to be addressed.. Again I can say dump the stone blocks under the speakers, and for sure make sure you have a good carpet out in front of the speakers to truly effect the bass response and soundstage. Just start with that and drop the speakers with spikes right on the floor as step #1…. Placement of the speaker will become more critical in the room than any of this.      
Nothing. Spike the speakers to the floor. Forget about the 'dimes', the object is to couple the speakers to the floor. Otherwise, you are trying to couple and then de-couple. One will work, the other doesn't.
Buconero is right.........and wrong!
Spike the speakers directly to the wooden floorboards.
The objective is NOT to 'couple' the speakers to the floor, but to DE-COUPLE them whilst at the same time creating a stable, unmoving, balanced speaker box.
The tiny contact area of the spikes will not allow medium to low-frequency sound transfer from either the speakers to the floorboards and vice-versa whilst 3 spikes will prevent any rocking.