Your question is a bit vague that will not encourage a lot of responses.
These are you speakers?
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What kind of floors will the speaker be on? Bare wood? Concrete? Carpet? Rug? Other?
Just out of curiosity, what is the other equipment in your system?
What are the Dimensions of the Room?
Generally Speaker Spikes are also referred to as Carpet Spikes, they are meant to reach down through thick carpet or rugs to the solid floor underneath.
Alternately, you would put a granite base under the Spikes to protect a finished wood floor. Though there are Spike Shoes, small metal disks, that can be placed under the Spikes to protect a wood floor.
Following on with that, I would be inclined to ask,
in your mind, what is the purpose of the Granite base?
Speaker Spikes concentrate the weight of the speakers on very small points, so the Weight Per Square Inch is very high.
The Granite base would be, to some extent, for Isolation, however, the Spikes themselves would be for Coupling. Coupling meaning to make such concentrated contact between the speakers and the floor that they are essential coupled into one thing.
If you are on a Floating Floor, it is possible for the Spikes to couple to that floor which is akin to a drum head, and cause the entire floor to resonate, is a situation like this, you might want to explore Decoupling the speakers and floor. Also, with a Floating Floor, it is possible to drive vibration down in the floor where it will then travel back up into your equipment cabinet and cause your components to vibrate, which may or may not be a problem.
So, we need some more details about what you are actually doing and why to determine if your method will be effective.
Likely, if you are simply trying to spare your nice wood floor from scratches, then a granite base might have value, but you have to ask, what will you put between the Granite Base and the Floors? That is will the underside of the granite have small feet, Felt, Rubber, Foam, or other?
Again, far too few details on what you have and what you are trying to accomplish for anyone to comment.
Steve/bluewizard