I agree with Eric, it is complicated and floor does transfer sound. I tried to couple (spikes) and decouple (Vibrapods) and cannot say one way is better than another - just different sound. I moved recently from wooden floor/basement home to one on the slab with ceramic tiles and resonances are completely gone, but it might be caused by different dimensions of the room as well - back wall 2x further away (less of the room effect at bass frequencies). Vibrapods and such make speaker less stable - important with kids. Spikes over large/wide granite slab on isolation (like Vibrapods) might work well. They also sell in gardening stores, heavy as hell, garden concrete columns/pedestals - very cheap and way better than stands (if you need them), as long as you can tolerate such atrocity in your room.
To couple, or not to couple, that is the question
There seems to be a fundamental difference of opinion between those who would couple their speakers to the floor (e.g., with spikes), and those who would decouple them (e.g., with springs). I’ve gone both ways, but have found that I prefer the latter; I’ve currently got Sorbothane feet attached to my tower speakers, so that they wobble or "float"—much like the Townshend Platforms videos show for that similar, but more expensive, approach. My ears are the final arbiters of my listening experience, so they rule my choices. But my mind likes to have a theoretical explanation to account for my subjective preferences.
That’s where the question comes in. A very knowledgable audiophile friend insists that what I prefer is precisely the opposite of what is best: that ideally, the speaker enclosure should be as rigid and immovable as possible so that the moving cones of the drivers can both most efficiently and most accurately create a sound front free of the inevitable colorations that would come from fighting against a moving cabinet. He says that transients will be muddied by the motion of the cabinet set up by the motion of the speaker cones. And this makes perfect sense to me in terms of my physical intuitions. It’s perhaps analogous to the desirability of having a rigid frame in a high-performance vehicle, which allows the engineers to design the suspension without having to worry too much about the complex interactions with a flexing chassis.
Am I just deluded, then, in preferring a non-rigid interface between speaker and floor? Or does it depend on the kind of floor? (I get that most advice seems to favor decoupling from a suspended wood floor, and coupling to a slab; my floor is hardwood, but not exactly "suspended" as the underflooring structure is very rigid.) Or are there trade offs here, as there usually are in such options: do I gain something (but what, and how?) even as I lose something else (i.e., clean transients, especially in bass tones)?
The ears will win this contest, but I like to have my mind on board if possible. So thanks for any input you may have on this question.