Speakers is the first piece of gear in need of relative isolation /coupling/decoupling/ damping to control not only external vibrations but internal resonance...
If you had money buy the excellent platform ghprentice recommended, loved by all it seems, or use basics sciences for a lesser but very evident audible results (at no cost for me) ...
The cement floor is coupled to the earth. The earth moves. My audio room has been on a cement slab most of the decades I have been an audiophile. Cars, trucks, lightning strikes, workmen, nearby footfalls, small movements in the earth. I own a seismometer, it is easy to discern the day from the night on it, from the background noise. The first day I owned it there was a boom from a lightning strike about two miles away... wow, did the concrete slab shake.