After the excellent suggestions of
mitch2
I will only add that the coupling/decoupling -process worked well for me with thick concrete slab, granite plate, bamboo plate, oak thick plate sorbothane plate, cork plate , shungite plate under the speakers ... all integrated one above the other in the order your ears will dictate😊 ...
My damping of speakers with a load worked well too but is not practical for most ...I used a load tuned to 100 grams ( 80 pounds of concrete) over the speakers and a set of springs compressed by it with another set of springs over the sandwich plates and directly under the speakers , which is then compressed also by the load, as the set of springs above which is compressed only by the concrete load , but more compressed because of the speakers weight added to it ... These two unequally compressed set of springs work well to decrease resonance and not only vibrations ... It can be tuned by ears near 100 grams easily ...
Mechanical vibration/resonance controls is so impactful that it is hard to believe ...
Spikes dont work compared to this above ...