You are right ...
This is why to a damping tuned heavy load on top of the speakers and to a complex sandwich of materials under the speakers ( oak plate-sorbothane-granite plate-shungite plate-bamboo plate-cork plate) i add a set of 4 springs UNDER the damping load +the speaker weight , and to this i add a new set of springs ABOVE the speakers and under the damping load...
The two sets of springs then differently tuned by different compressive force by the difference of mass decreased resonance and improved a lot compared to a singular springs set under the speakers withoyut any coupling/$decoupling sandwich, without damping load and without another sets of springs compressed above the speakers by the load only .....
It is not doable in living room with children... Esthetic and stability problem ...
Only a a dedicated room ...
But at peanuts costs it was efficient for S.Q. a lot ...People underestimate resonance/vibrations problem , even the speakers designers...What they can do at low coast that will not appear unesthetical ?
Another misconception: "depends on the spring rate and the mass": that is called a SWINGER for good reason. at resonance frequency, amplitude will be infinite. Try driving your car with spring only.
That is were the DAMPER comes in. Now you have a system of spring, damper and mass, and can be tuned to KILL vibrations.
This has NOTHING to do with the vibrations the emitted sound is producing ('will vibrate even if suspend the speaker in the air'). It has to do with the vibration the mass off the speaker is COUPLING to the floor (not those of the soundwave).