I used 2 set of Springs with damping load for each speakers ( rectangular wood box type 2-way) ... The damping load must be fine tuned exactly by ears in few listening experiments arount + or - 100 grams or less than 1/4 of lbs over the speakers top with around 80 pounds in my case and the load is weighting on 4 springs which are located on top of the speakers on a granite plate (on sorbothane plate) for better stabilty and i also use 4 springs under the speakers too .... The differential compression between the two set of springs, one set is compressed only by the load, the other is compressed by the speakers weight +the load, this differential help resonance control of the speakers a lot by decreasing it ...
I also used a mix of granite plates between cork plate and sorbothane plate and Bamboo plate, quartz feet, under the set of springs/ speakers/second set of spring/85 lbs of dense cement block as damping load on top...
Then it is not only about isolating the speakers from the room and other components and external vibrations isolation but also about damping and decreasing internal resonance effect ...three tasks instead of one...
The end result is stunning... It makes everybody understand that the mechanical control part of audio system matter at least as the electrical and acoustical embeddings control parts...
But it is impractical to do it for most people with children in a living room the way i did it... I describe it for those without children in a dedicated audio room with box speakers because the cost is very low....
Anyway NO ONE know the huge negative effect of vibrations without and BEFORE any experience with the rightful way to limit it... Even after experiencing it it is difficult to believe so much powerful vibrations affect S.Q. Spikes alone are no comparison at all....