As I understand isolation, one is dealing with resonance frequencies. Above that frequency vibrations are turned into heat, but below that they amplify the vibration. Solid isolators typically rely on psi by having a narrow point to the earth ultimately which make the weight above it have greater pressure and thus resistance to motion.
I have tried perhaps 12 different soft or rubbery feet and rejected them all for stealing the dynamic or pace of the music. I have used many spring systems whether they be actual springs, like pole magnets, some combination of springs, or bladders inflated with air or air and oil and with or without heavy mass above the spring. Some of these have satisfied me for some time, but ultimately they too rob the music of dynamics. There are non-resonance systems that are very expensive. One of these, the Halcyonic active isolation base has motion sensors and voice coils which reverse the phase of the vibrations and cancel it. These are outstanding.
Finally there are efforts to tie the component to the earth. Goldman long ago use two soft feet and one solid under the transformer. Tip-toes made of aluminum were the first of these. There have since been countless versions made of most metals, plastics, and hard rubbers. I like brass best but everyone has their own preferences. Their placement under the component is a crucial experiment.
Recently, there are the Syn. Research MIGs. These are solid and made of iron. They are cup shape and can be used with the round side up or down. Two configurations are recommended by SR-two round sides up and one down or the reverse. These must be experimented with extensively to optimize, but I very much like them. I certainly do not understand how these feet work as they ring if standing alone but not under components.
Finally, there are StillPoints. These are solid devices with multiple balls within that are configured to make vertical motions into horizontal motions. They are very effective and lend a vibrancy to the music that I only got with the Halcyonics before and then only for the three components I could afford to so isolate. Now with everything on StillPoints Racks or Component Stands, I get a complete system benefit.
Much to my surprise, the SR MIGs on the StillPoint Racks still add greatly to the realism of the music.
I am elaborating on my personal experiences here and fully expect that others' tastes and systems may not respond identically.
