Theaudiotweak: sorry if I wasn't clear. I did not mean that Sorbothane doesn't react to/affect all frequencies. Clearly it must, but it reacts to/affects them differently. Sorbothane absorbs higher frequencies more than lower frequencies. As a result, it lowers the overall system resonance frequency. How a Sorbothane-floated system responds to vibration depends on the frequency of that vibration.
Sorbothane lowers a system's resonance frequency by absorbing vibrations above that frequency. The farther above the system resonance frequency an incoming vibration is, the more of it will be absorbed. This absorbed vibration is largely converted to heat, *not* released later as vibration.
OTOH, Sorbothane tends not to absorb vibrational energy below the system resonance frequency. At those frequencies, it seems to act less like a damper and more like a coupling device.
If you want to lower the natural resonance frequency of a system, (ie, to reduce exposure to support-borne vibrations above that frequency) then the appropriate Sorbothane feet should have reasonably predictable results. This is what I wanted to do with my equipment rack, which is sitting on a suspended wood floor that is easily excited by my speakers. Floating the rack on Sorbothane yielded greater clarity, faster attacks and a quieter background at all frequencies above 30 Hz or so. Frequencies below that, as best I can tell, are slightly amplified but seem about as clear as before. This is consistent with the worksheet on Sorbothane's website, which calculated that I'd have a system resonance frequency of about 28 Hz.
If, OTOH, a component is intended to be *producing* multi-frequency vibrations, as a loudspeaker is, we would predict that placing any vibration damper beneath it would impair its performance. That was exactly my experience with Sorbothane beneath our floorstanders. Attacks were severely dulled. Very bad.
Sorry to Bundeel for highjacking his thread with such a lengthy post. Enjoy the music!