Don Hills
Addicted to Fun and Learning
... Townshend's idea is a bit different than other people. They contend the speaker sends out bass notes, which come back to a speaker via the floor causing movement. Enough movement to equal the movement of tweeters which can smear or blur sound. So decoupling is to prevent this from occurring. They have this video to show what they have in mind. Also in some cases vibration from other sources can interfere with the speaker providing sound cleanly. My question would be if the amount of movement is enough to really make an audible difference. ...
It's not enough to assume that the baffle (and therefore the tweeter) moves back and forth a similar amount to the movement of the tweeter diaphragm. You also need to take into account the frequency of the movement. In theory, it would impart a doppler effect on the tweeter output. In practice, it's simply inaudible. For proof, look at any fullrange driver, where the problem of bass moving the treble source back and forth is hundreds of times worse. If it was that audible, fullrange drivers would sound awful. Or any coaxial driver, where the cone forms a waveguide for the tweeter.