Agear, I suggest the following easy experiment. Place on a normal office table a component that has a fan (which is neither very quiet not very noisy), e.g. a computer or an external hard-drive. After turning on the component, place your elbows on the table and a finger in each of your ear and listen to the vibrations generated by the fan that travel through the table. Then, place a cushion between your elbow and the table and listen again.
I predict the following outcome:
1) When resting on the table using your elbows you will hear very clearly and loudly these vibrations. (There is a decently strong coupling between our ears and the medium conducting the vibrations.)
2) When placing a cushion between your elbows and the table you will hear these vibrations significantly less. (The coupling has been significantly reduce in this situation.)
3) When removing your elbows from the table you will hear the fan but not the vibration generated by the fan that travel through the table. (There is no coupling in this situation).
Obviously, in the experiment suggested above the elbows play the same role the spikes play in an audio system.
The simple experiment suggested above should illustrate to everyone that spikes do not isolate. On the contrary, spikes increase the coupling between the spiked audio component and the surface on which this audio component rests. (In fact, even poor spikes like our elbows provide a decent amount of coupling!)
It is important to note, however, that this is not necessarily a bad thing. For example, increasing the coupling can be beneficial for subwoofers or speakers with large bass drivers. The large mass of the floor and the strong coupling between the floor and speaker provides a very strong foundation for the bass drivers, viz. the movements of the driver are less likely to induce movements of the cabinet of the speaker/subwoofer. (The strong coupling between floor and speaker will also change the spectrum of resonant frequencies of the floor and also of the speaker - because of the added mass and the change in geometry. Depending on the situation and also on the listener this may affect the sound positively, negatively or not at all.)
The problem with most spikes is that they allow vibrations to go in both directions. That is, not only from the speakers into the floor but also from the floor into the speakers. This effect is not desirable. The reason is that one wants to hear the music reproduced by the speakers, i.e. not the music produced by the speaker and modulated by spectrum of resonant frequencies of the floor.
