With respect to the issue of decoupling subs from a floor, I think that even very inert cabinets may experience some transfer of vibration, depending on the sub, the floor, and the volume level of the sub. There is plenty of anecdotal evidence that room vibrations can be reduced slightly with some kind of isolation material between a sub and a suspended wood floor, although some subs may already have feet which achieve the same result.
I have tried putting a lightweight object on the polished surface of my piano black PB16's, which are very inert seeming and heavy (175lbs). And, I have observed that object sliding slightly at high volumes. Similarly, as Marc mentioned, subs can skate slightly on a smooth or polished surface such as wood or marble. So, the completely inert seeming cabinet may be a little deceptive with respect to the transfer of energy to another surface.
This isn't something I would worry about at all under normal circumstances. But, if a sub sliding is a problem, or if excessive tactile energy is experienced on a suspended wood floor, or rattling is occurring in other parts of the room with a suspended wood floor, decoupling the sub from the floor is certainly one potential solution.
GUIDE TO SUBWOOFER CALIBRATION AND BASS PREFERENCES
* The Guide linked above is a comprehensive guide to Audio & HT systems, including:
Speaker placements & Room treatments; HT calibration & Room EQ; Room gain; Bass
Preferences; Subwoofer Buyer's Guide: Sealed/ported; ID subs; Subwoofer placement.
Last edited by mthomas47; 12-15-2017 at 04:50 PM.