Added Track Audio isolation footers to my 7's with 2 buddies on Sunday, coupled to my concrete floor below carpet. Immediate effect was profound - tighter and clearer bass, greater detail, clarity and high-end extension from the m/t speakers as the bass notes were no longer muddying it. Spikes are adjustable, which came in handy to correct a slight unevenness in the floor. Speakers are now about 1.5" off the floor.
NOTE: Had to order 3/8-16 adapters for the spikes, per Albert. However, it turned out they didn't fit the existing t-connectors on the speaker bottoms. We had to replace these smaller T-connectors with 3/8 connectors found at the local hardware store. Pretty much of a PITA, making the installation a lot longer than it really should have been.