I'm passing this on in case it might be of use to someone. Last night I experienced a very clear case of floor coupling, in which my amp was making the floor resonate...it was causing problems with my tone. My rig: Component rack (SWR Grand Prix, Presonus Compressor, Stewart World 1.2) Flite Sound 1x15 Line out into a Bose PAS w/one woofer module. Venue: Our usual practice room, which is maybe 8x12 feet. Bare wood floor, built-in cabinets and shelves, old house. Last night at practice I was hearing a lot of boominess down low, specifically from about the low C on down. Weird...I hadn't changed anything. Then it struck me...normally I have my speaker sitting on a dense foam pad (one of those 2x2 ft jigsaw-edged things you can get a Home Depot) and neglected to put it down when we unloaded after our last gig. I rectified that, and bingo...boominess gone. The floor had been reinforcing the low end, and not in a good way. If you've got any kind of weirdness going on with the overall balance of your sound, it might be due to floor coupling. Try isolating your cabinet and see what happens.