I agree with Al and rpeyton80 about the woofer being on the floor. This brings up another important point: The actual placement of the subwoofer relative to the listener is not critical. This is because human hearing can't distinguish the source (location) of very low frequencies.

This thread reminds me of something I've been wondering: How critical is the nature of the surface upon which the subwoofer rests? I have mine sitting directly on the carpet and have wondered what would happen if I were to put a piece of plywood under it to keep the sound waves from being absorbed by the carpet. Any informed opinions?