One of my friends has a dual Servodrive contrabass setup and it literally makes your shirt flap in movies like Pearl Harbor and TS2. Even though the bass can literally clobber you, it still remains defined with things like bass guitar. Far and away the best sub setup I've heard. Each unit is about 2x2x3 with 2 15" active drivers with the servo between them and 2 18" PR's. Each unit is fed with about 500-800 watts. My single SVS 2039 can rumble the wood floor but I never get this kind of air movement. I've heard the B4+ also and although very impressive it didn't do this either. If your sub setup can do this, give us some info on what you're running and the room size/openings.