Are you using boundary reinforcement? Put them ON or very close to the back wall 12" or less, ideally six inches or less. Put them in the corners as well. Walk around the room and see if bass increases close to boundaries. If so, it is your room, if not, I would have said check woofer polarity. And obviously both woofers function correctly? I have had Cornwall I, II and III and all shake the couch as the volume goes up gradually. Something ain't right.