Chess,
The house is a only few years old, one of those hastily-assembled suburbia specials. The basement has cement under the carpet. The walls are relatively thin drywall, presumably with wood for the loads. Our old place was an apartment building, although the construction was quite solid there.
It's very bizarre...I actually can't move the sub much farther out into the room, because the driver fires backwards to reflect bass off the walls, and moving it out decreases bass output markedly without much help on the vibration. To describe the AX500, imagine an M40 backwards, with the driver and control panel on the broad baffle facing the wall.
Essentially, in the bigger room I'm getting less clean bass, and far more mechanical vibration of the walls and other speakers. My electronics are on a sturdy rack.
If I remember, you use an EP350. Do you get much shaking of the walls? I am considering a trial purchase to see if a front-firing sub corrects the problem, barring any suggestions that work.
