My couch is about 4 feet out from the wall. The sub is almost against the wall, so you can walk betweent the sub and the couch. Let me just say that I've always heard a corner is the most efficient placement for a subwoofer, but I didn't have any corners available to place it, so behind the couch was the next best place.
And yes, now I have to turn it way down or all I hear is bass slamming into my back. Makes it nice when I do feel like watching a movie a little hot though. When I want the people down the street to wonder where the helicopter crashed!