Have you used a frequency/tone CD w/SPL meter ...

For someone trying to get a handle on the whats and whys on their rooms bass response I think they are invaluable. Especially so when initially setting up speakers. FWIW, I suspect very few who are really serious about set up are without one.

What surprised me most when I first starting using one was the extent of bass abnormalities that could be cured by simply moving the speakers or listening chair a little bit. I had heard folks talk about small movments making big differences but I thought they were FOS.

Huge changes in bass response depending on small changes in seating position. Less than 12" forward or back affected bass by as much 10db.
Everyone should try it if possible. Cheers,
Spencer

Ditto to Newbee & Sbank's responses. The small differences in listening position will be particularly true in small to mid sized rooms, especially ones where the dimensions reinforce the same frequencies (a cube is the extreme example where the opposing surfaces are equally spaced). The meter was also instructive to me since, for example, my initial views of a flat bass response were really not correct.