>>The sub is 10' from the corner behind the sectional to the center of the dustcap.... three feet to the wall where the eqpt. closet is. The ceiling height is 8' 4".
Hmmm. That doesn't work out at all
The graph didn't mention crossover frequency... there's no chance you were crossing the mains over at 40 Hz, were you ? Doesn't seem likely -- that's the kind of thing HK owners do, and I don't think you have an HK...
The bigger thing nagging at me is that there are some big up/down spikey things going on in the response curve but it's not really all THAT bad. The problem may be nothing more than the combination of a decent midrange sub and a small room which doesn't give much reinforcement below 40 Hz, that being a combination which doesn't give you much output in the "wow did you feel that ?" frequency range. Perversely enough the 350 in a larger room would probably be quite a bit more satisfying because of the room reinforcement at lower frequencies.
I'm having a tough time believing that the BFD is really going to make a big difference except by using it to boost the 20-35 Hz region, where a larger room would give you some reinforcement. It may be time for someone who lives near Mark and has one of those "flat below 20 hz" subs to pay a visit and see if an EP500, SVS or VTF-3 fixes the problem.
I would like to understand that suckout at 38 Hz though, just in case that is also affecting your lower frequencies. I do think the sub in the corner gave you a better starting point for BFD-ing than the sub by the radiator and from your earlier graphs it definitely eliminated the 38 Hz hole.
It probably is worth trying the "sub in the center of the room" placement, maybe even on the coffee table. JohnK (I think) said that you won't get much effective room gain that way but your room is only giving you gain in the "boom" frequencies, not the "holy $#%" frequencies anyways.
