OB driver suitablity, room modes

[dtkky]

Hi all,
What sort of Qms should we look for in choosing an OB driver? I know that the Qts shpuld be ~0.7-1.0 and it should have a generous Xmax. My instinct tells me Qms should be fairly high so that it does't flop around too much. and if it's low, we should use current drive. Tell me if I'm wrong.

I'm using Gefco X-6100 in dipole configuration (4 per side in 80cm x 110cm baffle) to cover 250 hz down to 30 hz. My room is 3m wide and 4.2m long with 3m cathedral ceiling. Using pink noise and measuring from the listening positon near the back wall, I get peaks at 40 hz on both channels (about +12dB left and +6 db left) and a notch at 63 hz -6db but only on the left. This seems to be quite consistent regardless of speaker position. What's going on here?

For my room, what's a good freq. to use to cross over to a monopole subwoofer?

Thanks
David Tan