Changed Speaker Placement NOW BOOMY

I recently dealt with this problem as well and unfortunately there is no easy solution if you are unable to move things around. The cheapest and best solution is to move the speakers out from the wall behind them and/or move the listening position forward/back in the room until you have an even response. In my room having the speakers 2' vs 2.5' off the wall made the difference.

I have also tried room treatment using 4" acoustic bass trap panels in combo with bass trap wedge foam. IME minor room treatment like this helps a little but in the end will not cut it unless you are willing to go all out.

Finally, other things you can try other than changing speakers are port stuffing (probably wouldn't work too well on your Thiels) or some sort of parametric EQ. If you have a highly adjustable subwoofer you can also try to adjust the phase, polarity, and cutoff such that it cancels out the offending boom from your speakers without affecting the other frequencies too much. Good luck!

Timlub - There is a pretty good article here : http://www.ethanwiner.com/acoustics.html

It shows that my material (John Manville 817) has two times higher absorption coefficient at 125Hz than lighter 814 material (similar to common Owens Corning). It is still pretty bad for lower frequencies unless I'll go 4". Problem then is cost and WAF.

I'm not sure if reflections come from vaulted area. I think it is mostly from tall walls. I can hear echo, when clapping hands and also get better imaging at lower sound levels (echo dies faster). I had problems with previous speakers (Paradigm) resonating on upper bass frequency that was most likely multiple of bass refleks tuning. My Hyperions don't do that (why?).

Hi Kijanki,
I asked about hearing from you vault from dealing with pro sound equiptment. Back in the old days, I actually built several systems for night clubs and church's. Inevitably, I had to deal with sound reflection and absortion from high ceilings. Without fail, when we damped upper reflections, the room was better and you could hear the difference at floor level.
I can't answer the differences between your Hyperions vs Paradigm. I've never sat in front of Hyperions, but they look great.

Lots of varying info. How will you decide what to take as advice? ;-)

Everest: amazon.com/Master-Handbook-Acoustics-Alton-Everest/
Toole: amazon.com/Sound-Reproduction-Acoustics-

"I've never sat in front of Hyperions, but they look great."

Timlub, you make me feel better. The only thing I didn't like about Hyperions was black piano finish and coffin like shape. Now it is slowly growing on me. I even realized that possible scratches on black piano finish can be easily repaired by piano repair/restoration shop while scratches on wood veneer are almost impossible to erase.