Hipper
Addicted to Fun and Learning
I'm seeing a little bit of evidence below 80 Hz in your first measurement, but nothing that's outside of what I see from measurement variation. Your second measurement though shows a big difference. You definitely tapped into some issues with the additional corners.
Do you have a post-EQ graph?
RE: decay times, those are mostly down due to the reduction in amplitude, and will see a similar result from multi-sub + EQ. Do bass traps reduce decay even if amplitude isn't affected? That I don't know. Bass traps work to make the room appear larger, like adding stuffing inside a speaker. A room acoustician would have to answer that.
I have (currently) four GIK Tri-traps, and went with them because after measuring my space, I couldn't fit the soffit traps. I didn't see any changes below 80 Hz with those.
Post EQ:
This was done by applying filters created by REW to the ten Parametric EQ of a Behringer DEQ2496.
And the spectogram of the EQ'd signal (again, 40Hz is mostly traffic noise):
This is the various stages of adding bass traps: