It is several years since I used REW together with Umik 1, windows version and it helped me alot with placing treatment in my room to cure SBIR problems. But, I also think your meaurements look ”odd”. That mode around 30 Hz from the waterfall looks to linger on ”forever”. If you have a large window area behind those curtains it feels likely a length mode 30 Hz would just pass right through the curtain and window area, not bounce back and forth in the room and build up such a mode.
Is it is possible to borrow another laptop, perhaps a windows based one, and make new measurements?
Otherwise, a personal reflection; you have good gear and a very nice looking room. So if there’s any truth in the measurements you have made so far, this shows good gear and a nice looking room doesn’t guarantee good sound. The interaction speaker positions <=> surrounding reflection areas <=> listening position often influences bass sound a lot more than good versus less good gear. Speaker directivity and toe in are other variables to remember, impact can be seen in REW's ETC diagram and has to do with SBIR.
I understand you don’t want to change anything in your room, so I would start with simple things which requires no money and little of efforts. That would be to move the microphone forward and sideways at ear height at least 1 m and not place it on anyhting that can resonate at 30 Hz. Any change? If yes, a move of speakers and/or listening position can mean improvement. (A shot in the dark, -if your couch under the leather cushions is constructed around a sealed empty plywood box, it could be a resonating box, porly damped at 30 Hz.) A simple ”real” floor standing tripod, instead of the little one you got together with the mic, can be a good investment. Always mark out your measuring positions with a tape mark on the floor and number it so you know which measurement it goes along with.
My basement room has a concrete shell 20-50 cm (8”-20”) thick. A change of 1 m shows a substantial change in mode strength. I realised before I started out with treatment that the 3 lowest length modes would be next to impossible to treat with any common purchaseable and visually acceptable ”acoustical fixes”. So, careful positioning of speakers and listening place was treatment # 1 at no cost. # 2 for 4 th length mode at around 86 Hz and 2nd width mode at 82 Hz were limp membrane traps + DIY helmholtzes of substantial areas (but not very deep). # 3 (later on) were arrays of subs at front and back wall. So, I don’t fully agree with what Matt wrote ”The only good option is to treat the source. Damp the length mode reflection”. Check first how it sounds with a repositioning of speakers and / or listening position. Important to remember is that the best position for mid and treble element is seldom the best for low bass element. To lessen bass problems 2 subs, 1 at the front and 1 at back wall can improve a lot at listening position versus length modes. 2 separated at front and 2 separated at back wall and you can reach an even bass across the width of the room. The subs would take up less volume than any useful acoustical treatment, probably less money (and no / little rebuilding …) An EQ instead is cheap, could improve on 1 more or less fixed position but not overall in the room.
First things first though, check out if the measurements show true or false results.
