Ceiling treatment. DIY BASF basotect 4".
DIY Arquen diffusers for covering rear wall.
I bought wood for making PRD difusers but later decided for styropor (styrodur). Much easier to work with. And cheaper too.
Glasswool on the test. Unfortunately it didn't work on usual places.
Testing a foam used in car industry. Not effective as I thought. On the bright side, room had new car smell for a short period of time.
Rockwool wrapped in gardening cloth and ready to use. Turned out the best place is between speakers and not in corners.
Covering a window behind screen with rockwool blocks.
DIY PRD diffusers. This was really time consuming but cheap! Only $15 per piece. At this point I didn't know styropor manufacturer offers CNC cutting. What a revelation! More on that later.
Time for covering side walls. This will be a hybrid absorber/diffuser.
Painting and sorting.
Glasswool covered with two layers of cloth.
Heavy lifting time. Diffusers waiting for montage.
Enveloping is now great even that side surrounds are pretty close. Probably KEF's Uni-Q drivers are helping as well. However, this didn't help much for 2-channel low end.
Fake rack on the opposite side for better symmetry.
Two Helmholtz resonators (each 60 L). They lowered peak by 2d at 45 Hz (room mode) but caused ringing in the time domain. Floyd Toole was right!
Testing wood panels targeted to 45 Hz and placed on top of rockwool absorbers. Very little or no effect but can be useful to prevent sucking up HF.
Huge DIY membrane absorbers on the test. These were borrowed. Advertised as very effective. Didn't help much here. This is one strange room!
The rest of styropor was used to build much simpler diffuser. Super easy.
Gave up achieving good stereo sound using just two speakers. Adding third sub confirmed more subs can be effective.
BAD panel replica. Took me a week to drill those 850 holes. I think I lost weight!
Last and probably least: more difusers. This time cubes were bought precisely sliced. I just glued them together. Still, took me 30 minutes for one 7x7 panel.
Rack from behind: bad cable management.