Help with room treatment

[Mindscapes]

Hello!

I'm looking for help in evening out my room decay times and L and R imbalances.

The room has the following characteristics:

• Width: 11.80 m
• Lenght: 4.84 m
• Height 3.14 m
• Total volume 179.2 m3
• Front windows covered by drapes

The speakers are a pair of Kef Q7 meta with the following placement:

• Listening position: 1.90 m from back wall
• Listening height: around 85 cm
• Speakers distance from front wall: 88 cm
• UniQ height: 88.5 cm
• Speaker center to speaker center: 2.17 m
• Speaker center to listening position: 2.25 m
• Speakers toe-in: around 15° from pointing straight at the wall, firing slightly behind my head.

As you can see in the attached pictures, right now i have only my front wall treated with 6 120x60 panels made of 120kg/m rockwool and one 120x60x10 (i know, not the best density for this application). Speakers are off center and firing along the short wall as this is the placement that gave me both the shortest decay i could manage and avoided a very nasty room width null in the bass region when my listening position was centered and the speakers where firing along the long wall. All this to say that i tried various listening and speakers position both firing along the short and long wall and this one is the one that gives me the shortest decay and straightest FR of the bunch, but left me with asymmetry to manage.

From my limited understanding, besides the long decay in the lowest frequencies that i'm managing with the Room Shaper plugin, my main problem from the rt60 graph are quite longer decays in the 150-350 hz region, high energy streaks i can see in the spectrograms too. There's also the ceiling bounce at around 8 ms in the etc which would improve with a cloud, but implementing that would be problematic. Theres also something at 3ms in the left etc i can't pinpoint. I don't have anything near or in between the speakers besides the amps and dac on the floor.

I was thinking of making three big absorbtion panels, 180x120x20, with two 40 kg/m rockwool 6cm deep panels inside separated by 8 cm air between them. I would put two between the speakers and the listening position, about 1 m to the left and right of the sofa, a sort of faux walls to restore a bit of symmetry, and one centered behind the listening position.

I can also make two 120x120x20 perforated panels absorbers with a fairly wide Q to target the 150/300 hz zone, and treat the two front corners of the room.

Would this be sensible treatment or can i do better? I will make my panels, so i can quite manage the cost and am open to various suggestions. I can do whatever with the room besides removing the wardrobe and shelves.

Thanks for the help!