OK, Audio Wizards - and especially those of you who have built listening rooms, or altered existing rooms for audio. Everything that I’ve read tells me that parallel walls are problematic, but most of the time there’s nothing to be done about it. I’m carving off some space from my home office for a listening room. It’s the smallest of Steve’s room dimensions with an 8’ ceiling: 9’ wide by 11’ long. I’m attaching a drawing of an idea to make the long walls non-parallel. There’s nothing that I can do about the other walls, floor or ceiling. As you can see, I have a couple of things going for me with the closet opening along the front wall, a design that’s open to change, and the ability to add whatever absorbers or diffusers that I want. I have an idea that in a room this small, absorbers will be more important, especially in the corners. This little project may lead you to conclude that Wife Acceptance Factor is not an issue for me, and you would be correct. So this is just a little experiment. To avoid having a door into the room, I’m making the 3’ wall at the left front of the room moveable (on felt slides), but still able to hold treatment. So my question remains - is this a crazy idea with little chance of making a difference? Or something worth trying? Feedback, please.

If it were me, I would start with the Sabine equation and shoot for 0.5 ms.  Then you’ll know your problem areas. I should say problem areas aside from bass. Bass is a given and you’ll need some thick (10-12”) treatments to address 100hz and down. Depending on your surfaces, furniture, and decor, bass treatment may be sufficient. I’d start with bass treatments in the side corners and side walls, diffusion front and back walls.
A 2-4” cloud on the ceiling is nice but realistically your ceiling height will start getting pretty cramped with ceiling treatment. A thick rug with a pad under can be sufficient.
I thick this kind of treatment is more effective than trying to change your room dimensions. Or change your dimension by adding the thickness of the bass treatment.

Well, not exactly what I was hoping for, but it will have to do.