I would straddle 4" panels in the corners around the room. That would absorb A LOT more low end.
I can't on the ceiling to wall corners unfortunately since I have windows and lights on the sidewalls. The iso room window and the tracking room window are angled outside of the wall about 1-2' each kinda making a shelf ontop so I'm gonna just build a bass trap into the tops of them. I should be able to manage the floor to wall corners near the mix position as well. Think I'll also put a 6" trap on the wall beside the door and on the door itself in the control room since I won't be able to put a corner trap there.
Can you buy FRK by itself or does it only come with rigid fiberglass? Is it pretty much shinny thin cardboard? Maybe I could just put a layer of thin cardboard covered with something like tinfoil or plastic bags? Should I have a bass trap reflective if it's to the left behind the mix position aimed towards me?
Sweet I'll throw some skylines on the back wall infont of the 12" thick bass trap!
Think for the tracking room I might put some velcro on the reflection points so I could switch between diffusion and absorption. So I can experiment and have some options. Gonna put some 3' wide floor to ceiling bass traps in the corners. Be sweet if the whole ceiling was a giant broadband absorber depending on how much isolation I would get out of it.
Thanks again for all the help!