Have now completed acoustic treatment prototyping.
I had a real problem with bass modes in my screen 'alcove' in the front of the room so I choose to treat the entire alcove with 4" mineral wool (covered with 1" linacoustic - cheaper than GOM)
2'x6'x4" bass traps in the rear corners; and
48" high panels of 1" linacoustic on the side walls (just cut pieces of linacoustic - have not framed them yet)
See before and after RT60 and Freq response below (note before is red, after blue)
Please note that I have 4 subs in 1/3 2/3 positions on the front and rear walls.
Have to say the RT60 may be a bit low. I may scale back the side panels a bit.
However, the room sounds very good, albeit a bit dead. Whenever I listen in a room like this I like to say that it ruins all my recordings. I hear every error in mix, artificial reverb, MP3 (my library is in iTunes) encoding compression, etc. But when a recording is good, its great!
All comments welcome!