Hi JC, thanks for you interest, and the choice Ferris quote
In my case, I consulted with an acoustics expert early on and determined the coverage of the walls. Each acoustic expert has their own "special sauce", as its been said, to achieve the best results. Having nearly completed all my OC703 install, I think the room is good but probably not optimum.
The best case scenario is to take the time to use REW software to actually measure your room and then adjust your treatments accordingly. You can also consult with several different firms that offer acoustics assistance. The two I've seen on the forum are GIK Acoustics and Erskine design. Both offer levels of consulting to help optimize the acoustics treatments of your room.
I'd say due to time constraints that I am dropping out at the 90% good level and getting fabric installed so I can complete this and the family can start using the theater after a long several year construction.
In general, my treatments follow a couple standard rules. The front wall is the "RC" sandwich often used which uses a membrane trap to catch some stray lower frequencies. The side walls provide an anechoic path (no reflection) from the front speakers to the front row seats. The top of the walls at the surrounds are not treated (above 5 feet and 7 feet back) to allow a more lively surround. Speakers are mounted 2 feet above ear level from the first row, which follows THX. It might have been better to put these right above ear level though.
Back wall is primarily for bass so it is 4" thick and covered in poly as the poly will reflect higher frequencies.
So is it overkill and do I have too much absorption - I'd say possibly on the side walls. Is it better than watching TV in the living room? Heck yeah.