How you treat your room is somewhat based on what type of speakers you have, monopole, dipole, omni. For example, a “dead” front wall is not ideal for dipoles.
To your OP, we typically suggest wide-band absorption at the middle of the back wall about 4’ wide (maybe wider) with diffusers flanking left and right.
Question: Sound Treatment behind the Listener?
I have treated the 1st and 2nd reflection points and I have sound panels between my speakers. I also have tube traps in all 4 corners, but I am not sure what (if any) should be done with the wall behind the listener.
That wall presently has a DIY rack system that holds about 5000-6000 cd’s. I believe it helps scatter the sound. But I’m not sure if that is the right approach.
So, what are you guys using on that wall? Diffusion, Absorbtion, Reflection? Anything else?
I would appreciate your thoughts.
ozzy