Backwall wall behind my back treatment.

Its a hard concretetype wall.

Perhaps a long pile rug ? Or a acousticmatt of pressed foam ? On the rearwall. ?

Maybe 3 inches thick of some rigid fiberglass covered in a nice fabric. Ask at the acoustics circle at audiocircle.com and hopefully Ethan Winer of Realtraps will chime in. Be sure to describe the rest of your room also and pictures would even be better.

Thanks Warnerwh ! Shall go there :)

If you are within inches of the rear wall you should leave it untreated. Your brain cannot tell he difference between the direct and reflected sound if the wave path distances are virtually the same.