Still vaguely exploring acoustic treatment solutions. We'll put the reduction of bass on one side for the moment, and concentrate on >120Hz. The first problem is: way too much direct reflection off the walls. So I figure the logical place to start would be to cover the whole of the front wall (behind the front speakers), and the side and rear walls up to ear height, with some sort of absorber. Not altogether happy at the idea of paying >£8 a square foot for 4" Auralex pyramids, so I've been hunting around for alternative absorbers, and have come across Rockwool "rigid and semi-rigid slabs". Extrapolating from Rockwool's figures, I reckon a 100mm thick slab of RW5 would absorb virtually everything above 150Hz, with an absorption of 0.75 at 120Hz, and still above 0.5 even at 100Hz. Not too shabby. Does anyone have experience of using RW5 (or perhaps RW3) slabs as an acoustic treatment (NOT as soundproofing)? If so, can you tell me if it has to be set in a wood or metal frame, or if it's possible for the more rigid versions (e.g. RW5) to be glued to a wall?