miroslav
Cosmic Cowboy
I believe his thinking is that the CD's would bring back some reflection...
...He could rip out all the foam and it wouldn't be any louder outside because it's the mass of the walls that is doing whatever muting there is.
Yeah, I know that's where his thinking was...and I suggested why bother...just remove the foam and you get hard surfaces.
Really...he can just rip out 80% of that foam, leaving just a few random pieces to pick up some of the high-end reflections but without sucking the life out of the space (muffled vocals)...and then like others suggested, bring some rigid fiberglass for low end trapping.
For more volume control...add more sheet-rock.
Thing is...it ain't a big booth...so adding sheets of this and that will leave him with a tight space....which I think he's aware of and part of the reason he isn't following up in that direction. As I already said...he looks like he has the space to build it out to a bigger booth, which may be his only salvation if he must have good sound control but also some decent sound quality.