Big DIY Basement and HT project

[bigpants_ku]

Mike,

I read with interest that research on soundproofing gypsum walls.

I noticed all tests were done with gypboard on both sides of the wall,

with bunches of variation (2 layers, alternating studs, etc etc).

In my situation, (picture at base of this post) I've got a closet back

there behind the media wall with a cement wall on 2 sides of it, and I

want to prevent all that concrete from bouncing sound that leaks into

that room back out of it (all without messing with the concrete walls

if possible). Since this is a "hidden" room, that means I don't

have to put sheetrock on the back of that wall if I don't want

to. Since sheetrock on both sides transmits sound through and

negates the insulation for the most part as was proved in that project,

I wonder if (since this is not alternating studs, etc) leaving the

gypboard off of the back side and covering the heck out of it with

thick fiberglass (and plastic?) would work better than insulating the

gap and sheetrocking (even double thickness) on each side...?)

Thanks! Here's the pic: