Few problems; the insulation will act as an air gap, so placing it on both sides of even SOLID concrete blocks will make a 3-leaf wall (see the top "before you post" link this forum) -
Those dB ratings are STC or rW ratings, both of which ignore bass frequencies below 125 hZ; so it's easy to sound like you're GREAT when you don't have to do any "heavy lifting" - meaning, no importance AT ALL given to low frequencies.
Once again, there is no "magic bullet" I know of - sound isolation takes mass-air-mass, the more of each the better. So spending high $$ on "special" panels is generally a waste of money; the cheapest mass is the best mass, insulation within a wall isn't really critical (it is necessary, but density isn't real important) - decoupling between the inner and outer mass IS important, and intentionally (or otherwise) building more than two centers of mass between you and the sounds you don't want will cause VERY noticeable lessening of isolation at lower frequencies, with (usually) an improved MID range isolation.
HTH... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
