Very good resorce for sound absobtion class ratings
Came across this wikki page about class ratings for sound transmission through walls etc.
I live in Canada so never seen this before could be useful for someone building an audio room or need sound proofing solutions. This will give you some guide as to what each system will give you against a class rating system. Seems I need class 63 looks like that's going to be costly double wall system. ;-)