If you contact a company called Roxul @ 1-800-265-6878, they can give you the actual acoustical Performance absorption co-efficients at the frequencies-125, 250, 500, 1000, 2000 and 4000 Hz. I am looking right now at their spec list that they faxed to me and have just recently installed it in the ceiling of my new control room along with 1/2" drywall suspended and isolated from the ceiling joists with 1/2" blue dense foam board strips between, furring strips screwed on edge with screws countersunk and installed perpendicular to the ceiling joists every 16"...3" "Roxul" rock wool (also known as rotten cotton) then another layer of drywall. Definately deadens the sound between the two rooms. The rotten cotton comes in 1", 1.5",2",3" and 4" with different accoustic ratings per frequency per thickness. Definately worth checking out!
PAULIII