Placing wool behind panels is pretty much products whole idea. Low to mid frequency absorbtion is pretty same that bare wool. Behind panels doesn't absorbt high frequencies as effective, that is usually only good thing when big areas are covered so you won't absorbt high end too much.Can I use the rockwool 2" or 4" behind the perforated panels or should I frame and hang them in front?
It is esthetically nice to hide the rockwool behind but my doubt is, will it still be acoustically effective as absorbers? I have visited my friend's HT where he has used them behind perforated boards and it is working there.Clap echos are not there.Clarity of voice is quite good too.No measurements done in the room though. Must I increase the rockwool thickness (to make it more effective) in case I place them behind the boards?
Most gyptones measurements are made without and with 2" wool behind panels.
As you can see using 2" wool behind panel will save some space against just huge air gap.