Ethan!

1. Is it true that you can get 100% absorption down to about 50Hz from a porous absorber when it's 30cm/1foot thick? I read this somewhere but it sounds strange... Why on earth would you in that case build complex hangers, panels..or like in Steve Albini's studio..combine large membranes with an airgap down to the basement to let low frequencies out of the studio room?

2. I read somewhere that when you have about 30cm/1 foot of free space on a wall you can use fluffy fibreglass all the way instead of rigid and get the same results. Is that true..and if so, how does that work? I thought one inch of rigid fibreglass was the same as 5-6 inches of the fluffy insulation ..

Please help me with this! Because I have space to use and lots of mineral wool :o)

Daniel Sterner, Gothenburg, Sweden

100 percent absorption down to 50 Hz with only one foot thick fluffy insulation sounds awfully optimistic. Most anechoic chambers are "totally dead" down to only 100 Hz, and the absorber wedges they use are huge, like three feet thick. However, you don't need 100 percent absorption to make a huge improvement in the response and ringing. Even 25 percent absorption will make quite a large difference.

--Ethan