Originally Posted by Sebastian Vera
I looked the coefficient abssorptions tables of Owens RFG and found that 703 4"thick mounted on wall (I guess this means no air gap) has 0,84 at 125hz. Same FG same thickness but with 16" of air gap has 0,65 at that frq. I was specting to find more absorption because of the gap. Ethan specially Sugested the gap in order to trap waves with longer length.
I think that the lower absorption at 125 is a resoult of the lost of linearity cause of the air gap and that at lower frq there would be more absorption.
By the other hand I was surpriced of the 703 6" mounted on the wall, looks like really near a full band absorber I'm gonna try them for early reflection points!
From data souirces that I trust, gapping up to around 2:1 provides good, as in flat increase in low end absorption. A 16" gap means a 4:1 ratio.
Yes, 6" of 703 is pretty good. 4" with a 2" will provide similar results. In my part of world, f you have 6" available for depth, ~6" of Roxul Safe N Sound or similar product will provide the same acoustic performance at a fraction of cost.