Design parameters for absorption panels?

Some inquiries in regard to those bespoken panels... I do not intend to discuss any particular panel absorber or a particular design but concentrate on the parameters that goes into designing them. However, it's probably worth to mention that my goal in the end is to design lightweight and portable panels (2'x4' in 2", 3" or 4" depths somewhat similar in looks to these two) why I consider the mass to efficiency ratio very important. (I will soon post more about my room and the planned treatment in another topic.) Now on to the parameters... I've come up with four possible panel absorber configurations that I would like to discuss. They are denoted "A", "B", "D" and "C" below (the cross-section cutaway illustrations are purely schematic and not to scale).

Type "A" Summary: This is the basic and most common configuration for panel absorbers: A single sheet of isolation mounted in a frame and hung with a space between it and the wall. This is a simple and fairly straightforward case were the panel more or less inherit the isolations acoustic properties why it usually comes down to selecting the right isolation material and thickness. However, from this configuration I would like to learn how to control and balance the absorption/reflectivity between the high and low end. Questions: * Obviously wrapping panels in cloth or canvas for aesthetically reasons and as barrier against the fiberglas/rockwool is ideal and very common. What cloth to choose to keep the HF absorption at a minimum? * What can be done to increase the HF reflectivity of the panel? A thin sheet (4 mm) of plywood mounted on the front underneath the cloth wrapping, would probably be good but maybe a bit to heavy? Cardboard/paperboard/foamcore instead of plywood? Or heavy paper? * The best compromise and rule of thumb is to keep the space from the wall equal to the thickness of the isolation, e.g. 2" of isolation is spaced 2" from the wall, to boost the efficiency compared to mounting it directly against the wall. But how big will that boost be?

Type "B" Summary: This configuration is similar to Type "A" above but with two layers of isolation with the possibly of having different material density and thickness for each layer. With this configuration I would like to learn what happen if several isolation materials is used together. Questions: * If two sheets of identical isolation is layered what will the acoustic properties be? Will it be the same as a similar isolation sheet of twice the thickness, eg. two 1" 703 sheets equals one 2" 703 sheet? * If two isolation sheets of different densities and/or thickness is used in what order should they be layered? My gut feeling tells me by absorption coefficient. That is the sheet with most HF absorption in front of the sheet with highest LF absorption, based on the assumption that LF waves not absorbed penetrate the first layer while HF waves not absorbed reflects. Or am I completely off the track (or is it "standing outside the wrong ballpark)?

Type "C" Summary: This configuration is similar to Type "B" above but with the layers spaced apart forming an internal air cavity. The idea is that the first layer in conjunction with the cloth/paper/cardboard act as a membrane while the second layer act as a damper and the air as a spring. It's intended to be mounted in a similar fashion, spaced from the wall, as Type "A" and "B". Questions: * Since the important thing in a membrane panel is the membrane mass using high density isolation as first layer may work as substitute for plywood or hard board, albeit not equal to them? * Will the membrane-cavity-damper combination still work to some degree despite not being mounted directly to the wall? * So will this work as a hybrid design? Working both according to the pressure principle (at least to some extent) in addition to the velocity principle (as the other panels above)? * Will there be a benefit to this configuration compared to Type "B"? Or will it not be worth it?

Type "D" Summary: I guess most forum members recognize this final configuration as a variation on John's bass trap design. A panel a with plywood back and isolation attached to the cloth front. Questions: * How do I calculate the efficiency of this design when picking the isolation density, thickness and depth of air gap? * Would a such design work according to pressure or just velocity (the gap filling the same role as the wall distance for a Type "A" panel)?