rumonkey2 said:
thanks scott, more or less confirming what I was initially thinking& helping me visualize it. But, why a gap behind panels (and how) & may have problems on throw wall...planning on painted wall screen. But I have also been thinking about painted canvas - which I could then hang on panel - or, possibly back w/ insulating material? Does that make sense???
When you mount a porous absorber with a gap behind you get a boost in performance... as a practical matter a gap +/- = to panel thickness is about the maximum gap worth considering. Obviously this is not always "doable", but when space allows, take the free ride and get more bang for your buck.
With ceiling panels its a snap, you just adjust the hangers to allow the panels to hang down a bit. With our firm's upholstered mineral fiber panels the easy way is to stand the upper hanger hook off the wall [+/- 4" for a 4" panel] and then add a short length of plastic / cardboard tube behind the lower portion of the panel - or a small block of packing foam and some double sided tape works well. You can't see any of this from the front side, so the panel appears to "hover" a few inches off the wall.
Something similar should work for most any panel you buy or build, but foam panels are a special case and may require some sort of stiffening to the back side to keep things from getting floppy. I know of folks who have glued foam panels to grill like panels of thin plastic, or MDF to get stiffness and leave the backside acoustically transparent and then done something like the technique described above. "Eggcrate" drop in ceiling grid return grills might work well for that application.
In corner mounting simply hang/lean the panel so that both backside edges touch a room boundary [wall/ceiling/floor] - don't allow a gap around the edges in this case as there is an extra boost of absroption that comes from capturing a wedge of air behind a corner panel.
A screen on an absorptive substrate is a pretty neat idea... you are going to have a lot of square footage there to work with and extensive front wall absorption is a well known and respected design tool for improving small room critical listening.
Will the screen be acoustically transparent? If not, might you need to consider the screen acting as a membrane / resonate absorber. I'd get help calculating that potential factor before proceeding with the concept given it is so large a device it could have a profound impact - put a big hole in the room resoanance where you don't want / need one. Sort of like putting a big notch in your EQ at an presently unknown frequency and finding out after the build if it is beneficial... or not.
If I were to make such a device I'd try to use an acoustically transparent screen if practical and in any event make the absorber backing thick so that it functions broadband [on lows as well as highs]. Assuming a 3 lbs. pcf semi-rigid fiberglass substrate like 703 then I'd go at least 4" thick. If thickness is a criticality you could go with 705 [6 lbs. FG - at twice the cost] and get in the neighborhood of 4" 703 performance with only 3".
In both cases gapping would improve performance - if you have the room to spare.