jonessy
I had terrible luck here.
After an extensive reply I pushed the submit button, and the forum replied with a critical error.
I even couldn't recover it from my cache.
Just a short version.
I have experience with any kind of room (from small to concert , pop-concert, theaters, huge tv studios, factories, whatever) but that doesn't answer your question.
Main difference:
Small room acoustics: strongly defined by modal acoustics.
Large rooms: more defined by geometric acoustics (modes themselves are very dense in audio range)
The formulas you know (Sabine, Eyring, whatever) you can better apply for geometric than modal acoustics. So there's no problem.
Basically you can use any wool as for small room acoustics.
Important is:
The further you distance a board from a wall the better low frequent absorption becomes.
However when you continue increasing the distance this effect disappears and reverses.
The same board at very long distance will act as a board in a diffuse field showing poor low frequent absorption.
As a rule of thumb: A board in a diffuse field will show comparable absorption as a 50% thick board directly mounted against a wall (from low to mid).
Further important:
The low frequent gain by diffraction/edge effect (mostly in studiogroups wrongly confused with edge surface absorption) will diminish also in a free field versus closer to wall mounting.
In other words: absorption in a free/diffuse field is less to much less efficient for low to mid.
Your boxes with backing substitute the lack of a close by reflecting wall which is good if you hang them far from boundaries.
I should use ceiling tiles in those boxes with a cavity. Advantage: you can buy them in lots of finishes, they are self supporting until large sizes etc.
You can partly fill the cavity with cheaper wool if you like.
The total thickness or cavity depth is to be defined in function of the absorption spectrum you want.
Look at Bob Golds page:
http://www.bobgolds.com/AbsorptionCoefficients.htm
As long as you don't give a location (as I suggested) it has no sense for me or others to give possible links to possible producers or materials.
jonessy:
I just remembered that knightfly put it even in the rules:
knightfly wrote:This means -
No location, no answer.
It helps yourself and others to read them.
) is about to become a gran-papa for the third time, love the kids but hate the further proof of "old fart" status. 