Thought we could add value to this stickie. Dave proposed a "gobo" wall, or self standing diffusion/absorption panel, suitable when permanent walls are compromised by whatever. Ductboard is a glass matrix typically folded into air and heat runs from the furnace. Diffusers may assume any one of three products from PI at this time.
Dave could you explain what the "soundboard back" might be made from ?
Assuming the "gobo" is standing in corner and diffusion of sorts, is provided on wall between adjacent corners, might a more simple "gobo", fabric covered frame enclosure of ductboard or Roxul, suffice ?
As for front and back diffusion, many a professional and AC users have embraced the loose filled void created from simple ply radiused along major (8') or minor (4') axis and applied to front and rear walls. I wonder the merits of such as opposed to new found materials ?
Further yet, I've heard some terrific 6' tall rear loaded horns of late, and they benefited greatly from ceiling treats. These were simple and multiple(hung one behind the other) framed absorptive(Roxul) materials, angulated (facing proud toward speaker) hung in side to side rows just before the speakers to above the sitting area. Talk about staging. These achieved a sound/image we can only dream all recordings are made from. I don't see these discussed frequently and wonder how speaker "specific" such treatment becomes ?
Dave, thanks for the dialog. This is how things happen.
Let's pick them off:
Soundboard is, well - soundboard. A dedicated fiberboard known throughout the building trades. It is made by about 10 different companies. Celotex is a premium version of it - http://www.blueridgefiberboard.com/pages/soundstop.php
Also, the WFBB (white faced building board) is an excellent general material for this type of construction and is easy to finish http://www.blueridgefiberboard.com/pages/white-faced-building-board.php
Any of the low density fiberboards will be OK for this application - http://www.supressproducts.com/soundproofing-articles/Sound-Deadening-Board.html
Sure, a simple frame will suffice. I just hate lifting and toting things around when I can roll 'em.
If you want to make a polycylinderical diffuser here is the easy way: take 2 - 1"x2" wood strips (cleats) and cut a 30 degree bevel on one side. Mount them vertically to the wall, floor to ceiling with the bevels facing inward with a distance of 3'6" to 3'10" apart. Take a piece of 1/8" masonite and pop it between the angled faces of the cleats, Voila - polycylinderical diffuser. Polys are easy to build and not particularly applicable for what we are trying to do here: create a realistic image. Polys are designed to create broadband diffusion to eliminate slap echoes (direct returns) in larger spaces. They can be used on side walls or behind the listening space, but don't expect great results. They can also be filled with FG, Roxul or polyfill to create some local bass trapping, too. Do NOT put them on a front wall between the speakers. They will smear the superpositions (summations and reflected frequency nodes) along the radius - just the thing we don't want for precise imaging. We want to disrupt (breakup) the superpositions to prevent comb filtering and reinforcement. Go here and download the .cdf player and watch how waves interact. It will visually explain how modes and frequencies sum: http://demonstrations.wolfram.com/SuperpositionOfSoundWaves/
Fun things to do when you're bored - http://demonstrations.wolfram.com/topic.html?topic=Acoustics&limit=20
Ceilings are boundaries and need to be treated as such. Everyone worries about floor bounce, but few people think of the ceiling as the
biggest source of HF time domain distortion. What is usually the driver that is the closest to the ceiling? The tweeter - and the midrange or bass/mid is usually below it exascerbating the crossover group delay problem. Point sources still suffer from this with the bottom portion of the driving cone being farther away that the HF element. Bummer. First reflection point spot absorption is the order of the day in these spots. Don't forget about the first reflection point at the ceiling/sidewall, ceiling/frontwall and ceiling/rearwall intesections, either. More superposition generators that totally hose imaging. One caveat to absorption - use only enough to get the job done. No one wants to listen long in a space that is unnaturally dead. Remember that a room is an energy system that should track the energy input into the room in an uncorrellated manner - ie. no direct reflections - but with diffuse energy to not rob the senses.
The best listening room is one with good dimensions, no 90 degree intersections at first order reflection and appropriate treatment. OF course "appropriate treatment" is where SAF, musical tastes, and budget intersect.