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Thanks for getting things started Dave. I'm going to ask, where DO you start ? I like low listening level dynamics and don't want things "damped". I'll take a slant here and ask what one should consider, having no room treatments at all with OB speakers. These do most everything REAL well with no apparent bass loading. At 8' on center 5' from front wall, in a 14 X 23' room, imaging and dynamics with a mere 1" toe-in, gives me little to complain about. If treatments are psycho-acoustical, where does one begin what appears to be an empirical effort to make "improvement" ? You made it wide open Dave, so hope this isn't a stretch.
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 ?
Cool.......you've just "diffused" half of my reading material. . There is so much yap re polys especially pertaining to "smaller" rooms. These include "highly" acclaimed room specialists. Claim is they make the room feel larger as in "wider"......so we are now approaching psycho-acousticsAs for unwanted "dead rooms".......seems diffusion is primary followed by judicious construction of absorptive panels ie. start with covered "ductboard" to the primary reflective areas. (For the OB types, this would include area just behind and beside the speakers, as in the area just forward. Effectively, we have "primary reflective front" (not discounting top), and "primary reflective rear"). Having constructed these panels, they just MIGHT require additional (thicker or larger) "layers" be added.Do all these "panels" benefit from "standoffs" ie airspace between their rear surface and mounting wall ? Does a "soundstop" type board add merit to the "ductboard" for further "layering" of these reflective treatments ? Further, if the previous is true, would the first place to administer additional "layering" be at primary reflective surfaces (as opposed to room's rear walls) ?As for the Diffusers, new and old, front and rear, would they be just as affective built into movable frames ala "gobos" as they would hung or pasted to the walls and further, when and where is "wider and/or taller" affective with diffusion ?
A poly WILL make the room feel wider... it will also make every instrument or voice do the same thing. Highly acclaimed room specialists go in and out of vogue kind of like wide ties. I just try to do what works and if I have to eat my words or revise my thinking I'll do that. There are a lot of guys still stuck in live end, dead end, too.Once again, I always recommend absorption for the primary (first order) reflection points. Doesn't have to be a big panel usually in smaller rooms like we typically have, either. My room has 42" high x 48" wide panels on the side walls. I'm thinking that they "may be" a little too big and will try some smaller ones when I do the room remodel. Ceiling panels should be absorbent, too. They DO NOT HAVE TO BE 4" - 6" thick, either. Mine are 1" thick 8# density ductboard. Any absorbent will be more effective when mounted away from the boundary surface. A 1" spacing does wonders, especially with ductboard. The spacing turns the ductboard into a diaphragmatic absorber and extends the LF cutoff. Our foam diffusers benefit from spaced mounting for the same reason. You can extend the low frequency absorption by mass loading diaphragms, too. Anything from cardboard (lower mids), 1/8" masonite (upper bass) down to 3/4" plywood (LF) can be used. Remember that the rule of thumb is for at least on dimension of the panel to be 1/4 WL of the target frequency for highest efficiency. Bottom line is that any suspended mass will burn up energy. And one more time: the tricorner wall/wall/ceiling intersection behind the speakers, any speakers is one of the first places I treat in any room with 90 degree corners. It is a megaphone for comb filtering and other bad ju-ju.Soundboard has a lot of uses, but not so much for layering with absorbents unless you are building a bass trap. The added reactive mass helps in those instances.I always recommend that treatment be made easily moveable - frames or panels or whatever that can be hung on picture hangers, hook rails orpinned into position. I am all about T-pins for lightweight treatments. Fixed treatment locks the room into a single use mode and that sucks if you move your listening position.Dave
I believe the wall/wall/ceiling is supposed to be an absorber - does the gap from the absorber to the boundary still apply, and does it change when the ceiling is a cathedral type? How big should they be? Is bigger generally better or there any guidelines depending on the room size or frequencies that are desired to be controlled?
"You can extend the low frequency absorption by mass loading diaphragms, too. Anything from cardboard (lower mids), 1/8" masonite (upper bass) down to 3/4" plywood (LF) can be used. Remember that the rule of thumb is for at least on dimension of the panel to be 1/4 WL of the target frequency for highest efficiency. Bottom line is that any suspended mass will burn up energy." Dave.....the above implies that w.o. bass traps, one should consider dual purpose diffusion. Simply applying, for instance, T's, to the front/rear walls, is not enough. They should first be applied to 3/4" ply(other) and ideally stand free of the wall surface. If this is correct and there is no other single purpose LF trapping, how does one know(w.o. analysis) how big (area) these self built panels need be ? Room's cubic volume ? "And one more time: the tricorner wall/wall/ceiling intersection behind the speakers, any speakers is one of the first places I treat in any room with 90 degree corners. It is a megaphone for comb filtering and other bad ju-ju." Does this apply to any wall/ceiling corner intersect other than 90 degree ? For instance, my front and rear walls are "bayed"(the exception, but planned as a pseudo-horn) have 2- 145 degree angulation creating a "mouthed corner", so not as abrupt as the atypical dead-ended 90 degree corner..... When employed, is the ductboard sufficient for the tri-cornered application or should it be backed with a "mass-loading" ply or other material as you mention for dual purpose diffusion ?
So on the attachment you would be recommendeding illustration "D"? (not A -since you called it "type A" mounting.(Also, I think the Type A refers to protocol for absorption measurement procedures in facilities where they place the object flush against the wall. -but that is all from memory, and it has been known to be faulty... So "modified type A" is when they add this little bit of space?)
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.htmlSure, 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=20Ceilings 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.How's that?<><Dave
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