[dBe]

EDIT: Let's try this one one more time.  If we can discuss pertinent room treatments without having to reinvent the wheel this can be a great thread.

Onward and upward.

Dave

**************************************************

This will be a place where anyone and everyone can post about PI audio group room treatments: their uses and results.   This must NOT become a place to rival the Acoustics Circle.  Rob runs a great forum over there and we need to respect the boundaries already in place.  Please keep it sane and not delve off into other waters.  This is also not "Rudimentary Acoustics 010".  Please try to do a little homework and remember: Google is a great search engine - available 24/7.  Most of us mere mortals aren't.

It is my hope that we can all learn from each other here.  I have years of experience in acoustical design, application, measurements and room analysis, but acoustics can be a very dry topic and Beranek, Augspurger, Don and Carol Davis, Floyd E. Toole, Earl Geddes,  et all have pretty well defined what goes on in a room, but remember, even these people have areas where they agree to disagree in application and measurement methods.  In the final analysis, what works, WORKS.  A point to remember is that different musical tastes are often served best with different treatment schemes.  I don't even want to go down the road to aesthetics.    This is the place where science and art can come together, so if someone has a good way to build something or make thangs purdy, by all means- speak up!

If you come up with a good or better way to do things, please speak up.  Post pictures when possible so we all may benefit.

Thanks.

Dave 

 

[dBe]

The Room as an Energy System

First thing we have to establish is what the function of the room is in quality music playback.

The room should provide a convenient, comfortable place to sit and derive the greatest amount of enjoyment for the listener.  This means different things to different people, obviously, and this can be a place to read a good book, have a cool drink and soak up the musical ambience or a place to do hard core, "they are here and I can see down the vocalists throat" listening. 

My question to the readers of this initial post is an easy one to ask:  How deep should we go here?

I am going to make some assumptions and guess that we are somewhere in the middle.  Please correct me if I'm off base here.

With this in mind where should I go into acoustical studies?  Room modes?  Reflections?  System setup?  Room dynamics as a whole?  My gut feeling from Tazar's post is that reflections are probably where this should start, but to me killing the pressure node in room corners is the first place I start.  Boomy rooms will benefit very little from reflection control because the microdynamics revealed with reflection control are swamped by the LF energy excess.

Give me some feedback and I'll try to address them as we go along.

One final note (musical pun, here):  do not take anything that I say here as audio gospel.  The science is the science.  That does not change.  What does change is utilizing that science in a reasonable, systematic approach to solve acoustical problems.  It is the approach that is the dynamic element in room design, especially when the SOAF (significant other acceptance factor) is in play.  Feel free to challenge my approach.  It is but one of several that will work and work well.  What I look for in a room is what Randy described in his post - making the room AND the speakers disappear and the performers so close you can touch 'em... IF that is what the recording portrays.  I seldom use the word "accuracy", because that is a non sequitur when it comes to something as subjective as musical enjoyment, but getting close to the recording and the emotion that recording evokes is what I am all about.

Dave 

[tasar]

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.

[dBe]

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.

No, this is the kind of question that I was looking for to begin the whole thing.  Just starting out with a generic "room treatment" topic really doesn't work because there are way too many variables.

I had hoped to add more last week, but the zaniness around here continues.  Gayle had gall bladder surgery on Monday and her recovery isn't going very well.  I didn't think one person could barf as much as she has.  I know: Eeeeewwwwwwwww!  Then my oldest daughter and husband had to fly out to California for his Dad's heart valve replacement surgery... he's not doing to well either    Anyway, we have two very active grandchildren here until they get back.  Top this off with a pile of orders (thanks for being patient, everyone) and I am frazzeled.  It has been a difficult couple of months here in Albuquerque.  Nothing major, but life's little petty problems that have to be taken care of with no time to do them in.  All of this to say:  I'll be writing more during the next few days as time permits.  I may begin a though, leave it in midbrain and then come back later to finish it.  I will get it done soon though.

Thanks for the direction - let's see where that leads us 

Dave

[dmccombs]

Wow, you left this one wide open, and its a great topic.  I have been wanting to post something suggesting a direction for this, but I keep coming back to my specific issues/questions.

Like many, I started with the good suggestions in the Acoustic Forum about Absorbtion.  Treating the Bass issues seems key to hearing the rest of the frequencies.  I have bass traps in my corners and this made a huge difference.  I upgrade speakers last week so I have been trying different absorption and diffusion to get the best sound.  I tried pulling out one bass trap on the front wall and everything got boomy.  Even the mids and highs sounded muddy.  what a great lessen.   

Most agree that first reflections should be covered.  One area that seems vague is weather the ceiling should be treated.  Maybe that could be a topic of discussion a some point.

Then there are the diffusers.  I have some of Igor's diffusers and they make a big difference.  The placement options seems endless.  Maybe some strategy could be developed on where to place these first as starting points?

I guess I would suggest giving a high level view of absorption and diffusers effects and strategies on how to tune a room.  All rooms are different, but if we had an attack plan that would be beneficial.

LOL, so many topics, so little time....

Darrell
www.mach2music.com

[dBe]

When I treat a room I start by measuring it and doing a mode analysis.  I have specialized software for this but there are a number of good freeware versions on the net.  Here is an easy one to use:  http://www.bobgolds.com/Mode/RoomModes.htm:  As a matter of fact if you all don't know about the FRD Consortium you need to:  http://forum.speakerplans.com/frd-consortium-linktools_topic14489.html  The RRC is a really good visualization tool for simple rooms.  Here is a fun toy to help visualize room interaction.  This one is only 2-D.  Click on the 3-D button to see into a room mode: http://www.falstad.com/ripple/  Be sure to activate boundaries, too.  There are some other applets on the site that you can play with to get an idea of what is going on in rooms.   

In my next post I'll go into an easy to do, but difficult to hide, way to work on the major room modes.

Dave 

[tasar]

Great Dave, I've been poking around, sniffing the bushes. I plan to have some of your panels shipping, so looking for, not "typical", but "atypical" set of panels for the "basic" rectangular listening room. Front corners/sides, primary reflection points and basic rears. YIKES !

Dave

[tasar]

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 ?

[dBe]

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.

How's that?

<><

Dave

[tasar]

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-acoustics

As 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 ?

[dBe]

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-acoustics

As 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

[SoCalWJS]

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?

[tasar]

  "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 ?

[dBe]

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?

The material that I used for my intersection traps is 9/16" soundboard covered with a thin raw cotton batt about an 1/8" thick.  Any fabric will be OK as long as it doesn't have a rubberized backing.  Size should be from about 16" to 36" on a side (triangular) depending upon room size.  I find that 20 -24" works very well in most rooms.  Fit them as flush to the walls as possible on each side.  Fill the cavity formed behind them and then you are done.

Cathedral ceilings are better but still have the 90 degree corner formed by the fron and side wall.  You will be amazed at the improvement.

Dave

[dBe]

Still failed.  I'll try a seperate post.

Arrrgggggghhhhhhhhhhhhhhhhhh.  I hate it when the forum software is smarter than me.......

Dave

[dBe]

  "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 ?

******************** OK - here is the deal:  The software does not like some of the hyperlinks I tried to add, so trust me when I say that a modified Type A mounting is mounting the appliance on a 3/4" - 1" thick furring strip...

*******************




I believe in dual purpose everything when it comes to room treatment where possible.  When applying any type of absorbent or semi-rigid material the reactivity of the appliance can be greatly improved by using the spaced mounting method.  Mounting with a 3/4" - 1" space is called a "Modified Type A" mounting.  Here are some other examples form a worthy competitor:

Just going to a piece of 3/4" ply at the onset is not a great idea without listing to and measuring the room to determine the problem areas.  If it is a mid to upper bass problem, it might be better to use a more flexible, less dense material.  The low bass is where the mass of a heavier loading material can be very beneficial.  Mounting them with a Mod A is the deal, though.

 

"how does one know(w.o. analysis) how big (area) these self built panels need be ? Room's cubic volume ?"  If only.  There are too many variables in rooms and room construction methods to give a short answer other than measure it or listen to it with a calibrated ear.  After doing this for a while it is pretty easy to determine the problem areas through listening tests, but to really nail it one should use any of the freeware room measurement software that is available.  I can tell you this, though: all modes terminate in the corners (boundary intersections) of rooms.  That is why you will see tube traps and corner absorbers of other types in most well designed rooms.  The other locations fro trapping is at 1/4WL (midwall and ceiling) and other nodes.  Check out some of the Java applets and the devices at the site I listed above:  http://demonstrations.wolfram.com/topic.html?topic=Acoustics&limit=20  Visualization is our friend, especially if you don't want to build a wave tank like I did to figure a lot of this out.

 

Your front corner intersections still have the wall to ceiling angle.  You are WAY ahead with the angled wall, though.  Could be that a simple absorbent strip 1' wide at the ceiling wall intersection will do the trick.  Better yet, diffusers fromjust below midwall to the ceiling like I showed in the drawings I sent are THE deal for those areas.  Since you have the Super V's a bit more "cut 'n' try" approach is going to be needed in your room.  You can tell us what works with them.  Open baffles are completely different animals from monopoles.

 

Same goes for the mass loading of corner treatment.  You gotta try it to suit the construction of the room as well as the speaker's characteristics.  Poured walls are way different from 2x4 or 2x6 frame construction.  Wood studs are different from metal studs.  Each room is a specific problem waiting to be solved. 

 

The best place for an amateur acoustician to start is with a good book on acoustics and measurement software.  The principles are easy once the physics are understood.


Dave

[dBe]

Here are basic mounting types:





What a struggle.

Dave

[TRADERXFAN]

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?)

[dBe]

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?)

Yes and no -  modified "Type A" is with a 3/4" - 1" spacing - the furring strips can be anywhere behind the material and are usually limited to 2 verticals.  Type D is with the furring strips surrounding the material creating a cavity behind the material with a top, bottom and 2 sides essentially creating a sealed (except for the characteristics of the material) cavity.  The Type D fixes the material at its' extremities.

BTW, The software deleted my last post in response to Dave (tasar)  I'm about to give up on that one.  I tried 4 times to get it to post correctly.  I'll try an edit later this evening when I get back to the house.

Dave

[nottaway]

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.

How's that?

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Dave

Hi John,

What width do the plywood panels need to be if the strips are above referenced distance apart?

Nicholas