I am remodeling my family room and want to make it a better “listening” environment for stereo and a future multi-channel system. Many years ago I read Earl Geddes book “Premium Home Theater” and one of my big takeaways was his recommendation to use CLD to absorb bass while preserving midrange and treble liveliness. Although Geddes also recommends CLD for sound isolation it is not the highest priority for me since one corner of my room has an open ½ flight of stairs to the kitchen with no good way to enclose it.
I am planning to incorporate CLD into the ceiling, the front wall and one sidewall using isolation clips, 7/8” steel hat channel plus 2 layers of drywall with visco-elastic mastic. My room is about 8ft x 14ft x 24ft.
Is high mass of the constraining layers needed for optimum bass absorption? There seems to be plenty of data (and science) indicating that high mass is very important for sound isolation (which makes sense) but I don’t know if that is also the case for low frequency absorption. Lightweight ½” drywall is readily available and I would consider that a diy project; however, installing 4ft x 14 ft sheets of high density 5/8” drywall on the ceiling is more than I want to tackle and I would hire that out. (All butt joints can be avoided by using 14 ft lengths.)
Any other thoughts on my plan would also be appreciated.
I am planning to incorporate CLD into the ceiling, the front wall and one sidewall using isolation clips, 7/8” steel hat channel plus 2 layers of drywall with visco-elastic mastic. My room is about 8ft x 14ft x 24ft.
Is high mass of the constraining layers needed for optimum bass absorption? There seems to be plenty of data (and science) indicating that high mass is very important for sound isolation (which makes sense) but I don’t know if that is also the case for low frequency absorption. Lightweight ½” drywall is readily available and I would consider that a diy project; however, installing 4ft x 14 ft sheets of high density 5/8” drywall on the ceiling is more than I want to tackle and I would hire that out. (All butt joints can be avoided by using 14 ft lengths.)
Any other thoughts on my plan would also be appreciated.
Damping via CLD requires movement. Mass alters that, but less so at bass frequencies. Don't make the constrained layer so thick that it moves too freely without producing heat.
Sounds sensible.
Thanks AllenB.
Intuitively it seems to make sense that more mass and higher flexural stiffness would result in less flex and thus less absorption. On the other hand, if there is too little resistance to flex it might start absorbing some of the higher frequencies that I want to preserve.
I am currently considering using Green Glue for the constrained layer. It seems quite pricey so economics should help me avoid overdoing it. Interestingly, it is quite a bit less pricey than some of the other visco-elastic materials discussed in the speaker forum such as Sikaflex and 2K Urethane but of course I will be using much greater quantities.
Intuitively it seems to make sense that more mass and higher flexural stiffness would result in less flex and thus less absorption. On the other hand, if there is too little resistance to flex it might start absorbing some of the higher frequencies that I want to preserve.
I am currently considering using Green Glue for the constrained layer. It seems quite pricey so economics should help me avoid overdoing it. Interestingly, it is quite a bit less pricey than some of the other visco-elastic materials discussed in the speaker forum such as Sikaflex and 2K Urethane but of course I will be using much greater quantities.
Not much danger in flexing walls absorbing high and upper mids.
In fact the flexing will absorb upper and lower bass like a diaphragm membrane absorber.
What you call CLD, I call a layer of Mass Loaded Vinyl (MLV) mistakenly trapped between two layers of drywall (such as QuietRock). It works but that layer would much more effective left loose and floppy like a shower curtain behind the drywall. If in doubt, just look at the many illustrations and articles online.
Here is a thread where I posted a few things.
The Search For A Simple Solution With Paper Thin Walls -
Audionirvana.org
If you just want to add mass there are extra dense drywall/gypsum board products out there just for that purpose, you may have to special order.
To use MLV on an existing wall I plan on using simple wood furring (1/2" x 2" approx.) secured to existing studs, covered over with MLV (not stretched), cover that with material of choice, drywall, decorative plywood and so forth.
If you want to get a little fancy you can try using resilient hat channels in lieu of wood furring, or deeper furring that allows a layer of rock wool between the furring strips.
An air-space layer on one or both sides of the MLV allows it to work even better.
Mass Loaded Vinyl MLV | Soundproofing Products
An externally hosted image should be here but it was not working when we last tested it.
To recap: Flexure of MLV and or drywall and or thin plywood is what absorbs sound energy, as non-intuitive as that sounds, it's true.
Analogy, which absorbs more energy the baseball bat or the catcher's mitt?
The baseball bat transfers energy effectively to the ball and reverses it's direction and out of the ball park if you get lucky.
The catcher and his mitt absorbs the ball's energy thereby halting it's forward progression.
So ask yourself if you want bass energy bouncing around your room (in an opposite direction of the source), or have the walls absorb that energy and thereby preventing it from escaping and disturbing people outside of the room?
Sound Barrier/MLV-FAQs dispels the myths about MLV
Last edited:
Mass Loaded Vinyl and the Correct Uses for It
Mass Loaded Vinyl and the Correct Uses for It | Acoustical Solutions
Mass Loaded Vinyl and the Correct Uses for It | Acoustical Solutions
First, if you have a large area (the stairs) that you cannot enclose, you will always have sound rolling through there, no matter what you do. From there it will travel your house at it's own whim and will. This will almost certainly defeat any attempt at sound proofing the theatre area.
IF you are concerned about vibration on the floor above, CLD might make sense on your ceiling. In that case you don't want flex of any kind so mass+CLD makes sense. The idea of low mass and relying upon CLD is probably mistaken because CLD itself relies on some movement, which is what you're trying to block.
For the rest of it, I think more conventional methods using sound absorbers and diffusers would make more sense, conditioning the sound in the room to limit echos and resonances. While this won't prevent sound from travelling up your stairs it will at least limit the unwanted sounds before they escape.
The good news is that in-room sound management is usually a lot cheaper and easier to do. You can often do an adequate job with strategically positioned artwork, furniture and curtains. It doesn't have to look like the inside of a recording studio, unless you want it to.
A solid connection is going to transmit more energy, flex and air-spring dampening action are your friend.
Just look at the STC (Sound Transmission Coefficient) ratings on a few typical assemblies.
High Quality Metal Furring Hat Channel for Resilient Sound Clips | TMsoundproofing.com
How to Keep the Noise Down - GreenBuildingAdvisor
Regarding the open stairwell, I currently have one in my house because I have not yet built a wall and put in a door.
However, it is much more livable upstairs (stereo is downstairs) than my old house because almost all of the frequencies go up the stairwell and can be heard upstairs. This is far less annoying than in my old home where only the bass would go upstairs and it would be Boom Boom Boom.
My recommendation is that if you currently can hear everything upstairs and choose not to completely soundproof, leave it as be. Treat only what you have to in order to get good sound.
As much as I know or think I know living with the Devil you know is better than creating a new evil demon.
Last edited:
Thank you kach22i and Douglas Blake for your input.
Perhaps my post wasn't clear in what I am trying to accomplish. Preventing sound transmission to other parts of the house is not my objective. My main objective for this project is to greatly diminish the amount of low frequency sound that is reflected back into the family room. I want to do this to avoid the amplification of some low frequencies and the nulls in other low frequencies that are caused by room modes.
When a CLD wall is pressurized, the wall flexes and the mastic between the layers undergoes shear deformation (effectively converting sound energy into heat.) It is important that the mastic be predominantly viscous rather than elastic; otherwise the mastic will store that energy and release it back to the room as it returns to its original shape when the sound pressure is at its minimum.
This is the extent of my very limited understanding of CLD. What I don't understand is the relationship between the mass and flexural strength of the constraining layers and the frequency range where it is effective.
Perhaps my post wasn't clear in what I am trying to accomplish. Preventing sound transmission to other parts of the house is not my objective. My main objective for this project is to greatly diminish the amount of low frequency sound that is reflected back into the family room. I want to do this to avoid the amplification of some low frequencies and the nulls in other low frequencies that are caused by room modes.
When a CLD wall is pressurized, the wall flexes and the mastic between the layers undergoes shear deformation (effectively converting sound energy into heat.) It is important that the mastic be predominantly viscous rather than elastic; otherwise the mastic will store that energy and release it back to the room as it returns to its original shape when the sound pressure is at its minimum.
This is the extent of my very limited understanding of CLD. What I don't understand is the relationship between the mass and flexural strength of the constraining layers and the frequency range where it is effective.
If you check some of the other threads, you'll discover I experimented with CLD a long time ago in speaker cabinets. Your assessment of the goal is essentially correct. The idea is to actively counter any tendency to flex --or worse flex while flexing-- with a bonded viscous layer. I can tell you it works beautifully on speaker cabinets... you would never feel vibration on the ones I built.
I can't swear to how well that translates into room acoustics. But I've seen a couple of home theatres where it was used and my reaction was kind of "Meh", not impressed. There may have been some reduction but I doubt it was what people claim... because those rooms still had lots of echos and nodes to deal with.
The goal of limiting physical low frequency vibration... the kids feet tingling on the floor upstairs when the death star explodes... makes more sense for CLD since most viscous goos (Decidamp, Green Glue, etc.) are in fact very slow moving and unable to respond to higher frequencies. Those higher frequencies don't shake the structure but they do become echos to be dealt with by other means.
I'm not sure I can give you a good recommendation other than a nice carpet with good quality underpadding. Again, the open stairs pretty much defeat any other measures.
You have more than three choices, but I will post just three to keep it simple.
WallDamp - Technical | Acoustic Sciences Corporation
An externally hosted image should be here but it was not working when we last tested it.
The above is disappointing, building an inner skin isn't going to specifically address bass, but will help, just not as much as I may have indicated earlier by STC - live and lean.
Soundoctor PROJECT 1139
The unfinished corner bass absorber above is championed by some, and poo pooed by others. I'm personally undecided.
And now the Acoustic Fields diaphragmatic absorber.
VIDEO
How To Build A Bass Trap – Acoustic Fields
Everyone is selling something in their own niche, it's hard to tell the flowers from the bull patties - sorry.
EDIT-1:
A fourth option, science backed and perhaps your best choice.
My little barn -
Audionirvana.org
Hard to believe, but those acrylic things can be ordered to treat specific bass frequencies, look it up.
Helmholtz resonators
SMT Wing Diffusors vs. QRD Diffusors? Effective? | What's Best Audio and Video Forum. The Best High End Audio Forum on the planet!
Absorbing too much bass will deaden the room and the sound, spreading the bass energy around (diffusion) so that it's inoffensive may be an attractive option.
Last edited:
AllenB,
Thanks for alerting me to resonant frequency issue.
Douglas Blake,
Your comment about not being impressed by CLD treated rooms does have me concerned. Although there are plenty of results reported on STC and transmission loss with various wall assemblies, I've seen no data on low frequency absorption using CLD. Do you think the folks in the forum on building speakers might have data on that?
kach22i,
Even though the first chart you show with relatively low transmission loss in the Green Glue wall assembly that doesn't necessarily mean that it won't help with my objective. I'm not so much concerned with how much bass is transmitted but I am concerned with limiting reflections back into the room. For that same reason I don't think the #4 option you show would work for me. A high mass, high stiffness brick wall would likely reflect most of the bass back into my room -- the opposite of what I want to accomplish.
Thanks for alerting me to resonant frequency issue.
Douglas Blake,
Your comment about not being impressed by CLD treated rooms does have me concerned. Although there are plenty of results reported on STC and transmission loss with various wall assemblies, I've seen no data on low frequency absorption using CLD. Do you think the folks in the forum on building speakers might have data on that?
kach22i,
Even though the first chart you show with relatively low transmission loss in the Green Glue wall assembly that doesn't necessarily mean that it won't help with my objective. I'm not so much concerned with how much bass is transmitted but I am concerned with limiting reflections back into the room. For that same reason I don't think the #4 option you show would work for me. A high mass, high stiffness brick wall would likely reflect most of the bass back into my room -- the opposite of what I want to accomplish.
Effect of Mass and Stiffness on Resonant Frequency, Reflections and CLD Energy Absorption
From what I have learned on this forum along with some additional information here’s a short summary of the factors that could affect my project. Given my limited understanding of the subject some of this may not be correct.
Lowering the Resonant Frequency of the constraining layers should help to minimize the occurrence of resonance. Increasing the mass of the wall and lowering the stiffness would help reduce Resonant Frequency.
Reducing the strength of reflections into the “listening” room should be helped by decreasing the stiffness and mass of the constraining layers.
Increasing the flexing of the wall should help increase the energy absorption via CLD. Increased flexing (and thus increased energy absorption) should be helped by decreasing the mass and stiffness of the constraining layers.
The damping compound that is used between the constraining layers should be more viscous than elastic so that energy is absorbed rather than returned to layers.
Conclusion: I will plan to use ½” lightweight drywall for my constraining layers. The lightweight drywall may not be ideal for reducing Resonant Frequency but should help CLD effectiveness. I’ve not decided on mastic yet but Green Glue is a possibility. I may also contact the manufacturer of my favorite interior / exterior caulk “Tower Tech 2” that is described as “urethane modified acrylic …. Internally plasticized…… with 800% elongation and excellent adhesion”.
From what I have learned on this forum along with some additional information here’s a short summary of the factors that could affect my project. Given my limited understanding of the subject some of this may not be correct.
Lowering the Resonant Frequency of the constraining layers should help to minimize the occurrence of resonance. Increasing the mass of the wall and lowering the stiffness would help reduce Resonant Frequency.
Reducing the strength of reflections into the “listening” room should be helped by decreasing the stiffness and mass of the constraining layers.
Increasing the flexing of the wall should help increase the energy absorption via CLD. Increased flexing (and thus increased energy absorption) should be helped by decreasing the mass and stiffness of the constraining layers.
The damping compound that is used between the constraining layers should be more viscous than elastic so that energy is absorbed rather than returned to layers.
Conclusion: I will plan to use ½” lightweight drywall for my constraining layers. The lightweight drywall may not be ideal for reducing Resonant Frequency but should help CLD effectiveness. I’ve not decided on mastic yet but Green Glue is a possibility. I may also contact the manufacturer of my favorite interior / exterior caulk “Tower Tech 2” that is described as “urethane modified acrylic …. Internally plasticized…… with 800% elongation and excellent adhesion”.
Okay, here's the thing... CLD construction is not intended to manage reflections or echos inside a room. It's purpose is to prevent cabinetry or walls from vibrating with changes in air pressure (sound). It is thus a sound proofing technique.
I experimented with this on a pair of home brew speakers way back in the 1970s and, yes, there are threads to read in the "Mult-iWay" forum where I've been looking into this for a new design I hope to get into this summer.
The reason I find this less impressive in room design is that unlike in a speaker where you experience the effect from the outside, you are standing inside the managed area. The effects are very different. It's a little hard to describe (as is all hearing) but my thought was that while it will limit vibrations on walls and floors adjoining the room, it does little or nothing for the room itself.
In your case you have this big opening leading out of the room. So I would find any benefit from CLD questionable at best, since the sound from that room is just going to bounce around in your house as it sees fit anyway.
To say it directly ... In your case it just strikes me as a waste of money.
Option #4 is not someone else's room, it's the Helmholtz Resonators.
The barn's masonry walls trap bass energy inside similar to typical basement construction.
Stud walls and furring on masonry flex via the drywall sheathing to absorb bass energy with air spring action.
RE: the construction chart using green glue, MLV and other stuff, as you can see there are slight improvements across the board, but nothing bass specific.
You want bass specific, then Helmholtz resonators and the Acoustic Fields box are your winners - in my opinion.
Last edited:
Exactly, I agree.
sondans, you are a candidate for room acoustic treatments (the fewer the better), and not construction solutions.
Is your family room below grade?
Is so then we have a vastly different situation here, and there are different remedies.
Such as what Joe Pittman did.
The Search For A Simple Solution With Paper Thin Walls -
Audionirvana.org
Joe Pittman;n129561 said:
Last edited:
I've eaten dinner and had some time to think about this situation.
There is a chance that with an unsealed half flight of stairs to kitchen connecting the listening room will not allow the room to be sufficiently energized or pressurized to take full advantage of something read in a book that applies to an optimized ideal or ultimate room.
Think of when they were trying to make steam engines safer, the darn boilers were blowing up and killing people. They wanted to know at what pressure the boiler would blow, so a team buried the steam engine and kept feeding.................it never blew up.
They dug the boiler up and inspected it, and discovered a small leak.
This leak lead to the implementation of steam valves that would leak out excess pressure and prevent the rupture of the boiler.
This stairway opening is your steam valve, you may never develop enough pressure in the stereo room to activate the diaphragmatic flexing of the CLD drywall system.
You don't know until you test the stereo system in the room first.
Gotta define a problem if you want to fix it.
Don't fix it if it isn't broken.
There is a chance that with an unsealed half flight of stairs to kitchen connecting the listening room will not allow the room to be sufficiently energized or pressurized to take full advantage of something read in a book that applies to an optimized ideal or ultimate room.
Think of when they were trying to make steam engines safer, the darn boilers were blowing up and killing people. They wanted to know at what pressure the boiler would blow, so a team buried the steam engine and kept feeding.................it never blew up.
They dug the boiler up and inspected it, and discovered a small leak.
This leak lead to the implementation of steam valves that would leak out excess pressure and prevent the rupture of the boiler.
This stairway opening is your steam valve, you may never develop enough pressure in the stereo room to activate the diaphragmatic flexing of the CLD drywall system.
You don't know until you test the stereo system in the room first.
Gotta define a problem if you want to fix it.
Don't fix it if it isn't broken.
Last edited:
Okay, I gotta point this out...
Constrained Layer Damping is about preventing vibration and resonance.
See the effects in THIS VIDEO (started at the relevant part)
To postulate allowing some movement or flexibility so as to deliberately activate the gum layer is to completely undo its effectiveness. The minute the three layer construct vibrates, its effectiveness is gone.
Thus CLD is a sound proofing technique intended to prevent sound from traversing from one side of the multi-layer construct to the other... to keep the sound from getting out of the treated area.
This is NOT a sound treatment for use inside a listening area. It can't be tuned to absorb bass or prevent unwanted reflections. In fact, a CLD treated wall is (in my observations) often somewhat more reflective than ordinary drywall, and may require even more aggressive treatments in the room.
I ran into a similar perspective problem when I began using Sorbothane feet under subwoofers and larger floorstanders. Sorbothane is a viscous gel that aids in preventing mechanical coupling of the woofer's vibration to the structure of the building. It works by allowing the speaker to move independently of the floor for a very small distance.
Everyone immediately rushed to test this stuff and promptly came back to me declaring "It makes no difference at all", "Everything sounds the same" and "What a waste of money".
I asked if they measured in the next room or the neighbour's apartment...
"No, why would I do that?" ...
The answer was that the gooey little disks under their speakers were not for them... they were for the neighbours. The goal was to prevent bass notes from travelling through the structure and annoying the heck out of everyone else.
The goal of CLD is the same... it is not intended to improve sound in the listening room. It is a way to give your neighbours some relief.
Sometimes you just got to look at these things the right way...
Constrained Layer Damping is about preventing vibration and resonance.
See the effects in THIS VIDEO (started at the relevant part)
To postulate allowing some movement or flexibility so as to deliberately activate the gum layer is to completely undo its effectiveness. The minute the three layer construct vibrates, its effectiveness is gone.
Thus CLD is a sound proofing technique intended to prevent sound from traversing from one side of the multi-layer construct to the other... to keep the sound from getting out of the treated area.
This is NOT a sound treatment for use inside a listening area. It can't be tuned to absorb bass or prevent unwanted reflections. In fact, a CLD treated wall is (in my observations) often somewhat more reflective than ordinary drywall, and may require even more aggressive treatments in the room.
I ran into a similar perspective problem when I began using Sorbothane feet under subwoofers and larger floorstanders. Sorbothane is a viscous gel that aids in preventing mechanical coupling of the woofer's vibration to the structure of the building. It works by allowing the speaker to move independently of the floor for a very small distance.
Everyone immediately rushed to test this stuff and promptly came back to me declaring "It makes no difference at all", "Everything sounds the same" and "What a waste of money".
I asked if they measured in the next room or the neighbour's apartment...
"No, why would I do that?" ...
The answer was that the gooey little disks under their speakers were not for them... they were for the neighbours. The goal was to prevent bass notes from travelling through the structure and annoying the heck out of everyone else.
The goal of CLD is the same... it is not intended to improve sound in the listening room. It is a way to give your neighbours some relief.
Sometimes you just got to look at these things the right way...
Douglas,
I watched the entire video. Excellent! Thanks for sharing that.
I agree with you that “Constrained Layer Damping is about preventing vibration and resonance.” However, the vibrating panels of the speaker box would generate sound both inside and outside the box and neither would be desirable. The same reasoning would apply to a much bigger box, such as a listening room. CLD should dampen vibrating room walls as well, which would reduce sound reflected back into the room as well as sound transmitted into the next part of the wall assembly to the adjoining space. At about 34:30 the “teacher” states that “damping eats up resonant energy in frictional losses as the shear inside the material produces frictional heat transfer …. to get rid of some of that energy. ‘ That is consistent with what Allen and I believe CLD is supposed to do.
A vibrating panel will produce sound waves on both sides of the panel with the sound 180 deg out of phase from one side to the other. Whether a speaker box or room you would want to dampen that vibration.
The video did leave me with some questions about my about whether or not CLD in a listening room should target a higher or lower resonant frequency? Since Resonant Freq = sqrt(stiffness/mass) do I want to target Low Freq (low stiffness/high mass) or High Freq(high stiffness/low mass). It sure seemed like the “teacher” was targeting high frequency/low mass. Assuming that acoustic pressure inside a speaker box is very much greater than a listening room perhaps you can make the wall much stiffer and still flex them even with high frequencies. In a listening room you want the walls to reflect mid/highs and flex/absorb lows. I'm still thinking as Alan suggested previously that you want less stiffness in CLD for a room or you may have trouble generating enough low frequency pressure to flex the CLD and would end up reflecting both high and low frequencies back into the room.
In your design of speakers, what did you target for resonant frequency?
I watched the entire video. Excellent! Thanks for sharing that.
I agree with you that “Constrained Layer Damping is about preventing vibration and resonance.” However, the vibrating panels of the speaker box would generate sound both inside and outside the box and neither would be desirable. The same reasoning would apply to a much bigger box, such as a listening room. CLD should dampen vibrating room walls as well, which would reduce sound reflected back into the room as well as sound transmitted into the next part of the wall assembly to the adjoining space. At about 34:30 the “teacher” states that “damping eats up resonant energy in frictional losses as the shear inside the material produces frictional heat transfer …. to get rid of some of that energy. ‘ That is consistent with what Allen and I believe CLD is supposed to do.
A vibrating panel will produce sound waves on both sides of the panel with the sound 180 deg out of phase from one side to the other. Whether a speaker box or room you would want to dampen that vibration.
The video did leave me with some questions about my about whether or not CLD in a listening room should target a higher or lower resonant frequency? Since Resonant Freq = sqrt(stiffness/mass) do I want to target Low Freq (low stiffness/high mass) or High Freq(high stiffness/low mass). It sure seemed like the “teacher” was targeting high frequency/low mass. Assuming that acoustic pressure inside a speaker box is very much greater than a listening room perhaps you can make the wall much stiffer and still flex them even with high frequencies. In a listening room you want the walls to reflect mid/highs and flex/absorb lows. I'm still thinking as Alan suggested previously that you want less stiffness in CLD for a room or you may have trouble generating enough low frequency pressure to flex the CLD and would end up reflecting both high and low frequencies back into the room.
In your design of speakers, what did you target for resonant frequency?
Have you considered the effect if the resonance is critically or over-damped?
Where this changes is when you apply it to something. The purpose gets defined and the goals become situationally dependent.
This is an electrical equivalent to the wall panel, the input terminals are the room.
