I originally made a similar post in the Room Acoustics forum; however, there appears to be a lot more discussion of CLD in this forum. (Pretend the room is a big speaker enclosure – just kidding.)
I am remodeling my family room and want to make it a better “listening” environment for stereo and future multichannel. About ten years ago I read Earl Geddes excellent book “Premium Home Theater” and one of my big takeaways was his recommendation to use CLD in a listening room to absorb bass while preserving midrange and treble liveliness. Although Geddes also recommends CLD for sound isolation - that is not my objective, since one corner of the room has an open ½ flight of stairs up to the middle level of our home with no good way to enclose it.
Tentative plan is to incorporate CLD into the ceiling, the front wall and one sidewall of the 8 x 14 x 24ft room. Sound isolation clips would be attached to studs/ joists with 7/8” steel hat channel attached a maximum 4’oc and spaced a maximum 2’ apart. Two layers of lightweight ½” drywall separated by a suitable damping compound (Green Glue?) would be attached to the hat channel.
Is this a worthwhile endeavor to hopefully preclude the need for standalone bass absorbers, multiple subwoofers, room correction software, trial & error measurements, etc?
Is this a good design? Am I on the right track with the following design assumptions?
Increase the flexing of the constraining layers (and thus energy absorption via CLD) by decreasing the stiffness and mass of the constraining layers.
Reduce the strength of reflections into the “listening” room by decreasing the stiffness and mass of the constraining layers.
The damping compound that is used between the constraining layers should have very good adhesion and be more viscous than elastic so that energy is absorbed rather than returned to layers.
Minimize the Resonance Frequency of constraining layers by increasing mass and decreasing stiffness.
I am remodeling my family room and want to make it a better “listening” environment for stereo and future multichannel. About ten years ago I read Earl Geddes excellent book “Premium Home Theater” and one of my big takeaways was his recommendation to use CLD in a listening room to absorb bass while preserving midrange and treble liveliness. Although Geddes also recommends CLD for sound isolation - that is not my objective, since one corner of the room has an open ½ flight of stairs up to the middle level of our home with no good way to enclose it.
Tentative plan is to incorporate CLD into the ceiling, the front wall and one sidewall of the 8 x 14 x 24ft room. Sound isolation clips would be attached to studs/ joists with 7/8” steel hat channel attached a maximum 4’oc and spaced a maximum 2’ apart. Two layers of lightweight ½” drywall separated by a suitable damping compound (Green Glue?) would be attached to the hat channel.
Is this a worthwhile endeavor to hopefully preclude the need for standalone bass absorbers, multiple subwoofers, room correction software, trial & error measurements, etc?
Is this a good design? Am I on the right track with the following design assumptions?
Increase the flexing of the constraining layers (and thus energy absorption via CLD) by decreasing the stiffness and mass of the constraining layers.
Reduce the strength of reflections into the “listening” room by decreasing the stiffness and mass of the constraining layers.
The damping compound that is used between the constraining layers should have very good adhesion and be more viscous than elastic so that energy is absorbed rather than returned to layers.
Minimize the Resonance Frequency of constraining layers by increasing mass and decreasing stiffness.
I think you have the perspective backwards Allen ... the whole idea is that the constraining layer prevents movement and vibration and thus limits the re-transmission of sound.
Allowing the panels to move in order to activate the constraining layer totally undoes the entire purpose of sound damping.
I'm in agreement with Allen on this issue. High sound pressure causes the CLD to flex, which creates shear strain between the layers and plastic deformation of the damping compound which is converted to heat energy. Low sound pressure (when the wave is 180 degrees out of phase) causes flex in the opposite direction, and more shear strain, deformation, and conversion to heat.
CLD will not work if the mastic is fully elastic since the energy of deformation will be fully returned to the room as the CLD "springs" back when the wave is 180 deg out of phase.
CLD will not work if the mastic is fully elastic since the energy of deformation will be fully returned to the room as the CLD "springs" back when the wave is 180 deg out of phase.
Hi, sondans
I used Green glue in remodeling my living / sound room. It works very well and isolation of the beams from the plywood or sheet rock is the way to go. I made sound adsorbing panels using Corning 700 series 2' x 4' fiberglass panels. The 700 series has different densities, do a little reading as for which grade will work for your purpose. Another material is cotton matting (recycled blue jeans).
Steve Guttenberg ( audio club member ) shot a video of my speaker project and room construction. Perhaps some of this info would be helpful to you.
YouTube
Good luck with your project
Joe
I used Green glue in remodeling my living / sound room. It works very well and isolation of the beams from the plywood or sheet rock is the way to go. I made sound adsorbing panels using Corning 700 series 2' x 4' fiberglass panels. The 700 series has different densities, do a little reading as for which grade will work for your purpose. Another material is cotton matting (recycled blue jeans).
Steve Guttenberg ( audio club member ) shot a video of my speaker project and room construction. Perhaps some of this info would be helpful to you.
YouTube
Good luck with your project
Joe
Yes that is the principle as described many times.
But that is not the purpose. You do not use this stuff to treat sound inside a room. It's not a giant bass trap. You use it to keep sound from getting out of a room... to render the walls more inert to prevent sound from passing through them.
It is sound proofing not room treatment. Inside the room itself CLD will make little or no noticeable difference.
Then: As I've explained repeatedly, now across two forums, in your case you have this large stair case rising to the mains of your house that you cannot reasonably enclose... this is going to let sound out of the room, and into the rest of the house no matter what you do.
Seriously, go ahead and do it if you want. But there are far better ways of wasting your money.
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Nope. You are thinking about the wall absorbing sound... it won't do that. It will block sound from passing through itself, but it does that by reflecting the sound back into the room. In fact, it could make room modes worse because it is still a hard smooth surface.
There is a very real difference between sound proofing and sound treatment. Sound proofing attempts to stop sound from escaping, sound treatment attempts to deal with echos and reflections inside the room.
If you want to kill room modes you basically have two choices ... diffusion or absorption, neither of which is a function of CLD. The difference in room modes noted by gedlee is far more likely to be due to changing the size of the room.
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So what happens if you laminate a panel of plywood to a thick panel of Aluminum with lots of bolts and no glue? It still damps, right? the movement of the two panels is constrained. each panel has a different resonant frequency yet they aren’t allowed to move relative to each other. So what happens? It’s not a sum of the two resonant frequencies. I assure you if you tap it, the aluminum won’t ring like a bell, the way it would if it were’‘t attached to the plywood. And the plywood won’t resonate the way it would if not attached to the alúminum.
Hmm, isn't a "Bass Trap" something designed to "drain"/"sink" specific modal build-up (pass-band) in specific locations within a room?
To some extent (depending on the application) the layer designed to be the "visco" layer between the two panels (wall and floating-damper) could do this (though to what degree would be anyone's guess). Ex. 3/4" sheet rock wall with 1/2" carpet pad with 1 1/2" of stacked sheet rock floating on carpet pad. (..carpet pad and glue would have to be very good as far as fire-proofing though.) Just having that 1/2" air-space between the wall and the panel is going to "sink" at least some of the boundary build-up between all room "edges".
Beyond that of course you are also suppressing the walls from generating additional pressure as the walls "flex".
It might be more interesting though to treat the wall itself from "stud-to-stud" as it's own tuned bass-trap in addition to the above. (..better sealing and then doing a "tuned labyrinth" inside each wall cavity.)
To some extent (depending on the application) the layer designed to be the "visco" layer between the two panels (wall and floating-damper) could do this (though to what degree would be anyone's guess). Ex. 3/4" sheet rock wall with 1/2" carpet pad with 1 1/2" of stacked sheet rock floating on carpet pad. (..carpet pad and glue would have to be very good as far as fire-proofing though.) Just having that 1/2" air-space between the wall and the panel is going to "sink" at least some of the boundary build-up between all room "edges".
Beyond that of course you are also suppressing the walls from generating additional pressure as the walls "flex".
It might be more interesting though to treat the wall itself from "stud-to-stud" as it's own tuned bass-trap in addition to the above. (..better sealing and then doing a "tuned labyrinth" inside each wall cavity.)
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IMHO you should start your project with some basic calculations, if you are triyng to convert sounwaves into heat with mechanical frictions. Walls surfaces can be considered as passive radiators that mechanically convert mechanical motion into heat in the spider, therefore the restriced BW abilities inherant to the mechanical construciton of the radiator (yes, a radiator acutated by the air) will be your early approach in the quest of the soundwaves capture no ?
A kind of T&S calculation without any electrcicity
A kind of T&S calculation without any electrcicity
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I believe so, often seen used in room corners, I don't understand why, who's listening position is in the corner?
Interesting, references please. Can the bass build up in a corner then propagate back into the room?
Agreed that the premise is to prevent movement/vibration. But in a real world system, does it not result in *some* amount of movement to shear the constrained layer?
I would think that any vibrational energy in a CLD panel would tend to be transformed, no matter how that energy was imparted into the panel.
I could see where the layers would need to be designed differently for this purpose than those in a panel for a speaker enclosure. There's less incident energy (or should I say pressure?) across the room and no direct excitation by the connection to the driver frame, etc.
I would consider a speaker baffle as a direct radiator when excited by coupling to the driver frame. There's no "escaping" sound due to this portion of the system energy.
If I'm not mistaken, it's more significant than the amount of energy transmitted by enclosure panels vibrating due to internal pressures.
First principles. Model a volume as a resonator and corners are where the energy piles up.
Say it in as many ways as you want, you're not getting it: CLD works by maximizing vibration into a highly lossy medium, whereupon its converted into heat. Fiberglass insulation damping works exactly the same way on a fiber level (vibrations turned into heat), albeit not as spatially efficient, if easier on the wallet. If the energy is coupled into the panel and converted into heat, how is it able to reflect or transmit?
Drywall-green glue-drywall is a CLD, albeit not a great one, as the drywall panels themselves aren't terribly stiff (but lossy unto themselves), but proof is in the pudding in that it works pretty well.
So a CLD absorber panel would ideally:
1.) acoustically couple VERY well to the air. If it's reflecting it's not coupling.
2.) convert coupled energy into heat.
I haven't make an absorber panel as such but pretty clear what Earl is advocating. OP -- think hard about using *thin* *stiff* materials for the CLD sandwich, you want them to be very low loss (to maximize transmission into the loss/shear layer)
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^ Yup! It would matter in terms of transmission to another room and dumping absorption there an effective way of pulling energy out of the modes, but if you're not begin bothered at the listening position, then it's not an issue. If you're designing a room for as large of a "sweet spot" as possible, then I'd argue it's where you want to focus.
Perhaps I missed the thrust of your question.
Perhaps I missed the thrust of your question.
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