I simply made sure it was a 'glue rich' layer (wetted both sides), so I'm sure it was very thin when dry. I suppose this doesn't meet the definiton of CLD. I was working on another paradigm, at least conceptually if not in reality) where having adjoining layers of different density can diffuse energy, not truly convert to heat. My outer layer was 18mm baltic birch, and my inner layer that my vendor called 'ultralite', a very low density particle board. The ultralite would be low density and seemed to have a low velocity accoustically, the BB is relatively high velocity, and the soft glue is extremely low. Real data would, of course, be very helpful.
Real Data on this is very scarce.
The only in depth examination I've seen (other than my own) is in This Video. The meat of the materials and constrained layer discussion starts at about 25 minutes in.
It should not surprise anyone that we reached similar conclusions.
Of interest is how identical sized panels of MDF and Plywood exhibit a very different resonant tone. I've been thinking that using different materials might be an advantage since a sound that might excite one of them may not excite the other, increasing the resistance to box wall transmissions.
Clearly the elasticity of the constraining layer is a crucial part of this technique. The pull back of the elastic layer actually opposes vibrations. Too thin and it's just glue, too thick and it won't present a sufficient resistance to vibration.
Getting all this right, without real data, is pretty much a hit and miss game, right now.
The only in depth examination I've seen (other than my own) is in This Video. The meat of the materials and constrained layer discussion starts at about 25 minutes in.
It should not surprise anyone that we reached similar conclusions.
Of interest is how identical sized panels of MDF and Plywood exhibit a very different resonant tone. I've been thinking that using different materials might be an advantage since a sound that might excite one of them may not excite the other, increasing the resistance to box wall transmissions.
Clearly the elasticity of the constraining layer is a crucial part of this technique. The pull back of the elastic layer actually opposes vibrations. Too thin and it's just glue, too thick and it won't present a sufficient resistance to vibration.
Getting all this right, without real data, is pretty much a hit and miss game, right now.
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I am glad to hear you say that because I know very well that there is scant real data on this subject. I always want to see how one actually would measure these effects - because, honestly I was never able to do it after several attempts.
It has been my experience that damping the structure works best. I guess that I have said that before, but my point is that we really don't know how any of this works.
Specifically to the video, damping the material is fine, but show that this makes a measurable difference to the sound radiation.
The poly boards that I use have the most internal damping that I have seen in any material and everyone should be using it. But oh yea, did I mention that it costs 10X MDF. A bit of a downside.
As you may have noticed my own experiments with this predate the video by some 40 years (oh, man, do I feel old writing that!). I had kept detailed notes of each test but they were lost in a house fire along side the speakers themselves.
My neighbour in the duplex decided to dump frozen french fries into boiling oil and took out both our houses.
I am thus forced to do this from memory, which we all know can be somewhat unreliable at times. That is why I was so happy to see an attempt at real examination in that video. I will agree that his conclusions leave a few gaps to be filled in... but I can tell you that from my own build the sound quality was about half an inch short of amazing. It was good enough that I had people asking me to build them a set and paying a premium price for them. I was even approached by a major speaker manufacturer for more information on the technique... just before my neighbour got stupid.
I don't know if any of those early builds are still around or not.
About the only way to measure box sounds would be with REW or some other microphone driven platform, placing the microphone very close to the enclosure and taking measurements of box radiation. Measure the sound field, measure near the box, subtract, and whatever remains is the box.
The accelerometer used in the video did not exist when I was working on this. But I did get some pretty good readings by simply attaching a microphone to the panels and catching the results on a scope. My detached panel tests, similar to those in the video showed about the same results... but of course within the limits of a much cruder testing technique.
About the only real thing I can tell you is that I never once noticed any vibration on the exterior of my cabinets, and we did push them pretty hard at times.
Afterthought... I really hope the absence of valid data does not deter us from exploring a better method. I would hope it would encourage us to finish the work and fill in the gaps.
My neighbour in the duplex decided to dump frozen french fries into boiling oil and took out both our houses.
I am thus forced to do this from memory, which we all know can be somewhat unreliable at times. That is why I was so happy to see an attempt at real examination in that video. I will agree that his conclusions leave a few gaps to be filled in... but I can tell you that from my own build the sound quality was about half an inch short of amazing. It was good enough that I had people asking me to build them a set and paying a premium price for them. I was even approached by a major speaker manufacturer for more information on the technique... just before my neighbour got stupid.
I don't know if any of those early builds are still around or not.
About the only way to measure box sounds would be with REW or some other microphone driven platform, placing the microphone very close to the enclosure and taking measurements of box radiation. Measure the sound field, measure near the box, subtract, and whatever remains is the box.
The accelerometer used in the video did not exist when I was working on this. But I did get some pretty good readings by simply attaching a microphone to the panels and catching the results on a scope. My detached panel tests, similar to those in the video showed about the same results... but of course within the limits of a much cruder testing technique.
About the only real thing I can tell you is that I never once noticed any vibration on the exterior of my cabinets, and we did push them pretty hard at times.
Afterthought... I really hope the absence of valid data does not deter us from exploring a better method. I would hope it would encourage us to finish the work and fill in the gaps.
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LOL... that too.
In another thread, I have what may become an alternative use for CLD, a wall that actually rings when tapped. This you can see in REW as a big out of phase bulge at about 100hz. If we decide to go that way to solve that problem I'll be sure to post the results either here and/or in the other thread.
Troublesome wall echo
In another thread, I have what may become an alternative use for CLD, a wall that actually rings when tapped. This you can see in REW as a big out of phase bulge at about 100hz. If we decide to go that way to solve that problem I'll be sure to post the results either here and/or in the other thread.
Troublesome wall echo
I posted some data from Swedac in a previous thread: Constrained layer damping adhesive Tip: Check out the diagram for 1 solid 24 mm plywood shees versus 2 x 12 mm with the goo as 1 mm thick constrained layer in between.
Avoid very high strength glues. In genereal these turn hard after curing = transmits vibrations readily, doesn't dampen them. Something that stays rubbery with hardness 20-50 Shore A or so after curing should be OK, these can have an elangation at break around 3-6 times (possible stretching before they brake).
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Setting aside the fact that it is also acting as an adhesive that locates the panels with respect to each other, what does elasticity bring to the table?
Okay good question ...
Take two flexible sticks... like rulers or thin wood... line up the ends... then bend it into a curve. Even the smallest curvature will result in the ends of the inner piece projecting outward from the ends of the outer piece. This is an artefact of the different radii of curve. The inner piece flexes on a smaller radius than the outer piece. Of course reversing the curvature will have the end of the other piece sticking out.
By applying a viscous bonding material between the two pieces you produce an elastic reaction that opposes the end displacement making it much harder to curve the pieces.
The result is that any tendency to bend back and forth with changes in pressure inside the box is greatly reduced, producing an almost completely non-resonant cabinet.
A secondary effect is that the viscous layer between them also tends to dampen any local vibrations such as a tendency to flex more in the centre than at the edges.
You can see this demonstrated, in the video I've been posting ... YouTube
Take two flexible sticks... like rulers or thin wood... line up the ends... then bend it into a curve. Even the smallest curvature will result in the ends of the inner piece projecting outward from the ends of the outer piece. This is an artefact of the different radii of curve. The inner piece flexes on a smaller radius than the outer piece. Of course reversing the curvature will have the end of the other piece sticking out.
By applying a viscous bonding material between the two pieces you produce an elastic reaction that opposes the end displacement making it much harder to curve the pieces.
The result is that any tendency to bend back and forth with changes in pressure inside the box is greatly reduced, producing an almost completely non-resonant cabinet.
A secondary effect is that the viscous layer between them also tends to dampen any local vibrations such as a tendency to flex more in the centre than at the edges.
You can see this demonstrated, in the video I've been posting ... YouTube
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Ah the joys of language.
Elasticity is like a spring. It stores energy when stretched, then returns all this energy to the other parts of the system when released.
visco-elasticity is where some of the energy deforming the elastic material is converted to heat. The "spring" (and the CLD speaker wall) does not stretch as far as it would with no losses.
The CLD wall has similar losses as it returns to its original position, so it does not fully return to the initial position. However a resonance from a tap is a decaying sine wave (see oscilloscope in video) pushing the wall one way then back the other. So the speaker wall ends up very nearly in its initial position. Too close for us to notice the difference.
The hope of CLD construction is to find a visco-elastic material with high energy loss that stretches significantly as the wall vibrates. Too stiff (like those used with steel) and it acts like a hard glue (no losses) with MDF/plywood. Too soft and the losses are too small to damp MDF/plywood walls much. Wall stiffness(thickness) and damping layer thickness matter here as well.
hence the interest in doing studies with real materials.
Hope that adds clarity and not confusion.
Maybe a word from a specialist source is useful.
The Difference Between Elastic Materials and Viscoelastic Materials - www.sorbothane.com
The material in the damping layer needs to create as large a damping force as possible in order to dissipate the energy in the cabinets bending waves as quickly as possible. This information for a viscoelastic material is contained in a nomogram. Here at the bottom of the technical datasheet is an example plus how to read it from the company of the product in the video but for a different material. It is missing for the DC30 product and sorbothane which suggests these products are not marketed at engineers.
The reason we need a nomogram to make comparisons is because the damping performance varies strongly with frequency and temperature. Different viscoelastic materials are optimised for different jobs. We need a large damping force at room temperature over the frequency range of the lowest few cabinet resonances which is normally 500-2000 Hz. The size of the damping force follows from both the loss factor and the stiffness so we need to consider how these properties vary with frequency at room temperature and their product. The loss factor alone is insufficient.
Ideally we want high stiffness and high loss for cabinet walls but, unfortunately, high loss materials tend to be weak so we need to use a combination of materials. CLD is one way of doing this but others are to embed strong fibres in a weak strongly dissipative material. The video by the way showed a significant increase in damping but not a high level of damping. The resonant frequency was also a bit low although not to the extent of being wholly irrelevant.
A challenge for DIY folk wishing to use CLD for speaker cabinets is to find damping materials that work well, are available for DIYers to purchase and are not expensive. If folk here do work with a product like decidamp DC30 which lacks a nomogram it would be useful to post details of a knock test on a test piece like that shown in the video. A mic rather than an accelerometer/vibrometer is likely fine. As well as a decay plot the material and dimensions of the structural and constraining layer of the test piece would likely help in making comparisons.
Another issue is the strength and longevity of the bond between the layers. This needs to be strong for CLD to work unlike, say, isolation which will still work OK with a weak bond.
The reason we need a nomogram to make comparisons is because the damping performance varies strongly with frequency and temperature. Different viscoelastic materials are optimised for different jobs. We need a large damping force at room temperature over the frequency range of the lowest few cabinet resonances which is normally 500-2000 Hz. The size of the damping force follows from both the loss factor and the stiffness so we need to consider how these properties vary with frequency at room temperature and their product. The loss factor alone is insufficient.
Ideally we want high stiffness and high loss for cabinet walls but, unfortunately, high loss materials tend to be weak so we need to use a combination of materials. CLD is one way of doing this but others are to embed strong fibres in a weak strongly dissipative material. The video by the way showed a significant increase in damping but not a high level of damping. The resonant frequency was also a bit low although not to the extent of being wholly irrelevant.
A challenge for DIY folk wishing to use CLD for speaker cabinets is to find damping materials that work well, are available for DIYers to purchase and are not expensive. If folk here do work with a product like decidamp DC30 which lacks a nomogram it would be useful to post details of a knock test on a test piece like that shown in the video. A mic rather than an accelerometer/vibrometer is likely fine. As well as a decay plot the material and dimensions of the structural and constraining layer of the test piece would likely help in making comparisons.
Another issue is the strength and longevity of the bond between the layers. This needs to be strong for CLD to work unlike, say, isolation which will still work OK with a weak bond.
Viscoelastic material still exhibits elastic properties, but it does them slowly. Unlike a rubber band that snaps back at you and makes a good slingshot, Decidamp and Sorbothane do not snap back. They do return to shape and the initial deformation is very fluid but they tend to remain in a stressed state longer.
As the scope showed in the video, that first impact pulse is about the same no matter what the material is. The big question is what happens with subsequent half cycles. Viscous rubbers dissipate the energy, they don't return it.
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"Decidamp® SP150 is easy to apply by simply spraying, rolling or trowelling onto surfaces. .....
Decidamp® SP150 is a superior extensional damping compound suitable to be applied directly to structures (steel, fibreglass and alloys)".
The above quote from the Pyrotek link, makes no recommendation for Decidamp® SP150 used in a constrained layer, or on non-rigid substrates e.g. mdf, plywood. This supports the reservations of andy19191.