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Constrained layer damping

Arnandsway

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Sep 13, 2018
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#1
Hi all,

For a while I've been busy trying to design a speaker for the first time. So I have learned a lot these last few months and I know it is only the surface of knowledge.
Now, my focus has shifted towards the enclosure itself and in this proces I came across this video which involved constrained layer damping, from someone probably some of you already know. (See the vid below.) It is a very interesting video for sure, so I recommend to watch it. I've linked it with a timestamp from where he shows what the effect is of dampening etc.

He explained how it can help to dampen the speaker enclosure very well.
And he also showed two products that could be used, Sorbothane (rubbery sheets very expensive though!)and Pyrotek Decidamp DC30 (two component paste as a adhesive and constrained layer). Unfortunately this product is not available in Europe, so I can't get my hands on it.

So my question to the experienced engineers/designers: do you know of alternative ways or products that could reach the same goal?

 

617

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#2
There are some good discussions from Earl Geddes on this subject on diyAudio. His recommendation is two braces from opposite sides of the enclosure overlapping, with a flexible adhesive holding them together. The idea is that you transfer the motion of the cabinet walls (in/out) into a shearing motion over a large surface area of flexible adhesive. This is essentially what CLD does - it puts a lossy, gummy material between two layers of structural material which are moving relative to one another. The differential motion between the outer layers is damped by the inner layer.

I am pretty skeptical of the conventional damping assessments looking at decay of impacts on the cabinet. The KEF LS50 whitepaper has some really good information, but essentially what they did was make a really small well braced cabinet, but undersize the braces and install them with a layer of flexible adhesive. KEF of course didn't do a 'knuckle wrap' test, or look at impact decay or use a stethoscope, they made a computer model of the cabinet rigidity vibrating at different frequencies.

Also I'm not sure what your aim is but I would steer you away from voigt pipes and full range drivers. Too many compromises.
 

Shadrach

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#3
I built laminate panel for my speakers. I used half inch marine ply and made what is best described as a tray. I filled the tray with the product below. You do in fact need to slightly over fill. Then I used another panel of quarter inch marine ply to so the Dum Dum was trapped between the panels.
Total panel thickness one and one quarter inches.
There is a theoretical problem though. Such a construction will act as a capacitor.
For the baffle I used a one and a half inch thick kitchen worktop made from composite blocks.
These are 60 liter enclosures with the crossover mounted outside the cabinet.
There are two horizontal braces and one vertical inside the enclosure.
Just an idea for you to think about.


https://www.morrisminorspares.com/b...-5kg-tin-no-longer-available-use-t18n-p828706
 

Arnandsway

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Sep 13, 2018
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#4
There are some good discussions from Earl Geddes on this subject on diyAudio. His recommendation is two braces from opposite sides of the enclosure overlapping, with a flexible adhesive holding them together. The idea is that you transfer the motion of the cabinet walls (in/out) into a shearing motion over a large surface area of flexible adhesive. This is essentially what CLD does - it puts a lossy, gummy material between two layers of structural material which are moving relative to one another. The differential motion between the outer layers is damped by the inner layer.

I am pretty skeptical of the conventional damping assessments looking at decay of impacts on the cabinet. The KEF LS50 whitepaper has some really good information, but essentially what they did was make a really small well braced cabinet, but undersize the braces and install them with a layer of flexible adhesive. KEF of course didn't do a 'knuckle wrap' test, or look at impact decay or use a stethoscope, they made a computer model of the cabinet rigidity vibrating at different frequencies.

Also I'm not sure what your aim is but I would steer you away from voigt pipes and full range drivers. Too many compromises.
Thanks for the info. I'm reading through the thread right now. This one.
Next is to find which glue to use as a constraining layer. Titebond Melamine or Sikaflex 292 is what I found in this thread, mentioned bij Gedlee.

I wonder now though it would be worthwhile to CLD the whole enclosure? I agree that the methodology used in the video seems uncrompehensive but the panels did sound much well dampened where the resonance frequency lowered.

PS. Not planning on using full range drivers. ;)
 

Arnandsway

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#5
I built laminate panel for my speakers. I used half inch marine ply and made what is best described as a tray. I filled the tray with the product below. You do in fact need to slightly over fill. Then I used another panel of quarter inch marine ply to so the Dum Dum was trapped between the panels.
Total panel thickness one and one quarter inches.
There is a theoretical problem though. Such a construction will act as a capacitor.
For the baffle I used a one and a half inch thick kitchen worktop made from composite blocks.
These are 60 liter enclosures with the crossover mounted outside the cabinet.
There are two horizontal braces and one vertical inside the enclosure.
Just an idea for you to think about.


https://www.morrisminorspares.com/b...-5kg-tin-no-longer-available-use-t18n-p828706
Are your panels 1,25" (~3,1 cm)? That seems very thick. My speakers will be monitors of about ~14L, for which I don't think this isn't necessary. I plan to run them to 100 hz anyways and cross them over to subs.

The problem with this Dum-dum (however funny the name is) is that we don't know if the acoustic dampening properties actually help reduce the ones relevant. Per say they could dampen 30-60 hz but if the dominant resonance is around 150 hz, the CLD in ths case would be irrelevant.
 

Shadrach

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#6
Are your panels 1,25" (~3,1 cm)? That seems very thick. My speakers will be monitors of about ~14L, for which I don't think this isn't necessary. I plan to run them to 100 hz anyways and cross them over to subs.

The problem with this Dum-dum (however funny the name is) is that we don't know if the acoustic dampening properties actually help reduce the ones relevant. Per say they could dampen 30-60 hz but if the dominant resonance is around 150 hz, the CLD in ths case would be irrelevant.
Yes they are one and a quarter inches thick. The front baffle is one and a half.
For an enclosure of 14 liters none of what I've done is relevant.;)
 
Joined
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#7
I have watched many of that guys videos on jet engines and drones. They are interesting and he obviously is a very intelligent person.

But note that he call a single driver set up the "2nd best speaker in the world" His "Best speaker in the World" is(was) a bass shaker motor on a panel or at least was for a while. In my not particularly humble opinion, he ought to stick to drone and jets. (Very good videos and ideas!) The notion of a bass or whatever it was , loose attachable motor being the best there is and the above are both absurdities on the face of it.

I have a lot of audiophile friends who like single driver speakers and disrespect crossovers. If I am in a frisky mood I tell them ," yeah, they are great if you don't mind having no top octave , no bottom two octave , lots of IM distortion and modulation, and not terribly much dynamic range."

The laws of physic aren't suspended because you buy a Lowther, a Voxativ nor any of the newer versions. They do work GREAT with tube amps though.;)



I am not sure that constrained layer damping is even worthwhile if you build your enclosures solidly enough. I think it is more intended for rooms and less for speaker enclosures. If you apply horizontal grade Formica (laminate , horizontal grade is thicker) with the appropriate adhesive you get a composite material that performs pretty well. This material is stronger and more isotropic than wood veneers because it does not have grain nor fiber structure. The vertical grade is thinner. If you were to laminate the inside too it would be really stiff , even if the core was just mdf.

It will probably be difficult to find an adhesive that will remain flexible for a long time. You could mimic Sorbothane with polyurethane or silicone caulk. Silicone has less peel strength the poly urethane. Both are pricey but should even be available in Europe. Silicone is more resistant to attack and polymerization crosslinking (ie age related stiffening) than polyurethane. There are PUs that have Silicone too.

Might be overkill. But sometimes overkill is fun.:):rolleyes:
 
Last edited:

Wombat

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#8
I used this on the inside of the braced MDF panels of my 14 cu.ft. enclosures. The result was a very dull, low level, 'thunk' from the knuckle-test. A big improvement.
 
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