Constrained layer damping adhesive

... it looks like a mostly relevant read - later in the thesis "5-layer" CLD is mentioned

Thank you for the reference, quite informative, "5 layer" CLD does look like it is worth consideration but it was not clear to me that this is what you had in mind.
My comments were about "3 layer" because this seemed to be the context of the discussion, I expect it's easily the most common method for speakers.
The review discussion in the paper supports my comments for a 3 layer system, as far as my initial read reveals.

Geddes claims to use...

Seems very reasonable but not common AFAIK. Do you have a link for this one too?

Best wishes
David
 
if I remember correctly Geddes somewhere says he uses a similar damping bracing technique, may cite yet another patent, and doesn't seem to think it hard to avoid the specific patent claims if he considers any valid - I wasn't clear on his position there
 
I found this: 3M VHB tape. It's a double sided visco elastic tape. Seems like an easy way to experiment with CLD.  3M? VHB? Tape 4905 Clear, 1/2 in x 72 yd 20.0 mil, 18 per case

An externally hosted image should be here but it was not working when we last tested it.


It's about 10 euro for a square meter in 0.2 mm thickness. And can be bought on Ebay and Aliexpress in small quantities. According to 3M it is the world toughest double sided tape. It's used in automotive to control vibration.

Could be interesting.
 
Although the structure may seem effective at attenuating vibration, at 5mm I suspect that it is working as a sandwich with an intermediate floating isolation layer, rather than true CLD.

With true CLD structures (which should work better with thin damping layers), it should be possible to screw through all of the layers, while retaining most of the vibration attenuation. If putting screws through the layers impairs the vibration attenuation abilities, the structure likely isn't CLD.

At least when using Green Glue, keeping the damping layer thickness under 2mm appears to work better - 1.5mm should be fine.
This is in response to an old thread on Constrained Layer Damping.
I'm writing because I think you have it wrong.
CLD works by shearing the damping material (CLD dead material/glue/elastomer/whatever - big boys even use lead (I have - not for speakers) - this shearing requires relative motin between the inner and outer "stiff" members.
Basically - you want the inner and outer stiff member to be as stiff as possible, and then the damping material to be as "dead" (highly damped) as possible.
If you are screwing through both layers of the "stiff layers" - relative motion is obviously being restricted.
Screwing though both layers - does create an overall stiffer structure, and the CLD material between layers will add damping - just not in the pretty CLD style.
The "standard" CLD approach is - stiff inner member supporting load, dead damping layer, and then thin but very stiff outer member.
This is how it is done in airplanes - like Boeing and Airbus.
Not trying to be a dick - just trying to be helpful.
If you have a system that works - that is cool - speakers are not as weight constrained as airplanes! - but optimized - this is the approach you want.

I am 35 year shock and vibe engineer - everything from Space Shuttle (old one and new one!) to mining equipment etc. This is how it is done at Boeing and Airbus, where CLD is used like "band aids" to solve resonance problems.

Just fyi -

Best
 
Enclosed is a pdf in Swedish from the company Swedac AB. This old pdf has been taken down from their site now but I have a saved copy of it. Swedac specalizes in acoustics and vibration damping. Vibration Damping | Swedac Their ”goo” DG-A2 is used by some loudspeaker building companies. The pdf is readable by Scandinavians (and possibly Dutch people?).

DG-A2 is an acrylic based compound like Green Glue, containing 68% water. Of interest is its shear strength of 1,10 N/mm², their recommendation of applying a 1 mm layer with spatula before the sheets are put under pressure of about 0,5 Kp/cm² for 4-6 hours at 20 deg C. For best damping the sheets should be of equal thickness but differences up to 1:3 has shown good damping as well. Because of the viscoelastic properties of the damping layer, the total thickness should for symmetric layers be increased by 50%, for assymetric layers by 30%, -this compared to 1 solid sheet and if one wants to keep the same bending strength as for the solid sheet.

So, if one can find a ”goo” with shear strength around 1,1 N/mm², it should be roughly equivalent to DG-A2 as long as it doesn’t harden over time. (I myself used a "special glue" from Loctite / Henkel when i built my speakers.)

Some translations for the diagrams: Odämpad = undamped, Dämpad = damped, Förlustfaktor = loss factor, Efterklangsförlopp = decay rate, Dämpskiktets = the damping layer, Reduktionstal = reduction factor (number)
 

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It was mentioned that Dr. Geddes uses titebond melamine. He doesn't use it and doesn't suggest using it. He has mentioned that he uses a two part shore a poyurethane. It's been mentioned in other threads, by other members, that sikaflex marine as well as sikabond construction may be good substitutes.
 
Hi Alfaman1: Thank you for your comments. I've mostly experimented with CLD for speakers, tonearms, turntables, and phono cartridges.

While I agree that the connection between the outer and inner layers should not prevent horizontal (shearing) motions from occurring, I have found the damping effectiveness to be augmented by some measure of vertical compression, hence my previous comment about "screwing through all of the layers". (Granted, this could be an artifact of the particular structural and damping materials that I have worked with.)

If the screws are inserted from the inner layer (inside the speaker cabinet), and the screwholes are made a little larger than the screw shafts, vertical compression can be added without completely taking away the inner layer's freedom of horizontal motions (don't over-tighten the screws). For the same reason, I prefer pan, truss, round, or button screw head types rather than flat or oval screw heads.

If you feel that even this is excessively limiting the inner layer's freedom of horizontal motions, I'd like to hear about your experiences.
 
Hi folks.
The original discussion was about green glue.
I assume the type of gg mentioned is the super runny snot recommended for use between layers of drywall, but where i live they also sell gg sealant. This item is supposed to be applied at the drywall joints, which i assume would mean it is less runny.
Anyone had experience using the gg sealant?
I will be using it in my sound room when i get to the drywall stage but have not opened the tubes yet to see it's consistency.
 
For my next build I have been looking for CLD materials and vapour barrier glue seems very promising. It never really dries and remains very viscoelastic - you can stretch it and it returns to its original shape, but very slowly. Its also extremely sticky and seems to hold plywood sheets together really well.

I haven't done any scientific testing of course, but I build several different CLD bracing and panel prototypes using various materials (leftovers from my house build) which I have then been bending, vibrating, bouncing stuff off of them etc in various ways just to see, hear and feel what happens.

Here's what I have "tested", all of them sandwiched between two sheets of 6 mm birch plywood:

- Reference single sheet plywood
- Reference two sheets of plywood glued together with normal PVA wood glue

- 1 mm felt covered bitumen glued with contact glue: Clearly more damped than the references, but still very "bouncy" compared to the best samples

- 1 mm felt covered bitumen glued with Pattex all purpose glue: Same as with contact glue

- Silicone: Super bouncy, like a trampoline, zero damping

- Non-expanding PU foam glue ("perimeterkleber" here in Germany, meant for gluing styrofoam to concrete walls): Average damping, very difficult to use

- Pure contact glue: Little difference to PVA glue, almost no damping

- Five layers of aluminium tape: Very low damping

- Soudal MS polymer flexible "extra strong"construction adhesive: Very little difference to the PVA reference, very little, if any, damping

- 3M VHB tape: Average damping, good strong bond

- Lugato Fester Halt acrylic sealant: Good damping, very strong bond

- 1 layer of butyl tape: Good damping

- 2 layers of butyl tape: Very good damping, test pieces seem "dead"

- Bitumen based "cold glue" (used to glue bitumen roof shingles): Very good damping, strong bond but long curing time, test pieces seem "dead"

- Vapour barrier glue: Very good damping, test pieces seem "dead"


So there you have it. Maybe this helps someone. I think it would be interesting to make a couple of test boxes and measure them with an oscilloscope and acceleration sensor for example in addition to listening. I might do this, but I'd first have to buy an oscilloscope and learn how to use it...
 
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Thank you, Kimi, for sharing these very interesting results. Quite recently I tried researching which glue is suitable for that task myself and also stumbled over Bostik bitumen cold glue. However, in the datasheets was written that only bricks, concrete and so on are suitable substrates. I just assume they didnt have CLD in mind when writing those. In your experience, does it stick well to wood and metal, too? I am also concerned about the odor since it is bitumen after all and speakers usually go to the living room. Is there any noticealbe odor left after letting it dry for, say, a month?


That vapour barrier glue also sounds interesting. Do you remember which glue you used exactly? I am from Austria and quite likely they sell the same stuff here. Does this stick well to wood and metal and is there any issue with odors?
 
Thank you, Kimi, for sharing these very interesting results. Quite recently I tried researching which glue is suitable for that task myself and also stumbled over Bostik bitumen cold glue. However, in the datasheets was written that only bricks, concrete and so on are suitable substrates. I just assume they didnt have CLD in mind when writing those. In your experience, does it stick well to wood and metal, too? I am also concerned about the odor since it is bitumen after all and speakers usually go to the living room. Is there any noticealbe odor left after letting it dry for, say, a month?


That vapour barrier glue also sounds interesting. Do you remember which glue you used exactly? I am from Austria and quite likely they sell the same stuff here. Does this stick well to wood and metal and is there any issue with odors?

Hi Troy,

I haven't tried the bitumen glue with metal, but I'm rather sure that it sticks to anything. Especially well to skin.

My bitumen glue is a solvent free one from Mem and even when fresh it has very little smell and already after a couple of days doesn't smell at all.

I brushed on two layers of it to both plywood pieces letting them dry a few hours between layers and then applied third layer, clamped the pieces together with a few spring clamps and let them dry for a day or so. I can't pull the pieces apart.

The vapourbarrier glue is Domofix Dampfbremsenkleber polyacrylat-dispersion. It doesn't smell at all even if I stick my nose right in to the glue line (it says Geruchsneutral on the cartridge, too). Again I haven't tried it with any metals, but it's also so bloody sticky that I'm sure it works with almost everything.
 
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