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Constrained layer damping adhesive
Constrained layer damping adhesive
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Old 22nd July 2019, 03:50 PM   #71
Adhoc1 is offline Adhoc1
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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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File Type: pdf Swedac DG-A2 dämplim.pdf (33.1 KB, 15 views)

Last edited by Adhoc1; 22nd July 2019 at 04:01 PM.
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Old 22nd July 2019, 04:03 PM   #72
BradH is offline BradH
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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.
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Old 22nd July 2019, 05:07 PM   #73
jcarr is offline jcarr  United States
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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.
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Old 27th July 2019, 04:10 PM   #74
BradH is offline BradH
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By the way, Adhoc, I wanted to thank you for your info here and in other posts. One of the best versed in CLD for speaker building.
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Old 27th July 2019, 09:36 PM   #75
Top Shelf is offline Top Shelf  Canada
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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.
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Old 27th July 2019, 11:13 PM   #76
ScottG is offline ScottG  United States
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I'm pretty sure that I remember from my childhood:

-runny snot dry's hard.

Not a good long term solution.
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