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Multi-Way Conventional loudspeakers with crossovers

constrained layer damping with MDF and Ply
constrained layer damping with MDF and Ply
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Old 26th April 2015, 04:58 PM   #71
twinter is offline twinter  United States
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Per Gedlee, the "core" damping layer is generally very compliant compared to the stiff bottom base and top constraining layers. For example, Green Glue is very compliant, almost a liquid, as it has to deal with sheetrock wall resonances in the 5 to 20 Hz range. Depending on construction, loudspeaker wall resonances start around 160 Hz and greater. Most commercially available resin/polymer vibration damping products are not provided with sufficient technical information to ensure an informed selection for thick wall plywood & MDF applications. The SWEDAC DG-A2 product I referenced earlier is an exception, supplying good thorough specifications. Numerous patents, bucoo, have been applied for damping resins in the last 20 years. These are generally are for polyurethane or epoxy resins. These patents are published with very informative information enclosed. Including damping loss factors plotted versus temperature, Tg's, formulations, etc. However, this information has not carried over into the application information for consumer, commercial, and industrial damping products. Frustratingly the technology is here, just not being broadcast.

If I had to guess on a current widely available product for the damping layer in CLD for loudspeaker walls, the Sikaflex line of polyurethane adhesives look promising. Maybe Sikaflex 292 or other similar products in that family. Why? 1) It a polyurethane which has natural damping characteristics. 2) It has a glass temperature, Tg of -40C (found on one of the product datasheets) which corresponds to a damping range in the vicinity of room temperature. 3) It has a Shore A hardness of 55. In one of the patents by Henkel (see link below), they were developing a line of polyurethane resins with effective damping in the 10 to 400 Hz range at room temperature. The resins had Shore A hardnesses mainly in the 40 to 60 range. Hardness is not the same as stiffness, but for compliant materials there is a relationship. 4) Sika lists "Vibration and sound damping properties" in the product datasheet (not MSDS) for the 292 adhesive. I e:mailed the Sika technical department for clarification or measurement data of the damping properties. They replied that the damping properties for Sikaflex 292 were not measured. Again, the technical information provided by Sika does not guarantee that Sikaflex 292 is a very good selection for damping in a CLD application.

Patent US20120115998 - Adhesives with acoustic damping effect - Google Patents


Others have mentioned other products for CLD that have been effective for them, such as Titebond Melamine Glue (our Gedlee) and DAP Alex Plus. They're definitely worthwhile to consider. Being retail products, they offer little technical information in their product datasheets to help with any assessment.

Last edited by twinter; 26th April 2015 at 05:27 PM.
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Old 26th April 2015, 06:35 PM   #72
gedlee is offline gedlee  United States
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I gave up on the melamine glue a long time ago. I developed my own adhesive that sounds an awful lot like the Silaflex you describe above. Basically it is the filler that yields good damping - lots of small particles rubbing against one another.
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Old 2nd May 2015, 01:22 AM   #73
xandresen is offline xandresen
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I documented a CLD technique I use for cabinets in an HTG thread this March. Suitable for home builders.

http://www.htguide.com/forum/showthread.php?42597-Constrained-layer-cabinet-walls-%28bathroom-tile-as-constraining-layer%29

I once built a pair of similar cabinets using Green Glue. Was a disaster. The inner and outer layers seemed decoupled, the Green Glue added much mass, resulting in flexy walls with low resonant frequencies. Green Glue never dries (consistancy is sort of like vasoline jelly) and soaks a bit into the MDF so you can't get it off and start over.
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Old 9th May 2015, 04:01 PM   #74
twinter is offline twinter  United States
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Located two companies in the USA with vibration damping products that are effective for plywood and mdf panel applications, Pyrotek Noise Control and Soundown. These products are commercial/industrial products, which is reflected in their prices and order sizes. These products are not inexpensive, but will perform. No blind guesswork with the associated hoping and praying that it works.

Pyrotech Noise Control - Decidamp Line :
Decidamp, Aluminium Vibration Damping Panels

Constrained Layer Damping Products

Damping Compound, Decidamp DC30; #17051066-3; 2 parts: 11 kg total, US$188
http://www.pyroteknc.com/download/De...%2009_13EC.pdf

Self Leveling Compound, Decidamp SLC; #1705108-1-C; 2 parts: 14 kg total; US$199
http://www.pyroteknc.com/download/De...15ratioSLF.pdf

Damping Layer Roll with polyester fiber outer layers, Decidamp FDF; #175053024, 2.5mm X 1.2m X 2.45m (dimensions from rep) ; #17053024; US$94
http://www.pyroteknc.com/download/De...142IP_logo.pdf

Extensional Damping Products

Damping Tiles, 12" X 12"
http://www.pyroteknc.com/download/De...1014adhesv.pdf

Decidamp Tile, 3/8" Thickness; #17051084; US$19 ea.
Decidamp Tile, 1/2" Thickness; #17051085; US$25 ea.
Decidamp Tile, 5/8" Thickness; #17051086; US$32 ea.



Soundown
Soundown Vibration Damping Sheets and Tiles -
Products may take up to 6 weeks delivery if importation is required.

Constrained Layer Damping Products

Viscoelastic Glue DG-A 2; SWEDAC; Water base acrylic; US$56/gal
http://www.soundown.com/Product%20Line/Adobe/dgaweb.pdf
http://www.revintage.se/dga2.pdf
SWEDAC Swedish Acoustic Products Innovation AB

Damping layer SWEDAC DG-U 6, SWEDAC, 2 part polyurethane - 11.5 kg total; US$259
http://www.revintage.se/dgu6.pdf

Extensional Damping Products

Damping Tiles, 12" X 12"
http://www.soundown.com/images/2.3/d...10%201%20A.pdf

Damping Tile, 3/8" Thickness; US$19 ea.
Damping Tile, 5/8" Thickness; US$30 ea.

Last edited by twinter; 9th May 2015 at 04:14 PM.
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Old 13th February 2018, 07:25 PM   #75
Patrick Bateman is offline Patrick Bateman  United States
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For the past five years, I've been using mortite mostly. I'm REALLY happy with the results. Particularly with 3D printed enclosures, it makes a night and day difference.

I use a layer of mortite on the inside wall of the enclosure, covered with an additional layer of fiberglass.

This thread has me thinking there's room for improvement.

First, it sounds like the inner and outer layer of the sandwich should be identically stiff.

Second, the part I don't really understand is why I should use a polyurethane glue instead of mortite. Mortite is soft, it never gets hard, it's readily available and it's cheap. What's not to like?

I understand that mortite WILL harden if exposed to air for a few months, but I never let that happen. The sandwich is airtight.
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Old 13th February 2018, 09:09 PM   #76
xandresen is offline xandresen
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Patrick
constrained layer damping (CLD) occurs

1.when we force the inner layer to flex. generally this requires panel stiffness on both sides of that layer. having owned several fiberglass boats, plain fiberglass is not a stiff panel material. boats use a stiff core panel (often plywood or end grain balsa) inside the fiberglass when they need a stiff flat panel.

2. when the inner layer has what is called "viscoelastic" properties. This means it changes shear flexure from bending into heat, rather than acting as a near perfect spring (MDF, Baltic Birch, etc.).
The suggestion of Sitkaflex 292 polyurethane adhesive is based on data sheet indications that it may have this property, in the right amounts, after it sets up. I do not know if this is true. Each poly product is likely to be different so try one's choice in a test panel.

Polys need moisture to cure.

One possible issue: I have used a different Sitkaflex poly adhesive/caulk in boat building. Trying to spread a uniform thickness layer of that one would have been difficult.

I am not familiar with Mortite so can't comment on it. As I mentioned, I did try Green Glue which never hardens. It decoupled the inside and outside cabinet layers. A CLD construction bonds all three layers tightly together.
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