Yes I think you're right the data doesn't even vary a little from tests 10-24, just 'zero'.
Anyway, I'm curious if the constraining layers stiffness and thickness important or only stiffness? I presume constraining layers stiffness is more important than thickness (or mass).
E.g. Would two different constraining layer materials (say 3mm steel vs. 18mm plywood) have the same ideal damping layer, provided they have the same stiffness?
I wish there were an online calculator where you enter the constraining layer young's modulus and thickness and it will tell you the damping layer thickness to use
Anyway, I'm curious if the constraining layers stiffness and thickness important or only stiffness? I presume constraining layers stiffness is more important than thickness (or mass).
E.g. Would two different constraining layer materials (say 3mm steel vs. 18mm plywood) have the same ideal damping layer, provided they have the same stiffness?
I wish there were an online calculator where you enter the constraining layer young's modulus and thickness and it will tell you the damping layer thickness to use
Last edited:
I already said that it was the stiffness that matters. Since stiffness varies with thickness for a given material it is clear that the material and thickness can vary as long as the stiffness is the same. Generally the required composite stiffness depends on the application.
Generally the stiffness of the constrained layer is negligible, so all that matters is the stiffness of the two outside layers in parallel. Its all really basic statics of materials. Statically the damping layer is irrelevant.
Generally the stiffness of the constrained layer is negligible, so all that matters is the stiffness of the two outside layers in parallel. Its all really basic statics of materials. Statically the damping layer is irrelevant.
Sorry didn't see that, I haven't read this whole thread.
Knowing that stiffness is all that matters, once could find a good commercial example of layer damping then scale the stiffness to damping thickness ratio for a new composite.
E.g. I have seen commercial CLD steel consisting of two 1.5mm skins of stainless steel with a 0.05mm damping core. Knowing the stiffness of 1.5mm steel compared to 18mm plywood we can scale up the damping thickness accordingly, right?
Calculating the optimal damping layer thickness would take several equations, graphs and/or nomograms. See work by David I. G. Jones among others.
The optimal shear forces required in the damping layer will depend on the stiffness of the base and constraining layers. The shear forces generated will will depend on the material shear modulus (stiffness), and the thickness of the damping layer itself.
The optimal damping layer thickness for CLD will vary with the shear modulus (shear stiffness) of the damping material. Of course the damping layer will have to be in a certain range. The lower stiffness damping material will require a thinner layer, and the more stiff damping material will require a thicker layer. We're looking at a damping layer thickness range of approximately 1/2 mm to 5 mm.
See pages 3 and 4 of the link:
http://www.acoustics.asn.au/conference_proceedings/AAS2008/papers/p69.pdf
Damping depends on viscoelastic behavior of the polymer, not elastic behavior. This damping behavior occurs in the glass-to-rubber transition temperature range for the material. Polyurethanes and butyl rubber can have transition temperatures ranges around 20C/72F. This corresponds to a glass temperature, Tg, around -20C to -40C. Not all polyurethanes are well damped. Those that are damped are for a limited temperature range. Damping is indicated by the damping loss factor, tan delta, and related to the Bashore rebound test for resilience. Understanding glass temperatures, transition temperatures, modulus of elasticity varying with temperature, and loss factor varying with temperature is critical to understanding damping behavior of polymers.
Pure epoxies are not naturally well damped. Also, they're Tg's that are too high for damping at room temperature, 20C. However agents such as flexibilizers can be added to add damping and low the Tg to achieve significant damping at room temperature. See Noisetek products, and other numerous patent and research papers.
http://www.bnam2012.com/papers/Kinnari_24.pdf
Example of a damping product for CLD with informative specifications:
http://www.revintage.se/dga2.pdf
Akustik ljudisolering bullerdämpning ljuddämpning vibrationsisolering
Last edited:
That pretty much nails the subject - thanks.
For making speaker enclosure I think that just using some form of CLD is far more important than worry about if it is "optimum". Don't let seeking "the best" be the enemy of "the better".
I also find damped cross bracing to be very effective, maybe more so than CLD, although the techniques are similar.
For making speaker enclosure I think that just using some form of CLD is far more important than worry about if it is "optimum". Don't let seeking "the best" be the enemy of "the better".
I also find damped cross bracing to be very effective, maybe more so than CLD, although the techniques are similar.
This sounds right.
How do we define the required DIFFERENCE in stiffness between the core and the skin for effective damping?
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.
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:
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.
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.
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/Decidamp DC30 122IP_ 09_13EC.pdf
Self Leveling Compound, Decidamp SLC; #1705108-1-C; 2 parts: 14 kg total; US$199
http://www.pyroteknc.com/download/DecidampSLC192IP_160415ratioSLF.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/Decidamp FDF 142IP_logo.pdf
Extensional Damping Products
Damping Tiles, 12" X 12"
http://www.pyroteknc.com/download/DecidampTile182IP_231014adhesv.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 Line/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/damping tile 2010 1 A.pdf
Damping Tile, 3/8" Thickness; US$19 ea.
Damping Tile, 5/8" Thickness; US$30 ea.
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/Decidamp DC30 122IP_ 09_13EC.pdf
Self Leveling Compound, Decidamp SLC; #1705108-1-C; 2 parts: 14 kg total; US$199
http://www.pyroteknc.com/download/DecidampSLC192IP_160415ratioSLF.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/Decidamp FDF 142IP_logo.pdf
Extensional Damping Products
Damping Tiles, 12" X 12"
http://www.pyroteknc.com/download/DecidampTile182IP_231014adhesv.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 Line/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/damping tile 2010 1 A.pdf
Damping Tile, 3/8" Thickness; US$19 ea.
Damping Tile, 5/8" Thickness; US$30 ea.
Last edited:
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.
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.
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.
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.
Has anyone investigated the use of "Acoustical sealant".
You know, the black sticky messy goop used for sealing vapour barrier to wood in construction? It never dries.
I was thinking of using it between the drywall and resilient channel in my garage as a further step for sound isolation.
The last house i built had a closed sub built into the 17' tall wall. I used pieces of drywall with acoustical sealant and mass loaded the backside of the outer drywall with them, as well as between the studs and drywall.
You know, the black sticky messy goop used for sealing vapour barrier to wood in construction? It never dries.
I was thinking of using it between the drywall and resilient channel in my garage as a further step for sound isolation.
The last house i built had a closed sub built into the 17' tall wall. I used pieces of drywall with acoustical sealant and mass loaded the backside of the outer drywall with them, as well as between the studs and drywall.
Last edited:
Glueing two 9mm plywood layers with Titebond carpenters glue (100% surface coverage) gives you an 18mm layer of plywood. carpenter's glue is a hard glue.
Sitkaflex 292
You would be the pioneer.
you would have to make a test panel and try it, comparing it to a similar panel glued up with carpenters glue.
Part of the experiment is you need a way to spread a layer of Sitkaflex that is fairly uniform in thickness. Nearly all of the surface of the plywood layers needs to be bonded, not just the high spots. If Sitkaflex is like other marine polyurethane sealant/adhesives I have used, it is thick and very messy, not easy to spread out smooth.
No one can say what adhesive thickness you should try. A guess might be 1 or 2mm.
Finally Sitkaflex cures using moisture from it's surroundings so it might take weeks for it to cure between two layers of plywood,
Good luck. I spent much time experimenting with my method.
Last edited:
Haha, true
Thanks for the advice. Sitkaflex sounds like too much for me, especially because of the unknown time to cure.
There is the guy on the forum who made a very sophisticated 3-way design with heavy usage of CLD. I think he was mentioned in this thread, too. He used self-adhesive silicone buttons to control the thickness of the CLD layer (He used Bostic V60). Well, Bostic is not available here but i can source green glue and copy the method with silicone buttons to control the height. Is green glue a good candidate for this kind of job in terms of vibration dampening properties and its thickness/ease of application?
I am thinking about 2-3mm thickness.