I'm interested in constrained layer damping for bass and mid boxes. I have a handful of materials I can test: Green Glue, silicone caulking, various glues with and without additives, lead shot, kitty litter... and I'm interested in running some experiments to see how well they each do across the audio band.
Here's what I've got in mind:
- Driver: Dayton full range exciter
- The usual measurement of frequency response and distortion with REW + measurement mic
- ~1/2" thick pieces of wood in a sandwich roughly imitating normal cabinet dimensions + inner bracing, with multiple identically sized sandwiches made up varying the constrained layer material
I know temperature is important. I figure since we're listening to speakers at room temperature, that's where I'll test, and I can measure and record with an infrared cooking thermometer.
What else should I be looking at? Very high volume? Very low?
Here's what I've got in mind:
- Driver: Dayton full range exciter
- The usual measurement of frequency response and distortion with REW + measurement mic
- ~1/2" thick pieces of wood in a sandwich roughly imitating normal cabinet dimensions + inner bracing, with multiple identically sized sandwiches made up varying the constrained layer material
I know temperature is important. I figure since we're listening to speakers at room temperature, that's where I'll test, and I can measure and record with an infrared cooking thermometer.
What else should I be looking at? Very high volume? Very low?
I like the idea of using an exciter to trigger the cabinet vibrations.
1) I wouldn't use "pieces of wood". Use ply. The results will be more applicable to the cabinets (most) people actually build.
2) It seems that you are thinking of CLD for the walls, but apparently it is more effective on cross braces. Makes sense: the middle of a panel will have the largest amount of motion, so if you put a CLD brace on that point...
e.g. see this (particularly figure 21):
https://www.kefdirect.com/media/wysiwyg/documents/ls50/ls50_white_paper.pdf
...and maybe skim this thread for good bits.
Measuring sound output from speaker cabinet walls
e.g. posts 26, 66 and 71, are tips from a dude whose doctorate / work is in the field.
Post 1 and post 75 have many links and articles that may help.
If that is too much reading, the core point from the thread might be:
"I have to admit that I was never able to convince myself with actual data that all this [cabinet work] was necessary, it just seemed like good engineering in the absence of any data."
1) I wouldn't use "pieces of wood". Use ply. The results will be more applicable to the cabinets (most) people actually build.
2) It seems that you are thinking of CLD for the walls, but apparently it is more effective on cross braces. Makes sense: the middle of a panel will have the largest amount of motion, so if you put a CLD brace on that point...
e.g. see this (particularly figure 21):
https://www.kefdirect.com/media/wysiwyg/documents/ls50/ls50_white_paper.pdf
...and maybe skim this thread for good bits.
Measuring sound output from speaker cabinet walls
e.g. posts 26, 66 and 71, are tips from a dude whose doctorate / work is in the field.
Post 1 and post 75 have many links and articles that may help.
If that is too much reading, the core point from the thread might be:
"I have to admit that I was never able to convince myself with actual data that all this [cabinet work] was necessary, it just seemed like good engineering in the absence of any data."
This page is showing me a targeted ad for cat litter. LOL.
The page linked at the start of that thread: Loudspeaker construction seemed pretty informative. Still plenty more in the rest of the thread to digest...
Most of the scrap wood I have around the garage is MDF, but there might be some ply. Maybe both would be interesting. Other dimensions of the comparison that I've thought might be interesting:
- Measurement of the cross product of fillers { sand, lead shot, bentonite cat litter, ...? } x adhesives { caulk, epoxy, wood glue, Elmer's, Green Glue, ...? }
- Evaluation in terms of cost per dB reduction
- Evaluation in terms of weight added per dB reduction
I might also need to look at what minimum size of sandwich will be necessary for meaningful results. It would be nice to be able to test tiny little bits of this on like a 1" or 2" square, but I could think of many reasons in terms of modal behavior and surface area vs. bass response that it might not work out like that. We'll see.
The page linked at the start of that thread: Loudspeaker construction seemed pretty informative. Still plenty more in the rest of the thread to digest...
Most of the scrap wood I have around the garage is MDF, but there might be some ply. Maybe both would be interesting. Other dimensions of the comparison that I've thought might be interesting:
- Measurement of the cross product of fillers { sand, lead shot, bentonite cat litter, ...? } x adhesives { caulk, epoxy, wood glue, Elmer's, Green Glue, ...? }
- Evaluation in terms of cost per dB reduction
- Evaluation in terms of weight added per dB reduction
I might also need to look at what minimum size of sandwich will be necessary for meaningful results. It would be nice to be able to test tiny little bits of this on like a 1" or 2" square, but I could think of many reasons in terms of modal behavior and surface area vs. bass response that it might not work out like that. We'll see.
Regarding walls vs. braces, I see the reasoning, and that would seem to agree with the popular wisdom (backed up by some amount of DIY testing) that in, say, a car audio application with Dynamat, only about 30% of the surface area of interest needs to be treated with CLD in order to get 90+% of the benefit. I'm actually going to try to keep that out of the picture for this experiment and just do one sandwich at a time, leaving it up to a followup experiment to figure out how/where that's best applied inside an actual enclosure (assuming that all other things being equal, a more effective CLD layer would still be more effective regardless whether it's in the corner, in the middle of a side, or on a brace, even if one of those approaches is clearly superior to the others in absolute terms).
... although ...
there's also not much to stop me from using the exciter on one of my existing (gigantic) DIY MDF enclosures in the living room, with just half the sandwich made up for each experiment. I'll have to think about that.
... although ...
there's also not much to stop me from using the exciter on one of my existing (gigantic) DIY MDF enclosures in the living room, with just half the sandwich made up for each experiment. I'll have to think about that.
+1 on what jesh said.
I get the impression that mass loading works best when the cabinet is light (as per the BBC experiments), so the ratio of panel weight:goo weight is high.
Post 14 here shows a flimsy speaker that I mass loaded with several things, including a heavy paste made largely from kitty litter + bulk glue.
The application of a few kilos of paste made a mild improvement vs. a stock cabinet. If I'd applied it to a more solidly built cab, I think the improvement would have been less.
Unknown sensor in port
I get the impression that mass loading works best when the cabinet is light (as per the BBC experiments), so the ratio of panel weight:goo weight is high.
Post 14 here shows a flimsy speaker that I mass loaded with several things, including a heavy paste made largely from kitty litter + bulk glue.
The application of a few kilos of paste made a mild improvement vs. a stock cabinet. If I'd applied it to a more solidly built cab, I think the improvement would have been less.
Unknown sensor in port
Maybe that one bears some explanation.
Bentonite clay on a budget - Try 100% Kitty litter |
http://qualia.webs.com/newdampingfactors.htm
- note bentonite - described in that page as pure clay cat litter as well - listed towards the bottom with one of the best damping factors, just short of purpose-made wood and tungsten putty.
Bentonite clay on a budget - Try 100% Kitty litter |
http://qualia.webs.com/newdampingfactors.htm
- note bentonite - described in that page as pure clay cat litter as well - listed towards the bottom with one of the best damping factors, just short of purpose-made wood and tungsten putty.
The Qualia listing is referring to isophthalic polyester resin filled with bentonite clay granules (kitty litter). Approximately 3:2 ratio of bentonite clay:resin by volume:volume. The granules settle in the wet resin, so adjust component compositions to achieve a thin 1mm smooth resin top layer. This results in a thick, hard, damped composite for extensional damping, not constrained layer damping.
Last edited:
Nice, thank you.
Did you ever post a direct link to it? I see mention of it in this thread: Cabinet bracing: measurements? which looks helpful and closely related, but in a quick search I haven't found my way back to the particular articles you're mentioning yet.
Did you ever post a direct link to it? I see mention of it in this thread: Cabinet bracing: measurements? which looks helpful and closely related, but in a quick search I haven't found my way back to the particular articles you're mentioning yet.
The damping materials for constrained layer damping (CLD) and extensional damping of loudspeaker enclosure, are quite different. A loudspeaker speaker is basically a structure, with its 3/4" or so stiff walls. Unlike the thin walls of automobile panels.
For most effective extensional damping of structures, the damping material should be:
1) 1/2 to 1 times the thickness of the base panel, even greater thickness is more effective,
2) optimally, the damping material should be fairly stiff, with the modulus of elasticity of the damping material should be similar to the base panel (surprisingly), within +-50% is best, though 1/5th works
3) the damping factor of the damping material should be greater than 0.1, with 0.4 to 0.6 best, damping factor = 1/Q
4) the damping material should be firmly attacked to the base panel, no flexible adhesive here, you want the damping material to flex when the base panel vibrates
Constrained Layer Damping (CLD), typically a 3 layer system (can be more layers)
1. Outer stiff wall
2. Middle thin 2 to 4 millimeter adhesive elastic layer, loaded in shear when vibrating
3. Inner stiff wall
Previous related threads on this forum
constrained layer damping with MDF and Ply
how to brace a speaker cabinet?
Woofer choice : maple or mdf ?
Cabinet structure MDF vs HDF
Measuring sound output from speaker cabinet walls
Last edited:
Twinter: Do you think that I could add a 1 to 3 mm layer of Bentonite Resin on a 1mm thick aluminum panel for extensional damping or is the Resin Bentolite mix too granular? Do you know what the Young Modulus of the resin mix is? i would be surprised if it is 1% of aluminum. However, after researching i found that even 3 x thickness would be ok even with a Youngs Modulus of 1% the Aluminum Modulus. If it is 10 percent I could get away with 1 mm thickness of resin bontonite.
Newpaton2, as you alluded, a 1 mm layer of bentonite & resin would be questionable due to the size of the bentonite granules. Possible a 3 mm layer would work if you slight ground and sieved the bentonite granules to a small diameter.
Though for 1 mm thick aluminum panels, standard automotive panel damping sheets or mastic should be effective.
General note here for applying epoxy to aluminum. The aluminum oxide surface layer that forms on aluminum to give it some good corrosion resistance in mild ambient conditions, also can make adhesion of paints and epoxies difficult. Surface prep with an etching solution or sanding immediately before application is sometime required. The aluminum oxide forms fairly quickly, so you can't surface prep a day ahead.
Though for 1 mm thick aluminum panels, standard automotive panel damping sheets or mastic should be effective.
General note here for applying epoxy to aluminum. The aluminum oxide surface layer that forms on aluminum to give it some good corrosion resistance in mild ambient conditions, also can make adhesion of paints and epoxies difficult. Surface prep with an etching solution or sanding immediately before application is sometime required. The aluminum oxide forms fairly quickly, so you can't surface prep a day ahead.
Thanks twinter. I tried the polyester bentonite and didnt get good results. Probably because i didnt use isopthalic resin. I ordered some so i will be testing again soon. Yes , i needed to grind to dust to get thinner layers. This time around i will do some testing on metal strips before coating the whole loudspeaker.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.