A comparison of the effectivity of different speaker panel damping products

[mcdn]

Thanks, had seen the AH article previously. It is a big gulp but can skip forward to the conclusion if not looking for a science lesson. It does mention part of the issue with building and measuring in that stiffness is critical. However, really need to measure to know when stiff is stiff enough. CLD techniques have a comparable but add even more complexity.

I thought the takeaway was pretty clear, in that if you have 19mm (3/4") MDF panels, gluing 100mm x 38mm (4" x 1.5") MDF strips to them would make each section of the panel behave independently. Using hardwood strips would allow you to make them approx 50mm x 19mm for the same result as they are 3 times stiffer than MDF (12GPa vs 4GPa). Aluminium strips could be even smaller as it is 70GPa, but they are harder to fix to MDF.

Adding more strips seems to work up to the point where your panel is about 20% covered in strips, beyond which it closely approximates a thicker panel.

We can probably trust the computer analysis that far. Given the effectiveness of simple strips I'd certainly want measurements before adding anything fancy like cross bracing, what do you think?

 

[Rick Sykora]

I thought the takeaway was pretty clear, in that if you have 19mm (3/4") MDF panels, gluing 100mm x 38mm (4" x 1.5") MDF strips to them would make each section of the panel behave independently. Using hardwood strips would allow you to make them approx 50mm x 19mm for the same result as they are 3 times stiffer than MDF (12GPa vs 4GPa). Aluminium strips could be even smaller as it is 70GPa, but they are harder to fix to MDF.

Adding more strips seems to work up to the point where your panel is about 20% covered in strips, beyond which it closely approximates a thicker panel.

We can probably trust the computer analysis that far. Given the effectiveness of simple strips I'd certainly want measurements before adding anything fancy like cross bracing, what do you think?

Thanks for sharing and good to know the sims are productive. It is not an insignificant effort but at least the result seems worthwhile. As @fluid mentioned, brace for lower frequencies and dampen higher ones. In my experience, bracing lower ones can result in higher resonances, so panels are resonating lower, start with bracing until you can make inaudible or use damping to do so. The challenge is where that line might be drawn and knowing which damping solution is most effective at reducing it. So still will need to do that testing.

P.S. also agree about takeaway for a adding strips to a panel. My comment was more about cross bracing but, in any case, measuring to validate will still be key to right-sizing the brace.

 

[Thomas_A]

With respect to CLD, I found Swedacs glue dg-a2 effective.

Damping Glue DG A2 | Swedac

Speaker enclosure vibrations - a few measurements with accelerometer

There are been quite a number of threads dealing with vibrations in speaker cabinets, both in relation to "speaker feet" and vibrations in enclosures themselves. I recently took out my ACH01 accelerometer to do some measurements, both speaker feet and enclosures. There was some initial...

www.audiosciencereview.com

 

[mcdn]

Cross bracing (as opposed to window bracing) has always seemed to me to be prone to bending modes in the brace itself. The approach @Rick Sykora and @fluid suggest has to be right: use window/strip bracing to push panel resonances up to frequencies that can be effectively damped by stuffing (~500Hz for denim felt or melamine foam), so that they never excite the panels in the first place.

 

[cavedriver]

@Rick Sykora I filled the plastic front panels somewhat at random with 300g per panel of polyester filler ("builder's bog"), which sets like stone. I also glued lengths of 10mmx30mm hardwood to the side panels.

I read about a guy that used some Richlite pressed paper boards to stiffen the insides of a boxy speaker cabinet. He apparently had access to scraps because the stuff is insanely expensive otherwise. I bought some to make some speaker stands so I also got a piece of their 3/4" thick material to test on some old Snell's that I have. The problems is that richlite is insanely dense and doesn't take glue that well, and I'm not sure what size pieces to use. The speakers are Snell E/III's which are about 31" tall and about 11" deep and have maybe only 1 interior brace to begin with. I also suspect I could get the same result with 1/2" material, and sure with some other product that's a lot cheaper than richlite.

 

[mcdn]

@cavedriver, Richlite has video on gluing it:

TL;DR, use epoxy, and don't clamp too hard or you will squeeze the epoxy out of the joint (not a problem if you are laminating it, but they clearly show an appropriate quantity to use)

 

[cavedriver]

@cavedriver, Richlite has video on gluing it:

TL;DR, use epoxy, and don't clamp too hard or you will squeeze the epoxy out of the joint (not a problem if you are laminating it, but they clearly show an appropriate quantity to use)

yeah, I corresponded with an applications engineer at richlite when I bought the material. They were really down on the bond strength even with the glue they recommended, which was something called T-88. The write-up I found used a glue that's now sold as Grizzly Glue Xpress, which is apparently a simple polyurethane glue, but I can't remember if the guy used a thin layer like he was trying to stiffen the panel, or a thick layer like he was trying to create a CLD scenario.

Grizzly Xpress

Grizzly Xpress, a cartridge-loaded thixotropic (semi-gel) polyurethane adhesive, is strong, yet bonds quickly. Order today!

www.grizzlyglue.com

 

[mcdn]

yeah, I corresponded with an applications engineer at richlite when I bought the material. They were really down on the bond strength even with the glue they recommended, which was something called T-88. The write-up I found used a glue that's now sold as Grizzly Glue Xpress, which is apparently a simple polyurethane glue, but I can't remember if the guy used a thin layer like he was trying to stiffen the panel, or a thick layer like he was trying to create a CLD scenario.

Grizzly Xpress

Grizzly Xpress, a cartridge-loaded thixotropic (semi-gel) polyurethane adhesive, is strong, yet bonds quickly. Order today!

www.grizzlyglue.com

I’m not sure you want to worry about bond strength so much as its stiffness, which slow setting epoxy is good for. This isn’t a structural application after all. CLD is a whole different level of complexity to analyse and get right. But hey! Maybe do one speaker as CLD and another as a stiff connection and measure both!

 

[cavedriver]

I’m not sure you want to worry about bond strength so much as its stiffness, which slow setting epoxy is good for. This isn’t a structural application after all. CLD is a whole different level of complexity to analyse and get right. But hey! Maybe do one speaker as CLD and another as a stiff connection and measure both!

I was more thinking that with vibration and a poor bond the glue joint might just fail entirely after a couple years and the block just fall right off, haha. But also, it seems like if stiffness is the goal even a good hardwood or maybe some bamboo flooring scraps I have laying around, would work just well.

 

[mcdn]

It took some digging because richlite don't publish it on their website, but its elastic modulus is about 11GPa (https://www.surfacematter.co.uk/files/Richlite-BS-EN-Technical-Data-Sheet.pdf). So yeah, same as hardwood.