Yeah cork or Nidacore. But really the simple Weicon 310M Flex CLD )or PL300 if you have to go cheap) are more or less the same with a whole lot less hassle. If I were building a box today with what I'm seeing above, it would an inner 1/4" MDF box glued to outer 1/2" MDF box with the 310M Flex, probably solid bracing, 2 layers of wool batting, and maybe some Rezonix. Though I'm unsure how that last will interact with a CLD cabinet. Might have to check that out. This would be a very straightforward construction most any DIY'er can do.
My layman's thinking on the 3/4" ply, solid braced, sub box w/1/4" cork and 1/4" outer panel was that after the 3/4" panels were braced, the panels produced two separate resonances.
I reasoned that the more compliant 1/4" panel coupled to the sub box w/1/4" cork would further dissipate those remaining resonances and perhaps work to cancel each other within the compliant layer(s). I am going to use a troweled polyurethane adhesive to bond the cork and the outer panel to the 3/4" sub box. With the exception of the cork (cheap) I have the walnut finished outer panels on hand anyway, so going to give it a whirl.
Got on board with your test early on and I appreciate your efforts on this Brandon. Great work!
Phil.
I reasoned that the more compliant 1/4" panel coupled to the sub box w/1/4" cork would further dissipate those remaining resonances and perhaps work to cancel each other within the compliant layer(s). I am going to use a troweled polyurethane adhesive to bond the cork and the outer panel to the 3/4" sub box. With the exception of the cork (cheap) I have the walnut finished outer panels on hand anyway, so going to give it a whirl.
Got on board with your test early on and I appreciate your efforts on this Brandon. Great work!
Phil.
I like your thinking, I'm just pointing out that the measured evidence so far doesn't show that mechanism being dominant, at least compared to other simpler methods like simply gluing two pieces of MDF together with Weicon 310M or Loctite PL300. But certainly it is a good performer if you want to go through the hassle.
I would suggest not using polyurethane, at least not any variant that cures hard. Also I'm not sure a sub box will benefit from all this. You can see below the main box resonance that response drops drastically and stiffness is all that matters. For a sub I would use good quality 1/2" plywood very well braced.
I would suggest not using polyurethane, at least not any variant that cures hard. Also I'm not sure a sub box will benefit from all this. You can see below the main box resonance that response drops drastically and stiffness is all that matters. For a sub I would use good quality 1/2" plywood very well braced.
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Or, for an easier (but uglier) look, maybe an inner 1/2" MDF box with skins glued onto the outside? The baffle could just be made extra, extra thick to kill any flex.
I know these are sort of data dumps, and unless you open plots in separate browser tabs to flip back and forth and comparing them, not so east to digest. So maybe a summary of what I'm seeing so far. I should add my observations apply to any woofer duty that is not a subwoofer. For subs, it seems to me 1/2" or 3/4" plywood well braced is all you really need.
1) MDF is actually pretty good. I would use it over plywood for anything except a subwoofer
2) simply gluing two pieces of MDF together with a softer adhesive like Weicon 310M Flex Classic or Loctite PL300 works really well as a simple CLD
3) a sandwich of MDF and Nidacore or cork works well too (again glued with the 310M Flex or PL300) but I'm not sure most people will want to deal with the hassle
4) CLD bracing with 33% overlap has a small edge over solid bracing, but any bracing at all really drops that main box resonance
5) melamine foam or 100% wool batting is the way to go for lining the box
6) Resonix is a nice cherry on top if you can swing the extra cost
Things that were not impressive: XPS foam in a CLD, hard polyurethane adhesives like PL Premium, crappy plywood, coating the interior with any supposed vibration absorbing compound.
1) MDF is actually pretty good. I would use it over plywood for anything except a subwoofer
2) simply gluing two pieces of MDF together with a softer adhesive like Weicon 310M Flex Classic or Loctite PL300 works really well as a simple CLD
3) a sandwich of MDF and Nidacore or cork works well too (again glued with the 310M Flex or PL300) but I'm not sure most people will want to deal with the hassle
4) CLD bracing with 33% overlap has a small edge over solid bracing, but any bracing at all really drops that main box resonance
5) melamine foam or 100% wool batting is the way to go for lining the box
6) Resonix is a nice cherry on top if you can swing the extra cost
Things that were not impressive: XPS foam in a CLD, hard polyurethane adhesives like PL Premium, crappy plywood, coating the interior with any supposed vibration absorbing compound.
If I understand what you are saying, that is actually how I've done the test boxes: inner box built as normal with wood glue, then each outer panel glued one at a time. The problem with that method is all the outer panels have to be custom dimensions because of the adhesive and it doesn't look that great. I actually wanted to try the reverse, build the outer box (1/2" MDF) as normal with wood glue so the dimensions are exact. Than glue panels (1/4" MDF?) to the interior with one of the good adhesives. If performance is still on par that would be a lot easier than how I've done it so far.
Has been my experience that trowel grade flooring adhesive (the poly) doesn't cure "hard". I've seen removal of older flooring installs that show the adhesive as having a property more closely resembling a firm rubber consistency. It was comical to see the fellas trying to chisel the flooring up along the glue line only to see the chisel rebounding with each hammer blow. It's tough stuff.
Just to be clear(er), my sub box isn't a subwoofer enclosure. It's the inner enclosure of a 2-way design. More along the line of 454Casull thinking ... sans the "ugly" part.
Just to be clear(er), my sub box isn't a subwoofer enclosure. It's the inner enclosure of a 2-way design. More along the line of 454Casull thinking ... sans the "ugly" part.
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Yeah, it's just that if you have good bracing on the inside, you then have to deal with lots of spaces to "fill in" with the CLD panels.
I was going to add the bracing after the inner panels are glued in. Thoughts?
I have considered that, and should really test it. My thinking so far though is you want the inner panels to be enclosed by the CLD and not radiating to the outside. Whereas if I glued the panels up first, the inner ones would be exposed to the outside, though only the edges, and some inner panels would actually be glued to outer panels, again being able to transmit to the outside. Would certainly be easier if you could glue the panels up first then put the box together as you normally would and still get the same benefit as box-within-a-box.
I think it would be better to brace the main structure which is already more rigid. Otherwise you should lose much of the benefit of bracing (higher stiffness & resonant modes), and besides, doesn't CLD function better if it's allowed to vibrate? According to what I've read, energy is dissipated as a result of shear deformation - which is minimized if both sides are extremely stiff.
https://earglobal.com/media/9891/understandingdampingtechniques.pdf
Long story short - super stiff main structure (exoskeleton, if you will) with CLD applied wherever possible. Of course, the beauty of the testing is that I can be proven wrong!
I don't know if I'm misunderstanding this, but it sounds like this is a double-box construction, not a single box with CLD.
Bracing is so positive I have a hard time abandoning it just to allow the CLD to "do the work" as it were. But as part of a proof-of-concept I will be building a new box with some of the lessons learned, and I decided I will measure the box first without bracing, then with bracing. Just to be sure.
My thoughts on how to brace, what should be the rigid structure, etc.... I see it as first trying to kill sound transmission at the source box, which is the interior box since it sees the woofer radiation. So that should be braced IMO, but maybe doesn't have to be real thick. Then we have the dampening layer, then an outer box, which at this point is hopefully seeing much less energy than a solid box. It's really there to provide a constraining layer, but that is about it.
Brandon, I wonder if you might find this paper interesting at this point:
whitepaper-audibility-of-cabinet-panel-resonances/
whitepaper-audibility-of-cabinet-panel-resonances/
I'll post full results this weekend, but just wanted to share some early results of my tapped port for dampening the port resonances. The port is based of my Precision port clone. I added square taps around the centerline. First plot compares results with taps open, then wrapped with wool batting, then duct tape over the wool to create a more or less sealed cavity. Second plot compares the final taped version vs the standard Precision port. The resonance at @1.3khz is the predicted first resonance. The broader resonance above that to about 3.5khz is a little unaccounted for.
