The largest panels are the most important no matter where they are.
I CLD the front and back AND structurally brace them as well. But my braces are cross braces, not on-panel braces (which don;t work any better than CLD. If you consider that CLD works by shear in a panel, the shear is much smaller than the displacement say of the center of the panel. This larger displacement will have more effect as a cross brace because of the great excursion that results.
Enclosures have been shown to not radiate significantly at HFs, it's only the lower freqs where the lowest panel modes exist. So damp those panel modes and you have a good solution. You don't want an inner box that is too soft because its resonance will suck out the energy from the woofer at this resonance. The enclosure should be stiff, light and well damped. This makes wood not such a good choice, although not terrible in the case of BB for example. I use poly boards as they have a stiffness to weight ratio much higher than BB.
I CLD the front and back AND structurally brace them as well. But my braces are cross braces, not on-panel braces (which don;t work any better than CLD. If you consider that CLD works by shear in a panel, the shear is much smaller than the displacement say of the center of the panel. This larger displacement will have more effect as a cross brace because of the great excursion that results.
Enclosures have been shown to not radiate significantly at HFs, it's only the lower freqs where the lowest panel modes exist. So damp those panel modes and you have a good solution. You don't want an inner box that is too soft because its resonance will suck out the energy from the woofer at this resonance. The enclosure should be stiff, light and well damped. This makes wood not such a good choice, although not terrible in the case of BB for example. I use poly boards as they have a stiffness to weight ratio much higher than BB.
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Thank you @gedee, very informative.
Your point that the centre of the panel flexes more than the edges is well taken and I do agree it can be a problem.
On larger panels a cross brace can actually serve two functions: First it clearly does stiffen the panel but it also takes the out of phase push, pull of opposing panels flexing and uses one to cancel the other. This, I think, is fairly well known.
In my original effort I never once noticed vibration on the outer cabinets and those speakers got pushed pretty hard. But it clearly is something to consider for my new design.
Now, I'm thinking that, within reason, a combination of measures might be most effective.
Thank you.
Your point that the centre of the panel flexes more than the edges is well taken and I do agree it can be a problem.
On larger panels a cross brace can actually serve two functions: First it clearly does stiffen the panel but it also takes the out of phase push, pull of opposing panels flexing and uses one to cancel the other. This, I think, is fairly well known.
In my original effort I never once noticed vibration on the outer cabinets and those speakers got pushed pretty hard. But it clearly is something to consider for my new design.
Now, I'm thinking that, within reason, a combination of measures might be most effective.
Thank you.
Now tie that brace to another brace at 90 degrees between the front and back and all modes are stiffened and damped. My experience is that it is very effective. Although the cross brace took some six different parts to make and had to be assembled very carefully. Remember that it is better to dampen that to stiffen.
I can see how a cross brace like that would be complex to fit, unless it was part of the initial design of the enclosure. I recently did some work in a couple of older towers where they had produced about the same effect with a single piece of wood fitted to the inside of the cabinet, but with 4 largish round holes in the corners. Seemed to work quite well...
But, I'm still on the fence about the "better to dampen than stiffen" debate... I'm going to have to give that one some more thought.
But, I'm still on the fence about the "better to dampen than stiffen" debate... I'm going to have to give that one some more thought.
Canadian fellow on 1 st page of this thread ( the one with bi-junction name, not the other) got mad with that
Canadian fellow on 1 st page of this thread ( the one with bi-junction name, not the other) got mad with that
Yeah well, I'm not that fellow. Just because we are Canadian doesn't me we are the same person. As a matter of fact there are about 38 million of us.
I asked for information and discussion ... wouldn't it be rather stupid of me to get all upset at the answers to my own questions?
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3-way active, time aligned, constrained layer construction
Many of the issues discussed in this thread were addressed in the above build report. The even distribution of the damping layer is solved by a heavy duty press and extrusion approach as detailed in post #13 of the link. I put together a mini-me model (below) to illustrate the fitting of the panels to achieve a box-within-a-box construction. Interestingly, the damping layer is still compliant after 8 years. I have never succeeded in pulling even the smallest panel sample apart. The split in the mdf is due to a screw holding the panels. There are no screws in the actual build. Even though I have built many enclosures since, this is my favourite and best performing. It was a challenging build.
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Hello Bon ...
Thanks for your response. I've had a quick scan through your other thread. I'll give it a more thorough read in a day or two.
I'm not planning anything even remotely so exotic. Tentatively a pair of 8 inch 3 ways to put on stands. I haven't even started sketching yet but I would imagine it will be basically a box with the right holes in it.
When I did the constrained layer build in 1979, I pre-cut the panels to size and positioned them before mounting into my cabinets. To get the silicone layer even I used a small grouting trowel, then placed strips of 1/8" plastic at the corners while clamping and curing, to keep the thickness I wanted. Finally I assembled the cabinets by gluing, using a joining technique much like yours. The overall wall thickness was 1 1/8" and they weighed a ton.
There is a picture in one of my earlier posts. It was pretty ordinary looking, as speakers go, but yeah, like you said... best result. The sound from them was pretty amazing.
For this new build I'm contemplating a very similar construction. 2 X 3/8 mdf with a 1/8" silicone or decidamp layer between.
I'm gathering that a lot of people don't understand the CLD concept. They mistake it for isolation, which it isn't or they take it as padding, also not what it is. It's not even stiffening. In fact it is a way of killing resonance in the speaker walls so they don't sound "boxy" at all.
I don't know if I will still use internal bracing or if the bracing I use will be of the conventional kind... I would appreciate guidance on that one.
I would also appreciate any materials or preparation recommendations you can make for the constraining layers.
Very impressive speakers, btw.
Thanks for your response. I've had a quick scan through your other thread. I'll give it a more thorough read in a day or two.
I'm not planning anything even remotely so exotic. Tentatively a pair of 8 inch 3 ways to put on stands. I haven't even started sketching yet but I would imagine it will be basically a box with the right holes in it.
When I did the constrained layer build in 1979, I pre-cut the panels to size and positioned them before mounting into my cabinets. To get the silicone layer even I used a small grouting trowel, then placed strips of 1/8" plastic at the corners while clamping and curing, to keep the thickness I wanted. Finally I assembled the cabinets by gluing, using a joining technique much like yours. The overall wall thickness was 1 1/8" and they weighed a ton.
There is a picture in one of my earlier posts. It was pretty ordinary looking, as speakers go, but yeah, like you said... best result. The sound from them was pretty amazing.
For this new build I'm contemplating a very similar construction. 2 X 3/8 mdf with a 1/8" silicone or decidamp layer between.
I'm gathering that a lot of people don't understand the CLD concept. They mistake it for isolation, which it isn't or they take it as padding, also not what it is. It's not even stiffening. In fact it is a way of killing resonance in the speaker walls so they don't sound "boxy" at all.
I don't know if I will still use internal bracing or if the bracing I use will be of the conventional kind... I would appreciate guidance on that one.
I would also appreciate any materials or preparation recommendations you can make for the constraining layers.
Very impressive speakers, btw.
I thought all Canadians were the same then eh!
Yeah... and we all know each other ... go figure.
I made a number of test panels with mdf and different constrained layer materials. After protracted measurements and subjective testing, the glazing silicone was the winner by my judgement. It is also relatively affordable. It is designed for the extreme pressure loading experienced in aquariums, and wind loading in high rise building construction. As I mentioned previously, it has maintained its flexibility over 8 years.
I consider structural bracing as essential in addition to the CLD. I also added a layer of extensional damping layer to all interior surfaces. It didn't seem to do any harm. I don't think it is possible to over-damp the actual enclosure.
I came to the same conclusion first time around... It's probably what I will use this time also.
Decidamp was pretty impressive in that video, so it's also a contender.
That's pretty good. No issues with it letting go?
There is always a point of excess ... but within reason I can see the benefits of both CLD and internal bracing. As I said in an earlier post, at the very least it will make a stronger box.
Thank you for your response.
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I know from experience that a saw blade will rip the damping layer right out. If the contact area with the sawblade is significant, the blade can stall, or worse, grab and throw the panel. All of this has happened to me. It needs very precise fence positioning to leave the blade just shy (~0.5mm) of any damping layer.
Post #151? Good cabinet, very strange driver layout. I can't see they would have imaged very well?
A "thinner" layer of the constrained viscoelastic layer should be better than a "thicker" layer. It dampens vibration due too shearing forces ("twist and tear"). Damping = converting energy from the vibrations /movements into heat. The shearing forces should be more substantial inside a thin layer compared to a thicker one. -As the inner wall (substrate ) expands / acts on it and the outer layer "holds back". The constrained layer will be compressed from the inside and streched towards the outside of its thicknes, "mangled" one could say. A thicker layer will be less mangled than a thinner one.
(I used a 0,8 mm thick layer of non hardening MS polymer between 2 sheets of 22 mm (7/8") hard particle board. The sheets were oversized, glued together prior to cutting to size. With a thin layer there was no problems at all with sawing and routing. My experience is that MS polymer adheres better to wood than silicone. Also, MS polymer is paintable while silicone is not. For a controlled low thickness one can use some strings of fishing line etc streched across the sheets together with a spatula / trowel, pull out the strings when the polymer has been applied. Drill some holes for nails close to the edges of the oversized sheets so they don't glide away from each other when clamps are applied. MS polymer cures with moisture, so dampen the outer sheet with a wet sponge just before inserting the nails and clamping the sheets together. Curing time for skin formation of MS polymer varies, about 15 minutes is usual so one has to act quite quickly. Total curing time is about 24 h.)
(I used a 0,8 mm thick layer of non hardening MS polymer between 2 sheets of 22 mm (7/8") hard particle board. The sheets were oversized, glued together prior to cutting to size. With a thin layer there was no problems at all with sawing and routing. My experience is that MS polymer adheres better to wood than silicone. Also, MS polymer is paintable while silicone is not. For a controlled low thickness one can use some strings of fishing line etc streched across the sheets together with a spatula / trowel, pull out the strings when the polymer has been applied. Drill some holes for nails close to the edges of the oversized sheets so they don't glide away from each other when clamps are applied. MS polymer cures with moisture, so dampen the outer sheet with a wet sponge just before inserting the nails and clamping the sheets together. Curing time for skin formation of MS polymer varies, about 15 minutes is usual so one has to act quite quickly. Total curing time is about 24 h.)
That accords with what I worked out on the first build. The goal is to provide an opposing force to panel resonances. The viscus layer has to be thin enough to actively resist flexing of the panel but thick enough to provide a good bond between layers. I somehow came to the conclusion that with GE Silicone 1/8" was the best.
Also if you watched the video I linked to, I believe he came to similar conclusions.
The MS Polymer you suggest sounds interesting. I'll add it to my "To be investigated" list. Thank you.
Back in approximately 2004, I built four of Wayne Parham's Studio 2 Pi speakers, using double layers for the front baffle and the back. At the time, North Creek Music was selling a 'soft' glue intended for damping multilayer cabinets, so I used that. The cabinets turned out very well. I also braced internally with wood curtain rods. Those cabinets are quite dead.
Some years later, George Short (North Creek's owner) was no longer offering the soft glue. I called him to see if he didn't like it anymore, and he said that it worked very well but he wasn't selling a lot of it. I could buy it at Walmart in small quantities. I just looked and it appears to still be available:
https://www.walmart.com/ip/Aleene-s...l5=9032140&wl6=106119632769&wl7=&wl8=&veh=sem
If you are doing some tests, I would include this -- It applies like PVA wood glue.
Skip
Some years later, George Short (North Creek's owner) was no longer offering the soft glue. I called him to see if he didn't like it anymore, and he said that it worked very well but he wasn't selling a lot of it. I could buy it at Walmart in small quantities. I just looked and it appears to still be available:
https://www.walmart.com/ip/Aleene-s...l5=9032140&wl6=106119632769&wl7=&wl8=&veh=sem
If you are doing some tests, I would include this -- It applies like PVA wood glue.
Skip
Thank you Skip Pack for your response.
I took a quick look at your link and will add it to the list.
But a question... it does need some thickness and elasticity for constrained layers to work. I'm wondering how resiliant this is and if a decent layer (1/8" or so) can be bult up without problems.
I took a quick look at your link and will add it to the list.
But a question... it does need some thickness and elasticity for constrained layers to work. I'm wondering how resiliant this is and if a decent layer (1/8" or so) can be bult up without problems.
Apologies if this has already been determined but I don't yet understand what is the ideal material (and thickness) for the speaker panels when used in CLD.
The same materials and dimensions as below (22mm hard particle board) or different materials and thicknesses such as plywood and thinner hardboard (HDF) panels?
The same materials and dimensions as below (22mm hard particle board) or different materials and thicknesses such as plywood and thinner hardboard (HDF) panels?
From my experience (admittedly a long time ago) and what appears to be the general consensus of builders the inner layer should be MDF. The outer layer can be plywood or MDF. Plywood offers some advantage in that it can be sanded and finished very nicely where MDF will require either vinyl wrap or veneer to give you a nice looking speaker.
My build was MDF-Silicone-MDF and then I veneered them for a nice oak wood finish.
If you watched the video I linked to (from the beginning) he spends a lot of time on discussing various materials. I'm not sure I agree 100% but it is a pretty thorough dissertation.
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