Javs' Modular Tower WMTW - 15FH520 / Beyma 12P80ND-V2 / TPL-150H - Page 3 - AVS Forum | Home Theater Discussions And Reviews
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post #61 of 68 Old 09-12-2017, 10:12 PM - Thread Starter
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Originally Posted by Mpoes12 View Post
Rigid isn't necessarily good in a midrange box. The midrange boxes should be fairly lossy in the sense that they should absorb and dissipate a good amount of the energy. Rigid is good for low frequencies where the boxes operate largely as pressure vessels.

Small doesn't mean that it doesn't need damping. Those sections will still resonate and still allow a bit of sound to leak through. CLD is most beneficial in the mid and high frequency section. It actually serves no benefit for low frequencies at all. At low frequencies (those below the resonant frequency of the enclosure walls) the dictating factor is the rigidity of the walls. Even mass doesn't matter, if you can believe it. Mass can even make matters worse. Raising the mass lowers the resonant frequency. Since it's so difficult to dissipate large low frequency energy through a lossy box it makes more sense to raise the resonant frequency and raise rigidity. It's more effective and keeping the negative effect of the resonance out of the operating range and this out of the area that matters.

I can't remember the resonances I was picking up in my large sub boxes with the accelerometer. I want to say they were centered pretty high, in the 100's of hz.

Because your boxes are operating up pretty high I guess I might still try to push up the rigidity/stiffness as much as possible to get those resonances as high as possible. Bracing helps too. While at very low frequencies the braces don't have the ability to fully subdivide the panels, that is true at higher frequencies.

If the resonances are sufficiently high the CLD will damp the resonances and be of benefit. I don't think you wasted effort necessarily. It's just in sub boxes where it's a counterproductive waste. It may not provide as much benefit as it would in the midrange boxes.

There is a lot of misinformation with regard to acoustic transmission loss. My own understanding originally came from the diyaudio forum and this one. I misunderstood, misinterpreted, and largely was misinformed and thus built a lot of silly boxes. It was only recently when I began studying the phenomena for soundproofing that I had the full understanding I have today. I read a lot of scientific journal arrivals and engineering texts specifically on transmission loss rather than sound proofing to better understand the physics. I stumbled on a number of papers focused on TL in speaker boxes and saw the parallel with that and soundproofing.
Thanks!

I will endeavour with adding a few CLD strips into my mid range and HF boxes then since it will have benefit there the most.

This is kinda what's happening so far anyway, the panels are going in to areas where I feel the bracing is not adding anything or can be improved.












Will add some into the walls of the mid and HF chambers too.




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post #62 of 68 Old 09-12-2017, 10:43 PM
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Looks good.

What are those tiles? What are they made of?

What's the plan for the front baffle. The CLD front baffle is probably among the best ideas. My speakers were designed with CLD front and rear baffles. When I talked with the designer about this he had indicated that his research had shown this to be optimal. He later switched to adding CLD to the side, top, and bottom panels and I did the same with mine. I used urethane sheet scrape he had leftover from his composite enclosures and I adhered it with a modified urethane casting medium with a 30 durometer stiffness and talc powder. I took before and after measurements with an accelerometer and I remember being both impressed and disappointed. It absolute terms it made a big difference. I had overly high expectations and was surprised to see so little impact at lower frequencies.

I don't feel confident in my measurements from that time but I did find that I had a slightly smoother response. I know when I took them I had averaged 6 measurements before and after to look for differences. What I found was very small. I didn't look at the waterfall which I suspect is the more likely area to show a difference.


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post #63 of 68 Old 09-13-2017, 12:36 AM - Thread Starter
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Quote:
Originally Posted by Mpoes12 View Post
Looks good.

What are those tiles? What are they made of?

What's the plan for the front baffle. The CLD front baffle is probably among the best ideas. My speakers were designed with CLD front and rear baffles. When I talked with the designer about this he had indicated that his research had shown this to be optimal. He later switched to adding CLD to the side, top, and bottom panels and I did the same with mine. I used urethane sheet scrape he had leftover from his composite enclosures and I adhered it with a modified urethane casting medium with a 30 durometer stiffness and talc powder. I took before and after measurements with an accelerometer and I remember being both impressed and disappointed. It absolute terms it made a big difference. I had overly high expectations and was surprised to see so little impact at lower frequencies.

I don't feel confident in my measurements from that time but I did find that I had a slightly smoother response. I know when I took them I had averaged 6 measurements before and after to look for differences. What I found was very small. I didn't look at the waterfall which I suspect is the more likely area to show a difference.
Those are just 9mm MDF sheets cut down to 20cm sq tiles for ease... Some of the areas in my boxes vary in size, that was the size that would fit pretty much everywhere I wanna put them. so the main panels in the enclosures are 18mm and these are half that, which I read someone was good to do so each panel has different characteristics of resonance and they wont interact/reinforce each others resonance.

Yeah the front baffle, that's going to be double layer 19mm MDF, so I could well use the Sika 11FC on bonding those two together, I trust in the strength of the adhesive for this, when it dries there is no way I can pull the panels apart yet it definitely remains rubbery and soft. Might do a test and then do some roundovers on it to see how it behaves.

Your second paragraph is one reason I am not stressing over trying out the method too much, at worst it will do something and improve on something somewhere. I tried to make sure the boxes had pretty good bracing up until I decided a bit of CLD couldn't hurt thanks to Steve earlier in this thread. Thanks Steve!

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post #64 of 68 Old 09-13-2017, 04:40 AM
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Ok guys so I am trying to wrap my head around the CLD concepts and what I am not sure about is the optimal type of materials for the CLD panels. Adhok gave me a reply a few post back, but I didn't understand what he said. It is my understanding that you can use 3/4" ply or 3/4" MDF for the CLD panels, and what matters is the adhesive that you use to attach these panels inside the enclosure. Is this correct?
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post #65 of 68 Old 09-13-2017, 06:43 AM
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I didnt see this mentioned anywhere, although I may have missed it, but what will you gain going to a bigger center channel?

I only ask because things are very slowly starting to pick back up for me which means my builds will finally start making saw dust. I looked at building a center channel with similar parts but wont have the center channel as my L/R. So I thought about building a center channel similar to the one you have now. I know I wouldnt need a 15" version at all considering my L/R will only have 10's. But re-reading this thread had me wondering. PLUS every time I try and use a CD I seem to love the TPL's more. Also are you selling your designs?

I ask because in the future I was going to ask for some help in building your 3way 12" design and passive Xo. BUT if your selling this design then I will not bother you with my questions. Either way thanks again and very happy to have read this thread again.
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post #66 of 68 Old 09-13-2017, 02:19 PM
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If I'm fully understanding CLD, the constrained elastomer layer being sheared by the vibrations of the rigid constraining layers absorbs the energy of the vibrations reducing the vibration amplitude. Shearing forces would be lateral in the constrained layer. Differences in the constraining layers would enhance this shearing property in the panels. Adding CLD would add mass that could lower the frequency, but the 2nd contraining layer might also stiffen the panel and work to raise the frequency. B&W's flagship cabinets are very ridgid and dead. Knuckle rap test sounds like knuckle bones only. They do use CLD techniques, but mostly extreme bracing. More than most of us would be willing to implement. They also have a lot of proprietary tech and mesuring equipment. I'm a big fan, but not spending the ridiculous amounts asked for new or used B&W speakers. Check the prices for 30 to 40 year old speakers with kid dented drivers lol.

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post #67 of 68 Old 09-13-2017, 06:58 PM
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Quote:
Originally Posted by Steve Hanna View Post
If I'm fully understanding CLD, the constrained elastomer layer being sheared by the vibrations of the rigid constraining layers absorbs the energy of the vibrations reducing the vibration amplitude. Shearing forces would be lateral in the constrained layer. Differences in the constraining layers would enhance this shearing property in the panels. Adding CLD would add mass that could lower the frequency, but the 2nd contraining layer might also stiffen the panel and work to raise the frequency. B&W's flagship cabinets are very ridgid and dead. Knuckle rap test sounds like knuckle bones only. They do use CLD techniques, but mostly extreme bracing. More than most of us would be willing to implement. They also have a lot of proprietary tech and mesuring equipment. I'm a big fan, but not spending the ridiculous amounts asked for new or used B&W speakers. Check the prices for 30 to 40 year old speakers with kid dented drivers lol.


Hi Steve. I think most of what you said is right. However there is some debate about the different materials part. I read the exact opposite in some fairly old engineering books and papers. I asked Dr Geddes and a friend who engineers satellite parts. They both said they believe that old belief came from a need to be able to model and predict behavior and having same material for constraining layers makes that much easier. That isn't an issue today. Dr Geddes felt that different materials might have the advantage of non-identical coincident frequencies. That would certainly be a good thing.

Based on what I've read and measured from an accelerometer, it seems the effect is mostly noticeable at the point of resonances. Both the coincident frequency and panel critical frequency. It has less and sometimes no effect at other frequencies, especially below the critical frequency.

From what I was told recently, doubling the layers makes a material 8 times stiffer! When in a CLD panel that isn't true and for the purposes of estimating, it's more like 4 times stiffer if both layers are a like material. I've found a few articles testing this and it seems the exact amount can vary a lot, some were only slightly stiffer than a single layer and others were close to the full 8 times stiffer.

I actually think Magico and Wilson have some of the most advanced enclosures around. B&W has claimed a lot of incorrect things that they argued were proven in their lab but later seemed unsubstantiated and proven wrong. They made a big thing about dimpled ports but that was later proven to make things worse not better. They had a speaker with a funky shaped interior to diffuse sound but that too was later shown to make things worse and not better. Their bracing techniques have been tested as well and better approaches have been shown. Given what literature exists on CLD I also think they misuse it in their speakers. I used to lust after 800 series speakers but as of late I've lost respect for their engineering.


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post #68 of 68 Old 09-13-2017, 08:27 PM
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The Matrix 800 series had extremely well braced and knuckle rap dead cabinets. Stereo Review testing seemed to show the same using their taped on acceleration sensor. The later 800 series not as good. BTW Be tweeter diaphragms are better than vacuum deposited diamond IMHO. Even used 40 year old Matrix speakers are way over priced because they are B&W.

DIY from now on. If you can do it right, you sbould be able to surpass B&W. We've got the design and testing tools now to really excell. Javs has the drivers.

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