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  • Constrained layer

    What is everyone using for a constrained layer?

  • #2
    I'm not. With good bracing it's not required, nor is massively heavy construction.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • analogkid455
      analogkid455 commented
      Editing a comment
      Yeah, I did find a bunch of threads on it and mostly they ended with, don't bother. Bracing it is. One question though. Do you see benefit in using two different materials for cabinet walls, say, one layer mdf and another layer birch plywood?

    • DanW
      DanW commented
      Editing a comment
      If we assume the purpose is to reduce sound radiation from the enclosure panels any sufficient bracing would eliminate the need to get fancy. If you want to go down a rabbit hole you could read up on Statistical Energy Analysis.

      "Simple" calculations can find the resonance frequencies of individual homogeneous panels, but once you interconnect the panels and add cutouts, bracing, etc the assumptions that allow simplification are no longer valid. Personally I break up the largest dimensions of panels with bracing and when possible have the bracing offset from mid-span. A thin brace across the mid-span is at the null for the 2nd harmonic across that span and has minimal impact for that resonance.

      If I were to use multiple materials it would be for reasons unrelated to enclosure sound radiation, like better fastener holding of plywood for the front baffle or the aesthetics of hardwoods.

  • #3
    Thanks Dan. No rabbit hole for me. I am happy to use bracing. Easier the better. Off-setting them I did not think of. Thanks for that tip!

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    • #4
      Not that you asked, but on topic...a few small side to side braces and front to back braces is way more effective than one window brace placed in the middle. The only advantage a window brace(s) has is to help keep a tall tower type speakers square and straight (not bowing in or out along its height). That's pretty much the only time I use window braces. To your original question, as far as constrained layer panels go, IMHO that is beyond the law of deminishing returns and very difficult to impliment correctly.
      Craig

      I drive way too fast to worry about cholesterol.

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      • billfitzmaurice
        billfitzmaurice commented
        Editing a comment
        I never use window braces either. Fully 1/3 of their material ends up where it's not doing any good. I seldom use spline braces, because they pale in effectiveness compared to panel to panel bracing. I only use them where I need something and a panel to panel brace isn't possible.

      • analogkid455
        analogkid455 commented
        Editing a comment
        Thanks Craig and Bill. Noted.

    • #5
      https://www.audiocircle.com/index.php?topic=70291.0
      craigk

      " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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      • analogkid455
        analogkid455 commented
        Editing a comment
        Good read. Thank you.

    • #6
      I just let my cabinets sing

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      • #7
        Originally posted by analogkid455 View Post
        What is everyone using for a constrained layer?
        It's a good question since the viscoelastic materials that are fairly readily available have generally been developed for different applications that tend to move more and at lower frequencies. I have made one or two half hearted attempts to both define what is wanted and to find suppliers of materials but with little to no progress. The former is probably the more important and I hope to make more progress in a few months. If you get anywhere with your search please post back.

        Bracing some parts of a speaker can reduce the unwanted sound radiated by a cabinet but in general it makes little difference. The reasons for this are generally not well understood by DIY folk (but are by engineers in industry) who seem to associate a stiffer cabinet that deflects less with a quieter one. I have started working on an article to explain the physics involved but, as usual, have gone off on a bit of a tangent but one that is related to progressing the article. I am also struggling with the practical side of the web but need to get on top of it to join the modern world.

        BTW if you think bracing might be the answer go look for some genuine evidence to support it. That is, evidence involving sound radiation and not just some accelerometer measurements and a lot of hand waving.

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        • analogkid455
          analogkid455 commented
          Editing a comment
          Thanks for the comment. Something to consider.

      • #8
        My stick built windowpane braces give me a warm feeling. They are based on light aircraft construction, I have 30 years in aircraft maintenance.

        My last three projects use windowpane braced 1/2" and 3/8" thick cabinets. I'm happy.

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        • billfitzmaurice
          billfitzmaurice commented
          Editing a comment
          Quite right. Panel radiation can only occur in relation to panel vibration. No vibration, no radiation. Minimal vibration, minimal radiation. Constrained layer construction does have it's uses, such as between layers of sheet rock on walls as opposed to having studs on eight inch centers, but where speakers are concerned not really. FWIW I am an engineer in the industry.

        • djg
          djg commented
          Editing a comment
          Engineers and mechanics, often at odds. Not that we are, just a saying.

      • #9
        You might find this thread of interest. It is an approach to a very solid little cabinet.

        https://techtalk.parts-express.com/f...r-build-thread

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        • #10
          My B12 speaker uses 5 mm plywood with 3 layer Sonic Barrier adhered to the inside for damping. I believe this qualifies as a constrained layer design. Unfortunately, without building an identically shaped traditional box for comparison I can't really say if it works well or not.

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          • billfitzmaurice
            billfitzmaurice commented
            Editing a comment
            Damping the inside of the cabinet serves a very different purpose. It does very little in terms of reducing panel vibration, although that varies with the panel thickness and mass. If it's car sheet metal it does a lot. If it's 3/4" MDF it's hardly anything. OTOH a single brace connecting the middle of two opposing panels has the same effect as doubling the panel thicknesses. With adequate bracing you can get the equivalent of 2 inch construction using half-inch material.

          • Billet
            Billet commented
            Editing a comment
            I think that constrained layers and damping are intended to absorb vibrations. Bracing pushes the resonant frequency of the panels higher, possibly to a point where the wood internally absorbs the vibrations.

        • #11
          Originally posted by Billet View Post
          My B12 speaker uses 5 mm plywood with 3 layer Sonic Barrier adhered to the inside for damping. I believe this qualifies as a constrained layer design.
          A "constrained layer" is sandwiched and to do it correctly is a lot of work. So something like mdf, viscoelastic damping, mdf. I have a. big box of 1/8" butyl rubber damping stuff like BillF is referring to and I make sure to brace well, usually 3/4" mdf. (Just attaching to panels, not sandwiched.) It may or may not make a difference, but it's not hurting anything. I'm not building PA stuff so don't care if it is heavy.

          Comment


          • billfitzmaurice
            billfitzmaurice commented
            Editing a comment
            That butyl sheet is different from what he's talking about, which is foam sandwiched over butyl. It works as far as damping internal reflections is concerned, but IME no better than plain foam. I've got a lot of butyl sheet on hand too. I lined my car doors with it when I had the liners off to install crossovers, and I lined the rear package shelf. Every time I have a reason to remove any of the plastic interior trim I line it as well. I've seen guys line their entire car floor with it, but the liner under my carpet is 1/2" thick, so I haven't bothered with that.

            As to using it in speakers, I've made two identical speakers, one with it and one without. They measured the same, but of course they were well braced. I even lined an entire front loaded midbass horn with it to see the effect. It had none.

          • Billet
            Billet commented
            Editing a comment
            The 3 layer Sonic Barrier has a solid sheet of material with a thin layer of foam sandwiched between the solid sheet and the enclosure panel. I believe it actually is a constrained layer.
            Last edited by Billet; 09-08-2022, 07:48 PM. Reason: clarified some details about the solid sheet of material

          • billfitzmaurice
            billfitzmaurice commented
            Editing a comment
            It's a constrained layer when sandwiched between two higher density layers.

        • #12
          I used floor tile mounting tape to bond two layers of MDF together on my Continuums. Not very thick at all, but it would allow some movement. I've used that method on two project baffles between two 1/2" mdf layers.

          More interested in whether it will last. Also quick and clean compared to buttering up with titebond.

          Comment


          • #13
            My current build. Transverse windowpane, rear panel one stiffener plus a brace to the weakest part of the baffle,

            Click image for larger version

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            • #14
              Well since we have BillF in one corner and andy19191 in the other, I might as well jump in the ring! I made a brief summary of my testing here https://www.diyaudio.com/community/t...2#post-7090874. Bottom line to me, as shown by my testing, bracing has only partial effect on the primary panel resonance region, and something more should be done. There must be some form of damping, not just stiffening. My CLD method is stupid simple. There is no support for the idea that you can stiffen a wood box so the primary panel resonance region is above the passband of the midrange. It's not happening. Since the results on my website are a wall of words, I've decided to start a YT channel to better communicate what I've found so far. The first two videos are just about my method, no results, but I'm on vacation for 3 weeks and hoping to put out the bracing and panel material testing.


              ~Brandon
              Please donate to my Waveguides for CNC and 3D Printing Project!!
              Please donate to my Monster Box Construction Methods Project!!
              Soma Sonus

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              • billfitzmaurice
                billfitzmaurice commented
                Editing a comment
                I totally agree that moving the panel resonance above the passband is a red herring. While it may occur as a by-product of bracing that's not what prevents panel sourced coloration. The taming of panel vibration is. You can accomplish the same thing with pure mass, for instance, making the cabinet of six inch thick reinforced concrete. That sucker isn't going to vibrate, and the lack of panel sourced coloration isn't due to the panel resonant frequency being above the passband. Using damping and bracing in tandem may give a better result than bracing alone, but if it does IME that indicates that the bracing was too widely spaced and/or the panels too thin. Even with four inch spans between braces 1/8" plywood panels are going to vibrate...unless you bend them.

              • analogkid455
                analogkid455 commented
                Editing a comment
                Wow, a lot of good info you got there on your page, Augerpro. I just went through it all but will have to go back over it to digest it all. Thank you for all your hard work!

            • #15
              analogkid455 - although Augerpro says his website is a "wall of words" I suggest reading his page​​ (wall of words) on box construction methods since you are interested in the topic. (Go to the Soma Sonus link in his signature).

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