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How ManyPoints of Contact for a Removable Baffle?

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  • #16
    We did this with two of our recent designs. If you have a good gasket, it isn't as difficult as you might think. Our build was also translam.

    On the bookshelf design, we only used 4 points. We initially had an air leak in one, but when we took it apart we figured out the gasket had moved out of place in assembly. Once that was fixed, 0 leaks.


    On the tower design we had a top and bottom unit separated. The bottom had 8 points and I think the top had 6.


    The towers arent finished in that photo, but the mounting hasn't changed, just the woofer and baffle finish.

    We have had no problems with air getting out. By far the most important consideration was having threaded inserts to allow us to tighten without worry of stripping the wood.

    Comment


    • #17
      Originally posted by ohaple View Post
      We have had no problems with air getting out. By far the most important consideration was having threaded inserts to allow us to tighten without worry of stripping the wood.
      This is what I am most worried about. On the R/L TM cabs, they have that 1" tab going all along the side. I am doing 6 (3 on each side) and don't have any worries there. I am slighting concerned if I do the tap in nuts that I will split the BB Ply. That's why I was going for attaching to the internal bracing.

      Comment


      • #18
        Just a note on that- you could add a natural wood square dowel to the rear of the tab for a binder in case the ply would split for whatever reason. This is insurance in this case that it will stay solid, and the insert will clamp to the wood, not the ply this way. I've seen plywood separate a whole lot easier than I thought it would.

        Bummer on the sub- would have liked to hear your impressions.

        Later,
        Wolf
        "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
        "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
        "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
        "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

        *InDIYana event website*

        Photobucket pages:
        http://photobucket.com/Wolf-Speakers_and_more

        My blog/writeups/thoughts here at PE:
        http://techtalk.parts-express.com/blog.php?u=4102

        Comment


        • #19
          Originally posted by Ironman129 View Post

          This is what I am most worried about. On the R/L TM cabs, they have that 1" tab going all along the side. I am doing 6 (3 on each side) and don't have any worries there. I am slighting concerned if I do the tap in nuts that I will split the BB Ply. That's why I was going for attaching to the internal bracing.
          We used the self-threading screw in inserts. We had no issues with splitting the birch ply with the inserts. Just make sure you are drilling the appropriate hole for the insert.Sometimes if we are worries about the strength of a hole we will also soak in some superglue. Not sure if it helps, but it makes us feel better about it.

          Comment


          • #20
            Originally posted by ohaple View Post

            We used the self-threading screw in inserts. We had no issues with splitting the birch ply with the inserts. Just make sure you are drilling the appropriate hole for the insert.Sometimes if we are worries about the strength of a hole we will also soak in some superglue. Not sure if it helps, but it makes us feel better about it.
            ^ this, in particular screw in over smash in (you're damaging the material / losing material for insert grip by doing that far more than screw in) and for pre-drill, should be no brainer to always do that, using the smallest appropriate hole which is typically specified by the insert notes or descriptions, at-least the ones I've looked at.

            Well applied Hot Glue also works exceedingly well with MDF. From experiments it'll peel off the MDF material instead of just coming off in most cases, probably because MDF is so incredibly porous. No idea about Hot Glue on BB, but plenty here likely do know.

            You could easily do a piece of scrap matching your configuration as a test.

            Gorilla glue I do find is in fact one of the toughest, best holding / highest strength, longest lasting wood glues from several I've used.

            Experts around here have likely used more exotic or less well known glues that may be even better, but they'd need to speak to that.

            And to go absolute Rambo on it if I needed or wanted to - I'd use Minwax Wood filler w/hardner, pack it in the insert hole, screw the insert in, scrape off the excess. It'll hold the wood itself together and become a part of that piece of wood until the sun burns out or something else breaks first. That stuff is liquid wood. Love it, you just have to get used to how to work with it, particularly hardener amount vs filler for timing purposes. Grab a fan though. Smelly stuff, well worth it though. Using it to cover and repair some MDF edges right now actually.
            Feel free to rip my assumptions apart when wrong, or fix if close.

            Passive Radiators:
            All PR(s) Vd must be at-least double all woofer(s) Vd. Calc = Sd x Xmax to get Vd for all PR(s) and all woofer(s). A combined PR(s) Vd equal or > than a combined woofer(s) Vd is usable.
            Woofer(s) with large Xmax vs Sd, all PR(s) with Xmax at-least double all woofer(s) Xmax is usable.
            A PR max weight is said to be its Mms x3

            PR Systems - tight focus with key parameters.
            PR Speaker Design - thorough coverage.

            Comment


            • #21
              Originally posted by Wolf View Post
              Just a note on that- you could add a natural wood square dowel to the rear of the tab for a binder in case the ply would split for whatever reason. This is insurance in this case that it will stay solid, and the insert will clamp to the wood, not the ply this way. I've seen plywood separate a whole lot easier than I thought it would.

              Bummer on the sub- would have liked to hear your impressions.

              Later,
              Wolf
              This makes a lot of sense and will allow to place them anywhere I need too!

              Comment


              • #22
                Going off of your guy's ideas, I can just add dowels or block of mdf in these corners. That would all be glued to 2 points and tap the threaded inserts in to that. That way I don't have to worry about splitting the BB Ply and it still should be nice and solid. (forgive the free hand drawing in "paint" but it should convey the idea).
                Attached Files

                Comment


                • #23
                  ^ that'll keep it simple, add even more strength in certain areas and MDF pre-drills like butter. Should do nicely. With them being relatively tiny they probably won't affect the internal volume ft^3 and tuning to any noticeable degree.
                  Feel free to rip my assumptions apart when wrong, or fix if close.

                  Passive Radiators:
                  All PR(s) Vd must be at-least double all woofer(s) Vd. Calc = Sd x Xmax to get Vd for all PR(s) and all woofer(s). A combined PR(s) Vd equal or > than a combined woofer(s) Vd is usable.
                  Woofer(s) with large Xmax vs Sd, all PR(s) with Xmax at-least double all woofer(s) Xmax is usable.
                  A PR max weight is said to be its Mms x3

                  PR Systems - tight focus with key parameters.
                  PR Speaker Design - thorough coverage.

                  Comment


                  • #24
                    Yes, just don't use MDF for the blocks. MDF is way weaker than the ply
                    John H

                    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                    Comment


                    • #25
                      Since you've got access to a cnc why not just route a groove on the back side of the baffle and use an o-ring or some spline as your gasket?

                      Comment


                      • #26
                        What if.... the tweeter is mounted from the front in the normal way, after the baffle surface between the woofers is recessed an inch or so. Then make a removable section that goes in front of the tweeter. No need to make it air tight this way, and only a minimal amount of strength would be needed.

                        Comment


                        • #27
                          In my extensive experience in working with MDF as a general utility material in my garage, unrelated to speakers, where they mostly see far more stress than the proposed 8 blocks this project will ever experience, I believe using MDF for the blocks would work fine.

                          With that said though, if OP has scrap ply available, can cut the blocks to the sizes he needs, can pre drill without splitting them, there's no reason not to use ply and just be done with it, which at this point he may well be approaching because he just wants to get it done and have it be air tight, and move on



                          ************************************************** ******************
                          Long winded - Just skip this section if MDF blocks have been discarded as option:
                          ************************************************** ******************

                          Specifically, minimum 2" squared MDF blocks, Gorilla glued on two sides each, pre drilled with at-least one of several methods mentioned to reinforce insert hole strength should do for this application.

                          My hypothesis (some of which promoted to theory (for me) from my own experience described above) as to why includes:
                          • they're simply holding a baffle butt against the cabinet tight. They're not supporting the entire baffle + driver mass, because
                          • the backing ply dados support the entire baffle mass in many directions, assuming a nice tight fit, because
                            • we can assume a tight fit (providing support) as this is literally about air tightness. Without that it will leak, becoming moot until it does meet this criteria.
                          • limited forces the blocks will experience, including outward pressure.
                            • the number of bolts further spreading the overall, already limited load all the blocks will experience individually.
                          • each MDF block well glued on 2 sides each.
                          • blocks of adequate size. I'm thinking 2" squared based on the size of the insert will leave plenty of meat for the block strength they actually need to provide for their purpose, based on all the above.
                          • well treated insert holes providing a very solid bolt to baffle connection, preventing the MDF from tearing out.
                          Added Strength:
                          Reinforcing MDF by orders of magnitude is a simple procedure when needed by simply using Wood Hardener. Although for their purpose in this project scope I don't think it's needed, it's available, viable, cheap and works incredibly well.

                          There are folks (including expert builders) around this board that actually soak their entire baffle, like a bath, in Wood Hardener, for the purpose of strengthening not just the entire baffle, but in particular small sections or strips of MDF. Soaking 2" blocks wouldn't take much hardener, doable in a small pan or bucket with just enough to do the job.

                          Examples of super thin weak areas reinforced with hardener, and some told me theirs are way thinner in these areas, and the hardener did the trick even in those extreme cases, allowing sanding and interaction without these tiny strips (weak when just raw MDF) being affected or damaged. This matches my experience when building my LCR.

                          Thin in tower MTM section of an MTMWWx2PR config
                          Click image for larger version  Name:	ThinMat1.Tower.MTM.Section.png Views:	1 Size:	748.1 KB ID:	1390391
                          ‚Äč
                          Thin in CC same config except horizontal and even thinner

                          Click image for larger version  Name:	ThinMat2_CC.png Views:	1 Size:	538.2 KB ID:	1390392

                          Just another long winded 2-1/2c on the matter.
                          Last edited by Thump; 10-13-2018, 03:50 PM. Reason: Updated sig
                          Feel free to rip my assumptions apart when wrong, or fix if close.

                          Passive Radiators:
                          All PR(s) Vd must be at-least double all woofer(s) Vd. Calc = Sd x Xmax to get Vd for all PR(s) and all woofer(s). A combined PR(s) Vd equal or > than a combined woofer(s) Vd is usable.
                          Woofer(s) with large Xmax vs Sd, all PR(s) with Xmax at-least double all woofer(s) Xmax is usable.
                          A PR max weight is said to be its Mms x3

                          PR Systems - tight focus with key parameters.
                          PR Speaker Design - thorough coverage.

                          Comment


                          • #28
                            Originally posted by Thump View Post
                            In my extensive experience in working with MDF as a general utility material in my garage, unrelated to speakers, where they mostly see far more stress than the proposed 8 blocks this project will ever experience, I believe using MDF for the blocks would work fine.
                            Thanks. I have scrap of both. I was thinking 1.5" squares of 3/4" mdf or ply. I could double it up if that would help. Make 1.5" cubes, but then I will need 3" connector bolts to make it through the 1" baffle and 1.5" block.

                            Comment


                            • #29
                              Originally posted by Ironman129 View Post

                              Thanks. I have scrap of both. I was thinking 1.5" squares of 3/4" mdf or ply. I could double it up if that would help. Make 1.5" cubes, but then I will need 3" connector bolts to make it through the 1" baffle and 1.5" block.
                              What final connection strategy did you settle regarding inserts and bolts? I'm trying to determine why the bolt needs to go all the way through the block to its backside.
                              Feel free to rip my assumptions apart when wrong, or fix if close.

                              Passive Radiators:
                              All PR(s) Vd must be at-least double all woofer(s) Vd. Calc = Sd x Xmax to get Vd for all PR(s) and all woofer(s). A combined PR(s) Vd equal or > than a combined woofer(s) Vd is usable.
                              Woofer(s) with large Xmax vs Sd, all PR(s) with Xmax at-least double all woofer(s) Xmax is usable.
                              A PR max weight is said to be its Mms x3

                              PR Systems - tight focus with key parameters.
                              PR Speaker Design - thorough coverage.

                              Comment


                              • #30
                                I have a bunch of the T-Nuts:

                                https://www.parts-express.com/10-32-...-pcs--081-1088

                                but they are all #10-32. I like the added surface area of the connecting bolts both those are 1/4" So I thought I would do threaded inserts. I can use the connecting bolts and It won't interfere with the waveguide, so I think it should be all good.

                                Comment

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