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  • Cabinet stiffening. . .

    Is it OK to put a 1/4" HDF Peg Board panel in the center from front to back for the full height of the cabinet (attached by glue/nail gun on all sides) with (6) evenly vertically spaced 3-1/4 inch holes drilled into it and (2) smaller holes between the big holes in a 6.5"wide X 9.5" deep X 30.5" tall cabinet made of 3/4" MDF? (interior dimensions).

    Looks EXACTLY like a 6 cylinder diesel engine head gasket. (accidental - just wound up that way as my brain said to do it that way).

    Just wondering because I just did that and before I glue it all up I'd like to know what the effects of ANY early reflections from the woofer upon it will look like and if I should take up knitting again instead of using hole saws and beer for fun.

    Thanks!

    Steve.



  • #2
    Steve, I don't think it will really add that much stiffness as doubled(tripled) thickness strips glued-up to the sides of your cabinet. Maybe if you doubled-up 1/4" pegboard or plain Masonite you'd add rigidity if you did it correctly. I'm not that good at thinking about "space-framing" for internal bracing. Hence my sub-woofer being named "The Norge" after the early 1950's compact 'fridges that weighed half a ton!!! (But ran 'til the 1990's! Them and Crosley's!)
    Your idea is good, but I think you need stouter bracing material. I could be wrong...been wrong before!

    Comment


    • #3
      Originally posted by Whitneyville1 View Post
      Steve, I don't think it will really add that much stiffness as doubled(tripled) thickness strips glued-up to the sides of your cabinet. Maybe if you doubled-up 1/4" pegboard or plain Masonite you'd add rigidity if you did it correctly. I'm not that good at thinking about "space-framing" for internal bracing. Hence my sub-woofer being named "The Norge" after the early 1950's compact 'fridges that weighed half a ton!!! (But ran 'til the 1990's! Them and Crosley's!)
      Your idea is good, but I think you need stouter bracing material. I could be wrong...been wrong before!
      Dude!

      I am not trying to be difficult nor contrary but after having considered "Engineered Floor Trusses" I thought that it might be suitable for cabinet stiffening while consuming far less internal volume?

      Still learning ...

      Thanks for the favor of your reply. (I'll try posting pics later).



      Comment


      • #4
        Best/most efficient way to brace is to run about 3/4"-1" dowels (or sq. stock) between opposite panels (side-to-side, front-to-back, ... ). Staggered spacing is good as well.

        Comment


        • #5
          Honestly you can probably do better bracing in the manner Chris describes. But, your method *may* offer some wall damping from the relatively flexible peg board.
          Francis

          Comment


          • #6
            Originally posted by Steve Lee View Post
            Is it OK to put a 1/4" HDF Peg Board panel in the center from front to back for the full height of the cabinet (attached by glue/nail gun on all sides) with (6) evenly vertically spaced 3-1/4 inch holes drilled into it and (2) smaller holes between the big holes in a 6.5"wide X 9.5" deep X 30.5" tall cabinet made of 3/4" MDF? (interior dimensions).
            Assuming the intention is to make the cabinet quieter then bracing should aim to stiffen the front baffle in order to reduce the power (force * velocity component normal to baffle) being put into vibrating the cabinet. Once energy is in the cabinet damping will remove it while stiffness will not whatever DIYers beliefs may be to the contrary.

            The obvious way to stiffen your cabinet is with horizontal panels just above and below the low frequency drivers. Holes drilled as required. There might be a case for one or two more away from the driver/s depending on driver arrangement.

            A vertical panel connecting front baffle and rear panel would also stiffen the front baffle but the large cutouts to go around the drivers would weaken it. Is this what you are proposing?

            A vertical panel connecting the side walls would have minimal effect on stiffening the baffle and is likely to be of little benefit.

            Dowels between front and back centres are likely to do little good and could make matters worse. They will add little stiffness because the centres are the least stiff part of the baffle. When the front baffle moves forward/back the rear panel will follow it adding little stiffness. However a fair amount of mass will have been added by the dowel leading to the main front baffle mode likely falling in frequency not increasing. A panel with holes is likely to perform significantly better.

            Dowels side to side and top to bottom will do little to stiffen the baffle, will likely add new low frequency modes and be of little benefit.


            Comment


            • #7
              Panel to panel bracing with dowels, be they round, square or rectangular, is the best bracing method. You can use so-called window braces, or shelf braces, but they're heavier, more complicated and no more effective. Most of their material ends up not having any effect.
              A single dowel connecting the centers of opposing panels imparts stiffness equal to doubling the panel thickness. More work even better, but there is a point of diminishing returns. I've found even with pro-touring grade subwoofers made of 1/2" BB plywood dowels need not be spaced closer than 6 inches apart, nor less than six inches from the cabinet corners.
              www.billfitzmaurice.com
              www.billfitzmaurice.info/forum

              Comment


              • #8
                Originally posted by andy19191 View Post

                Assuming the intention is to make the cabinet quieter then bracing should aim to stiffen the front baffle in order to reduce the power (force * velocity component normal to baffle) being put into vibrating the cabinet. Once energy is in the cabinet damping will remove it while stiffness will not whatever DIYers beliefs may be to the contrary.

                The obvious way to stiffen your cabinet is with horizontal panels just above and below the low frequency drivers. Holes drilled as required. There might be a case for one or two more away from the driver/s depending on driver arrangement.

                A vertical panel connecting front baffle and rear panel would also stiffen the front baffle but the large cutouts to go around the drivers would weaken it. Is this what you are proposing?

                A vertical panel connecting the side walls would have minimal effect on stiffening the baffle and is likely to be of little benefit.

                Dowels between front and back centres are likely to do little good and could make matters worse. They will add little stiffness because the centres are the least stiff part of the baffle. When the front baffle moves forward/back the rear panel will follow it adding little stiffness. However a fair amount of mass will have been added by the dowel leading to the main front baffle mode likely falling in frequency not increasing. A panel with holes is likely to perform significantly better.

                Dowels side to side and top to bottom will do little to stiffen the baffle, will likely add new low frequency modes and be of little benefit.

                Sometimes I wonder if narrow cabinets can sound better because they brace the front panel better, closer to the woofer cutouts.
                Francis

                Comment


                • #9
                  Originally posted by fpitas View Post

                  Sometimes I wonder if narrow cabinets can sound better because they brace the front panel better, closer to the woofer cutouts.
                  The loudest unwanted mode is often the one involving the woofer bouncing on the baffle with the rest of the cabinet moving in sympathy. It is not only among the lowest in frequency, efficiently driven by the vibration of the drivers but also radiates strongly at the listener. A narrow baffle not only stiffens the baffle but also reduces the radiating area facing the listener making the task of good design easier in this respect. Whether a wide or narrow baffle if a cabinet is competently designed with respect to damping and stiffening where it is actually beneficial it should be possible to make the radiation from the cabinet effectively inaudible at the listening position. That is, if done well it largely ceases to be a factor in the sound quality of speakers.

                  Comment


                  • #10
                    Originally posted by andy19191 View Post
                    Whether a wide or narrow baffle if a cabinet is competently designed with respect to damping and stiffening where it is actually beneficial it should be possible to make the radiation from the cabinet effectively inaudible at the listening position. That is, if done well it largely ceases to be a factor in the sound quality of speakers.
                    andy19191 - I am glad you posted. I was following the recent thread at Diyaudio.com and saw your recommendation "to brace effectively with struts one should triangulate. For example, connecting the centres of adjacent rather than opposite panels" and was going to link to it. These conversations tend to digress into technical issues that may not be "audible at the listening position". In a few bullet points, how would you recommend designing a competently designed speaker in terms of damping and stiffness?

                    Comment


                    • #11
                      Originally posted by fpitas View Post

                      Sometimes I wonder if narrow cabinets can sound better because they brace the front panel better, closer to the woofer cutouts.
                      In my previous reply I assumed cabinets would be well designed with respect to making them quieter. On the other hand, if there is no effective damping and the cabinet is braced raising the frequency of the lowest resonances to where they are more audible and intrusive then I think there may well be something in what you suggest. A wide 12" 3 way monitor in comparison with a narrow 2 x 8" 3 way tower would make a nice example to develop.

                      Comment


                      • #12
                        Originally posted by fpitas View Post
                        Sometimes I wonder if narrow cabinets can sound better because they brace the front panel better, closer to the woofer cutouts.
                        If unbraced a narrower baffle would be better than wider, because the narrower baffle has less unbraced area. How close the sides are to the woofer cutouts is immaterial. The problem you run into with a large woofer is you have to contend with not being able to place braces as close to each other as you'd like. A trick I've used with large front mounted woofers is to run a brace from four of the driver bolt hole locations to the back, screwing the driver to not only the baffle but right through it into the braces. That makes the baffle/back/driver assembly a rigid structure.

                        www.billfitzmaurice.com
                        www.billfitzmaurice.info/forum

                        Comment


                        • #13
                          Originally posted by a4eaudio View Post

                          andy19191 - I am glad you posted. I was following the recent thread at Diyaudio.com and saw your recommendation "to brace effectively with struts one should triangulate. For example, connecting the centres of adjacent rather than opposite panels" and was going to link to it. These conversations tend to digress into technical issues that may not be "audible at the listening position". In a few bullet points, how would you recommend designing a competently designed speaker in terms of damping and stiffness?
                          That depends on the type of speaker. Subwoofers, 3 ways and 2 ways have different sound radiation issues to address with cabinet design and there is often more than one approach that could be used effectively. This requires something more than a few bullet points if it is to be presented effectively. In particular it needs examples with quantified evidence from detailed predictions and/or measurements.

                          I and one or two others with engineering backgrounds have posted on cabinet stiffness, damping, mass, isolation,... in the past but to little practical effect it would seem. In posts like this people without engineering backgrounds (i.e. most) have difficulty distinguishing between suggestions with a solid engineering basis and those without when there is disagreement. There is an understandable tendency to look to well established DIY speaker enthusiasts with a strong web presence. These people tend not to have an engineering background and tend to propagate recipes they assess to have worked before. Sometimes this assessment has been subjective. This has allowed one or two of the less important aspects of speaker design to become the norm despite being relatively poor in an engineering sense.

                          The odd specific design aspect like the OPs may benefit from a bullet point or two but the much larger subject of how to design speaker cabinets to be quiet requires rather more.

                          Comment


                          • a4eaudio
                            a4eaudio commented
                            Editing a comment
                            "I and one or two others with engineering backgrounds have posted on cabinet stiffness, damping, mass, isolation,..."
                            Yes, I have appreciated your many posts, even though some of it goes over my head and agree that most people don't try to incorporate the science. I figure if it can be presented in bullets then people would be likely to try. If it is more nuanced (which of course it is) then it may be too much effort and they'll just go with what is on someone's website or YouTube video.

                        • #14
                          Originally posted by andy19191 View Post
                          Dowels between front and back centres are likely to do little good and could make matters worse. They will add little stiffness because the centres are the least stiff part of the baffle. When the front baffle moves forward/back the rear panel will follow it adding little stiffness. However a fair amount of mass will have been added by the dowel leading to the main front baffle mode likely falling in frequency not increasing. A panel with holes is likely to perform significantly better.

                          Dowels side to side and top to bottom will do little to stiffen the baffle, will likely add new low frequency modes and be of little benefit.
                          Originally posted by billfitzmaurice View Post
                          Panel to panel bracing with dowels, be they round, square or rectangular, is the best bracing method. You can use so-called window braces, or shelf braces, but they're heavier, more complicated and no more effective. Most of their material ends up not having any effect.
                          A single dowel connecting the centers of opposing panels imparts stiffness equal to doubling the panel thickness. More work even better, but there is a point of diminishing returns. I've found even with pro-touring grade subwoofers made of 1/2" BB plywood dowels need not be spaced closer than 6 inches apart, nor less than six inches from the cabinet corners.
                          Dowels, no dowels, center brace, no center brace...

                          ~Brandon 8O
                          Please donate to my Waveguides for CNC and 3D Printing Project!!
                          Please donate to my Monster Box Construction Methods Project!!
                          DriverVault
                          Soma Sonus

                          Comment


                          • andy19191
                            andy19191 commented
                            Editing a comment
                            Indeed. So how would a reader determine which is correct, whether both are addressing the same issue, how much it matters,...

                        • #15
                          OP merrily ignores all input and goes on with his project as planned . . .

                          Comment


                          • djg
                            djg commented
                            Editing a comment
                            I've done that.

                          • Steve Lee
                            Steve Lee commented
                            Editing a comment
                            Obviously - you have copious builds under your belt.

                            My hat is off to you.

                            :D
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