How Do You Brace a Sub Box

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  • Bing Fung
    Ultra Senior Member
    • Aug 2000
    • 6521

    How Do You Brace a Sub Box

    As most of you know I have been wanting to build a sub for a while now and was posed for the sono. Since then, I have played with the idea of a sub box that is 24"w x 20"h x 20.3"d. that would give me the same volume as the Sono I was designing (130L). The driver is to be placed along the 24" width with the port on the same baffle face.

    What are some general guide lines to bracing this box internally?

    Should the bracing run parrallel to the baffle or perpendicular, does it matter?

    What should the general spacing be?

    I was planning on using 3/4 MDF, should I step up to 1" instead?

    What is the easiest and simplest cut out to use on the bracing to calculate volume displacement? i.e. a circle would be the simplest in my mind but leaves too much material in the brace.




    Bing
    Bing
  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15261

    #2
    Hi Bing,

    It's a tradeoff between weight and rigidity. Actually, the main goal should be getting all panel resonances well above the highest frequency you plan to use. Personally, I'm a proponent of layered up 3/4" MDF; minimum of two layers for backs and sides, 3 layers for the front. But, as ThomasW will attest, I am a sick man. (though stout of back, shoulder, and arm, from picking up, working on, and moving these speaker cabinets.

    I've used bracing for building small speakers, using prefab cabinets as a starting point, such as the Woodstyle boxes available from Madisound. In those cases I've used oak, glued on edge, parallel to the panels, and also braces front to back, and side to side. The B&W matrix thing is the ultimate way to go. But,when you start getting to larger panel sizes, you wind up with a lot of braces, and perhaps not the panel mass and damping that you need. That's why speakrs like Avalon's and Hales are made with such "riduclous" panel sizes.
    If you can get 1" MDF in your area, use that as a minimum, and consider a matrix type bracing system, with 3/4" MDF as a minimum. Parts Express has those 3 cubic foot cabinet kits for subwoofers that aren't bad, they're 1", with 1" matrix braces. That's a pretty good starting point.

    Good luck with your project.

    Best regards,

    Jon




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    Comment

    • Andrew Pratt
      Moderator Emeritus
      • Aug 2000
      • 16507

      #3
      Bing what happened to the SonoSub idea? They are a lot easier to build




      Comment

      • ThomasW
        Moderator Emeritus
        • Aug 2000
        • 10934

        #4
        Hi Bing

        I assume this question is a function of you're wanting to build a "fine furniture" finished sub

        Jon has pretty much given you the best description of what to do. I'll add a little. But first here's an example of a well designed "box"



        Use doubled 3/4" MDF for the "body" of the box. Use 3/4" ply for the bracing. This will keep the weight down (well sort of!).




        theAudioWorx
        Klone-Audio

        IB subwoofer FAQ page


        "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

        Comment

        • Bing Fung
          Ultra Senior Member
          • Aug 2000
          • 6521

          #5
          I'm waffeling again Andrew! I started thinking that it would be nice to do something furniture grade. It's not to say the Sono is out, I'm just exploring the options. The box design I have come up with will look good as an end table. ok, maybe I'm experiencing SAF.

          Here is the prelim Autocad drawing. I haven't worked out were all the bracing will go. That's the B&W 603 on the right for perspective. If it looks like the B&W ASW 4000, that's because it is sort of modeled after it. Also with this I can place in a built in KG-5230 300W sub amp.






          Bing
          Bing

          Comment

          • Bing Fung
            Ultra Senior Member
            • Aug 2000
            • 6521

            #6
            Wow! That is beautiful Thomas, if I had your skill no doubt I would attempt that.

            It seems like the doubled 3/4 is the way to go, that is going to be one heavy sub built like that.

            I notice the Ariel sub does not have plywood laminated to the back side of the baffle for speaker attachment. Is it totally nessesary, or do you guys know of a different trick to prvent T-nuts from stripping in the MDF?




            Bing
            Bing

            Comment

            • ThomasW
              Moderator Emeritus
              • Aug 2000
              • 10934

              #7
              Bing

              Check out the following,

              The domain name Audioinnovation.com is for sale. Call BuyDomains at 844-896-7299 to get a price quote and get your business online today!


              Click on "speaker projects" then click on picture to the right of the "TC Sounds speaker" Dan's got a step by step picture tutorial for cabinet construction. Now this IS a little "overbuilt" but this should give you the general idea.

              The only guaranteed method to keep T-nuts from slipping is to use the ply layer (or something else with a wood grain) behind the baffle.

              Manufacturers don't use T-nuts, they just use wood screws.

              You can also simply glue small blocks of wood (not MDF) to the back of the baffle, where each screw will come through. I frequently glue on 1"X1" blocks of 3/4" oak, and set the T-nuts in them. You don't get the "stiffening" benefit from the ply using this method.




              theAudioWorx
              Klone-Audio

              IB subwoofer FAQ page


              "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

              Comment

              • Lexman
                Super Senior Member
                • Jun 2000
                • 1777

                #8
                Personally, I started with a 2 X 4 band just between the driver and the ports on the front side of my velex subs. I then used 1 X 2 cross supports across all horizontal sides, attached to the 2 X 4s. From the center, I also attached 1 X 2s going top to bottom. If that makes sense. My boxes are structurally stable, and I have NOT heard one bit of cabinet instability. Solid as a rock.

                Lex





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                Comment

                • ThomasW
                  Moderator Emeritus
                  • Aug 2000
                  • 10934

                  #9
                  Hi Lex,

                  Yes crossbracing or diagonal bracing of as many internal surfaces as possible is effective. Then tieing the opposing surfaces together with 1"X2" does result in a pretty stiff box. That's what Jon was describing is his post, when we are using preassembled aftermarket boxes from "Woodstyle". These boxes are sold by many of the DIY suppliers, and are easily identified by the use hardwood quarter round (usually oak or walnut) molding for the joints.

                  This is actually the only way to effectively brace preassembled boxes. The gusset method seen in the links I posted is only possible when scratch building a box.

                  Either method will work. The gusset is actually a bit easier to do, although it doesn't look that way. It helps to have a dado blade. Just cut dado's (slots) spaced 4-8" apart on all the internal surfaces. Then the gussets simply slide in place as the cabinet wall are glued up. The patterns cut into the gussets themselves, don't need to be as elaborate as detailed in the examples.

                  Sometimes tieing the crossbracing or diagonal bracing together can be a challenge, if the driver openings are small, or if there are a lot crossbraces.




                  theAudioWorx
                  Klone-Audio

                  IB subwoofer FAQ page


                  "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                  Comment

                  • Bing Fung
                    Ultra Senior Member
                    • Aug 2000
                    • 6521

                    #10
                    Ahh, to dato or not to dato was to be my next question Thomas.

                    Well, I'm certainly going to have a crack at desiging this box, That will be the easy part. Actual construction is another issue. Are the 3/4 sheets of MDF just laminated with glue or are they screwed together as well?

                    Thanks for the Link Thomas. I have not had a chance to read it yet, I'll do that tonight.




                    Bing
                    Bing

                    Comment

                    • ThomasW
                      Moderator Emeritus
                      • Aug 2000
                      • 10934

                      #11
                      They MUST be glued together, in some fashion. There are many "techniques" for this.

                      Some put a sheet of 60LB felt paper(aka "tar paper") between the MDF layers, then screw together using lots of screws. The "tar paper" adhesive itself, will glue the wood together. Doesn't hurt to let the pieces sit out in the sun for a day to heat-up.

                      Others use a floor mastic (adhesive), put on with a notched trowel like the ones used for floor tile.

                      Both these create what is called "constrained layer damping". This is where a "isolating layer" is placed between two ridged layers. Makes for a very dead/inert box.

                      Jon likes to make a "sandwich". He will use 2-3/4" layers of MDF separated by a layer of 1/4" "tempered" Masonite. This gets REAL heavy quickly!

                      If that's too exotic then use TiteBond II, and pressure (weight) to hold the pieces together while the glue dries. Glue rough cut pieces together, then cut to size. Trying to laminate precision cut pieces is problematic because the glue makes the pieces of wood want to "slide" apart.




                      theAudioWorx
                      Klone-Audio

                      IB subwoofer FAQ page


                      "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                      Comment

                      • Lexman
                        Super Senior Member
                        • Jun 2000
                        • 1777

                        #12
                        Thanks for the advice Thomas! Great information on internal construction too. I have thought about building another 2 subs, then selling the one's I have completed. I might yet But not now.

                        Lex





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                        Comment

                        • marc seals
                          Junior Member
                          • Sep 2000
                          • 19

                          #13
                          """"Regarding the T-Nut question""""

                          I used a nice glob/dollop of Basin/Tile adhesive caulk on, around, and over my T-nuts. This stuff is pretty strong and also has a little flex to it. I have removed and reinstalled my Shiva at least 5 times so far with nary a problem. I would also think that a decent epoxy would work as good also.
                          I am sure that the plywood method works as well but it is an extra step that MAY not be nessecary, at least from my experience with MY sonosub.
                          Good luck with whatever method you decide upon!

                          Comment

                          • Bing Fung
                            Ultra Senior Member
                            • Aug 2000
                            • 6521

                            #14
                            I though about hammering in the T-nut abd then applying a liberal amount of epoxy around the nut and area. Thanks,

                            Thomas, I had a read of Daniel's site. For his box he just used 1" MDF. Do you think I could get away with doing the same using a 12" driver? it would certainly make the job easier.




                            Bing
                            Bing

                            Comment

                            • ThomasW
                              Moderator Emeritus
                              • Aug 2000
                              • 10934

                              #15
                              Marc's right on track with using glue to help hold the "T-nuts". This is actually SPO (standard operating procesure) for all the Klone-Audio/AudioWorx projects, I just forgot to mention it. 5-minute epoxy works well for this application.

                              If you want to use more braces then of course the thickness of the walls can be decreased. It's a trade-off, thicker walls fewer braces, thinner walls more braces




                              theAudioWorx
                              Klone-Audio

                              IB subwoofer FAQ page


                              "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                              Comment

                              • Bing Fung
                                Ultra Senior Member
                                • Aug 2000
                                • 6521

                                #16
                                Alrighty then! carry on...

                                Thomas, when factoring in Volume displacement of the hardware, Does the port volume get calculated as total displacement of tube OD x Length or is it OD minus ID x Length?

                                In case that's not clear, is the air inside the tube length counted as displace volume of the tube as well, as if the tube is a solid?




                                Bing
                                Bing

                                Comment

                                • ThomasW
                                  Moderator Emeritus
                                  • Aug 2000
                                  • 10934

                                  #17
                                  Hi Bing

                                  Yes, you are correct. It's best to consider the port as a "solid". So it must be factored into the items deducted from internal volume.

                                  Now if someone is using monster ports 8"-10", and they are long, then there is some "fudge" factor that comes into play. If not the size of the box becomes huge.

                                  Understand that varying items 10-15% won't have a significant impact on the operation of a ported system. I know people tend to fixate on details but "ballpark" is usually close enough for most people's hearing




                                  theAudioWorx
                                  Klone-Audio

                                  IB subwoofer FAQ page


                                  "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                                  Comment

                                  • Bing Fung
                                    Ultra Senior Member
                                    • Aug 2000
                                    • 6521

                                    #18
                                    Thanks Thomas!

                                    Lex, Thomas, Andrew, Jon, I love this site, The S/N ratio for me is increditably high, thanks for having me




                                    Bing
                                    Bing

                                    Comment

                                    • Lexman
                                      Super Senior Member
                                      • Jun 2000
                                      • 1777

                                      #19
                                      wowie, that makes us feel good Bing, thanks. :B

                                      I was thinking on this glueing vs. screwing, and aside from the screwings we get day in and day out, lol. I REALLY REALLY believe that it's necessary to screw layers of MDF/Ply, whatever to insure a complete compression of the boards surfaces. Maybe compression is the wrong word, but complete contact. I just think it's very difficult to put enough weight on it to equal the pounds per square inch achieved by screwing in a close pattern one layer to the other. Along with gluing of course! The screws simply allow the boards to "become one" in the gluing process, and effectively have little impact once the glue is dried. Of course, you leave them anyway for added strength.

                                      And about these T-nuts, what the hell is a T-Nut? lol. I am familiar with the T-Bone. I probably know what they are, but just don't know them by that name.

                                      Lex





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                                      Comment

                                      • Bing Fung
                                        Ultra Senior Member
                                        • Aug 2000
                                        • 6521

                                        #20
                                        Good point on the screws and getting screwed Lex. LOL

                                        Here is a pic courtesy of Pat Sun's page.

                                        Let me reaqaint you to the humble T-Nut






                                        Bing
                                        Bing

                                        Comment

                                        • Patrick Sun
                                          Super Senior Member
                                          • Aug 2000
                                          • 1380

                                          #21
                                          Lex, here's a few pix of a t-nut in use:

                                          Photo 1

                                          Photo 2

                                          Photo 3




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