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The Foam Core Forte

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  • The Foam Core Forte

    Project Description:
    A 2.1 semi-portable boom box using foam core for the enclosure.

    Design Goals:
    I've been messing around with the idea of creating a compact stereo unit ever since our other high priced bluetooth unit started giving us trouble; cutting out, disconnecting intermittently, etc. The project goal was to create a relatively compact, very affordable speaker that covers from ~40hz on up, with hi-fi quality sound.

    Driver Selection:
    (1) Tang Band W3-1876S 3" Mini Subwoofer
    (2) Dayton CE65W-8 2-1/2" Shielded Extended Range

    Enclosure Design and Assembly:
    Taking inspiration from builds in another online DIY forum for audio, the enclosure is constructed out of foam core. I included my CAD layout of all the cut pieces in the photos below. The foam core allowed me to complete the whole build in days rather than weeks if I had used MDF, hardwood, or plywood. I simulated the enclosure sizes for the drivers as well as the port specs for the subwoofer in Unibox. I glued the foam core together with good old white Elmer's school glue. The drying time isn't great but i feel like the bond it gives on foam core is really strong. The plate amp and drivers are held in place with 8/32 threaded inserts and black allen head machine screws. The Elmer's didn't do such a great job adhering the threaded inserts to the foam core, so I came back with some Titebond III on all of them, which seemed to do the trick.

    Plate Amp and PS:
    The plate amp I used is based on the TPA3118 class D chip. There are two chips. One putting out 2x30 watts to the CE65's, and the other gives 60 watts to the sub. It's running off of a 120W laptop power supply. This combo is more than enough to drive the CE65's and the 1876S.

    Even though the CE65's only reach to ~16khz and this speaker isn't as compact as our old bluetooth, it beats the pants off of it in every way. The CE65's can play so much louder and cleaner with the 1876 picking up from 40-150hz. Jazz and vocals sound great with accurate reproduction of plucked bass notes and piano as well. I can say I'm already very happy with it. Hopefully it gets even better with a little break-in time on the drivers.
    Like my Dad always says, "I know enough to be dangerous!"

  • #2
    More Photos
    Like my Dad always says, "I know enough to be dangerous!"


    • #3
      Last set
      Like my Dad always says, "I know enough to be dangerous!"


      • #4
        Cool project. What foam did you use? Are the braces wood or foam?

        Soma Sonus


        • #5
          How do you cut the foam?
          Isn't it about time we started answering rhetorical questions?

          Paul Carmody's DIY Audio Projects
          Twitter: @undefinition1


          • #6
            Originally posted by Paul Carmody View Post
            How do you cut the foam?

            I've done some foam core projects. I used a straight-edge and a utility knife to cut it. The stuff is pretty cheap at Wal-Mart, Hobby-Lobby and some of the dollar stores.
            "We're speaker geeks, not speaker nerds. Nerds make money!" Marty H
            Bismarck, North Dakota
            My Current System: Jolida SJ502A, Squeezebox Touch, and Carmody Sunflowers
            My Garage System:Marantz 2238B and Nano-Neos


            • #7
              Very interesting! Where did you get the 2.1 amp from?
              That material looks to be a great way to quickly model something, too.

              How thick are your foam core boards? How dense is it? do the walls flex when you lift it with the top handle?
              I see some at Walmart that are 3/16", but that seems quite thin...


              • #8
                If you work anywhere with a marketing department, they often will have posterboards on foamcore that are discarded after events. I have an effectively limitless supply of the stuff from my company. Scroungers- SCROUNGE!


                • #9
                  Originally posted by andykriech View Post
                  Very interesting! Where did you get the 2.1 amp from?
                  Go to the popular auction site and search for 2.1 plate amp. It'll be the first thing that comes up. It does look pretty cool, I wonder how it dissipates heat though, doesn't look to have a heat sink.


                  • #10
                    Thanks Augerpro and Andykriech! It's foam core board like others have said. It's a center core of foam with a layer of paper bonded to each side. It's pretty rigid stuff even at only 3/16" thick. The bracing is all the same 3/16" foam core. Also, most of the enclosure is two layers for extra rigidity and to help the threaded inserts have enough meat to grab onto. There's no flex when I grab the handle on top due to the fender washers I used to sandwich the top piece of foam core. You're right! This stuff gives you a ton of flexibility to model enclosures fast and cheap. Badman nailed it too. If you can scrounge your projects get even cheaper. This project can easily be done for under $100. And I've scrounged a bunch of 1/2" thick foam core for another project.

                    The amp is from the big E auction site. Just search "TPA3118 HIFI subwoofer amplifier".

                    Paul C and Mikejennens, I've used a utility knife too but I've found that an x-acto knife with a #11 blade gives the best control. I use a starret 12" ruler for most cuts or a 24" straight edge for longer cuts. The most important thing is to try to cut the foam core so the edges are as square to the faces as possible otherwise you end up with weaker joints.
                    Like my Dad always says, "I know enough to be dangerous!"


                    • #11
                      Jeff F, the TPA3118 chip has a thermal pad on the bottom of the chip which actually heatsinks through the pcb itself. In addition I think this design benefits from the aluminum plate also helping to pull some heat off of the pcb. The 3118 is a pretty efficient chip as well, so it won't produce a ton of heat unless you really take it to its limits with a 24V power supply, 4 ohm loads and full volume listening. I'm running 19.5V with a 4ohm sub and 8ohm stereo pair of drivers. That said I haven't fully tested this amps longevity but looking forward to putting some hours on it at moderate listening levels.

                      Here's a photo of the exposed circuitry. Quite a complicated, but apparently well done layout.
                      Click image for larger version

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                      Last edited by jwjarch; 08-30-2017, 12:53 PM. Reason: Added amplifier image and info.
                      Like my Dad always says, "I know enough to be dangerous!"