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Building a center speaker using urethane foam contruction

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  • Building a center speaker using urethane foam contruction

    After decades of negotiations, I finally get to build some speakers for a home theater. My family room (12'x16') is gutted, the plan is to build in shelving unit (photo attached). I can build it but using blackmail tactics with my wife, no speaker then no shelving unit. Wink

    The rear speaks will be Dayton CS620W In-wall speakers, no room a bookshelf speaker, the sub will be a ported design using Dayton 12" RSS315HF-4. The LR speakers will be Tango MT or AviaTrix Sealed MT Bookshelf speakers, most likely the Tango since they are only 15" tall.

    But even I admit, putting a AviaTrix under the TV is just ugly. One option still under negotiations, make the center channel built in.

    What I really want, a sound/speaker bar similar Dayton BS36 mounted directly under the TV, I may just buy buy and re-wire it for a center channel. But the drivers look so cheap....

    So my concept is, make a sound bar using 8# or 16# density Urethane foam (source US Composites) . The 16# density foam is quite hard with a compressive strength of 580 psi, it is hard as oak. The 8# density foam is similar to a soft wood.

    My problem, I cannot find any center speaker designs using ~3" drivers which I can adapt. I do have experience working with the foam, I did make a few subwoofer boxes for cars in a failed commercial venture, they were about 1/2 the weight of MDF boxes. I will do a followup post on my adventures using foam for speakers boxes.

    If anyone with experience in building speakers is interested in this project, I may be able to offer a prototype box for testing.

  • #2
    You built that shelf unit from scratch?


    • #3
      Why foam core construction?

      Using foam core allows for curve surfaces. An ideal application would be a cylinder shape down firing sub-woofer box. Cover it with veneer and a wood top/bottom or even a granite top and you got a nice looking cabinet. You could also make a bar height cocktail table for your home theater. Another advantage is the superior strength of a cylinder, pipes are round for a reason. Another application would be guitar speakers, using foam is ~1/2 the weight of MDF.

      What is the acoustics characteristics of foam?

      No clue.

      My adventures with foam construction.

      I tried a commercial venture making sub boxes for cars, it failed due to the complexity of multiple pouring of the foam, I did not have foam injection equipment to pour the foam in one application, I used plastic cups and a milk shake mixers and could not fill the mold with one pouring of foam. . I use aluminum flashing from Home Depot for the outer skin. As the foam rose and set, it would pull in the flashing material which created distortion in the box. I solved the problem but labor cost were ridiculous.

      What did work, I use felt carpeting padding for the inside of the box. I used carpet tape and polyurethane gorilla glue to seal up the padding.The urethane foam is attached directly to the padding. I also used 3/4" pvc pipe for structural strength. I cut holes in the padding and sealed them up with glue. The foam would fill the pipes making them directly embedded into the structure. I am unsure if the pipes were completed filled, i doubt it.

      I also tried to make the front (baffle) and back of the speakers foam core with a hard board (3/16" ?) skin, this added alot of complexity. For a home down firing subwoofer, I would suggest using 3/4" MDF. It would be much simpler to just make a foam cylinder then attach the front/back after the foam has cured. You could embedded bolts into the foam and then glue and bolt on the MDF panels.

      The outer skin should be applied after the foam has set. You make get air pockets formed which have to be filled (Bondo) for a smooth surface. Gluing veneer to the foam should work and look great. You can also paint the foam.

      well thanks for reading, I will answer any questions if anyone is interested.


      • #4
        Originally posted by Millstonemike View Post
        You built that shelf unit from scratch?
        Sorry for not being clear, I am using the photo as a model. I have a bunch of cabinet doors that I will use, the rest is cabinet making 101 with lots of molding. I made something similar. I will post photos when completed.