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Twin Sub Project

I'm building a slightly modified pair of JR's Twin Subs, using the same GRS 12SW-4HE  subwoofers and Dayton SPA250 plate amps.   Thanks, JR, for sharing this info in the other thread. 

Here is the basic plan: 3.1 cu. ft, 1.5" thick walls, and an adjustable external port coming out the top/rear of box. Provide a small area on the top/front of box to place a pair of satellite speakers that will be large enough to hide the ugly looking port just behind it. Adjust the length of port for best sound with the particular satellite speaker used.



joeybutts
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Comments

  • Panel glue-up: The total 1.5" thickness was formed by gluing two 3/4" thick panels together to form rabbets along all edges.


  • edited April 28

    Glue up: 4 panels have been glued up, but the baffle and one side panel have not been glued in place yet. Not sure if I am going to glue or screw the baffles in place.


    joeybutts6thplanettajanes
  • Baffle: I bolted the woofer temporarily in place & then marked the areas for routing out clearance scallops. The woofer hole was cut with a jig saw at a 20 degree bevel because the 8 mounting holes were very close to the edge. I felt that the bevel was needed to provide greater strength to support the woofer. But it blocks air flow. The scallops should help to restore the flow, yet retain the strength around the mounting holes and T-nuts. I also epoxied the T-nuts in place to keep them from falling out.


    kenrhodesSteve_Leejoeybutts6thplanet
  • Nifty project.

    I seen the price for a sheet of 3/4" plywood. I'm not building anything.

  • I like your beveled hole. That's an interesting solution to woofers with screw holes close to the edge.

    joeybutts
  • Hot swappable ports are a nice feature.

    Particle board is the only affordable cabinet material these days so its back to the future . . .

  • Thanks, guys. Much appreciated. Luckily, I purchased this particle board several years ago, at substantially lower prices. So I am using NOS particle board for this project!

    At double thickness, this is going to be a heavy one. Using my uncalibrated bathroom scales, I am guestimating 90 lbs per sub, not including plate amps. The plate amps are 12 lbs each, which would bring it up to 102 lbs, so I think I will be putting the amps in separate boxes.

  • Build in some kind of handles?

  • Might want to add a removable port end flare. It would be fun to test with and without

     John H, thanks to JP I did get that email
  • @Kornbread said:
    Build in some kind of handles?

    Do you mean like a tool chest? Not a bad idea. Then I could install locking style casters to roll them around.
    https://www.homedepot.com/p/Husky-26-in-W-x-18-in-D-Standard-Duty-4-Drawer-Rolling-Tool-Cabinet-in-Gloss-Black-HKST98066BK/309580736?MERCH=REC--pip_sem_mobile--300372967--309580736--N

    rjj45
  • @jhollander said:
    Might want to add a removable port end flare. It would be fun to test with and without

    Good idea. Do they make flares that fit 4" ID PVC sch 40 pipes? Or would this be a DIY thing. I have not checked into this yet. I've done NF measurements of ports with and without flares on one speaker system. When I cranked the volume up high I could actually see a turbulant "break point" where the port tuning shifted from about 30 at low volumes to about 50Hz or so at higher volumes.

  • You would have to DIY. My preferred method is to use a flush trim bit on the inside of the PVC then do a round over. Probably have to make a outer sleeve clamp to the port to keep it from moving.

     John H, thanks to JP I did get that email
  • @4thtry said:

    @Kornbread said:
    Build in some kind of handles?

    Do you mean like a tool chest? Not a bad idea. Then I could install locking style casters to roll them around.
    https://www.homedepot.com/p/Husky-26-in-W-x-18-in-D-Standard-Duty-4-Drawer-Rolling-Tool-Cabinet-in-Gloss-Black-HKST98066BK/309580736?MERCH=REC--pip_sem_mobile--300372967--309580736--N

    Since the box is double-wall, I was thinking simply use the router and cut an appropriately sized slot in the right locations.

  • Is there going to be any side-2-side bracing or just the double thick walls? Bill Fizzy would be put off.

    joeybuttsrjj45
  • Oh no! Placing subs right under the satellites? The Big Fizzy will be pooping in his panties!

    4thtryjoeybutts
  • "Ah, just use enough PL Premium to fill in the cracks, it'll be okay."

    joeybutts
  • @PWRRYD said:
    Oh no! Placing subs right under the satellites? The Big Fizzy will be pooping in his panties!

    Paul Hales being interviewed by Scott W. It's over 1 hour long and somewhat boring. But fast forward to 53:30 and watch the last 10 minutes of the vid, where they discuss the multi-sub concept and "kick drum bass in the butt." Subs located elsewhere just do not sound "right" to my ears.

    dcibelPWRRYD
  • @PWRRYD said:
    Is there going to be any side-2-side bracing or just the double thick walls? Bill Fizzy would be put off.

    No bracing. Double thick walls or bust. Going to line the walls with 1/2" fiberglass (Armstrong pebble 2x4 panels at Menards) and that should be good enough.

  • @jhollander said:
    You would have to DIY. My preferred method is to use a flush trim bit on the inside of the PVC then do a round over. Probably have to make a outer sleeve clamp to the port to keep it from moving.

    The biggest roundover bit that I currently have is 3/4" Not sure if that would be enough. Think I'll pick up a pair of Precision PSP-41F 4" inside flares (PE 268-377). They will not slip onto 4" schedule 40 PVC, but I should be able to cobble together some type of adapter to make this work. Those flares have a much bigger radius.

    rjj45
  • While "good" router bits are pretty expensive, Yonico has inexpensive 1", 1-1/4", 1-1/2" round overs on Amazon.

    rjj45
  • @a4eaudio said:
    While "good" router bits are pretty expensive, Yonico has inexpensive 1", 1-1/4", 1-1/2" round overs on Amazon.

    I'd imagine that personal safety and following the proper multi-pass procedures would be extremely important when using roundover bits of this size. I've never used a bit this large, so I would have to study the matter thoroughly before attempting to use one of these. But thanks for the tip.

  • edited April 29

    No doubt! I thought the 3/4" was a little scary the first time I used it. I'm sure my buddy who just bought a mill and lathe would just laugh...

  • I have the 1-1/2 round over bit. I used it in my router table on low speed for the C-Cake project. I made very shallow passes. Given some time I could make make you a flare.

     John H, thanks to JP I did get that email
  • I have some 4" flares laying around I can donate to the cause. You'll be at the gathering next weekend, right.

  • @jhollander said:
    I have the 1-1/2 round over bit. I used it in my router table on low speed for the C-Cake project. I made very shallow passes. Given some time I could make make you a flare.

    Thanks for the offer John! Looks like Eric has solved my problem. After measuring the flares, I'll make up a pair of small wooden adapter rings to fit the flares onto the ends of the PVC pipes. Should look really cool, like a vintage locomotive smoke stack! :)

  • @6thplanet said:
    I have some 4" flares laying around I can donate to the cause. You'll be at the gathering next weekend, right.

    Thanks, Eric. Yes, I'll be there.

    6thplanet
  • Progress report: Scallops are done.

    I glued mounting rings onto the 4" PVC couplers and gave them a 3/4" radius roundover. This should work well for the inside radius because, according to the LDC, the internal radius should be smaller than the external radius for the best performance.

    The couplers will be glued into the cabinet holes using 100% silicone sealer. There will be approximately 3" of gluing surface along the perimeter of the mounting hole, so this should hold the chimney firmly in place once the silicone sets up. I haven't glued them in yet as I am low on silicone and need to pick up another tube tomorrow.


  • So you do or don't need the flares? If so, you only need 2?

  • Yes, only 2 needed for the external end of the 4" PVC pipes. The above shows the two smaller 3/4" radius internal flares, which are now done.

    6thplanet
  • Had good luck with Gorilla glue, or poly glue for plastic to wood. With a double wall, I like to router a step maybe half way into the wall so the pvc can be butted up against that and glued in place. After the glue dries, router a roundover in the outer layer of ply.

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