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Cloning a cab Sunn/Yamaha 2-15" (to be lighter) project

Discussion in 'Amps and Cabs [BG]' started by JoeVictim, Aug 14, 2012.

  1. 001-1.


    I have this old Yamaha cab (Sunn clone). The cab is MASSIVE, in both tone and weight. The idea is to try to get the cabinet to weigh around 30-40lbs without anything inside. I am talking about shaving a lot of weight off this bad boy.

    The current construction includes 1.25" thick panels of MDF. I know there is a savings to be had right there, but I am concerned that going to a 1/2" panel may require additional bracing.

    I am looking for design ideas to try and capture the tone without the weight. Any help would be appreciated.
  2. I think the only way you are getting down to that weight is with composite materials, and a better design.

    Mike Arnopol recently build this greenboy Dually 215 that weighed in at 39 pounds. I might get in touch with him and see what kind of options he can incorporate.

  3. I'm actually looking for advice on bracing and actual construction. The cab sounds amazing, I just don't want to lug around a 1.25" thick cab.
  4. Korladis

    Korladis Banned Supporting Member

    You might save a bit by using 3/4" ply for the baffles, back and sides, and 1/2" ply for the port sections.
  5. I'm guessing I'll lose some rigidity. Anything I need to do to compensate?
  6. will33


    May 22, 2006
    You might not hit the weight goal in your first post but you can take a lot of weight off this thing.

    1/2" Arauco ply, available as some Lowes, is good stuff. Has thicker, even plys including the outside plys, no paper thin veneer and is a good 20% lighter than baltic birch.

    The drawbacks are, it only has one "pretty" side. Or rather useable, not really pretty. You're going to cover it....big deal. Have to figure around that when cutting. It can tend to warp some if you cut all the panels first, leave them laying around for a week or 2 before you start the build. If you cut and build as you go, it won't do that. The box will sort of force itself to stay square along the way and you won't end up with a warped box.

    You can do the whole thing in 1/2 if you make it double thickness just where the drivers, wheels, and probably handles mount.

    Crossbracing like in the pic below ends up being stronger while using less wood than spines. May still need a spine here or there depending on how things are laid out in there.

    That odd shaped brace in the middle of your port. Use that as a template and make 3 of them. Evenly space them through the port on the new cab.

    Use internal measurements of your cab to figure the dimensions for the new 1/2" ply cab. The new one will then be a clone on the inside where it counts. The overall exterior dimensions will be slightly less than this one.

    1-1/4" MDF.....Geez. Shouldn't have a problem shaving a lot of weight off that thing. Even going in all Baltic Birch, it'll be even sturdier and still weigh much, much less than that thing.


    You can cut strips from your plywood stock and double them up to make 1" x 1" square bracing sticks instead of buying all that dowel. Glue them wherever they happen to intersect out in the middle there.
  7. Thanks will33. One last kink in the hose, on the left side of the port where it disappears, it actually runs at an angle towards the back corner of the cab. It looks like a folded horn design. So there is going to be about an inch gap between the back panel and where the port runs almost parallel. This "crossboard" of the folded horn stops about 3 inches from the side panel. " L-- " kinda like that. I can snap pics if that doesn't make sense. My mind can be abstract sometimes.
  8. Toastfuzz


    Jul 20, 2007
    Pittsburgh, PA
    You should look up Greenboy's plans for his 1515/66, and brace similar to that. If I remember correctly they're similar to my 12/6's which was easy to install, only its stronger in the middle/spine to accommodate the taller cab.
  9. will33


    May 22, 2006
    May include some spines there on the inside of the "L". Or make the braces that run inside the port so they "wrap around" and continue along the back wall to support the L.

    Pic or simple drawing might help. I'd be inclined to extend the port brace that's visible in the wrap around variety. Build from the baffle towards the back. The L would be the 3rd from the last piece installed. It's braces that aren't visible in the front pic 2nd to the last. Putting the back on last.
  10. Balog


    Mar 19, 2009
    Mukilteo, WA
    Did Sunn make a folded horn? This more seems like a straight up Yamaha design than a Sunn clone. That being said, good luck with your build. :)
  11. will33


    May 22, 2006
    I don't know much about horns but it wouldn't be a folded horn technically. Might be some hybrid between a slot loaded port type thing. Might have some horn loading of the rear wave reaching into the low mids maybe. It's not long enough to be a bass horn.

    OP, can swiss cheese the port braces and any spines you use to shed a little more weight. The spines will be stronger if you make them 3" wide or more and perforate them than it will using smaller strips.
  12. I'll have to wait until I'm home to come up with anything, but thank you for trying to lend a hand. I really appreciate everyone coming to my aid.

    An aerial view, taking the top panel off would look something like V----back panel
    l =========\--------l
    l--------------/------l < port

    Edit: the double line is the weird port/wall thing that I'm trying to tell ya about.l

    The speakers would be inside the "house shape". The bottom piece would be the front of the cab with the speakers pointing "down" on your screen. The only other thing to note is that there is a divider piece that runs parallel, but is not the same piece as the port brace in pic two.
  13. Ah man, it didn't space out right...
  14. will33


    May 22, 2006
    I get what you mean. I'd just put little "port divider" pieces between the L and the back wall that line up with the port dividing brace you can see in your front pic.

    When bracing the inside of the cab, just use the inside of the L as the back wall to attach the crossbraces on the inside of the speaker compartment to.
  15. For starters, use high grade 1/2" plywood such as baltic birch. Don't skimp on this.

    The bracing shown above is the right idea, but is nasty to implement beyond a drawing.
    Use 1/2" ply scrap ripped into splines 1" wide.
    Glue the splines vertical on the outer wall at 6" ~ 8" intervals.
    Glue the cross braces to the splines, and to each other where they cross in mid-cab.
    This method avoids the micro-precision length cuts required to accurately fit a round dowel between two panels.

    Further weight saving is realized by drilling relief holes in the bracing.
    This is a time consuming and very tedious process, even with a drill press.
    I did this with my bass horns because the bracing is large and the weight savings substantial.

    MDF weighs 49 pounds per cubic foot. A 4x8 x3/4" sheet weighs 98 pounds on my beam balance scale.
    Half-inch baltic is 0.445" thick and weighs 39.8 pounds per cubic foot.
    Arauco 1/2" ply is 33.6 pounds.
  16. will33


    May 22, 2006
    Excuse the crude drawings...

    From the top I imagine the port to be something like this. Shaded area being the port path.


    I'd make braces the same shape as the inside of the port path. Something like this...


    Using 1/2", I'd make 3 of those and space them evenly in the port. Would look something like this from the front.....


    And Viola....a braced port.


    Baltic Birch is stiffer, easier to work with than the Arauco. Heavier, but still come in way lighter than what you've got. Maybe use the birch on the baffle and any other stress areas, like using a piece to double the thickness where the wheels mount, making the crossbraces out of it, etc. Could use Arauco on the rest.
  17. ^ Nice. That makes total sense. Besides the extra bracing for the port, Is there an argument for spline vs. cross bracing? At this point, I think I got the right people looking at this thread. Thanks for all the help so far, everyone.
  18. will33


    May 22, 2006
    Crossbracing is stronger and uses less wood (less weight). Spline is good and easier to build. Bgavin's description of using a combination of the 2 would likely make the easiest and stiffest build.

    I use plywood strips doubled up to crossbrace instead of buying all that dowel and drilling relief holes in the panels, etc. I glue a little block on the wall for the crossbraces to sit on/attach to. Much easier to assemble than lining up all those holes, etc.

    Could use splines to stiffen the individual panels. Then can use fewer crossbraces to connect opposing panels.
  19. will33


    May 22, 2006
    BB can use less bracing than Arauco because it's already stiffer. Putting all the bracing in is tedious and time-consuming. If you did the whole thing out of BB, it'd be an easier build. Going the Arauco way means a lot more work for a little bit of weight savings.

    I've done things like PA tops and monitor wedges out of arauco and it works good. Something that's going to get slammed like a bass cab needs at least some birch in it.
  20. "Q"


    Feb 9, 2010
    Sacramento, CA

    The ply will be stronger than dowels, have more contact area with the side of the box and be much less prone to warping too.

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