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Composite Cab DIY

Discussion in 'Amps and Cabs [BG]' started by dug dog, Apr 21, 2009.

  1. Greetings y'all.

    For the past couple of years I've been whining about lifting and carting my rig. Nothing new there. It's not the world's greatest rig, but it's what I have- Yorkville Y400B rated at 400W into 4ohm load. Two cabs- Yorkville BC210 with 2 16ohm drivers giving 8 ohms (according to Yorkville it weighs 52 pounds) and a sealed Sovtek cabinet that houses an Eminence Delta 15A. The internal volume of the Sovtek is about 4700 cubic inches (approx. 77 litres). and using my highly unscientific methods it weighs about 47 pounds. (Already, I can hear a bunch of people wondering what I'm complaining about. "Fifty pounds is nothing!"). Compared to hauling around an 810 fridge, fifty pounds IS nothing.

    Nonetheless, a couple of months ago I decided to look into lightening the load - micro head, neo drivers, lightweight cabs, the whole shebang. I've been checking it all.

    Along the way, I came across the Zaclite composite build thread http://www.talkbass.com/forum/showthread.php?t=432560. Mighty impressive stuff. A 210 cab weighing in at 22 pounds! Damn!

    I gave some thought to trying to duplicate Zac's efforts, but was reluctant to do any stinky, messy fibreglass work. (That's how we spell fiberglass in The Great White North.) Somewhere, I read about making composite panels using pink rigid foam sandwiched between thin plywood sheets. To satisfy my curiosity, I decided to build a cab using this technique. For simplicity's sake, I figured I'd just replicate the Sovtek box so as to avoid porting and, this way, I could use the existing plywood baffle from the Sovtek which is held in place by screws.

    Like most first builds, I learned more about how NOT to do it, but, overall, the results were most promising.

    Here's the old Sovtek box made of 5/8 MDF.

    And here's the replacement.


    The old box, loaded, weighed 47 pounds and the new one, loaded with the same baffle and driver weighs 30 pounds. I still haven't added paint/ duratex/ rat fur, corners or edge protection (which will be needed all around the whole box due to the somewhat fragile nature of the wooden edges) and that will add a couple of pounds.

    Here's a shot of the panel.


    I used 1 inch foam and the wood is sold as door skins at the lumber yard. It's 3 ply stuff and comes in 3X7 foot sheets. I glued the sandwiches together using Weldbond Plus.

    Here's a shot of the interior



    More to follow.
  2. Interesting approach.

    I'd be concerned about the structural strength of the cabinet, but good luck with finishing the build.

    I would have tried building a box with just some regular ply (13mm or something similar), which would also have been quite a bit lighter than the MDF the sovtek is made of.

    Oh, and sterotypical condicending "wimp" comment :p
  3. Stumbo

    Stumbo Wherever you go, there you are. Commercial User

    Feb 11, 2008
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  4. greenboy


    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Hey dug dog,

    Yeah I talked about foam core panels in Zac's thread and elsewhere. More weight shaving to be had once you get rolling, I'm sure. Falling back to thinner foam, a unitized bracing/join design that gets rid of some wood weight or at least trades it for rigidity, and hooks into the baffle...

    Your work here looks real good - I like the way you stepped the side panels. Color me envious ; }
  5. Thanks for the throwing in the "wimp" bit! I'd have been disappointed (Insert winky smiley icon here. Must figure out how to do that.)

    I finished the cab up last week and took it out to jam with my yahoo buddies. This is not necessarily a ringing endorsement, but it sounded every bit as good as the original cab.

    As far as strength and structural integrity goes, I'm a bit nervous about banging it into things, but the box is stronger and stiffer than you might think- there's no problem with the cab supporting my full body weight (about 165 lbs.). Granted, if you whack the original box with a baseball bat you're gonna get sore wrists, while the new box would probably be reduced to toxic kindling.

    Back to the actual build, I wasn't sure what would be the best way to join up the sides, as a butt joint would leave an exposed pink foam end. So, I cut the outside skin long enough to cover the end of the panel attached to it and did the same thing for the back. Here's a shot of the back to give an idea of what I'm trying to explain.


    Not so easy to make out in this shot of the corner.


    What I found out after it was too late is that if you build a big panel first and then cut it down to size on the table saw, you can cut nice mitred joints. There IS a tendency for the door skin stuff to splinter a bit, but I'm told splintering can be greatly reduced by applying low tack painter's masking tape to your cut line before running it through the saw.
  6. For sure.......

    I didn't mention that the actual box, aside from the panels, was assembled with PL Premium. If I had built oversized panels first and then cut them down to size, I could have had much better fitting joints and could probably cut about a pound of PL out of the equation!

    As for the thickness of the foam, the only reason to go for thinner is to reduce pack size. As I recall from Zac's thread, INCREASING the thickness gives exponential improvements in rigidity.

    What do you think? 40 pound fEar 15?
  7. pathdoc2


    Oct 16, 2002
    Allen, TX
    Cool project. I like the idea of a lightweight cab.
  8. greenboy


    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Yep, that's true - not only Zac's research but also stuff I've seen linked on home and marine sites bears that out. Actually ply foamcore is commercially available too, and I've seen figures for torsional and sheer strength.

    But I see a lot of runners in there used for joining. If instead they were replaced with kind of an aircraft-drilled girdled frame that supplies both glue surface for joins, and rigidity and vibrational damping across panels, it could be a good tradeoff and would contribute to the monocoque nature of this project - especially when high force long-excursion woofers are part of the mix.

    We're already practically there when using lighter varieties of plywood. It could go down quite a bit lower than that, maybe 30 pounds including hardware.
  9. Thirty pounds would be SO SWEET. I'm not sure if I've seen any weight measurements on your 15/6.
  10. Petebass


    Dec 22, 2002
    QLD Australia
    Nice work Dug Dog! Reminds me of the Flite cabs.

    I agree with greenboy that some extra planning could have reduced the wood framing and got the weight down further. But if the goal was just to make something lighter than what you had before, you've succeeded so well done! I guess if getting weight to an absolute minimum was a priority, then you'd bite the bullet and go with fiberglass.

    I really want to build a Fiberglass cab but unfortunately my priorities are elsewhere at the moment. I'll get around to it one day ............
  11. seamonkey


    Aug 6, 2004
    Nice work - very innovative.

    I had a similar idea using standard stick sizes for an outside skeleton:


    If figured solid wood edges would help with the average road durability. Drops always seem to hit an edge.

    I didn't put in any bracing, it wouldn't be hard to add. It is in sketchup so you can resize to any width and height.

    In investigating foam, I found the rigid roofing grade foam would probably work the best. It's strong enough to stand on.

    On the ply chipping - I found a rail type plunge saws to be ideal, and very safe. In constructing kitchen and bathroom cabinets I would never use a table saw again. There is no chipping. Festool, Makita, Dewalt, make them. Now the price may seem steep but they are so much safer, especially for musicians who need their fingers.
  12. Thanks all for the kind words.

    Mr. C. Monkey: I banged around a similar idea myself and I agree it would likely be much more road worthy. When I started to look at all the sticks I thought I'd need, I thought it might get to be a tad heavy, but don't really know how much. It might be well worth some extra pounds for the increased durability- just a matter of figuring out how MUCH more weight. I also have some concern in this day and age about finding nice, straight sticks. I've bought some pine stuff that seemed OK until I cut it!

    Nonetheless, I think your idea is definitely worth trying. (Gonna have to figure out how to run Sketch Up.)
  13. Just realized I don't have to learn Sketch Up to look at your model in 3D. I think it looks like a great plan. Gonna be doing a bit of brainstorming for sure.
  14. seamonkey


    Aug 6, 2004
    I didn't figure out weight. I would probably start with poplar (tulip wood)
    I used a lot of it for internal framing for home cabinets and it seems solid and light. Easy to work with, mills, fastens and glues fine. I could find lots of straight pieces. The sizes I used you can find already kiln dried so you wouldn't have to rip it.

    Someday I'll build one myself, but it's back to home projects for a while.
  15. Crockettnj


    Sep 2, 2005
    North NJ
    Dug, how's the foal core cab holding up?
  16. Petebass


    Dec 22, 2002
    QLD Australia
    Huh, baby horse? :p
  17. This cab hasn't really seen too much action as my current music project has me singing and not playing bass. Also, once I determined that the construction method was viable, I figured I'd build something that would be a better performer (fEarful or Bill Fitz design) and, so, never got around to adding protection for the edges and corners. As a result, the dozen or so times I've taken it out, I've pretty much babied it.
    Once I got looking at other cab designs, I started to look long and hard at my entire rig and have been pretty much mired down ever since, not knowing which way to go, how much money to spend, etc.. Right now, I'm thinking pretty hard (again) about some type of fEar based set up. I'm also realizing that if I'm gonna build something, I have to get off my donkey before it gets too cold.
  18. newbold


    Sep 21, 2008
    I wonder how this approach to materials would fare on a Bill Fitzmaurice design.
  19. I gave that a long look and I think it would be doable, but there are some caveats. The first would be the overall size increase. If you use panels that are 1 inch foam with 1/8 inch skin on each side versus 1/2 inch plywood, then a square box gets bigger by an inch and a half in direction. Not such a big deal, but if you were to build the internal bits of a BFM design (horn, baffle), then you'd be increasing the size by even more in order to keep the interior volumes the same.
    The other tricky bit is the assembly. I just built a BFM Jack 110, and after gluing each joint, I'd shoot it with a brad nailer which was super handy. I have no idea how much holding power a brad would have in a composite, but I'm guessing not much. So I'm thinking that you'd have to get a bit more creative with clamping techniques using guide boards, which would be more time consuming, but not impossible. I eventually came to the conclusion that the simplest way to do it (for me) would be to compromise and build the bottom, front, back and internals from plywood and then use composite for the sides and top. I actually did some sketchup models of a couple of modular takes on the Omni 15 but have since decided that the fEar approach will probably work best for me.
  20. Crockettnj


    Sep 2, 2005
    North NJ
    it'd require some redesign. You would have to account for the added thickness of the panels, as Bills designs are nearly all using 1/2" ply. HOwever, you'd have to be careful not to alter the dimensions of throat/internal volume/horns in doing so. Certainly could be done, but would require some mental gymnastics first.

    Foal core. hehehe. good one!

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