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DIY Lightweight Composite Cab Build

Discussion in 'Amps and Cabs [BG]' started by zac2944, May 8, 2008.


  1. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    After much thought, I have decided to design and build a lightweight bass cab using composite construction. The plan is to build a ported 2x10" with tweeter that is significantly lighter than anything available and strong enough to stand up to light gigging and rehearsals. Here are some of the ideas that motivated me to investigate the feasibility of such a project:

    • With all these new 500W+ bass amps under 4lbs that can fit into your gig bag pocket why not build a super lightweight cab to go with it?
    • My cabs are much more durable than I need them to be. Can I trade some of that durability for weight savings?
    • New light weight neo drivers, same old heavy plywood construction.
    • I'm an engineering dork at heart, and while exotic construction might not be necessary, I find it pretty cool.
    • I enjoy building stuff, and don't see the point in building something similar to what is already out there.

    Is it feasible? I don't see why not. People have been building high performance airplanes, boats, surfboards, race cars, etc with composite construction for years (since early 1970's). Will it be cost effective and easy to build? Given the cost of some high end cabs out there it might be cost effective, but it will take a lot more time and effort than building with traditional methods.

    I focused on a construction method known to homebuilt airplane builders as Rutan Moldless Composite Sandwich Construction. This is the method used to build Rutan(Burt) Aircrafts, and is detailed in a nice little book of the same title. I found a copy on the web for about $20 . The method is pretty simple in concept. You create a sandwich of fiberglass/epoxy, foam, fiberglass/epoxy. This gives you a sandwich panel with two stiff and strong skins on the outside that are separated by a lightweight core. This arrangement takes advantage of the fact that when you apply a load to something like an airplane wing or in this case a panel on a bass cab, the majority of the stress occurs at the outer surfaces.

    Any weight savings realized with composite construction will only effect a portion of the cabs overall weight. The best I could figure, for a typical Neo 210 the weight from plywood is about 60% of the total weight of the cab, the driver weight is about 20% of the total, and the other 20% or so is from the hardware,tweeter,ports,carpet,x-over, etc. These numbers came from a spreadsheet model that I came up with. They are estimates and averages and very from cab to cab. Let's say for the sake of argument that the average Neo 210 is 44lbs. That means that the drivers weigh about 9lbs, the plywood weighs about 26lbs, and everything else adds up to about 9lbs. By my calculations, I should be able to reduce that 26lbs of plywood to 8lbs of fiberglass/epoxy and foam. I can also reduce the weight of hardware, crossover to something like 5lbs. This beings me to a 22lb cab. That's half the weight of the 44lb average. I've done some experimenting and figure that I'll be 10% higher, so I've set my design goal to 25lbs.

    Here's some background info on some of the neo 210's out there compared to my design.
    210comparisontable.

    More to come in just a bit.
     
  2. mjolnir

    mjolnir Thor's Hammer 2.1.3beta Supporting Member

    Jun 15, 2006
    Houston, TX
    I'm very interested to see where this goes. Subscribed.
     
  3. Bassic83

    Bassic83

    Jul 26, 2004
    Texas, USSA
    Sounds a little like Flite cabs. I'd love to see this work for you, good luck! I'm definitely subscribed. Different is good- how can I think outside the box when they never let me out of the box to begin with? :D
     
  4. quickervicar

    quickervicar Supporting Member

    Jul 21, 2006
    Lancaster, PA
    Eden's Nemesis line was created with your concerns in mind. You can have lightweight and great performance. Go for it!
     
  5. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    My design goal has been set. A 25lb 2x10".

    Here's a summery of what I've planned:

    2 x Eminence 2510 (vertically aligned)
    1 x 4 driver piezo tweeter array (vertically aligned, ala BFM cabs)
    1 x epoxy/fiberglass/foam moldless composite cab
    2 x epoxy/fiberglass molded composite ports

    Here's a view of the baffel:
    cabcaddrawing3-1.

    I'll finish it off with fairing compound (epoxy and glass microspheres) over the outer epoxy, sand that smooth, and then paint. I'll use the standard plastic corners, rubber feet, and strap handle on top.

    Since working with epoxy is very temperature dependant, I chose to start my build with the tweeter array. It is still too cold here in MA for the epoxy. 70-75 is a good working temperature.

    After testing a bunch of piezo tweeters I picked out four good ones, cut them buy hand with a cheap $3 plastic miter box and glued them up with plastic cement.

    IMG_0909-1.
    IMG_0915.

    More to come in a bit.
     
  6. JonathanD

    JonathanD

    Dec 13, 2006
    Atlanta, GA
    Just posting to say great in theory, and if it works in practice watch out world. Revolution could ensue
    Jonathan
     
  7. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    I've never seen one, but I've heard that Flite used thin plywood over foam construction. Same idea, different materials. I considered this method too, but ruled it out.
     
  8. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    I doubt that this construction method could ever be scaled for commercial use. It is too labor intensive and the results greatly dependent on the ability of the builder. Thanks for the kind words though.
     
  9. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    A note on the piezo tweeters. I chose the piezos because they are very lightweight, require no crossover, and IMO sound pretty nice when arrayed.
     
  10. word up on the nemesis cab, I have a 1 12 nemesis cab , it is about 40lbs on its side and then I put a.....wait for it....a Markbass 102p on top on its side as well. The markbass 2 10 weighs 34lbs, and I run it with a GK1001rbII and it slams, it is as tall as an 810 cab and it sounds as big. weighs 74lbs

    Nice
     
  11. subscribed. very interested to see how this turns out.. good luck!
     
  12. subscribed
    Light weight is good!
     
  13. ::::BASSIST::::

    ::::BASSIST:::: Progress Not Perfection.

    Sep 2, 2004
    Vancouver, BC Canada
    I hate to throw a monkey wrench into this but its likely that the tone will not be as good. There is a reason Flite cabs dont sell well. The flexible nature of the fibreglass (etc) will allow the cabs walls to move too much when your pumping decent wattage thru it. Definitely more than plywood. If you brace the hell out of it, it may help, but then there goes the weight savings.

    Anyway, I hope I am wrong. Kjung mentioned something about this in relation to Flite cabs quite a long time ago... why I remember I dont know.

    I love lightweight stuff so again, here's hoping!
     
  14. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    With the piezo array finished I moved on to the ports. As you can see in the baffle drawing, the port design is a bit different then normal round or shelf ports. I did this for two reasons. One was to save space on the baffle to fit the tweeter array, and the other was because they look cool and would be fun to build from epoxy/fiberglass.

    Since these parts are small I chose to do them in my workshop and built a small oven for curing for extra foam and a 100W light. The oven was not necessary, but helped to speed up the full cure time.
    IMG_2535.

    The ports were not built with sandwich construction, but rather epoxy/fiberglass over a mold. To build my mold I used printer to print a template of the port profile. Then I cut to pieces of plastic scrap to the template. I placed pieces of foam between the two plastic templates and used a knife to cut the foam to the profile. Once I had enough foam profiles I glued them up with hot melt, wrapped the glued up block with cardboard, glued on a base, filleted the interior corners with dry micro (epoxy mixed with glass microspheres into a paste), and then covered the mold surface with packaging tape. The packaging tape keeps the epoxy from sticking to the mold and helps create a smooth finished surface.

    IMG_2512. IMG_2506.
    IMG_2510. IMG_2537.

    Once the molds were done it was time to layup some glass. I'm using West Systems Epoxy for this project. I have set up a special table for working with epoxy. It is just a $7 piece of 2'X4' melamine board I got from Home Depot. Epoxy won't stick to melamine and it is easy to keep clean. Here you can see some glass ready for layup. You have to have everything ready to go before you mix epoxy. Once you mix, the clock starts ticking. Take too long and it will set up on you before you are finished with the layup.

    IMG_25331. IMG_25401.

    For these parts I using two layers of some cheap Bondo brand galss I got at an auto parts store. It is a 6oz/sq.yrd. simple weave. Nothing fancy. I'm saving my fancy glass for the cab! Once laid up, into the oven for a few hours to bake. Here they are after a few hours:

    IMG_2542. IMG_2543.

    All that was left to do then was to remove the mold, trim the rough edges, fair the surfaces with dry micro, sand and paint.

    IMG_2544. IMG_2558.
     
  15. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Your hope is fulfilled!:cool:

    Seen any competitive wooden race cars lately? Stiffness/weight ratio is job one for that application. But money talks, and doing cabs really well is gonna cost a bundle.
     
  16. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    I understand your concern and this is something I have researched and experimented with quite a bit. If all you are used to is single wall fiberglass construction like you might see with a fiberglass canoe, pickup truck cap, etc. then you might not understand what I'm talking about. Sandwich construction is a totally different animal and can be made very stiff, and even stiffer then plywood yet still weigh much less. When you're dealing with sandwich construction, yous material stiffness is a function of the square of the distance between the skins. Here's is a great article that addresses stiffness of sandwich composites vs. plywood. I have done some basic testing to compare plywood to composite sandwich and I'm happy with the results.
     
  17. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    +1

    Without going into carbon fiber, most of the cost to build a cab is from labor. BTW, I'll be sure to post a complete cost analysis once I'm done.
     
  18. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Possibly all you need are molded ribs on the back surface. You can also do foam stringers like modern surfboards or sailboards use. Relatively cheap, light, and quite labor-intensive.:crying:


    Also, to the OP: if I remember correctly from some prior boat building hobby work, there are epoxies which are designed to cure in lower temperatures ... might let you get started sooner, if you like.

    West System makes the hardener component in a few flavors, including an accelerated one for colder temps. As usual, there's a tradeoff in the end result though. I'm planning on doing mine in an autoclave, but I likely will just hire out the whole layup process since there's a ton of world class composites talent where I live.

    It's funny, but I'm much more comfortable with this technology than with woodworking. Good on ya, Zac!
     
  19. OrionManMatt

    OrionManMatt

    Feb 17, 2004
    Houston
    Subscribed.

    Had you chosen 2x12's I would be emailing you for a quote. :)
     
  20. Nope... a foam core composite can be and is stronger than laminated wood with no flex - very rigid. Certainly lighter per volume. Boats and Plans are just the obvious applications. Graphite and polymers, a family member of the technology, are very stable... just look at the Status basses.

    Go forth and build the box. It will eventually be the cutting edge. The real reason it is not in the market place is: 1. labor costs (time and skill) and 2. material expense.