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Another Composite cab build - inspired by Zac

#21
mcrracer said:
Petebass said:
I used the same foam as Zac, Extruded Polystyrene (XPS). Please not this is not the stuff they use for broccoli boxes and beanbag filler. That's Expanded Polystyrene and they're very different foams.

I looked up XPS and one of the listings by one of the companies here in the States is Styrofoam. Is that what your panels were, Styrofoam covered in Fiberglass? Thanks
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Isn't styrofoam the stuff they used to use to package fast food? If so, then I suspect styrofoam is a word used to describe any type of polystyrene, as most of the fast food packaging I was was expanded polystyrene. The chemicals in the resin will dissolve expanded polystyrene, so you'll know pretty quickly if you've bought the wrong one.

Mike, yes I modelled the cab before building it, using WinISd among other things.

Lo-Freq, I will eventually build a BIG cab using this method. Having done it on a smallish cab, I can now see that BIG cabs is where there's going to be real weight savings. I'm thinking a 2x12 next, and possibly a 4x10 or 6x10 after that.
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#23
mcrracer said:
Did your material come in sheets? What size sheets? Approx price per sheet? Trying to make sure I am looking at the same thing here before buying any. Thanks
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Yep the stuff I bought came in sheets of 2400mm x 600mm. The brand name I used was "Foamular" and it's marketed as an insulation foam. I can only help you with Australian prices... I paid aprox AUS$40 per sheet.

From memory Zac got his from Home Depot and it was aprox US$10 per sheet, but I'm not sure what size.
 
#26
dug dog said:
Nice job, Pete.

I remember someone saying something like, "At 3am, every pound feels like 5 pounds."
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I agree wholeheartedly..... especially with obstacles such as stairs and drunks making it harder. On a personal level, several motorbike crashes and sporting injuries have also taken their toll, and I’m sure I’m not the only bass player in that situation.
 
#28
knuckle_head said:
So - how do the front edges hold up to load in/out? Is it worth laying in a 'ding' layer of some other material - say a 1/4" ply frame?

As you got near-zero flex on the panels do you think a slightly thinner foam could be used?
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I'm not keen on adding any extra reinforcement, partly because as it will undoubtedly add weight, and secondly because I challenged myself to use no wood on this cab whatsoever. Believe me, I was very tempted to do so several times. It made attaching corner protectors, handles, the grill etc much more challenging without any wood to work with.

So far the front edges are holding up fine, as is the whole cab. It seems strong enough to me to withstand the sort of hits a cab takes during "normal" use. I'm also noticing that you tend to bump the lighter cab less often because the lack of weight makes it easier to manoeuvre. And also the the lack of mass and momentum on the lighter cabs makes for much less impact when for example I do bump it as I'm walking through a doorway. The "Hit" doesn't seem as hard, and that's good for both the cab and the doorway.

On a cab this size, I probably could have used thinner foam. I used 1" foam, Zac used 3/4 inch foam. Here in Australia I found my choices for foam thickness rather limited. For a larger cab, I'd probably stick with 1" foam.

But before you go thinner, just remember there is no real weight penalty for going thicker. The physics is such that the stiffness of the panel is proportional to the square of the foam core thickness. In other words, doubling the core thickness (100% increase) increases strength by 400%, but only adds a tiny bit of weight. That's a pretty good ratio, a gift even. The only down side is thicker foam makes your cab's external dimensions that tiny big larger.
 
#32
Petebass said:
I don't see why it wouldn't work.

From memory they had a shelf port? That might need a little bit of planning to work out how to build, but I'm sure it's possible. If not an equivalent round port could be used. Personally I'd also ditch the heavy EV driver and go for a Kappalite or Deltalite 15" speaker.
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i actually thought a 3015 non lf
 
#33
We had a bass players GTG in Sydney on the weekend so I bought my composite cab along for everyone to check out. Aussiemark was the first to grab it and what he did next sent luthier Phil Mailloux running for his video camera (that's his French Canadian accent you can hear). the resulting video clip demonstrates the weight of the cab... or rather the lack of weight:-



People seemed to dig the tone too, which I was pleased to hear. the consensus seemed to be that my composite 1x12 was comparable to the other big-name 1x12's there, only much lighter. Mission accomplished! :hyper:
 
#34
Great feedback! And hilarious video clip. Looks like a "prop" cabinet instead of a real one. You know?

I've already started gathering the materials needed to build a composite cab of this type too. It should answer several people's question about how this construction method will hold up in a bigger cab. Running a pair of 15's and a HF compression driver. Looking at roughly 3.5ft^3 for this one. I'll make a build thread once the epoxy resin and fiberglass arrives from US Composites.

Cheers,

Zach
 
#36
rpsands said:
Hey,

I realize you guys are using fiber glass for this stuff, but does anyone have any thoughts on using sheets of ABS plastic sheets? Just found this when fiddling around:

http://www.professionalplastics.com/ABSSHEETFORMINGGRADE

Seems like .04 sheets of 4x8 are less than 20 bucks apiece. Would that be stuff enough with foam in between?
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I have no idea! It's a bit hard to tell from the website exactly what this material is. I'm one of those guys who needs to touch and feel something to get a feel for whether or not it's suitable.

I guess anything can work as long as you've got a way to create a strong bond between the sheet and the foam. the whole sheet of plastic/fiberglass/thin ply/whatever has to bond strongly to the whole face area of the foam. If not the sandwich won't hold. If there's an adhesive that bonds strongly to this plastic sheet AND doesn't dissolve the foam, then this might work.

FWIW I was a fiberglass virgin before this build. I'd never touched the stuff, knew nothing about it and was therefore scared of it. I shouldn't have worried - I managed OK and most people with a bit of common sense should also manage.
 
#37
Hmm, I might give this a shot. I'll start a thread if I can get myself up to it.

It's ABS... "Sheets are produced in monolayer and co-extruded multilayer ABS (Acrylonitrile-Butadiene-Styrene)"

http://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene

Well ok that's not that informative since it's a plastic that can make anything from foam peanuts to legos. I get the impression it's basically plastic. And at .04 it can be rolled up so it's probably not very stuff. The hope would be it'd be a resilient enough surface for the foam.

Can you think of any way to tell if contact cement would melt foam?
 
#38
rpsands said:
It's ABS... I get the impression it's basically plastic. And at .04 it can be rolled up so it's probably not very stuff. The hope would be it'd be a resilient enough surface for the foam.
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ABS is a commodity plastic. It's widely available, in a good variety of colors, finishes, and thicknesses. Another sheet compound you can find around is Kydex (trademark), which is a blend of acrylic and PVC. It's a little harder and stiffer than ABS, but more expensive.

Either of these would make a durable covering for a speaker cabinet. I covered some monitors with Kydex years ago, and found it to be quite tough, and abrasion-resistant. The only problems that developed were where I had left an uncovered edge; those tended to get caught and peeled back over the years.

Re: using ABS for the outer layers of a foam sandwich - the stiffness of the panel will be largely dependent on the tensile strength of the skin, and the distance between skins (foam thickness). I don't have the time to dig up numbers, but feel safe in saying the tensile strength of ABS is way below epoxy-fiberglass. Perhaps you could compensate by using thicker foam. It would be an interesting experiment.


Can you think of any way to tell if contact cement would melt foam?
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It's the solvents in the cement that melt the foam; stuff like xylol, toluene... But there are non-flammable contact cements that are water-based. I'd think those should work.
 
#40
Yeah, I was thinking of doing something nuts like using 2" foam or something. It's interesting that the tensile (that's pulling/stretching, right?) is the determiner, so something like ABS might work -- it bends easily but won't stretch very easily at all. One upside is I think it'd be much lighter than fiberglass, and might be more durable to impacts.

I think I'll shelve that as an idea -- another idea I had was to cut down on labor by using the ABS on the inside and using 1/8" plywood on the outside. Seems like a possible angle. Is there anything wrong with using different tensile strength materials for skin?
 

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