Composite Construction

Message

alexclaber · #1 Post by **alexclaber** » Sat Aug 25, 2007 8:44 am

In the past I'd been planning to build my next cab using foamcore ply or something similar but in the end shelved those ideas due to sourcing difficulties. I recently came across a company that supplies composite products for boat building so am now thinking about building the cab using dense 1/2" foam panels instead of plywood and then covering the foam with fibreglass or carbon fibre fabric before epoxying it.

Any thoughts?

Alex

#2 Post by **Bill Fitzmaurice** » Sat Aug 25, 2007 9:14 am

Fiberglas lacks adequate stiffness without extensive bracing, and there go you weight savings. Carbon fiber is adequately stiff, doesn't come cheap. You'll turn a 40 hour $100 build into an 80 hour $500 build.

Mikey · #3 Post by **Mikey** » Sat Aug 25, 2007 1:41 pm

alexclaber wrote:Any thoughts?

Bill has purposely designed these cabinets to be as light as possible while still retaining more-than-adequate strength. Compare their weight with "similar" commercial offerings. If you want to knock a little weight off of your cabs, just use 3/8" ply for the horn path, as others have done with great success.

JMHO

bgavin · #4 Post by **bgavin** » Sat Aug 25, 2007 1:46 pm

Making all the internal plates (except baffle) from 3/8" would be a 25% weight savings on a significant amount of wood. I do have to ask if it is worth the extra effort, dados, etc.

FTR, my T39 in 24" external width is 74 pounds naked. No finish, no screws, no driver, no hardware. It is mostly American Birch, with braces made from 1/2" BB scraps.

Mikey · #5 Post by **Mikey** » Sat Aug 25, 2007 2:34 pm

Bruce wrote:Making all the internal plates (except baffle) from 3/8" would be a 25% weight savings on a significant amount of wood. I do have to ask if it is worth the extra effort, dados, etc.

The extra steps to use the 3/8" ply would be far less time-consuming than attempting other exotic methods to trim a bit of weight, undoubtedly.

I can understand that there would be reasons for wanting the cabinets as light as possible. People with physical handicaps (such as bad backs) want to lift as little as possible. People who fill their little import cars to the brim to haul their gear to gigs need to keep their total weight down. People who frequently have to haul their gear up and down stairs want to haul as little weight as possible. Cabs on sticks or being flown would also benefit from lighter weight.

For most of us, the relatively light weight of Bill's designs is a plus. For some, the possibility of making them even lighter is an absolute necessity.

alexclaber · #6 Post by **alexclaber** » Sat Aug 25, 2007 5:51 pm

Mikey wrote:People who frequently have to haul their gear up and down stairs want to haul as little weight as possible.

That'll be everyone gigging smaller UK venues then!

From what Bill's said the cost will be prohibitive but I will double-check. I have considered 9mm ply but it would require quite a low more bracing.

Chopping up pieces of foam, gluing them together and then covering in carbonfibre doesn't seem any harder than building in ply, though more time consuming. I'd be willing to do it for the weight saving if the material cost is not obscene.

Alex

Mikey · #7 Post by **Mikey** » Sat Aug 25, 2007 6:35 pm

Alex, only the very largest of Bill's designs could really be considered "heavy". Which cabinet is it that you are trying to make lighter?

alexclaber · #8 Post by **alexclaber** » Sun Aug 26, 2007 5:44 am

The Omni 15TB. It's already a light cab for its output so if I have to go the way of 1/2" ply that'll be fine. I'm just perennially curious...

Alex

Harley · #9 Post by **Harley** » Sun Aug 26, 2007 10:38 am

alexclaber wrote:The Omni 15TB.

My Omni15 std weighs 28kg The TB version would be similar as the area of wood is almost the same.

bgavin · #10 Post by **bgavin** » Sun Aug 26, 2007 11:05 am

28kg/62 pounds is not unreasonable at all in a vertical configuration.

All my cabs seem to come in heavier that everybody elses. For example, my naked T39/24" is 74 pounds. This is American Birch (yuck) with a few BB pieces, all in 1/2". Scale is a very accurate beam balance type, and not suspected to be inaccurate.

Harley · #11 Post by **Harley** » Sun Aug 26, 2007 12:58 pm

bgavin wrote:All my cabs seem to come in heavier that everybody elses. For example, my naked T39/24" is 74 pounds. This is American Birch (yuck) with a few BB pieces, all in 1/2". .

My cabs are from Italian Poplar so yes they'd be way lighter than yours.

I have to carpet the poplar though as it is quite soft and dings easy. It would not take paint finish and stand up to the knocks.

Oh....and I just realised my O15 does not have the APT tweeter in it, that would add a couple of kgs as well

Wes Whitmore · #12 Post by **Wes Whitmore** » Tue Aug 28, 2007 12:09 pm

I have a Ampeg neo cab that is also made of Italian Poplar. It's some 27 lbs loaded with 2 10s, grills, corners, handles, lpad, etc. Its also carpeted. Finding the poplar is another story.
Wes

Sydney · #13 Post by **Sydney** » Tue Aug 28, 2007 12:59 pm

Poplar is one of the dominate trees in WV and less than a dollar a board foot rough cut.
I have 1000 bd ft of poplar ship lap for interior walls and trim.
When I had my property timbered, a few years back - Poplar was a large part of the stands. Used extensively in furniture w a thin veneer.

Harley · #14 Post by **Harley** » Tue Aug 28, 2007 1:28 pm

Wes Whitmore wrote: Finding the poplar is another story.
Wes

I thought it would have been more poplar there