For those wanting to build carbon fiber cabinets...

Whitey80

Whitey80

Senior Audioholic
It can be very difficult to get good results without a large autoclave to create a strong and air free part.

Now first off, I am no speaker builder, but I have heard many a person expressing desire to build cabinets out of carbon mat. I have built many gas tanks, seats and fenders for motorcycles from fiberglass and carbon, which have much more complex shapes than a speaker cab, so this should be no problem for a simple cabinet.

First off, you need a buck. Generally this is either made from wood or styrofoam. For gas tanks and other complete enclosures, I use styrofoam, as once the final piece is made, I can use gasoline to break it down to liquid and it is quick to shape. For a speaker cabinet, I will recommend this same process as well. You must make two that are identical.

Now, since this isn't a motorcycle part, and weight is not a factor, I would suggest first building it up with woven fiberglass mat.
Over your buck, lay alternating layers of resin and glass, making sure to use a roller to force out any possibly trapped air bubbles in the process. The baffle face should be layed very thick for strength, but for resonant properties, I'm not entirely sure of how thick the rest of the cabinet will need to be, that would be best left to the engineers here to figure out. I'm just a laborer.

On a buck, after laying your final layer of glass, test fit your carbon sheets, (compound curves can be tricky, and I don't recommend them for the beginner, Stick with a simple round-backed cabinet) once you are certain of fitment, lay your resin and mat, then top layer of resin.

Here comes the trick, after initial drying, but not fully cured, place playground sand into large metal containers at 400 degrees for 20-30 minutes. pull out and mix with equal part of room temperature sand. Cover all sides of part with heavy black trash bag and place in tub or other container large enough. Pour sand (should be between 120 and 140 by now, so wont melt plastic) and pour in all around wrapped part (should be flat face down). Let stand for 60 minutes, until completely cool. Put sand back into containers to repeat process for next part you are making.

The heat and weight of the sand forces the resin into the carbon weave, which is the trickiest bit, the resin penetrates and bonds with the fiberglass far easier. once pieces are complete, use your saw, or router, whichever you normally use to cut the holes for your drivers. once holes are cut, pour in gasoline, which will break the styrofoam down to a gel which can be poured out and PROPERLY disposed of.

After this, a run over with 800 then 1200g wet sanding will smooth it perfectly and a finish buffing with a cutting compound will polish it up beautifully for you.


This is seemingly a far better process for smaller bits, as a bookshelf speaker, but if you have the space, and money, a floorstander is exactly the same.

Hope this helped a guy or two venture out and build something new, good luck guys!



 
skyline_123

skyline_123

Audioholic
Thanks for the write up! I've made my fair share of carbon fiber parts but I've never heard of doing anything like this. Your work looks beautiful so it obviously works well. The main problem with trying to lay carbon fiber is getting a smooth, wrinkle free finish. I'm curious though, will the bags leave any sort of wrinkles in the resin? I'm assuming that's why you let the resin dry partially?
 
Whitey80

Whitey80

Senior Audioholic
Thanks for the write up! I've made my fair share of carbon fiber parts but I've never heard of doing anything like this. Your work looks beautiful so it obviously works well. The main problem with trying to lay carbon fiber is getting a smooth, wrinkle free finish. I'm curious though, will the bags leave any sort of wrinkles in the resin? I'm assuming that's why you let the resin dry partially?
It's over the complex curves that the layout of the mat becomes tricky to avoid wrinkling or over separation of the weave. Certain weaves lay better and have a slight pliability to them without making the weave look overly distorted. When I have an over-ninety angle, curving in, like on the knee indents and the tunnels of gas tanks, I will overlay, paying careful attention to the pattern to keep it as proper looking as possible.

The trash bag method will leave very slight marks in the resin, not a lot since it is allowed to dry first, but that is a reason for having to use 800g in the cleanup process.
 
G

gkaste

Junior Audioholic
Wow, very neat. Would love to try this some day.

Anyone know a place who can make the foam cores? Using a CNC machine or something? Making two things identical by hand are pretty difficult, at least for me.
 
Whitey80

Whitey80

Senior Audioholic
Wow, very neat. Would love to try this some day.

Anyone know a place who can make the foam cores? Using a CNC machine or something? Making two things identical by hand are pretty difficult, at least for me.
keep it simple. Flat front baffle, curved back. Measure and cut both blokcs to equal boxes, then make a template from cardboard for the curved back (a piece of board with the "U" shape that you would like the cabinet to be). Use that to as a guide while carving down foam with a knife. Running it up and down the piece as you go to make sure there are no high spots.
 
annunaki

annunaki

Moderator
How well does cf and the resin bond with other materials such as mdf or ply? Will it work similar to fiberglass resins and make a strong bond?

I can see using ply for baffle rings and or the baffle with the cf making up the rear of the enclosure, or making a braced skeleton of the enclosure from ply and wrapping in cf.

The thing that concerns me with cf is resonance. Because it is extremely lightweight the resonance point will most likely be shifted higher into the crucial upper midrange. This is why I am asking about using a braced skeleton.

A constrained layer damping system employing CF may be a viable alternative to audibly remove resonance however and get away with fewer actual layers??
 
Whitey80

Whitey80

Senior Audioholic
How well does cf and the resin bond with other materials such as mdf or ply? Will it work similar to fiberglass resins and make a strong bond?

I can see using ply for baffle rings and or the baffle with the cf making up the rear of the enclosure, or making a braced skeleton of the enclosure from ply and wrapping in cf.

The thing that concerns me with cf is resonance. Because it is extremely lightweight the resonance point will most likely be shifted higher into the crucial upper midrange. This is why I am asking about using a braced skeleton.

A constrained layer damping system employing CF may be a viable alternative to audibly remove resonance however and get away with fewer actual layers??
I like the way you think buddy!
Using a skeleton would increase overall rigidity substantially, in the spaces between, the finished and cured carbon/glass composite will have a resistance to flexing far greater than that of wood at any thickness.

I have absolutely 0 knowledge about how it will actually affect the cabinet resonance.... I just know how to build things with it.
I use System2000 epoxy resin from Fiberglast. It bonds with carbon, kevlar and fiberglass and will penetrate and bond with the MDF as well. There are Poly resins that most people use for fiberglass that also bonds with wood, but I am uncertain as to it's abilities beyond that.

I suppose the most likely cure for these issues in speaker-building will be to build a standard MDF cabinet and use a single finishing layer of carbon to "make it pretty"! But it's a lot more fun to try something new and see if it can work.

edit - Isn't the Kef Blade made from composite mat? Maybe looking into that more deeply will reveal some tricks.

edit again! - The Blade is most definitely made from fiberglass....as is the upper portion of the B&W D series, so this does work, with the right engineering knowledge.
 
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lsiberian

lsiberian

Audioholic Overlord
That sounds a lot more dangerous than woodworking. I like the idea of using carbon fiber as a finish more than the structure.
 
Whitey80

Whitey80

Senior Audioholic
I thought gas and styrofoam made a fire starter? Would be a nice byproduct of the process I suppose.
Home made napalm, basically. A highly-flamable gelatinous liquid.
And to think, I've been wasting it by letting SafetyKleen take it away :(
 
annunaki

annunaki

Moderator
The heads of the B&W enclosures are made of marlan which is a high density non resonant material. They work very well as mid-bass enclosures but is much different than fiberglass.
 
B

Bishopdante

Audiophyte
This sand trick is an interesting method!

I would suggest that the idea that cabinet weight is not a concern outside motorsport or aerospace would be quite incorrect, and is the chief reason why I am investigating carbon cabinets: lots of audio equipment needs to be moved. Live sound reinforcement gear is typically very heavy because of the cabinets.

One very interesting part of using foam is that it would not necessarily need removing. Employing two skins of carbon either side of structural foam can produce a very stiff structure, and also would also potentially help dampen resonances.

One company employing carbon cabinets for hifi is Wilson benesch.

The idea of making a cabinet extremely stiff is to cut out panel deflection, eliminating compliance completely. From what I have found riding carbon fiber bicycles is that they are really not resonant. This is down to the epoxy, if agitated they just make a "click" sound, although the area involved in tubing is fairly small. Given a thick panel, I doubt there'd be much in the way of resonance, and there are opportunities to make the panel in corrugated or formed shapes to add strength and reduce resonance or flexibility.

Sent from my SM-N9005 using Tapatalk
 
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