Carbon Fiber as an alternative to wood for cabs?

[Cobra]

I'm wondering if there is any experimentation being done with alternative materials for cab construction, especially carbon fiber, but also other natural or man-made composites?
Just thinking outside the box of conventional wisdom, from improving tone, to cost & manufacturing issues...

[stokes]

They use carbon fiber in acoustic guitar construction and it sounds very good.I wonder tho,how cost effective it would be to build a cab,and how much the acoustic properties would suffer with a one half inch slab compared to the thinner stuff used for the guitar body.

[Enzo]

I can't imagine how it could remotely compete with wood for cabs. Slab of wood, saw to size, glue together. Carbon fiber I don't think comes in slabs at the lumber yard, you have to build it up, don;t you?

[Steve Conner]

I know car audio guys use fiberglass to make odd-shaped cabinets that fit into spare wheel wells, footwells and the like. It's convenient because they can actually use the car itself as the mould.

Also, newer PA speakers like the small Mackies and JBLs have plastic cabinets.

Carbon fiber is really expensive and has to be built up by hand the same way as fiberglass. However it's incredibly light and strong. (You wouldn't need a half-inch slab of it, even if you could get one.)

A carbon fiber bass cabinet with neodymium drivers would be an interesting experiment

[tubeswell]

Wood is easier for most people to work with tool- and technology-wise and its cheaper, simpler, more abundant and easier on your immune system. Also solid timber resonates better. Carbon-fibre might be lighter but its manufacture is messier, more intensive, resource-hungry and toxic process and you still don't get something necessarily as robust as a timber cab, because carbon fibre is prone to brittleness (and the fumes stink more than wood glue). But if you accept those limitations, then go for it.

[Diablo]

Carbon fiber is around $25/lb. I think you could build a cab out of some very fancy wood for that amount of scratch. Carbon fiber is light though....

[black_labb]

on www.talkbass.com someone made a composite cab using foam panels coated with wither fibreglass, carbon fibre or just epoxy. cant remember what it was exactly. cameout very light and stiff.
guitar cabs often sound "better" with the timbers resonance, but that resonance takes away from the low end delivered by the speaker, and can muddy up the sound by not having as clean a signal in the low end. of course alot of these things are desireable for some styles of guitar.

[Mullard Man]

I've played several high end Ovation Adamas guitars with carbon fiber tops. They sounded great, but a little different than the typical high end woods (mainly spruce, mahogany, and maple).

I think with proper design, a carbon fiber cab would be great. The problem would have to be cost. Like others have said, it won't be cheap.

[R.G.]

Two issues: flexibility and safety.

Flexibility:
Unless laid-up carbon fiber is thick, it's more flexible than you want for speaker cab sides. However, with a laid-up material, you are free to make the sides be something other than solid slabs. A tube of material retains a high fraction of a solid bar of the same material while being much, much lighter. The reason wood is strong for its weight is that it's composed of long, reasonably empty tubes of cellulose, the remnants of the original cell structure left after the water dries out of it. Making the sides of cabs out of tubes of carbon fiber, or two sheets interconnected with a web of reinforcements between them would make for a very light, but still incredibly stiff panel. Very good for speaker cabs. This could be made even stiffer by internal bracing inside the cab - like, a web of braces inside that nearly fills the cavity, leaving no more than a few inches between any two braces. This would use the compression/rarefaction of the air in the cabinet on the walls to reinforce one another, because an internal pressure would put the internal braces in tension, and a rarefaction would put the internal braces in compression; both walls would be trying to go in opposite directions and the braces would reinforce the other side.

I can envision some ... very ... expensive but light speaker cabs...

Then there's safety. Using epoxy composites for speaker cabs is one thing, but using it for cabs which have AC power going into them is another. Unless specially compounded, epoxies are not flame retardant, and would not make a safe enclosure from fire hazards unless coated by metal or some other resistant coating inside. Wood over X mm thick does qualify as it's well understood how much temperature/air/etc is needed to cause wood to burn per thickness. Not using either metal or wood/wood composition over X mm would cause a sincere round of testing at any safety testing lab, probably doubling or tripling the testing costs.

[wrathfuldeity]

It would be interesting, the ability shape a cab would be endless and if one hit on a good sounding design. If tooled and set up for mass production produced it could be economical verses good tone wood and hand craftsmanship. A one off design could be relatively easy...like building a "feather light canoe" which is basically done by shaping a mould out of stryofoam then covered with plaster of paris and waxed with parifin to release the mold...however much toxic petro chemicals involved. Perhaps, if laid up with some fiberglass or kevlor and incorporating stiffing structural design it should be basically indestructable and generally flameproof. Other products are snowboards and ski are basically laid up exotics and they are stiff and you'd have to fire up a torch to get them to burn. Though one problem might be if the cab is light and you have 4x12 stack...you would have to figure out how to keep from bouncing off the stage....maybe add some 80 lbs sand bags.

[R.G.]

... and generally flameproof. Other products are snowboards and ski are basically laid up exotics and they are stiff and you'd have to fire up a torch to get them to burn.

Don't get too excited about that. Both polyester and epoxy resins in their natural states are burnable, and support combustion in air. You have to mix flame retardants into them to get them to not support combustion. I once saw a guy use a heat gun on a block of polyester to soften it. It got too hot and started burning, fanned by the heat gun.

It's possible to make them be flame resistant, but you have to work at it.

[Chuck H]

R.G., how did that polyester resin burn when you saw it? Ive seen hardened polyester resin on fire. It goes up like a cross between gun powder and a tinder box

Alot of "5 way surround", computer and even some industrial speakers are made with plastics. Most use an infrastructure as R.G. described. But IMHO there is something lacking in their tone compared to old wooden console speakers. It may have to do with weight and stability. I mean, you can make a plastic cab stable from a structural integrity standpoint. But simply being less firmly planted on a surface seems to detriment the tone to my ears. My theory is that tiny sypathetic vibrations in the lighter weight materials cause phase cancellations. It's just an untested theory. But I do know that some guys change out the thin 5/16" baffles on their Fender combos for true 1/2 stock to get a more solid tone. And it works.

The original notion was to build a great cab more cheaply. But at this stage of the game I agree that wood is still the way to go. Even with wood there are density designations. I don't know much about it but pine is like 39 to 40 and poplar is 40 to 43. Both sound good. Only one exotic wood is similar in density and thats canary wood. Which doesn't look all that special to shell out coin for it. From my experiments, and any reports I've seen from others, higher density woods just don't sound as good. Redwood has excellent acoustical properties. But good, dry heart wood has become very expensive for such a bland looking wood. You would also have to build with thinner stock.

Thinner stock may be the key to getting better tone from the higher density exotic woods. I haven't tried it because the thinner stock won't support the standard 1/2" bullnose router on the corners and still make a strong box. You would have to go with a smaller bullnose and have custom corners made to pull it off well.

Chuck

[R.G.]

R.G., how did that polyester resin burn when you saw it? Ive seen hardened polyester resin on fire. It goes up like a cross between gun powder and a tinder box

It was...um... exciting, to say the least. You know that old term, "fire drill"?...

Alot of "5 way surround", computer and even some industrial speakers are made with plastics. Most use an infrastructure as R.G. described. But IMHO there is something lacking in their tone compared to old woodenconsole speakers. It may have to do with weight and stability. I mean, you can make a plastic cab stable from a structural integrity standpoint. But simply being less firmly planted on a surface seems to detriment the tone to my ears. My theory is that tiny sypathetic vibrations in the lighter weight materials cause phase cancellations. It's just an untested theory. But I do know that some guys change out the thin 5/16" baffles on their Fender combos for true 1/2 stock to get a more solid tone. And it works.

The theoretically perfect speaker baffle and cabinet are completely rigid and do not transmit sound at all, and do not move. You are correct that there is a remaining issue with the CF cabinets I mentioned - they're too light, and the sound pressure from the speakers can literally move them back and forth. I ... think... but cannot verify that such speakers would sound better if bolted down so they can't move. Industrial plastic speakers leak sound from all over. I believe you have to fill the plastic holes with an acoustically absorptive material to keep the leakage down. And the plastics don't come anywhere near the rigidity of CF.

When I designed the enclosure for the Workhorse Pony (30W, 1-12) I specified 3/4" hardwood plywood, baffle glued into a routed groove in the sides and top. It came out well for a 12" in such a small cabinet. Flexing baffle boards become secondary speakers, and as such do the phase cancellation thing you mention at the resonances of the various sub-areas, so it may sound good at one place but bad at another, depending on what frequencies are being reinforced.

The original notion was to build a great cab more cheaply. But at this stage of the game I agree that wood is still the way to go. Even with wood there are density designations.

Very true. The best compromise for a speaker which is not taken on the road is probably MDF. MDF is not your ordinary particle board. It's dense, acoustically dead, and heavy. Very little sound gets out of it. High end hifi speakers are usually partly or mostly MDF for that reason. It's modestly cheap, easy to work. About the only things wrong with MDF are
- it's HEAVY, which is a reflection of being acoustically dead
- mechanical strength is not as good as plywood or normal lumber, so it breaks on the road
- water absorption can degrade it rapidly.

All of those last are killers for musical instrument speakers, so you don't see it much. But a Marshallesque 4x12 made of MDF and properly reinforced inside would likely be a very good sounding speaker. You just couldn't move it...

Thinner stock may be the key to getting better tone from the higher density exotic woods.

Since we use very thin panels of wood in acoustic guitars and since MI speakers are sound PROducers, not REPROducers, I'd say you're dead on. The speaker cab is part of the musical instrument for us.

[Baxthorpe]

Dagnabbit! Man-made materials for speaker cabs? What a new idea ... nobody here old enough to remember those 1940s Bakelite radios?

[Enzo]

As a matter of fact, I am pretty darn familiar with Bakelite.