Cabinet materials - why not more diversity?

[Christopher]

Hmmm, I think the vaccuum idea is sound in principle but I wouldn't want to try to make it work. If I'm not mistaken, (and I often am) using double glaze for sound requires larger separation because they are separated by argon, not a vaccuum. Were it a vaccuuum, the gap could be very small. For the vaccuum to work however, in our case the layers would have to be mechanically held apart and sealed by something strong and flexible enough to take the strain of the vaccuum, accousticly inert enough not to transmit the sound and perfectly bonded so as not to leak. A pretty big engineering task for sure.

As for how to build the design in question using vaccuum bagged composite sandwich, there are a few things to consider. Firstly I wouldn't bother with Kevlar(aramid) or carbon for several reasons. Kevlar isn't really all that stiff. Most applications use it because it takes a lot to make it fail. It is a freakishly tough material and a real bitch to work with. I only use it in combination weaves for the skin of the board where impact resistance is required. The fan cowls on jet engines use it to contain fragments in case of a blade failure.

Carbon's main advantage is the ability to mould compound curves where aluminum would be very difficult. Beleive it or not, aluminum actually has a better stength to weight ratio. I can only suppose that carbon is used in the floor panels of aircraft due to bonding problems between aluminum and the honeycomb. I'm sure that there are some exceptions, but anywhere I have seen these types of panels made with aluminum skin, they have always used balsa core, which alows a much larger bonding area. I have never had much success bonding aluminum to anything that will flex much, and I have gone through the whole etching proceess with only medeocre results.

The two reasons to use vaccuum bagging are the ability to clamp the entire assembly, which is very usefull when making fabric or core material conform to tight curves, and it allows a better fibre to resin ratio, which in turn increases strength to weight.

The final point to consider is that of core thickness. If you double the distance between the inner and outer skins you square the strengh. Thus, the only way to really take advantage of this method would be to either build 2 sandwiches (glass fiber/core-cell/glass fiber) and then separate them by and bond them to a thick core, or build a sandwich which has several layers of core-cell bonded to each other. You can get core materials much thicker, but you'd never bend them around the curve we're talking about.

All in all, I guess all the trouble may be worth it if you can push the resonant freq out of the audible range, but I can't comment on that.

For overall stiffness, I think it's pretty hard to beat poured plaster or concrete or Steve's stacked MDF.

I think one of the most promising cabinet materials are the inert poured resins being used in some of the flagship speakers. I can't recall which ones off hand though.( Watt maybe) The guy on this forum who seems to have the best handle on polymers and plastics is SY. I'm kind of curious what the acoustic properties of the synthetic wine corks are. Would it be a suitable core, and could it be used by the hobbyist?

I guess that was more than 2 cents worth eh?

Chris

[rwagter]

How about using GLARE, sandwich construction of aluminum (0,4 mm) and glassfiber.
The new airbus A380 is build from it, it's outerhull is only 3-4 mm thick !!!!

The process is like this: make a mould, put layers of aluminum (very clean with primer for gleu) and fiberglass on top of eachother with layer of epoxy in between en compress. For the best result compression should be under high temperatur where he epoxy gets very liquid and forces any airbubles out of the construction. Voila

[Christopher]

I'd never heard of this until your post, but I suspected that there were other reasons for using this as it would be no stronger or lighter than a single sheet of aluminum the same thickness as the GLARE laminate. I did a quick google search, and the reason for GLARE is that it seems to be highly superior in the fatigue department. For our needs, not a concern.

But I'm diggin' everyone coming up with all these unique ideas, maybe we'll hit a good one yet. Something that occured to my a while ago (mostly for rapid prototyping) would be double layered drywall. It's cheap, easy to work with using simple tools, and quite rigid. As a real cabinet, you could even build an inner and outer cabinet and separate them with some kind of damping foam.

How's that?

BTW don't ever try heating room temp cure epoxy to make it flow better. It'll cure in the pot right before your eyes and start to smoke. Bad thing. It also will kill the strength of the epoxy. You can heat a finsished laminate to get a higher strength finished product, but you really have to know what you're doing. I've done it by accident while working wet epoxy on carbon fiber in bright sunlight, I can't say if it was any stronger than normal, all my boards break eventually, I build them very light and sail them like they're made of rock.

Chris

[pinkmouse]

Originally posted by EC8010


Is that a barrel of Fullers ESB (Extra Strong Bass)?

Actually, it was ( ) a barrel of Honeydew! And as I was a bit bored yesterday, it is now actually becoming a sub

I have cut the hole in the top for a driver, measured the volume, and now all I have to do is a bit of calculating and stuffing. Pics will follow!

[Da5id4Vz]

The great thing about your subwoofer design is that you need to keep removing fluid from it until its tuned, and then start all over again.

Do lagers sound better than stout?

[EC8010]

"Now I've been to one world fair, a picnic and a rodeo and that's the stupidest thing I've heard come over a set of earphones."

I don't remember that line. Perhaps it was Major Kong's strong accent?

[Da5id4Vz]

It was his response to receiving the attack order. The another part of the quote is "Are you sure you’ve got today’s codes right"

[purplepeople]

Originally posted by Christopher
... Firstly I wouldn't bother with Kevlar(aramid) or carbon for several reasons. Kevlar isn't really all that stiff. Most applications use it because it takes a lot to make it fail. It is a freakishly tough material and a real bitch to work with. I only use it in combination weaves for the skin of the board where impact resistance is required. The fan cowls on jet engines use it to contain fragments in case of a blade failure.

... I'm kind of curious what the acoustic properties of the synthetic wine corks are. Would it be a suitable core, and could it be used by the hobbyist?

Yes, in recumbent bikes, Kevlar is used as the outside layer to protect the rider from objects puncturing into the fairing during crashes. The carbon is the actual structural material. Still, it would make for a dent-proof enclosure, if you could get past the hideous cost.

I like the idea of the synth cork. Utilizing the natural damping characteristics is interesting. What about other damping materials as a core?

Sand. Not a lot, but enough to separate inside and outside with energy absorption. You'd have to make a box in a box and fill the gap with sand. Vibrate it with the woofer as low as possible to settle it while filling completely.

Silicone in the gap. Or heavy machine grease. Or that expanding foam stuff they using plumbing.

What if you just patterned the interior after an anechoic chamber?

:)ensen.
Fearful that I've gone off the deep end of an empty pool...

[7V]

I found this and thought of this thread.
Harmony in light metal

[SY]

I'm kind of curious what the acoustic properties of the synthetic wine corks are. Would it be a suitable core, and could it be used by the hobbyist?

Wups, didn't see this until today. Sorry. In any case, it's the wrong material (polyethylene, closed cell). Too soft, too difficult to process without monster extruders. The best for diy would still be polyurethane.