Cylindrical cabinet? (revisited)

[Ian Hall]

I did some searching and found a bit of discussion on this topic, but not in this particular vein.

I'm getting back into playing after a long hiatus due to an injury, and have been thinking about possible designs for an ultra-light cabinet for at home and possibly jam session use. By ultra light, I mean 20lbs or less. I'm thinking a single neo 10 would probably do the trick. I have a lot of trouble lifting, and it seems even the smallest commercial cabs are slightly out of my comfort zone.

As I mentioned, this discussion has already been had regarding traditional-use cabinets, but I think a cylinder design could hold a real advantage in the ultra-light cab category. Although square/rectangular cabinets make the most sense practicality wise (stacking, ease of construction, etc.), they don't really make a lot of sense structurally. In fact, they make almost no sense structurally... it's just that the other advantages of traditional boxes are significant enough that it's worth it to put up with the added weight.

The best strength to weight ratio would come in a sphere or cylinder, and a sphere is out of the question as far as ease of construction goes. A cylinder, however, isn't excessively difficult.

I'm waiting on some hard numbers from one of the engineers at work, but I'm thinking that assuming the cylinder's length is at least 1.5 times its diameter, a serious weight savings could be had. The longer the cylinder is in comparison to its diameter, the greater the potential improvement over a traditional cabinet in regards to weight vs. overall rigidity. Too long, and you end up with a completely silly looking cabinet, as opposed to a moderately silly looking cabinet. I'm thinking 2 to 1 might be a good ratio.

I was hoping that perhaps some of the more knowledgable folks here could give me some suggestions as far as numbers for my coworker to plug into the analysis. Coming up with total pressure isn't an issue, I'm more concerned about resonance. I'm thinking that running 20Hz to 2khz should be enough, but I'm unsure on that.

The design I'm looking at right now would be several layers of carbon fiber fabric laid with epoxy resin using a large cardboard tube as a temporary form. I'm going to probably use a balloon in the back end to make a spherical closure for the back of the box, that way I don't have to have a heavy back plate to muck up my efforts towards light weight. I'm thinking I'll add some internal spars to prevent resonance from flexure, and a square front baffle to prevent my cab from becoming a tire without a car.

If you're having any trouble envisioning it, think giant carbon fiber cigar tube, with a square cap.

Another point I'd really appreciate some advice on, would be whether the edges of the square baffle extending out past the tube body could cause any strange effects. I'm also wondering if some type of mass-dampening coating would be necessary on the inside, to mitigate any ringing from high frequencies. I'm hoping that perhaps the analysis from my coworker might answer that question for me, but he is no loudspeaker designer.

I was also thinking that if someone just couldn't get over the goofy looks, a reasonably sturdy false box could be built around the outside, adding only a couple of pounds of weight.

[T-Bird]

Hi.

There's been plenty of tube subs, the giant Bose "SubTube" or what ever that was called, comes to mind first when talking about MI/PA duty.

Of course the shelves of the cheapo-audio stores are filled with tube car subs with speakers on each end.

Genelec has a spiral "drum" studio sub, You might want to look into that design to copy from.

As an engineer I don't see too much advantage in using a tube, or sphere (there's those around as well) for MI use, but that might be a fun project .

Good luck in making a half sphere or a dome of any kind with CF, at least if looks are of any concern.

You're talking about 110, but with a frequency response (f3 I assume) starting from 20 Hz. IMHO better to aim for around 50 or 60 Hz, but I'm just a hobbyist, not a pro.
Or You have to be prepared to drop a crapload of money into one, not to mention a few KW's of amplifier power.

Regards
Sam

[Nev375]

Ever consider using a bass drum shell as a prototype?

[dbase]

I used a "Bazooka" car sub woofer tube once and it sounded ok, The only problem, I had to drag a 40 lb 12 volt car battery around with it.

[vbchaos]

I once was in a studio to record - and the engineer there had build an own bass cab. He used plastic water pipes of a diameter perfectly fitting to 10inch speakers. 4 of these pipes, combined 2 next to each other on above, so you get the layout of a usual 4x10, but extremely light!! And this thing sounded very very good.
In the back the cab was totally sealed with plywood. I found a picture of this little masterpiece - unfortunately, no real good one, but maybe you get the idea

Edit: The amp above is a dynacord FOH-mixing panel from approx 1955. 4 channels, all tube. This is what they had back these days to fire up a complete concert Damn it, that little thing sounded sooooooo great as bass-amp

[billfitzmaurice]

Cylinders do have a very high strength to weight ratio. However, they also have a very low internal volume to pack space ratio, so what you lose in weight you gain in bulk for equal results.