DIY Cab bracing question

[doublestop]

Hi guys,

I want to build a lightweight cab (composite fEarful 15/6).

Is it a good idea to make it stiffer by 'connecting' the panels of the cab, on the inside?

Let's say that inside the cab, I have some thin sticks running
- from the front panel to the back panel
- from the top panel to the bottom panel
- from one side panel to the other side panel.

Sticks of wood, or aluminium, or composite material. Or even off-the-shelff carbon rods. These do not weigh much, don't take up much volume but will make the cab much stiffer.

Right? Or am I missing something and is it better to make each panel stiffer by means of the usual bracing ?

Answers, ideas?

[Bmorefoozler]

The intent of bracing is to stiffen the middles of the panels from flexing, so if your method would do so with virtually no "losses" it sounds good to me....

But I'm no expert, I jsut stayed in a Holdiay in Express and read a lot.

[rpsands]

I would stick to the usual bracing. All the panels are connected by the spine and girdle braces. No need for more from what I've seen.

You could certainly use a different bracing scheme, but Greenboy researched the hell out of his, and anything you do would be unlikely to be much better. Incremental improvements perhaps.


edit: I see you're doing a composite. Definitely worth reconsidering in this case. Depends on how thick the panels are!

[Zooberwerx]

You may want to check the Acme / Andy Lewis website for ideas. I believe there are also some Acme demos on youtube in which he explains the principles of enclosure resonance. FWIW, the Acme enclosures are braced to the extent that the panels actually bow outwards to some degree.

Riis

[dug dog]

Since you're building a composite cab, a good answer is "It depends."

When Zac did his fiberglass/foam composite cabs he felt that the panels were sufficiently stiff that they required no extra bracing. Of course, his cabs weren't as big as a 15/6. You've probably read his threads on here, so you know that the thickness of the core will greatly affect the stiffness of the panels, so, again, it depends.

From what I've seen, the bracing method you're suggesting is a tried and true approach.

[greenboy]

When I get into the two-woofer fEarful models I do run one side-to-side and one back-to-back brace that ties into the girdles and spines. Larger panels and a good spot to put them, works out perfectly. The unitized girdles and spines is a great way to stiffen panels, and it's also a way to keep any surface area from being large enough to become a resonance problem.

What type of composite? That determines how you might want to proceed.

[greenboy]

Here's another thing from the fEarful wiki, about bracing: http://www.talkbass.com/wiki/index.php/Bracing

[doublestop]

Thanks all.

The composite will be a core of XPS foam, with toplayers of expoxy/carbon or expoxy/glass fibre.

Actually, I am thinking about carbon on the inside and glass on the outside, not sure yet.

[I hope to collaborate with some guys in my region who build lightweight, race class sailing boats for a living. Catamarans, made of carbon.]

[dug dog]

If you can share resources with those kind of people, you'll be in good shape. They'll have lots of know-how and good material sources as well as the "tools of the trade".

[Codger]

Originally Posted by doublestop

Sticks of wood, or aluminium, or composite material. Or even off-the-shelff carbon rods. These do not weigh much, don't take up much volume but will make the cab much stiffer.

You're trying to raise the resonant frequency of each panel. As noted, Acme does it by stressing the panels outward but you could stress them inward just as well. Someone suggested trying arrow shafts. I couldn't figure out how to attach and stress them. Let us know if it works out.

[doublestop]

I'll let you know if this works out. If so, I'll post pictures.

Thanks for all suggestions and hints.