Cabinet bracing 101

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I just finished reading a thread about cabinets, materials and some talk of bracing as well. True to my habit it only served to fuel my curiosity.

Earl (GedLee), Dave (Planet10) and som other valued members had a really good discussion going on what makes a good bracing for a cabinet.
Let's see if we can have a good thread that focuses on the bracing issue itself.

Three major bracing techniques were discussed.
Cross bracing with dowels, regular shelf braces and shelf bracing in the form of a "backbone" for the baffle including driver coupling to the brace.

Everyone seemed to be after the same goal but somehow they could not agree on the best solution.
There is some interesting information that indicates that the backbone of Planet10's designs is a stiff stucture. GedLee had some compelling arguments why dowels is the best soulution and the more common looking shelf braces never really got off the ground once these two got into it.

Now, aiming for the best bang for the buck would point me in the direction of Earls findings but things aren't really that cut and dry.
Physics would seem to indicate that the shortest path between supports is crucial to resonance frequencies in panels. Adding a dowel as a cross brace will effectivly half the pathlenght in every direction of the panel making it very effective. Reapeat this and you should reach a point of diminishing returns after a number of iterations.

A "backbone" or shelf could be seen as an infinite number of iterations with dowels running in a straight line. The concept of the "I-beam" is introduced.

There's no question in my mind that a properly placed dowel will will win hands down when it comes to mass vs effect. A stick really is negligeable weight wise.
At first glance this would seem to indicate the dowel to be the most cost effective solution but since we are hobbyists this isn't necessarily so.

We buy sheet materials by the sheet and a lot of the time we will have some spare material leftovers. Dowels are best realised with something like a oak rod or similar and the average sheet material will not be the best option for this.

So the price might not be the deciding factor for a hobbyist. The cross bracing will have a definate advantage over the "backbone", bracing of multiple panels when theree dowels are used running in X, Y and Z directions.
Or does it?
The I-beam with panels attached will transfer the force quite well.
When the side panels wants to flex (vibrate) the desired curvature of the panel will pull the adjoinging panels towards itself causing tension. The I-beam will resist this due to the "backbone". I'm sure there are other structural mechanics involved as well but suddenly I'm not entirely convinced that the cross brace is the #1 contender?
Attaching a shelf might be far easier than a rod as well, especially when you start thinking about using three rods and connecting them in the middle.

Now, enter acoustic theory and preassure waves in the cabinet.
The dowels will be sort of acoustically transparent due to their small pysical size and shape. A big sheet of ply will not be quite as invisible.
Do we really want invisible?
By routing large holes in the ply you get two internal distances spread over the internal panel surface. Could this possibly mitigate some issues with standing waves?
Keeping the holes edges sharp will likely introduce some form of diffraction but this doesn't have to be a bad thing since we want to reduce unified pressure waves. Imagine using diffusors in a cabinet to break up standing waves.
Bass notes will be considered large wavelength compared to the edges and diffraction will not be an issue.
Could it possibly be that this might actually reduce the need for internal damping for mid to HF notes?

A lot of questions and I welcome the input if anyone can shed some light on this.
I'm no stranger to math and physics even though it's been years since I flexed the physics part of the brain.

I guess in the end either way should work but I really enjoy understanding the fine prints regarding stuff like this.

So how much is good enough? When does it become an exercise in futility?
A quick check of the numbers from my own upcoming build would indicate the cabinet weighing about 200 times the moving mass of the woofer.
I don't se much amplitude in the cabinet happening concearning mechanical transfer from the driver. Exciting the resonance of the baffle will make it a whole different animal I imagine but that should be a non-issue if the the resonance frequency is high enough.

So, lots of questions. Any answers out there? :D
 
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Can you post the URL to the discussion between Earl & Dave?

Listen, the buyer wants the best product they can obtain for their money. The seller wants to earn money and lots of them. So, whom is the smarter one here? Most often the seller. As buyers we like to be fooled. All the time. :rolleyes:

Everybody could learn a lesson around this: The Power of the Placebo Effect in Audio & Beyond | Audioholics

I used to believe in the heavy braced & stiff cabinet for loudspeakers.
The matrix structure in B&W loudspeakers was the holy grail for me. Never used it though. Dislike the sound of B&W speakers...

Been in the audio DIY business for 30 years now and I believed in everything, also snake oil related. One should ask oneself: where's the proof for a given claim? Stick to common sense and don't fool yourself. This is money business! :shhh:

Where's the real proof for all that bracing in loudspeakers will pay off?

So right now I'm building a 4pi loudspeaker with two dowels in each cabinet for the bracing. Now I believe that this type of bracing is sufficient. I even built a 3pi sub without bracing! In the common audio world this is pure madness to build like this! I prefer my form of madness. :joker:

The more time and money we put into our hobby/projects the better we believe they get. :santa:

Let's see what's coming up regarding bracing. :spin:
 
I think this is the thread I was thinking of. Discussion arising from Geddes loudspeaker

You touch on my favorite subject and that's the question when enough is enough. Where is the point where diminishing returns seriously kick in?
I'm hoping some well versed people will chime in and give us their $0.02.

I whish I could remember how I used to do FEM modelling, that would have been nice.
 
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