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From a purely strength standpoint, round "corners" are stronger than square corners.

But seriously, we are talking sub boxes here...what exactly are you bracing against? How much pressure do you think even a huge 21" speaker is producing inside a box, that you need oak 1 by 4 for?

Bracing is *mostly* for stability and resonance issues...not because the box is going to have elephants stomp on it, hold up a house, or control a small C-4 blast!

Sure, I've seen boxes "blow up" before, but that's because they were made by retarded kids that think you can run 10,000 watts off a stock alternator, and that box + hole + speaker = bass.

Boxes don't need to be 1000lbs and 3 layers thick all around. Sure it helps, but a better design beats overbuilding any day.

On a lighter note, overbuilding is easier and takes less thought. I know I've done it myself when it was just easier to way overbuild then to think out the best plan.
 

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That's great if we are building the box to withstand external pressures...but part of bracing is to divide large panels into smaller sections so the resonance will be out of an audio range.

IMHO, dowels or 2X2 build a strong box, but not one that divides the larger panels into smaller sections.

Also, I feel that the dividers should be asymmetrical so you aren't dividing a 2' panel into two equal 1' panels (for example).

Sure these boxes are strong, and sure an elephant can use it as a step-stool, but I feel that we need to build rigid and non-resonant...which will still be strong.

Look at NeoDan style boxes. He's got the right idea.






 

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If you use 2x2 like a 4 pane window frame why can't it be used just like an mdf brace to divide larger panels into smaller ones?

I would have thought 2x2 mitred and glued/screwed into a 4 pane panel would have been stiffer/stronger than a 1" thick MDF equivalent?
Overkill, but that works perfectly.


/shrug

Mine seems to be doing ok with it. Resonance was the first thing on my mind when I decided to brace it the way I did. That, and my wallet. Since I use plywood instead of MDF for health reasons, I reckoned I could probably get away with the minimal bracing in a box that size. There are stretches in there that I think do resonate either in the operating range or just above it, but I'm ok with the way it sounds.

Part of that project was to work out my woodworking rust before I went on to try more complicated designs. That sub was part of my first DIY project in a good 15 years.
A lot of stuff that people do for bracing has never been measured for effectiveness. The advantage of a rounded brace (arch) is that it distributes weight from the center point out to the sides, so that in a bridge you can use a lot less material to support a high load capacity on the bridge.

As lonely raven pointed out, we are not dealing with elephants or huge inward pressures in subs. In a sub, the idea is to divide a panel up into smaller subsections with resonant frequencies outside the subs passband.

In theory, a dowel across the middle of a panel will divide it into 4 smaller panels and there is no need for windowpane style bracing. I have not seen any real world testing to show this and people much more knowledgeable than I sit on both sides of the fence/debate. It would be interesting to build a box with a T brace so one side gets a dowel style brace and the other a windowpane style brace and then measure for the resulting resonant frequency.

If weight were an issue, it would be more of a challenge to find effective bracing that significantly reduces the sub's weight, but I bet you could do so with composite materials like carbon fiber.

Edit: the key to any bracing is the value of the Young's Modulis parallel to the panel you are trying to brace. The higher the Young's Modulus, the stiffer the material and the more effective it becomes as a bracing material. Also, just because one material is a little stiffer than another does not mean it will translate into a measurable difference in the end product, so oak vs ply may make no difference.
I disagree.

In subwoofers you aren't necessarily trying to make smaller panels, but pillar type bracing should have much the same effect. You are trying to make the resonances much higher in frequency so that they are out of the pass band and stiffen the panels as much as possible to minimize any panel vibration or flex. In the examples that you showed the strongest reinforcement and stiffening from the bracing is in the corners of the box where the box is already the strongest and most resistant to flexing or resonance, but notice that Dan also added or left in the pillar type of bracing. The strengthening in the middle of the panels is less substantial with a large circle type brace and that is where it is needed most. A few strategically placed 2x2's or large dowels near the center of the cabinet walls would probably more effectively stiffen the center of the panels and combat flex while raising the resonances up in frequency as compared to that type of brace. There is still a lot of disagreement though. IMO you want the most material towards the center of the large panels not the edges. I also do not like MDF for bracing. It flexes too easily IMHO.
Sorry, I seem to have been ranting. :hissyfit:

I think we need measurements to truly settle this, and I agree that 2" X 2" or dowels will do some damping of the panels. I think I really just wanted to get the point across that we are not building bomb disposal boxes, but audio boxes. We need to think in audio, not bridges.
 

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If you use 2x2 like a 4 pane window frame why can't it be used just like an mdf brace to divide larger panels into smaller ones?

I would have thought 2x2 mitred and glued/screwed into a 4 pane panel would have been stiffer/stronger than a 1" thick MDF equivalent?
Overkill, but that works perfectly.


/shrug

Mine seems to be doing ok with it. Resonance was the first thing on my mind when I decided to brace it the way I did. That, and my wallet. Since I use plywood instead of MDF for health reasons, I reckoned I could probably get away with the minimal bracing in a box that size. There are stretches in there that I think do resonate either in the operating range or just above it, but I'm ok with the way it sounds.

Part of that project was to work out my woodworking rust before I went on to try more complicated designs. That sub was part of my first DIY project in a good 15 years.
A lot of stuff that people do for bracing has never been measured for effectiveness. The advantage of a rounded brace (arch) is that it distributes weight from the center point out to the sides, so that in a bridge you can use a lot less material to support a high load capacity on the bridge.

As lonely raven pointed out, we are not dealing with elephants or huge inward pressures in subs. In a sub, the idea is to divide a panel up into smaller subsections with resonant frequencies outside the subs passband.

In theory, a dowel across the middle of a panel will divide it into 4 smaller panels and there is no need for windowpane style bracing. I have not seen any real world testing to show this and people much more knowledgeable than I sit on both sides of the fence/debate. It would be interesting to build a box with a T brace so one side gets a dowel style brace and the other a windowpane style brace and then measure for the resulting resonant frequency.

If weight were an issue, it would be more of a challenge to find effective bracing that significantly reduces the sub's weight, but I bet you could do so with composite materials like carbon fiber.

Edit: the key to any bracing is the value of the Young's Modulis parallel to the panel you are trying to brace. The higher the Young's Modulus, the stiffer the material and the more effective it becomes as a bracing material. Also, just because one material is a little stiffer than another does not mean it will translate into a measurable difference in the end product, so oak vs ply may make no difference.
I disagree.

In subwoofers you aren't necessarily trying to make smaller panels, but pillar type bracing should have much the same effect. You are trying to make the resonances much higher in frequency so that they are out of the pass band and stiffen the panels as much as possible to minimize any panel vibration or flex. In the examples that you showed the strongest reinforcement and stiffening from the bracing is in the corners of the box where the box is already the strongest and most resistant to flexing or resonance, but notice that Dan also added or left in the pillar type of bracing. The strengthening in the middle of the panels is less substantial with a large circle type brace and that is where it is needed most. A few strategically placed 2x2's or large dowels near the center of the cabinet walls would probably more effectively stiffen the center of the panels and combat flex while raising the resonances up in frequency as compared to that type of brace. There is still a lot of disagreement though. IMO you want the most material towards the center of the large panels not the edges. I also do not like MDF for bracing. It flexes too easily IMHO.
Sorry, I seem to have been ranting. :hissyfit:

I think we need measurements to truly settle this, and I agree that 2" X 2" or dowels will do some damping of the panels. I think I really just wanted to get the point across that we are not building bomb disposal boxes, but audio boxes. We need to think in audio, not architecture.
 
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