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Old 4th October 2008, 10:59 PM   #1
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Default Bracing the cabinet

I've seen a lot of cabinet braces that go across the cabinet from side to side but haven't seen any that brace the baffle front to back (yet).
Any reason?
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Old 4th October 2008, 11:13 PM   #2
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Bracing opposing sides of the cabinet to one another does very little to raise the resonant frequencies of either panel. The most effective way to raise the resonant frequency is to make the panel much thicker. This makes the panel behave like a beam where one surface is in compression while the opposite surface is in tension. The easy way to do this is to put a board on edge against the panel. You want the braces to bisect the panels parallel to the longest dimension of the panel.
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Old 4th October 2008, 11:15 PM   #3
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Default Re: Bracing the cabinet

Quote:
Originally posted by Lewis Moon
I've seen a lot of cabinet braces that go across the cabinet from side to side but haven't seen any that brace the baffle front to back (yet).
Any reason?
You haven't been looking in the right places?

Click the image to open in full size.

Some points (assumming a rectangular box):

1/ a brace should touch 4 walls or at least have a wide contact area (ie a dowel from side-to-side doesn't do much).

2/ it needs to be stiff (ie avoid particle board or MDF)

3/ a brace should be placed such that it divides a panel into 2 subpanels that form dissimilar rectangles with a greater aspect ratio than the original panel (ie don't put a brace dead centre and they are best if they run the long dimension (ie the ubiquitous shelf brace is not the most effective way to do things)

4/ if the subpanels in 3 are trapezoids instead of rectangles, even better.

dave
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Old 4th October 2008, 11:21 PM   #4
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Probably because the sides often have a greater surface area than the baffle, so greater benefit comes from bracing the sides.
Also, the baffle commmonly has drivers all over it, making siting a brace more tricky.
Furthermore, this panel-to-panel bracing topology only works optimum if the panels are identical in flexing characteristics, and the baffle with large holes, and moving diaphragms in it, would not vibrate with the same frequency and amplitude as the back wall, so the brace would transfer further vibrations to the side pointed at you.

I'm talking about the dowel type brace here, not the best but easy to install retrospectively.

I believe they would benefit from intersecting another such brace, or two (all 3 dimensions, contradictory as it is with the above), because they would have the tendency to work like a string on a guitar, particularly catastrophic if the half wave frequency of this is the same as one in the panels. I've fought this with damping foam, but don't really know if it worked, may install a top-to-bottom brace.
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Old 4th October 2008, 11:43 PM   #5
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The baffle is the panel that needs the most bracing since you have cut big holes in it...

Attached is a picture from an AES paper... higher numbers are better

dave
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File Type: gif panel-bracing-strategies.gif (24.7 KB, 218 views)
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Old 4th October 2008, 11:54 PM   #6
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For this reason I use an extra thick baffle, and attach slanted braces between the drivers.

This data is reassuring, I've got two dowels and a bunch of widthwise braces. The dowels seem to have have little effect on the reasonant frequency of the panels, but surely would improve the stiffness at lower frequencies? Good for sub duty?
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