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Old 5th May 2006, 06:35 AM   #1
gwgjr31 is offline gwgjr31  United States
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Join Date: Feb 2006
Location: Boston, MA
Default how much bracing is enough

So, after digging deeper through the forums, I've come to realize that I need to add bracing to the sealed box that I've been building for a 15" driver. The box is 18"x18"x21" internal and is constructed out of 3/4" MDF. The MDF is framed with 2x2 poplar. I've attached a picture of the partially constructed box. My original plan was to finish the box with 1/4" plywood. I'm considering either adding assorted cross bracing between the internal surfaces, enclosing the entire box in 1/2"+ plywood/MDF, or both (if really necessary).

My question is, how much is enough. I know there is some point of diminishing returns here, but I don't know where it is. I want the sub to be sufficiently sturdy, but I'd also like to be able to move this thing on my own.

Thanks!
Gary
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Old 5th May 2006, 06:57 AM   #2
lndm is offline lndm  Australia
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My opinion is...

Bracing is good as it adds stiffness with little extra mass. Extra mass would negate the stiffness, therefore, laminating your panels brings an improvement, but bracing is much more effective than that when done right.

When I built my first boxes, I used to think of resonance in so far as how much there was, and how strong the box needed to be to reduce the resonance to an acceptable level.

In practice, bracing increases the frequencies of the resonances. In some cases this can make the box sound worse.

When building a subwoofer, this situation is quite fortunate. Applying enough bracing to raise the resonances out of the passband will fix your problem. Also, keeping your panels small in comparison to a wavelength at the higher frequencies in your passband might make life easier.

As far as cross braces between panels versus braces glued along a single panel, I have found the latter has helped me more effectively so far.
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