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Discussion Starter · #1 ·
I'm building a 16x16 sealed sub out of 3/4 inch mdf and was just wondering if I still needed bracing in the center or if it was small enough to get away with none. Thanks!
 

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HTS Moderator , Reviewer
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That's a fairly small box and you're using .75" MDF to build it, so you may be able to get away without any bracing. What driver and amp did you have in mind?
 

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Elite Shackster , HTS Moderator Emeritus
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Yes, yes, and yes.

I just made some satellite speakers that are about 4x5x7 and I can feel them flexing (and sadly hear them resonating). Those are a cheap prototype, I will have bracing in the final build.

As to a sub, you also need to break up panel resonances. Since you are looking at a cube there, breaking those up will help immensely.

I would build up structure in the corners (like a solid triangular brace) along the "depth", direction the driver points and have one mid panel with either one giant hole or 2 holes about 2/3 of the way back. Overall you aren't adding that much volume, but the results will be noticeable.

Good luck.
 

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Discussion Starter · #4 ·
@theJman I'm using a Bash 300 and a CSS Trio 12

@Anthony can you explain a little more about the triangular bracing and placement? Do you mean in the corners farthest away from the driver?
 

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Elite Shackster , HTS Moderator Emeritus
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For a small box, I'd use at least the one "partition" (the one I described with one large hole or two smaller ones like an 8). That basically adds a perimeter rib all the way around in one direction. In your case, this would have to be across the back of the driver, since you couldn't fit it any other way. I would locate the divider such that it wasn't on an even multiple (1/2, 1/4, etc), but rather an odd one (1/3 or 2/3 of the length from the front). This prevents the remaining resonance modes from being the same frequencies and building on one another. In your case, with a small enclosure, the 1/3 point from the back is probably good, and generally just avoid the exact middle.

As for the other thing I mentioned. I was talking more of a cleat, or corner fillet. It would end up being a triangle of wood that would run along the 4 edges making up the top and sides. It stiffens up the corners, which (like the panel divider mentioned earlier) drives up the resonant frequencies, hopefully out of the subwoofer range. It also makes assembly easier, since you have a nice surface to screw into from the inside.

Code:
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(Really crude ASCII drawing, those are top and side with the brace in the corner, should be a 45 degree angle)

For max effect, any stiffening material should be glued along its entire length and pinned or screwed (since clamps might be tough for some of the shapes. The end result is that you don't really have any sides that are a regular flat board, free to resonate.

I would also stuff the sub, and if it's in the budget, line the insides with 1" acoustic foam. You should end up with a nice tight sound.
 

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@theJman I'm using a Bash 300 and a CSS Trio 12

@Anthony can you explain a little more about the triangular bracing and placement? Do you mean in the corners farthest away from the driver?
Even using something such as 1/2" quarter round along the corners inside can have a tremendous impact on reducing any flex in the box.
 

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Because it's relatively easy and inexpensive to brace the inside of a box like that, just do it! The beauty of DIY is you can attend to those little details. Air tightness and rigidity are keys to a great sounding sealed sub. I like to stuff mine full of duct putty, along all the joints and in all the corners. No sharp corners inside my subs. If you were using 1" MDF, I'd say you could skip bracing. With 3/4" not worth it.
 

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Elite Shackster , HTS Moderator Emeritus
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I have some tiny 2 driver full range speakers (5"x6"x7" approx). I didn't brace the prototype boxes, but you can really feel the sides flexing when the volume is up. The final version will be a tad larger and braced much better.
 
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