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Discussion Starter · #1 ·
I'm about to build two ported enclosures for my new Sundown Zv4 12 inch subs. I'm in the planning stages and realized my least favorite part of building subwoofers is the interlocking bracing.

At what point do you not need to brace the insides? I'm thinking about building the walls of the enclosure three inches thick.

Do you need to brace with walls 3" thick?
 

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Wow! 3 inch thick walls. That box is going to be quite heavy, no?

Anyways, with 3" walls there might be enough surface space that is glued together and it wouldn't call for much internal bracing. I always take a simplistic approach to bracing myself. However, I usually use plenty of glue/screws or count on the slot port (if building a ported box) to provide enough protection. I would think that some sort of bracing would always be necessary. I could be wrong, though.
 

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There is nothing that dictates that you have to use interlocking bracing made from MDF. You can use dowels, allthread, scrap wood, angle iron, whatever. The purpose of bracing is to reduce panel resonance. If you brace the center of a panel you have moved the resonant frequency of that panel way up. ROT is bracing within 12" of wall or other bracing.

3" thick walls is going to be extremely heavy - almost regardless how small the box is. Single 3/4" wall thickness, double up the baffle, and use some 1" dowel and glue in place. The glue joint almost always is stronger than the wood itself.
 

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Great answers so far, I will just jump on the bandwagon and say 3" walls is probably too much especially when we are only talking 12" drivers. I used 1.5" sides and back with 2.25" front baffle for the 18" LMS Ultra but I also braced inside. This relatively small enclosure at about 4cuft internal still weighed about 115 lbs and for the first layer I used Ultra Light MDF.

Use 1" hardwood dowels as BD55 suggested, MUCH easier to do than interlocking braces which are more for show when you put up your build thread.
 

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Great answers so far, I will just jump on the bandwagon and say 3" walls is probably too much especially when we are only talking 12" drivers. I used 1.5" sides and back with 2.25" front baffle for the 18" LMS Ultra but I also braced inside. This relatively small enclosure at about 4cuft internal still weighed about 115 lbs and for the first layer I used Ultra Light MDF.

Use 1" hardwood dowels as BD55 suggested, MUCH easier to do than interlocking braces which are more for show when you put up your build thread.
That's unusually "light". My build with a 15" driver in an 18" cube with internal amp (1" walls and 1.5" baffle) came out over 120 lbs... The driver and amplifer was 25 lbs each.

My 12" subwoofer build in a 18x18x19" box with 0.75" walls and 1.5" baffle came over 75 lbs.
 

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That's unusually "light". My build with a 15" driver in an 18" cube with internal amp (1" walls and 1.5" baffle) came out over 120 lbs... The driver and amplifer was 25 lbs each.

My 12" subwoofer build in a 18x18x19" box with 0.75" walls and 1.5" baffle came over 75 lbs.
The weight I posted was ONLY for the enclosure, it was probably actually closer to 125 lbs and with the LMS Ultra loaded in it was well over 200 lbs.
 

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Discussion Starter · #7 ·
This enclosure will be slot ported.

The reason I want the walls so thick is because the box has to be 23"w x 21"d x 31"h. If I build it with .75" MDF then it will be too big, over 6 cubic feet.

If I use 3" walls, I can get it down to about 2.5 cubic feet.

I've used dowels for bracing in this box and wasn't really impressed.



This box was an 18" cube with 2.25 thick walls. It ended up being over 110 pounds just for the enclosure. I used threaded rods for bracing.

 

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No wonder you weren't impressed with dowelling on the ported box; there isn't nearly enough bracing. I see all sorts of open panel faces that would then be free to resonate.

I also don't understand how using 3/4" walls gets you 6 cuft while 3" walls gets you 2.5 cuft......color me confused.
 

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Discussion Starter · #9 ·
A slot port box that is 31.5 wide, 23.75 height and 21.75 deep. 3/4 MDF, port width 1.5 inches and port length yields a 6.886 cubic foot box tuned to 15.6.

The same size box on the outside with 3" thick MDF and a 19" port length yields a 3.428 cubic foot box tuned to 21.37 hz.
 

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Another down side, have you considered how much a 3" baffle would choke off your drivers? You'd need some serious chamfer to get to a reasonable clearance around the parts of the motor that need breathing. I don't see a single reason to do 3", or anything over 3/4" or 1", frankly. Even if the box were a size of a room, bracing and 1" walls would be enough.

There is nothing that dictates that you have to use interlocking bracing made from MDF. You can use dowels, allthread, scrap wood, angle iron, whatever. The purpose of bracing is to reduce panel resonance. If you brace the center of a panel you have moved the resonant frequency of that panel way up. ROT is bracing within 12" of wall or other bracing.

3" thick walls is going to be extremely heavy - almost regardless how small the box is. Single 3/4" wall thickness, double up the baffle, and use some 1" dowel and glue in place. The glue joint almost always is stronger than the wood itself.
+1
 

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Discussion Starter · #11 ·
The 3" of baffle will be in front of the woofer, not behind it.

So having a heavy enclosure doesn't help it? I would think it would be better to have a heavier vs lighter enclosure.

I wish I had an accelerometer I could attach to the different boxes I have to measure vibrations.
 

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No, you are absolutely right that having a heavy enclosure helps. However, heavy and rigid aren't necessarily always mutually inclusive attributes. Both can work together to make sure the maximum amount of output is available, but there is a point of diminishing returns on weight. I would take rigid over heavy any day. For example, you could have a light but rigid enclosure that walks all over the place from the sub's output. Throw some weight on top of it and you're done - and your back thanks you.

If you want to go thick and heavy, go right ahead. The box will inherently be rigid due to the amount of material. And like you said, weight is a good thing with a sub. I'm just saying you don't have to do that to have great results.
 

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Discussion Starter · #13 ·
Maybe I'll try making it 1.5" thick with a 3" baffle and use 2x4's to brace the interior. I had to move my sealed 2.25 thick all the way around enclosure with a dolly because it was so heavy.

I was in the decking section of the local hardware store the other day and came up with an idea with (i don't know what they are called) metal pieces that join 2x4's together.
 

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You mean "joist hanger"?


I don't think that will do what you want. Those are designed to support shearing forces. Simply screwing and gluing would do what you want.
 

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Discussion Starter · #15 ·
Yup, that's it. I guess back to the drawing board.

Has anyone ever used concrete boards for building boxes? I think it's in the plumbing section of the hardware store. It almost looks like sheetrock.
 

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At the risk of being deemed "wrong" again - my 2 cents=== It is " necessary " to brace a subwoofer enclosure when the design dictates it. If you design the cab properly there is no "need" for bracing as the will inherently have all the support it needs. As I have stated on the other forum recently I have hundreds of sub boxes out there and have yet to brace any of them (primarily car audio cabinets with multiple drivers) When in doubt go thicker is my train of thought- design the port to be structural - Heavy is a good thing for subs, I have a 15 that wont sit still, and a newly built 18 that weighs over 200 pounds that dances also. At any rate , just wanted to chime in
 

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Discussion Starter · #17 ·
So your 200lb sub dances around? I built a 1.8 cube with a 3" thick front baffle and this thing walks all over the place. I'm planning on adding weight on top of the box to see how much weight it takes to stop it from moving around.
 
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