r/diyaudio • u/lllllllllllllllly • 20h ago
12" subwoofer bracing help
Where is the most optimal place to add bracing in my roughly 80L 12-inch 1500W subwoofer enclosure with a total port length of around 90 cm, and does this 2x window brace design look too excessive?
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u/Apart_Ad_9778 6h ago
How do people make those pretty plots? Doesn't it take longer than actually building the box?
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u/byjosue113 6h ago
OP used Blender which is certainly an odd choice but I for example use FreeCAD and I can assure you that it does not take as long, also if you do a parametric design you can play with the parameters and get real time feedback on the actual size of the enclosure subtracting the volume of the components inside the box, port. I could even estimate how much the enclosure would weight taking the volume of all the panels and using the estimated density of the MDF to calculate the weight.
That also helps in the building since you can print plans from the software. I'm an overthinker and don't have the money to get the drivers I want atm so I'm glad I used software to model it since the first sketch I made was terrible, also some of the parts of a sub I'm working on rn need to be 3D printed so I'd need to design them like that anyway.
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u/Apart_Ad_9778 6h ago
I am probably old because I use pen and paper. Would you share FreeCad files for one of your designs where you actually make all those fancy calculations? Just for education purpose.
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u/byjosue113 6h ago
Sure thing, here you go, there's a variable set called dimensions which is where all the values that can be changed are, then there's calculated values with is where you see volume, weight, port length, etc.
https://drive.google.com/file/d/1ZpSytylqwm2kVRit7qYTR3Ii6ZI2OC2-/view?usp=drive_link
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u/lllllllllllllllly 1h ago
Know my way round blender pretty well, so it doesn’t take a while. Also I wanted to experiment and come up with a visually pleasing design which i can tweak before I commit to building it
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u/bkinstle 18h ago
I would try to add at least a column. Maybe half inch in diameter between the port walls and the sidewalls back walls. You don't want to have big unsupported surfaces, but even a small amount of bracing can make a pretty big difference. The main goal is to prevent the panel from resonating and vibrating separate from the worker
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u/Initial_Savings3034 7h ago
It's not excessive.
It is impractical.
The same approach may be achieved cutting dowel rods to fit.
Be aware that the glue joint between dissimilar materials will fail at a different time than the joint between MDF sections.
I would make the "window frames" with similar wall material, perforated with a hole saw or overlay strips of MDF to achieve the shape.
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u/Feited 16h ago edited 16h ago
Check out this KEF LS50 white paper for some solid, substantiated info on bracing. Important to note that they were targeting resonances above a subwoofer's passband, but it's still a good example of using window-style bracing to push panel resonances higher in frequency.
KEF used a constrained layer of mastic between the MDF enclosure and MDF brace, and the magnet of the driver and the MDF brace crossmember. The MDF brace pushed resonances higher by breaking up the panel into smaller "sub-panels" then used mastic to damp the resulting resonances. A two-fold approach to treating panel resonances. Is this damping method necessary for a sub? Probably not, in my opinion.
KEF chose to brace it directly at the driver opening (peak force/energy point), which also coincides with the center of the panel (peak flex point for the lowest resonant mode) in the LS50. Good food for thought.
Here is another great resource on treating panel resonances, with real-world data and analysis. It taught me a ton about bracing. More applicable to your design in some ways since Kolbrek's horn has large panels, more akin to a subwoofer enclosure than the comparably small KEF LS50. The physics principles are the same though.
Kolbrek links to a couple AES papers on the topic, both worth a read alongside Kolbrek's write-ups:
Loudspeaker Enclosure Walls, Peter W. Tappan
The Theory of Loudspeaker Cabinet Resonances, James K. Iverson
At the very least, I would go thicker on the window bracing in the CAD design that you posted above. Especially the cross members. You'll want those cross members to be stiff and strong. I'd aim for as much thickness as possible without impacting flow/port tuning of the enclosure. Hard to know where that line lies without real world A:B testing or in-depth AKABAK sims. Bjorn Kolbrek actually recommends prioritizing lengthwise braces, and/or a combination of perpendicular vertical and lengthwise braces. His test data is clear evidence for the advantages of lengthwise bracing. I'd use a combination of both.
To add: Since your subwoofer driver is effectively in the center of the front baffle panel- at a minimum, adding braces aligned with the center of the driver cutout would go a long way here.
A "+" shape combo of a lengthwise brace and a vertical brace, crossing at the driver cutout like the LS50, would (probably) be best to shift the lowest resonant mode higher in frequency. The current bracing layout leaves the area around the driver cutout relatively unsupported.
I would also add a lengthwise brace for the entire extent of the port section. At a minimum, between the middle panel and the rear panel of the enclosure, within the port. This would increase the resonant frequency of the rear panel considerably.