DIY Subwoofer Box

Hi everyone! Looking for tips, tricks, knowledge and advice on diy subs.

I currently have two 18 inch subs that I’m looking to build a box for. I picked up the pair from a guy that used to build PA systems as a side gig. Unfortunately he did not remember the model or specs of the woofers. They were sitting in his garage collecting dust, but completely unused. No stampings or stickers on the subs lead to any distinct model. From as far as I could dig and guess, they are probably an average PA subwoofer that likely fall off around 40 hz, and can handle 300-500W a piece. For 50 bucks for the pair, I sent it just because.

Eventually I plan to upgrade to dual Dayton Ultimax 18’s and swap the drivers. I figure as long as I’m going to do this, I should build the box to the Ultimax specifications.

I am a bit crazy and want to build a dual opposed, single front vented box, that will double as my entertainment center-tv stand. I will work on posting my CAD pictures and maybe file if that’s possible shortly. I am completely new to this so any advice will help. I designed the box based of of specs from win isd for dual ultimax 18’s.

Any thoughts on why that would be a bad idea for the time being?!

Model was made with 1 inch thick material. I may use 3/4 unless ill-advised. It also does not show any bracing. I would plan one brace between the woofers and port. The giant opening and whole through the middle would serve as a rack mount, and wiring access.


I would try and get as much information on the subs as possible, and see what the specs are so you can tune your box accordingly (for the daytons you want to put in there). I would just lookup tutorials and then adapt them to your needs. Also always make sure to over engineer the box to higher standards rather then skimp on the box, it can end up making a big difference. Also with the dual opposed design, you will need about double the power to get to a specific spl compared to other designs. You might also want to look into that.

Also check out some isobaric designs, that might be something to look into

When I ran win isd I uploaded the Ultimax parameters so it should be optimized for those.

I definitely want to do opposed woofers to eliminate as many vibrations as possible. I’ll jump on my laptop now and upload what I’ve done so you can get an idea for the madness I plan to dive into.

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Edited the original post. Let me know if there are any issues viewing the pictures that I need to resolve :slight_smile:

Gotcha, I was envisioning a setup where you would have the woofers magnet to magnet to increase output, but yeah I don’t foresee any issues with the design as long as you go with what you planned

Edit: didn’t see you said ported, my bad

Ah no worries! Thanks for the input.