How to Build a Simple Sub Box

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Building a box for your subwoofer is one of the best ways to put your peronal touch on a car's audio system. Whether it's a basic cubic box or a precisely designed kerfed / ported box, making sure your sub gets the appropriate enclousure for your needs can make a world of difference.

This step by step shows the process to build a basic sealed box.

In my case, I picked up a sub/amp/box combo on Craigslist for pretty cheap, however the box was slightly too big to fit into the trunk of my 1997 240sx (only a 15" opening). So, motivated to make my purchase work, I decided to build a box: Spending less than $50 for the materials.

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Step 1: Planning: Figuring out cubic feet

Before you start anything, you need to look at the sub you are using. Subwoofers recommend a min. / max. cubic feet enclosure. 

In this case, I was using an Infinity Kappa 12.1 which recommends a .75 - 1.25 cubic foot Sealed box. Reading some reviews, I chose to go with 1 cubic foot. (sealed vs. ported depends on your preferences. Sealed gives you a harder/punchier bass, ported gives you a wider range and can be heard from further distances. Read up more on sealed vs. ported if you're unsure on what you would like)

To figure out the cubic feet of the interior of the box you are designing, you multiply Length x Width x Height and divide by 1728
In this example, the exterior of this box is 10" x 16" x 16"
Keep in mind the thickness of materials -  3/4" on each side = 1.5"
8.5 x 14.5 x 14.5 = 1787 Divided by 1728 = 1.03 cubic feet

*Depth of the box should be judged by the depth of the subwoofer + 2" minimum*
aleitt1 year ago
Excellent information. How does it sound ? I want to build the exact enclosure to slide under the rear seat of my pickup. Do you think the box being ported would make a big difference ? That might be too complicated for a beginner like me.
Thanks !
jondneumann (author)  aleitt1 year ago
It sounds pretty good. It's a very modest set up compared to my last system (2 Alpines, I also had 2 Kickers before that). If you're going to port the box, read up on different techniques and the size of the port. That will matter greatly. It also depends on what type of music you like (ported can be louder, but offer less "punch". theyre good for rap, techno or "rolling bass"). But on a box like this, I've seen people use a 2"-3" circle port, made out of PVC. Just make sure everything is sealed (liquid nails or silicone).
gmatta2 years ago
very nice my friend. I was wanting to do something like this but instead be a portable sound system. not to be rude, but I think you meant to put "excess." I just thought I'd let you know now that way people don't start complaining about it later. but I found this very helpful. thanks :))
jondneumann (author)  gmatta2 years ago
Thanks for the correction, sir. I didn't catch that one. Updated!
Da Nugesta2 years ago
Absolutely amazing job! Made it look so easy :) I have built a few boxes in my time (Alpine 8, Mutant 12 and my latest was an 18 inch Fi BL!) Those are the ones that spring to mind.. You have done a much better job! Keep up the great work and possibly do more subwoofer instructables :)

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