Introduction: Custom Underseat Subwoofer Box

About: All around DIY enthusiast. I love everything from woodworking, metal working, to fishing rod building!

This tutorial is of an underseat subwoofer box, I have recently completed. This is most definitely not an exhaustive tutorial whatsoever. It is just an overlook at the process. These custom sub boxes, have so much work involved, that a full tutorial would be extremely long. If you guys want to see a full tutorial, show me the support and I will make one if it interests you guys! :)

Step 1: Measurements/Floorboard Template

The first step is to take measurements of the area that the box will go. I have already predetermined what the airspace inside the box will need to be based on the subwoofers parameters. However, the bottom will be a false bottom, to keep from fiber-glassing the trucks floorboard. With that said, I needed to measure where the false bottom needs to sit. I used a jig that I made in order to trace the shape of the floorboard onto MDF. This step is not necessary. You can certainly just square cut the front piece to fit around the tranny hump, but I like to make everything neat and some what factory looking.

Step 2: Beginning of Fabrication

In this step I cut all my MDF panels. I left a lot of things out here, as it is a sub box tutorial, and not a woodworking tutorial. If you guys want a full tutorial then I will include all woodworking tips as well. Anyways, the basics here is using my template for the floorboard to make my cut for the front panel, and using my measurements for the rest of the panels. I then predrilled holes with a countersink bit for wood screws, and glued all panels together between a generous amount of wood glue. The second picture shows all panels glued and screwed together. The round part is the port. That would be a whole other tutorial. I also used a roundover bit on my router to smooth out my edges.

Step 3: Fiberglass

On this top panel, I added a nice flow coat of fiberglass resin. This is because it is angled for the seat allowance, and I want to make these seams as strong as possible. This step is easy. You simply mix up the resin per instructions, then pour a layer over the top. I used a duct tape border to keep it from flowing down the sides.

Step 4: "Body Work"

The next step is to do what I call the "bodywork". This involves using bondo to fill in all screw holes, seams, and low spots in the fiberglass resin. Just use a bondo scraper to apply it as smooth as possible. After it sets up, you will spend a couple hours sanding. This is a painted box, so all flaws will show through. I used 80 grit to knock the high spots down, then 120 and 220 to smooth it out. You will end up with a perfectly smooth finish.

Step 5: Prime/Test Fit

In this step, I prime the box and test fit the woofer to make sure that all is well before painting. The bottom is left unprimed, as it will be covered in carpet. It is a downfiring sub box, so the sub is on the bottom.

Step 6: Paint

This is the fun part. You get to see the almost complete project. I painted this one with a color match red. The truck it went in was a red GMC. He wanted black splatter paint on it, but that is pretty self explanatory.

Step 7: Final Touches

This is where I added the subwoofers decal as well as my decal. Also, the underneath was lined with carpet, and the entire edge on bottom was lined with felt strip, to prevent it from scraping the trucks carpet. LED lights were also installed at this point. It is ready to be installed and the box is complete.