by Paul Sanders
Adding a new car subwoofer to your stereo system can really enrich the sound quality that you experience in your vehicle. Once you've chosen your subwoofer, you'll need to place it in an enclosure. A subwoofer enclosure provides a box of trapped air for the subwoofer speaker to push against. That air provides resistance for the speaker cone, which lets it vibrate properly to produce deep, rich bass. With a few simple tools, you can put together your own subwoofer box.
Determine the box volume. Your subwoofer will specify the exact air volume, in cubic feet, required for the best performance.
Calculate the internal volume by subtracting the thickness of the MDF from your dimensions. Then multiply the height, width and depth to get the volume. If your subwoofer enclosure is wedge-shaped, you may need to do more complex calculations for its volume.
Convert the volume from cubic inches to cubic feet by dividing the volume in inches by 1728.
Adjust the dimensions of the subwoofer enclosure to achieve the volume specified by the manufacturer. Change your sketch to match the new dimensions. It's best to make the sides of the subwoofer box larger to overlap the edges of the front, top, bottom and back panels.
Cut MDF pieces for the subwoofer box. You'll need just one piece for each side of the subwoofer enclosure, except the front. Cut two identical pieces for the front panel.
Trace and cut a hole for the subwoofer speaker. Your subwoofer may include a template to trace a hole for both the subwoofer and the mount on the front panel of the box. Follow specific instructions for your subwoofer.
Cut a rectangular hole for the terminal cup. This hole will be on the back panel of your subwoofer enclosure and will hold the terminal that accepts speaker wire from your amplifier.
Pre-drill holes in the MDF for the screws. Pre-drill matching holes for the 2-inch screws where each MDF panel overlaps an adjacent panel. Where you place the holes is up to you, but use a minimum of two holes per joint.
Fasten the panels together. Glue the two front panels together to form the double front panel that the subwoofer speaker will rest on.
Lay one of the side panels flat and glue the edges of the top, bottom, front and back panels perpendicular to it. Use clamps to hold the pieces together while the glue dries. Glue the other side panel on top to complete the subwoofer enclosure, making sure that all the sides are square.
Fasten the 2-inch screws through the predrilled holes. Wipe up any glue that seeps onto the outside of the subwoofer box.
Run silicone caulk along the inside seams of the subwoofer box and let it dry for a day.
Insert the speaker terminal cup. Run a bead of caulk around the edge of the hole in the back panel of the subwoofer enclosure and insert the cup. Fasten it with the 1/2-inch screws.
Insert the subwoofer speaker. Test the opening for the subwoofer by inserting the speaker dry. If the subwoofer doesn't fit properly, sand down the edges of the opening until it fits the subwoofer snugly.
Mark the location of the mounting holes on the speaker and remove it. Pre-drill the holes for the screws.
Connect the wires from the terminal to the subwoofer speaker.
Run a bead of non-hardening caulk around the edge of the opening and insert the subwoofer.
Fasten the speaker to the front panel with 1/2-inch screws.
Install the subwoofer enclosure in your car. Run the appropriate speaker wire from your stereo and connect it to the terminal on the back of the subwoofer box. Secure the subwoofer to your vehicle so that it doesn't slide around.