Published on September 5th, 2012 | by Gearhead Diva0
Build a Subwoofer Box for Your Car
You’re putting together an awesome stereo system for your car. You’ve bought everything but the subwoofer, but you’re not sure whether you want to spend the extra money on buying a sub box that is prebuilt, or save a pretty penny by building it yourself. You’d really like to save that money and build the box yourself, but how? Read on, my friend, and you’ll see that the hardest part of this process is deciding what brand and size sub(s) to buy rather than building an enclosure!
Make the Box Out of Medium Density Fiberboard (MDF)
Wait, I said I was going to save you money. Yes, I did, but not at the expense of a quality build. Plywood is cheaper than MDF because it is plywood. It is several plies, or sheets, of thin wood glued and pressed together. With the thumping of a good subwoofer, the bonds between these sheets can loosen and develop an annoying rattle. So, go with 3/4″ MDF.
Tools and Materials You’ll Need
- Enough MDF to complete the project.
- Wood/drywall screws – about 100 should do. You’ll want 4 – 6 to mount each sub, and enough to space about 6″ apart when assembling the box. You want them 1 1/4″ long.
- Wood glue or clear silicone sealant – air leaks are bad.
- Drill – preferably cordless, their clutch allows them to stop immediately.
- 1/8″ drill bit
- Phillips screwdriver tip for the drill.
- Speaker terminals – 1 per subwoofer
- 14-gauge speaker wire
- Compass or speaker template
Calculate the Box Size You Need
If you buy really high-quality speakers, they usually come with a spec sheet that details ideal box dimensions to get quality sound from your subs. As an example of this, the spec sheet for the MTX Thunder 9500 15″ sub calls for a speaker box with an internal volume of 134.9 cubic inches.
Sometimes even with quality speakers, you won’t find box volume listed in the specs. But there are websites that can make the calculations for you. Here are some calculators available for free. You’ll need to check the spec sheet for Qt, Vas, Fb, Fs, and a few other specs.
- The DIY Audio and Video website has a good calculator to use for calculating ideal box volume.
- If your speaker’s spec sheets show a listing for enclosure displacement, you can use the speaker box volume calculator at the DIY Audio and Video website to find the best measurements for your box. Remember, this is for INTERNAL volume, not external measurements. You need to account for the thickness of the MDF being used.
- The12volt.com has a number of calculators listed on their page for both ported and unported enclosures. They also have calculators for impedance loads.
Measure, Measure Again and Then Cut
I have been told by master carpenters hundreds of times: “Measure two or three times before cutting. It reduces mistakes.” And it does. Once you’ve got your ideal box dimensions decided upon from the calculators above, lay out your MDF sheet(s), and start measuring and marking. Then measure again just to make sure you were correct. Mark the pieces so you know what one goes where. Be sure to include internal bracing for added strength. Once you have all of the pieces measured and marked, cut them out.
Use the compass or speaker template to create the circle to cut for the speaker opening and the port, if you plan on using one. Use the drill (or a hole saw) to make an opening for the jigsaw blade to cut out the speaker opening. Next, decide which side you’re going to put the speaker terminals on (back, top, side) and make the opening for the terminals.
Assemble Your Speaker Enclosure
First, make sure all the pieces fit together properly without using the glue or sealant. With that decided and any corrections required made, it’s time to complete the assembly for real. Lay out the bottom piece and drill pilot holes 6 – 8″ inches apart. Run a bead of glue or silicone along the mating edge of one of the sides, hold it in place, and secure it with the screws. Repeat this process for the internal braces, top, front, and the other side.
With the box completely built, but no speakers in it, run a bead of glue or silicone along the insides of all the joints for added sealing. If you used silicone, let it dry overnight. The acids in the silicone fumes can damage your speaker drivers. Also, after applying the sealing bead is a great time to either paint, or cover the enclosure so it looks good. Paint or cover to either blend in or contrast with the location the box will sit in your car.
Mount the Speaker in the Box
Place the speaker in the opening and drill pilot holes. Once everything is properly dried, hold the speaker in the opening and connect the speaker wires from the speaker terminals. Run a bead of sealer (preferably non-silicone) around the outer edge of the speaker basket and place the speaker in the box, lining up the mounting holes. Mount the speaker in place with at least four screws. Larger speakers should use more screws so as to not warp the basket. Allow it all to dry and install it in your vehicle.
Now “turn it up to 11!”
Photo credit: mlg9770