How to Build a Subwoofer Box ...and save some money, too.

Erin Blanton — Jul 01, 2003

Article contents
Page 1.   Tools and materials
Page 2.   Choosing your sub and designing the enclosure
Page 3.   Constructing the subwoofer enclosure
Page 4.   Finishing and customizing your subwoofer encl

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Click on the photos to enlarge.

	Step 1. We started by measuring and cutting the main pieces of MDF for the front, sides, back and top of the box, using a table saw with a carbide-tipped blade. Don't have a table saw? Don't worry. If you purchase your MDF at any large home improvement store, they should be able to cut it for you for a small fee. You could also use a jigsaw, but your cuts may not be quite as smooth (and smooth, flat cuts help to ensure that the box seals well). We cut seven pieces total — top and bottom, two sides, the back, and two identical pieces for the front (since it was to be a double thickness).
	Step 2. After the pieces are cut to size, use a compass, or the template that may be included in your subwoofer's packaging, to mark the woofer cutout on one of the identical front pieces.
	Step 3. If you choose to use a double-thickness of MDF for the front panel (this method is recommended — it provides an extremely strong, non-resonant mounting surface for the sub), fasten the two identical front pieces together using plenty of carpenter's glue and several sheet metal screws. Also, the double thickness will serve to strengthen the box as a whole. (If you don't use a double thickness of MDF for the mounting surface, you should definitely plan to use bracing elsewhere in the box for added strength. In fact, it's never a bad idea to use bracing no matter what, especially if your box is larger than a cubic foot. The box will be subjected to extreme internal pressure, so the stronger it is, the better. The easiest way to add bracing is with 2"x2" strips of lumber. Glue and screw these along at least two of your box's internal seams before attaching the top and bottom.)
	Step 4. Using a drillpress, we made a hole near the inside edge of the circle we had traced, large enough for our jigsaw blade to fit in. If you don't have a drillpress, simply use your handheld drill and a large bit.

	We jigsawed out the circle, and the woofer cutout was complete.
	Step 5. We followed the same drilling/jigsawing procedures to make a rectangular hole in the box's back panel. This would hold the terminal cup, which we installed next. After running a bead of silicon caulk around the edge of the terminal cup (available from Crutchfield, item number # 0732531034, $4.00), we screwed it into place using 1/2" sheet metal screws.
	We jigsawed out the circle, and the woofer cutout was complete.
	Step 6. Since the back and front pieces were now complete, it was time to fasten everything together. Note: the largest sides of the box should overlap each of the smaller sides to provide the greatest strength. For our box, that meant that the sides were fastened to the front and back first, and the top and bottom were added last. Because MDF can be prone to splitting, we pre-drilled holes for the screws in each of the pieces to be fastened together.
	After pre-drilling the holes, we squeezed plenty of carpenter's glue between the pieces. The glue, not the screws, is what will ultimately seal the box together, so don't be afraid to pour it on.
	Then, we fastened the pieces together using our cordless drill and 2" drywall screws. Some of the glue will squeeze out during this step — you can wipe it off the outside of the box using a wet rag, but it's OK to leave it on the inside edges (it'll actually help with the seal).
	After you put together the front, back, and sides, you may find that the box is a little out of square — we did. When you screw the top or bottom on, it should pull things back into alignment. Ours gave us just a little bit of trouble, though, so we used a furniture clamp to get things straightened out.
	After you've glued-and-screwed the sides, front, back, top, and bottom, you're just about done.
	The next step is to drop the subwoofer in and make sure it fits. If the box has gotten a bit out of square, you may find that the sub is now a tight fit — if so, use coarse sandpaper or a rasp to enlarge the opening a little.
	Step 7. With the subwoofer in place, we used a pencil to mark the screw hole locations, then removed the subwoofer and pre-drilled holes for the mounting screws.
	Step 8. To make double sure that everything was sealed up, we waited for the glue to dry and ran a bead of silicon caulk over all of the box's internal seals. We used a hand-held tube of caulk, since it would be tough to get a caulk gun down inside the box at this point. Let the caulk cure for 12-24 hours before putting the subwoofer back in. Some silicon caulk releases acetic acid fumes while curing, which have the potential to destroy subwoofer surrounds.
	Step 9. After the caulk had cured, we hooked up speaker wires from the terminal cup to the subwoofer and placed the subwoofer back in the box, using non-hardening rope caulk (found in the weatherstrip section of the hardware store) to seal it down. Don't use regular caulk for this — you'll need to pull that sub someday, and if you glue it to the box with silicon caulk it'll be tough to get out.
	Once the sub was in place, we fastened it down using 3/4" sheet metal screws, and our box was complete.