Building Your Own Subwoofer Enclosure
For my example I'm building a small enclosure to suit a single 12" JBL subwoofer to go into a Honda Civic hatchback. Because the enclosure is only 2.4 cubic foot with a single 12", I'm making it out of 16mm MDF.
Note: There is now a video version of this tutorial located here. It uses slot ports instead of aeroports.
Step 1 - Make sure everything fits
Once you've got the MDF at home and all your tools ready get out the tape measure and check the cuts are correct. The guys at the timber yard are usually pretty good, but its worth while double checking.
Test assemble the enclosure by sitting the panels next to each other, it will give a good indication of weather everything will fit.
WHOOPS ! Seems the timberyard guys got a bit generous with the side panels, so lets mark the excess flab for cutting.
You could do these cuts with the jigsaw, but if you're in a hurry nothing beats a nice 3-horsepower ripsaw with a depth guide.
Nice and neat, off comes the excess materials. Save those offcuts ! We'll be using those later.
Step 2 - Cutting The Baffles
The baffle is the sheet of wood with a hole punched thru it to mount the woofer or the ports. You'll need templates for these.
The best template for marking out the woofer hole in the baffle is to use the packaging in the box it came mounted in. Its the right size to hold the woofer in transit and makes a great template for marking the holes !
Unfortunately I didnt have the sub or box to use for a template, so I used an old baffle that had 12"s mounted into it !
Lay the template on your baffle board, line it up and mark with a pencil.
Mark your ports in the same way. This enclosure will have its ports firing into the side of the car, and sub firing up, so I'm marking the ports on one of the ends. I've used the PVC tube we'll be using for ports as the template.
Be carefull cutting the port holes ! Make them too big and the ports won't fit snuggly and will fall out. Make them too small and the port wont fit.
Its better to make
Because this enclosure is being covered with carpet I've used the outside of the PVC for marking, which means the holes have to be slightly bigger than the pipes outer diameter to allow the carpet to be rolled inwards. This hides the carpets cut edge inside the box and allows a snug port fitment as the carpet takes up the slack.
Next drill a guidehole. I'm using a 3/8" wood bore as its a nice size to allow the jigsaw blade to get in there, you can use whatever size you have that fits. Seen here, I'm lining the edge of the bore up with the cut marking.
Guidehole punched. Perfect ! Now you can get in there with the jigsaw and carefully cut along the line.
Here's the finished punched out hole, nice 'n' messy. Keep the bit you just cut out, you need it later.
Next step is to get onto the edge with your router. The edge needs routing because the underside of the basket tapers inwards, and your baffle will need to too otherwise the woofer wont fit !
The finished port baffle. Cut & clean routed, the nicely routed lip follows the contour of the port flare we'll be making later, so it'll sit flush.
Step 3 - Building the Chamber & Bracing
I got a little carried away with the gluing and screwing and forgot to take most of the photo's ! But its pretty easy:
1. Hold two sheets where they should roughly be (an extra pair of hands helps here), I prefer one side and the base. Use the 2.5mm bit (or whatever is handy) drill guide holes down thru the two pieces, to the approx. depth of your screws. This will prevent cracking when you screw it all together. A spacing of around 3-4" between holes is a good rule of thumb.
2. Using your driver bit, screw the top and side together loosely.
Next, get one of the ends, position it and drill more tap holes to attach it to the base and sides. Then screw it loosely. Do the next side drilling the taps and screwing.
3. With the final end drill the tap holes, but then remove it and apply glue to its edges. Now place it inside and screw it, this time snugging the screws down tight. Remove one sides screws, glue its edges, then screw down snuggly. Repeat for the remaining two panels.
Note: You want to achieve a firm clean seal between the edges with no gaps. When getting rid of the gaps don't worry too much if there's a bit of overhang or daggy edges. You can clean those up later with a plane.
What you end up with will look like this, ready for the top.
Remember those offcut pieces I told you not to throw out ? They're now your bracing. Bracing is used around the baffles to add strength and to the floor panel as it is large and prone to flex. Attach the bracing use a healthy dose of PVA glue and tack it using some light MDF nails.
I've used the sub hole "biscuit" and the two short edges from the side panel to reinforce the sub baffle. The port "biscuits" are attached between the ports to brace the port baffle. The long sections from the side panels are attached to the base in a V configuration to add strength to that panel.
Step 5 - Completed
All thats left to do now is attach the baffle, clean it up and add some ports.
To attach the baffle, lay it ontop the completed cabinet, line it up and drill your guide holes. Again, 3-4" gaps are fine, drill the guides to the depth of the fastener. Remove the baffle, apply the adhesive to the top edges, replace the baffle and screw it down snuggly.
Once its in one piece, you may wish to clean up any overhangs with a plane. Small cracks, screw tops, etc. can now be covered up with building bog or painter caulk, then sanded down for a super smooth finish.
Here's our completed enclosure without ports:
From here you can coat the enclosure with a layer of fibreglass resin then paint it, or wrap it with carpet or vinyl.