How to Build Your Own Subwoofer

The woofer is the key to the cabinet size

Choice abounds when it comes to building your own subwoofer. There's the choice of building a sub for your vehicle or home theater. There's the choice of shape of the cabinet, from traditional rectangle to round. There's the type of subwoofer, with eight subwoofer types being known. And then there's the material employed for the box or enclosure: everything from traditional plywood to granite. Thankfully, there's much in the way of help in terms of instructions, parts and software on the Internet. And the savings of DIY are profound, up to 90 percent less than a comparable manufactured subwoofer.

Things You'll Need

• Loudspeaker
• Speaker design software
• Thiele/Small (T/S) parameters
• 1-inch birch plywood
• Table or power saw
• Power drill
• Furniture clamps
• Router or circular saw attachment
• Wood glue
• Wood screws
• Silicone caulk
• Acoustic foam
• Sanding block
• Plate amplifier
• Speaker wire

Instructions

Planning a Sealed Box

1. Pick the loudspeaker/driver. The biggest size speaker will not only produce more bass, but will determine the dimensions of the speaker box/cabinet. A 15-inch diameter is optimum for a home theater; 12 inches is the same for a vehicle.

2. Use speaker design software. For example, WinISD is a free, popular download for Windows computers. A lot of science and engineering goes into subwoofer design; take advantage of what's out there to help.

3. Get the Thiesle/Small parameters for your loudspeaker/driver. T/S parameters are included with the purchase of any quality loudspeaker, and can also be obtained from the Thiele/Small website. (See Resources.) T/S parameters are all the acoustic and design measurements necessary for creating the cabinet or box.

4. Buy acoustic foam to dampen the resonance of the box.

Assembling the Subwoofer

1. Print out the plans as generated by the speaker-building software.

2. Get one-inch birch plywood. Birch plywood was the material of the Altec-Lansing "Voice of the Theater," the most famous speaker ever made. Cut the box panels from this plywood as indicated by the plans. Use a table saw, or have a store cut the pieces to size for a small fee.

3. Assemble the side panels, bottom panel and brace. Test fit first, then glue the panels together with wood glue. Next, 2-inch wood or drywall screws further secure each joint. Clamp this assembly with furniture clamps, and let it dry thoroughly, six to eight hours.

4. Make the cut out for the back panel. This is where the plate amplifier is installed. Dry fit the back panel to the cabinet. If flush, glue and screw the rear panel to the cabinet. Clamp and let dry for eight hours.

5. Attach the top panel. Apply glue, and further secure with wood screws. Clamp and let dry for 12 hours.

6. Apply a bead of clear silicone rubber caulk to all interior joints. Allow to dry for 10 to 12 hours. Then glue acoustic foam to all interior surfaces of the box.

7. Cut out the circle for the loudspeaker to fit in the front panel. Use a hole saw, router or circle cutter in a drill press.

8. Glue and screw the front panel to the box. Clamp the front panel. Caulk the inside seams of the front panel, using the openings in the front and rear panel for access. Allow 12 hours for the silicone rubber caulk to thoroughly dry.

Finishing the Subwoofer Box

1. Sand the finished cabinet by hand with a sanding block while the caulk is drying. Fill the countersunk screw holes with wood putty. Re-sand once more.

2. Install plate amplifier in the back panel. Using 12-gauge cable (lamp cord), connect the cable to the speaker contacts on the plate amp. The cable should be eight inches longer than the cabinet depth to have room to connect it to the loudspeaker/driver.

3. Finish the cabinet with stain, paint or wood veneer to finish and protect it. Remember, this as much a piece of furniture as it is an electronic component. (This step can likely be skipped if building a vehicle subwoofer.)

4. Connect the cables from the amp to the loudspeaker/driver, and install the driver in the front panel. Use Phillips wood screws to secure it, and apply a bead of non-drying caulk between the front panel and the speaker perimeter to provide an airtight seal.

5. Position the subwoofer wherever bass performance is best in a home theater, or where there's sufficient room in a vehicle.

Tips & Warnings

• Positioning can be most anywhere. Bass frequencies have no directionality to the human ear.

References

• DIYsubwoofers: DIY Plans and Designs for Subwoofers of All Types
• DIYAudioProjects: Do-It-Yourself Information on Subwoofers

Resources

• Thiele/Small: The T/S Parameters Database
• WinISD: Free Software Download of Speaker Building Software