How to Build a Powered Subwoofer
The crowning touch to a home theater is the installation of a subwoofer. The subwoofer delivers the subsonic thrills that are experienced in a movie theater by low-end effects that are felt as much as heard, and the subwoofer is what brings these to life. Though it is a challenging undertaking, building your own powered subwoofer is among the most satisfying tasks for a do-it-yourself-er. While there are many considerations from the shape of the enclosure to size of the loudspeaker, there are abundant plans online, and cost savings you will realize, that will bring you a thrilling result.
Things You'll Need
- Speaker driver
- Plate amplifier
- 3/4-inch to 1-inch MDF
- 3/4-inch plywood
- PVC pipe
- Power drill
- Router or circular saw attachment
- Speaker wire
- Silicon caulk
- Non-drying caulk
- Wood screws
Pick the size loudspeaker that will be housed in the cabinet. Popular sizes range from 8 inches to 18 inches, and the best bass response will be produced by 12-inch, 15-inch or 18-inch loudspeakers. Then, armed with the Thiele/Small parameters that dictate the enclosure size for a bass reflex or sealed speaker design, pick your cabinet materials to begin building the powered subwoofer for your home theater.
Choose a plate amplifer. A plate amplifier allows for free movement of the sub, and usually includes the crossover in its purchase. It mounts inside the speaker box. For these reasons, a plate amp is both cost effective and convenient. You can also choose one that perfectly matches power output to the power handling capacities of the loudspeaker you're using in the sub. There are excellent Web sources such as partsexpress.com.
MDF (Medium Density Fiberboards) is preferred over plywood because of its higher density. Whichever is chosen, 3/4-to-1-inch thickness is advised. Often in DIY enclosures, the top and bottom of the cabinet will be MDF and the sides, back and front will be plywood. If the shape of the design is cylindrical rather than square, Sonotube is good for the enclosure, with the top and bottom being MDF.
PVC pipe is often very good for creating a port. The port or vent greatly aids in the reproduction of low-frequency sound by extending the low-frequency range of a speaker box. Bass reflex/ported designs therefore feature a lower cutoff frequency than a sealed-enclosure system using the same driver, and also offer lower distortion and higher power handling. Instead, their sound can be more "boomy" than that of enclosed boxes, and that is where greater science and engineering come into play.
Once you've decided on a design, sealed or ported, use winISD (or another software design program) to map out your cabinet. Then, assemble the cabinet pieces, including one piece the same size as the top and bottom to use as a brace in any design using a loudspeaker/driver 10 inches or larger.
Dry-fit the enclosure. This is to ensure that the terminal cup and/or plate amp will fit the driver or any bracing. Once it all fits, glue the sides to the top, bottom and brace. Apply the glue to each side of the joining pieces. Smooth the glue with your finger, and clamp the boards in place. Let it dry for 30 minutes minimum, but follow the instructions for your particular glue. Next, set the back piece in place and mark the location of the terminal cup and plate amp. Cut the terminal cup hole, test fit, and notch out a bit of bracing if the terminal cup or amp need more room. Glue the back piece in place, clamp it, and let the cabinet dry at least eight hours.
Fit the front board, and mark the position of the loudspeaker. Also mark the ports if the design is for a ported subwoofer. Cut the holes for the speaker (and port). Make certain everything on the front panel clears the bracing. Before connecting the front panel, run a bead of silicone caulking over all inside edges. Then glue and clamp the front panel without the loudspeaker in place, and let it dry at least eight hours. Lastly, caulk the front panel (go through the plate amp hole on the back ) and leave the caulking to dry for at least 24 hours. Silicon caulking emits gases as it drys that can eat through speaker surrounds.
Install the amplifier in the cabinet. Silicon caulk the amplifier around its perimeter.
Install the loudspeaker. Screw it down and run a bead of non-drying caulk around the surround frame.
Sand, finish, and apply any veneer to the cabinet you like.
Tips & Warnings
- There is definitely science at work in creating any powered subwoofer design. Powered designs are best in a sealed enclosure, so much of the expertise required for ported sub design is moot. Using a free program called winISD, which can be downloaded from their Web site, makes your work quite easy. See the resources for the winISD link.
- Always use generous amounts of glue and silicone sealant in constructing the cabinet. Positively no air should escape the cabinet except through the port.
- Make sure the plate amplifier is matched to the ratings of the loudspeaker/driver.