Directions to build a ported subwoofer are all over the Internet because a ported subwoofer box is probably the most popular form of subwoofer, whether manufactured or self-made. Building one is a do-it-yourself project that involves impressive engineering expertise. After all, there is a good reason why top brands can exceed £1,950 per speaker. Thankfully, Internet help allows anyone with the patience and initiative to build their own quality subwoofer for about 10 per cent of the manufactured cost. Doing this produces a quality subwoofer that will reproduce the most earth-shaking bass frequencies of a cinema or concert hall.
- Skill level:
Things you need
- 3/4-inch to 1-inch birch plywood
- Sabre saw
- Power drill
- Router or circular saw attachment
- Wood glue
- Wood screws
- PVC pipe
- PVC elbows
- PVC flares
- PVC cement
- Silicone caulk
- Binding posts
- Speaker wire
Choose a 12-inch loudspeaker/driver. This is the most important component of any subwoofer box design.
Thiele/Small parameters are normally provided with good loudspeaker/drivers. If yours do not come with them, download them from the thielesmall.com website (see Resources), which is a database of over 5,000 loudspeakers.
Download speaker-building software. Many programs exist for both PCs and Macs, but winISD is among the best regarded, and it is free for Windows-based computers.
Get the Critical Components
Buy 24-inch diameter Sonotube (or other concrete form material) as the box material. Sonotube is very dense, coated cardboard used as a mould for pouring concrete columns. Round subwoofers eliminate many of the problems encountered during the tuning of a subwoofer box.
Use a sabre saw to cut a 23-inch piece of the Sonotube.
Peel one and one-half inches of the waxy polymer interior coating from both inside ends of the Sonotube segment.
Smooth and taper the ends of the Sonotube. This eases installation of the wooden end caps. Use a hand file to do this.
Apply auto body undercoating to the tube interior (except on the prepared ends of the tube) to help reduce resonance.
Glue or spray acoustic one-inch damping material on the inside surface of the tube, except on the ends where the wood caps will go.
Build a Round Box
Cut three 24-inch diameter circles from three-quarter inch medium density fiberboard (MDF) or birch plywood. These circles will be glued together for both the bottom and top of the cabinet. Cut a fourth circle 26 to 28 inches in diameter; this will serve as the tabletop.
Glue two wood circles together using a good quality wood glue to create the top and bottom of the subwoofer. Clamp around the perimeter of the circles with C-clamps. Remove the clamps after one hour, but allow six to eight hours for the glue to dry thoroughly.
Install the speaker top piece. Apply a generous amount of glue to the inch of bare interior surface, and insert the smaller diameter end into the tube. Counter sink wood screws every three inches around the tube perimeter to further bond the top to the tube. Once the glue is dry, apply silicone caulk around the inside seam to make a complete seal.
Prepare the remaining wood circle for the loudspeaker, the ports and the binding posts. Use a router or circular jig to make the cuts. Cut two four-inch circles next to each other in the top third of the wood circle, and cut out the 12-inch circle below them for the loudspeaker. Make two half-inch diameter cutouts for the binding posts. Maximise space between each of the items.
Build the "U" shaped ports from three-inch inside diameter PVC pipe. Use a hacksaw to cut two 16-inch lengths. Glue 90-degree PVC elbows with PVC cement. Cut two four-inch lengths of pipe and glue them to the open ends of the PVC elbows. Glue two additional PVC elbows to the three-inch PVC lengths, turning each elbow down to form a U shape. Glue a 13- to 14-inch length of pipe to the open end of the second PVC elbow to complete the U shape. The ports will end directly over the loudspeaker/driver after installation.
Install the PVC ports on one side of the bottom circle. Insert the bare ends of the U-shaped ports into the small holes in the panel and cap them from the opposite sides with pipe flares. Glue and screw the pipe flares to the surface of the wood bottom. Apply silicone caulk around the PVC pipes on the interior side of the wood bottom.
Install the loudspeaker on the opposite side of the bottom from the ports. Use wood screws plus non-drying silicone caulk to affix the driver to the panel. Insert the binding posts from the same side and connect 12-gauge wire from the posts to the respective tabs on the speaker's rear. Glue additional foam backing around the backside of the panel for further damping. Apply wood glue to the open end of the tube, insert the panel flush with the tube bottom and further secure the bottom with wood screws counter sunk around the tube's diameter.
Install three 3-inch screw-on feet to the base and finish the cabinet in your choice of fabric, paint or wood veneer.
Construct the End Caps
Tips and warnings
- For less than £130, this subwoofer design will extend below 20 Hz and output sound pressure levels in the low 120 dB range. A separate power amp must be connected to this subwoofer.
- Use generous amounts of glue and caulking on all seams of a subwoofer box. No air should escape the box except through the port.
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