How to Make a Bandpass Sub Box

By Sean Russell

RMS is a measurement of speaker power.
i Hemera Technologies/ Images

Those interested in pumping up the bass may consider the bandpass sub box design. In this design, the subwoofer mounts inside of a dual-chambered box. The box is separated by a sealed chamber and a ported chamber. The circular port hole of a bandpass box forces sound into a narrow frequency range, creating maximum bass. Bandpass sub box design works well with bass-heavy genres of music such as hip-hop, hard rock and electronic. Not all subwoofers are designed for the bandpass configuration. Consult the owner's manual for the loudspeaker to verify a bandpass configuration will work for your specific subwoofer.

Determining Subwoofer Box Dimensions

Step 1

Consult your specific subwoofer owner manual for manufacturer recommended enclosure specifications including size, enclosure volume and required air space.

Step 2

Measure the height of your subwoofer from the bottom of the magnet to the rim of the sub face. The easiest way to measure the height accurately is by placing the subwoofer upon a level surface with the magnet-end touching the ground. Add two-inches to the subwoofer height. This will be the depth of the enclosed portion of your dual-chambered bandpass sub box.

Step 3

Consult the owner manual’s mounting template for required volume within the second ported chamber of the box. The mounting template will also advise on the recommended height and width of the box.

Step 4

Sketch the dimensions of the sub box on a piece of paper, using the correct height, width and depth dimensions as whole and separated by the chamber. Use this template during the build.

Step 5

Subtract the thickness of the fiberboard from each dimension (height, width and depth) to determine the internal dimensions.

Step 6

Calculate the cubic volume based on the internal dimensions of the sub box using this formula: height x width x depth = cubic volume. Refer to the manufacturer's recommended dimensions, and adjust as needed.

Building The Bandpass Box

Step 1

Measure the correct dimensions for each of the six sides of the external enclosure on the fiberboard and, with a pencil, draw cut lines to fit those dimensions. Use the same technique to measure the size of the internal panel the subwoofer will mount onto.

Step 2

Cut the fiberboard to size using the jigsaw along the pencil lines.

Step 3

Trace the circumference of the circular subwoofer face using the subwoofer face template, included in the owner manual, on the center of the interior panel of the box.

Step 4

Cut out the drawn circle using the jigsaw.

Step 5

Trace the shape of the speaker terminal cup on the enclosed portion of the box’s back panel. Note where the magnet’s location will be in the enclosed compartment of the box, because that is where the wires connect from the subwoofer to the terminal cup. Cut out the terminal cup shape.

Step 6

Squeeze a bead of caulking along the rear perimeter of the terminal cup before screwing it into place using the sheet metal screws.

Step 7

Measure the circumference of the port hole on the lower portion of the sub box’s ported chamber, and cut out the port shape.

Step 8

Insert a port tube (which can also be made from PVC pipe) into the port hole until the wide outer lip of the tube rests on the box. Use hot glue to secure it in place.

Step 9

Glue the box to shape using the wood glue liberally. Do not secure the top side of the enclosed chamber in place until the rest of the box has dried. Once dry, future assure air tightness for the box by pre-drilling pilot holes, and then screwing in the woodscrews.

Step 10

Mount the subwoofer through the open side of the soon-to-be enclosed chamber with the face pointing towards the port hole. The magnet side will face up. Secure the loudspeaker with sheet metal screws.

Step 11

Wire the positive and negative speaker wire from the input on the magnet basket to the contacts of the speaker terminal cup.

Step 12

Finish the box by gluing and then screwing the final panel of the enclosed chamber into place.