Subwoofer Box Calculator

Start by choosing your enclosure type. Select Sealed for a simpler build with tight, accurate bass, or choose Ported if you want louder output and deeper extension at a specific tuning frequency.

Next, select the number of subwoofers, the driver diameter, and enter the recommended volume per subwoofer from your manufacturer's specifications. This number is usually listed in the owner's manual or on the product page as the recommended sealed or ported volume in cubic feet.

Choose your material thickness. Most builders use 3/4 inch MDF. If you selected a ported enclosure, enter your desired tuning frequency in hertz and the diameter of the port tube you plan to use.

Click Calculate Box Dimensions to see the total volume breakdown, suggested external dimensions, a panel cut list, and the number of 4 by 8 sheets of MDF you will need. For ported enclosures, the calculator also shows port length and warns you if the estimated port velocity is high enough to cause noise.

Sealed enclosures are the simplest to build and the most forgiving of small measurement errors. The airtight chamber acts as a spring behind the subwoofer cone, controlling its motion and producing tight, well defined bass. Sealed boxes roll off gradually below their resonant frequency, which means they still produce output at very low frequencies, just at reduced levels.

Ported enclosures use a tuned port (a tube or slot) that allows air to move in and out of the box. At the tuning frequency, the port's output reinforces the subwoofer's output, resulting in significantly higher SPL (sound pressure level) in that range. Below the tuning frequency, however, the subwoofer becomes unloaded and output drops sharply. This means ported boxes are louder in their tuned range but need careful design to avoid damage from frequencies below the port tuning.

For music listening and sound quality builds, many enthusiasts prefer sealed enclosures. For SPL competitions, movies, and maximum output, ported enclosures are the popular choice. Both designs work well when built to the manufacturer's recommended specifications.

The tuning frequency of a ported enclosure determines where the port produces its maximum output. A box tuned to 35 Hz will have peak port output at 35 Hz, with the combined output of the port and subwoofer creating a bump in the response around that frequency.

Lower tuning frequencies (25 to 30 Hz) produce deeper, more subsonic bass that you feel more than hear. This is ideal for home theater and music genres that emphasize deep bass. Higher tuning frequencies (35 to 45 Hz) produce louder, more punchy bass that is easier to hear and stands out in a car environment with road noise.

The tuning frequency also affects port length. Lower tuning requires a longer port, and larger port diameters also require more length. If the calculator shows a port length that would not fit inside your enclosure, you can increase the tuning frequency, reduce the port diameter, or consider using a slot port instead of a round tube.

Use MDF (medium density fiberboard) for most subwoofer enclosures. It is denser than plywood, which helps absorb panel vibrations and prevent rattles. MDF also cuts cleanly and takes paint or carpet covering well. The downside is weight, but for a stationary car audio installation, the extra mass is actually beneficial.

Apply wood glue to every joint before screwing the panels together. Use drywall screws or wood screws spaced about 4 to 5 inches apart along each joint. After assembly, run a bead of silicone caulk along every interior seam to ensure an airtight seal.

For the subwoofer cutout, use a router with a circle jig or a jigsaw with a compass guide. The cutout should match the mounting hole diameter specified by the subwoofer manufacturer, not the cone diameter. Many builders also use a flush trim router bit to create a recessed mounting surface so the subwoofer sits flush with the baffle.