How thick should the walls of a sealed subwoofer box be?

For most home and car subwoofers, 18 mm (3/4 inch) MDF or quality plywood is the sweet spot. Larger 15-inch and 18-inch drivers benefit from 18 to 25 mm walls plus internal bracing to stop panel flex.

Does a sealed box need internal bracing?

Yes for anything from a 12-inch driver upward, and it never hurts on smaller boxes. Bracing ties opposite panels together so they cannot flex, which keeps the energy in the cone instead of the walls for tighter, cleaner bass.

How important is it to get the internal volume exactly right?

Important, but not to the millilitre. Sealed boxes are forgiving, and being within a few percent of the target net volume keeps the system Q (Qtc) and F3 essentially on target. Our plans are solved to the exact net volume for each driver.

How to build a sealed subwoofer box (step by step)

A practical, beginner-friendly walkthrough of building a sealed subwoofer enclosure — from choosing the right internal volume to cutting, bracing, sealing and mounting the driver.

A sealed (closed) subwoofer box is the simplest, most accurate way to mount a subwoofer. There is no port to tune, the low-frequency roll-off is gentle, and the transient response is tight. This guide walks through building one the right way.

1. Start from the driver, not the box

The single most important number is the net internal volume the driver wants to see, which depends on its Thiele-Small parameters (Vas, Qts, Fs). Too small and the bass gets peaky and shy on extension; too large and it gets boomy and loses control. Every plan on this site is already solved to the correct net volume and a target system Q (Qtc ≈ 0.7 for a maximally flat response).

2. Cut accurately

Mark and cut your panels to whole-millimetre dimensions. The two ways to do it:

Print & tape: print the full-size 1:1 templates at 100%, butt the A4 sheets together, lay them on the board, trace and cut with a jigsaw or router.
CNC: feed the DXF cut files to a CNC and it cuts every outline, the driver cutout and the brace holes in one pass.

Either way you get exactly the same box.

3. Brace it

Panel flex is the enemy of clean bass. Internal braces tie opposite walls together so the box stays rigid. Round drilled holes in the braces (at standard hole-saw sizes) keep them light and let air move freely between chambers while adding huge stiffness.

4. Glue, seal and clamp

Assemble with wood glue on every joint and clamp until dry. A sealed box must be airtight — any leak changes the tuning and adds noise. Run a bead of sealant along the internal seams, and gasket the driver and any connector plate.

5. Mount the driver and test

Wire up the driver, drop it into the pre-sized cutout, and bolt it down onto a gasket. Power it up at low volume first and listen for air leaks or buzzes before pushing it.

That’s it — a rigid, airtight, correctly-sized sealed box that lets your subwoofer do exactly what it was designed to do.

Frequently asked questions

How thick should the walls of a sealed subwoofer box be?: For most home and car subwoofers, 18 mm (3/4 inch) MDF or quality plywood is the sweet spot. Larger 15-inch and 18-inch drivers benefit from 18 to 25 mm walls plus internal bracing to stop panel flex.
Does a sealed box need internal bracing?: Yes for anything from a 12-inch driver upward, and it never hurts on smaller boxes. Bracing ties opposite panels together so they cannot flex, which keeps the energy in the cone instead of the walls for tighter, cleaner bass.
How important is it to get the internal volume exactly right?: Important, but not to the millilitre. Sealed boxes are forgiving, and being within a few percent of the target net volume keeps the system Q (Qtc) and F3 essentially on target. Our plans are solved to the exact net volume for each driver.