A sealed box acts like an air spring behind the cone. Its size sets the total Q of the system (Qtc), and Qtc sets the shape of the bass: lower is deeper and more controlled, higher is louder around resonance but boomier.
How this calculator works
Vb = Vas / ((Qtc / Qts)² − 1)
Fc = Fs · √(1 + Vas / Vb)Vb is the net internal volume, after the driver and any bracing are subtracted.
A Qtc of 0.707 gives the flattest response (a Butterworth alignment). Between 0.5 and 0.6 the box gets bigger and the bass rolls off earlier but more gently, which suits sound-quality builds and cars with strong cabin gain. Around 0.8 to 1.0 the box is small and punchy, with a bump near Fc.
Before you build
- This is net volume. Add the driver's displacement and bracing to get the gross volume, then panel thickness for the outside size. The box volume guide walks through it.
- Check cone travel at your amplifier power in the full calculator; sealed boxes are forgiving but long-throw drivers still have limits.
- Not sure sealed is right? Read sealed vs ported.