Subwoofer Box Calculator — Sealed & Ported Enclosures

Thiele-Small (T/S) parameters describe the electromechanical properties of a loudspeaker driver. The key ones for enclosure design are Fs (resonant frequency in Hz), Qts (total Q factor) and Vas (equivalent compliance volume in litres). These are published in driver datasheets.

Sealed enclosures are simpler to build, have better transient response and a gentler roll-off below cutoff. Ported enclosures extend bass lower and produce more output near the tuning frequency but roll off sharply below it. Drivers with Qts below 0.4 typically suit ported; those from 0.4 to 0.7 suit sealed; around 0.4 either works.

Qtc is the total system Q of a driver in a sealed enclosure. A Qtc of 0.707 (Butterworth alignment) gives the flattest possible response with no bass peak before roll-off. Lower values give flatter but less extended bass. Higher values add a bass hump that can sound boomy.

Yes. Bracing, the driver magnet and port tube all displace internal volume. Add approximately 10-15% to the calculated net volume to compensate. The calculator shows net internal volume — your external box should be larger.