Thiele-Small Box Volume Calculator

Thiele-Small (T/S) parameters are a set of measured electromechanical properties that describe a loudspeaker driver's low-frequency behaviour, named after Neville Thiele and Richard Small. The three used most for box design are Fs (free-air resonance), Vas (equivalent compliance volume) and Qts (total Q factor). They let a designer predict how a driver behaves in any enclosure.

For a maximally flat sealed alignment (Qtc 0.707), the box volume is Vb = Vas / ((0.707 / Qts)^2 - 1), valid when Qts is below 0.707. This calculator uses that relation for the sealed suggestion. Smaller boxes raise the system Q and resonance; larger boxes approach free-air behaviour.

A widely used vented (quasi-Butterworth) approximation gives Vb = 20 * Vas * Qts^3.3, with the port tuned to Fb = Fs * (Vas / Vb)^0.31. This calculator reports both the sealed and vented suggested volumes so you can compare enclosure types for your driver.

As a rough guide, drivers with Qts below about 0.4 suit vented boxes; Qts around 0.4 to 0.7 suit sealed boxes; and high-Qts drivers (above 0.7) often suit free-air or infinite-baffle mounting. The Qts is the single most useful parameter for choosing enclosure type, so check your driver's datasheet value.

No. These are alignment approximations to give a sound starting volume. A complete design accounts for port dimensions and air velocity, driver displacement limits, box losses, and baffle effects, and is best confirmed with a full simulation. Always treat the output as a starting point and verify before building.