How do I calculate sealed box volume?

Vb = Vas / ((Qtc/Qts)² − 1), where Vas and Qts are the driver's parameters and Qtc is your chosen system Q (0.707 is a flat default).

Can a box be too big or too small?

Yes. Too small raises Qtc/Fc (boomy, less extension); too large lowers system Q and can over-extend a driver below tuning. Model the response and excursion to stay in safe limits.

What size box does my subwoofer need?

Box size depends on the driver's Thiele/Small parameters (Vas, Qts, Fs). Enter your driver to get sealed and ported volume, tuning and F3 instantly.

There is no single 'right' box size — it follows from the driver's Thiele/Small parameters. The compliance-equivalent volume (Vas), total Q (Qts) and resonance (Fs) set how large the box should be and how low it will play.

Sealed box by target Qtc

For a sealed box you pick a target system Q (Qtc). Qtc 0.707 (Butterworth) is maximally flat and a safe default; lower Qtc means a bigger box and tighter bass, higher Qtc a smaller box with a bump. The required volume is Vb = Vas / ((Qtc/Qts)² − 1).

Ported box

A ported box is usually larger and tuned near the driver's resonance. A common starting estimate is Vb ≈ 20·Vas·Qts^3.3 with tuning Fb ≈ Fs·(Vas/Vb)^0.31, then refined against the modelled response.

Pick a driver from the database, or enter your own T/S parameters, and the designer computes both sealed and ported boxes with the −3 dB point and full response.

Frequently asked

How do I calculate sealed box volume?: Vb = Vas / ((Qtc/Qts)² − 1), where Vas and Qts are the driver's parameters and Qtc is your chosen system Q (0.707 is a flat default).
Can a box be too big or too small?: Yes. Too small raises Qtc/Fc (boomy, less extension); too large lowers system Q and can over-extend a driver below tuning. Model the response and excursion to stay in safe limits.