Speaker Box Calculator

Subwoofer Box Volume from T/S Parameters

Every driver has Thiele-Small specs that describe how it behaves in an enclosure. Given Vas, Qts, and Fs, you can estimate a sealed or ported box volume before cutting wood.

Sealed Enclosure Volume

$$V_c = \frac{V_{as}}{(Q_{tc}/Q_{ts})^3 - 1}$$

For a Butterworth alignment, $Q_{tc} \approx 0.707$.

Ported Enclosure and Port Length

Ported volume uses a QB3-style alignment. Port length follows the same formula as our dedicated port tool:

$$L = \frac{23562.5 \times D^2}{V \times F^2} - k \times D$$

Related tools: Port Length Calculator and Delay Reverb Calculator.

Frequently Asked Questions

What is Vas?

Vas is the equivalent air compliance volume of the driver suspension. It is listed on most subwoofer spec sheets in liters.

Sealed or ported: which should I pick?

Sealed boxes are simpler and tighter. Ported boxes can play louder near the tuning frequency but need correct port dimensions.

Can I size a box from external dimensions?

Yes. Enter outer width, height, depth, and panel thickness. The tool subtracts wall material and reports net internal volume.

Why does port length matter?

Port length sets the tuning frequency with a given box volume and port diameter. Too short or too long shifts bass response.

Are these results exact?

They are starting points for DIY builds. Driver placement, bracing, and port flare all shift real-world response slightly.

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Subwoofer Box Volume from T/S Parameters

Sealed Enclosure Volume

Ported Enclosure and Port Length

Frequently Asked Questions

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