Speaker box calculator
Sealed and ported enclosure design from three Thiele/Small parameters — box volume, tuning, port length, and an honest response preview.
Volumes are net internal volume — add driver displacement, bracing and port volume on top. Fill/stuffing makes a sealed box act ~10–15% bigger.
Sealed boxes: pick a Qtc
A sealed box turns the driver into a second-order high-pass with total Q of Qtc. The box volume follows directly: Vb = Vas / ((Qtc/Qts)² − 1), with Fc = Fs·Qtc/Qts. Qtc 0.707 (Butterworth) is maximally flat; 0.577 trades extension for the best transient behavior; approaching 1.0 sounds punchier but rings and rolls off higher. Qtc below your driver's Qts is physically impossible — the tool flags it.
Ported boxes: volume and tuning
A ported (bass-reflex) box adds a Helmholtz resonator that extends response roughly half an octave deeper for the same driver, at the cost of steeper rolloff (24 dB/oct) and less control below tuning. The classic QB3-family starting point for drivers with Qts ≈ 0.2–0.4: Vb ≈ 15·Vas·Qts^2.87, Fb ≈ 0.42·Fs·Qts^−0.96. Port length comes from the Helmholtz condition with end correction: L = S·c² / (4π²·Fb²·Vb) − 1.46·r.
FAQ
Sealed or ported for my driver?
If you enter Qes, the tool shows EBP = Fs/Qes: under ~50 favors sealed, over ~100 favors ported, between works either way. High-Qts drivers (>0.5) generally want sealed or very large ported boxes.
Why does my port need to be so long?
Low tuning + small box + wide port = long port. Options: smaller diameter (watch chuffing — keep port area up for high-excursion drivers), a passive radiator, or accepting a larger box.
How accurate is the response preview?
The sealed curve is the exact second-order response for your Qtc. The ported curve is an idealized 4th-order alignment sketch — real ported response depends on losses and the exact alignment, so treat it as a shape guide, not a measurement.