Speaker box designer

Enter the driver’s Thiele/Small parameters from its data sheet (or start from one of the generic examples), pick a box type, and the designer sizes the box, plots how it will behave, and gives you the panels to cut.

How to use it

Driver. Fs, Vas, Sd and Re are needed, and two of Qts, Qes and Qms (or BL with Qms). Leave Qts or BL blank to have them derived. The line under the fields shows what follows from them: moving mass and compliance, BL, the reference efficiency and 1 W / 1 m sensitivity, and the efficiency bandwidth product (EBP = Fs/Qes) — below about 50 a driver suits a sealed box, above about 100 a vented one.
Box.
- Sealed — pick a target Qtc (0.707 is the flattest; 0.5–0.6 is tight and needs a bigger box; above 0.8 it peaks) or type your own volume. Vb = Vas/((Qtc/Qts)² − 1).
- Vented — the alignments are the classic Thiele/Small fourth-order high-pass polynomials, solved for a loss-free box and then plotted with your box losses (QL, 7 is typical): QB3 (quasi-Butterworth third order) for Qts below 0.383 — a small box tuned above Fs; B4 (Butterworth) is exact at Qts = 0.383; BB4 (Keele’s "boom box", two identical second-order sections, tuned to Fs) wants a bass boost; C4 (Chebyshev) for Qts above 0.383 — a bigger box tuned below Fs, with a ripple that grows with Qts. Or type your own Vb and Fb.
- Band-pass (4th order) — a sealed chamber behind the driver and a ported chamber in front; only the port radiates. From S (0.7 flat, 0.6 and 0.5 give more gain over a narrower band) and the Q of the driver on its rear chamber: Vf = (2·S·Qts)²·Vas, Vr = Vas/((Qbc/Qts)² − 1), Fb = Qbc·Fs/Qts.
Port. Round tubes or slots, one or several. The length is the effective length Leff = Sp·c²/(4π²·Fb²·Vb) less the end corrections (0.85·r for a flanged end, 0.61·r for a free one; a slot uses the radius of a circle of the same area, plus a little when it runs along a wall). The tool also gives the port air speed at your drive power and the area that keeps it under 17 m/s, about where chuffing starts.
Plots. SPL at 1 m in half space for √(P·Re) volts, the peak cone excursion against Xmax, group delay, impedance (measure the real box’s impedance peaks to check the tuning), and port air speed. They come from a lumped-element model of the driver (Re, Le, BL, Mms, Cms, Rms) coupled to the box, so the SPL plot matches the textbook transfer functions when Le is zero.
Build it. The internal volume is the net volume plus the driver, the port and any bracing; it is shaped to the proportions you choose (the golden ratio 0.62 : 1 : 1.62 by default), and the panel thickness turns it into outside dimensions and a cut list in millimetres and inches. Plan the sheet layout in the cut list optimiser.

The model has no baffle step, no room gain and no voice-coil heating, so expect the real box to be a few decibels off in places. Box stuffing makes a sealed box act bigger and lowers QL.

The example drivers are generic: typical, self-consistent figures for each size, not any manufacturer’s driver. For the crossover, the active filter designer does Linkwitz–Riley pairs; check a finished box with the audio oscilloscope or spectrum analyser, and the room with room acoustics.

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