BoxwrightIn short
- One engine, written once, with every formula sourced. The app and this site’s calculators use it; the site’s JavaScript port is tested against the engine on 963 inputs to 1e-9.
- 338 reference vectors run on every build: hand-worked values, edge cases, and 79 values published by manufacturers and in papers. Every one must pass within its own tolerance.
- A separate Python reference agrees with the engine on more than 4,000 values to 1e-9. 26 deliberate bugs (a sign, a constant) were each caught by the tests.
- 7 real designs compared with Hornresp 60.60.
Against Hornresp
Hornresp is a free simulator many builders treat as the reference. We entered the same drivers (from their datasheet Fs, Qes, Qms, Vas, Sd and Re) and the same boxes in both, at 2.83 V, half space, 1 m, QL 7.
| Driver | Box | Largest SPL difference | Largest excursion difference | Fb engine / Hornresp |
|---|---|---|---|---|
| JL Audio 12W3v3-4 | Sealed 35.4 L | 0.04 dB | 0.4 % | – |
| JL Audio 12W3v3-4 | Ported 49.6 L, 100 cm² × 36 cm | 0.61 dB | 2.6 % | 36.85 / 36.48 Hz (+1.0 %) |
| SB Acoustics SB23NRXS45-8 | Ported 40 L, 50 cm² × 20 cm | 0.62 dB | 2.0 % | 37.97 / 37.97 Hz (+0.0 %) |
| Scan-Speak 18W/8531G00 | Sealed 20 L | 0.03 dB | 0.4 % | – |
| Dayton RSS265HF-4 | Ported 55 L, 80 cm² × 30 cm | 0.52 dB | 1.5 % | 34.05 / 33.90 Hz (+0.5 %) |
| Peerless SLS-P830669 | Sealed 60 L | 0.08 dB | 0.7 % | – |
| JL Audio 10TW3-D4 | Sealed 17 L | 0.03 dB | 0.5 % | – |
- Sealed boxes agree within 0.1 dB and 1 %.
- Ported boxes read up to 0.6 dB lower far below tuning (at 15 Hz, where output is already about 25 dB down) and within 0.3 dB in the useful band. Hornresp treats the port as its own sound source; our model, like Small’s, sums cone and port at one point.
- Tuning agrees within 1 %. Hornresp’s implied port end correction is 1.46 to 1.62 × radius; our default (one flanged, one free end) is 1.46.
Not compared yet: bandpass boxes, passive radiators and port air speed.
Against published values
These are values a manufacturer or an author printed, worked out again by this site’s calculator code:
| Source | Value | Published | Our result | Tolerance | Result |
|---|---|---|---|---|---|
| JL Audio 12W3v3-4 | Qts from Qes and Qms | 0.444 | 0.444 | ± 0.006 | ✓ within |
| JL Audio 12W3v3-4 | Sealed Qtc | 0.830 | 0.835 | ± 0.006 | ✓ within |
| JL Audio 12W3v3-4 | Sealed Fc | 50.2 Hz | 50.2 Hz | ± 0.1 Hz | ✓ within |
| JL Audio 12W3v3-4 | Sealed F3 | 43.7 Hz | 43.7 Hz | ± 0.1 Hz | ✓ within |
| JL Audio 12W3v3-4 | Slot port tuning | 30.0 Hz | 29.5 Hz | ± 1 Hz | ✓ within |
| Scan-Speak Technote 07 | Sealed volume for Qtc 0.707 | 13.63 L | 13.63 L | ± 0.01 L | ✓ within |
| Scan-Speak Technote 07 | Sealed volume for Qtc 0.707 | 17.79 L | 17.79 L | ± 0.01 L | ✓ within |
| Scan-Speak Technote 07 | Port length, 6 cm port | 21.7 cm | 21.0 cm | ± 1 cm | ✓ within |
| Scan-Speak Technote 07 | Port length, 6 cm port | 24.6 cm | 24.4 cm | ± 1 cm | ✓ within |
| Scan-Speak Technote 07 | Port length, 6 cm port | 51.9 cm | 51.5 cm | ± 1 cm | ✓ within |
| Scan-Speak 18W/8531G00 | Sealed volume for Qtc 0.707 | 23.0 L | 23.0 L | ± 0.5 L | ✓ within |
| SB Acoustics SB23NRXS45-8 | Fs from Mms and Cms | 27.00 Hz | 26.98 Hz | ± 0.16 Hz | ✓ within |
| SB Acoustics SB23NRXS45-8 | Vas from Cms and Sd | 94.0 L | 93.8 L | ± 1.5 L | ✓ within |
| Peerless SLS-P830669 | Fs from Mms and Cms | 31.48 Hz | 31.48 Hz | ± 0.19 Hz | ✓ within |
| usenclosure.com | Port length, 4 in port, 1.5 ft³, 35 Hz | 15.50 in | 15.36 in | ± 0.15 in | ✓ within |
The tolerance is the printed rounding, or the scatter the source states. The full set of verified values, by source:
| Source | What is checked | Vectors |
|---|---|---|
| JL Audio 12W3v3-4 specifications (authorised retailer copy) | Qts, Bl, efficiency, sensitivity, sealed Fc, Qtc and F3, slot port tuning, net volume | 9 |
| Scan-Speak Technote 07, box alignments | Sealed volumes, QB3 and SC4 boxes, port lengths, Fs, Qes, Rms, Zmax | 17 |
| SB Acoustics SB23NRXS45-8 datasheet | Qts, Vas, Fs, Qes, Rms | 5 |
| Dayton Audio RSS265HF-4 specifications | Qts, Fs, Vd | 3 |
| Peerless SLS-P830669 datasheet | Qts, Vas with Small’s air constants, Fs, Qes, Sd | 5 |
| audioXpress, “Voice Coil Focus: Quasi-Alignment Families” | QB3 alignment table at QL 10 | 6 |
| Speakerbench, alignment theory | B4, LR4, IB4, BL4 and CD4 alignments at QL ∞, 10 and 7 | 15 |
| Small, R. H., “Vented-Box Loudspeaker Systems” Parts I–IV, JAES 21 (1973) | Butterworth and Bessel coefficients | 2 |
| usenclosure.com, enclosure formulas | Sealed F3/Fc table, port length | 9 |
| audiojudgement, 4th-order bandpass design (Dickason example) | 4th-order bandpass worked example | 8 |
What we promise
- Box formulas (Qtc, Fc, F3, port length, volumes, wiring): exact to the formula, 1e-9.
- Against Hornresp: sealed within 0.1 dB, ported within 0.7 dB from 15 to 100 Hz, tuning within 1 %.
- Against datasheets: within the sheet’s own rounding. When a sheet disagrees with itself, the app tells you instead of picking a side (see the datasheet check).
- Estimates are labelled: slot port end corrections, cabin gain and the port-noise limits.
Why WinISD or another calculator shows a different number
We have not compared against WinISD: there is no official download any more to test with. When two programs disagree, it is almost always one of these:
- Net or gross volume. Some calculators take the inside size of the box. Boxwright wants net: the driver, port and bracing out.
- Port end correction. Programs use anything from 0.6 to 0.85 × radius per end, or let you choose. One end flanged or free moves the tuning by a few percent.
- Box losses (QL). We use QL 7 for ported boxes, Small’s typical value. A lossless model gives a slightly different F3 and a sharper response.
- Air constants. We use 343 m/s and 1.204 kg/m³ (20 °C). Small used 345 m/s and 1.18 kg/m³.
- Which F3. −3 dB from the flat line, or −3 dB below the peak. We show both and say which.
- The driver numbers. Two programs with two different datasheet versions will disagree. Check the sheet first with the datasheet check.
Found a number that looks wrong?
Write to hello@mufatech.com with the driver, the box and what you expected. If it is our mistake, it becomes a test first, then a fix, and it stays in the test set.
Sources
- Hornresp (D. McBean), version 60.60
- JL Audio 12W3v3-4 specifications (authorised retailer copy)
- Scan-Speak 18W/8531G00 datasheet
- Scan-Speak Technote 07, box alignments
- SB Acoustics SB23NRXS45-8 datasheet
- Dayton Audio RSS265HF-4 specifications
- Peerless SLS-P830669 datasheet
- audioXpress, “Voice Coil Focus: Quasi-Alignment Families”
- Speakerbench, alignment theory
- Small, R. H., “Vented-Box Loudspeaker Systems” Parts I–IV, JAES 21 (1973)
- usenclosure.com, enclosure formulas
- audiojudgement, 4th-order bandpass design (Dickason example)
Results are design estimates. Check the driver’s datasheet and your amplifier’s minimum load before you build.
Checked against the sources: October 27, 2026