An open, community-owned loudspeaker enclosure simulator that runs in any browser.
Speaker design belongs to everyone who builds.
OpenISD is a modern, free, open-source replacement for WinISD — a tool to design sealed, vented, bandpass, and passive-radiator enclosures from a driver's Thiele/Small parameters. No install, no licence key, runs in any browser. Validated against the closed-form physics, with a self-test that proves it on every load.
It started as a quick spike, and it has come a long way since. The physics engine (packages/engine/src/) is now clean and modular, with a full unit, golden, and browser test suite checked against the exact closed-form solutions. Two rough spots from the prototype days remain, and both are tracked in the open: some duplicated structure on the data-scraper side, and the engine's input-validation boundary — incomplete input can still produce a NaN instead of a clear error. If someone calls this "vibe-coded", VIBE_CODING.md is the reply: it asks what that phrase is supposed to mean, then lays out — trait by trait, with evidence — the tests and guardrails that keep OpenISD honest, and where it still falls short. The plan for turning the remaining fixes into checks the build runs automatically is in PLAN.md and SDLC.md.
WinISD has been abandoned and is closed source, so there is no way to move it forward. OpenISD exists to build a modern, open alternative — compatible with WinISD's file formats (and others), and answering the many complaints about the old tool. The long-term goal is something that doesn't rot when I drop dead or lose interest — a tool that stays trustworthy because the rules that keep it clean are enforced by the build, not by memory.
I am looking for a band of the willing to move this thing forward. Please volunteer your time with ideas, feedback, and pull requests.
I am a software engineer with 40 years of experience and would like to do the right thing here and have a bit of fun at the same time.
My bio, CV and all my Hackaday projects can be found on my personal page https://johnlon.github.io/
But I need your help; that's the whole point!
Runs in your browser — nothing to install if you don't want to. Mobile layout is a known gap — contributions welcome.
To install for offline use (PWA):
- Chrome / Edge / Android: open the site, click the install icon in the address bar (or the ⋮ menu → "Install OpenISD")
- iOS Safari: tap the Share button → "Add to Home Screen"
Once installed the app works without an internet connection.
The main simulator. Driver and enclosure controls sit on the left; the response graphs fill the right. Everything is live: change the box volume, drag the vent length, swap the driver or the box type, and every curve — SPL, cone excursion, impedance, group delay — redraws on the same keystroke. There is no "calculate" button and no waiting. That instant feedback is what makes exploring a design fast and genuinely fun — you can feel how each parameter pushes the response around instead of guessing.
The speaker-design tool landscape is a graveyard. WinISD has been abandoned since 2016 and is Windows-only. Basta, Unibox, the old spreadsheets — fragmented and dead. The web calculators that filled the gap mostly can't be trusted at the frequencies that matter.
The Thiele/Small math has been public since the 1970s. The knowledge is open; the tools are not. OpenISD exists to close that gap, and to do it once, together, instead of as another solo project that dies in a year.
- Box types: sealed, vented (bass-reflex), 4th-order bandpass, passive radiator
- Curves: SPL, driver + PR cone excursion, port air velocity, group delay, impedance magnitude & phase, transfer-function phase, max SPL, max power
- Design aids: EBP box-type gauge, Qtc / QB3-B4 alignment helpers, vent length ↔ tuning solver, passive-radiator Fp tuning + mass auto-tune, multiple drivers (series / parallel)
- Files: import and export WinISD
.wdrdriver files; save/load whole projects as JSON
What-If editor. Click any driver to open its Thiele/Small parameters (Fs, Qts, Qes, Vas, Sd, Re, Le, Xmax, Pe) for inline editing. Nudge a value and the graphs respond immediately — the same live loop as the box controls — so you can ask "what if this driver had a lower Fs?" or "a bigger Vas?" and see the answer at once. Derived quantities (Bl, Mms, Cms, EBP) recompute as you type. It is a scratchpad: nothing you try here changes the shared library entry until you explicitly Save to My Drivers.
WinISD is the canonical reference tool. OpenISD's default mode replicates its simulation output. But OpenISD goes further in several areas:
| WinISD 0.7 | OpenISD | |
|---|---|---|
| Platform | Windows-only desktop app | Any browser, no install |
| Source | Closed, abandoned 2016 | Open source, MIT licence |
| Circuit model | Simplified acoustic-domain only (Le excluded from SPL/GD) | Both WinISD-compatible and full gyrator with Le (switchable) |
| Box losses | Ql + Qa via hidden "Advanced→" popup | Ql + Qa with practical stuffing guide |
| Cursor / readout | Mouse hover only | Hover + right-click snap to peak/trough + lock + Hz input |
| Design compare | Not supported | Pin any design, overlay curves |
| State persistence | Manual project files | Auto-saves to browser storage |
| Filter / EQ | Yes | Yes |
| Passive radiator | WinISD-style inputs | WinISD and T/S modes, switchable |
WinISD computes SPL and group delay using a simplified acoustic-domain model where voice-coil inductance (Le) does not affect the simulation — only the impedance plot. OpenISD defaults to this mode so cross-checks against WinISD are exact.
The Full gyrator mode includes Le throughout: the driver's electrical back-impedance becomes frequency-dependent, which is physically correct and matters when Le is large (>1 mH) or when accuracy above a few hundred Hz is needed. Group delay peak frequency shifts by ~2 Hz in the demo driver (Le = 0.7 mH) — a real physical difference, not a bug in either tool.
Switch between modes in the Signal & drivers panel → Circuit model.
Every model is validated against the exact closed-form solutions:
- the sealed box reproduces
fc = Fs·√(1+Vas/Vb),Qtc = Qts·√(1+Vas/Vb)to < 0.03 dB - the passband asymptotes to the driver's reference sensitivity
- the vented box rolls off at 24 dB/oct with two impedance peaks straddling Fb
The app runs these as a self-test in your browser console on load, and they run in
CI from test/engine.test.mjs. If the physics is wrong, the test goes red — in
public. See CONTRIBUTING.md for the model, and
VIBE_CODING.md for the full accounting of the guardrails.
- Hosted: https://openisd.app/ — nothing to install
- PWA / offline: see the install instructions in the callout above
- Local dev:
npm install && npm run dev— opens athttp://localhost:5173 - Build:
npm run build— output goes todist/, serve with any static host
drivers/ holds community-contributed .wdr files. Got a driver OpenISD
doesn't? Import its spec sheet, check the numbers, and open a PR with the .wdr.
Every spec sheet added is a gift to the next builder — this shared library is the
whole point.
Driver library browser. Search thousands of community-contributed drivers, or narrow the list by type (sub, woofer, mid, tweeter, PR, coax…), by Fs, by Sd, by nominal impedance, or by source. Pick one and it loads straight into the current design, so the graphs redraw around the real driver you're considering — making it easy to audition candidate drivers against the same box in seconds.
Define Driver Model. Enter a driver OpenISD doesn't have yet, straight from its datasheet. Fields are grouped (Thiele/Small, piston/acoustic, electrical, motor/large-signal, voice coil/thermal) and the "what each graph needs" legend at the top highlights exactly which values a given chart depends on — so you can see what's required for the curves you care about and skip the rest. Enter two of Qts/Qes/Qms and the third is calculated for you; the same goes for Sd ↔ cone diameter. Once saved, the driver behaves like any other — drop it into a box and the graphs update live.
Newcomers welcome — you do not need to be an acoustician. The physics engine lives
in packages/engine/src/; a new box type or filter is a weekend and a pull request. Start
with CONTRIBUTING.md and the backlog.
Yes. The entire app runs in your browser — there is no backend, no server, no account. The physics engine is client-side JavaScript; your designs never leave your machine unless you choose to share them.
The intention is to keep it that way for as long as it's feasible. Any feature that genuinely required a backend would be a large, explicit architectural decision — not a default direction. The goal is that as much of the app's functionality remains free as long as that's feasible. If a backend turns out to be necessary for something, that's a decision for the community to make together. The source is MIT-licensed; if the maintainers vanish, fork it and carry on.
MIT — forever. See LICENSE. OpenISD can never be closed up, taken away, or left behind a login. If the maintainers vanish, fork it and carry on.