WinISD vs RokketBox: Which Subwoofer Simulator Should You Use?
WinISD has been the go-to free subwoofer simulation tool for over two decades. The name still comes up in every forum thread, every build log, every "what should I use?" question. That reputation is earned - in 2005 it was genuinely the best tool available, and the core physics it implements is correct. But the audio world has moved on, and a simulator that has not had a meaningful update since 2016 shows its age in ways that matter when you are trying to design a box in 2026.
This is not a hit piece on WinISD. It is a direct comparison between what WinISD does, what it does not do, and where RokketBox fills the gaps. Both tools are free. Both simulate the same physics. The differences are in workflow, platform support, depth of modelling, and what you get at the end.
If you have been using WinISD and wondering whether it is worth switching, read on. If you are new to subwoofer simulation and trying to pick a starting point, this article will help you choose.
What WinISD Does Well
WinISD's core simulation engine is solid. It models sealed, vented, and bandpass enclosures using the standard Thiele-Small framework and produces the curves you need: frequency response, group delay, cone excursion, port velocity, and impedance. For most common design scenarios - a 12-inch driver in a ported box tuned to 35 Hz - it gives you accurate, trustworthy results.
The driver database is WinISD's strongest card. It ships with thousands of drivers already loaded: Dayton, JL Audio, Sundown Audio, Fi Audio, Rockford Fosgate, TC Sounds, and hundreds more. For most builders, your driver is already in the library. You pick it from a list and you are simulating within 30 seconds of opening the application.
The community knowledge base built around WinISD is also substantial. Thousands of forum posts, build threads, and YouTube tutorials reference WinISD screenshots. If you get stuck, there is almost certainly an answer somewhere in a decade-old thread. That institutional knowledge has real value.
For its core purpose - entering T/S parameters and generating a frequency response curve - WinISD is accurate and well-understood. The physics is Thiele-Small all the way down, the same foundation that every other simulation tool uses.
The Problems With WinISD in 2026
The elephant in the room is platform support. WinISD is a Windows application. It does not run on macOS. It does not run natively on Linux. If you are on a Mac - which is now the majority platform for creative and professional work - your options are Wine (with varying compatibility), a Windows virtual machine, or a second machine. None of these run reliably — Wine compatibility varies by WinISD version, and a VM adds hardware overhead just to open a subwoofer simulator.
The last public release of WinISD was version 0.50a7, dated 2016. In the ten years since, subwoofer drivers have evolved, simulation techniques have advanced, and user interface expectations have shifted dramatically. The application still runs, but it shows its age in the interface, the workflow, and the modelling depth.
Specific gaps that matter for modern builds:
No cut sheet generation. WinISD tells you the dimensions you need. It does not produce a panel cut list, port routing diagram, or build specification. You take the numbers, do the geometry yourself, and figure out port routing manually. Every builder does this, but it is hours of work that does not need to be manual.
No port routing geometry. WinISD calculates port length from the Helmholtz equation. It has no concept of whether that port physically fits inside the enclosure. A 45 cm port in a 30 cm deep box is not a problem WinISD will catch - it just gives you the number and lets you discover the issue at build time. There is no collision detection, no fold routing, no check that the port and driver can coexist in the box.
No thermal or Le modelling. The impedance curve in WinISD uses an ideal voice coil inductance model. Real drivers do not behave this way - the high-frequency impedance rise is shallower than an ideal inductor predicts because of eddy current effects. The difference matters for bandpass enclosures and for accurate impedance-based power delivery calculations. WinISD also does not model BL compression at high excursion, which means its SPL prediction at high power is optimistic compared to real-world behaviour.
Interface friction. Driver entry is manual and library management is clunky by modern standards. If your driver is not in the database, you enter parameters through dialog boxes that feel like 2003. Changing a parameter and re-simulating is not instantaneous - it requires deliberate steps rather than live updating.
No optimiser. WinISD is a simulator, not an optimiser. You propose a design; it tells you what it does. Finding the optimal volume and tuning for a specific driver is a manual process of iteration: try 50 litres, look at the curve, try 55 litres, compare. With a good understanding of Thiele-Small theory you can home in quickly, but there is no automated search.
What RokketBox Does Differently
RokketBox is browser-based. No download, no installation, no operating system dependency. It runs on Windows, macOS, Linux, and any device with a modern browser — relevant because WinISD has no macOS build and uneven Wine support.
The simulation engine goes deeper than WinISD in several areas. RokketBox uses a hybrid approach: the full simulation paths for vented and bandpass enclosures build an electroacoustic equivalent circuit and solve it at each of 500 frequency points, while the sealed path and optimizer use closed-form transfer functions for speed. Non-linear effects — BL compression and port turbulence — are handled via iterative convergence loops that feed back into each circuit solution. You can read the full technical breakdown in Inside the RokketBox Simulation Engine.
Specific modelling differences:
Leach parallel R-L model for voice coil impedance. The Leach semi-inductance model replaces ideal inductor behaviour with a lossy parallel R-L element, producing an impedance rise that is shallower than a pure inductor. This matches measured driver impedance curves more accurately, especially above 200 Hz where bandpass response is sensitive to the impedance shape. For more detail, see voice coil inductance modelling.
BL compression at high excursion. RokketBox models the falloff in motor force as the voice coil moves out of the magnetic gap. At Xmax, BL has typically dropped 30-50% from its rest value. The SPL curve reflects this - the output compresses rather than following the linear prediction, which is what you would actually measure. WinISD assumes constant BL throughout the excursion range. See Motor Force: BL Isn't Constant for the detailed analysis.
Iterative port turbulence. Port velocity and port impedance are mutually dependent. RokketBox solves this iteratively at each frequency point rather than treating it as a one-pass calculation. The result is accurate compression modelling at high drive levels, rather than raising a flag when velocity exceeds a threshold and stopping there.
The optimiser. Enter your driver parameters or select from the database, set your constraints (maximum box dimensions, target tuning range, port type preference), choose a weight preset (SPL, SQ, or Balanced), and the optimiser explores the design space using Latin hypercube sampling. It evaluates thousands of configurations in seconds, scores them against your goals, and returns the best design. This is the step that takes hours of manual iteration in WinISD.
Port routing and collision detection. RokketBox's geometry engine checks whether the calculated port physically fits inside the enclosure given the driver's physical depth, the box dimensions, and the required fold type. Straight, L-fold, C-fold, and U-fold routing are all checked against the actual 3D constraints of the design. Configurations where the port collides with the driver or cannot route through the box are rejected before they reach the results. See Port Routing Collision Detection for how this works.
Cut sheet generation. The build output from RokketBox is a complete panel cut list with all dimensions, port routing specifications, corner strip positions, and (where applicable) kerf bend specifications for curved ports. This goes straight to the table saw — dimensions, port routing, and corner strip positions are already worked out.
Cabin gain simulation. For vehicle installs, RokketBox includes a cabin gain model with selectable vehicle presets (Sedan, SUV, Hatchback, Truck) or a custom cabin volume input. The dashed SPL line shows the combined in-cabin response rather than the anechoic prediction. Designing for a car without accounting for cabin gain — which adds significant output at and below the cabin's resonance frequency — produces a box tuned for the wrong environment. WinISD has no cabin gain model. Read more in Cabin Gain: The Free Bass You're Not Accounting For.
Side-by-Side Feature Comparison
| Feature | WinISD | RokketBox |
|---|---|---|
| Platform | Windows only | Browser (all platforms) |
| Last updated | 2016 | Active |
| Sealed simulation | Yes | Yes |
| Vented simulation | Yes | Yes |
| Bandpass (4th order) | Yes | Yes |
| Driver database | Large (thousands of drivers) | Growing |
| Manual T/S parameter entry | Yes | Yes |
| Frequency response | Yes | Yes |
| Impedance curve | Yes | Yes |
| Group delay | Yes | Yes |
| Cone excursion | Yes | Yes |
| Port velocity | Yes | Yes |
| Voice coil inductance model | Ideal (Le as pure inductor) | Leach parallel R-L (semi-inductance) |
| BL compression at high excursion | No | Yes (iterative) |
| Iterative port turbulence | No | Yes |
| Enclosure optimiser | No | Yes (LHS + refinement) |
| Port routing geometry | No | Yes (straight, L-fold, C-fold, U-fold) |
| Port collision detection | No | Yes |
| Cut sheet generation | No | Yes |
| Kerf bend specifications | No | Yes |
| Cabin gain simulation | No | Yes |
| 3D box preview | No | Yes |
| Weight presets (SPL/SQ/Balanced) | No | Yes |
| Free to use | Yes | Free (account required for optimizer and bandpass) |
The honest note on the driver database: WinISD's library is larger and more comprehensive. RokketBox's database is growing but does not yet cover the full range of drivers that WinISD has accumulated over two decades. If your specific driver is not in RokketBox's database, you enter the T/S parameters manually - the same workflow as WinISD, just less frequently needed as the database grows.
Who Should Use Each Tool
Use WinISD if:
You are on Windows and comfortable with the workflow. You want the largest driver database available in a free tool. You are doing a quick feasibility check and do not need cut sheet output. You are familiar with the tool from previous builds and the manual workflow works for you.
WinISD is not broken. If your process is "simulate in WinISD, then work out the panel dimensions and port routing manually," that process still works. The physics is correct and the curves are trustworthy for standard scenarios.
Use RokketBox if:
You are on macOS or Linux and WinISD is not a native option. You want the optimiser to find the best design rather than iterating manually. You need a cut sheet at the end of the design process - dimensions, panel sizes, port routing, all ready for the workshop. You want cabin gain simulation for a vehicle install. You are building a bandpass enclosure and want the more accurate impedance modelling for the coupled-chamber response. You are designing a high-excursion build at near-rated power and want BL compression reflected in the simulation. You want port routing verified geometrically before you cut wood.
The two tools are not mutually exclusive. Some builders use WinISD to quickly check if a driver is suited to sealed vs vented using the large database, then switch to RokketBox for the detailed design and cut sheet. That is a reasonable workflow.
Moving From WinISD to RokketBox
If you have been using WinISD and want to try RokketBox, the transition is straightforward. You already know how to read the curves - RokketBox shows the same plots with the same meaning.
Finding your T/S parameters: If your driver is in RokketBox's database, select it. If not, the core Thiele-Small parameters from WinISD (Fs, Qts, Qes, Qms, Vas, Re, BL, Xmax, Sd, Mms) go into the same fields in RokketBox with the same names and units. RokketBox also uses additional parameters its physics engine needs (Cms, Rms, nominal impedance, efficiency, Vd, number of voice coils) — these are on the same driver form. Le is optional; Pe is a separate driver-level field. If you are not sure what any of these parameters mean, Understanding Thiele-Small Parameters covers them in detail.
What to expect from the curves: The frequency response shape will be similar to WinISD for most scenarios. The impedance curve will differ slightly at high frequencies because RokketBox uses the Leach parallel R-L model rather than an ideal inductor. The RokketBox curve is the closer match to what you would measure with a real impedance analyser.
The group delay plot will match in shape but RokketBox's curve is smoother — primarily because it differentiates the real and imaginary components of the transfer function separately using a Savitzky-Golay filter, which avoids the phase-wrapping artefacts that atan2-based approaches produce. The denser 500-point sweep also contributes; WinISD's coarser resolution can produce stair-step artefacts in the group delay curve at low frequencies. The Group Delay Explained post covers what these numbers mean and which values are actually audible.
Port velocity is calculated by both tools, but RokketBox's iterative turbulence model means the velocity at high power levels accounts for the non-linear compression that occurs when turbulence increases port impedance. WinISD's velocity calculation is linear and does not account for this feedback. In practice, for most builds operating well below rated power, the difference is small.
Starting a design: Open RokketBox, enter or select your driver, pick an enclosure type, and the simulator is live immediately. Adjust volume and tuning frequency with the sliders and watch all five plots update in real time. When you are ready to optimise, switch to the Optimiser tab, set your constraints, choose a preset, and run. The result comes back in seconds with full port routing and dimension specifications.
For ported box starting points, the ported box calculator gives you a quick Helmholtz-based estimate of port length for any volume, tuning, and area combination. The sealed box calculator does the same for Qtc-based volume calculations. The port length calculator handles the full end-correction calculation including flanged and unflanged corrections. These are useful for quick checks; the full simulation in RokketBox gives you the complete picture including excursion limits, turbulence, and cabin gain.
The physics underlying both tools is the same. What changes is platform access, modelling depth at high excursion, the presence of an optimiser, and whether the design process ends with numbers or a build-ready cut sheet.