Guide
Create FRD and ZMA files – with REW, ARTA or ATB
To simulate a crossover you need two measurements of every driver: the frequency response (FRD) and the impedance (ZMA). Both are plain text files that every common measurement program writes. Here is what matters when measuring and where the programs keep the export.
What the files contain
One line per frequency: the frequency in Hz, then the value (FRD: sound pressure in dB, ZMA: impedance in Ω), then optionally the phase in degrees. Comment lines start with *, #, ; or !, depending on the program.
The file extension is only a hint: .frd, .zma and .txt contain the same format. Crover recognises from the contents whether a file looks like impedance data and warns about swapped files.
* Freq(Hz) SPL(dB) Phase(deg)
200.0 86.41 -12.7
211.9 86.52 -14.1
…What matters when measuring
- Measure in the finished cabinet: the baffle, the driver position and the edges (baffle step, diffraction) shape the frequency response; the box volume shapes the impedance.
- Set a window (gate) for the frequency response so room reflections drop out. Below a few hundred hertz the window is too short; there one usually adds a near-field measurement – or accepts that the simulation is less accurate in the bass.
- Measure all drivers of a speaker with the same microphone position and the same timing reference if the measured phase should contain their time differences. Otherwise let the phase be derived from the magnitude and enter the acoustic offset by hand.
- Use the same drive voltage for every way (e.g. 2.83 V) and levels in dB SPL – then the woofer and tweeter levels relate correctly.
REW (Room EQ Wizard)
REW measures frequency response and impedance in the same measurement dialog (“SPL” or “Impedance”). “File → Export → Export measurement as text” exports it; the file has frequency, value and phase. For the FRD set the window (IR Windows) first so the exported response is gated.
Measuring impedance with REW, step by step
ARTA and LIMP
ARTA measures the frequency response from the impulse response; after setting the window you export it from the File menu (Export) as a text file in FRD format. The impedance is measured by its sister program LIMP, which saves and exports ZMA files directly. The exact menus are in the ARTA and LIMP manuals.
ATB precision
ATB precision also measures frequency response and impedance and exports both as text files. What the export is called in your version is in the ATB manual; all that matters is the result: frequency, value and phase in columns.
A quick check before you simulate
- Frequency range: does the file cover the range the driver plays in – with an octave to spare around the crossover frequency?
- Level: are the woofer and tweeter curves at a plausible height relative to each other?
- Impedance: is the minimum above resonance roughly at Re (DC resistance)? Much higher often means a wrong sense resistor value or swapped inputs.
How Crover reads the files: file formats and the import in the manual. Measured or derived phase – what changes: phase in the manual. Why the baffle shapes the frequency response: The baffle step explained.