Hi John,
The current Thiele-Small parameter calculator in REW is excellent for small-signal linear modeling. I would love to request an extension of this tool into the large-signal domain, specifically optimized for micro-transducers like 6mm–15mm dynamic earphones.
Since REW already supports dual-channel impedance measurements, it has the perfect mathematical foundation to capture real-time voltage and current (V/I). Implementing a software-based system identification method would allow users to map non-linear driver behavior safely at this miniature scale.
Scale & Hardware Constraints for Earphones
Because earphone drivers have incredibly low moving mass (often around 0.02 grams) and low power handling, standard large-signal measurement setups designed for subwoofers do not scale down safely. For an earphone, large-signal excursion happens at tens of milliwatts, not watts. The hardware loopback circuit would consist of:
1 The Drive Source: A low-noise dedicated headphone amplifier (like an Objective2) providing a clean voltage sweep up to ~1V–2V RMS max. This provides enough headroom to overcome the series resistance of the measurement jig while keeping the power dropped across the fragile voice coil within safe, non-destructive thresholds (approx. 50mW–100mW).
2 High-Resolution V/I Sensing: Because earphone nominal impedances are higher (typically 16Ω to 32Ω) and the current flow is tiny, the series current-sense resistor (\(R_{sense}\)) would scale upward to roughly 1.0 to 4.7 Ohms to maintain a healthy signal-to-noise ratio into the line inputs.
3 Protection Scaling: The safety voltage dividers on the loopback sensing lines would only need a small attenuation factor (e.g., 2:1) to match the interface's max input limits, preserving critical dynamic range for ultra-low back-EMF tracking.
By running an adaptive tracking filter using this low-power V/I input configuration, REW could extract and plot the following metrics:
1. Dynamic Parameter Curves
• Bl(x) curves showing motor strength drop over tiny, sub-millimeter excursions.
• Cms(x) / Kms(x) curves tracking the non-linear stiffness of the fragile diaphragm suspension.
• Le(x, i) mapping variable inductance against position and micro-amperage current.
• Non-linear distortion plots scaled cleanly in fractions of a millimeter.
2. Micro-Thermal Tracking
• Real-time Tv monitoring via delta-Re shifts during the test sweep to monitor voice coil temperature changes at milliwatt levels.
• Thermal compression profiling over continuous exposure.
3. Motor Symmetry Analysis
• Xsym calculation to pinpoint structural diaphragm or voice coil alignment offsets, which are critical for matching left/right IEM channels.
Implementing a software layer capable of scaling down to these ultra-low current levels would make REW an incredibly complete tool for headphone modifiers, IEM engineers, and micro-driver acoustics enthusiasts.
Thank you for considering this expansion!
Oliver
The current Thiele-Small parameter calculator in REW is excellent for small-signal linear modeling. I would love to request an extension of this tool into the large-signal domain, specifically optimized for micro-transducers like 6mm–15mm dynamic earphones.
Since REW already supports dual-channel impedance measurements, it has the perfect mathematical foundation to capture real-time voltage and current (V/I). Implementing a software-based system identification method would allow users to map non-linear driver behavior safely at this miniature scale.
Scale & Hardware Constraints for Earphones
Because earphone drivers have incredibly low moving mass (often around 0.02 grams) and low power handling, standard large-signal measurement setups designed for subwoofers do not scale down safely. For an earphone, large-signal excursion happens at tens of milliwatts, not watts. The hardware loopback circuit would consist of:
1 The Drive Source: A low-noise dedicated headphone amplifier (like an Objective2) providing a clean voltage sweep up to ~1V–2V RMS max. This provides enough headroom to overcome the series resistance of the measurement jig while keeping the power dropped across the fragile voice coil within safe, non-destructive thresholds (approx. 50mW–100mW).
2 High-Resolution V/I Sensing: Because earphone nominal impedances are higher (typically 16Ω to 32Ω) and the current flow is tiny, the series current-sense resistor (\(R_{sense}\)) would scale upward to roughly 1.0 to 4.7 Ohms to maintain a healthy signal-to-noise ratio into the line inputs.
3 Protection Scaling: The safety voltage dividers on the loopback sensing lines would only need a small attenuation factor (e.g., 2:1) to match the interface's max input limits, preserving critical dynamic range for ultra-low back-EMF tracking.
By running an adaptive tracking filter using this low-power V/I input configuration, REW could extract and plot the following metrics:
1. Dynamic Parameter Curves
• Bl(x) curves showing motor strength drop over tiny, sub-millimeter excursions.
• Cms(x) / Kms(x) curves tracking the non-linear stiffness of the fragile diaphragm suspension.
• Le(x, i) mapping variable inductance against position and micro-amperage current.
• Non-linear distortion plots scaled cleanly in fractions of a millimeter.
2. Micro-Thermal Tracking
• Real-time Tv monitoring via delta-Re shifts during the test sweep to monitor voice coil temperature changes at milliwatt levels.
• Thermal compression profiling over continuous exposure.
3. Motor Symmetry Analysis
• Xsym calculation to pinpoint structural diaphragm or voice coil alignment offsets, which are critical for matching left/right IEM channels.
Implementing a software layer capable of scaling down to these ultra-low current levels would make REW an incredibly complete tool for headphone modifiers, IEM engineers, and micro-driver acoustics enthusiasts.
Thank you for considering this expansion!
Oliver
