This disclosure describes an active, direct, and real-time method for the measurement of moving coil transducer, e.g., as utilized in a speaker, parameters. Two charged electrodes made of graphite are attached to the moving coil transducer. A positive electrode is attached as small ring at the base of a cone of the speaker or as a small ring around a spider of the cone. A negative electrode is disposed on a magnet of the moving coil transducer. The positive electrode moves with vibration of the coil while the negative electrode remains stationary. A supply voltage is applied to the electrodes. The circuit also includes an analog to digital converter (ADC) and a resistor in series with the ADC. Current measured across the series resistor is calibrated against moving coil excursion and is used subsequently to determine the excursion of the moving coil transducer.
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Smedegaard, Michael and Asfaw, Michael, "Electrostatic excursion sensing in a moving coil transducer", Technical Disclosure Commons, (November 20, 2018)