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Reluctance Force Modeling and Compensation

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In the case of an electrodynamic loudspeaker, the reluctance force is purely a nonlinear addition to the Lorentz force. It generates second harmonic and intermodulation distortions and very low--frequency components in the force applied to the moving assembly. Being able to accurately model and then compensate this force is one of the building blocks for a feedforward system designed to linearize an electrodynamic loudspeaker. This work investigates the reluctance force formulation and proposes a more accurate model for motor structures with a shorting ring and compensation algorithm that does not require root finding or model inversions. The compensation is applied to two drive units and shown to reduce both harmonic and intermodulation distortion by around 18 dB between direct current and 1 kHz. Compensation results using parameters fitted to measured and simulated electrical impedances are compared. Finally there is a brief discussion on the implications of the results for shorting ring design.

JAES Volume 70 Issue 3 pp. 177-184; March 2022
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