Control of loudspeakers using disturbance-observer-type velocity estimation

A new approach to obtain sensorless velocity feedback for loudspeakers is developed. The back electromotive force (back-EMF) of the moving coil is estimated by using a disturbance-observer-type estimator based on the coil current measurement. The cone velocity of a loudspeaker can be obtained based on its proportionality to the back-EMF. Instead of relying on the coupled mechanical dynamics as reported in previous work, the proposed velocity estimation is based on the precise knowledge of electrical impedance, which makes it more robust to changes in acoustic loading. The proposed approach enables the development of a robust velocity controller for a subwoofer without an expensive velocity measuring device. Experimental results demonstrated that closed-loop velocity control using the proposed scheme of velocity estimation achieved a performance comparable to that obtained by using measured velocity feedback. The proposed approach can be easily adapted to other moving-coil-type linear actuators.