Hybrid controller for mid‐power audio application

Abstract

Driving current of a moving coil loudspeaker, fed from a switched voltage-mode audio amplifier, display non-ideal transfer characteristic relative to the reference audio signal. This is chiefly due to the effective speaker voice coil electrical impedance and phase lag provided by the output filter. This study investigates the deviation in the transfer characteristics from the ideal constant gain and zero-lag properties and proposes a hybrid controller to mitigate the drawback. The hybrid controller comprises a sliding-mode controlled amplifier (SMCA) which has a non-linear control law and ensures maximal command following among voltage-mode algorithms, realisable under switching frequency and filter size constraints. Additionally, a linear controller fine-tunes the speaker current and its design is based on the transfer function of the SMCA and loudspeaker, which are least-square approximated from experimental frequency response data. A 20 W amplifier, driving a 4 Ω speaker load, is developed and experimental results obtained there from establishing the improved electric to acoustic signal conversion using the hybrid controller.