In this paper, the feasibility of using voice coil back-emf signal as feedback information for closed loop control was investigated. A dual voice coil closed-box subwoofer system is use to demonstrate the effectiveness of back-emf feedback control. A second order filter is developed to extract the velocity information from the coil back-emf signal. A PD controller is well suited for reducing the harmonic distortion and extending the subwoofer bass response. Experimental results verified that the proposed control scheme effectively extended the bass response of the subwoofer system by one octave and at the same time reduced harmonic distortion by more than 6 dB. The proposed feedback and control scheme can be easily implemented using inexpensive analog components, which can further reduce the cost and complexity of the system.

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