An equalizer is described which extends the low-frequency response of a closed-box loudspeaker system. The equalizer consists of an auxiliary active filter that converts the overall system response to that of a fourth-order Butterworth alignment. The method used to realize the equalizer is general and can be extended to transfer functions other than fourth-order Butterworth. The circuit realization requires knowledge of the resonance frequency and total quality factor of the closed-box system.
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