In general, Loudspeakers operate on voltage-drive mode.
However, since the sound pressure produced by the loudspeaker is proportional to the current flowing through the voice coil, current-drive mode is more suitable for loudspeaker operation. When the loudspeaker operates on current-drive mode, sound pressure distortion appears at low frequencies. The reason of the distortion is speaker resonance. The impedance of the loudspeaker is likely to be recognized as a fixed value. But the impedance of the speaker continues to vary with frequency variation and especially becomes large value in resonance frequency band. large impedance value causes the distortion.
Sound pressure of loudspeaker distortion degrades sound quality. In order to improve sound quality resonance compensation is needed. So analog resonance compensation circuits are used in current-drive audio system. However, there are several weaknesses in the analog resonance compensation circuit. The range of adjustable frequencies is too narrow to use and accuracy is poor because of using analog circuit elements.
In the paper, we propose digital resonance compensation circuit design using digital signal processing to strengthen the weaknesses of analog resonance compensation circuit. The circuit is designed based on principle of pole shifting using SigmaDSP audio processor and software tool SigmaStudio. The circuit is designed signal sum of state variable filter’s low, band, high pass outputs. The circuit can control varying the Q and frequency by external input through general purpose input and output SigmaDSP function. In the experiment, adjustable frequency range is 50 to 150 ㎐. But it is possible to operate at the more higher frequency. Comparing designed circuit with analog resonance compensation circuits, adjustable frequency range is more than twice and accuracy of the circuit increase. So It can be used widely for speakers classified as low frequencies in current-drive audio system.