A novel method for the equalization of loudspeakers and other audio systems using IIR (infinite impulse response) parametric filters is presented. The main characteristic of the proposed filter design method resides in the fact that the equalization structure is planned from the beginning as a chain of SOSs (second-order sections), where each SOS is a low-pass, high-pass, or peak filter, defined by its parameters. The algorithm combines a direct search method with a heuristic parametric optimization process where constraints on the values could be imposed in order to obtain practical implementations. A psychoacoustic model based on the detection of peaks and dips in the frequency response has been employed to determine which ones need to be equalized, reducing the filter order without noticeable effect. The first computed sections of the designed filter are the ones that correct the response more effectively, allowing scalable solutions when hardware limitations exist or different degrees of correction are needed. The method has been validated with subjective testing and compared with other methods. Its results could be applied to passive and multiway active loudspeakers.
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