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The Mirror Filter-A New Basis for Linear Equalization and Nonlinear Distortion Reduction of Woofer Systems

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A new filter structure derived from the nonlinear differential equation and switched into the electrical path enables the reduction of nonlinear distortions of loudspeakers caused by displacement of varying parameters (force factor, stiffness, and inductance) and Doppler effect. Simultaneously, this filter is used for optimizing the linear frequency response (resonance frequency and Q-factor) and for realizing an effective protection against destruction. Unlike feedback systems, no permanent sensor is required. To adjust the filter parameters to the actual loudspeaker automatically, an iterative method is presented which is based on the electrical or acoustical measurement of the overall transfer response. Both the filter and the auxiliary systems for protection and adjustment are implemented in a DSP 56001 and result in a self-learning distortion reduction system. This system was tested on different loudspeakers. Results are contrasted to the listening impression and possible consequences to loudspeaker design are discussed.

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