METHOD FOR DESIGNING A MODAL EQUALIZER FOR A LOW FREQUENCY AUDIBLE RANGE ESPECIALLY FOR CLOSELY POSITIONED MODES

The present invention relates to a method for designing a modal equalizer ( 5 ) for a low frequency audible range, typically for frequencies below 200 Hz for a predetermined space ( 1 ) (listening room) and location ( 2 ) (location in the room) therein, in which method modes to be equalized are determined at least by center frequency and decay rate of each mode, creating a discrete-time description of the determined modes, and determining equalizer filter coefficients on the basis of the discrete-time description of the determined modes, and forming the equalizer ( 5 ) by means of a digital filter by defining the filter coefficients on the basis of the properties of the modes. In accordance with the invention following method steps are used: forming a mode detection function (G(Omega)), defining the highest peak angular frequency Omegap of the function (G(Omega)), making AR analysis of predefined order for solving the poles of the mode representing the highest peak angular frequency, selecting the pole closest to point ejOmegap on the unit circle, determining the decay time of the mode and if is over a predetermined level, designing a modal correction filter for this mode, and repeating this procedure until no decay time exceeds over the predetermined level, and each individual filter obtained in previous stages of the method is combined to a cascaded filter.