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 .OMEGA..sub.p 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
e.sup.j.OMEGA.p 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.