This paper introduces an automatic decision method for designing parameters of inverse filters to simplify realization of a high-performance sound reproduction system. The reproduced performance depends on several design parameters of the inverse filters that cancel the effect of room transfer functions (RTFs). Therefore, a method of determining the sample lengths of impulse responses of RTFs is proposed. In the proposed method, a suitable sample length of the impulse response is determined based on autocorrelation function (ACF) . The results of numerical simulations using real data reveal that the proposed method can determine suitable sample lengths while maintaining reproduction performance.