This paper presents a multichannel dereverberation algorithm that only uses coherent acoustic channels. In the framework of multi-input/output inverse theorem (MINT), the equalization performance varies depending on the length of the input acoustic channels. However, only the portion of observed channel that resemble the true acoustic channel contributes to performance enhancement when measurement error is accounted. Hence, the proposed algorithm derives the frequency dependent viable channel length (VCL) from the coherence analysis of Monte Carlo observations of a single acoustic channel. The VCL of the room impulse response (RIR) is determined by the portion where the stochastic characteristic of multiple observations is highly coherent. Experiments are conducted to compare the equalization performance of the subband MINT algorithm depending on the length of the input RIR. The equalization performance using frequency dependent VCL is as good as the one obtained using the maximum length of the measured channel, while its complexity is significantly reduced.