Design of stereo reproduction system for cars is very specific because of cabin acoustical response and non-symmetrical loudspeakers positions. This behavior has motivated various researches aiming at improving listening conditions with the help of signal processing. Based on time-frequency analysis, a new spectral equalization is presented, considering independently the direct sound and the diffuse field spectra. This method allows an efficient correction based on spatial characteristics of the sound field. A perceptive justification was undertaken thanks to listening tests analyzed with multidimensional tools.