Abstract: The stereophonic sound image for an off-center listener is analysed theoretically and experimentally. The results show that, the sound image direction for an off-center listener depends on frequency. When listener departs from center position to some distance x_max or the frequency of signal is higher than a limit f_max, the sound image may locate outside the arrangement of the stereophonic loudspeaker pair. Therefore the spatial information of stereo is spoiled. It is also proved that x_max is inversely proportional to f_max, or conversely. A narrow span of loudspeaker pair or adding a front loudspeaker (as in 5.1 ch system) can enlarge listening area and stabilize sound image.