Stereo inter-loudspeaker level differences steer perceived sound location between speakers.

Evidence

In a traditional stereo arrangement, the subject faces two loudspeakers positioned in front, each at an angle of about 30° from straight ahead. If both loudspeakers radiate the same sound pressure level at the same time, a summing localization occurs and the sound is perceived as coming from a location midway between the two loudspeakers. If the sound pressure level from the right loudspeaker is 30 dB higher than that from the left speaker, the sound is perceived as originating in the direction of the right loudspeaker. This means that a dependence of the location of the perceived sound is obtained in a manner similar to that shown in Fig. 15.12 for lateralization. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1721