Relative loudspeaker amplitudes shift the perceived direction of a phantom image.

Evidence

Both speakers driven with different amplitudes: This is shown in Figure 7.2(c). In this case, both speakers are providing different signals to both ears. The composite wave due to the sum of the two signals from the speakers at each ear is no longer identical. This makes the phase shift between the two ears somewhere between the first two cases. This phase shift will be dependent on the relative amplitudes of the two loudspeakers, because this determines the composite wave’s amplitude and phase. The resulting phase shift is identical to the phase shift due to a sound source that is between the center position and the physical loudspeaker positions. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2202

Categorization

• DEFINE: Introduces the amplitude-panning mechanism by which inter-ear phase shift is manipulated to steer a virtual source.
• XREF: Connects to the book’s earlier treatment of interaural phase difference as a primary localization cue.