Distance perception of a nearby virtual sound source reproduced by a linear loudspeaker array

When a virtual sound source is reproduced by a linear loudspeaker array, listeners can perceive not only the direction of the source, but also its distance. Control over perceived distance has often been implemented via the adjustment of various acoustic parameters, such as loudness, spectrum change, and the direct-to-reverberant energy ratio; however, there is a neglected yet powerful cue to the distance of a nearby virtual sound source that can be manipulated for sources that are positioned away from the listener's median plane. By extending the manipulation of interaural level difference (ILD) to lower frequencies than what is typical for such lateralized sources, a very strong means becomes available for controlling perceived distance of sources at close range, within the listener's peripersonal space (within arm's reach). Of course, the ILD of a virtual source reproduced by a line array will not be identical to that of a real monopole, due to many physical limitations such as finite aperture, spatial aliasing and stationary phase approximation. Using an ideal rigid sphere as a model of the variation in head-related transfer functions at close range, this paper identifies the effects of these artifacts on perception of the nearby virtual source.