Sound Source and Loudspeaker Base Angle Dependency of Phantom Image Elevation Effect

Hyunkook Lee

doi:10.17743/jaes.2017.0028

Abstract

Early studies found that, when identical signals were presented from two loudspeakers equidistant from the listener, the resulting phantom image was elevated in the median plane and the degree of the elevation increased with the loudspeaker base angle. However, sound sources used in such studies were either unknown or limited to noise signals. In order to investigate the dependencies of the elevation effect on sound source and loudspeaker base angle in details, the present study conducted listening tests using eleven natural sources and four noise sources with different spectral and temporal characteristics for seven loudspeaker base angles between 0° and 360°. The elevation effect was found to be significantly dependent on the sound source and base angle. Results generally suggest that the effect is stronger for sources with transient nature and a flat frequency spectrum than for continuous and low-frequency-dominant sources. Theoretical reasons for the effect are also discussed based on head-related transfer function measurements. It is proposed that the perceived degree of elevation would be determined by a relative cue related to the spectral energy distribution at high frequencies, but by an absolute cue associated with the acoustic crosstalk and torso reflections at low frequencies.

Highlights

It is widely known that the localization of sound source placed in the median plane is governed by spectral cues
With regards to the vertical localization of individual frequencies, Pratt [10] reported that a higher frequency tone was localized at a higher position than a lower frequency one when it was presented from a single loudspeaker in the median plane
The present study aimed to investigate the sound source dependency of the phantom image elevation effect

Summary

Introduction

It is widely known that the localization of sound source placed in the median plane is governed by spectral cues. Studies confirmed that the head-related transfer function (HRTF) above about 3 kHz plays the main role in the median plane localization of broadband signals [1,2,3]. Research further suggests that notch frequencies between 6 and 12 kHz in the HRTF have particular importance for vertical localization [4,5,6]. Gardner [8] and Algazi et al [9] showed that torso reflections produce spectral notches in the HRTF below 3 kHz, which are additional localization cues for an elevated source. Blauert [16] found, from an experiment using 1/3-octave band noise signals reproduced from loudspeakers placed at the front, rear, side, and overhead positions that frontal localization was mainly associated with the 4 kHz band, back with the 1 kHz band, and above with the

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