Directional loudness of narrow-band noises in an anechoic sound field

Abstract

In order to investigate the effect of sound incidence angle on loudness across a larger set of parameters than have been used in most previous studies, a listening experiment was carried out using a loudspeaker setup in an anechoic chamber. Eight subjects, whose absolute hearing thresholds and head-related transfer functions (HRTFs) were measured, participated in a total of 22 sessions each. On each trial their task was to judge which of two narrow-band noises sounded louder. These judgments were used in an adaptive procedure to find loudness matches between a frontal reference location and seven other sources, positioned both in the horizontal and median planes. Sound incidence angle, center frequency, and overall SPL were varied in the procedure. The results show that loudness is not constant over sound incidence angles, with matches varying over a range of 10 dB, and showing considerable frequency dependency. The pattern of results also varies substantially between subjects, but can be accounted for by interindividual variations in the listeners’ HRTFs. [Work Kjær Sound & Vibration Measurement A/S.]