The direction of a sound source in relation to the listener significantly affects the loudness of the sounds it produces, especially in the horizontal plane, where interaural time difference (ITD) is the main localization cue. There is growing awareness of this phenomenon of directional loudness sensitivity (DLS); this has to be taken into account for audio reproduction systems, especially for multichannel. This effect has only been studied for sounds generated and presented directly over headphones, which are not natural listening conditions. The present study aims at investigating this effect on low-frequency noises originating from real sources. Twenty subjects assessed the loudness of stimuli that were presented by both loudspeakers arranged at various locations within a listening room and by a recording with a dummy head and then virtually reproduced through headphones. Results show that the directional loudness sensitivity (DLS) is in agreement with the previously revealed ITD effect. Moreover, the DLS was higher when stimuli were reproduced over headphones than over loudspeakers, specifically when frontal sources were located at a short distance from the listeners. One hypothesis for this effect relies on visual cues that were available to the listeners only when sounds were reproduced over loudspeakers, providing information about the source distance. Listeners were also aware that sounds were reproduced on loudspeaker or headphones, possibly involving different loudness assessments, leading to DLS differences.
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