| Towards approximately above 500 Hz sound waves, Torso(especially the shoulder) can produce apparent reflection effect. And torso reflection provide a certain contribution for lateral plane sound localization. The shoulder reflection is controlled by the ear gradually occlusion(frequency shielding) at frequencies around 3kHz beginning; And ear occlusion(frequency shielding) is obvious at frequencies above 5kHz, So the shoulder reflection of sound source localization can be ignored. Therefore, it is considered that shoulder reflection has significant elevation cues at low frequency. Especially, shoulder reflection providing recognition of the presence of low-frequency cues are more important for listeners with hearing loss at higher frequencies.In addition to the frequency, shoulder reflection is affected by other cues, Including shoulder shape and individual size(such as the neck height, shoulder width, the head relative to shoulder position and so on), Shoulder reflection caused by the listener’s head rotation unconsciously in the process of the sound source localization in the auditory system. To analyze the effect of different factors on the shoulder reflection, This paper presents the half ellipsoidal model,which described individual shoulder characteristics, With ellipsoidal head and cylindrical neck consisting of head-neck-shoulder model(HNS).Compared with snowman model(HAT) and head-neck-torso model(HNT), The shoulder reflection of three models are compared and analyzed by means of HRTFs.Head Related Transfer Function(HRTF) describes the sound source to the ears of the transfer process, The sound source localization cues before mentioned are calculated and analyzed by HRTF. Because of the simplified model contains the structure of the neck, whose shape is more complex, Only numerical simulation approach(such as boundary element method, BEM) is adopted to solve their HRTFs. In order to facilitate the practical application, this paper also put forward geometrical acoustic simulation method to simulate shoulder reflection. It can be used to analog shoulder reflection quickly on the HRTFs of without shoulder and without neck model. Although shoulder reflection has an effect mainly to lateral different elevations, This article also give the result of the horizontal and median plane, to analyze the combined effects of the shoulder reflection on HRTFs.Finally, the different shoulder reflection on the lateral localization cues of the near-field HRTF is investigated by the psychoacoustic experiment. It includes :1)HNS model, which has individual physiological structure size, compared with original HNT model, the experiment is used to evaluate the difference between HNS and HNT model of lateral sound source elevation localization; While another experiment is designed to investigate the effect of the precise individual shoulder reflection on lateral elevation localization. 2)Investigating the change of shoulder reflection caused by head rotation impact on lateral elevation localization. 3) Investigating the head forward or back offset relative to Torso(or the shoulder) impact on anterolateral and rear side sound source elevation localization. 4) Investigating simplified geometric acoustic model, compared with the HNS model, can provide lateral elevation localization cues or not. the results showed that, compared to the HNS and HNT models, the HNS model improved the sound source localization cues at low elevation, and the precise size of individual shoulder has no significant difference at lateral elevation localization. The head forward or back offset relative to the shoulder has not improved front/back confusions; Shoulder rotation has little effect on the sound source localization information; The result of psychoacoustic experiments between Geometric acoustic model and HNS model indicating that the shoulder reflection of Geometry acoustic model can provide lateral elevation cues partly. |
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