We proposed a simple method using IIR filters to approximate head-related transfer functions (HRTFs) for realizing sound images localization, previously. However, front-rear judgement errors, the sounds that simulated the rear sound images were symmetrically localized on the interaural axis, were increased in comparison with the FIR filters. In this paper we set up some design conditions which were taken account of the specified frequency bands 500 Hz to 2 kHz and 8 kHz to 12.5 kHz, which play a important role in the rear sound localization, in the approximation process of the HRTFs. Sound localization experiments on the horizontal plane were carried out using the design conditions with 2-loudspeaker reproduction. As a result, the accuracy of rear sound localization was improved in consideration of the specified frequency bands.
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