Spatial audio quality factors for headphone evaluation

Comparison of acoustic characteristics of headphones is a major concern during design or product selection. There are several specifications for the acoustic characteristics, such as frequency response, impedance, sensitivity, and so on. They rarely provide hints for a comparison between devices. In addition, spatial impression is a major subjective attribute for evaluations of a sound field, it has not been considered enough for evaluations of headphones. In this study, we focused on the comparison of headphones by acoustical measurements to find the acoustical factors that explain the spatial audio quality reproduced by headphones. Power and phase spectrum, and acoustic parameters such as the maximum amplitude of the interaural cross-correlation function (IACC) and the interaural time delay (ITD) were calculated from the impulse response. Four music pieces and one natural sound were sent through the headphones and recorded through a head and torso simulator (HATS) with binaural microphones. The recorded signals were analyzed by factors extracted from the interaural cross-correlation function (IACF). There are three factors extracted from the IACF. They are IACC, ITD, and the width of the IACF. The different frequency response represented in the specification of each headphone was confirmed by the magnitude spectrum of the impulse response. The difference of spatial audio quality among headphones was represented by the IACF factors.