In head-related transfer functions (HRTFs), spectral cues due to the individual pinna geometry are known to contribute to elevation perception and externalization. The pinna component of an HRTF is referred to as a pinna-related transfer function (PRTF). Some headphone concepts aim to excite individual PRTF cues by placing the headphone transducer away from the traditional position on the interaural axis, e.g. tilted in front of the pinna. However, it is not clear to which extent the individual PRTF is preserved when the pinna is placed inside a headphone cup enclosed by a baffle and a cushion. In this study, multiple prototype setups successively approximating a headphone cup and allowing for variable transducer positions are analyzed using a set of silicone pinna replicas. PRTF perturbations are analyzed in near field measurements and the impact of headphone cup acoustics is discussed. Based on the observation that the perturbations are systematic, an equalization scheme restoring the free field PRTF based on the median of measurements with several pinnae is proposed.
