Measurement of acoustic transmission properties of a handset with a piezoelectric vibrator using a head and torso simulator

Abstract

This paper presents equalizing an acoustic transmission property from a handset with a piezoelectric vibrator at a pinna to an eardrum with that of a normal headphone by hearing the measured sound through a head and torso simulator (HATS). Recently, a piezoelectric vibrator that vibrates a pinna to produce sounds was adopted as a receiver of smartphones to improve perceived quality within noisy environments. The HATS, used for handset testings in accordance with ITU-T recommendations, has a silicon-rubber pinna simulator to reproduce realistic acoustic properties with its human-like shape and stiffness. However, the handset with the built-in piezoelectric vibrator is beyond the scope and was not tested on the HATS before. This paper clarifies the difference of frequency responses between the pinna simulator and the real pinna based on a subjective assessment that adjusts the loudness of pure tones through the pinna simulator to be equalized auditorily to those through the real pinna. We used B&K HATS Type 4128-D. The results indicated a flat response for the pinna simulator, while a low-pass-like response for the real pinna with a cutoff at 1.5 kHz. Thereby, the actual sound can be simulated from the sound measured by the HATS with the responses.