Measurements of Transmission Characteristics Related to Bone-Conducted Speech Using Excitation Signals in the Oral Cavity

Abstract

Purpose Psychoacoustical studies on transmission characteristics related to bone-conducted (BC) speech, perceived by speakers during vocalization, are important for further understanding the relationship between speech production and perception, especially auditory feedback. For exploring how the outer ear part contributes to BC speech transmission, this article aims to measure the transmission characteristics of bone conduction focusing on the vibration of the regio temporalis (RT) and sound radiation in the ear canal (EC) due to the excitation in the oral cavity (OC). Method While an excitation signal was presented through a loudspeaker located in the enclosed cavity below the hard palate, transmitted signals were measured on the RT and in the EC. The transfer functions of the RT vibration and EC sound pressure relative to OC sound pressure were determined from the measured signals using the sweep-sine method. Results Our findings obtained from the measurements of five participants are as follows: (a) the transfer function of the RT vibration relative to the OC sound pressure attenuated the frequency components above 1 kHz and (b) the transfer function of the EC relative to the OC sound pressure emphasized the frequency components between 2 and 3 kHz. Conclusions The vibration of the soft tissue or the skull bone has an effect of low-pass filtering, whereas the sound radiation in the EC has an effect of 2–3 kHz bandpass filtering. Considering the perceptual effect of low-pass filtering in BC speech, our findings suggest that the transmission to the outer ear may not be a dominant contributor to BC speech perception during vocalization.