Intelligibility of bone-conducted speech detected on the scalp assessed by mono-syllable articulation and speech transmission index.

Bone-conduction microphones (BCMs) can detect speaker's voices with high signal-to-noise ratio even under extremely noisy environments. However, it is sometimes accompanied by discomfort and esthetic problems because BCMs are ordinarily attached to the front of the neck (larynx). In order to solve such problems, we have been developing a novel BCM systems built in a hard hat [2]. To develop this BCM system, characteristic of bone-conducted speech detected on the scalp need to be clarified. In this study, intelligibilities of bone-conducted speech detected at several locations on the head and neck were assessed by mono-syllable articulation tests and the speech transmission index (STI), objective measure of signal transmission quality. The results obtained indicated that the forehead and the vertex showed better articulation and STI than the mastoid process of the temporal bone, the mandibular condyle and occiput. Additionally, the larynx, commonly used in existing BCM systems, showed lower scores than others. These results suggest that attenuation of high-frequency components are smaller at the forehead and the vertex, and indicate the practicability of these locations as the BCM placement.