Speech Intelligibility with a Bone Vibrator

Abstract : The FELIN project (Foot soldier with Integrated Equipment and Connectivity) of the French Military Procurement Agency aims at gearing tomorrow's foot soldier with "flexible and maneuvering" equipment. Among its requirements is that foot soldiers are fitted with a communications headband operating through bone conduction. The main advantage of listening through bone conduction is that it allows for the transmission of information to the soldier, while leaving the soldier's ears free to perceive the surrounding environment. This device is light, not bulky, and is quite comfortable. This laboratory assessment compared the voice intelligibility scores of a prototype bone conduction device with those obtained by Peltor's (trademark) militarized COMTAC-type headset. The COMTAC headset is a hearing device (i.e., fitted with two microphones, left and right, to reproduce a spatial hearing capability). Both technologies allow for orientation in space using acoustic cues. Tests were performed in silence and in operationally realistic noise conditions (reproducing the noisy environment inside an armored vehicle). Voice material consisted of nonsense CVC words (Consonant-Vowel-Consonant) spoken by two speakers of different genders. In silence, the prototype bone vibrator headband and the COMTAC headset obtained the same intelligibility score. In noise, the performance of the prototype headband was slightly lower than that of the COMTAC headset. One of the reasons for this is that in a noisy environment, finding the right position for the vibrator to obtain optimal hearing is difficult, and the voice transmission level is too low. In brief, bone conduction technology (reduced here to the mere listening function) has an appreciable initial potential, based on the performance obtained in silence. However, design improvements will be needed to reach the voice levels required for intelligibility in loud environments (notably for use in armored vehicles).