Measurement of vocal doses in virtual classrooms

This work shows the results of a preliminary study about the determination of the optimal acoustical conditions for speakers in small classrooms. An experiment was carried out in a laboratory facility with 22 untrained talkers, who read a text passage from "Goldilocks" during two minutes under 13 different acoustical conditions, that combined different kind of background noise and virtual classroom acoustics. Readings from the vocal fold vibrations were registered with an Ambulatory Phonation Monitor device. The speech signal from the talker in the center of the facility was picked up with a head-worn microphone, convolved in real time with the impulse response of the chosen classroom, and reproduced through 29 loudspeakers placed around the subject. In particular, two different primary school classrooms were selected, with very low and very high reverberation time and, for each of them, two speaker positions. The acoustic of the classrooms was simulated with Odeon 9.0. Environmental noise recorded in quiet classrooms, traffic, and babble noise were considered as sources of disturbing noise during experimentation. Several acoustical parameters were calculated from the impulse response measured with an artificial head (corresponding to the mouth-ears path) placed at the talker position while simulating the classrooms. Time histories of the vocal fold vibration readings, with the trend of the fundamental frequency and an estimation of the sound pressure level, sampled every 50 ms, were obtained. From these data the vocal doses Time dose, Vocal Loading Index, Distance Dose, Energy Dissipation Dose, and Radiated Energy Dose were calculated and correlated with the acoustical features of the classrooms.