Intelligibility assessment in elementary school classrooms from binaural room impulse responses measured with a childlike dummy head

In a classroom, especially for those intended for small children, speech intelligibility is a basic issue for learning efficacy. As it is well known, applying articulation tests (AT’s) is the best way to assess room’s speech intelligibility. However, the technique is expensive and takes a rather long time to be completed. In this paper, a new technique to assess classroom speech intelligibility is presented, which does not require the application of AT’s inside the classroom. The room binaural impulse response, produced by a sweep sine signal and emitted by an artificial speaker (AS), is recorded with a dummy head. Since small children are involved, the binaural recording was performed with a childlike dummy head, with a size corresponding, roughly, to that of a 10 years old child. The binaural measurements were also made using an adult dummy head for comparison purposes. The measured binaural impulse responses were convolved with anechoic signals containing the enunciation of monosyllables. The background noise measured in the room is then added and the result is convolved again with a headphone impulse response, generating an acoustical virtual reality – the auralizations. The resulting binaural signals are applied to subjects of the same age in virtual AT’s. To validate the technique, actual AT’s using the same anechoic lists of monosyllables emitted by the AS inside the classroom were performed. The technique was applied in three schools to students of different level classrooms. The results show that the proposed technique presents good reliability to assess classroom intelligibility when the measurements are made with the childlike dummy head. For virtual AT’s obtained with the adult dummy head, however, it was verified that the children ability to recognize the monosyllables was much lower than that with the childlike dummy head. This is a consequence of the pronounced differences between the head related impulse responses for an adult and a child, resulting in distinct binaural impulse responses.