Listening efficiency in real and simulated university classrooms

The present study examines how reverberation, background noise level and type, affect both speech reception performance and the perceived effort of students in a university classroom. The classroom has a volume of 198 m3 and a reverberation time in occupied conditions of 0.6 s, complying with the target value of the DIN 18041 standard. Diagnostic Rhyme Tests (DRT) in the Italian language were proposed to a group of 26 normal-hearing young adults: half of them native (Italian), the other half non-native (German) speakers. Data on speech intelligibility (SI) and response time (RT) were collected. The two quantities were combined in the joint metric of listening efficiency, effectively describing the interplay of perceptual and cognitive processes in speech reception performance. The experiment took firstly place in situ, where the distinct effects a speech-shaped stationary noise and a fluctuating (ICRA) noise with the same short-term STI were determined. Afterwards, acoustic simulations of the classroom setting were carried out, and the resulting binaural impulse responses used for laboratory experiments with headphones. Simulations and in-situ measurements were compared in terms of STI, SI and RT; then, listening tests under controlled conditions were accomplished with a selection of background noise levels and reverberation times.