The Effect of Sound Source Direction on Speech Intelligibility in Rooms

Speech intelligibility has traditionally been measured using an omni-directional microphone. However, we know that human hearing is not omni-directional. This paper investigates the effect of source direction on speech intelligibility to better understand the real world situation. An experimental methodology was designed to objectively, assess speech intelligibility using the Speech Transmission Index Public Address (STIPA) methodology. The subject based assessment of speech used male recordings of phonetically balanced word lists, which were scored by each individual participant. The experiment was undertaken under several conditions, in terms of signal to noise and reverberation. In addition, analyses of the subject based intelligibility scores were divided into native and non-native English speakers. Finally, the participants undertook the experiment both facing towards and facing away from the sound source. The results of the research are presented in the paper which suggests there was a reduction in speech intelligibility for the non-native English speakers when facing away from the loudspeaker under noisy conditions.