In room acoustics, one of the most used parameters for evaluating the speech intelligibility is the Speech Transmission Index (STI). the experimental evaluation of this STI generally employ an artificial speaker (binaural head) and listener (artificial mouth). In this study, the influence on the measurements of the emission directivity of the artificial mouth was investigated for different acoustic environments and we have found that, in many cases ( i.e. big rooms or systems of telecommunications ) the results is not sensitive to modifications of the directivity; on the contrary, inside cars, the shape of the whole balloon of directivity is important for determining correct and comparable values and the different mouth studied gives really different results in the same situation. Afterwards we measured, in an anechoic room, the 3D directivities of a statistical population of speakers. The post-processing of the results enabled us to determine the average and the standard deviation of human speech directivity. ficial mouths’ one These results constitute a valuable source of information for assessing the compliances of artificial mouth to reality.
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