Release from masking of speech intelligibility due to fluctuating ambient noise in open-plan offices

The sensitivity of intelligibility to ambient noise modulation is analyzed in this paper by means of two laboratory tests. The first one consists of measuring release from masking using acoustic samples composed of speech noise synthesized in the laboratory, but also real signals measured in two open plan offices. The Speech Reception Threshold values obtained from the experiment for the synthetic signals are compared with the literature. Those obtained for the real samples show significant differences as a function of the open-plane office. Secondly, a new indicator based on the calculation of the speech transmission index (IEC 60268-16, 2011) is proposed, by taking into account the modulation of the ambient noise in the 4 Hz octave band. Simultaneously, a second intelligibility experiment is performed, resulting in a very good correlation between the intelligibility scores and the new indicator. To complete the evaluation, the sound samples of the first test are reused to demonstrate that the indicator is a good descriptor of release from masking due to the modulation of ambient noise for the synthetic signals and that it is capable of classifying work spaces in terms of level of distraction.