Noise annoyance in open plan offices: influence of the presence of multiples intelligible speakers.

Speech noise is a major cause of annoyance in open-plan offices. The purpose of this research was to assess the quality of existing tools for predicting the nuisance potential of speech and highlight possibilities for improvement. The ways in which speech sounds influence noise annoyance were thus investigated. To this end, experiments were carried out based on classical mental tasks, with concurrent objective and subjective measurements of the increase in mental workload caused by ambient speech. First, the effect of speech intelligibility was studied. Indeed, some argue for the use of a speech intelligibility measure, the Speech Transmission Index (STI), to predict noise annoyance in open-plan offices. Results confirmed the increase in disruption caused by speech made more intelligible. However, the STI was incapable of predicting noise annoyance for fluctuating background sounds, which are usual in open-plan offices. An alternative was then provided that accounted for the temporal variability seen in actual office sound environments. The predictive ability of this measure was assessed for varied tasks. The resulting effects were small when compared with individual differences in susceptibility to speech noise. However, they indicated that allowing for level fluctuations in the sound environment is essential to quantifying the induced noise annoyance. Moreover, it appeared that subjective measurements of noise annoyance were a critical complement to objective measurements for identifying certain causes of noise annoyance.