Compared effects of overall level and speech intelligibility on self-reported fatigue in open-plan offices : a laboratory study

It seems now accepted that speech noise in open plan offices is the main source of annoyance for employees. The aim of the present study is to test in a laboratory the effect of different sound conditions representative of ambient noise in open plan offices, while the participants perform a task closer to the everyday open-plan office work. Forty-five subjects between 18 and 58 years old participated to the experiment. They were exposed to four controlled sound conditions, made of intelligible speech superimposed to babble noise: equivalent modulation index MAeq and overall level LAeq were the two control factors (two levels each). The duration of the experiment for each condition was equivalent to the duration of half a workday (four hours for each condition). The task consisted in writing a review of four newspapers. During each half-day, the self-reported mental fatigue and the perception of sound environment were evaluated several times. The statistical analyses were performed with respect to three factors, the two sound characteristics (MAeq and LAeq) and the time of the day. The results show that a high intelligibility, which corresponds to a high MAeq value, significantly increased the fatigue experienced by the participants. Lastly, the results of this experiment were compared to a previous experiment conducted by Kostallari et al. We concluded that, for all sound conditions, in both experiments, speech noise has a higher impact on the mental fatigue of the participants, compared to stationary noise or to the ?speech like? amplitude-modulated noise.