It is currently accepted that noise is one of the most important annoyance factors in open-space offices. However, noise levels measured in open spaces of the tertiary sector rarely exceed 65 dB(A). It, therefore, appears necessary to develop a tool that can be used to assess the noise environment of these offices and identify the parameters to be taken into consideration when assessing the noise annoyance. This article presents a questionnaire to be filled by people working in such environment, and a case study in different open plan offices. The majority of the 237 respondents consider that the ambient noise level in their environment is high and that intelligible conversations between their colleagues represent the main source of noise annoyance. This annoyance was significantly correlated with their evaluation of sound intensity, which could not be represented by A-weighted level measurements.

In this paper a series of numerical simulations of the effect of turbulence on the propagation of acoustic waves in the atmosphere are presented. First the technique of representing the turbulence as a set of realizations of a random field generated by a limited number of Fourier modes is described. Through each individual realization, the acoustic waves are propagated in a wide-angle parabolic approximation to obtain the sound-pressure level. Ensemble averaging is then performed to compute the statistical properties of the acoustic field: mean sound-pressure level, intensity fluctuations, and amplitude distributions. The method is applied first to a nonrefractive atmosphere, both in the presence of a rigid boundary and of an impedance ground, and then to an upward refractive atmosphere with an impedance ground. The model, which contains no adjustable parameters, is tested using the experimental data of Parkin and Scholes, Daigle, and Wiener and Keast. Good agreement between numerical simulations and experiments is obtained.

Even for low noise levels, employees working in open-plan offices declare they are disturbed by different sound sources and especially by intelligible speech. This paper presents two experiments that aim at studying the effects of sound sources on task performance and cognitive load. In the first experience, thirty-five individuals were assigned a serial memorization task in four noise conditions: printers, intelligible speech, non-intelligible speech and phone rings. Noise annoyance was assessed by measuring task performance and cognitive workload (NASA-TLX). Although there was no significant difference between intelligible speech, unintelligible speech and phone ring tone signals in terms of annoyance, the performance in a memory task decreased in the presence of intelligible speech. In the second experiment, the relevance of a new intelligibility index was evaluated. This index was derived from SIIt as defined by Rhebergen et al. (2006) to deal with fluctuating noise as speech babble. Fifty-five subjects performed a serial memory task in four STIt (non-stationary STI) conditions (from 0.38 to 0.69) while STI values were kept constant (around 0.36). No significant difference appeared between the decreases in performance observed with multiple levels of intelligibility. However, an inter-individual variability appeared in performance measurements. The best performers seemed to be less affected by the high level of intelligibility condition than the other ones.

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