Measurement uncertainty and unicity of single number quantities describing the spatial decay of speech level in open-plan offices
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The ISO 3382-3 standard (2012) defines single number quantities (SNQs) which evaluate the acoustic quality of open-plan offices, but does not address the issue of measurement uncertainties. This study focusses on the SNQs present in this standard related to spatial decay of speech, i.e. D 2S , L pAS4m and r c. The aim is to provide additional information to the limited literature on the measurement uncertainties of these SNQs by use of both analytical developments and a stochastic approach based on simulations. The accuracy of the analytical developments was studied thanks to simulations of the sound propagation within a series of offices (1 layout, 16 acoustic configurations with different screen heights and different acoustic qualities of screens and ceiling). The SNQs obtained in the simulations cover a wide range: D 2S between 3.4 and 7.5 dB(A), L pAS4m between 40.6 and 51.9 dB(A) and r c between 2.5 and 14.7 m. Therefore, the simulations are representative of a broad set of acoustic qualities. Estimated uncertainties have a magnitude of 0.4 dB(A) for D 2S and vary between 0.4 and 0.7 dB(A) for L pAS4m and between 0.2 and 1.5 m for r c over a measurement path comprising 7 measurement positions. The simulations also raise the question of describing the acoustic quality of an office using a single value for the indicators. The results of the simulations show that in some cases, D 2S values significantly depend on the measurement path, leading to a strong increase of its measurement uncertainty if a unique value is to be considered.
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