Spatial decay rate of speech in open plan offices: the use of D2,S and Lp,A,S,4m as building requirements

Invited paper

Remy Wenmaekers

Eindhoven University of Technology

Tuesday 2 june, 2015, 15:20 - 15:40

0.9 Athens (118)

In 2012, new room acoustic parameters for open plan offices were introduced in the ISO 3382-3 standard. While concepts like the spatial decay rate and speech privacy have been used already in judging open plan office designs, now the standard provides an internationally agreed measurement procedure. Four single number ratings are proposed: the decay rate of speech, D<sub>2,S</sub>, the A- weighted sound pressure level of speech at a distance of 4 m, L<sub>p,A,S,4m</sub>, the distraction distance, r<sub>D</sub> (above which the Speech Transmission Index, STI, falls below 0.50), and the average A-weighted background noise level, L<sub>p,A,B</sub>. These new parameters are increasingly used in drawing up requirements for new buildings. The intention of the ISO 3382-3 is to evaluate all four single number ratings, because each parameter controls different acoustic quality aspects. In particular D<sub>2,S</sub> and L<sub>p,A,S,4m</sub> should always be used together. In this paper, measurement data of various rooms are discussed to find out whether requirements for D<sub>2,S</sub> and L<sub>p,A,S,4m</sub> would guarantee the desired reduction in speech level over distance. Results are compared to the classification system as suggested by Virjonen et al.. It is found that the measured decay rate of speech can be relatively low (D<sub>2,S</sub> < 7 dB), while the absolute speech level L<sub>p,A,S</sub> is below a class B rated trend line with D<sub>2,S</sub> > 10 dB and L<sub>p,A,S,4m</sub> < 50 dB. Also, it is found that for judging speech transmission between zones in typical flex offices, multiple decay rates are found. Based on these findings, it is suggested to formulate building requirements based on a combination of D<sub>2,S</sub> and L<sub>p,A,S,4m</sub> as a maximum target curve for values of L<sub>p,A,S</sub>.

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