Spatial decay rate of speech in open plan offices: the use of D2,S and Lp,A,S,4m as building requirements
Invited paper
Eindhoven University of Technology
Tuesday 2 june, 2015, 15:20 - 15:40
0.9 Athens (118)
Abstract:
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>.