  Open-plan offices (OPOs) have been around for more than half a century now,
chronicling the vicissitudes of workplace topography amongst other factors.
This paper addresses one such factor - the sound environment in occupied OPOs
in relation to several objective workplace parameters, using measurements in
contemporary OPOs and comparisons with studies over the last 50 years.
Omnidirectional and binaural sound measurements were conducted in 43 offices
during typical working hours. The results describe variation in several
acoustic and psychoacoustic metrics, and present statistical models that
predict these metrics as a function of the number of workstations in offices.
LA,eq of 53.6 dB is typical for occupied OPOs, with spectral slope of
approximately -4 dB/octave. LA,eq values do not vary much over the workplace
parameters studied (e.g., floor plate area, work activity, etc), except for
-2.7 dB and -4.1 dB differences between offices with/without carpeting, and
offices with ceiling absorption but with/without carpeting, respectively; most
likely from reduced floor impact noise leading to speech level reduction. Sound
fluctuation, as characterised by the metric Noise Climate (NCl: LA10 - LA90)
and the psychoacoustic Fluctuation Strength (FS), decreases significantly with
increasing number of workstations in OPOs. This suggests lesser auditory
distraction in larger offices, which needs further investigation. In terms of
historical trends, OPOs have become quieter over the years, especially
background noise quantified as LA90, although there are several subtleties.
Overall, current findings can inform several OPO design perspectives including
policy documents, provide values for laboratory simulations of OPO acoustic
environments, help interpret subjective impressions of OPO occupants, etc.
