  The zones of quiet in pure-tone diffuse sound fields have been studied
extensively in the past, both theoretically and experimentally, with the well
known result of the 10\,dB attenuation extending to about a tenth of a
wavelength. Recent results on the spatial-temporal correlation of broadband
diffuse sound fields are used in this study to develop a theoretical framework
for predicting the extension of the zones of quiet in broadband diffuse sound
fields. This can be used to study the acoustic limitations imposed on local
active sound control systems such as an active headrest when controlling
broadband noise. Spatial-temporal correlation is first revised, after which
derivations of the diffuse field zones of quiet in the near-field and the
far-field of the secondary source are presented. The theoretical analysis is
supported by simulation examples comparing the zones of quiet for diffuse
fields excited by tonal and broadband signals. It is shown that as a first
approximation the zone of quiet of a low-pass filtered noise is comparable to
that of a pure-tone with a frequency equal to the center frequency of the
broadband noise bandwidth.
