  Late reverberation involves the superposition of many sound reflections
resulting in a diffuse sound field. Since the spatially resolved perception of
individual diffuse reflections is impossible, simplifications can potentially
be made for modelling late reverberation in room acoustics simulations with
reduced spatial resolution. Such simplifications are desired for interactive,
real-time virtual acoustic environments with applications in hearing research
and for the evaluation of hearing supportive devices. In this context, the
number and spatial arrangement of loudspeakers used for playback additionally
affect spatial resolution. The current study assessed the minimum number of
spatially evenly distributed virtual late reverberation sources required to
perceptually approximate spatially highly resolved isotropic and anisotropic
late reverberation and to technically approximate a spherically isotropic
diffuse sound field. The spatial resolution of the rendering was systematically
reduced by using subsets of the loudspeakers of an 86-channel spherical
loudspeaker array in an anechoic chamber. It was tested whether listeners can
distinguish lower spatial resolutions for the rendering of late reverberation
from the highest achievable spatial resolution in different simulated rooms.
Rendering of early reflections was kept fixed. The coherence of the sound field
across a pair of microphones at ear and behind-the-ear hearing device distance
was assessed to separate the effects of number of virtual sources and
loudspeaker array geometry. Results show that between 12 and 24 reverberation
sources are required.
