Spatial fluctuations in measures for spaciousness

In room acoustics, several measures have been defined that are supposed to quantify the apparent source width (ASW) in a hall, being one of the percep tual cues related to spaciousness. The most common ones are the lateral ene rgy fraction (LF), i.e., the ratio between lateral and omnidirectional earl y energy, and the interaural cross correlation coefficient (IACC), all to b e calculated from measured or simulated impulse responses. [Several version s of the LF are known in literature, having different names, generalized he re as lateral energy fraction.] According to a method proposed by Berkhout et al. [J. Acoust. Soc. Am. 102, 2757-2770 (1997)], for a fixed source posi tion impulse responses have been measured along an array of closely spaced microphone positions in several halls. The above measures, when calculated from these impulse responses, show large fluctuations with small variations in microphone position due to interference of the different components of the wave field to which the human ear is apparently insensitive. A revision of the measures is discussed, which contributes to the suppression of the interference effects. In order to assess their perceptual significance, the fluctuations have to be related to just-noticeable differences (jnd's) in ASW. Since very different jnd values are given in the literature, the autho rs advise that new experiments should be conducted on this point. (C) 2001 Acoustical Society of America.