Interaural cross-correlation (IACC), lateral fraction (LF), and low- and high-frequency sound levels (G) as measures of acoustical quality in concert halls

Abstract

Interaural cross-correlation coefficient (IACC) and lateral efficiency (LF) as correlates with subjective ratings [see companion paper, L. Beranek, ‘‘Determination of categories of acoustical quality in concert halls’’ (this session)] were analyzed. To make IACC sensitive to quality ratings, a multi-octave-band average was developed, based on Blauert et al. [Acustica 59, 292] and on a subjectively derived set of equal ASW contours that showed the 0.5, 1.0, and 2.0 octave bands to be of equal importance. This IACC3 was divided into IACCE3 integrated over first 0.08 s after arrival of the direct sound, and IACCL,3 same, 0.08 to 1 s. Subjective judgments were also made to determine the effects of increased sound levels of symphonic music at frequencies above and below 355 Hz on apparent source width ASW. IACCE3 and GL both appear important for determining ASW. The measured quantity [1−IACCE3] alone was found to separate the 17 concert halls of this study for which IACC data were available into the same three category groups as those determined from the interviews. Lateral fraction (LF) was found to extend over a very small range and there were so many overlaps among halls when separation into three rating groups was attempted that LF was judged not to be suitable for rating acoustical quality.