Judgments of noticeable differences in sound fields of concert halls caused by intensity variations in early reflections.

In concert halls early reflections combine with the direct sound and with reverberation to determine the subjective rating of a room's acoustics. Of interest is how variations in the amplitudes of these early reflections are related to the subjectively just-noticeable differences (jnd) in several important acoustical parameters for their wide range encountered in existing halls. Investigated were four subjective parameters, apparent source width (ASW), loudness, intimacy and clarity, which are related to the physical measurements, [1-IACC(E3)], G, ITDG, and C80, defined mathematically in Beranek [Concert and Opera Halls: How They Sound (Acoustical Society of America, New York, 1996)]. Forty-eight types of sound fields were chosen in which to make variations in the amplitudes of early reflections and were reproduced electro-acoustically by multiple loudspeakers in an anechoic chamber. The results indicate that ASW and loudness are more sensitive to changes in the levels of early reflections, and were the primary parameters investigated. Although the number of subjects available with enough experience in listening classical music is limited and the measured jnd is an initial estimation, the jnd of [1-IACC(E3)] is measured as 0.065+/-0.015 in variations of sound field structures and the jnd of G was measured as 0.25+/-0.15 dB, which is consistent with the results of previous studies.