To ensure good sound environments in architectural spaces, the Architectural Institute of Japan is currently developing a standard and its design guidelines of sound absorption. In this standard, upper limits of reverberation time are recommended for three types of rooms intended for speech and communication with sound reinforcement systems, which are derived from the criteria of equivalent floor absorption coefficient. To validate the criteria, we conducted an auditory experiment in the sound fields reproduced in an anechoic room based on geometric room acoustic simulation. Assuming the source-to-receiver distance equals the mean free path, the room impulse responses were obtained for rectangular rooms having three room volumes from 300 to 30 000 m3 and five absorption criteria. Twenty-four subjects evaluated speech listening difficulty for the 15 room conditions. The results of the listening difficulty ratings (LDR) suggest that the proposed criteria are generally appropriate for small- to medium-sized rooms but possibly lead to a higher LDR in large rooms due to lack of early reflected sounds. In addition, a relatively good correspondence was confirmed between the clarity C50 and LDR, but there were systematic differences between the theoretical and simulated values of C50.
Chen et al. (Wed,) studied this question.