Abstract
Details of the acoustic improvement of a large hall are described. Though the reverberation time of this hall was rather short for an orchestral music, it was not altered keeping in mind the multi-purpose use of the hall. Therefore only adding some early reflections was attempted for the acoustic improvement of this hall. In order to know where reflectors should be set up to get more early reflections, the following subjective tests were carried out in the hall using an anechoic chamber music tape as the source of test signals. The sound fields to be judged were produced by a loudspeaker in the center of the stage and one or two loudspeakers fed delayed signals for simulated early reflections. Paired comparison tests of the different sound fields were carried out. It was concluded from above subjective tests that median-plane as well as lateral reflection would contribute to the acoustic improvement of this hall. Based on above findings, the shape of the side walls was altered to get lateral reflections while movable over-stage reflectors were installed to get more early reflections. The acoustics of this hall had certainly improved, and which was confirmed by comparing dummy head recordings taken before and after the above improvement. Generally for the acoustic improvement of large halls it is necessary to increase both spatial-impression and loudness, therefore lateral and median-plane reflection would be useful. This was also supported by other experiments in anechoic chamber on the subjective effects of adding median-plane reflection.
