A design principle for the sound reinforcement system of an open‐field stage

Abstract

If loudspeakers radiate sound from images which lie behind the imaginary walls of an open‐field auditorium, the audience can hear sounds in a simulated indoor auditorium. This principle was applied to an open‐field stage in Hyogo Prefecture, Japan. In order to supply simulated reflections over all of the audience seats, four positions for the loudspeakers were selected, two on each side of the stage symmetrically. Two poles 18 m in height were built close to the stage, and two other 12 m high poles were kept at some distance from the stage. Two loudspeakers were installed at each position, one for the seats near the stage, and the other for the more distant seats so that everyone in the audience would be able to receive at least one simulated reflection within a suitable delay‐time after arrival of the direct sound from the stage. In order to arrange delay‐time for each loudspeaker, four channels of digital delay‐machines were used. The suitable delay‐times were determined by psychoacoustical experiments according to the sound‐pressure level, delay‐time, and direction of the reflected sound in relation to the direct sound.