On Microphone Positioning in Electroacoustic Reverberation Enhancement Systems

Microphone positioning is one of the most important and difficult issues when designing a reverberation enhancement system. This paper first analyses the microphone position relative to the system loudspeakers. It is shown how a microphone can be placed as close to the corresponding loudspeaker as 0.2 times the reverberation distance while keeping almost the same efficiency as that of the diffuse field hypothesis. Results from measurements show that microphone signals are adequately decorrelated when microphones are separated by a distance of the same order as the reverberation distance. The microphone position relative to the stage is then examined. In non-regenerative systems using electronic reverberation, it is shown that microphones have to be placed relatively close to the stage (not further than the reverberation distance) and/or that time variant filters must be used for the decays not to be double-sloped. Acoustic feedback is always far from being negligible in these systems. If no time variant filters are used, the number of channels must be large for the statistical properties of the electroacoustic contribution to be more or less similar to that of a "normal" passive response.