Prediction of howling for a sound system in an acoustical environment with both reverberant and direct sounds

Abstract

Prediction of howling is a key technology for a howling suppression design for a sound system with a loudspeaker and microphone. A howling occurrence prediction method for a sound system in a reverberant room has already been presented [J. Ohga, J. Sakaguchi, ‘‘Prediction of howling of a sound system in a reverberant room,’’ W. C. Sabine Centennial Symposium (ASA, New York, 1994), 2aAAd4]. It is apparently useful for ordinary public address systems whose distances of loudspeakers from microphones are large. However, this result was not perfect because the direct sound component is not negligible in hands-free telephones or teleconference systems whose loudspeakers and microphones are set close to each other. This report gives a quantitative howling occurrence prediction method for a sound system in an acoustical environment with both reverberant and direct sounds. The following design parameters are obtained: (1) the increase of howling occurrence level from the power average value, (2) the level occurrence probability, and (3) the critical level chart given by an equation as a function of direct and reverberant sounds ratio. Prediction results for particular examples are compared with calculations of sound-field transfer functions. Results confirmed that it is practical.