PURPOSE: To previously detect and suppress howling, by providing a phase controller which changes the phase of a loudspeaker system at a fixed cycle, switching section which processes microphone output signals divided into plural frequency bands, average energy detecting section, attenuating quantity controlling section, and attenuating section.
CONSTITUTION: The output of a microphone amplifier 12 is inputted in a band dividing section composed of (n) pieces of BPFs 111∼11n. A switching section 121 time-divides a frequency band signal from the BPF111 synchronously to the cycle of a phase control section 14. The energy of a time division signal from the switching section 121 is detected at an average energy detecting section 131 and an attenuating quantity control section 141 compares the energy and finds the ratio of the highest value to the lowest value. When the ratio exceeds a threshold, the control section 141 causes an attenuating section 151 to increase the attenuating quantity. The above-mentioned operations are made similarly to each band. The frequency band signal processed in such a way is changed in phase at a fixed cycle at the phase control section 14 after the signal is added to each other at an adder section 13, and made loud by an amplifier 15 and loudspeaker 16.
FURUKAWA HIROMOTO
NAONO HIROYUKI
