| 摘要 |
PURPOSE:To suppress the howling by installing a secondary source on the outer circumference at an open end of a duct then producing a sound wave of reverse phase from that of a sound wave sent from the open end and cancelling the sound waves each other. CONSTITUTION:More than two detection microphones 13a, 13b are arranged in the longitudinal direction in a duct 12. A secondary source 14c is installed on the outer circumference at an open end 15 of the duct 12. A sound wave of reverse phase from that of a sound wave being sent out from the open end 15 is produced from the secondary source 14c corresponding to the output from the detection microphones 13a, 13b, then they are cancelled each other. Consequently, the howling can be suppressed.
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