ACTIVE SILENCING CONTROLLER FOR DUCT

摘要

PROBLEM TO BE SOLVED: To prevent dust from clinging to a sound absorbing material and remove the dust that may cling thereto by providing an air outlet near the surface of the sound absorbing material and in a position upstream of the sound absorbing material. SOLUTION: An opening 8a is formed in the inner surface of a duct 8, and a loudspeaker 13 emits secondary sound waves to the duct 8 from the opening 8a. A sound absorbing material 15 is placed to face the opening 8a. The distance 2L from the opening 8a to the surface 15a of the sound absorbing material 15 facing the opening 8a exceeds 0% of the wavelength of a sound wave of a maximum target frequency for active silencing control but does not exceeds 70%.