PURPOSE: To provide a high-efficient passive control means through a simple control circuit and to reduce the generation of noise of a fan by a method wherein a sounding means is operated through conversion of a phase of a frequency determined by a detecting means and a produced sound is inputted to a receiving level regulating control means to effect passive control.
CONSTITUTION: Since it is already known that at the noise source of an air- conditioner, noise emitted mainly from the suction side is loud, in a passive control method, two noise receiving means 9 located between a bell mouth 17 and a filter 2 concentrically and on a diagonal line and along the stream line of a flow and sounding means 8 placed in positions facing each other are provided. A sensor 10 for detecting the number of revolutions of an impeller and a sensor 4 for the source frequency of a motor are mounted as a detecting means. Rotation noise and electromagnetic noise from an impeller 3 are eliminated in a way that regulation is effected by a control means until the level thereof is reduced in the position of the noise receiving means 9 to a lower-most value by means of a sonic wave having an opposite to that of a noise source emitted from the sounding means 8 and the same amplitude as that thereof.
SHIMOIDE SHINICHI
OKABE SHINYA
