Active noise reduction of blade-passing frequency tone radiated from a centrifugal blower

The blade-passing frequency noise, abbreviated to BPF noise, radiated from a centrifugal blower, exhibits an extremely high level in the power spectrum of blower-radiated noise and dominates the overall noise level. In the present research, therefore, attention is focused on the BPF noise and two kinds of active control methods are applied to reduce the BPF noise level. One is an active noise source cancellation method and the other is an active noise reduction in the transmission passage. The assumed extent of the BPF noise source is replaced by flat plates which are driven by piezoelectric actuators, and the noise level of BPF can be reduced effectively without any influence on the other frequency components. In the noise reduction in the transmission passage, a small-sized loud speaker is used as a secondary source. The noise level of BPF can be reduced remarkably even in the highrotation region, as usually expected.