Abstract
We studied noise reduction mechanism of an axial-flow fan by means of active noise control (ANC) system. Desired reduction has already been attained for fundamental frequency (300Hz) and its second harmonic (600Hz) at a position of error microphone. However similar noise reduction has not necessarily been obtained at other positions. The reason is that there is a difference of propagation characteristics between noise and secondary sound in anechoic room. By changing the number of speakers for ANC system, noise reduction level and sound pressure level of secondary sound were measured in an anechoic room. We confirmed the correlation between the difference of propagation characteristics and noise reduction effect and therefore we succeeded in attaining noise reduction at the other positions in addition to that at the error microphone.
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