| 摘要 |
PROBLEM TO BE SOLVED: To continuously change and adjust a phase of a detection signal of noise which is detected by a microphone, to drive a speaker and to actively reduce noise. SOLUTION: The detection signal of noise detected by the microphone 8 is given to a low pass filter 62 and is given to first and second active all pass circuitsϕ1 andϕ2 composing a phase variable circuit 65. Variable resistances VR2 and VR4 can continuously change and adjust the phases. Output from a stage 1B in the middle of the low pass filter is given to the second active all pas circuitϕ2. Respective outputs of the filter circuit 62 and the first and second active all pass circuitsϕ1 andϕ2 are mixed in a mix circuit 72 and the speaker 11 is driven. Noise is actively extinguished in a diffraction region 32 at an upper part of a sound barrier 5 with sound from the speaker 11. COPYRIGHT: (C)2004,JPO
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