Patent ID: 7492911

Claim:
A noise reducing device comprising: a first microphone disposed at a control point set at an outer side of a sound barrier that reduces noise emitted from a noise source; a second microphone disposed at an inner side of the sound barrier and including a directivity in a predetermined direction so as to pick up the noise that is emitted from the noise source and made incident from a diagonal direction with respect to the sound barrier; computing means that computes, on the basis of the output of the first microphone and the output of the second microphone, a filter factor with an explicit method so that the noise at the control point is reduced; a filter that outputs a control signal digitally filtered on the basis of the filter factor computed by the computing means and the output of the second microphone; a control sound source in which unidirectional linear array of plural loudspeakers are arranged in a predetermined direction and which is disposed so that a control sound configured by sound emitted from the linear array of plural loudspeakers is diffracted at an upper edge of the sound barrier and reaches the control point; and an input circuit that inputs, to the linear array of plural loudspeakers and in correspondence to the arrangement order of the linear array of plural loudspeakers, the control signal and a delay control signal in which the control signal is delayed by predetermined times in correspondence to the direction in which the noise is made incident at the sound barrier.