Active noise attenuating device

An active noise attenuating device comprising:

• a first microphone provided in a propagation path of a noise which detects the noise and generates a detection signal;
• a loudspeaker provided in the propagation path of the noise;
• control means for producing a control signal on the basis of the detection signal supplied by the first microphone, the control signal being supplied to the loudspeaker so that the loudspeaker produces an interference sound having the same amplitude as the noise detected by the first microphone and a phase opposite to the noise at a control point in the noise propagation path;
• a high pass filter connected in the path of the control signal between the control means and the loudspeaker, the high pass filter having a cut-off frequency within a low frequency range that the loudspeaker is unable to reproduce and which corresponds to a frequency component of the control signal at which a coherence value is rapidly reduced, the coherence value indicating linearity between input and output of the active noise attenuating device;
• a second microphone provided in the vicinity of the control point in the noise propagation path, the second microphone monitoring an amount of noise attenuated by application of the interference sound;
• and
• adaptive control means for controlling the control means by compensating an operational factor thereof in correspondence with the amount of noise attenuated by application of the interference sound on the basis of the detection signals from the respective first and second microphones.