Abstract: An active noise control apparatus comprises a secondary sound source for generating sound canceling noise emitted from a noise source, first and second microphones sequentially arranged between the noise source and the secondary sound source at a predetermined distance in a direction from the noise source to the secondary sound source, a coefficient multiplier for multiplying an output signal of the second microphone by a coefficient corresponding to a ratio of a transfer function of the first microphone with respect to the secondary sound source to that of the second microphone with respect thereto, a subtracter for obtaining a difference between a multiplication resultant signal and an output signal of the first microphone, and a signal processor for outputting a secondary sound signal obtained by multiplying the difference signal with a predetermined coefficient to the secondary sound source.

Abstract: An adaptive type active noise cancellation apparatus comprises a first sensor for detecting a noise generated by a noise source and outputting a detection signal, a filter having a predetermined filter coefficient and filtering the output signal from the first sensor by using the predetermined filter coefficient and outputting a filtered signal, a speaker for receiving the filtered signal and generating a sound corresponding to the filtered signal, an active noise cancellation control system for actively canceling a noise at a control target point by using the sound generated by the speaker, a second sensor, arranged at the control target point, for detecting a sound at the control target point and outputting a detection signal, and an adaptive control system for receiving the output signals from the first and second sensors and adaptively updating the filter coefficient in accordance with a change in state of a system to which the active noise cancellation control system is applied.