Active noise reduction system

1 . An active noise reduction system, comprising:

a canceling sound output device configured to output a canceling sound for canceling a noise;

an error microphone configured to generate an error signal based on the noise and the canceling sound; and

a controller configured to control the canceling sound output device based on the error signal,

wherein the controller includes:

a control signal generation unit including a control filter configured to generate a control signal for controlling the canceling sound output device; and

a sound field learning unit including a secondary path filter that represents an estimation value of a transfer function of a secondary path from the canceling sound output device to the error microphone,

the control filter and the secondary path filter are configured to be adaptively updated, and

the controller is configured to differentiate a timing of an adaptive update of the control filter and a timing of an adaptive update of the secondary path filter,

wherein in a case where a fluctuation of the secondary path filter according to the adaptive update thereof has converged, the controller alternately performs the adaptive update of the control filter and the adaptive update of the secondary path filter, and

in a case where the fluctuation of the secondary path filter according to the adaptive update thereof has not converged, the controller repeats the adaptive update of the secondary path filter without the adaptive update of the control filter until the fluctuation of the secondary path filter according to the adaptive update thereof converges.

2 . An active noise reduction system, comprising:

a canceling sound output device configured to output a canceling sound for canceling a noise;

an error microphone configured to generate an error signal based on the noise and the canceling sound; and

a controller configured to control the canceling sound output device based on the error signal,

wherein the controller includes:

a control signal generation unit including a control filter configured to generate a control signal for controlling the canceling sound output device; and

a sound field learning unit including a secondary path filter that represents an estimation value of a transfer function of a secondary path from the canceling sound output device to the error microphone,

the control filter and the secondary path filter are configured to be adaptively updated, and

the controller is configured to differentiate a timing of an adaptive update of the control filter and a timing of an adaptive update of the secondary path filter,

wherein the control signal generation unit further includes an auxiliary secondary path filter that represents the estimation value of the transfer function of the secondary path, and

the controller is configured to

determine whether a fluctuation of the secondary path filter according to the adaptive update thereof has converged, and

update the auxiliary secondary path filter by copying a value of the secondary path filter to the auxiliary secondary path filter in a case where the fluctuation of the secondary path filter according to the adaptive update thereof has converged.

3 . The active noise reduction system according to claim 2 , wherein the controller is configured to determine whether the fluctuation of the secondary path filter according to the adaptive update thereof has converged based on a variation in at least one of an amplitude of the secondary path filter and a phase of the secondary path filter.

4 . The active noise reduction system according to claim 2 , wherein one of the canceling sound output device and the error microphone is installed in an occupant seat of a vehicle,

another of the canceling sound output device and the error microphone is installed in a portion of the vehicle other than the occupant seat, and

the controller is configured to

stop the adaptive update of the secondary path filter in a case where the fluctuation of the secondary path filter according to the adaptive update thereof has converged,

determine whether the transfer function of the secondary path has changed based on a state of the occupant seat in a state where the adaptive update of the secondary path filter is stopped, and

resume the adaptive update of the secondary path filter in a case where the transfer function of the secondary path has changed.

5 . The active noise reduction system according to claim 4 , wherein the controller is configured to

acquire a plurality of variations among a variation in a front-and-rear position of the occupant seat, a variation in a height of the occupant seat, and a variation in an inclination angle of a reclining portion of the occupant seat,

set a first threshold and a second threshold for each of the plurality of variations, the second threshold being smaller than the first threshold, and

determine that the transfer function of the secondary path has changed in a case where at least one of the plurality of variations is greater than the first threshold and a case where all of the plurality of variations are greater than the second threshold.

6 . The active noise reduction system according to claim 2 , wherein at least one of the canceling sound output device and the error microphone is installed in a vehicle cabin of a vehicle, and

the controller is configured to

stop the adaptive update of the secondary path filter in a case where the fluctuation of the secondary path filter according to the adaptive update thereof has converged,

determine whether the transfer function of the secondary path has changed based on an open/close state of a window of the vehicle cabin in a state where the adaptive update of the secondary path filter is stopped, and

resume the adaptive update of the secondary path filter in a case where the transfer function of the secondary path has changed.

7 . The active noise reduction system according to claim 1 , wherein the sound field learning unit further includes a primary path filter that represents an estimation value of a transfer function of a primary path from a noise source to the error microphone,

the primary path filter is configured to be adaptively updated, and

the controller is configured to normalize an adaptive update amount of the secondary path filter and an adaptive update amount of the primary path filter using a common normalization divisor.

8 . The active noise reduction system according to claim 7 , wherein the primary path filter is configured to be adaptively updated based on a reference signal corresponding to the noise,

the secondary path filter is configured to be adaptively updated based on the control signal, and

the common normalization divisor includes a norm of a signal vector of the reference signal and a norm of a signal vector of the control signal.

9 . The active noise reduction system according to claim 2 , further comprising a reference microphone provided separately from the error microphone,

the reference microphone is configured to generate a determination signal based on at least the noise,

the controller is configured to

stop the adaptive update of the secondary path filter in a case where the fluctuation of the secondary path filter according to the adaptive update thereof has converged,

determine whether the transfer function of the secondary path has changed based on the error signal and the determination signal in a state where the adaptive update of the secondary path filter is stopped, and

resume the adaptive update of the secondary path filter in a case where the transfer function of the secondary path has changed.

10 . The active noise reduction system according to claim 9 , wherein the controller includes a second control signal generation unit that is provided separately from the control signal generation unit, and

a microphone corresponding to the second control signal generation unit is used as the reference microphone.

11 . The active noise reduction system according to claim 9 , wherein the controller is configured to determine that the transfer function of the secondary path has changed in a case where a difference between the error signal and the determination signal is equal to or greater than a first reference value and a temporal variation in the error signal is equal to or greater than a second reference value.

12 . The active noise reduction system according to claim 11 , wherein the controller is configured to determine that the transfer function of the secondary path has changed in a case where the difference between the error signal and the determination signal is equal to or greater than the first reference value, the temporal variation in the error signal is equal to or greater than the second reference value, and the error signal is equal to or greater than a third reference value.

13 . An active noise reduction system, comprising:

a canceling sound output device configured to output a canceling sound for canceling a noise;

an error microphone configured to generate an error signal based on the noise and the canceling sound; and

a controller configured to control the canceling sound output device based on the error signal,

wherein the controller includes:

a control signal generation unit including a control filter configured to generate a control signal for controlling the canceling sound output device; and

a sound field learning unit including a secondary path filter that represents an estimation value of a transfer function of a secondary path from the canceling sound output device to the error microphone,

the control filter and the secondary path filter are configured to be adaptively updated,

the controller includes a plurality of control channels each including the control signal generation unit and the sound field learning unit, and

the controller is configured to differentiate a timing of an adaptive update of the secondary path filter in each of the control channels.