Active noise reducing device, mobile device, and active noise reducing method

1. An active noise reducing device that reduces noise in a predetermined space, the active noise reduction device comprising:

a plurality of reference signal input units that accepts inputs of a plurality of reference signals correlating with the noise;

a combined-reference-signal generation unit that generates a combined reference signal from the plurality of reference signals which is input;

an adaptive filter unit that applies an adaptive filter to the combined reference signal generated, to generate a cancel signal;

a cancel signal output unit that outputs the cancel signal generated;

an error signal input unit that accepts input of an error signal corresponding to a residual sound resulting from interference between the noise and a cancel sound source generating a cancel sound corresponding to the cancel signal;

a simulated acoustic transmission characteristic filter unit that generates a filtered combined reference signal by correcting the combined reference signal with a simulated transmission characteristic in which an acoustic transmission characteristic from the cancel signal output unit to the error signal input unit is simulated; and

a filter coefficient update unit that updates a coefficient of the adaptive filter in succession based on the error signal and the filtered combined reference signal generated, wherein the combined-reference-signal generation unit includes

a plurality of filters that is applied respectively to the plurality of input reference signals, and

an adder that adds up the plurality of reference signals to which the plurality of filters is applied respectively, to generate the combined reference signal, and

wherein the plurality of filters includes

a filter with a passband of frequencies having mainly structure borne noise that is applied to a reference signal output by an acceleration sensor out of the plurality of reference signals, and

a filter with a passband of frequencies having mainly air borne noise that is applied to a reference signal output by a microphone out of the plurality of reference signals.

2. The active noise reducing device according to claim 1 , wherein at least one of the plurality of filters is a bandpass filter.

3. The active noise reducing device according to claim 2 , wherein one of the plurality of filters is a low-pass filter.

4. The active noise reducing device according to claim 1 , wherein the plurality of filters characteristically has respective passbands not overlapping with each other.

5. The active noise reducing device according to claim 1 , wherein

the error signal is input from an error signal source disposed in the predetermined space into the error signal input unit, and

each of the plurality of reference signals is input from a reference signal source disposed outside the predetermined space.

6. The active noise reducing device according to claim 5 , wherein the reference signal source is one of an acceleration sensor and a microphone.

7. A mobile device, comprising:

the active noise reducing device according to claim 1 ;

a reference signal source that outputs the plurality of reference signals, wherein the reference signal source includes the acceleration sensor and the microphone; and

an error signal source that outputs the error signal into the error signal input unit.

8. The mobile device according to claim 7 , wherein

the mobile device is a vehicle

the predetermined space is a space in a vehicle interior, and

the noise is road noise.

9. An active noise reducing method for reducing noise in a predetermined space, the active noise reducing method comprising:

generating a combined reference signal from a plurality of reference signals correlating with the noise;

applying an adaptive filter to the combined reference signal generated, to generate a cancel signal;

generating a filtered combined reference signal by correcting the combined reference signal with a simulated transmission characteristic in which an acoustic transmission characteristic of a cancel signal output unit that outputs a cancel sound generated by a cancel sound source corresponding to the cancel signal to an error signal input unit that accepts input of an error signal corresponding to a residual sound resulting from interference between the cancel sound and the noise; and

updating a coefficient of the adaptive filter in succession based on the error signal and the filtered combined reference signal generated,

wherein the generating of the combined reference signal includes

applying a plurality of filters respectively to the plurality of reference signals, and

adding up the plurality of reference signals to which the plurality of filters is applied respectively to generate the combined reference signal, and

wherein the applying the plurality of filters includes

applying a filter with a passband of frequencies having mainly structure borne noise to a reference signal output by an acceleration sensor out of the plurality of reference signals, and

applying a filter with a passband of frequencies having mainly air borne noise to a reference signal output by a microphone out of the plurality of reference signals.