Patent Publication Number: US-2022230620-A1

Title: Active noise control device and vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-007148 filed on Jan. 20, 2021, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an active noise control device and a vehicle. 
     Description of the Related Art 
     JP H06-059688 A discloses an active noise canceling device. The active noise canceling device disclosed in JP H06-059688 A includes a sound generating device, a sound detection sensor, and a vibration sensor. The sound generating device is disposed in a space where noise is to be canceled. The sound detection sensor is disposed in the space where noise is to be canceled. The vibration sensor is provided for each of a plurality of vibration sources of several vibrations propagating in the space where noise is to be canceled. The active noise canceling device disclosed in JP H06-059688 A further includes a vibration signal generating means and a driving means. The vibration signal generating means generates a vibration signal having an opposite phase to the sound detected by the sound detection sensor, based on the output signals of the plurality of vibration sensors. The driving means drives the sound generating device based on the vibration signal. 
     SUMMARY OF THE INVENTION 
     However, in JP H06-059688 A, noise cannot always be reduced suitably when a change occurs in the characteristics of the sound generating device. 
     An object of the present invention is to provide an active noise control device and a vehicle that can reduce noise suitably. 
     An active noise control device according to an aspect of the present invention causes an actuator to output a canceling sound based on a control signal in order to reduce noise in a vehicle compartment of a vehicle. The active noise control device includes a control signal generating unit including a first adaptive filter configured to generate the control signal by performing a filtering process on a reference signal corresponding to the noise, an identifying unit configured to identify a peak frequency in an impedance frequency characteristic that is a frequency characteristic of impedance of the actuator, a peak frequency storage unit configured to store an initial peak frequency that is the peak frequency in the impedance frequency characteristic in an initial state, a first determination unit configured to determine whether or not a difference between the peak frequency currently identified by the identifying unit and the initial peak frequency stored in the peak frequency storage unit is greater than or equal to a threshold value, and a control unit configured to change a characteristic of the control signal generated by the control signal generating unit when the first determination unit determines that the difference is greater than or equal to the threshold value. 
     A vehicle according to another aspect of the present invention includes the active noise control device as described above. 
     According to the present invention, it is possible to provide an active noise control device and a vehicle which can reduce noise suitably. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an outline of active noise control; 
         FIG. 2  is a block diagram illustrating a part of a vehicle equipped with an active noise control device according to an embodiment; 
         FIG. 3  is a block diagram illustrating an example of a control signal generating unit; 
         FIG. 4  is a block diagram illustrating an example of an identifying unit; 
         FIG. 5  is a graph illustrating examples of impedance frequency characteristics of an actuator; 
         FIG. 6  is a block diagram illustrating another example of the identifying unit; 
         FIG. 7  is a block diagram illustrating an example of an impedance characteristic identifying unit; 
         FIG. 8  is a diagram illustrating an example of a table; 
         FIG. 9  is a flowchart illustrating an example of operations of an active noise control device according to an embodiment; and 
         FIG. 10  is a flowchart illustrating an example of operations of an active noise control device according to an embodiment. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Preferred embodiments of an active noise control device and a vehicle according to the present invention will be described in detail below with reference to the accompanying drawings. 
     Embodiment 
     An active noise control device and a vehicle according to an embodiment will be described with reference to  FIGS. 1 to 10 .  FIG. 1  is a diagram illustrating an outline of active noise control. 
     An active noise control device  10  causes an actuator  16  to output a canceling sound for reducing noise (vibration noise) in a vehicle compartment  14  of a vehicle  12 . 
     The noise in the vehicle compartment  14  may include, for example, road noise. Road noise is noise that is transmitted to an occupant in the vehicle compartment  14  when a wheel vibrates due to force received from the road surface and the vibration of the wheel is transmitted to the vehicle body via a suspension. 
     The vehicle  12  is provided with a vibration sensor that detects vibration of the vehicle  12 . That is, the vehicle  12  is provided with an acceleration sensor  18  that detects vibration of the vehicle  12 . The signal r detected by the acceleration sensor  18  is supplied to the active noise control device  10  as a reference signal r. That is, the signal r indicating vibration is supplied to the active noise control device  10  as the reference signal r. Although the case where the signal detected by the acceleration sensor  18  is used as the reference signal r is illustrated in  FIG. 1 , the present invention is not limited thereto. A signal correlated with the vibration of the vehicle  12  can be appropriately used as the reference signal r. That is, a signal corresponding to the noise can be appropriately used as the reference signal r. 
     A microphone  20  is further provided in the vehicle compartment  14 . The microphone  20  detects residual noise (cancellation error noise) due to interference between the noise and the canceling sound output from the actuator  16 . The residual noise detected by the microphone  20  is supplied to the active noise control device  10 . That is, an error signal e detected by the microphone  20  is supplied to the active noise control device  10 . 
     The active noise control device  10  generates a control signal u for outputting a canceling sound from the actuator  16 , based on an error signal e detected by the microphone  20  and the reference signal r. More specifically, the active noise control device  10  generates the control signal u such that the error signal e detected by the microphone  20  is minimized. Since the actuator  16  outputs the canceling sound based on the control signal u that minimizes the error signal e detected by the microphone  20 , the noise in the vehicle compartment  14  can be suitably canceled out by the canceling sound. In this way, the active noise control device  10  can reduce noise transmitted to an occupant in the vehicle compartment  14 . 
     Incidentally, when the characteristic of the actuator  16  has changed over time or the like, the noise in the vehicle compartment  14  cannot always be cancelled out suitably. As a result of intensive studies, the inventors of the present application have conceived the active noise control device  10  as described below. 
       FIG. 2  is a block diagram illustrating a part of a vehicle equipped with the active noise control device according to the present embodiment. 
     As shown in  FIG. 2 , the active noise control device  10  includes a computation unit  22 , a storage unit  30 , and an output unit  32 . 
     The computation unit  22  may be configured by a processor such as a CPU (Central Processing Unit), a DSP (Digital Signal Processor), or the like. However, the present invention is not limited to this feature. A DDS (Direct Digital Synthesizer), a DCO (Digitally Controlled Oscillator), or the like can be included in the computation unit  22 . In addition, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or the like can be included in the computation unit  22 . 
     The storage unit  30  may be configured by a volatile memory (not illustrated) and a nonvolatile memory (not illustrated). Examples of the volatile memory include, for example, a RAM or the like. Examples of the nonvolatile memory include, for example, a ROM, a flash memory, or the like. Data or the like may be stored, for example, in the volatile memory. Programs, tables, maps, and the like may be stored, for example, in the nonvolatile memory. The storage unit  30  may include a peak frequency storage unit  70 , an abnormality information storage unit  72 , and a table  74 . 
     The output unit  32  may be configured by an output interface circuit or the like. 
     The computation unit  22  includes a control signal generating unit  34 , an identifying unit  24 , a first determination unit  26 , a second determination unit  27 , and a control unit  28 . The control signal generating unit  34 , the identifying unit  24 , the first determination unit  26 , the second determination unit  27 , and the control unit  28  can be realized by the computation unit  22  executing a program stored in the storage unit  30 . 
     The active noise control device  10  may be supplied with the reference signal r. The reference signal r can be supplied from, for example, the acceleration sensor  18  (see  FIG. 1 ), but is not limited thereto. As described above, a signal correlated with the vibration of the vehicle  12  can be appropriately used as the reference signal r. That is, a signal corresponding to the noise can be appropriately used as the reference signal r. 
     As described above, the microphone  20  that detects the residual noise due to interference between the noise and the canceling sound is provided in the vehicle compartment  14  (see  FIG. 1 ). That is, the microphone  20  for detecting the error signal e is provided in the vehicle compartment  14 . 
     As described above, the vehicle compartment  14  (see  FIG. 1 ) is provided with the actuator  16  that outputs a canceling sound based on the control signal u. As examples of the actuator  16 , there may be cited a speaker. 
       FIG. 3  is a block diagram illustrating an example of a control signal generating unit. 
     The control signal generating unit (filter unit)  34  includes an adaptive filter  36 , an acoustic characteristic filter  38 , and a filter coefficient updating unit  40 . 
     The adaptive filter (first adaptive filter)  36  generates a control signal u by performing a filtering process on the reference signal r. As the adaptive filter  36 , for example, an FIR (Finite Impulse Response) filter or the like can be used, but the present invention is not limited to this feature. The filter coefficient W of the adaptive filter  36  is updated by the filter coefficient updating unit  40  as described later. The FIR filter generates the control signal u by performing a convolution operation on the reference signal r. 
     The acoustic characteristic filter  38  corrects the reference signal r by performing a filtering process on the reference signal r according to an acoustic characteristic (transfer characteristic) from the actuator  16  to the microphone  20 . The acoustic characteristic from the actuator  16  to the microphone  20 , that is, a transfer characteristic Ĉ, is obtained in advance. 
     The filter coefficient updating unit  40  updates the filter coefficient W of the adaptive filter  36  based on the error signal e acquired by detecting the residual noise by the microphone  20  and the reference signal r corrected by the acoustic characteristic filter  38 . More specifically, the filter coefficient updating unit  40  updates the filter coefficient W of the adaptive filter  36  such that the error signal e acquired by detecting the residual noise by the microphone  20  is minimized. When the filter coefficient W is updated, for example, a filtered-X LMS algorithm can be used, but the present invention is not limited to this feature. 
     In this manner, the adaptive filter  36  generates a control signal u by performing a filtering process on the reference signal r corresponding to the noise. As shown in  FIG. 2 , the control signal u generated by the control signal generating unit  34  is supplied to the actuator  16  via a power amplifier  15 . 
     The identifying unit  24  identifies a peak frequency (resonance frequency) f0 in an impedance frequency characteristic that is a frequency characteristic of the impedance of the actuator  16 . 
       FIG. 4  is a block diagram illustrating an example of an identifying unit. 
     The identifying unit  24  shown in  FIG. 4  includes a voltage detecting unit  46 , a current detecting unit  48 , an impedance frequency characteristic calculating unit  50 , and a peak frequency identifying unit  52 . 
     The voltage detecting unit  46  detects a voltage signal Vspk which is a time waveform signal of a voltage applied to the actuator  16 . As shown in  FIG. 2 , the time waveform signal of the voltage supplied from the power amplifier  15  to the actuator  16  is also supplied to the active noise control device  10 . That is, the voltage signal Vspk is also supplied to the active noise control device  10 . The voltage detecting unit  46  detects the voltage signal Vspk thus supplied. 
     The current detecting unit  48  detects a current signal Ispk which is a time waveform signal of a current consumed in the actuator  16 . As shown in  FIG. 2 , a current detector  17  that detects a current consumed by the actuator  16  is connected to the actuator  16 . The current detector  17  detects a current consumed in the actuator  16  and supplies a current signal Ispk, which is a time waveform signal of the current, to the active noise control device  10 . The current detecting unit  48  detects the current signal Ispk supplied from the current detector  17 . 
     The impedance frequency characteristic calculating unit  50  calculates an impedance frequency characteristic of the actuator  16  based on the voltage signal Vspk and the current signal Ispk. More specifically, the impedance frequency characteristic calculating unit  50  calculates the impedance frequency characteristic of the actuator  16  by performing Fourier transform. 
       FIG. 5  is a graph illustrating examples of impedance frequency characteristics of an actuator. The horizontal axis in  FIG. 5  indicates frequency. The vertical axis in  FIG. 5  indicates the impedance of the actuator  16 . The solid line in  FIG. 5  shows an example of the impedance frequency characteristic of the actuator  16  in the initial state. The dotted line in  FIG. 5  shows an example of the impedance frequency characteristic of the actuator  16  after the actuator  16  has changed over time. 
     The peak frequency identifying unit  52  identifies a peak frequency f0 by performing frequency analysis on the impedance frequency characteristic calculated by the impedance frequency characteristic calculating unit  50 . That is, the peak frequency identifying unit  52  scans the impedance frequency characteristic calculated by the impedance frequency characteristic calculating unit  50 , and identifies the frequency at which the impedance of the actuator  16  is maximized as the peak frequency f0. Thus, the peak frequency f0 in the impedance frequency characteristic of the actuator  16  is identified. 
       FIG. 6  is a block diagram illustrating another example of the identifying unit. 
     The identifying unit  24  shown in  FIG. 6  includes an impedance characteristic identifying unit  54 , a Fourier transform unit  56 , and the peak frequency identifying unit  52 . 
     The impedance characteristic identifying unit  54  identifies an impedance characteristic of the actuator  16 . 
       FIG. 7  is a block diagram illustrating an example of an impedance characteristic identifying unit. 
     The impedance characteristic identifying unit  54  includes an adaptive filter  60 , a filter coefficient updating unit  62 , and a calculator  64 . 
     The adaptive filter (second adaptive filter)  60  outputs a simulated voltage signal Vspk′ by performing a filtering process on a current signal Ispk that is a time waveform signal of a current consumed in the actuator  16 . The filter coefficient Wspk of the adaptive filter  60  is different from the filter coefficient W of the adaptive filter  36 . Therefore, the filtering process performed by the adaptive filter  60  is different from the filtering process performed by the adaptive filter  36  described above. 
     The calculator  64  calculates a difference between the voltage signal Vspk, which is a time waveform signal of the voltage applied to the actuator  16 , and the simulated voltage signal Vspk′. The calculation result of the calculator  64  is supplied to the filter coefficient updating unit  62 . 
     The filter coefficient updating unit  62  updates the filter coefficients Wspk of the adaptive filter  60  so as to minimize the difference between the simulated voltage signal Vspk′ and the voltage signal Vspk, which is a time waveform signal of the voltage applied to the actuator  16 . 
     Thus, the filter coefficient Wspk of the adaptive filter  60  becomes a value corresponding to the impedance characteristic of the actuator  16 . That is, the impedance characteristic of the actuator  16  is identified by the impedance characteristic identifying unit  54 . 
     The Fourier transform unit  56  performs the Fourier transform on the adaptive filter  60  to obtain an impedance frequency characteristic of the actuator  16 . That is, the Fourier transform unit  56  obtains the impedance frequency characteristic of the actuator  16  by performing the Fourier transform on the adaptive filter  60  having the filter coefficient Wspk corresponding to the impedance characteristic of the actuator  16 . 
     The peak frequency identifying unit  52  identifies the peak frequency f0 by frequency analyzing the impedance frequency characteristic obtained by the Fourier transform unit  56 . That is, the peak frequency identifying unit  52  scans the impedance frequency characteristic calculated by the Fourier transform unit  56 , and identifies a frequency at which the impedance of the actuator  16  is maximized as the peak frequency f0. Thus, the peak frequency f0 in the impedance frequency characteristic of the actuator  16  is identified. As described above, the peak frequency f0 in the impedance frequency characteristic may be obtained using the adaptive filter  60 . 
     An initial peak frequency f0org, which is a peak frequency in the impedance frequency characteristic in an initial period, is stored in advance in the peak frequency storage unit  70 . The initial period is a period before the actuator  16  is changed over time. Specifically, the initial period may be, for example, a period when the active noise control device  10  was installed on the vehicle  12 , but is not limited thereto. The initial peak frequency f0org may be measured, for example, when the active noise control device  10  was installed on the vehicle  12 , but is not limited thereto. 
     The first determination unit  26  determines whether or not the difference between the peak frequency f0 currently identified by the identifying unit  24  and the initial peak frequency f0org stored in the peak frequency storage unit  70  is greater than or equal to a threshold value TH. 
     The control unit  28  performs the following control, when the first determination unit  26  determines that the difference between the peak frequency f0 currently identified by the identifying unit  24  and the initial peak frequency f0org stored in the peak frequency storage unit  70  is greater than or equal to the threshold value TH. That is, in such a case, the characteristic of the control signal u generated by the control signal generating unit  34  is changed. 
     The characteristic of the control signal u can be performed by switching the acoustic characteristic Ĉ applied to the acoustic characteristic filter  38 , but is not limited thereto. 
       FIG. 8  is a diagram illustrating an example of a table. As shown in  FIG. 8 , the table  74  stores a plurality of acoustic characteristics Ĉ corresponding to the respective peak frequencies f0. The reference character Ĉ0 denotes an acoustic characteristic when the peak frequency is f00. The reference character Ĉ1 denotes an acoustic characteristic when the peak frequency is f01. The reference character Ĉn denotes an acoustic characteristic when the peak frequency is f0n. The reference character f0 is used when describing a peak frequency in general, and the reference signs f00 to f0n are used when describing individual peak frequencies. The reference character Ĉ is used when describing an acoustic characteristic in general. The reference characters Ĉ0 to Ĉn are used when describing individual acoustic characteristics. 
     The control unit  28  can change the characteristic of the control signal u generated by the control signal generating unit  34 , by appropriately switching according to the peak frequency f0 the acoustic characteristics Ĉ applied by the acoustic characteristic filter  38 . That is, the control unit  28  reads out the acoustic characteristic Ĉ corresponding to the current peak frequency f0 from the table  74 , and applies the acoustic characteristic Ĉ read out from the table  74  to the acoustic characteristic filter  38 . In this way, the characteristic of the control signal u generated by the control signal generating unit  34  is changed. 
     The second determination unit  27  can determine whether or not the peak frequency f0 is within a predetermined range of frequency. 
     When the second determination unit  27  determines that the peak frequency f0 is not within the predetermined range of frequency, the control unit  28  causes the control signal generating unit  34  to stop generating the control signals u. That is, when the peak frequency f0 changes significantly, the control unit  28  stops the generation of the control signal u by the control signal generating unit  34 . 
     When the second determination unit  27  determines that the peak frequency f0 is not within the predetermined range of frequency, the control unit  28  stores in the abnormality information storage unit  72 , information indicating that an abnormality has occurred in the characteristic of the actuator  16 . 
     When the second determination unit  27  determines that the peak frequency f0 is not within the predetermined range of frequency, the control unit  28  causes an information display device  68  provided in the vehicle  12  to display information indicating that the abnormality has occurred in the characteristic of the actuator  16 . 
     The output unit  32  notifies a failure diagnosis device  66  of information indicating that the abnormality has occurred in the characteristic of the actuator  16 . When the failure diagnosis device  66  is connected to the vehicle  12 , the control unit  28  notifies the failure diagnosis device  66  of information indicating that the abnormality has occurred in the characteristic of the actuator  16  via the output unit  32 . 
       FIG. 9  is a flowchart illustrating an example of operations of the active noise control device according to the present embodiment. 
     In step S 1 , the identifying unit  24  identifies the peak frequency f0 in the impedance frequency characteristic of the actuator  16 . Thereafter, the process transitions to step S 2 . 
     In step S 2 , the first determination unit  26  determines whether or not the difference between the peak frequency f0 currently identified by the identifying unit  24  and the initial peak frequency f0org stored in the peak frequency storage unit  70  is greater than or equal to the threshold value TH. When the difference is greater than or equal to the threshold value TH (YES in step S 2 ), the process proceeds to step S 3 . When the difference is less than the threshold value TH (NO in step S 2 ), the process shown in  FIG. 9  is completed. 
     In step S 3 , the control unit  28  changes the characteristic of the control signal u. As described above, the characteristic of the control signal u can be changed by switching the acoustic characteristics Ĉ applied to the acoustic characteristic filter  38 , but is not limited to this. Upon carrying out these steps, the process shown in  FIG. 9  is brought to an end. 
       FIG. 10  is a flowchart illustrating an example of operations of the active noise control device according to the present embodiment. 
     In step S 11 , the second determination unit  27  determines whether or not the peak frequency f0 is within a predetermined range of frequency. When the peak frequency f0 is not within the predetermined range of frequency (NO in step S 11 ), the process transitions to step S 12 . If the peak frequency f0 is within the predetermined range of frequency (YES in step S 11 ), the process shown in  FIG. 10  is completed. 
     In step S 12 , the control unit  28  stops generating the control signal u by the control signal generating unit  34 . Thereafter, the process proceeds to step S 13 . 
     In step S 13 , the control unit  28  stores information indicating that an abnormality has occurred in the characteristic of the actuator  16  in the abnormality information storage unit  72 . Thereafter, the process transitions to step S 14 . 
     In step S 14 , the control unit  28  causes the information display device  68  provided in the vehicle  12  to display information indicating that the abnormality has occurred in the characteristic of the actuator  16 . Upon carrying out these steps, the process shown in  FIG. 10  is brought to an end. 
     As described above, in the present embodiment, it is determined whether or not the difference between the peak frequency f0 currently identified by the identifying unit  24  and the initial peak frequency f0org stored in the peak frequency storage unit  70  is greater than or equal to a threshold value TH. When it is determined that the difference is greater than or equal to the threshold value TH, the characteristic of the control signal u generated by the control signal generating unit  34  is changed. Consequently, according to the present embodiment, it is possible to provide the active noise control device  10  that is capable of suitably canceling noise in the vehicle compartment  14  even when a change occurs in the characteristic of the actuator  16  due to a change over time or the like, and thus capable of suitably reducing noise. 
     Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made thereto without departing from the essence and gist of the present invention. 
     The above-described embodiments can be summarized in the following manner. 
     The active noise control device ( 10 ) causes the actuator ( 16 ) to output the canceling sound based on the control signal (u) in order to reduce noise in the vehicle compartment ( 14 ) of the vehicle ( 12 ), and includes the control signal generating unit ( 34 ) including the first adaptive filter ( 36 ) configured to generate the control signal by performing a filtering process on the reference signal (r) corresponding to the noise, the identifying unit ( 24 ) configured to identify the peak frequency (f0) in an impedance frequency characteristic that is a frequency characteristic of impedance of the actuator, the peak frequency storage unit ( 70 ) configured to store the initial peak frequency (f0org) that is the peak frequency in the impedance frequency characteristic in an initial state, the first determination unit ( 26 ) configured to determine whether or not a difference between the peak frequency currently identified by the identifying unit and the initial peak frequency stored in the peak frequency storage unit is greater than or equal to the threshold value (TH), and the control unit ( 28 ) configured to change a characteristic of the control signal generated by the control signal generating unit when the first determination unit determines that the difference is greater than or equal to the threshold value. According to such a configuration, when the difference becomes equal to or greater than the threshold value due to a change over time or the like, the characteristic of the control signal generated by the control signal generating unit is changed. Consequently, according to such a configuration, it is possible to provide an active noise control device that is capable of suitably canceling noise in the vehicle compartment even in a case where a change occurs in the characteristic of the actuator due to a change over time or the like, and thus capable of suitably reducing noise. 
     The identifying unit may include the voltage detecting unit ( 46 ) configured to detect a voltage signal (Vspk) that is a time waveform signal of a voltage applied to the actuator, the current detecting unit ( 48 ) configured to detect the current signal (Ispk) that is a time waveform signal of a current consumed by the actuator, the impedance frequency characteristic calculating unit ( 50 ) configured to calculate the impedance frequency characteristic based on the voltage signal and the current signal, and the peak frequency identifying unit ( 52 ) configured to identify the peak frequency by performing frequency analysis on the impedance frequency characteristic. According to such a configuration, the peak frequency can be identified based on the impedance frequency characteristic. 
     The identifying unit may include the impedance characteristic identifying unit ( 54 ) configured to calculate an impedance characteristic of the actuator, wherein the impedance characteristic identifying unit includes the second adaptive filter ( 60 ) configured to output the simulated voltage signal (Vspk′) by performing a filtering process that is different from the filtering process performed by the first adaptive filter, on a current signal that is a time waveform signal of a current consumed by the actuator, and the second filter coefficient updating unit ( 62 ) configured to update the filter coefficient (Wspk) of the second adaptive filter so as to minimize a difference between the simulated voltage signal and a voltage signal that is a time waveform signal of a voltage applied to the actuator, and the identifying unit further includes the Fourier transform unit ( 56 ) configured to perform a Fourier transform on the second adaptive filter to obtain the impedance frequency characteristic, and a peak frequency identifying unit configured to perform frequency analysis on the impedance frequency characteristic obtained by the Fourier transform unit to identify the peak frequency. 
     The active noise control device may further include the second determination unit ( 27 ) configured to determine whether or not the peak frequency is within a predetermined frequency range, wherein, when the second determination unit determines that the peak frequency is not within the frequency range, the control unit is configured to cause the control signal generating unit to stop generating the control signal. According to such a configuration, since the generation of the control signal is stopped when the peak frequency in the impedance frequency characteristic of the actuator significantly changes, it is possible to prevent an increase in noise or the like caused by a failure, an abnormality, or the like of the actuator. 
     The active noise control device may further include the second determination unit configured to determine whether or not the peak frequency is within a predetermined frequency range, and the abnormality information storage unit ( 72 ) configured to store information indicating that an abnormality has occurred in a characteristic of the actuator when the second determination unit determines that the peak frequency is not within the frequency range. According to such a configuration, information indicating that an abnormality has occurred in the actuator can be used for failure diagnosis or the like. 
     When the second determination unit determines that the peak frequency is not within the frequency range, the control unit ( 28 ) may be configured to cause the information display device ( 68 ) provided at the vehicle to display information indicating that the abnormality has occurred in the characteristic of the actuator. According to this configuration, since the information indicating that an abnormality has occurred in the characteristic of the actuator can be displayed on the information display device, the user can notice that an abnormality has occurred in the characteristic of the actuator based on the display of the information display device. 
     The active noise control device may further include the output unit ( 32 ) configured to notify the failure diagnosis device ( 66 ) of information indicating that the abnormality has occurred in the characteristic of the actuator. According to this configuration, since the information indicating that an abnormality has occurred in the characteristic of the actuator can be supplied to the failure diagnosis device, an accurate failure diagnosis can be performed by the failure diagnosis device. 
     The active noise control device may further include the table ( 74 ) containing the plurality of acoustic characteristics (Ĉ) corresponding to the respective peak frequencies, the acoustic characteristic filter ( 38 ) configured to correct the reference signal by performing a filtering process on the reference signal in accordance with any of the acoustic characteristics contained in the table, and the first filter coefficient updating unit ( 40 ) configured to update the filter coefficient (W) of the first adaptive filter, based on the error signal (e) acquired by detecting residual noise due to interference between the noise and the canceling sound by the microphone ( 20 ) and the reference signal corrected by the acoustic characteristic filter, wherein the control unit may be configured to change the characteristic of the control signal generated by the control signal generating unit, by switching the acoustic characteristics applied to the acoustic characteristic filter according to the peak frequencies. According to such a configuration, since the acoustic characteristic in the acoustic characteristic filter is switched in accordance with the peak frequency, the characteristic of the control signal can be accurately changed without requiring complicated signal processing. That is, according to such a configuration, it is possible to prevent the control of the vibration of the noise from becoming unstable, and it is possible to suitably reduce the noise. 
     The actuator may be a speaker. 
     The vehicle includes an active noise control device as described above.