Patent Publication Number: US-2023146577-A1

Title: Storage medium, microphone, and engine speed acquisition device

Description:
TECHNICAL FIELD 
     The present invention relates to an active acoustic control program for causing an operation processing device to execute a process of generating a control signal for outputting a canceling sound from a speaker provided in a vehicle compartment in order to reduce noise in the vehicle compartment, a microphone for detecting a cancellation error noise used when causing the operation processing device to execute the process in accordance with the active acoustic control program, and an engine rotational speed acquisition device for detecting an engine rotational speed used when causing the operation processing device to execute the process in accordance with the active acoustic control program. 
     BACKGROUND ART 
     JP 2012-131244 A discloses that a portable terminal is used as an active acoustic control device. An active acoustic control program is installed on the portable terminal. In addition, the portable terminal downloads a transfer characteristic of noise suitable for a vehicle from a server. 
     SUMMARY OF THE INVENTION 
     JP 2012-131244 A does not discuss a technique capable of reducing noise in a vehicle compartment, regardless of the type of a vehicle, by installing an active acoustic control program on a device that is readily available to anyone. 
     The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an active acoustic control program that can reduce noise in a vehicle compartment, regardless of the type of a vehicle, by installing on a device that is readily available to anyone. Also, another object of the present invention is to provide a microphone that detects cancellation error noise used when causing the operation processing device to execute the process in accordance with the active acoustic control program, and an engine rotational speed acquisition device that detects an engine rotational speed used when causing the operation processing device to execute the process in accordance with the active acoustic control program. 
     An active acoustic control program according to a first aspect of the present invention is downloaded using a communication device that transmits and receives data to and from a server. The active acoustic control program causes an operation processing device to execute a process of generating a control signal that causes a speaker provided in a vehicle compartment of a vehicle to output a canceling sound in order to reduce noise in the vehicle compartment, and the active acoustic control program includes a basic signal generating unit configured to generate a basic signal corresponding to the noise generated from a noise source, an adaptive notch filter configured to adaptively perform signal processing on the basic signal to generate the control signal, an error signal input unit configured to input an error signal corresponding to a cancellation error noise of the noise and the canceling sound output from the speaker based on the control signal, an identifying unit configured to identify a transfer characteristic of a sound in a space of the vehicle compartment to generate a correction value, a reference signal generating unit configured to generate a reference signal by correcting the basic signal based on the correction value, and a filter coefficient updating unit configured to sequentially update a filter coefficient of the adaptive notch filter based on the error signal and the reference signal in a manner that the error signal is minimized. 
     A second aspect of the present invention is a microphone that detects the cancellation error noise used when causing the operation processing device to execute the process in accordance with the active acoustic control program according to the first aspect above, wherein the microphone is connected by wire or wirelessly to a device on which the active sound control program downloaded using the communication device is installed, and the microphone is detachably mounted in the vehicle compartment. 
     A third aspect of the present invention is an engine rotational speed acquisition device that acquires a engine rotational speed used when causing the operation processing device to execute the process in accordance with the active acoustic control program according to the first aspect above, wherein the engine rotational speed acquisition device is connected by wire or wirelessly to the device, and is detachably mounted in the vehicle compartment. 
     According to the present invention, it is possible to reduce noise in the vehicle compartment, regardless of the type of the vehicle, by installing the active acoustic control program on the device that is readily available to anyone. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating an overview of active acoustic control; 
         FIG.  2    is a block diagram of a smartphone and an in-vehicle system; 
         FIGS.  3 A and  3 B  are diagrams showing examples of installation positions of microphones in a vehicle compartment; 
         FIG.  4    is a block diagram of an active acoustic control device; 
         FIG.  5    is a block diagram of the active acoustic control device; 
         FIG.  6    is a table indicating orders of components of vibration frequency corresponding to the number of cylinders of an engine. 
         FIG.  7    is a table showing values of control filter coefficients corresponding to respective predetermined frequencies; 
         FIG.  8 A  is a flowchart illustrating the flow of an active noise control process; 
         FIG.  8 B  is a flowchart illustrating the flow of a setting process; 
         FIG.  8 C  is a flowchart illustrating the flow of the setting process; 
         FIG.  8 D  is a flowchart illustrating the flow of the setting process; 
         FIG.  9    is a diagram illustrating a smartphone; 
         FIG.  10    is a diagram illustrating the smartphone; 
         FIG.  11    is a diagram illustrating the smartphone; 
         FIG.  12    is a diagram illustrating the smartphone; 
         FIG.  13    is a diagram illustrating the smartphone; 
         FIG.  14    is a diagram illustrating the smartphone; 
         FIG.  15    is a diagram illustrating the smartphone; 
         FIG.  16    is a diagram illustrating the smartphone; 
         FIG.  17    is a block diagram of an active acoustic control device; 
         FIG.  18    is a block diagram of an active acoustic control device; 
         FIG.  19 A ,  FIG.  19 B , and  FIG.  19 C  are diagrams illustrating examples of installation positions of microphones in a vehicle compartment; 
         FIG.  20    is an image diagram of active noise control; 
         FIG.  21    is a block diagram of a smartphone, an in-vehicle system, and a vehicle information acquisition device; 
         FIGS.  22 A and  22 B  are diagrams showing examples of installation positions of the vehicle information acquisition device in the vehicle compartment; 
         FIG.  23    is a block diagram of a smartphone and an in-vehicle system; and 
         FIG.  24    is a block diagram of an active acoustic control device. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     First Embodiment 
       FIG.  1    is a diagram illustrating an overview of active acoustic control performed by an active acoustic control device  10 . 
     The active acoustic control device  10  outputs a canceling sound from a speaker  16  provided in a vehicle compartment  14  of a vehicle  12 , and reduces engine muffled sounds (hereinafter referred to as noise) transmitted to vehicle occupant in the vehicle compartment  14  due to vibration of an engine  18 . The active acoustic control device  10  generates a control signal u 0  for outputting a canceling sound from the speaker  16  based on an error signal e corresponding to a sound collected by a microphone  20  provided in the vehicle compartment  14  and an engine rotational speed Ne detected by an engine rotational speed sensor  19 . The error signal e is a signal corresponding to a cancellation error noise in which the canceling sound and the noise are combined at a position of the microphone  20 . The engine  18  corresponds to a drive source of the present invention, and the engine rotational speed sensor  19  corresponds to an engine rotational speed acquisition device of the present invention. 
       FIG.  2    is a block diagram of a smartphone  22  and an in-vehicle system  24  installed in the vehicle  12 . 
     The smartphone  22  downloads an active acoustic control program from a server  26  via the Internet  28 . The downloaded active acoustic control program is installed on the smartphone  22 . The smartphone  22  corresponds to a communication device of the present invention. 
     The smartphone  22  has two terminals, i.e., an external connection terminal and an earphone/microphone terminal (neither of which is shown), as terminals to be connected to an external device. The smartphone  22  is connected to the in-vehicle system  24  and the microphone  20  by wire, and is connected to the engine rotational speed sensor  19  by air (wirelessly). 
     In the case that the smartphone  22  is connected to the engine rotational speed sensor  19  by wire, the smartphone  22  may be connected to the in-vehicle system  24  wirelessly. In addition, in recent years, some smartphones  22  do not have an earphone/microphone terminal, and in this case, the microphone  20  may also be connected wirelessly. 
     The engine rotational speed sensor  19  is connected to an on-board diagnostics (OBD) connector  112  provided in the vehicle  12 . The OBD connector  112  is connected to an in-vehicle ECU via a CAN or a K line. From the OBD connector  112 , vehicle information such as an engine rotational speed, a water temperature, a voltage, and a boost pressure can be acquired from the OBD connector. 
     The engine rotational speed sensor  19  may be connected to the in-vehicle system  24  by wire such as USB. In this case, the engine rotational speed sensor  19  acquires information on the engine rotational speed flowing through the CAN via the in-vehicle system  24 . 
     Further, the engine rotational speed sensor  19  need not necessarily be provided, but the smartphone  22  may estimate the engine rotational speed based on a DC voltage variation of the vehicle  12  for charging the smartphone  22  or the like. 
     The microphone  20  is installed in the vehicle compartment  14  such that it is easily detachable by a user.  FIGS.  3 A and  3 B  are views showing an example of the installation position of the microphone  20  in the vehicle compartment  14 . If the vehicle  12  is a right-hand drive vehicle, the microphone  20  is fixed to the left side surface (vehicle center side) of a headrest  15   a  of a driver&#39;s seat  15  with a double-sided tape or the like, as shown in  FIG.  3 A . 
     The position where the microphone  20  is set is not limited to the position shown in  FIG.  3 A . For example, as shown in  FIG.  3 B , the microphone  20  may be fixed to the left side surface (vehicle center side) of a seat back  15   b  of the driver&#39;s seat  15  by a double-sided tape or the like. If the automobile  12  is a left-hand drive vehicle, the microphone  20  is provided on a right side surface of the headrest  15   a  or the seat back  15   b  of the driver&#39;s seat  15 . 
     Returning to  FIG.  2   , the smartphone  22  includes an operation processing device  29 , a memory  30 , a storage  31 , a microphone  32 , a display  34 , a touch panel  36 , an acceleration sensor  37 , a mobile communication module  38 , a wireless LAN communication module  40 , and a short-range (near field) wireless communication module  42 . The acceleration sensor  37  corresponds to an acceleration detecting unit according to the present invention. 
     The operation processing device  29  is, for example, a processor such as a central processing unit (CPU) or a microprocessing unit (MPU). The memory  30  is, for example, a non-transitory or transitory tangible computer-readable recording medium such as a ROM or a RAM. The storage  31  is, for example, a non-transitory tangible computer-readable recording medium such as a hard disk or a solid state drive (SSD). 
     When the active acoustic control program is installed on the smartphone  22 , the active acoustic control program is stored in the storage  31 . The smartphone  22  functions as the active acoustic control device  10  when the operation processing device  29  performs active acoustic control processing in accordance with the active acoustic control program stored in the storage  31 . 
     The microphone  32  collects sounds around the smartphone  22 . The display  34  is, for example, a display device using liquid crystal, organic electroluminescence (organic EL), or the like. The touch panel  36  is a pointing device that detects a position on the display  34  touched by a user&#39;s finger or the like. The acceleration sensor  37  detects the acceleration acting on the smartphone  22 . When the smartphone  22  is in the vehicle compartment  14 , the acceleration detected by the acceleration sensor  37  can be regarded as the acceleration of the vehicle  12 . 
     The mobile communication module  38  is a module that communicates with a base station  28   a  connected to the Internet  28  by cellular communication. The wireless LAN communication module  40  is a module that communicates with an access point  28   b  connected to the Internet  28  by wireless LAN communication such as Wi-Fi (registered trademark). Thus, the smartphone  22  can transmit and receive data to and from the server  26  via the Internet  28 . The short-range wireless communication module  42  is a module that communicates with the in-vehicle system  24  by short-range wireless communication such as Bluetooth (registered trademark). 
     The in-vehicle system  24  includes an operation processing device  43 , a memory  44 , a sound source  45 , a display  46 , a touch panel  48 , a short-range wireless communication module  50 , and an amplifier  53 . 
     The operation processing device  43  is, for example, a processor such as a central processing unit (CPU) or a microprocessing unit (MPU). The memory  44  is a non-transitory or transitory tangible computer-readable recording medium such as a ROM or a RAM. The sound source  45  is, for example, a non-transitory tangible computer-readable recording medium such as a hard disk or a solid state drive (SSD), and stores information such as music or guidance voices for car navigation. 
     The display  46  is, for example, a display device using liquid crystal, organic electroluminescence (organic EL), or the like. The touch panel  48  is a pointing device that detects a position on the display  46  touched by a user&#39;s finger or the like. The short-range wireless communication module  50  is, for example, a module that communicates with the engine rotational speed sensor  19 , the smartphone  22 , and the like by short-range wireless communication such as Bluetooth (registered trademark). Instead of wireless communication, wired communication such as USB may be used for communication with the engine rotational speed sensor  19 , the smartphone  22 , and the like. 
     The in-vehicle system  24  is connected to the speaker  16  via the amplifier  53 . The in-vehicle system  24  and the speaker  16  are connected by wire. The in-vehicle system  24  and the speaker  16  may be wirelessly connected to each other. The operation processing device  43  outputs a sound source signal for outputting music or voices stored in the sound source  45  from the speaker  16 . The sound source signal is amplified by the amplifier  53  and output to the speaker  16 . The operation processing device  43  transmits the control signal u 0  transmitted from the smartphone  22  (active acoustic control device  10 ) to the amplifier  53 . The control signal u 0  may be directly transmitted from the smartphone  22  (active acoustic control device  10 ) to the amplifier  53 . The control signal u 0  is amplified by the amplifier  53  and output to the speaker  16 . Thus, the canceling sound for canceling the noise is output from the speaker  16  together with the music and voices of the sound source. 
     [Active Acoustic Control Device] 
       FIGS.  4  and  5    are block diagrams of the active acoustic control device  10 . In the active acoustic control device  10 , a SAN (Single-frequency Adaptive Notch) filter, which is a notch filter, is used as an adaptive digital filter. A filtered-X LMS (Least Mean Square) algorithm is used to update the coefficients of the SAN filter. The active acoustic control device  10  according to the present embodiment performs active noise control as active acoustic control. Before performing an active noise control process (hereinafter referred to as an ANC processing), the active acoustic control device  10  of the present embodiment performs identification processing of identifying a transfer characteristic C (hereinafter referred to as a secondary path transfer characteristic C) of sound in a transfer path (hereinafter referred to as a secondary path) from the speaker  16  to the microphone  20 . Hereinafter, the active noise control performed by the active acoustic control device  10  of the present embodiment will be referred to as active noise control of a prior identification type. Note that the transfer path from the speaker  16  to the microphone  20  is referred to as a secondary path, whereas the transfer path from the engine  18  to the microphone  20  is referred to as a primary path below. 
       FIG.  4    shows a block diagram of the active acoustic control device  10  during the ANC process.  FIG.  5    shows a block diagram of the active acoustic control device  10  during the identification process. The active acoustic control device  10  switches between the ANC processing and the identification processing by a processing switching unit  51 . 
     (ANC Processing) 
     Signal processing performed by the active acoustic control device  10  during the ANC processing will be described with reference to  FIG.  4   . The active acoustic control device  10  includes a basic signal generating unit  52 , a control signal generating unit  54 , an error signal input unit  56 , a reference signal generating unit  58 , and a control filter coefficient updating unit  60 . The control signal generating unit  54  corresponds to an adaptive notch filter of the present invention, and the control filter coefficient updating unit  60  corresponds to a filter coefficient updating unit and an identifying unit according to the present invention. 
     The basic signal generating unit  52  generates basic signals xc and xs based on the engine rotational speed Ne. The basic signal generating unit  52  includes a frequency detecting circuit  52   a , a cosine signal generator  52   b , and a sine signal generator  52   c.    
     The frequency detecting circuit  52   a  detects a vibration frequency f that is a fundamental frequency of noise (muffled sound) generated in synchronization with rotation of an output shaft of the engine  18 . The muffled sound of the engine  18  is a vibration radiation sound generated by transmitting an exciting force generated by the rotation of the engine  18  to the vehicle body, and thus is a vibration noise having a remarkable frequency characteristic synchronized with the rotational speed of the engine  18 . For example, in the case where the engine  18  is a 4-cycle 4-cylinder engine, an excitation vibration with the engine  18  as a base point occurs, due to a torque fluctuation caused by gas combustion occurring every ½ rotation of the output shaft of the engine  18 . As a result, noise is generated in the vehicle compartment  14 . 
     The vibration frequency f is detected based on the engine rotational speed Ne. The engine rotational speed Ne can be converted into a rotational frequency fe by a following equation. 
         fe [Hz]= Ne [rpm]/60 [sec] 
     For example, in the case that the engine rotational speed Ne is 6000 [rpm], the rotational frequency fe is 100 [Hz]. 
     In the case that the engine  18  is a four-cycle engine, ignition is performed once per two rotations in each cylinder. For example, if the engine rotational speed Ne is 6000 [rpm] in the four-cylinder engine  18 , the vibration frequency f is as follows. 
     
       
         
           
             
               f 
               [ 
               Hz 
               ] 
             
             = 
             
               
                 
                   100 
                   [ 
                   Hz 
                   ] 
                 
                 × 
                 
                   1 
                   2 
                 
                 × 
                 4 
               
               = 
               
                 2 
                 ⁢ 
                 0 
                 ⁢ 
                 0 
               
             
           
         
       
     
     That is, the vibration frequency f of the four-cylinder engine  18  has a secondary component of the rotational frequency fe.  FIG.  6    is a table showing orders of components of the vibration frequency f corresponding to the number of cylinders of the engine  18 . The vibration frequency f can be obtained by multiplying the rotational frequency fe by an order corresponding to the number of cylinders of the engine  18 . 
     The cosine signal generator  52   b  generates a basic signal xc (=cos(2πft)) which is a cosine signal of the vibration frequency f. The sine signal generator  52   c  generates a basic signal xs (=sin(2πft)), which is a sine signal of the vibration frequency f. Here, t denotes time. 
     The control signal generating unit  54  generates a control signal u 0  based on the basic signals xc and xs. The control signal generating unit  54  corresponds to an adaptive notch filter according to the present invention. The control signal generating unit  54  includes a first control filter  54   a , a second control filter  54   b , and an adder  54   c.    
     In the control signal generating unit  54 , a SAN filter is used as a control filter. 
     The first control filter  54   a  has a filter coefficient W 0 . The second control filter  54   b  has a filter coefficient W 1 . The filter coefficients W 0  and W 1  are optimized by being adaptively updated by the control filter coefficient updating unit  60  described later. 
     The basic signal xc filtered by the first control filter  54   a  and the basic signal xs filtered by the second control filter  54   b  are added by the adder  54   c  to generate the control signal u 0 . The speaker  16  is controlled based on the control signal u 0 , and the canceling sound is output from the speaker  16 . 
     The reference signal generating unit  58  generates reference signals r 0  and r 1  based on the basic signals xc and xs. The reference signal generating unit  58  includes a first secondary path filter  58   a , a second secondary path filter  58   b , a third secondary path filter  58   c , a fourth secondary path filter  58   d , an adder  58   e , and an adder  58   f.    
     In the reference signal generating unit  58 , a notch filter is used as a secondary path filter. A coefficient C{circumflex over ( )} of the secondary path filter (hereinafter, referred to as a secondary path filter coefficient C{circumflex over ( )}) is obtained in an identification processing described below. 
     The first secondary path filter  58   a  has a secondary path filter coefficient C 0 {circumflex over ( )} that is a real part of the secondary path filter coefficient C{circumflex over ( )} (=C 0 {circumflex over ( )}+iC 1 {circumflex over ( )}). The second secondary path filter  58   b  has a filter coefficient −C 1 {circumflex over ( )} obtained by inverting the polarity of the imaginary part of the secondary path filter coefficient C{circumflex over ( )}. The third secondary path filter  58   c  has filter a coefficient C 0 {circumflex over ( )} which is a real part of the secondary path filter coefficient C{circumflex over ( )}. The fourth secondary path filter  58   d  has a filter coefficient C 1 {circumflex over ( )} which is an imaginary part of the secondary path filter coefficient C{circumflex over ( )}. 
     The basic signal xc filtered by the first secondary path filter  58   a  and the basic signal xs filtered by the second secondary path filter  58   b  are added by the adder  58   e  to generate a reference signal r 0 . The basic signal xs filtered by the third secondary path filter  58   c  and the basic signal xc filtered by the fourth secondary path filter  58   d  are added by the adder  58   f  to generate a reference signal r 1 . 
     That is, by the reference signal generating unit  58 , the reference signals r 0  and r 1  are generated by correcting the basic signals xc and xs based on the secondary path filter coefficient C{circumflex over ( )} that is the correction value. 
     The error signal input unit  56  inputs the error signal e corresponding to the cancellation error noise collected by the microphone  20 . The cancellation error noise is a sound obtained by synthesizing the noise d input to the microphone  20  and the canceling sound y input to the microphone  20 . The error signal input unit  56  may input the error signal e corresponding to the cancellation error noise collected by the microphone  32  mounted on the smartphone  22 . 
     The control filter coefficient updating unit  60  updates the filter coefficients W 0  and W 1  of the control signal generating unit  54  based on the reference signals r 0  and r 1  and the error signal e. The control filter coefficient updating unit  60  adaptively updates the filter coefficients W 0  and W 1  based on the filtered-X LMS algorithm. The control filter coefficient updating unit  60  includes a first control filter coefficient updating unit  60   a  and a second control filter coefficient updating unit  60   b.    
     The first control filter coefficient updating unit  60   a  and the second control filter coefficient updating unit  60   b  update the filter coefficients W 0  and W 1  based on the following equations. In the equations, n denotes a time step (n=0, 1, 2, . . . ), and μ0 and μ1 denote step size parameters. 
         W 0( n+ 1)= W 0( n )−μ0× e ( n )×{ C 0{circumflex over ( )}( n )× xc ( n )− C 1{circumflex over ( )}( n )× xs ( n )}
 
         W 1( n+ 1)= W 1( n )−μ1× e ( n )×{ C 0{circumflex over ( )}( n )× xs ( n )+ C 1{circumflex over ( )}( n )× xc ( n )}
 
     The filter coefficients W 0  and W 1  are optimized by repeatedly updating the filter coefficients W 0  and W 1  by the control filter coefficient updating unit  60 . In the active acoustic control device  10  using the SAN filter, the update equations for the filter coefficients W 0  and W 1  are configured by four arithmetic operations and do not include a convolution operation. Therefore, it is possible to suppress a computational load due to update processing of filter coefficients W 0  and W 1 . 
     (Identification Processing) 
     Signal processing performed during the identification processing by the active acoustic control device  10  will be described with reference to  FIG.  5   . 
     In the identification processing, identification sounds of predetermined frequencies fm (=f 0 , f 1 , . . . , fm−1) are output from the speaker  16 , and the secondary path transfer characteristic C at that time is identified. White noise, pink noise, or sine sweep is used as an identification sound. 
     In the identification processing, the secondary path transfer characteristic C of each predetermined frequency fm is identified as a secondary path filter coefficient C{circumflex over ( )}. The identification processing is performed when the engine  18  is stopped. During the identification processing, the filter coefficient of the first secondary path filter  58   a  is fixed to 1, the filter coefficient of the second secondary path filter  58   b  is fixed to 0, the filter coefficient of the third secondary path filter  58   c  is fixed to 1, and the filter coefficient of the fourth secondary path filter  58   d  is fixed to 0. 
     The frequency detecting circuit  52   a  outputs predetermined frequencies fm (=f 0 , f 1 , . . . , fm−1). The cosine signal generator  52   b  generates the basic signal xc which is a cosine signal having the predetermined frequency fm. The sine signal generator  52   c  generates the basic signal xs which is a sine signal having the predetermined frequency fm. 
     The basic signal xc is output as an identification signal x. The speaker  16  is controlled based on the identification signal x and an identification sound is output from the speaker  16 . 
     The error signal input unit  56  inputs a noise signal xC corresponding to the identification sound collected by the microphone  20 . The noise signal xC is input to an adder  64 . 
     The basic signal xc filtered by the first control filter  54   a  and the basic signal xs filtered by the second control filter  54   b  are added by the adder  54   c  to generate the control signal u 1 . The polarity of the control signal u 1  is inverted by an inverter  62 , and the inverted signal is input to the adder  64 . The adder  64  generates a virtual error signal e′ which is a difference between the noise signal xC and the control signal u 1 . 
     The control filter coefficient updating unit  60  adaptively performs signal processing on the filter coefficients W 0  and W 1  of the control signal generating unit  54  based on the reference signals r 0  and r 1  and the virtual error signal e′. 
     The first control filter coefficient updating unit  60   a  and the second control filter coefficient updating unit  60   b  update the filter coefficients W 0  and W 1  based on the following equations. 
         W 0( n+ 1)= W 0( n )−μ0× e ′( n )× xc ( n )
 
         W 1( n+ 1)= W 1( n )−μ1× e ′( n )× xs ( n )
 
     In the identification processing, the frequency detecting circuit  52   a  sweeps the predetermined frequencies fm, and the control filter coefficient updating unit  60  adaptively updates the filter coefficients W 0  and W 1  for a predetermined time at each of the predetermined frequencies fm. The adaptively updated filter coefficient W 0  is recorded as the filter coefficient C 0 {circumflex over ( )} for each of the predetermined frequencies fm, and the adaptively updated filter coefficient W 1  is recorded as the filter coefficient C 1 {circumflex over ( )} for each of the vibration frequencies f.  FIG.  7    is a table showing values of control filter coefficients C 0 {circumflex over ( )} and C 1 {circumflex over ( )} corresponding to respective predetermined frequencies f 0 , f 1 , . . . , fa−1. The control filter coefficient updating unit  60  during the identification processing corresponds to an identifying unit according to the present invention. 
     [Active Noise Control Processing in Smartphone] 
       FIG.  8 A  is a flowchart showing the flow of active noise control processing in the smartphone  22 . 
     When the active acoustic control program is installed on the smartphone  22 , the active acoustic control application can be used in the smartphone  22 .  FIG.  9    is a diagram illustrating the smartphone  22  in which an initial screen  34   a  is displayed on the display  34 . When the active acoustic control program is installed on the smartphone  22 , an icon  35   a  of the active acoustic control application is displayed in the initial screen  34   a . When the user taps the icon  35   a , the active acoustic control application is activated, and the operation processing device  29  performs active noise control processing. The active noise control processing is repeatedly performed with a predetermined period until an ANC OFF operation, which will be described later, is performed by the user. 
     In step S 1 , the operation processing device  29  displays an ANC ON operation screen  34   b  on the display  34 , and the process proceeds to step S 2 .  FIG.  10    is a diagram illustrating the smartphone  22  in which the ANC ON operation screen  34   b  is displayed on the display  34 . The ANC ON operation screen  34   b  includes an ANC ON button  35   b , a checkbox  35   c , and a setting button  35   r.    
     In step S 2 , the operation processing device  29  determines whether or not a setting operation has been performed by the user. If the setting operation has been performed, the process proceeds to step S 3 , and if the setting operation has not been performed, the process proceeds to step S 4 . If the user taps the setting button  35   r , the operation processing device  29  determines that a setting operation has been performed by the user. 
     In step S 3 , the operation processing device  29  performs setting process to be described later, and the process proceeds to step S 4 . 
     In step S 4 , the operation processing device  29  determines whether or not an ANC ON operation has been performed by the user. If the ANC ON operation has been performed, the process proceeds to step S 5 , and if the ANC ON operation has not been performed, the process returns to step S 2 . If the user taps the ANC ON button  35   b , the operation processing device  29  determines that the ANC ON operation has been performed by the user. 
     In step S 5 , the operation processing device  29  determines whether or not a checkbox to skip identification processing is checked. If the checkbox to skip identification processing is checked, the process proceeds to step S 10 , and if the checkbox to skip identification processing is not checked, the process proceeds to step S 6 . In the ANC ON operation screen  34   b  of  FIG.  10   , if the user taps the checkbox  35   c  to check and then taps the ANC ON button  35   b , the operation processing device  29  determines that the checkbox to skip the identification processing is checked. 
     In step S 6 , the operation processing device  29  performs the identification processing, and the process proceeds to step S 7 . 
     In step S 7 , the operation processing device  29  displays an identification processing notification screen  34   f  on the display  34 , and the process proceeds to step S 8 .  FIG.  11    is a diagram illustrating the smartphone  22  in which the identification processing notification screen  34   f  is displayed on the display  34 . In the identification processing notification screen  34   f , a message is displayed to inform the user that the identification processing is in progress and that a noise sound is generated. As a result, a sense of discomfort or anxiety to the user caused by the generation of the noise sound is suppressed. 
     In step S 8 , the operation processing device  29  determines whether or not the identification processing has been completed. If the identification processing is completed, the process proceeds to step S 9 , and if the identification processing is not completed, the process returns to step S 6 . 
     In step S 9 , the operation processing device  29  displays an identification processing end notification screen  34   g  on the display  34 , and the process proceeds to step S 10 .  FIG.  12    is a diagram illustrating the smartphone  22  in which the identification processing end notification screen  34   g  is displayed on the display  34 . On the identification processing end notification screen  34   g , a message is displayed to notify the user that the identification processing has ended and that the ANC processing will be performed. 
     In step S 10 , the operation processing device  29  performs the ANC processing, and the process proceeds to step S 11 . 
     In step S 11 , the operation processing device  29  displays an ANC processing notification screen  34   h  on the display  34 , and the process proceeds to step S 12 .  FIG.  13    is a diagram illustrating the smartphone  22  in which the ANC processing notification screen  34   h  is displayed on the display  34 . On the ANC processing notification screen  34   h , an image for notifying the user that the ANC processing is being performed is displayed. Further, an ANC OFF button  35   q  is displayed on the ANC processing notification screen  34   h.    
     In step S 12 , the operation processing device  29  determines whether or not an ANC OFF operation has been performed. If the ANC OFF operation is performed, the active noise control processing is terminated. If the ANC OFF operation is not performed, the process returns to step S 10 . If the user taps the ANC OFF button  35   q , the operation processing device  29  determines that the ANC OFF operation is performed by the user. 
       FIG.  8 B ,  FIG.  8 C  and  FIG.  8 D  are flowcharts illustrating the flow of a setting process performed in step S 3 . As described above, the setting process is performed if the user taps the setting button  35   r  illustrated in  FIG.  10    and performs a setting operation. For example, the setting operation is performed when the active acoustic control application is activated for the first time after the active noise control program is installed on the smartphone  22 , or when the number of microphones  20  is changed, or when a vehicle is replaced, or the like. 
     In step S 21 , the operation processing device  29  displays a number-of-engine-cylinders input screen  34   c  on the display  34 , and the process proceeds to step S 22 .  FIG.  14    is a diagram illustrating the smartphone  22  in which the number-of-engine-cylinders input screen  34   c  is displayed on the display  34 . The number-of-engine-cylinders input screen  34   c  includes a number-of-engine-cylinders input section  35   d , a help button  35   e , and a go-to-next-screen button  35   f.    
     In step S 22 , the operation processing device  29  inputs 0 for an argument m and an argument n, and proceeds to step S 23 . 
     In step S 23 , the operation processing device  29  determines whether or not a help operation has been performed. If the help operation is performed, the process proceeds to step S 29 , and if the help operation is not performed, the process proceeds to step S 24 . If the user taps the help button  35   e , the operation processing device  29  determines that the help operation has been performed by the user. 
     In step S 24 , the operation processing device  29  determines whether or not the input of the number of cylinders of the engine  18  for the number-of-engine-cylinders input section  35   d  by the user has been completed. If the input of the number of cylinders of the engine  18  has been completed, the process proceeds to step S 25 , and if the input has not been completed, the process proceeds to step S 26 . 
     In step S 25 , the operation processing device  29  increments the argument m, that is, increases the numerical value of the argument m by 1, and proceeds to step S 28 . 
     In step S 26 , the operation processing device  29  determines whether or not a go-to-next-screen operation is performed by the user. If the go-to-next-screen operation is performed, the process proceeds to step S 27 , and if the go-to-next-screen operation is not performed, the process proceeds to step S 28 . When the user taps the go-to-next-screen button  35   f , the operation processing device  29  determines that the go-to-next-screen operation is performed by the user. 
     In step S 27 , the operation processing device  29  increments the argument n, and the process proceeds to step S 28 . 
     In step S 28 , the operation processing device  29  determines whether or not the product of the argument m and the argument n is 0. If the product of the argument m and the argument n is 0, the process returns to step S 23 , and if the product of the argument m and the argument n is not 0, the process proceeds to step S 40 . 
     In step S 29  to which the process proceeds if it is determined in step S 23  that the help operation has been performed by the user, the operation processing device  29  determines whether or not the argument m is 0. If the argument m is 0, the process proceeds to step S 30 , and if the argument m is not 0, the process returns to step S 23 . 
     In step S 30 , the operation processing device  29  displays a search screen  34   d  on the display  34 , and proceeds to step S 31 .  FIG.  15    is a diagram illustrating the smartphone  22  in which the search screen  34   d  is displayed on the display  34 . The search screen  34   d  includes a vehicle name input section  35   g , a grade input section  35   h , and a search button  35   j.    
     In step S 31 , the operation processing device  29  inputs 0 for an argument l, the argument m, and the argument n, respectively, and then proceeds to step S 32 . 
     In step S 32 , the operation processing device  29  determines whether or not the input of the vehicle name for the vehicle name input section  35   g  by the user has been completed. If the input of the vehicle name has been completed, the process proceeds to step S 33 , and if the input has not been completed, the process proceeds to step S 34 . 
     In step S 33 , the operation processing device  29  increments the argument l, and the process proceeds to step S 38 . 
     In step S 34 , the operation processing device  29  determines whether or not the input of the grade for the grade input section  35   h  by the user has been completed. If the input of the grade has been completed, the process proceeds to step S 35 , and if the input has not been completed, the process proceeds to step S 36 . 
     In step S 35 , the operation processing device  29  increments the argument m, and the process proceeds to step S 38 . 
     In step S 36 , the operation processing device  29  determines whether or not the search operation has been performed by the user. If the search operation has been performed, the process proceeds to step S 37 , and if the search operation has not been performed, the process proceeds to step S 38 . If the user taps the search button  35   j , the operation processing device  29  determines that the search operation has been performed by the user. 
     In step S 37 , the operation processing device  29  increments the argument n, and the process proceeds to step S 38 . 
     In step S 38 , the operation processing device  29  determines whether or not the product of the argument l, the argument m, and the argument n is 0. If the product of the argument l, the argument m, and the argument n is 0, the process returns to step S 32 , and if the product of the argument l, the argument m, and the argument n are not 0, the process proceeds to step S 39 . 
     In step S 39 , the operation processing device  29  receives the number of cylinders of the engine  18  corresponding to the input vehicle name and grade from the server  26 , and proceeds to step S 40 . 
     In step S 40 , the operation processing device  29  displays number-of-speakers/number-of-microphones input screen  34   e  on the display  34 , and the process proceeds to step S 41 .  FIG.  16    is a diagram illustrating the smartphone  22  in which the number-of-speakers/number-of-microphones input screen  34   e  is displayed on the display  34 . The number-of-speakers/number-of-microphones input screen  34   e  includes a number-of-speakers input section  35   k , a number-of-microphones input section  35   m , a checkbox  35   n , and an end button  35   p.    
     In step S 41 , the operation processing device  29  inputs 0 for the argument l and the argument m, and the process proceeds to step S 42 . 
     In step S 42 , it is determined whether or not the input of the number of speakers  16  for the number-of-speakers input section  35   k  by the user has been completed. If the input of the number of speakers  16  has been completed, the process proceeds to step S 43 , and if the input has not been completed, the process proceeds to step S 44 . 
     In step S 43 , the operation processing device  29  increments the argument l, and the process proceeds to step S 46 . 
     In step S 44 , the operation processing device  29  determines whether or not the input of the number of microphones  20  for the number-of-microphones input section  35   m  by the user has been completed. If the input of the number of microphones  20  has been completed, the process proceeds to step S 45 , and if the input has not been completed, the process proceeds to step S 47 . 
     In step S 45 , the operation processing device  29  increments the argument m, and the process proceeds to step S 51 . 
     In step S 46 , the operation processing device  29  determines whether or not the product of the argument l and the argument m is 0. If the product of the argument l and the argument m is 0, the process proceeds to step S 50 , and if the product of the argument l and the argument m is not 0, the process proceeds to step S 47 . 
     In step S 47 , the operation processing device  29  determines whether or not a checkbox to use the microphone  32  of the smartphone  22  has been checked by the user. If the checkbox to use the microphone  32  of the smartphone  22  is checked, the process proceeds to step S 48 , and if the checkbox to use the microphone  32  of the smartphone  22  is not checked, the process proceeds to step S 49 . If the user taps and checks the checkbox  35   n , the operation processing device  29  determines that the checkbox to use the microphone  32  is checked. 
     In step S 48 , the operation processing device  29  determines to perform the active noise control process using the microphone  32  mounted on the smartphone  22 , and the process proceeds to step S 50 . 
     In step S 49 , the operation processing device  29  determines not to perform the active noise control process using the microphone  32  mounted on the smartphone  22 , and the process proceeds to step S 50 . 
     In step S 50 , the operation processing device  29  determines whether or not the product of the argument l and the argument m is 0. If the product of the argument l and the argument m is 0, the process returns to step S 42 , and if the product of the argument l, the argument m, and the argument n is not 0, the setting process is ended. 
     [Active Acoustic Control Device Using FIR Filter] 
     Hereinafter, an active acoustic control device  66  using an FIR filter will be described as a comparative example with respect to the active acoustic control device  10  using the SAN filter of the present embodiment. 
       FIG.  17    is a block diagram of the active acoustic control device  66  using an FIR filter. In the active acoustic control device  66 , an FIR (Finite Impulse Response) filter is used as an adaptive digital filter. A filtered-X LMS algorithm is used to update the filter coefficients of the FIR filter. 
     The active acoustic control device  66  includes a basic signal generating unit  68 , a control signal generating unit  70 , a reference signal generating unit  72 , an error signal receiving unit  74 , and a control filter coefficient updating unit  76 . 
     The basic signal generating unit  68  generates a basic signal x based on the engine rotational speed Ne. The basic signal generating unit  68  includes a frequency detecting circuit  68   a  and a cosine signal generator  68   b.    
     Similarly to the frequency detecting circuit  52   a  of the active acoustic control device  10  of the present embodiment, the frequency detecting circuit  68   a  detects the vibration frequency f of the engine  18  in accordance with the engine rotational speed Ne and the number of cylinders of the engine  18 . 
     The cosine signal generator  68   b  generates a basic signal x (=cos(2πft)) which is a cosine signal of the vibration frequency f. Here, t denotes time. When the number of taps of the FIR filter is N, a time-series signal vector X(n) of a basic signal x(n) at a time step n is defined by the following equation. 
         X ( n )=[ x ( n ), x ( n− 1), x ( n− 2), . . .  x ( n−N+ 1)] T    
     The control signal generating unit  70  generates a control signal u 0  based on the time-series signal vector X of the basic signal x. In the control signal generating unit  70 , an FIR filter which is an adaptive filter is used as a control filter. The control filter coefficient W is optimized by being updated by the control filter coefficient updating unit  76  described later. 
     The control filter coefficient W(n) at the time step n is expressed by the following equation. 
         W ( n )=[ w   0 ( n ), w   1 ( n ), w   2 ( n ), . . . , w   N−1 ( n )] T    
     The control signal u 0 ( n ) at time step n is expressed by the following equation: In the following equation, “*” indicates a convolution sum. 
         u 0( n )=Σ i=0   N−1   w   i ( n )× x ( n−i )= W ( n )* X ( n )= W ( n ) T   ×X ( n )
 
     Further, the time-series vector U 0 ( n ) is expressed by the following equation. 
         U 0( n )=[ u 0( n ), u 0( n− 1), u 0( n− 2), . . . , u 0( n−N+ 1)] T    
     The basic signal x filtered by the control signal generating unit  70  is output as the control signal u 0 . The speaker  16  is controlled based on the control signal u 0 , and the canceling sound is output from the speaker  16 . 
     The reference signal generating unit  72  generates a reference signal r based on the basic signal x. The reference signal generating unit  72  includes a secondary path filter. The value of the secondary path filter coefficient C{circumflex over ( )} is stored in the server  26  for each vehicle type, and is downloaded from the server  26  to the active acoustic control device  66 . The secondary path filter coefficient C{circumflex over ( )}(n) at time step n is expressed by the following equation: 
         C {circumflex over ( )}( n )=[ c   0 {circumflex over ( )}( n ), c   1 {circumflex over ( )}( n ), c   2 {circumflex over ( )}( n ), . . .  c   N−1 {circumflex over ( )}( n )] T  
 
     The reference signal r(n) at time step n is expressed by the following equation. In the following equation, “*” indicates a convolution sum. 
         r ( n )=Σ i=0   N−1   c   i {circumflex over ( )}( n )× x ( n−i )= C {circumflex over ( )}( n )* X ( n )= C {circumflex over ( )}( n ) T   ×X ( n )
 
     Further, the time series vector R(n) is expressed by the following equation. 
         R ( n )=[ r ( n ), r ( n− 1), r ( n− 2), . . . , r ( n−N+ 1)] T    
     The error signal receiving unit  74  receives an error signal e corresponding to the cancellation error noise collected by the microphone  20 . The error signal e is a signal corresponding to a cancellation error noise in which the canceling sound and the noise are combined at the position of the microphone  20 . 
     The control filter coefficient updating unit  76  updates the filter coefficient W of the control signal generating unit  54  based on the reference signal r and the error signal e. The control filter coefficient updating unit  60  updates the control filter coefficient W based on the filtered-X LMS algorithm. The control filter coefficient updating unit  76  updates the control filter coefficient W based on the following equation. 
     
       
         
           
             
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     In the control filter coefficient updating unit  76 , the control filter coefficient W is optimized by repeatedly updating the control filter coefficient W. Since the update equation of the control filter coefficient W includes a convolution operation, a computational load due to the update processing of the control filter coefficient W increases. 
     [Operation and Advantageous Effects] 
     It is expected that active noise control for reducing noise in the vehicle compartment  14  can be performed using equipment that is readily available to anyone. Therefore, it is conceivable that an active acoustic control program is downloaded from the server  26  on the smartphone  22 , and the smartphone  22  is caused to perform active noise control. 
     In the active acoustic control device  66  using the FIR filter of the comparative example, the convolution operation is included in the update equation for updating the control filter coefficient W by the control filter coefficient updating unit  76 . Therefore, if active noise control is performed by the active acoustic control device  66 , the load of operation processing becomes large, and the amount of memory used also becomes large. Therefore, the smartphone  22  functioning as the active acoustic control device  66  is required to include the operation processing device  29  capable of performing high-speed operation processing and the large-capacity memory  30 . That is, an inexpensive smartphone  22  cannot function as the active acoustic control device  66 , and the active noise control process cannot be performed by a device that is readily available to anyone. 
     Further, in the active acoustic control device  66  using the FIR filter of the comparative example, the secondary path filter coefficient C{circumflex over ( )} is downloaded from the server  26 . Since the identification of the secondary path transfer characteristic C is not performed by the active acoustic control device  66 , it is possible to reduce the load of the operation processing of the operation processing device  29  accompanying the identification processing, and the use amount of the memory  30 . Since the secondary path transfer characteristic C is different for each vehicle type, the secondary path filter coefficient C{circumflex over ( )} corresponding to the secondary path transfer characteristic C for each vehicle type is stored in the server  26 . Therefore, the active acoustic control device  66  cannot suppress noise in the vehicle compartment  14  of a certain type of vehicle, unless the secondary path filter coefficient C″ for the vehicle type is stored in the server  26 . That is, a user using a vehicle type for which the secondary path filter coefficient C{circumflex over ( )} is not stored in the server  26 , cannot cause the smartphone  22  to function as the active acoustic control device  66 . 
     Therefore, the present embodiment causes the smartphone  22  on which the active acoustic control program is installed to function as the active acoustic control device  10  using the SAN filter. In the active acoustic control device  10 , the update equation for updating the control filter coefficient W by the control filter coefficient updating unit  60  is composed of four arithmetic operations and does not include a convolution operation. 
     Therefore, in the case that active noise control is performed by the active acoustic control device  10 , it is possible to suppress the computational load due to an update processing of the control filter coefficient W. Therefore, the smartphone  22  functioning as the active acoustic control device  10  is not required to include the large-capacity memory  30  and the operation processing device  29  equipped with a processor capable of high-speed operation processing. Therefore, even an inexpensive smartphone  22  can be made to function as the active acoustic control device  10 , and the active noise control processing can be performed by a device that is easily available to anyone. 
     In the present embodiment, the active acoustic control device  10  identifies the secondary path transfer characteristic C and generates the filter coefficients C 0 {circumflex over ( )} and C 1 {circumflex over ( )} as correction values by the control filter coefficient updating unit  60 . The filter coefficients C 0 {circumflex over ( )} and C 1 {circumflex over ( )} are identified based on the identification sounds at the plurality of predetermined frequencies fm. Accordingly, since the smartphone  22  functioning as the active acoustic control device  10  can identify the secondary path transfer characteristic C, the smartphone  22  can function as the active acoustic control device  10  regardless of the vehicle type of the vehicle  12 . 
     Further, in the present embodiment, the active acoustic control device  10  generates the basic signals xc and xs by the basic signal generating unit  52  based on the number of engine cylinders and the engine rotational speed Ne. Accordingly, the active acoustic control device  10  can reduce the sound having the vibration frequency f which is a fundamental frequency of the noise in the vehicle compartment  14 . 
     In the present embodiment, the microphone  20  is detachably attached in the vehicle compartment  14 . Thus, when the user changes to another vehicle  12 , the user can remove the microphone  20  from the original vehicle  12  and attach the microphone  20  to the other vehicle  12 . Therefore, if the smartphone  22  on which the active acoustic control program is installed is brought into the other vehicle  12 , the active noise control can be performed for the other vehicle  12  by the smartphone  22 . 
     Second Embodiment 
     In the active acoustic control device  10  according to the first embodiment, the identification processing is performed in a state where an identification sound (noise sound) is output from the speaker  16 , before the ANC processing is performed. On the other hand, in the active acoustic control device  10  of the second embodiment, the ANC processing and the identification processing are performed in parallel, and the identification processing is performed without using an identification sound. Hereinafter, the active noise control performed by the active acoustic control device  10  according to the present embodiment will be referred to as active noise control of a constant identification type. 
     [Active Acoustic Control Device] 
       FIG.  18    is a block diagram of the active acoustic control device  10  according to the second embodiment. The active acoustic control device  10  includes a basic signal generating unit  78 , a control signal generating unit  80 , a first estimated cancellation signal generating unit  82 , an estimated noise signal generating unit  84 , a reference signal generating unit  86 , a second estimated cancellation signal generating unit  88 , an error signal receiving unit  90 , a primary path filter coefficient updating unit  92 , a secondary path filter coefficient updating unit  94 , and a control filter coefficient updating unit  96 . 
     The basic signal generating unit  78  generates basic signals xc and xs based on the engine rotational speed Ne. The basic signal generating unit  78  includes a frequency detecting circuit  78   a , a cosine signal generator  78   b , and a sine signal generator  78   c . The processing performed by the basic signal generating unit  78  is the same as the processing performed by the basic signal generating unit  52  of the active acoustic control device  10  of the first embodiment. 
     The control signal generating unit  80  generates the control signals u 0  and u 1  based on the basic signals xc and xs. The control signal generating unit  80  includes a first control filter  80   a , a second control filter  80   b , a third control filter  80   c , a fourth control filter  80   d , an adder  80   e , and an adder  80   f.    
     In the control signal generating unit  80 , a SAN filter is used as a control filter. The first control filter  80   a  has a filter coefficient W 0 . The second control filter  80   b  has a filter coefficient W 1 . The third control filter  80   c  has a filter coefficient −W 0 . The fourth control filter  80   d  has a filter coefficient W 1 . The control filters are optimized by updating the filter coefficients W 0  and W 1  by the control filter coefficient updating unit  96  described later. 
     The basic signal xc filtered by the first control filter  80   a  and the basic signal xs filtered by the second control filter  80   b  are added by the adder  80   e  to generate the control signal u 0 . The speaker  16  is controlled based on the control signal u 0 , and the canceling sound is output from the speaker  16 . The basic signal xs filtered by the third control filter  80   c  and the basic signal xc filtered by the fourth control filter  80   d  are added by the adder  80   f  to generate the control signal u 1 . 
     The first estimated cancellation signal generating unit  82  generates an estimated cancellation signal y 1 {circumflex over ( )} based on the control signals u 0  and u 1 . The first estimated cancellation signal generating unit  82  includes a first secondary path filter  82   a , a second secondary path filter  82   b , and an adder  82   c.    
     In the first estimated cancellation signal generating unit  82 , a SAN filter is used as a secondary path filter. The secondary path filter coefficient C{circumflex over ( )} is adaptively updated by the secondary path filter coefficient updating unit  94  described later. 
     The first secondary path filter  82   a  has a filter coefficient C 0 {circumflex over ( )} which is a real part of the secondary path filter coefficient C{circumflex over ( )}(=C 0 {circumflex over ( )}+iC 1 {circumflex over ( )}). The second secondary path filter  82   b  has a filter coefficient C 1 {circumflex over ( )} which is an imaginary part of the secondary path filter coefficient C{circumflex over ( )}. The control signal u 0  filtered by the first secondary path filter  82   a  and the control signal u 1  filtered by the second secondary path filter  82   b  are added by the adder  82   c  to generate an estimated cancellation signal y 1 {circumflex over ( )}. The estimated cancellation signal y 1 {circumflex over ( )} is an estimated signal of a signal corresponding to the canceling sound y input to the microphone  20 . 
     The estimated noise signal generating unit  84  generates an estimated noise signal d{circumflex over ( )} based on the basic signals xc and xs. The estimated noise signal generating unit  84  includes a first primary path filter  84   a , a second primary path filter  84   b , and an adder  84   c . In the estimated noise signal generating unit  84 , a SAN filter is used as a primary path filter. The coefficient H{circumflex over ( )} of the primary path filter (hereinafter referred to as a primary path filter coefficient H{circumflex over ( )}) is adaptively updated by the primary path filter coefficient updating unit  92  described later. 
     The first primary path filter  84   a  has a filter coefficient H 0 {circumflex over ( )} that is a real part of a coefficient H{circumflex over ( )} (=H 0 {circumflex over ( )}+iH 1 {circumflex over ( )}) of the primary path filter. The second primary path filter  84   b  has a filter coefficient −H 1 {circumflex over ( )} obtained by inverting the polarity of the imaginary part of the primary path filter coefficient H{circumflex over ( )}. The basic signal xc filtered by the first primary path filter  84   a  and the basic signal xs filtered by the second primary path filter  84   b  are added by the adder  84   c  to generate an estimated noise signal d{circumflex over ( )}. The estimated noise signal d{circumflex over ( )} is an estimated signal of a signal corresponding to the noise d input to the microphone  20 . 
     The reference signal generating unit  86  generates reference signals r 0  and r 1  based on the basic signals xc and xs. The reference signal generating unit  86  includes a third secondary path filter  86   a , a fourth secondary path filter  86   b , a fifth secondary path filter  86   c , a sixth secondary path filter  86   d , an adder  86   e , and an adder  86   f.    
     In the reference signal generating unit  86 , a SAN filter is used as a secondary path filter. The secondary path filter coefficient C{circumflex over ( )} is adaptively updated by the secondary path filter coefficient updating unit  94  described later. 
     The third secondary path filter  86   a  has a filter coefficient C 0 {circumflex over ( )} that is a real part of the secondary path filter coefficient C{circumflex over ( )} (=C 0 {circumflex over ( )}+iC 1 {circumflex over ( )}). The fourth secondary path filter  86   b  has a filter coefficient −C 1 {circumflex over ( )} obtained by inverting the polarity of the imaginary part of the secondary path filter coefficient CA. The fifth secondary path filter  86   c  has a filter coefficient C 0 {circumflex over ( )} that is the real part of the secondary path filter coefficient C{circumflex over ( )}. The sixth secondary path filter  86   d  has a filter coefficient C 1 {circumflex over ( )} that is the imaginary part of the secondary path filter coefficient C{circumflex over ( )}. 
     The basic signal xc filtered by the third secondary path filter  86   a  and the basic signal xs filtered by the fourth secondary path filter  86   b  are added by the adder  86   e  to generate a reference signal r 0 . The basic signal xs filtered by the fifth secondary path filter  86   c  and the basic signal xc filtered by the sixth secondary path filter  86   d  are added by the adder  84   c  to generate a reference signal r 1 . The filter coefficients C 0 ″, C 1 {circumflex over ( )}, and −C 1 {circumflex over ( )} correspond to correction values of the present invention. 
     The second estimated cancellation signal generating unit  88  generates an estimated cancellation signal y 2 {circumflex over ( )} based on the reference signals r 0  and r 1 . The second estimated cancellation signal generating unit  88  includes a fifth control filter  88   a , a sixth control filter  88   b , and an adder  88   c.    
     In the second estimated cancellation signal generating unit  88 , a SAN filter is used as a control filter. The fifth control filter  88   a  has a filter coefficient W 0 . The sixth control filter  88   b  has a filter coefficient W 1 . The control filters are optimized by updating the filter coefficients W 0  and W 1  by the control filter coefficient updating unit  96  described later. 
     The reference signal r 0  filtered by the fifth control filter  88   a  and the reference signal r 1  filtered by the sixth control filter  88   b  are added by the adder  88   c  to generate an estimated cancellation signal y 2 {circumflex over ( )}. The estimated cancellation signal y 2 {circumflex over ( )} is an estimated signal of a signal corresponding to the canceling sound y input to the microphone  20 . 
     The error signal receiving unit  90  receives an error signal e corresponding to the cancellation error noise collected by the microphone  20 . The error signal e is a signal corresponding to a cancellation error noise in which the canceling sound and the noise are combined at a position of the microphone  20 . 
     The error signal e received by the error signal receiving unit  90  is input to an adder  98 . The polarity of the estimated noise signal d{circumflex over ( )}generated by the estimated noise signal generating unit  84  is inverted by an inverter  100 , and the estimated noise signal d{circumflex over ( )} is input to the adder  98 . The polarity of the estimated cancellation signal y 1 {circumflex over ( )}generated by the first estimated cancellation signal generating unit  82  is inverted by an inverter  102 , and the inverted signal is input to the adder  98 . By the adder  98 , a virtual error signal e 1  is generated. 
     The estimated noise signal d{circumflex over ( )}generated by the estimated noise signal generating unit  84  is input to an adder  104 . The estimated cancellation signal y 2 {circumflex over ( )}generated by the second estimated cancellation signal generating unit  88  is input to the adder  104 . By the adder  104 , a virtual error signal e 2  is generated. 
     The primary path filter coefficient updating unit  92  updates the primary path filter coefficient H{circumflex over ( )}(=H 0 {circumflex over ( )}+iH 1 {circumflex over ( )}) based on the basic signals xc and xs, and the virtual error signal e 1 . The primary path filter coefficient updating unit  92  updates the primary path filter coefficient H{circumflex over ( )} based on a filtered-X LMS (Least Mean Square) algorithm. The primary path filter coefficient updating unit  92  includes a first primary path filter coefficient updating unit  92   a  and a second primary path filter coefficient updating unit  92   b.    
     The first primary path filter coefficient updating unit  92   a  and the second primary path filter coefficient updating unit  92   b  update the filter coefficients H 0 {circumflex over ( )} and H 1 {circumflex over ( )} based on the following equations. In the equations, n denotes the time step (n=0, 1, 2, . . . ), and μ 0  and μ 1  denote the step size parameters. 
         H 0{circumflex over ( )}( n+ 1)= H 0{circumflex over ( )}( n )−μ0 ×e 1( n )× xc ( n )
 
         H 1{circumflex over ( )}( n+ 1)= H 1{circumflex over ( )}( n )−μ1 ×e 1( n )× xs ( n )
 
     A transfer characteristic H of the primary path (hereinafter referred to as a primary path transfer characteristic H) is identified by repeatedly updating the primary path filter coefficient H{circumflex over ( )} by the primary path filter coefficient updating unit  92 . In the active acoustic control device  10  using the SAN filter, the update equations for the primary path filter coefficient H{circumflex over ( )} are configured by four arithmetic operations and do not include a convolution operation. Therefore, it is possible to suppress a computational load due to update processing of the primary path filter coefficient H{circumflex over ( )}. 
     The secondary path filter coefficient updating unit  94  updates the secondary path filter coefficient C{circumflex over ( )} (=C 0 {circumflex over ( )}+iC 1 {circumflex over ( )}) based on the control signals u 0  and u 1 , and the virtual error signal e 1 . The secondary path filter coefficient updating unit  94  updates the secondary path filter coefficient C{circumflex over ( )} based on the filtered-X LMS algorithm. The secondary path filter coefficient updating unit  94  includes a first secondary path filter coefficient updating unit  94   a  and a second secondary path filter coefficient updating unit  94   b.    
     The first secondary path filter coefficient updating unit  94   a  and the second secondary path filter coefficient updating unit  94   b  update the filter coefficients C 0 {circumflex over ( )} and C 1 {circumflex over ( )} based on the following equations. In the equation, μ 2  and μ 3  indicate the step size parameters. 
         C 0{circumflex over ( )}( n+ 1)= C 0{circumflex over ( )}( n )−μ2 ×e 1( n )×{ W 0( n )× xc ( n )+ W 1( n )× xs ( n )}
 
         C 1{circumflex over ( )}( n+ 1)= C 1{circumflex over ( )}( n )−μ3 ×e 1( n )×{− W 0( n )× xs ( n )+ W 1( n )× xc ( n )}
 
     The secondary path transfer characteristic C is identified by repeatedly updating the secondary path filter coefficient C{circumflex over ( )} by the secondary path filter coefficient updating unit  94 . In the active acoustic control device  10  using the SAN filter, the update equations for the secondary path filter coefficient C{circumflex over ( )} are configured by four arithmetic operations and do not include a convolution operation. Therefore, it is possible to suppress a computational load due to update processing of the secondary path filter coefficient C{circumflex over ( )}. 
     The control filter coefficient updating unit  96  updates the filter coefficients W 0  and W 1  based on the reference signals r 0  and r 1 , and the virtual error signal e 2 . The control filter coefficient updating unit  96  updates the control filter coefficient W based on the filtered-X LMS algorithm. The control filter coefficient updating unit  96  includes a first control filter coefficient updating unit  96   a  and a second control filter coefficient updating unit  96   b.    
     The first control filter coefficient updating unit  96   a  and the second control filter coefficient updating unit  96   b  update the filter coefficients W 0  and W 1  based on the following equations. In the equations, μ 4  and μ 5  denote the step size parameters. 
         W 0( n+ 1)= W 0( n )−μ4× e 2( n )×{ C 0( n )× xc ( n )− C 1( n )× xs ( n )}
 
         W 1( n+ 1)= W 1( n )−μ5× e 2( n )×{ C 0( n )× xs ( n )+ C 1( n )× xc ( n )}
 
     The control filter W is optimized by repeatedly updating the filter coefficients W 0  and W 1  by the control filter coefficient updating unit  96 . In the active acoustic control device  10  using the SAN filter, the update equations for the filter coefficients W 0  and W 1  are configured by four arithmetic operations and do not include a convolution operation. Therefore, it is possible to suppress a computational load due to update processing of filter coefficients W 0  and W 1 . 
     [Active Noise Control Processing by Smartphone] 
     In the active acoustic control device  10  of the present embodiment, it is not necessary to perform the identification processing before the ANC processing. Therefore, among the active noise control process performed by the smartphone  22  of the first embodiment, the process from step S 5  to step S 9  in  FIG.  8 A  is not performed by the smartphone  22  of the present embodiment. 
     In the ANC ON operation screen  34   b  displayed on the display  34  of the smartphone  22  according to the present embodiment, only the ANC ON button  35   b  is displayed, and the checkbox  35   c  and the like are not displayed. Other processes are the same as those of the active acoustic control device  10  according to the first embodiment. 
     [Operation and Advantageous Effects] 
     The present embodiment causes the smartphone  22  on which the active acoustic control program is installed to function as the active acoustic control device  10  using the SAN filter. In the active acoustic control device  10 , the update equations for updating the primary path filter coefficient H{circumflex over ( )} by the primary path filter coefficient updating unit  92 , the update equations for updating the secondary path filter coefficient C{circumflex over ( )} by the secondary path filter coefficient updating unit  94 , and the update equations for updating the control filter coefficient W by the control filter coefficient updating unit  96 , are configured by four arithmetic operations and do not include a convolution operation. 
     Therefore, in the case that active noise control is performed by the active acoustic control device  10 , it is possible to suppress the computational load due to an update processes of the primary path filter coefficient H{circumflex over ( )}, the secondary path filter coefficient C{circumflex over ( )}, and the control filter coefficient W. Therefore, the smartphone  22  functioning as the active acoustic control device  10  is not required to include the operation processing device  29  capable of performing high-speed operation processing and the large-capacity memory  30 . Therefore, even an inexpensive smartphone  22  can be made to function as the active acoustic control device  10 , and the active noise control processing can be performed by a device that is easily available to anyone. 
     Further, in the active acoustic control device  10  of the present embodiment, since the identification processing is performed simultaneously during the ANC processing, even if the primary path transfer characteristic H and/or the secondary path transfer characteristic C may change during the ANC processing, the primary path transfer characteristic H and/or the secondary path transfer characteristic C can be identified. 
     Third Embodiment 
     In the first embodiment and the second embodiment, the active acoustic control device  10  generates the control signal u 0  for controlling one speaker  16  based on the error signal e input from one microphone  20 . In the third embodiment, the active acoustic control device  10  generates control signals u 0 [ l ] (l=0, 1, . . . , l−1) for controlling l speakers  16  based on error signals e[m] (m=0, 1, . . . , m−1) input from m microphones  20 . 
     The microphones  20  are installed in the vehicle compartment  14  such that they are easily detachable by the user.  FIGS.  19 A,  19 B, and  19 C  are views showing examples of installation positions in which two microphones  20  are installed in the vehicle compartment  14 . If the vehicle  12  is a right-hand drive vehicle, as shown in  FIG.  19 A , one microphone  20  is fixed to the right side surface (vehicle outside) of the headrest  15   a  of the driver&#39;s seat  15  with double-sided tape or the like, and another microphone  20  is fixed to the left side surface (vehicle outside) of a headrest  17   a  of a passenger&#39;s seat  17  with double-sided tape or the like. If the vehicle  12  is a left-hand drive vehicle, one microphone  20  is provided on the left side surface of the headrest  15   a  of the driver&#39;s seat  15 , and another microphone  20  is provided on the right side surface of the headrest  17   a  of the passenger&#39;s seat  17 . 
     The positions where the microphones  20  are set are not limited to the positions shown in  FIG.  19 A . For example, if the vehicle  12  is a right-hand drive vehicle, one microphone  20  may be fixed to the left side surface (vehicle center side) of the headrest  15   a  of the driver&#39;s seat  15  with double-sided tape or the like, and another microphone  20  may be fixed to the left side surface of a headrest  13   a  at the center of the rear seat  13  with double-sided tape or the like, as shown in  FIG.  19 B . In the case where the vehicle  12  is a left-hand drive vehicle, one microphone  20  may be provided on a right side surface of the headrest  15   a  of the driver&#39;s seat  15 , and another microphone  20  may be provided on a right side surface of the headrest  13   a  at the center of the rear seat  13 . 
     Further, as shown in  FIG.  19 C , one microphone  20  may be fixed to the left side surface (vehicle center side) of the headrest  15   a  of the driver&#39;s seat  15  with double-sided tape or the like, and another microphone  20  may be fixed to the rear side surface of the headrest  13   a  at the center of the rear seat  13  with double-sided tape or the like. If the vehicle  12  is a left-hand drive vehicle, one microphone  20  may be provided on the right side surface of the headrest  15   a  of the driver&#39;s seat  15 . 
       FIG.  20    is an image diagram of active noise control using a plurality of microphones  20  and a plurality of speakers  16 . 
     There are m transfer paths (primary paths) from the engine  18  to the microphones  20 , each of which has a primary path transfer characteristic H (H[ 0 ] to H[m−1]). Therefore, the active acoustic control device  10  requires m primary path filter coefficients H{circumflex over ( )}[ 0 ] to H{circumflex over ( )}[m−1] corresponding to the respective primary path transfer characteristics H. 
     There are (l×m) transfer paths (secondary paths) from each of the speakers  16  to each of the microphones  20 , and each of the paths has a secondary path transfer characteristic C (C[0, 0] to C[l−1, m−1]). Therefore, the active acoustic control device  10  requires (l×m) secondary path filter coefficients C{circumflex over ( )}[0, 0] to C{circumflex over ( )}[l−1, m−1] corresponding to the respective secondary path transfer characteristics C. 
     Since there are 1 speakers  16 , the active acoustic control device  10  needs to generate 1 control signals u 0  (u 0 [ 0 ] to u 0 [ l −1]) to be input to the respective speakers  16 . Therefore, the active acoustic control device  10  requires 1 control filter coefficients W (W[ 0 ] to W[l−1]). 
     That is, the numbers of the primary path filter coefficients H{circumflex over ( )}, the secondary path filter coefficients CA, and the control filter coefficients W are determined according to the number of the speakers  16  and the number of the microphones  20 . 
     In the active acoustic control device  10  of the present embodiment, each of the filter coefficients is updated based on the MEFX (Multiple Error Filtered-X)-LMS algorithm. Hereinafter, the update equations of the control filter coefficient W in the active noise control of a prior identification type described in the first embodiment, and the update equations of the primary path filter coefficient H{circumflex over ( )}, the secondary path filter coefficient C{circumflex over ( )}, and the control filter coefficient W in the active noise control of a constant identification type described in the second embodiment, will be described, respectively. 
     [Filter Coefficient Update Equations in Active Noise Control of Prior Identification Type] 
     Update equations of the control filter coefficients W 0 [ j ] and W 1 [ j ] for generating the control signal u 0 [ j ] input to the j-th speaker  16  is expressed by the following equations. Here, it is assumed that xc, xs are the basic signals, C[j, k]{circumflex over ( )} is the secondary transfer filter coefficient corresponding to the transfer characteristic C[j, k] of the sound in the transfer path from the j-th speaker  16  to the k-th microphone  20 , and e[k] is the error signal input to the k-th microphone  20 . In the equations, n denotes the time step (n=0, 1, 2, . . . ), and μ 0  and μ 1  denote the step size parameters. 
         W 0[ j ]( n+ 1)= W 0[ j ]( n )−μ0 ×E   k=0   m−1   e [ k ]( n )×Σ k=0   m−1   {C 0[ j,k ]( n )× xc ( n )− C 1[ j,k ]( n )× xs ( n )}
 
         W 1[ j ]( n+ 1)= W 1[ j ]( n )−μ1×Σ k=0   m−1   e [ k ]( n )× E   k=0   m−1   {C 0[ j,k ]( n )× xs ( n )+ C 1[ j,k ]( n )× xc ( n )}
 
     [Filter Coefficient Update Equation in Active Noise Control of Constant Identification Type] 
     Update equations of the primary path filter coefficient H[k]{circumflex over ( )}(=H 0 [ k ]{circumflex over ( )}+iH 1 [ k ]{circumflex over ( )}) corresponding to the transfer characteristic H[k] of the sound in the transfer path from the engine  18  to the k-th microphone  20  are shown by the following equations. Here, it is assumed that xc and xs are the basic signals, and e 1 [ k ] is the virtual error signal of the k-th microphone  20 . In the equations, n denotes the time step (n=0, 1, 2, . . . ), and μ 0  and μ 1  denote the step size parameters. 
         H 0[ k ]{circumflex over ( )}( n+ 1)= H 0[ k ]{circumflex over ( )}( n )−μ0 ×e 1[ k ]( n )× xc ( n )
 
         H 1[ k ]{circumflex over ( )}( n+ 1)= H 1[ k ]{circumflex over ( )}( n )−μ1 ×e 1[ k ]( n )× xs ( n )
 
     Update equations of the secondary path filter coefficient C[j, k]{circumflex over ( )}(=C 0 [ j, k ]{circumflex over ( )}+iC 1 [ j, k ]{circumflex over ( )}) corresponding to the transfer characteristic C[j, k] of the sound in the transfer path from the j-th speaker  16  to the k-th microphone  20  are expressed by the following equations. Here, it is assumed that xc and xs are the basic signals, e 1 [ k ] is the virtual error signal of the k-th microphone  20 , and W[j] (=W 0 [ j ]+iW 1 [ j ]) is the control filter coefficient for generating the control signal u 0 [ j ] to be input to the j-th speaker  16 . In the equations, μ 2  and μ 3  indicate the step size parameters. 
         C 0[ j,k ]{circumflex over ( )}( n+ 1)= C 0[ j,k ]{circumflex over ( )}( n )−μ2× e 1[ k ]( n )×{ W 0[ j ]( n )× xc ( n )+ W 1[ j ]( n )× xs ( n )}
 
         C 1[ j,k ]{circumflex over ( )}( n+ 1)= C 1[ j,k ]{circumflex over ( )}( n )−μ3×[ k ]{circumflex over ( )}( n )×{− W 0[ j ]( n )× xs ( n )+ W 1[ j ]( n )
 
     Update equations of the control filter coefficients W 0 [ j ] and W 1 [ j ] used for generating the control signal u 0 [ j ] input to the j-th speaker  16  are expressed by the following equations. Here, it is assumed that xc, xs are the basic signals, C[j, k]{circumflex over ( )} is the secondary path filter coefficient corresponding to the transfer characteristic C[j, k] of the sound in the transfer path from the j-th speaker  16  to the k-th microphone  20 , and e 2 [ k ] is the virtual error signal of the k-th microphone  20 . In the equations, μ 4  and μ 5  denote the step size parameters. 
         W 0[ j ]( n+ 1)= W 0[ j ]( n )−μ4× E   k=0   m−1   e 2[ k ]( n )×Σ k=0   m−1   {C 0[ j,k ]( n )× xc ( n )− C 1[ j,k ]( n )× xs ( n )}
 
         W 1[ j ]( n+ 1)= W 1[ j ]( n )−μ5×Σ k=0   m−1   e 2[ k ]( n )× E   k=0   m−1   {C 0[ j,k ]( n )× xs ( n )+ C 1[ j,k ]( n )× xc ( n )}
 
     [Operation and Advantageous Effects] 
     In the active acoustic control device  10  of the present embodiment, the numbers of the primary path filter coefficients H{circumflex over ( )}, the secondary path filter coefficients C{circumflex over ( )}, and the control filter coefficients W are determined according to the number of the speakers  16  and the number of the microphones  20 . Accordingly, the active acoustic control device  10  of the present embodiment can appropriately perform active noise control in accordance with the number of speakers  16  and the number of microphones  20 . 
     Fourth Embodiment 
     In the first to third embodiments, the smartphone  22  on which an active acoustic control program is installed is caused to function as the active acoustic control device  10 . In contrast, in the present embodiment, a vehicle information acquisition device  106  on which an active acoustic control program is installed is caused to function as the active acoustic control device  10 . 
       FIG.  21    is a block diagram of a smartphone  22 , an in-vehicle system  24 , and the vehicle information acquisition device  106 . In the present embodiment, detailed description of the same configurations as those in the first to third embodiments will be omitted. 
     The vehicle information acquisition device  106  is connected to the smartphone  22  by wire. The vehicle information acquisition device  106  is connected to the in-vehicle system  24  by wire. The vehicle information acquisition device  106  may be wirelessly connected to the smartphone  22  and the in-vehicle system  24 . 
     The active acoustic control program is downloaded from the server  26  to the smartphone  22  via the Internet  28 , and the active acoustic control program is transmitted from the smartphone  22  to the vehicle information acquisition device  106 . The active acoustic control program transmitted from the smartphone  22  is installed on the vehicle information acquisition device  106 . 
     The information of the ANC processing and the identification processing may be displayed on the display  46  of the in-vehicle system  24  or may be displayed on the display  34  of the smartphone  22 . 
     The vehicle information acquisition device  106  includes an operation processing device  107 , a memory  108 , a storage  109 , and a short-range wireless communication module  110 . 
     The operation processing device  107  is, for example, a processor such as a central processing unit (CPU) or a microprocessing unit (MPU). The memory  108  is, for example, a non-transitory or transitory tangible computer-readable recording medium such as a ROM or a RAM. The storage  109  is, for example, a non-transitory tangible computer-readable recording medium such as a flash memory. 
     When the active acoustic control program is installed on the vehicle information acquisition device  106 , the active acoustic control program is stored in the storage  109 . The operation processing device  107  functions as the active acoustic control device  10  when the operation processing device  107  performs active acoustic control processing in accordance with the active acoustic control program stored in the storage  109 . 
     The short-range wireless communication module  110  is a module that performs communication by short-range wireless communication such as Bluetooth (registered trademark). If the vehicle information acquisition device  106  is wirelessly connected to the smartphone  22  and the in-vehicle system  24 , the short-range wireless communication module  110  is used to communicate with the smartphone  22  and the in-vehicle system  24 . 
     The vehicle information acquisition device  106  is connected to an on-board diagnostics (OBD) connector  112  provided in the vehicle  12 . The OBD connector  112  is connected to an in-vehicle ECU via a CAN or a K line. From the OBD connector  112 , vehicle information such as an engine rotational speed, a water temperature, a voltage, and a boost pressure can be acquired. 
     The vehicle information acquisition device  106  is connected to the microphone  20  by wire. The vehicle information acquisition device  106  and the microphone  20  may be wirelessly connected to each other. 
     The vehicle information acquisition device  106  can be installed in the vehicle compartment  14  such that it can be easily detachable by the user.  FIGS.  22 A and  22 B  are views showing an example of an installation position of the vehicle information acquisition device  106  in the vehicle compartment  14 . As shown in  FIG.  22 A , the vehicle information acquisition device  106  is fixed to a center lower cover  23  at a lower portion of a steering wheel  21  with double-sided tape or the like. A wire  106   a  extends from the vehicle information acquisition device  106 , and the vehicle information acquisition device  106  is connected to the smartphone  22  and the in-vehicle system  24  by the wire  106   a.    
     The position where the vehicle information acquisition device  106  is set is not limited to the position shown in  FIG.  22 A . For example, as shown in  FIG.  22 B , it may be fixed to a side surface of a center console  25  with double-sided tape or the like. 
     [Operation and Advantageous Effects] 
     In the present embodiment, the vehicle information acquisition device  106  is connected to the OBD connector  112 . Thus, the vehicle information acquisition device  106  can acquire the engine rotational speed Ne from the in-vehicle ECU. 
     Further, the vehicle information acquisition device  106  is detachably attached in the vehicle compartment  14 . Thus, when the user changes to another vehicle  12 , the user can remove the vehicle information acquisition device  106  from the original vehicle  12  and attach the vehicle information acquisition device  106  to the other vehicle  12 . Therefore, if the vehicle information acquisition device  106  on which the active acoustic control program is installed is attached to the other vehicle  12 , the active noise control can be performed in the other vehicle  12  by the vehicle information acquisition device  106 . 
     Fifth Embodiment 
     In the first to third embodiments, the smartphone  22  on which the active acoustic control program is installed is caused to function as the active acoustic control device  10 . In contrast, in the present embodiment, the in-vehicle system  24  on which the active acoustic control program is installed is caused to function as the active acoustic control device  10 . 
       FIG.  23    is a block diagram of a smartphone  22  and an in-vehicle system  24 . In the present embodiment, detailed description of the same configurations as those in the first to third embodiments will be omitted. 
     The in-vehicle system  24  is connected to the smartphone  22  by wire. The in-vehicle system  24  may be wirelessly connected to the smartphone  22 . 
     An active acoustic control program is downloaded from the server  26  to the smartphone  22  via the Internet  28 , and the active acoustic control program is transmitted from the smartphone  22  to the in-vehicle system  24 . The active acoustic control program transmitted from the smartphone  22  is installed in the in-vehicle system  24 . 
     The information of the ANC processing and the identification processing may be displayed on the display  46  of the in-vehicle system  24  or may be displayed on the display  34  of the smartphone  22 . 
     The in-vehicle system  24  is connected to the engine rotational speed sensor  19  and the microphone  20  by wire. The in-vehicle system  24  may be wirelessly connected to the engine rotational speed sensor  19  and the microphone  20 . 
     [Operation and Advantageous Effects] 
     In this embodiment, the downloading of the active acoustic control program from the server  26  is performed by the smartphone  22  including a mobile communication module  38  and a wireless LAN communication module  40 . Then, the downloaded active acoustic control program is transmitted from the smartphone  22  to the in-vehicle system  24 , and the active acoustic control program is installed on the in-vehicle system  24 . Accordingly, even in the in-vehicle system  24  in which the mobile communication module or the wireless LAN communication module is not included, the active acoustic control program can be installed, and the in-vehicle system  24  can function as the active acoustic control device  10 . 
     Sixth Embodiment 
     In the first to fifth embodiments, the active acoustic control device  10  performs active noise control in the active acoustic control. In contrast, in the present embodiment, an active acoustic control device  10  performs active sound effect control in addition to the active noise control. In the active sound effect control, a sound effect simulating the engine sound is output from the speaker  16  in accordance with the engine rotational speed Ne. Thereby, for example, it is possible to give a vehicle occupant of the vehicle  12  feelings of comfort and acceleration. 
       FIG.  24    is a block diagram of the active acoustic control device  10 . The active acoustic control device  10  includes an active noise control unit  113  that performs active noise control and an active sound effect control unit  114  that performs active sound effect control. The configuration of the active acoustic control device  10  according to any one of the first to fourth embodiments is used as the configuration of the active noise control unit  113 . The active sound effect control unit  114  corresponds to a sound effect generating unit of the present invention. 
     The active sound effect control unit  114  includes a frequency detecting circuit  116 , a harmonic signal generating unit  118 , a waveform storage unit  120 , and a control signal generating unit  122 . 
     The frequency detecting circuit  116  detects a vibration frequency f in the same manner as the frequency detecting circuit  78   a  of the first embodiment. The harmonic signal generating unit  118  generates a harmonic signal fh that is four times, five times, or six times the vibration frequency f. The waveform storage unit  120  stores waveform data having different amplitudes and phases for respective harmonic signals fh. The control signal generating unit  122  generates a control signal v 0  based on the waveform corresponding to the harmonic signal fh. 
     The control signal u 0  output from the active noise control unit  113  and the control signal v 0  output from the active sound effect control unit  114  are added by an adder  124 . The speaker  16  is controlled based on the control signal u 0  and the control signal v 0 . Thus, a sound effect imitating an engine sound is output from the speaker  16  together with a canceling sound for reducing noise. 
     [Operation and Advantageous Effects] 
     The active acoustic control device  10  according to the present embodiment includes the active noise control unit  113  and the active sound effect control unit  114 . Thus, a sound effect imitating an engine sound can be output from the speaker  16  together with a canceling sound for reducing noise. 
     [Modifications] 
     In the first to sixth embodiments, the vibration frequency f is detected based on the engine rotational speed Ne. There is a high correlation between the acceleration of the vehicle  12  and the engine rotational speed Ne. Therefore, the vibration frequency f may be detected based on the acceleration of the vehicle  12  detected by the acceleration sensor  37  of the smartphone  22  in the vehicle compartment  14 . 
     The engine rotational speed Ne also has a high correlation with the speed of the vehicle  12 . Therefore, an accumulated value of acceleration of the vehicle  12  detected by the acceleration sensor  37  of the smartphone  22  in the vehicle compartment  14  may be set as the vehicle speed, and the vibration frequency f may be detected based on the speed. 
     Terms of Computer in the Present Application 
     In the present application, a computer refers to a machine that automatically performs complex calculations or operations according to a given procedure. In particular, it refers to an electric machine that can continuously perform input/output, calculation or operation, conversion, and the like of digital data using an electronic circuit or the like, and can be used for various purposes by a person or the like describing and giving detailed processing procedures. 
     Generally, a device classified as a computer itself includes a personal computer (PC) that is a general purpose computer for personal use, a server or a mainframe that is a large-scale and high-performance computer used in an information system or the like of a company, a supercomputer that is an ultrahigh-performance computer used for scientific and technical calculation or the like, and so on. Also, electrical machines that handle information and data often incorporate a type of computer in some form. 
     Therefore, in the present application, a computer shall include a communication device of every kind such as a mobile phone, a smartphone, and a tablet terminal, and an electronically controlled home electric appliance and an industrial machine such as a video recorder, a digital television, a digital camera, a game machine, and a vehicle control device. 
     That is, a computer in the present application includes an input/output device that exchanges data with the outside, a storage device that records data, a control device that executes a program and controls an execution state of the program and a state of each device, a computation device or an operation device that calculates and processes data, and the like. 
     Among them, the storage device may be divided into a main storage device used for temporary storage and an external storage device (auxiliary storage device) used for permanent storage. 
     The control device and the computation device may be integrated as one device or a semiconductor chip, and this may be used as a processing device (or a central processing unit, a CPU, or a processor). 
     The calculation procedure of a computer is recorded and given (concept of a stored-program computer), and this is called a computer program or simply a program. 
     Terms of Operation Processing Device in the Present Application 
     An operation processing device is a central processing unit (CPU, microprocessing unit, MPU, processor) in which transistors and semiconductor elements are integrated. The operation processing device is one of the main components of a computer, and is a device that performs control of other devices and circuits, calculation of data, and the like. This is a device that combines a computation device with a control device. In recent years, a microprocessor (MPU: Micro-Processing Unit) integrated on a single IC chip is used. 
     The operation processing device sequentially reads (fetches) a program of a machine language stored in a main memory (RAM) one by one through a bus, interprets the contents of the program to determine (decode) an operation to be performed, and drives an internal circuit to actually execute processing. The operation processing device includes a control unit that interprets instructions and instructs other circuits to perform operations, and a computation unit (ALU: Arithmetic and Logic Unit) that performs logic operations and arithmetic operations, a register for temporarily storing data, an interface circuit for communicating with the outside, and the like. 
     Further, in order to fill an excessively large difference in speed and capacity between the register and the main memory, a cache memory having both a speed and a capacity intermediate between those of the two memories is often incorporated. 
     Terms of Main Storage Device in the Present Application 
     The main storage device is also referred to as a “main memory”, a “memory”, or a “RAM”. The main storage device is directly connected to a central processing unit (CPU) through electric wiring or the like on a board. The main storage device is a storage device that can be directly read and written by a command of the CPU, and stores a program code that is being executed, data necessary for current processing, and the like. The main storage device is much faster in read/write operation than an external storage device (storage), but is generally several orders of magnitude smaller in capacity than the external storage device because of its high unit price. 
     A DRAM (Dynamic RAM), which is a kind of RAM (Random Access Memory) of a semiconductor storage device (semiconductor memory), is mostly used as a main storage device (main memory) in a modern computer, and has a characteristic that stored contents are lost when energization to the device is stopped by turning off a power supply of the device. Therefore, as basic operation, a storage is used for permanent storage of data and programs, and when the computer is started, a necessary program or the like is read into a main memory and executed. Many modern CPU products incorporate a storage circuit called a “cache memory” which is faster than the DRAM, but this is used only as a temporary storage location for speeding up communication with the DRAM, and the operation cannot be explicitly controlled with a program. 
     Terms of Storage in the Present Application 
     The storage is also referred to as an “external storage device”, an “external storage unit”, or an “auxiliary storage device”. Storage is one of the major components of a computer and is a device that permanently stores data. A magnetic disk (hard disk or the like), an optical disk (CD/DVD/Blu-ray (registered trademark) Disc or the like), a flash memory storage device (USB memory/memory card/SSD (solid state drive) or the like), a magnetic tape or the like corresponds to the storage. 
     The storage generally refers to a storage device in which stored contents are maintained without being energized, and is used for fixedly storing programs, data, and the like used by a computer over a long period of time. In addition to this, a main storage device (main memory, memory) for storing data by a semiconductor element or the like is incorporated in the computer, and when a user starts a program and processes data, a necessary program is called from the storage to the memory and used. 
     When devices mounted on the same computer are compared with each other, the storage has a storage capacity which is some orders of magnitude larger than that of the memory (several tens to several thousands times), and cost per capacity is some orders of magnitude smaller, but time required for reading and writing is some orders of magnitude longer. 
     Technical Idea Obtained from Embodiment 
     A description will be given below concerning technical concepts that are capable of being grasped from the above-described embodiments. 
     The active acoustic control program downloaded using the communication device ( 22 ) that transmits and receives data to and from the server ( 26 ), the active acoustic control program causing the operation processing device ( 29 ) to execute a process of generating a control signal that causes the speaker ( 16 ) provided in the vehicle compartment ( 14 ) of the vehicle ( 12 ) to output a canceling sound in order to reduce noise in the vehicle compartment, the active acoustic control program including the basic signal generating unit ( 52 ) configured to generate a basic signal corresponding to the noise generated from a noise source, the adaptive notch filter ( 54 ) configured to adaptively perform signal processing on the basic signal to generate the control signal, the error signal input unit ( 56 ) configured to input an error signal corresponding to a cancellation error noise of the noise and the canceling sound output from the speaker based on the control signal, the identifying unit ( 60 ) configured to identify a transfer characteristic of a sound in a space of the vehicle compartment to generate a correction value, the reference signal generating unit ( 58 ) configured to generate a reference signal by correcting the basic signal based on the correction value, and the filter coefficient updating unit ( 60 ) configured to sequentially update a filter coefficient of the adaptive notch filter based on the error signal and the reference signal in a manner that the error signal is minimized. 
     In the above-described active acoustic control program, the device on which the active acoustic control program downloaded using the communication device is installed may include the microphone ( 32 ), the microphone may detect the cancellation error noise, and the identifying unit may identify a transfer characteristic of a sound having a frequency of the basic signal in a transfer path from the speaker to the microphone to generate the correction value. 
     In the above-described active acoustic control program, the device on which the active acoustic control program downloaded using the communication device is installed may be connected to the microphone ( 20 ), the microphone may detect the cancellation error noise, and the identifying unit may identify a transfer characteristic of a sound having a frequency of the basic signal in a transfer path from the speaker to the microphone to generate the correction value. 
     In the above-described active acoustic control program, the device on which the active acoustic control program downloaded using the communication device is installed may include the number-of-engine-cylinders input section ( 35   d ) configured to receive an input of information about a number of engine cylinders, the engine rotational speed acquisition device ( 19 ) configured to detect an engine rotational speed may be connected to the device on which the active acoustic control program is installed, and the basic signal generating unit may generate the basic signal based on the number of engine cylinders and the engine rotational speed. 
     In the above-described active acoustic control program, the device on which the active acoustic control program downloaded using the communication device is installed may include the number-of-speakers input section ( 35   k ) configured to receive an input of information about a number of speakers, and the number-of-microphones input section ( 35   m ) configured to receive an input of information about a number of microphones, and a number of correction values and a number of filter coefficients are determined according to the number of speakers and the number of microphones. 
     In the above-described active acoustic control program, the device on which the active acoustic control program downloaded using the communication device is installed may include the number-of-engine-cylinders input section configured to receive an input of information about a number of engine cylinders, and the acceleration detecting unit ( 37 ) configured to detect an acceleration, and the basic signal generating unit may generate the basic signal based on the number of engine cylinders and the acceleration. 
     The above-described active acoustic control program may further include the sound effect generating unit ( 114 ) configured to generate a second control signal that causes the speaker to output a sound effect, based on the engine rotational speed. 
     In the above-described active acoustic control program, the operation processing device may be caused to function as a sound effect generating unit configured to generate a second control signal that causes the speaker to output a sound effect, based on the acceleration or a speed of the vehicle. 
     The microphone that detects the cancellation error noise used when causing the operation processing device to execute the process in accordance with the above-described active acoustic control program, wherein the microphone is connected by wire or wirelessly to a device on which the active sound control program downloaded using the communication device is installed, and the microphone is detachably mounted in the vehicle compartment. 
     The engine rotational speed acquisition device ( 106 ) that acquires a engine rotational speed used when causing the operation processing device to execute the process in accordance with the above-described active acoustic control program, wherein the engine rotational speed acquisition device is connected by wire or wirelessly to the device, and is detachably mounted in the vehicle compartment. 
     REFERENCE SIGNS LIST 
     
         
           12 : vehicle 
           14 : vehicle compartment 
           16 : speaker 
           20 ,  32 : microphone 
           18 : engine (noise source) 
           19 : engine rotational speed sensor (engine rotational speed acquisition device) 
           22 : smartphone (communication device) 
           26 : server 
           29 : operation processing device 
           35   d : number-of-engine-cylinders input section 
           35   k : number-of-speakers input section 
           35   m : number-of-microphones input section 
           37 : acceleration sensor (acceleration detection unit) 
           52 : basic signal generating unit 
           54 : control signal generating unit (adaptive notch filter) 
           56 : error signal input unit 
           58 : reference signal generating unit 
           60 : control filter coefficient updating unit (filter coefficient updating unit, identifying unit) 
           106 : vehicle information acquisition device (engine rotational speed acquisition device) 
           114 : active sound effect control unit (sound effect generating unit)