Active noise control device

Abstract

The present invention provides an active noise control device. The active noise control device (10) includes a secondary path filter coefficient updating unit (40). When it is determined that the phase characteristic of the secondary path filter with an initial value as the coefficient is not similar to the phase characteristic of the secondary path filter with a previous value as the coefficient, the secondary path filter coefficient updating unit (40) uses the coefficient of the secondary path filter after the last update as the last value to update the coefficient of the secondary path filter. Thus, even if the transfer characteristic changes, the noise can be reduced.

Description

Technical Field

[0001] The invention relates to an active noise control device. Background Art

[0002] Japanese Patent Publication No. 2008-239098 discloses a technique for causing a speaker to output a cancelling sound for cancelling noise. The noise is transmitted from a transmission shaft to the interior of a vehicle. A control signal for outputting the cancelling sound from a speaker is generated by processing a reference signal generated based on the rotation frequency of the transmission shaft by an adaptive filter. The adaptive filter is updated based on an error signal and a reference signal. The error signal is a signal output from a microphone disposed in the vehicle compartment. The reference signal is a signal generated by correcting the reference signal using a correction value. Summary of the invention

[0003] In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2008-239098, the transfer characteristics of the canceling sound between the speaker and the microphone are measured in advance, and the measured transfer characteristics are used as the correction value of the reference signal. Therefore, if the transfer characteristics change, the noise may not be reduced.

[0004] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an active noise control device that can reduce noise even if the transfer characteristic changes.

[0005] The technical scheme of the present invention is an active noise control device, which performs active noise control for controlling a speaker according to an error signal, wherein the error signal changes according to a synthesized sound of noise transmitted from a vibration source and a cancelling sound output from the speaker for cancelling the noise, and the active noise control device comprises a reference signal generating unit, a control signal generating unit, an estimated noise signal generating unit, a first estimated cancelling signal generating unit, a first virtual error signal generating unit, a secondary path filter coefficient updating unit, and an initial value table, wherein the reference signal generating unit generates a reference signal corresponding to a control target frequency; the control signal generating unit processes the reference signal using a control filter as an adaptive notch filter to generate a control signal for controlling the speaker; the estimated noise signal generating unit processes the reference signal using a primary path filter as an adaptive notch filter to generate an estimated noise signal; the first estimated cancelling signal generating unit processes the control signal using a secondary path filter as an adaptive notch filter to generate a first estimated cancelling signal; the first virtual error signal generating unit generates a secondary path filter coefficient updating unit according to the error signal; The secondary path filter coefficient updating unit adaptively updates the coefficients of the secondary path filter in sequence according to the control signal and the first virtual error signal so as to minimize the magnitude of the first virtual error signal; the initial value table stores the initial values ​​of the coefficients of the secondary path filter in a table form in correspondence with the frequencies; the secondary path filter coefficient updating unit performs the following processing: before updating the coefficients of the secondary path filter, determining whether the phase characteristics of the secondary path filter when the initial values ​​corresponding to the frequencies in the initial value table are used as the coefficients of the secondary path filter are similar to the phase characteristics of the secondary path filter after the coefficient updating unit last updates the coefficients; if it is determined that they are similar, updating the coefficients of the secondary path filter using the initial values ​​as the last values; if it is determined that they are not similar, updating the coefficients of the secondary path filter using the coefficients of the secondary path filter after the coefficient updating unit last updates the coefficients as the last values.

[0006] The active noise control device of the present invention can reduce noise even if the transfer characteristics change.

[0007] The above-mentioned objects, features and advantages will be easily understood from the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1FIG. 2 is a diagram for explaining an overview of active noise control performed in the active noise control device.

[0009] Figure 2 This is a block diagram of an active noise control device using the method proposed by the present inventors.

[0010] Figure 3 is a block diagram of an active noise control device.

[0011] Figure 4 is a diagram showing a secondary path filter on the complex plane.

[0012] Figure 5 is a diagram showing a secondary path filter on the complex plane.

[0013] Figure 6 This is a diagram that explains the table.

[0014] Figure 7 : is a flowchart showing the flow of the filter coefficient update process.

[0015] Figure 8 It is a graph showing the phase characteristics of the secondary path transfer characteristic and the phase characteristics of the secondary path filter.

[0016] Fig. 9 Graph showing the sound pressure level of the noise in the vehicle cabin when no active noise control is performed and when active noise control is performed using a secondary path filter.

[0017] Fig.10 Graph showing the sound pressure level of the noise in the vehicle cabin when no active noise control is performed and when active noise control is performed using a secondary path filter. DETAILED DESCRIPTION

[0018] [First embodiment]

[0019] Figure 1 2 is a diagram for explaining an overview of active noise control performed in active noise control device 10 .

[0020] The active noise control device 10 causes a speaker 16 provided in a vehicle cabin 14 of a vehicle 12 to output a cancelling sound. The cancelling sound cancels out the engine roar (hereinafter referred to as noise) transmitted to the occupant due to the vibration of the engine 18, thereby reducing the sound pressure of the noise. The active noise control device 10 receives an error signal e and an engine speed Ne. The error signal e is a signal output from a microphone 22 that detects a cancelling error noise described later. The engine speed Ne is a detection value detected by an engine speed sensor 24. The active noise control device 10 generates a control signal u0 based on the error signal e and the engine speed Ne. The active noise control device 10 outputs the control signal u0 to the speaker 16, and the speaker 16 outputs the cancelling sound based on the control signal u0. The cancelling error noise is a synthesized sound of the cancelling sound and the noise at the position of the microphone 22. The microphone 22 is provided on a headrest 20a of a seat 20 provided in the vehicle cabin 14. Accordingly, the microphone 22 is provided near the ear of the occupant.

[0021] [Regarding the active noise control device of the prior art]

[0022] In the prior art, an active noise control device is proposed. The active noise control device uses an adaptive notch filter (for example, a SAN (Single-frequency Adaptive Notch) filter) with a small amount of computational processing.

[0023] In the active noise control device of the prior art, first, a reference signal x is generated, which has the frequency of the noise to be eliminated. Hereinafter, the frequency of the noise to be eliminated is referred to as the control target frequency. Next, the active noise control device generates a control signal u0 by performing signal processing on the reference signal x using a control filter W, wherein the control filter W is an adaptive notch filter.

[0024] The filter W is updated and controlled by an adaptive algorithm (eg, LMS (Least Mean Square) algorithm) to minimize the error signal e output from the microphone 22. As a result of canceling the noise by canceling the sound, the sound pressure of the sound input to the microphone 22 decreases, and the error signal e also decreases.

[0025] There is a transfer characteristic C in the transfer path of the sound from the speaker 16 to the microphone 22. The cancellation sound output from the speaker 16 is different in phase from the cancellation sound input to the microphone 22. In order to cancel the noise by the cancellation sound at the position of the microphone 22, it is necessary to output the cancellation sound from the speaker 16 in consideration of the phase of the cancellation sound input to the microphone 22. The speaker 16 outputs the cancellation sound according to the control signal u0. The control signal u0 is a signal processed by the control filter W.

[0026] The active noise control device of the prior art identifies the transfer characteristic C as the filter C ^ in advance. Then, the active noise control device of the prior art updates the control filter W using the reference signal x after the signal processing by the filter C ^. This control is called Filtered-X type. In addition, the electronic circuit characteristics of the speaker 16 and the electronic circuit characteristics of the microphone 22 are included in the transfer characteristic C.

[0027] The filter C^ is a fixed filter identified in advance. Therefore, when the transfer characteristic C changes, the phase characteristic of the filter C^ and the phase characteristic of the transfer characteristic C may deviate greatly. In this case, when the control filter W is updated, the control filter W may diverge. In addition, the canceling sound output from the speaker 16 may amplify the noise, and the canceling sound output from the speaker 16 may become an abnormal sound.

[0028] Therefore, the present inventors proposed a method for making the filter C^ follow the change of the transfer characteristic C in active noise control without previously evaluating the transfer characteristic C. The present invention further improves the method proposed by the present inventors. The following is a general description of an active noise control device 100 using the method proposed by the present inventors.

[0029] Figure 2 1 is a block diagram showing an active noise control device 100 using a method proposed by the present inventors. Hereinafter, the transmission path of sound from the engine 18 to the microphone 22 is referred to as a primary path. Also, hereafter, the transmission path of sound from the speaker 16 to the microphone 22 is referred to as a secondary path.

[0030] The active noise control device 100 includes a reference signal generating unit 26, a control signal generating unit 28, a first estimated cancellation signal generating unit 30, an estimated noise signal generating unit 32, a reference signal generating unit 34, a second estimated cancellation signal generating unit 36, a primary path filter coefficient updating unit 38, a secondary path filter coefficient updating unit 40, and a control filter coefficient updating unit 42.

[0031] The reference signal generating unit 26 generates reference signals xc and xs according to the engine speed Ne. The reference signal generating unit 26 includes a frequency detecting circuit 26a, a cosine signal generator 26b, and a sine signal generator 26c.

[0032] The frequency detection circuit 26a detects the control target frequency f. The control target frequency f is the vibration frequency of the engine 18 detected based on the engine speed Ne. The cosine signal generator 26b generates a reference signal xc (=cos(2πft)) as a cosine signal of the control target frequency f. The sine signal generator 26c generates a reference signal xs (=sin(2πft)) as a sine signal of the control target frequency f. Here, t represents time.

[0033] The control signal generating unit 28 generates control signals u0 and u1 based on the reference signals xc and xs. The control signal generating unit 28 includes a first control filter 28a, a second control filter 28b, a third control filter 28c, a fourth control filter 28d, an adder 28e, and an adder 28f.

[0034] The control signal generating unit 28 performs signal processing on the reference signals xc and xs using the control filter W as a SAN filter. The control filter W has a filter W0 for the reference signal xc and a filter W1 for the reference signal xs. The coefficient W0 of the filter W0 and the coefficient W1 of the filter W1 are updated in the control filter coefficient updating unit 42 described later, thereby optimizing the control filter W.

[0035] The first control filter 28a has a filter coefficient W0. The second control filter 28b has a filter coefficient W1. The third control filter 28c has a filter coefficient -W0. The fourth control filter 28d has a filter coefficient W1.

[0036] The reference signal xc processed by the first control filter 28a and the reference signal xs processed by the second control filter 28b are added by the adder 28e to generate the control signal u0. The reference signal xs processed by the third control filter 28c and the reference signal xc processed by the fourth control filter 28d are added by the adder 28f to generate the control signal u1.

[0037] The control signal u0 is converted into an analog signal by the digital-analog converter 17, and is output to the speaker 16. The speaker 16 outputs a canceling sound based on the control signal u0.

[0038] The first estimated cancellation signal generating unit 30 generates a first estimated cancellation signal y1^ based on the control signals u0 and u1. The first estimated cancellation signal generating unit 30 includes a first secondary path filter 30a, a second secondary path filter 30b, and an adder 30c.

[0039] The first estimated cancellation signal generation unit 30 processes the control signals u0 and u1 by the secondary path filter C^, which is a SAN filter. The secondary path filter coefficient update unit 40 described later updates the coefficient (C0^+iC1^) of the secondary path filter C^, thereby identifying the secondary path transfer characteristic C as the secondary path filter C^.

[0040] The filter coefficient of the first secondary path filter 30a is the real part C0^ of the coefficient of the secondary path filter C^. The filter coefficient of the second secondary path filter 30b is the imaginary part C1^ of the coefficient of the secondary path filter C^. The control signal u0 after the signal processing by the first secondary path filter 30a and the control signal u1 after the signal processing by the second secondary path filter 30b are added by the adder 30c to generate the first estimated cancellation signal y1^. The first estimated cancellation signal y1^ is an estimated signal equivalent to the cancellation sound y input to the microphone 22.

[0041] The estimated noise signal generator 32 generates an estimated noise signal d^ based on the reference signals xc and xs. The estimated noise signal generator 32 includes a first primary path filter 32a, a second primary path filter 32b, and an adder 32c.

[0042] The estimated noise signal generating unit 32 performs signal processing on the reference signal xc through the primary path filter H ^ as the SAN filter. The transfer characteristic H of the primary path is identified as the primary path filter H ^ by updating the coefficient (H0 ^ + iH1 ^) of the primary path filter H ^ by the primary path filter coefficient updating unit 38 described later. Hereinafter, the transfer characteristic H of the primary path is referred to as the primary path transfer characteristic H.

[0043] The filter coefficient of the first primary path filter 32a is the real part H0^ of the coefficient of the primary path filter H^. The filter coefficient of the second primary path filter 32b is -H1^ obtained by reversing the polarity of the imaginary part of the coefficient of the primary path filter H^. The reference signal xc processed by the first primary path filter 32a and the reference signal xs processed by the second primary path filter 32b are added by the adder 32c to generate an estimated noise signal d^. The estimated noise signal d^ is an estimated signal equivalent to the noise d input to the microphone 22.

[0044] The reference signal generator 34 generates reference signals r0 and r1 based on the reference signals xc and xs. The reference signal generator 34 includes a third secondary path filter 34a, a fourth secondary path filter 34b, a fifth secondary path filter 34c, a sixth secondary path filter 34d, an adder 34e, and an adder 34f.

[0045] The reference signal generating unit 34 processes the reference signals xc and xs by the secondary path filter C^, which is a SAN filter. The secondary path filter coefficient updating unit 40 described later updates the coefficient (C0^+iC1^) of the secondary path filter C^, thereby identifying the transfer characteristic C of the secondary path as the secondary path filter C^. Hereinafter, the transfer characteristic C of the secondary path is referred to as the secondary path transfer characteristic C.

[0046] The filter coefficient of the third secondary path filter 34a is the real part C0^ of the coefficient of the secondary path filter C^. The filter coefficient of the fourth secondary path filter 34b is -C1^ obtained by inverting the polarity of the imaginary part of the coefficient of the secondary path filter C^. The filter coefficient of the fifth secondary path filter 34c is the real part C0^ of the coefficient of the secondary path filter C^. The filter coefficient of the sixth secondary path filter 34d is the imaginary part C1^ of the coefficient of the secondary path filter C^.

[0047] The reference signal xc processed by the third secondary path filter 34a and the reference signal xs processed by the fourth secondary path filter 34b are added by the adder 34e to generate the reference signal r0. The reference signal xs processed by the fifth secondary path filter 34c and the reference signal xc processed by the sixth secondary path filter 34d are added by the adder 34f to generate the reference signal r1.

[0048] The second estimated cancellation signal generating unit 36 ​​generates a second estimated cancellation signal y2^ based on the reference signals r0 and r1. The second estimated cancellation signal generating unit 36 ​​includes a fifth control filter 36a, a sixth control filter 36b, and an adder 36c.

[0049] In the second estimated cancellation signal generation unit 36, the reference signals r0 and r1 are subjected to signal processing by the control filter W, which is a SAN filter. The filter coefficient of the fifth control filter 36a is W0. The filter coefficient of the sixth control filter 36b is W1.

[0050] The adder 36c adds the reference signal r0 processed by the fifth control filter 36a and the reference signal r1 processed by the sixth control filter 36b to generate a second estimated cancellation signal y2^. The second estimated cancellation signal y2^ is an estimated signal corresponding to the cancellation sound y input to the microphone 22.

[0051] The analog-to-digital converter 44 converts the error signal e output from the microphone 22 from an analog signal to a digital signal.

[0052] The error signal e is input to the adder 46. The polarity of the estimated noise signal d ^ generated by the estimated noise signal generating unit 32 is inverted by the inverter 48. The estimated noise signal -d ^ after the polarity inversion is input to the adder 46. The polarity of the first estimated cancellation signal y1 ^ generated by the first estimated cancellation signal generating unit 30 is inverted by the inverter 50. The first estimated cancellation signal -y1 ^ after the polarity inversion is input to the adder 46. The estimated noise signal -d ^ and the first estimated cancellation signal -y1 ^ are added to each other by the adder 46 to generate the first virtual error signal e1. The adder 46 corresponds to the first virtual error signal generating unit of the present invention.

[0053] The estimated noise signal d ^ generated by the estimated noise signal generating unit 32 is input to the adder 52. The second estimated cancellation signal y2 ^ generated by the second estimated cancellation signal generating unit 36 ​​is input to the adder 52. The estimated noise signal d ^ and the second estimated cancellation signal y2 ^ are added by the adder 52 to generate the second virtual error signal e2. The adder 52 corresponds to the second virtual error signal generating unit of the present invention.

[0054] The primary path filter coefficient updating unit 38 adaptively updates the coefficients of the primary path filter H^ in sequence based on the LMS algorithm to minimize the magnitude of the first virtual error signal e1. The primary path filter coefficient updating unit 38 includes a first primary path filter coefficient updating unit 38a and a second primary path filter coefficient updating unit 38b.

[0055] The first primary path filter coefficient updating unit 38a and the second primary path filter coefficient updating unit 38b update the filter coefficients H0^ and H1^ according to the following formula: n in the formula represents a time step (n=0, 1, 2, ...), and μ0 and μ1 represent step size parameters.

[0056] H0^ n+1 =H0^ n -μ0×e1 n ×c n

[0057] H1^ n+1 =H1^ n -μ1×e1 n × n

[0058] The primary path transfer characteristic H is identified as the primary path filter H^ by repeatedly updating the filter coefficients H0^ and H1^ by the primary path filter coefficient updating unit 38. In the active noise control device 100 using the SAN filter, the update formula of the coefficient of the primary path filter H^ is composed of four arithmetic operations and does not include a convolution operation, so the calculation load caused by the update process of the filter coefficients H0^ and H1^ can be suppressed.

[0059] The secondary path filter coefficient updating unit 40 adaptively updates the coefficients of the secondary path filter C^ in sequence according to the LMS algorithm so as to minimize the magnitude of the first virtual error signal e1. The secondary path filter coefficient updating unit 40 includes a first secondary path filter coefficient updating unit 40a and a second secondary path filter coefficient updating unit 40b.

[0060] The first secondary path filter coefficient updating unit 40a and the second secondary path filter coefficient updating unit 40b update the filter coefficients C0^ and C1^ according to the following formula: μ2 and μ3 in the formula represent step size parameters.

[0061] C0^ n+1 =C0^ n -μ2×e1 n ×u0 n

[0062] C1^ n+1 =C1^ n -μ3×e1 n ×u1 n

[0063] The secondary path filter coefficient updating unit 40 repeatedly updates the filter coefficients C0^ and C1^, thereby identifying the secondary path transfer characteristic C as the secondary path filter C^. In the active noise control device 100 using the SAN filter, the update formula of the filter coefficients C0^ and C1^ is composed of four arithmetic operations and does not include a convolution operation, so the calculation load caused by the update process of the filter coefficients C0^ and C1^ can be suppressed.

[0064] The control filter coefficient updating unit 42 adaptively updates the coefficients W0 and W1 of the control filter W in sequence according to the LMS algorithm so as to minimize the magnitude of the second virtual error signal e2. The control filter coefficient updating unit 42 includes a first control filter coefficient updating unit 42a and a second control filter coefficient updating unit 42b.

[0065] The first control filter coefficient updating unit 42a and the second control filter coefficient updating unit 42b update the filter coefficients W0 and W1 according to the following formula: μ4 and μ5 in the formula represent step size parameters.

[0066] W0 n+1 =W0 n -μ4×e2 n ×r0 n

[0067] W1 n+1 =W1 n -μ5×e2 n ×r1n

[0068] The control filter W is optimized by repeatedly updating the filter coefficients W0 and W1 by the control filter coefficient updating unit 42. In the active noise control device 100 using the SAN filter, the update formula of the filter coefficients W0 and W1 is composed of four arithmetic operations and does not include a convolution operation. Therefore, the calculation load caused by the update process of the filter coefficients W0 and W1 can be suppressed.

[0069] [About improvements]

[0070] The present invention will be described with respect to the improved features of the active noise control device 100 using the method proposed by the present inventors.

[0071] Figure 3 1 is a block diagram of the active noise control device 10 of the present embodiment. The active noise control device 10 of the present embodiment includes the active noise control device 100 using the method proposed by the present inventors as the signal processing unit 54. The active noise control device 10 also includes an initial value table 56, an update value table 58, a result value table 60, an initial value table operation unit 62, an update value table operation unit 64, a result value table operation unit 66, and an end state determination unit 68.

[0072] The active noise control device 10 has an operation processing device and a storage device which are not shown in the figure. The operation processing device has, for example, a processor such as a central processing unit (CPU), a microprocessor (MPU), and a memory composed of ROM, RAM, etc. The storage device is, for example, a hard disk, a flash memory, etc. The active noise control device 10 may not have a storage device. The active noise control device 10 sends and receives data with the storage device on the cloud through communication. The signal processing unit 54, the initial value table operation unit 62, the update value table operation unit 64, the result value table operation unit 66 and the end state determination unit 68 are implemented by executing the program stored in the storage device by the operation processing unit.

[0073] The initial value table 56 is a table-shaped memory area provided in the ROM. The initial values ​​of the filter coefficients C0^ and C1^ of the secondary path filter C^ described later are stored in the initial value table 56. The update value table 58 is a table-shaped memory area provided in the RAM. The update values ​​of the filter coefficients C0^ and C1^ are stored in the update value table 58. The result value table 60 is a table-shaped memory area provided in the ROM. The result values ​​of the filter coefficients C0^ and C1^ are stored in the result value table 60.

[0074] The initial value table operation unit 62 performs writing of initial values ​​to the initial value table 56 , etc. The updated value table operation unit 64 performs writing of updated values ​​to the updated value table 58 , etc. The result value table operation unit 66 performs writing of result values ​​to the result value table 60 , etc.

[0075] The end state determination unit 68 determines the end cause of the active noise control. There are three reasons for the end of the active noise control. The first is a normal end due to the stop of the engine 18, the second is an abnormal end due to an abnormality in the active noise control, and the third is a divergent end due to the divergence of the active noise control.

[0076] The updating process of the filter coefficients C0 ^ and C1 ^ performed by the secondary path filter coefficient updating unit 40 of the present embodiment is partially different from the updating process of the filter coefficients C0 ^ and C1 ^ performed by the secondary path filter coefficient updating unit 40 of the active noise control device 100 described above.

[0077] First, in this embodiment, the secondary path filter coefficient update unit 40 performs the determination described below before updating the filter coefficients C0^ and C1^. The secondary path filter coefficient update unit 40 determines whether the phase characteristic of the secondary path filter C^ after the last coefficient update is similar to the phase characteristic of the secondary path filter C^ with the update value as the coefficient. Since this determination is performed before updating the filter coefficients C0^ and C1^, the secondary path filter C^ after the last coefficient update can also be said to be the current secondary path filter C^. The update value corresponds to the control object frequency f obtained based on the current engine speed Ne. The update value is stored in the later-described Figure 6 In the update value table 58. In the following, the secondary path filter C^ after the last coefficient update is sometimes referred to as the last value secondary path filter C^. In addition, the secondary path filter C^ with the update value as the coefficient is sometimes referred to as the update value secondary path filter C^, where the update value corresponds to the control object frequency f obtained according to the current engine speed Ne.

[0078] When the phase difference θ between the phase characteristic of the previous value secondary path filter C^ and the phase characteristic of the updated value secondary path filter C^ is less than 15°, the secondary path filter coefficient update unit 40 determines that the phase characteristics of the two are similar. When the phase difference θ between the phase characteristic of the previous value secondary path filter C^ and the phase characteristic of the updated value secondary path filter C^ is greater than 15°, the secondary path filter coefficient update unit 40 determines that the phase characteristics of the two are not similar.

[0079] Figure 4: is a diagram showing the secondary path filter C^ on the complex plane. Point P represents the position of the previous value secondary path filter C^. Point Q and point R represent the position of the updated value secondary path filter C^. The phase difference θ can be obtained based on the following formula.

[0080]

[0081] The filter coefficients C0^ and C1^ of the previous value secondary path filter C^ are input to C0^n and C1^n in the above formula, respectively. The filter coefficients C0^ and C1^ of the updated value secondary path filter C^ are input to C0^(f)_u and C1^(f)_u in the above formula, respectively.

[0082] For example, in the update value secondary path filter C ^ located at Figure 4 At point Q shown in FIG. 1 , the phase difference θq between the updated secondary path filter C^ and the previous secondary path filter C^ is less than 15°. Therefore, the secondary path filter coefficient update unit 40 determines that the phase characteristic of the previous secondary path filter C^ is similar to the phase characteristic of the updated secondary path filter C^.

[0083] For example, in the update value secondary path filter C ^ located at Figure 4 At point R shown in FIG. 1 , the phase difference θr between the updated secondary path filter C^ and the previous secondary path filter C^ is greater than 15°. Therefore, the secondary path filter coefficient update unit 40 determines that the phase characteristic of the previous secondary path filter C^ is not similar to the phase characteristic of the updated secondary path filter C^.

[0084] Whether the phase characteristic of the previous value secondary path filter C ^ and the phase characteristic of the updated secondary path filter C ^ are similar to each other may be determined as follows.

[0085] Figure 5 is a diagram showing the secondary path filter C^ on the complex plane. Figure 5 As shown, the complex plane is divided into 12 regions S1 to S12 at a predetermined angle of 30°.

[0086] When the updated value secondary path filter C^ and the previous value secondary path filter C^ are located in the same region, the secondary path filter coefficient update unit 40 determines that the phase characteristics of the two are similar. When the updated value secondary path filter C^ and the previous value secondary path filter C^ are located in different regions, the secondary path filter coefficient update unit 40 determines that the phase characteristics of the two are not similar.

[0087] For example, in updating the value of the secondary path filter C ^ lie in Figure 5In the case of the point Q shown in FIG. 1 , the point Q is located in the same region S2 as the point P which is the position of the previous value secondary path filter C^. Therefore, the secondary path filter coefficient update unit 40 determines that the phase characteristic of the previous value secondary path filter C^ is similar to the phase characteristic of the updated value secondary path filter C^.

[0088] For example, in the updated value secondary path filter C^ is located at Figure 5 In the case of the point R shown in FIG. 1 , the point R is located in a region S1 different from the point P which is the position of the previous value secondary path filter C^. Therefore, the secondary path filter coefficient update unit 40 determines that the phase characteristic of the previous value secondary path filter C^ is not similar to the phase characteristic of the updated value secondary path filter C^.

[0089] When it is determined that the phase characteristic of the previous value secondary path filter C^ is similar to the phase characteristic of the updated value secondary path filter C^, the secondary path filter coefficient update unit 40 of the present embodiment performs the following processing. That is, the first secondary path filter coefficient update unit 40a of the secondary path filter coefficient update unit 40 and the second secondary path filter coefficient update unit 40b of the secondary path filter coefficient update unit 40 respectively update the filter coefficients C0^ and C1^ according to the following formula.

[0090] C0^(f) n+1 =C0^(f)_u-μ2×e1 n ×u0 n

[0091] C1^(f) n+1 =C1^(f)-u-μ3×e1 n ×u1 n

[0092] The update values ​​C0^(f)_u and C1^(f)_u corresponding to the control object frequency f are respectively input to the first item (hereinafter referred to as the pre-update value) on the right side of the above formula. The control object frequency f is the control object frequency f obtained based on the engine speed Ne at the time of this update (time step n+1). The filter coefficients C0^ and C1^ at the latest update time point among the filter coefficients C0^ and C1^ at which the engine speed Ne at the time of update is the same as the engine speed Ne at the time of this update are respectively input to the pre-update value.

[0093] When it is determined that the phase characteristic of the previous value secondary path filter C^ is not similar to the phase characteristic of the updated value secondary path filter C^, the secondary path filter coefficient updating unit 40 of the present embodiment updates the filter coefficients C0^ and C1^ in the first secondary path filter coefficient updating unit 40a and the second secondary path filter coefficient updating unit 40b according to the following formula.

[0094] C0^ n+1 =C0∧ n -μ2×e1 n ×u0 n

[0095] C1∧ n+1 =C1∧ n -μ3×e1 n ×u1 n

[0096] The filter coefficients C0^n and C1^n updated at the last update (time step n) are respectively input as the pre-update values ​​of the above formula. In this case, the filter coefficients C0^n and C1^n at the latest update time point among the filter coefficients C0^n and C1^ updated in the past are respectively input as the pre-update values. The engine speed Ne when the filter coefficients C0^n and C1^n input as the pre-update values ​​are updated is different from the engine speed Ne at the time of this update.

[0097] The secondary path filter coefficient update unit 40 uses the updated filter coefficients C0^ and C1^ as filter coefficients of the third secondary path filter 34a, the fourth secondary path filter 34b, the fifth secondary path filter 34c and the sixth secondary path filter 34d of the reference signal generation unit 34.

[0098] [Update of filter coefficients of secondary path filter]

[0099] Figure 6 This is a diagram that explains the table. Figure 6 As shown, the initial value table 56 stores the initial value C0 in a table format. ^ (f)_i, C1 ^ (f)_i. Initial value C0 ^ (f)_i, C1 ^ (f)_i is associated with the frequency and stored in the initial value table 56. Figure 6 As shown, the update value table 58 stores the update value C0 in a table format. ^ (f)_u, C1 ^ (f)_u. Update value C0 ^ (f)_u, C1 ^ (f)_u is associated with the frequency and stored in the update value table 58. Figure 6 As shown, the result value table 60 stores the result value C0 in a table format. ^ (f)_r, C1 ^ (f)_r. Result value C0 ^ (f)_r, C1 ^(f)_r is stored in the result value table 60 in correspondence with the frequency.

[0100] The initial value C0 stored in the initial value table 56 ^ (f)_i, C1 ^ (f)_i is set according to any one of the following (i) to (vi).

[0101] (i) Measured values ​​of secondary path transfer characteristics C at each frequency

[0102] (ii) Phase Characteristics of Measured Values ​​of Secondary Path Transfer Characteristics C at Each Frequency

[0103] (iii) Estimated value of the secondary path transfer characteristic C after supplementation based on the measured value of the secondary path transfer characteristic C at a representative frequency

[0104] (iv) Phase characteristics of the estimated value of the secondary path transfer characteristic C after supplementation based on the measured value of the secondary path transfer characteristic C at a representative frequency

[0105] (v) The estimated value of the secondary path transfer characteristic C is estimated by the following formula:

[0106] C0^(f)=a(f)×cos(-2πfT)

[0107] C1^(f)=a(f)×sin(-2πfT)

[0108] Here, T is the time it takes for sound to reach the microphone 20 from the speaker 16, and a is the amplitude constant.

[0109] (vi) A convenient smaller value (when no specific initial value is set for the sake of system setting efficiency, etc.)

[0110] Figure 7 is the filter coefficient C0 ^ 、C1 ^ Flow chart of the update process of the filter coefficients C0^ and C1^. Each time active noise control is implemented, the update process of the filter coefficients C0^ and C1^ is executed.

[0111] In step S1, the update value table operation unit 64 writes the initial value stored in the initial value table 56 into the update value table 58 as the update value. Figure 6 That is, the update value table operation unit 64 writes the initial value corresponding to each frequency as the update value corresponding to each frequency into the update value table 58. Thereafter, the process proceeds to step S2.

[0112] In step S2, the frequency detection circuit 26a included in the signal processing unit 54 detects the control target frequency f. Thereafter, the process proceeds to step S3.

[0113] In step S3, the secondary path filter coefficient update unit 40 reads the update value ( Figure 6 After that, the process proceeds to step S4.

[0114] In step S4, the secondary path filter coefficient update unit 40 determines whether the phase characteristic of the previous value secondary path filter C^ and the phase characteristic of the updated value secondary path filter C^ are similar. If it is determined that the phase characteristic of the previous value secondary path filter C^ and the phase characteristic of the updated value secondary path filter C^ are similar, the process proceeds to step S5. If it is determined that the phase characteristic of the previous value secondary path filter C^ and the phase characteristic of the updated value secondary path filter C^ are not similar, the process proceeds to step S6.

[0115] In step S5, the secondary path filter coefficient update unit 40 inputs the update value corresponding to the control target frequency f at the time of this update into the pre-update value of the update formula to update the filter coefficients C0 ^ and C1 ^. Thereafter, the process proceeds to step S7.

[0116] In step S6, the secondary path filter coefficient update unit 40 inputs the filter coefficients C0 ^ and C1 ^ updated last time into the pre-update values ​​of the update formula to update the filter coefficients C0 ^ and C1 ^. Thereafter, the process proceeds to step S7.

[0117] In step S7, the update value table operation unit 64 writes the updated filter coefficients C0 ^ and C1 ^ into the update value table 58 corresponding to the control target frequency f. Figure 6 After that, the process proceeds to step S8.

[0118] In step S8, the end state determination unit 68 determines whether the active noise control has ended. If the active noise control has not ended, the process returns to step S2, and if the active noise control has ended, the process proceeds to step S9.

[0119] In step S9, the end state determination unit 68 determines whether the active noise control has ended normally. If it is determined that the active noise control has ended normally, the process proceeds to step S10. If it is determined that the active noise control has ended abnormally or diverged, the process proceeds to step S12.

[0120] In step S10, the initial value table operation unit 62 determines whether rewriting of the initial value in the initial value table 56 is permitted. If rewriting of the initial value table 56 is permitted, the process proceeds to step S11. If rewriting of the initial value table 56 is not permitted, the update process of the filter coefficients C0 ^ and C1 ^ is terminated.

[0121] In step S11, the initial value table operation unit 62 rewrites the initial values ​​corresponding to the frequencies in the initial value table 56 with the updated values ​​corresponding to the frequencies in the updated value table 58 ( Figure 6 Then, the update process of the filter coefficients C0^ and C1^ is terminated.

[0122] In step S12, the result value table operation unit 66 writes the update value corresponding to each frequency in the update value table 58 into the result value corresponding to each frequency in the result value table 60 ( Figure 6 Then, the update process of the filter coefficients C0^ and C1^ is terminated.

[0123] The initial value table 56 and the result value table 60 can be copied to a personal computer or the like connected to the vehicle 12. Therefore, in the event that an abnormality or divergence occurs in the active noise control, by comparing the update value stored in the initial value table 56 with the result value stored in the result value table 60, the cause of the abnormality or divergence in the active noise control can be verified.

[0124] [Effects]

[0125] The secondary path characteristic C differs depending on the frequency of the cancelling sound. In order to more accurately identify the secondary path characteristic C, it is necessary to update the filter coefficients C0 ^ and C1 ^ of the secondary path filter C ^ according to the frequency of the cancelling sound.

[0126] In the present embodiment, the active noise control device 10 is provided with an initial value table 56 and an update value table 58. As a result, the active noise control device 10 can set the initial values ​​of the filter coefficients C0^ and C1^ according to the frequency. In addition, the active noise control device 10 can update the filter coefficients C0^ and C1^ according to the frequency using the update values ​​stored in the update value table 58. Since the initial values ​​are set according to the frequency, the active noise control device 10 can significantly improve the noise cancellation performance in the initial period after the start of active noise control. Since the filter coefficients C0^ and C1^ are updated according to the frequency, the active noise control device 10 can more accurately identify the secondary path characteristic C as the secondary path filter C^. Accordingly, the active noise control device 10 can improve the noise cancellation performance.

[0127] However, when the filter coefficients C0^ and C1^ are updated according to the frequency, the number of updates of the filter coefficients C0^ and C1^ corresponding to the frequency corresponding to the engine speed Ne with a low occurrence frequency is small, so the progress of learning is slow. Therefore, the secondary path filter C^ may deviate greatly from the secondary path transfer characteristic C. In this case, the noise reduction performance of the active noise control device 10 may be reduced, and abnormal sound may be output from the speaker 16.

[0128] Next, use Figure 8 and Fig. 9 To illustrate the increase in noise pressure due to active noise control.

[0129] Figure 8 Graph showing the phase characteristics of the secondary path transfer characteristic C and the phase characteristics of the secondary path filter C^. Figure 8 In FIG. 1 , the thick line represents the phase characteristic of the secondary path transfer characteristic C, and the thin line represents the phase characteristic of the secondary path filter C. Here, the phase characteristic of the secondary path filter C is set to 0° at all frequencies.

[0130] Fig. 9 is the sound pressure level of the noise in the cabin 14 without active noise control and the Figure 8 A graph showing the sound pressure level of the noise in the cabin 14 when the secondary path filter C^ performs active noise control. Fig. 9 In FIG. 1 , the thick line indicates the sound pressure level when active noise control is not performed, and the thin line indicates the sound pressure level when active noise control is performed using the secondary path filter C .

[0131] like Figure 8 As shown, at frequencies near 66 [Hz], 100 [Hz], and 130 [Hz], the phase characteristic of the secondary path filter C ^ and the actual secondary path transfer characteristic C have a phase difference of 180°. A frequency near 66 [Hz] is equivalent to an engine speed near 2000 [RPM]. A frequency near 100 [Hz] is equivalent to an engine speed near 3000 [RPM]. A frequency near 130 [Hz] is equivalent to an engine speed near 3800 [RPM]. Fig. 9 As shown, the sound pressure level of the noise when the active noise control is performed becomes higher at the engine speed around 2000 [RPM], the engine speed around 3000 [RPM], and the engine speed around 3800 [RPM] than the sound pressure level of the noise when the active noise control is not performed.

[0132] The engine speed Ne rarely increases or decreases sharply. Figure 8As shown, the secondary path transfer characteristic C changes continuously with respect to the change in frequency, so when the change in frequency is not abrupt, the change in phase characteristic is also not abrupt. When the frequency changes by 1 [Hz], the phase characteristic of the secondary path transfer characteristic C does not change by more than 10°.

[0133] Therefore, when learning of the update value of the update value table 58 does not progress, the phase characteristic of the previous value secondary path filter C^ may be closer to the phase characteristic of the secondary path transfer characteristic C than the phase characteristic of the update value secondary path filter C^.

[0134] Therefore, in the active noise control device 10 of the present embodiment, the secondary path filter coefficient update unit 40 determines whether the phase characteristic of the updated value secondary path filter C ^ is similar to the phase characteristic of the previous value secondary path filter C ^. And, when it is determined that the phase characteristic of the updated value secondary path filter C ^ is similar to the phase characteristic of the previous value secondary path filter C ^, the secondary path filter coefficient update unit 40 updates the filter coefficients C0 ^ and C1 ^ as follows. That is, the secondary path filter coefficient update unit 40 inputs the update values ​​C0 ^(f)_u and C1 ^(f)_u corresponding to the control object frequency f into the pre-update values ​​of the update formula to update the filter coefficients C0 ^ and C1 ^. On the other hand, when it is determined that the phase characteristic of the updated value secondary path filter C ^ is not similar to the phase characteristic of the previous value secondary path filter C ^, the secondary path filter coefficient update unit 40 updates the filter coefficients C0 ^ and C1 ^ as follows. That is, the secondary path filter coefficient updating unit 40 updates the filter coefficients C0 ^n and C1 ^n by inputting the filter coefficients C0 ^n and C1 ^n updated last time (at time step n) into the pre-update values ​​of the update formula.

[0135] Fig.10 : is a graph showing the sound pressure level of the noise in the vehicle cabin 14 when no active noise control is performed and the sound pressure level of the noise in the vehicle cabin 14 when the active noise control of the present embodiment is performed. Fig.10 In FIG. 1 , the thick line indicates the sound pressure level when the active noise control is not performed, and the thin line indicates the sound pressure level of the noise when the active noise control according to the present embodiment is performed.

[0136] In the active noise control of this embodiment, the filter coefficients C0^ and C1^ of the secondary path filter C^, which can suppress the characteristics from greatly deviating from the secondary path transfer characteristic C, are input with the values ​​before the update of the update formula of the filter coefficients C0^ and C1^. Fig.10 As shown, in the active noise control of the present embodiment, it is possible to suppress the sound pressure level of noise from increasing compared to the case where the active noise control is not performed.

[0137] The active noise control device 10 of the present embodiment can improve the convergence performance of the active noise control. Therefore, the active noise control device 10 of the present embodiment can improve the noise cancellation performance in the early stage after the start of the active noise control, and can suppress the generation of abnormal sound in the vehicle cabin 14 even in a state where the secondary path filter C ^ has not converged. In addition, the active noise control device 10 of the present embodiment can improve the quietness in the vehicle cabin 14 after the secondary path filter C ^ has converged.

[0138] In addition, in the active noise control device 10 of the present embodiment, in the secondary path filter coefficient updating unit 40, when the phase difference θ between the phase characteristic of the previous value secondary path filter C^ and the phase characteristic of the updated value secondary path filter C^ is less than 15°, it is determined that the phase characteristics of the two are similar. Accordingly, in the active noise control device 10 of the present embodiment, it is possible to accurately determine whether the phase characteristic of the previous value secondary path filter C^ and the phase characteristic of the updated value secondary path filter C^ are similar.

[0139] In addition, in the active noise control device 10 of the present embodiment, in the secondary path filter coefficient updating unit 40, when the updated value secondary path filter C^ and the previous value secondary path filter C^ are located in the same region on the complex plane, it is determined that the phase characteristic of the previous value secondary path filter C^ and the phase characteristic of the updated value secondary path filter C^ are similar. Accordingly, the active noise control device 10 of the present embodiment can simplify the determination of whether the phase characteristic of the previous value secondary path filter C^ and the phase characteristic of the updated value secondary path filter C^ are similar.

[0140] [Other implementation methods]

[0141] In the first embodiment, the active noise control device 10 includes the initial value table 56 and the update value table 58, but may not include the update value table 58. In this case, the secondary path filter coefficient update unit 40 determines whether the phase characteristic of the previous value secondary path filter C ^ is similar to the phase characteristic of the secondary path filter C ^ with the initial value as the coefficient. The initial value is a value corresponding to the control target frequency f stored in the initial value table 56. When it is determined that the phase characteristic of the previous value secondary path filter C ^ is similar to the phase characteristic of the secondary path filter C ^ with the initial value as the coefficient, the secondary path filter coefficient update unit 40 inputs the initial value of the initial value table 56 as the pre-update value of the update formula to update the filter coefficients C0 ^ and C1 ^. When it is determined that the phase characteristic of the last value secondary path filter C^ is not similar to the phase characteristic of the secondary path filter C^ with the initial value as the coefficient, the secondary path filter coefficient update unit 40 inputs the filter coefficients C0^ and C1^ updated last time into the pre-update value of the update formula to update the filter coefficients C0^ and C1^. And, whenever the filter coefficients C0^ and C1^ are updated, the initial value table operation unit 62 rewrites the initial value of the initial value table 56 to the updated filter coefficients C0^ and C1^.

[0142] [Technical ideas that can be obtained according to the implementation method]

[0143] The following describes the technical ideas that can be grasped from the above-mentioned embodiments.

[0144] An active noise control device (10) performs active noise control by controlling a speaker (16) based on an error signal, wherein the error signal changes based on a synthesized sound of noise transmitted from a vibration source and a cancelling sound output from the speaker (16) for cancelling the noise, the active noise control device (10) comprising a reference signal generating unit (26), a control signal generating unit (28), an estimated noise signal generating unit (32), a first estimated cancelling signal generating unit (30), a first hypothetical error signal generating unit (46), a secondary path filter coefficient updating unit (40), and an initial value table (56). , wherein the reference signal generating unit (26) generates a reference signal corresponding to a control object frequency; the control signal generating unit (28) uses a control filter as an adaptive notch filter to perform signal processing on the reference signal to generate a control signal for controlling the speaker; the estimated noise signal generating unit (32) uses a primary path filter as an adaptive notch filter to perform signal processing on the reference signal to generate an estimated noise signal; the first estimated cancellation signal generating unit (30) uses a secondary path filter as an adaptive notch filter to perform signal processing on the control signal to generate a first estimated cancellation signal; The first hypothetical error signal generating unit (46) generates a first hypothetical error signal according to the error signal, the first estimated cancellation signal and the estimated noise signal; the secondary path filter coefficient updating unit (40) adaptively updates the coefficients of the secondary path filter in sequence according to the control signal and the first hypothetical error signal so as to minimize the magnitude of the first hypothetical error signal; the initial value table (56) stores the initial values ​​of the coefficients of the secondary path filter in a table form in a corresponding relationship with the frequency, and the secondary path filter coefficient updating unit performs the following processing: when updating the coefficients of the secondary path filter Before updating the coefficients, it is determined whether the phase characteristics of the secondary path filter when the initial value corresponding to the frequency in the initial value table is used as the coefficient of the secondary path filter is similar to the phase characteristics of the secondary path filter after the secondary path filter coefficient updating unit last updated the coefficients. If it is determined that they are similar, the initial value is used as the last value to update the coefficients of the secondary path filter. If it is determined that they are not similar, the coefficients of the secondary path filter after the secondary path filter coefficient updating unit last updated the coefficients are used as the last value to update the coefficients of the secondary path filter.

[0145] In the above-mentioned active noise control device, it may be that, when a phase difference between a phase characteristic of the secondary path filter when the initial value corresponding to the frequency in the initial value table is used as the coefficient of the secondary path filter and a phase characteristic of the secondary path filter after the secondary path filter coefficient updating unit last updates the coefficient is less than a predetermined angle, the secondary path filter coefficient updating unit determines that the phase characteristic of the secondary path filter when the initial value corresponding to the frequency in the initial value table is used as the coefficient of the secondary path filter is similar to the phase characteristic of the secondary path filter after the secondary path filter coefficient updating unit last updates the coefficient.

[0146] In the above-mentioned active noise control device, a complex plane may be divided into a plurality of regions at a predetermined angle, and when, on the complex plane, a phase characteristic of the secondary path filter when the initial value corresponding to the frequency in the initial value table is used as the coefficient of the secondary path filter and a phase characteristic of the secondary path filter after the coefficient updating unit last updated the coefficient are located in the same region, it is determined that the phase characteristic of the secondary path filter when the initial value corresponding to the frequency in the initial value table is used as the coefficient of the secondary path filter and the phase characteristic of the secondary path filter after the coefficient updating unit last updated the coefficient are similar.

[0147] In the above-mentioned active noise control device, it is also possible to have an update value table (58) and an update value table operation unit (64), wherein the update value table (58) stores the update value of the coefficient of the secondary path filter in a table form in a corresponding relationship with the frequency; the update value table operation unit (64) writes the initial value of the initial value table as the update value into the update value table when the active noise control starts, and writes the coefficient of the secondary path filter updated by the secondary path filter coefficient update unit in the active noise control as the update value into the update value table, and the secondary path filter coefficient update unit performs the following processing: Process: Before updating the coefficient of the secondary path filter, determine whether the phase characteristic of the secondary path filter when the update value corresponding to the frequency in the update value table is the coefficient of the secondary path filter is similar to the phase characteristic of the secondary path filter after the secondary path filter coefficient updating unit last updated the coefficient; if it is determined that they are similar, use the update value as the last value to update the coefficient of the secondary path filter; if it is determined that they are not similar, use the coefficient of the secondary path filter after the secondary path filter coefficient updating unit last updated it as the last value to update the coefficient of the secondary path filter.

[0148] The active noise control device may further include an initial value table operation unit (62) for rewriting the initial value in the initial value table to the update value in the update value table when the active noise control is terminated.

[0149] The active noise control device may include a reference signal generating unit (34), a second estimated cancellation signal generating unit (36), a second hypothetical error signal generating unit (52), a control filter coefficient updating unit (42) and a primary path filter coefficient updating unit (38), wherein the reference signal generating unit (34) uses the secondary path filter to perform signal processing on the reference signal to generate a reference signal; the second estimated cancellation signal generating unit (36) uses the control filter to perform signal processing on the reference signal to generate a second estimated cancellation signal; The second hypothetical error signal generating unit (52) generates a second hypothetical error signal according to the second estimated cancellation signal and the estimated noise signal; the control filter coefficient updating unit (42) adaptively updates the coefficient of the control filter in sequence according to the reference signal and the second hypothetical error signal so as to minimize the size of the second hypothetical error signal; the primary path filter coefficient updating unit (38) adaptively updates the coefficient of the primary path filter in sequence according to the reference signal and the first hypothetical error signal so as to minimize the size of the first hypothetical error signal.

Claims

1. An active noise control device (10) for performing active noise control by controlling a speaker (16) based on an error signal, wherein the error signal changes based on a synthesized sound of noise transmitted from a vibration source and a cancelling sound output from the speaker (16) for cancelling the noise, The active noise control device (10) is characterized in that: The invention comprises a reference signal generating unit (26), a control signal generating unit (28), an estimated noise signal generating unit (32), a first estimated cancellation signal generating unit (30), a first hypothetical error signal generating unit (46), a secondary path filter coefficient updating unit (40) and an initial value table (56), in, The reference signal generating unit (26) generates a reference signal corresponding to the frequency of the control object; The control signal generating unit (28) performs signal processing on the reference signal using a control filter as an adaptive notch filter to generate a control signal for controlling the speaker; The estimated noise signal generating unit (32) performs signal processing on the reference signal using a primary path filter as an adaptive notch filter to generate an estimated noise signal; The first estimated cancellation signal generating unit (30) performs signal processing on the control signal using a secondary path filter as an adaptive notch filter to generate a first estimated cancellation signal; The first virtual error signal generating unit (46) generates a first virtual error signal based on the error signal, the first estimated cancellation signal and the estimated noise signal; The secondary path filter coefficient updating unit (40) adaptively updates the coefficients of the secondary path filter in sequence according to the control signal and the first hypothetical error signal, so as to minimize the magnitude of the first hypothetical error signal; The initial value table (56) stores the initial values ​​of the coefficients of the secondary path filter in a corresponding relationship with the frequencies in a table form. The secondary path filter coefficient updating unit performs the following processing: Before updating the coefficient of the secondary path filter, determining whether the phase characteristic of the secondary path filter when the initial value corresponding to the frequency in the initial value table is used as the coefficient of the secondary path filter is similar to the phase characteristic of the secondary path filter after the secondary path filter coefficient update unit last updated the coefficient, If it is determined to be approximate, the coefficients of the secondary path filter are updated using the initial value as the previous value. If it is determined that the coefficients are not similar, the coefficients of the secondary path filter are updated using the coefficients of the secondary path filter after the coefficient update unit last updated the coefficients as last values.

2. The active noise control device according to claim 1, It is characterized in that When a phase difference between a phase characteristic of the secondary path filter when the initial value corresponding to the frequency in the initial value table is used as the coefficient of the secondary path filter and a phase characteristic of the secondary path filter after the secondary path filter coefficient updating unit last updated the coefficient is less than a prescribed angle, the secondary path filter coefficient updating unit determines that the phase characteristic of the secondary path filter when the initial value corresponding to the frequency in the initial value table is used as the coefficient of the secondary path filter is similar to the phase characteristic of the secondary path filter after the secondary path filter coefficient updating unit last updated the coefficient.

3. The active noise control device according to claim 1, It is characterized in that A complex plane is divided into a plurality of regions at a prescribed angle. When, on the complex plane, the phase characteristic of the secondary path filter when the initial value corresponding to the frequency in the initial value table is the coefficient of the secondary path filter and the phase characteristic of the secondary path filter after the secondary path filter coefficient updating unit last updated the coefficient are located in the same region, it is determined that the phase characteristic of the secondary path filter when the initial value corresponding to the frequency in the initial value table is the coefficient of the secondary path filter and the phase characteristic of the secondary path filter after the secondary path filter coefficient updating unit last updated the coefficient are similar.

4. The active noise control device according to any one of claims 1 to 3, It is characterized in that An update value table (58) and an update value table operation unit (64) are provided, wherein: The update value table (58) stores the update values ​​of the coefficients of the secondary path filter in a corresponding relationship with the frequencies in a table form; The update value table operation unit (64) writes the initial value of the initial value table as the update value into the update value table when the active noise control starts, and writes the coefficient of the secondary path filter updated by the secondary path filter coefficient update unit in the active noise control as the update value into the update value table, The secondary path filter coefficient updating unit performs the following processing: Before updating the coefficient of the secondary path filter, determining whether the phase characteristic of the secondary path filter when the update value corresponding to the frequency in the update value table is used as the coefficient of the secondary path filter is similar to the phase characteristic of the secondary path filter after the coefficient was last updated by the secondary path filter coefficient update unit, If it is determined to be approximate, the coefficients of the secondary path filter are updated using the updated value as the previous value, If it is determined that the coefficients are not similar, the coefficients of the secondary path filter are updated using the coefficients of the secondary path filter after the coefficient update unit last updated the coefficients as last values.

5. The active noise control device according to claim 4, It is characterized in that An initial value table operation unit (62) is provided, and when the active noise control is terminated, the initial value table operation unit (62) rewrites the initial value of the initial value table to the update value of the update value table.

6. The active noise control device according to any one of claims 1 to 3, It is characterized in that The invention comprises a reference signal generating unit (34), a second estimated cancellation signal generating unit (36), a second hypothetical error signal generating unit (52), a control filter coefficient updating unit (42) and a primary path filter coefficient updating unit (38), wherein: The reference signal generating unit (34) uses the secondary path filter to perform signal processing on the reference signal to generate a reference signal; The second estimated cancellation signal generating unit (36) performs signal processing on the reference signal using the control filter to generate a second estimated cancellation signal; The second virtual error signal generating unit (52) generates a second virtual error signal based on the second estimated cancellation signal and the estimated noise signal; The control filter coefficient updating unit (42) adaptively updates the coefficients of the control filter in sequence according to the reference signal and the second hypothetical error signal so as to minimize the magnitude of the second hypothetical error signal; The primary path filter coefficient updating unit (38) adaptively updates the coefficients of the primary path filter in sequence according to the reference signal and the first hypothetical error signal so as to minimize the magnitude of the first hypothetical error signal.

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