JP5226226B2 - Active noise control device - Google Patents

Description

  The present invention cancels noise generated when a vehicle is traveling on a road (road) and entering the inner and outer ears of a passenger in a vehicle interior, so-called road noise, by canceling sound (secondary noise) having a phase opposite to that of the road noise. The present invention relates to an active noise control device for silencing.

  Recently, the tire pressure monitoring system that measures the pressure and temperature of the vehicle's tires and sends it to the receiver on the vehicle side to alert the driver when the vehicle side detects that the tire pressure is below the specified value. (TPMS: Tire Pressure Monitoring System) has been proposed and partially put into practical use.

  In this case, for example, in a direct TPMS, a module having a pressure / temperature sensor, a signal processing chip, a UHF transmitter, and the like is integrally attached to a valve (air inlet) of each tire of the vehicle.

  In Patent Document 1, the functions of the above-described TPMS, a tire cavity resonance reduction device having an FFT analysis means for analyzing tire cavity resonance sounds, and a synthesized sound data generation means are integrated into one chip and arranged on a tire. Thus, it is described that road noise related to tire cavity resonance sound having a peak at about 200 to 300 Hz can be reduced while downsizing the apparatus and omitting duplication of functions.

  Further, as road noise, the vibration of the wheel received from the road (road) while the vehicle is traveling is transmitted to the vehicle body via the suspension, and is excited by acoustic resonance characteristics in a closed space such as a passenger compartment, and is about 40 Hz. There is also known a noise (also referred to as drumming noise) that has a peak and has a bandwidth of about 20 to 150 Hz and enters the inner and outer ears of passengers in the passenger compartment.

  In Patent Document 2, pseudo noise data is read based on tire pressure setting information, and pseudo noise data is convolved with an adaptive filter to generate a control signal, and a synthesized sound of control sound (cancellation sound) and noise based on the control signal. Is detected as an error, and the filter coefficient of the adaptive filter is determined so that the error is minimized, so that the noise generated when the vehicle rides on a protrusion on the road surface can be silenced or reduced. Have been described.

JP 2006-64822 A JP 2003-216163 A

  By the way, as shown in FIG. 6, the inventors of this application have found that the peak of the frequency of road noise that must be silenced due to the change in the tire air pressure of the vehicle greatly deviates.

  In the example of FIG. 6, the peak frequency of the noise characteristic 100 indicated by a solid line at a specific position in the vehicle, approximately 40 [Hz], is shifted to the peak frequency of the noise characteristic 102 indicated by a dotted line, approximately 35 [Hz]. I understand.

  When a shift occurs in the frequency peak of road noise based on a change in tire pressure of the vehicle, the noise reduction techniques disclosed in Patent Documents 1 and 2 according to the above prior art can effectively reduce noise. This may not be possible, and the silencing effect may be greatly reduced or worsened. Furthermore, control may become unstable and abnormal noise may be generated.

  The present invention has been made in consideration of the above-described problems. Even if a change occurs in the tire air characteristics such as the tire pressure or the tire air temperature of the vehicle, the invention is stable and optimal following the change in the tire air characteristics. It is an object of the present invention to provide an active noise control device having a novel configuration that enables efficient noise control.

  The active noise control device according to the present invention comprises a sound detection means for receiving a synthesized sound of a road noise in the vehicle interior and the road noise canceling sound output from the sound output means, and outputting as an error signal; Control means for generating a control signal so as to minimize the error signal output from the sound detection means and supplying the control signal to the sound output means, and the load output from the sound output means based on the control signal The active noise control apparatus that silences the road noise by the noise canceling sound has the following features (1) to (6).

  (1) Tire air characteristic detecting means for detecting tire air characteristics; and control characteristic changing means for changing the control characteristics of the control means based on the tire air characteristics detected by the tire air characteristic detecting means. It is characterized by that.

  According to the present invention, since the control characteristic changing unit changes the control characteristic of the control unit based on the tire air characteristic detected by the tire air characteristic detecting unit, a change occurs in the tire air characteristic of the vehicle. Even so, stable and optimum noise control can be performed following the change in tire air characteristics.

  (2) In the invention having the feature (1), the control means converts the reference signal having the frequency of the road noise peak or a frequency near the peak into the control signal, and the reference signal as the control signal. A filter reference signal converted by an error path simulation characteristic from the sound output means to the sound detection means, and a filter coefficient update means for supplying the error signal to update a filter coefficient of the adaptive filter, and the control characteristic The changing means changes the frequency of the reference signal and the error path simulation characteristic as the control characteristic based on the tire air characteristic detected by the tire air characteristic detecting means.

  According to the present invention, the frequency of the reference signal supplied to the adaptive filter and the error path simulation characteristic forming the filtered reference signal supplied to the filter coefficient updating means are changed based on the tire air characteristic. Therefore, the canceling sound can be suitably generated by the feedforward type active noise control device.

  (3) In the invention having the above feature (2), when the tire air characteristic is a tire air pressure, the control characteristic changing means is configured to change the reference signal when the tire air pressure is lower than a specified air pressure range. When the frequency is changed to a constant low frequency, the error path simulation characteristic is changed to a characteristic corresponding to the constant low frequency, and the tire air pressure is within the specified air pressure range, the reference signal When the frequency is changed to a constant medium frequency, the error path simulation characteristic is changed to a characteristic corresponding to the constant medium frequency, and the tire air pressure is higher than the specified air pressure range, the frequency of the reference signal is changed. Is changed to a constant high frequency, and the error path simulation characteristic is changed to a characteristic corresponding to the constant high frequency.

  According to the present invention, when the tire air pressure is lower than the specified air pressure range, the tire spring characteristic is relatively lowered, so that the resonance frequency is lowered. In addition, the error path simulation characteristic is changed to a characteristic corresponding to the constant low frequency. On the other hand, when the tire air pressure is higher than the specified air pressure range, the tire spring characteristic is relatively increased, so that resonance occurs. Considering the increase in frequency, the frequency of the reference signal is changed to a constant high frequency, the error path simulation characteristic is changed to a characteristic corresponding to the constant high frequency, and the tire air pressure is within a specified air pressure range. The frequency of the reference signal is changed to a fixed medium frequency, and the error path simulation characteristic is changed to a characteristic corresponding to the fixed medium frequency. It is possible to maintain the silencing effect that meet the change of the tire air pressure can be selected reference signal and the error path simulates characteristics in response to changes in tire pressure.

  (4) In the invention having the feature (2), the control characteristic changing unit increases the step size parameter of the filter coefficient updating unit when the tire air characteristic cannot be detected by the tire air characteristic detecting unit. It is characterized by that.

  According to the present invention, when the tire air characteristic of at least one tire cannot be detected, the step size parameter of the filter coefficient updating means is increased, so that the sensitivity (silence effect) of the control characteristic is lowered. Can be controlled in a wide band, and even if the resonance frequency changes, a certain silencing effect can be obtained.

  (5) In the invention having the feature (1), the control means is a filter circuit that converts the error signal into the control signal, and the control characteristic changing means is detected by the tire air characteristic detection means. Further, the filter coefficient of the filter circuit is changed as the control characteristic based on the tire air characteristic.

  The present invention can also be applied to a feedback type active noise control apparatus.

  (6) In the invention having any one of the features (1), (2), (4), and (5), the tire pressure characteristic is tire pressure or tire air temperature.

  According to the present invention, since the control characteristic is changed based on the tire air characteristic (tire pressure or tire air temperature, etc.), even if a change occurs in the tire air characteristic of the vehicle, the change in the tire air characteristic is changed. Stable and optimal mute (sound reduction) control can be performed following the above.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a feedforward type active noise control device 10 according to an embodiment of the present invention mounted on a vehicle 12.

  The active noise control device 10 basically includes an ACECU (adaptive noise control ECU) 20 that outputs a control signal (cancellation sound signal) Sc for silencing road noise, and a tire mounted on the rim of each tire 14. 14 includes a TPMS (Tire Pressure Monitoring System) transmitter 16 that transmits tire pressure and tire air temperature, and a TPMS ECU 18 that receives the tire pressure and tire air temperature transmitted from the TPMS transmitter 16 and transfers them to the ANC ECU 20.

  Each ECU is an electronic control unit and includes a microcomputer or the like. The microcomputer includes a CPU, ROM (including EEPROM), RAM, timer (clocking means), A / D converter, D / A converter, etc., and the CPU executes and processes a program recorded in the ROM. It operates as various function realization means.

  The speaker 24 is fixedly arranged, for example, on a kick panel or the like on the front door side (not shown) of the vehicle 12, and the microphone 30 is fixedly arranged, for example, on a vehicle compartment ceiling at the center of the vehicle 12.

  The ANC ECU 20 is based on a control characteristic changer 32 that changes the control characteristic of the ANC ECU 20 in accordance with the tire pressure and tire air temperature supplied from the TPMS ECU 18, and based on a command such as the frequency f from the control characteristic changer 32. A reference signal generator 34 that generates a sine wave and a cosine wave that coincide with the reference signal Sr, and an error path simulation characteristic (simulated transmission) that is a transfer characteristic simulating an error path (transmission path) C from the speaker 24 to the microphone 30. A filter (error path simulation filter) 36 having a characteristic and a gain and phase at a control frequency for each frequency (control frequency) f, a filtered reference signal r (n) that is an output of the filter 36, and a microphone 30. Is supplied with the error signal e (n) detected by the error signal e (n) by the LMS calculation or the like. A filter coefficient updater 40 that updates the filter coefficient of the adaptive filter (in this case, the adaptive notch filter) 38 so that the detection sound (noise) at the position of the microphone 30 is minimized. Adaptive noise control for outputting a control signal Sc (Sc = y (n)), which is a noise canceling sound signal, from the adaptive filter 84 is performed.

  The error path simulation characteristics are measured in advance at center frequencies flo, fmid, and fhi, which will be described later, and stored in the filter 36 or the control characteristic changer 32 as a table.

  The control signal Sc output from the ANC ECU 20 is output to the vehicle interior of the vehicle 12 through the speaker 24 as a canceling sound for road noise in the vehicle interior. In this way, the road noise in the passenger compartment is silenced by the canceling sound generated by the control signal Sc that adaptively changes in accordance with the change in tire air pressure.

  The active noise control apparatus 10 according to this embodiment is basically configured and operates as described above.

  Next, a more detailed operation of the above embodiment will be described with reference to a flowchart shown in FIG. Here, the CPU that executes the program according to this flowchart is the CPU of the ANC ECU 20. Further, the processing according to this flowchart is repeatedly executed at predetermined time intervals while the vehicle 12 is traveling.

  In step S1, the ANCECU 20 sequentially acquires the current air pressure of each tire 14 from the TPMS ECU 18, and calculates the average air pressure Ap when the air pressure of the four tires 14 can be acquired, for example.

  In practice, the TPMS ECU 18 sends a request signal to the TPMS transmitter 16 attached to each tire 14 to transmit the current tire pressure and tire air temperature, and based on this request signal, each TPMS transmitter 16 The tire air pressure and tire air temperature of the tire 14 to which is attached are measured, and a response signal is returned to the TPMS ECU 18.

  The ANC ECU 20 acquires the tire air pressure from the TPMS ECU 18 in this way, and calculates the average air pressure Ap.

  Next, the average air pressure Ap of the four tires for 14 minutes is compared with a predetermined air pressure B determined in advance. Here, the range of the prescribed air pressure B is an air pressure between the prescribed minimum air pressure Blo and the prescribed maximum air pressure Bhi (Blo ≦ B ≦ Bhi).

  Therefore, in step S2, it is compared whether or not the average air pressure Ap is lower than the specified minimum air pressure Blo. If the average air pressure Ap is lower (Ap <Blo), the average air pressure Ap is lower than the specified air pressure B as a control characteristic of the ANC ECU 20 in step S4. In this case, a control characteristic a to be described later is selected.

  In step S2, if the average air pressure Ap is not lower than the specified minimum air pressure Blo, it is compared in step S3 whether or not the average air pressure Ap is lower than the specified maximum air pressure Bhi. If it is lower (Ap <Bhi), the specified air pressure Ap is specified. In step S5, a control characteristic b, which will be described later, corresponding to the range of the prescribed air pressure B is selected as the control characteristic of the ANNCUCU 20.

  In step S3, when the average air pressure Ap is not lower than the specified maximum air pressure Bhi (Ap ≧ Bhi), in step S6, the control characteristic c to be described later when the control pressure of the ANCEC 20 is higher than the specified air pressure B is selected. The

  In step S1, if even one of the four tires 14 cannot acquire the air pressure, the average air pressure Ap of the four tires is unknown, and a control characteristic d described later is selected.

  FIGS. 3A to 3D show sensitivity functions of the ANC ECU 20 to which the selected control characteristics a to d are applied. The horizontal axis of the sensitivity function is frequency, and the vertical axis is sound pressure [dB]. In this embodiment, the center frequencies of the control characteristics a, b, c, and d are the center frequencies flo, fmid, fhi, and fx, respectively.

  Here, the magnitude relationship between the center frequencies is set as flo <fmid <fhi. In this embodiment, the center frequency fx related to the control characteristic d takes any value of flo, fmid, or fhi.

  When the tire pressure decreases, the tire spring characteristics decrease and the resonance frequency (center frequency of road noise) decreases. When the tire pressure increases, the tire spring characteristics increase and resonance frequency (center frequency of road noise). Has gained knowledge.

  Based on this knowledge, when the control characteristic a is selected in step S4 and the center frequency flo is set by the control characteristic changer 32, the reference signal generator 34 generates a sine wave and cosine wave of the center frequency flo. A reference signal Sr is generated and supplied to the adaptive filter 38 and the filter 36. On the other hand, an error path simulation characteristic at the center frequency flo is set in the filter 36 by a command from the control characteristic changer 32.

  Similarly, when the control characteristic b is selected in step S5 and the center frequency fmid is set by the control characteristic changer 32, the reference signal generator 34 causes the reference signal of the sine wave and cosine wave of the center frequency fmid to be set. Sr is generated and supplied to the adaptive filter 38 and the filter 36. An error path simulation characteristic at the center frequency fmid is set in the filter 36.

  When the control characteristic c is selected in step S6 and the center frequency fhi is set by the control characteristic changer 32, the reference signal generator 34 causes the reference signal of the sine wave and cosine wave at the center frequency fhi. Sr is generated and supplied to the adaptive filter 38 and the filter 36. An error path simulation characteristic at the center frequency fhi is set in the filter 36.

  In this way, by setting the control characteristics a to d and performing the above-described adaptive noise control in the ANC ECU 20, for example, with respect to the noise characteristic 100 indicated by a solid line with a peak frequency of about 40 [Hz] shown in FIG. When the control characteristic b with fmid = 40 [Hz] is selected, a reduced noise characteristic 100A indicated by a one-dot chain line in FIG. 4 in which the noise corresponding to the sensitivity function is reduced is obtained.

  Similarly, when the control characteristic a with flo = 35 [Hz] is selected with respect to the noise characteristic 102 with the peak frequency of about 35 [Hz] shown in FIG. 6, although not shown, it corresponds to the sensitivity function. Improved noise characteristics can be obtained.

  Although the negative peak value (cancellation amount) shown in FIG. 3D is small, the broadband control characteristic d is actually the control characteristic as the control characteristic a to c {the frequency of the reference signal Sr and the reference signal respectively. The error path transfer characteristic (gain and phase) at the center frequency f that matches the frequency of Sr} is selected, and the value of the step size parameter of the LMS algorithm is increased, and at the same time, the control signal Sc (Sc = y ( n)) can be set by reducing the output (gain).

  In this embodiment, the adaptive filter 38 is an adaptive notch filter, and, as is well known, the updated filter coefficient h (n + 1) includes the filter coefficient h (n) before the update and the filter coefficient updater 40 to the microphone 30. Is calculated as h (n + 1) = h (n) −μe (n) r (n) from the error signal e (n), the filtered reference signal r (n), and the step size parameter μ. .

  In step S1, when the air pressures of all the four tires 14 cannot be acquired, the ANC ECU 20 performs adaptive noise control with the resume function as the center frequency fix that sets the last used center frequency in the control characteristic d. Alternatively, the adaptive noise control itself is stopped.

  When the air pressures of the four tires 14 cannot be acquired, the average air pressure Ap of the air pressures with the acquired number is calculated. Then, it is determined whether or not the average air pressure Ap is within the range of the specified air pressure B in the same manner as in steps S2 and S3. Frequency) as the center frequency fx, and a more flattened control characteristic d shown in FIG. 3D may be selected as the sensitivity function.

  Further, the control characteristics may be changed based on the air pressure of at least one tire 14 instead of the average air pressure Ap.

  Furthermore, instead of the average air pressure Ap, the control characteristic may be changed by determining whether the air pressure is higher or lower than the range of the specified air pressure B by majority.

  FIG. 5 shows the configuration of a feedback type active noise control apparatus 10A according to another embodiment of the present invention.

  In this active noise control apparatus 10A, the ANCECU 20 is replaced with a control filter 50 that is a feedback filter. As the control filter 50, for example, an FIR filter or an IIR filter is employed.

  In this active noise control apparatus 10A, the control characteristic changer 32A changes the filter coefficient of the control filter 50 to a filter coefficient that is measured in advance so that the error signal e is minimized based on the tire air pressure supplied from the TPMS ECU 18.

  When the flowchart of FIG. 2 is applied, according to the tire average air pressure Ap, the control characteristic changer 32A changes the three control filters 50 with fixed filter coefficients corresponding to the control characteristics ac to the control characteristic d. A total of six filters of the three control filters 50 whose filter coefficients are fixed at the corresponding three center frequencies flo, fmid, and fhi can be switched and used.

  As described above, according to the above-described embodiment, the synthesized sound of the road noise in the vehicle interior and the road noise canceling sound output from the speaker (sound output means) 24 is received and output as the error signal e. A microphone (sound detection means) 30, an ACECU (control means) 20 or a control filter (control means) 50 that generates a control signal Sc and supplies it to the speaker 24 so that the error signal e output from the microphone 30 is minimized. The active noise control devices 10 and 10A for canceling the road noise by the canceling sound of the road noise output from the speaker 24 based on the control signal Sc include a TPMS transmitter 16 and a TPMS ECU 18 (tire Air pressure detecting means) and the tire air pressure detected by the TPMS ECU 18. , And a ANCECU20 or control characteristics changing unit for changing the control characteristics a~d of control filter 50 (the control characteristics changing means) 32, 32A.

  According to the active noise control devices 10 and 10A, based on the tire air pressure detected by the TPMS ECU 18, for example, the tire average air pressure Ap, the control characteristics changers 32 and 32A control characteristics a to d of the ANC ECU 20 and the control filter 50, respectively. Therefore, even if a change occurs in the tire air pressure of the vehicle 12, stable and optimum noise control can be performed following the change in the tire air pressure.

  Here, as shown in FIG. 1, the ANC ECU 20 converts the reference signal Sr having the peak frequency of the road noise or a frequency frequency near the peak into a control signal Sc, and the reference signal Sr from the speaker 24 to the microphone 30. A filter coefficient updater (filter coefficient updating means) for supplying the filter reference signal r (n) and the error signal e (n) converted by the filter 36 according to the error path simulation characteristics up to and updating the filter coefficient of the adaptive filter 38 40, and the control characteristic changer 32 uses the frequency f of the reference signal Sr and the error path simulation characteristic of the filter 36 as the control characteristics a to d based on the tire average tire pressure Ap detected by the TPMS ECU 118. Therefore, the feedforward type active noise control device 1 is changed. In it is possible to generate a canceling sound.

  The control characteristic changer 32 takes into account that when the tire average air pressure Ap is lower than the range of the specified air pressure B, the spring characteristic of the tire is relatively lowered, so that the resonance frequency is lowered, and the frequency f of the reference signal Sr is considered. Is a constant center frequency (low frequency) flo, and the tire average air pressure Ap is within the range of the specified air pressure B, the frequency f of the reference signal Sr is set to a constant center frequency (medium frequency) fmid, and the tire air pressure is When the air pressure is higher than the range of the specified air pressure B, the frequency characteristic of the reference signal Sr is set to a constant center frequency (high frequency) fhi in consideration of an increase in the resonance frequency because the spring characteristic of the tire relatively increases. Therefore, the reference signal Sr corresponding to the change in the tire pressure can be selected, and the silencing effect corresponding to the change in the tire pressure can be maintained.

  Further, when the tire pressure cannot be detected by the TPMS ECU 18, the control characteristic changer 32 increases the step size parameter of the filter coefficient updater 40 and decreases the output gain. Although the effect is low, it is possible to control in a wide band, so that a certain silencing effect can be obtained even if the resonance frequency changes.

  In the active noise control devices 10 and 10A according to the above-described embodiments, the tire air pressure is detected as the tire air characteristic and the control characteristic is changed, but the tire air temperature is substituted for the tire air pressure. The configuration can be changed so as to change the control characteristics by detecting the above.

  In addition, the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

It is a block diagram which shows the structure of the active noise control apparatus which concerns on one Embodiment of this invention. It is a flowchart with which it uses for operation | movement description of the example of FIG. 3A to 3D are explanatory diagrams of control characteristics set according to tire air pressure. It is a characteristic view explaining the road noise before and behind mute. It is a block diagram which shows the structure of the active noise control apparatus which concerns on other embodiment of this invention. FIG. 6 is a characteristic diagram of road noise before mute for use in explaining the problem of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 10A ... Active type noise control apparatus 12 ... Vehicle 16 ... TPMS transmitter 18 ... TPMS ECU
20 ... ANC ECU 24 ... speaker 30 ... microphone 32, 32A ... control characteristic changer 38 ... adaptive filter 40 ... filter coefficient updater 50 ... control filter

Claims (4)

Sound detection means for receiving a synthesized sound of road noise in the vehicle interior and the road noise canceling sound output from the sound output means and outputting it as an error signal; and the error signal output from the sound detection means Control means for generating a control signal to be minimized and supplying the control signal to the sound output means, and mute the road noise by the canceling sound of the road noise output from the sound output means based on the control signal In an active noise control device,
Tire air characteristic detecting means for detecting tire air characteristics;
Control characteristic changing means for changing the control characteristic of the control means based on the tire air characteristic detected by the tire air characteristic detecting means;
With
The control means includes
An adaptive filter for converting a reference signal having a frequency at or near the peak of the road noise into the control signal, and a filtered reference signal obtained by converting the reference signal by an error path simulation characteristic from the sound output means to the sound detection means And a filter coefficient updating unit that is supplied with the error signal and updates a filter coefficient of the adaptive filter,
The control characteristic changing means includes
When the tire air characteristic can be detected by the tire air characteristic detection means, based on the tire air characteristic, as the control characteristic, the frequency of the reference signal and the error path simulation characteristic are changed,
When the tire air characteristic cannot be detected by the tire air characteristic detection unit, the step size parameter of the filter coefficient update unit is increased as compared with the case where the tire air characteristic can be detected. An active noise control device characterized in that the frequency is changed to a broadband control characteristic. Sound detection means for receiving a synthesized sound of road noise in the vehicle interior and the road noise canceling sound output from the sound output means and outputting it as an error signal; and the error signal output from the sound detection means Control means for generating a control signal to be minimized and supplying the control signal to the sound output means, and mute the road noise by the canceling sound of the road noise output from the sound output means based on the control signal In an active noise control device,
Tire air characteristic detecting means for detecting tire air characteristics;
Control characteristic changing means for changing the control characteristic of the control means based on the tire air characteristic detected by the tire air characteristic detecting means;
With
The control means includes
An adaptive filter for converting a reference signal having a frequency at or near the peak of the road noise into the control signal, and a filtered reference signal obtained by converting the reference signal by an error path simulation characteristic from the sound output means to the sound detection means And a filter coefficient updating unit that is supplied with the error signal and updates a filter coefficient of the adaptive filter,
The control characteristic changing means includes
When the tire air characteristic can be detected by the tire air characteristic detection means, based on the tire air characteristic, as the control characteristic, the frequency of the reference signal and the error path simulation characteristic are changed,
The active noise control device, wherein when the tire air characteristic cannot be detected by the tire air characteristic detection means, the control by the control means is stopped. The active noise control device according to claim 1 or 2,
The tire noise characteristic is tire pressure or tire air temperature. The active noise control device according to claim 3,
When the tire air characteristic is tire pressure,
The control characteristic changing means includes
When the tire air pressure is lower than a specified air pressure range, the frequency of the reference signal is changed to a constant low frequency, the error path simulation characteristic is changed to a characteristic corresponding to the constant low frequency, and the tire When the air pressure is within the prescribed air pressure range, the frequency of the reference signal is changed to a constant medium frequency, the error path simulation characteristic is changed to a characteristic corresponding to the constant medium frequency, and the tire When the air pressure is higher than the specified air pressure range, the frequency of the reference signal is changed to a constant high frequency, and the error path simulation characteristic is changed to a characteristic corresponding to the constant high frequency. Active noise control device.

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