Active noise reduction system

Abstract

The present invention relates to an active noise reduction system that reduces noise in an interior space of a moving body. The active noise reduction system includes a controller configured to control a counter sound output device. The controller is configured to generate a first counter estimation signal as an estimation signal of a counter sound at a position of an error detector based on a reference signal, generate a second counter estimation signal as an estimation signal of the counter sound at a position of a head of an occupant by adjusting a time delay and an amplitude of the first counter estimation signal based on a reference distance, and update a control filter for controlling the counter sound output device based on the second counter estimation signal.

Description

Technical Field

[0001] The present invention relates to an active noise reduction system that reduces noise by canceling out sound interference noise that is out of phase with the noise. Background Technology

[0002] Typically, active noise cancellation systems reduce noise by canceling out noise interference with sound that is out of phase with the noise. For example, an active noise cancellation system includes: a canceling sound output device configured to output canceling sound to cancel out noise; an error detector configured to detect an error between the noise and the canceling sound and generate an error signal corresponding to the error; and a controller configured to control the canceling sound output device based on the error signal.

[0003] For example, JP2021-162849A discloses a loudspeaker that outputs canceled sound, a microphone that outputs an error signal, and an active noise controller that generates a control signal based on the error signal to make the loudspeaker output canceled sound.

[0004] In traditional active noise cancellation systems, the area with high control effectiveness (high noise reduction effect) is limited to a portion of the area surrounding an error detector, such as a microphone. Therefore, if the occupant's head position changes, the noise at the occupant's head position may not be adequately reduced. Summary of the Invention

[0005] In view of the above background, the object of the present invention is to provide an inexpensive active noise cancellation system that can effectively reduce noise at the occupant's head position even if the occupant's head position changes.

[0006] To achieve this objective, one aspect of the present invention provides an active noise cancellation system 11 for reducing noise in the interior space (carriage 5) of a moving body (vehicle 1), the active noise cancellation system comprising: a reference signal generator (vibration sensor 12) configured to generate a reference signal corresponding to the noise; a canceling sound output device (speaker 13) configured to output a canceling sound for canceling the noise; an error detector (error microphone 14) configured to detect an error between the noise and the canceling sound and generate an error signal corresponding to the error; and a reference distance detector 15 configured to detect as a signal from the canceling sound output. The reference distance is the distance from the output device to the occupant's head position; and a controller 16 is configured to control the canceling sound output device based on the reference signal, the error signal, and the reference distance, wherein the controller is configured to: generate a first cancellation estimation signal based on the reference signal, the first cancellation estimation signal being an estimation signal of the canceling sound at the position of the error detector; generate a second cancellation estimation signal by adjusting the time delay and amplitude of the first cancellation estimation signal based on the reference distance, the second cancellation estimation signal being an estimation signal of the canceling sound at the occupant's head position; and update a control filter W based on the second cancellation estimation signal, the control filter being a filter for controlling the canceling sound output device.

[0007] According to this aspect, by updating the control filter based on the second cancellation estimation signal (an estimated signal of the cancellation sound at the occupant's head position), the characteristics of the control filter can be changed to follow changes in the occupant's head position. Therefore, even if the occupant's head position changes, noise at the occupant's head position can be effectively reduced. Furthermore, the second cancellation estimation signal is generated by adjusting the time delay and amplitude of the first cancellation estimation signal (an estimated signal of the cancellation sound at the error detector's position). Therefore, it is not necessary to use a computationally intensive filter to generate the second cancellation estimation signal. Thus, the computational load on the controller can be reduced, and the controller can be composed of a relatively inexpensive processor.

[0008] In the above aspects, preferably, the controller is configured to: set a correction coefficient corresponding to the reference distance; and correct the update amount of the control filter by multiplying the update amount of the control filter by the correction coefficient.

[0009] Based on this, the update amount of the control filter can be adjusted according to the reference distance, so that the update amount of the control filter can be maintained at an appropriate value.

[0010] In the above aspects, preferably, the controller is configured to adjust the amplitude of the first cancellation estimation signal by using an amplitude adjustment coefficient that decreases as the reference distance increases, and the correction coefficient is set to be the reciprocal of the amplitude adjustment coefficient.

[0011] Based on this, when the amplitude adjustment coefficient decreases as the reference distance increases, the correction coefficient can be increased. Therefore, excessive reduction in the update amount of the control filter can be prevented, thereby maintaining the update performance of the control filter.

[0012] In the above aspects, preferably, the controller is configured to adjust the amplitude of the first cancellation estimation signal by using an amplitude adjustment coefficient that decreases as the reference distance increases, and the correction coefficient is set such that the product of the amplitude adjustment coefficient and the correction coefficient is less than 1.

[0013] Based on this, when the update accuracy of the control filter decreases with increasing reference distance, excessive increases in the update amount of the control filter can be suppressed. Therefore, the performance of the control filter can be prevented from deteriorating due to the update of the control filter.

[0014] In the foregoing, preferably, the controller is configured to store a correction coefficient table that defines the relationship between the reference distance and the correction coefficients.

[0015] In this respect, since the correction coefficient can be freely set according to the reference distance, the degree of freedom in setting the correction coefficient can be increased.

[0016] In the foregoing, preferably, the controller is configured to: update an estimate of the transmission characteristics of the canceling sound; and generate the first canceling estimate signal by correcting the reference signal based on the updated estimate of the transmission characteristics of the canceling sound.

[0017] Based on this, when the change in the transmission characteristics of sound is compensated for, the change in the transmission characteristics of sound can be learned to compensate for, and a first compensation estimation signal can be generated based on the learning result. Therefore, noise at the occupant's head position can be reduced more effectively.

[0018] In the foregoing, preferably, the canceling sound output device and the error detector are installed in the headrest 6a of the occupant seat 6 disposed in the interior space, and the controller is configured to generate the second canceling estimation signal by adjusting only the time delay and the amplitude of the first canceling estimation signal.

[0019] Based on this aspect, the cancellation sound output device, the error detector, and the occupant's head can be brought sufficiently close to each other. Therefore, most of the cancellation sound reaches the error detector and the occupant's head directly from the cancellation sound output device, thereby increasing the dependence of the cancellation sound on time delay and distance attenuation. Therefore, by adjusting only the time delay and amplitude of the first cancellation estimation signal, the second cancellation estimation signal can be generated with high accuracy.

[0020] Therefore, based on the above aspects, it is possible to provide an inexpensive active noise cancellation system that can effectively reduce noise at the occupant's head position even if the occupant's head position changes. Attached Figure Description

[0021] Figure 1 This is a schematic diagram showing a vehicle to which the active noise cancellation system according to the first embodiment is applied;

[0022] Figure 2 This is a functional block diagram showing the active noise cancellation system according to the first embodiment;

[0023] Figure 3 This is a schematic diagram illustrating the noise reduction mechanism and prerequisites according to the first embodiment;

[0024] Figure 4 It is a graph showing the effect of reducing road noise;

[0025] Figure 5 This is a functional block diagram illustrating the active noise cancellation system according to the second embodiment; and

[0026] Figure 6 A table of correction coefficients according to the second embodiment is shown. Detailed Implementation

[0027] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In this specification, the “^” (swirl) shown together with the symbols each represents an identified value or an estimated value. The “^” is shown above the symbols in the drawings and formulas, but after the symbols in the text of the specification.

[0028] (First Implementation)

[0029] First, refer to Figures 1 to 4 The first embodiment of the present invention is described.

[0030] <Active Noise Cancellation System 11>

[0031] Figure 1This is a schematic diagram showing a vehicle 1 (an example of a moving body) applying an active noise reduction system 11 (hereinafter referred to as "noise reduction system 11") according to a first embodiment. When the wheels 2 vibrate due to forces received from the road surface S and the vibration of the wheels 2 is transmitted to the vehicle body 4 via the suspension 3, road noise d is generated in the passenger compartment 5 (an example of the interior space of the moving body). The noise reduction system 11 according to the first embodiment is a feedback-controllable active noise control device (ANC device) for reducing such road noise d. More specifically, the noise reduction system 11 reduces road noise d by generating a canceling sound y that is out of phase with the road noise d and causing the generated canceling sound y to interfere with the road noise d. In another embodiment, the noise reduction system 11 can reduce noise other than the road noise d generated when the vehicle 1 is in motion (e.g., aerodynamic noise transmitted from the underbody attached to the lower surface of the vehicle body 4).

[0032] See Figure 1 and Figure 2 The noise reduction system 11 includes: a vibration sensor 12 (an example of a reference signal generator) configured to generate a reference signal x corresponding to road noise d; a plurality of speakers 13 (an example of a canceling sound output device) configured to generate a canceling sound y for canceling road noise d; a plurality of error microphones 14 (an example of an error detector) configured to detect an error (synthetic sound) between road noise d and canceling sound y and generate an error signal e corresponding to the detected error; and a reference distance detector 15 configured to detect the distance from the plurality of speakers 13 to the head position of the occupant (hereinafter referred to as "reference distance L"). r "); and controller 16, which is configured to base on reference signal x, error signal e, and reference distance L r To control multiple speakers 13.

[0033] Figure 2 The symbol H in m This represents the transmission characteristics (transmission characteristics of the primary path) of road noise d from the noise source (in this embodiment, the road surface S) to each error microphone 14. Figure 2 The symbol C in m This represents the transmission characteristics (transmission characteristics of the secondary path) of the canceled sound y from speaker 13 to each error microphone 14.

[0034] <Vibration Sensor 12>

[0035] Reference Figure 1The vibration sensor 12 of the noise reduction system 11 is mounted, for example, in at least one suspension 3. The vibration sensor 12 detects the acceleration of the suspension 3 based on road noise d and generates a reference signal x based on the acceleration of the suspension 3. In another embodiment, the vibration sensor 12 may be mounted in a location other than the suspension 3 of the vehicle 1. In another embodiment, a reference microphone (not shown) may generate the reference signal x based on road noise d.

[0036] <Speaker 13>

[0037] The speakers 13 of the noise reduction system 11 are installed, for example, in the headrests 6a of the passenger seats 6 located in the passenger compartment 5. In another embodiment, the speakers 13 may be installed in a location other than the headrests 6a of the passenger seats 6.

[0038] <Error Microphone 14>

[0039] The error microphones 14 of the noise reduction system 11 are installed, for example, in the headrest 6a of the passenger seat 6. In another embodiment, the error microphones 14 may be installed in a location other than the headrest 6a of the passenger seat 6.

[0040] <Reference Distance Detector 15>

[0041] The reference distance detector 15 of the noise reduction system 11 is, for example, comprised of an occupant monitoring system, which includes an occupant camera that captures images of the occupants. The reference distance detector 15 detects the reference distance L based on the images of the occupants captured by the occupant camera. r and the detected reference distance L r The output is sent to controller 16. In another embodiment, reference distance detector 15 may include direct detection of reference distance L. r Distance sensor.

[0042] <Controller 16>

[0043] The controller 16 of the noise reduction system 11 is composed of an electronic control unit (ECU) that includes a processing unit (CPU, MPU, etc.) and a storage device (ROM, RAM, etc.). The controller 16 can be composed of a single piece of hardware or a unit composed of multiple pieces of hardware.

[0044] Reference Figure 2 The controller 16 includes a first A / D conversion unit 21, a control signal output unit 22, a D / A conversion unit 23, a second A / D conversion unit 24, an acoustic characteristic update unit 25, a reference signal correction unit 26, an acoustic characteristic adjustment unit 27, an adjustment amount determination unit 28, and a control filter update unit 29 as functional components. Figure 2The symbol "ADA" in it represents "Adaptive".

[0045] <The first A / D conversion unit 21>

[0046] The first A / D conversion unit 21 of the controller 16 converts the analog reference signal x output from the vibration sensor 12 into a digital reference signal x, and outputs the digital reference signal x to the control signal output unit 22, the acoustic characteristic update unit 25, and the reference signal correction unit 26. Hereinafter, the "reference signal x" not described represents the reference signal x that has passed through the first A / D conversion unit 21.

[0047] <The control signal output unit 22>

[0048] The control signal output unit 22 of the controller 16 includes a control filter W. A finite impulse response filter (FIR filter) is used for the control filter W. In another embodiment, a single-frequency adaptive notch filter (SAN filter) can be used for the control filter W. The control signal output unit 22 generates a control signal u by filtering the reference signal x using the control filter W, and outputs the generated control signal u to the D / A conversion unit 23 and the acoustic characteristic update unit 25.

[0049] <The D / A conversion unit 23> <000×0214>The D / A conversion unit 23 of the controller 16 converts the digital control signal u output from the control signal output unit 22 into an analog control signal u, and outputs the analog control signal u to the speaker 13. Therefore, the speaker 13 generates a cancellation sound y according to the control signal u.

[0051] <The second A / D conversion unit 24>

[0052] The second A / D conversion unit 24 of the controller 16 converts the error signal e output from the error microphone 14 from an analog signal into a digital signal, and outputs the converted error signal e to the acoustic characteristic update unit 25. Hereinafter, the "error signal e" not described represents the error signal e that has passed through the second A / D conversion unit 24.

[0053] <The acoustic characteristic update unit 25>

[0054] The acoustic characteristic update unit 25 of the controller 16 updates the estimated value of the acoustic characteristics in the vehicle compartment 5 based on the reference signal x, the control signal u, and the error signal e. The acoustic characteristic update unit 25 includes a cancellation estimation signal generation unit 31, a noise estimation signal generation unit 32, and an adder 33.

[0055] The cancellation estimation signal generation unit 31 includes a secondary path filter unit 35 and a secondary path update unit 36.

[0056] The secondary path filter unit 35 includes a secondary path filter C^. The secondary path filter C^ is a transmission characteristic C of the canceled sound y from the speaker 13 to the error microphone 14. m The filter corresponding to the estimated value. The FIR filter is used for the secondary path filter C^. In another embodiment, the SAN filter can be used for the secondary path filter C^.

[0057] The secondary path filter unit 35 generates the cancellation estimation signal y^ by filtering the control signal u using the secondary path filter C^. m1 Cancel the estimated signal y^ m1 This is the estimated signal of the canceled sound y at the position of the error microphone 14 (hereinafter referred to as the "microphone position"). The secondary path filter unit 35 converts the generated canceled estimated signal y^ m1 Output to adder 33.

[0058] The secondary path update unit 36 ​​uses an adaptive algorithm, such as the Least Mean Square (LMS) algorithm, to update the secondary path filter C^. More specifically, the secondary path update unit 36 ​​updates the secondary path filter C^ such that the virtual error signal e1 (described later) output from the adder 33 is minimized.

[0059] The noise estimation signal generation unit 32 includes a primary path filter unit 38 and a primary path update unit 39.

[0060] The primary path filter unit 38 includes a primary path filter H^. The primary path filter H^ is related to the transmission characteristics H of the path noise d from the noise source to the error microphone 14. m The filter corresponding to the estimated value. An FIR filter is used for the primary path filter H^. In another embodiment, a SAN filter can be used for the primary path filter H^.

[0061] The primary path filter unit 38 generates a noise estimation signal d^ by filtering the reference signal x using a primary path filter H^. The noise estimation signal d^ serves as the road noise d at the microphone location. m The estimated signal is then used as the road noise d at the occupant's head position. e The primary path filter unit 38 outputs the generated noise estimation signal d^ to the adder 33 and the control filter update unit 29.

[0062] The primary path update unit 39 uses an adaptive algorithm, such as the LMS algorithm, to update the primary path filter H^. More specifically, the primary path update unit 39 updates the primary path filter H^ such that the virtual error signal e1 (described later) output from the adder 33 is minimized.

[0063] Adder 33 converts the error signal e and the cancellation estimation signal y^ m1 The virtual error signal e1 is generated by adding the noise estimation signal d^ together with the noise estimation signal d^. The adder 33 outputs the generated virtual error signal e1 to the cancellation estimation signal generation unit 31 and the noise estimation signal generation unit 32.

[0064] <Reference Signal Correction Unit 26>

[0065] Similar to the cancellation estimation signal generation unit 31, the reference signal correction unit 26 of the controller 16 includes a secondary path filter C^. When the secondary path filter C^ is updated in the cancellation estimation signal generation unit 31, the updated secondary path filter C^ is output to the reference signal correction unit 26, and the secondary path filter C^ is updated in the reference signal correction unit 26. That is, the secondary path filter C^ set in the reference signal correction unit 26 is not a fixed value, but a value that is continuously updated based on the signal from the cancellation estimation signal generation unit 31.

[0066] Reference signal correction unit 26 generates cancellation estimation signal y^ by filtering the reference signal x. m2 (First cancellation estimation signal). More specifically, the reference signal correction unit 26 generates the cancellation estimation signal y^ by correcting the reference signal x based on the updated secondary path filter C^. m2 And the offsetting estimated signal y^ m1 Similarly, cancel out the estimated signal y^ m2 This is the estimated signal of the canceled sound y at the microphone location. The reference signal correction unit 26 will use the generated canceled estimated signal y^ m2 Output to acoustic characteristic adjustment unit 27.

[0067] <Acoustic Characteristic Adjustment Unit 27>

[0068] The acoustic characteristic adjustment unit 27 of the controller 16 adjusts the cancellation estimation signal y^ m2 The time delay and amplitude (distance attenuation) are used to generate the cancellation estimation signal y^ e1 (Example of the second cancellation estimation signal). Cancellation estimation signal y^ e1 This is the estimated signal to cancel out the sound y at the occupant's head position. The acoustic characteristic adjustment unit 27 will generate the cancellation estimation signal y^ e1 The output is sent to the control filter update unit 29.

[0069] The acoustic characteristic adjustment unit 27 includes a delay unit 41 and an amplitude adjustment unit 42. The delay unit 41 uses the delay characteristic Z... -d To adjust the cancellation estimation signal y^ m2 The time delay. More specifically, the delay unit 41 will cancel the estimated signal y^ m2 The delay is d samples. The amplitude adjustment unit 42 adjusts the cancellation estimation signal y^ using an amplitude adjustment coefficient a. m2 The amplitude. More specifically, the amplitude adjustment unit 42 adjusts the amplitude by canceling the estimated signal y^ m2 The amplitude adjustment factor 'a' is used to adjust the cancellation estimation signal y^. m2 The range.

[0070] <Adjustment Amount Determination Unit 28>

[0071] The adjustment amount determination unit 28 of the controller 16 is based on the reference distance L output from the reference distance detector 15. r The adjustment amount of the time delay in the acoustic characteristic adjustment unit 27 is determined. More specifically, the adjustment amount determination unit 28 determines the delay characteristic Z of the delay unit 41 according to the following formula (1). -d Incidentally, in equation (1), "round" indicates rounding to an integer, "c" in equation (1) indicates the speed of sound, and "F" in equation (1) indicates the speed of sound. S " " indicates the sampling frequency.

[0072]

[0073] The adjustment amount determination unit 28 is based on the reference distance L output from the reference distance detector 15. r The amplitude adjustment amount in the acoustic characteristic adjustment unit 27 is determined. More specifically, the adjustment amount determination unit 28 determines the amplitude adjustment coefficient a of the amplitude adjustment unit 42 according to the following formula (2). Incidentally, in the following formula (2), "L" m “ represents the distance from a speaker 13 to the corresponding error microphone 14. N (N = 1, 2, ...) in the following formula (2) represents the parameter used to adjust the amplitude, and “σ” in the following formula (2) represents the adjustment constant (a constant with a relatively small value to prevent the denominator on the right side of the following formula (2) from becoming zero and to prevent the amplitude from becoming too large).

[0074]

[0075] It can be clearly seen from equation (2) above that the amplitude adjustment coefficient a is set to vary with the reference distance L. r It decreases as it increases.

[0076] <Control Filter Update Unit 29>

[0077] The control filter update unit 29 of controller 16, like the control signal output unit 22, includes a control filter W. The control filter update unit 29 is based on the cancellation estimation signal y^ output from the acoustic characteristic adjustment unit 27. e1 The control filter W is updated. The control filter update unit 29 includes a control filter unit 45, an adder 46, and a control update unit 47.

[0078] The control filter unit 45 uses the control filter W to cancel the estimated signal y^ e1 Filtering is performed to generate the cancellation estimate signal y^ e2 Cancel the estimated signal y^ e2 It is the estimated signal that cancels out the sound y at the occupant's head position, similar to the cancellation estimated signal y^. e1 Cancel the estimated signal y^ e2 It can be represented by the following formula (3).

[0079]

[0080] Adder 46 cancels the estimated signal y^ e2 The virtual error signal e is generated by combining the noise estimation signal d^ with the signal d. e Adder 46 will generate a virtual error signal e e Output to control update unit 47.

[0081] The control update unit 47 updates the control filter W using an adaptive algorithm such as the LMS algorithm. More specifically, the control update unit 47 updates the control filter W such that the virtual error signal e output from the adder 46... e minimize.

[0082] When the control filter W is updated in the control filter update unit 29 in this manner, the updated control filter W is output to the control signal output unit 22, and the control filter W is updated in the control signal output unit 22. That is, the control filter W set in the control signal output unit 22 is not a fixed value, but a value that is continuously updated based on the signal from the control filter update unit 29.

[0083] <Noise Reduction Mechanism and Prerequisites>

[0084] Next, we will refer to Figure 3 Describe the noise reduction mechanism and prerequisites of noise reduction system 11. Figure 3 Each curve p in the figure represents the wavefront of the road noise d (the surface with uniform sound pressure of the road noise d) transmitted from the noise source.

[0085] The head position of an occupant (e.g., the driver) can change significantly in the fore-aft direction depending on the occupant's driving posture, but it cannot change in the vertical direction. Therefore, with each speaker 13 and corresponding error microphone 14 installed in the headrest 6a of the occupant seat 6, the estimated occupant's head position and the error microphone 14 are located at approximately the same height. Road noise d is transmitted from the occupant's feet to their head in the passenger compartment 5. Therefore, if the occupant's head position and the error microphone 14 are located at approximately the same height, the estimated road noise d at the microphone position is... m Road noise at the head position of the occupants e They are essentially equal. That is, regarding the road noise d, the following equation (4) is satisfied.

[0086] d e ≈d m (4)

[0087] Since equation (4) is satisfied, the noise estimation signal d^ can be used simultaneously as the road noise d at the microphone location. m The estimated signal and road noise at the occupant's head position d e The estimated signal.

[0088] Incidentally, with each speaker 13 and its corresponding error microphone 14 installed in the headrest 6a of the occupant seat 6, the reference distance L r The cancellation sound y at the occupant's head position can change significantly with a significant change in the front-to-back direction. e It also changes significantly due to the effects of time delay and distance decay.

[0089] Thus, the controller 16 adjusts the cancellation estimation signal y^ m2 The time delay and amplitude (distance attenuation) are used to generate the cancellation estimation signal y^ e1 In other words, controller 16 adjusts the position of the microphone to cancel out the sound y. m The time delay and amplitude (distance attenuation) are used to estimate the canceled sound at the occupant's head position. e That is, regarding the canceling sound y, the following equation (5) is satisfied.

[0090] y e ≈ay m Z -d (5)

[0091] Adjusting the microphone position in this way to cancel out the sound y m The time delay and amplitude (distance attenuation) can be used to accurately estimate the canceled sound y at the occupant's head position. e Therefore, it can effectively reduce road noise at the head position of the occupants.

[0092] To use this noise reduction mechanism, preferably, most of the canceling sound y travels directly from each speaker 13 to the corresponding error microphone 14 and the corresponding occupant's head position, thus increasing the dependence of the canceling sound y on time delay and distance attenuation. In other words, the prerequisite for using this noise reduction mechanism is that each speaker 13, the corresponding error microphone 14, and the corresponding occupant's head position are sufficiently close to each other.

[0093] <Effects of the First Implementation Method>

[0094] According to the first embodiment, the controller 16 updates the primary path filter H^ and the secondary path filter C^ based on the reference signal x and the error signal e. In other words, the controller 16 updates the estimated acoustic characteristics of the interior space based on the reference signal x and the error signal e. Therefore, even if the acoustic characteristics of the interior space change according to the displacement of each error microphone 14, the characteristics of the control filter W can be changed to follow the change in acoustic characteristics. Therefore, the error microphones 14 can be arranged on a movable part such as the headrest 6a, and thus closer to the occupant's head position.

[0095] Additionally, the area with high control effect (sound reduction effect) of the noise reduction system 11 is limited to the area around each error microphone 14 (see Figure 1 (Circle A in the diagram). Therefore, when the occupant's head moves away from the error microphone 14 due to the occupant's driving posture, the control effect of the noise reduction system 11 that the occupant can perceive may be reduced.

[0096] Thus, the controller 16 uses a reference distance L r Adjusting the cancellation estimation signal y^ m2 The time delay and amplitude of (canceling the estimated signal y at the microphone location) are used to generate the canceled estimated signal y^. e1 (The estimated signal of the canceled sound y at the occupant's head position), and based on the canceled estimated signal y^ e1 The control filter W is updated. Therefore, the characteristics of the control filter W can be changed to follow changes in the occupant's head position. Thus, when the occupant's head leaves the error microphone 14, the reduction in the control effect of the noise reduction system 11 that the occupant can perceive can be suppressed.

[0097] Incidentally, when reducing broadband noise, the noise reduction system 11 can use an FIR filter to cancel the estimated signal y^ m2 Filtering is performed to generate the cancellation estimate signal y^ e1 However, if the cancellation estimation signal y^ is generated in this way using an FIR filter... e1 Then it is used to generate the cancellation estimation signal y^e1 The computational load on controller 16 increases.

[0098] In this way, controller 16 adjusts only the cancellation estimation signal y^ m2 The delay characteristic Z -d The amplitude adjustment coefficient 'a' is used to generate the cancellation estimation signal y^ e1 Therefore, even when reducing broadband noise, it is not necessary to use an FIR filter to generate the cancellation estimate signal y^. e1 Therefore, when reducing broadband noise, the cost of generating the cancellation estimation signal y^ can be significantly reduced. e1 The computational load of controller 16.

[0099] Figure 4 This is a graph showing the effect of reducing road noise d at the occupant's head position (more specifically, the occupant's ear position). For example... Figure 4 As shown, when the noise reduction of this embodiment (i.e., the noise reduction system 11 based on the occupant's head position update control filter W) is ON, it can reduce road noise d in a wide frequency band compared to the case where conventional noise reduction (i.e., the noise reduction system without considering the occupant's head position update control filter W) is ON and the case where noise reduction is OFF.

[0100] <Modified Example of the First Embodiment>

[0101] In the first embodiment, the controller 16 adjusts only the cancellation estimation signal y^ m2 The delay characteristic Z -d And the amplitude adjustment coefficient a. If the aforementioned preconditions of the noise reduction mechanism (the preconditions that the speaker 13, the corresponding error microphone 14, and the corresponding occupant's head position are sufficiently close) cannot be met, the controller 16 can not only adjust the cancellation estimation signal y^ m2 The delay characteristic Z -d It has an amplitude adjustment coefficient 'a', and can also adjust its other parameters.

[0102] (Second Implementation)

[0103] Next, we will refer to Figure 5 and Figure 6 The second embodiment of the present invention is described below. Descriptions overlapping with the description of the first embodiment of the present invention are appropriately omitted.

[0104] <Active Noise Cancellation System 51>

[0105] Figure 5This is a functional block diagram showing the active noise reduction system 51 (hereinafter referred to as "noise reduction system 51") according to the second embodiment. Except for the control filter update unit 54 and the adjustment amount determination unit 55 of the controller 53, the components of the noise reduction system 51 are the same as those of the noise reduction system 11 according to the first embodiment. Therefore, a description of these components will be omitted. Figure 5 The symbol "ADA" in the text stands for "Adaptive".

[0106] <Control Filter Update Unit 54>

[0107] The control filter update unit 54 of the controller 53 includes a control filter unit 56, an adder 57, an estimated signal correction unit 58, and a control update unit 59. The configuration of the control filter unit 56 and the adder 57 of the control filter update unit 54 is the same as that of the control filter unit 45 and the adder 46 of the control filter update unit 29 according to the first embodiment. Therefore, a description of these components will be omitted.

[0108] The estimated signal correction unit 58 corrects and cancels the estimated signal y^ by using a correction coefficient b. e1 The estimated signal correction unit 58 corrects the canceled estimated signal y^ e1 Output to control update unit 59.

[0109] The control update unit 59 updates the control filter W using an adaptive algorithm such as the LMS algorithm. More specifically, the control update unit 59 updates the control filter W such that the virtual error signal e output from the adder 57... e Minimize. For example, control update unit 59 updates control filter W according to equation (6). Incidentally, “μ” in equation (6) represents the step size parameter.

[0110]

[0111] As is clear from equation (6) above, the control update unit 59 updates the control filter W by adjusting the update amount (μe^) e (n)(r*aZ -d C^)) is multiplied by the correction factor b to correct the update amount of the control filter W.

[0112] <Adjustment Amount Determination Unit 55>

[0113] The adjustment amount determination unit 55 of the controller 53 is based on the reference distance L output from the reference distance detector 15. r To set the correction coefficient b. The following describes the method for setting the correction coefficient b of the adjustment amount determination unit 55.

[0114] <Method 1 for setting the correction factor b>

[0115] When the amplitude adjustment coefficient a changes with the reference distance L r As the value increases and decreases, the update amount of the control filter W also decreases. If the update amount of the control filter W decreases excessively, the update performance (learning speed) of the control filter W may deteriorate.

[0116] Thus, the adjustment amount determination unit 55 sets the correction coefficient b to the reciprocal of the amplitude adjustment coefficient a, in order to reduce the dependence of the update amount of the control filter W on the amplitude adjustment coefficient a. Therefore, as the amplitude adjustment coefficient a changes with the reference distance L... r When the value decreases as the value increases, the correction coefficient b can be increased. Therefore, it is possible to prevent the update value of the control filter W from decreasing excessively, thereby maintaining the update performance of the control filter W.

[0117] <Method 2 for setting the correction factor b>

[0118] When the reference distance L r When this condition is increased, the aforementioned preconditions for the noise reduction mechanism (the preconditions that the speaker 13, the corresponding error microphone 14, and the corresponding occupant's head position are sufficiently close) may not be met. Therefore, the update accuracy of the control filter W may deteriorate.

[0119] Thus, the adjustment amount determination unit 55 sets the correction coefficient b so that the product of the amplitude adjustment coefficient a and the correction coefficient b is less than 1. Therefore, at the reference distance L r In the case of an increase, it is possible to prevent the update amount of the control filter W from increasing excessively. Therefore, it is possible to avoid the performance of the control filter W deteriorating due to the update of the control filter W.

[0120] <Method 3 for setting the correction factor b>

[0121] See Figure 6 The adjustment amount determination unit 55 stores the correction coefficient table T, which defines the reference distance L. r The relationship between the amplitude adjustment factor a and the correction factor b. Similar to method 2 for setting the correction factor b, the correction factor b is set, for example, in such a way that the product of the amplitude adjustment factor a and the correction factor b is less than 1.

[0122] The adjustment amount determination unit 55 determines the amount based on the reference distance L. r The correction factor b is set using the correction factor table T. By using the correction factor table T in this way, the correction factor b can be determined based on the reference distance L. r The correction factor b can be set freely, thus increasing the degree of freedom in setting the correction factor b.

[0123] <Effects of the Second Implementation>

[0124] The controller 53 according to the second embodiment is set to correspond to the reference distance L. r The correction coefficient b is used, and the update amount of the control filter W is corrected by multiplying the update amount of the control filter W by the correction coefficient b. Therefore, the update amount of the control filter W can be corrected based on the reference distance L. r This is used to adjust the update amount of the control filter W, thereby maintaining it at an appropriate value.

[0125] The specific embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various modifications and changes can be made within the scope of the present invention.

Claims

1. An active noise cancellation system, the active noise cancellation system being used to reduce noise in the internal space of a moving body, the active noise cancellation system comprising: A reference signal generator, the reference signal generator being configured to generate a reference signal corresponding to the noise; A noise cancellation output device configured to output a noise cancellation sound for canceling the noise; An error detector is configured to detect the error between the noise and the canceled sound, and to generate an error signal corresponding to the error; A reference distance detector, configured to detect a reference distance as the distance from the canceling sound output device to the occupant's head position; as well as A controller configured to control the cancelling sound output device based on the reference signal, the error signal, and the reference distance. The controller is configured as follows: A first cancellation estimation signal is generated based on the reference signal, wherein the first cancellation estimation signal is an estimated signal of the cancellation sound at the position of the error detector; A second cancellation estimation signal is generated by adjusting the time delay and amplitude of the first cancellation estimation signal based on the reference distance. The second cancellation estimation signal is an estimated signal of the cancellation sound at the head position of the occupant. and The control filter is updated based on the second cancellation estimation signal. The control filter is a filter used to control the cancellation sound output device.

2. The active noise cancellation system according to claim 1, wherein, The controller is configured to: Set a correction coefficient corresponding to the reference distance; and The update amount of the control filter is corrected by multiplying the update amount of the control filter by the correction coefficient.

3. The active noise reduction system according to claim 2, wherein, The controller is configured to adjust the amplitude of the first cancellation estimation signal by using an amplitude adjustment coefficient that decreases as the reference distance increases, and The correction factor is set to be the reciprocal of the amplitude adjustment factor.

4. The active noise reduction system according to claim 2, wherein, The controller is configured to adjust the amplitude of the first cancellation estimation signal by using an amplitude adjustment coefficient that decreases as the reference distance increases, and The correction coefficient is set such that the product of the amplitude adjustment coefficient and the correction coefficient is less than 1.

5. The active noise reduction system according to claim 2, wherein, The controller is configured to store a correction coefficient table that defines the relationship between the reference distance and the correction coefficients.

6. The active noise cancellation system according to any one of claims 1 to 5, wherein, The controller is configured to: Update the estimated value of the transmission characteristics of the canceled sound; and The first cancellation estimate signal is generated by correcting the reference signal based on the updated estimate of the transmission characteristics of the cancellation sound.

7. The active noise cancellation system according to any one of claims 1 to 5, wherein, The sound cancellation output device and the error detector are installed in the headrest of the occupant seat located in the interior space, and The controller is configured to generate the second cancellation estimation signal by adjusting only the time delay and the amplitude of the first cancellation estimation signal.

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