Active noise reduction device

Abstract

To correctly determine whether a transfer function of a secondary path has changed.SOLUTION: An active noise reduction device 1 comprises: a cancelling sound output device 21 that outputs cancelling sound y1 for cancelling noise d1; an error microphone 23 that generates an error signal e1 on the basis of the noise d1 and the cancelling sound y1; and a control unit 25 that controls the cancelling sound output device 21 on the basis of the error signal e1. The control unit 25 includes a control filter W1 that generates a control signal u1 for controlling the cancelling sound output device 21, and a secondary path filter C^1 that indicates an estimated value of a transfer function of a secondary path from the cancelling sound output device 21 to the error microphone 23. The active noise reduction device 1 further includes a reference microphone 24 that is provided separate from the error microphone 23. The reference microphone 24 generates a signal for determination e2 on the basis of at least noise d2. The control unit 25 determines whether the transfer function of the secondary path has changed on the basis of the error signal e1 and the signal for determination e2.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an active noise reduction device that reduces noise by interfering with noise with a cancellation sound having a phase opposite to that of the noise.

Background Art

[0002] In recent years, efforts have been actively made to consider people in vulnerable positions such as the elderly and children among traffic participants and to provide such people with access to a sustainable transportation system. Toward the realization thereof, research and development for further improving traffic safety and convenience have been attracting attention through the development related to the habitability of vehicles.

[0003] In order to improve the habitability of a vehicle, it is preferable to reduce noise in the vehicle interior. Therefore, research and development of an active noise reduction device that reduces noise by interfering with noise with a cancellation sound having a phase opposite to that of the noise have been actively conducted.

[0004] For example, Patent Document 1 discloses an active noise reduction device including a secondary path filter (see “filter 14c for creating a filtered X signal” in Patent Document 1) that shows an estimated value of a transfer function of a secondary path.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the active noise reduction device as described above, when the transfer function of the secondary path changes and the difference between the transfer function of the secondary path and the secondary path filter becomes large, there is a risk that the noise reduction effect will deteriorate or, conversely, the noise will be amplified. Therefore, a technique for adaptively updating the secondary path filter when the transfer function of the secondary path changes is known. When adopting such a technique, in order to perform the adaptive update of the secondary path filter at an appropriate timing, it is required to accurately determine whether or not the transfer function of the secondary path has changed.

[0007] In view of the above background, an object of the present invention is to provide an active noise reduction device capable of accurately determining whether or not the transfer function of the secondary path has changed. Subsequently, it is an object to contribute to the development of a sustainable transport system.

Means for Solving the Problems

[0008] In order to solve the above problems, an aspect of the present invention is an active noise reduction device (1) including a cancellation sound output device (21) that outputs cancellation sound for canceling noise, an error microphone (23) that generates an error signal (e1) based on the noise and the cancellation sound, and a control device (25) that controls the cancellation sound output device based on the error signal. The control device includes a control filter (W1) that generates a control signal (u1) for controlling the cancellation sound output device, and a secondary path filter (C^1) that indicates an estimated value of the transfer function of the secondary path from the cancellation sound output device to the error microphone. The active noise reduction device further includes a reference microphone (24) provided separately from the error microphone. The reference microphone generates a determination signal (e2) based on at least the noise, and the control device determines whether or not the transfer function of the secondary path has changed based on the error signal and the determination signal.

[0009] According to this aspect, it is possible to accurately determine whether or not the transfer function of the secondary path has changed based on the error signal and the determination signal. Therefore, the adaptive update of the secondary path filter can be executed at an appropriate timing.

[0010] In the above aspect, a second noise cancellation output device (22) provided separately from the noise cancellation output device is further provided, and the control device includes a second control filter (W2) that generates a second control signal (u2) for controlling the second noise cancellation output device, and the second control filter may be adaptively updated based on the determination signal.

[0011] According to this aspect, the second control filter can be adaptively updated using the determination signal generated by the reference microphone. Therefore, compared with the case where a microphone for generating a determination signal and a microphone for generating a signal for adaptively updating the second control filter are provided separately, the number of components can be reduced.

[0012] In the above aspect, the control device includes a second secondary path filter (ĉ2) indicating an estimated value of the transfer function of the second secondary path from the second noise cancellation output device to the reference microphone, and the control device may determine whether the transfer function of the second secondary path has changed based on the error signal and the determination signal.

[0013] According to this aspect, based on the error signal and the determination signal, it is possible to determine not only whether the transfer function of the secondary path has changed, but also whether the transfer function of the second secondary path has changed. Therefore, compared with the case where signals for determining changes in the transfer function of the secondary path and signals for determining changes in the transfer function of the second secondary path are generated by separate components, the number of components can be reduced.

[0014] In the above aspect, the control device determines that the transfer function of the secondary path has changed when the difference between the error signal and the determination signal is equal to or greater than a first reference value and the amount of change in the error signal over time is equal to or greater than a second reference value, and determines that the transfer function of the second secondary path has changed when the difference between the error signal and the determination signal is equal to or greater than the first reference value and the amount of change in the determination signal over time is equal to or greater than the second reference value.

[0015] According to this aspect, based on the error signal and the determination signal, it is possible to easily determine whether or not the transfer function of the secondary path has changed and whether or not the transfer function of the second secondary path has changed. Therefore, the computational load on the control device can be reduced.

[0016] In the above aspect, the control device may determine that the transfer function of the secondary path has changed when the difference between the error signal and the determination signal is equal to or greater than a first reference value and the amount of change in the error signal over time is equal to or greater than a second reference value.

[0017] According to this aspect, based not only on the difference between the error signal and the determination signal but also on the amount of change in the error signal over time, it is possible to determine whether or not the transfer function of the secondary path has changed. As a result, when the transfer function of the secondary path from the noise canceling output device to the reference microphone changes, it is possible to avoid misjudging that the transfer function of the secondary path from the noise canceling output device to the error microphone has changed. Also, based on the difference between the error signal and the determination signal and the amount of change in the error signal over time, it is possible to easily determine whether or not the transfer function of the secondary path has changed. Therefore, the computational load on the control device can be reduced as compared with the case of determining whether or not the transfer function of the secondary path has changed based on the similarity between the error signal and the determination signal.

[0018] In the above aspect, the control device may determine that the transfer function of the secondary path has changed when the difference between the error signal and the determination signal is equal to or greater than the first reference value, the amount of change in the error signal over time is equal to or greater than the second reference value, and the error signal is equal to or greater than a third reference value.

[0019] Even when the transfer function of the secondary path has not changed, the error signal may change slightly. When determining the change in the transfer function of the secondary path using only the first reference value and the second reference value, in order to exclude such a slight change in the error signal, it is required to increase the second reference value. However, if the second reference value is increased in this way, the accuracy of determining the change in the transfer function of the secondary path may decrease. According to the above aspect, by determining the change in the transfer function of the secondary path using a third reference value in addition to the first reference value and the second reference value, it is possible to exclude such a slight change in the error signal without increasing the second reference value. Therefore, it is possible to accurately determine the change in the transfer function of the secondary path.

[0020] In the above aspect, the active noise reduction device may further include a second noise cancellation output device (22) provided separately from the noise cancellation output device, and the control device may include a second secondary path filter (C^2) indicating an estimated value of the transfer function of the second secondary path from the second noise cancellation output device to the reference microphone.

[0021] According to this aspect, the reference microphone can be used to control the second noise cancellation output device. Therefore, the number of components can be reduced as compared with the case of controlling the second noise cancellation output device using a microphone other than the reference microphone.

Advantages of the Invention

[0022] According to the above aspects, it is possible to provide an active noise reduction device capable of accurately determining whether or not the transfer function of the secondary path has changed.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification, the "ˆ" (hat) appended to various reference numerals indicates an identified value or an estimated value. "ˆ" is attached above various reference numerals in the drawings, but is attached after various reference numerals in the text.

[0025] <Vehicle 3> FIG. 1 is a schematic diagram showing a vehicle 3 to which an active noise reduction device 1 (hereinafter abbreviated as "noise reduction device 1") according to an embodiment is applied. The vehicle 3 is, for example, a four-wheel automobile.

[0026] A plurality of passenger seats 5 and 6 are arranged in the passenger compartment 4 of the vehicle 3. The plurality of passenger seats 5 and 6 include a first passenger seat 5 and a second passenger seat 6. For example, the first passenger seat 5 is a passenger seat, and the second passenger seat 6 is a driver's seat. In other embodiments, a seat other than the passenger seat (for example, the driver's seat or the rear seat) may be used as the first passenger seat 5, or a seat other than the driver's seat (for example, the passenger seat or the rear seat) may be used as the second passenger seat 6. That is, the combination of the first passenger seat 5 and the second passenger seat 6 can be freely determined.

[0027] Each passenger seat 5, 6 (hereinafter simply referred to as "passenger seats 5, 6") has a seat cushion 7 and a reclining portion 8 that is disposed above and behind the seat cushion 7 and rotates with respect to the seat cushion 7. The reclining portion 8 has a seat back 9 and a headrest 10 fixed to the upper end of the seat back 9.

[0028] The front-rear position of the passenger seats 5, 6, the height of the passenger seats 5, 6, and the inclination angle of the reclining portion 8 of the passenger seats 5, 6 are adjusted by an electric motor (not shown) in response to an operation by the passenger on a seat position operation portion (not shown). That is, the passenger seats 5, 6 are configured by so-called power seats.

[0029] <Noise reduction device 1> The noise reduction device 1 is an ANC device (Active Noise Control Device) for reducing the noise d generated in the vehicle compartment 4 of the vehicle 3. More specifically, the noise reduction device 1 generates cancellation sounds y1, y2 having a phase opposite to that of the noise d, and reduces the noise d by causing the generated cancellation sounds y1, y2 to interfere with the noise d.

[0030] For example, the noise d to be reduced by the noise reduction device 1 is road noise caused by the vibration of the wheels due to the force from the road surface. Note that the noise d to be reduced by the noise reduction device 1 may be noise other than the above road noise (for example, drive system noise caused by the vibration of a drive source such as an internal combustion engine or an electric motor).

[0031] The noise reduction device 1 includes a plurality of speakers 21, 22 that output cancellation sounds y1, y2 for canceling the noise d, a plurality of microphones 23, 24 that generate error signals e1, e2 based on the noise d and the cancellation sounds y1, y2, and a control device 25 that controls the plurality of speakers 21, 22 based on the error signals e1, e2.

[0032] <Plurality of speakers 21, 22> The plurality of speakers 21, 22 includes a first speaker 21 (an example of a noise cancellation output device) that outputs a noise cancellation y1 and a second speaker 22 (an example of a second noise cancellation output device) that outputs a noise cancellation y2. The second speaker 22 is provided separately from the first speaker 21.

[0033] The first speaker 21 is provided at a position corresponding to the first passenger seat 5 and in a portion other than the first passenger seat 5. For example, the first speaker 21 is provided on the floor in front of the first passenger seat 5 or on the door on the side of the first passenger seat 5. In other embodiments, the first speaker 21 may be provided on the first passenger seat 5.

[0034] The second speaker 22 is provided at a position corresponding to the second passenger seat 6 and in a portion other than the second passenger seat 6. For example, the second speaker 22 is provided on the floor in front of the second passenger seat 6 or on the door on the side of the second passenger seat 6. In other embodiments, the second speaker 22 may be provided on the second passenger seat 6.

[0035] <A plurality of microphones 23, 24> The plurality of microphones 23, 24 includes a first microphone 23 (an example of an error microphone) and a second microphone 24 (an example of a reference microphone). The second microphone 24 is provided separately from the first microphone 23.

[0036] The first microphone 23 is provided at an arbitrary position on the first passenger seat 5. For example, the first microphone 23 is provided on the headrest 10 of the reclining portion 8 of the first passenger seat 5. In other embodiments, the first microphone 23 may be provided at a position corresponding to the first passenger seat 5 and in a portion other than the first passenger seat 5.

[0037] Referring to FIG. 2, the first microphone 23 generates an error signal e1 based on the noise cancellation y1, the noise cancellation y2, and the noise d1 (the noise d at the position of the first microphone 23). In other embodiments, the first microphone 23 may generate the error signal e1 based on only the noise cancellation y1 and the noise d1.

[0038] Referring to FIG. 1, the second microphone 24 is provided at any position of the second passenger seat 6. For example, the second microphone 24 is provided on the headrest 10 of the reclining portion 8 of the second passenger seat 6. In other embodiments, the second microphone 24 may be provided at a position corresponding to the second passenger seat 6 and in a portion other than the second passenger seat 6.

[0039] Referring to FIG. 2, the second microphone 24 generates an error signal e2 (an example of a determination signal) based on the noise cancellation y1, the noise cancellation y2, and the noise d2 (the noise d at the position of the second microphone 24). In other embodiments, the second microphone 24 may generate the error signal e2 based only on the noise cancellation y2 and the noise d2.

[0040] Note that C1 in FIG. 2 indicates the transfer function of the secondary path from the first speaker 21 to the first microphone 23, and H1 in FIG. 2 indicates the transfer function of the primary path from the noise source to the first microphone 23. Similarly, C2 in FIG. 2 indicates the transfer function of the secondary path from the second speaker 22 to the second microphone 24, and H2 in FIG. 2 indicates the transfer function of the primary path from the noise source to the second microphone 24. These transfer functions C1, H1, C2, and H2 correspond to the sound field in the passenger compartment 4.

[0041] <Control device 25> The control device 25 is constituted by a computer having an arithmetic processing unit (a processor such as a CPU or an MPU) and a storage device (a memory such as a ROM or a RAM). The control device 25 may be constituted as one piece of hardware, or may be constituted as a unit composed of a plurality of pieces of hardware.

[0042] A reference signal r corresponding to the noise d is input to the control device 25. The reference signal r is input to the control device 25 from, for example, a reference microphone (not shown) that generates the reference signal r from the noise d. In other embodiments, the reference signal r may be input to the control device 25 from a vibration sensor (not shown) that detects vibrations corresponding to the noise d, or may be input to the control device 25 from a component other than the reference microphone or the vibration sensor.

[0043] Referring to FIG. 2, as functional components, the control device 25 includes a first control signal generation unit 31, a first sound field learning unit 32, a second control signal generation unit 33, a second sound field learning unit 34, a sound field change determination unit 35, a convergence determination unit 36, and an update processing unit 37. The first control signal generation unit 31 and the first sound field learning unit 32 correspond to the first speaker 21 and the first microphone 23. The second control signal generation unit 33 and the second sound field learning unit 34 correspond to the second speaker 22 and the second microphone 24.

[0044] <The first control signal generation unit 31> The first control signal generation unit 31 of the control device 25 includes a first control filter unit 41, a first auxiliary secondary path filter unit 42, and a first control update unit 43.

[0045] The first control filter unit 41 is constituted by a control filter W1. The control filter W1 is constituted by an FIR filter (finite impulse response filter). In other embodiments, the control filter W1 may be constituted by a SAN filter (single frequency adaptive notch filter) or the like.

[0046] The first control filter unit 41 generates a control signal u1 for controlling the first speaker 21 by performing filter processing on the reference signal r by the control filter W1. The first control filter unit 41 outputs the generated control signal u1 to the first speaker 21 and the first sound field learning unit 32. Accordingly, the first speaker 21 generates a cancellation sound y1 corresponding to the control signal u1 output from the first control filter unit 41.

[0047] The first auxiliary secondary path filter unit 42 is constituted by an auxiliary secondary path filter Ĉ1p. The auxiliary secondary path filter Ĉ1p is a filter indicating an estimated value of the transfer function C1 of the secondary path. The auxiliary secondary path filter Ĉ1p is constituted by an FIR filter. In other embodiments, the auxiliary secondary path filter Ĉ1p may be constituted by a SAN filter or the like.

[0048] The first auxiliary secondary path filter section 42 corrects the reference signal r by subjecting the reference signal r to filter processing by the auxiliary secondary path filter C^1p. The first auxiliary secondary path filter section 42 outputs the corrected reference signal r to the first control update section 43.

[0049] The first control update section 43 adaptively updates the control filter W1 using an adaptive algorithm such as the LMS algorithm (Least Mean Square Algorithm). More specifically, the first control update section 43 adaptively updates the control filter W1 so that the error signal e1 output from the first microphone 23 is minimized.

[0050] <First sound field learning section 32> The first sound field learning section 32 of the control device 25 includes a first anti-noise estimation signal generation section 51, a first secondary path update section 52, a first noise estimation signal generation section 53, a first primary path update section 54, a first anti-noise estimation signal inversion section 55, a first noise estimation signal inversion section 56, and a first virtual error signal generation section 57.

[0051] The first anti-noise estimation signal generation section 51 is constituted by the secondary path filter C^1. The secondary path filter C^1 is a filter showing an estimated value of the transfer function C1 of the secondary path, similar to the auxiliary secondary path filter C^1p. The secondary path filter C^1 is constituted by, for example, an FIR filter. In other embodiments, the secondary path filter C^1 may be constituted by a SAN filter or the like.

[0052] The first anti-noise estimation signal generation section 51 generates an anti-noise estimation signal y^1 indicating an estimated value of the anti-noise y1 by subjecting the control signal u1 to filter processing by the secondary path filter C^1. The first anti-noise estimation signal generation section 51 outputs the generated anti-noise estimation signal y^1 to the first anti-noise estimation signal inversion section 55.

[0053] The first secondary path update unit 52 adaptively updates the secondary path filter C^1 using an adaptive algorithm such as the LMS algorithm. More specifically, the first secondary path update unit 52 adaptively updates the secondary path filter C^1 so that the virtual error signal ev1 (details will be described later) output from the first virtual error signal generation unit 57 is minimized.

[0054] The first noise estimation signal generation unit 53 is constituted by the primary path filter H^1. The primary path filter H^1 is a filter that shows an estimated value of the transfer function H1 of the primary path. The primary path filter H^1 is constituted by, for example, a FIR filter. In other embodiments, the primary path filter H^1 may be constituted by a SAN filter or the like.

[0055] The first noise estimation signal generation unit 53 generates a noise estimation signal d^1 indicating an estimated value of the noise d1 by performing filter processing on the reference signal r by the primary path filter H^1. The first noise estimation signal generation unit 53 outputs the generated noise estimation signal d^1 to the first noise estimation signal inversion unit 56.

[0056] The first primary path update unit 54 adaptively updates the primary path filter H^1 using an adaptive algorithm such as the LMS algorithm. More specifically, the first primary path update unit 54 adaptively updates the primary path filter H^1 so that the virtual error signal ev1 (details will be described later) output from the first virtual error signal generation unit 57 is minimized.

[0057] The first cancellation noise estimation signal inversion unit 55 inverts the polarity of the cancellation noise estimation signal y^1 output from the first cancellation noise estimation signal generation unit 51. The first cancellation noise estimation signal inversion unit 55 outputs the cancellation noise estimation signal y^1 with the inverted polarity to the first virtual error signal generation unit 57.

[0058] The first noise estimation signal inversion unit 56 inverts the polarity of the noise estimation signal d^1 output from the first noise estimation signal generation unit 53. The first noise estimation signal inversion unit 56 outputs the noise estimation signal d^1 with the inverted polarity to the first virtual error signal generation unit 57.

[0059] The first virtual error signal generation unit 57 generates a virtual error signal ev1 by adding together the error signal e1 output from the first microphone 23, the anti-noise estimation signal ŷ1 that has passed through the first anti-noise estimation signal inversion unit 55, and the noise estimation signal d̂1 that has passed through the first noise estimation signal inversion unit 56. The first virtual error signal generation unit 57 outputs the generated virtual error signal ev1 to the first secondary path update unit 52 and the first primary path update unit 54.

[0060] <The second control signal generation unit 33> The second control signal generation unit 33 of the control device 25 is provided separately from the first control signal generation unit 31. The second control signal generation unit 33 includes a second control filter unit 61, a second auxiliary secondary path filter unit 62, and a second control update unit 63.

[0061] The second control filter unit 61 generates a control signal u2 (an example of a second control signal) for controlling the second speaker 22 by performing filter processing on the reference signal r with a control filter W2 (an example of a second control filter). The second auxiliary secondary path filter unit 62 is constituted by an auxiliary secondary path filter Ĉ2p indicating an estimated value of the transfer function C2 of the secondary path. The second auxiliary secondary path filter unit 62 corrects the reference signal r with the auxiliary secondary path filter Ĉ2p and outputs the corrected reference signal r to the second control update unit 63. The second control update unit 63 adaptively updates the control filter W2 so that the error signal e2 output from the second microphone 24 is minimized.

[0062] <The second sound field learning unit 34> The second sound field learning unit 34 of the control device 25 is provided separately from the first sound field learning unit 32. The second sound field learning unit 34 includes a second anti-noise estimation signal generation unit 71, a second secondary path update unit 72, a second noise estimation signal generation unit 73, a second primary path update unit 74, a second anti-noise estimation signal inversion unit 75, a second noise estimation signal inversion unit 76, and a second virtual error signal generation unit 77.

[0063] The second cancellation sound estimation signal generation unit 71 is configured by a secondary path filter Ĉ2 (an example of a second secondary path filter) that indicates an estimated value of the transfer function C2 of the secondary path. The second cancellation sound estimation signal generation unit 71 generates a cancellation sound estimation signal ŷ2 that indicates an estimated value of the cancellation sound y2 by performing filter processing on the control signal u2 using the secondary path filter Ĉ2. The second secondary path update unit 72 adaptively updates the secondary path filter Ĉ2 so that the virtual error signal ev2 (details will be described later) becomes minimum.

[0064] The second noise estimation signal generation unit 73 is configured by a primary path filter Ĥ2 that indicates an estimated value of the transfer function H2 of the primary path. The second noise estimation signal generation unit 73 generates a noise estimation signal d̂2 that indicates an estimated value of the noise d2 by performing filter processing on the reference signal r using the primary path filter Ĥ2. The second primary path update unit 74 adaptively updates the primary path filter Ĥ2 so that the virtual error signal ev2 (details will be described later) becomes minimum.

[0065] The second cancellation sound estimation signal inversion unit 75 inverts the polarity of the cancellation sound estimation signal ŷ2. The second noise estimation signal inversion unit 76 inverts the polarity of the noise estimation signal d̂2. The second virtual error signal generation unit 77 generates a virtual error signal ev2 by adding together the error signal e2 output from the second microphone 24, the cancellation sound estimation signal ŷ2 that has passed through the second cancellation sound estimation signal inversion unit 75, and the noise estimation signal d̂2 that has passed through the second noise estimation signal inversion unit 76.

[0066] <Sound field change determination unit 35> The sound field change determination unit 35 of the control device 25 determines whether or not the transfer function C1 of the secondary path has changed based on the error signal e1 and the error signal e2. Note that the method of determination by the sound field change determination unit 35 will be described later.

[0067] <Convergence determination unit 36> The convergence determination unit 36 of the control device 25 determines whether or not the fluctuations accompanying the adaptive update of the secondary path filter Ĉ1 have converged based on the secondary path filter Ĉ1. Note that the method of determination by the convergence determination unit 36 will be described later.

[0068] <Update processing unit 37> Based on the determination results of the sound field change determination unit 35 and the convergence determination unit 36, the update processing unit 37 of the control device 25 determines the order and timing of adaptive updates of the filter. The method of determination by the update processing unit 37 will be described later.

[0069] <Sound field change determination process> Next, the sound field change determination process by the sound field change determination unit 35 will be described. The sound field change determination process is a process for determining whether or not the transfer function C1 of the secondary path has changed.

[0070] Referring to FIG. 3, when the sound field change determination process is started, the sound field change determination unit 35 acquires the error signal e1 from the first microphone 23 and acquires the error signal e2 from the second microphone 24 (step ST1).

[0071] Next, the sound field change determination unit 35 calculates the signal level L1 of the error signal e1 and the signal level L2 of the error signal e2 (step ST2). For example, the sound field change determination unit 35 may use the sum of the squares of the error signal e1 within a certain time as the signal level L1 of the error signal e1, or may use the sum of the absolute values of the error signal e1 within a certain time as the signal level L1 of the error signal e1. The same applies to the signal level L2 of the error signal e2.

[0072] Next, the sound field change determination unit 35 determines whether or not the absolute value of the difference between the signal level L1 of the error signal e1 and the signal level L2 of the error signal e2 is equal to or greater than the first reference value R1 (step ST3). If the absolute value of the difference between the signal level L1 of the error signal e1 and the signal level L2 of the error signal e2 is less than the first reference value R1 (step ST3: No), the sound field change determination unit 35 determines that the transfer function C1 of the secondary path has not changed (step ST4).

[0073] When the absolute value of the difference between the signal level L1 of the error signal e1 and the signal level L2 of the error signal e2 is equal to or greater than the first reference value R1 (step ST3: Yes), the sound field change determination unit 35 determines whether the amount of change ΔL1 in the signal level L1 of the error signal e1 over time (for example, the difference between the current value and the previous value of the signal level L1 of the error signal e1) is equal to or greater than the second reference value R2 (step ST5). When the amount of change ΔL1 in the signal level L1 of the error signal e1 over time is less than the second reference value R2 (step ST5: No), the sound field change determination unit 35 determines that the transfer function C1 of the secondary path has not changed (step ST4).

[0074] When the amount of change ΔL1 in the signal level L1 of the error signal e1 over time is equal to or greater than the second reference value R2 (step ST5: Yes), the sound field change determination unit 35 determines whether the signal level L1 of the error signal e1 is equal to or greater than the third reference value R3 (step ST6). When the signal level L1 of the error signal e1 is less than the third reference value R3 (step ST6: No), the sound field change determination unit 35 determines that the transfer function C1 of the secondary path has not changed (step ST4). When the signal level L1 of the error signal e1 is equal to or greater than the third reference value R3 (step ST6: Yes), the sound field change determination unit 35 determines that the transfer function C1 of the secondary path has changed (step ST7).

[0075] As shown by the dashed two-dot line in FIG. 1, when the reclining portion 8 of the first passenger seat 5 is reclined, the position of the first microphone 23 provided in the reclining portion 8 of the first passenger seat 5 changes. Accordingly, the transfer function C1 of the secondary path changes, and the difference between the transfer function C1 of the secondary path and the secondary path filter Ĉ1 temporarily increases. Therefore, the control effect of the noise reduction device 1 temporarily decreases, and the signal level L1 of the error signal e1 increases.

[0076] Referring to FIG. 4, for example, when the reclining portion 8 of the first passenger seat 5 is reclined at time t1, the signal level L1 of the error signal e1 increases significantly with respect to the signal level L2 of the error signal e2. Accordingly, all the determinations in steps ST3, ST5, and ST6 described above become Yes. Therefore, the sound field change determination unit 35 can determine that the transfer function C1 of the secondary path has changed.

[0077] Note that the sound field change determination unit 35 can determine whether or not the transfer function C2 of the secondary path has changed based on the error signal e1 and the error signal e2 by the same process as the above-described sound field change determination process. For example, the sound field change determination unit 35 determines that the transfer function C2 of the secondary path has changed when the absolute value of the difference between the signal level L1 of the error signal e1 and the signal level L2 of the error signal e2 is equal to or greater than the first reference value R1, and the amount of change ΔL2 in the signal level L2 of the error signal e2 over time is equal to or greater than the second reference value R2, and the signal level L2 of the error signal e2 is equal to or greater than the third reference value R3. The sound field change determination unit 35 determines that the transfer function C2 of the secondary path has not changed in other cases.

[0078] <Convergence determination process> Next, the convergence determination process by the convergence determination unit 36 will be described. The convergence determination process is a process for determining whether or not the fluctuation (hereinafter abbreviated as "fluctuation of the secondary path filter C^1") associated with the adaptive update of the secondary path filter C^1 has converged.

[0079] Referring to FIGS. 5 and 6, when the convergence determination process is started, the convergence determination unit 36 acquires the amplitude A and the phase P of the secondary path filter C^1 (step ST11). For example, the convergence determination unit 36 acquires the maximum value of the amplitude of the impulse response of the secondary path filter C^1 as the amplitude A of the secondary path filter C^1. Further, the convergence determination unit 36 acquires the delay sample number Sd corresponding to the maximum value of the amplitude of the impulse response of the secondary path filter C^1 as the phase P of the secondary path filter C^1. Note that by multiplying the delay sample number Sd by the sampling time Ts, the delay time ΔT (the time T when the first speaker 21 outputs the cancellation sound y1) 0from the time T when the amplitude of the impulse response of the secondary path filter C^1 reaches its maximum value max until the time) is calculated. That is, the convergence determination unit 36 uses the delay sample number Sd corresponding to the delay time ΔT as the phase P of the secondary path filter C^1.

[0080] Next, the convergence determination unit 36 calculates the change amount ΔA of the amplitude A of the secondary path filter C^1 (for example, the difference between the current value and the previous value of the amplitude A of the secondary path filter C^1). Further, the convergence determination unit 36 calculates the change amount ΔP of the phase P of the secondary path filter C^1 (for example, the difference between the current value and the previous value of the phase P of the secondary path filter C^1) (step ST12).

[0081] Next, the convergence determination unit 36 determines whether the change amount ΔA of the amplitude A of the secondary path filter C^1 is less than the amplitude threshold value AT (step ST13). If the change amount ΔA of the amplitude A of the secondary path filter C^1 is greater than or equal to the amplitude threshold value AT (step ST13: No), the convergence determination unit 36 determines that the fluctuation of the secondary path filter C^1 has not converged (step ST14).

[0082] If the change amount ΔA of the amplitude A of the secondary path filter C^1 is less than the amplitude threshold value AT (step ST13: Yes), the convergence determination unit 36 determines whether the change amount ΔP of the phase P of the secondary path filter C^1 is less than the phase threshold value PT (step ST15). If the change amount ΔP of the phase P of the secondary path filter C^1 is greater than or equal to the phase threshold value PT (step ST15: No), the convergence determination unit 36 determines that the fluctuation of the secondary path filter C^1 has not converged (step ST14). If the change amount ΔP of the phase P of the secondary path filter C^1 is less than the phase threshold value PT (step ST15: Yes), the convergence determination unit 36 determines that the fluctuation of the secondary path filter C^1 has converged (step ST16).

[0083] As described above, the convergence determination unit 36 executes the convergence determination process based on both the change amount ΔA of the amplitude A and the change amount ΔP of the phase P of the secondary path filter C^1. As a result, compared with the case where the convergence determination process is executed based on only one of the change amount ΔA of the amplitude A and the change amount ΔP of the phase P of the secondary path filter C^1, it is possible to accurately determine whether or not the variation of the secondary path filter C^1 has converged.

[0084] <Update Process> Next, the update process by the control device 25 will be described. The update process is a process for updating the control filter W1, the secondary path filter C^1, the primary path filter H^1, and the auxiliary secondary path filter C^1p.

[0085] Referring to FIG. 7, when the update process is started, the sound field change determination unit 35 executes the above-described sound field change determination process. That is, the sound field change determination unit 35 determines whether or not the transfer function C1 of the secondary path has changed based on the error signal e1 and the error signal e2 (step ST21).

[0086] When the transfer function C1 of the secondary path has changed (step ST21: Yes), the update processing unit 37 sets the state of the secondary path filter C^1 to the state requiring update (step ST22) and proceeds to step ST23. When the transfer function C1 of the secondary path has not changed (step ST21: No), the update processing unit 37 proceeds to step ST23 without executing the process of step ST22.

[0087] Next, the update processing unit 37 updates the execution count Cnt (initial value = 0) of the update process to Cnt + 1 (step ST23) and determines whether or not the execution count Cnt is an odd number (step ST24).

[0088] When the execution count Cnt is even (step ST24: No), the first control update unit 43 adaptively updates the control filter W1 (step ST25). Next, the first control filter unit 41 generates a control signal u1 using the adaptively updated control filter W1 and outputs the generated control signal u1 to the first speaker 21. In response, the first speaker 21 outputs an anti-noise y1 (step ST26).

[0089] When the execution count Cnt is odd (step ST24: Yes), the update processing unit 37 determines whether the state of the secondary path filter Ĉ1 is set to the state where update is required (step ST27). When the state of the secondary path filter Ĉ1 is not set to the state where update is required (step ST27: No), the processes of step ST25 and step ST26 are executed in the same manner as when the execution count Cnt is even (step ST24: No).

[0090] When the state of the secondary path filter Ĉ1 is set to the state where update is required (step ST27: Yes), the first secondary path update unit 52 adaptively updates the secondary path filter Ĉ1, and the first primary path update unit 54 adaptively updates the primary path filter Ĥ1 (step ST28).

[0091] Next, the convergence determination unit 36 determines whether the variation of the secondary path filter Ĉ1 has converged by executing the above-described convergence determination process (step ST29).

[0092] When the variation of the secondary path filter Ĉ1 has converged (step ST29: Yes), the update processing unit 37 updates the auxiliary secondary path filter Ĉ1p with the value of the secondary path filter Ĉ1 by copying the value of the secondary path filter Ĉ1 to the auxiliary secondary path filter Ĉ1p (step ST30).

[0093] Next, the first control filter unit 41 generates a control signal u1 by means of the temporarily fixed control filter W1 (the control filter W1 adaptively updated in the previous update process), and outputs the generated control signal u1 to the first speaker 21. In response to this, the first speaker 21 outputs an anti-noise y1 (step ST31).

[0094] When the variation of the secondary path filter Ĉ1 has not converged (step ST29: No), the update processing unit 37 updates the execution count Cnt to Cnt + 1 without updating the auxiliary secondary path filter Ĉ1p according to the value of the secondary path filter Ĉ1 (step ST32). Next, by executing step ST31 described above, the first control filter unit 41 outputs the control signal u1 to the first speaker 21, and the first speaker 21 outputs the anti-noise y1.

[0095] When either step ST26 or step ST31 ends, the update process ends, and the next update process (a new update process) is executed after a predetermined time. However, the value of the execution count Cnt is retained as it is even after the update process ends, and is used in the next update process.

[0096] In addition, if the variation of the secondary path filter C^1 does not converge in the current update process (step ST29: No), the update processing unit 37 will set the state of the secondary path filter C^1 to the state requiring update in the next update process (step ST22). Also, if the variation of the secondary path filter C^1 does not converge in the current update process (step ST29: No), the execution count Cnt is updated twice in step ST32 of the current update process and step ST23 of the next update process, so that step ST24 of the next update process becomes Yes. As a result, in the next update process, similar to the current update process, the secondary path filter C^1 is adaptively updated (step ST28), and it is determined whether the variation of the secondary path filter C^1 has converged (step ST29). Thus, in this embodiment, until the variation of the secondary path filter C^1 converges, the control filter W1 is not adaptively updated, and the adaptive update of the secondary path filter C^1 and the determination of whether the variation of the secondary path filter C^1 has converged are repeated.

[0097] The control device 25 repeatedly executes the above update process at regular intervals. In the update process, the control device 25 determines whether the variation of the secondary path filter C^1 has converged (step ST29). If the variation of the secondary path filter C^1 has converged (step ST29: Yes), the control device 25 stops the adaptive update of the secondary path filter C^1. In the next update process, the control device 25 determines whether the transfer function C1 of the secondary path has changed based on the error signal e1 and the error signal e2 with the adaptive update of the secondary path filter C^1 stopped (step ST21). If the transfer function C1 of the secondary path has changed (step ST21: Yes), the control device 25 resumes the adaptive update of the secondary path filter C^1 (steps ST22, ST27, ST28).

[0098] <Effect> The control device 25 may also determine whether the transfer function C1 of the secondary path has changed based on external information (for example, information regarding the position of the first occupant seat 5). However, if such a determination method is adopted, when external information cannot be received, it becomes impossible to determine whether the transfer function C1 of the secondary path has changed. When it is impossible to determine whether the transfer function C1 of the secondary path has changed, it is also conceivable that the control device 25 always adaptively updates the secondary path filter C^1 regardless of whether the transfer function C1 of the secondary path has changed. However, if such an update method is adopted, the computational load on the control device 25 increases. Therefore, it becomes necessary to configure the control device 25 with an expensive processor that can withstand such a large computational load, which may lead to an increase in the manufacturing cost of the noise reduction device 1.

[0099] Therefore, the control device 25 determines whether the transfer function C1 of the secondary path has changed based on the error signal e1 and the error signal e2. Thereby, even when external information cannot be received, it is possible to determine whether the transfer function C1 of the secondary path has changed. Also, by determining whether the transfer function C1 of the secondary path has changed, the secondary path filter C^1 can be adaptively updated only when the transfer function C1 of the secondary path has changed. Therefore, the computational load on the control device 25 can be reduced compared to the case where the secondary path filter C^1 is always adaptively updated.

[0100] The control device 25 may also determine whether the transfer function C1 of the secondary path has changed based only on the error signal e1 (for example, based only on the magnitude of the error signal e1). However, if such a determination method is adopted, when the transfer function C2 of the secondary path changes, there is a risk of misjudging that the transfer function C1 of the secondary path has changed.

[0101] Therefore, the control device 25 determines whether the transfer function C1 of the secondary path has changed based on the error signal e1 and the error signal e2. Thereby, it is possible to accurately determine that the transfer function C1 of the secondary path has changed, rather than the transfer function C2 of the secondary path.

[0102] <Modification Example> <In the above embodiment, the convergence determination unit 36 executes the convergence determination process based on both the change amount ΔA of the amplitude A and the change amount ΔP of the phase P of the secondary path filter C^1. In other embodiments, the convergence determination unit 36 may execute the convergence determination process based on only one of the change amount ΔA of the amplitude A and the change amount ΔP of the phase P of the secondary path filter C^1.>

[0103] <In the above embodiment, the convergence determination unit 36 obtains the maximum value of the amplitude of the impulse response of the secondary path filter C^1 as the amplitude A of the secondary path filter C^1 (step ST11). In other embodiments, the convergence determination unit 36 may calculate the amplitude A of the secondary path filter C^1 by the following formula (1). However, L in the following formula (1) indicates the total number of coefficients of the secondary path filter C^1, and n in the following formula (1) indicates the number of the coefficients of the secondary path filter C^1.>

Equation

[0104] <In the above embodiment, the convergence determination unit 36 determines whether or not the change amount ΔA of the amplitude A of the secondary path filter C^1 is less than the amplitude threshold AT (step ST13). In other embodiments, the convergence determination unit 36 may determine whether or not the state where the change amount ΔA of the amplitude A of the secondary path filter C^1 is less than the amplitude threshold AT continues for a predetermined time. Alternatively, the convergence determination unit 36 may determine whether or not the ratio of the current value of the amplitude A of the secondary path filter C^1 to the previous value of the amplitude A of the secondary path filter C^1 is equal to or less than a predetermined value. The same applies to the determination of the change amount ΔP of the phase P of the secondary path filter C^1.>

[0105] In the above embodiment, the update processing unit 37 copies the value of the secondary path filter C^1 to the auxiliary secondary path filter C^1p in accordance with the adaptive update of the secondary path filter C^1 (Steps ST28 to ST30). In other embodiments, the update processing unit 37 may copy the value of the secondary path filter C^1 to the auxiliary secondary path filter C^1p at a timing different from the adaptive update of the secondary path filter C^1 (for example, the timing of the adaptive update of the control filter W1).

[0106] Referring to FIG. 7, in the above first embodiment, when the variation of the secondary path filter C^1 has not converged (Step ST29: No), after the update processing unit 37 updates the execution count Cnt to Cnt + 1, the first speaker 21 outputs the cancellation sound y1 (Steps ST31, ST32). Referring to FIG. 8, in other embodiments, when the variation of the secondary path filter C^1 has not converged (Step ST29: No), the first speaker 21 may output the cancellation sound y1 without the update processing unit 37 updating the execution count Cnt to Cnt + 1 (Step ST31). That is, in other embodiments, the process of Step ST32 may be omitted. As a result, in the next update process, Step ST24 becomes No, and the control filter W1 is adaptively updated (Step ST25). Therefore, when the transfer function C1 of the secondary path changes, the adaptive update of the control filter W1 (Step ST25) and the adaptive update of the secondary path filter C^1 (Step ST28) are alternately executed.

[0107] In the above embodiment, the second microphone 24 is used as the reference microphone for generating the determination signal. In other embodiments, a dedicated reference microphone for generating the determination signal may be provided. In this case, the reference microphone may generate the determination signal based only on the cancellation sound y1 and the noise d. That is, the reference microphone may generate the determination signal based at least on the noise d.

[0108] In the above embodiment, the control device 25 executes an update process in order to adaptively update the control filter W1, the secondary path filter C^1, and the primary path filter H^1. In other embodiments, the control device 25 may execute an update process in order to adaptively update the control filter W2, the secondary path filter C^2, and the primary path filter H^2. In this case, it is preferable that the second microphone 24 is used as an error microphone and the first microphone 23 is used as a reference microphone.

[0109] In the above embodiment, the noise reduction device 1 is applied to the passenger compartment 4 of the vehicle 3. In other embodiments, the noise reduction device 1 may be applied to the interior space of a moving body other than the vehicle 3 (for example, a ship or an aircraft), or the noise reduction device 1 may be applied to the interior space of a stationary object (for example, a house).

[0110] Although the description of the specific embodiments has been completed above, the present invention is not limited to the above embodiments and modification examples, and can be widely modified and implemented.

Explanation of Reference Numerals

[0111] 1: Active noise reduction device 21: First speaker (an example of an anti-noise output device) 22: Second speaker (an example of a second anti-noise output device) 23: First microphone (an example of an error microphone) 24: Second microphone (an example of a reference microphone) 25: Control device C^1: Secondary path filter C^2: Secondary path filter (an example of a second secondary path filter) W1: Control filter W2: Control filter (an example of a second control filter) e1: Error signal e2: Error signal (an example of a determination signal) u1: Control signal u2: Control signal (an example of a second control signal)

Claims

1. An anti-noise output device that outputs anti-noise to cancel noise, An error microphone that generates an error signal based on the noise and the anti-noise, A control device that controls the anti-noise output device based on the error signal, comprising: The control device A control filter that generates a control signal for controlling the anti-noise output device, A secondary path filter that indicates an estimated value of the transfer function of the secondary path from the anti-noise output device to the error microphone, and is an active noise reduction device, Further comprising a reference microphone provided separately from the error microphone, The reference microphone generates a determination signal based on the noise and the anti-noise, The control device is an active noise reduction device that determines whether the transfer function of the secondary path has changed based on the error signal and the determination signal.

2. Further comprising a second anti-noise output device provided separately from the anti-noise output device, The control device includes a second control filter that generates a second control signal for controlling the second anti-noise output device, The second control filter is adaptively updated based on the determination signal, and the active noise reduction device according to claim 1.

3. The control device includes a second secondary path filter that indicates an estimated value of the transfer function of the second secondary path from the second anti-noise output device to the reference microphone, The control device is an active noise reduction device according to claim 2 that determines whether the transfer function of the second secondary path has changed based on the error signal and the determination signal.

4. The control device When the difference between the error signal and the determination signal is equal to or greater than a first reference value, and the amount of change in time of the error signal is equal to or greater than a second reference value, it is determined that the transfer function of the secondary path has changed, When the difference between the error signal and the determination signal is equal to or greater than the first reference value, and the amount of change in time of the determination signal is equal to or greater than the second reference value, it is determined that the transfer function of the second secondary path has changed, and the active noise reduction device according to claim 3.

5. The control device determines that the transfer function of the secondary path has changed when the difference between the error signal and the determination signal is equal to or greater than a first reference value, and the amount of change in time of the error signal is equal to or greater than a second reference value, and the active noise reduction device according to claim 1.

6. The active noise reduction device according to claim 5, wherein the control device determines that the transfer function of the secondary path has changed when the difference between the error signal and the determination signal is equal to or greater than the first reference value, the amount of temporal change of the error signal is equal to or greater than the second reference value, and the error signal is equal to or greater than the third reference value.

7. further comprising a second noise cancellation output device provided separately from the noise cancellation output device, The active noise reduction device according to claim 1, wherein the control device includes a second secondary path filter indicating an estimated value of the transfer function of a second secondary path from the second noise cancellation output device to the reference microphone.

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