Active noise reduction device

Abstract

To suppress reduction of a noise reduction effect at a user's ear position or amplification of noise at the user's ear position, when cancellation sound propagation distance is increased.SOLUTION: An active noise reduction device 1 comprises: a cancellation sound output device 21 that outputs a cancellation sound y to cancel out noise d; an error microphone 22 that generates an error signal e based on the noise d and the cancellation sound y; and a control device 23 that controls the cancellation sound output device 21 based on the error signal e. The control device 23 calculates cancellation sound propagation distance L from the cancellation sound output device 21 to the error microphone 22, and suppresses the change of the cancellation sound y based on the cancellation sound propagation distance L.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an active noise reduction device that reduces noise by interfering with the noise with a canceling sound that is in the opposite phase to the noise. [Background technology]

[0002] In recent years, efforts to provide vulnerable transport users, such as the elderly and children, with access to sustainable transport systems have been gaining momentum. To achieve this, research and development into vehicle comfort has been attracting attention to further improve transport safety and convenience.

[0003] In order to improve the comfort of a vehicle, it is preferable to reduce noise in the vehicle interior. Therefore, active noise reduction devices that reduce noise by interfering with the noise with a canceling sound that is in the opposite phase to the noise have been actively researched and developed.

[0004] Conventionally, an active noise reduction device includes a noise canceling output device (e.g., a speaker) that outputs a canceling sound to cancel out noise, an error microphone that generates an error signal based on the noise and the canceling sound, and a control device that controls the canceling output device based on the error signal (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-28474 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above-mentioned active noise reduction device, when either the noise canceling output device or the error microphone is provided on a movable part, the distance from the noise canceling output device to the error microphone (hereinafter referred to as the "noise canceling propagation distance") may increase as the movable part moves. When the noise canceling propagation distance increases in this way, the control device causes the noise canceling output device to output a large noise canceling sound in order to sufficiently reduce noise at the position of the error microphone that is farther away from the noise canceling output device. However, when the ears of a user (e.g., a vehicle occupant) are located closer to the noise canceling output device than the error microphone, if the noise canceling output device outputs a large noise canceling sound, the noise reduction effect at the position of the user's ear may be reduced or the noise may be amplified at the position of the user's ear.

[0007] In view of the above background, an object of the present invention is to suppress a decrease in the noise reduction effect at the user's ear position and an amplification of noise at the user's ear position when the noise cancellation propagation distance increases, and to contribute to the development of a sustainable transportation system. [Means for solving the problem]

[0008] In order to solve the above problem, one aspect of the present invention is an active noise reduction device (1, 61, 71) comprising a noise cancellation output device (21) that outputs a noise cancellation sound to cancel out noise, an error microphone (22) that generates an error signal (e) based on the noise and the noise cancellation sound, and a control device (23, 63, 73) that controls the noise cancellation output device based on the error signal, wherein the control device calculates a noise cancellation propagation distance (L) that is the distance from the noise cancellation output device to the error microphone, and suppresses a change in the noise cancellation sound based on the noise cancellation propagation distance.

[0009] According to this aspect, by suppressing the change in the silencing sound based on the silencing sound propagation distance, it is possible to suppress the silencing sound from increasing in response to an increase in the silencing sound propagation distance, thereby suppressing a decrease in the noise reduction effect at the user's ear position and an amplification of the noise at the user's ear position.

[0010] In the above aspect, the control device includes a control filter (W) that generates a control signal (u) for controlling the noise cancellation output device, a primary path filter (H^) that indicates an estimate of a transfer function from a noise source to the error microphone, and a secondary path filter (C^) that indicates an estimate of a transfer function from the noise cancellation output device to the error microphone, and the control filter is adaptively updated based on a virtual error signal (e2) that is generated based on the noise estimation signal (d^) generated by the primary path filter and the noise cancellation estimation signal (y^2) generated by the secondary path filter, and the control device may correct at least one of the noise estimation signal or the noise cancellation estimation signal in accordance with the noise cancellation propagation distance.

[0011] According to this aspect, by correcting the noise estimation signal and the cancellation-sound estimation signal used for adaptively updating the control filter in accordance with the cancellation-sound propagation distance, it is possible to prevent the control signal generated by the control filter from becoming excessively large.

[0012] In the above aspect, the control device may set a gain coefficient (α) that increases as the cancellation propagation distance increases, and may correct the cancellation estimation signal by multiplying the cancellation estimation signal by the gain coefficient.

[0013] According to this aspect, the magnitude of the canceling sound estimation signal can be easily changed by adjusting the gain coefficient, so that the magnitude of the canceling sound can be easily adjusted.

[0014] In the above aspect, the control device may set a gain coefficient (β) that decreases as the negating sound propagation distance increases, and correct the noise estimation signal by multiplying the noise estimation signal by the gain coefficient.

[0015] According to this aspect, the magnitude of the noise estimation signal can be easily changed by adjusting the gain coefficient, and therefore the magnitude of the cancellation sound can be easily adjusted.

[0016] In the above aspect, the control device may calculate the cancellation propagation distance based on the secondary path filter.

[0017] The secondary path filter indicates an estimate of the transfer function from the noise canceling device to the error microphone. Therefore, it is possible to calculate the noise canceling propagation distance, which is the distance from the noise canceling device to the error microphone, based on the secondary path filter. By calculating the noise canceling propagation distance based on the secondary path filter in this way, it is not necessary to provide a separate sensor or the like for calculating the noise canceling propagation distance, which can reduce costs.

[0018] In the above aspect, the secondary path filter may be configured by a finite impulse response filter, and the control device may calculate the noise cancellation propagation distance based on a delay time from the time when the noise cancellation output device outputs the noise cancellation to the time when the amplitude of the impulse response of the secondary path filter becomes maximum.

[0019] According to this aspect, the cancellation propagation distance can be easily calculated from the impulse response of the secondary path filter.

[0020] In the above aspect, the sound canceling output device may be provided in a passenger seat (6) of a vehicle (3), the error microphone may be provided in a portion of the vehicle other than the passenger seat, and the control device may calculate the sound canceling propagation distance based on the position of the passenger seat.

[0021] When the noise canceling output device is provided on the passenger seat and the error microphone is provided in a portion other than the passenger seat as described above, the noise canceling propagation distance also changes according to the change in the position of the passenger seat. Therefore, by calculating the noise canceling propagation distance based on the position of the passenger seat, the noise canceling propagation distance can be easily calculated without increasing the calculation load of the control device.

[0022] In the above aspect, the sound-canceling output device may be provided in a reclining portion (8) of the passenger seat, and the control device may calculate the sound-canceling propagation distance based on at least one of the fore-and-aft position of the passenger seat, the height of the passenger seat, and the inclination angle of the reclining portion.

[0023] According to this aspect, when the noise cancelling output device is provided in the reclining section close to the ear position of the occupant, the noise cancelling propagation distance can be easily calculated based on the above-mentioned data.

[0024] In order to solve the above problem, one aspect of the present invention is an active noise reduction device (81, 91) including a sound cancellation output device (21) that outputs a sound cancellation for canceling noise, an error microphone (22) that generates an error signal (e) based on the noise and the sound cancellation, and a control device (83, 93) that controls the sound cancellation output device based on the error signal, wherein the control device calculates a sound cancellation propagation distance (L) that is a distance from the sound cancellation output device to the error microphone, and may cause the sound cancellation output device to stop outputting the sound cancellation when the sound cancellation propagation distance is equal to or greater than a predetermined threshold value.

[0025] According to this aspect, when the silencing sound propagation distance is equal to or greater than the threshold, the silencing sound output device is caused to stop outputting the silencing sound, thereby reliably preventing the noise from being amplified at the user's ear position, thereby preventing the user from feeling uncomfortable about the silencing sound.

[0026] In the above aspect, the control device may include a secondary path filter (C^) indicating an estimate of a transfer function from the noise canceling output device to the error microphone, and may calculate the noise canceling propagation distance based on the secondary path filter.

[0027] The secondary path filter indicates an estimate of the transfer function from the noise canceling device to the error microphone. Therefore, it is possible to calculate the noise canceling propagation distance, which is the distance from the noise canceling device to the error microphone, based on the secondary path filter. By calculating the noise canceling propagation distance based on the secondary path filter in this way, it is not necessary to provide a separate sensor or the like for calculating the noise canceling propagation distance, which can reduce costs.

[0028] In the above aspect, the noise canceling output device may be provided in a passenger seat (6) of a vehicle (3), the error microphone may be provided in a part of the vehicle other than the passenger seat, and the control device may calculate the noise canceling propagation distance based on the position of the passenger seat.

[0029] When the noise canceling output device is provided on the passenger seat and the error microphone is provided in a portion other than the passenger seat as described above, the noise canceling propagation distance also changes according to the change in the position of the passenger seat. Therefore, by calculating the noise canceling propagation distance based on the position of the passenger seat, the noise canceling propagation distance can be easily calculated without increasing the calculation load of the control device.

[0030] In the above aspect, the sound deadening output device may be provided in a passenger seat (6) of a vehicle (3), and the control device may cause the sound deadening output device to stop outputting the sound deadening when the control device receives information that no passenger is seated in the passenger seat.

[0031] According to this aspect, it is possible to prevent an occupant sitting in another occupant seat from feeling uncomfortable due to the cancellation sound from the cancellation sound output device of an occupant seat in which no occupant is sitting. Effect of the Invention

[0032] According to the above aspect, when the noise canceling propagation distance increases, it is possible to suppress a decrease in the noise reduction effect at the user's ear position and an amplification of noise at the user's ear position. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a schematic diagram showing a vehicle to which an active noise reduction device according to a first embodiment is applied; [Diagram 2] FIG. 1 is a functional block diagram showing an active noise reduction device according to a first embodiment; [Diagram 3] Graph illustrating impulse response of a secondary path filter according to a first embodiment; [Figure 4] 1 is a table showing a gain coefficient table according to a first embodiment. [Diagram 5] FIG. 11 is a functional block diagram showing an active noise reduction device according to a second embodiment. [Figure 6] 13 is a table showing a gain coefficient table according to the second embodiment. [Figure 7] A functional block diagram showing an active noise reduction device according to a third embodiment. [Figure 8] FIG. 13 is a schematic diagram illustrating a coordinate system according to the third embodiment; [Figure 9] A functional block diagram showing an active noise reduction device according to a fourth embodiment. [Figure 10] A functional block diagram showing an active noise reduction device according to a fifth embodiment. [Figure 11] Flowchart showing update processing according to the fifth embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this specification, the "^" (hat) next to each symbol indicates an identified value or an estimated value. In the drawings, the "^" is placed above each symbol, but in the text, it is placed after each symbol.

[0035] (First embodiment) First, a first embodiment of the present invention will be described with reference to FIGS.

[0036] <Vehicle 3> 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 a first embodiment is applied. The vehicle 3 is, for example, a four-wheeled automobile.

[0037] A plurality of passenger seats 6 are arranged below a roof lining 5 within a passenger compartment 4 of a vehicle 3. Each passenger seat 6 (hereinafter simply referred to as a "passenger seat 6") has a seat cushion 7 and a reclining unit 8 that is arranged above and behind the seat cushion 7 and rotates relative to the seat cushion 7. The reclining unit 8 has a seat back 9 and a headrest 10 that is fixed to the upper end of the seat back 9.

[0038] The position of the passenger seat 6 in the fore-aft direction is adjusted by an electric motor (not shown) in response to the operation of a position memory button (not shown) by the passenger (an example of a user). The inclination angle of the reclining unit 8 is adjusted by an electric motor (not shown) in response to the operation of an adjustment lever (not shown) by the passenger. In other words, the passenger seat 6 is configured as a so-called power seat. In other embodiments, not only the position of the passenger seat 6 in the fore-aft direction and the inclination angle of the reclining unit 8 but also the height of the passenger seat 6 may be adjustable.

[0039] The passenger seat 6 is provided with a seating sensor 12 that detects whether or not an occupant is seated. The seating sensor 12 is, for example, configured with a load sensor that detects the load on the seat cushion 7 of the passenger seat 6. The passenger seat 6 is provided with a seat belt sensor 13 that detects whether or not the occupant has fastened the seat belt.

[0040] <Noise reduction device 1> The noise reduction device 1 is an ANC device (Active Noise Control Device) for reducing noise d generated in a passenger compartment 4 of a vehicle 3. More specifically, the noise reduction device 1 generates a canceling sound y that is in the opposite phase to the noise d, and reduces the noise d by causing the generated canceling sound y to interfere with the noise d.

[0041] For example, the noise d to be reduced by the noise reduction device 1 is road noise caused by vibration of the wheels 15 due to a force from the road surface S. Note that the noise d to be reduced by the noise reduction device 1 may be noise other than the above-mentioned road noise (for example, drive system noise caused by vibration of a drive source such as an internal combustion engine or an electric motor).

[0042] 1 and 2, the noise reduction device 1 includes a plurality of speakers 21 (an example of a noise reduction output device) that output a cancellation sound y for canceling out a noise d, a plurality of error microphones 22 that generate an error signal e based on the noise d and the cancellation sound y, and a control device 23 that controls the plurality of speakers 21 based on the error signal e.

[0043] <Speaker 21> 1, each speaker 21 (hereinafter simply referred to as "speaker 21") is provided in a headrest 10 of reclining portion 8 of passenger seat 6. In other embodiments, speaker 21 may be provided in a portion of reclining portion 8 of passenger seat 6 other than headrest 10 (e.g., seat back 9), or may be provided in a portion of passenger seat 6 other than reclining portion 8. Furthermore, in other embodiments, speaker 21 may be provided in a portion of vehicle 3 other than passenger seat 6.

[0044] <Error Mic 22> Each error microphone 22 (hereinafter simply referred to as "error microphone 22") is provided in a portion of the vehicle 3 other than the passenger seat 6. The error microphone 22 is provided, for example, in the roof lining 5. In other embodiments, the error microphone 22 may be provided in a B-pillar (not shown) or the like, or may be provided in the passenger seat 6.

[0045] <Control device 23> The control device 23 is configured 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 23 may be configured as a single piece of hardware, or may be configured as a unit consisting of multiple pieces of hardware.

[0046] Referring to FIG. 2, the control device 23 has, as functional components, a control signal generating unit 31, a first canceling estimated signal generating unit 32, a noise estimated signal generating unit 33, a second canceling estimated signal generating unit 34, a control filter updating unit 35, a distance calculating unit 36, a signal correcting unit 37, and a virtual error signal generating unit 38.

[0047] <Control signal generating unit 31> The control signal generating unit 31 of the control device 23 is configured with a control filter W. The control filter W is configured with, for example, an FIR filter (finite impulse response filter). In other embodiments, the control filter W may be configured with a SAN filter (single frequency adaptive notch filter) or the like.

[0048] A reference signal r corresponding to noise d is input to the control signal generating unit 31. The reference signal r is input to the control signal generating unit 31, for example, from 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 signal generating unit 31 from a vibration sensor (not shown) that detects vibrations corresponding to the noise d, or may be input to the control signal generating unit 31 from a component other than the reference microphone or the vibration sensor.

[0049] The control signal generating unit 31 generates a control signal u for controlling the speaker 21 by performing a filtering process on the reference signal r using the control filter W. The control signal generating unit 31 outputs the generated control signal u to the speaker 21 and the first canceling sound estimation signal generating unit 32. In response to this, the speaker 21 generates a canceling sound y according to the control signal u output from the control signal generating unit 31.

[0050] <First cancellation noise estimation signal generation unit 32> The first cancellation estimation signal generating unit 32 of the control device 23 includes a secondary path filter unit 41 and a secondary path updating unit 42.

[0051] The secondary path filter unit 41 is configured with a secondary path filter C^. The secondary path filter C^ is a filter that indicates an estimated value of a transfer function of a secondary path from the speaker 21 to the error microphone 22. The secondary path filter C^ is configured with, for example, an FIR filter. In other embodiments, the secondary path filter C^ may be configured with a SAN filter or the like.

[0052] The secondary path filter unit 41 generates a first cancellation estimation signal y^1 indicating an estimated value of the cancellation y by filtering the control signal u using the secondary path filter C^. The secondary path filter unit 41 outputs the generated first cancellation estimation signal y^1 to the virtual error signal generator 38.

[0053] The secondary path update unit 42 adaptively updates the secondary path filter C^ using an adaptive algorithm such as an LMS algorithm (Least Mean Square Algorithm). More specifically, the secondary path update unit 42 adaptively updates the secondary path filter C^ so that a first virtual error signal e1 (described in detail later) output from the virtual error signal generation unit 38 is minimized.

[0054] <Noise Estimation Signal Generator 33> The noise estimation signal generating unit 33 of the control device 23 includes a primary path filter unit 44 and a primary path updating unit 45 .

[0055] The primary path filter unit 44 is configured with a primary path filter H^. The primary path filter H^ is a filter that indicates an estimate of a transfer function of a primary path from a noise source to the error microphone 22. The primary path filter H^ is configured with, for example, an FIR filter. In other embodiments, the primary path filter H^ may be configured with a SAN filter or the like.

[0056] The primary path filter unit 44 generates a noise estimation signal d^ indicating an estimated value of the noise d by filtering the reference signal r using the primary path filter H^. The primary path filter unit 44 outputs the generated noise estimation signal d^ to the virtual error signal generator 38.

[0057] The primary path update unit 45 adaptively updates the primary path filter H^ using an adaptive algorithm such as an LMS algorithm. More specifically, the primary path update unit 45 adaptively updates the primary path filter H^ so that the first virtual error signal e1 output from the virtual error signal generation unit 38 is minimized.

[0058] <Second cancellation noise estimation signal generation unit 34> The second cancellation estimation signal generating unit 34 of the control device 23 is configured with a secondary path filter C^, similar to the first cancellation estimation signal generating unit 32. When the secondary path filter C^ is updated in the first cancellation estimation signal generating unit 32, the updated secondary path filter C^ is output to the second cancellation estimation signal generating unit 34, and the secondary path filter C^ is updated in the second cancellation estimation signal generating unit 34. That is, the secondary path filter C^ set in the second cancellation estimation signal generating unit 34 is not a fixed value, but a value that is successively updated based on the signal from the first cancellation estimation signal generating unit 32.

[0059] The second cancellation estimation signal generating unit 34 generates a second cancellation estimation signal y^2 indicating an estimated value of the cancellation y by performing a filter process on the reference signal r using the secondary path filter C^. The second cancellation estimation signal generating unit 34 outputs the generated second cancellation estimation signal y^2 to the control filter updating unit 35.

[0060] <Control filter update unit 35> The control filter update unit 35 of the control device 23 includes a control filter unit 47 and a control update unit 48 .

[0061] The control filter unit 47 is configured by a control filter W, similar to the control signal generating unit 31. The control filter unit 47 performs filtering on the second cancellation estimation signal y^2 by the control filter W. The control filter unit 47 outputs the second cancellation estimation signal y^2 after filtering to the signal correcting unit 37.

[0062] The control update unit 48 uses an adaptive algorithm such as an LMS algorithm to adaptively update the control filter W. More specifically, the control update unit 48 adaptively updates the control filter W so that a second virtual error signal e2 (described in detail later) output from the virtual error signal generation unit 38 is minimized.

[0063] When the control filter W is updated in the control filter update unit 35 in this manner, the updated control filter W is output to the control signal generation unit 31, and the control filter W is updated in the control signal generation unit 31. In other words, the control filter W set in the control signal generation unit 31 is not a fixed value, but a value that is successively updated based on the signal from the control filter update unit 35.

[0064] <Distance calculation unit 36> The distance calculation unit 36 ​​of the control device 23 calculates the canceling sound propagation distance L (hereinafter, abbreviated as "propagation distance L") from the speaker 21 to the error microphone 22 based on the secondary path filter C^ constituting the second canceling sound estimation signal generation unit 34. The distance calculation unit 36 ​​outputs the calculated propagation distance L to the signal correction unit 37. The method of calculating the propagation distance L by the distance calculation unit 36 ​​will be described later.

[0065] <Signal correction unit 37> The signal correction unit 37 of the control device 23 is provided between the control filter update unit 35 and the virtual error signal generation unit 38. The signal correction unit 37 has a gain coefficient α. The signal correction unit 37 corrects the second cancellation estimation signal y^2 by multiplying the second cancellation estimation signal y^2 by the gain coefficient α. The signal correction unit 37 outputs the corrected second cancellation estimation signal y^2 to the virtual error signal generation unit 38. A method of correcting the second cancellation estimation signal y^2 by the signal correction unit 37 will be described later.

[0066] <Virtual error signal generator 38> The virtual error signal generating unit 38 of the control device 23 has a first polarity inverting unit 51, a second polarity inverting unit 52, a first adder 53, and a second adder 54.

[0067] The first polarity inversion unit 51 inverts the polarity of the first cancellation estimation signal y^1 output from the first cancellation estimation signal generation unit 32. The second polarity inversion unit 52 inverts the polarity of the noise estimation signal d^ output from the noise estimation signal generation unit 33.

[0068] The first adder 53 generates a first virtual error signal e1 by adding together the error signal e output from the error microphone 22, the first canceling estimation signal y^1 passed through the first polarity inversion unit 51, and the noise estimation signal d^ passed through the second polarity inversion unit 52. The first adder 53 outputs the generated first virtual error signal e1 to the first canceling estimation signal generation unit 32 and the noise estimation signal generation unit 33.

[0069] The second adder 54 generates a second imaginary error signal e2 by adding together the noise estimation signal d^ output from the noise estimation signal generation unit 33 and the second cancellation estimation signal y^2 output from the signal correction unit 37. The second adder 54 outputs the generated second imaginary error signal e2 to the control filter update unit 35.

[0070] <Calculation of propagation distance L> Next, a method for calculating the propagation distance L by the distance calculation unit 36 ​​will be described.

[0071] 3 illustrates an example of an impulse response of the secondary path filter C^ constituting the second cancellation estimation signal generator 34. The time T max is delayed by a delay time ΔT from the time T0 when the speaker 21 outputs the canceling sound y. This delay time ΔT is expressed by the following formula (1). However, ΔT in the following formula (1) e indicates the processing time of the electronic circuit constituting the control device 23, and ΔT s indicates the propagation time of the cancellation sound y from the speaker 21 to the error microphone 22. ΔT = ΔT e +ΔT s ...(1)

[0072] On the other hand, the propagation distance L is expressed by the following formula (2): Note that c in the following formula (2) represents the speed of sound (approximately 340 m / s). The value of c in the following formula (2) is known. L = ΔT s ×c...(2)

[0073] The following formula (3) is obtained from the above formula (1) and the above formula (2), and the following formula (4) is obtained from the following formula (3). max is the number of samples corresponding to the delay time ΔT (hereinafter, "the number of delay samples n max "), and n in the following formula (4) e is the processing time ΔT of the electronic circuit constituting the control device 23. e The number of samples corresponds to the following equation (4): sa indicates the sampling time. e and T sa is a known value. L = (ΔT - ΔT e )×c...(3) L=(n max -n e )×T sa ×c...(4)

[0074] The distance calculation unit 36 ​​first calculates the delay sample number n from the impulse response of the secondary path filter C^.max Next, the distance calculation unit 36 ​​determines the determined number of delay samples n max In this manner, the distance calculation unit 36 ​​calculates the propagation distance L by substituting the delay time ΔT (more specifically, the number of delay samples n corresponding to the delay time ΔT). max ) to calculate the propagation distance L.

[0075] <Correction of the second cancellation estimated signal y^2> Next, a method of correcting the second cancellation estimation signal y^2 by the signal corrector 37 will be described. 4, the signal correction unit 37 stores a gain coefficient table T1. The gain coefficient table T1 is a table showing the relationship between the propagation distance L and the gain coefficient α. The gain coefficient table T1 is set so that the gain coefficient α is 1 when the propagation distance L is a minimum value (for example, 10 cm). The gain coefficient table T1 is set so that the gain coefficient α increases as the propagation distance L increases.

[0076] The signal correction unit 37 sets the gain coefficient α by referring to the gain coefficient table T1 based on the propagation distance L calculated by the distance calculation unit 36. For example, the signal correction unit 37 sets the gain coefficient α so that the gain coefficient α is 1 when the propagation distance L is at a minimum value, and the gain coefficient α increases as the propagation distance L increases.

[0077] The signal correction unit 37 multiplies the second cancellation estimation signal y^2 by the gain coefficient α to correct the second cancellation estimation signal y^2 in accordance with the propagation distance L. As described above, when the propagation distance L is a minimum value, the gain coefficient α is set to 1. Therefore, even if the signal correction unit 37 multiplies the second cancellation estimation signal y^2 by the gain coefficient α, the second cancellation estimation signal y^2 does not increase or decrease.

[0078] On the other hand, when the propagation distance L is greater than the minimum value, the gain coefficient α is set to a value greater than 1. Therefore, when the signal correcting unit 37 multiplies the second cancellation estimation signal y^2 by the gain coefficient α, the second cancellation estimation signal y^2 is amplified according to the propagation distance L. More specifically, as the propagation distance L increases, the gain coefficient α increases, and therefore the amount of amplification of the second cancellation estimation signal y^2 also increases.

[0079] <Suppression of changes in cancellation y> As described above, when the propagation distance L is greater than the minimum value, the signal correcting unit 37 corrects the second cancellation estimation signal y^2, so that the second cancellation estimation signal y^2 is amplified in accordance with the propagation distance L. In response to this, the second cancellation estimation signal y^2 becomes larger relative to the noise estimation signal d^. Therefore, the control updating unit 48 adaptively updates the control filter W so that the second virtual error signal e2 becomes smaller. As a result, the cancellation y output from the speaker 21 becomes smaller compared to the case where the signal correcting unit 37 does not correct the second cancellation estimation signal y^2 (the cancellation y becomes larger in accordance with an increase in the propagation distance L), and the change in the cancellation y in accordance with an increase in the propagation distance L is suppressed (the amount of change in the cancellation y in accordance with an increase in the propagation distance L decreases). In addition, "suppressing the change in the canceling sound y in response to an increase (change) in the propagation distance L" includes both "reducing the amount of change in the volume of the canceling sound y in response to an increase (change) in the propagation distance L" and "not changing the volume of the canceling sound y even if the propagation distance L increases (changes)."

[0080] <Effects> 1, speaker 21 is provided in reclining section 8 of passenger seat 6, and error microphone 22 is provided in a portion other than passenger seat 6. In this configuration, when reclining section 8 is reclined, propagation distance L (distance from speaker 21 to error microphone 22) increases (see two-dot chain line in FIG. 1). When propagation distance L increases in this manner, control device 23 causes speaker 21 to output a large canceling sound y in order to sufficiently reduce noise d at the position of error microphone 22 that is farther away from speaker 21.

[0081] However, when the reclining section 8 is tilted back as described above, the occupant's ears are closer to the speaker 21 than the error microphone 22, and may be outside the sound reduction target range A that is set around the error microphone 22. If the speaker 21 outputs a large canceling sound y in a state in which the occupant's ears are outside the sound reduction target range A in this way, there is a risk that the effect of reducing the noise d at the position of the occupant's ears will be reduced, or the noise d will be amplified at the position of the occupant's ears.

[0082] Therefore, the control device 23 suppresses the change in the canceling sound y based on the propagation distance L. This makes it possible to suppress the canceling sound y from increasing in accordance with an increase in the propagation distance L. This makes it possible to suppress a decrease in the effect of reducing the noise d at the position of the passenger's ears and an amplification of the noise d at the position of the passenger's ears.

[0083] Moreover, unnecessary changes in the sound canceling effect y can be suppressed, and a decrease in the effect of reducing the noise d at the position of the passenger's ears can be more effectively suppressed.

[0084] In addition, the control device 23 corrects the second cancellation estimation signal y^2 used for adaptively updating the control filter W in accordance with the propagation distance L. This makes it possible to prevent the control signal u generated by the control filter W from becoming excessively large.

[0085] Second embodiment Next, an active noise reduction device 61 according to a second embodiment of the present invention (hereinafter, abbreviated as "noise reduction device 61") will be described with reference to Figures 5 and 6. Note that components other than a signal correction unit 64 of a control device 63 are similar to those in the first embodiment, so the same reference numerals as in the first embodiment are used in the drawings and descriptions thereof will be omitted.

[0086] <Signal correction unit 64> 5, the signal correction unit 64 of the control device 63 is provided between the noise estimation signal generation unit 33 and the virtual error signal generation unit 38. The signal correction unit 64 has a gain coefficient β. The signal correction unit 64 corrects the noise estimation signal d^ by multiplying the noise estimation signal d^ by the gain coefficient β. The signal correction unit 64 outputs the corrected noise estimation signal d^ to the virtual error signal generation unit 38.

[0087] 6, the signal correction unit 64 stores a gain coefficient table T2. The gain coefficient table T2 is a table showing the relationship between the propagation distance L and the gain coefficient β. The gain coefficient table T2 is set so that the gain coefficient β is 1 when the propagation distance L is a minimum value (for example, 10 cm). The gain coefficient table T2 is set so that the gain coefficient β decreases as the propagation distance L increases.

[0088] The signal correction unit 64 sets the gain coefficient β by referring to the gain coefficient table T2 based on the propagation distance L calculated by the distance calculation unit 36. For example, the signal correction unit 64 sets the gain coefficient β so that the gain coefficient β is 1 when the propagation distance L is at a minimum value, and the gain coefficient β decreases as the propagation distance L increases.

[0089] The signal correction unit 64 multiplies the noise estimation signal d^ by a gain coefficient β to correct the noise estimation signal d^ in accordance with the propagation distance L. As described above, when the propagation distance L is at its minimum value, the gain coefficient β is set to 1. Therefore, even if the signal correction unit 64 multiplies the noise estimation signal d^ by the gain coefficient β, the noise estimation signal d^ does not increase or decrease.

[0090] On the other hand, when the propagation distance L is greater than the minimum value, the gain coefficient β is set to a value smaller than 1. Therefore, when the signal correction unit 64 multiplies the noise estimation signal d^ by the gain coefficient β, the noise estimation signal d^ is attenuated in accordance with the propagation distance L. More specifically, as the propagation distance L increases, the gain coefficient β decreases, and therefore the amount of attenuation of the noise estimation signal d^ also increases.

[0091] <Suppression of changes in cancellation y> As described above, when the propagation distance L is greater than the minimum value, the signal correction unit 64 corrects the noise estimation signal d^, so that the noise estimation signal d^ attenuates in accordance with the propagation distance L. In response to this, the second cancellation estimation signal y^2 becomes larger relative to the noise estimation signal d^. Therefore, the control update unit 48 adaptively updates the control filter W so that the second virtual error signal e2 becomes smaller. As a result, the cancellation y output from the speaker 21 becomes smaller compared to the case where the signal correction unit 64 does not correct the noise estimation signal d^ (the cancellation y becomes larger in accordance with an increase in the propagation distance L), and the change in the cancellation y in accordance with an increase in the propagation distance L is suppressed (the amount of change in the cancellation y in accordance with an increase in the propagation distance L decreases).

[0092] <Effects> The control device 63 corrects the noise estimation signal d^ used for adaptively updating the control filter W in accordance with the propagation distance L. This makes it possible to prevent the control signal u generated by the control filter W from becoming excessively large.

[0093] <Modification> In the first embodiment, the control device 23 corrects the second cancellation estimation signal y^2 in accordance with the propagation distance L, and in the second embodiment, the control device 63 corrects the noise estimation signal d^ in accordance with the propagation distance L. In other embodiments, the control devices 23 and 63 may correct both the second cancellation estimation signal y^2 and the noise estimation signal d^ in accordance with the propagation distance L.

[0094] Third embodiment Next, an active noise reduction device 71 according to a third embodiment of the present invention (hereinafter, abbreviated as "noise reduction device 71") will be described with reference to Figures 7 and 8. Note that components other than a distance calculation unit 74 of a control device 73 are similar to those in the first embodiment, so the same reference numerals as in the first embodiment are used in the drawings and descriptions thereof will be omitted.

[0095] <Distance calculation unit 74> 7, seat position information I1 is input to distance calculation unit 74 of control device 73 from passenger seat 6. Seat position information I1 includes information relating to the front-to-rear position of passenger seat 6 and information relating to the tilt angle of reclining portion 8 of passenger seat 6. It is preferable that seat position information I1 be updated when the above-mentioned position memory button or adjustment lever (neither of which are shown) is operated.

[0096] The distance calculation unit 74 calculates the propagation distance L based on the seat position information I1 input from the passenger seat 6. Hereinafter, a method for calculating the propagation distance L by the distance calculation unit 74 will be described.

[0097] 8 illustrates an example of a coordinate system for calculating the propagation distance L. In this coordinate system, a point directly below the error microphone 22 and at the same height as the seat cushion 7 is set as the origin P. In this coordinate system, the X-axis is set horizontally from the origin P toward the rear, and the Y-axis is set vertically from the origin P toward directly above.

[0098] In this coordinate system, the coordinates (xm, ym) of the error microphone 22 are obtained by the following formula (5). Note that Hm in the following formula (5) indicates the vertical distance from the seat cushion 7 to the error microphone 22. In this embodiment, since the height of the passenger seat 6 does not change, Hm in the following formula (5) is a known value. (xm, ym) = (0, Hm)...(5)

[0099] In the above coordinate system, the coordinates (xs, ys) of speaker 21 are obtained by the following formula (6). Note that Ds in the following formula (6) indicates the distance from origin P to rotation center Q of reclining unit 8 (rear end of seat cushion 7), Lr in the following formula (6) indicates the distance from rotation center Q of reclining unit 8 to speaker 21, and θ in the following formula (6) indicates the angle between reclining unit 8 and the horizontal direction. Lr in the following formula (6) is a known value. (xs, ys)=(Ds+Lr×cosθ, Lr×sinθ)...(6)

[0100] From the above formula (5) and formula (6), the following formula (7) is obtained.

number

[0101] The distance calculation unit 74 calculates the distance Ds based on the seat position information I1 (particularly, information related to the front-rear position of the passenger seat 6). The distance calculation unit 74 acquires the angle θ based on the seat position information I1 (particularly, information related to the tilt angle of the reclining portion 8 of the passenger seat 6). The distance calculation unit 74 calculates the propagation distance L by substituting the distance Ds and the angle θ into the above formula (7).

[0102] <Effects> The control device 73 calculates the propagation distance L based on the position of the passenger seat 6. This makes it possible to easily calculate the propagation distance L without increasing the calculation load of the control device 73.

[0103] <Modification> In the third embodiment, the signal correction unit 37 corrects the second cancellation estimation signal y^2, as in the first embodiment. In other embodiments, the signal correction unit 37 may correct the noise estimation signal d^, as in the second embodiment. Furthermore, in other embodiments, the signal correction unit 37 may correct both the second cancellation estimation signal y^2 and the noise estimation signal d^.

[0104] In the third embodiment, the distance calculation unit 74 calculates the propagation distance L using a coordinate system having the origin P at a point directly below the error microphone 22. In other embodiments, the distance calculation unit 74 may calculate the propagation distance L using a coordinate system different from the above coordinate system (for example, a coordinate system having the origin P at a point other than the point directly below the error microphone 22).

[0105] In the third embodiment, the distance calculation unit 74 calculates the propagation distance L based on the position of the passenger seat 6 in the front-rear direction and the tilt angle of the reclining unit 8. In another embodiment, when the height of the passenger seat 6 changes, the distance calculation unit 74 may calculate the propagation distance L based on the position of the passenger seat 6 in the front-rear direction, the height of the passenger seat 6, and the tilt angle of the reclining unit 8. Furthermore, in another embodiment, the distance calculation unit 74 may calculate the propagation distance L based on only one of the position of the passenger seat 6 in the front-rear direction, the height of the passenger seat 6, or the tilt angle of the reclining unit 8. In other words, the distance calculation unit 74 may calculate the propagation distance L based on at least one of the position of the passenger seat 6 in the front-rear direction, the height of the passenger seat 6, and the tilt angle of the reclining unit 8.

[0106] (Fourth embodiment) Next, an active noise reduction device 81 (hereinafter, abbreviated as "noise reduction device 81") according to a fourth embodiment of the present invention will be described with reference to Fig. 9. Note that components other than the control device 83 are similar to those in the first embodiment, so the same reference numerals as in the first embodiment are used in the figure and descriptions thereof will be omitted. Regarding the control device 83, descriptions of contents that overlap with those in the first embodiment will also be omitted.

[0107] <Control device 83> The control device 83 has, as functional components, a control signal generating unit 84 and a distance calculating unit 85. Note that the distance calculating unit 85 is similar to the distance calculating unit 74 according to the third embodiment, and therefore a description thereof will be omitted.

[0108] <Control signal generating unit 84> The control signal generating unit 84 of the control device 83 has a control filter unit 87 , a secondary path filter unit 88 , and a control updating unit 89 .

[0109] The control filter unit 87 is configured with a control filter W. The control filter W is configured with an FIR filter. In other embodiments, the control filter W may be configured with a SAN filter or the like.

[0110] The control filter unit 87 generates a control signal u by performing filtering on the reference signal r using a control filter W. The control filter unit 87 outputs the generated control signal u to the speaker 21. In response to this, the speaker 21 generates a cancellation sound y according to the control signal u output from the control filter unit 87.

[0111] The secondary path filter unit 88 is configured with a secondary path filter C^p. The secondary path filter C^p is a filter that indicates an estimated value of a transfer function of a secondary path from the speaker 21 to the error microphone 22. The secondary path filter C^p is configured with an FIR filter. In other embodiments, the secondary path filter C^p may be configured with a SAN filter or the like. The secondary path filter C^p is a fixed value.

[0112] The secondary path filter unit 88 generates a cancellation estimation signal y^ indicating an estimated value of the cancellation y by filtering the reference signal r using the secondary path filter C^p. The secondary path filter unit 88 outputs the generated cancellation estimation signal y^ to the control update unit 89.

[0113] The control update unit 89 uses an adaptive algorithm such as an LMS algorithm to adaptively update the control filter W. More specifically, the control update unit 89 updates the control filter W so that the error signal e output from the error microphone 22 is minimized.

[0114] <Stop / continue output of mute y> The distance calculation unit 85 calculates the propagation distance L based on the seat position information I1 input from the passenger seat 6. The distance calculation unit 85 outputs the calculated propagation distance L to the control update unit 89.

[0115] When the propagation distance L is equal to or greater than a predetermined threshold value Lt, the control update unit 89 stops adaptively updating the control filter W using the adaptive algorithm. In addition, the control update unit 89 gradually decreases the coefficient of the control filter W by updating the control filter W according to the following equation (8), and then sets the coefficient of the control filter W to 0. W(t+1)=ηW(t), η<1...(8) As a result, the canceling sound y output from the speaker 21 gradually attenuates, and then the output of the canceling sound y from the speaker 21 stops.

[0116] On the other hand, when the propagation distance L is less than the threshold value Lt, the control update unit 89 continues to adaptively update the control filter W using an adaptive algorithm. Therefore, the output of the canceling sound y from the speaker 21 also continues.

[0117] The control update unit 89 receives seating information I2 from the seating sensor 12 of the passenger seat 6. The seating information I2 is information indicating whether or not an occupant is seated in the passenger seat 6.

[0118] When seating information I2 indicating that an occupant is not seated in the occupant seat 6 is received from the seating sensor 12, the control update unit 89 stops adaptively updating the control filter W and stops outputting the canceling sound y from the speaker 21, in the same manner as when the propagation distance L is greater than or equal to the threshold value Lt.

[0119] On the other hand, when seating information I2 indicating that an occupant is seated in the occupant seat 6 is received from the seating sensor 12, the control update unit 89 continues to adaptively update the control filter W and continues to output the canceling sound y from the speaker 21, in the same manner as when the propagation distance L is less than the threshold value Lt.

[0120] <Effects> When the propagation distance L is equal to or greater than the threshold value Lt, the control device 83 stops the speaker 21 from outputting the canceling sound y. This reliably prevents the noise d from being amplified at the user's ear position. This prevents the user from feeling uncomfortable about the canceling sound y.

[0121] In particular, in this embodiment, the secondary path filter C^p has a fixed value and is not updated according to changes in the acoustic characteristics in the vehicle interior 4, so that the noise d is likely to be amplified at the user's ear position. Therefore, by stopping the output of the canceling sound y from the speaker 21, the effect of suppressing the amplification of the noise d at the user's ear position is remarkable.

[0122] <Modification> In the fourth embodiment, the control update unit 89 determines whether to cause the speaker 21 to stop outputting the canceling sound y based only on the information from the seating sensor 12. In another embodiment, the control update unit 89 may determine whether to cause the speaker 21 to stop outputting the canceling sound y based on both the information from the seating sensor 12 and the information from the seat belt sensor 13. For example, when the control update unit 89 receives information from the seating sensor 12 that an occupant is seated in the occupant's seat 6 and receives information from the seat belt sensor 13 that the occupant has fastened the seat belt, the control update unit 89 may cause the speaker 21 to continue outputting the canceling sound y. On the other hand, in other cases, the control update unit 89 may cause the speaker 21 to stop outputting the canceling sound y. This makes it possible to suppress the speaker 21 from continuing to output the canceling sound y when the seating sensor 12 erroneously detects that an occupant is seated in the occupant's seat 6 (for example, when a heavy baggage is placed on the occupant's seat 6).

[0123] Furthermore, in another embodiment, the control update unit 89 may determine whether or not to cause the speaker 21 to stop outputting the canceling sound y based on information from an in-vehicle monitoring camera (not shown) that captures images of the occupants.

[0124] In the fourth embodiment, the configuration for causing the speaker 21 to stop outputting the canceling sound y when information is received that no occupant is seated in the occupant seat 6 is applied to the noise reduction device 81 in which the secondary path filter C^p is a fixed value. In other embodiments, the above-described configuration may be applied to a noise reduction device in which the secondary path filter C^ is adaptively updated (for example, the noise reduction devices 1, 61, 71 according to the first to third embodiments).

[0125] Fifth embodiment Next, an active noise reduction device 91 (hereinafter, abbreviated as "noise reduction device 91") according to a fifth embodiment of the present invention will be described with reference to Figures 10 and 11. Note that components other than the control device 93 are similar to those in the first embodiment, so the same reference numerals as in the first embodiment are used in the figures and descriptions thereof will be omitted. Regarding the control device 93, descriptions of contents that overlap with those in the first embodiment will also be omitted.

[0126] 10, the control device 93 has, as functional components, a control signal generating unit 94, a canceling estimated signal generating unit 95, a noise estimated signal generating unit 96, a virtual error signal generating unit 97, and an update processing unit 98. The components of the control signal generating unit 94 are similar to the components of the control signal generating unit 84 according to the fourth embodiment, so the same reference numerals as in the fourth embodiment are used in the drawing, and a description thereof will be omitted. The components of the canceling estimated signal generating unit 95 and the noise estimated signal generating unit 96 are similar to the components of the first canceling estimated signal generating unit 32 and the noise estimated signal generating unit 33 according to the first embodiment, so the same reference numerals as in the first embodiment are used in the drawing, and a description thereof will be omitted.

[0127] <Virtual error signal generator 97> The virtual error signal generating unit 97 of the control device 93 includes a first polarity inverting unit 101, a second polarity inverting unit 102, and an adder 103.

[0128] The first polarity inversion unit 101 inverts the polarity of the canceling estimated signal y^ output from the canceling estimated signal generation unit 95. The second polarity inversion unit 102 inverts the polarity of the noise estimated signal d^ output from the noise estimated signal generation unit 96.

[0129] The adder 103 generates a virtual error signal e' by adding together the error signal e, the canceling estimated signal y^ passed through the first polarity inversion unit 101, and the noise estimated signal d^ passed through the second polarity inversion unit 102. The adder 103 outputs the generated virtual error signal e' to the canceling estimated signal generation unit 95 and the noise estimated signal generation unit 96.

[0130] <Update processing unit 98> The update processing unit 98 of the control device 93 executes an update process for updating updatable filters (in this embodiment, the control filter W, the secondary path filter C^p, the secondary path filter C^, and the primary path filter H^). The update processing unit 98 may repeatedly execute the update process at predetermined time intervals. Details of the update process will be described below.

[0131] <Update process> 11, when the update process is started, the update processing unit 98 updates the number of executions Cnt of the update process (initial value=0) to Cnt+1 (step ST1).

[0132] Next, the update processing unit 98 judges whether the execution count Cnt is an odd number (step ST2). If the execution count Cnt is an even number (step ST2: No), the update processing unit 98 causes the secondary path update unit 42 to adaptively update the secondary path filter C^ and the primary path update unit 45 to adaptively update the primary path filter H^ (step ST3).

[0133] Next, the update processing unit 98 updates the secondary path filter C^p to C^ by copying the secondary path filter C^ adaptively updated in step ST3 to the secondary path filter C^p (step ST4). Next, the control filter unit 87 generates a control signal u by a temporarily fixed control filter W (the control filter W adaptively updated in the previous update process) and outputs the generated control signal u to the speaker 21. In response to this, the speaker 21 outputs a cancellation sound y (step ST5).

[0134] If the execution count Cnt is an odd number (step ST2: Yes), the update processing unit 98 calculates the propagation distance L based on the secondary path filter C^ (step ST6). The method of calculating the propagation distance L by the update processing unit 98 is similar to the method of calculating the propagation distance L by the distance calculation unit 36 ​​according to the first embodiment, and therefore the description thereof will be omitted.

[0135] Next, the update processing unit 98 judges whether the propagation distance L is equal to or greater than a predetermined threshold Lt (step ST7). If the propagation distance L is equal to or greater than the predetermined threshold Lt (step ST7: Yes), the update processing unit 98 causes the control update unit 89 to stop adaptively updating the control filter W and stops outputting the canceling sound y from the speaker 21 (step ST8).

[0136] If the propagation distance L is less than the threshold value Lt (step ST7: No), the update processing unit 98 causes the control update unit 89 to continue adaptively updating the control filter W. The control filter unit 87 generates a control signal u by the adaptively updated control filter W, and outputs the generated control signal u to the speaker 21. In response to this, the speaker 21 outputs a canceling sound y (step ST9).

[0137] When any one of step ST5, step ST8, and step ST9 is completed, the update process ends, and a new update process is executed after a predetermined time. However, the value of the execution count Cnt is retained even after the update process ends, and is used for the new update process.

[0138] <Effects> As in the fourth embodiment, the control device 93 stops the output of the canceling sound y from the speaker 21 when the propagation distance L is equal to or greater than the threshold Lt. This can reliably suppress the amplification of the noise d at the user's ear position. Therefore, it is possible to suppress the user from feeling uncomfortable about the canceling sound y. In addition, by copying the adaptively updated secondary path filter C^ to the secondary path filter C^p, the secondary path filter C^p always has a correct value. Therefore, even if the passenger seat 6 moves in a state where the propagation distance L is less than the threshold Lt, it is possible to reduce noise more stably and to the maximum extent. Furthermore, by alternately performing sound field learning and noise control, it is possible to calculate the propagation distance L based on the secondary path filter C^ and determine whether the propagation distance L is equal to or greater than the threshold Lt without significantly increasing the calculation load.

[0139] <Modification> In the above first to fifth embodiments, the noise reduction devices 1, 61, 71, 81, 91 are applied to the passenger compartment 4 of the vehicle 3. In other embodiments, the noise reduction devices 1, 61, 71, 81, 91 may be applied to the interior space of a moving body other than the vehicle 3 (for example, a ship or an aircraft), and the noise reduction devices 1, 61, 71, 81, 91 may be applied to the interior space of a fixed object (for example, a house).

[0140] Although the specific embodiment has been described above, the present invention is not limited to the above embodiment and its modified examples, and can be modified in a wide range of ways. [Explanation of symbols]

[0141] (First embodiment) 1: Active noise reduction device 3: Vehicle 6: Passenger seat 8: Reclining section 21: Speaker (an example of a noise cancelling output device) 22: Error microphone 23: Control device d: Noise y :Cancellation sound e: error signal L: Sound propagation distance u : Control signal W: Control filter H^: Primary path filter C^: Secondary path filter d^: Noise estimation signal y^2: Second cancellation estimation signal (an example of a cancellation estimation signal) e2: Second virtual error signal (an example of a virtual error signal) α: Gain coefficient β: Gain coefficient ΔT: Delay time Second embodiment 61: Active noise reduction device 63: Control device Third embodiment 71: Active noise reduction devices 73: Control device (Fourth embodiment) 81: Active noise reduction device 83: Control device Fifth embodiment 91: Active noise reduction devices 93: Control device

Claims

1. A noise canceling output device that outputs a canceling sound to cancel noise; an error microphone for generating an error signal based on the noise and the cancellation sound; A control device that controls the noise canceling device based on the error signal, The control device includes: Calculating a noise canceling propagation distance, which is a distance from the noise canceling output device to the error microphone; An active noise reduction device that suppresses the change in the noise cancellation based on the noise cancellation propagation distance.

2. The control device includes: a control filter for generating a control signal for controlling the noise canceling device; a first-order path filter providing an estimate of the transfer function from a noise source to the error microphone; a secondary path filter that indicates an estimate of a transfer function from the noise canceling device to the error microphone; The control filter is adaptively updated based on a virtual error signal generated based on a noise estimation signal generated by the primary path filter and a cancellation estimation signal generated by the secondary path filter; 2. The active noise reduction device according to claim 1, wherein the control device corrects at least one of the noise estimation signal or the canceling estimation signal in accordance with the canceling propagation distance.

3. The control device includes: A gain coefficient is set so that the gain coefficient increases as the sound canceling propagation distance increases, 3. An active noise reduction device according to claim 2, wherein the estimated noise cancellation signal is corrected by multiplying the estimated noise cancellation signal by the gain coefficient.

4. The control device includes: A gain coefficient is set so that the gain coefficient decreases as the elimination sound propagation distance increases, 3. An active noise reduction device according to claim 2, wherein the noise estimation signal is corrected by multiplying the noise estimation signal by the gain coefficient.

5. The active noise reduction system of claim 2 , wherein the control device calculates the cancellation propagation distance based on the secondary path filter.

6. the secondary path filter is a finite impulse response filter; The control device calculates the noise canceling propagation distance based on a delay time from the time when the noise canceling output device outputs the noise canceling to the time when the amplitude of the impulse response of the secondary path filter becomes maximum. The active noise reduction device according to claim 5.

7. The noise cancelling output device is provided in a passenger seat of a vehicle, the error microphone is provided in a portion of the vehicle other than the passenger seat, 2. The active noise reduction system according to claim 1, wherein the control device calculates the sound cancelling propagation distance based on a position of the passenger seat.

8. The noise cancelling device is provided in a reclining portion of the passenger seat, 8. The active noise reduction device according to claim 7, wherein the control device calculates the sound cancelling propagation distance based on at least one of the position of the passenger seat in the fore-and-aft direction, the height of the passenger seat, and the inclination angle of the reclining portion.

9. A noise canceling output device that outputs a canceling sound to cancel noise; an error microphone for generating an error signal based on the noise and the cancellation sound; A control device that controls the noise canceling device based on the error signal, The control device includes: Calculating a noise canceling propagation distance, which is a distance from the noise canceling output device to the error microphone; An active noise reduction device that causes the noise canceling output device to stop outputting the noise canceling when the noise canceling propagation distance is equal to or greater than a predetermined threshold value.

10. The control device includes: a secondary path filter that provides an estimate of a transfer function from the noise canceling output device to the error microphone; 10. The active noise reduction system of claim 9, further comprising: a secondary path filter that calculates the cancellation propagation distance based on the secondary path filter.

11. The noise cancelling output device is provided in a passenger seat of a vehicle, the error microphone is provided in a portion of the vehicle other than the passenger seat, 10. The active noise reduction system of claim 9, wherein the control device calculates the sound cancellation propagation distance based on a position of the passenger seat.

12. The noise cancelling output device is provided in a passenger seat of a vehicle, 12. An active noise reduction device according to claim 1, wherein the control device causes the noise cancelling output device to stop outputting the noise cancelling when the control device receives information that an occupant is not seated in the occupant seat.

Images