Active noise control system

Abstract

The present invention provides an "active noise control system" that switches characteristics without obstruction according to the displacement of an object. An adaptive filter (1111-1113) outputs a cancellation sound from a speaker (12), a selector (1116) selects the outputs of a plurality of auxiliary filters (1115) respectively corresponding to different positions, a subtractor (1114) subtracts the selected output from the output of a microphone (13) and outputs it as an error signal to the adaptive filter, and a position detection device (14) detects the position of the user's head. A transfer function in which the error signal is estimated to be 0 when noise is cancelled at the corresponding position is preset in the auxiliary filter (1115). When the auxiliary filter (1115) corresponding to the position close to the user's head changes, a switching control unit (112) gradually increases the frequency of selecting the output of the auxiliary filter (1115) by the selector (1116) to 100% in stages.

Description

Technical Field

[0001] The present invention relates to a technology of active noise control (ANC; Active Noise Control) for reducing noise by radiating noise cancellation sounds for canceling noise. Background Art

[0002] As a technology of active noise control for reducing noise by radiating noise cancellation sounds for canceling noise, the following technology is known: a microphone and a speaker arranged near a noise cancellation position are provided, and an adaptive filter that generates a noise cancellation sound output from the speaker for an output signal of a noise source or a signal simulating the output signal is provided. In the adaptive filter, a signal obtained by correcting the output of the microphone using an auxiliary filter is used as an error signal, and the transfer function is adaptively set.

[0003] Here, in this technology, a transfer function that is pre-learned for the auxiliary filter and corrects the difference between the transfer function from the noise source to the noise cancellation position and the transfer function from the noise source to the microphone, and the difference between the transfer function from the speaker to the noise cancellation position and the transfer function from the speaker to the microphone is set. By using such an auxiliary filter, noise is canceled at a noise cancellation position different from the position of the microphone.

[0004] In addition, a group of a microphone, a speaker, an adaptive filter, and an auxiliary filter corresponding to two noise cancellation positions is provided, and the above-described technology is used to output a noise cancellation sound for canceling noise at the corresponding noise cancellation position in each group, whereby a technology for canceling noise generated from a noise source at two noise cancellation positions is also known (for example, Patent Document 1).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-72770 Summary of the Invention

[0008] When the technology of canceling noise at a noise cancellation position different from the position of the microphone using the above-described auxiliary filter is applied to cancel noise that a user can hear, if the user's head deviates from the noise cancellation position as the user moves, sometimes the noise that the user can hear cannot be canceled well.

[0009] Therefore, the transfer function of the auxiliary filter is pre-learned for a plurality of different noise cancellation positions. Along with the displacement of the user's head, the transfer function of the auxiliary filter is switched to the transfer function learned for the noise cancellation position corresponding to the position of the user's head, thereby enabling the elimination of the noise audible to the user regardless of the displacement of the user's head.

[0010] However, in this case, during the switching of the transfer function of the auxiliary filter, sometimes problems such as divergence of the adaptive filter or generation of noise in the noise cancellation sound may occur.

[0011] Therefore, the technical problem of the present invention is to provide an active noise control system that can smoothly switch the characteristics to cancel noise at the displaced position according to the displacement of the object for which noise is to be canceled.

[0012] In order to solve the above technical problems, the active noise control system of the present invention reduces the noise that can be heard by the object body. The active noise control system includes: a microphone; an adaptive filter that takes a noise signal representing noise as an input; a speaker that outputs a noise cancellation sound as an output of the adaptive filter; a plurality of auxiliary filters that take the noise signal as an input and are respectively provided corresponding to different positions; an error correction unit that corrects the microphone output signal, which is the output of the microphone, using the output of any one of the auxiliary filters and then outputs an error signal to the adaptive filter; a position detection unit that detects the position of the object body; and a switching control unit that, when the auxiliary filter corresponding to the position that matches the position of the object body detected by the position detection unit changes, uses the auxiliary filter corresponding to the position that matches the position of the object body as the switched auxiliary filter, controls the error correction unit to perform a switching operation, and the switching operation switches the signal output as the error signal from the error correction unit to the signal obtained by correcting the microphone output signal using the output of the switched auxiliary filter. Here, the adaptive filter uses the error represented by the error signal input from the error correction unit to execute a prescribed adaptive algorithm to update the transfer function of the adaptive filter. In addition, the following transfer functions are preset for the plurality of auxiliary filters, and the transfer functions are learned so that the error represented by the error signal becomes 0 when noise is canceled by the noise cancellation sound at the corresponding position. Further, the switching control unit uses the auxiliary filter whose output was used in the correction of the microphone output signal before the switching operation as the pre-switching auxiliary filter, and in the switching operation, gradually or stepwise reduces the ratio of the signal obtained by correcting the microphone output signal using the output of the pre-switching auxiliary filter and output as the error signal to 0%, and correspondingly, gradually or stepwise increases the ratio of the signal obtained by correcting the microphone output signal using the output of the switched auxiliary filter and output as the error signal to 100%.

[0013] According to such an active noise control system, it is possible to switch the auxiliary filter used in the generation of the error signal input to the adaptive filter to the switched auxiliary filter that can well cancel noise at the position that matches the position of the object body according to the change in the position of the object body. Therefore, it is possible to well cancel the noise that can be heard in the object body regardless of the shift of the object body.

[0014] In addition, during this switching, the ratio of the signal generated by the auxiliary filter before switching and output as an error signal is gradually or stepwise decreased, while the ratio of the signal generated by the auxiliary filter after switching and output as an error signal is gradually or stepwise increased. Therefore, divergence of the adaptive filter and generation of noise in the noise cancellation sound can be suppressed.

[0015] In addition, the active noise control system of the present invention reduces the noise audible to the target object, and is characterized by including: a microphone; an adaptive filter that takes a noise signal representing noise as an input; a speaker that outputs the output of the adaptive filter as a noise cancellation sound; a plurality of auxiliary filters that take the noise signal as an input and are respectively provided corresponding to different positions; an error correction unit that corrects the microphone output signal, which is the output of the microphone, using the output of any one of the auxiliary filters and outputs the result as an error signal to the adaptive filter; a position detection unit that detects the position of the target object; and a switching control unit that controls the error correction unit such that when the position of the target object detected by the position detection unit changes, two auxiliary filters, specifically, the two auxiliary filters corresponding to the two positions where the target object is located between the two positions corresponding to the two auxiliary filters, are used as a first mixed target auxiliary filter and a second mixed target auxiliary filter, and signals obtained by correcting the microphone output signal using the output of the first mixed target auxiliary filter and signals obtained by correcting the microphone output signal using the output of the second mixed target auxiliary filter are output from the error correction unit as the error signal at a switched ratio, where the switched ratio is a ratio determined based on the ratio of the distance between the position corresponding to the first mixed target auxiliary filter and the position of the target object to the distance between the position corresponding to the second mixed target auxiliary filter and the position of the target object.

[0016] The adaptive filter uses the error represented by the error signal input from the error correction unit to execute a prescribed adaptive algorithm to update the transfer function of the adaptive filter.

[0017] The following transfer functions are preset for the plurality of auxiliary filters, and the transfer functions are learned such that the error represented by the error signal becomes 0 when the noise is cancelled by the noise cancellation sound at the corresponding position. In addition, the following transfer functions are preset for the plurality of auxiliary filters, and the transfer functions are learned such that the error represented by the error signal becomes 0 when the noise is cancelled by the noise cancellation sound at the corresponding position.

[0018] According to such an active noise control system, even at a position where an auxiliary filter capable of well canceling noise is not prepared, two auxiliary filters whose positions between positions capable of well canceling noise become the position of the object body can be used to cancel the noise audible in the object body. Here, the adaptive filter uses the error represented by the error signal input from the error correction unit, and executes a prescribed adaptive algorithm to update the transfer function of the adaptive filter. In addition, the following transfer functions are preset for the plurality of auxiliary filters, and the transfer functions are learned so that the error represented by the error signal becomes 0 when the noise is canceled by the noise canceling sound at the corresponding position.

[0019] According to such an active noise control system, even if the position of the object body is a position where an auxiliary filter capable of well canceling noise is not prepared at that position, two auxiliary filters whose positions between positions capable of well canceling noise become the position of the object body can be used to cancel the noise audible to the object body.

[0020] Here, such an active noise control system may also be configured such that, in the switching control unit, in the switching operation, the ratio of the signal obtained by correcting the microphone output signal using the output of the first hybrid object auxiliary filter, which is output as the error signal from the error correction unit, to the signal obtained by correcting the microphone output signal using the output of the second hybrid object auxiliary filter, which is output as the error signal from the error correction unit, gradually or stepwise changes to the post-switching ratio.

[0021] Here, such an active noise control system may also be such that the object body is the head of a user sitting on a seat capable of being displaced within a prescribed range, and the positions where the head of the human body sitting on the seat at that position is located at the standard position, which are obtained for different positions of the plurality of seats within the displacement range, are respectively positions corresponding to each of the plurality of auxiliary filters.

[0022] In addition, the present invention also provides an active noise control system, which includes two systems, namely a first system and a second system. The systems include the microphone, the adaptive filter, the speaker, the plurality of auxiliary filters, and the error correction unit. Here, the plurality of auxiliary filters of the first system and the plurality of auxiliary filters of the second system are paired one by one. The positional relationship between the position corresponding to the paired auxiliary filter of the first system and the position corresponding to the auxiliary filter of the second system is the same as or approximate to the positional relationship between two specified positions fixed relative to the object. In addition, the adaptive filter of the first system and the adaptive filter of the second system use the error signal output by the error correction unit of the first system and the error signal output by the error correction unit of the second system to execute a specified adaptive algorithm to update the transfer function of the adaptive filter. Moreover, the following transfer functions are preset for the plurality of auxiliary filters of the first system and the plurality of auxiliary filters of the second system. The transfer function is learned such that when the noise cancellation sound output by the speaker of the first system and the speaker of the second system cancels the noise at the position corresponding to the auxiliary filter and the position corresponding to the auxiliary filter corresponding to this auxiliary filter, the error signal output by the error correction unit of the first system and the error signal output by the error correction unit of the second system become 0.

[0023] Here, in such an active noise control system, it may be that the object is the head of a user sitting on a seat that can be displaced within a specified range. The positions where the left ear of the human body sitting on the seat at different positions within the displacement range is located at the standard position, which are obtained for different positions of the seats within the displacement range, are respectively the positions corresponding to each of the plurality of auxiliary filters of the first system. The positions where the right ear of the human body sitting on the seat at different positions within the displacement range is located at the standard position, which are obtained for different positions of the seats within the displacement range, are respectively the positions corresponding to each of the plurality of auxiliary filters of the second system. The above-mentioned plurality of auxiliary filters of the first system and the above-mentioned plurality of auxiliary filters of the second system that are paired are the plurality of auxiliary filters of the first system and the plurality of auxiliary filters of the second system for which the corresponding positions have been obtained for the positions of the same seat.

[0024] In addition, the above-mentioned specified seat in the above active noise control system may be a seat in an automobile.

[0025] Advantages of the Invention

[0026] As described above, according to the present invention, there is provided an active noise control system that can seamlessly switch its characteristics to eliminate noise at the displaced position according to the displacement of the object for which noise is to be eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 FIG. is a block diagram showing the configuration of an active noise control system according to an embodiment of the present invention.

[0028] Figure 2 FIG. is a diagram showing the arrangement of speakers and microphones in an active noise control system according to an embodiment of the present invention.

[0029] Figure 3 FIG. is a block diagram showing the configuration of a noise control device according to an embodiment of the present invention.

[0030] Figure 4 FIG. is a diagram showing an example of the arrangement of learning microphones according to an embodiment of the present invention.

[0031] Figure 5 FIG. is a block diagram showing the configuration of learning the transfer function of an auxiliary filter according to an embodiment of the present invention.

[0032] Figure 6 FIG. is a diagram showing the switching operation of an auxiliary filter according to an embodiment of the present invention.

[0033] Figure 7 FIG. is a diagram showing the switching operation of an auxiliary filter according to an embodiment of the present invention.

[0034] Figure 8 FIG. is a diagram showing the switching operation of an auxiliary filter according to an embodiment of the present invention.

[0035] Figure 9 FIG. is a diagram showing another configuration example of an active noise control system according to an embodiment of the present invention.

[0036] Figure 10 FIG. is a diagram showing another configuration example of an active noise control system according to an embodiment of the present invention.

[0037] Figure 11 FIG. is a block diagram showing another configuration example of a noise control device according to an embodiment of the present invention.

[0038] REFERENCE MARK DESCRIPTION

[0039] 1... Active noise control system, 2... Noise source, 11... Noise control device, 12... Speaker, 13... Microphone, 14... Position detection device, 41... Learning microphone, 50... First-stage learning processing unit, 51... Second-stage learning processing unit, 61... Left speaker, 62... Left microphone, 63... Right speaker, 64... Right microphone, 65... Left signal processing unit, 66... Right signal processing unit, 111... Signal processing unit, 112... Switching control unit, 141... Camera, 501... First-stage learning estimation filter, 511... Second-stage learning fixed filter, 512... Second-stage learning variable filter, 513... Second-stage learning adaptive algorithm execution unit, 514... Second-stage learning subtractor, 651... Left first estimation filter, 652... Left second estimation filter, 661... Right first estimation filter, 662... Right second estimation filter, 1111... Variable filter, 1112... Adaptive algorithm execution unit, 1113... Estimation filter, 1114... Subtractor, 1115... Auxiliary filter, 1116... Selector. Detailed implementation

[0040] Hereinafter, embodiments of the present invention will be described.

[0041] Figure 1 The configuration of the active noise control system of this embodiment is shown.

[0042] As shown in the figure, the active noise control system 1 includes a noise control device 11, a speaker 12, a microphone 13, and a position detection device 14.

[0043] Moreover, the active noise control system 1 is a system mounted on an automobile, which takes the position of the head of a user riding in the automobile as an elimination point, and eliminates the noise generated by the noise source 2 at the elimination point.

[0044] In addition, as Figure 2 shown, the speaker 12 and the microphone 13 are arranged, for example, on the ceiling in front of the seat (the right front seat in the figure) where the user who is the object of noise elimination in the vehicle interior is seated.

[0045] In addition, the position detection device 14 is a device that detects the position of the user's head, and includes a camera 141 that captures the periphery of the target seat provided in front of the target seat shown in Figure 2 the figure, and a sensor (not shown) that detects the position of the seat of the target seat in the front-rear direction and the inclination of the backrest. Based on the image captured by the camera 141, the position of the seat of the target seat detected by the sensor, and the inclination of the backrest, the position of the user's head is detected.

[0046] Return to Figure 1, the noise control device 11 of the active noise control system 1 uses the noise signal x(n) representing the noise generated by the noise source 2 and the microphone error signal err(n) which is the sound signal picked up by the microphone 13, generates the cancellation signal CA(n) for canceling the noise generated by the noise source 2 at the cancellation point, and outputs it from the speaker 12.

[0047] Next, Figure 3 illustrates the configuration of the noise control device 11 of the active noise control system 1.

[0048] As shown in the figure, the noise control device 11 includes a signal processing unit 111 and a switching control unit 112.

[0049] The signal processing unit 111 includes: a variable filter 1111, an adaptive algorithm execution unit 1112, an estimation filter 1113 with a preset transfer function S ^ (z), a subtractor 1114, three auxiliary filters 1115 with preset transfer functions H1(z), H2(z), and H3(z) respectively, and a selector 1116 that selects and outputs one of the outputs of the three auxiliary filters 1115 according to the control of the switching control unit 112.

[0050] In the configuration of such a signal processing unit 111, the input noise signal x(n) is output as the cancellation signal CA(n) to the speaker 12 after passing through the variable filter 1111.

[0051] In addition, the input noise signal x(n) is respectively sent to the selector 1116 through the three auxiliary filters 1115. The selector 1116 selects one of the outputs of the three auxiliary filters 1115 according to the control of the switching control unit 112 and sends it to the subtractor 1114. The subtractor 1114 subtracts the output of the selector 1116 from the microphone error signal err(n) picked up by the microphone 13 for correction, and outputs it as an error to the adaptive algorithm execution unit 1112.

[0052] Next, the variable filter 1111, the adaptive algorithm execution unit 1112, and the estimation filter 1113 form a Filter-X adaptive filter. The estimation filter 1113 is preset with the estimated transfer characteristic S ^ (z) obtained by estimating the transfer function S(z) from the signal processing unit 111 to the microphone 13 through actual measurement etc. The estimation filter 1113 convolves the transfer characteristic S ^ (z) with the input noise signal x(n), and outputs it to the adaptive algorithm execution unit 1112.

[0053] Then, the adaptive algorithm execution unit 1112 convolves the transfer function S by the estimation filter 1113^ Taking the noise signal x(n) of (z) and the error output from the subtractor 1114 as inputs, an NLMS-based adaptive algorithm is executed, and the transfer function W(z) of the variable filter 1111 is updated so that the error becomes zero.

[0054] Next, the transfer functions H1(z), H2(z), and H3(z) of the respective auxiliary filters 1115 of the signal processing unit 111 are set by performing a first-stage learning process and a second-stage learning process in advance.

[0055] Here, the transfer functions H1(z), H2(z), and H3(z) of the three auxiliary filters 1115 respectively correspond to different cancellation points.

[0056] That is, the transfer function H1(z) is as shown in Figure 4 a of, and corresponds to the standard position of the user's head, i.e., the cancellation point P1, when the position of the target seat is set at a position D forward from the standard front-rear direction position. The transfer function H2(z) is as shown in Figure 4 b of, and corresponds to the standard position of the user's head, i.e., the cancellation point P2, when the position of the target seat is set at the standard front-rear direction position. The transfer function H3(z) is as shown in Figure 4 c of, and corresponds to the cancellation point P3 of the standard position of the user's head when the position of the target seat is set at a position D rearward from the standard front-rear direction position.

[0057] In addition, the first-stage learning process is performed in a configuration where the first signal processing unit is replaced with the Figure 5 first-stage learning processing unit 50 shown in a of and the microphone 13 is replaced with the learning microphone 41.

[0058] When learning the transfer function Hi(z) by setting i to any number among 1, 2, and 3, as shown in Figure 4 a, b, and c of, the learning microphone 41 is arranged at the cancellation point Pi. That is, when learning the transfer function H1(z), as shown in Figure 4 a of, the learning microphone 41 is arranged at the cancellation point P1. When learning the transfer function H2(z), as shown in Figure 4 b of, the learning microphone 41 is arranged at the cancellation point P2. When learning the transfer function H3(z), as shown in Figure 4 c of, the learning microphone 41 is arranged at the cancellation point P3.

[0059] Figure 5 The first-stage learning processing unit 50 shown in a of includes from Figure 3The signal processing unit 111 shown excludes the three auxiliary filters 1115, the selector 1116, and the subtractor 1114, and replaces the estimation filter 1113 with an estimation filter 501 for the first-stage learning with a set transfer function S v ^ (z), and constitutes an error input of the output of the learning microphone 41 to the adaptive algorithm execution unit 1112. Among them, the transfer function S v ^ (z) represents the transfer function from the first-stage learning processing unit 50 to the learning microphone 41.

[0060] Moreover, in such a configuration, the transfer function W(z) of the variable filter 1111 is converged and stabilized by the adaptive action of the adaptive algorithm execution unit 1112, and the converged and stabilized transfer function W(z) is obtained as the result of the first-stage learning process.

[0061] Next, the second-stage learning process is set in the configuration where the Figure 3 signal processing unit 111 is replaced with the Figure 5 second-stage learning processing unit 51 shown in b.

[0062] Figure 5 The second-stage learning processing unit 51 shown in b includes: a second-stage learning fixed filter 511 that sets the transfer function W(z) obtained as the result of the first-stage learning process as the transfer function, a second-stage learning variable filter 512, a second-stage learning adaptive algorithm execution unit 513, and a second-stage learning subtractor 514.

[0063] The noise signal x(n) input to the second-stage learning processing unit 51 is output to the speaker 12 after passing through the second-stage learning fixed filter 511.

[0064] In addition, the input noise signal x(n) is sent to the second-stage learning subtractor 514 after passing through the second-stage learning variable filter 512. The second-stage learning subtractor 514 subtracts the output of the second-stage learning variable filter 512 from the signal picked up by the microphone 13 and outputs it as an error to the second-stage learning adaptive algorithm execution unit 513.

[0065] And, in such a configuration, the transfer function H(z) of the second-stage learning variable filter 512 is converged and stabilized by the adaptive action of the second-stage learning adaptive algorithm execution unit 513, and the converged and stabilized transfer function H(z) is learned as the transfer function Hi(z) of the i-th auxiliary filter 1115.

[0066] Next, for Figure 3The switching operation performed by the switching control unit 112 of the noise control device 11 will be described.

[0067] Based on the position of the user's head at the target seat detected by the position detection device 14, the switching control unit 112 switches the auxiliary filter 1115 whose output is selected by the selector 1116 and sent to the subtractor 1114.

[0068] This switching is performed through the following process: Calculate Figure 4 the cancellation points P1, P2, and P3 of a, b, and c, and select the cancellation point closest to the position of the head detected by the position detection device 14. When the calculated cancellation point changes, the selector 1116 switches the output sent to the subtractor 1114 to the output of the auxiliary filter 1115 that is set with the transfer function Hx(z) corresponding to the calculated cancellation point Px.

[0069] That is, when Figure 4 among the cancellation points P1, P2, and P3 of a, b, and c, the cancellation point P1 is closest to the position of the head detected by the position detection device 14, the selector 1116 switches the output sent to the subtractor 1114 to the output of the auxiliary filter 1115 that is set with the transfer function H1(z). When the cancellation point P2 is closest to the position of the head detected by the position detection device 14, the selector 1116 switches the output sent to the subtractor 1114 to the output of the auxiliary filter 1115 that is set with the transfer function H2(z). When the cancellation point P3 is closest to the position of the head detected by the position detection device 14, the selector 1116 switches the output sent to the subtractor 1114 to the output of the auxiliary filter 1115 that is set with the transfer function H3(z).

[0070] In addition, this switching is performed in such a way that the output sent by the selector 1116 to the subtractor 1114 changes gradually from the output before switching to the output after switching.

[0071] That is, for example, if the output before switching sent by the selector 1116 to the subtractor 1114 is the output of the auxiliary filter 1115 that is set with the transfer function H1(z), and the output after switching is the output of the auxiliary filter 1115 that is set with the transfer function H2(z), then as Figure 6As shown in a) below, during the transition time length T(H1 - H2) from the preset transfer function H1(z) to the transfer function H2(z), the ratio RH1 of the output of the auxiliary filter 1115 with the transfer function H1(z) input to the subtractor 1114 is stepwise reduced from 100% to 0%, and the ratio RH2 of the output of the auxiliary filter 1115 with the transfer function H2(z) input to the subtractor 1114 is gradually increased while satisfying RH1 + RH2 = 100% until from 0% to 100%, and after passing through T(H1 - H2), it maintains 100% at the ratio RH2. In addition, in Figure 6 In a), the ratio RH1 is reduced from 100% at 10% intervals at regular time intervals until 0%, and the ratio RH2 is increased from 0% at 10% intervals until 100%.

[0072] Here, the ratio of the output of the auxiliary filter 1115 input to the subtractor 1114 is controlled by controlling the selection frequency of the output of the auxiliary filter 1115 before and after the switching of the selector 1116.

[0073] That is, for example, if the output of the auxiliary filter 1115 with the transfer function H1(z) is set to 80% and the output of the auxiliary filter 1115 with the transfer function H2(z) is set to 20%, the selector 1116 is made to repeatedly perform the following process: after selecting the output value of the auxiliary filter 1115 with the transfer function H1(z) 8 times, select the output value of the auxiliary filter 1115 with the transfer function H2(z) 2 times. Similarly, if the output of the auxiliary filter 1115 with the transfer function H1(z) is set to 50% and the output of the auxiliary filter 1115 with the transfer function H2(z) is set to 50%, the selector 1116 alternately selects the output value of the auxiliary filter 1115 with the transfer function H1(z) and the output value of the auxiliary filter 1115 with the transfer function H2(z).

[0074] In addition, the transition time length for performing the stepwise switching as above can also be set to be larger as the distance between the cancellation points Pj and Pk corresponding to the transfer functions Hj(z) and Hk(z) set in the auxiliary filter 1115 before and after the switching is larger. That is, for example, the distance between the cancellation points P1 and P3 is greater than Figure 4The distances between the cancellation points P1 and P2 and between the cancellation points P2 and P3 are eliminated. Therefore, the transition time length during the switching between the output of the auxiliary filter 1115 with the transfer function H1(z) set and the output of the auxiliary filter 1115 with the transfer function H3(z) set can be made longer than the transition time length during the switching between the outputs of the auxiliary filters 1115 with other transfer functions set.

[0075] In addition, the number of stages for changing the ratio of the output before switching to the output after switching of the output sent by the selector 1116 to the subtractor 1114 can be arbitrary. For example, Figure 6 as shown in the case of the switching from the output of the auxiliary filter 1115 with the transfer function H1(z) set to the output of the auxiliary filter 1115 with the transfer function H2(z) set in b of, during T(H1 - H2), the ratio R_H1 of the output of the auxiliary filter 1115 with the transfer function H1(z) input to the subtractor 1114 is reduced to 100%, 50%, 0%, and the ratio R_H2 of the output of the auxiliary filter 1115 with the transfer function H2(z) input to the subtractor 1114 can be increased to 0%, 50%, 100%.

[0076] The embodiments of the present invention have been described above.

[0077] Thus, according to the present embodiment, since the auxiliary filter 1115 used in the generation of the error signal input to the adaptive filter can be switched to the auxiliary filter 1115 that can cancel noise well at the cancellation point close to the position of the user's head according to the change in the position of the user's head, the noise that the user can hear can be canceled well regardless of the displacement of the user's head.

[0078] In addition, by gradually or stepwise reducing the ratio of the signal generated by the auxiliary filter 1115 before switching as the error signal output and gradually or stepwise increasing the ratio of the signal generated by the auxiliary filter 1115 after switching as the error signal output for this switching, the divergence of the adaptive filter and the generation of noise in the noise cancellation sound can be suppressed.

[0079] However, in the above embodiment, there is an elimination point P2 corresponding to the transfer function H2(z) between the elimination point P1 corresponding to the transfer function H1(z) and the elimination point P3 corresponding to the transfer function H3(z), and it can be expected that the transfer function H2(z) becomes an intermediate value between the transfer function H1(z) and the transfer function H3(z). Therefore, the switching between the output of the auxiliary filter 1115 in which the transfer function H1(z) is set and the output of the auxiliary filter 1115 in which the transfer function H3(z) is set in the above embodiment can also be performed via the transfer function H2(z).

[0080] That is, for example, when switching from the output of the auxiliary filter 1115 set with the transfer function H1(z) to the output of the auxiliary filter 1115 set with the transfer function H3(z), the selector 1116 can switch the output as follows: Figure 7 A or Figure 7 As shown in b, during the transition time length T(H1-H3) from the preset transfer function H1(z) to the transfer function H3(z), the ratio R_H1 of the output of the auxiliary filter 1115 set with the transfer function H1(z) input to the subtractor 1114 is reduced stepwise from 100% to 100%, and the ratio R_H2 of the output of the auxiliary filter 1115 set with the transfer function H2(z) input to the subtractor 1114 is increased stepwise from 100% to 100% while satisfying R_H1+R_H2=100%. 0% to 100%, and then, the ratio R_H2 of the output of the auxiliary filter 1115 with the transfer function H2(z) set to the input of the subtractor 1114 is reduced step by step from 100% to 00%, and the ratio R_H3 of the output of the auxiliary filter 1115 with the transfer function H3(z) set to the input of the subtractor 1114 is increased step by step from 0% to 100% while satisfying R_H2+R_H3=100%, and after T(H1-H3), R_H3 maintains 100%.

[0081] In addition, in the above embodiment, the position of the head detected by the position detection device 14 is Figure 4 When the elimination points a, b, c are between P1 and P2, or between P2 and P3, the outputs of the two auxiliary filters 1115 corresponding to the two elimination points adjacent to the position of the head detected by the position detection device 14 can be output to the subtractor 1114 in the selector 1116 at a ratio of the inverse of the distance between the corresponding elimination point and the position of the head detected by the position detection device 14, thereby using the two auxiliary filters 1115 and the selector 1116 to form a virtual auxiliary filter 1115 that simulates the transfer function obtained when the learning microphone 41 is configured at the position of the head detected by the position detection device 14 and learning is performed.

[0082] That is, for example, as Figure 8 shown in a, when the position Pr of the head detected by the position detection device 14 is between the cancellation points P1 and P2, and the ratio of the distance from the position Pr to the cancellation point P1 to the distance from the position Pr to the cancellation point P2 is 70:30, the ratio of the output of the auxiliary filter 1115 that sets the transfer function H1(z) corresponding to the cancellation point P1 input to the subtractor 1114 to the output of the auxiliary filter 1115 that sets the transfer function H2(z) corresponding to the cancellation point P2 input to the subtractor 1114 is set to 30:70, which is the reciprocal of the distance ratio 70:30, as the switched state. Then, for the case where the position of the head detected by the position detection device 14 changes from the position of the cancellation point P1 to the position Pr, as Figure 8 shown in b1 of Figure 8 or b2 of

[0083] shown in b2, in the switching control unit 112, the selector 1116 is switched to output as follows: the ratio R_H1 of the output of the auxiliary filter 1115 that sets the transfer function H1(z) input to the subtractor 1114 decreases stepwise from 100% to 300%, and the ratio R_H2 of the output of the auxiliary filter 1115 that sets the transfer function H2(z) input to the subtractor 1114 increases stepwise until it reaches 700% from 0% while satisfying R_H1 + R_H2 = 100%, and then the ratio R_H2 is maintained at 70%.

[0084] Accordingly, even when the position of the user's head is not the position of the auxiliary filter 1115 that is prepared to use this position as the corresponding cancellation point, the two auxiliary filters 1115 whose positions between the corresponding cancellation points become the position of the head can be used to effectively cancel the noise that the user can hear. Figure 9

[0085] Figure 9 In addition, in the above embodiment, the case of performing noise cancellation for the user of one seat in the vehicle is described, but this can also be, as shown in a, for each seat in the vehicle, a speaker 12, a microphone 13, a camera 141 of the position detection device 14, and a sensor are provided to perform noise cancellation for the users of each seat.

[0086] In addition, in the above-described embodiments, the noise signal x(n) input to the active noise control system 1 may also be an audio signal output from a noise source, a sound signal obtained by picking up the noise of the noise source with an additionally provided noise microphone, or a signal of the noise of the noise source generated by an additionally provided analog sound generation device.

[0087] That is, for example, in the case where the engine is used as the noise source, the engine sound picked up by an additional noise microphone may be used as the noise signal x(n), or the analog sound obtained by simulating the engine sound generated by an additionally provided analog sound generation device may be used as the noise signal x(n).

[0088] In addition, in the above-described embodiments, it may also be extended to set the positions corresponding to the left ear and the right ear of the target seat as two cancellation points, and cancel the noise at each cancellation point.

[0089] That is, in this case, as shown in Figure 10 a and Figure 10 b, a set of a left speaker 61 and a left microphone 62 for canceling the noise of the main left ear, and a set of a right speaker 63 and a right microphone 64 for canceling the noise of the main right ear are provided.

[0090] And, in the noise control device 11, a left signal processing unit 65 and a right signal processing unit 66 as shown in Figure 11 are provided instead of the signal processing unit 111.

[0091] The configuration of the left signal processing unit 65 is substantially the same as the configuration of the signal processing unit 111 shown in Figure 3 , but in the left signal processing unit 65, the left speaker 61 is connected instead of the speaker 12, and the left microphone 62 is connected instead of the microphone 13.

[0092] In addition, instead of the estimation filter 1113, a left first estimation filter 651 that takes the noise signal x(n) as an input and sends the output to the adaptive algorithm execution unit 1112, and sets the transfer function S 11 (z) of the estimation transfer characteristic S 11 ^ (z) from the left signal processing unit 65 to the left microphone 62, and the transfer function S 21 (z) of the estimation transfer characteristic S 21 ^The left second estimation filter 652 of (z). In addition, the error e1 output from the subtractor 1114 and the error e2 output from the subtractor 1114 of the right signal processing unit 66 are input to the adaptive algorithm execution unit 1112, and the transfer function W(z) of the variable filter 1111 is updated in the adaptive algorithm execution unit 1112 so that the errors e1 and e2 become 0.

[0093] In addition, the configuration of the right signal processing unit 66 is also Figure 3 substantially the same as the configuration of the signal processing unit 111 shown, but in the left signal processing unit 65, the right speaker 63 is connected instead of the speaker 12, and the right microphone 64 is connected instead of the microphone 13. In addition, instead of the estimation filter 1113, an estimation transfer characteristic S 22 (z) of the estimation transfer characteristic S 22 ^ (z) of the right first estimation filter 662 and an estimation transfer characteristic S 12 (z) of the estimation transfer characteristic S 12 ^ (z) of the right second estimation filter 662 are set. In addition, the error e2 output from the subtractor 1114 and the error e1 output from the subtractor 1114 of the right signal processing unit 66 are input to the adaptive algorithm execution unit 1112, and the transfer function W(z) of the variable filter 1111 is updated in the adaptive algorithm execution unit 1112 so that the errors e1 and e2 become 0.

[0094] And, in the switching control unit 112, in the same manner as in the case of the signal processing unit 111 shown Figure 3 , according to the position of the head of the user of the target seat detected by the position detection device 14, the selector 1116 of the left signal processing unit 65 and the right signal processing unit 66 selects the output and switches the auxiliary filter 1115 sent to the subtractor 1114.

[0095] In addition, the learning of the transfer functions of the respective auxiliary filters 1115 of the left signal processing unit 65 and the right signal processing unit 66 is also Figure 3 the same as that of the respective auxiliary filters 1115 of the signal processing unit 111 shown, and is set by performing a first-stage learning process and a second-stage learning process in advance.

[0096] However, in the first-stage learning process, the left learning microphone and the right learning microphone are used instead of the learning microphone 41. And when learning the transfer function H1(z), as Figure 4When the position of the target seat is set at a position that is a distance D forward from the standard front-rear position as shown in a of , the left learning microphone is arranged at the standard position of the user's left ear, and the right learning microphone is arranged at the standard position of the user's right ear. When learning the transfer function H2(z), as Figure 4 shown in b, when the position of the target seat is set at the standard front-rear position, the left learning microphone is arranged at the standard position of the user's left ear, and the right learning microphone is arranged at the standard position of the user's right ear. When learning the transfer function H3(z), as Figure 4 shown in c, when the position of the target seat is set at a position that is a distance D rearward from the standard front-rear position, the left learning microphone is arranged at the standard position of the user's left ear, and the right learning microphone is arranged at the standard position of the user's right ear.

[0097] Moreover, in the first-stage learning process when learning the transfer function Hi(z), the transfer functions of the variable filters 1111 of the left signal processing unit 65 and the right signal processing unit 66, which represent the disappearance of noise from the outputs of the left learning microphone and the right learning microphone 13, are learned. In the second-stage learning process, the transfer functions of the variable filters 1111 of the left signal processing unit 65 and the right signal processing unit 66 are fixed to the transfer functions learned in the first-stage learning process, and the transfer functions of the learning auxiliary filters that make the error e1 output from the subtractor 1114 of the left signal processing unit 65 and the error e2 output from the subtractor 1114 of the right signal processing unit 66 equal to 0, obtained in the state where each auxiliary filter 1115 and selector 1116 are replaced with the learning auxiliary filters, are determined as the transfer function Hi(z).

[0098] In addition, the above-described embodiment shows the case where there is only one noise source 2, but the above-described embodiment can also be applied to the case where there are multiple noise sources 2 by expanding the configuration of the noise control device 11 to consider the propagation of each noise source 2 to each cancellation point.

[0099] In addition, in the above-described signal processing unit 111, left signal processing unit 65, and right signal processing unit 66, the number of auxiliary filters 1115 is set to 3, but any number of 2 or more auxiliary filters 1115 can also be provided.

Claims

1. An active noise control system that reduces the noise audible to an object, characterized in that, comprising: a microphone; an adaptive filter that takes a noise signal representing noise as an input; a speaker that takes the output of the adaptive filter as a noise cancellation sound output; a plurality of auxiliary filters that take the noise signal as an input and are respectively provided corresponding to a plurality of different positions; an error correction unit that corrects a microphone output signal, which is the output of the microphone, using the output of any one of the auxiliary filters and outputs the corrected signal as an error signal to the adaptive filter; a position detection unit that detects the position of an object; and a switching control unit that, when the auxiliary filter corresponding to the position where the position of the object detected by the position detection unit matches changes, uses the auxiliary filter corresponding to the position where the position of the object matches as a switched auxiliary filter, controls the error correction unit, and performs a switching operation that switches the signal output as the error signal from the error correction unit to a signal obtained by correcting the microphone output signal using the output of the switched auxiliary filter, wherein the adaptive filter uses the error represented by the error signal input from the error correction unit to execute a prescribed adaptive algorithm to update the transfer function of the adaptive filter, a transfer function is preset for the plurality of auxiliary filters, and the transfer function is learned such that the error represented by the error signal becomes 0 when noise is cancelled by the noise cancellation sound at the corresponding position, the switching control unit uses the auxiliary filter whose output was used in the correction of the microphone output signal before the switching operation as a pre-switching auxiliary filter, and in the switching operation, gradually or stepwise reduces the ratio of the signal obtained by correcting the microphone output signal using the output of the pre-switching auxiliary filter to be output as the error signal to 0%, and correspondingly gradually or stepwise increases the ratio of the signal obtained by correcting the microphone output signal using the output of the switched auxiliary filter to be output as the error signal to 100%.

2. The active noise control system according to claim 1, wherein the object is the head of a user sitting on a seat that can be displaced within a prescribed range, the positions of the heads of the human bodies sitting on the plurality of different seats within the displacement range, when the heads are in a standard position, are respectively the positions corresponding to each of the plurality of auxiliary filters.

3. The active noise control system according to claim 2, wherein the prescribed seat is a seat in a vehicle.

4. The active noise control system according to claim 1, wherein the active noise control system includes two systems, a first system and a second system, and each system includes the microphone, the adaptive filter, the speaker, the plurality of auxiliary filters, and the error correction unit, A plurality of auxiliary filters of the first system and a plurality of auxiliary filters of the second system are established in one-to-one correspondence. The positional relationship between the positions corresponding to the established auxiliary filters of the first system and the positions corresponding to the auxiliary filters of the second system is the same as or approximate to the positional relationship between two specified positions fixed relative to the object body. The adaptive filter of the first system and the adaptive filter of the second system use the error signal output by the error correction unit of the first system and the error signal output by the error correction unit of the second system to execute a specified adaptive algorithm to update the transfer function of the adaptive filter. The following transfer functions are preset for the plurality of auxiliary filters of the first system and the plurality of auxiliary filters of the second system. The transfer function is learned so that when the noise cancellation sound output by the speakers of the first system and the second system cancels the noise at the position corresponding to the auxiliary filter and the position corresponding to the auxiliary filter corresponding to the auxiliary filter, the error signal output by the error correction unit of the first system and the error signal output by the error correction unit of the second system become 0.

5. The active noise control system according to claim 4, wherein The object body is the head of a user sitting on a seat that can be displaced within a specified range. For different positions within the displacement range of the seat, the positions where the left ear of the human body sitting on the seat at that position is in the standard position are respectively the positions corresponding to each of the plurality of auxiliary filters of the first system. For different positions within the displacement range of the seat, the positions where the right ear of the human body sitting on the seat at that position is in the standard position are respectively the positions corresponding to each of the plurality of auxiliary filters of the second system. The plurality of auxiliary filters of the first system and the plurality of auxiliary filters of the second system that are established in correspondence are the plurality of auxiliary filters of the first system and the plurality of auxiliary filters of the second system for which the corresponding positions are obtained for the same seat position.

6. The active noise control system according to claim 5, wherein The specified seat is a seat in a vehicle.

7. An active noise control system that reduces the noise audible to an object, characterized in that, Comprising: A microphone; An adaptive filter that takes a noise signal representing noise as an input; A speaker that outputs the output of the adaptive filter as noise cancellation sound; A plurality of auxiliary filters that take the noise signal as an input and are respectively provided corresponding to different positions; An error correction unit that corrects the microphone output signal, which is the output of the microphone, using the output of any one of the auxiliary filters and outputs it as an error signal to the adaptive filter; A position detection unit that detects the position of the object body; And The switching control unit controls the error correction unit so that when the position of the object detected by the position detection unit changes, two auxiliary filters, and specifically, the two auxiliary filters between two positions corresponding to the two auxiliary filters that become the position of the object, are used as the first hybrid object auxiliary filter and the second hybrid object auxiliary filter, and signals obtained by correcting the microphone output signal using the output of the first hybrid object auxiliary filter and signals obtained by correcting the microphone output signal using the output of the second hybrid object auxiliary filter are output from the error correction unit as the error signal at a switched ratio, where the switched ratio is a ratio determined based on the ratio of the distance between the position corresponding to the first hybrid object auxiliary filter and the position of the object to the distance between the position corresponding to the second hybrid object auxiliary filter and the position of the object. The adaptive filter uses the error represented by the error signal input from the error correction unit and executes a prescribed adaptive algorithm to update the transfer function of the adaptive filter. Transfer functions are preset for the plurality of auxiliary filters, and the transfer functions are learned so that the error represented by the error signal becomes 0 when noise is eliminated by noise cancellation sound at the corresponding positions.

8. The active noise control system according to claim 7, wherein In the switching operation, the switching control unit gradually or stepwise changes the ratio of the signal obtained by correcting the microphone output signal using the output of the first hybrid object auxiliary filter, which is output from the error correction unit as the error signal, to the signal obtained by correcting the microphone output signal using the output of the second hybrid object auxiliary filter, which is output from the error correction unit as the error signal, to the switched ratio.

9. The active noise control system according to claim 8, wherein The object is the head of a user seated on a seat that can be displaced within a prescribed range. The positions where the head of a human body seated on the seat located at each of the different positions within the displacement range is at the standard position, which are obtained for the positions of the plurality of seats, are the positions corresponding to each of the plurality of auxiliary filters.

10. The active noise control system according to claim 8, wherein The active noise control system includes two systems, a first system and a second system, and each system includes the microphone, the adaptive filter, the speaker, the plurality of auxiliary filters, and the error correction unit. The plurality of auxiliary filters of the first system and the plurality of auxiliary filters of the second system are paired one-to-one, and the positional relationship between the position corresponding to the paired auxiliary filter of the first system and the position corresponding to the auxiliary filter of the second system is the same as or approximate to the positional relationship with respect to two prescribed positions fixed relative to the object. The adaptive filter of the first system and the adaptive filter of the second system use the error signal output by the error correction unit of the first system and the error signal output by the error correction unit of the second system to execute a prescribed adaptive algorithm to update the transfer function of the adaptive filter. The following transfer functions are preset for the multiple auxiliary filters of the first system and the multiple auxiliary filters of the second system. The transfer function is learned so that when the noise cancellation sound output by the speakers of the first system and the speakers of the second system cancels the noise at the position corresponding to the auxiliary filter and the position corresponding to the auxiliary filter corresponding to the auxiliary filter, the error signal output by the error correction unit of the first system and the error signal output by the error correction unit of the second system become 0.

11. The active noise control system according to claim 10, wherein: The object is the head of a user seated on a seat that can be displaced within a prescribed range. The positions where the left ear of a human body seated on a seat located at different positions within the displacement range is in the standard position, which are obtained for the different positions within the displacement range, are respectively the positions corresponding to each of the multiple auxiliary filters of the first system. The positions where the right ear of a human body seated on a seat located at different positions within the displacement range is in the standard position, which are obtained for the different positions within the displacement range, are respectively the positions corresponding to each of the multiple auxiliary filters of the second system. The multiple auxiliary filters of the first system and the multiple auxiliary filters of the second system that are established to correspond are the multiple auxiliary filters of the first system and the multiple auxiliary filters of the second system for which the corresponding positions have been obtained for the positions of the same seat.

12. The active noise control system according to claim 11, wherein: The prescribed seat is a seat in an automobile.

13. The active noise control system according to claim 7, wherein: The object is the head of a user seated on a seat that can be displaced within a prescribed range. The positions where the head of a human body seated on a seat located at different positions within the displacement range is in the standard position, which are obtained for the different positions within the displacement range, are respectively the positions corresponding to each of the multiple auxiliary filters.

14. The active noise control system according to claim 13, wherein: The prescribed seat is a seat in an automobile.

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