Active noise reduction headrest and noise reduction method

Abstract

The invention discloses an active noise reduction headrest which comprises a microphone array, a secondary sound source and an active controller electrically connected with the microphone array, and the microphone array is arranged at a certain distance from the head. The invention further discloses an active noise reduction method. The method comprises the steps that S1, the noise reduction headrest system is built; s2, a coordinate system is established, microphone arrays are symmetrically arranged on the head, and the array form is linear; s3, arranging a head tracking device, and determining coordinates of a microphone and plane coordinates of a head motion range; s4, acquiring a sound pressure signal by using a microphone array, and calculating and analyzing an estimated value of a sound field signal of a noise reduction point at the human ear; s5, establishing a sound path model from the secondary sound source to the human ear noise reduction point by using an LMS algorithm; and S6, calling the sound path model by the active controller, operating an FxLMS algorithm to iteratively calculate a control signal, and outputting the control signal to realize noise control. The low-frequency line spectrum noise near the head is controlled, and the method can be widely applied to the field of noise control.

Description

Technical Field

[0001] The present invention relates to the field of noise control, and particularly to an active noise reduction headrest and a noise reduction method. Background Art

[0002] A typical application of local active (active) noise control is an active noise reduction headrest, simply referred to as an active headrest. The active headrest can be deployed on facilities such as seats, workstations, and beds near the head to obtain noise attenuation at the human ear and provide a low-noise working and living environment.

[0003] In existing research on active headrests, a microphone is usually pre-arranged at the human ear, and then a model is established using the secondary sound source and the sound pressure signal at the microphone. If the position to be controlled changes, it is necessary to re-set up a microphone at the human ear to establish an acoustic path model. Usually, positions are pre-divided within the head movement plane, and a large number of secondary path transfer functions at different positions of the human head are measured and stored at these positions for subsequent control phase calls. The main problems are as follows: The preparatory work before control is cumbersome, requiring the measurement and storage of a considerable number of secondary path transfer functions, and additional microphones need to be arranged everywhere during modeling; at the same time, the designed measurement schemes divide points at certain intervals within the head movement plane, so there will always be points missed at the intermediate positions of the divided grid. When the head moves to a position where the secondary path transfer function is not stored, the control performance will decline.

[0004] In addition, existing active headrests cannot capture the position of the human head. Only by accurately obtaining the corresponding noise reduction points can control be carried out for the noise reduction points. Otherwise, the control effect is not good, and technical measures need to be taken to obtain the coordinates of the noise reduction points when implementing control. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above background art, and provide an active noise reduction headrest and a noise reduction method, which can capture the position information of the human head in real time to obtain the coordinates of the noise reduction points, and build an active control system through a microphone array to achieve the control of low-frequency line spectrum noise near the head.

[0006] An active noise reduction headrest provided by the present invention includes a microphone array, a secondary sound source, and an active controller electrically connected to the microphone array. The microphone array is arranged at a certain distance from the head.

[0007] In the above technical solution, the microphone array is linear and arranged in multiple columns. The multiple-column microphone arrays are symmetrically distributed on the left and right sides of the head.

[0008] In the above technical solution, 2 microphone arrays are provided on each side of the head, and the distance between each microphone is equal.

[0009] In the above technical solution, a coordinate system is set with the center of the head as the origin, and the height of the microphone array is flush with the origin of the coordinate system.

[0010] In the above technical solution, the coordinate system is a three-dimensional rectangular coordinate system.

[0011] In the above technical solution, an installation structure higher than the head is provided behind the head. A head tracking device is provided at a position corresponding to the head on the installation structure. The head tracking device is connected to the active controller through a signal cable, and the multi-channel microphone array is respectively connected to both ends of the installation structure.

[0012] In the above technical solution, there are two secondary sound sources, which are respectively fixed on one side of the installation structure facing the head. The two secondary sound sources are symmetrically arranged on both sides behind the head, and the sound outlets of the secondary sound sources are arranged away from the installation structure.

[0013] In the above technical solution, the two secondary sound sources are located inside the microphone array.

[0014] The present invention also provides an active noise reduction method, including the following steps: S1. Build a noise reduction headrest system and connect the microphone, secondary sound source, head tracking device and active controller; S2. Take the center of the head as the origin to establish a three-dimensional rectangular coordinate system. Microphone arrays are symmetrically arranged on both the left and right sides of the head. The height of the microphone array is flush with the origin of the three-dimensional rectangular coordinate system, and the array form is linear. Multiple microphone arrays are symmetrically arranged on each side of the head; S3. Arrange a head tracking device above the head to determine the coordinates of each arranged microphone and the plane coordinates of the head movement range. The head tracking device captures the coordinates of the noise reduction point of the human ear in real time and inputs them to the active controller; S4. Use the microphone array to collect the sound pressure signals at the corresponding positions, and obtain the estimated value of the sound field signal at the noise reduction point of the human ear through calculation and analysis; S5. Excite the secondary sound source, use the sound field signal at the noise reduction point of the human ear, and establish an acoustic path model from the secondary sound source to the noise reduction point of the human ear based on the estimated value of the sound field at the noise reduction point of the human ear and the FIR (Finite Impulse Response) filter using the LMS (Least Mean Squares) algorithm, and store the acoustic path model in the active controller for calling during control; S6. When the control is turned on, the active controller calls the acoustic path model and runs the FxLMS (Filtered-X Least Mean Square) algorithm to perform iterative calculation to control the signal and output it. The control signal is transmitted to the secondary sound source to generate secondary sound waves that interfere and cancel with the sound waves of the noise source at the noise reduction point, thereby achieving noise control.

[0015] In the above technical solution, the specific process of step S4 is as follows: S41. Use a microphone array to collect the sound pressure signals at corresponding positions, and obtain the time-domain sound pressure signal vector of the original sound field at all microphone positions. ; S42. Use FFT (Fast Fourier Transform) to perform frequency-domain analysis on the collected original sound pressure signals, and obtain the frequency-domain sound pressure signal vector at all microphone positions. ; S43. Use the spherical approximate uniform sampling method to obtain plane wave vectors on the sphere with the origin of the space coordinate system as the center of the sphere and a radius of , within the range of the spatial pitch angle and the horizontal angle , and randomly and uniformly obtain a number of plane wave directions; S44. Decompose the frequency-domain sound pressure measured at each measurement point of the microphone array into the superposition of the aforementioned plane waves, so as to obtain the transfer matrix composed of plane waves in each direction : , where represents the wave vector in a certain direction, and represents the coordinate vector of the microphone array (1); S45. Solve the plane wave complex amplitude vector , construct the equation constrained by , where " " represents norm, is the noise estimate value, is the plane wave complex amplitude vector to be solved. Using the existing and , where is the frequency-domain sound pressure signal vector at all microphone positions , and setting according to actual needs, can be obtained; S46. Use a head tracking device to obtain the specific coordinates of the human ear and transmit them to the active controller for estimating the noise signal at the human ear coordinate points; S47. According to the obtained human ear coordinates and the equation , update to , calculate the frequency-domain sound pressure signal at the human ear coordinates , where is the transfer matrix of the sound field coordinate points to be estimated; S48. For the obtained , then by constructing the spectral method and the inverse Fourier transform, the time-domain sound pressure signal at the human ear coordinates can be obtained, and thus the estimated value of the sound field signal at the noise reduction point at the human ear is obtained.

[0016] The active noise reduction headrest and noise reduction method of the present invention have the following beneficial effects: 1. Estimate the noise signal at the noise reduction point using a linear microphone array. When performing active noise control, there is no need to place an additional microphone at the human ear as an error microphone, which can avoid the repetitive modeling and storage work of the pre-control acoustic path.

[0017] 2. Build an active control system through a microphone array. At the same time, use a head tracking device to accurately obtain the coordinates of the noise reduction point in real time and input them into the active control system, which can avoid the situation where the control effect is significantly reduced due to the head moving to a noise reduction point where the acoustic path model has not been established, and improve the noise reduction effect. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the overall structure of the active noise reduction headrest of the present invention; Figure 2 It is a schematic flowchart of the active noise reduction method of the present invention; Figure 3 It is a planar coordinate diagram of the head movement range in step 3 of the active noise reduction method of the present invention; Figure 4 It is a planar wave vector division diagram in step 6 of the active noise reduction method of the present invention; Figure 5 It is a simulation noise reduction effect diagram in step 13 of the active noise reduction method of the present invention. Detailed Embodiments

[0019] The present invention will be further described in detail below in conjunction with the drawings and embodiments, but this embodiment should not be construed as a limitation of the present invention.

[0020] To achieve the above object, the specific solution adopted by the present invention is as follows: The present invention combines a microphone array 1 and a head tracking device 4 for an active headrest, which is composed of a microphone array 1, a secondary sound source 2 (loudspeaker), an active controller 3, a head tracking device 4, etc. For the composition of each component, please refer to the appendix Figure 1 . Among them, the form and arrangement of the microphone array 1 need to meet the requirements shown in the drawings.

[0021] Embodiment 1 The signal input interface of the active controller 3 is connected to the microphone array 1 through a signal cable and supplies power to the microphone. The microphone collects the sound pressure signal in the sound field and inputs it to the active controller 3. The signal output interface circuit part in the active controller 3 integrates a power amplifier (not shown in the figure). The secondary sound source 2, in this embodiment, the secondary sound source 2 is a loudspeaker, is connected to the signal output interface of the active controller 3 through a signal cable, receives the output signal of the active controller 3 and emits sound.

[0022] The microphone arrays 1 are symmetrically distributed on the left and right sides of the head 5. The array form is linear, with two columns on each side, and there is no need to arrange microphones at the human ear. The active controller 3 is arranged near the head 5 at a position convenient for stable installation (such as the back of a chair, the head of a bed, etc.), connects other components, receives the noise signals collected by the microphone arrays 1, estimates the noise signals at the noise reduction points, and uses algorithms to iteratively calculate and output control signals. The secondary sound sources 2 are arranged on both sides of the head 5 to control the noise at the left and right ears respectively.

[0023] Embodiment 2 This embodiment is basically the same as Embodiment 1, and the differences are as follows: The head tracking device 4 is connected to the signal input interface in the active controller 3 through a signal cable, and inputs coordinate information to the active controller 3.

[0024] The head tracking device 4 is also arranged near the head 5 at a position convenient for stable installation (such as the back of a chair, the head of a bed, etc.).

[0025] Embodiment 3 The specific implementation steps of the active noise reduction method of the present invention are shown in the appendix Figure 2 .

[0026] 1. Build a noise reduction headrest system as shown in Figure 1 , and connect the microphones, secondary sound sources 2, head tracking device 4 and active controller 3.

[0027] 2. Take the center of the head 5 as the origin to establish a coordinate system. In this embodiment, the coordinate system is a three-dimensional rectangular coordinate system. The microphone arrays 1 are symmetrically arranged on the left and right sides of the head 5. The height of the microphone arrays 1 is flush with the origin of the coordinate system. The array form of the microphone arrays 1 is linear, with 2 columns of microphones on each side of the head 5. The distance between the near side of the microphone arrays 1 and the head 5 is 20 cm, and the distance between each microphone is 3 cm. There are a total of 12 microphones. Without changing the basic form of the microphone arrays 1, microphones can be added to expand the sound field reconstruction range.

[0028] 3. Arrange the head tracking device 4 above the head 5 to determine the coordinates of each arranged microphone, as well as the plane coordinates of the movement range of the head 5, as shown in the appendix Figure 3 . The head tracking device 4 captures the coordinates of the noise reduction points of the human ear in real time and inputs them to the active controller 3.

[0029] 4. Use the microphone arrays 1 to collect the sound pressure signals at the corresponding positions to obtain the time-domain sound pressure signal vector of the original sound field at the positions of 12 microphones .

[0030] 5. Use FFT to perform frequency-domain analysis on the collected original sound pressure signals to obtain the frequency-domain sound pressure signal vector at the positions of 12 microphones .

[0031] 6. Using the spherical surface approximate uniform sampling method, on the spherical surface with the origin of the space coordinate system as the center of the sphere and a radius of , the spatial elevation angle , horizontal angle range, obtain plane wave vectors, and randomly and uniformly obtain a total of 400 plane wave directions. The plane wave vectors are divided as shown in Appendix Figure 4 .

[0032] 7. Decompose the frequency-domain sound pressure measured at each measurement point of the microphone array 1 into the superposition of 400 plane waves with different directions and amplitudes. Thus, obtain the transfer matrix composed of plane waves in different directions:

[0033] where, represents the wave vector in a certain direction, and represents the coordinate vector of the microphone array.

[0034] 8. Solve the plane wave complex amplitude vector , construct the equation constrained by , where " " represents the norm, is the noise estimate value, is the plane wave complex amplitude vector to be solved. Using the existing and , where, is the frequency-domain sound pressure signal vector at all microphone positions. According to actual requirements, set , and can be obtained.

[0035] 9. Use the head tracking device 4 to obtain the specific coordinates of the human ear and transmit them to the active controller 3 for estimating the noise signal at the human ear coordinate point.

[0036] 10. According to the obtained human ear coordinates and the equation , update to , calculate the frequency-domain sound pressure signal at the human ear coordinates, where, is the transfer matrix of the sound field coordinate point to be estimated.

[0037] 11. For the obtained , then by constructing the spectral method and performing the inverse Fourier transform, the time-domain sound pressure signal at the human ear coordinates can be obtained. Steps 4 to 11 are to obtain the estimated value of the noise signal at the human ear.

[0038] 12. Energize the secondary sound source 2. By using the method described in the above steps 4 to 11, the sound field signal at the noise reduction point of the human ear can be obtained. Use the LMS algorithm to establish an acoustic path model from the secondary sound source 2 to the noise reduction point of the human ear by using the estimated signal and the FIR filter, and store the acoustic path model in the active controller 3 for calling during control.

[0039] 13. When the control is turned on, the active controller 3 calls the acoustic path model and runs the FxLMS algorithm to iteratively calculate and output the control signal. The control signal is transmitted to the secondary sound source 2 to generate secondary sound waves that interfere and cancel out with the sound waves of the noise source at the noise reduction point, realizing noise control. Attached Figure 5 is the simulated noise reduction effect obtained by using the present invention.

[0040] Compared with the original method of actually measuring the sound signal through a single microphone, the present invention proposes a source-leaning method with a microphone array 1 and a head tracking device 4 placed at a certain distance from the head, which can relieve the burden on the head and solve the problems of difficult determination of the noise reduction point caused by the change of the human head position and the acoustic path modeling problem of the active control system brought about by the position change. On the one hand, the head tracking device 4 is used to capture the position information of the human head 5 in real time to obtain the coordinates of the noise reduction point; on the other hand, the low-frequency noise signal at the noise reduction point is estimated by using the coordinate information and the microphone array 1, and then an active control system is built through the microphone array 1, which can realize the control of the low-frequency line spectrum noise near the head 5.

[0041] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

[0042] The content not described in detail in this specification belongs to the prior art well known to those skilled in the art.

Claims

1. An active noise reduction headrest, comprising a microphone array (1), a secondary sound source (2), and an active controller (3) electrically connected to the microphone array (1), characterized in that: The microphone array (1) is arranged at a certain distance from the head (5).

2. The active noise reduction headrest according to claim 1, characterized in that: The microphone array (1) is linear and arranged in multiple rows, and the multiple rows of microphone arrays (1) are symmetrically distributed on the left and right sides of the head (5).

3. The active noise reduction headrest according to claim 2, characterized in that: Two rows of microphone arrays (1) are provided on each side of the head (5), and the spacing between the microphones is equal.

4. The active noise reduction headrest according to claim 3, characterized in that: A coordinate system is set with the center of the head (6) as the origin, and the height of the microphone array (1) is flush with the origin of the coordinate system.

5. The active noise reduction headrest according to claim 4, characterized in that: The coordinate system is a spatial rectangular coordinate system.

6. The active noise reduction headrest according to claim 5, characterized in that: A mounting structure (6) higher than the head (5) is provided behind the head (5); a head tracking device (4) is provided at a position on the mounting structure (6) corresponding to the head (5); the head tracking device (4) is connected to the active controller (3) via a signal cable; and the multiple microphone arrays (1) are respectively connected to two ends of the mounting structure (6).

7. The active noise reduction headrest according to claim 6, characterized in that: The secondary sound sources (2) are two and are respectively fixed to one side of the mounting structure (6) facing the head (5); the two secondary sound sources (2) are symmetrically arranged on both sides behind the head; and the sound outlets of the secondary sound sources (2) are arranged away from the mounting structure (6).

8. The active noise reduction headrest according to claim 7, characterized in that: The two secondary sound sources (2) are located inside the microphone array (1).

9. An active noise reduction method, characterized in that: The steps include: S1, build a noise reduction headrest system, connect the microphone, the secondary sound source (2), the head tracking device (4) and the active controller (3); S2. With the center of the head (5) as the origin, a spatial rectangular coordinate system is established, and microphone arrays (1) are symmetrically arranged on the left and right sides of the head (5). The height of the microphone array (1) is flush with the origin of the spatial rectangular coordinate system, and the array form is linear. Multiple columns of microphone arrays (1) are symmetrically arranged on each side of the head (5); S3, arranging a head tracking device (4) above the head (5), determining the coordinates of each arranged microphone and the plane coordinates of the movement range of the head (5), and the head tracking device (4) captures the coordinates of the human ear noise reduction point in real time and inputs them into the active controller (3); S4, using the microphone array (1) to collect the sound pressure signal at the corresponding position, and obtaining an estimated value of the sound field signal at the noise reduction point at the human ear through calculation and analysis; S5, exciting the secondary sound source (2), using the sound field signal of the noise reduction point at the human ear, using the LMS algorithm based on the sound field estimation value of the noise reduction point at the human ear and the FIR filter to establish a sound path model from the secondary sound source (2) to the noise reduction point at the human ear, and storing the sound path model in the active controller (3) for reference during control; S6, when the control is turned on, the active controller (3) calls the sound path model and runs the FxLMS algorithm to iteratively calculate the control signal and output it. The control signal is transmitted to the secondary sound source (2) to generate secondary sound waves that interfere with the sound waves of the noise source at the noise reduction point, thereby achieving noise control.

10. The active noise reduction method according to claim 9, characterized in that: The specific process of step S4 is as follows: S41, using the microphone array (1) to collect the sound pressure signal at the corresponding position, and obtain the time domain sound pressure signal vector of the original sound field at all microphone positions ; S42, using FFT to perform frequency domain analysis on the collected original sound pressure signal to obtain the frequency domain sound pressure signal vector at all microphone positions ; S43, using the spherical approximate uniform sampling method, with the zero point of the spatial coordinate system as the center of the sphere and the radius On the spherical surface, the spatial pitch angle , horizontal angle Obtain plane wave vectors within the range, and obtain several plane wave directions randomly and uniformly; S44, decomposing the frequency domain sound pressure measured at each measuring point of the microphone array (1) into the superposition of the aforementioned plane waves, thereby obtaining a transfer matrix composed of plane waves in each direction : ， in, represents the wave vector in a certain direction, represents the coordinate vector of the microphone array (1); S45. Solving the plane wave complex amplitude vector , construct the equation Constrained by ,in" "express norm, is the noise estimate, is the complex amplitude vector of the plane wave to be solved. and ,in, is the frequency domain sound pressure signal vector at all microphone locations , set according to actual needs , can be obtained ; S46, using the head tracking device (4) to obtain specific coordinates of the human ear, and transmitting the coordinates to the active controller (3) for estimating the noise signal at the human ear coordinate point; S47, according to the acquired human ear coordinates and equation ,renew for , the frequency domain sound pressure signal at the human ear coordinates is calculated ,in, is the transfer matrix of the sound field coordinate points to be estimated; S48, for the obtained Then, the time domain signal of the sound pressure at the human ear coordinates can be obtained by constructing the spectrum method and inverse Fourier transform. , thereby obtaining an estimated value of the sound field signal at the noise reduction point at the human ear.

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