Gradient helical tube composite Helmholtz resonator sound absorption device and its adjustment method

Abstract

This invention provides a gradient helical tube composite Helmholtz resonator sound absorption device and its adjustment method, relating to the field of noise control technology. It solves the problem of existing technologies' difficulty in simultaneously achieving high low-frequency efficiency and broadband sound absorption within a limited space. The gradient helical tube composite Helmholtz resonator sound absorption device includes a gradient helical tube and multiple Helmholtz resonator units. The diameter of the gradient helical tube changes continuously along the sound wave propagation path. The multiple Helmholtz resonator units are connected in series at the ends of the gradient helical tube and disposed within the internal space enclosed by the gradient helical tube. This invention can broaden the sound absorption bandwidth and enhance low-frequency sound absorption performance through the composite structure of the gradient helical tube and multiple Helmholtz resonator units.

Description

Technical Field

[0001] This invention relates to the field of noise control technology, and in particular to a gradient helical tube composite multi-Helmholtz resonator sound absorption device and its adjustment method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Noise control, especially the suppression of low-frequency broadband noise, is a key challenge in many industrial sectors. Existing technologies, such as porous materials and resonant structures (e.g., Helmholtz resonators and micro-perforated panels), have inherent limitations in achieving "low-frequency, broadband, and efficient" sound absorption: porous materials and traditional micro-perforated panel structures rely on deep and large back cavities to improve low-frequency performance, resulting in bulky structures that contradict the trend of compactness and lightweight design in modern equipment; resonant structures such as Helmholtz resonators have extremely narrow sound absorption bandwidths, and simply connecting multiple resonant units in parallel to broaden the bandwidth drastically increases the complexity and space required by the system. Therefore, existing technologies struggle to simultaneously achieve high-efficiency low-frequency and broadband sound absorption within a limited space. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a gradient helical tube composite multi-Helmholtz resonator sound absorption device and its adjustment method that can solve or at least alleviate the above problems, which can broaden the sound absorption frequency band and enhance the low-frequency sound absorption performance through the composite structure of gradient helical tube and multiple Helmholtz resonator units.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a gradient helical tube composite Helmholtz resonator sound absorption device, comprising a gradient helical tube and a plurality of Helmholtz resonator units, wherein the diameter of the gradient helical tube changes continuously along the sound wave propagation path; the plurality of Helmholtz resonator units are connected in series at the ends of the gradient helical tube and disposed in the internal space enclosed by the gradient helical tube.

[0006] Preferably, the plurality of Helmholtz resonator units are connected in series, each Helmholtz resonator unit including a neck and a cavity, with the neck placed inside the cavity; the neck diameters of the plurality of Helmholtz resonator units decrease in a gradient, and the neck diameter of the first Helmholtz resonator unit connected in series with the gradient helical tube is equal to the end aperture of the gradient helical tube.

[0007] Preferably, the gradient helical tube is connected to the plurality of Helmholtz resonator units via an extension tube.

[0008] Preferably, the aperture variation of the gradient helical tube follows a linear variation law: ; In the formula: The total length of the gradient spiral tube after it has been unfolded, including the extension tube. h This refers to a certain position after the gradient helical tube has been unfolded. ; , H The overall height of the gradient helical tube is [missing information]. L The diameter of the helix. P For pitch, L e The length of the extended tube after it has been unfolded; The inlet diameter of the gradient helical tube is [missing information]. For the end aperture, After the gradient helical tube is unfolded The aperture at that location.

[0009] Preferably, the gradient helical tube, the extension tube, and the multiple Helmholtz resonator units are integrally made of metal or engineering plastic.

[0010] Secondly, the present invention provides an adjustment method for a gradient helical tube composite Helmholtz resonator sound-absorbing device, comprising the following steps: S1. Establish the gradient helical tube model and the multi-Helmholtz resonator model: Gradient helical tube model: Discretize the gradient helical tube along the direction of helical expansion as follows: For a straight pipe section with gradually changing cross-sectional area, the transfer matrix for each layer is: ; In the formula: For complex wave number, , Angular frequency, , Speed ​​of sound in air; The imaginary unit; The length of each micro-segment of straight pipe after discretization. , The total length of the gradient spiral tube after it is unfolded, including the extension tube; For dependent on local cross-sectional area acoustic impedance, , For air resistance, , air density, , After the gradient helical tube is unfolded The aperture at that location; Multi-Helmholtz resonator model: Each Helmholtz resonator unit includes a neck and a cavity, and the transfer matrix is: ; In the formula: For the neck transfer matrix, Let be the transfer matrix of the cavity. and These are the correction matrices; S2, Overall Transfer Matrix: ; In the formula: This is the total transfer matrix of the gradient solenoid; for N HR The total transfer matrix of a series structure of Helmholtz resonator units; S3. Calculate acoustic performance, specifically the surface acoustic impedance from the total transfer matrix. Reflection coefficient and sound absorption coefficient : , , ; In the formula: For the incident surface area of ​​the sound wave in the composite model, The inlet diameter of the gradient helical tube; The first element of the first row and first column of the total transfer matrix; The element in the second row and first column of the total transfer matrix; S4. Verify and optimize the design, calculate the sound absorption coefficient curve, and verify the sound absorption performance. If the expected results are not achieved, return to adjust the structural parameters of multiple Helmholtz resonator units and / or the geometric parameters of the gradient helical tube, and repeat steps S1 to S3 until the sound absorption coefficient curve reaches the expected results.

[0011] Preferably, in step S1, the transfer matrix of the neck Transfer matrix of cavity They are respectively: , ; In the formula: and These represent the neck length and cavity length of a Helmholtz resonator element, respectively. and These are the complex wave numbers for the neck and cavity, respectively. and These represent the neck impedance and cavity impedance of the Helmholtz resonator unit, respectively.

[0012] Preferably, neck impedance and cavity impedance They are respectively: , ; Where: neck radius , d neck,i For the first i Neck diameter of each Helmholtz resonator unit; cavity radius , d cavity The diameter of the cavity; and These are the cross-sectional areas of the neck and the cavity, respectively. This refers to the Prandtl number at standard atmospheric pressure. The specific heat capacity ratio of air; It is the kinematic viscosity of air.

[0013] Preferably, the complex wave number of the neck and the complex wave number of the cavity They are respectively: , ; In the formula: This indicates the characteristic thickness of the acoustic boundary layer.

[0014] Preferably, the correction matrix and They are respectively: , ; In the formula, and These are the correction lengths, and They are respectively: , ; In the formula: and The neck radius of each Helmholtz resonator unit is respectively. and cavity radius ; The transition radius at the junction of the neck and the cavity is given in the model. .

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention achieves wide bandwidth coverage by forming multiple high sound absorption resonance peaks in the low frequency band through the synergistic effect of multiple Helmholtz resonator units connected in series and gradient helical tubes. At the same time, the multiple Helmholtz resonator units are arranged in the internal space of the helical tube, and the overall thickness is much smaller than the corresponding sound wave wavelength, which has deep subwavelength characteristics and makes the structure compact and space utilization high.

[0016] 2. The gradient helical tube, extension tube, and multiple Helmholtz resonator units are manufactured in one piece from metal or engineering plastic, adaptable to a variety of engineering environments, and have good scalability and customizability.

[0017] 3. The adjustment method provided by this invention is based on the transfer matrix method, which can accurately predict sound absorption performance, support rapid parameter optimization, reduce design trial and error costs, and make the design method clear and controllable. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0019] Figure 1 A schematic diagram of the gradient helical tube composite Helmholtz resonator sound absorption device of Embodiment 1 or Embodiment 2 of the present invention is shown.

[0020] Figure 2 A schematic diagram of the gradient helical tube of Embodiment 1 or Embodiment 2 of the present invention is shown.

[0021] Figure 3 A schematic diagram of the extension tube of Embodiment 1 or Embodiment 2 of the present invention is shown.

[0022] Figure 4 A schematic diagram of the structure of multiple Helmholtz resonator units according to Embodiment 1 or Embodiment 2 of the present invention is shown.

[0023] Figure 5 A curve comparison diagram showing the effect of the number of units of the Helmholtz resonator in Embodiment 2 of the present invention on the sound absorption performance is shown, along with a magnified view of a portion of the gray area.

[0024] Figure 6 A curve comparison of the effect of different cavity diameters on the sound absorption performance of the Helmholtz resonator of Embodiment 2 of the present invention is shown, along with a magnified view of a portion of the gray area.

[0025] Figure 7 A curve comparison diagram showing the effect of different cavity lengths on the sound absorption performance of the Helmholtz resonator of Embodiment 2 of the present invention is shown, along with a magnified view of a portion of the gray area.

[0026] Figure 8 A curve comparison of the effect of different neck lengths on the sound absorption performance of the Helmholtz resonator of Embodiment 2 of the present invention is shown, along with a magnified view of a portion of the gray area.

[0027] Figure labeling: 1-gradient helical tube; 2-extension tube; 3-multiple Helmholtz resonator units. Detailed Implementation

[0028] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1 like Figures 1 to 4 As shown, the gradient helical tube composite multi-Helmholtz resonator sound absorption device (hereinafter referred to as the sound absorption device) provided by the embodiment of the present invention includes a gradient helical tube 1 and multiple Helmholtz resonator units 3, wherein the multiple Helmholtz resonator units 3 are connected in series at the end of the gradient helical tube 1 and arranged in the internal space enclosed by the gradient helical tube 1. The arrangement of multiple Helmholtz resonator units 3 in the internal space enclosed by the gradient helical tube 1 greatly improves the structural compactness and space utilization. In addition, the overall thickness of the multiple Helmholtz resonator units 3 arranged in the internal space enclosed by the gradient helical tube 1 is much smaller than the corresponding sound wave wavelength, possessing deep subwavelength characteristics, and realizing efficient sound absorption at the deep subwavelength scale. The gradient helical tube 1 and the multiple Helmholtz resonator units 3 are connected by an extension tube 2 (the length after unfolding is...). L e )connect.

[0031] The gradient helical tube 1 spirals upwards axially (around its central axis), forming a three-dimensional acoustic channel. The tube diameter changes continuously along the sound wave propagation path. Preferably, the diameter of the gradient helical tube 1 decreases continuously along the sound wave propagation path. The overall height of the gradient helical tube 1 is... H The diameter of the spiral is L The pitch is P The inlet orifice diameter of gradient helical tube 1 is... The end aperture is This forms a gradually changing acoustic impedance structure. The gradient helical tube 1 achieves continuous acoustic impedance variation through a gradually changing aperture, reducing reflection and enhancing sound energy entry. The aperture variation of the gradient helical tube 1 follows a preset function. As a preferred embodiment, the aperture variation of the gradient helical tube 1 adopts a linear variation law:

[0032] In the formula: The total length of the gradient spiral tube 1 after unfolding (including the length of the extension tube 2). h This refers to a certain position after the gradient helical tube has been unfolded. ; ; After the gradient helical tube is unfolded The aperture at that location.

[0033] Multiple Helmholtz resonator units 3 are connected in series at the end of the gradient helical tube 1, forming a multi-stage resonance system. The multiple Helmholtz resonator units 3 excite resonance peaks of different frequencies in the low-frequency range, forming a continuous sound-absorbing band. Through the sequential series connection of multiple Helmholtz resonator units 3 and their synergistic effect with the gradient helical tube 1, multiple high-absorption resonance peaks are formed in the low-frequency range, achieving wideband coverage. Each Helmholtz resonator unit includes a neck and a cavity, with the neck placed within the cavity. The geometric parameters of the neck and cavity can be specifically designed to achieve resonance responses at different frequencies. The cavity length is... L cavity The cavity diameter is d cavity The length of the neck is... L neck The diameter of the neck is d neck In a preferred embodiment, four Helmholtz resonator units are provided, with their neck diameters decreasing in a gradient (…). This is to achieve wideband impedance matching and thus superior sound absorption performance. As a preferred structural connection method, the neck diameter of the first Helmholtz resonator unit (connected to extension tube 2) is... Set to the end orifice diameter of gradient helical tube 1 Equal impedance is achieved to ensure a smooth transition of acoustic impedance, reduce sound wave reflection loss at the interface, and facilitate integrated manufacturing and compact structural design; while for other parameters ( L cavity , d cavity , L neck Each Helmholtz resonator unit is configured to be identical.

[0034] This invention integrates multiple tunable Helmholtz resonator units 3 with a gradient helical tube 1 exhibiting a phase delay effect, forming a multi-coupled sound absorption mechanism that provides stronger low-frequency control and a wider sound absorption bandwidth. In this embodiment, the gradient helical tube 1, the extension tube 2, and the multiple Helmholtz resonator units 3 can be integrally manufactured from metal or engineering plastics, adaptable to various engineering environments, and possessing good scalability and customizability.

[0035] Example 2 This invention also provides an adjustment method for a gradient helical tube composite multi-Helmholtz resonator sound absorption device, utilizing the gradient helical tube composite multi-Helmholtz resonator sound absorption device in Example 1. This embodiment employs the transfer matrix method, discretizing the gradient helical tube 1 into several straight tube segments with gradually varying cross-sectional areas. Each Helmholtz resonator unit is considered as a series connection between the neck and the cavity. Finally, the total transfer matrix is ​​obtained through matrix multiplication, and the sound absorption coefficient is calculated. This method can efficiently predict structural performance and supports parameter optimization. The adjustment method includes the following steps: S1. Establish the gradient helical tube model and the multi-Helmholtz resonator model.

[0036] Gradient helical tube model: Discretize gradient helical tube 1 along the helical expansion direction as follows: Straight pipe sections with gradually changing cross-sectional areas. The transfer matrix for each layer is: ; In the formula: The complex wave number (considering damping) is given. , Angular frequency, Speed ​​of sound in air; The imaginary unit; The length of each micro-segment of straight pipe after discretization. , This represents the total length of the spiral tube; It depends on the local cross-sectional area acoustic impedance, For air resistance, air density, , After spiral unfolding The model describes both the acoustic phase delay (specifically reflected in the trigonometric function terms) and the distributed viscous loss (specifically reflected in the complex wave terms).

[0037] Multi-Helmholtz resonator model: Each Helmholtz resonator unit includes a neck and a cavity, and its transfer matrix is: ; In the formula: and These are the transfer matrices for the neck and cavity, respectively; and These are the correction matrices.

[0038] and They are represented as follows: , ; In the formula: and These represent the neck length and cavity length of the Helmholtz resonator unit, respectively. and These represent the complex wavenumbers of the neck and cavity, respectively; and These represent the neck impedance and cavity impedance of the Helmholtz resonator unit, respectively. and They are respectively: , ; In the formula: Neck radius , d neck,i For the first i The neck diameter of a Helmholtz resonator unit; cavity radius ; and These represent the cross-sectional area of ​​the neck and the cross-sectional area of ​​the cavity, respectively. This refers to the Prandtl number at standard atmospheric pressure. The specific heat capacity ratio of air; It is the kinematic viscosity of air.

[0039] and They are respectively: , In the formula, This indicates the characteristic thickness of the acoustic boundary layer.

[0040] and They are respectively:

[0041] ; In the formula: and These are the correction lengths, ; In the formula, and The neck radius of each Helmholtz resonator unit is respectively. and cavity radius ; The transition radius at the junction of the neck and the cavity is given in this model. .

[0042] S2, the overall transfer matrix.

[0043] The acoustic model in this embodiment is constructed based on the transfer matrix method (TMM), which decomposes a complex composite structure into a series of cascaded basic acoustic units and describes the propagation of sound waves throughout the structure through matrix multiplication.

[0044] The total transfer matrix of the system is obtained based on the actual layout of the structure. For example, consider a gradient helical tube structure composed of four Helmholtz resonator units: ; In the formula: This is the total transfer matrix of the gradient solenoid; The total transfer matrix is ​​for a cascaded structure of four Helmholtz resonator units.

[0045] S3. Calculate acoustic performance.

[0046] Calculate surface acoustic impedance from the total transfer matrix Reflection coefficient and sound absorption coefficient : , , ; In the formula: The area of ​​the incident surface of the sound wave in this composite model; The first element of the first row and first column of the total transfer matrix; This is the element in the second row and first column of the total transfer matrix.

[0047] S4. Verification and Optimization Design.

[0048] The sound absorption coefficient curve is calculated using the above model to verify its sound absorption performance. If the expected results are not achieved, the structural parameters (neck diameter, neck length, cavity diameter, cavity length) of multiple Helmholtz resonator units 3 or the geometric parameters (aperture, pitch, helix diameter, and height) of the gradient helical tube 1 are adjusted, and steps S1 to S3 are repeated until the optimal design is obtained. The specific parameter adjustment methods can be optimized in conjunction with the specific case analysis later.

[0049] The debugging method in this embodiment not only provides more powerful low-frequency control capabilities and a wider sound absorption bandwidth, but also, through a clear mathematical model and design steps, transforms the design process of high-performance sound absorbers from "trial and error based on experience" to "precise and predictable", greatly improving design efficiency and success rate.

[0050] To further understand the content of this invention, the following explanation focuses on the influence of the number of elements in a Helmholtz resonator and the structural geometric parameters of the Helmholtz resonator on its sound absorption performance.

[0051] (I) The effect of the number of elements in a Helmholtz resonator on its sound absorption performance To verify and demonstrate the synergistic effect of the series design of multiple Helmholtz resonator units 3 on improving low-frequency sound absorption performance, this embodiment, while keeping the main structure of the gradient helical tube 1 unchanged, clearly demonstrates the performance advantages brought about by increasing the number of Helmholtz resonator units by comparing the sound absorption coefficients of composite structures with 1, 2, 3, and 4 series Helmholtz resonator units.

[0052] The structural parameters of the gradient helical tube composite multi-Helmholtz resonator are shown in Table 1. Figure 5 The number of elements in a Helmholtz resonator is shown (using...). (This indicates the influence of the value from 1 to 4 on the sound absorption performance of the structure.)

[0053] Table 1. Structural parameters of the gradient helical tube composite Helmholtz resonator

[0054] like Figure 5 As shown, while keeping the structure of the gradient helical tube 1 unchanged, the sound absorption performance can be adjusted by changing the number of units in the series-connected Helmholtz resonators. The research results indicate that: When the number of elements in the Helmholtz resonator increases from 1 to 4, the low-frequency sound absorption performance of the structure below 600 Hz is significantly improved. The first peak absorption frequency decreased from 171 Hz to 81 Hz, and the peak absorption coefficient increased from 0.6 to 0.85; Multiple Helmholtz resonator units 3 form a synergistic resonance effect, which connects multiple discrete resonance peaks to form a continuous broadband sound absorption band.

[0055] Therefore, the number of units in the Helmholtz resonator in this invention can be flexibly configured according to the actual low-frequency sound absorption requirements. The more units there are, the wider the low-frequency sound absorption bandwidth and the better the sound absorption effect.

[0056] (II) The Influence of Structural Geometric Parameters of Helmholtz Resonators on Sound Absorption Performance To delve into the mechanisms of action of various parameters within the structure of multiple Helmholtz resonator units 3 and achieve precise acoustic tuning, this embodiment uses a fixed gradient helical tube 1 structure (overall height) H 50mm, pitch P 10mm, spiral diameter LUnder the premise of 40mm, taking a composite structure of 4 Helmholtz resonator units as an example, the system changes various parameters of the structure of multiple Helmholtz resonator units (cavity diameter) d cavity Cavity length L cavity Neck length L neck This study investigated the influence of various parameters on the sound absorption curves. Using the controlled variable method, only one parameter of the structure of multiple Helmholtz resonator units was changed each time, and its independent effect on the sound absorption curves was observed. The changes in each parameter are shown in Table 2; the corresponding sound absorption curves for each parameter change are shown in the figure below. Figures 6 to 8 As shown.

[0057] Table 2. Detailed list of structural parameter variations for multiple Helmholtz resonator units.

[0058] The key geometric parameters of multiple Helmholtz resonator unit structures include cavity diameter, cavity length, and neck length. The influence of each parameter on sound absorption performance is as follows: (1) Adjustment of cavity diameter When the cavity diameter increases from 16 mm to 24 mm, the sound absorption curve shifts overall towards the low-frequency region, and the low-frequency sound absorption capability is enhanced. The cavity diameter mainly adjusts the acoustic compliance of the system by changing the cavity volume, thereby affecting the position of the resonant frequency.

[0059] (2) Adjustment of cavity length When the cavity length increases from 12 mm to 16 mm, the sound absorption curve also shows a trend towards lower frequencies, consistent with the effect of adjusting the cavity diameter. The cavity length and cavity diameter together determine the cavity volume and are key parameters for adjusting the resonant frequency.

[0060] (3) Regulation of neck length When the neck length increases from 6 mm to 10 mm, the acoustic quality of the system increases, the resonant frequency shifts to the lower frequency direction, and the low-frequency sound absorption performance is significantly improved.

[0061] The above parameters mainly affect the low-frequency sound absorption characteristics below 800 Hz, while having a smaller impact on the sound absorption performance in the mid-to-high frequency range. This indicates that the gradient helical tube 1 is mainly responsible for mid-to-high frequency sound absorption, while multiple Helmholtz resonator units 3 are specifically designed for precise control of low-frequency noise.

[0062] In practical design, the cavity diameter, cavity length, and neck length can be adjusted in a coordinated manner to achieve precise control over low-frequency sound absorption performance. For example, to achieve a lower resonant frequency, a combination of a larger cavity diameter and a longer neck length can be used; if space is limited, the design goal can be achieved by appropriately increasing the neck length or decreasing the cavity size. The multi-parameter adjustable design provided by this invention offers a flexible technical path for achieving compact low-frequency broadband sound absorption in different application scenarios.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for adjusting a gradient helical tube composite Helmholtz resonator sound-absorbing device, characterized in that, The gradient helical tube composite Helmholtz resonator sound absorption device includes a gradient helical tube and multiple Helmholtz resonator units. The diameter of the gradient helical tube changes continuously along the sound wave propagation path. The multiple Helmholtz resonator units are connected in series at the ends of the gradient helical tube and are arranged in the internal space enclosed by the gradient helical tube. The adjustment method of the gradient helical tube composite Helmholtz resonator sound absorption device includes the following steps: S1. Establish the gradient helical tube model and the multi-Helmholtz resonator model: Gradient helical tube model: Discretize the gradient helical tube along the direction of helical expansion as follows: For a straight pipe section with gradually changing cross-sectional area, the transfer matrix for each layer is: ； In the formula: For complex wave number, , Angular frequency, , Speed ​​of sound in air; The imaginary unit; The length of each micro-segment of straight pipe after discretization. , The total length of the gradient spiral tube after it is unfolded, including the extension tube; For dependent on local cross-sectional area acoustic impedance, , For air resistance, , air density, , After the gradient helical tube is unfolded The aperture at that location; Multi-Helmholtz resonator model: Each Helmholtz resonator unit includes a neck and a cavity, and the transfer matrix is: ； In the formula: For the neck transfer matrix, Let be the transfer matrix of the cavity. and These are the correction matrices; and They are respectively: ， ； In the formula, and These are the correction lengths, and These represent the neck impedance and cavity impedance of a Helmholtz resonator element, respectively. and They are respectively: ， ； In the formula: and The neck radius of each Helmholtz resonator unit is respectively. and cavity radius ; The transition radius at the junction of the neck and the cavity is given in the model. ; S2, Overall Transfer Matrix: ； In the formula: This is the total transfer matrix of the gradient helical tube; for N HR The total transfer matrix of a series structure of Helmholtz resonator units; S3. Calculate acoustic performance, specifically the surface acoustic impedance from the total transfer matrix. Reflection coefficient and sound absorption coefficient : ， ， ； In the formula: For the incident surface area of ​​the sound wave in the composite model, The inlet diameter of the gradient helical tube; The first element of the first row and first column of the total transfer matrix; The element in the second row and first column of the total transfer matrix; S4. Verify and optimize the design, calculate the sound absorption coefficient curve, and verify the sound absorption performance. If the expected results are not achieved, return to adjust the structural parameters of multiple Helmholtz resonator units and / or the geometric parameters of the gradient helical tube, and repeat steps S1 to S3 until the sound absorption coefficient curve reaches the expected results.

2. The adjustment method of the gradient helical tube composite multi-Helmholtz resonator sound absorption device according to claim 1, characterized in that, The plurality of Helmholtz resonator units are connected in series, each Helmholtz resonator unit including a neck and a cavity, with the neck placed inside the cavity; the neck diameters of the plurality of Helmholtz resonator units decrease in a gradient, and the neck diameter of the first Helmholtz resonator unit connected in series with the gradient helical tube is equal to the end aperture of the gradient helical tube.

3. The adjustment method of the gradient helical tube composite Helmholtz resonator sound absorption device according to claim 1, characterized in that, The gradient helical tube is connected to multiple Helmholtz resonator units via extension tubes.

4. The adjustment method of the gradient helical tube composite multi-Helmholtz resonator sound absorption device according to claim 3, characterized in that, The aperture of the gradient helical tube varies linearly. ； In the formula: The total length of the gradient spiral tube after it has been unfolded, including the extension tube. h This refers to a certain position after the gradient helical tube has been unfolded. ; , H The overall height of the gradient helical tube is [missing information]. L The diameter of the helix. P For pitch, L e The length of the extended tube after it has been unfolded; The inlet diameter of the gradient helical tube is [missing information]. The end aperture, After the gradient helical tube is unfolded The aperture at that location.

5. The adjustment method of the gradient spiral tube composite multi-Helmholtz resonator sound absorption device according to claim 3, characterized in that, The gradient helical tube, extension tube, and multiple Helmholtz resonator units are integrally made of metal or engineering plastic.

6. The adjustment method of the gradient helical tube composite Helmholtz resonator sound absorption device according to any one of claims 1 to 5, characterized in that, In step S1, the transfer matrix of the neck Transfer matrix of cavity They are respectively: ， ； In the formula: and These represent the neck length and cavity length of a Helmholtz resonator element, respectively. and These are the complex wave numbers for the neck and cavity, respectively.

7. The adjustment method of the gradient helical tube composite multi-Helmholtz resonator sound absorption device according to claim 6, characterized in that, Neck resistance and cavity impedance They are respectively: ， ； Where: neck radius , d neck,i For the first i Neck diameter of each Helmholtz resonator unit; cavity radius , d cavity The diameter of the cavity; and These are the cross-sectional areas of the neck and the cavity, respectively. This refers to the Prandtl number at standard atmospheric pressure. The specific heat capacity ratio of air; The viscosity is the kinematic viscosity of air.

8. The adjustment method of the gradient helical tube composite Helmholtz resonator sound absorption device according to claim 7, characterized in that, Complex wave number of the neck and the complex wave number of the cavity They are respectively: ， ； In the formula: This indicates the characteristic thickness of the acoustic boundary layer.

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