A frequency-adjustable modular low-frequency noise reduction structure

Abstract

This application discloses a frequency-adjustable modular low-frequency noise reduction structure in the field of environmental engineering technology, comprising several sound-absorbing units. Each sound-absorbing unit consists of a top plate, a hollow spiral pipe, a shell, and a bottom plate. The shell has a receiving cavity, which has a top plate and a bottom plate spaced apart vertically. The top plate has a through hole at its center, parallel to the bottom plate. A locking device is provided on the lower surface of the shell, and the bottom plate is assembled to the shell through the locking device. The hollow spiral pipe has a spiral structure and is located inside the receiving cavity of the shell, with a horizontal outlet communicating with the receiving cavity. The hollow spiral pipe is glued to the top plate, aligned with the center of the through hole in the top plate. This invention features modular assembly, convenient disassembly and assembly, and achieves frequency-adjustable sound absorption and noise reduction by replacing the bottom plate.

Description

Technical Field

[0001] This application relates to the field of environmental engineering technology, and in particular to a frequency-adjustable modular low-frequency noise reduction structure. Background Technology

[0002] Prolonged exposure to noisy environments can damage hearing, the cardiovascular system, the nervous system, and vision, interfering with normal life, work, and study, and potentially leading to various accidents. Therefore, a better solution to suppress and eliminate noise is urgently needed.

[0003] To address the problems encountered in traditional noise control engineering, several sound-absorbing structures have been proposed, such as porous material sound-absorbing structures, resonant sound-absorbing structures, and micro-perforated plate sound-absorbing structures. Porous material sound-absorbing structures include sound-absorbing plate structures, spatial sound absorbers, and sound-absorbing wedges; however, they only have good sound absorption effects on mid- and high-frequency noise, while low-frequency noise is difficult to absorb through sound-absorbing materials. Sound-absorbing structures that introduce resonant characteristics, due to their narrow bandwidth, only have a good sound absorption coefficient within the resonant frequency and a certain adjacent bandwidth, and this coefficient cannot be adjusted.

[0004] Application No. 202310302782.3 discloses an underwater sound-absorbing superstructure based on Helmholtz resonators, which occupies a large volume. Although it can achieve efficient broadband sound absorption through coupling, it sacrifices the overall thickness of the structure. At the same time, the entire structure cannot be disassembled, and its noise reduction effect will be greatly reduced once the frequency band to be denoised shifts. ZL201911036388 discloses a Helmholtz resonator and a low-frequency broadband sound absorption and noise reduction structure based on it, which combines multiple sound-absorbing units into a large sound-absorbing structure, which can achieve efficient low-frequency sound absorption. However, when the frequency band to be denoised shifts, it is not convenient to adjust the length and cross-sectional area of ​​the internal embedded tube to change the effective frequency band of the sound-absorbing structure.

[0005] To address the narrow operating bandwidth of sound-absorbing structures, existing solutions primarily involve arraying multiple sound-absorbing units to broaden the bandwidth. This is achieved by coupling multiple resonant systems with different resonant frequencies, thus reaching a wider operating bandwidth. This coupling method is direct and effective. However, with existing modular structures, once the structural parameters are fixed, the effective bandwidth is also determined. The inability to easily adjust structural parameters to change the effective bandwidth results in low reusability of the structure.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the overall background of this application and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this application is to provide a frequency-adjustable modular low-frequency noise reduction structure, which is modularly assembled and easy to disassemble and reassemble. By replacing the base plate, the frequency-adjustable sound absorption and noise reduction effect can be achieved.

[0008] To achieve the above objectives, this application employs the following technical solution:

[0009] This application provides a frequency-adjustable modular low-frequency noise reduction structure, including several sound-absorbing units, wherein the sound-absorbing unit is composed of a top plate, a hollow spiral pipe, a shell and a bottom plate;

[0010] The housing has a receiving cavity, which has a top plate and a bottom plate spaced apart in a vertical direction; the top plate has a through hole at its center, parallel to the bottom plate; the bottom surface of the housing is designed with an interlocking device, and the bottom plate is assembled with the housing through the interlocking device;

[0011] The hollow spiral pipe has a spiral structure and is located inside the receiving cavity of the shell, with its horizontal outlet connected to the receiving cavity; the hollow spiral pipe is glued to the top plate and aligned with the center of the perforation in the top plate.

[0012] In some embodiments, the outer diameter of the housing is less than or equal to the outer diameter of the top plate, and the difference between the inner and outer diameters of the housing ranges from 3 to 10 mm. The housing has a certain thickness to facilitate the provision of interlocking devices and screw holes on the cut surface for sealing and fastening.

[0013] In some embodiments, the shell wall is solid and connected to the top plate via an upper annular boundary, and the height of the shell is greater than the height of the hollow spiral duct. Even if the height of the hollow spiral duct is changed to adjust the acoustic impedance ratio, the thickness of the sound-absorbing unit will not increase.

[0014] In some embodiments, the bottom surface of the housing has four screw mounting holes spaced at 90-degree intervals, and annular grooves of a certain width and depth are provided between adjacent mounting holes. The base plate has four screws spaced at 90-degree intervals, and protruding annular grooves corresponding to the width and depth. This ensures a secure engagement between the two, guarantees airtightness, and allows for repeated disassembly; the screws achieve a reliable connection between the housing and the base plate. Through easy disassembly, materials of different thicknesses or rigidities can be used as the base plate for the frequency band requiring noise reduction.

[0015] In some embodiments, the neck length of the hollow spiral pipe, the input end radius a1, and the output end radius a1 of the hollow spiral pipe are... f Proportional to the structure. The hollow spiral pipe is housed inside the shell, making it less susceptible to damage from external interference, thus ensuring safety. The hollow spiral pipe extends the neck length without increasing the overall structural thickness, resulting in a low acoustic resonance frequency for this noise reduction structure.

[0016] In some embodiments, the outer diameter of the top plate is larger than the size of the hollow spiral pipe; the radius of the central perforation of the top plate is equal to the radius of the top plate.

[0017] In some embodiments, the base plate is made of PLA or spring steel.

[0018] In some embodiments, the base plate is made of PLA with a thickness ranging from 0.3mm to 2mm; the base plate is made of spring steel with a thickness ranging from 0.1mm to 0.4mm. In the actual manufacturing process of PLA, dimensions smaller than 0.3mm are difficult to process, and excessively thin materials are prone to damage; when the dimension is greater than 2mm, the sound absorption frequency band is almost identical to that produced by 2mm, but manufacturing costs are increased.

[0019] In some embodiments, the resonant frequency of the sound-absorbing unit is calculated using the following formula:

[0020]

[0021] Among them, M a R represents the acoustic quality formed by the hollow spiral duct. a Acoustic impedance, primarily representing the loss of sound energy, C couple The acoustic capacitance is formed by the coupling system created by the sealing of the shell (3) and the base plate (4).

[0022] In some embodiments, the sound absorption coefficient of the sound-absorbing unit is calculated as follows:

[0023] Z s =Z a S, where Z a For acoustic impedance, Z s Where is the acoustic impedance, and S is the cross-sectional area of ​​the incident surface of the sound-absorbing unit;

[0024] Relative acoustic impedance ratio Where ρ0 is the air density and c0 is the speed of sound;

[0025] Acoustic impedance Z a It has a real part and an imaginary part, represented by R. a X represents the real part. a Indicates the imaginary part.

[0026] Relative acoustic impedance ratio

[0027] Acoustic impedance ratio Acoustic impedance ratio

[0028] sound absorption coefficient

[0029] Compared with the prior art, the beneficial effects achieved by this disclosure are as follows:

[0030] 1. Through easy disassembly, materials with different thicknesses or stiffnesses can be replaced as the base plate for the frequency band requiring noise reduction, thereby changing the resonant frequency of the sound-absorbing unit; by modularizing multiple sound-absorbing units with different resonant frequencies, arrayed small-scale devices can be realized to absorb sound and reduce noise.

[0031] 2. By introducing an embedded spiral pipe, the size of the sound-absorbing unit is reduced, effectively solving the space occupation problem and reducing the volume of the sound-absorbing unit. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the sound-absorbing unit of the present invention;

[0034] Figure 2 This is an exploded view of the sound-absorbing unit of the present invention;

[0035] Figure 3 This is a schematic diagram of the housing portion of the present invention;

[0036] Figure 4 This is a schematic diagram of an embodiment of the present invention applied to a ventilation pipeline;

[0037] Figure 5 This is an acoustic-electric analogy diagram of the sound-absorbing unit of the present invention;

[0038] Figure 6 This is a flowchart of the finite element simulation analysis process of this invention;

[0039] Figure 7 This invention relates to a diagram showing how changing the neck length of a hollow spiral pipe adjusts the acoustic impedance ratio.

[0040] Figure 8 This invention relates to a diagram showing how changing the neck length of a hollow spiral pipe adjusts the sound absorption coefficient.

[0041] Figure 9 This invention relates to a diagram showing how the acoustic impedance ratio can be adjusted by changing the height of a hollow spiral pipe.

[0042] Figure 10 This invention relates to a diagram showing how the sound absorption coefficient can be adjusted by changing the height of the hollow spiral pipe.

[0043] Figure 11This invention relates to a diagram showing how the acoustic impedance ratio is adjusted by changing the shell height.

[0044] Figure 12 This invention relates to a diagram showing how the sound absorption coefficient can be adjusted by changing the shell height.

[0045] Figure 13 This invention relates to a diagram showing how the acoustic impedance ratio is adjusted by changing the thickness of the base plate.

[0046] Figure 14 This invention relates to a diagram showing how changing the thickness of the base plate adjusts the sound absorption coefficient.

[0047] Figure 15 This invention relates to a diagram showing the adjustment of acoustic impedance ratio by changing the damping of the base plate material.

[0048] Figure 16 This invention relates to a diagram showing the sound absorption coefficient adjustment achieved by changing the damping of the base plate material.

[0049] Figure 17 This is the low-frequency noise reduction transfer rate diagram of the present invention;

[0050] Figure 18 This is a transfer rate diagram for low-frequency noise reduction in the frequency band of 100Hz-160Hz, as described in this invention.

[0051] Figure 19 This is a plan view of the spiral pipe of the present invention.

[0052] Explanation of reference numerals in the attached figures:

[0053] 1-Top plate; 2-Hollow spiral pipe; 3-Shell; 4-Bottom plate. Detailed Implementation

[0054] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this disclosure or its application or use.

[0055] Example:

[0056] This embodiment provides a frequency-adjustable modular low-frequency noise reduction structure, including several sound-absorbing units. A schematic diagram of the overall structure of the sound-absorbing units is shown below. Figure 1 As shown, the structural decomposition diagram is as follows: Figure 2 As shown, the sound-absorbing unit consists of a top plate 1, a hollow spiral pipe 2, a shell 3, and a bottom plate 4;

[0057] The housing 3 has a receiving cavity, which has a top plate 1 and a bottom plate 4 spaced apart in a vertical direction; the top plate 1 has a through hole in the center, parallel to the bottom plate 4; the bottom surface of the housing 3 is designed with an interlocking device, and the bottom plate 4 is assembled with the housing 3 through the interlocking device;

[0058] The hollow spiral pipe 2 has a spiral structure and is located in the receiving cavity of the shell, with its horizontal outlet connected to the receiving cavity; the hollow spiral pipe 2 is glued to the top plate 1 and aligned with the center of the perforation of the top plate 1.

[0059] In one specific embodiment of the present invention, the outer diameter of the shell 3 is less than or equal to the outer diameter of the top plate 1, and the difference between the inner and outer diameters of the shell 3 is in the range of 3-10mm.

[0060] The shell 3 has a solid wall and is connected to the top plate 1 through an upper annular boundary. The height of the shell 3 is greater than the height of the hollow spiral pipe 2.

[0061] like Figure 3 As shown, the bottom surface of the housing 3 is provided with four screw mounting holes at 90-degree intervals, and a circular groove with a certain width and depth is provided between adjacent mounting holes. The base plate 4 is provided with four screws at 90-degree intervals, and a protruding circular ring corresponding to the width and depth.

[0062] In one specific embodiment of the present invention, the neck length of the hollow spiral pipe 2, the input end radius a1, and the output end radius a of the hollow spiral pipe 2 are... f The sound waves are directly proportional to the volume of the hollow spiral pipe 2. Located inside the housing 3, the hollow spiral pipe 2 is less susceptible to damage from external interference, ensuring safety. The hollow spiral pipe 2 features a spiral neck, extending its length without increasing the overall structural thickness, thus lowering the resonant frequency of the corresponding sound-absorbing unit. Sound waves enter through the perforations in the top plate 1, reach the hollow opening on the upper surface of the hollow spiral pipe 2, and then enter the receiving cavity formed by the housing 3 and the bottom plate 4 from the horizontal outlet of the hollow spiral pipe 2.

[0063] In one specific embodiment of the present invention, the outer diameter of the top plate 1 is larger than the size of the hollow spiral pipe 2; the radius of the central perforation of the top plate 1 is the radius of the top plate 1.

[0064] The base plate 4 is made of PLA or spring steel.

[0065] The base plate 4 is made of PLA with a thickness ranging from 0.3mm to 2mm; the base plate 4 is also made of spring steel with a thickness ranging from 0.1mm to 0.4mm. In the actual manufacturing process of PLA, dimensions smaller than 0.3mm are difficult to process, and too low a thickness leads to easy damage; when the dimension is greater than 2mm, the sound absorption frequency band is almost the same as that produced by 2mm, but the manufacturing cost will increase.

[0066] In one specific embodiment of the present invention, the approximate formula for calculating the resonant frequency of the sound-absorbing unit is as follows:

[0067]

[0068] Among them, M a R represents the acoustic mass formed by the hollow spiral pipe 2. a For acoustic impedance, C couple The acoustic capacitance is formed by the coupling system created by the sealing of the shell 3 and the base plate 4.

[0069] The acoustic-electric analogy is a theoretical method that connects acoustic vibration theory and circuit theory. Although circuits and sound vibrations belong to different fields, a careful study of their laws reveals that they share the same form of differential equations. Therefore, acoustic vibration systems can be analogized to circuit diagrams. Through this analogy, methods and tools from circuit theory can be used to analyze and understand the behavior of acoustic vibration systems. This analogy method is widely used in acoustics and electronic engineering, helping us to better understand and design acoustic systems.

[0070] The sound-absorbing unit in this invention is a basic acoustic vibration system. When the base plate is a hard surface, such as... Figure 5 The diagram shown is an acoustic-electric analogy of the sound-absorbing unit. There is an analogy between the acoustic vibration system and the circuit system. The air mass in the hollow spiral pipe 2, as the inertial term, can be compared to the inductance in the circuit, denoted as M. a Acoustic impedance primarily represents the ability of a structure to transmit sound wave energy, analogous to resistance in a circuit, and is denoted as R. a The air inside the cavity formed by the shell 3 and the base plate 4 is analogous to a capacitor in a circuit, denoted as C. a .

[0071] When the thickness of the base plate 4 connected to the shell 3 decreases, acoustically it can be considered as changing from a rigid boundary to a flexible boundary. The resulting additional acoustic volume is approximately... This generates acoustic-vibration coupling. Here, 'a' is the radius of the circular base plate 4, and 'D' is the bending stiffness of the base plate 4, which is affected by the thickness and material properties of the base plate 4. The total acoustic volume of this coupling system can be approximated as C. couple =C a +C addedWhen acoustic impedance is neglected, the resonant frequency of the device is approximately: Therefore, by changing the thickness of the base plate 4, the resonant frequency of the device can be adjusted, thereby affecting its sound absorption performance.

[0072] The acoustic-electric analogy method employs the lumped parameter method, thus limiting the frequency to low frequencies. In actual product design, the precise resonant frequency and sound absorption performance can be obtained through finite element numerical calculations.

[0073] In one specific embodiment of the present invention, the calculation process of the sound absorption coefficient of the sound-absorbing unit is as follows:

[0074] Z s =Z a S, where Z a For acoustic impedance, Z s Where is the acoustic impedance, and S is the cross-sectional area of ​​the incident surface of the sound-absorbing unit;

[0075] Relative acoustic impedance ratio Where ρ0 is the air density and c0 is the speed of sound;

[0076] Acoustic impedance Z a It has a real part and an imaginary part, represented by R. a X represents the real part. a Indicates the imaginary part.

[0077] Relative acoustic impedance ratio

[0078] Acoustic impedance ratio Acoustic impedance ratio

[0079] sound absorption coefficient

[0080] When the sound-absorbing unit resonates, X = 0. At this time, if R = 1, the sound absorption coefficient is α = 1, meaning the sound-absorbing unit achieves perfect sound absorption. Therefore, when observing the acoustic impedance ratio curve, first find the frequency corresponding to the acoustic impedance ratio X being 0. If the acoustic impedance ratio R corresponding to this frequency is closer to 1, the sound absorption effect is better. When the R value is equal to 1, perfect sound absorption is achieved, meaning that the incident sound energy is 100% dissipated.

[0081] To study the sound absorption performance of the designed sound-absorbing unit, numerical simulation was performed using finite element simulation software. For example... Figure 6 The diagram shows the specific flowchart for analyzing its sound absorption performance using finite element simulation software. The relevant steps are described below.

[0082] First, a model is established. Top plate 1, shell 3, and bottom plate 4 can all use cylinders as basic voxels. Parameter L0 is defined for the parametric sweep of the height of shell 3; parameter t1 is defined for the parametric sweep of the thickness variation of bottom plate 4; damping is defined to represent the damping coefficient of bottom plate 4; the neck length of the hollow helical pipe 2 is set to be the same as the radius of the input end circle a1 and the radius of the output end circle a... f It is proportional to the distance, and the parameter distance is defined.

[0083] To establish the geometric model of the helical pipe, the initial angle is represented by theta_0, which is fixed at 0. The termination angle is represented by theta_f, where theta_f = 2n1.

[0084] in, The number of turns in the helical pipe is determined. A larger n1 results in a longer effective length of the helical pipe. A larger distance results in a shorter neck length for the hollow helical pipe 2. Therefore, the neck length of the hollow helical pipe 2 is adjusted by modifying the value of distance; a parameter h2 is defined to parameterize the height of the hollow helical pipe 2 during scanning.

[0085] Next, the material properties are defined. The materials of the top plate 1, hollow spiral pipe 2, shell 3 and bottom plate 4 are set to polylactic acid (PLA), which is a commonly used material in 3D printing and has good mechanical strength. The fluid inside the central hole of the top plate 1, the spiral pipe 2 and the hollow sound-absorbing cavity inside the shell are defined as air. The specific parameters of the materials are shown in Table 1.

[0086]

[0087]

[0088] Table 1

[0089] After setting the material properties, add the corresponding physical fields and boundary conditions. Here, three physical fields are used: pressure acoustics, thermoviscous acoustics, and solid mechanics.

[0090] After completing the mesh generation, the corresponding studies are added. This simulation example mainly studies the sound absorption performance of the sound-absorbing unit under frequency domain conditions, so the study conditions are selected as frequency domain, with a frequency range of 20-200Hz and a frequency step of 1Hz. Parametric scans can be added to the study, which can be used to explore the influence of parameter changes on sound absorption performance and acoustic impedance.

[0091] When investigating the effect of the neck length of the hollow spiral pipe 2 on the sound absorption performance and acoustic impedance, different distances were scanned because the distance affects the neck length of the hollow spiral pipe 2. Figure 7The figure shows the acoustic impedance curve. The greater the distance, the shorter the neck length of the hollow spiral pipe 2, and the shorter the acoustic channel inside, the smaller the corresponding acoustic impedance. Figure 8 The diagram shows the sound absorption curve. As the distance increases, the neck length of the hollow spiral pipe 2 becomes shorter, the peak frequency of sound absorption gradually increases, and the peak value of sound absorption also increases slightly. The main reason for this is that the neck length of the hollow spiral pipe 2 becomes shorter, the air mass inside the hollow spiral pipe 2 decreases, and the characteristic frequency of the sound absorption unit shifts to a higher frequency.

[0092] When investigating the effect of the height of the hollow spiral duct 2 on its sound absorption performance, the height of the hollow spiral duct 2 changed. Figure 9 The curve shown is the change curve of acoustic impedance ratio. The higher the height of the hollow spiral pipe 2, the lower the corresponding acoustic impedance ratio, and the sound absorption performance will be slightly improved. Figure 10 The sound absorption curve is shown. It can be seen that as the height of the hollow spiral pipe 2 increases, the peak frequency of sound absorption gradually increases from 33Hz to 36Hz, and the peak value of sound absorption also increases slightly. However, the device is not sensitive to the change of this geometric parameter overall.

[0093] When investigating the effect of the height of shell 3 on sound absorption performance, the height of shell 3 changed. Increasing the height of shell 3 reduced the overall acoustic volume of the structure, thus lowering the corresponding acoustic damping ratio. For example... Figure 11 The figure shows the curve of acoustic impedance ratio change. This will simultaneously lower the resonant frequency and slightly increase the peak sound absorption, as shown below. Figure 12 As shown.

[0094] When the thickness t1 of the base plate 4 changes, all other parameters of the sound-absorbing unit remain unchanged, and the change curve of the acoustic impedance ratio is as follows: Figure 13 As shown, when the thickness of the base plate 4 increases, the stiffness of the base plate 4 increases, and the peak frequency of sound absorption of the sound-absorbing unit gradually increases, with a slight increase in amplitude. (See below.) Figure 13 As shown, the acoustic impedance ratio decreases as the thickness of the base plate 4 gradually increases. Therefore, adjusting the thickness of the base plate 4 is used to achieve a frequency band shift for noise reduction.

[0095] When investigating the effects of different materials on sound absorption performance and acoustic impedance ratio, such as Figure 15 As shown, when the specifications of the sound-absorbing unit remain unchanged, the sound absorption frequency remains almost constant as the damping coefficient of the base plate 4 material changes. When the damping increases, the corresponding acoustic impedance ratio will be larger, so the peak sound absorption value will also decrease slightly. However, overall, the sound absorption performance is not sensitive to changes in the damping parameter. Figure 16 The figure shows the sound absorption coefficient curves of a single device designed in this invention under different damping coefficient conditions.

[0096] To investigate the frequency band adjustable by changing the thickness of the base plate 4 for a single sound-absorbing unit, based on scanning calculations of the above parameters, the perforated top plate 1 was set to have a radius of 49 mm and a thickness of 3 mm. The outer radius of the shell 3 was 49 mm, the inner radius was 46 mm, and the height was 28 mm. The height of the hollow spiral pipe 2 was 10 mm. The distance was set to 13. PLA was used as the bottom material. The thickness of a single sound-absorbing unit is only about 32 mm, much smaller than the wavelength of the incident sound; therefore, this sound-absorbing unit is subwavelength. Modeling of this part was performed. After fixing the top plate 1 and the hollow spiral pipe 2, the top plate 1 was fixed to the upper annular boundary of the shell 3. The base plate 4 was then assembled with the shell 3 using an interlocking device to obtain a complete sound-absorbing unit. The frequency bands with a sound absorption coefficient above 0.5 were investigated when the thickness of the base plate 4 varied from 0.3 mm to 2 mm.

[0097] As shown in Table 2, the data clearly demonstrates that by adjusting the bottom thickness as proposed in this invention, the range of sound absorption frequencies can be effectively controlled.

[0098] PLA bottom thickness Frequency range with sound absorption coefficient of 0.5 and above 0.3mm 23.5Hz-38.5Hz 0.4mm 36.8Hz-52.5Hz 0.5mm 51.3Hz-67.2Hz 0.6mm 66Hz-82Hz 0.7mm 80Hz-96.6Hz 0.8mm 92.8Hz-109.2Hz 0.9mm 104Hz-116Hz 1.0mm 113Hz-131Hz 1.1mm 121Hz-138Hz 1.2mm 127Hz-144.5Hz 1.3mm 132Hz-149Hz 1.4mm 136Hz-152.4Hz 1.5mm 139Hz-154.5Hz 1.6mm 141Hz-156.5Hz 1.7mm 142.5Hz-158Hz 1.8mm 144Hz-159Hz 1.9mm 145.5Hz-160Hz 2.0mm 147Hz-161Hz

[0099] Table 2

[0100] In the simulation, six sound-absorbing units with different resonant frequencies were obtained by using six PLA materials of different thicknesses as the base plate, such as... Figure 4 The units shown are installed on the ventilation duct, with thicknesses of 0.50mm, 0.55mm, 0.60mm, 0.65mm, 0.70mm, and 0.75mm respectively. All six sound-absorbing units have identical structural parameters except for the bottom. The perforated front panel has a radius of 49.5mm and a thickness of 3mm, a cavity height of 28mm, and a spiral tube height of 10mm. The distance is set to 13.

[0101] as follows Figure 17 As shown, the percentage of transmitted sound energy for the six sound-absorbing units is obtained. The percentage of transmitted sound energy is obtained by dividing the transmitted sound energy by the incident sound energy. The effective noise reduction frequency band (i.e., the frequency range corresponding to a transmittance of less than 0.5) is 63Hz-108Hz. Obviously, the smaller the percentage of transmitted sound energy, the greater the sound energy loss, and thus the better the noise reduction effect.

[0102] In another simulation example, for noise reduction in the 100Hz-160Hz frequency band, the following scheme is proposed: Eight PLA materials of different thicknesses are used as the base plate, with thicknesses of 0.8mm, 0.92mm, 1.08mm, 1.26mm, 1.42mm, 1.58mm, 1.74mm, and 1.92mm respectively. All other structural parameters are the same. The radius of the top plate 1 is 49mm, the outer diameter of the shell 3 is 49mm, the inner diameter is 46mm, and the height is 28mm. The height of the spiral pipe 2 is 10mm, and the distance is set to 13. Finite element simulation software calculations show that the sound absorption and noise reduction system composed of eight arrayed sound-absorbing units can achieve effective noise reduction in the 97Hz-169Hz frequency band. Figure 18 The percentage of sound energy transmitted is shown. At a frequency of 146 Hz, the sound pressure level attenuation can reach 25.2 dB.

[0103] For base plate 4, the greater its thickness, the greater its rigidity, and the higher the overall acoustic resonant frequency of the device. When the thickness exceeds the upper limit, base plate 4 can be considered a rigid wall, and its corresponding resonant frequency will no longer change.

[0104] Figure 19 As shown, a plan view of the spiral pipe is drawn to explain the input and output ends.

[0105] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to explain the relative positional relationship and movement between components in a specific orientation. If the specific orientation changes, the directional indication will also change accordingly. These terms are used only for the convenience of describing this application and for simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0106] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this disclosure / application, unless otherwise stated, "a plurality of" means two or more.

[0107] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0108] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A frequency adjustable modular low frequency noise reduction structure, characterized in that, It includes several sound-absorbing units, each of which consists of a top plate (1), a hollow spiral pipe (2), a shell (3), and a bottom plate (4); The housing (3) has a receiving cavity, which has a top plate (1) and a bottom plate (4) arranged at intervals along the vertical direction; the top plate (1) has a perforation in the center, parallel to the bottom plate (4); the bottom surface of the housing (3) is designed with an interlocking device, and the bottom plate (4) is assembled with the housing (3) through the interlocking device; by replacing the bottom plate with materials of different thicknesses or different stiffnesses, the resonant frequency of the sound-absorbing unit can be changed; The hollow spiral pipe (2) has a spiral structure and is located in the receiving cavity of the shell. The horizontal outlet is connected to the receiving cavity. The hollow spiral pipe (2) is glued to the top plate (1) and is aligned with the center of the perforation of the top plate (1). The base plate is made of PLA or spring steel; The base plate is made of PLA with a thickness ranging from 0.3mm to 2mm; the base plate is made of spring steel with a thickness ranging from 0.1mm to 0.4mm. When the thickness of the base plate (4) connected to the shell (3) decreases, acoustically it can be considered as changing from a rigid hard boundary to a flexible boundary, and the resulting additional acoustic capacity is approximately... And generate acoustic vibration coupling; where a is the radius of the circular base plate (4) and D is the bending stiffness of the base plate (4), which is affected by the thickness of the base plate (4) and the material properties.

2. The frequency-adjustable modular low-frequency noise reduction structure according to claim 1, characterized in that, The outer diameter of the shell (3) is less than or equal to the outer diameter of the top plate (1), and the difference between the inner and outer diameters of the shell (3) is 3-10 mm.

3. The frequency-adjustable modular low-frequency noise reduction structure according to claim 1, characterized in that, The shell (3) has a solid wall and is connected to the top plate (1) through the upper annular boundary. The height of the shell (3) is greater than the height of the hollow spiral pipe (2).

4. The frequency-adjustable modular low-frequency noise reduction structure according to claim 1, characterized in that, The bottom surface of the housing (3) is provided with four screw mounting holes at 90-degree intervals, and a circular groove with a certain width and depth is provided between adjacent mounting holes. The base plate (4) is provided with four screws at 90-degree intervals, and a protruding circular ring corresponding to the width and depth.

5. The frequency-adjustable modular low-frequency noise reduction structure according to claim 1, characterized in that, The neck length and the radius of the input end circle of the hollow spiral pipe (2) and the radius of the output end circle Proportional.

6. The frequency-adjustable modular low-frequency noise reduction structure according to claim 1, characterized in that, The outer diameter of the top plate (1) is larger than the size of the hollow spiral pipe (2); the radius of the central perforation of the top plate is equal to the radius of the top plate. .

7. The frequency-adjustable modular low-frequency noise reduction structure according to claim 1, characterized in that, The formula for calculating the resonant frequency of the sound-absorbing unit is as follows: ， in, The acoustic quality formed by the hollow spiral pipe (2) Acoustic resistance, which primarily represents the loss of sound energy, The acoustic capacitance is formed by the coupling system created by the sealing of the shell (3) and the base plate (4).

8. The frequency-adjustable modular low-frequency noise reduction structure according to claim 7, characterized in that, The calculation process for the sound absorption coefficient of the sound-absorbing unit is as follows: ， in, Acoustic impedance, Acoustic impedance, It is the cross-sectional area of ​​the incident surface of the sound-absorbing unit; Relative acoustic impedance ratio , in, air density, The speed of sound waves; acoustic impedance There are real and imaginary parts, using Indicates the real part, Indicates the imaginary part. Relative acoustic impedance ratio ; Acoustic impedance ratio Acoustic impedance ratio ; sound absorption coefficient .

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