CN117877451A - A frequency-adjustable modular low-frequency noise reduction structure - Google Patents

Abstract

The application discloses a frequency-adjustable modularized low-frequency noise reduction structure in the technical field of environmental engineering, which comprises a plurality of sound absorption units, wherein each sound absorption unit consists of a top plate, a hollow spiral pipeline, a shell and a bottom plate; the shell is provided with a containing cavity, and the containing cavity is provided with a top plate and a bottom plate which are arranged at intervals along the vertical direction; a perforation is arranged in the center of the top plate and is parallel to the bottom plate; the bottom surface of the shell is provided with a snapping device, and the bottom plate is assembled with the shell through the snapping device; the hollow spiral pipeline is of a spiral structure and is positioned in the accommodating cavity of the shell, and the horizontal outlet is communicated with the accommodating cavity; the hollow spiral pipe is connected with the top plate through gluing and is aligned with the perforation center of the top plate. The invention has the advantages of modularized assembly, convenient disassembly and assembly, and frequency-adjustable sound absorption and noise reduction effects by replacing the bottom plate.

Description

A frequency-adjustable modular low-frequency noise reduction structure

Technical Field

The present application relates to the field of environmental engineering technology, and in particular to a frequency-adjustable modular low-frequency noise reduction structure.

Background technique

Working in a noisy environment for a long time will cause damage to the human hearing, cardiovascular system, nerves and vision, interfere with people's normal life, work and study, and may cause various accidents. Therefore, a better solution is urgently needed to suppress and eliminate noise.

In order to solve the problems encountered in traditional noise control projects, some sound absorption structures have been proposed, such as porous material sound absorption structure, resonant sound absorption structure and micro-perforated plate sound absorption structure. The porous material sound absorption structure includes sound absorption plate structure, spatial sound absorption body and sound absorption wedge, but they only have good sound absorption effect on medium and high frequency noise, and low frequency noise is difficult to absorb through sound absorption materials. By introducing the sound absorption structure with resonance characteristics, due to the narrow bandwidth of the resonance structure itself, it only has a good sound absorption coefficient within the resonance frequency and a certain adjacent bandwidth, and it cannot be adjusted.

Application No. 202310302782.3 discloses an underwater sound-absorbing superstructure based on Helmholtz resonance, 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. Once the frequency band to be reduced is offset, its noise reduction effect will be greatly reduced. ZL201911036388 discloses a Helmholtz resonator and a low-frequency broadband sound absorption and noise reduction structure based on it. Multiple sound absorption units are combined into a larger sound absorption structure, which can achieve efficient low-frequency sound absorption. However, when the frequency band to be reduced is offset, it is impossible to conveniently adjust the length and cross-sectional area of the internal embedded tube to change the effective frequency band of the sound absorption structure.

In order to solve the problem of narrow working frequency band of sound absorption structure, the existing solution is mainly to array multiple sound absorption units to widen the sound absorption frequency band. Multiple resonance systems with different resonance frequencies are coupled to achieve a wider working frequency band. This coupling method is direct and effective. However, for the existing modular structure, once its structural parameters are fixed, the frequency band of action is also determined. Since it is impossible to easily adjust the structural parameters to change the frequency band of action, the reusability of the structure is not high.

The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the application and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to ordinary technicians in the field.

Summary of the invention

The purpose of the present application is to provide a frequency-adjustable modular low-frequency noise reduction structure, which is modularly assembled and easy to disassemble and assemble, and can achieve the effect of frequency-adjustable sound absorption and noise reduction by replacing the bottom plate.

In order to achieve the above objectives, this application is implemented by adopting the following technical solutions:

The present application provides a frequency-adjustable modular low-frequency noise reduction structure, comprising a plurality of sound absorbing units, wherein the sound absorbing units are composed of a top plate, a hollow spiral pipe, a shell and a bottom plate;

The shell has a housing cavity, and the housing cavity has a top plate and a bottom plate arranged at intervals in the vertical direction; a through hole is provided in the center of the top plate, parallel to the bottom plate; a bite device is designed on the bottom surface of the shell, and the bottom plate is assembled with the shell through the bite device;

The hollow spiral pipe is a spiral structure, located in the accommodating cavity of the shell, and the horizontal outlet is connected to the accommodating cavity; the hollow spiral pipe is connected to the top plate by gluing and is aligned with the center of the perforation of the top plate.

In some embodiments, the outer diameter of the shell is less than or equal to the outer diameter of the top plate, and the difference between the inner and outer diameters of the shell is in the range of 3-10 mm. The shell has a certain thickness, which is convenient for setting a bite device and screw holes on the cut surface for sealing and fastening.

In some embodiments, the shell wall is solid, 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 pipe. Even if the height of the hollow spiral pipe is changed to adjust the acoustic impedance ratio, the thickness of the sound absorbing unit will not be increased.

In some embodiments, the lower bottom surface of the shell is provided with four screw mounting holes at intervals of 90 degrees, and a circular channel with a certain width and depth is provided between adjacent mounting holes, and the bottom plate is provided with four screws at intervals of 90 degrees, and a protruding circular ring corresponding to the width and depth. It is ensured that the two can be firmly engaged, airtight, and can be repeatedly disassembled; the shell and the bottom plate are reliably connected by screws. Through simple disassembly, for the frequency band that needs noise reduction, materials with different thicknesses or different rigidity can be replaced as the bottom plate.

In some embodiments, the neck length of the hollow spiral pipe is proportional to the input end circle radius _a1 and the output end circle radius _af of the hollow spiral pipe. The hollow spiral pipe is arranged inside the shell, which is not easily damaged by external interference factors, and the safety is guaranteed. The hollow spiral pipe extends the length of the neck without increasing the thickness of the overall structure, so that the noise reduction structure has a low acoustic resonance frequency.

In some embodiments, the outer diameter of the top plate is larger than the size of the hollow spiral pipe; the central perforation radius of the top plate is

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

In some embodiments, the bottom plate is made of PLA, and the thickness is set in the range of 0.3mm-2mm; the bottom plate is made of spring steel, and the thickness is set in the range of 0.1mm-0.4mm. In the actual production process of PLA, the size below 0.3mm is not easy to process, and the thickness is too low to cause easy damage; when the size is greater than 2mm, the sound absorption frequency band is almost the same as that of 2mm, but the manufacturing cost will increase.

In some embodiments, the calculation formula of the resonant frequency of the sound absorbing unit is as follows:

Wherein, _Ma is the acoustic mass formed by the hollow spiral pipe, _Ra is the acoustic resistance, which mainly represents the loss of acoustic energy, and _Ccouple is the acoustic capacitance formed by the coupling system formed by the closed shell (3) and the bottom plate (4).

In some embodiments, the calculation process of the sound absorption coefficient of the sound absorption unit is as follows:

_Zs = _ZaS , where _Za is the acoustic impedance, _Zs is the acoustic impedance ratio, and S is the cross-sectional area of the incident surface of the sound absorbing unit;

Relative acoustic impedance ratio Among them, ρ ₀ is the air density, c ₀ is the speed of the sound wave;

The acoustic impedance _Za has a real part and an imaginary part. _Ra represents the real part and _Xa represents the imaginary part.

Relative acoustic impedance ratio

Acoustic resistivity ratio Acoustic impedance ratio/>

Sound absorption coefficient

Compared with the prior art, the present invention has the following beneficial effects:

1. Through easy disassembly, for the frequency band that needs noise reduction, materials with different thickness or stiffness can be replaced as the bottom plate to change the resonance frequency of the sound-absorbing unit; by modularizing multiple sound-absorbing units with different resonance frequencies, arrayed small-scale devices can be realized to absorb sound and reduce noise;

2. By introducing the embedded spiral pipe, the size of the sound absorbing unit is reduced, which effectively solves the problem of space occupation and reduces the volume of the sound absorbing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

FIG1 is a schematic diagram of a sound absorbing unit of the present invention;

FIG2 is an exploded schematic diagram of a sound absorbing unit of the present invention;

FIG3 is a schematic diagram of a housing portion of the present invention;

FIG4 is a schematic diagram of an embodiment of the present invention applied to a ventilation pipeline;

FIG5 is an acoustic-electric analog diagram of the sound absorbing unit of the present invention;

FIG6 is a finite element simulation analysis flow chart of the present invention;

7 is a diagram showing the acoustic impedance ratio of changing the neck length of the hollow spiral pipe according to the present invention;

FIG8 is a diagram showing the sound absorption coefficient of the present invention by changing the neck length of the hollow spiral pipe;

FIG9 is a diagram showing the acoustic impedance ratio of the present invention when changing the height of the hollow spiral pipe;

FIG10 is a diagram showing the sound absorption coefficient of the present invention by changing the height of the hollow spiral pipe;

11 is a diagram showing the acoustic impedance ratio of the present invention when the housing height is changed;

FIG12 is a diagram showing the sound absorption coefficient of the present invention when the height of the housing is changed;

13 is a diagram showing the acoustic impedance ratio of the present invention when the thickness of the bottom plate is changed;

14 is a diagram showing the sound absorption coefficient of the present invention when the thickness of the bottom plate is changed;

15 is a diagram showing the acoustic impedance ratio of the present invention by changing the damping of the bottom plate material;

FIG16 is a diagram showing the sound absorption coefficient of the present invention by changing the damping of the bottom plate material;

FIG17 is a diagram of the low frequency noise reduction transmissibility of the present invention;

FIG. 18 is a diagram of the low-frequency noise reduction transmissibility of the present invention for the frequency band 100 Hz-160 Hz.

FIG. 19 is a plan view of the spiral pipeline of the present invention.

Description of reference numerals:

1-top plate; 2-hollow spiral pipe; 3-shell; 4-bottom plate.

Detailed ways

The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present disclosure and its application or use.

Example:

This embodiment provides a frequency-adjustable modular low-frequency noise reduction structure, including a plurality of sound absorbing units, the overall schematic diagram of the sound absorbing unit structure is shown in FIG1 , and the structural decomposition schematic diagram is shown in FIG2 . The sound absorbing unit is composed of a top plate 1, a hollow spiral pipe 2, a shell 3 and a bottom plate 4;

The housing 3 has a housing cavity, and the housing cavity has a top plate 1 and a bottom plate 4 arranged at intervals in the vertical direction; a through hole is provided in the center of the top plate 1, which is parallel to the bottom plate 4; a bite device is designed on the bottom surface of the housing 3, and the bottom plate 4 is assembled with the housing 3 through the bite device;

The hollow spiral pipe 2 is a spiral structure, located in the accommodating cavity of the shell, and the horizontal outlet is connected to the accommodating cavity; the hollow spiral pipe 2 is connected to the top plate 1 by gluing and is aligned with the center of the perforation of the top plate 1.

In a specific implementation of the 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 3-10 mm.

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

As shown in FIG3 , the lower bottom surface of the shell 3 is provided with four screw mounting holes at intervals of 90 degrees, and an annular channel with a certain width and depth is provided between adjacent mounting holes, and the bottom plate 4 is provided with four screws at intervals of 90 degrees and a protruding annular ring corresponding to the width and depth.

In a specific implementation of an embodiment of the present invention, the neck length of the hollow spiral pipe 2 is proportional to the input end circle radius _a1 and the output end circle radius _af of the hollow spiral pipe 2. The hollow spiral pipe 2 is arranged inside the shell 3, and is not easily damaged by external interference factors, and the safety is guaranteed. The hollow spiral pipe 2 adopts a spiral neck, which extends the length of the neck without increasing the thickness of the overall structure, so that the resonance frequency of the corresponding sound absorption unit is reduced. The sound wave enters from the perforation of the top plate 1, arrives at the hollow opening on the upper surface of the hollow spiral pipe 2, and enters the accommodating cavity formed by the shell 3 and the bottom plate 4 from the horizontal outlet of the hollow spiral pipe 2.

In a specific implementation of the 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 bottom plate 4 is made of PLA or spring steel.

The bottom plate 4 is made of PLA, and the thickness is set in the range of 0.3mm-2mm; the bottom plate 4 is made of spring steel, and the thickness is set in the range of 0.1mm-0.4mm. In the actual production process of PLA, the size below 0.3mm is not easy to process, and the thickness is too low to cause easy damage; when the size is greater than 2mm, the sound absorption frequency band is almost the same as that of 2mm, but the manufacturing cost will increase.

In a specific implementation of the embodiment of the present invention, the approximate calculation formula of the resonant frequency of the sound absorbing unit is as follows:

Wherein, _Ma is the acoustic mass formed by the hollow spiral pipe 2, _Ra is the acoustic resistance, and _Ccouple is the acoustic capacity formed by the coupling system formed by the closed shell 3 and the bottom plate 4.

The acoustic-electric analogy is a theoretical method that relates acoustic vibration theory and circuit theory to each other. Although circuits and sound vibrations belong to different fields, when their laws are carefully studied, it can be found that they have the same form of differential equations in mathematics. Therefore, the acoustic vibration system can be analogized by means of a circuit diagram. Through this analogy, the methods and tools in circuit theory can be used to analyze and understand the behavior of the acoustic vibration system. This analogy method is widely used in the fields of acoustics and electronic engineering, and can help us better understand and design acoustic systems.

The sound absorbing unit in the present invention is a basic sound vibration system. When the bottom plate is a hard bottom surface, as shown in FIG5 , the sound-electric analogy diagram of the sound absorbing unit is an analogy relationship between the sound vibration system and the circuit system. The air mass in the hollow spiral pipe 2 is an inertia term, which can be analogized to the inductance in the circuit, denoted as _Ma ; the acoustic resistance mainly represents the ability of the structure to transmit sound wave energy, which is analogized to the resistance in the circuit, denoted as _Ra ; the air in the cavity surrounded by the shell 3 and the bottom plate 4 is analogized to the capacitance in the circuit, denoted as _Ca.

When the thickness of the bottom plate 4 connected to the shell 3 becomes thinner, it can be considered that the rigid boundary changes into a flexible boundary in acoustics, and the additional acoustic capacitance brought about by this is approximately And produce acoustic vibration coupling. Where a is the radius of the circular bottom plate 4, D is the bending stiffness of the bottom plate 4, which is affected by the thickness and material properties of the bottom plate 4. The total acoustic capacitance of the coupling system can be approximated as C _couple = _Ca + C _added . When the acoustic resistance is not considered, the resonant frequency of the device is approximately Therefore, by changing the thickness of the bottom plate 4, the resonant frequency of the device can be adjusted, thereby affecting its sound absorption performance.

When using the acoustic-electric analogy method, the lumped parameter method is used, so the frequency is limited to low frequency. In actual product design, its precise resonant frequency and sound absorption performance can be obtained through finite element numerical calculation.

In a specific implementation of the embodiment of the present invention, the calculation process of the sound absorption coefficient of the sound absorption unit is as follows:

_Zs = _ZaS , where _Za is the acoustic impedance, _Zs is the acoustic impedance ratio, and S is the cross-sectional area of the incident surface of the sound absorbing unit;

Relative acoustic impedance ratio Among them, ρ ₀ is the air density, c ₀ is the speed of the sound wave;

The acoustic impedance _Za has a real part and an imaginary part. _Ra represents the real part and _Xa represents the imaginary part.

Relative acoustic impedance ratio

Acoustic resistivity ratio Acoustic impedance ratio/>

Sound absorption coefficient

When the sound absorption unit resonates, X=0. At this time, if R=1, the sound absorption coefficient is α=1, that is, the sound absorption 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 occurs, that is, the incident sound energy is 100% dissipated.

In order to study the sound absorption performance of the designed sound absorption unit, numerical simulation was performed using finite element simulation software. As shown in Figure 6, a specific flow chart for analyzing its sound absorption performance using finite element simulation software is shown below. The relevant steps are introduced.

First, a model is established. The top plate 1, shell 3 and bottom plate 4 can all use cylinders as basic voxels. The parameter _L0 is defined for the parametric scan of the height of the shell 3; the parameter _t1 is defined for the parametric scan of the thickness change of the bottom plate 4; damping is defined to represent the damping coefficient of the bottom plate 4; the neck length of the hollow spiral pipe 2 is set to be proportional to the input end circle radius _a1 and the output end circle radius _af , and the parameter distance is defined.

In order to establish the spiral pipe geometric model, theta_0 is used to represent its initial angle, and theta_0 is fixedly set to 0. Theta_f is used to represent its terminal angle, and theta_f＝2n ₁ .

in, Determines the number of turns of the spiral pipe. The larger _{n 1} is, the longer the effective length of the spiral pipe is. The larger distance is, the shorter the neck length of the hollow spiral pipe 2 is. Therefore, the neck length of the hollow spiral pipe 2 can be adjusted by modifying the value of distance; the parameter h ₂ is defined for parametrically scanning the height of the hollow spiral pipe 2.

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). This material is a common material used in 3D printing and has good mechanical strength. The internal fluids in the central circular hole of the top plate 1, the spiral pipe 2, the hollow sound absorption cavity inside the shell and other areas are defined as air. The specific parameters of the materials are shown in Table 1.

Table 1

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.

After completing the meshing, add the corresponding study. In this simulation example, the sound absorption performance of the sound absorption unit in the frequency domain is mainly studied, so the study condition is selected as the frequency domain, where the frequency domain range is 20-200Hz, and the frequency step is 1Hz. In the study, you can add a parametric sweep, and through the sweep, you can explore the impact of parameter changes on sound absorption performance and acoustic impedance.

When exploring the effect of the neck length of the hollow spiral duct 2 on the sound absorption performance and acoustic impedance, because the distance affects the neck length of the hollow spiral duct 2, different distances are scanned. Figure 7 shows the acoustic impedance curve. The larger the distance, the shorter the neck length of the hollow spiral duct 2, and the shorter the sound channel therein, the smaller the corresponding acoustic resistance. Figure 8 shows the sound absorption curve. As the distance increases, the neck length of the hollow spiral duct 2 becomes shorter, the sound absorption peak frequency gradually increases, and the sound absorption peak also increases slightly. The main reason is that the neck length of the hollow spiral duct 2 becomes shorter, and the air mass inside the hollow spiral duct 2 decreases, causing the characteristic frequency of the sound absorption unit to move toward high frequency.

When exploring the effect of the height of the hollow spiral pipe 2 on the sound absorption performance, the height of the hollow spiral pipe 2 changes. Figure 9 shows the change curve of the acoustic impedance ratio. The higher the height of the hollow spiral pipe 2, the smaller the corresponding acoustic impedance ratio, and the sound absorption performance will be slightly improved. Figure 10 shows the sound absorption curve. It can be seen that as the height of the hollow spiral pipe 2 increases, the sound absorption peak frequency will gradually increase from 33Hz to 36Hz, and the sound absorption peak will also increase slightly, but the device is generally insensitive to changes in this geometric parameter.

When investigating the effect of the height of the shell 3 on the sound absorption performance, the height of the shell 3 changes. When the height of the shell 3 is increased, the acoustic capacity of the overall structure is reduced, and the corresponding acoustic impedance ratio is reduced. FIG11 is a curve showing the change of the acoustic impedance ratio. At the same time, the resonance frequency is reduced, and the sound absorption peak value is slightly increased, as shown in FIG12.

When the thickness _t1 of the bottom plate 4 changes, the other parameters of the sound absorbing unit remain unchanged, and the acoustic impedance ratio change curve is shown in FIG13. When the thickness of the bottom plate 4 increases, the rigidity of the bottom plate 4 increases, and the sound absorption peak frequency of the sound absorbing unit gradually increases, and the amplitude rises slightly. As shown in FIG13 below, when the thickness of the bottom plate 4 gradually increases, the acoustic impedance ratio also decreases. Therefore, the frequency band shift of noise reduction is achieved by adjusting the thickness of the bottom plate 4.

When exploring the influence of different materials on the sound absorption performance and acoustic impedance ratio, as shown in FIG15, when the specifications of the sound absorption unit remain unchanged, as the damping coefficient of the bottom plate 4 material changes, its sound absorption frequency remains almost unchanged. When the damping increases, the corresponding acoustic impedance ratio will increase, so the sound absorption peak value will also decrease slightly, but overall, the sound absorption performance is not sensitive to the change of the damping parameters. As shown in FIG16, the sound absorption coefficient curve of a single device designed by the present invention under different damping coefficient conditions.

In order to study the frequency band that a single sound absorbing unit can adjust by changing the thickness of the bottom plate 4, combined with the scanning calculation of the above parameters, the radius of the perforated top plate 1 is set to 49mm and the thickness is 3mm. The outer radius of the shell 3 is 49mm, the inner radius is 46mm, the height is 28mm, and the height of the hollow spiral pipe 2 is 10mm. Set the distance to 13. PLA is used as the bottom material. The thickness of a single sound absorbing unit is only about 32mm, which is much smaller than the wavelength of the incident sound, so the sound absorbing unit is sub-wavelength. Model the part, fix the top plate 1 to the upper annular boundary of the shell 3 after the top plate 1 and the hollow spiral pipe 2 are fixed, and assemble the bottom plate 4 and the shell 3 through the bite device to obtain a complete sound absorbing unit. The frequency bands where the sound absorption coefficient is above 0.5 when the thickness of the bottom plate 4 changes from 0.3mm to 2mm are studied respectively.

As shown in Table 2, it can be clearly seen from the table data that by adjusting the bottom surface thickness proposed in the present invention, the sound absorption frequency range can be effectively adjusted.

PLA bottom thickness Frequency range where the sound absorption coefficient is 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

Table 2

In the simulation, six different thicknesses of PLA materials were used as the bottom plate to obtain six sound absorbing units with different resonance frequencies, which were installed on the ventilation duct as shown in Figure 4. The thicknesses were 0.50mm, 0.55mm, 0.60mm, 0.65mm, 0.70mm, and 0.75mm, respectively. The structural parameters of the six sound absorbing units were the same except for the bottom. The radius of the perforated front panel was 49.5mm, the thickness was 3mm, the cavity height was 28mm, the spiral tube height was 10mm, and the distance was set to 13.

As shown in Figure 17 below, the pass-through sound energy percentages of the six sound absorbing units are obtained. The pass-through sound energy percentage 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 the pass rate less than 0.5) is 63Hz-108Hz. Obviously, the smaller the pass-through sound energy percentage, the greater the sound energy loss, that is, the better the noise reduction effect.

In another simulation example, the following scheme is given for noise reduction in the frequency band of 100Hz-160Hz: eight PLA materials of different thicknesses are used as the bottom plate, with thicknesses of 0.8mm, 0.92mm, 1.08mm, 1.26mm, 1.42mm, 1.58mm, 1.74mm, and 1.92mm respectively. The other structural parameters are all 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. It is calculated by finite element simulation software that the sound absorption and noise reduction system composed of eight sound absorption units array can achieve effective noise reduction in the frequency band of 97Hz-169Hz, that is, the corresponding pass-through sound energy percentage shown in Figure 18. At a frequency of 146Hz, the sound pressure level attenuation can reach 25.2dB.

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

As shown in Figure 19, a plan view of the spiral pipeline is drawn to explain the input end and the output end.

In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only used to explain the relative position relationship, movement, etc. between the components in a certain posture. If the specific posture changes, the directional indication will also change accordingly. It is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present application.

In addition, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the feature. In the description of this disclosure/application, unless otherwise specified, "plurality" means two or more.

In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood by specific circumstances.

The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims (10)

1. The modularized low-frequency noise reduction structure with the adjustable frequency is characterized by comprising a plurality of sound absorption units, wherein each sound absorption unit consists of a top plate (1), a hollow spiral pipeline (2), a shell (3) and a bottom plate (4);

the shell (3) is provided with a containing cavity, and the containing cavity is provided with a top plate (1) and a bottom plate (4) which are arranged at intervals along the vertical direction; a through hole is arranged in the center of the top plate (1) and is parallel to the bottom plate (4); the lower bottom surface of the shell (3) is provided with a snapping device, and the bottom plate (4) is assembled with the shell (3) through the snapping device;

the hollow spiral pipeline (2) is of a spiral structure and is positioned in the accommodating cavity of the shell, and the horizontal outlet is communicated with the accommodating cavity; the hollow spiral pipeline (2) is connected with the top plate (1) through gluing and is aligned with the perforation center of the top plate (1).

2. The frequency-adjustable modularized low-frequency noise reduction structure according to claim 1, wherein the outer diameter of the shell (3) is smaller than or equal to the outer diameter of the top plate (1), and the difference between the inner diameter and the outer diameter of the shell (3) is 3-10mm.

3. The frequency-adjustable modular low-frequency noise reduction structure according to claim 1, characterized in that the housing (3) wall is solid, the top plate (1) is connected by an upper annular boundary, the height of the housing (3) is greater than the height of the hollow helical duct (2).

4. The frequency-adjustable modularized low-frequency noise reduction structure according to claim 1, wherein four screw mounting holes are formed in the lower bottom surface of the shell (3) at intervals of 90 degrees, circular ring channels with certain width and depth are formed between adjacent mounting holes, and four screws at intervals of 90 degrees and protruding circular rings corresponding to the width and the depth are arranged on the bottom plate (4).

5. The frequency-tunable modular low frequency noise reducing structure according to claim 1, wherein the neck length of the hollow helical tube (2) and the input end radius a of the hollow helical tube (2) ₁ Output end radius a _f Proportional to the ratio.

6. The frequency-tunable 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 helical duct (2); the center perforation radius of the top plate is the radius of the top plate

7. The frequency tunable modular low frequency noise reducing structure of claim 1, wherein the base plate is made of PLA or spring steel.

8. The frequency tunable modular low frequency noise reducing structure according to claim 7, wherein the base plate is PLA and has a thickness ranging from 0.3mm to 2mm; the bottom plate is made of spring steel, and the thickness setting range is 0.1mm-0.4mm.

9. The frequency-tunable modular low-frequency noise reduction structure according to claim 1, wherein a formula for calculating a resonance frequency of the sound absorption unit is as follows:

wherein M is _a The acoustic mass, R, formed for a hollow helical pipe (2) _a Is acoustic resistance, acoustic resistance mainly representing loss of acoustic energy, C _couple The sound volume formed by the coupling system is formed by the shell (3) and the bottom plate (4) in a sealing way.

10. The frequency tunable modular low frequency noise reduction structure of claim 9, wherein the sound absorption coefficient of the sound absorption unit is calculated as follows:

Z _s ＝Z _a S，

wherein Z is _a Is acoustic impedance, Z _s S is the sectional area of the incident surface of the sound absorption unit for the acoustic impedance;

relative specific acoustic impedance ratio

Wherein ρ is ₀ For air density, c ₀ Is the speed of the sound wave;

acoustic impedance Z _a With real and imaginary parts, e.g. R _a Representing the real part, X _a Representing the imaginary part of the system,

relative specific acoustic impedance ratioSpecific acoustic resistivity->Ratio of sound resistance->Sound absorption coefficient->