Gradable frequency modulation type low and medium frequency silencing element and design method thereof

Abstract

The invention provides a graded frequency modulation medium and low frequency silencing element and a design method thereof.The graded frequency modulation medium and low frequency silencing element comprises a hollow outer shell, a first micro-perforated plate is arranged on one side wall of the outer shell, an inclined cabin is arranged in the outer shell, and the inclined cabin is defined by a second micro-perforated plate and a plurality of side plates; the side plates, the second micro-perforated plate and the first micro-perforated plate divide an inner cavity of the outer shell into two independent areas, and the first micro-perforated plate and the second micro-perforated plate are each provided with a shading plate capable of moving in a push-pull mode in a matched mode. When the light shielding plate is pushed and pulled, the sound absorption coefficient of the low-and-medium-frequency noise elimination element is adjusted by shielding the perforation rate of the first micro-perforated plate and the second micro-perforated plate. According to the low and medium frequency noise elimination element, the inclined cavity is introduced in design, the effective cavity depth is increased, and the thickness of the cavity of the noise elimination element can be reduced while the same low and medium frequency sound absorption performance is kept.

Description

Technical Field

[0001] The present invention relates to the technical field of noise control, and particularly relates to a mid-low frequency noise elimination element with hierarchical frequency modulation and a design method thereof. Background Art

[0002] In the noise control of ship cabins, mid-low frequency noise has always been a difficult point to control. Since the wavelength of mid-low frequency noise is relatively long, traditional porous sound-absorbing materials need to reach a thickness equivalent to the wavelength to achieve efficient sound absorption. However, the actual material thickness on ships is relatively thin at present, resulting in poor low-frequency sound absorption effect. Generally speaking, thick sound-absorbing materials cannot be used in the vibration and noise reduction of ship cabins. Therefore, the thickness of the low-frequency sound absorption structure should be minimized to avoid occupying too much cabin space.

[0003] On a certain ship, the problem of "when the power station diesel generator is running, the air noise at the air inlet is relatively large, and there is a resonance phenomenon when people speak" was found. According to the analysis of the air noise test results of the actual ship, mid-low frequency noise is the main noise source. Since the wavelength of mid-low frequency noise is relatively long and the diffraction effect is obvious, traditional porous sound-absorbing bodies such as sound-absorbing cotton, mineral wool, and sponge need to reach a thickness equivalent to the wavelength to achieve efficient sound absorption. However, due to reasons such as space and weight limitations on ships at present, the material thickness is relatively thin, and the mid-low frequency sound absorption effect is poor.

[0004] Because the structure of traditional noise elimination elements is fixed, there is often a deviation between the effective working frequency band of the element and the actual application. In actual applications, a series of mufflers usually need to be designed for selection, with a long design and production cycle and high costs. Summary of the Invention

[0005] The main purpose of the present invention is to provide a mid-low frequency noise elimination element with hierarchical frequency modulation and a design method thereof, aiming to reduce the thickness of the cavity of the noise elimination element while maintaining the same mid-low frequency sound absorption performance.

[0006] To achieve the above purpose, the present invention provides a mid-low frequency noise elimination element with hierarchical frequency modulation, including a hollow outer shell. One side wall of the outer shell is a first micro-perforated plate. An inclined cabin is arranged inside the outer shell and is formed by enclosing a second micro-perforated plate and multiple side plates. The multiple side plates, the second micro-perforated plate, and the first micro-perforated plate divide the internal cavity of the outer shell into two independent regions. The first micro-perforated plate and the second micro-perforated plate are both provided with light-shielding plates that can be pushed and pulled. When the light-shielding plates are pushed and pulled, the sound absorption coefficient of the mid-low frequency noise elimination element is adjusted by blocking the perforation rate of the first micro-perforated plate and the second micro-perforated plate.

[0007] Preferably, the first micro-perforated plate and the second micro-perforated plate are arranged in parallel.

[0008] Preferably, the included angle between the side plates and the inner side wall of the outer shell is 15°-45°.

[0009] Preferably, both the first micro-perforated plate and the second micro-perforated plate are square plates.

[0010] Preferably, the diameter of the perforations on the first micro-perforated plate and the second micro-perforated plate is 0.5 mm to 2 mm, and the thickness of the first micro-perforated plate and the second micro-perforated plate is 0.5 mm to 2 mm.

[0011] Preferably, the light-shielding plates are connected to the first micro-perforated plate and the second micro-perforated plate through sliding bearings.

[0012] Preferably, the first micro-perforated plate and the second micro-perforated plate are arranged in multiple rows and multiple columns uniformly.

[0013] Preferably, the height of the outer housing is less than or equal to 60 mm.

[0014] Preferably, the inclined chamber is provided with multiple layers to expand the frequency adjustment range.

[0015] The present invention also proposes a design method for a medium and low frequency sound-absorbing element with adjustable frequency grading based on the above, including the following steps: Conduct an air noise test on the area where the sound-absorbing device is to be installed to obtain the frequency range with the most prominent noise; By adjusting the areas of the two light-shielding plates covering the first micro-perforated plate and the second micro-perforated plate, test the sound absorption coefficient of the medium and low frequency sound-absorbing element in different shielding states, and select the optimal perforation rate of the first micro-perforated plate and the second micro-perforated plate according to the frequency range with the most prominent noise of the sound-absorbing device to be installed; According to the selected optimal perforation rate of the first micro-perforated plate and the second micro-perforated plate, adjust the areas of the two light-shielding plates covering the first micro-perforated plate and the second micro-perforated plate, and then install the adjusted medium and low frequency sound-absorbing element on the peripheral wall of the air inlet.

[0016] The medium and low frequency sound-absorbing element with adjustable frequency grading proposed by the present invention has the following beneficial effects: 1) Compared with the existing medium and low frequency sound-absorbing materials on actual ships, the present invention reduces the thickness of the sound-absorbing material by increasing the effective chamber depth while maintaining the same medium and low frequency sound absorption performance; 2) By introducing movable light-shielding plates, the absorption bandwidth of the absorber of the present medium and low frequency sound-absorbing element is greatly improved; 3) The present invention can be used for experimental verification of medium and low frequency noise absorption, saving the trouble of designing a series of mufflers for selection in the traditional method, shortening the design and production cycle, reducing costs, and thus providing verification elements and technical support for medium and low frequency noise control.

[0017] 4) The medium and low frequency noise elimination element of the present invention has strong implementability and great military value; in addition, in actual construction, it can be customized according to different noise spectrums and has broad application prospects. Description of the Drawings

[0018] Figure 1 Schematic diagram of the sound insulation model of a single micro-perforated plate in the prior art; Figure 2 Schematic diagram of the sound insulation model of two micro-perforated plates in the prior art; Figure 3 Cross-sectional schematic diagram of the medium and low frequency noise elimination element with hierarchical frequency modulation of the present invention; Figure 4 Three-dimensional schematic diagram of the medium and low frequency noise elimination element with hierarchical frequency modulation of the present invention; Figure 5 Three-dimensional schematic diagram of the equivalent model of the medium and low frequency noise elimination element with hierarchical frequency modulation of the present invention; Figure 6 Three-dimensional schematic diagram of the model of the medium and low frequency noise elimination element with a general series structure in the prior art; Figure 7a Schematic diagram of the first micro-perforated plate of the medium and low frequency noise elimination element with hierarchical frequency modulation of the present invention in the first shielding state of the light shielding plate; Figure 7b Schematic diagram of the first micro-perforated plate of the medium and low frequency noise elimination element with hierarchical frequency modulation of the present invention in the second shielding state of the light shielding plate; Figure 7c Schematic diagram of the first micro-perforated plate of the medium and low frequency noise elimination element with hierarchical frequency modulation of the present invention in the third shielding state of the light shielding plate; Figure 7d Schematic diagram of the first micro-perforated plate of the medium and low frequency noise elimination element with hierarchical frequency modulation of the present invention in the fourth shielding state of the light shielding plate; Figure 8 Exploded three-dimensional schematic diagram of the medium and low frequency noise elimination element with hierarchical frequency modulation of the present invention; Figure 9 Graph of the sound absorption coefficient of the medium and low frequency noise elimination element with hierarchical frequency modulation of the present invention varying with frequency.

[0019] In the figures, 1 - the first micro-perforated plate, 2 - the side plate, 3 - the second micro-perforated plate, 4 - the sliding bearing, 5 - the light shielding plate, 6 - the back cavity, 7 - the micro-perforated plate, 8 - the rigid surface, 9 - the incident surface.

[0020] The realization of the object, functional features and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. Detailed Description of the Invention

[0021] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] It should be noted that in the description of the present invention, the orientation or positional relationship indicated by the terms "lateral", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention 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 should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0023] The present invention provides a mid-low frequency sound-absorbing element capable of hierarchical frequency modulation.

[0024] In this preferred embodiment, with reference to Figure 3 , a mid-low frequency sound-absorbing element capable of hierarchical frequency modulation includes a hollow outer shell. One side wall of the outer shell is the first micro-perforated plate 1. An inclined chamber is arranged inside the outer shell. The inclined chamber is formed by enclosing the second micro-perforated plate 3 and multiple side plates 2 (the side plates 2 are solid plates). The multiple side plates 2, the second micro-perforated plate 3 and the first micro-perforated plate 1 divide the inner cavity of the outer shell into two independent regions. The first micro-perforated plate 1 and the second micro-perforated plate 3 are both provided with light-shielding plates 5 that can be pushed and pulled. When the light-shielding plates 5 are pushed and pulled, the sound absorption coefficient of the mid-low frequency sound-absorbing element is adjusted by blocking the perforation rate of the first micro-perforated plate 1 and the second micro-perforated plate 3.

[0025] Five side surfaces of the outer shell are all solid plates, and only the position of the top plate, that is, the first micro-perforated plate 1, is perforated. The outer shell has a cuboid structure.

[0026] In this embodiment, the first micro-perforated plate 1 and the second micro-perforated plate 3 are arranged in parallel. The first micro-perforated plate 1 and the second micro-perforated plate 3 are both square plates. The included angle between the side plate 2 and the inner side wall of the outer shell is 15° - 45° (that is, β in the figure).

[0027] Specifically, the perforation diameter on the first micro-perforated plate 1 and the second micro-perforated plate 3 is 0.5 mm - 2 mm, and the thickness of the first micro-perforated plate 1 and the second micro-perforated plate 3 is 0.5 mm - 2 mm.

[0028] In this embodiment, the light-shielding plates 5 are both connected to the first micro-perforated plate 1 and the second micro-perforated plate 3 through sliding bearings. The first micro-perforated plate 1 and the second micro-perforated plate 3 are uniformly arranged with multiple rows and multiple columns. In this embodiment, for the convenience of illustration, 4 columns of perforations are taken as an example. In subsequent applications, according to requirements, the perforated plate can be made into 2 columns, 3 columns, 4 columns... n columns to meet the requirements of different frequency adjustments.

[0029] The height of the outer casing is less than or equal to 60 mm. The height of the outer casing is set in this way to meet the actual installation requirements.

[0030] The inclined compartments are arranged in multiple layers to expand the frequency adjustment range. When there are two inclined compartments, two second micro-perforated plates 3 are correspondingly arranged.

[0031] The schematic diagram of the traditional micro-perforated plate sound insulation model is as Figure 1 shown. The schematic diagram of the traditional double-layer micro-perforated plate series model composed of two series-connected micro-perforated plates is as Figure 2 shown. In this medium and low frequency silencing element, an inclined cavity is introduced into the rectangular cavity to design a medium and low frequency silencing element with adjustable grading frequency. The cross-sectional schematic diagram of the medium and low frequency silencing element with adjustable grading frequency is as Figure 3 shown, and the three-dimensional schematic diagram of the medium and low frequency silencing element with adjustable grading frequency is as Figure 4 shown.

[0032] Figure 3 In it, the side plate 2 is used to connect the first micro-perforated plate 1 and the second micro-perforated plate 3, and the original rectangular cavity inside the outer casing is divided into two irregular cavities with volumes V1 and V2. The side length of the square plate is represented by b. The side length of the first micro-perforated plate 1 is 2b1, the side length of the second micro-perforated plate 3 is 2b2. The plate thicknesses of the first micro-perforated plate 1 and the second micro-perforated plate 3 are t1 and t2 respectively. The distance between the first micro-perforated plate 1 and the second micro-perforated plate 3 is D1, the cavity wall angle is β, the total volume of the upper cavity is represented by V1, and the distance from the second micro-perforated plate 3 with a radius of b2 to the bottom is D2. Specifically, in this embodiment, b1 = 48 mm, b2 = 32 mm, d1 = d2 = t1 = 1 mm, t2 = 2 mm, D1 = 35 mm, and D2 = 15 mm are taken as examples for specific description. The number of micro-holes in each column on the micro-perforated plate is represented by N, and the diameter of each micro-hole is represented by d.

[0033] Figure 5 is the three-dimensional schematic diagram of the equivalent model of the medium and low frequency silencing element with adjustable grading frequency, Figure 6 is the three-dimensional schematic diagram of the medium and low frequency silencing element model of the general series structure. As Figure 5 shown, the equivalent model of the medium and low frequency silencing element with adjustable grading frequency is composed of two rectangular cavities connected by perforated plates. (Equivalent method: Ensure that the incident surface area of the equivalent model is the same as that of the original model, and the depth of the equivalent cavity is the same as that of the original model.) Under the condition of the same porosity, the absorption coefficients of the medium and low frequency silencing element with adjustable grading frequency, the equivalent model, and the ordinary model are calculated.

[0034] For the structure of the medium and low frequency silencing element with adjustable grading frequency, due to the irregular cavity shape, V is the volume of the formed cavity, and S is the cross-sectional area of the perforated plate. Therefore, the calculation formula for the equivalent cavity depth is as follows: (1) That is, the equivalent cavity depth is the ratio of the cavity volume to the perforated plate area. It can be obtained from the above formula (1) that the absorption coefficient of the mid-low frequency noise elimination element with adjustable frequency grading is close to the acoustic impedance of the perforated plate of the equivalent model, but there are differences compared with the ordinary model. (The main reason for the difference is that the incident surface areas of the upper and lower cavities are different). Therefore, compared with the equivalent structure, the mid-low frequency noise elimination element with adjustable frequency grading can effectively reduce the material thickness by increasing the depth of the effective chamber.

[0035] The perforation rate of the first micro-perforated plate 1 and the second micro-perforated plate 3 is p. The number of micro-holes is represented by N, the diameter of each micro-hole is represented by d (unit: mm), and the side length of the square plate itself is represented by b. The perforation rate p of the perforated plate is a percentage, which is the ratio of the perforated area to the total area of the plate. (2) Figures 7a to 7d As shown, for the first micro-perforated plate 1 in four working states, the perforation exposure rates are different. The design of this low-frequency noise elimination element is to push and pull the light-shielding plate 5 to change the perforation exposure rate, thereby adjusting the frequency.

[0036] Figure 8 It shows a three-dimensional schematic diagram of the structural decomposition of the mid-low frequency noise elimination element with adjustable frequency grading. This noise elimination element is mainly divided into two major parts in series. The upper part is an upper push-pull adjustment structure formed by the light-shielding plate 5 and the first micro-perforated plate 1, and the lower part is a lower push-pull adjustment structure formed by the light-shielding plate 5 and the second micro-perforated plate 3. These two push-pull structures are combined together to form a second-order push-pull structure. There are four columns of holes on the micro-perforated plate, which are evenly distributed. Figures 7a to 7d It shows four adjustment modes of the push-pull structure. The baffle blocks different numbers of small holes, changing the perforation rate of the panel. By combining the four modes of the upper and lower two-layer push-pull structures, 16 combined states of the perforation rate of this structure are formed, as shown in Table 1. The first micro-perforated plate 1 is above, and the second micro-perforated plate 3 is below.

[0037] Table 1 16 combination methods of the structural perforation rate

[0038] The perforation rate p of the micro-perforated plate is determined by formula (2): that is, the ratio of the hollow area to the area of the entire plate. Assume that the number of holes in the first micro-perforated plate 1 is 48, and the number of holes in each column of the second micro-perforated plate 3 is 20. Use matlab to calculate the perforation rates of 16 states, and the results are shown in Table 2.

[0039] Table 2 Perforation rates in different states (unit: percentage) (where: p1 is the perforation rate of the first micro-perforated plate 1, and p2 is the perforation rate of the second micro-perforated plate 3)

[0040] The graded frequency modulation mid - low frequency silencing element proposed by the present invention has the following beneficial effects: 1) Compared with the existing mid - low frequency sound - absorbing materials on actual ships, while maintaining the same mid - low frequency sound - absorption performance, the present invention reduces the thickness of the sound - absorbing material by increasing the depth of the effective chamber. 2) By introducing a movable light - shielding plate, the absorption bandwidth of the absorber of the present mid - low frequency silencing element is greatly improved. 3) The present invention can be used for experimental verification of mid - low frequency noise absorption, saving the trouble of designing a series of mufflers for selection in the traditional method, shortening the design and production cycle, reducing costs, and thus providing verification elements and technical support for mid - low frequency noise control.

[0041] 4) The present mid - low frequency silencing element has strong implementability and great military value; in addition, during actual construction, it can be customized according to different noise spectra and has a wide range of application prospects.

[0042] The present invention further proposes a design method for a graded frequency modulation mid - low frequency silencing element.

[0043] In this preferred embodiment, a design method for a graded frequency modulation mid - low frequency silencing element based on the above - mentioned is as follows: Step S10: Conduct an air - borne noise test on the area where the silencing device is to be installed to obtain the frequency range with the most prominent noise. Step S20: By adjusting the area where the two light - shielding plates 5 cover the first micro - perforated plate 1 and the second micro - perforated plate 3, test the sound - absorption coefficient of the mid - low frequency silencing element in different shielding states, and select the optimal perforation rates of the first micro - perforated plate 1 and the second micro - perforated plate 3 according to the frequency range with the most prominent noise of the silencing device to be installed. Step S30: According to the selected optimal perforation rates of the first micro - perforated plate 1 and the second micro - perforated plate 3, adjust the area where the two light - shielding plates 5 cover the first micro - perforated plate 1 and the second micro - perforated plate 3, and then install the adjusted mid - low frequency silencing element on the surrounding walls of the air inlet.

[0044] Taking the mid - low frequency noise control problem of the air inlet of a certain ship as an example, the mid - low frequency noise near the air inlet of the power station diesel generator is more prominent. First, conduct a noise test to obtain the characteristic frequency of the air inlet, then obtain a set of optimal perforation rates of the upper and lower perforated plates of the graded frequency modulation mid - low frequency silencing element through simulation calculation, then adjust the perforation rates of the upper and lower perforated plates of the adjustable - frequency mid - low frequency silencing element sample to the optimal values, lay it on the actual ship to complete the actual ship optimization construction, and then conduct a noise test on the air inlet. The specific steps are as follows: Step 1: Conduct chamber air noise tests on the middle part of the air inlet before improvement. The test frequency range is 20 Hz to 20,000 Hz. It can be seen that the noise is most prominent around 300 Hz and 800 Hz, and the sound pressure levels are 67 dB(A) and 75 dB(A) respectively. Step 2: Adjust the perforation rate of the present medium and low frequency silencing element. By adjusting the positions of the pins of the first micro-perforated plate 1 and the second micro-perforated plate 3, 16 states of the silencing element are tested. At state 10 (i.e., 50% of the perforations of the upper perforated plate are exposed, that is, 2 out of 4 columns of perforations are exposed, and 75% of the perforations of the lower perforated plate are exposed, that is, 3 out of 4 columns of perforations are exposed), the silencing element has the highest sound absorption coefficient around 300 Hz and 800 Hz. The curve of the sound absorption coefficient changing with frequency is as Figure 9 . A set of values of the perforation rates of the upper and lower perforated plates are obtained: the perforation rate of the first micro-perforated plate 1 is 0.82%, and the perforation rate of the second micro-perforated plate 3 is 1.15%.

[0045] Step 3: According to the analysis in Step 2, adjust the perforation rate of the upper perforated plate of a batch of tunable medium and low frequency silencing element samples to 0.82%, that is, 2 out of 4 columns of perforations are exposed, and adjust the perforation rate of the second micro-perforated plate 3 to 1.15%, that is, 3 out of 4 columns of perforations are exposed. Then, lay the sound absorption element samples on the surrounding walls of the air inlet.

[0046] After improvement, conduct chamber air noise tests on the same position in the middle of the air inlet under the same working conditions. The test frequency range is 20 Hz to 20,000 Hz. In the frequency range corresponding to the common working conditions of the power station diesel generator, determine the peak value of the frequency-vibration level curve. The frequencies corresponding to this peak value are around 300 Hz and 800 Hz, which are the characteristic frequencies of the air inlet. The test results show that before optimization, the sound pressure level at 300 Hz in the interference equipment room is 67 dB(A), and after optimization, it is 61 dB(A), and the optimization effect is greater than 5 dB. At 800 Hz, the sound pressure level is 75 dB(A), and after optimization, it is 67 dB(A), and the optimization effect is greater than 5 dB. The optimization scheme has achieved the expected effect. In subsequent actual ship applications, the tunable samples can be replaced with customized double-layer micro-perforated plate series sound absorption materials with the same non-adjustable perforation rate.

[0047] As can be seen from the above embodiments, the sound absorption material composed of the present medium and low frequency silencing element, when applied to the air inlet near the power station diesel generator, can effectively achieve the sound absorption effect in the medium and low frequencies. The present invention effectively reduces the material thickness by introducing an inclined cavity and using a mechanical push-pull device, and realizes the medium and low frequency advantages and frequency tunability.

[0048] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A medium and low frequency muffler element capable of graded frequency modulation, characterized in that: The invention comprises an outer shell with a hollow configuration, wherein one side wall of the outer shell is a first micro-perforated plate, an inclined cabin is arranged inside the outer shell, and the inclined cabin is enclosed by a second micro-perforated plate and a plurality of side plates, and the plurality of side plates, the second micro-perforated plate and the first micro-perforated plate divide the inner chamber of the outer shell into two independent areas, and the first micro-perforated plate and the second micro-perforated plate are both equipped with a shading plate that can be pushed and pulled and moved, and the shading plate adjusts the sound absorption coefficient of the medium and low frequency sound-absorbing element by blocking the perforation rate of the first micro-perforated plate and the second micro-perforated plate when being pushed and pulled.

2. The mid- and low-frequency muffler element capable of graded frequency modulation according to claim 1, characterized in that: The first micro-perforated plate and the second micro-perforated plate are arranged in parallel.

3. The mid- and low-frequency muffler element capable of graded frequency modulation according to claim 1, characterized in that: The angle between the side plate and the inner side wall of the outer shell is 15°~45°.

4. The mid- and low-frequency muffler element capable of graded frequency modulation according to claim 1, characterized in that: The first micro-perforated plate and the second micro-perforated plate are both square plates.

5. The mid- and low-frequency muffler element capable of graded frequency modulation according to claim 1, characterized in that: The diameter of the holes on the first micro-perforated plate and the second micro-perforated plate is 0.5 mm to 2 mm, and the thickness of the first micro-perforated plate and the second micro-perforated plate is 0.5 mm to 2 mm.

6. The mid- and low-frequency muffler element capable of graded frequency modulation according to claim 1, characterized in that: The shading plates are connected to the first micro-perforated plate and the second micro-perforated plate via sliding bearings.

7. The mid- and low-frequency muffler element capable of graded frequency modulation according to claim 1, characterized in that: The first micro-perforated plates and the second micro-perforated plates are evenly arranged in multiple rows and columns.

8. The mid- and low-frequency muffler element capable of graded frequency modulation according to claim 1, characterized in that: The height of the outer shell is less than or equal to 60 mm.

9. The mid- and low-frequency muffler element capable of graded frequency modulation according to any one of claims 1 to 8, characterized in that: The tilting cabin is provided with multiple layers to expand the frequency adjustment range.

10. A design method for a mid- and low-frequency muffler element capable of graded frequency modulation based on any one of claims 1 to 9, characterized in that: The following steps are involved: Conduct air noise tests on the area where the silencer is to be installed to obtain the frequency range where the noise is most prominent; By adjusting the area of ​​the first micro-perforated plate and the second micro-perforated plate covered by the two shading plates, the sound absorption coefficient of the low- and medium-frequency muffler elements under different shielding conditions is tested, and the optimal perforation rate of the first micro-perforated plate and the second micro-perforated plate is selected according to the frequency range in which the noise of the muffler device to be installed is most prominent; According to the selected optimal perforation rates of the first and second micro-perforated plates, the areas where the two shading plates cover the first and second micro-perforated plates are adjusted, and then the adjusted low- and medium-frequency silencer elements are installed on the walls around the air inlet.

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