Impedance combined silencer

Abstract

The invention relates to the technical field of silencers, and discloses an impedance combined silencer which comprises a shell with an inner cavity, an air outlet is formed in the side wall of the shell, an air inlet is formed in the bottom of the shell, a sheet type resistive silencing section, a reactive sound absorption resonant cavity and an expansion section which are communicated are sequentially arranged in the inner cavity, the sheet type resistive silencing section is communicated with the air outlet, and the reactive sound absorption resonant cavity is communicated with the expansion section. The expansion section communicates with the air inlet; the first cavity wall and the second cavity wall of the resistant sound absorption resonant cavity are provided with a plurality of holes communicating with the inner cavity and the resistant sound absorption resonant cavity, the first cavity wall and the second cavity wall are oppositely arranged, and the air outlet faces the first cavity wall and the second cavity wall. According to the reactive sound absorption resonant cavity, the cavity wall holes are used for guiding sound waves to be coupled into the reactive sound absorption resonant cavity, Helmholtz resonance is formed, low-frequency noise is effectively absorbed, medium-high frequency noise is further absorbed with the assistance of the sheet type resistive noise elimination section, then the noise elimination frequency band is effectively widened, and low-frequency and medium-high frequency cooperative noise elimination is achieved.

Description

Technical Field

[0001] This invention relates to the field of noise reduction technology, and in particular to an impedance combination type silencer. Background Technology

[0002] Noise pollution is becoming increasingly prominent among various industrial equipment, especially the noise generated during the operation of equipment such as transformers, motors, and fans. This noise not only affects the surrounding environment but also adversely impacts the health of personnel operating the equipment. To reduce noise pollution, silencers are typically installed at the air inlets and outlets of the equipment. Existing silencers are mainly classified into resistive silencers, reactive silencers, exhaust silencers, and active silencers based on their noise reduction principles. Among these, resistive silencers primarily absorb sound energy through porous sound-absorbing materials. They have advantages such as simple structure, low cost, and good absorption of mid-to-high frequency noise. Therefore, conventional plate-type resistive silencers are widely used in engineering, particularly suitable for controlling high-frequency noise generated by fan-type equipment.

[0003] However, conventional plate resistive mufflers lack the ability to absorb low-frequency noise, resulting in poor performance in low-frequency noise control. Summary of the Invention

[0004] This invention provides an impedance-combined silencer to solve the technical problem that the silencing frequency band of conventional plate resistive silencers is limited to the mid-to-high frequency range.

[0005] To solve the above-mentioned technical problems, the present invention provides an impedance combination silencer, which includes a shell with an inner cavity, an air outlet on the side wall of the shell, an air inlet at the bottom of the shell, and a plate-type resistive silencing section, an reactive sound-absorbing resonant cavity and an expansion section arranged sequentially in the inner cavity, wherein the plate-type resistive silencing section is connected to the air outlet and the expansion section is connected to the air inlet;

[0006] The first and second cavity walls of the resistive sound-absorbing resonant cavity are provided with a plurality of holes connecting the inner cavity and the resistive sound-absorbing resonant cavity. The first cavity wall and the second cavity wall are arranged opposite to each other, and the air outlet faces the first cavity wall and the second cavity wall.

[0007] In some embodiments, the aperture of the plurality of holes ranges from 0.1 to 0.8 cm, the total area of ​​the plurality of holes opened on the first cavity wall accounts for 10% to 25% of the total area of ​​the first cavity wall, and the total area of ​​the plurality of holes opened on the second cavity wall accounts for 10% to 25% of the total area of ​​the second cavity wall.

[0008] In some embodiments, the holes are arranged at equal intervals.

[0009] In some embodiments, the holes on the first cavity wall and the holes on the second cavity wall correspond one-to-one.

[0010] In some embodiments, the housing includes a perforated plate, sound-absorbing cotton, a damping layer, and a housing steel plate; the perforated plate, the sound-absorbing cotton, the damping layer, and the housing steel plate are arranged sequentially from the inside to the outside, wherein the end face of the perforated plate facing away from the inner cavity is connected to the sound-absorbing cotton, and the damping layer is located between the sound-absorbing cotton and the housing steel plate.

[0011] In some embodiments, a fixing component is further included; the fixing component includes a first fixing member and a second fixing member; one end of the first fixing member is connected to the top inner wall of the housing, and the other end is connected to the first end face of the resistive sound-absorbing resonant cavity; one end of the second fixing member is connected to the bottom inner wall of the housing, and the other end is connected to the second end face of the resistive sound-absorbing resonant cavity, the first end face and the second end face of the resistive sound-absorbing resonant cavity being opposite to each other.

[0012] In some embodiments, the sheet-type resistive silencing section includes a plurality of sheet-type silencing sheets with a perforated plate double-sided wrapped with sound-absorbing cotton structure; the same end of the plurality of sheet-type silencing sheets is vertically connected to the inner surface of the side wall of the housing, and the plurality of sheet-type silencing sheets are arranged vertically at equal intervals.

[0013] In some embodiments, the channel formed by the space between the plurality of sheet-type sound-absorbing plates is a sound-absorbing plate ventilation channel; the channel formed by the internal space of the resistive sound-absorbing resonant cavity is a cavity channel; the sound-absorbing plate ventilation channel is directly opposite the cavity channel.

[0014] In some embodiments, a transition elbow is further included; the transition elbow and the housing are integrally formed, and the transition elbow is adapted to the air inlet.

[0015] In some embodiments, the area of ​​the vertical cross-section of the expansion section is d1, and the area of ​​the transverse cross-section of the end of the transition elbow located inside the housing is d2, resulting in: 1.1d2 <d1<1.5d2。

[0016] Compared with the prior art, the impedance combination silencer of this invention has the following advantages:

[0017] This invention, through a series of interconnected structures—an expansion section, a reactive sound-absorbing resonant cavity, and a plate-type resistive silencer—within the inner cavity of the housing, allows airflow entering from the air inlet at the bottom of the housing to pass through each structure sequentially, achieving multi-stage noise reduction. The expansion section acts as a buffer zone, initially reflecting and attenuating sound energy. The reactive sound-absorbing resonant cavity, a low-frequency noise reduction structure, has several holes on its opposing first and second cavity walls connecting the inner cavity and the cavity, thus forming a Helmholtz-like resonance structure. When low-frequency sound waves from the airflow enter the reactive sound-absorbing resonant cavity through the holes in the cavity wall, they induce capacitive oscillations in the air column within the cavity. These oscillations couple with the mass effect of the air column within the channels, generating strong acoustic resonance in the low-frequency range and converting it into heat energy. This significantly absorbs noise in that frequency band, achieving a targeted and energy-dissipative low-frequency noise reduction effect. This overcomes the shortcomings of traditional plate-type resistive silencers in reducing low-frequency noise. Furthermore, before the airflow in the inner cavity dissipates from the air outlet of the shell, the mid-to-high frequency noise in the sound waves passing through the resistive silencing section can be reflected and absorbed, thereby achieving silencing of mid-to-high frequency noise. It can be seen that in this embodiment of the invention, the resistive sound-absorbing resonant cavity utilizes the cavity wall holes to guide sound waves into the resistive sound-absorbing resonant cavity and form a Helmholtz resonance, effectively absorbing low-frequency noise. The addition of a plate-type resistive silencing section further absorbs mid-to-high frequency noise, thus effectively broadening the silencing frequency band and achieving synergistic silencing of low and mid-to-high frequencies. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the impedance combination silencer provided in an embodiment of the present invention;

[0019] Figure 2 This is a comparison of the insertion loss simulation results of the impedance combined silencer and the resistive conventional silencer provided in the embodiments of the present invention;

[0020] Figure 3 This is a flow field simulation result diagram of the impedance combination silencer provided by the present invention;

[0021] Figure 4 This is a flow field simulation result diagram of the resistive conventional muffler provided by the present invention;

[0022] Figure 5 This is a partial schematic diagram of the impedance combination silencer provided by the present invention.

[0023] In the diagram, 100 is the shell; 101 is the perforated plate; 102 is the sound-absorbing cotton; 103 is the damping layer; 104 is the shell steel plate; 110 is the inner cavity; 111 is the sheet-type resistive silencing section; 1111 is the sheet-type silencing plate; 112 is the reactive sound-absorbing resonant cavity; 1121 is the first cavity wall; 1122 is the second cavity wall; 113 is the expansion section; 120 is the air outlet; 130 is the air inlet; 200 is the fixing component; 210 is the first fixing component; 220 is the second fixing component; 300 is the transition elbow; 310 is the channel section; and 320 is the arc-shaped section. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of this invention, it should be noted that the directional terms such as "center", "upper", "lower", "inner", and "outer" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0026] Furthermore, the terms "first" and "second" 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. Thus, the use of "first" and "second" to define a feature may explicitly or implicitly include one or more of that feature, and in the description of this invention, "at least" means one or more, unless otherwise explicitly specified.

[0027] In this invention, unless otherwise explicitly specified and limited, the terms "assembly," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can also refer to a mechanical connection; they can refer to a direct connection or a connection through an intermediate medium; or they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] See again Figures 1 to 4This invention provides an impedance-combined silencer, which includes a housing 100 with an inner cavity 110. The side wall of the housing 100 has an air outlet 120, and the bottom of the housing 100 has an air inlet 130. The inner cavity 110 is provided with a connected plate-type resistive silencing section 111, an reactive sound-absorbing resonant cavity 112, and an expansion section 113, wherein the plate-type resistive silencing section 111 is connected to the air outlet 120, and the expansion section 113 is connected to the air inlet 130.

[0029] The first cavity wall 1121 and the second cavity wall 1122 of the resistive sound-absorbing resonant cavity 112 are provided with a plurality of holes connecting the inner cavity 110 and the resistive sound-absorbing resonant cavity 112. The first cavity wall 1121 and the second cavity wall 1122 are arranged opposite to each other, and the air outlet 120 faces the first cavity wall 1121 and the second cavity wall 1122.

[0030] In this embodiment, the difference from conventional plate-type silencers lies in the inclusion of a reactive sound-absorbing resonant cavity 112 with a Helmholtz resonator-like structure in the impedance combination silencer. The two opposing cavity walls (first cavity wall 1121 and second cavity wall 1122) of the reactive sound-absorbing resonant cavity 112 each have several holes communicating with the inner cavity 110 of the housing 100 and the reactive sound-absorbing resonant cavity 112, and the air outlet 120 on the housing 100 faces the first cavity wall 1121 and the second cavity wall 1122. When noise in the airflow inside the housing 100 enters the reactive sound-absorbing resonant cavity 112 through the holes in the cavity wall, based on the Helmholtz resonance principle, the low-frequency noise in the airflow is reflected and resonates within the reactive sound-absorbing resonant cavity 112, converting sound energy into heat energy, thereby achieving noise reduction in the low-frequency range.

[0031] Meanwhile, when the airflow that does not enter the reactive sound-absorbing resonant cavity 112 in the inner cavity 110 (this part of the airflow includes low, mid and high frequency noise) and the airflow that moves out of the cavity wall of the reactive sound-absorbing resonant cavity 112 (this part of the airflow includes mid and high frequency noise) move to the plate resistive noise-absorbing section 111, they are further scattered, reflected and absorbed by the plate resistive noise-absorbing section 111, thereby achieving noise reduction of various frequency bands (i.e. low, mid and high frequency bands).

[0032] It should be noted that, in the embodiments of the present invention, low-frequency noise refers to noise with a frequency band between 400-750 Hz, and mid-to-high frequency noise refers to noise with a frequency band between 750-1200 Hz.

[0033] Specifically, the impedance-combined silencer includes a housing 100 with an inner cavity 110. Within the inner cavity 110 of the housing 100, a connected plate-type resistive silencing section 111, a reactive sound-absorbing resonant cavity 112, and an expansion section 113 are sequentially arranged. An air outlet 120 is provided on the side wall of the housing 100, and an air inlet 130 is provided at the bottom of the housing 100. The plate-type resistive silencing section 111 is connected to the air outlet 120, and the expansion section 113 is connected to the air inlet 130. When airflow enters the expansion section 113 through the air inlet 130, the expansion section 113 acts as a buffer space, reflecting the sound energy in the airflow to initially attenuate the sound energy of noise in various frequency bands.

[0034] The resistive sound-absorbing resonant cavity 112 includes a first cavity wall 1121 and a second cavity wall 1122 disposed opposite to each other. The first cavity wall 1121 is the cavity wall adjacent to the air inlet 130, and the second cavity wall 1122 is the cavity wall away from the air inlet 130. The air outlet 120 faces the first cavity wall 1121 and the second cavity wall 1122. Both the first cavity wall 1121 and the second cavity wall 1122 have several holes for connecting the inner cavity 110 of the housing 100 and the resistive sound-absorbing resonant cavity 112. The cavity walls of the resistive sound-absorbing resonant cavity 112 are made of steel plate. Therefore, the resistive sound-absorbing resonant cavity 112 forms a structure similar to a Helmholtz resonator. When a specific frequency component (referring to low-frequency noise between 400-750Hz) in the airflow at the expansion section 113 couples into the reactive sound-absorbing resonant cavity 112 through the holes in the first cavity wall 1121, acoustic resonance occurs within the cavity, thereby converting sound energy into heat energy or dissipating it through internal structural vibration energy, thus achieving low-frequency noise reduction. Therefore, the reactive sound-absorbing resonant cavity 112 in this embodiment of the invention enables the impedance-combined silencer to significantly reduce low-frequency noise that is difficult to eliminate with conventional plate-type resistive silencers, improving the silencer's adaptability in complex low-frequency noise source scenarios such as indoor transformers, fans, air conditioning units, and industrial equipment. Figure 2 As shown, the impedance-combined silencer of this invention significantly improves insertion loss in the 400Hz-750Hz frequency band, resulting in a noticeable improvement in low-frequency noise reduction. Furthermore... Figure 3 as well as Figure 4 As shown, the flow field distribution of the impedance combined silencer in this invention is basically the same as that of the conventional impedance silencer (conventional plate resistive silencer). The setting of the resistive sound-absorbing resonant cavity 112 does not affect the flow field performance and does not increase the pressure loss.

[0035] Furthermore, the inner cavity 110 of the housing 100 is also provided with a plate-type resistive noise-absorbing section 111 that connects to the air outlet 120. For the airflow in the inner cavity 110 that does not enter the resistive sound-absorbing resonant cavity 112 and the airflow exiting from the second cavity wall 1122 of the resistive sound-absorbing resonant cavity 112, before being dispersed from the air outlet 120, it will first pass through the plate-type resistive noise-absorbing section 111 located between the air outlet 120 and the resistive sound-absorbing resonant cavity 112, and be reflected multiple times by the plate-type resistive noise-absorbing section 111, thereby achieving energy dissipation of noise in various frequency bands.

[0036] As can be seen, the sequential arrangement of the expansion section 113, the resistive sound-absorbing resonant cavity 112, and the plate-type resistive silencing section 111 forms a multi-stage composite silencing structure with synergistic effects of low-frequency resonance and high-frequency sound absorption, significantly broadening the overall silencing frequency band and increasing the resistive silencing effect. Furthermore, by employing an impedance composite structure with an internal resistive sound-absorbing resonant cavity 112, low-frequency sound absorption performance can be effectively improved, low-frequency noise can be effectively controlled, compensating for the poor low-frequency performance of the sound-absorbing cotton 102, without affecting the flow field distribution and ventilation and heat dissipation performance.

[0037] In one embodiment, the aperture of the plurality of holes ranges from 0.1 to 0.8 cm, the total area of ​​the plurality of holes opened on the first cavity wall 1121 accounts for 10% to 25% of the total area of ​​the first cavity wall 1121, and the total area of ​​the plurality of holes opened on the second cavity wall 1122 accounts for 10% to 25% of the total area of ​​the second cavity wall 1122.

[0038] In this embodiment, both the first cavity wall 1121 and the second cavity wall 1122 are provided with a plurality of holes of the same diameter and opening ratio. The opening ratio is determined based on the ratio of the total area of ​​the holes to the total area of ​​the cavity walls. Therefore, the opening ratios of the holes in the first cavity wall 1121 and the second cavity wall 1122 are the same; that is, the ratio of the total area of ​​the holes in the first cavity wall 1121 to the total area of ​​the first cavity wall 1121 is the same as the ratio of the total area of ​​the holes in the second cavity wall 1122 to the total area of ​​the second cavity wall 1122.

[0039] Since the noise reduction frequency band that the resistive sound-absorbing resonant cavity 112 can achieve is closely related to its size parameters, the size parameters of the resistive sound-absorbing resonant cavity 112 (including the porosity of the holes on the cavity wall, the diameter of the holes, the volume of the resistive sound-absorbing resonant cavity 112, etc.) should be reasonably set according to the low-frequency noise reduction requirements of the resistive sound-absorbing resonant cavity 112.

[0040] Specifically, based on the low-frequency noise reduction requirements of the resistive sound-absorbing resonant cavity 112 between 400-750Hz, the aperture thickness of the hole is set to a range of 0.1-0.8 cm; the opening ratio thickness of the hole is set to a range of 10%-25%; the thickness of the first cavity wall 1121 and the second cavity wall 1122 is set to a range of 1-5 mm; and the thickness of the periphery sidewall of the resistive sound-absorbing resonant cavity 112 is set to a range of 0.5-2 cm.

[0041] Among them, the size parameters of the resistant sound-absorbing resonant cavity 112 and the resonant frequency to be anechoic must satisfy the following:

[0042]

[0043] In the formula, f r The resonant frequency to be silenced is represented by: C; the speed of sound in air is represented by: π (pi), which is 3.14; A represents the vertical cross-sectional area of ​​the airflow channel in the resistive sound-absorbing resonant cavity; k represents the porosity of the hole; V represents the volume of the resistive sound-absorbing resonant cavity; l represents the thickness of the first and second cavity walls; and d represents the aperture of the hole (the aperture is also the diameter of the hole).

[0044] Based on the resonant frequency range to be anechoic, the cavity wall pores, porosity, diameter, and volume of the resistive sound-absorbing resonant cavity 112 are set. This allows control over the frequency range of sound waves entering the resistive sound-absorbing resonant cavity 112 and precise matching with the main frequency band to be anechoic, enabling effective coupling of sound waves as they pass through the pores and exciting volume resonance within the resistive sound-absorbing resonant cavity 112, thereby achieving resonant absorption of the target low-frequency noise.

[0045] In one specific embodiment, such as Figure 1As shown, a cylindrical resistive sound-absorbing resonant cavity 112 is required to silence noise in the 500Hz frequency band. Based on the noise reduction requirement for 500Hz noise, the specific dimensional parameters of the resistive sound-absorbing resonant cavity 112 are set as follows: the diameter of the holes on the opposite side walls (first cavity wall 1121 and second cavity wall 1122) of the resistive sound-absorbing resonant cavity 112 is set to 0.6cm; the thickness of the first cavity wall 1121 and the second cavity wall 1122 is set to 1.5mm; the opening ratio of the holes is set to 12%; the cylindrical periphery sidewalls are made of steel plate, and the thickness of the steel plate is set to 1cm; the distance between the first cavity wall 1121 and the second cavity wall 1122 of the resistive sound-absorbing resonant cavity 112 is set to 40cm, where the distance between the first cavity wall 1121 and the second cavity wall 1122 represents the length of the resistive sound-absorbing resonant cavity 112; the area of ​​the vertical cross-section of the airflow direction in the internal cavity channel of the resistive sound-absorbing resonant cavity 112 is set to 0.14㎡, and the volume of the resistive sound-absorbing resonant cavity 112 is set to 0.056m³. 3 Therefore, noise with a frequency / band of 500Hz can be silencing.

[0046] More specifically, the holes are arranged at equal intervals. The holes on the first cavity wall 1121 and the holes on the second cavity wall 1122 correspond one-to-one.

[0047] In this embodiment, the holes on the first cavity wall 1121 are the first holes (not shown in the figure), and the holes on the second cavity wall 1122 are the second holes (not shown in the figure). The first and second holes correspond one-to-one. This design, on the one hand, allows sound waves to form a symmetrical transmission path and resonance field distribution during their entry into the resistive sound-absorbing resonant cavity 112. This facilitates a uniform and stable volumetric resonance effect between the first and second cavity walls 1121 and 1122, thereby improving resonance efficiency. On the other hand, it helps the two cavities form a mirror-coupled sound field, improving the coupling efficiency of sound waves entering the resonant cavity, thereby further enhancing the absorption capacity of low-frequency sound energy and strengthening the noise reduction performance of specific frequency bands (low frequencies in this invention). Furthermore, the equal spacing between the first and second holes avoids sound pressure concentration in localized areas, reducing the impact of acoustic hotspots on the cavity structure, thereby improving the stability and service life of the resistive sound-absorbing resonant cavity 112.

[0048] In one embodiment, such as Figure 1As shown, the housing 100 includes a perforated plate 101, sound-absorbing cotton 102, a damping layer 103, and a housing steel plate 104; the perforated plate 101, the sound-absorbing cotton 102, the damping layer 103, and the housing steel plate 104 are arranged sequentially from the inside to the outside, wherein the end face of the perforated plate 101 facing away from the inner cavity 110 is connected to the sound-absorbing cotton 102, and the damping layer 103 is located between the sound-absorbing cotton 102 and the housing steel plate 104.

[0049] In this embodiment, the housing 100 includes a perforated plate 101, sound-absorbing cotton 102, a damping layer 103, and a housing steel plate 104 arranged sequentially from the inside out, forming a multi-layer composite sound-absorbing structure with gradually changing impedance. Under the synergistic effect of each layer of materials, the noise attenuation capability can be improved. Among them, the perforated plate 101 is the innermost layer (i.e., the first layer). Since the perforated plate 101 has several holes, sound waves can pass through the perforated plate 101 and be driven into the sound-absorbing layer where the sound-absorbing cotton 102 is located by the airflow. The sound-absorbing cotton 102 is the second layer, connected to the end face of the perforated plate 101 facing away from the inner cavity 110. The sound-absorbing cotton 102 has a good porous structure. Through air resistance and pore friction, the sound energy of noise can be converted into heat energy, thus effectively absorbing the noise sound waves. The damping layer 103, as the third layer, is located between the sound-absorbing cotton 102 and the shell steel plate 104. The damping layer 103 can dissipate structural vibrations and some low-frequency sound waves, and can absorb solid noise or low-frequency sound energy transmitted from the inner wall of the shell 100. The shell steel plate 104, as the outermost (i.e., the fourth) load-bearing structure, provides overall rigid support, and at the same time plays a role in sound insulation and protection of the internal materials.

[0050] Specifically, the shell steel plate 104 has a thickness greater than 1.5 cm, providing sufficient mechanical strength and structural rigidity to ensure that the shell 100 does not deform or resonate under long-term conditions in complex aerodynamic environments. The sound-absorbing cotton 102 has a thickness greater than 5 cm and is made of glass wool or polyurethane wool. Its average sound absorption coefficient is greater than 0.7, and it has high porosity and fiber damping performance, giving it excellent mid-to-high frequency sound energy absorption capabilities. The perforated plate 101 has several holes of the same diameter, each hole having a diameter greater than 1 cm and a perforation rate greater than 20%, which can significantly improve the incident transmittance of sound waves, allowing sound energy to enter the sound-absorbing layer more fully for dissipation.

[0051] Through a multi-layered composite design, not only is a continuous attenuation path achieved from sound wave penetration to gradual absorption and then to sound energy isolation, but it also significantly improves noise absorption efficiency and enhances the ability to suppress low-frequency structural vibration noise. Furthermore, the nested layout structure is compact and easy to assemble, improving the overall mechanical strength and durability of the housing 100, making it suitable for long-term operation in high-intensity, complex acoustic environments.

[0052] In one embodiment, such as Figure 1 As shown, it also includes a fixing component 200; the fixing component 200 includes a first fixing member 210 and a second fixing member 220; one end of the first fixing member 210 is connected to the top inner wall of the housing 100, and the other end is connected to the first end face of the resistive sound-absorbing resonant cavity 112; one end of the second fixing member 220 is connected to the bottom inner wall of the housing 100, and the other end is connected to the second end face of the resistive sound-absorbing resonant cavity 112, the first end face and the second end face of the resistive sound-absorbing resonant cavity 112 are opposite to each other.

[0053] In this embodiment, the resistive sound-absorbing resonant cavity 112 is connected to the inner wall of the housing 100 via a fixing component 200 (specifically, it is connected to the perforated plate 101 via the fixing component 200), so that the resistive sound-absorbing resonant cavity 112 is suspended in the inner cavity 110 space of the housing 100, that is, the resistive sound-absorbing resonant cavity 112 is used as an independent acoustic unit. This arrangement can avoid the "sound bridge effect" caused by rigid contact between the resistive sound-absorbing resonant cavity 112 and the housing 100. In other words, if the resistive sound-absorbing resonant cavity 112 is directly attached to the housing 100, sound waves may propagate around the resistive sound-absorbing resonant cavity 112 through the structure of the housing 100, weakening its ability to absorb noise of a specific frequency.

[0054] Preferably, to improve the noise reduction effect of low-frequency noise, the resistive sound-absorbing resonant cavity 112 can be suspended and installed in the central region of the inner cavity 110 of the housing 100 by the fixing component 200. This allows the resistive sound-absorbing resonant cavity 112 to more evenly contact sound waves incident from all directions, thereby enabling the sound waves to fully resonate within the resistive sound-absorbing resonant cavity 112. Simultaneously, the gap between the resistive sound-absorbing resonant cavity 112 and the inner wall of the housing 100 can form an auxiliary air layer. Mid-to-high frequency noise in the sound waves continuously reflects and moves within this air layer, thereby enhancing the sound absorption effect of mid-to-high frequency noise.

[0055] Specifically, the fixing component 200 includes a first fixing member 210 and a second fixing member 220. The two opposite end faces of the resistive sound-absorbing resonant cavity 112 are respectively connected to the inner wall of the top of the housing 100 through the first fixing member 210 and to the inner wall of the bottom of the housing 100 through the second fixing member 220. The first fixing member 210 and the second fixing member 220 can overlap along their own length. The first fixing member 210 and the second fixing member 220 can be rigid connectors (such as metal brackets or high-strength plastic rods) or components with a certain degree of elasticity (such as damping alloy sheets or rubber-coated connecting rods). If a rigid material is used, sufficient load-bearing capacity must be ensured to prevent the resistive sound-absorbing resonant cavity 112 from shifting due to its own weight or airflow vibration. If an elastic material is used, the transmission of vibration of the housing 100 to the resistive sound-absorbing resonant cavity 112 can be reduced, thereby reducing the interference of structural sound transmission on the sound absorption effect.

[0056] The lengths of the first fixing member 210 and the second fixing member 220 need to be precisely designed according to the height of the inner cavity 110 of the housing 100 and the installation position of the resistive sound-absorbing resonant cavity 112. The ratio between the length of the first fixing member 210 and the distance from the top inner wall of the housing 100 to the first end face of the resonant cavity is 1:1; the ratio between the length of the second fixing member 220 and the distance from the bottom inner wall of the housing 100 to the second end face of the resonant cavity is 1:1. In this way, it can be ensured that the resistive sound-absorbing resonant cavity 112 is suspended at a preset height in the inner cavity 110 space (usually the central area of ​​the cavity, to maximize the contact efficiency with sound waves).

[0057] For the connection between the fixing component 200 and the inner wall of the housing 100, the connection between the top end of the first fixing member 210 and the inner wall of the top of the housing 100 can be achieved by bolting, welding (for metal housings 100), or embedded snap-fit ​​(for plastic housings 100); the connection between the bottom end of the second fixing member 220 and the inner wall of the bottom of the housing 100 is similar. If necessary, the connection point can be reinforced (e.g., by adding shims or reinforcing ribs) to prevent loosening due to vibration after long-term use.

[0058] Regarding the connection between the fixing component 200 and the resistive sound-absorbing resonant cavity 112, specifically the connection between the bottom end of the first fixing member 210 and the first end face of the resistive sound-absorbing resonant cavity 112, and the top end of the second fixing member 220 and the second end face of the resonant cavity, can adopt a threaded connection that is easy to disassemble and maintain, or an adhesive connection suitable for scenarios where frequent replacement is not required. The specific connection method can be designed according to actual setup requirements, and this application does not limit the connection method between the fixing component 200 and the resistive sound-absorbing resonant cavity 112. In addition, the first fixing member 210 and the second fixing member 220 are symmetrically distributed along the central axis of the resistive sound-absorbing resonant cavity 112 (i.e., the connection points are located at the center positions of the first end face and the second end face of the resonant cavity, respectively), ensuring that the resonant cavity is subjected to balanced forces when suspended, and avoiding tilting or swaying caused by the shift of the center of gravity.

[0059] Therefore, by adopting a structural arrangement with bidirectional fixation on the top and bottom inner walls, the resistive sound-absorbing resonant cavity 112 is stably suspended within the housing 100, avoiding positional displacement, resonance failure, or structural fatigue caused by long-term operation or external disturbances. Simultaneously, this arrangement also helps maintain a relative distance between the resistive sound-absorbing resonant cavity 112 and the inner cavity 110 of the housing 100, ensuring good sound field distribution conditions during sound wave coupling and contributing to maintaining the stability and consistency of the cavity's resonance performance.

[0060] In one embodiment, such as Figure 1 As shown, the sheet-type resistive sound-absorbing section 111 includes a plurality of sheet-type sound-absorbing sheets 1111 with a perforated plate double-sided wrapped with sound-absorbing cotton structure; the same end of the plurality of sheet-type sound-absorbing sheets 1111 is vertically connected to the inner surface of the side wall of the housing 100, and the plurality of sheet-type sound-absorbing sheets 1111 are arranged vertically at equal intervals.

[0061] In this embodiment, the sheet-type resistive silencing section 111 is composed of several sheet-type silencing sheets 1111, each consisting of a perforated plate double-sided wrapped with sound-absorbing cotton. These sheet-type silencing sheets 1111 are identical in specifications and dimensions. The sheet-type silencing sheet 1111, with its perforated plate double-sided wrapped with sound-absorbing cotton, is essentially a composite structure of a double-layer perforated plate and intermediate sound-absorbing cotton. This composite structure utilizes the perforated plate to scatter and partially reflect sound waves, while simultaneously guiding the sound waves to the intermediate sound-absorbing cotton layer for energy attenuation, thereby achieving noise control. The silencing requirements for specific frequency bands can be adapted by adjusting the perforation rate, the thickness of the sheet-type silencing sheet 1111, and the density of the sound-absorbing cotton. Therefore, this sheet-type resistive silencing section 111 possesses good adjustability and adaptability. For example, increasing the thickness of the sound-absorbing cotton enhances low-frequency noise reduction, while increasing the perforation rate makes it more sensitive to high-frequency noise, thus achieving the goal of "wideband coverage" silencing.

[0062] Specifically, the single-piece sound-absorbing sheet 1111 has a rectangular planar shape with rounded edges to reduce turbulent noise during airflow. The thickness of the sheet sound-absorbing sheet 1111 is set between 6-10 cm. The perforated plate of the sheet sound-absorbing sheet 1111 has several holes with a diameter greater than 1 cm and a perforation rate greater than 20% evenly distributed on it. This design ensures that sound waves can smoothly penetrate the perforated plate and enter the internal sound-absorbing cotton between the two layers of perforated plates, while maintaining the structural strength of the sheet sound-absorbing sheet 1111.

[0063] Sound-absorbing cotton, made of glass wool or polyurethane wool, is filled between two layers of perforated panels, with an average sound absorption coefficient greater than 0.8. The thickness of the sound-absorbing cotton is designed according to actual sound attenuation requirements. If necessary, the sound-absorbing cotton can be treated for moisture protection (such as wrapping it with glass cloth or aluminum foil) to prevent the sound absorption performance from deteriorating due to humidity changes during long-term use. The two layers of perforated panels are fixed by edge pressing or bolts to tightly wrap the sound-absorbing cotton, forming an integral rigid structure.

[0064] All the plate-type sound-absorbing plates 1111 are vertically welded or bolted to the inner surface of the side wall of the housing at the same end. If necessary, the connection points can be reinforced with stiffeners to ensure that the plate-type sound-absorbing plates 1111 do not shake or deform under the impact of airflow. The vertical connection design makes the plate-type sound-absorbing plates 1111 form a 90° angle with the side wall of the housing, so that the horizontal plane of the plate-type sound-absorbing plates 1111 is parallel to the airflow direction, thereby maximizing the contact area with sound waves.

[0065] Several sheet-type sound-absorbing plates 1111 are evenly arranged vertically (i.e., along the height of the housing 100) along the inner side of the housing 100. The spacing design needs to consider the height of the sound-absorbing plates and the target noise reduction frequency: for mid-to-high frequency noise, the spacing can be appropriately reduced (by increasing the density of the sheet-type sound-absorbing plates 1111 to improve sound wave reflection and absorption efficiency); for low-frequency noise, the spacing can be increased (by reducing airflow resistance and avoiding secondary noise). The vertically evenly spaced sheet-type sound-absorbing plates 1111 can maximize the sound absorption area within the limited space of the housing 100's inner cavity 110, making it particularly suitable for scenarios with limited installation space, such as duct silencing and small ventilation systems.

[0066] In one specific embodiment, the sheet-type resistive silencing section 111 is composed of several sheet-type silencing plates 1111 arranged at equal intervals. Each sheet-type silencing plate 1111 is a perforated plate double-sided wrapped with sound-absorbing cotton, and its length is 1m. The perforation diameter of the holes in the perforated plate is 1.5cm, with a perforation rate of 25%. The sound-absorbing cotton is ultrafine glass wool with an average coefficient of 0.8. The sheet-type silencing plates 1111 are arranged vertically at equal intervals and are parallel to the horizontal plane. This arrangement ensures uniform airflow distribution, facilitating heat dissipation, and avoids airflow deflection caused by asymmetrical structures, improving overall aerodynamic stability. The sheet-type silencing plates 1111 are 8cm thick, and to ensure effective ventilation and heat dissipation, the spacing between the sheet-type silencing plates 1111 (i.e., the ventilation channels) is set to 10cm. This ensures both high airflow throughput and reduced wind resistance, facilitating heat dissipation and stable system ventilation.

[0067] In one embodiment, the channel formed by the space between the plurality of sheet-like sound-absorbing plates 1111 is a sound-absorbing plate ventilation channel; the channel formed by the internal space of the resistive sound-absorbing resonant cavity 112 is a cavity channel; the sound-absorbing plate ventilation channel is directly opposite the cavity channel.

[0068] In this embodiment, when several sheet-type sound-absorbing plates 1111 are arranged vertically at equal intervals, the channel formed by the space between two adjacent sheet-type sound-absorbing plates 1111 is the sound-absorbing plate ventilation channel. Therefore, the upper and lower sides of the sound-absorbing plate ventilation channel are the perforated plate surfaces of the sheet-type sound-absorbing plates 1111, which are smooth and have uniform holes, serving as both the boundary for airflow and providing a path for sound waves to enter the sound-absorbing cotton. The two ends of the sound-absorbing plate ventilation channel are respectively connected to the air outlet 120 of the housing 100 and the inner cavity 110, forming a through airflow path.

[0069] The internal space of the resistive sound-absorbing resonant cavity 112 constitutes a cavity channel, the structure of which is determined by the shape of the shell 100 of the resistive sound-absorbing resonant cavity 112, and is usually a hollow structure (such as a cylindrical hollow cavity or a rectangular hollow cavity). Since the resistive sound-absorbing resonant cavity 112 is made of steel plate, the sound waves in the cavity channel are not directly absorbed by the resistive sound-absorbing resonant cavity 112, but rather the energy is dissipated through the resonance effect of the sound waves in the cavity channel. That is, when the frequency of the incident sound wave is consistent with the center frequency of the cavity channel (resistive sound-absorbing resonant cavity 112), the sound wave can resonate in the cavity channel, converting the energy into the vibration energy of the cavity wall and dissipating it, thereby achieving the silencing of noise at a specific frequency.

[0070] It should be noted that, as discussed in the foregoing embodiments, the center frequency setting of the resistive sound-absorbing resonant cavity 112 is related to the size setting of the resistive sound-absorbing resonant cavity 112, and will not be discussed again here. The center frequency of the resistive sound-absorbing resonant cavity 112, the resonance frequency to be anechoic, and the low-frequency anechoic requirements of the resistive sound-absorbing resonant cavity 112 all have the same meaning.

[0071] The ventilation channel of the silencer plate and the cavity channel are aligned linearly in space, or their axes coincide or are parallel. This allows the airflow from the cavity channel to directly enter the ventilation channel of the silencer plate, avoiding eddies and turbulence caused by channel misalignment. The ventilation channel of the silencer plate operates on the principle of resistive silencing (sound-absorbing cotton absorbs mid-to-high frequency noise), while the cavity channel operates on the principle of reactive silencing (resonance effect suppresses low-frequency noise). Their aligned arrangement ensures that noise first enters the cavity channel to silence low-frequency noise before passing through the ventilation channel to absorb mid-to-high frequency energy, forming a composite noise reduction chain that provides full coverage of both high and low frequencies. Compared to using only one structure, the composite noise reduction chain structure in this embodiment can significantly improve the overall noise reduction.

[0072] In summary, the direct alignment of the silencing plate ventilation channel and the cavity channel, through complementary acoustic principles, optimized airflow path, and collaborative structural design, not only enhances the broadband noise reduction effect but also reduces system energy consumption and maintenance costs. It is a highly efficient solution combining resistive and reactive silencing technologies, and is especially suitable for indoor substation industrial ventilation and other scenarios with high requirements for noise reduction range and operating efficiency.

[0073] In one embodiment, such as Figure 1 As shown, it also includes a transition elbow 300; the transition elbow 300 and the housing 100 are integrally formed, and the transition elbow 300 is adapted to the air inlet 130.

[0074] In this embodiment, the adapter elbow 300 is integrally formed with the housing 100. This integral forming avoids assembly errors or air leakage risks caused by multi-segment connections, improves overall sealing and mechanical strength, and simplifies manufacturing and assembly processes. The adapter elbow 300 includes a channel portion 310 and an arc-shaped portion 320 connected to the side wall of the channel portion 310. The channel portion 310 is adapted to the air inlet 130 at the bottom of the housing 100, and the channel portion 310 is used to guide air from the air inlet 130 into the interior of the housing 100. The arc-shaped portion 320 has an inwardly curved structure, with its arc center facing the direction of the resistive sound-absorbing resonant cavity 112 disposed inside the housing 100. The arc-shaped portion 320 and the channel portion 310 together form a curved airflow guiding path.

[0075] During airflow, air enters through the air inlet 130 at the bottom of the housing 100 and first moves vertically upward through the channel 310. Then, upon reaching the connection area between the channel 310 and the arc-shaped section 320, the airflow is guided by the curved structure of the arc-shaped section 320, sliding along its surface under the influence of inertia and the guiding surface, thus achieving a natural transition from vertical to horizontal direction. Guided by the arc-shaped section 320, the airflow direction achieves a smooth turn of approximately 90°, ultimately entering the subsequent expansion section 113, the resistive sound-absorbing resonant cavity 112, and the sheet-type resistive silencing section 111 in a horizontal direction, and is discharged through the air outlet 120 on the side wall of the housing 100.

[0076] By setting up an arc-shaped guide structure, the airflow smoothly changes direction after entering through the air inlet 130, avoiding the abrupt impact and turbulence that might be caused by right-angle bends, effectively reducing local resistance loss. Furthermore, if the airflow can enter the horizontally arranged expansion section 113 and the resistive sound-absorbing resonant cavity 112 stably and uniformly, the uniformity of the sound wave propagation path in the anechoic structure can be ensured, which is beneficial to the effective attenuation of noise in all frequency bands.

[0077] In one embodiment, such as Figure 1 as well as Figure 5As shown, the area of the vertical cross-section of the expansion section 113 is d1, and the area of the lateral cross-section of one end of the adapter elbow 300 located inside the housing 100 is d2, and there is: 1.1d2 < d1 < 1.5d2.

[0078] In this embodiment, the expansion section 113 is the space of the inner cavity 110 located between the resistive acoustic resonance cavity 112 and the side wall of the housing 100 inside the inner cavity 110. As Figure 5 shown, the length of the vertical cross-section of the expansion section 113 is denoted as L1, and the width of its vertical cross-section is denoted as L2, then d1 = L1×L2; the length of the lateral cross-section of one end of the adapter elbow 300 located inside the housing 100 (that is, the port cross-section of the channel portion 310 located in the inner cavity 110) is denoted as L3, and the width of its lateral cross-section is denoted as L4, then d2 = L3×L4. Since the area of the vertical cross-section of the expansion section 113 is larger than the outlet area of the adapter elbow 300 (the area difference between the two is specifically reflected as 1.1d2 < d1 < 1.5d2), the air flow expands after entering the expansion section 113, and the flow velocity slows down accordingly, which helps to convert the high-speed turbulent flow into low-speed laminar flow, thereby reducing the propagation speed and kinetic energy of noise. At the same time, the appropriate increase in the area of the expansion section 113 can, to a certain extent, break the standing wave conditions easily formed in the inner cavity 110 and reduce the noise enhancement effect caused by the superposition of standing waves and sound wave reflections.

[0079] In a specific embodiment, the vertical cross-section size of the expansion section 113 is 82 cm * 82 cm, and the lateral cross-section size of one end of the adapter elbow 300 located inside the housing 100 is 70 cm * 70 cm. That is, the vertical cross-sectional area of the expansion section 113 is 6724 cm 2 , and the lateral cross-sectional area of one end of the adapter elbow 300 located inside the housing 100 is 4900 cm 2 , meeting the structural setting requirements of "1.1d2 < d1 < 1.5d2". If the vertical cross-section d1 of the expansion section 113 is less than 1.1d2, or d1 is greater than 1.5d2 (that is, the area difference between the two is too small or too large), it is easy to form local air flow blockage and increased back pressure, resulting in vibration of the inner cavity 110 or damage to the housing 100; if the cross-section ratio is controlled within the range of "1.1d2 < d1 < 1.5d2", the problem of local air flow blockage and increased back pressure can be effectively avoided.

[0080] The working process of this invention is as follows: In this embodiment, an expansion section 113, a reactive sound-absorbing resonant cavity 112, and a plate-type resistive silencing section 111 are sequentially arranged in the inner cavity 110 of the housing 100. Airflow enters from the air inlet 130 at the bottom of the housing 100 and flows through each structure sequentially within the inner cavity 110, achieving multi-stage silencing. The expansion section 113 acts as a buffer zone, causing initial sound energy reflection and attenuation. The reactive sound-absorbing resonant cavity 112 serves as a low-frequency silencing structure. Its opposing first cavity wall 1121 and second cavity wall 1122 each have several holes connecting the inner cavity 110 and the reactive sound-absorbing resonant cavity 112, thus forming a Helmholtz-like resonant structure. When low-frequency sound waves contained in the airflow enter the resistive sound-absorbing resonant cavity 112 through the holes in the cavity wall, they induce capacitive oscillations in the air column within the cavity 112. This oscillation couples with the mass effect of the air column within the duct, generating strong acoustic resonance in the low-frequency range and converting it into heat energy. This significantly absorbs noise in this frequency band, achieving a targeted and energy-dissipative low-frequency noise reduction effect. This compensates for the shortcomings of traditional conventional plate-type resistive silencers in attenuating low-frequency noise. Furthermore, before the airflow in the inner cavity 110 exits through the outlet 120 of the housing 100, mid-to-high frequency noise in the sound waves passing through the resistive silencer section can be reflected and absorbed, thus achieving attenuation of mid-to-high frequency noise. As can be seen, in this embodiment of the invention, the resistive sound-absorbing resonant cavity 112 guides the sound waves to couple into the cavity through the cavity wall holes and forms a Helmholtz resonance, effectively absorbing low-frequency noise. The plate-type resistive noise-absorbing section 111 further absorbs mid-to-high-frequency noise, thereby effectively widening the noise-absorbing frequency band and realizing the coordinated noise reduction of low and mid-to-high frequencies.

[0081] In summary, the present invention provides an impedance combination silencer, which includes a housing 100 having an inner cavity 110, an air outlet 120 opened on the side wall of the housing 100, an air inlet 130 opened at the bottom of the housing 100, and a plate-type resistive silencing section 111, an reactive sound-absorbing resonant cavity 112, and an expansion section 113 arranged sequentially in the inner cavity 110, wherein the plate-type resistive silencing section 111 is connected to the air outlet 120, and the expansion section 113 is connected to the air inlet 130;

[0082] The first cavity wall 1121 and the second cavity wall 1122 of the resistive sound-absorbing resonant cavity 112 are provided with a plurality of holes communicating between the inner cavity 110 and the resistive sound-absorbing resonant cavity 112. The first cavity wall 1121 and the second cavity wall 1122 are arranged opposite to each other, and the air outlet 120 faces the first cavity wall 1121 and the second cavity wall 1122. The resistive sound-absorbing resonant cavity 112 of the present invention utilizes the cavity wall holes to guide sound waves to couple into the resistive sound-absorbing resonant cavity 112 and form Helmholtz resonance, effectively absorbing low-frequency noise. With the aid of the plate-type resistive noise-absorbing section 111, the mid-to-high frequency noise is further absorbed, thereby effectively widening the noise-absorbing frequency band and realizing the coordinated noise reduction of low frequency and mid-to-high frequency.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. An impedance-combined silencer, characterized in that, The device includes a housing with an inner cavity, an air outlet on the side wall of the housing, an air inlet at the bottom of the housing, and a connected plate-type resistive silencing section, an reactive sound-absorbing resonant cavity, and an expansion section arranged sequentially inside the inner cavity, wherein the plate-type resistive silencing section is connected to the air outlet, and the expansion section is connected to the air inlet. The first and second cavity walls of the resistive sound-absorbing resonant cavity are provided with a plurality of holes connecting the inner cavity and the resistive sound-absorbing resonant cavity. The first cavity wall and the second cavity wall are arranged opposite to each other, and the air outlet faces the first cavity wall and the second cavity wall.

2. The impedance combination silencer according to claim 1, characterized in that, The aperture of the plurality of holes ranges from 0.1 to 0.8 cm. The total area of ​​the plurality of holes opened on the first cavity wall accounts for 10% to 25% of the total area of ​​the first cavity wall, and the total area of ​​the plurality of holes opened on the second cavity wall accounts for 10% to 25% of the total area of ​​the second cavity wall.

3. The impedance combination silencer according to claim 2, characterized in that, The holes are spaced at equal intervals.

4. The impedance combination silencer according to claim 3, characterized in that, The holes on the first cavity wall and the holes on the second cavity wall correspond one-to-one.

5. The impedance combination silencer according to claim 1, characterized in that, The housing includes a perforated plate, sound-absorbing cotton, a damping layer, and a housing steel plate; the perforated plate, the sound-absorbing cotton, the damping layer, and the housing steel plate are arranged sequentially from the inside to the outside, wherein the end face of the perforated plate facing away from the inner cavity is connected to the sound-absorbing cotton, and the damping layer is located between the sound-absorbing cotton and the housing steel plate.

6. The impedance combination silencer according to claim 1, characterized in that, It also includes a fixing component; the fixing component includes a first fixing member and a second fixing member; one end of the first fixing member is connected to the top inner wall of the housing, and the other end is connected to the first end face of the resistive sound-absorbing resonant cavity; one end of the second fixing member is connected to the bottom inner wall of the housing, and the other end is connected to the second end face of the resistive sound-absorbing resonant cavity, the first end face and the second end face of the resistive sound-absorbing resonant cavity being opposite to each other.

7. The impedance combination silencer according to claim 1, characterized in that, The sheet-type resistive silencing section includes several sheet-type silencing sheets with a perforated plate double-sided wrapped with sound-absorbing cotton structure; the same end of several sheet-type silencing sheets is vertically connected to the inner surface of the side wall of the housing, and the several sheet-type silencing sheets are arranged vertically at equal intervals.

8. The impedance combination silencer according to claim 7, characterized in that, The channel formed by the space between the several sheet-type sound-absorbing plates is the sound-absorbing plate ventilation channel; the channel formed by the internal space of the resistive sound-absorbing resonant cavity is the cavity channel; the sound-absorbing plate ventilation channel is directly opposite the cavity channel.

9. The impedance combination silencer according to claim 1, characterized in that, It also includes a transition elbow; the transition elbow and the housing are integrally formed, and the transition elbow is adapted to the air inlet.

10. The impedance combination silencer according to claim 9, characterized in that, The area of ​​the vertical cross-section of the expansion section is d1, and the area of ​​the transverse cross-section of the end of the transition elbow located inside the shell is d2, therefore: 1.1d2 <d1<1.5d2。

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