KR101937343B1

KR101937343B1 - silencer

Info

Publication number: KR101937343B1
Application number: KR1020160023342A
Authority: KR
Inventors: 김승평; 김승국; 김준범
Original assignee: 김승평; 김승국; 김준범
Priority date: 2016-02-26
Filing date: 2016-02-26
Publication date: 2019-01-11
Also published as: KR20170100896A

Abstract

The noise included in the flowing fluid is primarily reduced by the noise reducing means provided in the pocket on the inlet side, and then some noise emitted from the noise reducing means is secondarily subjected to noise again Type first noise reduction member that reduces the noise by the noise reduction unit provided inside the other side, the side facing the inlet is opened on the side of the inner inlet of the housing so as to reduce the noise, A flow path formed between an outer surface of the first noise reducing member and an inner surface of the housing; And a second noise reduction unit provided on the inner surface of the housing to reduce the noise emitted through the first noise reduction member while passing noise along the flow path.
Accordingly, the efficiency of removing noise is maximized, so that the ejected fluid can be discharged in a state in which almost no noise is removed. In addition, the ambient environment also has the effect of creating a more mild environmental condition.

Description

Silencer {silencer}

More particularly, the present invention relates to a silencer, and more particularly, to a silencer which reduces noise primarily contained in a flowing fluid by means of a noise reduction means provided in the form of a pocket on the inlet side, So that the noise can be reduced once again in the course of passing through the muffler.

In general, silencers are classified into four types of sound absorbing type, expansion type, resonance type, and interference type according to a sound attenuation method for reducing noise.

The sound-absorbing silencer is a silencer that absorbs sound to reduce noise by installing a sound-absorbing material such as glass fiber that can absorb sound in a part of the duct, and the expansion type has an expansion part in the duct to expand and shrink sound waves, It is a silencer that reduces the noise.

In addition, the resonance type silencer is a silencer in which a neck portion is installed in a duct, a cavity is connected to the resonator to generate resonance, and the energy of the sound wave is absorbed by the air vibration of the cavity portion. In the interference type, Is a half-wavelength of the sound wave, and the noise is attenuated by the interference.

Prior art relating to a sound-absorbing silencer includes Korean Patent No. 10-0918700 (hereinafter referred to as "Prior Art Document 1"), Korean Patent No. 10-0924958 (hereinafter referred to as "Prior Art Document 2"), (Hereinafter referred to as 'Prior Art Document 3'), Korean Patent No. 10-1030440 (hereinafter referred to as 'Prior Art Document 4'), Korean Patent No. 10-0939702 Prior Art Document 5 ') and Korean Patent Publication No. 10-2013-0104852 (hereinafter referred to as "Prior Art Document 6").

Prior art relating to an expandable silencer is disclosed in Korean Patent No. 10-1016601 (hereinafter referred to as "Prior Art Document 7").

Prior art relating to a resonance type silencer includes a resonance space having a predetermined volume and a perforated plate having a plurality of through holes as disclosed in Korean Patent No. 10-0555375 (hereinafter referred to as "Prior Art Document 8"), A technique has been proposed in which sound waves are dissipated by the resonance action of the sound waves incident on the inside, thereby reducing noise without a sound absorbing material.

The prior art related to the sound absorber using sound absorption and resonance includes a low-mid-range sound control device having a compact structure and influencing the sound performance, as disclosed in Korean Patent No. 10-0632419 (hereinafter referred to as 'Prior Art Document 9' A technique such as a sound absorbing resonator type silencer which exhibits an effective sound absorbing performance in a frequency component and which has strong structural and tensile strength even when exposed to air has been proposed.

Korean Patent No. 10-0918700 Korean Patent No. 10-0924958 Korean Patent Publication No. 10-2010-0134274 Korean Patent No. 10-1030440 Korean Patent No. 10-0939702 Korean Patent Publication No. 10-2013-0104852 Korean Patent No. 10-1016601 Korean Patent No. 10-0555375 Korean Patent No. 10-0632419

However, all of the prior art documents 1 to 9 have a disadvantage in that the noise reduction efficiency is low by reducing the noise by the sound absorbing material or the resonance space provided on both sides in the course of the passage of the noise-containing fluid through the flow path.

That is, in the process of passing through the flow path formed in the longitudinal direction, noise is removed only by the sound absorbing material or the resonance space formed on both sides of the flow path, and thus noise reduction efficiency is low.

Accordingly, in order to increase the efficiency of noise reduction, it also has a conditional disadvantage that the length of the silencer must be increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method and apparatus for reducing noise contained in a flowing fluid by first reducing the noise by a noise reduction means provided in a pocket- Some noise is to provide a silencer that can reduce noise again in the course of passing through the channel again.

Another problem to be solved by the present invention is to make high frequency noise in noise absorbing material and low frequency noise in simultaneous dissipation of sound waves in resonance space.

Another problem to be solved by the present invention is to make the noise passing through the passageway significantly reduce the high frequency noise and the low frequency noise.

According to an aspect of the present invention, there is provided an electronic apparatus including an inlet formed at one side of a housing to allow noise to pass therethrough, a discharge port formed at an opposite side of the inlet formed with the discharge port, Wherein the silencer includes a pocket-type first noise reduction member for reducing noise by a noise reduction unit provided on the inner inlet side of the housing and a surface facing the inlet is opened and the other surface is closed; A flow path formed between an outer surface of the first noise reducing member and an inner surface of the housing; And a second noise reduction unit arranged to reduce the noise emitted through the first noise reduction member while passing noise along the flow path on the inner surface of the housing.

The first noise reduction member includes a front pierced plate having a plurality of pores formed on an open front surface thereof, and a sound absorbing material filled between the inner side surface and a plurality of pored holes provided at predetermined intervals.

The noise reduction unit includes a sound absorbing material filled in the first noise reduction member.

A plurality of partition plates having a plurality of perforations formed at predetermined intervals between the sound absorbing members and a curved guide plate having a plurality of perforations formed on an open front face of the first noise reducing member.

The noise reduction unit may include a sound absorption unit in which a sound absorption material is filled between at least one perforated plate formed in the first noise reduction member, and a first resonance space in which no sound absorption material is filled between the perforated plates.

The sound absorbing portion and the first resonance space are arranged in a plurality of one by one.

The second noise reduction unit includes respective pore diaphragms having a plurality of pores formed in a portion in contact with the flow path, and a sound absorbing material filled between the respective pore diaphragms and the housing.

The first noise reduction member may be provided with a dispersion plate having an arc-shaped curved surface formed with a plurality of perforations so that the noise introduced through the inlet may be uniformly dispersed into the first noise reduction member, .

A second resonant space is formed between the inner side surface of the housing and the sound absorbing material by a partition diaphragm, wherein the partition diaphragm further includes a plurality of perforations.

And a third resonance space is formed between the sound absorbing material and the flow path by a split partition plate, wherein the split partition plate is formed with a plurality of perforations.

Further comprising a plurality of noise line reduction portions between the first noise reduction member and the inlet so as to reduce a portion of the noise before the noise introduced into the inlet through the inlet is introduced into the first noise reduction member, A first line reduction portion filled with a sound absorbing material, and a first ring resonance space filled with a sound absorbing material are formed as front and rear ring housings. On the noise inlet side, a plurality of pores are formed, The diameter of the ring housing on the inlet side is wide and the diameter of the ring housing on the first noise reducing member side is gradually narrowed.

In the present invention, noise included in a flowing fluid is primarily reduced by noise reduction means provided in a pocket-like shape on the inlet side, and then some noise emitted from the noise reduction means passes through the oil passage again, So that the discharge efficiency can be maximized and the discharged fluid can be discharged in a state in which almost no noise is removed. In addition to this effect, the surrounding environment can also provide a more quiet environment condition Also has an effect.

In addition, in the sound-absorbing material, the low-frequency noise can maximize the noise elimination efficiency by allowing the sound waves to dissipate simultaneously in the resonance space.

In addition, the noise passing through the flow path can also remarkably reduce the high frequency noise and the low frequency noise, so that the noise itself can be completely removed.

1 is a sectional view for explaining a first embodiment of the present invention,
FIG. 2 is a sectional view for explaining a use state according to FIG. 1,
Fig. 3 is a sectional view for explaining another embodiment according to Fig. 1,
4 is a sectional view for explaining a second embodiment of the present invention,
4A is a graph showing measured values in Table 2,
FIG. 4B is a graph showing the measured values of FIG. 3,
4C is a graph comparing FIGS. 4A and 4B, FIG.
5 is a sectional view for explaining a third embodiment of the present invention,
6 is a sectional view for explaining a fifth embodiment of the present invention,
7 is a sectional view for explaining a sixth embodiment of the present invention,
8 is a sectional view for explaining a seventh embodiment of the present invention,
9 is a sectional view for explaining an eighth embodiment of the present invention.
10 is a sectional view for explaining a ninth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. The present invention is not limited to or limited by the embodiments.

FIG. 1 is a cross-sectional view for explaining a first embodiment of the present invention, and FIG. 2 is a sectional view for explaining a use state according to FIG.

An inlet 112 formed at one side of the housing 110 so as to allow noise to pass therethrough with the fluid such as air ducts or various equipment or facilities as shown in the figure and an outlet 112 formed at the opposite side of the inlet 112, And a flow path 115 provided inside the housing 110 between the inlet 112 and the outlet 114. The silencer 100 shown in FIG.

Here, the noise included in the fluid is divided into a high frequency noise of 600 to 4,800 Hz and a low frequency noise of 250 Hz or less.

Usually, high-frequency noise is removed to some extent by a sound-absorbing material, but in the case of low-frequency noise, it is generally reduced by using a resonance phenomenon due to a characteristic that is not reduced by a sound-absorbing material.

In the present invention, noise included in a flowing fluid is primarily reduced by noise reduction means provided in a pocket-like shape on the inlet side, and then some noise emitted from the noise reduction means passes through the oil passage again, So that it can be reduced once again.

The muffler 100 according to the present invention is constructed such that the noise reduction unit 10A provided on the side of the inner inlet 112 of the housing 110 faces the inlet 112 of the muffler 100, A first pocket-type noise reduction member 10 for reducing noise; A flow path 115 formed between the outer surface of the first noise reducing member 10 and the inner surface of the housing 110; And a second noise reduction unit 20 provided on the inner surface of the housing 110 to reduce the noise emitted through the first noise reduction member 10 while passing noise along the flow path 115. .

It is preferable that the open portion of the first noise reduction member 10 is formed to be wider than the diameter of the inlet port so that most of the noise introduced through the inlet port can be introduced.

The first noise reduction member 10 includes a front piercing plate 11 having a plurality of pores formed in an opened front face thereof and a plurality of pierced perforated plates 12 provided at a predetermined distance from the inner side face thereof, And that the sound absorbing material (A) is filled.

The noise reduction unit 10A included in the first noise reduction member 10 includes a sound absorption material A such as a glass fiber or the like which is filled in the first noise reduction member 10. [ At this time, the first noise reduction member is fixed to the inner surface of the housing by a plurality of conventional frames, a mounting stand, or a spacing support.

Accordingly, the noise introduced into the inlet formed at one side of the housing flows through the open portion of the pocket-shaped first noise reduction member, and at the same time, the high frequency noise during noise is reduced by sound absorption by the noise absorption member.

In addition, since the first noise reduction member is formed in a pocket shape so that the low-frequency noise included in the noise is also filled with the sound absorbing material therein, a part of the low-frequency noise is also generated in the first noise reduction member The sound waves due to the resonance action can be reduced while being dissipated.

At this time, the first noise reduction member reduces the noise of about 80% of the noise introduced into the pockets.

Meanwhile, a part of noise which is not removed from the first noise reduction member is reduced again by the second noise reduction unit in the process of passing through the flow passage.

The second noise reduction unit 20 includes a pair of piercing diaphragms 22 formed with a plurality of pores into which a part of noise in a process of passing through the flow path is formed at a portion in contact with the flow path 15, And a sound absorbing material A such as a conventional glass fiber filled between the perforated diaphragm 22 and the housing 110. [

As a result, a part of the noise that has not been reduced by the first noise reduction member is reduced again in the second noise reduction unit while passing through the passage, so that there is almost no noise in the fluid discharged through the discharge opening.

In addition, since the flow path is formed to surround the first noise reduction member, the noise passing through the flow path can be more efficiently reduced in the second noise reduction unit while passing through the flow path in the form of turning after passing through the first noise reduction member .

Accordingly, in the present invention, the noise introduced through the inlet is firstly reduced by the pocket-like first noise reducing member, and then, during the passage of a part of the noise emitted from the first noise reducing member, And is completely removed by the reduction portion, thereby making it possible to maximize the noise reduction efficiency.

In addition, the first noise reduction member has the advantage of increasing the overall noise reduction efficiency due to the condition that the noise absorbing material embedded in the pocket type can maximize the reduction efficiency of the low frequency noise due to the high frequency noise as well as the constant depth and area I have.

1 and 2 show an example of a conventional exhaust type, it is preferable to provide a common connection flange, a connection pipe, and the like in the inlet and the outlet.

3 is a cross-sectional view for explaining another embodiment according to FIG.

As shown in the figure, the noise reduction unit of the first noise reduction unit can further reduce the low frequency noise in the state where the sound absorption material is filled.

A plurality of partition plates (10A-1) having a plurality of pores are provided at predetermined intervals between the sound-absorbing material (A) of the noise-reducing section (10A) so as to further efficiently reduce noise introduced thereto, (10A-2) having a plurality of punched holes formed on the open front face of the guide plate (10).

That is, the noise introduced into the inlet of the housing is uniformly introduced into the noise reduction portion of the first noise reduction member through the punch of the guide plate, and the sound absorption material of the noise reduction portion is divided into a plurality of overlapping chambers by the plurality of partition plates Accordingly, the noise introduced into the perforations of the partition plates, in particular the low-frequency noise, is gradually reduced between the formation of the mutually overlapping chambers between the partition plate and the partition plate.

Thereby providing a condition that minimizes the total noise introduced into the first noise reduction member. At this time, the high frequency noise included in the noise can be minimized by the same principle as the low frequency noise.

4 is a cross-sectional view for explaining a second embodiment of the present invention.

As shown in the drawings, in the above-described configuration, it is possible to further reduce the low-frequency noise of the noise introduced into the first noise reduction member.

The noise reduction unit 10A includes a sound absorbing unit 10A1 for reducing high frequency noise by filling a sound absorbing material A between at least one formed perforated plate 10a formed at a predetermined interval in the first noise reducing member 10, And a first resonance space 10A2 for dissipating and reducing the sound waves of low frequency noise due to the resonance phenomenon because the sound absorbing material is not charged between the perforated plates 10a. At this time, the sound-absorbing portion and the first resonance space may be selectively positioned in the order as shown in (a) or (c) according to the necessary conditions.

The noise reduction unit provided inside the first noise reduction member is mixed with the sound absorption unit and the first resonance space so that the high frequency noise and the low frequency noise of the noise can be more efficiently reduced, And the like.

In addition, the experimental data for measuring the noise with reference to (a) of the second embodiment of the present invention are as follows.

Here, the measuring instrument (Noise Meter) used for measuring the noise is Japan of the country of manufacture, Rion of the manufacturer, and NA27 of the model name.

(b) is a layout diagram for measuring noise after supplying noise through a duct in a noise source where the noise is generated, and passing through the silencer 100. Fig.

[Table 1] is a chart showing the positions and conditions for supplying noise.

[Table 2] is the noise condition measured in a duct to which noise is supplied.

[Table 3] shows the positions and conditions measured by the silencer.

Table 4 shows the noise conditions measured by the silencer.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

As can be seen from the experimental data, as shown in the experimental data, the difference of 111.1 Leq of the noise No 1 to 78.8 Leq of No 1 on the discharge port side is about 30 Leq or more. As a result, it can be confirmed that the noise is remarkably reduced.

5, by arranging the sound absorbing portion 10A1 and the first resonance space 10A2 of the noise reducing portion 10A one at a time, the sound absorbing portion 10A1 and the first resonance space 10A2 are arranged one by one, It is possible to reduce the harmonic noise and the low frequency noise as much as possible.

This is because the incoming noise alternates between the sound absorption portion and the first resonance space, thereby further reducing the high frequency noise and the low frequency noise, thereby minimizing the noise itself.

6 is a cross-sectional view for explaining a fifth embodiment of the present invention.

As shown in the drawings, the noise introduced through the inlet port can be more uniformly introduced into the first noise reduction member.

The openings of the first noise reduction member 10 are formed in a circular arc shape having a plurality of perforations so that the noise introduced through the inlet port 112 can be uniformly dispersed and introduced into the first noise reduction member 10 The curved surface of which is formed by the dispersing plate 11A.

In other words, since the open portion of the first noise reduction member is relatively larger in diameter than the inlet, noise can be concentrated only in an area corresponding to the inlet, and therefore, in order to prevent this, The noise can be introduced into the open portion of the first noise reduction member in a form of evenly dispersed noise.

Accordingly, the noise is uniformly dispersed and introduced into the first noise reduction member, so that the noise can be further effectively reduced by the noise reduction unit provided therein.

7 is a cross-sectional view for explaining a sixth embodiment of the present invention.

As shown in the figure, in the above-described configuration, since the noise reduced by the second noise reduction unit in the exaggeration passing through the flow path without being reduced by the first noise reduction member includes some low-frequency noise, So that it can be reduced.

A second resonance space 30 is formed between the inner surface of the housing 110 and the sound absorbing material A so that the sound waves are dispersed by the resonance action of the low frequency noise introduced by the partition plate 32, ) Further comprises a plurality of pores through which noise may be introduced.

As a result, the high frequency noise is reduced in the second noise reduction portion through the flow path, and the low frequency noise can be completely removed by resonance in the second resonance space.

In addition, since the second resonance space is formed to surround the entire inside of the housing, the second resonance space also has a condition capable of more efficiently removing the low-frequency noise included in the noise passing through the passage.

8 is a cross-sectional view for explaining a seventh embodiment of the present invention.

As shown in FIG. 6, in the above-described configuration, the low-frequency noise is reduced in advance before the low-frequency noise passing through the flow path is introduced into the second noise reduction unit, as shown in FIG.

A third resonance space 40 is formed between the sound absorbing material A and the flow path 115 provided on the inner side surface of the housing 110 by the partition plate 22, Lt; / RTI >

In other words, before the high-frequency noise of the noise is reduced while passing through the channel by the sound-absorbing material of the second noise-reducing section, the low-frequency noise contained in the noise is transmitted through the perforation of the split diaphragm by the resonance action in the third resonance space, And then the high frequency noise is removed by the sound absorbing material which is the second noise reducing part.

Accordingly, the low-frequency noise of the noise passing through the passage is firstly removed from the third resonance space, and then the high-frequency noise is also removed from the second noise reduction section. This also completely removes the high-frequency noise and low- It has the condition that it can be.

In addition, the third resonance space is formed entirely in a portion where the flow path is formed, thereby further enhancing the efficiency of removing low frequency noise.

9 is a sectional view for explaining an eighth embodiment of the present invention.

As shown in the drawings, the noise reduction efficiency can be improved even when the inlet port has a large area or a diameter wider than that of the first noise reduction member.

A plurality of noise lines are provided between the first noise reduction member 10 and the inlet 112 so as to reduce a part of the noise before the noise introduced through the inlet 112 flows into the first noise reduction member 10. [ And further includes a reduction section (50).

The noise line reduction section 50 includes a first line reduction section 52 filled with a sound absorption material such as ordinary glass fiber or the like, a first line resonance space 54 in which no sound absorption material is filled, And a ring 55 on the inlet side is wide and a ring on the side of the first noise reduction member 10 is formed in a ring shape. The diameter of the housing 55 is gradually narrowed.

Therefore, even when the diameter of the inlet is wide or wider than the open portion of the first noise reducing member, the noise is reduced by the noise line reducing portion constituted by the plurality of ring housings provided in front of the first noise reducing member It is possible to smoothly guide the noise reduction member to the first noise reduction member, thereby maximizing the noise reduction efficiency.

In addition, the ring housing of the noise line reduction section further reduces the high frequency noise and the low frequency noise more effectively by the first line reduction section and the first line resonance space.

In addition, the first line reduction portion and the first line-plus space may be reversed from each other as required.

10 is a sectional view for explaining a ninth embodiment of the present invention.

As shown in the drawings, in the above-described configuration, Figs. 1 to 8 are described as an example suitable for a conventional exhaust type, and the present invention is also applicable to a fresh type.

In other words, the internal structure of the housing 110 has the same structure as that of the above-described various embodiments, and is not a mounting flange or a connecting pipe on the discharge port side, but a technical . At this time, the housing may be connected to an air supply facility by using a separate bracket or the like.

Accordingly, the noise introduced into the inlet side while the fluid passes through the flow path through the flow path can be minimized by the above-described operation.

10: First Noise Reduction Member 10A: Noise Reduction Unit
10A-1: partition plate 10A-2: guide plate
10A1: sound absorption portion 10A2: first resonance space
11: front pier plate 11A:
12: perforated plate 20: second noise reduction section
22: perforated diaphragm 30: second resonance space
32: compartment diaphragm 40: third resonance space
42: split diaphragm 50: noise line reduction section
52: first line reduction part 54: second line resonance space
55: ring housing 100: silencer
110: housing 112: inlet
114: discharge port 115:

Claims

A silencer including an inlet formed at one side of the housing to allow noise to pass therethrough, a discharge port formed at the opposite side of the inlet port, and a flow path provided inside the housing between the inlet port and the discharge port,
Wherein the silencer has a pocket-type first noise reduction member for reducing noise by a noise reduction unit provided on the inner inlet side of the housing and a surface facing the inlet is opened and the other surface is closed;
A flow path formed between an outer surface of the first noise reducing member and an inner surface of the housing; And
And a second noise reduction unit arranged to reduce the noise emitted through the first noise reduction member while passing noise along the flow path on the inner surface of the housing,
The first noise reduction member may include a front pierced plate having a plurality of pores formed in an open front face thereof, a sound absorbing material filled between the inner side face and a plurality of pierced pores formed at predetermined intervals,
Wherein a plurality of partition plates having a plurality of pores are formed at predetermined intervals between the sound absorbing members and a curved guide plate having a plurality of pores formed in an open front face of the first noise reducing member, .

delete

The method according to claim 1,
Wherein the noise reducing unit includes a sound absorbing material filled in the first noise reducing member.

The method according to claim 1,
Wherein the noise reduction unit includes a sound absorption unit in which a sound absorption material is filled between at least one perforated plate formed in the first noise reduction member, and a first resonance space in which no sound absorption material is filled between the perforated plates.

6. The method of claim 5,
Wherein the sound absorbing portion and the first resonance space are arranged so as to be arranged one after the other.

The method according to claim 1,
Wherein the second noise reduction portion includes a plurality of perforated diaphragms disposed in a portion contacting the flow path, and a sound absorbing material filled between the respective perforated diaphragms and the housing.

A silencer including an inlet formed at one side of the housing to allow noise to pass therethrough, a discharge port formed at the opposite side of the inlet port, and a flow path provided inside the housing between the inlet port and the discharge port,
Wherein the silencer has a pocket-type first noise reduction member for reducing noise by a noise reduction unit provided on the inner inlet side of the housing and a surface facing the inlet is opened and the other surface is closed;
A flow path formed between an outer surface of the first noise reducing member and an inner surface of the housing; And
And a second noise reduction unit provided on the inner surface of the housing to reduce the noise emitted through the first noise reduction member while passing noise along the flow path,
The first noise reduction member may include a front pierced plate having a plurality of pores formed on an open front side thereof, a sound absorbing material disposed between the inner side surface and a plurality of pierced pores formed at a predetermined interval,
The first noise reduction member is provided with a dispersion plate having an arc-shaped curved surface formed with a plurality of perforations so that the noise introduced through the inlet may be uniformly dispersed into the first noise reduction member, Wherein the muffler is a muffler.

9. The method according to claim 7 or 8,
And a second resonance space is formed between the inner side surface of the housing and the sound absorbing material by a partition diaphragm, wherein the partition plate is formed with a plurality of perforations.

9. The method according to claim 7 or 8,
And a third resonance space is formed between the sound absorbing material and the flow path by a split partition plate, wherein the split partition plate has a plurality of perforations formed therein.

9. The method according to any one of claims 1 to 7,
Further comprising a plurality of noise line reduction portions between the first noise reduction member and the inlet so as to reduce a portion of the noise before the noise introduced into the inlet through the inlet is introduced into the first noise reduction member, A first line reduction portion filled with a sound absorbing material, and a first ring resonance space filled with a sound absorbing material are formed as front and rear ring housings. On the noise inlet side, a plurality of pores are formed, Wherein the diameter of the ring housing on the inlet side is wide and the diameter of the ring housing on the first noise reducing member side is gradually narrowed.