JP2008164231A - Muffling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a muffling device capable of improving muffling effect while reducing ventilation resistance. <P>SOLUTION: This muffling device 1 comprises a body 2 formed into the hollow box-shape and having an air suction opening 3 and an air supply opening 4, a hollow cylindrical air suction tube 7 projecting into the body 2 from the air suction opening 3 and extending to the neighborhood of the air supply opening 4, and a hollow cylindrical air supply tube 13 projecting to the outside of the body 2 from the air supply opening 4 and inserted into a ventilation hole 21. The inside of the body 2 is communicated with the outside only through the air suction opening 3 and the air supply opening 4. A sound absorbing material 5 is disposed on an inner wall surface of the body 2. A spatial portion 15 communicated with an opening at the other end side of the air suction tube 7, is formed between an outer wall surface of the air suction tube 7 and an inner wall surface of the body 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a silencer for preventing outdoor noise from entering a room through a ventilation hole of a building.

  There is sound insulation performance as one of the living performances, and in addition to improving sound insulation performance of walls, windows, etc., improvement of sound insulation performance of ventilation holes is required, and various silencer devices in ventilation holes have been proposed, Since the ventilation hole is intended for ventilation, there is a demand for a silencer that can secure a predetermined ventilation amount and that can provide high noise reduction performance. In view of such circumstances, the applicants of the present invention have provided a hood on the outer wall surface of the ventilation hole that penetrates the wall of the building and a muffler in the ventilation hole in an air supply device (ventilation device) provided with a register on the inner wall surface. The silencer ventilation apparatus which provided the apparatus was proposed (refer the following patent document 1).

  On the other hand, various means have been proposed to give the hood in the air supply device a silence (see Patent Documents 2 to 4 below). The hood in this type of air supply device is provided with a frame-shaped flat plate at the edge of the cylinder that becomes the air supply port to be inserted into the ventilation hole, and an elliptical or square cover (hood body) is provided on this flat plate. By providing an air inlet opening at the lower part of the cover, air is supplied to the ventilation hole and the ventilation hole is protected from rain and wind.

  In patent document 2, the structure which provided the sound-absorbing material in the inner surface of the food | hood is employ | adopted. In patent document 3, the structure which formed the ventilation path with the sound-absorbing material is employ | adopted. In Patent Document 4, a configuration is adopted in which a ventilation path is meandered and a sound absorbing material is disposed along the ventilation path in order to enhance the noise reduction effect.

Japanese Patent No. 3664675 JP 2004-150523 A JP 2006-171254 A JP 58-156136 A

The silencing structure of Patent Document 2 has an advantage that the ventilation resistance is small because there is no obstruction in the ventilation path from the air supply opening to the air supply opening that is the insertion portion from the air supply opening to the ventilation hole at the lower part of the hood. Since the performance depends on the sound absorbing performance of the sound absorbing material on the inside of the hood, there is a problem that a high silencing effect cannot be expected.
In the silencing structure of Patent Document 3, although the shape of the air passage is devised, the silencing performance depends on the sound absorbing performance of the sound absorbing material on the inner surface of the hood. There is a problem that the effect cannot be expected.
In the silencing structure of the above-mentioned Patent Document 4, although the silencing effect can be enhanced because the air passage is meandering, there is a problem that the air resistance increases due to the meandering of the air passage.
In recent years, the Building Standards Law has mandated that buildings such as residences be provided with a structure that can ventilate indoor air at a rate of 1.5 times / hour or more from the viewpoint of health considerations, and the ventilation resistance is large. In order to obtain a necessary ventilation amount, the intake port or the intake port must be enlarged, resulting in a problem that the hood itself is increased in size.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a silencer that can enhance the silencing effect while reducing ventilation resistance.

In order to achieve the above object, the silencer of the present invention employs the following technical means.
(1) The present invention is a silencer provided on the outer wall surface side of a ventilation hole of a building, and is formed in a hollow box shape, and an intake opening for taking in outside air, and a supply for supplying the taken outside air into the ventilation hole. A main body having an air opening, a hollow cylindrical air intake cylinder that protrudes from the intake opening to the inside of the main body and extends to the vicinity of the air supply opening, and has one end connected to the intake opening and opened at the other end, A hollow cylindrical supply cylinder that protrudes from the supply opening to the outside of the main body and is inserted into the ventilation hole, and the inside of the main body is connected to the outside only through the intake opening and the supply opening. A space communicating with the inner wall surface of the main body is provided with a sound absorbing material, and communicates with the opening on the other end side of the intake cylinder between the outer wall surface of the intake cylinder and the inner wall surface of the main body. The part is formed.

According to the above configuration, the entire frequency range of noise from the outside is attenuated by the effect of restricting the diameter of the intake cylinder, and the intermediate frequency range is attenuated by the effect of sound diffusion in the space portion inside the main body. The mid-high frequency range is attenuated by the sound absorbing material. Therefore, since the sound attenuation effect in all regions can be obtained by the noise reduction effect of each part, a high noise reduction effect can be obtained.
In addition, since the conventional general expansion silencer has a structure in which a small passage and a large volume cavity are simply connected (see FIG. 9), pressure loss due to sudden expansion and contraction of the flow (change in the cross-sectional area of the flow). However, in the present invention, since the intake cylinder is built in the main body and the other end of the intake cylinder extends to the vicinity of the air supply opening, there is no pressure loss due to sudden expansion and contraction of the flow. Can be reduced.
Therefore, according to the present invention, the silencing effect can be enhanced while reducing the ventilation resistance. Further, since the ventilation resistance is small, the intake opening and the main body can be made small, and as a result, the entire apparatus can be made compact.

(2) In the above silencer, the cross-sectional area of the air intake passage of the intake cylinder is smaller than the cross-sectional area of the air supply passage of the supply cylinder, and the intake cylinder and the supply cylinder intersect with each other in the axial direction. The intake cylinder is disposed so that the other end faces the air supply opening, and is disposed at a position that substantially partially closes the air supply opening. The position of the other end of the intake cylinder is set so that the area of the portion of the opening facing the outflow position of the outside air from the intake cylinder is equal to or larger than the cross-sectional area of the air passage of the intake cylinder.

  Thus, since the other end of the intake cylinder is disposed so as to face the air supply opening, it is possible to more effectively suppress the occurrence of pressure loss due to sudden expansion and contraction. In addition, even when the intake cylinder is disposed at a position that substantially partially closes the intake opening in order to arrange the intake cylinder at such a position, it faces the outflow position of the outside air from the intake cylinder in the supply opening. Since the position of the other end of the intake cylinder is set so that the area of the portion to be filled is equal to or larger than the cross-sectional area of the ventilation path of the intake cylinder, the flow of outside air is not obstructed and the influence on the ventilation resistance is small.

(3) Moreover, in said silencer, the said intake cylinder has a sound-absorbing material surrounding the ventilation path.

  By providing the sound absorbing material also in the intake cylinder in this way, the high frequency range is attenuated in the process of passing through the intake cylinder, so that a higher noise reduction effect can be obtained.

(4) In the above silencer, the intake cylinder itself is made of a sound absorbing material.

  Since the intake cylinder itself is made of a sound absorbing material in this way, the partition of the intake cylinder and the sound absorbing material can be integrated, so that the structure can be simplified.

  According to the present invention, it is possible to obtain an excellent effect that the silencing effect can be enhanced while reducing the ventilation resistance.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

[First Embodiment]
In FIG. 1, the external appearance of the silencer 1 concerning 1st Embodiment of this invention is shown. 1A is a side view, and FIG. 1B is a rear view as viewed from the direction of arrow 1B in FIG.
This silencer 1 is provided on the outer wall surface side of a ventilation hole of a building, and as shown in FIG. 1, a hollow box-shaped main body 2, a hollow cylindrical intake cylinder 7, and a hollow cylindrical supply air And a cylinder 13.

FIG. 2 is a longitudinal sectional view showing a state in which the silencer 1 is installed on the outer wall surface side of the ventilation hole 21 that penetrates the wall 20 of the building. FIG. 3 is a cross-sectional view taken along the line III-III in FIG.
The main body 2 is formed in a hollow box shape, and includes an intake opening 3 for taking in outside air and an air supply opening 4 for supplying the taken outside air into the ventilation hole 21. The inside of the main body 2 communicates with the outside only through the intake opening 3 and the air supply opening 4.
In the present embodiment, the intake opening 3 is formed at the center of the bottom surface of the main body 2 in the width direction (left-right direction in FIG. 3) of the main body 2. The air supply opening 4 is formed at the center in the width direction of the main body 2 on the back surface of the main body 2.

A sound absorbing material 5 is provided on the inner wall surface of the main body 2. As the sound absorbing material 5, a porous material such as polyethylene foam, urethane foam, polyester foam, glass wool, or the like can be used. In the present embodiment, the sound absorbing material 5 is provided on almost the entire inner wall surface of the main body 2, but the range and thickness thereof are appropriately set according to the required noise reduction performance.
Since the main body 2 is configured as described above, the sound that reaches the main body 2 from outside via the intake cylinder 7 is attenuated in the middle and high frequency range by the action of the sound absorbing material 5.

As shown in FIGS. 2 and 3, the intake cylinder 7 is provided so as to protrude from the intake opening 3 into the main body 2 and extend to the vicinity of the air supply opening 4. One end of the intake cylinder 7 is connected to the intake opening 3 and opened at the other end. It is a hollow cylindrical member. A hollow portion of the intake cylinder 7 serves as a ventilation path 11 through which outside air taken in from the intake opening 3 is passed. Hereinafter, with respect to the intake cylinder 7, one end connected to the intake opening 3 may be referred to as an inlet, and the other end opened inside the main body 2 may be referred to as an outlet.
In the present embodiment, the intake cylinder 7 has a cylindrical shape extending vertically upward from the intake opening 3, and its outlet is cut in a horizontal plane.

The intake cylinder 7 is provided with a sound absorbing material 10 surrounding the air passage 11. Specifically, the intake cylinder 7 includes a cylindrical partition wall 9 and a sound absorbing material 10 provided on the cylindrical partition wall 9. The intake cylinder 7 shown in FIGS. 2 and 3 has a structure in which a sound absorbing material 10 is provided on the inner peripheral surface of the cylindrical partition wall 9, but a plurality of openings are provided in the cylindrical partition wall 9, and the sound absorbing material 10 is provided on the outer peripheral surface thereof. It is good also as a provided structure. As the sound absorbing material 10, a porous material such as urethane foam, glass wool, or the like can be used similarly to the sound absorbing material 5 provided on the main body 2.
Since the intake cylinder 7 is configured as described above, the sound from the outside is attenuated in the high frequency range by the sound absorbing material 10 when passing through the intake cylinder 7.

  As shown in FIG. 3, a space portion 15 that communicates with the opening on the other end side of the intake cylinder 7 is formed between the outer wall surface of the intake cylinder 7 and the inner wall surface of the main body 2. The space 15 is not filled with the sound absorbing material 5, and the sound that reaches the space 15 via the intake cylinder 7 from the outside is attenuated by diffusion. As a result, the intermediate frequency region is attenuated in the space portion 15. The volume of the space 15 is set according to the frequency range to be attenuated.

The supply cylinder 13 is a hollow cylindrical member that protrudes from the supply opening 4 to the outside of the main body 2 and is inserted into the ventilation hole 21. In the hollow portion of the supply cylinder 13, an air passage 14 through which the outside air flowing in from the supply opening 4 is passed. In the present embodiment, a hollow cylindrical sleeve member 22 is fitted into the ventilation hole 21, and the intake cylinder 7 is inserted into the ventilation hole 21 via the sleeve member 22.
In the present embodiment, the supply cylinder 13 has a cylindrical shape extending in the horizontal direction from the supply opening 4. Therefore, the intake cylinder 7 and the supply cylinder 13 are arranged so that their axial directions are orthogonal to each other. The cross-sectional area of the air passage of the intake cylinder 7 is smaller than the cross-sectional area of the air passage of the supply cylinder 13.

The intake opening 3 is provided with a gall or mesh intrusion prevention member 16 for preventing the entry of small animals such as insects.
Inlet portions 7 a and 13 a formed in a bell mouth shape (trumpet shape) are provided at the inlet of the intake cylinder 7 and the inlet of the supply cylinder 13. With such streamlined inlet portions 7a and 13a, the airflow resistance can be reduced and the air permeability can be improved. There is no effect on the muffling performance.

  According to the silencer 1 configured as described above, the entire frequency range of noise from the outside is attenuated by the effect of the restriction of the diameter of the intake cylinder 7, and the high frequency range is attenuated by the effect of the sound absorbing material 10 of the intake cylinder 7. The medium frequency range is attenuated by the effect of sound diffusion in the space 15 inside the main body 2, and the medium and high frequency range is attenuated by the sound absorbing material 5 provided inside the main body 2. Therefore, since the sound attenuation effect in all regions can be obtained by the noise reduction effect of each part, a high noise reduction effect can be obtained.

FIG. 4 shows a graph comparing the silencing performance of the silencing device 1 of the present invention and the conventional example. The sound performance frequency measurement range of the silencer 1 is 100 Hz to 5 kHz, and is defined in JIS A4706 and A1416. Here, “transmission loss” is an index representing the sound insulation performance (silence performance) of materials such as building walls and windows, and indicates that the higher the transmission loss, the higher the silence performance.
From FIG. 4, it can be seen that the silencer 1 of the present invention has a high transmission loss in almost all frequency ranges as compared with the conventional example, and exhibits an excellent silencing effect.
Further, in the sound insulation grade of JIS A4716, the conventional example is at the T1 level, whereas the silencer 1 of the present invention is at the T3 to T4 level. Therefore, in terms of standards, the silencer 1 of the present invention has a much higher noise reduction performance than the conventional example.

Further, as shown in FIG. 9, the conventional general expansion silencer has a structure in which a small passage and a large volume cavity are simply connected, and therefore, by rapid expansion and contraction of the flow (change in the cross-sectional area of the flow). Disturbance of flow occurs. As a result, the pressure loss increases, that is, the ventilation resistance increases.
On the other hand, in the silencer 1 of the present invention, since the outlet of the intake cylinder 7 is positioned in the vicinity of the air supply opening 4, there is no pressure loss due to sudden expansion and contraction of the flow, and the ventilation resistance can be reduced. it can.
Therefore, according to the silencer 1 of the present invention, the silencing effect can be enhanced while reducing the ventilation resistance. Further, since the ventilation resistance is small, the intake opening 3 and the main body 2 can be made small, and as a result, the entire apparatus can be made compact.

The intake cylinder 7 is preferably arranged as follows in order to reduce the influence on the ventilation resistance.
As shown in FIGS. 2 and 3, the outlet of the intake cylinder 7 is preferably arranged as close as possible to the air supply opening 4. Specifically, the outlet of the intake cylinder 7 is set to a position facing the air supply opening 4, and the portion of the outlet of the ventilation path 11 of the intake cylinder 7 closest to the air supply opening 4 is connected to the air supply opening 4. It is preferable to make the distance (the distance indicated by a in the figure) as short as possible. For example, the distance a is preferably within 40 mm, and more preferably within 20 mm.
Thus, since the outlet of the intake cylinder 7 is disposed at a position close to the air supply opening 4, it is possible to more effectively suppress the occurrence of pressure loss due to sudden expansion and contraction.

In addition, as shown in FIG. 3, the suction opening is set so that the area A2 of the portion of the air supply opening 4 facing the outflow position of the outside air from the intake cylinder 7 is not less than the cross-sectional area A1 of the air passage 11 of the intake cylinder 7. The position of the outlet of the cylinder 7 is preferably set. Here, “the area of the portion of the air supply opening 4 that faces the outflow position of the outside air from the intake cylinder 7” is the horizontal position at the height of the outlet of the intake cylinder 7 in this embodiment shown in FIG. This is the area A2 of the upper part when the air supply opening 4 is virtually cut by a smooth surface.
As shown in FIG. 3, when the inner diameter d ₀ of the intake cylinder 7 is about 60 mm, for example, the length L of the intake cylinder 7 that blocks the front of the intake opening 4 is smaller than the diameter d of the intake opening 4. , 0 <L ≦ 2d / 3 is preferably set.
When the intake cylinder 7 is arranged at a position close to the air supply opening 4, as shown in FIG. 2, the air supply opening 4 is partially partially blocked by the intake cylinder 7, By setting the position of the outlet of the intake cylinder 7 as described above, it is possible to secure a sufficient opening area for receiving the outside air from the intake cylinder 7 in the air supply opening 4. Therefore, the influence on the ventilation resistance can be reduced without hindering the flow of outside air.

  FIG. 5 shows the relationship between the length of the intake cylinder 7, the transmission loss, and the ventilation resistance. As shown in FIG. 5, the transmission loss increases with the length of the intake cylinder 7. On the other hand, the airflow resistance decreases as the length of the intake cylinder 7 increases, but conversely increases when it exceeds a certain length. In the above silencer 1, the length of the intake cylinder 7 is set to α with a small ventilation resistance. However, when priority is given to transmission loss, the length of the intake cylinder 7 is required to be longer than α. It can be set according to the air permeability and sound deadening performance.

[Second Embodiment]
FIG. 6 shows a silencer 1 according to the second embodiment of the present invention. 6A is an exploded perspective view, and FIG. 6B is a completed view.
In FIG. 6, the main body 2 includes a hollow casing and an upper casing 2 a having an entire lower opening, and a bottom plate 2 b that closes the lower opening of the upper casing 2 a. An air supply opening 4 is formed on the back surface of the upper casing 2 a, and a supply cylinder 13 is connected to the air supply opening 4. An intake opening 3 is formed in the bottom plate 2 b, and an intrusion prevention member 16 is attached to the intake opening 3.

Inside the main body 2, a sound absorbing material 5 provided on the inner wall surface of the main body 2 and an intake cylinder 7 connected to the intake opening 3 are arranged. The sound absorbing material 5 includes an upper portion 5a disposed on the upper inner wall surface of the main body 2, a side portion 5b disposed on the side inner wall surface of the main body 2, and a bottom portion 5c disposed on the bottom inner wall surface (bottom plate 2b) of the main body 2. .
The intake cylinder 7 itself is made of a sound absorbing material. For example, a porous material such as urethane foam is preferably used as the sound absorbing material.
In the present embodiment, the lower end of the side portion 5b and the outer end of the bottom portion 5c are connected, and the lower end of the intake cylinder 7 and the respective inner ends of the bottom portions 5c on both sides thereof are connected. The bottom part 5c and the side part 5b are united.

As shown in FIG. 6B, in the assembled state, a space portion 15 is formed between the outer wall surface of the intake cylinder 7 and the inner wall surface of the main body 2 as in the first embodiment.
In addition, regarding each member, about the structure and the feature point other than the point mentioned above, it is the same as that of 1st Embodiment mentioned above.
In the present embodiment, the intake cylinder 7, the bottom 5c, and the side 5b are integrated. However, the upper 5a and the side 5b may be integrated, and the intake cylinder 7 and the bottom 5c may be integrated. .

  According to this embodiment, since the intake cylinder 7 itself is made of a sound absorbing material, the partition wall of the intake cylinder 7 and the sound absorbing material can be integrated, so that the structure can be simplified.

[Other configuration example 1]
7A to 7D show another configuration example 1 of the silencer 1 of the present invention. (A)-(D) are the rear views of the silencer 1, respectively. In each of (A) to (D), the outlet of the intake cylinder 7 is positioned in the vicinity of the air supply opening 4.
In (A), two intake cylinders 7 and 7 are arranged at an interval in the width direction of the main body 2 (left-right direction in the figure). In (B), the intake cylinder 7 and the air supply opening 4 are both arranged at positions shifted in the same direction from the center in the width direction of the main body 2. In (C), the intake cylinder 7 and the air supply opening 4 are disposed at positions shifted in the opposite directions from the center in the width direction of the main body 2.

  By shifting the positions of the intake cylinder 7 and the air supply opening 4 as in (A) to (C), the volume balance of the space portion 15 (see FIG. 3) can be changed to increase the sound attenuation effect. In addition, when it is necessary to reduce the area of the air passage of the intake cylinder 7 in order to obtain a desired noise reduction performance, a necessary amount of ventilation is ensured by providing a plurality of intake cylinders 7 as shown in FIG. be able to.

  In (D), the intake cylinder 7 and the air supply opening 4 are both arranged at the same position in the width direction of the main body 2, but the intake cylinder 7 does not block the front of the air supply opening 4. Thus, the intake cylinder 7 may have a length that does not block the front of the air supply opening 4 as long as the required silencing performance and ventilation performance are satisfied.

  When the positions of the intake cylinder 7 and the air supply opening 4 are shifted from each other in the width direction of the main body 2 as shown in (A) and (C), in order to keep the airflow resistance low, the intake cylinder 7 The distance (distance indicated by b in the figure) between the portion of the outlet of the air passage 11 (see FIG. 3) closest to the air supply opening 4 and the portion of the air supply opening 4 closest to the intake cylinder 7 is made as short as possible. Is preferred. For example, the distance b is preferably within 40 mm, and more preferably within 20 mm.

[Other configuration example 2]
8A and 8B show another configuration example 2 of the silencer 1 of the present invention. In (A) and (B), the upper left is a rear view, the right is a side view, and the lower is a bottom view.
In the configuration example shown in FIG. 8, the cross-sectional shape of the intake cylinder 7 is an ellipse that is long in the width direction of the main body 2 in (A), and a rectangle that is long in the width direction of the main body 2 in (B).
By using the intake cylinder 7 having an elliptical or rectangular cross-sectional shape as described above, the depth dimension of the main body 2 (the horizontal dimension in FIG. 2) is small. Even if it is not obtained, the cross-sectional area can be increased to reduce the airflow resistance.

In addition, in the above-described first embodiment, the sound absorbing material of the intake cylinder 7 can be obtained when sufficient sound absorbing performance is obtained by the silencing action of the other parts of the silencer 1 without providing the sound absorbing material 10 of the intake cylinder 7. 10 may be omitted.
Further, in each of the above-described embodiments and configuration examples, the intake cylinder 7 is arranged in a direction in which the axial direction is vertical. However, the intake cylinder 7 is arranged in a direction in which the axial direction is inclined with respect to the horizontal direction or the horizontal direction. It may be arranged.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

1 is an external view of a silencer according to a first embodiment of the present invention. It is a longitudinal section of a silencer concerning a 1st embodiment of the present invention. It is III-III sectional drawing of FIG. It is the graph which compared the silencing performance about the silencer of this invention, and a prior art example. The relationship between the length of the suction cylinder, the transmission loss, and the ventilation resistance in the silencer of the present invention is shown. It is the disassembled perspective view and completion figure of the silencer concerning 2nd Embodiment of this invention. It is a figure which shows the other structural example 1 of the silencer of this invention. It is a figure which shows the other structural example 2 of the silencer of this invention. It is a schematic diagram of the conventional general expansion-type silencer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silencer 2 Main body 2a Upper casing 2b Bottom plate 3 Intake opening 4 Inlet opening 5 Inhalation material 5a Upper part 5b Side part 5c Bottom part 7 Intake cylinder 7a Inlet part 9 Cylindrical partition 10 Absorbing material 11 Ventilation path 13 Inlet part 13a Inlet part 14 Ventilation path 15 Space 16 Intrusion prevention member 20 Wall 21 Ventilation hole 22 Sleeve member

Claims (4)

A silencer provided on the outer wall surface of the ventilation hole of the building,
A main body formed in a hollow box shape and having an intake opening for taking in outside air, and an air supply opening for supplying the taken-in outside air to the ventilation hole;
A hollow cylindrical intake cylinder that protrudes from the intake opening to the inside of the main body and extends to the vicinity of the intake opening, and has one end connected to the intake opening and opened at the other end;
A hollow cylindrical supply cylinder that projects from the supply opening to the outside of the main body and is inserted into the ventilation hole, and
The inside of the main body communicates with the outside only through the intake opening and the air supply opening,
A sound absorbing material is provided on the inner wall surface of the main body,
A silencer characterized in that a space communicating with the opening on the other end side of the intake cylinder is formed between the outer wall surface of the intake cylinder and the inner wall surface of the main body. The cross-sectional area of the air passage of the intake cylinder is smaller than the cross-sectional area of the air passage of the supply cylinder,
The intake cylinder and the supply cylinder are arranged so that their axial directions intersect each other,
The intake cylinder is disposed so that the other end faces the air supply opening, and is disposed at a position that substantially partially closes the air supply opening,
The position of the other end of the intake cylinder is set so that an area of a portion of the air supply opening facing an outflow position of the outside air from the intake cylinder is equal to or larger than a cross-sectional area of a ventilation path of the intake cylinder. Item 2. A silencer according to Item 1.   The silencer according to claim 1 or 2, wherein the intake cylinder has a sound absorbing material surrounding the air passage.   The silencer according to claim 1 or 2, wherein the intake cylinder itself is made of a sound absorbing material.

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