JP2016006372A - Muffler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an effective muffler by utilizing a space which is located between a muffler disposed within a ventilation duct and a wall surface of the ventilation duct and which has not been used in the past.SOLUTION: A muffler 12 configured to be disposed on the half way of the ventilation duct is provided. Such a muffler comprises: a main silencer 12a; and a closing plate 14 that extends from a side wall surface of the main silencer to a wall surface of the ventilation duct when the muffler is disposed within the ventilation duct. Such the muffler includes a sub silencer 12b formed within a space defined by the side wall surface of the main silencer, the closing plate, and the wall surface of the ventilation duct when the muffler is disposed within the ventilation duct.

Description

  The present invention relates to a silencer, and more particularly, to a silencer for ventilation used in a tunnel ventilation facility or the like.

  Silencers used in tunnel ventilation equipment and the like are mainly used for the purpose of reducing noise generated by a ventilation fan and suppressing the emission of noise outdoors. For this reason, it is required to reduce noise in a wide band from a low frequency to a high frequency generated in the ventilation fan. Moreover, in a tunnel ventilation facility, a space for installing a silencer cannot often be secured widely, so that the flow velocity of airflow passing through the silencer is inevitably increased. Since airflow sound generated by airflow leads to a decrease in the performance of the silencer, it is necessary to suppress the generation of airflow sound. Furthermore, when the flow velocity of the airflow passing through the silencer increases, the pressure loss at the silencer also increases. If the pressure loss is large, it will lead to a decrease in ventilation fan performance such as a reduction in air volume. Therefore, it is required to keep the pressure loss of the silencer within an allowable value.

  Ventilation silencers need to be planned to provide a certain sound reduction performance under these several conditions.

  Conventional silencers for tunnel ventilation are almost always composed of a sound absorbing silencer. The sound absorption type silencer adjusts the volume reduction by adjusting the thickness of the sound absorbing layer and the length of the silencer so that the target volume reduction can be obtained. In general, for a standardized product as a general-purpose product, the model and quantity are selected according to the required processing air volume (passing air volume). A sound absorbing silencer can obtain a sound reduction effect in a wide frequency band, but generally has a low sound reduction performance in a low frequency band.

  On the other hand, the noise of the ventilation fan mainly includes noise having a specific frequency component in a relatively low frequency band such as blade passing sound, in addition to noise having a component in a relatively high frequency band such as airflow sound. The specific frequency component of the blade passing sound is a frequency component (blade passing frequency) calculated as a product of the rotational frequency of the fan and the number of blades and a harmonic frequency component that is a natural number multiple thereof.

  Noise that has passed through the ventilation silencer is attenuated over a wide frequency band, but if a sound absorbing silencer is used, specific frequency components such as wing passage noise cannot be reduced intensively. In addition, since the blade passing sound is composed of a relatively low frequency component, it is generally difficult to obtain a sufficient volume reduction with a sound absorbing silencer having a low sound reduction performance in a low frequency band. For this reason, in the noise after passing through the sound absorbing silencer, the wing passing sound remains as a main component, which may be annoying.

  To further reduce the noise level, extend the sound absorption silencer in the direction of air flow or increase the sound absorption material to obtain the required volume reduction, but this is included in the noise of the ventilation fan. If the frequency components other than the blade passing sound have already been sufficiently reduced, the performance of the silencer for other frequency components becomes excessive.

Japanese Patent No. 4731829 Japanese Patent No. 4403104

  In Patent Document 1, a combination of two types of sound absorbing silencers with different opening ratios (ratio of the opening area of the cylindrical outer plate after mounting the sound absorbing material to the opening area of the cylindrical outer plate before mounting the sound absorbing material) There has been proposed an apparatus that adjusts the aperture ratio and the ratio of the number of silencers installed so that the noise reduced by the silencer and the magnitude of self-noise generated from the silencer are approximately equal. However, a silencer with a large aperture ratio installed to reduce the passage flow rate of the silencer has a sound reduction performance in a relatively low frequency band, such as a blade passing sound of a ventilation fan, than a silencer with a small aperture ratio. Therefore, noise that has passed through a silencer with a large aperture ratio is not reduced as much as noise that has passed through a silencer with a small aperture ratio, and at the expense of noise reduction performance as a whole, it is reduced in relation to self-noise. The sound performance is also determined, and the degree of freedom in design is low.

  As a sound absorption type silencer installed in a tunnel, there is one using a rectifier having a sound reduction effect as in Patent Document 2 in order to supplement the performance of the silencer. In this rectifier, a continuous bent portion is required in the duct, but such a portion is not necessarily provided in the tunnel for duct ventilation, so that the application is limited.

  In the silencer for ventilation installed in the tunnel ventilation equipment, a sound absorption type silencer is often used, but due to the characteristics of the silencer, the component of the octave band center frequency 63 Hz to 125 Hz is not sufficiently reduced. A specific frequency component such as the blade passing sound of the included ventilation fan remains as a dominant component. If the sound absorbing silencer is extended in order to sufficiently reduce the noise in this frequency band, the silencer becomes larger and it is necessary to secure a large installation location, which increases both manufacturing costs and construction costs.

  Also, the tunnel ventilation equipment ducts may be very narrow. For this reason, the silencer is installed in two places, or the silencer is installed in a vertical duct that is difficult to construct. Even in that case, there is a problem that the manufacturing and construction costs increase.

  In a typical silencer, there is a tendency that the pressure loss increases as the sound reduction performance increases. Therefore, as the noise is reduced by the silencer, the pressure loss increases and the power of the ventilation fan for blowing air increases. Ventilation in road tunnels requires a large amount of power to transport a large amount of air over long distances, which increases operating costs. It is desirable to keep this as low as possible.

  The present invention aims to alleviate or eliminate at least some of the above problems.

  According to one embodiment of the present invention, a silencer configured to be installed in the middle of a ventilation duct is provided. Such a silencer includes a main silencer and a closing plate that extends from the side wall surface of the main silencer to the wall surface of the ventilation duct when the silencer is installed in the ventilation duct. In the silencer, when the silencer is installed in the ventilation duct, the sub silencer is formed in a space defined by the side wall surface of the main silencer, the closing plate, and the wall surface of the ventilation duct.

  According to one embodiment, the sub silencer is formed as a resonant silencer.

  According to one embodiment, the sub silencer is formed as a side branch silencer.

  According to one embodiment, the sub silencer is formed as a sound absorbing silencer.

According to one embodiment, the sub silencer is configured as a branch duct having a non-reflective end that absorbs sound waves and suppresses reflection at the innermost part of the space of the sub silencer.

  According to one embodiment, the installation position of the closing plate is configured to be changeable in the direction of the ventilation duct.

  According to one embodiment, when installed in a ventilation duct, a plurality of sub silencers are formed, and the plurality of sub silencers include a resonance type silencer, a side branch type silencer, a sound absorption type silencer, and a non-reflection type. It is configured by combining multiple types from the group consisting of sub silencers with branch ducts with ends installed.

  According to one embodiment, the sub silencer is configured such that sound waves can enter from both upstream and downstream sides of the airflow flowing in the ventilation duct.

  According to one embodiment, the silencer is configured to be placed in a ventilation duct formed by concrete or steel plate.

1 is a schematic diagram showing a silencer comprising a main silencer and a sub silencer according to an embodiment of the present invention. 1 is a schematic diagram showing a silencer comprising a main silencer and a sub silencer according to an embodiment of the present invention. 1 is a schematic diagram showing a silencer comprising a main silencer and a sub silencer according to an embodiment of the present invention. It is the schematic which shows the silencer by which the sub silencer is comprised by the resonance type silencer by one Embodiment of this invention. It is the schematic seen from the downstream of the ventilation duct by which a sub silencer is comprised by the resonance type silencer by one Embodiment of this invention, and a silencer is arrange | positioned. It is the schematic seen from the downstream of the ventilation duct by which a sub silencer is comprised by the resonance type silencer by one Embodiment of this invention, and a silencer is arrange | positioned. It is the schematic which shows the silencer by which the sub silencer is comprised by the side branch type silencer by one Embodiment of this invention. It is the schematic seen from the downstream of the ventilation duct by which sub silencer is comprised by the side branch type silencer by one Embodiment of this invention, and a silencer is arrange | positioned. It is the schematic which shows the silencer with which a sub silencer is comprised with a sound absorption type silencer by one Embodiment of this invention. 1 is a schematic diagram illustrating a sub-muffler configured as a branch duct having a non-reflective end according to an embodiment of the present invention. It is the schematic which shows the silencer by which a door is arrange | positioned at a sub silencer by one Embodiment of this invention. It is the schematic which shows the silencer by which a door is arrange | positioned at a sub silencer by one Embodiment of this invention. It is the schematic which shows the silencer by which sub silencer is comprised by the sound absorption type silencer and the resonance type silencer by one Embodiment of this invention. It is the schematic which shows the silencer by which sub silencer is comprised by the sound absorption type silencer and the resonance type silencer by one Embodiment of this invention. It is the schematic which shows the silencer by which sub silencer is comprised by the sound absorption type silencer and the resonance type silencer by one Embodiment of this invention. It is the schematic which shows the silencer by which the sub silencer is comprised by the side branch type silencer by one Embodiment of this invention. It is the schematic which shows the silencer by which the sub silencer is comprised by the side branch type silencer by one Embodiment of this invention. It is a figure which shows schematically the conventional silencer arrange | positioned in the ventilation duct of tunnel ventilation equipment. It is a graph which shows the sound reduction effect of the silencer by embodiment shown by FIG. It is a graph which shows the sound reduction effect of the silencer by embodiment shown by FIG.

  Embodiments of a silencer according to the present invention will be described below with reference to the accompanying drawings. In the accompanying drawings, the same or similar elements are denoted by the same or similar reference numerals, and redundant description of the same or similar elements may be omitted in the description of each embodiment. Further, the features shown in each embodiment can be applied to other embodiments as long as they do not contradict each other.

  FIG. 18 is a diagram schematically showing a conventional sound absorbing silencer 102 disposed in a ventilation duct 100 of a tunnel ventilation facility, and shows a cross section cut out in a horizontal plane parallel to the airflow passage direction. The sound absorbing silencer 102 is configured by combining a number of cell type or splitter type sound absorbing silencers. Here, the cell-type sound absorbing silencer is a silencer that uses a single or a plurality of cylindrical sound absorbing silencers whose cross section perpendicular to the airflow direction is approximately square. is there. A splitter type sound absorption silencer is a sound absorption silencer that uses one or more cylindrical sound absorption silencers whose cross-sectional shape is perpendicular to the airflow direction and has a relatively large aspect ratio. It is a vessel. The sound absorbing silencer 102 can be, for example, a silencer in which a sound absorbing material such as glass wool is mounted inside a cylindrical outer plate having a rectangular cross section. In the sound absorbing silencer 102, sound waves pass through the ventilation duct 100 together with air, and the sound waves are absorbed and silenced by the sound absorbing material.

  In general, when the conventional sound absorbing silencer 102 is installed in the ventilation duct 100, a space 104 exists between the sound absorbing silencer 102 and the wall surface of the ventilation duct 100 as shown in FIG. Therefore, the space between the sound absorbing muffler 102 and the wall surface of the ventilation duct 100 is covered with a closing plate 106 so that airflow and sound waves pass through the sound absorbing muffler 102.

  As described above, the sound absorbing silencer generally has a reduced sound reduction performance in a low frequency band. The noise of the ventilation fan contains a relatively low frequency component such as blade passing sound, and it is necessary to reduce this noise in order to reduce the noise. Therefore, in the embodiment of the present invention, effective silencing is realized by using the space 104 between the silencer 102 and the wall surface of the ventilation duct 100, which has not been conventionally used.

FIG. 1 is a schematic diagram showing the configuration of a silencer 12 according to an embodiment, and shows a cross section cut out in a horizontal plane parallel to the airflow passage direction. In such an embodiment, the silencer 12 includes a main silencer 12a. The main silencer 12a can be, for example, a conventional sound absorption silencer, and can be configured by combining a cell type or splitter type sound absorption silencer. In the present embodiment, the closing plate 14 is disposed from the upstream (inlet side) end of the main silencer 12a toward the inner wall surface of the ventilation duct 100. However, a closing plate is not provided at the downstream (exit side) end of the main silencer 12a. Therefore, an open space 18 is formed by the outer wall surface 16 of the main silencer 12 a, the closing plate 14, and the inner wall surface of the ventilation duct 100. The sound wave that has passed through the main silencer 12a wraps around the space 18 and functions as a sub silencer 12b that reduces the sound by effects such as resonance, interference, and sound absorption. In general, since a low-frequency sound wave is more easily diffracted, the sub silencer 12b is effective in silence of a relatively low frequency component such as a blade passing sound. Further, as will be described in detail below, the sub silencer 12b is formed as a resonance type silencer or a side branch type silencer, thereby reducing a specific frequency component such as a blade passing sound. It can be. On the other hand, the inlet of the sub-muffler 12b is located on the side of the outlet of the main muffler 12a, and almost no airflow flows through the sub-muffler 12b, so that almost no pressure loss occurs.

  As an embodiment, as shown in FIG. 2, the closing plate 14 can be configured to be installed and fixed at an arbitrary position along the flow direction of the airflow. Therefore, when the silencer is installed in the ventilation duct, the volume of the space 18 of the sub silencer 12b can be arbitrarily changed and fixed. In such a configuration, a space for airflow to enter the outside of the upstream end portion of the main silencer 12a is generated, and pressure loss may occur. Therefore, as one embodiment, as shown in FIG. 3, the installation position of the closing plate 14a located at the upstream end of the main silencer 12a is fixed, and the installation position is changed along the airflow direction. A possible closing plate 14b can be further provided. With this configuration, it is possible to prevent the occurrence of pressure loss and change the volume of the space 18 of the sub silencer 12b.

  FIG. 4 is a diagram showing an embodiment in which the sub silencer 12b is configured as a resonance silencer. FIG. 4 mainly shows the configuration of the sub silencer 12b. The main silencer 12a is the same as in FIG.

FIG. 4 shows a part of a cross section of the sub silencer 12b cut out in a horizontal plane parallel to the airflow direction. In the present embodiment, the sub silencer 12b configured as a resonance silencer includes a closing plate 14 extending from the upstream end of the main silencer 12a toward the inner wall surface of the ventilation duct 100, and the outside of the main silencer 12a. A resonance chamber 22 is formed by the wall surface 16, the inner wall surface of the ventilation duct 100, and the closing plate 14 c formed with the opening 20 extending from the downstream end of the main silencer 12 a toward the inner wall surface of the ventilation duct 100. The In the illustrated embodiment, the resonance type sub-muffler 12 b includes a resonance chamber 22 and an opening 20. Resonance of the sub muffler 12b exert maximum sound reduction effects at the resonant frequency f ₀ as shown by the following equation.
f ₀ = (c / 2π) √ (S / d · V)
Here, f ₀ is the resonance frequency [Hz], c is the speed of sound in the air [m / s], S is the opening cross-sectional area [m ² ], d is the opening length [m], and V is the volume of the resonance chamber. [M ³ ]. Frequency of sound reduction is not desired sound, for example, as the blade passing frequency is outstanding component of the noise of the ventilation fan and the resonance frequency f ₀ is matched, the volume V, the sectional area of the opening 20 S, the length of the opening 22 Adjust d.

  In one embodiment, a partition plate 24 may be installed in the resonance chamber 22, and a plurality of resonance-type sub silencers 12b may be configured around the main silencer 12a. FIG. 5 is a schematic view showing a silencer 12 including a sub silencer 12b formed as a resonance type silencer, as viewed from the downstream side of the airflow, according to an embodiment. As shown in FIG. 5, a plurality of openings 20 to the resonance chamber 22 can be provided around the main silencer 12a. A partition plate 24 (shown by a broken line in FIG. 5) is provided at an arbitrary location in the resonance chamber 22, and a plurality of resonance chambers 22 having different volumes are provided so that the resonance frequencies coincide with a plurality of frequencies, The sub-muffler 12b can be configured to reduce the frequency component. Further, the opening 20 to the resonance chamber 22 can be a circular or rectangular hole, or can be formed as a continuous slit 20a or an intermittent slit 20b as shown in FIG.

  In one embodiment, the volume of the resonance chamber 22 is adjusted so that the installation position of the closing plate 14 constituting the resonance type sub silencer 12b can be changed as shown in FIGS. The resonance frequency may be changed with

  FIG. 7 is a diagram showing an embodiment in which the sub silencer 12b is configured as a side branch type silencer. 7 mainly illustrates the configuration of the sub silencer 12b. The main silencer 12a is the same as that shown in FIGS.

FIG. 7 schematically shows a part of a cross section of the sub silencer 12b cut out in a horizontal plane parallel to the airflow direction. In the present embodiment, the sub silencer 12b configured as a side branch type silencer includes a closing plate 14 extending from the upstream end of the main silencer 12a toward the inner wall surface of the ventilation duct 100, and the main silencer 12a. A branch duct 26 is formed by the outer wall surface 16 and the inner wall surface of the ventilation duct 100. In the embodiment shown in FIG. 7, side branch type of sub silencer 12b is for maximum sound reduction effects at the resonant frequency f _r represented by the following formula.
f _r = (2n−1) · c / 4L
Here, _fr is the resonance frequency [Hz], c is the speed of sound [m / s], L is the length [m] of the branch duct 26, and n is a natural number (n = 1, 2, 3,...). . Frequency of sound reduction is not desired sound, for example, as the blade passing frequency is outstanding component of the noise of the ventilation fan and the resonance frequency f _r are the same, to adjust the length L of the branch duct 26. As shown in FIG. 8 in which a part of the silencer 12 is viewed from the downstream side, a plurality of side branches can be provided. At that time, a shielding plate 30 is provided in the openings 28 of some side branches, A plurality of side branches can be set apart from each other, and a partition plate 24 such as the resonance type sub-muffler 12b shown in FIG. 5 can be provided to divide the side branch.

  FIG. 9 is a diagram showing an embodiment in which the sub silencer 12b is configured as a sound absorption type silencer, and schematically shows a cross section of the sub silencer 12b cut out in a horizontal plane parallel to the airflow direction. In the present embodiment, the sub silencer 12b configured as a sound absorption type silencer includes a closing plate 14 extending from the upstream end of the main silencer 12a toward the inner wall surface of the ventilation duct 100, and the outside of the main silencer 12a. A space 18 is formed by the wall surface 16 and the inner wall surface of the ventilation duct 100. The sound absorbing material 32 is arranged on the inner wall surface of the space 18 to constitute the sound absorbing type sub silencer 12b. In this embodiment, a part of the sound wave that has passed through the main silencer 12a is reduced by entering the sound absorbing silencer that is the sub silencer 12b.

  FIG. 10 shows a silencer 12 according to an embodiment, and a non-reflection end 34 that absorbs sound waves and substantially suppresses reflection is disposed in the innermost part of the space 18 forming the sub silencer 12b. In the case of the sub silencer 12b provided with the non-reflection end 34 as in the present embodiment, a part of the sound wave that has passed through the main silencer 12a enters the sub silencer 12b provided with the non-reflection end 34. Since the sound wave reaching the inner part is absorbed by the non-reflecting end 34, the sound wave discharged from the sub silencer 12b is reduced. In such an embodiment, the sub silencer 12b on which the non-reflective end 34 is installed may be a sound absorption type sub silencer 12b. The position of the innermost part where the non-reflective end 34 is installed can be adjusted and changed in the direction in which the airflow flows, as shown in FIGS. The non-reflective end 34 can be constituted by, for example, a wedge-shaped sound absorbing structure or a simpler structure by attaching a sound absorbing material such as glass wool thicker than in normal use.

  FIGS. 11 and 12 partially show the silencer 12 according to one embodiment, and show a configuration in which a door 36 is provided on the closing plate 14 that forms the sub silencer 12b. In the embodiment of FIG. 11, the sub silencer 12b is configured as a resonance type silencer, and in the embodiment of FIG. 12, the sub silencer 12b is configured as a side branch type silencer. In the illustrated embodiment, the position of the closing plate 14a at the upstream end of the main silencer 12a is fixed, and the closing plate 14b arranged further downstream can be adjusted in the direction in which the airflow flows. is there. In the illustrated embodiment, an airtight door 36 is provided on both of the closing plates 14a and 14b. By installing such a door 36, the sub-muffler 12b can be used as a passage, and it becomes easy to check or the inside of the sub-muffler 12b can be easily checked. In the embodiment of FIG. 11, the door 36 may be installed on the closing plate 14 c where the opening 20 of the resonance chamber 22 is formed, and the opening 20 may be provided on the door 36.

13 and 14 show a silencer 12 according to an embodiment, and both a resonance type silencer and a sound absorption type silencer are used as the sub silencer 12b. In the illustrated embodiment, an opening 20 of the resonance silencer is formed in the innermost part of the sound absorption silencer. In such an embodiment, since the sound can be reduced by both the sound absorption effect by the sound absorption type silencer and the resonance effect by the resonance type silencer, the frequency is wider than that of the sub silencer having only the resonance type silencer. The range of sound waves can be reduced. As shown in FIG. 14, a sound absorbing silencer having a plurality of resonance frequencies can be configured by changing the position of the innermost part of each sound absorbing silencer constituting the sub silencer 12b. In such an embodiment, a plurality of resonance silencers having different resonance frequencies and a sound absorption silencer having different sound absorption effects due to different lengths can be configured. In such an embodiment, it is possible to reduce a plurality of frequency components such as a plurality of dominant frequencies, for example, a blade passing frequency which is a dominant component of the noise of the ventilation fan and its harmonics.

  FIG. 15 shows a silencer 12 according to an embodiment, and both a resonance type silencer and a sound absorption type silencer are used as the sub silencer 12b. In the illustrated embodiment, a resonance type sub silencer 12b is provided around the entrance side of the main silencer 12a, and a sound absorption type sub silencer 12b is provided around the exit side of the main silencer 12a. A resonance type sub-muffler 12b having an opening 20 in the innermost part of the device 12b is further provided. The resonance-type sub muffler 12b on the inlet side and the resonance-type sub muffler 12b on the outlet side are partitioned by a closing plate 14b. In such an embodiment, a plurality of excellent frequency components can be reduced by the resonance type sub silencer 12b having different resonance frequencies, and a wide range of noise can be reduced by the sound absorption type sub silencer 12b. In this embodiment, since airflow enters the resonance type sub silencer 12b around the inlet side of the main silencer 12a, some pressure loss occurs, but the airflow passing through the ventilation duct 100 is Since the flow velocity is smaller, the pressure loss is relatively small.

  FIGS. 16 and 17 partially show a silencer 12 according to an embodiment. A plurality of side branch type silencers are used as the sub silencer 12b, and the side branch type silencer is a main silencer 12a. It is provided in the vicinity of both the inlet side and the outlet side. In the illustrated embodiment, the side branch type sub silencer 12b disposed around the entrance side of the main silencer 12a and the side branch type sub silencer 12b disposed around the exit side of the main silencer 12a. Thus, different dominant frequency components can be reduced by making the lengths of the branch ducts 26 different. In the illustrated embodiment, the length of the branch duct 26 can be determined according to the frequency of the sound wave to be silenced. In the embodiment of FIGS. 16 and 17, airflow enters the side branch type sub silencer 12 b around the entrance side of the main silencer 12 a, so that some pressure loss occurs, but the ventilation duct 100 Since the airflow passing through the inside has a smaller flow velocity in the vicinity, the pressure loss is relatively small.

FIG. 19 is a graph showing the results of a model experiment that confirmed the sound reduction effect of the silencer 12 shown in FIG. 4 according to one embodiment. This graph is a graph showing the sound reduction effect by installing the sub silencer 12b when the resonance chamber 22 is arranged as a sub silencer 12b on a part of the outer periphery of the main silencer 12a. As in the conventional silencer shown in FIG. 18, the sound reduction effect is achieved by closing a space 104 formed between the silencer 102 and the wall surface of the ventilation duct with two closing plates 106 arranged at both ends thereof. FIG. 4 shows the difference between the sound pressure level in the case where the opening 20 is disposed in the closing plate 14c on the outlet side of the main silencer 12a as shown in FIG. In the graph of FIG. 19, a peak is seen in the vicinity of 200 Hz as the sound reduction effect. Since the design value of the resonance frequency f ₀ of the configured resonance type sub muffler 12b in this experiment was approximately 220 Hz, it is considered that the noise reducing effect of the resonance-type sub silencer errors Some were exhibited.

FIG. 20 is a graph showing the results of a model experiment in which the sound reduction effect of the silencer 12 shown in FIG. 7 which is an embodiment is confirmed. This graph is a graph showing the sound reduction effect by installing the sub silencer 12b when the branch duct 26 is arranged as a sub silencer 12b on a part of the outer periphery of the main silencer 12a. As in the conventional case shown in FIG. 18, the sound reduction effect is obtained when the space 104 formed between the silencer 102 and the wall surface of the ventilation duct is closed by two closing plates 106 arranged at both ends thereof. This is a difference between the sound pressure level and the sound pressure level when the opening 28 is used without providing a closing plate on the outlet side of the main silencer 12a as shown in FIG. In the graph of FIG. 20, a peak is observed near 190 Hz as a sound reduction effect. Since the design value of the resonant frequency f _r of the side branch type sub muffler 12b configured in this experiment was approximately 190 Hz, noise reducing effect of the side branch type sub muffler is considered to have been exhibited.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment. The features of the above-described embodiments can be combined or exchanged as long as they do not contradict each other.

12 silencer 12a main silencer 12b sub silencer 14 closing plate 16 outer wall 18 space 20 opening 22 resonance chamber 24 partition plate 26 branch duct 28 opening 30 shielding plate 32 sound absorbing material 34 non-reflective end 36 door 100 ventilation duct 102 Silencer 104 space 106 closing plate

Claims (9)

A silencer configured to be installed in the middle of a ventilation duct,
The main silencer,
When the silencer is installed in a ventilation duct, a closing plate extending from the side wall of the main silencer to the wall surface of the ventilation duct,
The silencer, wherein when the silencer is installed in a ventilation duct, a sub silencer is formed in a space defined by the side wall of the main silencer, the closing plate, and a wall surface of the ventilation duct.   2. The silencer according to claim 1, wherein the sub silencer is formed as a resonant silencer.   2. The silencer according to claim 1, wherein the sub silencer is formed as a side branch type silencer.   2. The silencer according to claim 1, wherein the sub silencer is formed as a sound absorbing silencer.   2. The silencer according to claim 1, wherein the sub silencer is configured as a branch duct having a non-reflective end that absorbs sound waves and suppresses reflection at the innermost part of the space of the sub silencer. ,Silencer   It is a silencer as described in any one of Claims 2 thru | or 4, Comprising: The silencer comprised so that the installation position of the said closing board can be changed in the direction of a ventilation duct.   The silencer according to any one of claims 1 to 6, wherein when installed in a ventilation duct, a plurality of the sub silencers are formed, and the plurality of sub silencers are resonant silencers, A silencer configured by combining a plurality of types from a group consisting of a side-branch silencer, a sound absorption silencer, and a sub silencer having a branch duct provided with a non-reflective end.   The silencer according to claim 7, wherein the sub silencer is configured such that sound waves can enter from both the upstream side and the downstream side of the airflow flowing in the ventilation duct.   9. The silencer according to any one of claims 1 to 8, wherein the silencer is configured to be placed in a ventilation duct formed of concrete or steel plate.

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