Air duct with silencer

Abstract

The invention provides an air duct with a silencer, which can effectively reduce sound propagating in the air duct when air from an air blower is sent out through the air duct. An air duct with a muffler is provided with: an air duct through which air blown from a blowing source flows; and a first silencer and a second silencer which reduce sound propagating in the air duct by using a passive silencing method, and the frequency bands of the reduced sound are different from each other. The first muffler having a lower frequency band of the reduced sound is disposed at a position closer to the blowing source, and the second muffler having a higher frequency band of the reduced sound is disposed at a position farther away from the blowing source. The frequency of the primary muffling peak of the second muffler is equal to or greater than a peak frequency at which the intensity of sound generated in the air duct is the maximum among the peak frequencies of sound generated in the air duct due to blowing in the air duct.

Description

Technical Field

[0001] The invention relates to an air duct with a muffler. Background Art

[0002] When air from an air conditioner or a blower is blown through an air duct such as a passage, noise caused by the operation of the blower, for example, can be transmitted to the air supply destination through the air duct. A technology for eliminating such noise at a midpoint of the air duct has been developed, and the technology described in Patent Document 1 can be cited as an example.

[0003] In the air conditioner described in Patent Document 1, a radial fan assembly is provided in an outdoor unit, and sucks in outdoor air to supply air to an indoor unit. At this time, the air supplied to the indoor unit passes through an air supply and exhaust passage, and a muffler (specifically, a silencer) provided in the air supply and exhaust passage reduces the sound propagating in the air supply and exhaust passage.

[0004] Previous technical literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2004-069173 Summary of the invention

[0007] Technical issues to be solved by the invention

[0008] When a muffler is installed in an air duct, it is usually installed on the upstream side of the air duct, for example, near the blower, because it is difficult to ensure installation space near the outlet of the air duct. On the other hand, the air supply volume is sometimes increased for the purpose of effectively supplying air, in which case the wind speed in the air duct increases. Sometimes, noise, especially high-frequency noise, is generated due to the increase in wind speed.

[0009] Then, if the above-mentioned noise is generated at a position downstream of the muffler in the air duct, the noise will propagate to the outlet of the air duct and be released from the outlet. Therefore, even if a muffler is arranged on the upstream side of the air duct, it is possible that the muffler function cannot be properly exerted on the above-mentioned noise generated on the downstream side thereof (i.e., the sound generated in the air duct due to air supply in the air duct), and the desired muffler effect cannot be obtained.

[0010] The present invention is completed in view of the above situation, and its subject is to solve the following purposes. That is, the purpose of the present invention is to provide an air duct with a silencer, which can solve the above problems and effectively reduce the sound propagating in the air duct when the wind from the blower is sent out through the air duct.

[0011] Means for solving technical problems

[0012] In order to achieve the above-mentioned object, the present invention has the following structure.

[0013] [1] An air duct with a silencer, comprising: an air duct for flowing air sent from an air source; and a first silencer and a second silencer, which use a passive silencer method to reduce sound propagating in the air duct, and the frequency bands of the reduced sounds are different from each other, the first silencer with a lower frequency band is arranged at a position closer to the air source, and the second silencer with a higher frequency band is arranged at a position farther from the air source, and the frequency of the primary silencer peak of the second silencer is above the following peak frequency, which is the peak frequency of the sound generated in the air duct due to air supply in the air duct, and the intensity of the generated sound becomes the maximum peak frequency.

[0014] [2] An air duct with a silencer according to [1], wherein, when the distance from the downstream end of the first silencer to the outlet of the air duct is set to L, the second silencer is arranged at a position where the distance from the downstream end of the second silencer to the outlet of the air duct is less than L / 2.

[0015] [3] An air duct with a silencer according to [1] or [2], wherein when the size of the space surrounded by the outer wall surface of the first silencer is set to the volume of the first silencer and the size of the space surrounded by the outer wall surface of the second silencer is set to the volume of the second silencer, the volume of the second silencer is smaller than the volume of the first silencer.

[0016] [4] The air duct with a muffler according to any one of [1] to [3], wherein the minimum value of the diameter of the air duct or the minimum value of the equivalent circle diameter of the air duct is 150 mm or less.

[0017] [5] An air duct with a silencer according to any one of [1] to [4], wherein the interior of the first frame of the first silencer and the interior of the second frame of the second silencer respectively include an inner silencer air duct constituting a part of the air duct, and at least one of the first frame and the second frame is entirely or partially made of resin material.

[0018] [6] The air duct with a silencer according to any one of [1] to [5], wherein a sound absorbing material made of a resin material is arranged in at least one of the first silencer and the second silencer.

[0019] [7] An air duct with a silencer according to any one of [1] to [6], wherein at least one of the first silencer and the second silencer has an expansion portion, the expansion portion has a cross-sectional dimension orthogonal to the extension direction of the air duct that is larger than an internal space of the air duct, and the internal space of the expansion portion includes an inner air duct of the silencer constituting a part of the air duct and a back space located outside the inner air duct of the silencer.

[0020] [8] An air duct with a silencer according to any one of [1] to [7], wherein the air duct passes through a wall separating two spaces, a first silencer is arranged in one of the two spaces, and a second silencer is arranged in the other space.

[0021] [9] The air duct with a silencer according to [8], wherein a wall separates an interior space of a room for accommodating people from the outside of the room, and the space where the second silencer is arranged is the interior space of the room.

[0022]

[10] The air duct with a silencer according to [8] or [9], wherein the second silencer is arranged at a position adjacent to a wall in another space.

[0023]

[11] An air duct with a silencer according to any one of [1] to

[10] , wherein the interior of the first silencer and the interior of the second silencer respectively include an inner silencer air duct constituting a part of the air duct, and the inner silencer air duct of the second silencer forms an end portion on the outlet side of the air duct.

[0024]

[12] The air duct with a muffler according to any one of [1] to

[11] , wherein the air duct is connected to an exhaust port of a fan as an air blowing source.

[0025] Effects of the Invention

[0026] In the air duct with silencer of the present invention, a first silencer with a lower silencer frequency band is arranged at a position closer to the blowing source, and a second silencer with a higher silencer frequency band is arranged at a position farther from the noise source. In addition, the frequency of the primary silencer peak of the second silencer is above the peak frequency at which the intensity of the sound generated in the air duct due to the air supply in the air duct becomes the maximum. Thus, when the air from the blower is sent out through the air duct, the sound propagated in the air duct can be effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram showing an air supply system using an air duct with a silencer according to an embodiment of the present invention.

[0028] Figure 2 It is a cross-sectional view of a first muffler included in an air duct with a muffler according to an embodiment of the present invention.

[0029] Figure 3 It is a cross-sectional view showing a first modified example of the first muffler.

[0030] Figure 4 It is a cross-sectional view showing a second modified example of the first muffler.

[0031] Figure 5 It is a cross-sectional view showing a third modified example of the first muffler.

[0032] Figure 6 This is a diagram showing a configuration for measuring the frequency spectrum of sound generated in an air duct.

[0033] Figure 7 It is a cross-sectional view of a second muffler included in the air duct with a muffler according to one embodiment of the present invention.

[0034] Figure 8 It is a schematic diagram showing the positional relationship between the first muffler and the second muffler.

[0035] Fig. 9 This is an explanatory diagram regarding the dimensions of each part of the first muffler used in the first embodiment.

[0036] Fig.10 This is an explanatory diagram regarding the dimensions of each part of the second muffler used in the first embodiment.

[0037] Fig.11 It is a graph which shows the noise reduction performance of each muffler used in the Example and the comparative example.

[0038] Fig.12 It is a graph showing the measurement results of the noise reduction effect in each of Example 1 and Comparative Examples.

[0039] Fig.13 It is a figure which shows the measurement result about the noise reduction effect in each test 1-3. DETAILED DESCRIPTION

[0040] The air duct with a muffler of the present invention is described in detail below with reference to the preferred embodiment shown in the accompanying drawings. In addition, the following embodiment is only an example given for the convenience of understanding the present invention and does not limit the present invention. That is, the structure of the present invention can be changed or improved according to the following embodiment as long as it does not deviate from its purpose.

[0041] Furthermore, the material and shape of each component used to implement the present invention can be arbitrarily set according to the purpose of the present invention and the technical level at the time of implementation of the present invention, unless otherwise specified. Furthermore, the present invention includes equivalents thereof.

[0042] Furthermore, in the present specification, a numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0043] Furthermore, in this specification, "orthogonal", "perpendicular" and "parallel" include the error range allowed in the technical field to which the present invention belongs. For example, "orthogonal", "perpendicular" and "parallel" in this specification refer to the range of less than ±10° relative to orthogonal, perpendicular or parallel in the strict sense. In addition, the error from orthogonal or parallel in the strict sense is preferably 5° or less, and more preferably 3° or less.

[0044] Furthermore, in the present specification, “same”, “identical”, and “equal” mean that the terms can include an error range that is generally allowed in the technical field to which the present invention belongs.

[0045] Furthermore, in this specification, “all”, “all” and “all” mean that, in addition to including 100% cases, they also include the error range that is generally allowed in the technical field to which the present invention belongs, for example, cases of more than 99%, more than 95% or more than 90%.

[0046] In addition, "noise reduction" in the present invention means reducing sound, and is a concept that includes both sound insulation and sound absorption. Sound insulation means shielding sound, in other words, not letting sound pass through. In addition, sound shielding includes reflection of sound (sound) and mutual cancellation of sound (sound). Sound absorption means reducing reflected sound, that is, absorbing sound (sound).

[0047] [Basic structure of the air duct with muffler of the present invention]

[0048] A basic structure of an air duct with a muffler according to an embodiment of the present invention (hereinafter referred to as the present embodiment) will be described with reference to the drawings.

[0049] In the following description, "air supply direction" refers to the direction in which the wind flows toward the outlet in the air duct, which is equivalent to the extension direction of the air duct. In addition, the downstream side refers to the outlet side of the air duct in the air supply direction, and the upstream side refers to the inlet side of the air duct (i.e., the side where the blowing source 10 described later is arranged).

[0050] The air duct with a muffler (hereinafter referred to as the air duct with a muffler 100) according to the present embodiment is used for an air supply system, and in particular, for an air supply system S for a building. The air supply system S is used to transport (supply) air to a predetermined space (e.g., a room, etc.) in a building for the purpose of achieving air conditioning or ventilation. Buildings include single-family houses, households in a collective housing such as an apartment, stores such as restaurants and shops, and facilities such as hospitals, department stores, and movie theaters.

[0051] In addition, "wind" refers to the flow (airflow) of artificial air or gas. There are no particular restrictions on the composition of the air or gas constituting the wind and the ratio of each component, and the following description assumes that normal air is blown.

[0052] like Figure 1 As shown, the air supply system S is composed of a blowing source 10 and an air duct 100 with a muffler. Figure 1 As shown, the air duct 100 with a muffler includes: an air duct 12 connected to an air source 10; and a muffler 20 for reducing the sound (noise) propagating in the air duct 12 when air is blown.

[0053] The air blowing source 10 is a device that has an electric motor such as a motor and is operated by starting the electric motor to blow air, specifically, a blower fan or a ventilation blower fan constituting an air conditioning device. As the fan, a well-known fan such as an axial flow fan (propeller fan), a Sirocco fan, a turbo fan, a centrifugal fan, and a line flow fan (registered trademark) can be used.

[0054] The air duct 12 is a flow path for the air sent from the blowing source 10 to flow. In the air duct 12, the portion other than the muffler 20 is formed by a cylindrical air duct forming member 14 such as a channel, a pipe or a hose. There is no particular limitation on the material and structure of the air duct forming member 14. From the viewpoint of easier laying of the air duct 12, for example, a flexible hose such as a vinyl hose, a flexible hose, and a corrugated hose (Ti Duct Hose) is preferably used as the air duct forming member 14.

[0055] Furthermore, a portion of the air duct 12 is located inside the muffler 20. In other words, the interior of the muffler 20 constitutes a portion of the air duct 12, namely, the muffler internal air duct 16 (see Figure 2 ).

[0056] In the present embodiment, the cross-sectional shape of the air duct 12 is, for example, circular or square. The cross-sectional shape of the air duct 12 is a cross-sectional shape whose normal line is the air supply direction at the position of the cross-sectional shape, i.e., the extension direction of the air duct 12. In addition, the cross-sectional shape of the air duct 12 is not particularly limited, and for example, it may be a quadrilateral other than a square, a polygon other than a quadrilateral, or an irregular shape. Furthermore, in the following description, "cross-sectional area" means the size of the cross-sectional shape, which represents the area of ​​the range surrounded by the outer edge of the cross-sectional shape.

[0057] One end (end on the upstream side) of the air duct 12 is connected to the exhaust port of the fan serving as the air blowing source 10. The other end (end on the downstream side) of the air duct 12 is disposed in a space in the building corresponding to the air supply destination. Figure 1As shown, the air supply destination in this embodiment is the interior of the room R (indoor space) where people are accommodated, and the interior space of the room R is separated from the exterior of the room R by a wall W. Figure 1 As shown, a fan as the air blowing source 10 is arranged in a space outside the room R (outdoor space).

[0058] That is, in the present embodiment, a portion of the air duct 12 is arranged along the wall W separating the indoor space and the outdoor space, and penetrates the wall W at a preferred position to enter the room R of the air supply destination. The indoor space and the outdoor space are two spaces adjacent to each other separated by the wall W, the outdoor space is equivalent to one of the two spaces, and the indoor space is equivalent to the other space.

[0059] The air duct 12 may be laid so as to send air from the outdoor air source 10 into the room R, and the path of the air duct 12 is not particularly limited.

[0060] As described above, a through hole is formed in the wall W for the air duct 12 (strictly speaking, the air duct forming member 14) to pass through. The size (diameter) of the through hole can be designed to a preferred value according to the building using the air supply system S, but is usually less than 150 mm. The minimum value of the diameter of the air duct 12 is made to correspond to the diameter of the above-mentioned through hole, as long as it is less than 150 mm. Among them, the diameter of the air duct 12 is the diameter of the circle when the cross-sectional shape of the air duct 12 is a circle, and is the equivalent circle diameter of the shape when the cross-sectional shape of the air duct 12 is other than a circle.

[0061] In addition, the size of the through hole is, for example, 150 mm or less in a shop and 100 mm or less in a house. Furthermore, when the air duct forming member 14 such as a duct and a hose is used in a house, the minimum value of the diameter of the air duct 12 is 50 mm or less. Furthermore, from the viewpoint of molding accuracy, the minimum value of the diameter of the air duct 12 is preferably 1 mm or more.

[0062] Furthermore, the wall W through which the air duct 12 passes may be a ceiling wall that separates the space behind the ceiling and the space below the ceiling (room) in the building. Alternatively, the wall may be an outer wall that separates the inside and outside of a room in the building. That is, the air duct 12 may be arranged along the outer wall of the building, and pass through the outer wall at a preferred position to enter the building (indoors).

[0063] During the start-up period of the fan as the blowing source 10, wind flows in the air duct 12 at a flow rate equivalent to the rated output of the motor of the fan, and the wind speed is, for example, about 9 m / s. That is, the wind speed in the air duct 12 is determined according to the specifications of the blowing source 10, and specifically, is set within a range determined according to the performance of the blowing source 10, etc.

[0064] In addition, the wind speed refers to the average wind speed in the cross section of each part of the air duct 12. The average wind speed in the cross section refers to the wind speed calculated based on the amount of air flowing in the air duct 12 per unit time (for example, 1 second) and the cross-sectional area of ​​the air duct, for example, the wind speed obtained by simply dividing the air volume by the cross-sectional area. The air volume can be measured by installing an anemometer at the outlet of the air duct 12 and measuring the wind speed using the anemometer.

[0065] The muffler 20 is a device that uses a passive muffler method to reduce the sound propagating in the air duct 12. The passive muffler method is a muffler method that is different from an active method such as active noise reduction (ANC) that outputs a controlled sound with a phase opposite to the sound (noise) of the muffler object to reduce noise. Specifically, the muffler 20 reduces noise by performing any one of sound absorption, resonance (acoustic resonance) or sound reflection in the muffler 20, or a combination of these.

[0066] In the present embodiment, the muffler 20 is composed of a plurality of mufflers including a first muffler 21 and a second muffler 22. The plurality of mufflers may be more than three mufflers. In this case, the muffler located on the most upstream side (the blowing source 10 side) is equivalent to the first muffler 21, and the muffler located on the most downstream side (the side opposite to the blowing source 10) is equivalent to the second muffler 22.

[0067] The frequency bands of the reduced sounds are different between the first muffler 21 and the second muffler 22. The difference in the frequency bands of the reduced sounds means that the frequencies of the primary muffler peaks (i.e., the frequencies of the muffler peaks with the lowest frequencies) are different in the muffler spectrum of the muffler. However, this is not limited to this, and the difference in the frequencies of the reduced sounds may be the main muffler frequency bands, specifically, the frequency bands where the muffler degree becomes above a specified value.

[0068] The sound attenuation spectrum of the muffler 20 indicates the sound attenuation degree of the muffler 20 at each frequency. The sound attenuation degree is a measure of the sound attenuation performance of the muffler 20, and the higher the sound attenuation performance is, such as the transmission loss or the sound absorption coefficient, the larger the value is. The transmission loss of the muffler 20 can be calculated based on the transmissivity measured by the sound tube measurement. In the sound tube measurement method, a measurement system of transmissivity and reflectivity using a four-terminal microphone (not shown) is made in accordance with "ASTM E2611-09: Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method" for evaluation. At this time, for example, if the inner diameter of the sound tube is set to 4 cm, it is possible to measure up to about 4000 Hz in the above-mentioned measurement system. In addition, the same measurement can be performed using WinZacMTX manufactured by Nihon Onkyo Engineering Co., Ltd.

[0069] Below, reference Figures 1 to 8 The structures of the first muffler 21 and the second muffler 22 are described below. Figures 2 to 5 7 and 7 are cross-sectional views of each muffler (including modified examples), and the cross-section of the muffler is a cross-section parallel to the air supply direction in the muffler, that is, the extending direction of the air duct.

[0070] (No. 1 muffler)

[0071] The first muffler 21 is a muffler that reduces the frequency band of sound at a lower level than the second muffler 22. Figure 1 As shown, the first muffler 21 is located at an upstream side of the second muffler 22 , that is, is arranged at a position closer to the air blowing source 10 than the second muffler 22 .

[0072] The first muffler 21 is used for the purpose of reducing the noise caused by the operating sound of the fan (hereinafter also referred to as the noise from the blowing source). Figure 1 As shown, the first muffler 21 is arranged at a position slightly away from the exhaust port and downstream of the exhaust port of the fan serving as the air blowing source 10. In addition, in the present embodiment, the first muffler 21 is arranged in the outdoor space in the same manner as the fan. Figure 1As shown, it is arranged in the middle of the part provided in the outdoor space in the air duct 12. Thus, the noise from the blowing source can be appropriately eliminated by the first muffler 21.

[0073] In addition, the installation position and installation method of the first muffler 21 are not particularly limited.

[0074] The structure of the first silencer 21 is designed so that its sound elimination spectrum corresponds to the spectrum of the noise from the blowing source, which can effectively reduce the noise from the blowing source. The spectrum of the noise from the blowing source is a sound spectrum that represents the intensity of the noise at each frequency (specifically, the noise amount or sound pressure, in dB). The intensity of the noise from the blowing source can be measured as follows: the exhaust port of the blowing source 10 is connected to the reverberation chamber through a channel or a hose, and the blowing source 10 is operated to deliver air at a constant air volume, and the intensity of the noise generated at this time is measured using a plurality of microphones dispersed in the reverberation chamber.

[0075] The first muffler 21 can be any muffler that reduces the noise from the air source, and its muffler method is not particularly limited, but the first muffler 21 of this embodiment reduces the noise by resonance (acoustic resonance) and sound absorption. Figure 2 As shown, the first muffler 21 includes a first frame 31 and a sound absorbing material 41 disposed in the first frame 31 , and performs noise elimination through resonance in the frame and sound absorption by the sound absorbing material 41 .

[0076] In this embodiment, if Figure 2 As shown, the first frame 31 is composed of a cylindrical portion 33 and an expansion portion 34. The cylindrical portion 33 is a cylindrical or square cylindrical portion, and is connected to an air duct forming component 14 extending from the blowing source 10 at one end thereof, and is connected to an air duct forming component 14 extending toward the outlet at the other end. That is, the interior of the cylindrical portion 33 of the first frame 31 constitutes a part of the air duct 12 (that is, the muffler internal air duct 16).

[0077] And, if Figure 2 As shown, a hole (hereinafter referred to as a communication hole 33 a ) penetrating the outer peripheral wall of the cylindrical portion 33 is formed in the central portion of the cylindrical portion 33 .

[0078] The expansion portion 34 is a box-shaped portion having a cavity (expansion space) inside whose cross-sectional area is expanded compared to the air duct 12. The cross-sectional area of ​​the expansion portion 34 is the size of the cross section of the expansion portion 34, and the cross section of the expansion portion 34 is a cross section whose normal line is the air supply direction at the position of the cross section, that is, the extension direction of the air duct 12.

[0079] In this embodiment, if Figure 2As shown in FIG. 1 , the expansion portion 34 is provided at a position surrounding the central portion of the cylindrical portion 33 in which the communication hole 33a is formed. Figure 2 As shown, the cylindrical portion 33 is provided in a state where it passes through the expansion portion 34 and both ends of the cylindrical portion 33 penetrate the side wall of the expansion portion 34. In other words, the internal space of the expansion portion 34 includes the muffler internal air duct 16 formed by the internal space of the cylindrical portion 33. In addition, the internal space of the expansion portion 34 includes the space located outside the cylindrical portion 33, that is, the back space 42. The back space 42 and the muffler internal air duct 16 are connected to each other through the connecting hole 33a formed in the cylindrical portion 33.

[0080] According to the above structure, the first frame 31 of the first muffler 21 functions as a resonance type muffler, in detail, as a Helmholtz resonance type muffler. That is, when the sound of the same frequency as the resonance frequency passes through the cylindrical portion 33 (i.e., the muffler internal air duct 16), the air in the connecting hole 33a vibrates, and the sound energy is converted into heat energy by the viscosity loss at this time. In this way, the first muffler 21 reduces noise by resonance in the first frame 31.

[0081] In addition, a resonance-type muffler can also absorb sound by converting sound energy into heat energy through the resonance of a membrane or a plate.

[0082] There is no particular limitation on the material constituting the first frame body 31, and metal materials, resin materials, paper materials, reinforced plastic materials, carbon fibers, etc. can be used. However, in order to ensure easy molding and design freedom and to be able to manufacture at a lower cost, the first frame body 31 is preferably made of a resin material.

[0083] As the resin material, for example, acrylic resin, polymethyl methacrylate, polycarbonate, polyamide-imide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, ABS resin (acrylonitrile, flame retardant ABS resin, butadiene, styrene copolymerized resin), polypropylene, triacetylcellulose (TAC: Triacetylcellulose), polypropylene (PP: Polypropylene), polyethylene (PE: Polyethylene), polystyrene (PS: Polystyrene), ASA (Acrylate Sthrene Acrylonitrile: acrylate-styrene-acrylonitrile) resin, polyvinyl chloride (PVC: Polyvinyl Chloride) resin and PLA (Polylactic Acid: Polylactic acid) resin, etc. can be cited.

[0084] Examples of reinforced plastic materials include carbon fiber reinforced plastics (CFRP: Carbon Fiber Reinforced Plastics) and glass fiber reinforced plastics (GFRP: Glass Fiber Reinforced Plastics).

[0085] Furthermore, the entire first frame 31 may be manufactured from a resin material by injection molding or the like. Alternatively, a portion of the first frame 31 may be formed from a material other than a resin material, and the remaining portion may be formed from a resin material. In this case, a portion of the first frame 31 may be formed from a metal plate or the like, and the portion may be vibrated to reduce noise.

[0086] Furthermore, in the first frame body 31 , a portion of the expansion portion 34 may be made of the same type of material as the edge portion thereof and have a thickness (plate thickness) different from that of the edge portion.

[0087] like Figure 2 As shown in FIG. 1 , the sound absorbing material 41 is filled in the expansion part 34 in the first frame 31, specifically, in the back space 42. In the present embodiment, the sound absorbing material 41 is in a cylindrical shape, and the cylindrical part 33 is arranged inside the expansion part 34. That is, the sound absorbing material 41 is arranged in the expansion part 34 in a state of surrounding the cylindrical part 33 constituting the muffler internal air duct 16. Then, if the sound in the muffler internal air duct 16 enters the back space 42 through the connecting hole 33a, the sound is absorbed by the sound absorbing material 41.

[0088] A material that converts sound energy into heat energy to absorb sound can be used as the sound absorbing material 41. The material constituting the sound absorbing material 41 is not particularly limited, and examples thereof include porous materials such as foam, foamed material, and nonwoven fabric sound absorbing material.

[0089] Specific examples of the foam and the foam material include foamed polyurethane foam such as CALMFLEX F of INOAC CORPORATION and polyurethane foam manufactured by Hikari Co., Ltd., soft polyurethane foam, ceramic particle sintered material, phenolic foam, melamine foam, insulating board, and polyamide foam.

[0090] Specific examples of nonwoven fabric sound absorbing materials include microfiber nonwoven fabrics such as Thinsulate from 3M Company, polyester nonwoven fabrics such as White Cuon from TOKYO BOUON CO., LTD. and QonPET from Bridgestone KBG Co., Ltd. (including nonwoven fabrics with a double-layer structure having a thin surface nonwoven fabric with high density and a back surface nonwoven fabric with low density), plastic nonwoven fabrics such as acrylic fiber nonwoven fabrics, natural fiber nonwoven fabrics such as wool and felt, meltblown nonwoven fabrics, metal nonwoven fabrics, glass nonwoven fabrics, floor mats, carpets, and the like.

[0091] In addition to the above, it is also possible to use a sound absorbing material composed of a material containing minute air, for example, various sound absorbing materials such as a sound absorbing material composed of glass wool, rock wool, gypsum board, wood wool cement board, and nanofiber-based fibers. As nanofiber-based fibers, for example, silica nanofibers and acrylic nanofibers such as XAI manufactured by Mitsubishi Chemical Corporation can be cited.

[0092] When a hydrophilic material (e.g., glass wool) is used as the material of the sound absorbing material 41, the sound absorbing material may mold when wind with high humidity flows in the muffler. In order to suppress the generation of such mold, the material of the sound absorbing material 41 is preferably a non-metallic material other than an inorganic material, specifically, a resin material, and more preferably a sound absorbing material 41 composed of hydrophobic resin fibers. In addition, as long as the sound absorbing material 41 is composed of a resin material, it is possible to suppress the scattering of glass fibers in the sound absorbing material made of glass wool.

[0093] Furthermore, the flow resistivity of the sound absorbing material 41 is preferably 1000 (Pa×s / m 2 )~100000(Pa×s / m 2 ). In the case where the sound absorbing material 41 is a laminated structure in which a plurality of layers are stacked, the flow resistance of the entire structure can be measured and the flow resistance ratio can be calculated based on the thickness of the entire structure.

[0094] The structure of the silencer for silencing by sound absorption may be other than the structure using the sound absorbing material 41. For example, it may be a structure that is composed of a plate or film that resonates when sound with a frequency close to the resonance frequency is incident, and converts sound energy into heat energy through internal loss of the plate or film to absorb sound.

[0095] Furthermore, a resonant sound absorbing structure made of a perforated plate can also be used. In this sound absorbing structure, when sound of the same frequency as the resonant frequency hits the air in the hole, the air in the hole portion vibrates, and the sound energy is converted into heat energy through the viscosity loss at this time.

[0096] In addition, a composite sound absorbing structure combining the above-mentioned sound absorbing structure and a sound absorbing material can also be used.

[0097] The structure of the first muffler 21 is not limited to the above-mentioned structure example, and may be other structures. Figure 3 Specifically, an opening 33b may be provided at the upstream side of the cylindrical portion 33, and the opening 33b and the back space 42 may be continuous with each other and bent into an L-shaped space (hereinafter referred to as the L-shaped space). The L-shaped space is adjacent to the muffler internal air duct 16 on one side of the muffler internal air duct 16. Then, the sound propagating in the muffler internal air duct 16 is reduced by the sound absorbing material 41 in the L-shaped space and the back space 42.

[0098] Furthermore, the first muffler 21 may be, for example, Figure 4 Specifically, the portion of the cylindrical portion 33 located in the expansion portion 34 is missing, and the muffler internal air duct 16 is surrounded by the sound absorbing material 41. In addition, in the cross section of the muffler internal air duct 16, a portion of the outer edge of the muffler internal air duct 16 is in contact with the sound absorbing material 41, and the remaining portion can be in contact with the inner wall of the expansion portion 34.

[0099] Furthermore, the first muffler 21 can be used as follows Figure 5 The present invention relates to a muffler having a structure of a porous plate 43 as shown in FIG. Specifically, the portion of the cylindrical portion 33 located in the expansion portion 34 is composed of the porous plate 43. The porous plate 43 is a fine perforated plate having a plurality of through holes with a diameter of about 100 μm, and sound absorption is performed through the fine holes and the space outside thereof (i.e., the back space 42). As the fine perforated plate, for example, an aluminum fine perforated plate such as SUONO manufactured by DAIKEN CORPORATION and a vinyl chloride resin fine perforated plate such as DI-NOC manufactured by 3M Company can be used.

[0100] (Second muffler)

[0101] The second muffler 22 is a muffler that reduces the frequency band of sound higher than the first muffler 21. Figure 1 As shown, the second muffler 22 is located at a position further downstream than the first muffler 21 , that is, is arranged at a position farther from the air blowing source 10 than the first muffler 21 .

[0102] The second muffler 22 is used for the purpose of reducing the noise generated in the air duct 12 by blowing air in the air duct 12 during the operation of the fan as the air source 10 (hereinafter also referred to as fluid noise). The fluid noise is noise generated in the air duct 12, especially noise generated in the downstream side of the first muffler 21, and has a peak in a frequency band higher than the noise from the air source (above 800 Hz, for example, around 1 kHz) in its spectrum (refer to Fig.11 The frequency spectrum of fluid noise is a sound spectrum that represents the intensity of fluid noise at each frequency (specifically, the amount of noise or sound pressure, in dB). Figure 6 The measurement system shown is used for the measurement.

[0103] If Figure 6 The measurement system shown in FIG. 1 is described, the air blowing source 10 and the inlet of the measuring muffler 60 are connected through an upstream side air duct 62 composed of a hose or the like, and a downstream side air duct 64 composed of a hose or the like extends from the outlet of the measuring muffler 60 to the reverberation chamber Z. Then, the air blowing source 10 is operated to supply air, and the air is made to flow through the upstream side air duct 62, the inside of the measuring muffler 60, and the downstream side air duct 64 at a constant air volume. At this time, the noise from the air blowing source is absorbed by the measuring muffler 60, and on the downstream side of the measuring muffler 60, mainly the fluid noise propagates in the air duct. Therefore, in the above state, the intensity of the sound released from the outlet of the downstream side air duct 64 can be measured by using a plurality of microphones dispersed in the reverberation chamber Z, so that the intensity of the fluid noise can be measured.

[0104] As described above, fluid noise is the sound generated in the air duct 12 due to air supply in the air duct 12. Therefore, even if the muffler 20 is arranged on the upstream side of the air duct 12, i.e., on the side close to the blowing source 10, it is difficult to reduce the fluid noise generated on the downstream side of the air duct 12 by the muffler 20, and the desired muffler effect may not be obtained.

[0105] Furthermore, in the frequency spectrum of fluid noise, as described above, the peak with the highest intensity (sound pressure) of fluid noise is located at a relatively high frequency (e.g., 1kHz), but the noise intensity at this peak tends to increase as the wind speed increases. In particular, in the air supply system S in a general residence or a store such as a restaurant, the air supply volume is increased for the purpose of improving the performance of air conditioning or ventilation. On the other hand, due to the limitation of the configuration space of the air duct forming component 14, the minimum value of the diameter of the air duct 12 becomes smaller, for example, sometimes set to less than 150mm. Therefore, in the air supply system S in recent years, the wind speed in the air duct 12 gradually increases, generating wind noise, and as a result, the intensity of the fluid noise tends to increase significantly.

[0106] Considering the above reasons, Figure 1 As shown, the second muffler 22 is arranged at a position farther from the blowing source 10 than the first muffler 21, and is arranged near the outlet of the air duct 12, that is, the air supply destination. Figure 1 As shown, the second muffler 22 is arranged in a space different from the space where the first muffler 21 is arranged, that is, an indoor space, that is, an internal space of the room R. In addition, the second muffler 22 is adjacent to the portion located on the most downstream side in the air duct forming member 14, and is arranged at a position closer to the downstream side than the portion, that is, arranged at the end (terminal portion) on the outlet side of the air duct 12. Thus, the fluid noise can be appropriately eliminated by the second muffler 22.

[0107] In addition, the installation position of the second muffler 22 is not limited to the above-mentioned position. Figure 1 As shown in FIG. 1 , as long as the first muffler 21 and the second muffler 22 are arranged in different spaces across the wall W, it is easier to ensure the installation space for each muffler than when two mufflers are arranged in one space. Figure 1 As shown, as long as the second muffler 22 is arranged at a position adjacent to the wall W in the indoor space, it is more preferable to arrange the second muffler 22 in the indoor space, and more specifically, it is easy to arrange it at a position where collision with a person can be avoided.

[0108] Furthermore, there is no particular limitation on the installation method of the second muffler 22. For example, a support tool such as a support bracket may be fixed to the wall W, and the second muffler 22 may be installed at a predetermined position by using the support tool.

[0109] The structure of the second muffler 22 is designed so that its silencing spectrum corresponds to the spectrum of the fluid noise, which can effectively reduce the fluid noise. Fig.11 As shown, the frequency of the primary silencer peak of the second silencer 22 is above the peak frequency of the fluid noise at which the intensity of the fluid noise becomes the maximum (hereinafter referred to as the peak frequency of the fluid noise). The frequency of the primary silencer peak of the second silencer 22 is the lowest order (most low frequency side) peak frequency in the silencer spectrum of the second silencer 22.

[0110] As described above, in this embodiment, the frequency of the primary silencer peak of the second muffler 22 is greater than the peak frequency of the fluid noise, and by arranging the second muffler 22 at a more downstream position in the air duct 12, the fluid noise can be appropriately reduced by the second muffler 22.

[0111] In addition, the peak frequency of the fluid noise changes according to the flow velocity (wind speed) of the wind flowing in the air duct 12. Among them, the peak frequency of the fluid noise at the minimum wind speed value (the wind speed during the fan startup, excluding the value when the fan is stopped) in the range of wind speeds that can be achieved by the fan as the blowing source 10 is set as the "peak frequency at the minimum wind speed". The frequency of the primary silencer peak of the second silencer 22 can be determined, for example, based on the peak frequency at the minimum wind speed. In this case, it only needs to be set to be greater than the peak frequency at the minimum wind speed.

[0112] The second muffler 22 can be used as long as it effectively reduces the fluid noise. There is no particular limitation on the muffler method. The second muffler 22 of this embodiment is the same as the first muffler 21, and reduces noise by resonance (acoustic resonance) and sound absorption. The basic structure of the second muffler 22 is roughly the same as the first muffler 21, except that the muffler frequency band is different and the size is smaller. That is, Figure 7 As shown, the second muffler 22 includes a second frame 32 and a sound absorbing material 41 disposed in the second frame 32 , and performs noise elimination through resonance in the frame and sound absorption by the sound absorbing material 41 .

[0113] And, if Figure 7 As shown, the second frame 32 has a cylindrical portion 35 whose internal space constitutes the muffler internal air duct 16 and an expansion portion 36 surrounding the central portion of the cylindrical portion 35. The muffler internal air duct 16 formed in the cylindrical portion 35 of the second frame 32 constitutes the terminal portion (end portion on the outlet side) of the air duct 12 as described above. In addition, the muffler internal air duct 16 in the second frame 32 is connected to the back space 42 of the expansion portion 36 through the connecting hole 35a formed in the central portion of the cylindrical portion 35. Thus, the second frame 32 functions as a Helmholtz resonator.

[0114] Furthermore, there is no particular limitation on the material constituting the second frame body 32, and for example, metal materials, resin materials, paper materials, reinforced plastic materials, and carbon fibers can be used. Furthermore, from the perspective of ensuring easy molding and freedom of design, and being able to manufacture at a lower cost, it is preferred that all or part of the second frame body 32 is made of a resin material. Examples of the resin material constituting the second frame body 32 are the same as the examples of the resin material constituting the aforementioned first frame body 31.

[0115] When a portion of the second frame body 32 is made of a material other than resin material and the remaining portion is made of resin material, the fluid noise can be reduced by making a portion of the second frame body 32 of a metal plate or the like and vibrating the portion.

[0116] Furthermore, in the second frame body 32 , a portion of the expansion portion 36 may be made of the same type of material as the edge portion thereof and have a different thickness (plate thickness) from the edge portion.

[0117] In addition, a sound absorbing material 41 is disposed in a back space 42 located outside the cylindrical portion 35 in the internal space of the expansion portion 36. Examples of materials constituting the sound absorbing material 41 provided in the second muffler 22 are the same as examples of materials constituting the sound absorbing material 41 provided in the first muffler 21, and the sound absorbing material 41 made of a resin material is particularly preferred.

[0118] In addition, the sound absorbing structure in the second muffler 22 may be a structure other than the structure using the sound absorbing material 41, and may be composed of a plate-like body or a film-like body that resonates by incident sound of a frequency close to the resonance frequency. In addition, a resonant sound absorbing structure composed of a perforated plate may also be used. In addition, a composite sound absorbing structure combining the above-mentioned sound absorbing structure and the sound absorbing material may also be used.

[0119] Furthermore, the muffler structure of the second muffler 22 is the same as that of the first muffler 21 and is not limited to Figure 7 The noise reduction structure shown, for example, can also be Figure 3 The side branch type muffler shown, Figure 4 The cavity-type muffler shown in the figure may utilize Figure 5 The muffler has a structure of a porous plate 43 as shown.

[0120] Furthermore, in this embodiment, Figure 1 It can be seen that the volume of the second muffler 22 is smaller than the volume of the first muffler 21. Among them, the volume of the first muffler 21 is the size of the space surrounded by the outer wall surface of the first muffler 21, in detail, the size of the space surrounded by the outer wall surface of the first frame 31, that is, the three-dimensional size of the first frame 31. And, the volume of the second muffler 22 is the size of the space surrounded by the outer wall surface of the second muffler 22, in detail, the size of the space surrounded by the outer wall surface of the second frame 32, that is, the three-dimensional size of the second frame 32. Thereby, the second muffler 22 arranged in the room can be made more compact while ensuring the use of the muffler effect of each muffler.

[0121] If described in more detail, the sound-absorbing material used for the muffler is usually larger in size (volume) relative to the wavelength of the sound of the muffler object, and the muffler effect is more effectively exerted. On the other hand, fluid noise is a sound in the high-frequency band, and its wavelength is relatively shortened, so even a muffler with a relatively small size can exert a high muffler effect on fluid noise. Therefore, by making the volume of the second muffler 22 smaller than the volume of the first muffler 21, it is possible to save the installation space of the second muffler 22 while maintaining a sufficient muffler effect. This effect is particularly significant when the second muffler 22 is configured in an indoor space.

[0122] Furthermore, in the present embodiment, the first muffler 21 and the second muffler 22 are disposed in the air duct 12, and the positional relationship of the two mufflers is such that a better muffler effect can be obtained. Figure 8 , the positional relationship between the first muffler 21 and the second muffler 22 in the air duct 12 is described.

[0123] In addition, Figure 8 In the figure, the air duct 12, the first muffler 21 and the second muffler 22 are simplified. In addition, for the convenience of illustration, the air duct 12 which is actually bent or laid while being bent is shown in FIG. Figure 8 In the figure, a path is virtually regarded as a straight line.

[0124] In the air duct 12, the distance from the downstream end of the first muffler 21 (specifically, the downstream end of the cylindrical portion 33) to the outlet of the air duct 12 is set to L. In this embodiment, Figure 8 As shown, the second muffler 22 is arranged at a position where the distance from the downstream end of the second muffler 22 (specifically, the downstream end of the cylindrical portion 35) to the outlet of the air duct 12 is less than L / 2. In other words, in the air duct 12 involved in this embodiment, the downstream end of the first muffler 21 and the downstream end of the second muffler 22 are separated by more than L / 2.

[0125] In order to reduce the intensity of the fluid noise by half, the interval between the first muffler 21 and the second muffler 22 needs to be at least L / 2. Therefore, as long as the above-mentioned positional relationship is maintained, the fluid noise can be well reduced by the second muffler 22 .

[0126] <<Other implementation methods>>

[0127] As mentioned above, the structure of the air duct with a muffler according to one embodiment of the present invention has been described, but the present invention is not limited to the above-mentioned embodiment, and other embodiments are conceivable.

[0128] In the above-mentioned embodiment, the first muffler 21 and the second muffler 22 are arranged in rooms located on opposite sides of each other across the wall W. However, this is not limited to this, and both the first muffler 21 and the second muffler 22 may be arranged in the same room. However, from the viewpoint of saving space for the second muffler 22 while maintaining a good muffler effect, the above-mentioned embodiment is more preferable.

[0129] In the above-mentioned embodiment, the second muffler 22 is arranged at the terminal portion of the air duct 12. In other words, the muffler internal air duct 16 in the second muffler 22 constitutes the end portion of the outlet of the air duct 12. However, it is not limited to this, and the second muffler 22 can be arranged at a position closer to the downstream side than the first muffler 21, or at a position closer to the upstream side than the outlet of the air duct 12.

[0130] In the above-mentioned embodiment, the first muffler 21 and the second muffler 22 are respectively provided with expansion parts 34 and 36, and the expansion parts 34 and 36 have internal spaces expanded more than the cross-sectional area of ​​the air duct. However, this is not limited to this, and only one of the first muffler 21 and the second muffler 22 may be provided with an expansion part.

[0131] In the above embodiment, the first frame 31 of the first muffler 21 and the second frame 32 of the second muffler 22 are each made of resin material. However, this is not limiting, and only one of the first frame 31 and the second frame 32 may be made of resin material.

[0132] Furthermore, in the above-described embodiment, the sound absorbing material 41 is disposed inside each of the first muffler 21 and the second muffler 22, and a resin material is cited as a preferred material for each of the sound absorbing materials 41. However, the present invention is not limited thereto, and only the sound absorbing material 41 provided inside either the first muffler 21 or the second muffler 22 may be formed of a resin material.

[0133] In the above-mentioned embodiment, as the structure of the muffler using the passive muffler method, the muffler 20 that reduces noise by resonance in the frame and sound absorption using a sound absorbing material is described, but the passive muffler method may also be a method other than resonance, sound absorption and reflection. For example, the following structure may be used: in a muffler that causes a part of the side wall of the frame (vibration part) to vibrate by sound hitting it, vibration-damping material is attached to the vibration part to suppress vibration, thereby reducing noise.

[0134] Example

[0135] Below, utilize embodiment to further specifically describe the present invention.As long as do not depart from the gist of the present invention, then can suitably change the material, usage amount, ratio, processing content and processing step etc. shown in the following embodiment.Therefore, the scope of the present invention should not be interpreted restrictively by the embodiment shown below.

[0136] <Example 1>

[0137] In the first embodiment, a device for reducing the noise from the blowing source is provided for the air duct provided to send the wind from the blowing source to the reverberation chamber. Fig. 9 The low frequency muffler 71 shown in the figure and the method for reducing fluid noise Fig.10 The high frequency muffler 81 is shown in the figure. As the blowing source, two DC (direct current) type blowers (manufactured by SANYO Electric Co., Ltd., model: 9BMC24P2G001) as air supply fans were used. Figure 1 Specifically, the low-frequency muffler 71 is arranged at a position closer to the air source than the high-frequency muffler 81 is.

[0138] The exhaust port of the blower and the upstream end of the low-frequency muffler 71 are connected by a transparent vinyl hose (manufactured by Chubu Vinyl Industry CO., LTD) as a duct forming member. The inner diameter of the vinyl hose is 28 mm, the outer diameter is 34 mm, and the total length of the hose used in Test 1 is 1.7 mm.

[0139] Furthermore, the downstream end of the low-frequency muffler 71 and the upstream end of the high-frequency muffler 81 are connected by a corrugated hose (manufactured by Tigers Polymer Corporation, product name: corrugated hose N type) as an air duct forming member. The inner diameter of the corrugated hose is 32.5 mm, the outer diameter is 37 mm, and the total length of the hose used in Test 1 is 2.0 m.

[0140] The low frequency muffler 71 corresponds to the first muffler of the present invention and is composed of Fig. 9 Specifically, a connecting hole 72a with a diameter of 20 mm is formed in the central part of a cylindrical portion 72 having an inner diameter of 28 mm, an outer diameter of 34 mm, and a total length of 228 mm. Then, a low-frequency muffler 71 is formed by surrounding the central part of the cylindrical portion 72 having the connecting hole 72a formed therein with a rectangular parallelepiped expansion portion 73. The height of the expansion portion 73 ( Fig. 9 , marked as d1), depth and total length ( Fig. 9 The volume of the frame of the low-frequency muffler 71 is 584 cm 3 Furthermore, the internal space of the expansion portion 73 becomes a closed space, and the communication hole 72a is closed by the expansion portion 73. Furthermore, the communication hole 72a is blocked by a sound absorbing material 74 (product name: QonPET) of Bridgestone KBG Co., Ltd.

[0141] The high frequency muffler 81 is equivalent to the second muffler of the present invention and is composed of Fig.10Specifically, the high-frequency muffler 81 is formed by arranging the expansion portion 83 between two annular portions 82 having an inner diameter of 28 mm and an outer diameter of 31 mm. The inner diameter and width of the expansion portion 83 ( Fig.10 In the figure, the lengths of the high-frequency silencer 81 are 168 mm, and the volume of the frame of the high-frequency silencer 81 is 310 cm. 3 Furthermore, an air duct (air duct in the muffler) having the same diameter as the inner diameter of the annular portion 82 and a sound absorbing material 84 surrounding the air duct are arranged in the expansion portion 83. The sound absorbing material 84 is made of a sound absorbing material (product name: QonPET) of Bridgestone KBG Co., Ltd.

[0142] Furthermore, in the first embodiment, the high-frequency silencer 81 is disposed at the terminal end of the air duct.

[0143] (Comparative Example)

[0144] In the comparative example, the structure of the high frequency muffler is different from that of the first embodiment. Although the high frequency muffler of the comparative example has a size difference, its structure is substantially the same as the low frequency muffler 71 of the first embodiment. That is, the high frequency muffler of the comparative example becomes Fig. 9 The structure shown in the figure has a cylindrical barrel portion with a connecting hole formed in the center and a rectangular expansion portion surrounding the center of the barrel portion. The inner diameter of the barrel portion is 28 mm, the outer diameter is 34 mm, the total length is 222 mm, and the diameter of the connecting hole is 20 mm. In addition, the height, depth and total length of the expansion portion are 75.8 mm, 75.8 mm and 62 mm respectively. In addition, the volume of the frame of the low-frequency muffler 71 is 501 cm 3 The internal space of the expansion part becomes a closed space. The communication hole is closed by the expansion part and blocked by the sound absorbing material 74 (product name: QonPET) of Bridgestone KBG Co., Ltd.

[0145] The structures other than the high-frequency muffler are the same between the comparative example and the first embodiment.

[0146] (Measurement of the muffler's noise spectrum)

[0147] The low frequency muffler 71 and high frequency muffler 81 of Example 1 and the high frequency muffler of the comparative example were measured for vertical incidence transmission loss spectrum as the anechoic spectrum by the sound tube measurement method in accordance with "ASTM E2611-09". The measurement results are shown in FIG. Fig.11 . Fig.11The horizontal axis represents the center frequency of the 1 / 3 octave band (in Hz), and the vertical axis on the left represents the transmission loss (in dB).

[0148] exist Fig.11 , together with the above-mentioned measurement results, there is shown a noise spectrum of the sound (ie, fluid noise) generated when wind flows in a corrugated hose with a total length of 2 m at a wind speed of 9.3 m / s. Fig.11 The vertical axis on the right side of represents the noise amount of the fluid noise (in dB).

[0149] from Fig.11 It is found that the noise reduction peak value (peak value of transmission loss) of each muffler satisfies the following relational expression (1).

[0150] fa1 <fb2<fx<fb1 (1)

[0151] In the above formula (1), fa1 is the silencing peak value (438 Hz) of the low frequency muffler 71 in Example 1, and fb2 is the silencing peak value (518 Hz) of the high frequency muffler in the comparative example. fx is the peak value (1250 Hz) of the noise spectrum of the fluid noise, and fb1 is the silencing peak value (1568 Hz) of the high frequency muffler 81 in Example 1.

[0152] That is, in Example 1, the primary silencer peak value of the high-frequency silencer 81 as the second silencer is the peak frequency of the fluid noise, specifically, the peak frequency at which the noise amount becomes the maximum. In contrast, in the comparative example, the primary silencer peak value of the high-frequency silencer is the peak frequency of the fluid noise that is less than the peak frequency at which the noise amount becomes the maximum.

[0153] (Measurement of the noise reduction effect)

[0154] In Example 1 and Comparative Example, air was blown from the blower so that the wind speed in the corrugated hose constituting the air duct was 9.1 m / s. Then, the noise released from the end of the air duct into the reverberation chamber was measured using a microphone installed in the reverberation chamber, thereby obtaining a noise spectrum indicating the amount of noise at each frequency. The measurement results are shown in Fig.12 . Fig.12 The horizontal axis represents the center frequency of the 1 / 3 octave band (in Hz), and the vertical axis represents the noise level (in dB).

[0155] In addition, Fig.12 , the noise spectrum of the fluid noise generated in the air duct under the above conditions is shown together with the above measurement results. Fig.12The noise spectrum when the blowing source and the air supply destination (reverberation chamber) are directly connected through a corrugated hose without a muffler in the air duct is shown as reference data. In this reference data, the wind speed flowing in the air duct is the same as that in Example 1 and the comparative example, which is set to 9.1m / s.

[0156] from Fig.12 It can be seen that in Example 1 and the comparative example, the noise corresponding to the peak value appearing near 450Hz in the reference data is removed by the low-frequency muffler. Therefore, in the noise propagating toward the outlet in the air duct, the high-frequency fluid noise generated on the downstream side of the low-frequency muffler dominates and has a greater impact on the overall noise.

[0157] Furthermore, in Example 1 and the comparative example, a high frequency muffler is provided on the downstream side of the low frequency muffler. Fig.12 As shown, in Example 1, the fluid noise can be effectively reduced, but in the comparative example, the fluid noise cannot be fully eliminated. As a result, in Example 1, the noise level measured in the reverberation chamber is 45.7 dB, and in the comparative example, the noise level measured is 49.4 dB. That is, it can be seen that a large noise reduction effect is obtained in Example 1, and a small noise reduction effect is obtained in the comparative example. That is, it is clear that by setting the primary noise reduction peak of the high-frequency silencer disposed on the downstream side of the air duct to be above the peak frequency at which the noise level becomes the largest among the peak frequencies of the fluid noise, the fluid noise can be effectively reduced and a high noise reduction effect can be obtained.

[0158] <Test on the noise reduction effect according to the location of the muffler>

[0159] Next, a description will be given of a test 1 conducted on the noise reduction effect according to the arrangement position of the muffler and tests 2 and 3 as comparative tests thereof.

[0160] (Test 1)

[0161] In Experiment 1, the same air duct with a muffler as in Example 1 was used. That is, in Experiment 1, Fig. 9 The low frequency muffler 71 shown in the figure is arranged closer to the blowing source than the high frequency muffler 81. Fig.10 The high-frequency muffler 81 shown in the figure is arranged at the terminal end of the air duct. Specifically, the distance from the downstream end of the low-frequency muffler 71 to the outlet of the air duct is set to L, and the high-frequency muffler 81 is arranged in a manner such that the distance from the downstream end of the high-frequency muffler 81 to the outlet of the air duct becomes less than L / 2.

[0162] (Test 2)

[0163] In Test 2, the high-frequency muffler 81 is arranged on the downstream side of the low-frequency muffler 71 and in the vicinity of the low-frequency muffler 71. Specifically, when the distance from the downstream end of the low-frequency muffler 71 to the outlet of the air duct is L, the high-frequency muffler 81 is arranged so that the distance from the downstream end of the high-frequency muffler 81 to the outlet of the air duct is greater than L / 2. Regarding other points, the same conditions are set between Test 2 and Test 1.

[0164] (Test 3)

[0165] In Test 3, the air source and the air supply destination (reverberation chamber) were directly connected via a bellows hose without using the low-frequency silencer 71 and the high-frequency silencer 81. The same conditions were set between Test 3 and Test 1 in other respects.

[0166] (Measurement of the noise reduction effect)

[0167] In each of the tests 1 to 3, the air was blown from the blower so that the wind speed in the bellows hose constituting the air duct was 9.1 m / s. In each test, the noise released from the end of the air duct into the reverberation chamber was measured using a microphone installed in the reverberation chamber, thereby obtaining a noise spectrum indicating the amount of noise at each frequency. The measurement results are shown in Fig.13 . Fig.13 The horizontal axis represents the center frequency of the 1 / 3 octave band (in Hz), and the vertical axis represents the noise level (in dB).

[0168] In addition, Fig.13 , together with the above-mentioned measurement results, there is shown a noise spectrum of the fluid noise generated in the air duct under the above-mentioned conditions.

[0169] from Fig.13 It can be seen that in the structure of Test 2, the fluid noise cannot be completely eliminated, and the residual fluid noise propagates to the reverberation chamber. On the other hand, in the structure of Test 1, the noise in the frequency band equivalent to the fluid noise is greatly reduced. If explained in more detail, in the frequency band affected by the fluid noise (specifically, 800Hz~2500Hz), when the structure of Test 2 is adopted, the noise amount of the fluid noise in the reverberation chamber is 49.5dB. In contrast, when the structure of Test 1 is adopted, the noise amount becomes 45.7dB, and the difference with Test 2 becomes -3.8dB. It can be seen that by ensuring that the interval between the low-frequency silencer 71 and the high-frequency silencer 81 is greater than the specified distance (specifically, L / 2) and making the high-frequency silencer 81 closer to the outlet of the air duct, the noise reduction effect is significantly improved.

[0170] As described above, the effects of the present invention are clearly demonstrated based on the results of Example 1 and Test 1 described above.

[0171] Description of Reference Numerals

[0172] 10-blowing source, 12-air duct, 14-air duct forming member, 16-air duct in muffler, 20-muffler, 21-first muffler, 22-second muffler, 31-first frame, 32-second frame, 33, 35-cylindrical portion, 33a, 35a-communication hole, 33b-opening portion, 34, 36-expansion portion, 41-sound absorbing material, 42-back space, 43-porous plate , 60-muffler for measurement, 62-upstream air duct, 64-downstream air duct, 71-muffler for low frequency, 72-cylindrical part, 72a-connecting hole, 73-expansion part, 74-sound absorbing material, 81-muffler for high frequency, 82-annular part, 83-expansion part, 84-sound absorbing material, 100-air duct with muffler, R-room, S-air supply system, W-wall, Z-reverberation chamber.

Claims

1. An air duct with a muffler, comprising: an air duct through which the air sent from the air blowing source flows; and The first muffler and the second muffler reduce the sound propagating in the air duct by a passive muffler method, and the frequency bands of the reduced sounds are different from each other. The first muffler having a lower frequency band is arranged at a position closer to the air blowing source. The second muffler having a higher frequency band is arranged at a position farther away from the air source. The frequency of the primary silencer peak of the second silencer is equal to or higher than a peak frequency at which the intensity of the generated sound reaches a maximum among peak frequencies of sound generated in the air duct due to air blowing in the air duct.

2. The air duct with a muffler according to claim 1, wherein: When the distance from the downstream end of the first muffler to the outlet of the air duct is L, the second muffler is arranged at a position where the distance from the downstream end of the second muffler to the outlet of the air duct is less than L / 2.

3. The air duct with a muffler according to claim 1, wherein: When the size of the space surrounded by the outer wall surface of the first muffler is the volume of the first muffler and the size of the space surrounded by the outer wall surface of the second muffler is the volume of the second muffler, the volume of the second muffler is smaller than the volume of the first muffler.

4. The air duct with a muffler according to claim 1, wherein: The minimum value of the diameter of the air duct or the minimum value of the equivalent circle diameter of the air duct is 150 mm or less.

5. The air duct with a muffler according to claim 1, wherein: The interior of the first frame of the first muffler and the interior of the second frame of the second muffler each include an internal muffler air duct constituting a part of the air duct. At least one of the first frame body and the second frame body is entirely or partially made of a resin material.

6. The air duct with a muffler according to claim 1, wherein: A sound absorbing material made of a resin material is arranged in at least one of the first muffler and the second muffler.

7. The air duct with a muffler according to claim 1, wherein: At least one of the first muffler and the second muffler has an expansion portion. The expansion portion has a cross-section perpendicular to the extension direction of the air duct, the cross-section having a size larger than the internal space of the air duct. The internal space of the expansion portion includes an internal muffler air duct constituting a part of the air duct and a back space located outside the internal muffler air duct.

8. The air duct with a muffler according to any one of claims 1 to 7, wherein: The air duct runs through the wall separating the two spaces. The first muffler is arranged in one of the two spaces, and the second muffler is arranged in the other space.

9. The air duct with a muffler according to claim 8, wherein: The wall separates the interior space of the room housing the person from the exterior of the room, The space where the second silencer is arranged is the internal space of the room.

10. The air duct with a muffler according to claim 8, wherein: The second muffler is arranged at a position adjacent to the wall in the other space.

11. The air duct with a muffler according to claim 1, wherein: The interior of the first muffler and the interior of the second muffler each include an inner muffler air duct constituting a part of the air duct. The muffler internal air passage of the second muffler forms an end portion on the outlet side of the air passage.

12. The air duct with a muffler according to claim 1, wherein: The air duct is connected to an exhaust port of a fan serving as the air blowing source.

Images