Silencer-equipped air duct

Abstract

Provided is a silencer-equipped air duct which makes it possible to improve silencing performance for low-frequency sounds while suppressing increase in size.　This silencer-equipped air duct is configured by disposing a silencer at an intermediate position of the air duct, wherein: the silencer comprises a silencer main body and a conversion mechanism that is housed within the silencer main body and coverts sound energy into heat energy; the air duct comprises a first air duct part formed within the silencer main body, a second air duct part located on the upstream side from the first air duct part, and a third air duct part located on the downstream side from the first air duct part; the acoustic impedance density of the internal space of the silencer main body is lower than the acoustic impedance densities of the respective internal spaces of the second air duct part and the third air duct part; and -1.97 < log10(αE / λ) < 0.76 is satisfied where αE is an effective propagation length determined on the basis of the characteristic of a sound wave propagation space within the silencer main body, and λ is the wavelength of sound of a frequency which is determined on the basis of the length of the first air duct part and at which the silencer main body resonates.

Description

Silencer-equipped air duct

[0001] The present invention relates to an air duct with a silencer, which is configured by arranging a silencer midway along the air duct.

[0002] When air from an air conditioner, a blower, or the like is blown through an air passage such as a duct, noise, etc., caused by the operation of the blower may be transmitted to the destination through the air passage. Techniques for silencing such noise at a position along the air passage have already been developed, and one example of such a technique is described in Patent Document 1.

[0003] In the air conditioner described in Patent Document 1, a radial fan assembly is provided in the outdoor unit, which takes in outdoor air and sends it to the indoor unit. At this time, the air sent to the indoor unit passes through an intake and exhaust duct, and a silencer (specifically, a muffler) provided in the intake and exhaust duct reduces the sound transmitted through the intake and exhaust duct.

[0004] Japanese Patent Application Laid-Open No. 2004-069173

[0005] When a silencer is provided in an air passage such as an intake or exhaust duct, the size of the silencer is limited depending on the size of a device such as an air conditioner or a blower, and the smaller the size of the silencer, the lower the sound silencing performance for low-frequency sounds (for example, 1000 Hz or lower). Therefore, there is a demand for such silencers to have improved sound silencing performance for low-frequency sounds, particularly for sounds at a first resonant frequency with high transmittance and sounds in a frequency band lower than the first resonant frequency. Note that the "sound at the first resonant frequency" refers to the lowest-frequency sound among sounds that resonate within the silencer.

[0006] Furthermore, the sound-absorbing materials typically used in silencers are inferior in their ability to silencing low-frequency sounds compared to their ability to silencing high-frequency sounds, and so increasing the volume of the sound-absorbing material is considered a way to improve the silencing performance for low-frequency sounds. However, this would result in an increase in the size of the silencer, making it unsuitable for use in situations where there are size restrictions.

[0007] The object of the present invention is to provide an air duct with a silencer that can solve the problems of the above-mentioned conventional technology, suppress an increase in size, and improve the noise reduction performance for low-frequency sounds.

[0008] In order to solve this problem, the present invention has the following configuration: [1] An air duct with a silencer configured by placing a silencer at a midpoint of the air duct, wherein the silencer has a silencer body and a conversion mechanism housed in the silencer body that converts sound energy into thermal energy, the air duct has a first air duct section formed inside the silencer body, a second air duct section located upstream of the first air duct section, and a third air duct section located downstream of the first air duct section, the acoustic impedance density of the internal space of the silencer body is smaller than the acoustic impedance densities of the internal spaces of the second air duct section and the third air duct section, and an effective propagation length determined based on the characteristics of the propagation space of sound waves inside the silencer body is defined as α Ｅ When the wavelength of the sound of the frequency at which the silencer body resonates is determined based on the length of the first air passage portion and is λ, -1.97<log １０ (α Ｅ [2] The silencer-equipped air duct according to [1], wherein the silencer main body is a housing, the cross-sectional area of ​​the housing is larger than the cross-sectional areas of the second air duct section and the third air duct section, and a rear space communicating with the air duct space in the first air duct section is provided inside the housing. [3] The silencer-equipped air duct according to [1] or [2], wherein the first air duct section has an air duct wall that separates the air duct space, and the air duct wall is provided with one or more openings that communicate the air duct space with the rear space. [4] The silencer-equipped air duct according to [1] or [2], wherein the total area of ​​all the opening areas of the one or more openings is A. １ The total area of ​​the air duct wall in contact with the air duct space is A ２ In this case, A １ and A ２ A for the sum of １[5] The silencer-equipped air duct according to any one of [1] to [3], wherein the ratio of the above is more than 10% and less than 85%. [5] The silencer-equipped air duct according to any one of [1] to [4], wherein the conversion mechanism is a sound-absorbing material. [6] The silencer-equipped air duct according to any one of [1] to [5], wherein the sound-absorbing material is positioned in the rear space so as to cover at least a part of the opening, and the opening is positioned at the center of the first air duct section in a first direction in which the first air duct section extends. [7] The silencer-equipped air duct according to any one of [1] to [6], wherein, when the length of the first air duct section in the first direction is L, the opening is positioned within L / 4 from the center of the first air duct section in the first direction. [8] The silencer-equipped air duct according to any one of [1] to [7], wherein an end of the first air duct section in a second direction intersecting the first direction in which the first air duct section extends forms part of an end of the housing in the second direction. [9] The silencer-equipped air duct according to any one of [1] to [8], wherein the air duct wall has a pair of walls facing each other across the air duct space in a direction intersecting the first direction in which the first air duct section extends.

[10] The silencer-equipped air duct according to any one of [1] to [9], wherein an opening is provided in each of the pair of walls.

[11] The silencer-equipped air duct according to any one of [1] to

[10] , wherein the silencer silences noise generated by the operation of a fan that sends air into the air duct.

[0009] According to the present invention, it is possible to provide an air duct with a silencer that is capable of improving the noise reduction performance for low frequency sounds while suppressing an increase in size.

[0010] FIG. 1 is a diagram showing an air blowing system in which an air duct with a silencer according to an embodiment of the present invention is used. FIG. 1 is a cross-sectional view showing the A-A cross section of the air duct with a silencer shown in FIG. 1. FIG. 2 is a cross-sectional view showing the B-B cross section of the air duct with a silencer shown in FIG. 2. FIG. 3 is a cross-sectional view showing the C-C cross section of the air duct with a silencer shown in FIG. 2. FIG. 4 is a diagram showing a first modified example of a silencer. FIG. 5 is a diagram showing a second modified example of a silencer. FIG. 6 is a diagram showing a sixth modified example of a silencer. FIG. 7 is a diagram showing a seventh modified example of a silencer. FIG. 8 is a diagram showing a relationship between frequency and log １０ (α Ｅ1 is a graph showing the relationship between log / λ and sound transmission loss through a silencer. １０ (α Ｅ 1 is a diagram showing the relationship between λ / λ) and transmission loss. FIG. 2 is a diagram showing the relationship between frequency and transmission loss in each of Comparative Example 1, Comparative Example 2, and Example 1. FIG. 3 is a diagram showing the relationship between aperture ratio and transmittance. FIG. 4 is a diagram showing the relationship between frequency and transmittance depending on the aperture position. FIG. 5 is a diagram showing the relationship between aperture position and transmittance at a first resonance frequency. FIG. 6 is a diagram showing the relationship between frequency and transmission loss determined depending on the position of the first air path section.

[0011] The silencer-equipped air duct of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings. Note that the following embodiment is merely an example given to facilitate understanding of the present invention and is not intended to limit the present invention. In other words, the configuration of the present invention can be modified or improved from the following embodiment without departing from the spirit of the present invention.

[0012] Furthermore, unless otherwise specified, the material and shape of each member used to implement the present invention can be arbitrarily set depending on the application of the present invention and the state of the art at the time of implementing the present invention. Furthermore, the present invention includes equivalents thereof.

[0013] Furthermore, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Furthermore, in this specification, "orthogonal" and "parallel" are intended to include the range of error acceptable in the technical field to which the present invention belongs. For example, "orthogonal" and "parallel" in this specification mean being within a range of less than ±10° from strictly orthogonal or parallel. Note that the error from strictly orthogonal or parallel is preferably 5° or less, and more preferably 3° or less. Furthermore, in this specification, the meanings of "same," "identical," "match," and "equal" may include the range of error generally acceptable in the technical field to which the present invention belongs. Furthermore, in this specification, the meanings of "any," "all," and "all" include not only the case of 100%, but also the range of error generally acceptable in the technical field to which the present invention belongs, and may include cases of 99% or more, 95% or more, or 90% or more.

[0014] Furthermore, "sound deadening" in the present invention means reducing sound, and is a concept that includes the meanings of both sound insulation and sound absorption. Sound insulation means blocking sound, in other words, not allowing sound to pass through. Sound insulation also includes the reflection of sound (acoustics) and the cancellation of sound (acoustics). Sound absorption means reducing reflected sound, in other words, absorbing sound (acoustics).

[0015] [Basic Configuration of Silencer-Equipped Air Passage of the Present Invention] The basic configuration of a silencer-equipped air passage according to one embodiment of the present invention (hereinafter referred to as this embodiment) will be described with reference to the drawings. In the following description, the first direction in which first air pass section 31 (see FIG. 1) extends is referred to as the X direction, the direction perpendicular to the X direction is referred to as the Y direction, and the second direction perpendicular to the X and Y directions is referred to as the Z direction. Furthermore, the upstream side refers to the inlet side of air passage 30 (i.e., the side where air source 10 (see FIG. 1), which will be described later, is arranged), and the downstream side refers to the outlet side of air passage 30.

[0016] The silencer-equipped air duct according to this embodiment (hereinafter referred to as the silencer-equipped air duct 100) is used in an air blowing system S. The air blowing system S is used, for example, to transport (blow) air to a predetermined space (e.g., a room) within a building for the purpose of air conditioning or ventilation. Buildings include detached houses, individual dwelling units in apartment complexes such as condominiums, stores such as restaurants and shops, and facilities such as hospitals, department stores, and movie theaters.

[0017] It should be noted that "wind" refers to an artificial flow of air or gas (air current). The composition of the air or gas that constitutes wind and the ratio of each component are not particularly limited, but the following description will be given assuming that normal air is being blown.

[0018] 1, the air blowing system S is configured with an air blowing source 10 (fan) and a silencer-equipped air duct 100. The silencer-equipped air duct 100 is configured by disposing a silencer 20 at a midpoint of an air duct 30. The detailed configuration of the silencer-equipped air duct 100 will be described later.

[0019] The air source 10 is a device that includes an electric motor such as a motor and is activated by the motor to blow air, specifically, a blower fan that constitutes an air conditioner or a ventilation fan. Known fans such as an axial fan (propeller fan), a sirocco fan, a turbo fan, a centrifugal fan, and a line flow fan (registered trademark) can be used as the fan.

[0020] [Air duct with silencer according to this embodiment] Next, an air duct with silencer 100 according to this embodiment will be described with reference to Figures 1 to 4. As shown in Figure 1, air duct with silencer 100 includes air duct 30 and silencer 20 that reduces sound (noise) propagating within air duct 30 when air is blown.

[0021] (Air Path) The air path 30 is a flow path through which the air blown from the air blower source 10 flows. As shown in FIG. 1 , the upstream end of the air path 30 (more specifically, the second air path section 32) is connected to the exhaust port of the air blower source 10, which is located outside the room, via a cylindrical upstream air path 12 (e.g., a duct, a pipe, a hose, etc.). The downstream end of the air path 30 (more specifically, the third air path section 33) is connected to the indoor space (room) inside the exterior wall W via a cylindrical downstream air path 14 (e.g., a duct, a pipe, a hose, etc.). The downstream air path 14 penetrates the exterior wall W of the building that separates the indoor space from the outdoor space and enters the room to which the air is blown. Note that the air blower source 10 is not limited to being located outdoors and may be located indoors (in a room), for example, and any location is possible.

[0022] As long as air passage 30 can be sent from outdoor air passage 10 into the room, it may be located anywhere between air passage 10 and exterior wall W, and may be attached to the housing of air passage 10, for example. Air passage 30 may be located in either the indoor or outdoor space. The materials and structures of upstream air passage 12 and downstream air passage 14 are not particularly limited, and flexible hoses such as vinyl hoses, flexible hoses, and tie duct hoses may be used.

[0023] As shown in FIG. 1, the air passage 30 has a first air passage section 31 formed inside the silencer 20, a second air passage section 32 located upstream of the first air passage section 31, and a third air passage section 33 located downstream of the first air passage section 31.

[0024] The first air path section 31 is formed inside the housing 21 (corresponding to the silencer main body). In other words, the first air path section 31 constitutes a part of the silencer 20. As shown in Fig. 3 , the first air path section 31 has an air path space 41 surrounded by four imaginary surfaces that define the outer edge of the first air path section 31, and an air path wall 42 that separates the air path space 41.

[0025] As shown in Figure 3, the air passage wall 42 has a pair of walls 42a, 42b arranged along two imaginary surfaces facing each other in the Y direction out of the four imaginary surfaces surrounding the air passage space 41, and a wall 42c arranged along one imaginary surface (the lower surface in Figure 3) located at one end in the Z direction.

[0026] 1, wall 42a is made up of two wall pieces arranged in the X direction with an opening 43a (described later) sandwiched therebetween, and wall 42b is made up of two wall pieces arranged in the X direction with an opening 43b (described later) sandwiched therebetween. Wall 42c forms part of the end of housing 21 (the lower wall of housing 21 in FIG. 3 ) (described later). Walls 42a, 42b, and 42c are flat, rigid walls that extend along the X direction.

[0027] Of the four imaginary surfaces surrounding the air passage space 41, the imaginary surface (the upper surface in FIG. 3 ) located on the opposite side of the wall 42 c in the Z direction does not have an air passage wall 42. In other words, one of the four imaginary surfaces surrounding the air passage space 41 is open, forming an opening 43 c.

[0028] The air passage wall 42 is provided with a plurality of openings 43a, 43b, and 43c (three in this embodiment) that connect the air passage space 41 with the rear space 23, which will be described later. The openings 43a, 43b, and 43c are located on three sides of the first air passage section 31 as shown in Fig. 1 , and more specifically, are located on the outer edge of the first air passage section 31 at one end in the Z direction (more specifically, the end opposite the wall 42c) and both ends in the Y direction.

[0029] As shown in FIG. 1, each of the pair of walls 42a, 42b has an opening. More specifically, opening 43a is provided in the center of wall 42a in the X direction, and opening 43b is provided in the center of wall 42b in the X direction.

[0030] As shown in FIG. 4 , when the length (total length) of the first air path section 31 in the X direction is L, the openings 43a, 43b are preferably located within L / 4 of the center of the first air path section 31 in the X direction. The "length L" of the first air path section 31 is equal to the distance from one X-direction end to the other X-direction end of the inner wall surface of the housing 21. Each of the openings 43a, 43b is provided so that the distance between a center line (median line) parallel to the Z direction that bisects the opening in the X direction and the center line (median line) of the first air path section 31 that is parallel to the Z direction and bisects the first air path section 31 in the X direction is within L / 4 in the X direction. In this embodiment, the center lines of the openings 43a, 43b and the center line of the first air path section 31 coincide in the X direction.

[0031] The openings 43a and 43b are more preferably located within L / 4.5 from the center of the first air passage section 31 in the X direction, and even more preferably within L / 5.

[0032] 3, the opening 43c is formed along one imaginary surface (the upper surface in FIG. 3) located at the other end in the Z direction (the end opposite to the wall 42c) of the four imaginary surfaces surrounding the air passage space 41, and is formed from one end to the other end of the first air passage section 31 in the X direction. That is, in the first air passage section 31, the entire area of ​​the one imaginary surface located at the other end in the Z direction is open to the rear space 23.

[0033] The total area of ​​the openings 43a, 43b, and 43c is A １ The total area of ​​the air passage wall 42 in contact with the air passage space 41 (specifically, the area of ​​the walls 42a, 42b, and 42c) is A ２ In this case, A １ and A ２ A for the sum of １ The ratio of A is preferably more than 10% and less than 85%. １ and A ２ A for the sum of １ The ratio of the opening area A to the opening area B is called the "opening ratio." １ The area of ​​the four virtual sides surrounding the air passage space 41 is A ０ In this case, A1=A ０ -A ２If the opening ratio is 10% or less, the degree to which the sound in the first air passage portion 31 can penetrate into the sound-absorbing material 22 in the rear space 23 decreases, and the sound-absorbing material 22 cannot be used effectively.

[0034] The aperture ratio is more preferably greater than 13% and less than 75%, and even more preferably greater than 16% and less than 65%.

[0035] The second air passage section 32 and the third air passage section 33 are cylindrical sections that surround an internal space through which air flows. As shown in FIG. 1 , the second air passage section 32 is a section that protrudes upstream from the upstream end of the silencer 20 in the X direction and is connected to the end of the upstream-side air passage 12. The third air passage section 33 is a section that protrudes downstream from the downstream end of the silencer 20 in the X direction and is connected to the end of the downstream-side air passage 14. In other words, the second air passage section 32 and the third air passage section 33 are part of the air passage 30 and also function as joints that connect the silencer-equipped air passage 100 to the upstream-side air passage 12 and the downstream-side air passage 14.

[0036] The first air path section 31 and the second air path section 32 are arranged side by side in the X direction, sandwiching the upstream wall (hereinafter also referred to as the upstream wall) of a pair of walls that face each other in the X direction and that constitute the housing 21. More specifically, the upstream end of the first air path section 31 is connected to the inner surface of the upstream wall of the housing 21, and the downstream end of the second air path section 32 is connected to the outer surface of the upstream wall of the housing 21. The first air path section 31 and the second air path section 32 communicate with each other via a through hole provided in the upstream wall of the housing 21.

[0037] The first air path section 31 and the third air path section 33 are arranged side by side in the X direction, sandwiching the downstream wall (hereinafter also referred to as the downstream wall) of a pair of walls that face each other in the X direction and that constitute the housing 21. More specifically, the downstream end of the first air path section 31 is connected to the inner surface of the downstream wall of the housing 21, and the upstream end of the third air path section 33 is connected to the outer surface of the downstream wall of the housing 21. The first air path section 31 and the third air path section 33 are in communication with each other via a through hole provided in the downstream wall of the housing 21.

[0038] In this embodiment, each of the first air path section 31, the second air path section 32, and the third air path section 33 is a linear air path section extending in the X direction, and the central axis of each air path section extends in the X direction and is located on the same imaginary line.

[0039] In this embodiment, the cross-sectional shape of air passage 30 (first air passage section 31, second air passage section 32, and third air passage section 33) is, for example, a square (rectangle). The cross section of air passage 30 refers to a cross section perpendicular to the extension direction of air passage 30. In this embodiment, the extension direction of air passage 30 is the X direction, and the cross section of air passage 30 refers to a plane extending in the Y direction and the Z direction. Note that the cross-sectional shape of air passage 30 is not particularly limited, and may be, for example, a circle, a square, a quadrangle other than a square, a polygon other than a quadrangle, or an irregular shape.

[0040] In the following description, "cross-sectional area" refers to the size of the cross section, and means the area of ​​the range surrounded by the outer edge of the cross section. In the first air duct section 31, it means the area of ​​the air duct space 41, and in the second air duct section 32 and the third air duct section 33, it means the area of ​​the internal space surrounded by each outer edge.

[0041] The first air passage section 31, the second air passage section 32, and the third air passage section 33 may have the same cross-sectional shape and cross-sectional area, or may have different shapes and / or different cross-sectional areas.

[0042] The material constituting the air passage 30 is not particularly limited, and metal materials, resin materials, paper materials, reinforced plastic materials, carbon fiber, etc. can be used. However, from the viewpoint of ensuring moldability and freedom of design, resin materials are preferred. Examples of resin materials include acrylic resin, polymethyl methacrylate, polycarbonate, polyamide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, ABS resin (acrylonitrile, flame-retardant ABS resin, butadiene, styrene copolymer synthetic resin), polypropylene, triacetylcellulose (TAC), polypropylene (PP), polyethylene (PE), polystyrene (PS), ASA (Acrylate Sthrene Acrylonitrile) resin, polyvinyl chloride (PVC) resin, and PLA (Polylactic Acid) resin. Examples of reinforced plastic materials include carbon fiber reinforced plastics (CFRP) and glass fiber reinforced plastics (GFRP).

[0043] (Muffler) Muffler 20 reduces noise propagating within air passage 30, and more specifically, muffles noise generated due to the operation of air blower source 10 sending air into air passage 30, more specifically, noise generated due to the rotation of a drive motor (not shown) of air blower source 10. Muffler 20 is provided for air passage 30, and is provided at a midpoint along air passage 30 as shown in FIG.

[0044] The silencer 20 has a housing 21 (corresponding to the silencer main body), the above-mentioned first air passage section 31 formed inside the housing 21, a rear space 23 that communicates with an air passage space 41 inside the first air passage section 31, and a conversion mechanism housed inside the housing 21 (more specifically, the rear space 23). The conversion mechanism is a mechanism that converts sound energy into thermal energy, and in this embodiment is a sound-absorbing material 22.

[0045] 1 , the housing 21 in this embodiment defines the outer edge of the silencer 20 and is a hollow rectangular parallelepiped (hexahedron) extending in the X direction. Of the six walls that make up the housing 21, a pair of walls that face each other in the X direction are each provided with a through-hole as described above, and the ends of the first air path section 31 and the second air path section 32 are connected to the through-hole on the upstream side, and the ends of the first air path section 31 and the third air path section 33 are connected to the through-hole on the downstream side wall.

[0046] In this embodiment, the cross section of the housing 21 perpendicular to the X direction is rectangular, and the cross-sectional shape is constant in the X direction. However, the cross-sectional shape of the housing 21 is not limited to this, and may be, for example, a circle, a quadrangle other than a square, a polygon other than a square, or an irregular shape, and may change in the X direction.

[0047] The cross-sectional area of ​​housing 21, more specifically, the cross-sectional area of ​​the internal space surrounded by housing 21, is larger than the cross-sectional area of ​​each of the internal spaces of second air path section 32 and third air path section 33. That is, in this embodiment, silencer 20 is an extension section that is larger than second air path section 32 and third air path section 33, and silencer-equipped air path 100 can also be said to be an air path equipped with an extension-type silencer.

[0048] 3, the first air path section 31 is in contact with one end of the housing 21 in the Z direction (the bottom wall of the housing 21 in FIG. 3) at the center of the housing 21 in the Y direction. Strictly speaking, as described above, the end (wall 42c) of the first air path section 31 in the Z direction forms part of the end of the housing 21 in the Z direction.

[0049] The material that constitutes the housing 21 is not particularly limited, and metal materials, resin materials, paper materials, reinforced plastic materials, carbon fiber, etc. can be used. The detailed types of materials are the same as those of the air passage 30, so explanation will be omitted.

[0050] As shown in Fig. 1, a rear space 23 is provided inside the housing 21, which communicates with the air passage space 41 in the first air passage section 31. The rear space 23 is the internal space surrounded by the housing 21 excluding the first air passage section 31, and as shown in Fig. 3, the rear space 23 surrounds the first air passage section 31 on three sides. The rear space 23 is separated from the air passage space 41 by walls 42a and 42b, and communicates with the air passage space 41 via openings 43a, 43b, and 43c.

[0051] A sound-absorbing material 22 is disposed in the rear space 23. As shown in Fig. 3 , the sound-absorbing material 22 surrounds the first air passage portion 31 on three sides and is disposed in the rear space 23 so as to cover at least a portion of each of the openings 43a, 43b, and 43c. In this embodiment, the sound-absorbing material 22 covers the entire area of ​​each of the openings 43a, 43b, and 43c, and fills the entire rear space 23.

[0052] The sound-absorbing material 22 may be one that absorbs sound by converting sound energy into thermal energy. Examples of materials that can be used for the sound-absorbing material 22 include porous materials such as foams, foam materials, and nonwoven fabric sound-absorbing materials. Specific examples of foams and foam materials include urethane foam such as Calmflex F manufactured by Inoac Corporation and urethane foam manufactured by Hikarisha, soft urethane foam, sintered ceramic particles, phenol foam, melamine foam, insulation board, and polyamide foam. Specific examples of nonwoven sound-absorbing materials include microfiber nonwoven fabrics such as 3M's Thinsulate, polyester nonwoven fabrics (including those with a two-layer structure having a high-density, thin nonwoven fabric on the front side and a low-density nonwoven fabric on the back side) such as Tokyo Bouon Co., Ltd.'s White Qon and Bridgestone KBG's QonPET, 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, and carpets. In addition to the above, various sound-absorbing materials can be used, such as sound-absorbing materials made of materials containing microscopic air particles, such as glass wool, rock wool, gypsum board, wood wool cement board, and sound-absorbing materials made of nanofiber fibers. Examples of nanofiber fibers include silica nanofibers and acrylic nanofibers such as XAI manufactured by Mitsubishi Chemical Corporation.

[0053] The silencer 20 configured as described above may be formed integrally with the air passage 30, or may be assembled to the air passage 30 as a separate component.

[0054] (Acoustic Impedance Density) The configuration of the silencer-equipped air duct 100 according to this embodiment will be described again from the perspective of acoustic impedance density.

[0055] Acoustic impedance density is a numerical representation of the ease of sound propagation. If the acoustic impedance density is Z, the density of the air (gas) flowing through the air passage 30 is ρ, the sound speed of the air (gas) is c, and the cross-sectional area is A, then Z = ρ × c / A holds. The unit of acoustic impedance density Z is rayl / m ２Let's say.

[0056] In this embodiment, the acoustic impedance density of the internal space of the housing 21 is smaller than the acoustic impedance density of each of the internal spaces of the second air path portion 32 and the third air path portion 33. In other words, the acoustic impedance density of the internal space of the housing 21 is set to Z ｓ and the acoustic impedance density of the internal space of the second air passage section 32 is Z ｉｎ and the acoustic impedance density of the internal space of the third air passage section 33 is Z ｏｕｔ When we define ｓ <Z ｉｎ , and Z ｓ <Z ｏｕｔ Meet the following.

[0057] The cross-sectional area A of the housing 21 means the cross-sectional area of ​​the internal space surrounded by the housing 21, and the cross-sectional area A of each of the second air passage section 32 and the third air passage section 33 means the cross-sectional area of ​​the internal space surrounded by the outer edge. ｓ , Z ｉｎ , and Z ｏｕｔ The same values ​​are applied to the density ρ and the sound velocity c used when calculating each of the above. Therefore, in this embodiment, the acoustic impedance density Z is a value determined only by the cross-sectional area A, and is inversely proportional to the cross-sectional area A. Since the cross-sectional area A of the housing 21 is the largest among the housing 21, the second airflow path section 32, and the third airflow path section 33, the acoustic impedance density Z of the housing 21 is ｓ becomes the smallest, and Z ｓ <Z ｉｎ , and Z ｓ <Z ｏｕｔ This will satisfy the following.

[0058] (Propagation Length) The silencer-equipped air passage 100 has an effective propagation length of α Ｅ and the wavelength of the sound in the air at the frequency at which the housing 21 resonates (specifically, the first resonant frequency) is λ, then −1.97<log １０ (α Ｅ / λ) < 0.76. Ｅ is determined based on the characteristics of the sound wave propagation space within the housing 21, and specifically, α Ｅ= 1 / Re[γ]. γ is a propagation constant determined by the characteristics of the medium, and is defined in the Journal of the Acoustical Society of Japan, Vol. 68, No. 9 (2012). Re[γ] is the real part of the propagation constant γ. The wavelength λ of the first resonant frequency is determined as λ = L / 2 based on the length L of the first air path section 31 (see FIG. 4). Note that the "sound of the first resonant frequency" refers to the sound with the lowest frequency among the length-induced resonances that occur in the first air path section 31 when the medium is air.

[0059] In the configuration in which the silencer 20 includes the sound absorbing material 22 as part of the silencer 20, the effective propagation length α Ｅ is α Ｅ = α × V s / V ｂ α is the propagation length of the sound absorbing material 22, and V ｓ is the volume of the sound absorbing material 22, and V ｂ is the volume of the back space 23. The propagation length α of the sound absorbing material 22 is calculated by α=1 / Re[γ], where γ is the propagation constant and Re[γ] is the real part of the propagation constant γ. In this embodiment, the effective propagation length α Ｅ is the effective propagation length determined based on the sound-absorbing material 22 inside the housing 21, and the wavelength λ is the wavelength of sound at a frequency (specifically, the first resonant frequency) at which the housing 21 resonates when it does not contain the sound-absorbing material 22.

[0060] The propagation constant γ can be determined by measuring using a transfer function method that uses an acoustic tube and two microphones. This method complies with JIS A1405-2, ISO 10534-2, and ASTM E 1050 standards. For example, an acoustic tube that uses the same measurement principle as the WinZac manufactured by Nittobo Acoustic Engineering Co., Ltd. can be used. This method allows the propagation constant to be measured over a wide spectral range.

[0061] The "casing 21 in a state where the sound-absorbing material 22 is not housed" means a state where the sound-absorbing material 22 is not disposed in the back space 23, and the back space 23 is hollow.

[0062] Effective propagation length α Ｅ When the sound absorbing material 22 is filled in the entire rear space 23 as in this embodiment, V ｓ / V ｂ is 1, so it matches the propagation length α. １０ (α Ｅ / λ) is inversely proportional to the acoustic resistance, specifically, log １０ (α Ｅ / λ) increases, the acoustic resistance decreases, and log １０ (α Ｅ / λ) becomes smaller, the acoustic resistance becomes larger.

[0063] [Operations and Effects of the Present Embodiment] The inventors have found that in the silencer-equipped air duct 100, −1.97<log １０ (α Ｅ It was found that by satisfying the condition (λ / λ) < 0.76, the sound deadening performance for low-frequency sounds of 1000 Hz or less is improved (see FIG. 14). In particular, it was revealed that when the above numerical conditions are satisfied, a sound deadening effect of a transmission loss of 3 dB or more, at which a person can recognize a reduction in sound, is exerted for sounds of a resonant frequency with high transmittance, more specifically, the first resonant frequency (850 Hz in FIG. 14), at which the sound is reduced. Furthermore, by configuring the silencer 20 so as to satisfy the above numerical conditions, it is no longer necessary to increase the volume of the sound-absorbing material housed in the silencer more than necessary, and therefore an increase in the size of the silencer (air duct with silencer) is suppressed. As described above, the air duct with silencer 100 can improve the sound deadening performance for low-frequency sounds (specifically, 1000 Hz or less) while suppressing an increase in size.

[0064] In addition, log １０ (α Ｅ When log(λ) becomes large and exceeds 0.76, the acoustic resistance decreases, and the sound absorption performance decreases. Furthermore, resonance occurs at the first resonance frequency within the silencer 20, and the desired sound absorbing effect cannot be obtained. １０ (α Ｅ When the ratio (λ) becomes small and becomes −1.97 or less, the sound absorbing material behaves in the same way as a rigid body, and the sound absorbing performance falls to the same level as a rigid body (i.e., the acoustic resistance increases), and the desired sound deadening effect cannot be obtained.

[0065] In addition, in the silencer-equipped air duct 100, −1.80<log １０ (αＥ / λ)<0.48, in which case a sound silencing effect of a transmission loss of 5 dB or more can be achieved for the sound of the first resonance frequency. １０ (α Ｅ It is most preferable that the relationship (λ / λ)<0.27 is satisfied, in which case a sound silencing effect with a transmission loss of 7 dB or more can be achieved for sound of the first resonance frequency.

[0066] In the silencer-equipped air duct 100 according to this embodiment, as shown in FIG. 2, the cross-sectional area of ​​the housing 21 is larger than the cross-sectional area of ​​each of the second air duct portion 32 and the third air duct portion 33, i.e., the silencer 20 forms an extended portion. As a result, Z ｓ <Z ｉｎ , and Z ｓ <Z ｏｕｔ A silencer that satisfies the relationship is realized.

[0067] 1, air passage wall 42 is provided with openings 43a, 43b, and 43c, which allow air passage space 41 to communicate with rear space 23, and sound in air passage space 41 can enter sound-absorbing material 22 in rear space 23, allowing silencer 20 to exhibit its silencing effect appropriately.

[0068] In addition, in the silencer-equipped air duct 100 according to this embodiment, the openings 43a, 43b, and 43c are １ and A ２ A for the sum of １ is more than 10% and less than 85%. As a result, as shown in Fig. 15 , the silencing effect of the silencer 20 is appropriately exhibited for sounds with frequencies lower than the first resonant frequency (355 Hz in Fig. 15 ).

[0069] 4, in silencer-equipped air duct 100 according to this embodiment, openings 43a and 43b are located at the center of first air duct section 31 in the X direction. As a result, openings 43a and 43b are provided at positions where the particle speed of air (wind) flowing through first air duct section 31 is fast, and sound-absorbing material 22 is disposed at these positions, making it possible to more effectively muffle sound at the first resonant frequency.

[0070] Furthermore, in silencer-equipped air duct 100 according to this embodiment, openings 43a, 43b are located within L / 4 from the center of first air duct section 31 in the X direction. This more effectively demonstrates the effect of providing openings 43a, 43b at positions where the particle speed of air (wind) flowing through first air duct section 31 is faster, thereby more effectively silencing sound of the first resonant frequency.

[0071] Furthermore, in silencer-equipped air duct 100 according to the present embodiment, as shown in Fig. 3, wall 42c located at the end of first air duct section 31 in the Z direction constitutes part of the end of housing 21 in the Z direction (the lower end in Fig. 3). This ensures a sufficient gap between the end of first air duct section 31 opposite wall 42c in the Z direction (i.e., opening 43c) and the end of housing 21 opposite wall 42c in the Z direction (the upper end in Fig. 3). As a result, the peak frequency of sound silencing in silencer 20 can be shifted to a lower frequency side (see Fig. 18) compared to when first air duct section 31 is disposed in the center of housing 21 in the Z direction as shown in Fig. 5.

[0072] Furthermore, in silencer-equipped air passage 100 according to the present embodiment, air passage wall 42 has a pair of walls 42a, 42b that face each other in the Y direction, sandwiching air passage space 41 therebetween. This allows the position of air passage space 41 in the Y direction to be determined by pair of walls 42a, 42b, and enables the air sent from air source 10 to be appropriately sent inside housing 21, i.e., in first air passage section 31.

[0073] Furthermore, in silencer-equipped air passage 100 according to this embodiment, openings 43a, 43b are provided in each of the pair of walls 42a, 42b, which allow sound from air passage space 41 to enter the areas of sound-absorbing material 22 adjacent to each of the pair of walls 42a, 42b, thereby allowing silencer 20 to exhibit its silencing effect appropriately.

[0074] Furthermore, silencer-equipped air duct 100 according to this embodiment silences noise generated by the operation of air blower source 10 that blows air into air duct 30. For example, silencer-equipped air duct 100 can provide a noise-reduction effect in an air blowing system that blows air into a predetermined space (e.g., a room) within a building for the purpose of air conditioning, ventilation, or the like.

[0075] [Other Embodiments] One embodiment of the silencer-equipped air duct of the present invention has been described above, but the above embodiment is merely an example to facilitate understanding of the present invention and does not limit the present invention. In other words, the present invention can be modified and improved without departing from the spirit of the present invention. Furthermore, it goes without saying that the present invention includes equivalents thereof.

[0076] In the above embodiment, the conversion mechanism for converting sound energy into thermal energy is the sound-absorbing material 22. However, this is not limited to this, and the conversion mechanism may not use the sound-absorbing material 22, but may instead use, for example, wall friction. Specifically, sound energy may be converted into thermal energy based on the surface roughness imparted to the wall surfaces that define the rear space 23 (i.e., the inner wall surfaces of the housing 21 and the outer wall surfaces of the air passage wall 42 shown in FIG. 3).

[0077] In the above embodiment, as shown in Fig. 3, the wall 42c forming the end of the first air passage portion 31 in the Z direction constitutes part of the end of the housing 21 in the Z direction (the lower wall of the housing 21 in Fig. 3). However, this is not limited to this, and the wall 42c may be disposed at a distance from the end of the housing 21 in the Z direction (the lower wall of the housing 21 in Fig. 5), as in the silencer 20A shown in Fig. 5. In this case, a sound-absorbing material 22A may be disposed in the space (rear space) between the wall 42c and the housing 21, as shown in Fig. 5.

[0078] 1, each of the pair of walls 42a, 42b is provided with one opening 43a, 43b. However, this is not limited thereto, and each of the pair of walls 42a, 42b may be provided with a plurality of openings. For example, each of the walls 42a, 42b may be made of punched metal or wire mesh provided with a plurality of through holes (openings).

[0079] In the above embodiment, as shown in Fig. 3, the sound absorbing material 22 fills the entire rear space 23. However, this is not limited to this, and as in the silencer 20B shown in Fig. 6, the sound absorbing material 22B may be disposed in only a part of the rear space 23. For example, as shown in Fig. 6, in each of the regions of the rear space 23 located on both sides in the Y direction across the air passage space 41, sound absorbing materials 22B that are sufficiently thinner in the Y direction than those regions may be disposed along the openings 43a, 43b.

[0080] Furthermore, as in the silencer 20C shown in FIG. 7, one or more communication holes 24C (communication passages) that connect the air passage space 41 and the rear space 23 and penetrate the sound absorbing material 22C may be provided in the sound absorbing material 22C.

[0081] In the above embodiment, the air passage wall 42 is provided with a plurality of openings 43a, 43b, and 43c, as shown in Fig. 1 . The openings 43a, 43b, and 43c are located on three sides of the first air passage section 31. More specifically, as shown in Fig. 3 , the openings 43a, 43b, and 43c are located on the outer edge of the first air passage section 31, at one end in the Z direction (opposite the wall 42c) and at both ends in the Y direction. However, this is not limited to this. For example, as in a silencer 20D shown in Fig. 8 , only the opening 43c may be provided in the air passage wall 42. In this case, no openings are provided in the air passage walls 42 located at both ends in the Y direction of the first air passage section 31, and as shown in Fig. 8 , the sound-absorbing material 22 may not be provided in areas of the rear space 23 that are located outside the air passage walls 42 in the Y direction.

[0082] In the above embodiment, the pair of walls 42a, 42b are rigid, flat walls extending along the X direction as shown in FIG. 4 . However, this is not limited thereto. As in the silencer 20E shown in FIG. 9 , the walls 42a, 42b may be rigid walls extending in a direction inclined with respect to the X direction. More specifically, as shown in FIG. 9 , the pair of walls 42a, 42b arranged upstream of the openings 43a, 43b in the X direction may extend at an inclination toward the outside in the Y direction (toward the rear space 23) as they extend downstream. On the other hand, the pair of walls 42a, 42b arranged downstream of the openings 43a, 43b in the X direction may extend at an inclination toward the inside in the Y direction (toward the air passage space 41) as they extend downstream.

[0083] In the above embodiment, the cross section of the housing 21 perpendicular to the X direction is rectangular as shown in Fig. 1, and the cross-sectional shape is maintained as a constant shape in the X direction. However, this is not limited to this, and the cross section of the housing may be circular, quadrilateral other than a square, polygonal other than a square, or irregular, and may change in the X direction. For example, as in the silencer 20F shown in Fig. 10, the cross section of the housing 21F perpendicular to the X direction may be polygonal, and the cross-sectional area may decrease toward the outside in the X direction (i.e., toward the second air path portion 32 and the third air path portion 33).

[0084] In the above embodiment, as shown in Fig. 1, the first air path section 31, the second air path section 32, and the third air path section 33 are each linear air path sections extending in the X direction, and the central axes of the air path sections all extend in the X direction and are located on the same imaginary line. However, this is not limited to this. As in a silencer 20G shown in Fig. 11, the direction in which the first air path section 31G extends (X direction) may be inclined with respect to the direction in which the second air path section 32G and the third air path section 33G extend. Furthermore, the configuration of the housing 21G that houses the first air path section 31G may be changed depending on the direction in which the first air path section 31G extends (X direction). For example, as shown in Fig. 11, the direction in which the housing 21G extends may be inclined with respect to the direction in which the second air path section 32G and the third air path section 33G extend.

[0085] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0086] Simulations 1 to 4 were carried out to examine the effects of the silencer-equipped air duct according to the present invention. The simulations were carried out using the acoustic module of finite element method calculation software COMSOL ver. 6.0 (COMSOL).

[0087] <Simulation 1> Simulation 1 was performed under three conditions (Comparative Examples 1 and 2, and Example 1). [Comparative Example 1] In Comparative Example 1, a calculation model of an air duct with a silencer was generated. The calculation model had the same configuration as that shown in FIGS. 1 to 4 in the above-described embodiment. Specifically, the dimensions of the first air duct section were set to a length of 200 mm (the dimension of length L in FIG. 4), a width of 21 mm (the length in the Y direction), and a height of 21 mm (the length in the Z direction). Openings (corresponding to openings 43a and 43b in FIG. 1) provided in each of a pair of walls facing each other in the Y direction (corresponding to walls 42a and 42b in FIG. 1) were positioned at the center of the first air duct section in the X direction, and the dimensions were set to a length of 140 mm (X direction) and a height of 21 mm (Z direction).

[0088] The entire back space is filled with sound-absorbing material, and the flow resistance of the sound-absorbing material is 18 Pa·s / m ２ The first resonance frequency of the silencer was set to 850 Hz, and the wavelength λ of the sound at that frequency was set to 100 mm (= L / 2). １０ (α Ｅ / λ) was 1.02.

[0089] The density ρ of the air flowing through the air duct is 1.29 kg / m ３ The sound velocity c of the sound propagating through the air was set to 340 m / s. The cross-sectional area of ​​the housing was set to 0.004 m ２ and the cross-sectional area of ​​each of the second air duct section and the third air duct section was set to 0.000441 m ２ As a result, the acoustic impedance density Zs of the internal space of the housing is set to 109650 rayl / m２ and the acoustic impedance density of the second air passage section Z ｉｎ , and the acoustic impedance density Z of the third air passage section ｏｕｔ is 994558 rayl / m ２ This is what happened.

[0090] [Comparative Example 2] In Comparative Example 2, the flow resistance of the sound absorbing material was set to 1,800,000 Pa·s / m ２ This resulted in log １０ (α Ｅ / λ) was −2.07. The other conditions were the same as those in Comparative Example 1.

[0091] [Example 1] In Example 1, the flow resistance of the sound absorbing material was set to 14384 Pa·s / m ２ This resulted in log １０ (α Ｅ / λ) was −0.76. The other conditions were the same as those in Comparative Example 1.

[0092] [Results of Simulation 1] A simulation was carried out on the relationship between the frequency of sound passing through the calculation model of the air duct with a silencer described above and the sound transmission loss due to the silencer, and the results are shown in FIGS.

[0093] In the simulation, sound (sound waves) emitted by the air source was incident on the entrance of the air duct with silencer (more specifically, the upstream end of the second air duct section), and the amplitude per unit area of ​​the sound reaching the exit of the air duct with silencer (more specifically, the downstream end of the third air duct section) was calculated (see Figure 1 for the calculation model). The amplitude per unit area of ​​the sound emitted by the air source was set to 1. Then, the transmission loss was calculated from the ratio of the amplitude of the sound emitted by the air source to the amplitude of the sound reaching the exit of the air duct with silencer.

[0094] FIG. 12 shows the relationship between frequency and log １０ (α Ｅ 13 is a graph showing the relationship between log / λ and transmission loss for a sound with a first resonance frequency of 850 Hz. １０ (α Ｅ14 is a diagram showing the relationship between frequency and transmission loss in each of Comparative Example 1, Comparative Example 2, and Example 1.

[0095] As shown in Fig. 13, at a first resonance frequency of 850 Hz, Comparative Examples 1 and 2 only achieved a sound deadening effect with a transmission loss of less than 3 dB, but Example 1 achieved a sound deadening effect with a transmission loss of 3 dB. As mentioned above, an increase in transmission loss of 3 dB or more means that the sound has been reduced to a level that can be recognized by humans. In other words, as shown in Fig. 13, Example 1 achieved a sound deadening effect with a transmission loss of -1.97<log １０ (α Ｅ It was found that by satisfying the condition of (λ / λ)<0.76, a sound deadening effect with a transmission loss of 3 dB or more can be obtained.

[0096] Furthermore, as shown in FIG. 14, in Example 1, the transmission loss is large in comparison with both Comparative Examples 1 and 2 in the low frequency sound of 1000 Hz or less including the first resonant frequency of 850 Hz, and it was found that the sound absorbing effect of the silencer is appropriately exhibited.

[0097] [Simulation 2] A calculation model with a different aperture ratio was generated based on the calculation model of Example 1. Specifically, the aperture ratio was changed by changing the width in the X direction of a pair of openings (corresponding to openings 43a and 43b in FIG. 1) formed in a pair of air passage walls sandwiching the first air passage section. Regardless of the aperture ratio, each of the pair of openings was positioned at the center of the first air passage section in the X direction. Unlike Example 1, Example 2 positioned the first air passage section at the center of the housing in the Z direction, as shown in FIG. 5. Furthermore, the space between the outer edges (four sides) of the first air passage section and the housing, i.e., the rear space, was filled with sound-absorbing material throughout the entire rear space.

[0098] [Results of Simulation 2] A simulation was performed on the relationship between the sound transmittance and the aperture ratio when sound of set frequencies (specifically, 355 Hz and 850 Hz) passed through a calculation model of an air duct with a silencer, and the results are shown in Fig. 15. Fig. 15 is a diagram showing the relationship between the aperture ratio and the transmittance, with the horizontal axis representing the aperture ratio and the vertical axis representing the transmittance. As shown in Fig. 15, when the aperture ratio is in the range of more than 10% and less than 85%, it was found that the transmittance of low-frequency sound, particularly that of 355 Hz, which is lower than the first resonant frequency of 850 Hz, is reduced.

[0099] [Simulation 3] Based on the calculation model of Example 1, a calculation model was created in which the positions in the X direction of a pair of openings (corresponding to openings 43a and 43b in FIG. 1) formed in a pair of air passage walls sandwiching the first air passage section were changed. Specifically, for each of the pair of openings, the distance in the X direction to the center line of the opening parallel to the Z direction was changed, with the center line parallel to the Z direction of the first air passage section as the reference. Note that the opening width in the X direction was set to 40 mm at each opening position.

[0100] [Results of Simulation 3] A simulation was performed to examine the relationship between the frequency of sound passing through a calculation model of an air duct with a silencer and the transmission loss of that sound when the opening position was changed, and the results are shown in Figures 16 and 17. Figure 16 is a diagram showing the relationship between frequency and transmittance for each opening position, with the horizontal axis representing frequency and the vertical axis representing transmittance. Figure 17 is a diagram showing the relationship between opening position and transmittance for sound of the first resonant frequency, with the horizontal axis representing the distance in the X direction from the center line of the first air duct section to the center line of the opening (hereinafter referred to as distance D), and the vertical axis representing transmittance at a first resonant frequency of 850 Hz.

[0101] As shown in Figure 16, when the distance D was set to 80 mm, the transmittance was high in the frequency band including the first resonant frequency of 850 Hz, with the first resonant frequency at its peak. On the other hand, as the distance D was shortened, the transmittance in the frequency band centered on the first resonant frequency of 850 Hz decreased, and when the distance D was 0 mm, the transmittance was found to be approximately the same as that in the low-frequency bands other than the first resonant frequency. This is presumably because the opening was positioned at a location where the particle velocity of the air flowing through the first air duct section was high, thereby reducing the transmittance in the frequency band centered on the first resonant frequency of 850 Hz. It was also found that, even when the distance D was set to 0 mm, the transmittance was high in the frequency band including the first resonant frequency of 850 Hz and in the frequency bands including the other resonant frequencies, as shown by the dashed-dotted line in Figure 16, when no sound-absorbing material was placed in the silencer.

[0102] It was found that, as the distance D was shortened, the transmittance in the frequency band centered on the first resonance frequency of 850 Hz decreased, while the transmittance in the frequency band centered on the second resonance frequency (near 1800 Hz) increased. In other words, it was found that the frequency of the silencing peak shifted to the lower frequency side as the distance D was shortened.

[0103] Furthermore, as shown in Figure 17, it was found that at a first resonant frequency of 850 Hz, the transmittance can be suppressed to 12% or less by setting the distance D to within L / 4 (in the case of Simulation 3, D = 50 mm).

[0104] [Simulation 4] A calculation model was generated based on the calculation model of Example 1, in which the position of the first air path section relative to the housing in the Z direction was changed. Specifically, the position of the end of the first air path section (corresponding to wall 42c in FIG. 3 ) in the Z direction was set in three patterns. In the first pattern, the end of the first air path section was set at one end of the housing (the lower end of housing 21 in FIG. 3 ) as shown in FIG. 3 . In the second pattern, the end of the first air path section was set at the center of the housing in the Z direction as shown in FIG. 5 . In the third pattern, the end of the first air path section was set at a position between the first and second patterns.

[0105] [Results of Simulation 4] A simulation was performed to examine the relationship between the frequency of sound passing through a calculation model of an air duct with a silencer and the transmission loss of that sound when the position of the end of the first air duct section was changed. The results are shown in Figure 18. Figure 18 is a diagram showing the relationship between frequency and transmission loss, determined depending on the position of the first air duct section in the Z direction, with the horizontal axis representing frequency and the vertical axis representing transmission loss. In Figure 18, the "bottom" indicated by the thick solid line refers to the case where the end of the first air duct section in the Z direction is located at the position of the first pattern. In Figure 18, the "center" indicated by the thin solid line refers to the case where the end of the first air duct section in the Z direction is located at the position of the second pattern. In Figure 18, the "intermediate" indicated by the dashed line refers to the case where the end of the first air duct section in the Z direction is located at the position of the third pattern. As shown in Figure 18, it was found that the frequency of the silencing peak shifted to a lower frequency as the position of the first air duct section in the Z direction moved from the center of the housing toward one end (bottom) of the housing.

[0106] The effects of the present invention are clear from the simulation results described above.

[0107] 10 Air blowing source (blower) 12 Upstream air passage 14 Downstream air passage 20, 20A, 20B, 20C, 20D, 20E, 20F, 20G Silencer 21, 21F, 21G Housing (silencer body) 22, 22A, 22B, 22C Sound absorbing material 23 Back space 24C Communication hole 30 Air passage 31, 31G First air passage section 32, 32G Second air passage section 33, 33G Third air passage section 41 Air passage space 42 Air passage wall 42a, 42b, 42c Wall 43a, 43b, 43c Opening 100 Air passage with silencer D Distance L Length S Air blowing system W Outer wall

Claims

1. In an air duct with a silencer configured by arranging a silencer at an intermediate position in the air duct, the silencer has a silencer body and a conversion mechanism that converts sound energy accommodated in the silencer body into thermal energy, the air duct has a first air duct portion formed inside the silencer body, a second air duct portion located upstream of the first air duct portion, and a third air duct portion located downstream of the first air duct portion, the acoustic impedance density of the internal space of the silencer body is smaller than the acoustic impedance density of the internal space of each of the second air duct portion and the third air duct portion, Let α be the effective propagation length determined based on the characteristics of the sound wave propagation space inside the muffler body Ｅ and when the wavelength of the sound of the frequency at which the silencer body resonates is λ, which is determined based on the length of the first air duct portion, -1.97 < log １０ (α Ｅ / λ) < 0.76, an air duct with a silencer.

2. the silencer body is a housing, the cross-sectional area of the housing is larger than the cross-sectional area of each of the second air duct portion and the third air duct portion, a back space communicating with the air duct space in the first air duct portion is provided inside the housing. The air duct with a silencer according to claim 1.

3. the first air duct portion has an air duct wall that partitions the air duct space, one or more openings communicating the air duct space and the back space are provided in the air duct wall. The air duct with a silencer according to claim 2.

4. Let the total area obtained by summing up the opening areas of all the openings of 1 or more be A １ and let the total area of the entire air passage wall in contact with the air passage space be A ２ When this is the case, A １ and A ２ The ratio of A １ to the sum of A is more than 10% and less than 85%. The air passage with a muffler according to claim 3

5. the conversion mechanism is a sound-absorbing material. The air duct with a silencer according to claim 3.

6. the sound-absorbing material is located in the back space so as to cover at least a part of the opening, the opening is located at the center of the first air duct portion in the first direction in which the first air duct portion extends. The air duct with a silencer according to claim 5.

7. The sound-absorbing material is located in the back space so as to cover at least a part of the opening, when the length of the first air duct portion in the first direction in which the first air duct portion extends is L, the opening is located within L / 4 from the center of the first air duct portion in the first direction. The air duct with a silencer according to claim 5.

8. an end of the first air duct portion in a second direction intersecting the first direction in which the first air duct portion extends constitutes a part of an end of the housing in the second direction. The air duct with a silencer according to claim 2.

9. the air duct wall has a pair of walls facing each other across the air duct space in a direction intersecting the first direction in which the first air duct portion extends. The air duct with a silencer according to claim 3.

10. the opening is provided in each of the pair of walls. The air duct with a silencer according to claim 9.

11. The air duct with a muffler according to any one of claims 1 to 10, wherein the muffler silences the sound generated due to the operation of a blower that sends air into the air duct.