Sound pressure reduction structure

Abstract

[Problem] To provide a sound pressure reduction structure that enables drainage of water in a resonance space while maintaining sound pressure reduction performance. [Solution] This sound pressure reduction structure comprises: a pipe line extending in a first direction; and a resonance pipe having an opening connected to the pipe line. The resonance pipe includes: a bottom wall facing the opening in a second direction intersecting the first direction; side walls connecting the opening to the bottom wall; and a porous member provided in an in-pipe space surrounded by the side walls and the bottom wall.

Description

Sound pressure reduction structure

[0001] This invention relates to a sound pressure reduction structure.

[0002] Sound pressure reduction structures are used in various fields to suppress noise. For example, there are many sound sources inside a car. Because quietness from noise both inside and outside the car is required, effective sound pressure reduction structures are necessary in automobiles.

[0003] For example, a technology has been proposed to reduce noise by utilizing resonance (see, for example, Japanese Patent Publication No. 2014-84782). Water may accumulate in this resonant space. The water accumulated in the resonant space is discharged, for example, through a drain hole.

[0004] Providing such drainage holes may affect the sound pressure reduction performance.

[0005] Therefore, the present invention aims to provide a sound pressure reduction structure that can discharge water from the resonant space while maintaining sound pressure reduction performance.

[0006] A sound pressure reduction structure according to one embodiment of the present invention comprises a conduit extending in a first direction and a resonant tube having an opening connected to the conduit. The resonant tube includes a bottom wall facing the opening in a second direction intersecting the first direction, a side wall connecting the opening to the bottom wall, and a porous member provided in the internal space of the tube surrounded by the side wall and the bottom wall.

[0007] This is a cross-sectional view showing an example of the configuration of a sound pressure reduction structure according to one embodiment of the present invention. This is a cross-sectional view showing an example of the configuration of the resonant tube shown in Figure 1A. This is a cross-sectional view showing another example of the configuration of the resonant tube shown in Figure 1B. This is a cross-sectional view showing another example of the configuration of the resonant tube shown in Figure 1B. This is a cross-sectional view showing an example of a sound pressure reduction structure according to a comparative example. This is a cross-sectional view showing an example of the configuration of a sound pressure reduction structure according to a modified example. This is a cross-sectional view showing an example of the configuration of the resonant tube shown in Figure 6A. This is a cross-sectional view showing another example of the configuration of the resonant tube shown in Figure 6B. This is a diagram for explaining the configuration of the sound pressure reduction structure used in the examples. This is a diagram showing the sound pressure reduction effect of the sound pressure reduction structures according to Examples 1 to 3. This is another diagram showing the sound pressure reduction effect of the sound pressure reduction structures according to Examples 1 to 3. This is a diagram showing the sound pressure reduction effect of the sound pressure reduction structures according to Examples 4 and 5. This is another diagram showing the sound pressure reduction effect of the sound pressure reduction structures according to Examples 4 and 5. This is a diagram showing the sound pressure reduction effect of the sound pressure reduction structure according to Example 6. This is another diagram showing the sound pressure reduction effect of the sound pressure reduction structure according to Example 6. This is a diagram showing the sound pressure reduction effect of the sound pressure reduction structure according to Example 7.

[0008] A sound pressure reduction structure according to one embodiment of the present invention comprises a conduit extending in a first direction and a resonant tube having an opening connected to the conduit. The resonant tube includes a bottom wall facing the opening in a second direction intersecting the first direction, a side wall connecting the opening to the bottom wall, and a porous member provided in the internal space of the tube surrounded by the side wall and the bottom wall.

[0009] According to the sound pressure reduction structure of this embodiment, a porous member is provided in the space inside the pipe, so water accumulated in the space inside the pipe is drawn up into the porous member. The water drawn up into the porous member becomes, for example, water vapor and diffuses into the pipe. Therefore, water accumulated in the space inside the pipe can be discharged without providing drainage holes or the like. Thus, it is possible to discharge water in the resonant space while maintaining sound pressure reduction performance. In this specification, "maintaining" sound pressure reduction performance is a concept that includes cases where the sound pressure reduction structure is slightly reduced to a degree that does not have a practical impact.

[0010] Embodiments of the present invention will be described below with reference to the drawings, but the technical scope of the present invention is not limited to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios. In this specification, "M to N" indicating a range means "M or greater and N or less". Unless otherwise specified, operations and measurements of physical properties, etc., are performed under room temperature (20 to 25°C) / relative humidity of 40 to 50%.

[0011] <Embodiment> [Configuration of sound pressure reduction structure] Figure 1A shows the configuration of a sound pressure reduction structure 1 according to one embodiment of the present invention. The sound pressure reduction structure 1 has a conduit 10 and a resonant tube 20 connected to the conduit 10.

[0012] The conduit 10 is a hollow member extending in a predetermined direction. A first open end 11 is provided at one end of the conduit 10 in the direction of extension, and a second open end 12 is provided at the other end. For example, sound incident on the conduit 10 from the first open end 11 propagates along the direction of extension of the conduit 10 and is radiated from the second open end 12. The resonant tube 20 is connected in a direction intersecting the direction of extension of the conduit 10. That is, in the sound pressure reduction structure 1, the length direction of the resonant tube 20 is provided in a direction intersecting the direction of extension of the conduit 10. The resonant tube 20 has an opening 20M at one end in the length direction. This opening 20M is connected to the conduit 10 at a position between the first open end 11 and the second open end 12. The resonant tube 20 is connected to the conduit 10, for example, via an adapter (not shown). In the following explanation, the direction of extension of the conduit 10 may be referred to as the Y direction, the direction of length of the resonant tube 20 as the Z direction, and the direction intersecting the Y and Z directions as the X direction. Here, the Y direction corresponds to one specific example of the first direction of the present invention, the Z direction to one specific example of the second direction of the present invention, and the X direction to one specific example of the third direction of the present invention. Figure 1A shows the YZ cross-section of the sound pressure reduction structure 1.

[0013] (Pipeline 10) Pipeline 10 has, for example, a rectangular prism shape. The XZ cross-section of pipeline 10 is, for example, a square. Pipeline 10 extending in the Y direction has a predetermined pipe diameter. The pipe diameter is the size of pipeline 10 in the Z direction. Pipeline 10 has, for example, a pipe diameter D at a position corresponding to the opening 20M of the resonance tube 20. Pipeline 10 has, for example, the same pipe diameter D from the first open end 11 to the second open end 12. The size of the pipe diameter of pipeline 10 may change between the first open end 11 and the second open end 12. The pipe diameter D is, for example, about 1 cm to 50 cm. The size of pipeline 10 in the Y direction is, for example, about 0.1 m to 5 m. Pipeline 10 has a predetermined primary resonance frequency. The primary resonance frequency of pipeline 10 is, for example, 50 Hz to 500 Hz.

[0014] The conduit 10 is made of, for example, a metal material or a resin material. Examples of metal materials include aluminum, titanium, magnesium, tungsten, iron, steel, chromium, chromium-molybdenum, nichrome-molybdenum, and alloys thereof. Examples of resin materials include polypropylene, polyethylene, acrylic resin, polymethyl methacrylate, polycarbonate, polyamide-imide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, triacetylcellulose, and others. Other materials such as carbon fiber reinforced plastic (CFRP), carbon fiber, and glass fiber reinforced plastic can also be used.

[0015] (Resonance Tube 20) Figure 1B shows an example of the XY cross-section of the resonance tube 20. The resonance tube 20 connected to the conduit 10 has a predetermined length (size in the Z direction in Figure 1A). The resonance tube 20 is, for example, a λ / 4 resonance tube. That is, the length of the resonance tube 20 is approximately 1 / 4 the length of the wavelength corresponding to any frequency of the sound wave propagating from the first open end 11 to the second open end 12 of the conduit 10. The resonance tube 20 has, for example, a rectangular prism shape, and the XY cross-section of the resonance tube 20 is, for example, a rectangle.

[0016] The resonant tube 20 has a bottom wall 21 and side walls 221, 222, 223, and 224. The bottom wall 21 is positioned opposite the opening 20M in the Z direction. That is, the other end of the resonant tube 20 in the direction of its length is closed. The bottom wall 21 has a rectangular planar shape. The side walls 221, 222, 223, and 224 connect the opening 20M to the bottom wall 21. For example, side wall 221 and side wall 223 face each other in the Y direction, and side wall 222 and side wall 224 face each other in the X direction. Each of the side walls 221, 222, 223, and 224 has a rectangular planar shape.

[0017] The bottom wall 21 and the side walls 221, 222, 223, and 224 are made of materials similar to those described for the pipe 10. The constituent materials of the bottom wall 21 and the side walls 221, 222, 223, and 224 may be the same as or different from the constituent materials of the pipe 10.

[0018] In the sound pressure reduction structure 1, the internal space 20T enclosed by the bottom wall 21 and side walls 221, 222, 223, and 224 is connected to the conduit 10 via an opening 20M. In such a sound pressure reduction structure 1, sound waves incident on the conduit 10 from the first open end 11 travel through the conduit 10 in the Y direction while being influenced by the internal space 20T near the opening 20M.

[0019] In this embodiment, a porous member 30 is provided in the internal space 20T of the resonant tube 20. When water accumulates in the internal space 20T, the porous member 30 absorbs the water and diffuses it into the conduit 10, for example, as follows. When the water accumulated in the internal space 20T wets a part of the porous member 30, this water is carried from the bottom wall 21 side to the opening 20M side by the capillary action of the porous member 30. At this time, the water vapor pressure of the porous member 30 near the opening 20M is higher than the water vapor pressure of the conduit 10, which is open at both ends, so water vapor diffuses from the porous member 30 into the conduit 10. The water vapor diffused into the conduit 10 is diffused to the outside of the conduit 10 through the first open end 11 and the second open end 12.

[0020] Such a porous member 30 is, for example, made of a sheet-shaped porous material. The porous material is a material having a plurality of fine pores, and it is preferable that adjacent pores are arranged in three-dimensional communication. This allows water absorbed by the porous member 30 to easily pass through the pores. It is preferable that the porous material has water absorption properties. Examples of porous materials include nonwoven fabrics, woven fabrics, sponges, and ceramics. It is preferable that the porous material is a material having a fibrous structure, and includes, for example, cotton, wool, silk, linen, rayon, cupro, nylon, aramid, polyvinyl chloride, polyester, acrylic, polyethylene, polypropylene, polyurethane, polylactic acid, acrylate, glass fiber, carbon fiber, or metal fiber. It is preferable that the porous material is a nonwoven fabric containing polyester and rayon, and more preferably 70% polyester and 30% rayon.

[0021] The porous member 30 is preferably adhered to at least one of the side walls 221, 222, 223, and 224. Thereby, since it becomes difficult for the porous member 30 to vibrate, it is possible to suppress a decrease in the sound pressure reduction performance due to the vibration of the porous member 30. The porous member 30 is preferably adhered from one end to the other end in the Z direction of the side wall 221 or the like. For example, the porous member 30 is continuously provided from one end to the other end in the Z direction of the side wall 221. Thereby, it becomes easier to suck up the water accumulated near the bottom wall 21 to the vicinity of the opening 20M. Further, the porous member 30 is preferably adhered to the bottom wall 21 as well. Thereby, it becomes easier to suck up the water accumulated near the bottom wall 21. The porous member 30 is preferably adhered to at least one of the side walls 221 and 223 facing each other in the Y direction. Thereby, the water sucked up to the vicinity of the opening 20M is easily diffused by the wind flowing through the conduit 10. In FIG. 1A, an example in which the porous member 30 is adhered to the side wall 221 on the second open end 12 side is shown, but the porous member 30 may be adhered to the side wall 223 on the first open end 11 side. The porous member 30 may be adhered to both the side walls 221 and 223.

[0022] A part of the porous member 30 preferably protrudes from the opening 20M into the conduit 10. Thereby, it becomes easier to diffuse the sucked-up water into the conduit 10.

[0023] The protruding amount P of the porous member 30 preferably satisfies the following formula (1). Thereby, the water sucked up by the porous member 3 is easily diffused into the conduit 10, and it is possible to suppress a decrease in the sound pressure reduction performance due to the protrusion of the porous member 30 into the conduit 10.

[0024]

[0025] In formula (1), the protruding amount P represents the distance from the position corresponding to the opening 20M to one end of the porous member 30 protruding into the conduit 10, and the pipe diameter D represents the size in the Z direction of the conduit 10 at the position corresponding to the opening 20M. The value of P / D is preferably 0.12 or less.

[0026] The porous member 30 is, for example, fixed in position in the internal pipe space 20T by an adhesive member 40 and is in close contact with the bottom wall 21 and the side wall 221. The adhesive member 40 is provided, for example, between the porous member 30 and each of the bottom wall 21 and the side wall 221. The adhesive member 40 is composed of, for example, a double-sided tape. Here, the adhesive member 40 corresponds to a specific example of the fixing member of the present invention. By using a double-sided tape as the adhesive member 40, the porous member 30 can be easily brought into close contact with the side wall 221 or the like.

[0027] The size S of the porous member 30 in the X direction ３０ is preferably less than or equal to the size S of the internal pipe space 20T in the X direction. ２０ This makes it easier to bring the porous member 30 into close contact with the side wall 221 or the side wall 223. One end of the porous member 30 in the X direction is in contact with, for example, the side wall 224. One end of the porous member 30 in the X direction may also be in contact with, for example, the side wall 222.

[0028] FIGS. 2, 3, and 4 show other examples of the XY cross-section of the resonance pipe 20. The porous member 30 may be disposed near the center in the X direction (FIG. 2). A plurality of porous members 30 may be provided in the internal pipe space 20T (FIG. 3). For example, two porous members 30 may be provided in the internal pipe space 20T, and one porous member 30 may be in contact with the side wall 222 and the other porous member 30 may be in contact with the side wall 224. One end of one porous member 30 in the X direction may be in contact with the side wall 224 and the other end may be in contact with the side wall 222 (FIG. 4).

[0029] [Function and Effect of the Sound Pressure Reduction Structure] In the sound pressure reduction structure 1, the sound wave incident on the pipe line 10 from the first open end 11 travels along the Y direction and is radiated from the second open end 12. At this time, interference of the sound wave occurs due to the resonance pipe 20 connected to the pipe line 10, and the sound pressure in a predetermined frequency band is reduced. In the present embodiment, since the porous member 30 is provided in the internal pipe space 20T of the resonance pipe 20, the water accumulated in the internal pipe space 20T is sucked up by the porous member 30. Therefore, the water accumulated in the internal pipe space 20T can be discharged without providing a drain hole or the like. Hereinafter, this function and effect will be described using a comparative example.

[0030] Figure 5 shows a sound pressure reduction structure 100 according to a comparative example. The resonant tube 200 of this sound pressure reduction structure 100 is not provided with a porous member (for example, the porous member 30 in Figure 1A). The resonant tube 200 has a drain hole 200H. In this respect, the sound pressure reduction structure 100 according to the comparative example differs from the sound pressure reduction structure 1 of this embodiment.

[0031] The drain hole 200H is provided, for example, in the bottom wall 21. When water accumulates in the internal space 200T of the resonant tube 200, the water is discharged from the drain hole 200H. In such a sound pressure reduction structure 100, the decrease in sound pressure reduction performance due to water accumulated in the internal space 200T is suppressed, but the sound pressure reduction performance decreases due to the drain hole 200H. Another possible method is to provide a valve in the drain hole 200H. In this method, with the valve closed, water gradually accumulates in the internal space 200T, and when the amount of water accumulated in the internal space 200T exceeds a threshold, the valve opens and the water in the internal space 200T is discharged. In this method, while the valve is closed, the sound pressure reduction performance changes due to the amount of water accumulated in the internal space 200T. Furthermore, while the valve is open, the sound pressure reduction performance decreases due to the drain hole 200H.

[0032] In contrast, in this embodiment, a porous member 30 is provided in the internal space 20T of the resonant tube 20, so water accumulated in the internal space 20T is drawn up to the porous member 30 and diffused into the conduit 10. Therefore, in the sound pressure reduction structure 1, water accumulated in the internal space 20T can be discharged without providing drainage holes. Consequently, drainage holes become unnecessary, and sound pressure reduction performance can be maintained. Thus, in the sound pressure reduction structure 1, it is possible to discharge water from the resonant space while maintaining sound pressure reduction performance.

[0033] In particular, when the resonant tube has a bent shape (not shown), it becomes difficult to drain water accumulated in the space inside the tube. In the sound pressure reduction structure 1 of this embodiment, a porous member 30 is provided in the space inside the tube 20T, so even when the resonant tube 20 has a bent shape, water accumulated in the space inside the tube 20T can be effectively drained.

[0034] Furthermore, it is preferable that the porous member 30 is in continuous contact with the side wall 221 and the like from one end to the other in the Z direction. This makes it easier to draw up water accumulated near the bottom wall 21 to the vicinity of the opening 20M.

[0035] Furthermore, it is preferable that a portion of the porous member 30 protrudes from the opening 20M into the conduit 10, and it is desirable that the amount P of protrusion of the porous member 30 satisfies the requirements of the above formula (1). This makes it easier for water absorbed by the porous member 30 to diffuse into the conduit 10, and suppresses the decrease in sound pressure reduction performance caused by the protrusion of the porous member 30 into the conduit 10. This is presumed to be because a boundary region exists in the conduit 10. The boundary region is the region located near the connection portion with the resonant tube 20. In this boundary region, the sound velocity is different from other regions in the conduit 10 due to the influence of air viscosity. Even if the porous member 30 protrudes into this boundary region, it is thought that the decrease in sound pressure reduction performance caused by the porous member 30 can be suppressed. It should be noted that the mechanism presumed above does not limit the technical scope of the present invention.

[0036] The following describes modified versions of the sound pressure reduction structure 1 described in the above embodiment. In order to avoid repetition, detailed explanations of configurations similar to those described in the above embodiment of the sound pressure reduction structure 1 will be omitted.

[0037] <Modified Version> Figure 6A shows the configuration of a modified sound pressure reduction structure 1A. In this modified sound pressure reduction structure 1A, the porous member 30 is in close contact with the side wall 221 by a partition 50. Except for this point, the modified sound pressure reduction structure 1A has the same configuration as the sound pressure reduction structure 1 of the above embodiment and produces the same effects. Here, the partition 50 corresponds to one specific example of the fixing member and pressing member of the present invention. A part of the porous member 30 may protrude from the opening 20M into the conduit 10 (see Figure 1A).

[0038] Figure 6B shows an example of the XY cross-section of the resonance tube 20. The partition 50 is, for example, a plate-like member having a rectangular planar (YZ plane) shape. The partition 50 is disposed, for example, at the center in the X direction of the internal space 20T of the tube. The partition 50 divides the internal space 20T into a first portion 20TA and a second portion 20TB. The first portion 20TA and the second portion 20TB are arranged side by side in the X direction with the partition 50 therebetween. The partition 50 is made of, for example, the same material as the resonance tube 20. The thickness (size in the X direction) of the partition 50 is, for example, about 0.1 mm to 10 mm.

[0039] For example, a porous member 30 is provided between the partition 50 and the side wall 221, and the partition 50 presses the porous member 30 against the side wall 221. Thereby, the porous member 30 adheres closely to the side wall 221.

[0040] The porous member 30 is provided, for example, in the first portion 20TA and the second portion 20TB. The size S in the X direction of the porous member 30 in the first portion 20TA ３０Ａ is preferably not more than the size S in the X direction of the first portion 20TA. ２０Ａ The size S in the X direction of the porous member 30 in the second portion 20TB ３０Ｂ is preferably not more than the size S in the X direction of the second portion 20TB. ２０Ｂ Thereby, it becomes easier to make the porous member 30 adhere closely to the side wall 221 in each of the first portion 20TA and the second portion 20TB.

[0041] Figure 7 shows another example of the XY cross-section of the resonance tube 20. The size S in the X direction of the porous member 30 in the first portion 20TA ３０Ａ may be the same as the size S in the X direction of the first portion 20TA. ２０Ａ The size S in the X direction of the porous member 30 in the second portion 20TB ３０Ｂ may be the same as the size S in the X direction of the second portion 20TB. ２０Ｂ

[0042] In the sound pressure reduction structure 1A according to the above modified example, a porous member 30 is provided in each of the first portion 20TA and the second portion 20TB of the resonant tube 20, so that water accumulated in the first portion 20TA and the second portion 20TB is drawn up to the porous member 30. Therefore, water accumulated in the first portion 20TA and the second portion 20TB can be discharged without providing drainage holes or the like.

[0043] Furthermore, in this sound pressure reduction structure 1A, since the first section 20TA and the second section 20TB each function as resonant tubes, the wavefront of the sound wave incident on the pipe 10 from the first open end 11 becomes more easily disturbed. Therefore, sound pressure can be reduced more effectively.

[0044] Furthermore, in this sound pressure reduction structure 1A, the porous member 30 is tightly attached to the side wall 221 by the partition 50, eliminating the need for adhesive members (for example, the adhesive member 40 in Figure 1A). Therefore, it is possible to reduce the number of parts and lower costs.

[0045] <Examples of Application> The sound pressure reduction structures 1 and 1A described in the above embodiments and modifications can be suitably used for various applications to reduce sound pressure. Since the sound pressure reduction structures 1 and 1A allow for drainage within the resonance space, it is preferable that they be mounted and used in a vehicle. Examples of applicable parts include, in the passenger compartment, the dash insulator, dash panel, floor carpet, spacers, door trim, sound-absorbing structure within the door trim, sound-absorbing structure within the compartment, instrument panel, instrument center box, instrument upper box, air conditioner housing, roof trim, sound-absorbing structure within the roof trim, sun visors, rear seat air conditioner ducts, cooling ducts for battery cooling systems in battery-equipped vehicles, cooling fans, center console trim, sound-absorbing structure within the console, parcel trim, parcel panel, seat headrests, front seat backs, rear seat backs, etc. Furthermore, in the trunk, it can be applied to the trunk floor trim, trunk board, trunk side trim, sound-absorbing structure within the trim, drafter cover, etc. Furthermore, it can be applied within the vehicle's frame and between panels, for example, to pillar trim and fenders. It can also be applied to components near the vehicle's engine.

[0046] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples.

[0047] 《Evaluation of Drainage Effect》 Under conditions of 25°C to 27°C and 50% to 60% relative humidity, 2.0 g of water was placed in a resonant tube, and the difference in drainage effect with and without a porous material was evaluated. In the resonant tube without a porous material, the amount of water decreased by 0.5 g, while in the resonant tube with a porous material, the amount of water decreased by 1.5 g. In other words, the drainage of water in the resonant tube was improved by the presence of the porous material. This is thought to be because the water accumulated in the resonant tube was drawn up by the porous material and diffused, for example, as water vapor.

[0048] 《Fabrication of Sound Pressure Reduction Structure》 The sound pressure reduction structure 1B shown in Figure 8 was fabricated as follows. Along the extending direction of the conduit 10, a back plate 61, a sound absorber 62, a speaker 63, a cylindrical tube 64, the conduit 10, and a microphone 67 were arranged. The back plate 61, sound absorber 62, speaker 63, and cylindrical tube 64 were placed on the first open end 11 side of the conduit 10, and the microphone 67 was placed on the second open end 12 side. The speaker 63 was fixed to the cylindrical tube 64 by a flange 68. The cylindrical tube 64 and the conduit 10 were connected using a flange 65 and a fitting 66. A reference microphone 69 was placed near the fitting 66. The resonant tube 20 was connected to the conduit 10 between the first open end 11 and the second open end 12. The distance in the Y direction between the center c of the resonant tube 20 and position 0 of the first open end 11 was 20 cm.

[0049] In sound pressure reduction structure 1B, a portion of the conduit 10 is inserted into the cylindrical pipe 64, and the first open end 11 of the conduit 10 is provided inside the cylindrical pipe 64. In sound pressure reduction structure 1B, only 0.12 m of the conduit 10 is inserted into the cylindrical pipe 64.

[0050] A 15 mm thick acrylic resin backplate 61 was used. A 50 mm thick White Cuon (registered trademark, manufactured by Tokyo Bouon Co., Ltd.) was used for the sound absorber 62. An FE103En (manufactured by Fostex) was used for the speaker 63. An acrylic resin cylindrical tube with an inner diameter of 10 cm was used for the cylindrical tube 64. The distance between flange 68 and flange 65 was 30 cm. The conduit 10 was a conduit with a square XZ plane with sides of 4.2 cm. That is, the tube diameter D was 4.2 cm. The size of the conduit 10 in the Y direction was 0.87 m. A resonant tube 20 was connected to the conduit 10 via an adapter (not shown).

[0051] Microphone 67 and reference microphone 69 were made using 378B02 (manufactured by PCB Piezotronics). Flanges 65 and 68 were made of acrylic resin with a thickness of 15 mm. Fitting 66 was made of acrylic resin with a thickness of 20 mm and a square opening with sides of 4.2 cm.

[0052] 《Evaluation of Sound Pressure Reduction Effect》 The FRF (Frequency Response Function) was measured in the sound pressure reduction structure 1B fabricated as described above. The specifications of the resonant tube differed in each example and comparative example. Table 1 below shows the specifications of the sound pressure reduction structure 1B used in each example and comparative example. In each example and comparative example, a λ / 4 resonant tube (tube length: 0.2 m, size in the X direction (S)) was used. ２０ ): 16mm was used.

[0053]

[0054] [Example 1] In Example 1, a porous member was placed in the internal space of a λ / 4 resonant tube. A sheet-like nonwoven fabric (70% polyester, 30% rayon) was used as the porous member. The size of the porous member in the X direction (S ３０ The protrusion was 4 mm. The porous member was positioned in the center of the internal space of the pipe in the X direction (see Figure 2). The porous member was attached in close contact with the side wall on the incident end side or the side wall on the radiating end side in the Y direction. The porous member was attached to the side wall using an adhesive. Double-sided tape was used as the adhesive. The porous member was attached continuously from one end to the other in the Z direction of the side wall. The protrusion amount P was 0. The FRF when the porous member was attached in close contact with the side wall on the incident end side of the sound wave was -34.3 dB. The FRF when the porous member was attached in close contact with the side wall on the radiating end side of the sound wave was -33.9 dB.

[0055] [Example 2] The FRF was measured in the same manner as in Example 1, except that the porous member was placed at one end of the internal space of the pipe in the X direction (see Figure 1B). The FRF was -34.5 dB when the porous member was in close contact with the side wall on the incident end side of the sound wave. The FRF was -34.3 dB when the porous member was in close contact with the side wall on the radiating end side of the sound wave.

[0056] [Example 3] The FRF was measured in the same manner as in Example 1, except that two porous members were placed in the space inside the pipe. The size of each of the two porous members in the X direction (S ３０The diameter was 4 mm. The porous members were placed at both ends of the internal space of the pipe in the X direction (see Figure 3). The FRF when the porous member was in close contact with the side wall on the sound wave incidence end was -34.0 dB. The FRF when the porous member was in close contact with the side wall on the sound wave radiation end was -33.7 dB.

[0057] [Example 4] Size of the porous member in the X direction (S ３０ The FRF was measured in the same manner as in Example 1, except that the size of the porous member in the X direction (S ３０ The diameter was 8 mm. The FRF when the porous material was in close contact with the side wall on the incident end of the sound wave was -33.5 dB. The FRF when the porous material was in close contact with the side wall on the radiating end of the sound wave was -33.1 dB.

[0058] [Example 5] Size of the porous member in the X direction (S ３０ The FRF was measured in the same manner as in Example 2, except that the size of the porous member in the X direction (S ３０ The diameter was 8 mm. The FRF when the porous material was in close contact with the side wall on the incident end of the sound wave was -34.0 dB. The FRF when the porous material was in close contact with the side wall on the radiating end of the sound wave was -33.8 dB.

[0059] [Example 6] Size of the porous member in the X direction (S ３０ The FRF was measured in the same manner as in Example 1, except that the size of the porous member in the X direction (S ３０ The width was 16 mm. That is, the porous material was in close contact with the entire surface of the side wall. The FRF when the porous material was in close contact with the side wall on the sound wave incidence end side was -33.8 dB. The FRF when the porous material was in close contact with the side wall on the sound wave radiation end side was -33.3 dB.

[0060] [Comparative Example 1] In Comparative Example 1, the porous member and adhesive member were not placed in the internal space of the λ / 4 resonant tube. Except for this, the FRF was measured in the same manner as in Example 1. The FRF was -34.7 dB.

[0061] [Comparative Example 2] In Comparative Example 2, no porous member was placed in the internal space of the λ / 4 resonant tube; only an adhesive member was placed. Except for this difference, the FRF was measured in the same manner as in Example 1. The FRF when the adhesive member was in close contact with the side wall on the sound wave incidence end was -33.9 dB. The FRF when the porous member was in close contact with the side wall on the sound wave radiation end was -33.9 dB.

[0062] [Comparative Example 3] In Comparative Example 3, a drain hole was provided in the bottom wall of the λ / 4 resonant tube. Except for this, the FRF was measured in the same manner as in Comparative Example 1. The FRF was -22.7 dB.

[0063] Examples 1 to 6, in which porous members were placed in the internal space of the pipe, showed a sound pressure reduction effect equivalent to that of Comparative Examples 1 and 2. In Comparative Example 3, in which a drainage hole was provided in the λ / 4 resonant pipe, the sound pressure reduction effect was reduced compared to Comparative Examples 1 and 2. From these results, it can be said that the sound pressure reduction structure according to Examples 1 to 6 allows for the discharge of water from the resonant space while maintaining the sound pressure reduction effect.

[0064] Next, for Examples 1 to 6, the FRF was measured while varying the P / D value.

[0065] Figures 9A and 9B show the relationship between P / D and FRF for Examples 1 to 3. Figure 9A shows the relationship between P / D and FRF when the porous member is in close contact with the side wall on the incident end side of the sound wave, and Figure 9B shows the relationship between P / D and FRF when the porous member is in close contact with the side wall on the radiating end side of the sound wave.

[0066] Figures 10A and 10B show the relationship between P / D and FRF in Examples 4 and 5. Figure 10A shows the relationship between P / D and FRF when the porous member is in close contact with the side wall on the incident end side of the sound wave, and Figure 10B shows the relationship between P / D and FRF when the porous member is in close contact with the side wall on the radiating end side of the sound wave.

[0067] Figures 11A and 11B illustrate the relationship between P / D and FRF in Example 6. Figure 11A shows the relationship between P / D and FRF when the porous member is in close contact with the side wall on the incident end side of the sound wave, and Figure 11B shows the relationship between P / D and FRF when the porous member is in close contact with the side wall on the radiating end side of the sound wave.

[0068] Figures 9A to 11B show a change in the sound pressure reduction effect when P / D is 0.24. In other words, a sufficient sound pressure reduction effect was confirmed when the above equation (1) was satisfied.

[0069] [Example 7] The FRF was measured in the same manner as in Example 1, except that the porous member was in close contact with the side wall by a partition. The space inside the pipe was divided into a first part and a second part aligned in the X direction by a partition. The porous member was placed so as to span the first part and the second part (Figure 6B). In this Example 7, the size of the porous member in the X direction (S ３０Ａ , S ３０Ｂ The FRF was measured by changing the S value. ２０Ａ , S ２０Ｂ It was 7 mm.

[0070] Figure 12 shows S of Example 7. ３０Ａ / S ２０Ａ S ３０Ｂ / S ２０Ｂ This shows the relationship between S and FRF. ３０Ａ / S ２０Ａ and S ３０Ｂ / S ２０Ｂ The arrangement of the porous members was adjusted so that the values ​​were the same. In Figure 12, the open circles represent the results for porous members arranged in a dry state, and the filled circles represent the results for porous members arranged in a wet state.

[0071] In Example 7, S ３０Ａ / S ２０Ａ and S ３０Ｂ / S ２０Ｂ A change in the sound pressure reduction effect was observed when the value was 1. In other words, a sufficient sound pressure reduction effect was confirmed when the size of the porous material in the X direction was less than or equal to the size of the space inside the pipe in the X direction. Also, S ３０Ａ / S ２０Ａ and S ３０Ｂ / S ２０Ｂ When the value is 1, a higher sound pressure reduction effect was observed in the wet porous material compared to the dry porous material. This is thought to be because the wet porous material adheres more easily to the side walls.

[0072] The sound pressure reduction structure of the present invention has been described above using embodiments, modifications, and examples. However, the present invention can be appropriately added, modified, and omitted by those skilled in the art within the scope of its technical concept. For example, the configuration, shape, and size of each part of the sound pressure reduction structure described in the above embodiments are examples, and other configurations, shapes, and sizes may be used.

[0073] For example, in the above embodiment, an example was described in which one resonance tube 20 is connected to the conduit 10, but multiple resonance tubes 20 may be connected to the conduit 10.

[0074] Furthermore, although a straight resonant tube 20 is shown in Figure 1A, for example, the resonant tube 20 may have a bent shape. The resonant tube 20 may also be composed of resonant tubes other than λ / 4 resonant tubes.

[0075] Furthermore, although the above embodiment describes an example in which the conduit 10 has a quadrilateral planar shape (XZ plane), the conduit 10 may have other planar shapes. For example, the conduit 10 may have a planar shape with five or more polygons, or it may have a planar shape such as a circle or an ellipse.

[0076] The following embodiments are also included in the scope of the present invention: a sound pressure reduction structure according to claim 1 having the features of claim 2; a sound pressure reduction structure according to claim 1 or 2 having the features of claim 3; a sound pressure reduction structure according to any one of claims 1 to 3 having the features of claim 4; a sound pressure reduction structure according to any one of claims 1 to 4 having the features of claim 5; a sound pressure reduction structure according to any one of claims 1 to 5 having the features of claim 6; a sound pressure reduction structure according to any one of claims 1 to 6 having the features of claim 7; a sound pressure reduction structure according to claim 7 having the features of claim 8; a sound pressure reduction structure according to claim 5 having the features of claim 9; a sound pressure reduction structure according to claim 9 having the features of claim 10; a sound pressure reduction structure according to claim 10 having the features of claim 11; a sound pressure reduction structure according to any one of claims 1 to 11 having the features of claim 12; a sound pressure reduction structure according to any one of claims 1 to 12 having the features of claim 13; a sound pressure reduction structure according to any one of claims 1 to 13 having the features of claim 14; a sound pressure reduction structure according to any one of claims 1 to 14 having the features of claim 15.

Claims

1. A sound pressure reduction structure comprising a conduit extending in a first direction and a resonant tube having an opening connected to the conduit, wherein the resonant tube includes a bottom wall facing the opening in a second direction intersecting the first direction, a side wall connecting the opening to the bottom wall, and a porous member provided in the internal space of the tube surrounded by the side wall and the bottom wall.

2. The sound pressure reduction structure according to claim 1, wherein the porous member has a sheet shape.

3. The sound pressure reduction structure according to claim 1, wherein the porous member is in close contact with at least one of a pair of side walls facing each other in the first direction.

4. The sound pressure reduction structure according to claim 3, wherein the porous member is in continuous contact with the side wall from one end to the other in the second direction.

5. The sound pressure reduction structure according to claim 4, further comprising a fixing member for fixing the position of the porous member so that the porous member is in close contact with the side wall.

6. The sound pressure reduction structure according to claim 5, wherein the fixing member includes an adhesive member for adhering the porous member to the side wall.

7. The sound pressure reduction structure according to claim 6, wherein a portion of the porous member is positioned to protrude from the opening into the conduit.

8. The sound pressure reduction structure according to claim 7, wherein the amount of protrusion P of the porous member satisfies the following formula (1). In equation (1), the protrusion amount P represents the distance from the position corresponding to the opening to one end of the porous member protruding into the pipeline, and the pipe diameter D represents the size of the pipeline in the second direction at the position corresponding to the opening.

9. The sound pressure reduction structure according to claim 5, wherein the fixing member includes a pressing member that presses the porous member against the side wall.

10. The sound pressure reduction structure according to claim 9, wherein the pressing member includes a partition that divides the internal space of the pipe into a first portion and a second portion, and the first portion and the second portion are arranged side by side in a third direction intersecting the first direction and the second direction.

11. The sound pressure reduction structure according to claim 10, wherein the porous member is provided in the first portion and the second portion, and in the first portion, the size of the porous member in the third direction is less than or equal to the size of the first portion in the third direction, and in the second portion, the size of the porous member in the third direction is less than or equal to the size of the second portion in the third direction.

12. The sound pressure reduction structure according to claim 1, wherein the size of the porous member in a third direction intersecting the first and second directions is less than or equal to the size of the internal space of the pipe in the third direction.

13. The sound pressure reduction structure according to claim 1, wherein the size of the resonant tube in the second direction is 1 / 4 of the wavelength corresponding to the resonant frequency of the conduit.

14. The sound pressure reduction structure according to claim 1, wherein the porous member has water absorption properties.

15. The sound pressure reduction structure according to claim 1, wherein the porous member includes a nonwoven fabric.

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