Sound pressure reducing structure

Abstract

[Problem] To provide a sound pressure reducing structure capable of reducing sound pressure near the primary resonance frequency of a pipeline while reducing installation space. [Solution] This sound pressure reducing structure comprises: a pipeline that has a first open end and a second open end in the extending direction; a first λ / 4 resonance pipe and a second λ / 4 resonance pipe that each have a resonance frequency which is higher than the primary resonance frequency of the pipeline and is lower than the secondary resonance frequency of the pipeline; and a connection part that is provided between the first open end and the second open end, connects the first λ / 4 resonance pipe and the second λ / 4 resonance pipe to the pipeline in a manner as to be disposed with a gap therebetween in the extending direction, and satisfies equation (1). The sound pressure reducing structure has: a change position b1 at which an acoustic impedance zb at the primary resonance frequency of the pipeline discontinuously changes along the extending direction; and a position a1 that is the closest to the first open end among a plurality of points of intersection between a differential zb' of the acoustic impedance zb and a differential za' of an acoustic impedance za of the pipeline at the resonance frequencies of the first λ / 4 resonance pipe and the second λ / 4 resonance pipe. The position of the connection part in the extending direction is between the position a1 and the change position b1.

Description

Sound pressure reduction structure

[0001] The present 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. Since quietness is required from noise both inside and outside the car, an effective sound pressure reduction structure is necessary for cars.

[0003] A sound pressure reduction structure has been proposed that includes a pipe and a λ / 4 resonance tube connected to the pipe (for example, JP 2015-169092 A). The λ / 4 resonance tube is connected in a branch-like manner to the side of the pipe in a direction intersecting the extension direction of the pipe. This λ / 4 resonance tube has, for example, the same resonance frequency as the primary resonance frequency of the pipe.

[0004] Since the resonance frequency of a λ / 4 resonance tube depends on the length of the tube, it is difficult to change the length of a λ / 4 resonance tube that is tuned to the same resonance frequency as the primary resonance frequency of the tube. This requires space around the tube to accommodate the λ / 4 resonance tube, which tends to increase the installation space for the sound pressure reduction structure.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a sound pressure reducing structure that can reduce sound pressure around the primary resonance frequency of a pipe while reducing the installation space.

[0006] a first λ / 4 resonance tube and a second λ / 4 resonance tube, each having a resonance frequency higher than a primary resonance frequency of the pipe and lower than a secondary resonance frequency of the pipe; and a connection portion provided between the first open end and the second open end, connecting the first λ / 4 resonance tube and the second λ / 4 resonance tube to the pipe so as to be spaced apart in the extension direction, and satisfying the following formula (1):

[0007]

[0008] In formula (1), L represents the size of the connection portion in the extension direction, and D represents the size of the pipe in the radial direction intersecting the extension direction at the position where the connection portion is provided.

[0009] 1-3 is a diagram showing the configuration of a sound pressure reduction structure according to an embodiment of the present invention, along with changes in acoustic impedance. FIG. 1 is a diagram showing a cross-sectional configuration of a connection portion between a conduit and a λ / 4 resonance tube shown in FIG. 1. FIG. 1 is a diagram showing an example of a planar configuration of the connection portion shown in FIG. 1. FIG. 3 is a diagram showing another example of a planar configuration of the connection portion shown in FIG. 3. FIG. 1-3 is a diagram showing the configuration of a sound pressure reduction structure according to Modification 1. FIG. 1-3 is a diagram showing the configuration of a sound pressure reduction structure according to Modification 2. FIG. 1-3 is a diagram for explaining the configuration of the sound pressure reduction structure used in Reference Examples 1-1 and 1-2. FIG. 1-3 is a diagram showing the evaluation results of the sound pressure reduction effect of Reference Example 1-1. FIG. 1-3 is a diagram showing the evaluation results of the sound pressure reduction effect of Reference Example 1-2. FIG. 1-3 is a diagram for explaining the configuration of the sound pressure reduction structure used in Reference Examples 2 to 5 and Examples 1 to 12. FIG. 1-3 is a diagram showing the evaluation results of the sound pressure reduction effect at 340 Hz for Reference Examples 2 to 5. FIG. 1-3 is a diagram showing the evaluation results of the sound pressure reduction effect at 200 Hz for Reference Examples 2 to 5. FIG. 1-3 is a diagram showing the evaluation results of the sound pressure reduction effect at 340 Hz for Examples 1 to 5. FIG. 1-3 is a diagram showing the evaluation results of the sound pressure reduction effect at 200 Hz for Examples 1 to 5. 1 is a diagram showing the evaluation results of the sound pressure reduction effect at 200 Hz for Examples 6 to 10. FIG. 2 is a diagram showing the evaluation results of the sound pressure reduction effect at 200 Hz for Examples 11 and 12.

[0010] a first λ / 4 resonance tube and a second λ / 4 resonance tube, each having a resonance frequency higher than a primary resonance frequency of the pipe and lower than a secondary resonance frequency of the pipe; and a connection portion provided between the first open end and the second open end, connecting the first λ / 4 resonance tube and the second λ / 4 resonance tube to the pipe so as to be spaced apart in the extension direction, and satisfying the following formula (1):

[0011]

[0012] In formula (1), L represents the size of the connection portion in the extension direction, and D represents the size of the pipe in the radial direction intersecting the extension direction at the position where the connection portion is provided.

[0013] According to the sound pressure reduction structure of this embodiment, the resonance frequencies of the first λ / 4 resonance tube and the second λ / 4 resonance tube are higher than the primary resonance frequency of the pipe. Therefore, the pipe length is shorter than that of a λ / 4 resonance tube having the same resonance frequency as the primary resonance frequency of the pipe. Furthermore, the connection portion connecting the first λ / 4 resonance tube and the second λ / 4 resonance tube to the pipe satisfies the above formula (1), and the position of the connection portion in the extension direction is between position a1 and change position b1. Therefore, sound pressure around the primary resonance frequency of the pipe is reduced. Furthermore, since the first λ / 4 resonance tube and the second λ / 4 resonance tube are arranged with a gap in the extension direction at the connection portion, the space occupied by the λ / 4 resonance tube is smaller than when a single λ / 4 resonance tube is arranged over the entire connection portion. Therefore, it is possible to reduce the installation space while reducing sound pressure around the primary resonance frequency of the pipe.

[0014] Hereinafter, embodiments of the present invention will be described 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 the convenience of explanation and may differ from the actual ratios. In this specification, the range "M to N" means "M or more and N or less." Furthermore, unless otherwise specified, operations and measurements of physical properties, etc. are performed under conditions of room temperature (20 to 25°C) and relative humidity of 40 to 50%.

[0015] 1 shows the configuration of a sound pressure reduction structure 1 according to one embodiment of the present invention, along with changes in acoustic impedance. The sound pressure reduction structure 1 has a conduit 10, a first λ / 4 resonance tube 21, a second λ / 4 resonance tube 22, and a connection portion 30. The first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are connected to the conduit 10 via the connection portion 30.

[0016] 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 extension direction, and a second open end 12 is provided at the other end. For example, sound entering the conduit 10 from the first open end 11 propagates along the extension direction of the conduit 10 and is radiated from the second open end 12. The first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are connected in a direction intersecting the extension direction of the conduit 10. That is, in the sound pressure reduction structure 1, the pipe lengths of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are set in a direction intersecting the extension direction of the conduit 10. A connection portion 30 connecting the conduit 10 to the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 is provided between the first open end 11 and the second open end 12 in the extension direction of the conduit 10. In the following description, the extension direction of the pipe 10 will be referred to as the Y direction, the pipe length direction of the first λ / 4 resonance pipe 21 and the second λ / 4 resonance pipe 22 will be referred to as the Z direction, and the direction intersecting the Y direction and the Z direction will be referred to as the X direction.

[0017] (Conduit 10) FIG. 2 shows an XZ cross section of the connection portion between the conduit 10 and the first λ / 4 resonance tube 21. Although not shown, for example, the connection portion between the conduit 10 and the second λ / 4 resonance tube 22 also has a configuration similar to the XZ cross section shown in FIG. 2. The conduit 10 has, for example, a square prism shape with four flat surfaces (flat surfaces 13, 14, 15, and 16). In the conduit 10, for example, flat surfaces 13 and 14 are arranged opposite each other in the Z direction, and flat surfaces 15 and 16 are arranged opposite each other in the X direction. For example, flat surface 14 has two slits spaced apart and extending in the Y direction, and adapters with through holes are provided in these slits. For example, the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are inserted into the through holes of the adapters. The XZ cross section of the conduit 10 is, for example, square.

[0018] The conduit 10 extending in the Y direction has a predetermined size in the radial direction, i.e., the Z direction. In other words, the radial size of the conduit 10 is the size of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 in the tube length direction. The radial size of the conduit 10 is, for example, the distance between the planes 13 and 14 that face each other in the Z direction. The conduit 10 has a radial size D, for example, at the position where the connection portion 30 is provided. The conduit 10 has the same radial size (size D) from the first open end 11 to the second open end 12, for example. The radial size D of the conduit 10 may vary from the first open end 11 to the second open end 12. The size D of the conduit 10 is, for example, approximately 1 cm to 50 cm.

[0019] The conduit 10 has a predetermined size in a width direction, i.e., the X direction, which intersects the extension direction and the radial direction. The width direction size of the conduit 10 is, for example, the distance between a plane 15 and a plane 16 that face each other in the X direction. The conduit 10 has a width direction size W10, for example, at a position where the connection portion 30 is provided. The conduit 10 has the same width direction size (size W10), for example, from the first open end 11 to the second open end 12. The width direction size W10 of the conduit 10 may vary from the first open end 11 to the second open end 12. The size W10 of the conduit 10 is, for example, approximately 1 cm to 50 cm.

[0020] The size of the conduit 10 in the Y direction is, for example, about 0.1 m to 5 m. The conduit 10 has a predetermined primary resonance frequency F ｂ The first resonance frequency F ｂ is, for example, 68 Hz to 3500 Hz.

[0021] The first resonance frequency F of the pipe 10 ｂ The acoustic impedance zb at varies along the Y direction. The dashed line in FIG. 1 indicates the first resonance frequency F ｂ The change in the acoustic impedance zb in the Y direction is shown. ｂThere is a position in the Y direction where the acoustic impedance zb changes discontinuously. Hereinafter, this position in the Y direction where the acoustic impedance zb changes discontinuously will be referred to as a change position b1. The change position b1 is, for example, the center position of the pipe 10 in the Y direction.

[0022] The conduit 10 is made of, for example, a metal material or a resin material. Examples of metal materials that can be used include aluminum, titanium, magnesium, tungsten, iron, steel, chromium, chromium molybdenum, nichrome molybdenum, and alloys thereof. Examples of resin materials that can be used include polypropylene, polyethylene, acrylic resin, polymethyl methacrylate, polycarbonate, polyamide-imide, polyarylate, polyetherimide, polyacetal, polyether ether ketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, and triacetyl cellulose. Other materials that can be used include carbon fiber reinforced plastic (CFRP), carbon fiber, and glass fiber reinforced plastic.

[0023] (First λ / 4 Resonance Tube 21 and Second λ / 4 Resonance Tube 22) The first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 connected to the pipeline 10 have a predetermined pipe length (size in the Z direction in FIG. 1 ). The pipe lengths of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are, for example, 0.05 m to 1 m. The first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 have, for example, the same pipe length. The first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 each have an opening at one end in the pipe length direction. The opening of each of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 is connected to the pipeline 10 via a connection part 30.

[0024] The other ends in the pipe length direction of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are closed. Therefore, a sound wave entering the pipe 10 from the first open end 11 travels in the Y direction through the pipe 10 while being influenced by the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 near the connection portion 30, and is emitted from the second open end 12. The openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 each have, for example, a rectangular planar shape (see FIG. 3 described later).

[0025] In this embodiment, the resonant frequencies F of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are a is the primary resonance frequency F of the pipe 10 ｂ and the second resonance frequency F ｃ For example, the first resonance frequency F ｂ When the frequency is about 200 Hz, the secondary resonance frequency F ｃ is about 390 Hz, and the resonant frequency F of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 is about 390 Hz. a is about 330 Hz to 350 Hz. ｂ In comparison with the case where λ / 4 resonance tubes having the same resonance frequency are used, the lengths of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 can be shortened, and the size of the sound pressure reduction structure 1 in the Z direction can be reduced. For example, if the resonance frequency of the first λ / 4 resonance tube 21 and the resonance frequency of the second λ / 4 resonance tube 22 are the same, and the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 each have a resonance frequency F a The resonance frequency of the first λ / 4 resonance tube 21 and the resonance frequency of the second λ / 4 resonance tube 22 may be different. In this case, the resonance frequency F a is the one having the higher (larger) resonance frequency out of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 .

[0026] The resonance frequency F of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 aThe acoustic impedance za of the pipe 10 at the resonant frequency F varies along the Y direction. a The change in the acoustic impedance za in the Y direction is shown. a The differential za' of the acoustic impedance za and the first resonance frequency F of the pipe 10 ｂ Among the multiple intersections of the differential za' of the acoustic impedance za and the differential zb' of the acoustic impedance zb, the position closest to the first open end 11 will be referred to as position a1 below.

[0027] The first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are arranged with a gap in the Y direction. For example, the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are arranged in this order from the first open end 11 side ( FIG. 1 ). The gap between the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 is a space configured to allow, for example, elements other than the sound pressure reduction structure 1 to be present. For example, air or the like is present in the gap between the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22.

[0028] The first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are made of, for example, the same material as that described for the above-mentioned pipe 10. The constituent material of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 and the constituent material of the pipe 10 may be the same as or different from each other.

[0029] (Connection portion 30) The connection portion 30 is a portion that connects the openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 to the pipeline 10. Due to the presence of this connection portion 30, the sound wave paths of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 and the sound wave path of the pipeline 10 are connected.

[0030] In this embodiment, the position of the connection portion 30 in the Y direction is provided between the position a1 and the change position b1 of the pipeline 10 (position a1 and change position b1 are not included). As a result, the first resonance frequency F ｂ A resonant frequency F aEven when the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 having the first resonance frequency F ｂ The surrounding sound pressure is effectively reduced.

[0031] 3 shows the planar (XY plane) shape of the connection portion 30. The openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 connected to the pipe 10 have, for example, the same size. The openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 each have a size W20 in the X direction and a size L20 in the Y direction.

[0032] At the connection portion 30, the opening of the first λ / 4 resonance tube 21 and the opening of the second λ / 4 resonance tube 22 are arranged in the Y direction with a gap of size G between them. At the connection portion 30, the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are arranged so that the position of the center of gravity C21 in the X direction is aligned with the position of the center of gravity C22.

[0033] The connection portion 30 has, for example, a rectangular planar shape (XY plane) and has predetermined sizes in the X and Y directions. The size of the connection portion 30 in the X direction is, for example, approximately the same as the X direction size W20 of the openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22. The size of this connection portion 30 in the X direction is smaller than the width direction size W10 of the pipe 10, but is preferably closer to the width direction size W10 of the pipe 10. The connection portion 30 is disposed, for example, approximately at the center of the pipe 10 in the X direction. For example, the centers of gravity C21 and C22 are disposed approximately at the center of the pipe 10 in the X direction.

[0034] The connection portion 30 has a predetermined size L in the Y direction. The size L of the connection portion 30 is, for example, the sum of the size of the openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 in the Y direction and the size G of the gap. In this embodiment, the size L of the connection portion 30 satisfies the following formula (1). In other words, the size L of the connection portion 30 in the Y direction is larger than half the size D of the duct 10. As will be described in detail later, this allows the sound pressure reduction structure 1 to reduce the primary resonance frequency F of the duct 10. ｂ The surrounding sound pressure is reduced.

[0035]

[0036] In formula (1), L represents the size of the connection portion 30 in the Y direction, and D represents the size of the pipeline 10 in the Z direction at the position where the connection portion 30 is provided.

[0037] Furthermore, in this connection portion 30, a gap is provided between the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22, so the space occupied by the λ / 4 resonance tube is smaller than when one λ / 4 resonance tube is arranged over the entire connection portion 30. It is preferable that the size G of the gap between the opening of the first λ / 4 resonance tube 21 and the opening of the second λ / 4 resonance tube 22 satisfies the following formula (2). As a result, the primary resonance frequency F of the pipe 10 ｂ The surrounding sound pressure can be reduced, and the space occupied by the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 in the connecting portion 30 can be reduced.

[0038]

[0039] In equation (2), L represents the size of the connection portion 30 in the Y direction, and G represents the size of the gap between the opening of the first λ / 4 resonance tube 21 and the opening of the second λ / 4 resonance tube 22 in the Y direction.

[0040] 4 shows another example of the planar (XY plane) shape of the connection portion 30. As shown in FIG. 4 , the openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 connected to the pipe 10 may have different sizes. For example, the opening of the first λ / 4 resonance tube 21 has a size L21 in the Y direction, and the opening of the second λ / 4 resonance tube 22 has a size L22 in the Y direction. In this case, the size of the opening of the second λ / 4 resonance tube 22 is preferably larger than the size of the opening of the first λ / 4 resonance tube 21. In other words, the size of the opening of the second λ / 4 resonance tube 22 arranged on the radiation end side is preferably larger than the size of the opening of the first λ / 4 resonance tube 21 arranged on the incident end side. This more effectively reduces the first-order resonant frequency F ｂIt is possible to reduce the surrounding sound pressure. [Effects of the Sound Pressure Reduction Structure] In the sound pressure reduction structure 1, sound waves incident on the duct 10 from the first open end 11 travel along the Y direction and are radiated from the second open end 12. In this embodiment, the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 connected to the duct 10 via the connection part 30 are radiated at the primary resonance frequency F ｂ and the second resonance frequency F ｃ A resonant frequency F lower than ａ As a result, the first resonance frequency F ｂ Compared to the case where a λ / 4 resonance tube having the same resonant frequency as the first λ / 4 resonance tube 21 is connected to the duct 10, the length of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 is shorter, and therefore the size of the sound pressure reduction structure 1 in the Z direction is reduced. This will be explained below.

[0041] The first resonance frequency F of the pipe 10 ｂ When reducing the surrounding sound pressure, the primary resonance frequency F ｂ However, since the resonance frequency of the λ / 4 resonance tube depends on its length, it is possible to use a λ / 4 resonance tube having the same resonance frequency as the primary resonance frequency F of the tube. ｂ In other words, in a sound pressure reduction structure having such a λ / 4 resonance tube, the size in the direction intersecting the extension direction of the pipe 10 (for example, the Z direction) also tends to be large.

[0042] In contrast to this, in this embodiment, the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 connected to the pipe 10 have a first resonance frequency F ｂ and the second resonance frequency F ｃ A resonant frequency F lower than ａ Therefore, the first resonance frequency F ｂ The lengths of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are shorter than those of the λ / 4 resonance tubes having the same resonant frequency as the first λ / 4 resonance tube 21. This reduces the size of the sound pressure reduction structure 1 in the Z direction.

[0043] Furthermore, since the size L of the connecting portion 30 in the Y direction satisfies the above formula (1), the primary resonance frequency F ｂ and the second resonance frequency F ｃ A resonant frequency F lower than ａ Even if the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 have the first resonance frequency F ｂ The sound pressure in the surroundings is reduced. This is presumably because the wavefront of the sound wave traveling in the Y direction through the duct 10 is easily disturbed by the connection part 30 that satisfies the formula (1), and the mismatch in acoustic impedance increases. Therefore, in the sound pressure reduction structure 1, the primary resonance frequency F ｂ It is possible to reduce the surrounding sound pressure. Note that the mechanism presumed as described above does not limit the technical scope of the present invention.

[0044] Furthermore, in the sound pressure reduction structure 1, the position of the connection portion 30 in the Y direction is set between the position a1 and the change position b1. This more effectively reduces the primary resonance frequency F ｂ It is possible to reduce the surrounding sound pressure.

[0045] In addition, since a gap is provided between the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 in the connection part 30, the space occupied by the λ / 4 resonance tubes is smaller than when one λ / 4 resonance tube is arranged in the entire connection part 30. Furthermore, since the wavefront of the sound wave traveling in the Y direction in the pipe 10 is disturbed near the openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22, the first resonance frequency F ｂ Therefore, it is possible to reduce the installation space of the sound pressure reduction structure 1 and more effectively reduce the sound pressure around the primary resonance frequency of the pipe.

[0046] In addition, by aligning the position of the center of gravity C21 and the position of the center of gravity C22 in the X direction, the primary resonance frequency F ｂFurthermore, by disposing the centers of gravity C21 and C22 at the center of the pipe 10 in the X direction, the primary resonance frequency F ｂ This makes it possible to reduce the surrounding sound pressure even more effectively.

[0047] In addition, in the sound pressure reduction structure, the transmission loss TL ｓｂ The larger the transmission loss TL, the more effectively the sound pressure is reduced. ｓｂ is the cross-sectional area of ​​the pipe S ０ is the same, the cross-sectional area S of the λ / 4 resonance tube ｂ The larger the cross-sectional area S ｂ is, for example, the sum of the opening areas of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22. In the sound pressure reduction structure 1 having a plurality of λ / 4 resonance tubes, specifically the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22, this cross-sectional area S ｂ Therefore, the primary resonance frequency F ｂ It is possible to reduce the surrounding sound pressure.

[0048]

[0049] In formula (4), S ０ is the cross-sectional area of ​​the pipe, S ｂ is the cross-sectional area of ​​the λ / 4 resonance tube, k is a constant, l ｂ represents the size of the pipe in the Y direction.

[0050] Furthermore, since the conduit 10 has a pair of opposing flat surfaces 13 and 14, the connecting portion 30 can be provided on one of the pair of flat surfaces 13 and 14 (flat surface 14 in FIG. 2). This increases the mismatch in acoustic impedance, and more effectively reduces the primary resonance frequency F ｂ It is possible to reduce the surrounding sound pressure.

[0051] The following describes modifications of the sound pressure reduction structure 1 described in the above embodiment. In order to avoid duplication of explanation, detailed descriptions of components similar to those of the sound pressure reduction structure 1 described in the above embodiment will be omitted.

[0052] <Modification 1> Fig. 5 shows the configuration of the main parts of a sound pressure reduction structure 1A according to Modification 1. Fig. 5 shows an example of the planar (XY plane) configuration of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 of the sound pressure reduction structure 1A. In the sound pressure reduction structure 1A, partitions (partitions 21P and 22P described below) are provided inside each of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22. Except for this point, the sound pressure reduction structure 1A according to Modification 1 has the same configuration as the sound pressure reduction structure 1 of the above embodiment and provides the same functions and effects.

[0053] The first λ / 4 resonance tube 21 has, for example, a partition 21P therein. The first λ / 4 resonance tube 21 has a plurality of spaces 201-216 separated in the X and Y directions by this partition 21P. The second λ / 4 resonance tube 22 has, for example, a partition 22P therein. The second λ / 4 resonance tube 22 has a plurality of spaces 217-232 separated in the X and Y directions by this partition 22P. The partitions 21P and 22P are made of, for example, the same material as the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22. The thickness of the partitions 21P and 22P is, for example, approximately 0.1 mm to 10 mm.

[0054] In the sound pressure reduction structure 1A according to the first modification, the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 also have a primary resonance frequency F ｂ and the second resonance frequency F ｃ A resonant frequency F lower than ａ Furthermore, the size L of the connection portion 30 in the Y direction satisfies the above formula (1). As a result, as in the above embodiment, the installation space can be reduced while the primary resonance frequency F ｂ It is possible to reduce the surrounding sound pressure.

[0055] Furthermore, in this sound pressure reduction structure 1A, the inside of each of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 is divided into a plurality of spaces 201 to 216, 217 to 232, so that the wavefront of the sound wave incident on the duct 10 from the first open end 11 is more likely to be disturbed, and the mismatch of the acoustic impedance becomes larger. Therefore, the primary resonance frequency Fｂ It is possible to reduce the surrounding sound pressure.

[0056] <Modification 2> Fig. 6 shows the configuration of the main parts of a sound pressure reduction structure 1B according to Modification 2. Fig. 6 shows an example of the planar (XY plane) configuration of the connection portion 30 of the sound pressure reduction structure 1B. In this connection portion 30, the center of gravity C21 of the first λ / 4 resonance tube 21 and the center of gravity C22 of the second λ / 4 resonance tube 22 are arranged so as to be offset in the X direction. Except for this point, the sound pressure reduction structure 1B according to Modification 2 has the same configuration as the sound pressure reduction structure 1 of the above embodiment and provides the same functions and effects.

[0057] In the connecting portion 30, it is preferable that the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are arranged at positions where they at least partially overlap in the X direction. This makes it possible to more effectively ｂ It is possible to reduce the surrounding sound pressure.

[0058] The center of gravity C21 of the first λ / 4 resonance tube 21 and the center of gravity C22 of the second λ / 4 resonance tube 22 are spaced a distance C in the X direction. In this case, it is preferable that the size W20 of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 in the X direction both satisfy the following formula (3). This more effectively adjusts the primary resonance frequency F of the tube 10. ｂ It is possible to reduce the surrounding sound pressure.

[0059]

[0060] In formula (3), C represents the distance in the X direction between the center of gravity C21 of the first λ / 4 resonance tube 21 and the center of gravity C22 of the second λ / 4 resonance tube 22, and W20 represents the size in the X direction of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22. There are no particular restrictions on the specific value of W20, but from the viewpoint of achieving an excellent sound pressure reduction effect, it is preferably 0.1 to 10 mm, more preferably 0.2 to 6 mm, even more preferably 0.3 to 5 mm, and particularly preferably 0.4 to 4 mm.

[0061] In the sound pressure reduction structure 1B according to the second modification, the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are also configured to have a primary resonance frequency F ｂand the second resonance frequency F ｃ A resonant frequency F lower than ａ Furthermore, the size L of the connection portion 30 in the Y direction satisfies the above formula (1). As a result, as in the above embodiment, the installation space can be reduced while the primary resonance frequency F ｂ It is possible to reduce the surrounding sound pressure.

[0062] <Application Examples> The sound pressure reduction structure 1 described in the above embodiment can be suitably used for reducing various sound pressures. Because the sound pressure reduction structure 1 can reduce installation space, it is preferably mounted on a vehicle for use. Examples of application areas include dash insulators, dash panels, floor carpets, spacers, door trim, sound-absorbing structures in door trim, sound-absorbing structures in compartments, instrument panels, instrument center boxes, instrument upper boxes, air conditioner housings, roof trim, sound-absorbing structures in roof trim, sun visors, rear seat air conditioning ducts, cooling ducts for battery cooling systems in battery-powered vehicles, cooling fans, center console trim, sound-absorbing structures in consoles, parcel trim, parcel panels, seat headrests, front seat backs, and rear seat backs. Furthermore, in the trunk, the sound pressure reduction structure can be applied to trunk floor trim, trunk boards, trunk side trims, sound-absorbing structures in trim, and drafter covers. The present invention can also be applied to the interior of the vehicle frame or between panels, such as pillar trim or fenders, and can also be applied to structures near the engine of a vehicle.

[0063] The present invention will be described in more detail below with reference to examples, although the technical scope of the present invention is not limited to the following examples.

[0064] [Reference Examples 1-1 and 1-2] The sound pressure reduction structure 100 shown in FIG. 7 was fabricated as follows. A backplate 41, a sound absorber 42, a speaker 43, a cylindrical pipe 44, the pipe 10, and a microphone 47 were arranged along the extension direction of the pipe 10. The backplate 41, the sound absorber 42, the speaker 43, and the cylindrical pipe 44 were arranged on the first open end 11 side of the pipe 10, and the microphone 47 was arranged on the second open end 12 side. The speaker 43 was fixed to the cylindrical pipe 44 with a flange 48. The cylindrical pipe 44 and the pipe 10 were connected using a flange 45 and a fitting 46. A λ / 4 resonance pipe 20 (pipe length: 0.238 m, size in the X direction: 20.1 mm, size in the Y direction: 31.0 mm, resonance frequency: 332 Hz) was connected to the pipe 10 between the first open end 11 and the second open end 12 via a connecting part 30.

[0065] In the sound pressure reduction structure 100 ( FIG. 7 ), a portion of the conduit 10 is inserted into the cylindrical pipe 44, and a first open end 11 of the conduit 10 is provided inside the cylindrical pipe 44. In the sound pressure reduction structure 100, the conduit 10 is inserted into the cylindrical pipe 44 by 0.12 m.

[0066] The back plate 41 was made of acrylic resin and had a thickness of 15 mm. The sound absorber 42 was made of White Qion (registered trademark, manufactured by Tokyo Bouon Co., Ltd.) and had a thickness of 50 mm. The speaker 43 was made of FE103En (manufactured by Fostex). The cylindrical tube 44 was made of acrylic resin and had an inner diameter of 10 cm. The distance between the flanges 48 and 45 was 30 cm. The conduit 10 was a square with an XZ plane and each side measuring 4.2 cm (see Figure 2). That is, the radial dimension D of the conduit 10 (X direction) was 4.2 cm. The dimension of the conduit 10 in the Y direction was 0.87 m. The primary resonance frequency F of this conduit 10 was ｂ is 201Hz, the secondary resonance frequency F ｃ The frequency was 390 Hz. A slit extending in the X and Y directions was provided in one of the planes (for example, plane 14 in FIG. 2 ) constituting the pipe 10. An adapter (not shown) with a through hole was placed in the slit, and the λ / 4 resonance tube 20 was connected to the through hole.

[0067] The microphone 47 used was a 378B02 (PCB Piezotronics). The microphone 47 was pre-calibrated to obtain a sound pressure of 94 dB (1 kHz). The flanges 45 and 48 were made of acrylic resin and 15 mm thick. The fitting 46 was made of acrylic resin and 20 mm thick, with a square opening measuring 4.2 cm on a side.

[0068] The specifications of the sound pressure reduction structure 100 used in Reference Examples 1-1 and 1-2 are shown in Table 1 below. When L / D is 0.5 or more, the connecting portion 30 satisfies formula (1).

[0069]

[0070] In the sound pressure reduction structure 100, the sound pressure reduction effect was evaluated as follows while changing the position of the connection portion 30 in the Y direction. First, a white noise signal was sent from a signal generating device to the speaker 43 of the sound pressure reduction structure 100. Then, the signal acquired by the microphone 47 was subjected to processing including FFT (Fast Fourier Transform) calculation processing. This resulted in measurement results of the sound pressure level. The frequency of the white noise signal was 100 to 4096 Hz. A system (manufactured by Siemens Corporation, SCADADSIII, SC310W) was used for the FFT calculation processing. The FFT calculation processing was set to a frequency range of 0 to 4096 Hz, a Hanning window, 30 averaging times, and 0% overlap.

[0071] The evaluation results of Reference Example 1-1 are shown in Fig. 8, and the evaluation results of Reference Example 1-2 are shown in Fig. 9. The horizontal axis in Fig. 8 and Fig. 9 represents the distance from the first open end to the center position c in the Y direction of the λ / 4 resonance tube 20, and the vertical axis represents the sound pressure level (SPL). When the center position c is at the first open end 11 of the conduit 10, it is set to 0 [m]. The reference value R of the sound pressure level is calculated by multiplying the first resonance frequency F of the conduit 10 when the center position c is at the change position b1. ｂ is the sound pressure level value.

[0072] In Reference Example 1-1, in which the connection portion 30 satisfies the above formula (1), the connection portion 30 is positioned between the position a1 and the change position b1, so that the primary resonance frequency F ｂ The surrounding sound pressure level hardly deteriorated from the reference value R. In contrast, in Reference Example 1-2 in which the connection part 30 does not satisfy the above formula (1), the primary resonance frequency F ｂ The ambient sound pressure level worsened from the reference value R.

[0073] [Reference Examples 2 to 5] The sound pressure reduction structure 200 shown in FIG. 10 was fabricated in the same manner as the sound pressure reduction structure 100. The sound pressure reduction structure 200 was fabricated in the same manner as Reference Examples 1-1 and 1-2, except that the first λ / 4 resonance tube 21 (tube length: 0.238 m) and the second λ / 4 resonance tube 22 (tube length: 0.238 m) were connected to the duct 10 via a connecting portion 30. The connecting portion 30 was provided from position L1 to position L2 in the Y direction. The gap between the opening of the first λ / 4 resonance tube 21 and the opening of the second λ / 4 resonance tube 22 was provided from position G1 to position G2 in the Y direction. Table 2 below shows the specifications of the sound pressure reduction structure 200 used in Reference Examples 2 to 5. In Reference Examples 2 to 5, the connecting portion 30 was disposed at a position not between position a1 and change position b1. In Table 2, the opening area of ​​the λ / 4 resonance tube represents the sum of the opening area of ​​the first λ / 4 resonance tube 21 and the opening area of ​​the second λ / 4 resonance tube 22. The resonance frequencies of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 used in Reference Examples 2 to 5 were almost the same.

[0074]

[0075] Comparative Example A sound pressure reduction structure according to a comparative example was fabricated in the same manner as in Examples 2 to 5, except that the λ / 4 resonance tube was not connected to the duct 10 .

[0076] The sound pressure reduction effect was evaluated in the sound pressure reduction structure 200. At this time, the sound pressure reduction effect was evaluated in the same manner as in Reference Examples 1-1 and 1-2, except that the position of the connecting portion 30 was fixed.

[0077] The evaluation results of Reference Examples 2 to 5 and the Comparative Example are shown in Figures 11 and 12. The vertical axis of Figure 11 represents the sound pressure level at 340 Hz, and the vertical axis of Figure 12 represents the sound pressure level at 200 Hz. At 340 Hz, which is close to the resonance frequency of the λ / 4 resonance tube, the sound pressure level was reduced in all of Reference Examples 2 to 5 compared to the Comparative Example. In particular, Reference Examples 2 to 4, which have a large opening area of ​​the λ / 4 resonance tube, reduced the sound pressure level more effectively than Reference Example 5. On the other hand, at 200 Hz, which is the primary resonance frequency Fb of the duct 10, all of Reference Examples 2 to 5 showed sound pressure levels that were approximately the same as the Comparative Example.

[0078] Examples 1 to 5 The sound pressure reduction structures 200 according to Examples 1 to 5 were created in the same manner as in Reference Examples 2 to 5, except that the connection portion 30 was provided between position a1 and change position b1. Table 3 below shows the specifications of the sound pressure reduction structures 200 used in Examples 1 to 5. In Table 3, the opening area of ​​the λ / 4 resonance tube is the sum of the opening area of ​​the first λ / 4 resonance tube 21 and the opening area of ​​the second λ / 4 resonance tube 22. In Example 2, the opening area of ​​the first λ / 4 resonance tube 21 was 182.5 mm ２ , the area of ​​the opening of the second λ / 4 resonance tube 22 is 60.8 mm ２ In Example 3, the area of ​​the opening of the first λ / 4 resonance tube 21 is 121.7 mm ２ , the area of ​​the opening of the second λ / 4 resonance tube 22 is 121.7 mm ２ In Example 4, the opening area of ​​the first λ / 4 resonance tube 21 is 73.3 mm ２ , the opening area of ​​the second λ / 4 resonance tube 22 is 170.0 mm ２ The resonance frequencies of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 used in Examples 1 to 5 were almost the same.

[0079]

[0080] The evaluation results of Examples 1 to 5 and the comparative example are shown in Figures 13 and 14. The vertical axis of Figure 13 represents the sound pressure level at 340 Hz, and the vertical axis of Figure 14 represents the sound pressure level at 200 Hz. In Examples 1 to 5, the primary resonance frequency F ｂAt 200 Hz, where G / L is 0.75, the sound pressure level was reduced by 4 dB or more compared to the comparative example. Even in Example 5, where G / L is 0.75, a sufficient sound pressure reduction effect at 200 Hz was confirmed. That is, even if the gap between the opening of the first λ / 4 resonance tube 21 and the opening of the second λ / 4 resonance tube 22 is increased, the primary resonance frequency F ｂ This shows that the present invention ensures freedom in placement of multiple λ / 4 resonance tubes with gaps between them, and can flexibly accommodate the size, shape, etc. of the space in which the sound pressure reduction structure is installed.

[0081] The sound pressure level at 200 Hz was 61.8 dB in Example 2, 61.3 dB in Example 3, and 60.5 dB in Example 4. In Examples 2 to 4, the sum of the area of ​​the opening of the first λ / 4 resonance tube 21 and the area of ​​the opening of the second λ / 4 resonance tube 22 was the same. In this case, it was confirmed that Example 4, in which the area of ​​the opening of the second λ / 4 resonance tube 22 arranged on the radiation end (second open end 12) side of the duct 10 was larger than the area of ​​the opening of the first λ / 4 resonance tube 21, was able to more effectively reduce the sound pressure at 200 Hz.

[0082] Furthermore, the opening area of ​​the λ / 4 resonance tube of Example 1 is almost the same as the opening area of ​​the λ / 4 resonance tube 20 of Reference Example 1-1. In Example 1, a sound pressure level reduction effect of about 2 dB was confirmed at 200 Hz compared to Reference Example 1-1.

[0083] [Examples 6 to 10] Sound pressure reduction structures 200 according to Examples 6 to 10 were created in the same manner as in Examples 1 to 5. Table 4 below shows the specifications of the sound pressure reduction structures 200 used in Examples 6 to 10. In Table 4, the opening area of ​​the λ / 4 resonance tube is the sum of the opening area of ​​the first λ / 4 resonance tube 21 and the opening area of ​​the second λ / 4 resonance tube 22. The resonance frequencies of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 used in Examples 6 to 10 were approximately the same. In Examples 6 to 8, the X-direction positions of the centers of gravity C21 and C22 were offset from each other. In Examples 9 and 10, the X-direction positions of the centers of gravity C21 and C22 were aligned. In Example 10, the centers of gravity C21 and C22 were located at positions other than the center of the X-direction of the pipe 10. In Example 11, the centers of gravity C21 and C22 were disposed at the center of the pipeline 10 in the X direction.

[0084]

[0085] The evaluation results of Examples 6 to 10 and the comparative example are shown in Figure 15. The vertical axis of Figure 15 represents the sound pressure level at 200 Hz. In Examples 6 to 10, the primary resonance frequency F ｂ The sound pressure level was reduced at 200 Hz, where C / W20 is 3.3, compared to the comparative example. Even in Example 6, where C / W20 is 3.3, a sufficient sound pressure reduction effect at 200 Hz was confirmed. It was confirmed that the sound pressure level at 200 Hz tends to decrease as C / W20 approaches zero, that is, as the positions of the centers of gravity C21 and C22 in the X direction approach each other. When C / W20 is zero and the centers of gravity C21 and C22 are located at the center in the width direction of the pipeline 10 (Example 10), the sound pressure level at 200 Hz was more effectively reduced.

[0086] [Examples 11 and 12] The sound pressure reduction structures 200 according to Examples 11 and 12 were fabricated in the same manner as in Examples 1 to 5. Table 5 below shows the specifications of the sound pressure reduction structures 200 used in Examples 11 and 12. In Table 5, the opening area of ​​the λ / 4 resonance tube is the sum of the opening area of ​​the first λ / 4 resonance tube 21 and the opening area of ​​the second λ / 4 resonance tube 22. The resonance frequencies of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 used in Examples 11 and 12 were approximately the same. In Examples 11 and 12, the positions of the centers of gravity C21 and C22 in the X direction were aligned. In Example 11, the centers of gravity C21 and C22 were positioned at positions other than the center of the pipe 10 in the X direction. In Example 12, the centers of gravity C21 and C22 were positioned at the center of the pipe 10 in the X direction.

[0087]

[0088] The evaluation results of Examples 11 and 12 and the comparative example are shown in Fig. 16. The vertical axis of Fig. 16 represents the sound pressure level at 200 Hz. In Examples 11 and 12, the primary resonance frequency F ｂ At 200 Hz, where W20 is 4 mm or less, the sound pressure level was reduced compared to the comparative example. In Examples 11 and 12, which had larger opening areas than Examples 9 and 10, the sound pressure level at 200 Hz was reduced more effectively. When the centers of gravity C21 and C22 were located at the center of the pipe 10 in the X direction (Example 12), the sound pressure level at 200 Hz was reduced more effectively. Furthermore, a comparison between Example 9 and Example 11, and a comparison between Example 10 and Example 12 reveals that when W20 is 4 mm or less, the effect of reducing the sound pressure level is particularly excellent.

[0089] The sound pressure reduction structure of the present invention has been described above using embodiments, modifications, and examples. However, those skilled in the art can appropriately add, modify, and omit aspects of the present invention within the scope of the technical concept. For example, the configurations, shapes, sizes, etc. of the components of the sound pressure reduction structure described in the above embodiments are merely examples, and other configurations, shapes, sizes, etc. may be used.

[0090] For example, in the above-described embodiment, an example in which one connection part 30 is provided in the pipeline 10 has been described, but a plurality of connection parts 30 may be provided in the pipeline 10. For example, a λ / 4 resonance tube is connected to the pipeline 10 via each of the plurality of connection parts 30.

[0091] Furthermore, for example, in the above embodiments, examples have been described in which the pipe lengths of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 are the same, but the pipe lengths of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 may be different from each other.

[0092] Furthermore, for example, in the above embodiments, examples have been described in which the openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 have a rectangular planar shape, but the openings of the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22 may have other planar shapes.

[0093] Furthermore, for example, in the above-described embodiment and the like, an example has been described in which the size of the opening of the first λ / 4 resonance tube 21 and the size of the opening of the second λ / 4 resonance tube 22 in the X direction are the same (size W20), but the size of the opening of the first λ / 4 resonance tube 21 and the size of the opening of the second λ / 4 resonance tube 22 in the X direction may be different. In this case, the size W20 in the above formula (3) may be the average of the size of the opening of the first λ / 4 resonance tube 21 and the size of the opening of the second λ / 4 resonance tube 22 in the X direction.

[0094] Furthermore, for example, in the above-described embodiments, the sound pressure reduction structures 1, 1A, 1B have been described as having two λ / 4 resonance tubes (the first λ / 4 resonance tube 21 and the second λ / 4 resonance tube 22), but the sound pressure reduction structures 1, 1A, 1B may have three or more λ / 4 resonance tubes. In such a case where three or more λ / 4 resonance tubes are present, the structure is considered to be within the scope of the present invention as long as it satisfies the provisions of the present invention when any two λ / 4 resonance tubes are assumed to be the first λ / 4 resonance tube and the second λ / 4 resonance tube.

[0095] In the above embodiment, the pipeline 10 has a quadrangular planar shape (XZ plane), but the pipeline 10 may have other planar shapes. For example, the pipeline 10 may have a polygonal planar shape with pentagons or more sides, or may have a planar shape such as a circle or an ellipse.

Claims

1. A pipe having a first open end and a second open end in an extension direction; a first λ / 4 resonance tube and a second λ / 4 resonance tube, each having a resonance frequency higher than a first resonance frequency of the pipe and lower than a second resonance frequency of the pipe; and a connection portion provided between the first open end and the second open end, connecting the first λ / 4 resonance tube and the second λ / 4 resonance tube to the pipe so as to be arranged with a gap in the extension direction, and satisfying the following formula (1); wherein the pipe has a change position b1 where an acoustic impedance zb at a first resonance frequency of the pipe changes discontinuously along the extension direction; and a position a1 among a plurality of intersection points between a differential za' of an acoustic impedance za of the pipe and a differential zb' of an acoustic impedance zb at the resonance frequencies of the first λ / 4 resonance tube and the second λ / 4 resonance tube, the position a1 being closest to the first open end, A sound pressure reducing structure, wherein a position of the connection portion in the extension direction is between the position a1 and the change position b1. In formula (1), L represents the size of the connection portion in the extension direction, and D represents the size of the pipeline in a radial direction intersecting the extension direction at the position where the connection portion is provided.

2. A sound pressure reduction structure as described in claim 1, wherein, in the connection portion, the first λ / 4 resonance tube and the second λ / 4 resonance tube are arranged at positions that satisfy the following formula (2). In formula (2), L represents the size of the connection portion in the extension direction, and G represents the size of the gap between the opening of the first λ / 4 resonance tube and the opening of the second λ / 4 resonance tube in the extension direction.

3. A sound pressure reduction structure as described in claim 1, wherein the first λ / 4 resonance tube and the second λ / 4 resonance tube are arranged in this order from the first open end side, and the size of the opening of the second λ / 4 resonance tube connected to the pipeline is larger than the size of the opening of the first λ / 4 resonance tube connected to the pipeline.

4. A sound pressure reduction structure according to claim 3, wherein the first open end is a sound incident end and the second open end is a sound radiating end.

5. A sound pressure reduction structure as described in claim 1, wherein the duct has a predetermined size in a width direction intersecting the extension direction and the radial direction, and the first λ / 4 resonance tube and the second λ / 4 resonance tube are arranged in a position where they at least partially overlap in the width direction.

6. A sound pressure reduction structure as described in claim 5, wherein the openings of the first λ / 4 resonance tube and the second λ / 4 resonance tube connected to the pipeline each have a size W20 in the width direction, and both sizes W20 satisfy the following formula (3). In formula (3), C represents the distance in the width direction between the center of gravity of the first λ / 4 resonance tube and the center of gravity of the second λ / 4 resonance tube.

7. A sound pressure reduction structure as described in claim 5, wherein the center of gravity of the first λ / 4 resonance tube and the center of gravity of the second λ / 4 resonance tube are located at the center of the width of the tube.

8. A sound pressure reduction structure as described in claim 5, wherein the center of gravity of the first λ / 4 resonance tube and the center of gravity of the second λ / 4 resonance tube are aligned in the width direction.

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