Sound absorbing structure and method for manufacturing sound absorbing structure

Abstract

This sound absorption structure comprises a multi-stage resonance box having a plurality of resonators arranged in a first direction. Each of the plurality of resonators has a resonance space extending in a second direction orthogonal to the first direction. The multi-stage resonance box includes: openings which are formed in a first resonator positioned at an end in the first direction among the plurality of resonators, and communicate the resonance space of the first resonator and the external space of the multi-stage resonance box; and communication port enabling communication between the resonance spaces of the resonators adjacent to each other in the second direction.

Description

Sound-absorbing structure and method for manufacturing the same

[0001] The present disclosure relates to sound absorbing structures and methods for manufacturing sound absorbing structures.

[0002] Non-Patent Document 1 describes a sound-absorbing structure that absorbs discrete frequency noise (discrete frequency sound) having multiple frequency peaks, such as the sound generated by a motor fan. This sound-absorbing structure is configured by laminating an upper layer in which multiple primary resonators are arranged in a lattice pattern and a lower layer in which multiple secondary resonators are arranged in a lattice pattern, with holes formed in the upper wall of the upper layer that communicate with each of the primary resonators, and holes formed in the partition wall between the upper and lower layers that communicate with each of the primary resonators in the upper layer and each of the secondary resonators in the lower layer. In other words, in this sound-absorbing structure, multiple two-stage resonators, in which primary and secondary resonators are connected in series, are arranged in a lattice pattern.

[0003] Journal of the Acoustical Society of Japan, Vol. 62, 2006, pp. 759-766

[0004] The sound-absorbing structure described in Non-Patent Document 1 has a thick and complex structure because it is constructed by laminating an upper layer in which a plurality of primary resonators are arranged in a lattice pattern and a lower layer in which a plurality of secondary resonators are arranged in a lattice pattern, which makes it difficult to arrange the structure in a narrow space and makes it difficult to manufacture.

[0005] An object of the present disclosure is to provide a sound-absorbing structure that can absorb discrete frequency noise, can be made thin, and can be easily manufactured, and a method for manufacturing a sound-absorbing structure.

[0006] [1] A sound-absorbing structure according to the present disclosure includes a multi-stage resonance box having a plurality of resonators arranged in a first direction, each of the plurality of resonators having a resonance space extending in a second direction perpendicular to the first direction, and the multi-stage resonance box has an opening formed in a first resonator located at an end of the plurality of resonators in the first direction, the opening connecting the resonance space of the first resonator to an external space of the multi-stage resonance box, and a communication opening connecting the resonance spaces of adjacent resonators in the second direction.

[0007] In this sound-absorbing structure, an opening is formed in the first resonator, and adjacent resonators are connected by a communication port. Therefore, when sound waves enter the resonance space of the first resonator through the opening, resonance occurs in the resonance space. Furthermore, when sound waves enter the resonance space of the adjacent resonator through the communication port, resonance occurs in the resonance space. As a result, the sound absorption peak is split into two, generating two sound absorption peaks, making it possible to absorb discrete frequency noise.

[0008] In this sound-absorbing structure, multiple resonators each having a resonance space extending in the second direction are arranged in the first direction. This prevents the structure from becoming thicker in a third direction perpendicular to the first and second directions. Furthermore, because the multi-stage resonance box can be manufactured in part or entirely by extrusion molding in the second direction, the structure can be easily manufactured.

[0009] [2] In the sound absorbing structure described in [1], the multi-stage resonance box may include a first resonator and a second resonator adjacent to the first resonator as the multiple resonators, and the communication opening may connect the resonance space of the first resonator to the resonance space of the second resonator. In this sound absorbing structure, the multi-stage resonance box includes the first resonator and the second resonator as the multiple resonators, and the resonance space of the first resonator is connected to the resonance space of the second resonator by the communication opening, so that two sound absorption peaks are generated. This makes it possible to absorb discrete frequency noise having two frequency peaks.

[0010] [3] In the sound-absorbing structure described in [1], the multi-stage resonance box may include, as the multiple resonators, a first resonator, a second resonator adjacent to the first resonator, and a third resonator adjacent to the second resonator, and the communication openings may include a first communication opening connecting the resonance space of the first resonator to the resonance space of the second resonator and a second communication opening connecting the resonance space of the second resonator to the resonance space of the third resonator. In this sound-absorbing structure, the multi-stage resonance box includes, as the multiple resonators, the first resonator, the second resonator, and the third resonator, and the resonance space of the first resonator is connected to the resonance space of the second resonator via the first communication opening, and the resonance space of the second resonator is connected to the resonance space of the third resonator via the second communication opening, thereby generating three sound absorption peaks. This makes it possible to absorb discrete frequency noise having three frequency peaks.

[0011] [4] In the sound absorbing structure according to any one of [1] to [3], each of the plurality of resonators may have a rectangular cross section perpendicular to the second direction. In this sound absorbing structure, the cross section perpendicular to the second direction of each of the plurality of resonators is rectangular, which allows the sound absorbing structure to be arranged efficiently.

[0012] [5] In the sound-absorbing structure according to any one of [1] to [4], the multi-stage resonance box may be formed of a cylindrical box portion having both ends open in the second direction. In this sound-absorbing structure, the multi-stage resonance box is formed of a cylindrical box portion having both ends open in the second direction, and therefore the multi-stage resonance box can be manufactured by extrusion molding in the second direction. When using the sound-absorbing structure, resonance can be generated in the resonance space of each resonator by blocking both ends of the cylindrical box portion in the second direction with another member, such as an object to be sound-absorbed.

[0013] [6] In the sound-absorbing structure according to any one of [1] to [4], the multi-stage resonance box may be configured with a cylindrical box portion having both open ends in the second direction and a first end portion that closes one end of the cylindrical box portion in the second direction. In this sound-absorbing structure, the multi-stage resonance box is configured with a cylindrical box portion having both open ends in the second direction and a first end portion that closes one end of the cylindrical box portion in the second direction. Therefore, the multi-stage resonance box can be manufactured by molding the cylindrical box portion by extrusion molding in the second direction and then joining the first end portion to the cylindrical box portion. When using the sound-absorbing structure, resonance can be generated in the resonance space of each resonator by closing the end of the cylindrical box portion opposite the first end portion in the second direction with another member, such as a sound-absorbing object.

[0014] [7] In the sound-absorbing structure according to any one of [1] to [4], the multi-stage resonance box may include a cylindrical box portion having both open ends in the second direction, a first end portion closing one end of the cylindrical box portion in the second direction, and a second end portion closing the end of the cylindrical box portion opposite the first end in the second direction. In this sound-absorbing structure, the multi-stage resonance box includes a cylindrical box portion having both open ends in the second direction, a first end portion closing one end of the cylindrical box portion in the second direction, and a second end portion closing the end of the cylindrical box portion opposite the first end in the second direction. Therefore, resonance can be generated in the resonance space of each resonator without modification. The multi-stage resonance box can be produced, for example, by molding the cylindrical box portion by extrusion molding in the second direction and then joining the first end and the second end portion to the cylindrical box portion.

[0015] [8] In the sound absorbing structure according to any one of [1] to [7], the opening may be a circular hole. In this sound absorbing structure, since the opening is a circular hole, it is possible to suppress a decrease in rigidity of the first resonator due to the opening.

[0016] [9] In the sound absorbing structure according to any one of [1] to [8], the multi-stage resonance box may have a plurality of openings. In this sound absorbing structure, the multi-stage resonance box has a plurality of openings, so that the first resonator can function as a plurality of resonators. This can enhance the sound absorbing effect.

[0017]

[10] In the sound absorbing structure according to [9], the openings may be arranged in the second direction. In this sound absorbing structure, since the openings are arranged in the second direction, it is possible to suppress an increase in the dimension of the multi-stage resonance box in the first direction due to the formation of the openings.

[0018]

[11] In the sound absorbing structure according to any one of [1] to

[10] , the communication opening may be a slit extending in the second direction. In this sound absorbing structure, since the communication opening is a slit extending in the second direction, the communication opening can be formed by extrusion molding in the second direction.

[0019]

[12] In the sound absorbing structure according to any one of [1] to

[11] , the communication opening may be formed by a partition wall that forms a boundary between adjacent resonators in the second direction and a communication opening protrusion that protrudes from the partition wall. In this sound absorbing structure, the communication opening is formed by the partition wall that forms the boundary between adjacent resonators in the second direction and the communication opening protrusion that protrudes from the partition wall, so that the depth of the communication opening can be increased. This allows the sound absorption characteristics to be improved at low frequencies.

[0020]

[13] In the sound absorbing structure according to any one of [1] to

[12] , the opening may be formed by an outer wall of the first resonator and a protruding portion protruding from the outer wall. In this sound absorbing structure, the opening is formed by the outer wall of the first resonator and the protruding portion protruding from the outer wall, so that the depth of the opening can be increased. This allows the sound absorption characteristics to be improved at low frequencies.

[0021]

[14] In the sound absorbing structure according to any one of [1] to

[13] , a plurality of multi-stage resonance boxes may be arranged in a first direction. In this sound absorbing structure, since a plurality of multi-stage resonance boxes are arranged in the first direction, it is possible to enhance the sound absorbing effect and to prevent the structure from becoming thick in a third direction perpendicular to the first and second directions.

[0022]

[15] A method for manufacturing a sound absorbing structure according to the present disclosure is a method for manufacturing a sound absorbing structure according to any one of [1] to

[14] , in which discrete frequency noise having multiple frequency peaks is acquired, and the sound absorbing structure is manufactured so that the multiple frequency peaks of the acquired discrete frequency noise become sound absorption peaks.

[0023] In this method for manufacturing a sound absorbing structure, discrete frequency noise having multiple frequency peaks is acquired, and a sound absorbing structure is manufactured so that the multiple frequency peaks of the acquired discrete frequency noise become sound absorption peaks. Therefore, the manufactured sound absorbing structure can absorb the discrete frequency noise. Moreover, because this method for manufacturing a sound absorbing structure manufactures the above-mentioned sound absorbing structure, a thin sound absorbing structure can be easily manufactured.

[0024] According to the present disclosure, discrete frequency noise can be absorbed, the thickness can be reduced, and the product can be easily manufactured.

[0025] FIG. 1 is a schematic perspective view showing a sound absorbing structure according to an embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1 . FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG. 1 . FIG. 4 is a schematic cross-sectional view corresponding to FIG. 2 , for explaining an example of a method for manufacturing the sound absorbing structure shown in FIG. 1 . FIG. 5 is a schematic cross-sectional view corresponding to FIG. 3 , for explaining an example of a method for manufacturing the sound absorbing structure shown in FIG. 1 . FIG. 6 is a schematic cross-sectional view corresponding to FIG. 3 , showing a sound absorbing structure according to Modification 1. FIG. 7 is a schematic cross-sectional view corresponding to FIG. 3 , showing a sound absorbing structure according to Modification 2. FIG. 8 is a schematic perspective view showing a sound absorbing structure according to Modification 3. FIG. 9 is a schematic cross-sectional view taken along line IX-IX in FIG. 8 . FIG. 10 is a schematic perspective view of a sound absorbing structure according to Modification 4. FIG. 11 is a schematic perspective view of a sound absorbing structure according to Modification 5. FIG. 12 is a schematic cross-sectional view taken along line XII-XII in FIG. 11 . FIG. 13 is a schematic cross-sectional view taken along line XIII-XIII in FIG. 11 . FIG. 14 is a schematic perspective view of the sound absorbing structure of Modified Example 6. FIG. 15 is a schematic cross-sectional view taken along line XV-XV in FIG. 14 . FIG. 16 is a schematic perspective view of the sound absorbing structure of Modified Example 7. FIG. 17 is a schematic perspective view of the sound absorbing structure of Modified Example 8. FIG. 18 is a schematic cross-sectional view taken along line XVIII-XVIII in FIG. 17 . FIG. 19 is a schematic perspective view of the sound absorbing structure of Modified Example 9. FIG. 20 is a graph showing the measurement results of Comparative Example 1. FIG. 21 is a graph showing the measurement results of Example 1. FIG. 22 is a graph showing the measurement results of Example 2. FIG. 23 is a graph showing the measurement results of Example 3. FIG. 24 is a graph showing the measurement results of Example 4. FIG. 25 is a graph showing the measurement results of Example 5. FIG. 26 is a graph showing the measurement results of Example 6. FIG. 27 is a graph showing the measurement results of Comparative Example 1 and Examples 1 and 4.

[0026] Hereinafter, embodiments of a sound-absorbing structure and a method for manufacturing a sound-absorbing structure according to the present disclosure will be described in detail with reference to the drawings. In the drawings, identical or corresponding parts are designated by the same reference numerals, and duplicate explanations will be omitted. Numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0027] [Sound-absorbing structure] Fig. 1 is a schematic perspective view showing a sound-absorbing structure according to an embodiment. Fig. 2 is a schematic cross-sectional view taken along line II-II in Fig. 1. Fig. 3 is a schematic cross-sectional view taken along line III-III in Fig. 1. As shown in Figs. 1 to 3, the sound-absorbing structure 1 according to this embodiment has a Helmholtz resonance structure. In other words, the sound-absorbing structure 1 absorbs sound by generating Helmholtz resonance. The sound-absorbing structure 1 has a multi-stage resonance box 2.

[0028] The multi-stage resonance box 2 has a first resonator 3, a second resonator 4, a plurality of openings 5, and a communication port 6. The first resonator 3 and the second resonator 4 are arranged in a first direction D1 and integrally formed. That is, the first resonator 3 and the second resonator 4 are adjacent to each other in the first direction D1. The first resonator 3 is also a resonator located at an end of the multi-stage resonance box 2 in the first direction D1.

[0029] The first resonator 3 is a resonator located at an end of the multiple resonators in the first direction D1 and generating Helmholtz resonance. The first resonator 3 has a resonance space 31 extending in a second direction D2 perpendicular to the first direction D1. The resonance space 31 is the internal space of the first resonator 3. A cross section of the resonance space 31 perpendicular to the second direction D2 is formed into a rectangular shape, and has the same shape throughout the second direction D2. If the direction perpendicular to the first direction D1 and the second direction D2 is defined as a third direction D3, the cross section of the resonance space 31 perpendicular to the second direction D2 is a cross section along the first direction D1 and the third direction D3.

[0030] The second resonator 4 is a resonator that generates Helmholtz resonance. The second resonator 4 has a resonance space 41 that extends in the second direction D2. The resonance space 41 is an internal space of the second resonator 4. A cross section of the resonance space 41 that is perpendicular to the second direction D2 is formed into a rectangular shape, and has the same shape throughout the entire area in the second direction D2.

[0031] The plurality of openings 5 ​​are formed in the first resonator 3, and connect the resonance space 31 of the first resonator 3 to the external space of the multi-stage resonance box 2. The resonance space 31 is connected to the external space of the multi-stage resonance box 2 only through the plurality of openings 5. Each of the openings 5 ​​(hereinafter simply referred to as "opening 5") is, for example, a hole formed in the outer wall of the first resonator 3. The openings 5 ​​are, for example, circular holes. The plurality of openings 5 ​​are arranged in the second direction D2.

[0032] The communication port 6 communicates the resonance space 31 of the first resonator 3 with the resonance space 41 of the second resonator 4. The resonance space 41 communicates with the resonance space 31 of the first resonator 3 only at the communication port 6. The resonance space 41 also communicates with the external space of the multi-stage resonance box 2 only via the communication port 6, the first resonator 3, and the multiple openings 5. The communication port 6 is, for example, a slit formed in a partition wall that forms a boundary between the first resonator 3 and the second resonator 4 and extending in the second direction D2. The communication port 6 extends, for example, over the entire area in the second direction D2.

[0033] More specifically, the multi-stage resonance box 2 is composed of a cylindrical box portion 21 having both open ends in the second direction D2, a first end portion 22 that closes one end of the cylindrical box portion 21 in the second direction D2, and a second end portion 23 that closes the end of the cylindrical box portion 21 opposite the first end portion 22 in the second direction D2.

[0034] The cylindrical box portion 21 defines therein a resonance space 31 for the first resonator 3 and a resonance space 41 for the second resonator 4. The cylindrical box portion 21 blocks the resonance space 31 and the resonance space 41 from directions perpendicular to the second direction D2 (directions along the first direction D1 and the third direction D3). With only the cylindrical box portion 21, the resonance space 31 and the resonance space 41 are open on both sides in the second direction D2.

[0035] The cylindrical box portion 21 is composed of a first bottom wall 21a, a second bottom wall 21b, a first top wall 21c, a second top wall 21d, a first side wall 21e, a second side wall 21f, and a partition wall 21g.

[0036] The first bottom wall 21a is a wall that closes the resonance space 31 of the first resonator 3 from one side in the third direction D3. The first bottom wall 21a is formed in a flat plate shape extending in the first direction D1 and the second direction D2, and is disposed on one side of the resonance space 31 in the third direction D3.

[0037] The second bottom wall 21b is a wall that closes the resonance space 41 of the second resonator 4 from one side in the third direction D3. The second bottom wall 21b is formed in a flat plate shape extending in the first direction D1 and the second direction D2, and is disposed on one side of the resonance space 41 in the third direction D3.

[0038] The first bottom wall 21 a and the second bottom wall 21 b are adjacent to each other in the first direction D1 and integrally formed, and the first bottom wall 21 a and the second bottom wall 21 b are formed as a flat plate extending in the first direction D1 and the second direction D2 as a whole.

[0039] The first top wall 21c is a wall that closes the resonance space 31 of the first resonator 3 from the side opposite the first bottom wall 21a in the third direction D3. The first top wall 21c faces the first bottom wall 21a in the third direction D3. The first top wall 21c is formed in a flat plate shape extending in the first direction D1 and the second direction D2, and is located on the side of the resonance space 31 opposite the first bottom wall 21a in the third direction D3. A plurality of openings 5 ​​are formed in the first top wall 21c.

[0040] The second top wall 21d is a wall that closes the resonance space 41 of the second resonator 4 from the side opposite to the second bottom wall 21b in the third direction D3. The second top wall 21d faces the second bottom wall 21b in the third direction D3. The second top wall 21d is formed in a flat plate shape extending in the first direction D1 and the second direction D2, and is disposed on the side of the resonance space 41 opposite to the second bottom wall 21b in the third direction D3.

[0041] The first top wall 21c and the second top wall 21d are adjacent to each other in the first direction D1 and integrally formed, and are formed as a flat plate extending in the first direction D1 and the second direction D2 as a whole.

[0042] The first side wall 21e is a wall that closes the resonance space 31 of the first resonator 3 from the side opposite to the second resonator 4 in the first direction D1. The first side wall 21e is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is arranged on the side of the resonance space 31 opposite to the second resonator 4 in the first direction D1.

[0043] The second side wall 21f is a wall that closes the resonance space 41 of the second resonator 4 from the side opposite the first resonator 3 in the first direction D1. The second side wall 21f faces the first side wall 21e in the first direction D1. The second side wall 21f is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is arranged on the side of the resonance space 41 opposite the first resonator 3 in the first direction D1.

[0044] The partition wall 21g is a wall that closes the resonance space 31 of the first resonator 3 from the second resonator 4 side in the first direction D1, and closes the resonance space 41 of the second resonator 4 from the first resonator 3 side in the first direction D1. In other words, the partition wall 21g is a wall that forms a boundary between the first resonator 3 and the second resonator 4, and is a wall that separates the resonance space 31 from the resonance space 41. The partition wall 21g faces the first side wall 21e and the second side wall 21f in the first direction D1. The partition wall 21g is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is arranged on the second resonator 4 side of the resonance space 31 of the first resonator 3 in the first direction D1, and on the first resonator 3 side of the resonance space 41 of the second resonator 4 in the first direction D1. A communication opening 6 is formed in the partition wall 21g.

[0045] The first end 22 is a wall that closes the resonance space 31 of the first resonator 3 and the resonance space 41 of the second resonator 4 from one side in the second direction D2. The first end 22 is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is arranged on one side of the resonance space 31 and the resonance space 41 in the second direction D2.

[0046] The second end 23 is a wall that closes the resonance space 31 of the first resonator 3 and the resonance space 41 of the second resonator 4 from the side opposite to the first end 22 in the second direction D2. The second end 23 faces the first end 22 in the second direction D2. The second end 23 is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is located on the side of the resonance space 31 and the resonance space 41 opposite to the first end 22 in the second direction D2.

[0047] The multi-stage resonance box 2 has enough self-supporting properties to maintain its shape in a stationary state. The multi-stage resonance box 2 is non-air permeable. The multi-stage resonance box 2 has at least one of a Shore A hardness of 40 to 100 and a Shore D hardness of 10 to 100. In this case, the Shore A hardness of the multi-stage resonance box 2 may be 50 to 100 or 60 to 100. Furthermore, the Shore D hardness of the multi-stage resonance box 2 may be 20 to 100 or 30 to 100.

[0048] The Shore A hardness of the multi-stage resonance box 2 can be measured using a durometer in accordance with JIS K6253-3; for example, a GS-709N TYPE A manufactured by Teclock Corporation can be used. The Shore D hardness of the multi-stage resonance box 2 can be measured using a durometer in accordance with JIS K6253-3; for example, a GS-720N TYPE D manufactured by Teclock Corporation can be used. If the allowable number of stacked test pieces specified in JIS K6253-3 (three or less) does not satisfy the specified measurement thickness (6 mm or more), more than three pieces can be stacked and measurement can be performed at the specified thickness.

[0049] The material of the multi-stage resonance box 2 includes, for example, elastomer such as thermoplastic elastomer, plastic, rubber, rubber-like material, or other resin.

[0050] Examples of elastomer materials include thermoplastic elastomers such as styrene block copolymer (SBC), polyolefin (TPO), polyurethane (TPU), polyester (TPC), polyamide (TPA), dynamically crosslinked (TPV), soft polyvinyl chloride (PVC), and acrylic.

[0051] Examples of plastic materials include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polyphenylene sulfide (PPS), polyurethane (PU), epoxy resin, phenolic resin, and melamine resin.

[0052] Examples of rubber materials include natural rubber (NR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), ethylene propylene rubber (EPM), ethylene propylene diene rubber (EPDM), silicone rubber, and urethane rubber.

[0053] Examples of rubber-like materials include UV-curable acrylic rubber-like materials.

[0054] The sound absorbing structure 1 configured in this manner can be manufactured by various methods, such as injection molding, extrusion molding, modeling using a 3D printer, and salt coagulation.

[0055] Here, a method for manufacturing the sound absorbing structure 1 using extrusion molding will be described with reference to Figures 4 and 5. Figure 4 is a schematic cross-sectional view corresponding to Figure 2, for explaining an example of a method for manufacturing the sound absorbing structure shown in Figure 1. Figure 5 is a schematic cross-sectional view corresponding to Figure 3, for explaining an example of a method for manufacturing the sound absorbing structure shown in Figure 1.

[0056] First, as shown in Figures 4 and 5, the cylindrical box portion 21 is formed by extrusion molding. In extrusion molding, the material of the cylindrical box portion 21 is extruded in the second direction D2. At this time, the communication opening 6 is a slit extending over the entire area in the second direction D2, so that the communication opening 6 can also be formed in the partition wall 21g of the cylindrical box portion 21 by extrusion molding the cylindrical box portion 21.

[0057] Next, a plurality of openings 5 ​​are formed in the first top wall 21c of the cylindrical box portion 21. The formation of the plurality of openings 5 ​​can be performed by, for example, a drilling method or a laser cutting method.

[0058] Next, the first end portion 22 and the second end portion 23 are joined to both ends in the first direction D1 of the cylindrical box portion 21. The first end portion 22 and the second end portion 23 can be joined to the cylindrical box portion 21 by, for example, adhesive bonding or welding. In this way, the sound-absorbing structure 1 is manufactured.

[0059] As described above, in the sound absorbing structure 1 according to this embodiment, a plurality of openings 5 ​​are formed in the first resonator 3, and adjacent first and second resonators 3 and 4 are connected to each other by the communication opening 6. Therefore, when sound waves enter the resonance space 31 of the first resonator 3 through the plurality of openings 5, resonance occurs in the resonance space 31. Furthermore, when sound waves enter the resonance space 41 of the adjacent second resonator 4 through the communication opening 6, resonance occurs in the resonance space 41. As a result, the sound absorption peak is split into two, generating two sound absorption peaks, making it possible to absorb discrete frequency noise having two frequency peaks.

[0060] In this sound-absorbing structure 1, the first resonators 3 and the second resonators 4, each having a resonance space 31 and a resonance space 41 extending in the second direction D2, are arranged in the first direction D1. This prevents the structure from becoming thicker in a third direction D3 perpendicular to the first direction D1 and the second direction D2. Furthermore, the cylindrical box portion 21 of the multi-stage resonance box 2 can be manufactured by extrusion molding in the second direction D2, making it easy to manufacture.

[0061] Furthermore, in this sound absorbing structure 1, the cross sections of the first resonator 3 and the second resonator 4 that are perpendicular to the second direction D2 are formed in a rectangular shape, so that the sound absorbing structure 1 can be arranged efficiently.

[0062] Furthermore, in this sound-absorbing structure 1, the multi-stage resonance box 2 is composed of a cylindrical box portion 21 that is open at both ends in the second direction D2, a first end portion 22 that closes one end of the cylindrical box portion 21 in the second direction D2, and a second end portion 23 that closes the end of the cylindrical box portion in the second direction D2 on the opposite side from the first end portion 22. Therefore, resonance can be generated in the resonance space of each resonator as is. Then, for example, the multi-stage resonance box 2 can be produced by molding the cylindrical box portion 21 by extrusion molding in the second direction D2 and then joining the first end portion 22 and the second end portion 23 to the cylindrical box portion 21.

[0063] Furthermore, in this sound absorbing structure 1, since the opening 5 is a circular hole, it is possible to suppress a decrease in the rigidity of the first resonator 3 due to the opening 5.

[0064] Furthermore, in this sound absorbing structure 1, the multi-stage resonance box 2 has a plurality of openings 5, so that the first resonator 3 can function as a plurality of resonators, thereby enhancing the sound absorbing effect.

[0065] In addition, in this sound-absorbing structure 1, since multiple openings 5 ​​are arranged in the second direction D2, the increase in dimension of the multi-stage resonance box 2 in the first direction due to the formation of multiple openings 5 ​​can be suppressed.

[0066] Furthermore, in this sound absorbing structure 1, the communication openings 6 are slits extending in the second direction D2, so that the communication openings 6 can be formed by extrusion molding in the second direction D2.

[0067] The present disclosure is not limited to the above-described embodiments, and modifications can be made as appropriate without departing from the spirit of the present disclosure.

[0068] For example, in the present disclosure, a multi-stage resonance box may be configured with a cylindrical box portion and a first end portion without having a second end portion.

[0069] [Modification 1] Fig. 6 is a schematic cross-sectional view corresponding to Fig. 3 and showing a sound absorbing structure of Modification 1. In the sound absorbing structure 1A shown in Fig. 6, a multi-stage resonance box 2A does not have the second end portion 23 of the first embodiment, but is composed of a cylindrical box portion 21 and a first end portion 22. Therefore, the resonance space 31 of the first resonator 3A and the resonance space 41 of the second resonator 4A are open on the side opposite to the first end portion 22 in the second direction D2.

[0070] In this sound-absorbing structure 1A, the multi-stage resonance box 2A is composed of a cylindrical box portion 21 that is open at both ends in the second direction D2 and a first end portion 22 that closes one end of the cylindrical box portion 21 in the second direction D2, so that the multi-stage resonance box 2A can be produced by molding the cylindrical box portion 21 by extrusion molding in the second direction D2 and then joining the first end portion 22 to the cylindrical box portion 21. When using the sound-absorbing structure 1A, resonance can be generated in the resonance space 31 of the first resonator 3A and the resonance space 41 of the second resonator 4A by closing the end of the cylindrical box portion 21 in the second direction D2 opposite the first end portion 22 with another member 24A such as a sound-absorbing object.

[0071] [Modification 2] Fig. 7 is a schematic cross-sectional view corresponding to Fig. 3 and showing a sound absorbing structure of Modification 2. In the sound absorbing structure 1B shown in Fig. 7, a multi-stage resonance box 2B does not have the first end portion 22 and the second end portion 23 of the first embodiment, but is formed by a cylindrical box portion 21. Therefore, the resonance space 31 of the first resonator 3B and the resonance space 41 of the second resonator 4B are open on both sides in the second direction D2.

[0072] In this sound-absorbing structure 1B, the multi-stage resonance box 2B is configured with a cylindrical box portion 21 that is open at both ends in the second direction D2, and therefore the multi-stage resonance box 2B can be produced by extrusion molding in the second direction D2. When using the sound-absorbing structure 1B, one end of the cylindrical box portion 21 in the second direction D2 is blocked with another member 24B such as a sound-absorbing object, and the other end of the cylindrical box portion 21 in the second direction D2 is blocked with another member 25B such as a sound-absorbing object, thereby generating resonance in the resonance space 31 of the first resonator 3B and the resonance space 41 of the second resonator 4B.

[0073] Furthermore, in the present disclosure, the multiple openings may be formed at any position on the first resonator as long as they communicate the resonance space of the first resonator with the external space of the multi-stage resonance box.

[0074] [Modification 3] Fig. 8 is a schematic perspective view showing a sound absorbing structure of Modification 3. Fig. 9 is a schematic cross-sectional view taken along line IX-IX shown in Fig. 8. In the sound absorbing structure 1C shown in Figs. 8 and 9, the multiple openings 5C are formed in the first side wall 21e, not in the first top wall 21c.

[0075] In this sound absorbing structure 1C as well, sound waves enter the resonance space 31 of the first resonator 3 through the multiple openings 5C, causing resonance in the resonance space 31. Furthermore, sound waves enter the resonance space 41 of the adjacent second resonator 4 through the communication opening 6, causing resonance in the resonance space 41. As a result, the sound absorption peak is split into two, causing two sound absorption peaks, making it possible to absorb discrete frequency noise having two frequency peaks.

[0076] Furthermore, in the present disclosure, the communication holes may have any number, any shape, etc., as long as they communicate the resonance spaces of the resonators adjacent to each other in the second direction.

[0077] [Variation 4] Fig. 10 is a schematic perspective view of a sound absorbing structure of Variation 4. In a sound absorbing structure 1D shown in Fig. 10, a communication opening 6D connecting the resonance space 31 of the first resonator 3 and the resonance space 41 of the second resonator 4 is a slit extending in the second direction D2, for example, extending over the entire area in the second direction D2. The communication opening 6D is formed by a partition wall 21g that forms a boundary between the first resonator 3 and the second resonator 4 adjacent to each other in the second direction D2, and a communication opening protrusion 62D that protrudes from the partition wall 21g. The communication opening protrusion 62D extends from the partition wall 21g toward the resonance space 41 of the second resonator 4. The extending direction of the communication opening protrusion 62D is not particularly limited, but is, for example, the first direction D1. In addition, the communication port protrusion 62D may extend from the partition wall 21g toward the resonance space 31 of the first resonator 3, or may extend from the partition wall 21g toward both the resonance space 41 of the second resonator 4 and the resonance space 31 of the first resonator 3.

[0078] In this sound absorbing structure 1D, the communication opening 6D is formed by the partition wall 21g that forms the boundary between the first resonator 3 and the second resonator 4 that are adjacent in the second direction D2, and the communication opening protrusion 62D that protrudes from the partition wall 21g, so that the depth of the communication opening 6D can be increased, thereby achieving sound absorption characteristics at low frequencies.

[0079] Furthermore, in the present disclosure, the openings may have any number, shape, etc., as long as they communicate with the resonance spaces of the resonators adjacent to each other in the second direction.

[0080] [Variation 5] FIG. 11 is a schematic perspective view of a sound absorbing structure of Variation 5. FIG. 12 is a schematic cross-sectional view taken along line XII-XII in FIG. 11. FIG. 13 is a schematic cross-sectional view taken along line XIII-XIII in FIG. 11. In the sound absorbing structure 1E shown in FIGS. 11 to 13, a plurality of openings 5E that connect the resonance space 31 of the first resonator 3 with the external space of the multi-stage resonance box 2 are arranged in the second direction D2. Each of the plurality of openings 5E is, for example, a circular hole. The plurality of openings 5E are formed by a first top wall 21c that forms the outer wall of the first resonator 3 and an opening protrusion 52E that protrudes from the first top wall 21c. The first top wall 21c is part of the outer wall of the first resonator 3. The opening protrusion 52E extends from the first top wall 21c toward the resonance space 31 of the first resonator 3. The extending direction of the opening protrusion 52E is not particularly limited, and may be, for example, the third direction D3. The opening protrusion 52E may extend from the first top wall 21c toward the external space of the multi-stage resonance box 2, or may extend from the first top wall 21c toward both the resonance space 31 of the first resonator 3 and the external space of the multi-stage resonance box 2. A plurality of holes are formed penetrating the first top wall 21c and the opening protrusion 52E, and these holes serve as a plurality of openings 5E. The communication opening 6E connecting the resonance space 31 of the first resonator 3 and the resonance space 41 of the second resonator 4 is formed by the partition wall 21g and a communication opening protrusion 62E protruding from the partition wall 21g, similar to the communication opening 6D of the sound absorbing structure 1D shown in FIG. 10 .

[0081] In this sound-absorbing structure 1E, the openings 5E are formed by the first top wall 21c that forms the outer wall of the first resonator 3 and the opening protrusions 52E that protrude from the first top wall 21c, so that the depth of the openings 5E can be increased, thereby improving the sound absorption characteristics at low frequencies.

[0082] [Variation 6] Fig. 14 is a schematic perspective view of a sound absorbing structure of Variation 6. Fig. 15 is a schematic cross-sectional view taken along line XV-XV in Fig. 14. In the sound absorbing structure 1F shown in Figs. 14 and 15, the first resonator 3 does not have multiple openings formed therein, but rather has a single opening 5F formed therein. The opening 5F is a slit formed in the first top wall 21c and extending in the second direction D2. The opening 5F extends, for example, over the entire area in the second direction D2.

[0083] In this sound absorbing structure 1F, the openings 5F are slits extending in the second direction D2, and therefore the openings 5F can be formed by extrusion molding in the second direction D2.

[0084] In addition, in the present disclosure, the multi-stage resonance box may have any shape, structure, etc., as long as it has a plurality of resonators arranged in the first direction.

[0085] [Variation 7] Fig. 16 is a schematic perspective view of a sound absorbing structure of Variation 7. In the sound absorbing structure 1G shown in Fig. 16, a multi-stage resonance box 2G has a first resonator 3G, a second resonator 4G, a plurality of openings 5G, and a communication opening 6G. The first resonator 3G and the second resonator 4G are arranged in a first direction D1 and are integrally formed.

[0086] The first resonator 3G has a resonance space 31G extending in the second direction D2. A cross section of the resonance space 31G perpendicular to the second direction D2 is formed in a triangular shape, and has the same shape throughout the entire area in the second direction D2.

[0087] The second resonator 4G has a resonance space 41G extending in the second direction D2. A cross section of the resonance space 41G perpendicular to the second direction D2 is formed in a triangular shape, and has the same shape throughout the entire area in the second direction D2.

[0088] A plurality of openings 5G are formed in the first resonator 3G, and connect the resonance space 31G of the first resonator 3G to the external space of the multi-stage resonance box 2G.

[0089] The communication port 6G communicates the resonance space 31G of the first resonator 3G with the resonance space 41G of the second resonator 4G.

[0090] More specifically, the multi-stage resonance box 2G is composed of a cylindrical box portion 21G having both ends open in the second direction D2, a first end (not shown) that closes one end of the cylindrical box portion 21G in the second direction D2, and a second end (not shown) that closes the end of the cylindrical box portion 21G opposite the first end in the second direction D2.

[0091] The cylindrical box portion 21G defines a resonance space 31G for the first resonator 3G and a resonance space 41G for the second resonator 4G inside the cylindrical box portion 21G. The cylindrical box portion 21G blocks the resonance space 31G and the resonance space 41G from directions perpendicular to the second direction D2 (directions along the first direction D1 and the third direction D3). With only the cylindrical box portion 21G, the resonance space 31G and the resonance space 41G are open on both sides in the second direction D2.

[0092] The cylindrical box portion 21G is composed of a first bottom wall 21Ga, a second bottom wall 21Gb, a first top wall 21Gc, a second top wall 21Gd, and a partition wall 21Gg.

[0093] The first bottom wall 21Ga is a wall that closes the resonance space 31G of the first resonator 3G from one side in the third direction D3. The first bottom wall 21Ga is formed in a flat plate shape extending in a direction inclined with respect to the first direction D1 and the third direction D3, and is disposed on one side of the resonance space 31G in the third direction D3.

[0094] The second bottom wall 21Gb is a wall that closes the resonance space 41G of the second resonator 4G from one side in the third direction D3. The second bottom wall 21Gb is formed in a flat plate shape that extends in a direction inclined toward the opposite side from the first bottom wall 21Ga, and is disposed on one side of the resonance space 41G in the third direction D3.

[0095] The first bottom wall 21Ga and the second bottom wall 21Gb are adjacent to each other in the first direction D1 and integrally formed. The first bottom wall 21Ga and the second bottom wall 21Gb are formed in a V-shape that widens toward one side in the third direction D3.

[0096] The first top wall 21Gc is a wall that closes the resonance space 31G of the first resonator 3G from the side opposite the first bottom wall 21Ga in the third direction D3. The first top wall 21Gc is formed in a flat plate shape extending in a direction inclined away from the first bottom wall 21Ga, and is disposed on the side of the resonance space 31G opposite the first bottom wall 21Ga in the third direction D3. A plurality of openings 5G are formed in the first top wall 21Gc.

[0097] The second top wall 21Gd is a wall that closes the resonance space 41G of the second resonator 4G from the side opposite the second bottom wall 21Gb in the third direction D3. The second top wall 21Gd is formed in a flat plate shape that extends in a direction inclined away from the second bottom wall 21Gb, and is disposed on the side of the resonance space 41G opposite the second bottom wall 21Gb in the third direction D3.

[0098] The first top wall 21Gc and the second top wall 21Gd are adjacent to each other in the first direction D1 and integrally formed. The first top wall 21Gc and the second top wall 21Gd are formed in a V-shape that widens toward the first bottom wall 21Ga and the second bottom wall 21Gb in the third direction D3. The tip of the first top wall 21Gc opposite to the second top wall 21Gd is connected to the tip of the first bottom wall 21Ga opposite to the second bottom wall 21Gb, and the tip of the second top wall 21Gd opposite to the first top wall 21Gc is connected to the tip of the second bottom wall 21Gb opposite to the first bottom wall 21Ga.

[0099] The partition wall 21Gg is a wall that closes the resonance space 31G of the first resonator 3G from the second resonator 4G side in the first direction D1, and closes the resonance space 41G of the second resonator 4G from the first resonator 3G side in the first direction D1. In other words, the partition wall 21Gg is a wall that forms a boundary between the first resonator 3G and the second resonator 4G, and separates the resonance space 31G from the resonance space 41G. The partition wall 21Gg is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is arranged on the second resonator 4G side of the resonance space 31G of the first resonator 3G in the first direction D1, and on the first resonator 3G side of the resonance space 41G of the second resonator 4G in the first direction D1. One end of the partition wall 21Gg in the third direction D3 is connected to the connection portion between the first bottom wall 21Ga and the second bottom wall 21Gb, and the other end of the partition wall 21Gg in the third direction D3 is connected to the connection portion between the first top wall 21Gc and the second top wall 21Gd. A communication opening 6G is formed in the partition wall 21Gg.

[0100] The first end portion is a wall that closes the resonance space 31G of the first resonator 3G and the resonance space 41G of the second resonator 4G from one side in the second direction D2. The first end portion is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is disposed on one side in the second direction D2 of the resonance space 31G and the resonance space 41G.

[0101] The second end is a wall that closes the resonance space 31G of the first resonator 3G and the resonance space 41G of the second resonator 4G from the side opposite the first end in the second direction D2. The second end faces the first end in the second direction D2. The second end is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is located on the side opposite the first end of the resonance space 31G and the resonance space 41G in the second direction D2.

[0102] In this sound-absorbing structure 1G, the first resonators 3G and second resonators 4G, each having a resonance space 31G and a resonance space 41G extending in the second direction D2, are arranged in the first direction D1. This prevents the structure from becoming thicker in a third direction D3, which is perpendicular to the first direction D1 and the second direction D2. Furthermore, the cylindrical box portion 21G of the multi-stage resonance box 2G can be manufactured by extrusion molding in the second direction D2, making it easy to manufacture.

[0103] In addition, in the present disclosure, the multi-stage resonance box may have three or more resonators.

[0104] [Variation 8] Fig. 17 is a schematic perspective view of a sound absorbing structure of Variation 8. Fig. 18 is a schematic cross-sectional view taken along line XVIII-XVIII in Fig. 17. In a sound absorbing structure 1H shown in Figs. 17 and 18, a multi-stage resonance box 2H includes a first resonator 3, a second resonator 4, a third resonator 7H, a plurality of openings 5, a communication port 6 (first communication port), and a second communication port 6H. The first resonator 3, the second resonator 4, and the third resonator 7H are arranged in this order in the first direction D1 and integrally formed. In other words, the first resonator 3 and the second resonator 4 are adjacent to each other in the first direction D1, and the second resonator 4 and the third resonator 7H are adjacent to each other in the first direction D1.

[0105] The third resonator 7H is a resonator that generates Helmholtz resonance. The third resonator 7H has a resonance space 71H that extends in a second direction D2 that is perpendicular to the first direction D1. The resonance space 71H is an internal space of the third resonator 7H. A cross section of the resonance space 71H perpendicular to the second direction D2 is formed into a rectangular shape, and has the same shape throughout the entire area in the second direction D2.

[0106] The second communication port 6H communicates the resonance space 41 of the second resonator 4 with the resonance space 71H of the third resonator 7H. The resonance space 71H is communicated with the resonance space 41 of the second resonator 4 only at the second communication port 6H. The resonance space 71H is also communicated with the external space of the multi-stage resonance box 2 only via the second communication port 6H, the resonance space 41, the communication port 6, the first resonator 3, and the multiple openings 5. The second communication port 6H is, for example, a slit formed in a partition wall forming a boundary between the second resonator 4 and the third resonator 7H and extending in the second direction D2. The second communication port 6H extends, for example, over the entire area in the second direction D2.

[0107] More specifically, the multi-stage resonance box 2H is composed of a cylindrical box portion 21H having both ends open in the second direction D2, a first end portion 22H that closes one end of the cylindrical box portion 21H in the second direction D2, and a second end portion 23H that closes the end of the cylindrical box portion 21H opposite the first end portion 22 in the second direction D2.

[0108] The cylindrical box portion 21H defines therein a resonance space 31 of the first resonator 3, a resonance space 41 of the second resonator 4, and a resonance space 71H of the third resonator 7H. The cylindrical box portion 21H blocks the resonance space 31, the resonance space 41, and the resonance space 71H from directions perpendicular to the second direction D2 (directions along the first direction D1 and the third direction D3). With only the cylindrical box portion 21H, the resonance space 31, the resonance space 41, and the resonance space 71H are open on both sides in the second direction D2.

[0109] The cylindrical box portion 21H is composed of a first bottom wall 21a, a second bottom wall 21b, a third bottom wall 21Hh, a first top wall 21c, a second top wall 21d, a third top wall 21Hi, a first side wall 21e, a second side wall 21Hj, a partition wall 21g, and a second partition wall 21Hk.

[0110] The third bottom wall 21Hh is a wall that closes the resonance space 71H of the third resonator 7H from one side in the third direction D3. The third bottom wall 21Hh is formed in a flat plate shape extending in the first direction D1 and the second direction D2, and is disposed on one side of the resonance space 71H in the third direction D3.

[0111] The first bottom wall 21 a, the second bottom wall 21 b, and the third bottom wall 21Hh are adjacent to each other in the first direction D1 and integrally formed, and the first bottom wall 21 a, the second bottom wall 21 b, and the third bottom wall 21Hh are formed as a whole in the shape of a flat plate extending in the first direction D1 and the second direction D2.

[0112] The third top wall 21Hi is a wall that closes the resonance space 71H of the third resonator 7H from the side opposite the third bottom wall 21Hh in the third direction D3. The third top wall 21Hi faces the third bottom wall 21Hh in the third direction D3. The third top wall 21Hi is formed in a flat plate shape extending in the first direction D1 and the second direction D2, and is disposed on the side of the resonance space 71H opposite the third bottom wall 21Hh in the third direction D3.

[0113] The first top wall 21c, the second top wall 21d, and the third top wall 21Hi are adjacent to each other in the first direction D1 and integrally formed, and the first top wall 21c, the second top wall 21d, and the third top wall 21Hi are formed as a flat plate extending in the first direction D1 and the second direction D2 as a whole.

[0114] The second side wall 21Hj is a wall that closes the resonance space 71H of the third resonator 7H from the side opposite the second resonator 4 in the first direction D1. The second side wall 21Hj faces the first side wall 21e in the first direction D1. The second side wall 21Hj is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is disposed on the side of the resonance space 71H opposite the second resonator 4 in the first direction D1.

[0115] The second partition wall 21Hk is a wall that closes the resonance space 41 of the second resonator 4 from the third resonator 7H side in the first direction D1 and closes the resonance space 71H of the third resonator 7H from the second resonator 4 side in the first direction D1. In other words, the second partition wall 21Hk is a wall disposed at the boundary between the second resonator 4 and the third resonator 7H and separates the resonance space 41 from the resonance space 71H. The second partition wall 21Hk faces the first side wall 21e and the second side wall 21Hj in the first direction D1. The second partition wall 21Hk is formed in a flat plate shape extending in the second direction D2 and the third direction D3 and is disposed on the third resonator 7H side of the resonance space 41 of the second resonator 4 in the first direction D1 and on the second resonator 4 side of the resonance space 71H of the third resonator 7H in the second direction D2. A second communication opening 6H is formed in the second partition wall 21Hk.

[0116] The first end portion 22H is a wall that closes the resonance space 31 of the first resonator 3, the resonance space 41 of the second resonator 4, and the resonance space 71H of the third resonator 7H from one side in the second direction D2. The first end portion 22H is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is disposed on one side in the second direction D2 of the resonance space 31, the resonance space 41, and the resonance space 71H.

[0117] The second end 23H is a wall that closes the resonance space 31 of the first resonator 3, the resonance space 41 of the second resonator 4, and the resonance space 71H of the third resonator 7H from the side opposite to the first end 22H in the second direction D2. The second end 23H faces the first end 22H in the second direction D2. The second end 23H is formed in a flat plate shape extending in the second direction D2 and the third direction D3, and is arranged on the side of the resonance space 31, the resonance space 41, and the resonance space 71H opposite to the first end 22H in the second direction D2.

[0118] In this sound-absorbing structure 1H, a multi-stage resonance box 2H has a plurality of resonators, namely, a first resonator 3, a second resonator 4, and a third resonator 7H. The resonance space 31 of the first resonator 3 and the resonance space 41 of the second resonator 4 are connected by a communication opening 6, and the resonance space 41 of the second resonator 4 and the resonance space 71H of the third resonator 7H are connected by a second communication opening 6H. Therefore, when sound waves enter the resonance space 31 of the first resonator 3 through the plurality of openings 5, resonance occurs in the resonance space 31. Furthermore, when sound waves enter the resonance space 41 of the adjacent second resonator 4 through the communication opening 6, resonance occurs in the resonance space 41. Furthermore, when sound waves enter the resonance space 71H of the adjacent third resonator 7H through the second communication opening 6H, resonance occurs in the resonance space 71H. As a result, the sound absorption peak is split into three, generating three sound absorption peaks, making it possible to absorb discrete frequency noise having three frequency peaks.

[0119] Furthermore, in this sound-absorbing structure 1H, the first resonator 3, the second resonator 4, and the third resonator 7H, each having a resonance space 31, a resonance space 41, and a resonance space 71H extending in the second direction D2, are arranged in the first direction D1. This prevents the structure from becoming thicker in a third direction D3 perpendicular to the first direction D1 and the second direction D2. Furthermore, the cylindrical box portion 21H of the multi-stage resonance box 2H can be manufactured by extrusion molding in the second direction D2, making it easy to manufacture.

[0120] In the present disclosure, the sound absorbing structure may have a plurality of multi-tiered resonance boxes arranged in the first direction. In this case, the sound absorbing structure may have the same number of multi-tiered resonance boxes or may have a different number of multi-tiered resonance boxes.

[0121] [Modification 9] Fig. 19 is a schematic perspective view of a sound absorbing structure of Modification 9. The sound absorbing structure 1J shown in Fig. 19 includes a plurality of multi-stage resonance boxes 2 arranged in the first direction D1. That is, in the sound absorbing structure 1J, a plurality of multi-stage resonance boxes 2 are arranged in the first direction D1. Each of the plurality of multi-stage resonance boxes 2 has a first resonator 3 and a second resonator 4 arranged in the first direction D1.

[0122] In this sound-absorbing structure, multiple multi-stage resonance boxes 2 are arranged in a first direction D1, thereby enhancing the sound-absorbing effect and preventing the structure from becoming thicker in a third direction D3 that is perpendicular to the first direction D1 and the second direction D2.

[0123] [Measurement of Sound Absorption Coefficient] Here, the inventors prepared sound absorbing structures of Comparative Example 1 and Examples 1 to 6, and measured the normal incidence sound absorption coefficient of each sound absorbing structure as follows: Apparatus name: 4206 type impedance tube (Brüel & Kjær) Measurement method: normal incidence sound absorption coefficient (based on JIS A 1405-1) Measurement range: 50 to 3500 Hz Measurement sample size: Φ98 mm (for low frequency measurement: measurement range 125 to 1600 Hz)

[0124] (Comparative Example 1) The sound absorbing structure of Comparative Example 1 included a single-stage resonance box with one resonator. The resonator had a resonance space extending in the second direction and an opening connecting the resonance space of the first resonator to the space outside the resonance box. The resonator was configured to generate a resonance of 580 Hz. The frequency of the resonance generated by the resonator was calculated based on the shape of the opening, the depth of the opening, the volume of the resonance space, etc. Measurement results of the sound absorption coefficient of the sound absorbing structure of Comparative Example 1 are shown in Figures 20 and 27. Figure 20 is a graph showing the measurement results of Comparative Example 1. Figure 27 is a graph showing the measurement results of Comparative Example 1 and Examples 1 and 4.

[0125] Example 1 The sound-absorbing structure of Example 1 includes a two-stage resonance box having first and second resonators arranged in a first direction, as in the sound-absorbing structure shown in FIGS. 1 to 3 . Each of the first and second resonators has a resonance space extending in a second direction perpendicular to the first direction. The two-stage resonance box includes a first resonator having a plurality of openings communicating the resonance space of the first resonator with an external space of the two-stage resonance box, and a communication opening communicating the resonance space of the first resonator with the resonance space of the second resonator. The plurality of openings are arranged in the second direction, and each of the openings is a circular hole. The communication opening is a slit extending across the entire area in the second direction. Each of the first and second resonators is configured to generate a resonance at 580 Hz. The frequency of the resonance generated in the first resonator is calculated based on the shape and depth of the openings, the volume of the resonance space of the first resonator, and other factors. The frequency of the resonance generated in the second resonator is calculated based on the shape of the communication opening, the depth of the communication opening, the volume of the resonance space of the second resonator, etc. Measurement results of the sound absorption coefficient of the sound absorbing structure of Example 1 are shown in Figures 21 and 27. Figure 21 is a graph showing the measurement results of Example 1.

[0126] Example 2 The sound absorbing structure of Example 2, like the sound absorbing structure of Example 1, was equipped with a two-stage resonance box having a first resonator and a second resonator arranged in a first direction. In the sound absorbing structure of Example 2, the first resonator was configured to generate a resonance at 580 Hz, and the second resonator was configured to generate a resonance at 320 Hz. Other than that, the sound absorbing structure was the same as the sound absorbing structure of Example 1. The measurement results of the sound absorption coefficient of the sound absorbing structure of Example 2 are shown in Figure 22. Figure 22 is a graph showing the measurement results of Example 2.

[0127] Example 3 The sound absorbing structure of Example 3, like the sound absorbing structure of Example 1, was equipped with a two-stage resonance box having a first resonator and a second resonator arranged in a first direction. In the sound absorbing structure of Example 3, the first resonator was configured to generate a resonance at 400 Hz, and the second resonator was configured to generate a resonance at 580 Hz. Other than that, the sound absorbing structure was the same as the sound absorbing structure of Example 1. The measurement results of the sound absorption coefficient of the sound absorbing structure of Example 3 are shown in Figure 23. Figure 23 is a graph showing the measurement results of Example 3.

[0128] Example 4 The sound absorbing structure of Example 4 was equipped with a three-tiered resonance box having a first resonator, a second resonator, and a third resonator arranged in a first direction, as in the sound absorbing structure shown in Figures 17 and 18 . Each of the first resonator, the second resonator, and the third resonator had a resonance space extending in a second direction perpendicular to the first direction. The three-tiered resonance box had a first resonator formed with a plurality of openings communicating the resonance space of the first resonator with an external space of the two-tiered resonance box, a first communication port communicating the resonance space of the first resonator with the resonance space of the second resonator, and a second communication port communicating the resonance space of the second resonator with the resonance space of the third resonator. The plurality of openings were arranged in the second direction, and each of the plurality of openings was a circular hole. Each of the first communication port and the second communication port was a slit extending across the entire area in the second direction. The first resonator, the second resonator, and the third resonator were each configured to generate a resonance of 580 Hz. The frequency of the resonance generated in the first resonator was calculated based on the shape of the opening, the depth of the opening, the volume of the resonance space of the first resonator, etc. The frequency of the resonance generated in the second resonator was calculated based on the shape of the first communication opening, the depth of the first communication opening, the volume of the resonance space of the second resonator, etc. The frequency of the resonance generated in the third resonator was calculated based on the shape of the second communication opening, the depth of the second communication opening, the volume of the resonance space of the third resonator, etc. Measurement results of the sound absorption coefficient of the sound absorbing structure of Example 4 are shown in Figures 24 and 27. Figure 24 is a graph showing the measurement results of Example 4.

[0129] Example 5 The sound absorbing structure of Example 5, like the sound absorbing structure of Example 4, was equipped with a three-stage resonance box having a first resonator, a second resonator, and a third resonator arranged in a first direction. In the sound absorbing structure of Example 5, the first resonator was configured to generate a resonance at 580 Hz, and the second and third resonators were each configured to generate a resonance at 400 Hz. Other than that, the sound absorbing structure was the same as the sound absorbing structure of Example 4. Measurement results of the sound absorption coefficient of the sound absorbing structure of Example 5 are shown in Figure 25. Figure 25 is a graph showing the measurement results of Example 5.

[0130] Example 6 The sound absorbing structure of Example 6, like the sound absorbing structure of Example 4, was equipped with a three-stage resonance box having a first resonator, a second resonator, and a third resonator arranged in a first direction. In the sound absorbing structure of Example 6, the first resonator was configured to generate a resonance at 580 Hz, the second resonator was configured to generate a resonance at 400 Hz, and the third resonator was configured to generate a resonance at 320 Hz. Other than that, the sound absorbing structure was the same as the sound absorbing structure of Example 4. The measurement results of the sound absorption coefficient of the sound absorbing structure of Example 6 are shown in Figure 26. Figure 26 is a graph showing the measurement results of Example 6.

[0131] [Measurement Results] As shown in Fig. 27, the sound absorbing structure of Comparative Example 1, which includes a single-stage resonance box with one resonator, generated only one sound absorption peak. In contrast, the sound absorbing structure of Example 1, which includes a two-stage resonance box with a first resonator and a second resonator, generated two sound absorption peaks, splitting the sound absorption peak into two. Furthermore, the sound absorbing structure of Example 4, which includes a three-stage resonance box with a first resonator, a second resonator, and a third resonator, generated three sound absorption peaks, splitting the sound absorption peak into three. From these results, it can be inferred that by including a multi-stage resonance box with multiple resonators connected to each other via communication openings, it is possible to generate sound absorption peaks equal to the number of resonators connected via the communication openings, and thus to absorb discrete frequency noise having frequency peaks equal to the number of resonators connected via the communication openings.

[0132] As shown in Figures 21 to 26, it was found that by providing a multi-stage resonance box with multiple resonators connected by communication ports, the sound absorption peaks that are generated are lower in frequency than the resonance frequencies generated by each resonator.

[0133] [Method for manufacturing sound-absorbing structure] From the above results, it is possible to calculate the resonance frequency generated in each resonator from the shapes of the openings and communication openings, the depths of the openings and communication openings, the volume of the resonance space of each resonator, etc., and it is also possible to identify the sound absorption peaks that will occur according to the calculated resonance frequencies generated in each resonator, so it is inferred that the sound-absorbing structure according to the present disclosure can be manufactured by the following method. That is, in the method for manufacturing a sound-absorbing structure according to the present disclosure, first an acquisition step is performed in which discrete frequency noise having multiple frequency peaks is acquired. Then, a manufacturing step is performed in which a sound-absorbing structure is manufactured so that the multiple frequency peaks of the discrete frequency noise acquired in the acquisition step become sound absorption peaks.

[0134] The manufacturing step can be performed, for example, as follows: First, a plurality of sound-absorbing structures are manufactured in advance, with different design conditions, such as the number of resonators constituting the multi-stage resonance box, the shapes of the openings and communicating holes, the depths of the openings and communicating holes, and the volume of the resonance space of each resonator, and the sound absorption peaks generated in each of the manufactured sound-absorbing structures are measured. At this time, the relationship between the design conditions of each sound-absorbing structure and the sound absorption peaks generated in each sound-absorbing structure is registered in a database such as a table. Then, when the discrete frequency noise is acquired in the acquisition step, this database is referenced to select design conditions that generate sound absorption peaks corresponding to the multiple frequency peaks of the acquired discrete frequency noise, and the sound-absorbing structure is manufactured under the selected design conditions.

[0135] In this method for manufacturing a sound absorbing structure, discrete frequency noise having multiple frequency peaks is acquired, and a sound absorbing structure is manufactured so that the multiple frequency peaks of the acquired discrete frequency noise become sound absorption peaks. Therefore, the manufactured sound absorbing structure can absorb the discrete frequency noise. Moreover, because this method for manufacturing a sound absorbing structure manufactures the above-mentioned sound absorbing structure, a thin sound absorbing structure can be easily manufactured.

[0136] The present disclosure can be used as a sound-absorbing structure and a method for manufacturing a sound-absorbing structure.

[0137] 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1J…sound absorbing structure, 2, 2A, 2B, 2G, 2H…multi-stage resonance box, 3, 3A, 3B, 3G…first resonator, 4, 4A, 4B, 4G…second resonator, 5, 5C, 5E, 5F, 5G…opening, 6, 6D, 6E, 6G…communication port (first communication port), 6H…second communication port, 7H…third resonator, 21…cylindrical box portion, 21a…first bottom wall, 21b…second bottom wall, 21c…first first wall, 21d…second second wall, 21e…first side wall, 21f…second side wall, 21g…dividing wall, 21G…cylindrical box portion, 21 Ga…first bottom wall, 21Gb…second bottom wall, 21Gc…first first wall, 21Gd…second second wall, 21Gg…zone wall, 21H…cylindrical box portion, 21Hh…third bottom wall, 21Hi…third top wall, 21Hj…second side wall, 21Hk…second zone wall, 22, 22H…first end portion, 23, 23H…second end portion, 24A…other component, 24B…other component, 25B…other component, 31, 31G…resonance space, 41, 41G…resonance space, 52E…opening protrusion, 62D, 62E…connecting port protrusion, 71H…resonance space, D1…first direction, D2…second direction, D3…third direction.

Claims

1. An acoustic absorption structure comprising a multi-stage resonance box having a plurality of resonators arranged in a first direction, each of the plurality of resonators having a resonance space extending in a second direction orthogonal to the first direction, the multi-stage resonance box including: an opening formed at a first resonator located at an end of the plurality of resonators in the first direction, the opening communicating the resonance space of the first resonator with an external space of the multi-stage resonance box; and a communication port communicating the resonance spaces of the resonators adjacent to each other in the second direction.

2. The multi-stage resonance box has, as the plurality of resonators, a first resonator and a second resonator adjacent to the first resonator, and the communication port communicates the resonance space of the first resonator with the resonance space of the second resonator. The acoustic absorption structure according to claim 1.

3. The multi-stage resonance box has, as the plurality of resonators, a first resonator, a second resonator adjacent to the first resonator, and a third resonator adjacent to the second resonator, and the communication port includes a first communication port communicating the resonance space of the first resonator with the resonance space of the second resonator and a second communication port communicating the resonance space of the second resonator with the resonance space of the third resonator. The acoustic absorption structure according to claim 1.

4. The cross-section of each of the plurality of resonators orthogonal to the second direction is formed in a rectangular shape. The acoustic absorption structure according to any one of claims 1 to 3.

5. The multi-stage resonance box is constituted by a cylindrical box portion having both ends open in the second direction. The acoustic absorption structure according to any one of claims 1 to 4.

6. The multi-stage resonance box is constituted by a cylindrical box portion having both ends open in the second direction and a first end portion closing one end of the cylindrical box portion in the second direction. The acoustic absorption structure according to any one of claims 1 to 4.

7. The multi-stage resonance box is constituted by a cylindrical box portion having both ends open in the second direction, a first end portion closing one end of the cylindrical box portion in the second direction, and a second end portion closing the other end of the cylindrical box portion in the second direction opposite to the first end portion. The acoustic absorption structure according to any one of claims 1 to 4.

8. The opening is a circular hole. The acoustic absorption structure according to any one of claims 1 to 7.

9. The multi-stage resonance box has a plurality of the openings. The acoustic absorption structure according to any one of claims 1 to 8.

10. The sound absorption structure according to claim 9, wherein the plurality of openings are arranged in the second direction.

11. The sound absorption structure according to any one of claims 1 to 10, wherein the communication port is a slit extending in the second direction.

12. The sound absorption structure according to any one of claims 1 to 11, wherein the communication port is formed by a partition wall forming a boundary of the resonators adjacent to each other in the second direction and a communication port protrusion protruding from the partition wall.

13. The sound absorption structure according to any one of claims 1 to 12, wherein the opening is formed by an outer wall of the first resonator and an opening protrusion protruding from the outer wall.

14. The sound absorption structure according to any one of claims 1 to 13, wherein a plurality of the multi-stage resonance boxes are arranged in the first direction.

15. A method for manufacturing a sound absorption structure, which is a method for manufacturing the sound absorption structure according to any one of claims 1 to 14, comprising: obtaining discrete frequency noise having a plurality of frequency peaks; and manufacturing the sound absorption structure such that the plurality of frequency peaks of the obtained discrete frequency noise become sound absorption peaks.

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