Sound-absorbing structure

Abstract

The objective is to provide a sound-absorbing structure that provides a large sound absorption effect over a wide frequency range against low-frequency noise, has a simple structure, can be made thin and lightweight, and has low manufacturing costs. [Solution] Multiple resonators 2 are arranged in a planar configuration. Each resonator 2 has a hollow box-shaped body 3, and an opening 5 is provided on one of the surfaces 3a constituting the box-shaped body 3. The multiple resonators 2 are arranged in a planar configuration such that the surfaces 3a on which the openings 5 ​​are provided are located in the same plane. At least some of the multiple resonators 2 have a different surface area between the surface 3a on which the openings 5 ​​are provided and the surface 3c facing it across the hollow portion 3b compared to the other resonators 2.

Description

[Technical Field]

[0001] This invention relates to a sound-absorbing structure. [Background technology]

[0002] In modern society, noise reduction measures are crucial for addressing noise generated by automobiles, aircraft, railways, construction sites, office buildings, and apartment complexes. In automobiles, in addition to engine noise, new noise sources such as road noise, tire pattern noise, wind noise, and motor noise have become apparent with electrification, and reducing in-vehicle noise is required to provide occupants with a quiet and comfortable space. Furthermore, in buildings such as office buildings and apartment complexes, appropriate sound absorption is necessary to improve indoor acoustics, such as improving the clarity of conversations and sounds from audio equipment. To solve these problems, sound-absorbing materials such as urethane foam and glass wool have traditionally been used. However, these materials have poor sound absorption performance at low frequencies, and thick materials are required to achieve sufficient sound absorption at low frequencies. From the perspective of improving fuel efficiency and saving space in vehicles, there is an increasing demand for compact sound-absorbing materials that effectively absorb low-frequency noise. Therefore, Patent Documents 1-2 and Non-Patent Documents 1-2 propose sound-absorbing structures having Helmholtz resonators that can exhibit a large sound absorption effect despite their small size.

[0003] The sound-absorbing structure described in Patent Document 1 comprises a plate-shaped member having a plurality of openings, a rigid wall, a rear air layer provided between the plate-shaped member and the rigid wall, and an extension member connected to the openings, wherein at least the extension portion of the extension member is housed in the rear air layer.

[0004] The sound-absorbing member described in Patent Document 2 has a plurality of cavities in which at least one of the shape and size differs from one another. The plate-like members that constitute the walls of the cavities included in the plurality of cavities have perforations that connect the inside and outside of the cavities. The surface of the plate-like members includes a first region in which a plurality of perforations are formed, and a second region adjacent to the first region in which no perforations are formed.

[0005] The sound-absorbing structure described in Non-Patent Document 1 has a configuration in which multiple Helmholtz resonators, each with a neck portion of different dimensions, are integrated.

[0006] The sound-absorbing structure described in Non-Patent Document 2 has a configuration in which multiple Helmholtz resonators, each with a circular planar shape, are arranged in a planar configuration. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2013-8012 [Patent Document 2] Japanese Patent Publication No. 2023-24421 [Non-patent literature]

[0008] [Non-Patent Document 1] “Compact broadband acoustic sink with coherently coupled weak resonances”, S. Huang, Z. Zhou, D. Li, T. Liu, X. Wang, J. Zhu, Y. Li, Science Bulletin 65 (2020), 373-379. [Non-Patent Document 2] “Broadening perfect sound absorption by composite absorber filled with porous material at low frequency”, B. Cheng, N. Gao, Y. Huang, H. Hou, Journal of Vibration and Control (2020),1-15. [Overview of the project] [Problems that the invention aims to solve]

[0009] While the configurations described in Patent Documents 1-2 and Non-Patent Documents 1-2 provide a certain degree of sound absorption, there is a greater desire for sound-absorbing structures that exhibit even greater sound absorption. Furthermore, the configuration described in Patent Document 1 has a narrow range of frequencies that can be absorbed. In the configuration described in Patent Document 2, the lack of a neck results in a small sound absorption effect, and in order to widen the range of frequencies that can be absorbed, it is necessary to form a large number of perforations, which increases the size and manufacturing cost.

[0010] The configuration described in Non-Patent Document 1 requires a large number of Helmholtz resonators to obtain a large sound absorption effect, resulting in high manufacturing costs. The configuration described in Non-Patent Document 2 has a narrow range of frequencies that can be absorbed.

[0011] Therefore, the object of the present invention is to provide a sound-absorbing structure that can achieve a large sound absorption effect over a wide frequency range against low-frequency noise, has a simple structure, can be made thinner and lighter, and has low manufacturing costs, and in particular exhibits high sound absorption characteristics in the 500Hz to 1000Hz frequency band, which is a challenge for reducing noise inside electric vehicles and improving the intelligibility of human conversations. [Means for solving the problem]

[0012] The sound-absorbing structure of the present invention is characterized in that a plurality of resonators are arranged in a planar manner, each resonator has a hollow box-shaped body, an opening is provided on one of the surfaces constituting the box-shaped body, the plurality of resonators are arranged in a planar manner such that the surfaces on which the openings are provided are located in the same plane, and at least some of the plurality of resonators have a surface area that is different from the surface on which the opening is provided and the surface facing the hollow portion. [Effects of the Invention]

[0013] According to the present invention, there is provided a sound-absorbing structure that can obtain a large sound-absorbing effect over a wide frequency range against low-frequency noise, has a simple structure, can be thinned and lightened, and has a low manufacturing cost. In particular, a sound-absorbing structure that exhibits high sound-absorbing characteristics in the frequency band of 500 Hz to 1000 Hz, which is a problem for reducing noise inside a vehicle of an electric vehicle and improving the audibility of human conversations, can be obtained.

Brief Description of the Drawings

[0014] [Figure 1] (A) is a perspective view showing a sound-absorbing structure according to an embodiment of the present invention, and (B) is a cross-sectional view thereof. [Figure 2] (A) is an enlarged perspective view of a resonator of the sound-absorbing structure shown in FIG. 1, and (B) is an enlarged cross-sectional view thereof. [Figure 3] It is a cross-sectional view showing a modified example of the sound-absorbing structure according to an embodiment of the present invention. [Figure 4] It is a cross-sectional view showing another modified example of the sound-absorbing structure according to an embodiment of the present invention. [Figure 5] (A) to (C) are enlarged plan views of resonators of still another modified example of the sound-absorbing structure according to an embodiment of the present invention. [Figure 6] It is a cross-sectional view showing a sound-absorbing structure according to another embodiment of the present invention. [Figure 7] It is a cross-sectional view of the sound-absorbing structure of Example 1 of the present invention. [Figure 8] It is a plan view of the sound-absorbing structure of Example 1 of the present invention. [Figure 9] It is a graph showing the relationship between the frequency and the sound absorption rate of the sound-absorbing structure of Example 1 of the present invention. [Figure 10] It is a graph showing the relationship between the frequency and the sound absorption rate of the sound-absorbing structure of Example 2 of the present invention. [Figure 11] It is a plan view of the sound-absorbing structure of Example 3 of the present invention. [[ID=3S]] [Figure 12] It is a graph showing the relationship between the frequency and the sound absorption rate of the sound-absorbing structure of Example 3 of the present invention. [Figure 13] It is a graph showing the relationship between the frequency and the sound absorption rate of the sound-absorbing structure of Example 4 of the present invention. [Figure 14] This graph shows the relationship between frequency and sound absorption coefficient of the sound-absorbing structure of Embodiment 5 of the present invention. [Figure 15] This graph shows the relationship between frequency and sound absorption coefficient of the sound-absorbing structure of Embodiment 6 of the present invention. [Figure 16] This graph shows the relationship between frequency and sound absorption coefficient of the sound-absorbing structure in Comparative Example 1. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described below with reference to the drawings. Figure 1(A) is a perspective view showing a sound-absorbing structure 1 according to one embodiment of the present invention, and Figure 1(B) is a cross-sectional view thereof. This sound-absorbing structure 1 has a configuration in which a plurality of resonators 2 are arranged in a planar arrangement. Figure 2(A) is an enlarged perspective view of a resonator 2 of the sound-absorbing structure 1, and Figure 2(B) is an enlarged cross-sectional view thereof. The resonator 2 has a hollow box body 3 and a porous material layer 4 arranged inside the box body 3. An opening 5 and a neck portion 6 are provided on one surface constituting the box body 3, specifically the top surface 3a located at the top of the drawing, and the resonator 2 constitutes a so-called Helmholtz resonator. The neck portion 6 is a hollow rectangular tube that protrudes from the inner circumference of the opening 5 toward the inside of the box body 3. The porous material layer 4 is arranged so as to overlap the surface of the box body 3 where the opening 5 and the neck portion 6 are provided (top surface) 3a and the surface opposite to it across the hollow portion 3b (bottom surface located at the bottom of the drawing) 3c. In the sound-absorbing structure 1 of this embodiment, each resonator 2 is arranged in a line such that their top surfaces 3a are located in the same plane. The area of ​​the planar shape of each resonator 2, in other words, the area of ​​the bottom surface 3c of each resonator 2, is not constant. At least some (preferably at least 2 / 3) of the resonators 2 have a different area of ​​the bottom surface 3c than the other resonators 2. Furthermore, as shown in the modified example in Figure 3, it is also possible to have a configuration in which the neck portion 6 is not provided in some of the resonators 2. Moreover, it is also possible to have a configuration in which the neck portion 6 is not provided in any of the resonators 2.

[0016] Preferably, the top surface 3a and neck portion 6 of the box body 3 are integrally formed. Because the box body 3 and neck portion 6 exhibit high sound absorption characteristics due to their shape, they can be constructed from various materials. For example, they can be formed from metal materials such as stainless steel (SUS) or aluminum, plastics (e.g., LDPE (low-density polyethylene), PE (polyethylene), PP (polypropylene), PET (polyethylene terephthalate), PVC (polyvinyl chloride), PLA (polylactic acid), ABS, PC (polycarbonate), and composite resins thereof), wood, etc. Preferably, the materials constituting the box body 3 and neck portion 6 have a Young's modulus of 1 MPa to 250 GPa. By constructing the resonator 2 with such highly rigid materials, sound waves do not pass through the components, and acoustic energy can be confined within the box body 3 at the resonant frequency, thereby achieving high sound absorption characteristics. The porous layer 4 has a flow resistance (per unit thickness) of 5000 Ns / m 4 ~100,000 Ns / m 4 It is preferable that the porous body layer 4 is made of a material with high sound absorption. For example, the porous body layer 4 is made of various foams such as polyurethane foam, melamine foam, and rubber sponge, as well as nonwoven fabric, woven fabric, felt, glass wool, etc. These materials may also be made from biomass raw materials. The box body 3 is not limited to a hollow cube or rectangular prism, but may be any hollow solid. The planar shape of the box body 3 may be a polygon other than a quadrilateral, a circle, or other irregular shape, and the top surface 3a and bottom surface 3c may be curved.

[0017] A Helmholtz resonator, such as the resonator 2 that constitutes the sound-absorbing structure 1 of this embodiment, generally has a resonant frequency f shown by the following equation (1). r It exhibits high sound absorption characteristics in this context.

[0018]

number

[0019] c represents the speed of sound, s represents the cross-sectional area of ​​the neck constituting the Helmholtz resonator, l represents the length (height) of the neck including the thickness of the opening, and V represents the volume of the resonator. In other words, by designing the resonator 2 to have a large neck length and volume, and a small neck cross-sectional area, the resonant frequency can be lowered, and high sound absorption characteristics at low frequencies can be achieved. For example, if the dimensions of the neck portion 6 are constant and the height of the resonator 2 is also constant, the resonant frequency can be adjusted while maintaining the overall dimensions of the sound-absorbing structure 1 by adjusting the area of ​​the planar shape of the resonator 2, specifically the area of ​​the bottom surface 3c. Furthermore, by forming the bottom surfaces 3c of the multiple resonators 2 constituting the sound-absorbing structure 1 to have different areas, high sound absorption characteristics can be achieved over a wide range of frequencies. Based on this idea, at least some of the multiple resonators 2 are set so that the area of ​​the bottom surface 3c is different from that of the other resonators 2. In the sound-absorbing structure 1 of this embodiment, for example, as shown in Figure 1(B), the area of ​​the bottom surface 3c of each resonator 2 is different. However, the configuration may be such that the area of ​​the base surface 3c is the same for some of the multiple resonators 2. Specifically, it is preferable that at least two-thirds of the multiple resonators 2 have a different base surface 3c area from the other resonators 2. That is, it is preferable that the number of resonators 2 with the same base surface 3c area is less than one-third of the total resonators 2.

[0020] The resonator 2 of the sound-absorbing structure 1 achieves excellent sound absorption not only through the sound absorption effect caused by the vigorous vibration of the air inside the hollow neck portion 6, but also through the action of the porous material layer 4 positioned inside the box body 3 opposite the neck portion 6. In particular, in this embodiment, the sound absorption effect is greatly enhanced because the porous material layer 4 is positioned so as to overlap the bottom surface 3c of the box body 3, which is opposite the top surface 3a where the opening 5 and the neck portion 6 are located, with the hollow portion 3b in between. For example, compared to a case where the porous material layer 4 is positioned away from the bottom surface 3c and closer to the top surface 3a, the sound absorption effect is particularly excellent when the porous material layer 4 overlaps the bottom surface 3c. Due to the action of the porous material layer 4 positioned in this way, the sound absorption performance of the sound-absorbing structure 1 is good even if the height H of the neck portion 6 is somewhat low. Being able to lower the height H of the neck portion 6 while ensuring sound absorption contributes to the miniaturization, weight reduction, and ease of manufacturing of the sound-absorbing structure 1. Specifically, because the neck portion 6 is short, it is easy to form by injection molding, additive manufacturing, etc. Thus, in order to obtain good sound absorption of the sound-absorbing structure 1 even if the height H of the neck portion 6 is somewhat low due to the action of the porous body layer 4, it is preferable that the height H of the neck portion 6 of the resonator 2 is smaller than the thickness T1 of the porous body layer 4. It is permissible for the height H of the neck portion 6 of some resonators 2 to be greater than the thickness T1 of the porous body layer 4, but it is preferable that 70% or more of the resonators 2 have a neck portion 6 height H smaller than the thickness T1 of the porous body layer 4, and it is more preferable that 80% or more exist. In order for the sound-absorbing structure 1 to exhibit sufficient sound absorption characteristics for low-frequency noise in the range of 500 Hz to 1000 Hz and to be thinner than conventional sound-absorbing materials, the thickness T2 of the resonator 2 is preferably 10 mm or more and 60 mm or less, and more preferably 20 mm or more and 50 mm or less. In order to maintain the manufacturability of the neck portion 6 while improving the sound absorption characteristics by combining the effects of the porous body layer 4 and the neck portion 6, the height H of the neck portion 6 is preferably 1 mm or more and 10 mm or less, and the width W1 of the neck portion 6 is preferably 3 mm or more and 10 mm or less. The width W2 of the resonator is preferably 3 to 10 times the width W1 of the neck portion 6.By setting the width W2 of the resonator within this range, a sufficient neck portion 6 is formed so that the resonator 2 exhibits high sound absorption characteristics through Helmholtz resonance. Furthermore, the ratio of the height H and width W1 of the neck portion 6 to the width W2 of the resonator is not excessively large, resulting in a design that is easy to manufacture. However, it is also possible to have a configuration in which the porous body layer 4 does not exist within the resonator 2. In addition, as shown in Figure 3, it is also possible to have a configuration in which only the opening 5 exists in some of the resonators 2 and the neck portion 6 does not exist. Moreover, it is also possible to have a configuration in which the neck portion 6 is not provided in any of the resonators 2. A certain degree of sound absorption effect can be obtained even in configurations without the porous body layer 4 or the neck portion 6.

[0021] To ensure the rigidity of the sound-absorbing structure 1 and the volume inside the box 3, the thickness T of each surface of the box 3 is preferably 0.5 mm or more and 5 mm or less, and more preferably 1 mm or more and 3 mm or less. The thickness T1 of the porous material layer 4 is preferably 6 mm or more and less than or equal to the height T3 inside the box 3, and more preferably 10 mm or more and 3 mm or less. The porous material layer 4 may fill the entire interior of the box 3. Here, the height T3 inside the box 3 is expressed as T3 = T2 - 2T, and is a value that depends on the thickness T2 of the resonator 2 and the thickness T of the box 3. No complicated work is required to adjust the thickness T1 of the porous material layer 4. The thickness T1 of the porous material layer 4 of multiple resonators 2 may be constant, but the thickness T1 of the porous material layer 4 of some of the resonators 2 may be different from the thickness T1 of the porous material layer 4 of the other resonators 2.

[0022] The main frequency range for sound absorption by the resonator 2 varies depending on the height H of the neck portion 6 in the direction perpendicular to the top surface 3a on which the opening 5 and the neck portion 6 are provided, and the area of ​​the planar shape of the resonator 2, i.e., the area of ​​the bottom surface 3c. In the sound-absorbing structure 1 of this embodiment, multiple types of resonators 2 with different bottom surface 3c areas are mixed together, so a large sound absorption effect can be obtained over a wide frequency range.

[0023] In the sound-absorbing structure 1 of this embodiment, as shown in Figure 1, adjacent resonators 2 are in close contact with each other without any gaps, so that a good sound absorption effect can be achieved throughout the entire sound-absorbing structure 1 without any leakage. However, as shown in Figure 4, there may be a gap between adjacent resonators 2, and it is preferable that the gap ΔW between resonators 2 is 0 mm or more and 5 mm or less. The planar shape of the box 3 of each resonator 2 is preferably a polygon that can fill the plane, such as a square, triangle, or hexagon. In addition, the cross-sectional shape (planar shape) perpendicular to the longitudinal direction of the neck portion 6 is not limited to a square as shown in Figures 1 and 2, but may be a circle as shown in Figure 5(A), a polygon other than a square (e.g., an octagon) as shown in Figure 5(B), or a star shape as shown in Figure 5(C). The sound-absorbing structure 1 of this embodiment can be manufactured by injection molding, additive manufacturing, machining, etc. of the aforementioned materials. Each component constituting the sound-absorbing structure 1 may be molded as a single unit, or they may be individually molded and then joined to each other by adhesive, heat welding, etc.

[0024] The sound-absorbing structure 1 of the present invention can be used in a wide range of applications to counter low-frequency noise. For example, by installing the sound-absorbing structure 1 of the present invention in vehicles, especially automobiles, noise such as road noise, tire pattern noise, wind noise, and motor noise transmitted inside the vehicle can be reduced, creating a comfortable interior space. Furthermore, by installing the sound-absorbing structure 1 of the present invention on the walls and ceilings of buildings such as office buildings and apartment complexes, excessive reverberation can be suppressed, improving the clarity of conversations and sounds from audio equipment, thus improving the acoustics of the room.

[0025] In the embodiment described above, the porous material layer 4 is placed inside the box 3 of all the resonators 2 of the sound-absorbing structure 1, but the structure is not limited to this configuration. As shown in the other embodiment illustrated in Figure 6, the porous material layer 4 can be placed inside the box 3 of only some of the resonators 2, and the porous material layer 4 can not be placed inside the box 3 of the other resonators 2. In particular, it is preferable that the porous material layer 4 is placed inside the box 3 of 55% or more of the resonators 2. However, it is also possible to have a configuration in which the porous material layer 4 is not provided in any of the resonators 2. [Examples]

[0026] Specific examples and comparative examples of the sound-absorbing structure 1 of the present invention are described below. [Example 1] The sound-absorbing structure 1 of Embodiment 1 of the present invention has a square planar shape with a length of approximately 100 mm and a width of approximately 100 mm. A cross-sectional view of this sound-absorbing structure 1 is shown in Figure 7, and a plan view is shown in Figure 8. This sound-absorbing structure 1 has a configuration in which nine resonators 2 are arranged in a 3x3 matrix. An opening 5 with a circular planar shape is provided on the top surface 3a of the box body 3 of each resonator 2. A hollow neck portion 6 is not formed that protrudes inward from the inner circumference of this opening 5 into the box body 3. The top surface 3a and bottom surface 3c of the box body 3, where the opening 5 is provided, face each other with a hollow portion 3b in between. The dimensions of each part of each resonator 2 are shown in Table 1.

[0027] [Table 1]

[0028] In this embodiment, the dimensions of the planar shape of each resonator 2 are different. The width of resonator 2 is the dimension in the X direction in Figure 8, and corresponds to the width W2 shown in Figure 2(B). The length of resonator 2 is the dimension in the Y direction in Figure 8. The area of ​​resonator 2 is the product of the width and the length of resonator 2. The height of the neck portion 6 corresponds to the height H shown in Figure 2(B). The width (diameter) of the neck portion 6 corresponds to the width W1 shown in Figure 2(B). The thickness of the opening 5 is synonymous with the thickness of the top surface 3a, and in each embodiment and comparative example described herein, it is equal to the plate thickness T shown in Figure 2(B), for example, 1.20 mm. In this embodiment, the height of the neck portion 6 + the thickness of the opening 5 is 1.2 mm, and the neck portion 6 is not provided. The width W1 of the neck portion 6 listed in Table 1 is the width (inner diameter) of the opening 5. The thickness of the porous body layer 4 corresponds to the thickness T1 in Figure 2(B). The thickness of resonator 2 corresponds to the thickness T2 in Figure 2(B). The ratio of (neck height + opening thickness) / porous layer thickness is (H+T) / T1. In the sound-absorbing structure 1 of this embodiment, a porous layer 4 is not provided in each resonator 2, and the thickness T1 of the porous layer 4 is 0, so (neck height + opening thickness) / porous layer thickness cannot be calculated. The sound absorption characteristics exhibited by the sound-absorbing structure 1 can be evaluated by the normal incidence sound absorption coefficient obtained from the transfer matrix method. The normal incidence sound absorption coefficient α is expressed by the following equation (2).

[0029]

number

[0030] Z air Z is the characteristic impedance of air. all This is the impedance of the entire sound-absorbing structure 1. all As shown in equation (3), the impedance Z of each resonator i This can be expressed as (1 ≤ i < 9).

[0031]

number

[0032] S allis the cross-sectional area of the entire sound-absorbing structure 1, S i represents the cross-sectional area of the i-th resonator. Further, the impedance Z of each resonator i is represented by the transfer matrix T of the resonator i as shown in Equation (4).

[0033] [Equation]

[0034] (T i ) 11 ,(T i ) 21 represent the 11-component and 21-component of the transfer matrix, respectively. The transfer matrix T i can be evaluated according to Non-Patent Documents 1 and 2. The relationship between the frequency and the normal incidence sound absorption rate of the sound-absorbing structure 1 of this embodiment is shown in FIG. 9. The average value of the normal incidence sound absorption rate of the sound-absorbing structure 1 of this embodiment at the frequencies of 500 Hz to 1000 Hz shown in FIG. 9 is 0.814. In the following description, the normal incidence sound absorption rate represented by Equation (2) is simply referred to as the sound absorption rate.

[0035] [Example 2] The sound-absorbing structure 1 of Example 2 of the present invention has a configuration similar to that of the sound-absorbing structure 1 of Example 1, but some of the resonators 2 have a neck portion 6. The dimensions of each part of this sound-absorbing structure 1 are shown in Table 2. The relationship between the frequency and the sound absorption rate of the sound-absorbing structure 1 of this embodiment is shown in FIG. 10. The average value of the sound absorption rate of the sound-absorbing structure 1 of this embodiment at the frequencies of 500 Hz to 1000 Hz shown in FIG. 10 is 0.839.

[0036] [Table 2]

[0037] [Example 3] The sound-absorbing structure 1 of Embodiment 3 of the present invention, like the sound-absorbing structures 1 of Embodiments 1 and 2, has different planar dimensions for each resonator 2. Each resonator 2 is provided with a neck portion 6, and the shape and dimensions of each neck portion 6 are constant. A plan view of this sound-absorbing structure 1 is shown in Figure 11. A porous material layer 4 is provided inside each resonator 2 of this embodiment, and the thickness of the porous material layer 4 is constant. The dimensions of each part of this sound-absorbing structure 1 are shown in Table 3. Figure 12 shows the relationship between frequency and sound absorption coefficient of the sound-absorbing structure 1 of this embodiment. The average sound absorption coefficient of the sound-absorbing structure 1 of this embodiment at frequencies from 500 Hz to 1000 Hz shown in Figure 12 is 0.868.

[0038] [Table 3]

[0039] [Example 4] The sound-absorbing structure 1 of Embodiment 4 of the present invention, like the sound-absorbing structure 1 of Embodiment 2, has different planar dimensions for each resonator 2, and the shape and dimensions of the neck portion of each resonator 2 are also different. A porous material layer 4 is provided inside each resonator 2 of this embodiment, and the thickness of the porous material layer 4 is constant. The dimensions of each part of this sound-absorbing structure 1 are shown in Table 4. Figure 13 shows the relationship between frequency and sound absorption coefficient of the sound-absorbing structure 1 of this embodiment. The average sound absorption coefficient of the sound-absorbing structure 1 of this embodiment at frequencies from 500 Hz to 1000 Hz shown in Figure 13 is 0.872.

[0040] [Table 4]

[0041] [Example 5] The sound-absorbing structure 1 of Embodiment 5 of the present invention, like the sound-absorbing structure 1 of Embodiment 1, has different dimensions for the planar shape of each resonator 2, and no neck portion 6 is provided in each resonator 2. A porous material layer 4 is provided inside each resonator 2 of this embodiment, and the thickness of the porous material layer 4 is constant. However, the area of ​​the planar shape of some of the resonators 2 is the same. Specifically, the area of ​​resonator 2 No. 2 and resonator 2 No. 4 are the same, the area of ​​resonator 2 No. 3 and resonator 2 No. 7 are the same, and the area of ​​resonator 2 No. 6 and resonator 2 No. 8 are the same. That is, there are 6 different planar shape areas among the 9 resonators 2. The dimensions of each part of this sound-absorbing structure 1 are shown in Table 5. Figure 14 shows the relationship between frequency and sound absorption coefficient of the sound-absorbing structure 1 of this embodiment. The average sound absorption coefficient of the sound-absorbing structure 1 of this embodiment at frequencies from 500 Hz to 1000 Hz shown in Figure 14 is 0.846.

[0042] [Table 5]

[0043] [Example 6] The sound-absorbing structure 1 of Embodiment 6 of the present invention has a configuration similar to the sound-absorbing structure 1 of Embodiment 5, where the dimensions of the planar shape of each resonator 2 are not uniform, and each resonator 2 is not provided with a neck portion 6. Furthermore, a porous material layer 4 is provided inside each resonator 2 of this embodiment, and the thickness of the porous material layer 4 is uniform. However, the dimensions of the planar shape of some of the resonators 2 are identical. Specifically, the dimensions of resonators 2 No. 2 and No. 3 are the same, the areas of resonators 2 No. 4 and No. 7 are the same, and the areas of resonators 2 No. 5, No. 6, No. 8 and No. 9 are the same. That is, among the nine resonators 2, there are four different planar shape dimensions and three different areas. The dimensions of each part of this sound-absorbing structure 1 are shown in Table 6. Figure 15 shows the relationship between frequency and sound absorption coefficient of the sound-absorbing structure 1 of this embodiment. The average sound absorption coefficient of the sound-absorbing structure 1 of this embodiment at frequencies from 500 Hz to 1000 Hz shown in Figure 15 is 0.781.

[0044] [Table 6]

[0045] [Comparative Example 1] The sound-absorbing structure 1 of Comparative Example 1 has a configuration similar to that shown in Figure 1, but the dimensions of the planar shape of each resonator 2 of the sound-absorbing structure 1 are constant, and the shape and dimensions of the neck portion of each resonator 2 are also constant. Furthermore, a porous material layer 4 is provided inside each resonator 2, and the thickness of the porous material layer 4 is constant. The dimensions of each part of this sound-absorbing structure 1 are shown in Table 7. Figure 16 shows the relationship between frequency and sound absorption coefficient of the sound-absorbing structure 1 of this comparative example. The average sound absorption coefficient of the sound-absorbing structure 1 of this comparative example at frequencies from 500 Hz to 1000 Hz shown in Figure 16 is 0.439.

[0046] [Table 7]

[0047] [result] Figures 9-10 and 12-16 compare the sound absorption coefficients of Examples 1-6 and Comparative Example 1 of the present invention. According to the sound absorption structure 1 of Examples 1-6 of the present invention, a high sound absorption coefficient is observed over a wide frequency range, and the average value of the sound absorption coefficient is a high value exceeding 0.75.

[0048] Referring to Figure 16, in Comparative Example 1, the sound-absorbing structure 1 achieves locally high sound absorption coefficients at some frequencies, but low sound absorption coefficients in many frequency bands. The average value of this sound absorption coefficient is below 0.5. This is thought to be because Comparative Example 1 only has one type of resonator 2, and all resonators 2 exhibit a large sound absorption effect in the same frequency band, while the sound absorption effect is poor in other frequency bands.

[0049] Compared to Comparative Example 1 described above, Examples 1 to 6 achieve a large sound absorption effect over a wide frequency band. Referring to Figure 9, although an opening 5 is provided on the top surface 3a, there is no neck portion 6 protruding from the top surface 3a which is 1.2 mm thick, and even in the configuration of Example 1, which does not have a porous body layer 4, a large sound absorption coefficient of 0.8 or more on average can be achieved, and furthermore, because the dimensions of the planar shape of each resonator 2 are different, a large sound absorption effect can be obtained over a wide frequency band.

[0050] According to Example 2, as shown in Figure 10, a greater sound absorption effect is obtained than in Example 1. This is thought to be because some of the resonators 2 are provided with neck portions 6 protruding from the top surface 3a. Furthermore, according to Example 3, as shown in Figure 12, an even greater sound absorption effect is obtained than in Examples 1 and 2. This is thought to be the effect of the porous material layer 4 placed in the resonators 2. Moreover, according to Example 4, as shown in Figure 13, a porous material layer 4 is placed in all of the resonators 2, and most of the resonators 2 are provided with neck portions 6, resulting in an even greater sound absorption effect. In addition, since the dimensions of the planar shape of each resonator 2 are different, and the dimensions of the neck portions 6 of many of the resonators 2 are also different, the frequency bands in which the sound absorption effect of each resonator 2 is particularly large are further varied, resulting in a more evenly distributed and large sound absorption effect across a wide frequency band.

[0051] In the sound-absorbing structure 1 of Example 5, the dimensions of the neck portion 6 of each resonator 2 are constant, and although the dimensions of the planar shape of each resonator 2 are different, the area of ​​the planar shape of some of the resonators 2 is the same. As shown in Figure 14, the sound absorption coefficient of the sound-absorbing structure 1 of Example 5 is smaller than that of the sound-absorbing structure 1 of Example 4, and there are frequency bands where the sound absorption coefficient is slightly lower. Nevertheless, a large sound absorption coefficient of 0.8 or higher on average can be obtained. When a sound absorption effect as large as that of Example 4 is not required, it is possible to simplify the manufacturing of the sound-absorbing structure 1 by matching the area of ​​the planar shape of some of the resonators 2, as in Example 5.

[0052] In the sound-absorbing structure 1 of Example 6 shown in Figure 15, the frequency range in which sound absorption is effective is wider compared to the sound-absorbing structure 1 of Comparative Example 1, but it is not sufficient compared to Examples 1 to 5. This is thought to be because there are only four possible dimensions for the planar shape of the resonator 2 (three possible areas), resulting in limited variation.

[0053] Thus, because the dimensions of the planar shape (bottom surface 3c) of each resonator 2 in the sound-absorbing structure 1 according to the present invention vary, a high sound absorption coefficient can be obtained over a wide frequency range (e.g., 500Hz to 1000Hz). Moreover, this high sound absorption coefficient can be achieved simultaneously with miniaturization (for example, reducing the width of the sound-absorbing structure 1 to 100mm or less and the thickness to 25mm or less), weight reduction, and ease of manufacturing. Since a large sound absorption effect can be obtained without significantly increasing the number of resonators 2, there is no need to increase the number of resonators 2 more than necessary, and the number of resonators 2 arranged in a matrix as shown in Figures 8 and 11 can be as few as nine. Note that the configuration is not limited to all resonators 2 having different planar shapes; the dimensions of some resonators 2 may be the same. However, comparing Example 5 and Example 6, in order to obtain a greater sound absorption effect over a wide frequency band, it is preferable that at least two-thirds of the multiple resonators 2 have a different base surface area 3c from the other resonators 2, and that less than one-third of the resonators 2 have the same base surface area 3c.

[0054] In such a sound-absorbing structure 1, if a porous layer 4 is provided in each resonator 2 and arranged to overlap the bottom surface 9c, a large sound absorption effect can be obtained, and the fluctuation of the sound absorption coefficient with respect to frequency changes can be made very small, resulting in a large average sound absorption coefficient. Furthermore, if a neck portion 6 is provided in the resonator 2, an even greater sound absorption effect can be obtained. Moreover, if the dimensions of the neck portions 6 of each resonator 2 are different, it is more effective to obtain a large sound absorption effect over a wide frequency band.

[0055] The present invention may have the following configurations. [1] Multiple resonators are arranged in a planar configuration, The resonator has a hollow box-shaped body, and an opening is provided on one of the surfaces constituting the box-shaped body. The multiple resonators are arranged side by side such that the surfaces on which the openings are provided are located in the same plane. A sound-absorbing structure characterized in that at least some of the multiple resonators have a different surface area between the surface on which the opening is provided and the surface on which the hollow portion is separated, compared to the other resonators. [2] The sound-absorbing structure according to [1], wherein at least some of the plurality of resonators have a neck portion that protrudes from the inner circumference of the opening toward the inside of the box. [3] The sound-absorbing structure according to [2], wherein at least some of the multiple resonators have different dimensions from the other resonators in the neck portion. [4] The sound-absorbing structure according to [2] or [3], wherein the box body and the neck portion are integrally formed. [5] The sound-absorbing structure according to any one of [2] to [4], wherein the box body and the neck portion are formed of metal or resin. [6] The sound-absorbing structure according to [1], wherein at least some of the plurality of resonators have a porous layer disposed inside the box, and the porous layer is disposed on the surface of the box that is opposite to the surface where the opening is provided, with the hollow portion in between. [7] The sound-absorbing structure according to any one of [2] to [5], wherein at least some of the plurality of resonators have a porous layer disposed inside the box, and the porous layer is disposed on the surface of the box that is opposite to the surface where the opening is provided, with the hollow portion in between. [8] The sound-absorbing structure according to [7], wherein the thickness of the porous layer of a plurality of resonators having the porous layer is greater than the height of the neck portion in the direction perpendicular to the opening and the surface on which the neck portion is provided. [9] The sound-absorbing structure according to any one of [6] to [8], wherein the thickness of the porous layer of a plurality of resonators having the porous layer is constant.

[10] The sound-absorbing structure according to any one of [6] to [8], wherein at least some of the plurality of resonators having the porous layer have a different thickness of the porous layer than the other resonators.

[11] The sound-absorbing structure according to any one of [6] to

[10] , wherein the porous layer is made of foam, nonwoven fabric, woven fabric, felt, or glass wool.

[12] The sound-absorbing structure according to any one of [1] to

[11] , wherein at least two-thirds of the plurality of resonators have a different surface area from the other resonators, with respect to the surface on which the opening is provided and the surface on which the hollow portion is separated.

[13] The sound-absorbing structure according to any one of [1] to

[12] , wherein the planar shape of the opening is rectangular, circular, or star-shaped.

[14] The sound-absorbing structure according to any one of [1] to

[13] , wherein the planar shape of each of the resonators is square, triangular, or hexagonal. [Explanation of Symbols]

[0056] 1. Sound-absorbing structure 2 resonator 3 box body 3a Top surface 3b Hollow part 3c Bottom 4. Porous layer 5 Openings 6. Neck section H Neck height W1 Neck width W2 width of the resonator T1 Thickness of the porous layer T2: Thickness of the resonator T3 Box Interior Height T Box body plate thickness

Claims

1. Multiple resonators are arranged in a planar configuration. The resonator has a hollow box-shaped body, and an opening is provided on one of the surfaces constituting the box-shaped body. The multiple resonators are arranged side by side such that the surfaces on which the openings are provided are located in the same plane. A sound-absorbing structure characterized in that at least some of the multiple resonators have a different surface area between the surface on which the opening is provided and the surface on which the hollow portion is separated, compared to the other resonators.

2. The sound-absorbing structure according to claim 1, wherein at least some of the multiple resonators have a neck portion that protrudes from the inner circumference of the opening toward the inside of the box.

3. The sound-absorbing structure according to claim 2, wherein at least some of the resonators among the plurality of resonators have different dimensions for the neck portion from the other resonators.

4. The sound-absorbing structure according to claim 2 or 3, wherein the box body and the neck portion are integrally formed.

5. The sound-absorbing structure according to claim 2 or 3, wherein the box body and the neck portion are formed of metal or resin.

6. The sound-absorbing structure according to claim 1, wherein at least some of the multiple resonators have a porous material layer disposed inside the box, and the porous material layer is disposed on the surface of the box that faces the surface where the opening is provided, with the hollow portion in between.

7. The sound-absorbing structure according to claim 2, wherein at least some of the plurality of resonators have a porous material layer disposed inside the box, and the porous material layer is disposed on the surface of the box that faces the surface where the opening is provided, with the hollow portion in between.

8. The sound-absorbing structure according to claim 7, wherein the thickness of the porous layer in a plurality of resonators having the porous layer is greater than the height of the neck portion in the direction perpendicular to the opening and the surface on which the neck portion is provided.

9. The sound-absorbing structure according to any one of claims 6 to 8, wherein the thickness of the porous layer in a plurality of resonators having the porous layer is constant.

10. The sound-absorbing structure according to any one of claims 6 to 8, wherein at least some of the plurality of resonators having the porous layer have a different thickness of the porous layer than the other resonators.

11. The sound-absorbing structure according to any one of claims 6 to 8, wherein the porous layer is made of foam, nonwoven fabric, woven fabric, felt, or glass wool.

12. The sound-absorbing structure according to any one of claims 1, 2, 3, 6, 7, or 8, wherein at least two-thirds of the plurality of resonators have a different surface area between the surface on which the opening is provided and the surface facing the hollow portion.

13. The sound-absorbing structure according to any one of claims 1, 2, 3, 6, 7, or 8, wherein the planar shape of the opening is rectangular, circular, or star-shaped.

14. The sound-absorbing structure according to any one of claims 1, 2, 3, 6, 7, or 8, wherein the planar shape of each of the resonators is square, triangular, or hexagonal.

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