Sound absorbing device and on-vehicle sound absorbing device

Abstract

A sound absorbing device according to the present disclosure comprises a sound absorbing member including: a first sound absorbing layer that includes a plurality of first acoustic metamaterials each provided with at least one sound absorbing part and absorbs sound in a first frequency band; and a second sound absorbing layer that is stacked on the first sound absorbing layer, includes a plurality of second acoustic metamaterials each provided with at least one sound absorbing part, and absorbs sound in a second frequency band lower than the first frequency band.

Description

Sound absorbing devices and in-vehicle sound absorbing devices

[0001] This disclosure relates to sound-absorbing devices and in-vehicle sound-absorbing devices.

[0002] Inside a moving vehicle, there is a type of noise known as road noise, which has strong peaks in specific frequency ranges. This road noise can interfere with conversations and listening to music for passengers inside the vehicle.

[0003] On the other hand, sound-absorbing members capable of absorbing sounds in a specific frequency band have been proposed using acoustic metamaterials (for example, Patent Document 1).

[0004] International Publication No. 2024 / 048130

[0005] However, conventionally, the configuration of sound-absorbing materials that effectively absorb driving noise heard by the user, as well as the method of positioning them relative to the user, had not been sufficiently considered.

[0006] Therefore, the present disclosure aims to provide a sound-absorbing device and an in-vehicle sound-absorbing device that can effectively absorb noise generated in a specific space.

[0007] The sound-absorbing device according to this disclosure comprises a sound-absorbing member having: a first sound-absorbing layer that includes a plurality of first acoustic metamaterials, each provided with one or more sound-absorbing parts, and absorbs sound in a first frequency band; and a second sound-absorbing layer laminated on the first sound-absorbing layer, each provided with one or more sound-absorbing parts, and absorbs sound in a second frequency band lower than the first frequency band.

[0008] This is a schematic diagram showing the configuration of an example sound-absorbing device using an acoustic metamaterial applicable to each embodiment of this disclosure. This is a diagram (perspective view) illustrating an example of the configuration of the acoustic metamaterial of the sound-absorbing device. This is a cross-sectional view showing a cross-section of the acoustic metamaterial. This is a schematic diagram illustrating an example of the shape of the neck portion in the acoustic metamaterial. This is a schematic diagram illustrating an example of the shape of the neck portion in the acoustic metamaterial. This is a schematic diagram illustrating an example of the shape of the neck portion in the acoustic metamaterial. This is a graph showing an example of the resonance frequency of each sound-absorbing part. This is a graph using a theoretical formula to explain that a high sound absorption coefficient can be obtained in a desired frequency band. This is a graph using a simulation to explain that a high sound absorption coefficient can be obtained in a desired frequency band. This is a schematic diagram showing the configuration of an example sound-absorbing device using an acoustic metamaterial. This is a schematic diagram illustrating an example of changing the angle of the sound-absorbing device relative to the user. This is a schematic diagram illustrating an example of changing the angle of the sound-absorbing device relative to the user. This is a schematic diagram illustrating an example of changing the distance of the sound-absorbing device relative to the user. This is a schematic diagram showing an example of the installation state of the sound-absorbing device according to the first embodiment. This is a schematic diagram showing the shape of an example of a cell according to the second embodiment. This is a schematic diagram showing an example of the configuration of a sound-absorbing device according to the second embodiment. This is a schematic diagram showing an example of the configuration of a cell as a sound-absorbing part made of acoustic metamaterial, which is used in a sound-transmitting layer applicable to the third embodiment. This is a schematic diagram showing an example of the configuration of a sound-absorbing device according to the third embodiment. This is a schematic diagram showing the configuration of each layer of the sound-absorbing device according to the third embodiment, viewed from the plane on which the cells are arranged. This is a schematic diagram showing the configuration of each layer of the sound-absorbing device according to the third embodiment, viewed from the plane on which the cells are arranged. This is a schematic diagram showing the shape of an example of a cell made of acoustic metamaterial for absorbing low-frequency sounds, applicable to the fourth embodiment. This is a schematic diagram showing the shape of an example of a cell made of acoustic metamaterial for absorbing mid-frequency sounds, applicable to the fourth embodiment. This is a schematic diagram showing the structure of an example of a sound-absorbing device according to the fourth embodiment. This is a schematic diagram showing the structure of an example of a sound-absorbing device according to the fourth embodiment. This is a schematic diagram showing the structure of an example of a sound-absorbing device according to the fourth embodiment. This is a schematic diagram showing the structure of an example of a sound-absorbing device according to the fourth embodiment.This is a schematic diagram showing an example of a sound-absorbing device according to each embodiment of the present disclosure mounted on a vehicle.

[0009] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the following embodiments, the same parts will be denoted by the same reference numerals, and redundant descriptions will be omitted.

[0010] The embodiments of this disclosure will be described below in the following order: 1. General description of this disclosure 1-1. Overview of this disclosure 1-2. Acoustic metamaterials 2. First embodiment of this disclosure 2-1. Existing technology 2-2. Arrangement of sound absorption device according to the first embodiment 3. Second embodiment of this disclosure 4. Third embodiment of this disclosure 5. Fourth embodiment of this disclosure 5-1. Modification of the fourth embodiment 6. Fifth embodiment of this disclosure

[0011] (1. General Explanation of the Disclosure) The technology related to this disclosure will be explained in general terms.

[0012] (1-1. Overview of the Disclosure) In this disclosure, sound-absorbing members are constructed using acoustic metamaterials (AMMs) configured to absorb sound in specific frequency bands. More specifically, in this disclosure, a sound-absorbing device is constructed by combining a first sound-absorbing member that absorbs sound in a first frequency band and a second sound-absorbing member configured to absorb sound in a second frequency band lower than the first frequency band, both constructed using acoustic metamaterials. By combining acoustic members that absorb sound in different frequency bands in this way, noise sounds in a specific space can be effectively absorbed.

[0013] Furthermore, this disclosure describes how, by positioning the sound-absorbing member appropriately for the user, a sound-absorbing device can be configured that more effectively absorbs noise in the space where the user is present.

[0014] (1-2. Acoustic Metamaterials) Here, we will describe acoustic metamaterials applicable to this disclosure.

[0015] A metamaterial refers to an artificially designed substance with properties that do not exist in nature, and an acoustic metamaterial refers to a metamaterial for sound. Sound-absorbing components made of acoustic metamaterials have high sound absorption performance and can be made lighter than iron, glass, rubber, etc.

[0016] The following explanation assumes that the sound to be absorbed is the driving noise inside a moving vehicle.

[0017] Generally, driving noise propagating within a vehicle (for example, driving noise with a frequency band of 20 Hz to 10,000 Hz) tends to decrease towards higher frequencies, peaking around 20 Hz. For driving noise in the low-frequency range (for example, from 40 Hz to 400 Hz), this noise is canceled by known active noise cancellation, which outputs a cancellation signal from the speaker.

[0018] On the other hand, road noise in the 200Hz to 1000Hz band (referred to as the mid-frequency band) may not be sufficiently canceled by active noise cancellation. As will be described later, the acoustic metamaterial of a sound-absorbing device can adjust the target frequency, which is the frequency of the sound to be absorbed, by appropriately adjusting its configuration. By setting the target frequency to, for example, a frequency band where active noise cancellation is less effective (e.g., 100Hz to 1000Hz), road noise can be effectively reduced.

[0019] The acoustic metamaterials applicable to each embodiment of this disclosure are described in detail below.

[0020] Figure 1 is a schematic diagram showing the configuration of an example of a sound-absorbing device using an acoustic metamaterial applicable to each embodiment of the present disclosure. As schematically shown in Figure 1, the sound-absorbing device 1 has a plurality of acoustic metamaterials 10. Among the plurality of acoustic metamaterials 10, the target frequency of a predetermined first acoustic metamaterial is different from the target frequency of a second acoustic metamaterial that is different from the first acoustic metamaterial. Note that the target frequencies of the acoustic metamaterials 10 being different means that the ranges of the target frequencies are shifted, and the entire range of the target frequencies may be shifted, or some of the ranges may overlap. In addition, among the plurality of acoustic metamaterials 10, there may be acoustic metamaterials 10 that have the same target frequency.

[0021] (Example of Acoustic Metamaterial Configuration) An example of the configuration of the acoustic metamaterial 10 of the sound-absorbing device 1 will be described with reference to Figures 2 and 3. Figure 2 is a diagram (perspective view) illustrating an example of the configuration of the acoustic metamaterial 10 of the sound-absorbing device 1. Figure 3 is a cross-sectional view showing a cross-section of the acoustic metamaterial 10. More specifically, Figure 3 is a cross-sectional view showing a cross-section when the acoustic metamaterial 10 is cut along the cutting line AA-AA in Figure 2.

[0022] The acoustic metamaterial 10 has a box-shaped cell 11. The acoustic metamaterial 10 has a plurality of sound-absorbing sections formed within the cell 11. The acoustic metamaterial 10 shown in Figure 2 has, for example, nine sound-absorbing sections 21A, 21B, 21C...21I. Note that if it is not necessary to distinguish between the individual sound-absorbing sections, they may simply be referred to as sound-absorbing sections 21. The nine sound-absorbing sections 21 are arranged, for example, in a grid pattern inside the cell 11. Note that the number of sound-absorbing sections 21 is just an example and may be other than nine.

[0023] The sound-absorbing section 21 is configured, for example, as a Helmholtz resonator. Specifically, the sound-absorbing section 21 has a tubular neck section with open ends at both ends, and a closed cavity (also called a cavity) that communicates with the neck section. Generally, the volume of the cavity is set to be larger than the volume of the neck section. When sound is taken in through the opening of the neck section, the air in the neck section is pushed into the cavity section, and the pressure inside the cavity increases due to the air being pushed into the cavity section, attempting to push the air back out. This movement is repeated alternately, causing the Helmholtz resonator to vibrate and produce sound. The Helmholtz resonator has the effect of absorbing the kinetic energy of sound centered on the resonating sound (sound at the resonant frequency), and this effect provides a sound-absorbing effect.

[0024] As shown in Figure 3, for example, the sound-absorbing section 21A has a cylindrical tubular neck section 211A and a cavity 210A, which is a closed space formed within the cell 11 and communicates with the neck section 211A. The neck section 211A has a first opening 223A, which is an open end to the outside of the cell 11, and a second opening 224A on the opposite side (located within the cavity 210A). Sound taken in from the first opening 223A is absorbed by the Helmholtz resonance principle described above.

[0025] In the examples shown in Figures 2 and 3, the neck portion 211A has a cylindrical tubular shape, but it may have other shapes, such as a triangular prism or a rectangular prism. Also, the shapes of the first opening 223A and the second opening 224A are not circular, but triangular or square. Furthermore, in the examples shown in Figures 2 and 3, the cavity 210A has a box shape. The cavity 210A may have other shapes, such as a spherical shape. However, from the viewpoint of arranging multiple sound-absorbing parts 21, the shape of the cavity 210A is preferably a cube or a rectangular parallelepiped. The same applies to the neck portion, cavity, first opening, and second opening of the other sound-absorbing parts 21.

[0026] Similarly, the sound-absorbing section 21B has a cylindrical tubular neck section 211B and a cavity 210B which is a closed space formed within the cell 11 and communicates with the neck section 211B. The neck section 211B has a first opening 223B which is an open end to the outside of the cell 11 and a second opening 224B on the opposite side (located within the cavity 210B). The sound-absorbing section 21C has a cylindrical tubular neck section 211C and a cavity 210C which is a closed space formed within the cell 11 and communicates with the neck section 211C. The neck section 211C has a first opening 223C which is an open end to the outside of the cell 11 and a second opening 224C on the opposite side (located within the cavity 210C).

[0027] If it is not necessary to distinguish between the neck portion, cavity, first opening, and second opening of each sound-absorbing section 21, they may be collectively referred to as the neck portion 211, cavity 210, first opening 223, and second opening 224, respectively.

[0028] As shown in Figure 3, for example, in the sound-absorbing section 21A, the neck section 211A has a shape with a predetermined taper, where the second opening 224A is smaller than the first opening 223A. This is the same for the other sound-absorbing sections 21B to 21I.

[0029] The acoustic metamaterial 10 can be obtained, for example, by molding a resin material using a 3D (Three-Dimensional) printer or a mold. In the acoustic metamaterial 10, the tapered neck shape may have the characteristic of being easy to create a draft taper when molding with a mold, and thus having excellent moldability. The material of the acoustic metamaterial 10 is not limited to resin, but may be metal, wood, surface-treated paper, foamed material, etc. Since the sound-absorbing device 1 including the acoustic metamaterial 10 can be installed in vehicles, etc., it is preferable that the material be lightweight. The applicant has previously filed a European patent application 22164643.3 for a Helmholtz resonator and an acoustic metamaterial having a Helmholtz resonator. The matters disclosed in that patent application are applicable to this application.

[0030] (Characteristics of the sound-absorbing section) In each embodiment, the resonance frequencies of the multiple (nine in the example of Figure 2) sound-absorbing sections 21 that constitute the acoustic metamaterial 10 are slightly different. Figure 4, and Figures 5A and 5B are schematic diagrams illustrating examples of the shape of the neck section 211.

[0031] As shown in Figure 4, when the neck portion 211 is viewed in cross-section, the length of the neck portion 211 is D1, the diameter of the first opening 223 is W1, and the diameter of the second opening 224 is W2. For example, by making at least one of D1, W1, and W2 different for each sound-absorbing portion 21, the resonant frequencies of each sound-absorbing portion 21 can be made different. The cross-sectional shape of each sound-absorbing portion 21 may also be changed.

[0032] For example, as shown in Figure 5A, when the neck portion 211 is viewed in cross-section, the resonant frequency can be changed by making the shape from the first opening 223 to the second opening 224 a convex tapered shape that curves slightly convex rather than straight, or by making it a concave tapered shape that curves slightly inward, as shown in Figure 5B.

[0033] Furthermore, the resonant frequency can also be changed by changing the diameter (area) of the first opening 223 and the second opening 224 in the neck portion 211, or by changing the volume of the cavity 210 in the sound-absorbing portion 21.

[0034] Figure 6 is a graph showing an example of the resonant frequencies of each sound-absorbing section 21. In the graph of Figure 6, the horizontal axis represents frequency, and the vertical axis represents acoustic impedance, indicating the ease of sound propagation. The dips in each line shown in Figure 6 correspond to the resonant frequencies of each sound-absorbing section 21. Thus, the resonant frequencies of the sound-absorbing sections 21A to 21I that constitute the acoustic metamaterial 10 are slightly different.

[0035] Figure 7 is a graph based on a theoretical formula to explain how a high sound absorption coefficient can be obtained in the desired frequency range. Figure 8 is a graph based on a simulation to explain how a high sound absorption coefficient can be obtained in the desired frequency range.

[0036] The graph in Figure 7 shows the resonant frequencies obtained by applying the known theoretical formula for a Helmholtz resonator to each sound-absorbing section 21. In the graph in Figure 7, the horizontal axis represents frequency, and the vertical axis represents sound absorption coefficient. The relationship between resonant frequency and sound absorption coefficient obtained by acoustic simulation using a computer is shown in the graph in Figure 8, which is a composite of the sound absorption characteristics of each sound-absorbing section 21. In the graph in Figure 8, the horizontal axis represents frequency, and the vertical axis represents sound absorption coefficient. As shown in the graphs in Figures 7 and 8, by slightly shifting the resonant frequency of each sound-absorbing section 21, a high sound absorption coefficient can be achieved in the required frequency band.

[0037] For example, with the acoustic metamaterial 10 having the characteristics shown in Figures 6 and 7, a sound absorption coefficient of 0.5 or higher can be obtained in the frequency band enclosed by the frame AR shown in the graph of Figure 8 (220 Hz to 320 Hz), and furthermore, a high sound absorption coefficient of 0.8 or higher can be obtained in the range of 260 Hz to 280 Hz.

[0038] (2. First Embodiment of the Disclosure) Next, the first embodiment of the Disclosure will be described.

[0039] (2-1. Existing Technology) Here, in order to facilitate understanding, we will briefly explain an existing sound absorption device using acoustic metamaterial 10.

[0040] Figure 9 is a schematic diagram showing the configuration of an example of a sound-absorbing device 1 using an acoustic metamaterial 10. In the example of Figure 9, the sound-absorbing device 1 is composed of cells 11 made of the acoustic metamaterial 10 arranged in a grid. The sound-absorbing device 1 has a sound-absorbing surface formed by providing first openings 223 of each cell 11 on the grid surface. The sound-absorbing device 1 absorbs sound in a predetermined frequency band through the first openings 223 provided on the sound-absorbing surface.

[0041] The magnitude of road noise within the vehicle cabin has peaks around 200 Hz and 800 Hz in the rear seat area, and around 800 Hz in the front seat area. Furthermore, the magnitude of road noise depends on the direction relative to the vehicle's direction of travel. More specifically, road noise is louder coming from the window closest to the seat and from the diagonal rear on the side of that window. For example, a user sitting on the left side of the rear seat relative to the direction of travel will hear more road noise coming from the window on their left and the diagonal rear on their left. Similarly, a user sitting on the left side of the front seat relative to the direction of travel will hear more road noise coming from the window on their left and the diagonal rear on their left.

[0042] Thus, the side windows of the vehicle are considered to be one of the sources of intrusion of driving noise. For example, by installing a sound-absorbing device 1 with the configuration shown in Figure 9 on the side windows of the vehicle, it is expected that the driving noise heard by the user will be reduced. However, in reality, it is difficult to install a sound-absorbing device 1 on a window that should be transparent.

[0043] Another example is to install sound-absorbing devices 1 on the headrest so as to cover the sides and rear of the head from which road noise originates. In this case, road noise to the user is reduced. On the other hand, by creating an enclosure around the sides and rear of the head from a state where there was nothing there, a sound amplification effect occurs in a specific frequency band (e.g., 500 Hz to 1 kHz) due to this enclosure. Due to this amplification effect, there is a possibility that there will be almost no difference between the state with and without sound-absorbing devices 1 installed.

[0044] In the first embodiment of this disclosure, by installing the sound-absorbing device 1 in an appropriate state for the user, the sound-absorbing effect of the acoustic metamaterial 10 can be maximized while reducing the amplification effect described above.

[0045] (2-2. Arrangement of the sound-absorbing device according to the first embodiment) In the first embodiment, the sound-absorbing effect of the sound-absorbing device 1 with respect to the user is maximized by optimizing the angle and distance of the sound-absorbing device 1 with respect to the user. Figures 10 and 11 are schematic diagrams illustrating an example of changing the angle of the sound-absorbing device 1 with respect to the user. Figure 12 is a schematic diagram illustrating an example of changing the distance of the sound-absorbing device 1 with respect to the user.

[0046] In the following explanation, unless otherwise specified, the "sound absorption device 1 using acoustic metamaterial 10" will be referred to simply as "sound absorption device 1".

[0047] Figures 10, 11, and 12, as well as Figure 13 (described later), show a view from above the user 300's head 301, with sound-absorbing devices 1R and 1L installed vertically on both sides of the user 300's head 301 (right ear 302R side and left ear 302L side). Each sound-absorbing device 1R and 1L has a structure in which acoustic metamaterial 10 is arranged in a grid pattern, as explained with reference to Figure 9, and is installed so that its sound-absorbing surface faces the user 300's head 301.

[0048] Furthermore, it is assumed that the sound-absorbing devices 1R and 1L are installed and used on the right ear 302R side and the left ear 302L side of the user 300, and these sound-absorbing devices 1R and 1L together may be considered as a single sound-absorbing device. In this case, the sound-absorbing devices 1R and 1L may be considered as sound-absorbing members that constitute the sound-absorbing device.

[0049] Figure 10 shows an example in which the angles of each sound-absorbing device 1R and 1L with respect to the user 300 are changed symmetrically around points 30R and 30L, which correspond to the user's right ear 302R and left ear 302L, respectively. In this case, even if the angles of each sound-absorbing device 1R and 1L are changed, no significant change in the amplification effect described above is observed. In other words, even if the devices are rotated around points 30R and 30L, which correspond to the user's right ear 302R and left ear 302L, the amplification effect of each sound-absorbing device 1R and 1L will still be present.

[0050] Figure 11 shows an example in which the angles of each sound-absorbing device 1R and 1L with respect to the user 300 are changed symmetrically around points 31R and 31L at the rear ends of the user 300, respectively. In this case, changing the angles of each sound-absorbing device 1R and 1L results in a significant change in the amplification effect compared to the example in Figure 10. More specifically, changing the angles of each sound-absorbing device 1R and 1L so that they open more towards the front of the head 301 reduces the amplification effect.

[0051] Figure 12 is a schematic diagram showing an example in which the distances of each sound-absorbing device 1R and 1L from the right ear 302R and left ear 302L are changed symmetrically, with each sound-absorbing device 1R and 1L fixed at a predetermined angle with respect to the user 300, centered on points 31R and 31L at the rear ends. In this case, the amplification effect decreases as each sound-absorbing device 1R and 1L moves away from the right ear 302R and left ear 302L.

[0052] Although not shown in the diagram, for example, when each sound-absorbing device 1R and 1L is installed inside the vehicle, it is assumed that a headrest is present behind the head 301. In this case, if there is a gap between the headrest and the rear end of each sound-absorbing device 1R and 1L relative to the user 300, the amplification effect does not change significantly with or without the headrest. On the other hand, if there is no gap between the headrest and the rear end of each sound-absorbing device 1R and 1L relative to the user 300, the amplification effect will be greater.

[0053] As shown in the results in Figures 10 to 12, by extending each sound-absorbing device 1R and 1L toward the front of the head 301 and installing them away from the head 301, it is possible to reduce the amplification effect caused by the head 301 being surrounded by each sound-absorbing device 1R and 1L. On the other hand, by moving each sound-absorbing device 1R and 1L away from the head 301, the sound absorption effect of each sound-absorbing device 1R and 1L on the user 300 will be reduced. Therefore, it is preferable to optimize the angle and distance of each sound-absorbing device 1R and 1L to maximize the degree of reduction in amplification effect and the degree of sound absorption effect.

[0054] Figure 13 is a schematic diagram showing an example of the installation state of the sound-absorbing devices 1R and 1L according to the first embodiment. As shown in Figure 13, the angle of each sound-absorbing device 1R and 1L with respect to the user 300, centered on the rear end points 31R and 31L, is set to a predetermined angle α (>0°; for example, 30°). Also, the distance from the rear end of each sound-absorbing device 1R and 1L to the headrest 303 is set to a predetermined distance Δd (>0; for example, 20 mm). It is preferable to set the angle α and distance Δd appropriately according to the environment in which each sound-absorbing device 1R and 1L is installed.

[0055] (3. Second Embodiment of the Present Disclosure) Next, a second embodiment of the present disclosure will be described. In the second embodiment, a sound-absorbing device 1 is constructed by arranging a plurality of cells 11 with gaps between adjacent cells 11. By arranging the cells 11 with gaps between them, it is possible to reduce the amplification effect caused by being surrounded by the sound-absorbing device 1.

[0056] Figure 14 shows cell 11 according to the second embodiment. MF This is a schematic diagram showing an example of the shape. In Figure 14, cell 11 MF This is shown in a perspective view taken from an oblique angle above.

[0057] In Figure 14, cell 11 MF It is configured to absorb sounds in the mid-range frequency band (for example, 500 Hz to 1 kHz). More specifically, cell 11 MF This includes four sound-absorbing sections 211, 212, 213, and 214, each with a different peak frequency for sound absorption. By combining the sound absorption characteristics of these four sound-absorbing sections 211 to 214, a configuration is achieved that absorbs sounds in the mid-range frequency band.

[0058] In the example shown in Figure 14, the sound-absorbing section 211 has a cavity 2101, a neck section 2111, and a first opening 2231. Similarly, the sound-absorbing sections 212, 213, and 214 each have cavities 2102, 2103, and 2104, neck sections 2112, 2113, and 2114, and first openings 2232, 2233, and 2234, respectively.

[0059] Among the sound absorption parts 211 to 214, the sound absorption part 211 has the cavity 2101 with the largest volume, and the volumes of the cavities 2102 of the sound absorption part 212, the cavity 2103 of the sound absorption part 213, and the cavity 2104 of the sound absorption part 214 decrease in this order. The neck parts 2111, 2112, 2113, and 2114, as well as the first openings 2231, 2232, 2233, and 2234, may also have different sizes, etc. sequentially. In addition, in FIG. 14, the second opening is omitted.

[0060] With such a configuration, the frequency of the peak of sound absorption is the lowest for the sound absorption part 211 among the sound absorption parts 211 to 214, and increases in the order of the sound absorption parts 212, 213, and 214.

[0061] Here, the cell 11 MF is preferably in a cubic shape or a rectangular parallelepiped shape, which makes it easy to arrange a plurality of cells 11 MF to form the sound absorption device 1.

[0062] FIG. 15 is a schematic diagram showing a configuration example of the sound absorption device 1a according to the second embodiment. Section (a) of FIG. 15 is shown by a perspective view of the sound absorption device 1a seen from an obliquely upward direction. As shown in section (a), the sound absorption device 1a is configured by arranging cells 11 MF in a lattice pattern.

[0063] Section (b) of FIG. 15 is a view of the sound absorption device 1a shown in section (a) seen from the sound absorption surface side where the first openings 2231 to 2234 are provided. In the sound absorption device 1a, each cell 11 MF is arranged with a gap 13 between adjacent cells 11 MF . At this time, for example, a spacer 12a or 12b is inserted between adjacent cells 11 MF to hold the gap 13 and connect the cells on both sides of the gap 13. Similarly, a gap 14 is also provided between the frame part 40 of the sound absorption device 1a and the cell 11 MF adjacent to the frame part 40 by a spacer 12c. MF In this way, each cell 11

[0064] MF ​Between and in each cell 11 in the peripheral area MF Gaps 13 and 14 are left between the head and the frame portion 40. These gaps 13 and 14 create an air passage between one surface of the sound-absorbing device 1a and the other surface, making it possible to reduce the sound amplification effect in a specific frequency band caused by the head 301 being surrounded by the left and right sound-absorbing devices 1a as described above.

[0065] Each cell 11 MF The spacing between them, and each cell 11 in the surrounding area MF The distance between the sound absorber and the frame 40 may be determined by, for example, a simulation based on the direction of arrival of the sound to be absorbed and the installation location of the sound absorber 1a, to select the optimal value that maximizes the sound absorption effect on both the left and right sides of the user 300.

[0066] As an example, referring to the arrangement in Figure 13, the simulation results show that for the sound-absorbing device 1L located to the left of the user 300, the amplification effect decreases as the gap narrows, and for the sound-absorbing device 1R located to the right of the user 300, the amplification effect decreases as the gap widens up to a certain interval, and beyond that interval, the degree of reduction in the amplification effect saturates. In this case, the gaps 13 and 14 may be selected to the minimum value for sound-absorbing device 1L, and to the value at the point of saturation for sound-absorbing device 1R.

[0067] (4. Third Embodiment of the Disclosure) Next, a third embodiment of the Disclosure will be described. Each cell 11 in the second embodiment described above MF In this arrangement, each cell 11 MF Each cell 11 in the middle and peripheral areas MF Gaps 13 and 14 are provided between the sound absorber 1a and the frame portion 40. As a result, sound from behind the sound absorber 1a passes through the gaps 13 and 14 and reaches the user 300 as transmitted sound. In the third embodiment, a sound-absorbing layer (called a transmitted sound absorption layer) is laminated on the back surface of the sound absorber 1a to absorb sound from behind the sound absorber 1a.

[0068] Figure 16 shows a cell 11 as a sound-absorbing part made of acoustic metamaterial 10, which can be used in a sound-transmitting layer applicable to the third embodiment. SIDE This is a schematic diagram showing an example configuration. In Figure 16, cell 11 SIDEThis is shown in a perspective view taken from an oblique upward direction. In Figure 16, the sound-absorbing devices 1a are stacked in the direction indicated by the arrow.

[0069] In Figure 16, the acoustic metamaterial 10 is a box-shaped cell 11 SIDE It has. In Figure 16, cell 11 SIDE The side on which the sound-absorbing device 1a is stacked is surface 50 TOP Also, surface 50 TOP Two faces, each containing two edges that share a vertex, are defined as face 50. SIDE-1 50 SIDE-2 Let's assume that.

[0070] Cell 11 SIDE is one cavity 210 CMN Includes. Also, cell 11 SIDE is surface 50 SIDE-1 in addition, one or more (four in this example) first openings 223 11 , 223 12 , 223 13 and 223 14 A similar feature is provided. Similarly, surface 50 SIDE-2 in addition, one or more (four in this example) first openings 223 21 , 223 22 , 223 23 and 223 24 A first opening 223 is provided. (The diagram is omitted, but each first opening 223 11 ~223 14 , 223 21 ~223 24 The neck portion is connected to each first opening 223 11 ~223 14 , 223 21 ~223 24 And the neck portion is cell 11 SIDE One cavity 210 CMN They share this. Note that the second opening is omitted in Figure 16.

[0071] For example, the first opening 223 11 , 223 12 , 223 13 and 223 14The sizes of the neck sections connected to each of them may be different. This allows for sound absorption in an appropriate frequency band. That is, cell 11 SIDE Then, each of the multiple first openings 223 11 ~223 14 , 223 21 ~223 24 and cavity 210 relative to the neck CMN Since it is considered common, the frequency band (peak frequency) that is absorbed will be single. On the other hand, there are multiple first openings 223 of different sizes. 11 ~223 14 , 223 21 ~223 24 and the neck portion, the first opening 223 11 ~223 14 , 223 21 ~223 24 Furthermore, different characteristic curves (e.g., peak value and / or base spread) can be given to each neck section, allowing for finer adjustments. Cell 11 SIDE For example, cell 11 MF The device may be configured to absorb sounds in the mid-range frequency band, which is the target of sound absorption.

[0072] Thus, cell 11 SIDE is surface 50 TOP The side surface 50 SIDE-1 and 50 SIDE-2 Each first opening 223 provided for 11 ~223 14 , 223 21 ~223 24 Therefore, cell 11 SIDE It absorbs sound passing through its sides. Therefore, cell 11 SIDE This is called a side-sound-absorbing acoustic metamaterial. On the other hand, each cell 11 provided in the sound-absorbing device 1a MF is cell 11 MF Because it absorbs sound reaching the plane on which it is arranged, it is called a planar sound-absorbing acoustic metamaterial.

[0073] FIG. 17 is a schematic diagram showing a configuration example of the sound absorption device 1b according to the third embodiment. FIG. 17 shows the sound absorption device 1b in a vertically standing state as a perspective view seen from an obliquely upward direction. The sound absorption device 1b includes a first layer 100 in which cells 11 MF are arranged in a lattice pattern and has a sound absorption surface, and a side sound absorption layer 110 in which cells 11 SIDE are arranged in a lattice pattern, and they are laminated. Note that the first layer 100 has the same configuration as the sound absorption device 1a described using FIG. 15.

[0074] FIGS. 18A and 18B are schematic diagrams of the configurations of the respective layers of the sound absorption device 1b according to the third embodiment as seen from the surface on which cells 11 MF or 11 SIDE are arranged. FIG. 18A shows the state of the first layer 100 as seen from the sound absorption surface side. As shown in FIG. 18A, the first layer 100 has the same configuration as the section (b) of FIG. 15.

[0075] FIG. 18B shows the side sound absorption layer 110 as seen from the upper right obliquely in the drawing with the side facing the first layer 100. As shown in FIG. 18B, each cell 11 SIDE does not have an opening on the surface facing the first layer 100, and each first opening 223 SIDE-2 is provided on the side surface 50 21 to 223 24 are provided. Although omitted in FIG. 18B, each first opening 223 SIDE is also provided on the surface 50 SIDE-1 on the lower side in the drawing of each cell 11 11 to 223 14 are provided.

[0076] Note that each cell 11 SIDE maintains a gap with an adjacent cell 11 SIDE by a spacer 15a. Also, each cell 11 SIDE at the peripheral part maintains a gap with the frame part 40 by a spacer 15b.

[0077] Referring to FIG. 17, with such a configuration, the reflected sound from another sound absorption device 1b (for example, the sound absorption device 1R in FIG. 13) provided facing the sound absorption device 1b (for example, the sound absorption device 1L in FIG. 13) is received by each cell 11 of the first layer 100MF Sound is absorbed by the sound absorber 1b. On the other hand, transmitted sound coming from behind the sound absorber 1b and passing through the gaps 13 and 14 of the first layer 100 is absorbed by the cells 11 of the side sound absorber layer 110. SIDE It absorbs sound.

[0078] Thus, by applying the sound-absorbing device 1b according to the third embodiment, it is possible to absorb both reflected and transmitted sound. Therefore, compared to, for example, the sound-absorbing device 1a according to the second embodiment, it is possible to achieve an even greater noise reduction effect.

[0079] Note that, as mentioned above, cell 11 SIDE Although it has been explained that sound-absorbing openings are provided on two sides, this is not limited to this example, and for example, a configuration in which openings are provided on only one side is also possible. However, cell 11 SIDE In contrast, by providing openings on two sides, cell 11 SIDE When arranged in a grid pattern, it is possible to absorb sound transmitted through almost all gaps, thereby achieving higher sound absorption performance.

[0080] (5. A Fourth Embodiment of the Disclosure) Next, a fourth embodiment of the Disclosure will be described.

[0081] In the second and third embodiments described above, the sound-absorbing device 1a or 1b was used to absorb sounds in the mid-range frequency band, such as 500 Hz to 1 kHz. On the other hand, it is known that driving noise propagating inside a vehicle also includes noise in the low-frequency band, such as 40 Hz to 400 Hz. Therefore, in the fourth embodiment, a sound-absorbing device is configured to absorb low-frequency sounds using an acoustic metamaterial 10, and this sound-absorbing device is combined with the sound-absorbing device 1a or 1b described above that absorbs sounds in the mid-range frequency band to form a single sound-absorbing device.

[0082] Figure 19A shows a cell 11 made of acoustic metamaterial 10 for absorbing low-frequency sounds, applicable to the fourth embodiment. LF This is a schematic diagram showing an example of the shape. In Figure 19A, cell 11 LF This is shown in a perspective view taken from an oblique angle above.

[0083] Cell 11 LF This basically refers to cell 11 for absorbing sounds in the mid-range frequency band, as explained using Figure 14. MF It has a configuration equivalent to that of cell 11. LF This consists of four sound-absorbing sections 21, each with a different peak frequency for sound absorption. 21 , 21 22 , 21 23 and 21 24 This includes these four sound-absorbing parts 21 21 ~21 24 By combining the various sound absorption characteristics, a configuration that absorbs low-frequency sounds is achieved.

[0084] In the example shown in Figure 19A, the sound-absorbing section 21 21 Cavity 210 21 , neck part 211 21 and the first opening 223 21 It has a sound-absorbing section 21. 22 , 21 23 and 21 24 Similarly, each has a cavity of 210. 22 , 210 23 and 210 24 , neck part 211 22 ,211 23 and 211 24 , and the first opening 223 22 , 223 23 and 223 24 It has [this feature]. Note that the second opening is omitted in the figure.

[0085] Sound-absorbing section 21 21 Of the 214, the sound-absorbing section 211 has the largest volume. 21 It has a sound-absorbing section 21 22 Cavity 210 22 , sound-absorbing section 21 23 Cavity 2103, sound-absorbing section 21 24 Cavity 210 24 The volume decreases in the following order. Neck portion 211 21 ,211 22 ,211 23 and 211 24 , and the first opening 223 21, 223 22 , 223 23 and 223 24 Similarly, the sizes and other characteristics may be varied sequentially.

[0086] With this configuration, the frequency of the sound absorption peak is at the sound absorption section 21 21 ~21 24 sound-absorbing section 21 21 Lowest, sound-absorbing section 21 22 , 21 23 , 21 24 The price increases in that order.

[0087] Figure 19B shows a cell 11 made of acoustic metamaterial 10 for absorbing sounds in the mid-range frequency band, applicable to the fourth embodiment. MF This is a schematic diagram showing an example of the shape. In Figure 19B, cell 11 MF This is shown by a perspective view taken from diagonally above. Note that the configuration of cell 11MF shown in Figure 19B is the same as that of cell 11 shown in Figure 14. MF Since the structure is identical to that of [previous text], the explanation here will be omitted.

[0088] In Figure 19A, cell 11 LF The size is width W LF Height H LF Depth D LF Let this be the case. In contrast, cell 11 shown in Figure 19B MF Its size is width W MF Height H MF Depth D MF Assume that this is the case. At this time, cell 11 LF and cell 11 MF The relationship between size and is, for example, W LF ×H LF ×D LF >W MF ×H MF ×D MF This is the result. Note that here, (W LF >W MF ) ∧ ( H LF >H MF ) ∧ ( D LF >D MF )

[0089] Figures 20A and 20B are schematic diagrams showing the structure of an example of a sound-absorbing device 1d according to the fourth embodiment. More specifically, Figure 20A is a cross-sectional view showing a cross-section of an example of a sound-absorbing device 1d, and Figure 20B is a cross-sectional view showing an example of a cross-section when the sound-absorbing device 1d is cut along the cutting line BB-BB in Figure 20A.

[0090] As shown in Figures 20A and 20B, cell 11 MF-1 , 11 MF-2 For the first layer 100 in which ... are arranged, cell 11 LF A second layer 120, in which the cells 11 are arranged, is stacked. LF That is, each first opening 223 of the second layer 120 21 ~223 24 These are provided in the sound-absorbing layer 130, where the sound-absorbing surface is formed, together with the first openings 2231 to 2234 of the first layer 100.

[0091] As shown in Figure 20B, cell 11 LF Each cavity 210 21 ~210 24 (In Figure 20B, cavity 210) 21 (The part is omitted) penetrates the first layer 100 and reaches the sound-absorbing layer 130. More specifically, the cavity 210 of the second layer 120 relative to the sound-absorbing layer 130 21 ~210 24 Holes are drilled at the corresponding positions, and each of these holes is a cavity 210 21 ~210 24 Each of these openings may be a corresponding cavity 210. 21 ~210 24 It is desirable that the opening size be greater than or equal to the size of the opening. In other words, the first layer 100 is provided with spaces that penetrate vertically through the first layer 100 in the diagram, corresponding to these holes.

[0092] In the examples of Figures 20A and 20B, cell 11 MF-2 For example, part of it is cavity 210 22 By being connected to the cavity 210, that part becomes 22 It is used as such. Cell 11 LF For example, the first opening 22322 and neck portion 211 22 And, cell 11 MF-2 Cavity 210 including part of 22 This results in the formation of a Helmholtz resonator.

[0093] By using such a configuration, it is possible to realize an acoustic metamaterial that absorbs both low-frequency and mid-frequency sounds from the same sound-absorbing surface.

[0094] Note that in Figure 20B, cell 11 LF For example, the neck portion 211 22 The length of the neck portion 211 is shorter than the depth of the first layer 100, but this is not limited to this example. 22 The length may be longer than the depth of the first layer 100. Neck portion 211 22 By making the length longer than the depth of the first layer 100, the neck portion 211 in the first layer 100 22 This makes it possible to eliminate the need for the surrounding space. For example, the neck portion 211 22 The length of the first layer 100 is made equal to the depth of the first layer 100, and the space that penetrates the first layer 100 vertically in the figure is the neck portion 211 22 This is sufficient. With this configuration, the cell 11 in the first layer 100 MF This can improve the design flexibility.

[0095] Furthermore, the positions of each boundary of each cavity 2101 to 2104 in the first layer 100 and each cavity 210 in the second layer 120 21 ~210 24 The positions of each boundary do not necessarily have to coincide.

[0096] The method for manufacturing the sound-absorbing device 1d according to the fourth embodiment will be described in general terms using Figures 21A and 21B. Figures 21A and 21B are schematic diagrams showing the structure of an example of the sound-absorbing device 1d according to the fourth embodiment. Figures 21A and 21B show the sound-absorbing device 1d or each layer of the sound-absorbing device 1d as a perspective view from diagonally above.

[0097] As shown in Figure 21A, the sound-absorbing device 1d is constructed by laminating a sound-absorbing layer 130, a first layer 100, and a second layer 120. As shown in sections (a), (b), and (c) of Figure 21B, respectively, the sound-absorbing device 1d can have a three-part structure consisting of the sound-absorbing layer 130, the first layer 100, and the second layer 120.

[0098] Cell 11 LF And, cell 11 MF The sizes are completely different. Therefore, according to existing technology, the frequency band of the sound absorption target is set to cell 11 MF The mid-range frequency band and cell 11 LF The choice was between the mid-range frequency band and the low-frequency band. In contrast, according to the fourth embodiment, by configuring the sound-absorbing device 1d with a three-part structure consisting of a sound-absorbing layer 130, a first layer 100, and a second layer 120, it becomes possible to absorb both mid-range and low-frequency sounds from the same sound-absorbing surface. This makes it possible to realize a sound-absorbing device that absorbs both mid-range and low-frequency sounds.

[0099] Furthermore, the sound-absorbing layers 130, the first layer 100, and the second layer 120 are each shaped to be manufactured using a mold, and mass production is facilitated by bonding the manufactured sound-absorbing layers 130, the first layer 100, and the second layer 120 together to form the sound-absorbing device 1d.

[0100] Furthermore, if the first layer 100 and the second layer 120 can be laminated in close contact, the surface of the second layer 120 in contact with the first layer 100, or the surface of the first layer 100 in contact with the second layer 120, may be left open. Similarly, if the sound-absorbing layer 130 and the first layer 100 can be laminated in close contact, the surface of the first layer 100 in contact with the sound-absorbing layer 130 may be left open.

[0101] (5-1. Modifications of the Fourth Embodiment) Next, modifications of the fourth embodiment of the present disclosure will be described.

[0102] (First Modification) The first modification of the fourth embodiment is an example in which the configuration of the sound-absorbing device 1a according to the second embodiment is combined with the sound-absorbing device 1d according to the fourth embodiment. More specifically, in the first modification of the fourth embodiment, the sound-absorbing device 1d shown in Figures 20A and 20B, and Figures 21A and 21B according to the fourth embodiment may be combined with the sound-absorbing device 1a according to the second embodiment shown in Figure 15.

[0103] As a first example of the first modification of the fourth embodiment, in at least the first layer 100 of the first layer 100 and the second layer 120, spacers 12a to 12c are used to form the sound-absorbing layer 130 and each cell 11, as described using section (b) of Figure 15. MF Gaps 13 and 14 may be provided between them. As a second example of the first modification of the fourth embodiment, the sound-absorbing layer 130 and the cell 11 in the first layer 100 MF The boundary and cell 11 in the second layer 120 LF A gap may be provided that penetrates the first layer 100 and the second layer 120 at the location where the positions of the two coincide.

[0104] This makes it possible to absorb sound across multiple frequency bands while reducing the amplification effect caused by sound reflection from other sound-absorbing devices installed in conjunction with the sound-absorbing device.

[0105] (Second Modification) The second modification of the fourth embodiment is an example in which the configuration of the sound-absorbing device 1b according to the third embodiment is combined with the second example of the first modification described above. More specifically, in the second modification of the fourth embodiment, for example, the sound-absorbing device 1d shown in Figures 20A and 20B, and Figures 21A and 21B according to the fourth embodiment may be combined with the sound-absorbing device 1b according to the third embodiment shown in Figure 17.

[0106] For example, the sound-absorbing layer 130 and the cell 11 in the first layer 100 MF The boundary and cell 11 in the second layer 120 LF A gap is provided between the first layer 100 and the second layer 120 at the location where it coincides with the boundary. Each cell 11 for absorbing sound from the side is positioned relative to the location of this gap. SIDEEach cell 11 such that the position of at least one gap between them coincides. MF , 11 LF and 11 SIDE Adjust the size and position.

[0107] In this case, cell 11 SIDE is cell 11 MF The sound in the mid-range frequency band that is the target of sound absorption, and cell 11 LF Either the low-frequency band sound that is the target of sound absorption or the cell 11 may be the target of sound absorption. SIDE The sound absorption target may include sounds in the mid-range and low-range frequency bands.

[0108] This makes it possible to absorb sound across multiple frequency bands while also absorbing sound that passes through the sound-absorbing device.

[0109] (Other Modifications) Not limited to the configurations of each of the modifications described above, for example, it is also possible to combine the configuration of the sound-absorbing device 1a according to the second embodiment with the configuration of the sound-absorbing device 1b according to the third embodiment for the sound-absorbing device 1d according to the fourth embodiment.

[0110] (6. Fifth Embodiment of the Disclosure) Next, a fifth embodiment of the Disclosure will be described. The fifth embodiment is an example in which the sound-absorbing device 1a, 1b, or 1d according to each embodiment of the Disclosure is mounted on a vehicle.

[0111] Figure 22 is a schematic diagram showing an example in which a sound-absorbing device 1a, 1b, or 1d according to each embodiment of the present disclosure is mounted on a vehicle 400. Figure 22 is a perspective view of the interior of a right-hand drive vehicle 400 as seen from above. In the following description, the sound-absorbing devices 1a, 1b, or 1d according to each embodiment will be collectively referred to as sound-absorbing device 1 (sound-absorbing devices 1R, 1L).

[0112] In Figure 22, a sound-absorbing device 1R is installed on the side of the user 3001's right ear 302R, and a sound-absorbing device 1L is installed on the side of the user 3001's left ear 302L in the driver's seat. The sound-absorbing devices 1R and 1L may be semi-fixed to the headrest 303 using a jig or the like, or they may be fixed to the headrest 303 in advance. Furthermore, the position and angle of the sound-absorbing devices 1R and 1L may be set appropriately according to the environment in which the sound-absorbing devices 1R and 1L are installed, as explained with reference to Figure 13. As a result, driving noise and other noises to the driver, user 3001 are reduced, and user 3001 can concentrate on driving without being disturbed by the driving noise of the vehicle 400.

[0113] In the passenger compartment of vehicle 400, sound-absorbing devices 1R and 1L may be installed in the passenger seat and the left and right rear seats in the same manner as in the driver's seat. This reduces road noise for users 3002, 3003, and 3004 in the passenger seat and the left and right rear seats, allowing each user 3002, 3003, and 3004 to enjoy conversations and music from the car audio system without being disturbed by road noise from vehicle 400. The same applies to user 3001 in the driver's seat.

[0114] In the above description, the sound-absorbing devices 1 according to each embodiment of this disclosure were described as being installed in the interior of a vehicle 400, but this is not limited to this example. For example, the sound-absorbing devices 1 according to each embodiment of this disclosure may be installed on sofas or walls in a house, or on seats in a movie theater, etc.

[0115] Furthermore, the effects described herein are merely illustrative and not limiting, and other effects may also occur.

[0116] Furthermore, this technology can also take the following configurations: (1) A sound-absorbing device comprising: a sound-absorbing member comprising: a first sound-absorbing layer comprising a plurality of first acoustic metamaterials each having one or more sound-absorbing parts, which absorb sound in a first frequency band; and a second sound-absorbing layer laminated on the first sound-absorbing layer, comprising a plurality of second acoustic metamaterials each having one or more sound-absorbing parts, which absorb sound in a second frequency band lower than the first frequency band; (2) The sound-absorbing device according to (1), wherein the one or more sound-absorbing parts of the second sound-absorbing layer are each provided penetrating the first sound-absorbing layer; (3) The sound-absorbing device according to (1), wherein each of the one or more sound-absorbing parts has a neck portion and a cavity portion leading to the neck portion. (4) The sound-absorbing device according to (3), wherein each of the plurality of first acoustic metamaterials and each of the plurality of second acoustic metamaterials each has a plurality of sound-absorbing parts including a neck portion and a cavity portion leading to the neck portion, and each of the plurality of sound-absorbing parts of the first acoustic metamaterial has a cavity portion of different volumes and absorbs sounds of different frequencies in the first frequency band, and each of the plurality of sound-absorbing parts of the second acoustic metamaterial has a cavity portion of different volumes and absorbs sounds of different frequencies in the second frequency band. (5) The sound-absorbing device according to (3) or (4), wherein the neck portion has a first opening which is an open end and a second opening which is disposed within the cavity portion, and each of the one or more sound-absorbing parts differs in at least one of the diameter of the first opening, the diameter of the second opening, the length of the neck portion, and the cross-sectional shape of the neck portion. (6) The sound-absorbing device according to any one of (1) to (5), wherein at least the first sound-absorbing layer of the first sound-absorbing layer and the second sound-absorbing layer are arranged such that adjacent first acoustic metamaterials from the plurality of first acoustic metamaterials are spaced apart.(7) The sound-absorbing device according to (6), wherein the second sound-absorbing layer is further configured such that adjacent acoustic metamaterials among the plurality of second acoustic metamaterials are arranged with gaps between them, and the position of at least one of the gaps in the first sound-absorbing layer corresponds to the position of the gap in the second sound-absorbing layer. (8) The sound-absorbing device according to (6) or (7), comprising two sound-absorbing members, each facing inward towards the first sound-absorbing layer and arranged at a predetermined distance apart, wherein the size of the gap in the first sound-absorbing layer differs between one of the two sound-absorbing members and the other sound-absorbing member. (9) The sound absorbing device according to any one of (1) to (8), further comprising: a plurality of third acoustic metamaterials each provided with one or more sound-absorbing sections, the third sound-absorbing layer absorbing sound in at least one of the first frequency band and the second frequency band, wherein each of the plurality of first acoustic metamaterials and the plurality of second acoustic metamaterials has an opening in the one or more sound-absorbing section provided on the surface of the first sound-absorbing layer, and each of the third acoustic metamaterials has an opening in the one or more sound-absorbing section provided on a surface perpendicular to the surface of the first sound-absorbing layer. (10) The sound absorbing device according to (9), wherein the third sound-absorbing layer is provided on the side opposite to the surface of the first sound-absorbing layer on which the opening is provided. (11) The sound-absorbing device according to any one of (1) to (10), comprising two sound-absorbing members, wherein the first sound-absorbing layers of the two sound-absorbing members face each other, the distance between the first sides of each is shorter than the distance between the second sides facing the first side, and there is a gap between the member positioned on each of the first sides and each of the first sides. (12) The sound-absorbing device according to (11), wherein the distance between the first sides is based on the distance between a person's ears.(13) An in-vehicle sound absorbing device comprising: two sound absorbing members, each comprising: a first sound absorbing layer which includes a plurality of first acoustic metamaterials each having one or more sound absorbing parts and absorbing sound in a first frequency band; and a second sound absorbing layer which is laminated on the first sound absorbing layer and comprises a plurality of second acoustic metamaterials each having one or more sound absorbing parts and absorbing sound in a second frequency band lower than the first frequency band, wherein the two sound absorbing members are respectively installed at the left and right ends of the headrest of a seat in a vehicle, such that the first sound absorbing layers face each other. (14) The in-vehicle sound absorbing device according to (13), wherein the distance between the first sides in the height direction of each of the two sound absorbing members is shorter than the distance between the second sides facing the first side of each, and the two sound absorbing members are arranged so that there is a gap between the headrest and each of the first sides.

[0117] 1, 1a, 1b, 1d, 1L, 1R Sound absorption device 10 Acoustic metamaterial 11, 11 LF ,11 MF ,11 MF-1 ,11 MF-2 ,11 SIDE Cells 12a, 12b, 12c Spacers 13, 14 Gap 21, 211, 212, 213, 214, 21 21 ,21 22 ,21 23 ,21 24 , 21A, 21B, 21C, 21D, 21E, 21F, 21G, 21H, 21I Sound absorption part 40 Frame part 100 1st layer 110 Side sound absorption layer 120 2nd layer 130 Sound absorption layer 210, 2101, 2102, 2103, 2104, 210 21 ,210 22 ,210 23 ,210 24 ,210A,210B,210C Cavity 211,2111,2112,2113,2114,211 21 ,211 22 ,211 23 ,211 24 , 211A, 211B, 211C Neck section 223, 2231, 2232, 2233, 2234, 223 21 ,22322 223 23 223 24 223A, 223B, 223C First opening 224, 224A, 224B, 224C Second opening 300 Yuza 301 Head 302L Left ear 302R Right ear 400 Carriage

Claims

1. A sound-absorbing device comprising: a sound-absorbing member having a first sound-absorbing layer comprising a plurality of first acoustic metamaterials each provided with one or more sound-absorbing parts, which absorb sound in a first frequency band; and a second sound-absorbing layer laminated on the first sound-absorbing layer, comprising a plurality of second acoustic metamaterials each provided with one or more sound-absorbing parts, which absorb sound in a second frequency band lower than the first frequency band.

2. The sound-absorbing device according to claim 1, wherein the one or more sound-absorbing portions of the second sound-absorbing layer are each provided penetrating the first sound-absorbing layer.

3. The sound-absorbing device according to claim 1, wherein each of the one or more sound-absorbing parts has a neck portion and a cavity portion connected to the neck portion.

4. The sound-absorbing device according to claim 3, wherein each of the plurality of first acoustic metamaterials and each of the plurality of second acoustic metamaterials each has a plurality of sound-absorbing portions including a neck portion and a cavity portion leading to the neck portion, each of the plurality of sound-absorbing portions of the first acoustic metamaterial has a cavity portion of a different volume and absorbs sounds of different frequencies in the first frequency band, and each of the plurality of sound-absorbing portions of the second acoustic metamaterial has a cavity portion of a different volume and absorbs sounds of different frequencies in the second frequency band.

5. The sound-absorbing device according to claim 3, wherein the neck portion has a first opening that is an open end and a second opening disposed within the cavity, and each of the one or more sound-absorbing portions differs in at least one of the diameter of the first opening, the diameter of the second opening, the length of the neck portion, and the cross-sectional shape of the neck portion.

6. The sound-absorbing device according to claim 1, wherein at least the first sound-absorbing layer of the first sound-absorbing layer and the second sound-absorbing layer are arranged such that adjacent first acoustic metamaterials are spaced apart from each other.

7. The sound-absorbing device according to claim 6, wherein the second sound-absorbing layer is arranged such that adjacent acoustic metamaterials among the plurality of second acoustic metamaterials are spaced apart, and the position of at least one of the gaps in the first sound-absorbing layer corresponds to the position of the gap in the second sound-absorbing layer.

8. The sound-absorbing device according to claim 6, comprising two sound-absorbing members, each with the first sound-absorbing layer facing inward and arranged at a predetermined distance apart, wherein the size of the gap in the first sound-absorbing layer differs between one of the two sound-absorbing members and the other sound-absorbing member.

9. A sound-absorbing device according to claim 1, further comprising: a plurality of third acoustic metamaterials, each having one or more sound-absorbing sections, the third sound-absorbing layer absorbing sound in at least one of the first frequency band and the second frequency band, wherein each of the plurality of first acoustic metamaterials and the plurality of second acoustic metamaterials has an opening in the one or more sound-absorbing section provided on the surface of the first sound-absorbing layer, and each of the third acoustic metamaterials has an opening in the one or more sound-absorbing section provided on a surface perpendicular to the surface of the first sound-absorbing layer.

10. The sound-absorbing device according to claim 9, wherein the third sound-absorbing layer is provided on the side opposite to the surface of the first sound-absorbing layer on which the opening is provided.

11. The sound-absorbing device according to claim 1, comprising two sound-absorbing members, wherein the first sound-absorbing layers of the two sound-absorbing members face each other, the distance between the first edges of each is shorter than the distance between the second edges facing the first edges, and there is a gap between the member positioned on each of the first edges and each of the first edges.

12. The sound-absorbing device according to claim 11, wherein the distance between the first sides is based on the distance between a person's ears.

13. An in-vehicle sound-absorbing device comprising: two sound-absorbing members, each having: a first sound-absorbing layer comprising a plurality of first acoustic metamaterials, each having one or more sound-absorbing parts, which absorb sound in a first frequency band; and a second sound-absorbing layer laminated on the first sound-absorbing layer, each comprising a plurality of second acoustic metamaterials, each having one or more sound-absorbing parts, which absorb sound in a second frequency band lower than the first frequency band; wherein the two sound-absorbing members are installed at the left and right ends of the headrests of the seats of a vehicle, with the first sound-absorbing layers facing each other.

14. The in-vehicle sound-absorbing device according to claim 13, wherein the distance between the first sides of each of the two sound-absorbing members in the height direction is shorter than the distance between the second sides opposite to each of the first sides, and the two sound-absorbing members are arranged so that there is a gap between the headrest and each of the first sides.

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