Noise absorption device and acoustic meta-material

Abstract

To provide a noise absorption device and acoustic meta-material that can absorb a sound having a wide frequency band.SOLUTION: A sound absorption device comprises a sound hole surface plate 11, a vibrator 16, a first frame member 12, a back plate 18, and a second frame member 17. The surface plate has a plurality of sound holes. The vibrator faces the surface plate. The first frame member is connected to the surface plate and the vibrator, and forms first internal spaces 22, 23 with the surface plate and the vibrator. The back plate faces the vibrator. The second frame member is connected to the back plate and the vibrator, and forms a second internal space 24 with the back plate and the vibrator. The vibrator comprises a film 14. The first frame member comprises a space division member 122 which divides the first spaces, and a structure forming a partial space 23 functions as a single-degree-of-freedom Helmholtz resonator. A structure forming a partial space 22 and the second internal space 24 functions as a two-degree-of-freedom Helmholtz resonator.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to sound absorbing devices and acoustic metamaterials. [Background technology]

[0002] Ordinary sound-absorbing materials have the advantages of being low cost, thin, and having a broad sound absorption band above 1 kHz, but they also have disadvantages such as being unable to be used in high temperature environments, deteriorating over time, glass wool-based sound-absorbing materials having a large environmental impact, and needing to be thick to be used in low frequency bands.

[0003] Helmholtz resonators are known as sound-absorbing devices that reduce noise and other sounds. A Helmholtz resonator is a container whose internal space is connected to the external space through a single sound hole. A Helmholtz resonator can attenuate the vibration energy of incident sound at the resonant frequency by causing resonance in the internal space due to sound entering through the sound hole. A Helmholtz resonator has a single degree of freedom system and therefore has unimodal sound absorption characteristics. Depending on the design, a Helmholtz resonator can be applied to low frequency bands.

[0004] From the viewpoint of widening the bandwidth of sound absorption characteristics, a two-degree-of-freedom Helmholtz resonator has been proposed. A two-degree-of-freedom Helmholtz resonator has a structure in which an elastic plate is added to a one-degree-of-freedom Helmholtz resonator so as to separate the internal space into two spaces. The elastic plate has a one-degree-of-freedom system, and the Helmholtz resonator has a one-degree-of-freedom system, and the coupling of the Helmholtz resonator and the elastic plate results in a two-degree-of-freedom system. A two-degree-of-freedom Helmholtz resonator has sound absorption characteristics with two separate sound absorption coefficient peaks. A valley characteristic (a drop in sound absorption coefficient) occurs between the two sound absorption coefficient peaks.

[0005] A sound absorbing device is required to have a sound absorbing effect over a wide frequency range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-160087 Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a sound absorbing device and an acoustic metamaterial that can absorb sounds over a wide frequency band. [Means for solving the problem]

[0008] The sound absorbing device according to the embodiment comprises a surface plate, a vibrating body, a first frame member, a back plate, and a second frame member. The surface plate has a plurality of sound holes. The vibrating body faces the surface plate. The first frame member is connected to the surface plate and the vibrating body, forming a first space between the surface plate and the vibrating body. The back plate faces the vibrating body. The second frame member is connected to the back plate and the vibrating body, forming a second space between the back plate and the vibrating body. The vibrating body comprises a membrane, a third frame member attached to the membrane, a central member attached to the membrane, and a connecting member connecting the third frame member and the central member. The first frame member comprises a space dividing member that divides the first space. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view showing a sound absorbing device according to an embodiment. [Figure 2] FIG. 2 is an exploded view showing the sound absorbing device according to the embodiment. [Figure 3] FIG. 2 is an exploded view showing the sound absorbing device according to the embodiment. [Figure 4] 1 is a cross-sectional view showing a sound absorbing device according to an embodiment. [Figure 5] FIG. 1 is a perspective view showing a part of a sound absorbing device according to an embodiment. [Figure 6] FIG. 1 is a perspective view showing a part of a sound absorbing device according to an embodiment. [Figure 7]FIG. 1 is a plan view showing a part of a sound absorbing device according to an embodiment. [Figure 8] FIG. 2 is a perspective view showing a support member according to the embodiment. [Figure 9] FIG. 4 is a plan view showing a support member according to the embodiment. [Figure 10] FIG. 1 is a plan view showing a part of a sound absorbing device according to a first embodiment. [Figure 11] FIG. 10 is a plan view showing a part of a sound absorbing device according to a second embodiment. [Figure 12] FIG. 11 is a plan view showing a part of a sound absorbing device according to a third embodiment. [Figure 13] FIG. 2 is a cross-sectional view showing a sound absorbing device according to a first comparative example. [Figure 14] FIG. 10 is a cross-sectional view showing a sound absorbing device according to a second comparative example. [Figure 15] FIG. 10 is a cross-sectional view showing a sound absorbing device according to a third comparative example. [Figure 16] FIG. 3 is a diagram showing the sound absorbing performance of the sound absorbing device according to the first embodiment. [Figure 17] FIG. 10 is a diagram showing the sound absorbing performance of the sound absorbing device according to the second embodiment. [Figure 18] FIG. 10 is a diagram showing a comparison of the sound absorbing performance of the sound absorbing device according to the third comparative example with the sound absorbing performance of the first example and the sound absorbing performance of the second example. [Figure 19] 4 is a diagram showing a comparison of the sound absorbing performance of a first example and the sound absorbing performance of a second example of the sound absorbing device according to the embodiment. FIG. [Figure 20] FIG. 10 is a diagram showing the sound absorbing performance of the sound absorbing device according to the third embodiment. [Figure 21] 10 is a diagram showing a comparison of the sound absorbing performance of a first example and the sound absorbing performance of a third example of the sound absorbing device according to the embodiment. FIG. [Figure 22] FIG. 1 is a perspective view showing an acoustic metamaterial according to an embodiment. [Figure 23] FIG. 1 is a perspective view showing a sound absorbing unit according to an embodiment. [Figure 24] FIG. 2 is an exploded view showing the sound absorbing unit according to the embodiment. [Figure 25] FIG. 2 is a perspective view showing a part of the sound absorbing unit according to the embodiment. [Figure 26]FIG. 2 is a perspective view showing a part of the sound absorbing unit according to the embodiment. [Figure 27] FIG. 1 is a perspective view showing an acoustic metamaterial according to an embodiment. [Figure 28] FIG. 1 is a perspective view showing a sound absorbing unit according to an embodiment. [Figure 29] FIG. 2 is a perspective view showing a part of the sound absorbing unit according to the embodiment. [Figure 30] FIG. 29 is a diagram showing the sound absorption characteristics of the sound absorbing unit shown in FIG. 28. [Figure 31] 29 is a diagram showing the sound absorption characteristics of the sound absorbing unit shown in FIG. 23 and the sound absorbing characteristics of the sound absorbing unit shown in FIG. 28 . [Figure 32] FIG. 1 is a perspective view showing an acoustic metamaterial according to an embodiment. [Figure 33] FIG. 33 is a perspective view showing the sound absorbing unit shown in FIG. 32. [Figure 34] FIG. 33 is a perspective view showing the sound absorbing unit shown in FIG. 32. [Figure 35] FIG. 33 is a perspective view showing a part of the sound absorbing unit shown in FIG. 32. [Figure 36] FIG. 33 is a perspective view showing a part of the sound absorbing unit shown in FIG. 32. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment will be described with reference to the drawings.

[0011] Fig. 1 schematically shows a sound absorbing device 10 according to an embodiment, Figs. 2 and 3 schematically show the sound absorbing device 10 in an exploded state, Fig. 4 schematically shows a cross section of the sound absorbing device 10, and Figs. 5, 6, 7, and 8 schematically show portions of the sound absorbing device 10. The sound absorbing device 10 is configured to absorb sound generated in an external space. The sound absorbing device 10 is used, for example, to reduce noise.

[0012] As shown in Figures 1 to 7, sound absorbing device 10 comprises sound hole surface plate 11, frame member 12, spacer 13, vibrating body 16, frame member 17, and back panel 18. Sound absorbing device 10 has, for example, an overall cylindrical shape. Below, an example will be shown in which each component of sound absorbing device 10 is circular. Instead of a circle, the shape of each component may be a polygon or a figure surrounded by an arbitrary closed curve. The terms cylinder, ring, ring member, and column can be simply read as tube, ring, ring member, and pillar.

[0013] The sound-hole surface plate 11 is, for example, a circular flat plate with a plurality of sound holes 111 formed therein. The diameter of the sound holes 111 is, for example, 0.1 mm or more and 20 mm or less. The diameter of the sound holes 111 is, for example, 0.2 times or less the diameter of the sound-hole surface plate 11 itself. For the sake of explanation, an XYZ Cartesian coordinate system is introduced here. The Y-axis is defined as a direction perpendicular to the main surface of the sound-hole surface plate 11, and the X-axis and Z-axis are defined as directions parallel to the main surface of the sound-hole surface plate 11. For the sake of explanation, the sound-hole surface plate 11 is defined as the upper side and the back plate 18 as the lower side, defining the top and bottom. Hereinafter, length and thickness refer to dimensions in the Y-axis direction (a direction parallel to the Y-axis).

[0014] The frame member 12 is, for example, a cylindrical member. In Figures 1 and 4, L1 indicates the length of the frame member 12. The spacer 13 is, for example, an annular member. The frame member 12 and the spacer 13 may be molded as a single unit. The vibrating body 16 is, for example, circular in shape as a whole. The vibrating body 16 faces the sound-hole surface plate 11 in the Y-axis direction. The frame member 17 is, for example, a cylindrical member. The cylindrical cross-sectional shape and cross-sectional area along the XZ plane do not necessarily have to be constant. In Figures 1 and 4, L2 indicates the length of the frame member 17. The back plate 18 is, for example, a circular flat plate. The frame member 17 and the back plate 18 may be molded as a single unit. The back plate 18 faces the vibrating body 16 in the Y-axis direction. The vibrating body 16 is located between the sound-hole surface plate 11 and the back plate 18.

[0015] The frame member 12 forms an internal space 21 between the sound-hole surface plate 11 and the vibrating body 16. The sound-hole surface plate 11 is connected to the frame member 12 so as to close a first open end of the frame member 12. The vibrating body 16 is connected to the frame member 12 via a spacer 13 so as to close a second open end of the frame member 12. The vibrating body 16 is separated from the sound-hole surface plate 11 by a length L1. The internal space 21 communicates with the external space via the sound hole 111. The sound hole 111 functions as a path through which sound generated in the external space enters the internal space 21 of the sound-absorbing device 10.

[0016] The frame member 12 includes an outer frame 121 and a space-dividing member (also referred to as a slit member) 122 provided inside the outer frame 121. The outer frame 121 and the space-dividing member 122 are cylindrical. The space-dividing member 122 divides the internal space 21 into subspaces 22 and 23. An annular bottom plate connects an end of the outer frame 121 to an end of the space-dividing member 122, and one end of the subspace 23 between the outer frame 121 and the space-dividing member 122 is closed. The space-dividing member 122 is not closed by the bottom plate. The open ends, which are the unclosed ends of the outer frame 121 and the space-dividing member 122, are connected to the sound-hole surface plate 11. The subspace 22 is a space surrounded by the sound-hole surface plate 11, the frame member 12, the spacer 13, and the vibrating body 16, and is in contact with the vibrating body 16. The subspace 23 is a space surrounded by the sound-hole surface plate 11 and the frame member 12. The subspace 23 is a space separated from the subspace 22 and is isolated from the vibrating body 16. The subspace 23 is provided so as to surround the subspace 22, that is, the subspace 23 is located outside the subspace 22. Note that a configuration in which the subspace 23 is located inside the subspace 22 is also possible.

[0017] 7, the dashed lines schematically show the positions where the sound hole surface plate 11 contacts the space dividing member 122. The sound holes 111 located inside the dashed lines function as paths through which sounds generated in the external space enter the subspace 22. The sound holes 111 located outside the dashed lines function as paths through which sounds generated in the external space enter the subspace 23.

[0018] As shown in Figures 2 to 4, the frame member 17 forms an internal space 24 between the vibrating body 16 and the back plate 18. The internal space 24 is a closed space surrounded by the vibrating body 16, the frame member 17, and the back plate 18. The internal space 24 is separated from the internal space 21 and the external space. The vibrating body 16 is connected to the frame member 17 so as to close a first open end of the frame member 17. The back plate 18 is connected to the frame member 17 so as to close a second open end of the frame member 17. The vibrating body 16 is spaced a length L2 from the back plate 18.

[0019] The connection between two components (for example, the connection between the sound hole surface plate 11 and the frame member 12) may be performed by any means, such as bonding using an adhesive or fixing using fasteners such as bolts described below.

[0020] As shown in FIGS. 3 and 4 , the vibrating body 16 includes a membrane 14 and a support member 15 that supports the membrane 14. The membrane 14 is, for example, a circular thin film. The membrane 14 can be made of an elastic material such as polyvinyl chloride (PVC), silicone rubber, fluororubber, silicone rubber, acrylic rubber, ethylene propylene rubber, or ethylene vinyl acetate copolymer. As shown in FIGS. 3 , 4 , and 8 , the support member 15 includes a frame member 151, a central member 152 located inside the frame member 151, and a connecting member 153 that connects the frame member 151 and the central member 152. The frame member 151 and the central member 152 of the support member 15 are attached to the membrane 14. The frame member 151 and the central member 152 may be attached to the membrane 14 by, for example, bonding using an adhesive or double-sided tape, or by fixing using a magnet. For example, the membrane 14 may be fixed to the central member 152 by sandwiching the membrane 14 between a rubber magnet attached to the central member 152 and another rubber magnet attached to the center of the top surface of the membrane 14. The frame member 151 may be, for example, an annular member, and the central member 152 may be, for example, a cylindrical member. The center of gravity of the central member 152 may be located on the central axis of the sound absorbing device 10 (indicated by the dashed line in FIG. 4). The connecting member 153 may be a beam member extending radially (in a direction perpendicular to the Y-axis). The connecting member 153 supports the central member 152 so that it can vibrate relative to the frame member 151. The central member 152 is supported by the connecting member 153 so that it can vibrate in the Y-axis direction.

[0021] The structure of the support member 15 shown in FIG. 8 is one example. The connecting member 153 may have any structure as long as it can support the central member 152 so that it can vibrate relative to the frame member 151. In the example shown in FIG. 9, the connecting member 153 includes straight beam members 1531 and 1532 and an arc-shaped beam member 1533. A first end of the beam member 1531 is connected to the frame member 151, a second end of the beam member 1531 is connected to a first end of the beam member 1533, a first end of the beam member 1532 is connected to a second end of the beam member 1533, and a second end of the beam member 1532 is connected to the central member 152. Note that there may be two or more connecting members 153.

[0022] As shown in FIGS. 3 and 4 , in the vibrating body 16, the membrane 14 is located on the frame member 12 side, and the support member 15 is located on the frame member 17 side. The outer edge of the upper surface of the membrane 14 is connected to the frame member 12 via the spacer 13, the outer edge of the lower surface of the membrane 14 is connected to the upper surface of the frame member 151 of the support member 15, the center of the lower surface of the membrane 14 is connected to the upper surface of the central member 152 of the support member 15, and the lower surface of the frame member 151 of the support member 15 is connected to the frame member 17. The spacer 13 is provided so that the vibrating body 16 (specifically, the membrane 14) does not come into contact with the space dividing member 122 of the frame member 12. Note that a configuration in which the membrane 14 is located on the frame member 17 side and the support member 15 is located on the frame member 12 side is also possible. Alternatively, the vibrating body 16 may include two membranes 14 and two support members 15. These membranes 14 are attached to the support member 15 such that one membrane 14 is provided on the upper surface side of the support member 15 and the other membrane 14 is provided on the lower surface side of the support member 15 .

[0023] The vibrating body 16 vibrates in response to sound entering the subspace 22. Specifically, the membrane 14 vibrates in response to sound entering the subspace 22, and the vibration of the membrane 14 causes the central member 152 of the support member 15 to vibrate. The vibrating body 16 has two sound absorption characteristics. The first sound absorption characteristic is obtained when the central member 152 vibrates in the Y-axis direction, causing the membrane 14 to vibrate in accordance with the vibration of the central member 152. The second sound absorption characteristic is obtained by the vibration of the membrane 14 itself (membrane vibration). A portion of the membrane 14 is attached to the support member 15, and the remaining region of the membrane 14 is capable of membrane vibration. The second sound absorption characteristic occurs in a higher frequency band than the first sound absorption characteristic. In this embodiment, the second sound absorption characteristic is mainly utilized.

[0024] In the sound absorbing device 10 having the above-described configuration, the structure forming the partial space 23 (specifically, the sound-hole surface plate 11 and the frame member 12) functions as a Helmholtz resonator with one degree of freedom. The partial space 23 is a closed space for forming a Helmholtz resonator with one degree of freedom. Furthermore, the structure forming the partial space 22 and the internal space 24 functions as a Helmholtz resonator with two degrees of freedom. Specifically, the structure forming the partial space 22 (specifically, the sound-hole surface plate 11, the frame member 12, the spacer 13, and the vibrating body 16) functions as a Helmholtz resonator with one degree of freedom, and the vibrating body 16 (specifically, the structure forming the internal space 24) adds a single degree of freedom. The coupling between the Helmholtz resonator and the vibrating body 16 results in a two-degree-of-freedom system. A Helmholtz resonator with two degrees of freedom has sound absorption characteristics with two separate sound absorption coefficient peaks.

[0025] The single-degree-of-freedom system corresponding to the vibrating body 16 can be designed based on the mass of the membrane 14, the rigidity of the membrane 14, the rigidity of the connecting member 153, and the rigidity of the air spring formed by the internal space 24 as an air layer. The mass and rigidity of the membrane 14 can be adjusted, for example, by the shape of the central member 152 and the thickness and material of the membrane 14. The mass of the membrane 14 specifically refers to the mass of the region of the membrane 14 where membrane vibration is possible. As the dimensions of the central member 152 increase, the mass of the membrane 14 decreases and the rigidity of the membrane 14 increases. The membrane 14 has viscoelasticity, which can generate a damping effect that has the greatest impact on the sound absorption effect. The damping effect can be adjusted by changing the support conditions of the membrane 14 or by providing membranes 14 on both sides of the support member 15. The support conditions of the membrane 14 are explained below. Because the membrane 14 is attached to the central member 152, the boundary conditions of membrane vibration change depending on the vibration mode of the central member 152. This change can be used to adjust the damping effect. Specifically, the boundary conditions change depending on the frequency of the vibration mode. As the frequency of the vibration mode decreases, the membrane 14 is less constrained by the central member 152 (membrane 14 becomes more flexible), resulting in a stronger damping effect. Conversely, as the frequency of the vibration mode increases, the membrane 14 becomes more constrained by the central member 152 (membrane 14 becomes less flexible), resulting in a weaker damping effect. In the second sound-absorbing characteristic achieved by membrane vibration, changing the stiffness of the connecting member 153 only slightly changes the natural frequency. However, changing the stiffness of the connecting member 153 affects the boundary conditions of membrane vibration and can be included as a design element to fine-tune the damping effect. The stiffness of the air spring created by the internal space 24 can be adjusted by changing the thickness L2 of the frame member 17 and can be effectively used as a parameter to adjust the natural frequency of a single-degree-of-freedom system. It is also possible to divide the membrane 14 by attaching the connecting member 153 to the membrane 14 to change its natural frequency. The number of divisions changes depending on the number of connecting members 153 bonded to the membrane 14, and the natural frequency can be changed.

[0026] An embodiment using the second sound absorption property has the following features: Design and adjustment are easy. For example, the natural frequency can be determined by designing the shape of the central member 152 and the material and thickness of the membrane 14. The natural frequency can also be changed by attaching the connecting member 153 to the membrane 14. Damping can be achieved by attaching the membrane 14 to the support member 15. From the viewpoint of energy dissipation, the combination of membrane 14 and support member 15 is more preferable than a simple elastic plate, and does not require the addition of vibration-damping material. The damping effect can also be adjusted by changing the boundary conditions of the membrane 14 using the central member 152 and connecting members 153. The membrane 14 serves two purposes: to provide an acoustic wall effect and to provide the above-mentioned damping. By providing membranes 14 on both sides of the support member 15, it is possible to strengthen the damping effect.

[0027] The sound absorbing performance of the sound absorbing device 10 according to the embodiment will be described. Here, the results of measuring the sound absorption characteristics of the sound absorbing device 10 according to three examples, each having a different support member 15 structure, will be described. FIG. 10 schematically illustrates the sound absorbing device 10 according to the first example, FIG. 11 schematically illustrates the sound absorbing device 10 according to the second example, and FIG. 12 schematically illustrates the sound absorbing device 10 according to the third example. As shown in FIG. 10, the first example has one connecting member 153. As shown in FIG. 11, the second example has two connecting members 153. As shown in FIG. 12, the third example has a larger central member 152 than the first example. The structure of the support member 15 shown in FIG. 10 is referred to as Structure A1, the structure of the support member 15 shown in FIG. 11 is referred to as Structure B1, and the structure of the support member 15 shown in FIG. 12 is referred to as Structure A2. Except for the structure of the support member 15, the first to third examples are the same. The sound-hole surface plate 11 has a diameter of 54 mm and a thickness of 1 mm. The sound hole surface plate 11 has 61 sound holes 111 arranged in a honeycomb pattern. The diameter of the sound holes 111 is 1 mm. In the first and second embodiments, the frame member 12 is 36 mm thick, and the bottom plate of the frame member 12 is 2 mm thick. The spacer 13 is 3 mm thick. In this case, the length of the subspace 22 is 39 mm, and the length of the subspace 23 is 34 mm. In the third embodiment, the frame member 12 is 26 mm thick, and the bottom plate of the frame member 12 is 2 mm thick. The spacer 13 is 3 mm thick. In this case, the length of the subspace 22 is 29 mm, and the length of the subspace 23 is 24 mm. The membrane 14 is made of silicone rubber and has a thickness of 0.5 mm. In this case, the membrane 14 is translucent. The support member 15 is made of ABS (Acrylonitrile Butadiene Styrene). The support member 15 in Figure 10 has the structure shown in Figure 8, and the frame member 151 has an outer diameter of 60 mm, an inner diameter of 54 mm, and a thickness of 3 mm. The central member 152 has a diameter of 20 mm and a thickness of 3 mm. The connecting member 153 has a thickness of 1.5 mm and a width of 3 mm. The connecting member 153 is positioned in line with the center of the central member 152 in the Y-axis direction, and the membrane 14 and the connecting member 153 do not come into contact. The support member 15 in Figure 11 has two connecting members 153.12, the diameter of the central member 152 is 30 mm. The thickness of the frame member 17 is 3 mm, and the thickness of the back plate 18 is 5 mm.

[0028] Measurements were also conducted on sound absorbing devices according to the first, second, and third comparative examples, which will be described below. The sound absorbing devices according to Comparative Examples 1, 2, and 3 correspond to parts of the sound absorbing device 10 according to the embodiment. As shown in FIG. 13 , the sound absorbing device according to Comparative Example 1 is a Helmholtz resonator including a sound hole surface plate 31, a frame member 32, and a back plate 33. The sound hole surface plate 31 is similar to the sound hole surface plate 11, the frame member 32 is similar to the outer frame 121 of the frame member 12, and the back plate 33 is similar to the back plate 18. The sound hole surface plate 31 is connected to the frame member 32 so as to close the first open end of the frame member 32, and the back plate 33 is connected to the frame member 32 so as to close the second open end of the frame member 32. An internal space is formed by the sound hole surface plate 31, the frame member 32, and the back plate 33. As shown in FIG. 14 , the sound absorbing device according to Comparative Example 2 includes a vibrating body 41, a frame member 42, and a back plate 43. Vibrating body 41 is similar to vibrating body 16, frame member 42 is similar to frame member 17, and back plate 43 is similar to back plate 18. As shown in Fig. 15, the sound absorbing device of the third comparative example is a coupling of the sound absorbing device of the first comparative example and the sound absorbing device of the second comparative example, and functions as a Helmholtz resonator with two degrees of freedom. The sound absorbing device of the third comparative example corresponds to sound absorbing device 10 without space dividing member 122.

[0029] Fig. 16 shows a schematic diagram of the measurement results of the sound absorbing performance of the first example. In Fig. 16, the solid line shows the measurement results of the sound absorbing performance of the sound absorbing device 10 according to the embodiment, the dashed line shows the measurement results of the sound absorbing device according to the first comparative example, the dashed line shows the measurement results of the sound absorbing performance of the sound absorbing device according to the second comparative example, and the dotted line shows the measurement results of the sound absorbing performance of the sound absorbing device according to the third comparative example. Note that lengths L1 and L2 were measured as shown in the figure.

[0030] As shown in FIG. 16, the sound absorbing device of the third comparative example exhibits a valley characteristic (a drop in the sound absorption coefficient) between two sound absorption coefficient peaks. In contrast, the sound absorbing device 10 of this embodiment suppresses the valley characteristic that occurs in the sound absorbing device of the third comparative example, resulting in a higher sound absorption effect over a wider frequency band. The sound absorption frequency band where the sound absorption coefficient is 0.85 or higher is wider, from 633 Hz to 1155 Hz (522 Hz width). The sound absorption frequency band where the sound absorption coefficient is 0.8 or higher is 544 Hz, and the sound absorption frequency band where the sound absorption coefficient is 0.7 or higher is 588 Hz. The sound absorbing device 10 is only 11 mm thicker than the Helmholtz resonator shown in FIG. 13, yet its sound absorption performance is significantly improved compared to the Helmholtz resonator.

[0031] FIG. 17 shows a schematic diagram of the measurement results of the sound absorbing performance of the second example. In FIG. 17, the solid line shows the measurement results of the sound absorbing performance of the sound absorbing device 10 according to the embodiment, the dashed line shows the measurement results of the sound absorbing device according to the first comparative example, the dashed line shows the measurement results of the sound absorbing performance of the sound absorbing device according to the second comparative example, and the dotted line shows the measurement results of the sound absorbing performance of the sound absorbing device according to the third comparative example. The measurements here used a support member having the structure shown in FIG. 11, i.e., a support member with higher membrane support rigidity. It can be seen from FIG. 17 that the sound absorbing device 10 according to the embodiment suppresses the valley characteristics that occur in the sound absorbing device according to the third comparative example, and thus has a higher sound absorption effect over a wider frequency band.

[0032] The difference between the sound absorbing device 10 according to the embodiment and the sound absorbing device according to the third comparative example is that the sound absorbing device 10 includes a space dividing member 122 that is provided on the frame member 12 and divides the internal space 21. Therefore, it can be seen that providing the space dividing member 122 on the frame member 12 makes it possible to effectively suppress the valley characteristics that occur in the sound absorbing device according to the third comparative example.

[0033] FIG. 18 shows the measurement results (solid line) for the sound absorbing device according to the third comparative example shown in FIG. 16 and the measurement results (dashed line) for the sound absorbing device according to the third comparative example shown in FIG. 17 , and FIG. 19 shows the measurement results (solid line) for the sound absorbing device 10 according to the embodiment shown in FIG. 16 and the measurement results (dashed line) for the sound absorbing device 10 according to the embodiment shown in FIG. 17 . From FIG. 18 , it can be seen that the sound absorbing performance of the sound absorbing device according to the third comparative example is highly dependent on the membrane support stiffness of the support member included in the vibrating body 41. From FIG. 19 , it can be seen that the sound absorbing performance of the sound absorbing device 10 according to the embodiment is dependent on the membrane support stiffness of the support member 15. In both cases, the sound absorbing performance is higher when the membrane support stiffness is low. As such, with the sound absorbing device 10 according to the embodiment, it is possible to adjust the level at which the valley characteristics are suppressed by changing the membrane support stiffness.

[0034] FIG. 20 shows a schematic diagram of the sound-absorbing performance measurement results for the third example. In FIG. 20, the solid line indicates the sound-absorbing performance measurement results for the sound-absorbing device 10, the dashed line indicates the sound-absorbing performance measurement results for the sound-absorbing device of the first comparative example, the dashed-dotted line indicates the sound-absorbing performance measurement results for the sound-absorbing device of the second comparative example, and the dotted line indicates the sound-absorbing performance measurement results for the sound-absorbing device of the third comparative example. The measurements here use a support member 15 with the structure shown in FIG. 12 , i.e., a support member 15 with a larger central member 152. FIG. 20 confirms that the sound-absorbing device 10 according to the embodiment suppresses the valley characteristic that occurs in the sound-absorbing device of the third comparative example, thereby providing a higher sound-absorbing effect over a wider frequency range. The sound-absorption coefficient peak near 700 Hz corresponds to the first sound-absorbing characteristic described above.

[0035] Fig. 21 shows the measurement results (dashed line) for the sound absorbing device 10 according to the embodiment shown in Fig. 16 and the measurement results (solid line) for the sound absorbing device 10 according to the embodiment shown in Fig. 20. Fig. 21 confirms that the sound absorption frequency band changes depending on the shape and length L1 of the central member 152 included in the support member 15. Therefore, it is possible to adjust the sound absorption frequency band by changing the shape of the central member 152.

[0036] The valley characteristic varies depending on the material of the membrane 14. For example, when a membrane made of PVC (PVC membrane) is used as the membrane 14, the valley characteristic is smaller than when a membrane made of silicone rubber (silicone membrane) is used as the membrane 14. However, PVC membranes have the disadvantage of not being usable in high-temperature environments. On the other hand, silicone membranes are heat-resistant and can be used in high-temperature environments. Furthermore, silicone membranes, being heat-resistant materials, are resistant to deterioration over time. The sound-absorbing device 10 according to the embodiment has a sufficiently high sound absorption effect over a wide frequency range, even when a silicone membrane is used as the membrane 14, as shown in Figures 16, 17, and 20.

[0037] In this embodiment, a combination of a membrane 14 and a support member 15 is used as the vibrating body 16. This facilitates the design of the natural frequency. Furthermore, by providing the frame member 12 with a space-dividing member 122, the valleys that occur between sound absorption coefficient peaks can be suppressed, even when a heat-resistant material such as silicone rubber is used for the membrane 14, thereby achieving a high sound absorption effect across a wide frequency band. Even when the structural strength of the support member 15 is increased as shown in FIG. 11 , as shown in FIG. 17 , the difference in the valley suppression effect between the third comparative example and the sound absorbing device 10 is significant. This enables the sound absorbing device 10 of this embodiment to be applied to devices requiring structural strength. Here, the term "heat-resistant material" refers to materials with higher heat resistance than PVC, such as silicone rubber, fluororubber, acrylic rubber, ethylene-propylene rubber, ethylene-vinyl acetate copolymer, and materials with these structures. Examples of heat-resistant materials include elastic materials. Examples of heat-resistant materials include resins. Examples of heat-resistant materials include materials with a melting point exceeding 200 degrees Celsius. The heat-resistant material preferably has a heat resistance temperature (high temperature usage limit) of 150°C or higher, and more preferably 200°C or higher. When a silicon film is used as film 14 and the components other than film 14 are also made of highly heat-resistant materials, sound absorbing device 10 can be used in high-temperature environments, such as environments of approximately 100°C or higher and 200°C or lower. The heat-resistant material can be selected appropriately depending on the environmental temperature, light irradiation conditions, the presence or absence of an organic solvent atmosphere, the presence or absence of moisture, etc.

[0038] As described above, the sound absorbing device 10 according to this embodiment comprises the sound-hole surface plate 11 having a plurality of sound holes 111, the vibrating body 16 facing the sound-hole surface plate 11, the frame member 12 connected to the sound-hole surface plate 11 and the vibrating body 16 and forming an internal space 21 between the sound-hole surface plate 11 and the vibrating body 16, the back plate 18 facing the vibrating body 16, and the frame member 17 connected to the back plate 18 and the vibrating body 16 and forming an internal space 24 between the back plate 18 and the vibrating body 16. The vibrating body 16 comprises a membrane 14 and a support member 15 that supports the membrane 14. The support member 15 comprises a frame member 151 attached to the membrane 14, a central member 152 attached to the membrane 14, and a connecting member 153 that connects the frame member 151 and the central member 152. The frame member 12 comprises a space-dividing member 122 that divides the internal space 21 into partial spaces 22 and 23.

[0039] In the above configuration, the structure that constitutes the subspace 22 and the internal space 24 functions as a Helmholtz resonator with two degrees of freedom, and the structure that constitutes the subspace 23 functions as a Helmholtz resonator with one degree of freedom, and the combination of these makes it possible to obtain a high sound absorption effect over a wide frequency band. Specifically, the structure that constitutes the subspace 23 suppresses the valley characteristic between the two sound absorption coefficient peaks that are generated by the structures that constitute the subspace 22 and the internal space 24, thereby obtaining a high sound absorption effect over a wide frequency band.

[0040] Using a combination of the membrane 14 and the support member 15 as the vibrating body 16 makes it easy to design the natural frequency of the sound absorbing device 10. Furthermore, by adjusting the natural frequency of the support member 15, it is possible to adjust the damping effect and further improve the valley characteristics.

[0041] When the membrane 14 is made of a heat-resistant material such as silicone rubber, the sound absorbing device 10 can be used, for example, in high-temperature environments where general sound-absorbing materials cannot be used. When the membrane 14 is made of a heat-resistant material such as silicone rubber, the valley characteristics deteriorate compared to when the membrane 14 is made of PVC. As described above, the valley characteristics are suppressed by the structure that forms the subspace 23, so a high sound absorption effect can be obtained over a wide frequency range even when a heat-resistant material is used for the membrane 14. Silicone rubber does not deteriorate over time, allowing the sound absorbing device 10 to be used for long periods of time and has a low environmental impact. Furthermore, the sound absorbing device 10 can be used in environments where the structural strength of the support member 15 is required.

[0042] Furthermore, since the sound absorbing device 10 has a hollow structure, it can be manufactured using a small amount of material, thereby reducing the environmental impact.

[0043] The above-described sound absorbing device 10 can be used as each of the multiple units that make up an acoustic metamaterial, which may also be called a sound absorbing device or a sound absorbing system.

[0044] FIG. 22 schematically illustrates an acoustic metamaterial 100 according to an embodiment. As shown in FIG. 22, the acoustic metamaterial 100 includes a plurality of sound absorbing units 60. The sound absorbing units 60 are arranged periodically (in a honeycomb pattern in this example). The sound absorbing units 60 are fixed to one another using, for example, bands (not shown). Except for the external shape, each sound absorbing unit 60 has the same configuration as the sound absorbing device 10 described with reference to FIGS. 1 to 7. The sound absorbing units 60 have a hexagonal prism shape overall in order to be arranged in a honeycomb pattern.

[0045] Fig. 23 shows a schematic diagram of the sound absorbing unit 60, Fig. 24 shows a schematic diagram of the sound absorbing unit 60 in an exploded state, and Fig. 25 and Fig. 26 show a schematic diagram of a portion of the sound absorbing unit 60. As shown in Figs. 23 to 26, the sound absorbing unit 60 includes a sound hole surface plate 61, a frame member 62, a vibrating body 66, and a frame member 67.

[0046] The sound hole surface plate 61 is a hexagonal flat plate with multiple sound holes 611. The sound hole surface plate 61 corresponds to the sound hole surface plate 11 described above with a hexagonal outer frame added. Holes 612 for inserting bolts are provided at the outer edge of the sound hole surface plate 61.

[0047] The frame member 62 corresponds to the above-described frame member 12 with hexagonal outer frames added to the upper and lower ends thereof. Therefore, a detailed description of the frame member 62 will be omitted. The outer frame located at the lower end also functions as the above-described spacer 13. The outer edge of the frame member 62 is provided with holes 621 and 622 for inserting bolts.

[0048] The vibrating body 66 includes a membrane 64 and a support member 65 that supports the membrane 64. The membrane 64 corresponds to the membrane 14 described above, and the support member 65 corresponds to the support member 15 described above with a hexagonal outer frame added. Therefore, a detailed description of the vibrating body 66 will be omitted. A hole 651 for inserting a bolt is provided on the outer edge of the support member 65.

[0049] The sound hole surface plate 61 is connected to the frame member 62 so as to close the first open end of the frame member 62, and the vibrating body 66 is connected to the frame member 62 so as to close the second open end of the frame member 62.

[0050] The frame member 67 corresponds to a combination of the above-described frame member 17 and back plate 18 to which a hexagonal outer frame has been added. Therefore, a detailed description of the frame member 67 will be omitted. Holes 671 for inserting bolts are provided on the outer edge of the frame member 67. The vibrating body 66 is connected to the frame member 67 so as to close the open end of the frame member 67.

[0051] The sound hole surface plate 61, frame member 62, vibrating body 66, and frame member 67 are fixed together by inserting bolts into holes 612, 621, 622, 651, and 671 and screwing nuts onto the bolts.

[0052] The acoustic metamaterial 100 having the above-described configuration can effectively absorb sounds such as noise.

[0053] Fig. 27 schematically shows an acoustic metamaterial 200 according to an embodiment. As shown in Fig. 27, the acoustic metamaterial 200 includes a plurality of sound absorbing units arranged in a honeycomb pattern, including a plurality of sound absorbing units 70 and a plurality of sound absorbing units 80. The sound absorbing units 70 and the sound absorbing units 80 are arranged alternately. The arrangement pattern shown in Fig. 27 is an example. The number of sound absorbing units 70 may be different from the number of sound absorbing units 80.

[0054] The sound absorbing unit 70 is the same as the sound absorbing unit 60 described with reference to Figures 23 to 26. Therefore, a description of the sound absorbing unit 70 will be omitted.

[0055] FIG. 28 schematically illustrates a sound-absorbing unit 80, and FIG. 29 schematically illustrates a portion of the sound-absorbing unit 80. As shown in FIGS. 28 and 29, the sound-absorbing unit 80 includes a fabric 81, a support member 82, and a frame member 83. The fabric 81 can be a fabric containing aramid fiber, such as polyparaphenylene terephthalamide fiber. It may be a woven fabric made of a single material, or a blended fabric containing such fiber can be used. The fabric 81 is stretched over an annular support member 82. The support member 82 supports the fabric 81. The fabric 81 is connected to the frame member 83 via the support member 82 so that the fabric 81 covers the open end of the frame member 83. The support member 82 is fixed to the frame member 83 using, for example, a combination of bolts and nuts. An internal space is formed by the fabric 81 and the frame member 83. To maintain the shape of the fabric 81, the fabric 81 may be sandwiched between punched metal.

[0056] Figure 30 shows the results of measuring the sound absorption characteristics of sound absorbing unit 80. As shown in Figure 30, sound absorbing unit 80 using fabric 81 exhibits a high sound absorption effect at 1.2 kHz or higher. It can also be seen that the sound absorption effect increases as the air layer of sound absorbing unit 80 becomes longer.

[0057] 21, 30, and 31, the sound absorbing effect of the sound absorbing unit 70 is high in the frequency band where the sound absorbing effect of the sound absorbing unit 80 is low. Therefore, the acoustic metamaterial 200 can achieve a high sound absorbing effect over a wide frequency band. Specifically, the sound absorbing unit 70 exhibits a high sound absorption coefficient from approximately 600 Hz to approximately 1100 Hz, and the sound absorbing unit 80 exhibits a high sound absorption coefficient from approximately 1100 Hz to approximately 2700 Hz. When the sound absorbing characteristics of the sound absorbing unit 70 and the sound absorbing unit 80 are combined, the frequency band in which reflected sound is reduced to one-fourth or less extends to approximately 600 Hz to approximately 2700 Hz.

[0058] Fig. 32 schematically illustrates an acoustic metamaterial 300 according to an embodiment. As shown in Fig. 32, the acoustic metamaterial 300 includes a plurality of sound absorbing units 90 arranged in a honeycomb pattern.

[0059] 33 and 34 schematically show a sound absorbing unit 90. As shown in FIGS. 33 and 34, the sound absorbing unit 90 includes a sound hole surface plate 91, a frame member 92, a vibrating body 96, a frame member 97, and a cloth 93. The sound absorbing unit 90 is the same as the sound absorbing unit 60 described with reference to FIGS. 23 to 26, except that the shape of the frame member 92 differs from that of the frame member 62 and that a cloth 93 is provided. In other words, the sound hole surface plate 91 has the same configuration as the sound hole surface plate 61, the vibrating body 96 has the same configuration as the vibrating body 66, and the frame member 97 has the same configuration as the frame member 67. Therefore, a description of the sound hole surface plate 91, the vibrating body 96, and the frame member 97 will be omitted. The cloth 93 can be, for example, a cloth containing aramid fiber.

[0060] FIG. 35 schematically shows the sound absorbing unit 90 without the fabric 93, and FIG. 36 schematically shows the sound absorbing unit 90 without the sound hole surface plate 91 and the fabric 93. As shown in FIGS. 35 and 36, the frame member 92 is an extension of the frame member 62 to add an area for arranging the fabric 93. The frame member 92 includes a base portion 921 corresponding to the frame member 62 and an extension portion 922 provided around the base portion 921. The extension portion 922 has a structure in which an internal space is formed by the extension portion 922 and the fabric 93. The internal space formed by the extension portion 922 and the fabric 93 is a space separated from the internal spaces 21 and 24 shown in FIG. 4. The fabric 93 is connected to the extension portion 922 so as to close the open end of the extension portion 922, and the end of the extension portion 922 to which the fabric 93 is not connected is closed. The extension portion 922 is provided with partition walls 923 that divide the internal space into multiple subspaces. If the wavelength of the maximum frequency in the frequency range that is desired to be absorbed by the fabric 93 is λ, the dividing wall 923 is arranged so that the representative length is λ / 4.

[0061] The fabric 93 and the extended portion 922 of the frame member 92 have sound absorbing performance equivalent to that of the sound absorbing unit 80 described with reference to Fig. 28. Therefore, according to the acoustic metamaterial 300, similar to the acoustic metamaterial 200, a high sound absorbing effect can be obtained over a wide frequency band.

[0062] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0063] 10...sound absorbing device, 11...sound hole surface plate, 111...sound hole, 12...frame member, 121...outer frame, 122...space dividing member, 13...spacer, 14...membrane, 15...support member, 151...frame member, 152...central member, 153...connecting member, 1531, 1532, 1533...beam member, 16...vibrating body, 17...frame member, 18...back plate, 21...internal space, 22, 23...partial space, 24...internal space, 31...sound hole surface plate, 32...frame member, 33...back plate, 41...vibrating body, 4 2...frame member, 43...back panel, 60,70...sound absorbing unit, 61...sound hole surface plate, 611...sound hole, 62...frame member, 64...membrane, 65...support member, 66...vibrating body, 67...frame member, 612,621,622,651,671...hole, 80...sound absorbing unit, 81...cloth, 82...support member, 83...frame member, 90...sound absorbing unit, 91...sound hole surface plate, 92...frame member, 93...cloth, 96...vibrating body, 97...frame member, 100,200,300...acoustic metamaterial.

Claims

1. a surface plate having a plurality of sound holes; a vibrator facing the surface plate; a first frame member connected to the front panel and the vibrating body and forming a first space between the front panel and the vibrating body; a back plate facing the vibrator; a second frame member connected to the back plate and the vibrating body and forming a second space between the back plate and the vibrating body; Equipped with the vibrating body includes a membrane, a third frame member attached to the membrane, a central member attached to the membrane, and a connecting member connecting the third frame member and the central member, the first frame member includes a space dividing member that divides the first space; Sound absorbing device.

2. the vibrating body is connected to the first frame member via a spacer so that the vibrating body does not come into contact with the space dividing member; 2. The sound absorbing device according to claim 1.

3. the space dividing member divides the first space into a first subspace and a second subspace isolated from the vibrating body, The second partial space is provided to surround the first partial space.

2. The sound absorbing device according to claim 1.

4. the space dividing member divides the first space into a first subspace and a second subspace isolated from the vibrating body, The first partial space is provided to surround the second partial space.

2. The sound absorbing device according to claim 1.

5. the connecting member supports the central member so as to be vibrable relative to the third frame member; 2. The sound absorbing device according to claim 1.

6. the third frame member and the central member are attached to a first region of the membrane; The sound absorbing characteristics generated by vibration of a second region of the membrane, which is different from the first region, are utilized to reduce the sound entering the first space through the sound hole.

2. The sound absorbing device according to claim 1.

7. the connecting member is attached to the membrane; 2. The sound absorbing device according to claim 1.

8. a support member constituted by the third frame member, the central member, and the connecting member has a first surface and a second surface opposite to the first surface, and the membrane includes a first membrane provided on the first surface side of the support member and a second membrane provided on the second surface side of the support member; 2. The sound absorbing device according to claim 1.

9. the central member is adhered to the membrane; 2. The sound absorbing device according to claim 1.

10. the central member is secured to the membrane using a magnet; 2. The sound absorbing device according to claim 1.

11. The membrane is made of a heat-resistant material.

2. The sound absorbing device according to claim 1.

12. The membrane is made of silicone rubber.

12. A sound absorbing device according to claim 11.

13. a plurality of first sound absorbing units; a plurality of second sound absorbing units; Equipped with Each of the plurality of first sound absorbing units comprises the sound absorbing device according to claim 1; each of the plurality of second sound absorbing units includes a cloth and a fourth frame member connected to the cloth, and a third space is formed by the cloth and the fourth frame member; Acoustic metamaterials.

14. Equipped with multiple sound-absorbing units, Each of the plurality of sound absorbing units comprises the sound absorbing device according to claim 1 and a fabric, a third space is formed by the fabric and the first frame member included in the sound absorbing device, and the third space is separated from the first space and the second space; Acoustic metamaterials.

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