sound absorbing device

Abstract

To provide a sound absorption device capable of absorbing sound over a wide frequency band.SOLUTION: A sound absorbing device according to one embodiment comprises a surface plate, a back plate, a membrane, and a support member. The surface plate has sound holes. The back plate faces the surface plate. The membrane is provided between the surface plate and the back plate. The support member supports the membrane. The support member includes a first frame attached to the membrane, a first member located inside the first frame and attached to the membrane, and a connecting member connecting the first frame and the first member. The sound absorption device further comprises a second frame and a third frame. The second frame forms a first space between the surface plate and the membrane. The third frame forms a second space between the back plate and the membrane.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a sound absorbing device. [Background technology]

[0002] 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 generating 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.

[0003] 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 peaks.

[0004] In a two-degree-of-freedom Helmholtz resonator, a valley characteristic (a drop in the sound absorption coefficient) occurs between two sound absorption peaks. To suppress the valley characteristic, a method of attaching damping material to the elastic plate has been proposed. However, applying damping material to the elastic plate appropriately requires trial and error. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6510653 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a sound absorbing device that can absorb sounds in a wide frequency band. [Means for solving the problem]

[0007] A sound absorbing device according to one embodiment comprises a front panel, a back panel, a membrane, and a support member. The front panel has sound holes. The back panel faces the front panel. The membrane is provided between the front panel and the back panel. The support member supports the membrane. The support member includes a first frame attached to the membrane, a first member attached to the membrane and positioned inside the first frame, and a connecting member connecting the first frame and the first member. The sound absorbing device further comprises a second frame and a third frame. The second frame forms a first space between the front panel and the membrane. The third frame forms a second space between the back panel and the membrane. [Brief explanation of the drawings]

[0008] [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] 1 is a cross-sectional view showing a sound absorbing device according to an embodiment. [Figure 4] FIG. 2 is a perspective view showing a support member according to the embodiment. [Figure 5] 6 is a graph showing the sound absorption characteristics of a combination of a membrane and a support member according to an embodiment. [Figure 6] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 7] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 8] 10A and 10B are diagrams illustrating vibration modes of a membrane and support member combination according to an embodiment. [Figure 9] FIG. 2 is a perspective view showing a support member according to the embodiment. [Figure 10] FIG. 2 is a perspective view showing a support member according to the embodiment. [Figure 11]10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 12] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 13] FIG. 4 is a plan view showing a support member according to the embodiment. [Figure 14] FIG. 4 is a plan view showing a support member according to the embodiment. [Figure 15] FIG. 4 is a plan view showing a support member according to the embodiment. [Figure 16] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 17] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 18] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 19] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 20] 10A and 10B are diagrams illustrating the arrangement of a central member of a support member according to an embodiment. [Figure 21] FIG. 2 is a perspective view showing a support member according to the embodiment. [Figure 22] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 23] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 24] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 25] 10A and 10B are diagrams illustrating the arrangement of a central member of a support member according to an embodiment. [Figure 26] FIG. 2 is a perspective view showing a support member according to the embodiment. [Figure 27] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 28] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 29] 10A and 10B illustrate vibrations of a membrane and support member combination according to an embodiment. [Figure 30A] FIG. 1 is a perspective view showing a structure for measuring the sound absorption characteristics of a surface plate according to an embodiment. [Figure 30B] FIG. 2 is an exploded view showing a structure for measuring the sound absorption characteristics of a surface plate according to an embodiment. [Figure 30C] FIG. 2 is an exploded view showing a structure for measuring the sound absorption characteristics of a surface plate according to an embodiment. [Figure 31] FIG. 2 is a plan view showing the structure of the surface plate according to the embodiment. [Figure 32] 6 is a graph showing the results of measuring the sound absorption characteristics of the surface plate according to the example. [Figure 33] 34 is a graph showing a plot of Helmholtz resonance frequency versus thickness L1 obtained from FIG. 33. [Figure 34A] FIG. 1 is a perspective view showing a structure for measuring the sound absorption characteristics of a combination of a membrane and a support member according to an embodiment. [Figure 34B] FIG. 1 is an exploded view showing a structure for measuring the sound absorption characteristics of a combination of a membrane and a support member according to an embodiment. [Figure 34C] FIG. 1 is an exploded view showing a structure for measuring the sound absorption characteristics of a combination of a membrane and a support member according to an embodiment. [Figure 35] FIG. 2 is a plan view showing a combination of a membrane and a support member according to the first embodiment. [Figure 36] 6 is a graph showing the results of measuring the sound absorption characteristics of a combination of a film and a support member according to Example 1. [Figure 37] 37 is a graph showing a plot of the natural frequency of the first sound absorption characteristic against the thickness L2 obtained from FIG. 36. [Figure 38] FIG. 4 is a diagram for explaining a method for determining a combination of thicknesses L1 and L2 according to the first embodiment. [Figure 39] 4 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 1. [Figure 40] 4 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 1. [Figure 41] 6 is a graph showing the results of measuring the sound absorption characteristics of a combination of a film and a support member according to Example 1. [Figure 42] 42 is a graph showing a plot of the natural frequency of the first sound absorption characteristic against the thickness L2 obtained from FIG. 41. [Figure 43]FIG. 4 is a diagram for explaining a method for determining a combination of thicknesses L1 and L2 according to the first embodiment. [Figure 44] 4 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 1. [Figure 45] 4 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 1. [Figure 46] FIG. 10 is a graph showing the specific acoustic impedance in a comparison between a case where the membrane is doubled and a case where the membrane is tripled, according to Example 1. [Figure 47] FIG. 3 is a plan view showing a state in which a weight is attached to a support member according to the first embodiment. [Figure 48] 6 is a graph showing the results of measuring the sound absorption characteristics of a combination of a film and a support member according to Example 1. [Figure 49] FIG. 4 is a plan view showing four types of support members used to verify changes in natural frequency due to changes in the shape of the connecting member according to the first embodiment. [Figure 50] 6 is a graph showing the results of measuring the sound absorption characteristics of a combination of a film and a support member according to Example 1. [Figure 51] FIG. 10 is a plan view showing a combination of a membrane and a support member according to a second embodiment. [Figure 52] 10 is a graph showing the results of measuring the sound absorption characteristics of a combination of a film and a support member according to Example 2. [Figure 53] 53 is a graph showing the natural frequency of the second sound absorption characteristic versus the thickness L2 obtained from FIG. 52. [Figure 54] FIG. 10 is a diagram for explaining a method for determining a combination of thicknesses L1 and L2 according to the second embodiment. [Figure 55] 6 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 2. [Figure 56] 6 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 2. [Figure 57] 6 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 2. [Figure 58] FIG. 10 is an exploded view showing a sound absorbing device according to a third embodiment. [Figure 59]10 is a graph showing the results of measuring the sound absorption characteristics of a combination of a film and a support member according to Example 3. [Figure 60] 60 is a graph showing the natural frequency of the second sound absorption characteristic versus the thickness L2 obtained from FIG. 59. [Figure 61] FIG. 10 is a diagram for explaining a method for determining a combination of thicknesses L1 and L2 according to the third embodiment. [Figure 62] 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 3. [Figure 63] 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 3. [Figure 64] 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 3. [Figure 65] FIG. 10 is a graph showing the specific acoustic impedance of the sound absorbing device according to Example 2 compared with that of the sound absorbing device according to Example 3. [Figure 66] FIG. 10 is a perspective view showing a support member according to a fourth embodiment. [Figure 67] 10 is a graph showing the results of measuring the sound absorption characteristics of a combination of a film and a support member according to Example 4. [Figure 68] 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 4. [Figure 69] 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 4. [Figure 70] 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 4. [Figure 71] 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 4. [Figure 72] 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 4. [Figure 73] FIG. 10 is a diagram showing the specific acoustic impedance of the sound absorbing device according to the fourth embodiment. [Figure 74] 1 is a perspective view showing a sound absorbing device according to an embodiment. [Figure 75] 1 is a perspective view showing a sound absorbing device according to an embodiment. [Figure 76] 1 is a perspective view showing a sound absorbing device according to an embodiment. [Figure 77]FIG. 2 is an exploded view showing the sound absorbing device according to the embodiment. [Figure 78] FIG. 1 is a cross-sectional view showing a sound absorbing device according to a related art. [Figure 79] 10 is a graph showing the sound absorption characteristics of a sound absorbing device according to the related art. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings. Similar components are designated by similar reference numerals throughout the drawings, and redundant explanations will be omitted.

[0010] First, a sound absorbing device according to the related art will be briefly described.

[0011] FIG. 78 schematically illustrates a sound absorbing device 50 according to the related art. As shown in FIG. 78, the sound absorbing device 50 includes a surface panel 51, a frame 52, an elastic plate 53, and a back panel 54. The surface panel 51 has a sound hole 511. The back panel 54 faces the surface panel 51. The surface panel 51 is connected to the frame 52 so as to close a first open end of the frame 52, and the back panel 54 is connected to the frame 52 so as to close a second open end of the frame 52. The elastic plate 53 is provided between the surface panel 51 and the back panel 54 and is supported by the frame 52 so as to be able to vibrate. The surface panel 51, the frame 52, and the elastic plate 53 form an internal space 57, and the back panel 54, the frame 52, and the elastic plate 53 form an internal space 58. The internal space 57 communicates with the external space via the sound hole 511. The sound hole 511 functions as a path through which sound generated in the external space enters the internal space 57 of the sound absorbing device 50.

[0012] The sound absorbing device 50 has a two-degree-of-freedom system. Specifically, the combination of the sound hole 511 and the internal space 57 constitutes a vibration system with one degree of freedom, and the combination of the back panel 54 and the internal space 58 constitutes a vibration system with one degree of freedom.

[0013] Figure 79 shows a schematic diagram of the sound absorption characteristics of sound absorbing device 50. Because sound absorbing device 50 has a two-degree-of-freedom system, it has sound absorption characteristics with two sound absorption coefficient peaks and a valley characteristic (a drop in sound absorption coefficient) between the two sound absorption coefficient peaks, as shown in Figure 79. Such a valley characteristic can be suppressed by attaching a vibration-damping material to elastic plate 53, as shown by the arrow in Figure 79. Adding vibration-damping material to elastic plate 53 strengthens the damping effect, thereby suppressing the valley characteristic.

[0014] When a damping material is applied to the elastic plate 53, a change in the natural frequency occurs along with a damping effect. The natural frequency indicates the frequency at which the sound absorption coefficient reaches its peak. In particular, when the elastic plate 53 is thin, the damping effect and the change in the natural frequency become large. For this reason, the design of the sound absorbing device 50 requires trial and error.

[0015] Next, a sound absorbing device according to an embodiment will be described.

[0016] Figures 1 to 3 show a schematic diagram of the overall configuration of a sound absorbing device 10 according to one embodiment. Specifically, Figure 1 shows the external appearance of the sound absorbing device 10, Figure 2 shows the sound absorbing device 10 in an exploded state, and Figure 3 shows a cross section of the sound absorbing device 10. The sound absorbing device 10 is configured to absorb at least a portion of the sound generated in an external space.

[0017] As shown in FIGS. 1 to 3, the sound absorbing device 10 comprises a face plate 11, a frame 12, a membrane 13, a support member 14, a frame 15, and a back plate 16.

[0018] The top plate 11 is a perforated plate, specifically a circular flat plate with multiple sound holes 111. The top plate 11 may have only one sound hole 111. 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 top plate 11, and the X and Z axes are defined as directions parallel to the main surface of the top plate 11. In the following, thickness and height refer to dimensions in the Y axis direction (direction parallel to the Y axis).

[0019] The back plate 16 is a circular flat plate, and is provided opposite the front plate 11 in the Y-axis direction. The frames 12 and 15 are cylindrical members. The thickness of the frame 12 is represented as L1, and the thickness of the frame 15 is represented as L2.

[0020] The membrane 13 is a circular thin film and is provided between the front panel 11 and the back panel 16. The support member 14 supports the membrane 13. As shown in FIG. 4, the support member 14 includes a frame 141, a central member 142 located inside the frame 141, and a connecting member 143 that connects the frame 141 and the central member 142. The frame 141 and the central member 142 are attached to the membrane 13 by, for example, adhesive or double-sided tape. The frame 141 is annular, and the central member 142 is cylindrical. The connecting member 143 may be a beam member extending radially (perpendicular to the Y-axis). The connecting member 143 supports the central member 142 so that it can vibrate relative to the frame 141. The central member 142 is supported by the connecting member 143 so that it can vibrate in the Y-axis direction.

[0021] The frame 12 forms an internal space 31 between the surface plate 11 and the membrane 13. The internal space 31 is a space surrounded by the surface plate 11, the frame 12, and the membrane 13. The surface plate 11 is connected to the frame 12 so as to close a first open end of the frame 12. The membrane 13, attached to the support member 14, is connected to the frame 12 so as to close a second open end of the frame 12. This separates the surface plate 11 and the membrane 13 by a length L1. The internal space 31 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 31 of the sound absorbing device 10.

[0022] The frame 15 forms an internal space 32 between the back plate 16 and the membrane 13. The internal space 32 is a space surrounded by the back plate 16, the frame 15, the membrane 13, and the support member 14. The membrane 13 is connected to the frame 15 via the support member 14 so as to close a first open end of the frame 15. The back plate 16 is connected to the frame 15 so as to close a second open end of the frame 15. This leaves a distance L2 between the combination of the membrane 13 and the support member 14 and the back plate 16. The internal space 32 is separated from the internal space 31 and the external space.

[0023] The connection between the two components (for example the connection between the face plate 11 and the frame 12) may be made by adhesive, for example. The frame 15 and the back plate 16 may be integrally molded.

[0024] 3, the film 13 is provided on the surface of the support member 14 facing the frame 12. Alternatively, the film 13 may be provided on the surface of the support member 14 facing the frame 15. The film 13 may also be provided on both surfaces of the support member 14. Specifically, the film 13 may include a first film provided on the surface of the support member 14 facing the frame 12 and a second film provided on the surface of the support member 14 facing the frame 15.

[0025] In this embodiment, a combination of a membrane 13 and a support member 14 is used instead of the elastic plate 53 used in the related art. The combination of the membrane 13 and the support member 14 has sound absorption characteristics including a first sound absorption characteristic and a second sound absorption characteristic, as shown in FIG. 5. The first sound absorption characteristic is obtained by vibrating the central member 142 in the Y-axis direction, as shown in FIG. 6, and vibrating the membrane 13 in accordance with the vibration of the central member 142. The second sound absorption characteristic is obtained by vibrating the membrane 13 itself (membrane vibration), as shown in FIG. 7. A portion of the membrane 13 is bonded to the support member 14, and the remaining region of the membrane 13 is capable of membrane vibration. Hereinafter, a configuration that primarily utilizes the first sound absorption characteristic will be referred to as the first configuration, and a configuration that primarily utilizes the second sound absorption characteristic will be referred to as the second configuration. The support member 14 in the first and second configurations may have the same structure.

[0026] Figure 8 shows the vibration modes of the combination of the membrane 13 and the support member 14. As shown in Figure 8, many vibration modes occur. The vibration modes that provide sound absorption properties are modes in which the membrane 13 is not divided into regions and the entire membrane 13 vibrates in the same direction, such as the first vibration mode and the fourth vibration mode. This is because these modes are easily excited by vibrations when sound waves are incident perpendicularly. The first sound absorption property is obtained by the first vibration mode, and the second sound absorption property is obtained by the fourth vibration mode. On the other hand, for example, the second vibration mode is obtained when the membrane 13 is divided into two regions and the phases are different in the two regions. For this reason, vibrations are not easily excited by sound waves incident perpendicularly, and sound absorption properties cannot be obtained. The same is true for sound waves incident at an angle.

[0027] The first embodiment will be described in detail.

[0028] As described above, the support member 14 includes the frame 141, the central member 142 positioned inside the frame 141, and the connecting members 143 that support the central member 142 so that it can vibrate relative to the frame 141, and the frame 141 and the central member 142 are bonded to the membrane 13. With this configuration, the mass of the central member 142, the rigidity of the membrane 13, the rigidity of the connecting members 143, and the rigidity of the air spring formed by the internal space 32 as an air layer can create a single-degree-of-freedom system similar to that of the sound-absorbing device 50 according to the related art. Therefore, compared to the related art described above, designing the natural frequency is easier, and designing for low-frequency bands is also possible. Furthermore, the damping effect, which has the greatest impact on sound absorption, can be generated by the viscoelasticity of the membrane 13, eliminating the need for additional vibration-damping material.

[0029] The design of a single-degree-of-freedom system can be achieved by adjusting the mass of the central member 142, the rigidity of the membrane 13, the rigidity of the connecting members 143, and the rigidity of the air spring created by the internal space 32. The damping effect can be adjusted by the material and thickness of the membrane 13. In particular, the thickness of the membrane 13 has little effect on the natural frequency, so adjusting the thickness of the membrane 13 allows the damping effect to be adjusted without significantly changing the natural frequency. The mass of the central member 142 can be changed by changing its shape, and the rigidity of the connecting members 143 can be changed by changing their shape. Therefore, the natural frequency of the single-degree-of-freedom system can be easily adjusted. Note that in the sound-absorbing device 10 that uses a combination of the membrane 13 and the support member 14, the influence of the air spring rigidity created by the internal space 32 is greater than in related technologies that use an elastic plate 53. Therefore, the rigidity of the air spring created by the internal space 32 can be effectively used as a parameter for adjusting the natural frequency. The rigidity of the air spring created by the internal space 32 depends on the thickness L2 of the frame 15.

[0030] In summary, the sound absorbing device 10 according to the first embodiment has the following features. For example, the natural frequency can be determined by designing the central member 142 and the connecting member 143 of the support member 14 and the membrane 13. Damping can be achieved by attaching the membrane 13 to the support member 14. From the viewpoint of energy dissipation, the combination of membrane 13 and support member 14 is more preferable than the elastic plate 53 used in the related art, and does not require the addition of vibration-damping material. The membrane 13 has two roles: it provides an acoustic wall effect (acoustically separating the internal space 31 from the internal space 32) and it also provides the damping described above. Changing the thickness of the membrane 13 is effective for adjusting the damping effect.

[0031] The following describes variations of the support member 14. As variations of the support member 14, variations in the shape of the connecting member 143 are possible.

[0032] In the support member 14 according to the first variation, the connecting members 143 are straight beam members, as shown in Figures 4, 9, and 10. In the example shown in Figure 9, the support member 14 includes two connecting members 143, and in the example shown in Figure 10, the support member 14 includes four connecting members 143.

[0033] In the sound absorbing device 10 using the support member 14 according to the first variation, the design parameters include the following: Radius and thickness of the central member 142 Width, thickness, and number of connecting members 143 ·Material and thickness of membrane 13 Frame 15 thickness L2

[0034] The radius and thickness of the central member 142 contribute to the mass parameter of the single-degree-of-freedom system. The shape of the central member 142 is not limited to a cylinder, but may be other shapes such as a ring. The width, thickness, and number of connecting members 143 contribute to the stiffness parameter of the single-degree-of-freedom system. The material and thickness of the membrane 13 contribute to the stiffness parameter and viscosity parameter of the single-degree-of-freedom system. If the membrane 13 is used alone (i.e., without the support member 14), the mass parameter and stiffness parameter of the single-degree-of-freedom system will be strongly dependent on the material and thickness of the membrane 13, making it difficult to design the mass parameter and stiffness parameter of the single-degree-of-freedom system. Combining the membrane 13 and the support member 14 makes it easier to design the mass parameter and stiffness parameter of the single-degree-of-freedom system. The thickness L2 of the frame 15 is the thickness of the internal space 32 and contributes to the stiffness parameter of the single-degree-of-freedom system.

[0035] It should be noted that the connecting member 143 does not need to be adhered to the membrane 13. Furthermore, the mass of the central member 142 can be finely adjusted by attaching a thick tape or metal piece to the central member 142.

[0036] In the first embodiment, the primary vibration mode is utilized. Therefore, there are no restrictions on the number of connecting members 143. As the number of connecting members 143 increases, the rigidity of the single-degree-of-freedom system naturally increases, and the natural frequency also increases. In designing the sound absorbing device 10, the natural frequency is determined according to the sound absorption band (the frequency band to be absorbed), and the above design parameters, including the number of connecting members 143, are determined based on the determined natural frequency.

[0037] Fig. 11 shows the results of analyzing the vibration of combinations of membrane 13 and support member 14 for support member 14 having one connecting member 143 as shown in Fig. 4, support member 14 having two connecting members 143 as shown in Fig. 9, and support member 14 having four connecting members 143 as shown in Fig. 10. The vibration analysis results shown in Fig. 11 show that the natural frequency is 218 Hz for support member 14 having one connecting member 143 as shown in Fig. 4, 462 Hz for support member 14 having two connecting members 143 as shown in Fig. 9, and 635 Hz for support member 14 having four connecting members 143 as shown in Fig. 10. It can be seen from the vibration analysis results that the natural frequency increases as the number of connecting members 143 increases.

[0038] The connecting members 143 may be bonded to the membrane 13. Even when the connecting members 143 are bonded to the membrane 13, as shown in Fig. 12, increasing the number of connecting members 143 increases the rigidity and the natural frequency. In the vibration analysis results shown in Fig. 12, the natural frequency is higher than the value shown in Fig. 11 because the height of the connecting members 143 is doubled.

[0039] 13 to 15 , in the support member 14 according to the second variation, the connecting member 143 includes straight beam members 1431 and 1432 and an arc-shaped beam member 1433, with a first end of the beam member 1431 connected to the frame 141, a second end of the beam member 1431 connected to a first end of the beam member 1433, a first end of the beam member 1432 connected to a second end of the beam member 1433, and a second end of the beam member 1432 connected to the central member 142. In the example shown in FIG. 13 , the support member 14 includes one connecting member 143, in the example shown in FIG. 14 , the support member 14 includes two connecting members 143, and in the example shown in FIG. 15 , the support member 14 includes four connecting members 143.

[0040] In the sound absorbing device 10 using the support member 14 according to the second variation, the design parameters include the following: Radius and thickness of the central member 142 Width, thickness, and number of beam members 1431 and 1432 Width, thickness, angle θ, and number of beam members 1433 ·Material and thickness of membrane 13 Frame 15 thickness L2

[0041] The radius and thickness of the central member 142 contribute to the mass parameter of the single-degree-of-freedom system. The shape of the central member 142 is not limited to a cylinder, but may be other shapes such as a ring. The width, thickness, and number of beam members 1431 and 1432 contribute to the stiffness parameter of the single-degree-of-freedom system. The width, thickness, angle θ, and number of beam members 1433 contribute to the stiffness parameter of the single-degree-of-freedom system. Because the beam member 1433 extends in the circumferential direction, its length can be increased. The length of the beam member 1433 corresponds to the angle θ of the beam member 1433. Increasing the length of the beam member 1433 reduces the stiffness of the connecting member 143 and lowers the natural frequency of the first vibration mode. Therefore, the second variation can lower the natural frequency of the first vibration mode compared to the first variation, making it suitable for low-frequency design. The material and thickness of the membrane 13 contribute to the stiffness parameter and viscosity parameter of the single-degree-of-freedom system. The thickness L2 of the frame 15 is the thickness of the internal space 32, and contributes to the stiffness parameter of the one-degree-of-freedom system.

[0042] The force from the connecting member 143 to the central member 142 is applied obliquely to the Y-axis direction, causing the central member 142 to rotate slightly and move in translation in the Y-axis direction, allowing the membrane 13 to vibrate appropriately in the Y-axis direction.

[0043] Fig. 16 shows the results of vibration analysis when the support member 14 has two connecting members 143 as shown in Fig. 14 and when the support member 14 has four connecting members 143 as shown in Fig. 15. Fig. 16 confirms that translational motion in the Y-axis direction occurs appropriately.

[0044] Although the central member 142 has been shown as being circular when viewed in the Y-axis direction, the central member 142 may also be ring-shaped or polygonal when viewed in the Y-axis direction.

[0045] Next, the second embodiment will be described in detail.

[0046] As described above, the support member 14 includes the frame 141, the central member 142 positioned inside the frame 141, and the connecting member 143 that supports the central member 142 so that it can vibrate relative to the frame 141. The frame 141 and the central member 142 are bonded to the membrane 13. With this configuration, a single-degree-of-freedom system similar to that of the sound-absorbing device 50 of the related art can be created by adjusting the mass of the membrane 13, the rigidity of the membrane 13, the dimensions of the central member 142, and the rigidity of the air spring provided by the internal space 32 as an air layer. The effective area of ​​the membrane 13 can be changed by adjusting the dimensions of the central member 142, thereby changing the mass and rigidity of the membrane 13. The effective area of ​​the membrane 13 indicates the area within which the membrane can vibrate. Therefore, compared to the sound-absorbing device 50 of the related art, designing the natural frequency is easier, enabling design in low-frequency bands. Furthermore, the damping effect, which has the greatest impact on sound absorption, can be achieved by the viscoelasticity of the membrane 13, eliminating the need for additional vibration-damping material. The damping effect can be adjusted by providing membranes 13 on both sides of the support member 14 or by changing the support conditions of the membrane 13. The support conditions of the membrane 13 are described below. Because the membrane 13 is bonded to the central member 142, the boundary conditions of the membrane vibration change depending on the vibration mode of the central member 142. 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 13 is less constrained by the central member 142 (the membrane 13 becomes more easily movable), thereby increasing the damping effect. Conversely, as the frequency of the vibration mode increases, the membrane 13 is more easily constrained by the central member 142 (the membrane 13 becomes less easily movable), thereby weakening the damping effect. As described above, in the second embodiment, membrane vibration is utilized, so changing the shape of the connecting member 143 only slightly changes the natural frequency. However, changing the shape of the connecting member 143 affects the boundary conditions of the membrane vibration and can be included as a design element for fine-tuning the damping effect.

[0047] The design of the single-degree-of-freedom system can be achieved by adjusting the mass of the membrane 13, the rigidity of the membrane 13, the rigidity of the central member 142, and the rigidity of the air spring due to the internal space 32. Furthermore, since the membrane 13 has viscoelasticity, additional damping is unnecessary. Furthermore, the damping effect can be fine-tuned by changing the shape of the connecting member 143. In other words, the mass and rigidity of the membrane 13 can be changed by changing the shape of the central member 142 and the thickness and material of the membrane 13, thereby easily changing the natural frequency of the single-degree-of-freedom system. Furthermore, the damping effect can be fine-tuned by changing the shape of the connecting member 143. The influence of the air spring rigidity due to the internal space 32 is greater than that of the elastic plate 53 used in related art. Therefore, the rigidity of the air spring due to the internal space 32 can be effectively used as a parameter for adjusting the natural frequency. Furthermore, the natural frequency can be changed by dividing the membrane 13 by adhering the connecting member 143 to the membrane 13. The number of divisions can be changed by adjusting the number of connecting members 143 adhered to the membrane 13, thereby changing the natural frequency.

[0048] The sound absorbing device 10 according to the second embodiment 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 142 and the material and thickness of the membrane 13. By bonding the connecting member 143 to the membrane 13, the natural frequency can also be changed. Damping can be achieved by attaching the membrane 13 to the support member 14. From the viewpoint of energy dissipation, the combination of the membrane 13 and the support member 14 is more preferable than the elastic plate 53 used in the related art, 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 13 using the central member 142 and the connecting members 143. The design of the support member 14 to adjust the damping effect by changing the boundary conditions of the membrane 13 using the central member 142 and the connecting members 143 can be implemented by varying the connecting members 143, as in the first embodiment. The membrane 13 serves two purposes: to provide an acoustic wall effect and to provide the above-mentioned damping. By providing membranes 13 on both sides of the support member 14, it is possible to strengthen the damping effect.

[0049] Figure 17 shows the analysis results of the vibration of the combination of membrane 13 and support member 14. In Figure 17, the left side shows the analysis results when the effective area of ​​membrane 13 is small, and the right side shows the analysis results when the effective area of ​​membrane 13 is large. As the dimensions of central member 142 become smaller, the effective area of ​​membrane 13 increases. Figure 17 confirms that the natural frequency of membrane vibration is lower when the effective area of ​​membrane 13 is larger.

[0050] FIG. 18 shows the analysis results of vibrations of combinations of membrane 13 and support member 14 for two connecting members 143 with different shapes. The left side of FIG. 18 shows the analysis results of vibrations of combinations of membrane 13 and support member 14 when the connecting member 143 is thin, and the right side of FIG. 18 shows the analysis results of vibrations of combinations of membrane 13 and support member 14 when the connecting member 143 is thick. When the connecting member 143 is thin, the frequency of the first sound absorption characteristic is 218 Hz, and the frequency of the second sound absorption characteristic is 845.7 Hz. When the connecting member 143 is thick, the frequency of the first sound absorption characteristic is 264 Hz, and the frequency of the second sound absorption characteristic is 847.7 Hz. Thus, the frequency of the first sound absorption characteristic changes depending on the shape of the connecting member 143, but the frequency of the second sound absorption characteristic changes very little. From Figure 18, it can be seen that when the frequency of the first sound absorption characteristic is higher, membrane vibration is inhibited and displacement in the vicinity of the connecting member 143 is reduced. In other words, it can be seen that when the thickness of the connecting member 143 is greater, which increases the frequency of the first sound absorption characteristic, the bonding conditions of the membrane 13 are strengthened. Strengthening the bonding conditions of the membrane 13 reduces the vibration speed of the membrane vibration and reduces the damping effect. In this way, by changing the frequency of the first sound absorption characteristic by changing the shape of the connecting member 143, it is possible to fine-tune the damping effect without significantly changing the frequency of the second sound absorption characteristic used in the second form.

[0051] Figure 19 shows the analysis results of vibration of the combination of membrane 13 and support members 14 when connecting members 143 are bonded to membrane 13. Figure 19 confirms that the number of divisions of membrane 13 changes according to the number of support members 14 bonded to membrane 13, and the natural frequency also changes.

[0052] The support member 14 according to the third variation has a shape according to the design method exemplified in Figures 20 and 25. As described above, the natural frequency of membrane vibration depends on the effective area of ​​the membrane 13. The support member 14 according to the third variation makes it possible to greatly change the effective area of ​​the membrane 13, and therefore makes it possible to greatly change the natural frequency of membrane vibration.

[0053] Fig. 21 schematically shows an example of a support member 14 according to a third variation in accordance with the design method shown in Fig. 20. As shown in Fig. 21, the support member 14 includes a frame 141, three central members 142, and three connecting members 143. The central members 142 are arranged at positions that are equidistant from one another and at the same distance from the center of the support member 14. Each central member 142 is supported relative to the frame 141 by a corresponding connecting member 143.

[0054] In FIG. 20, R denotes the radius of the circle 211 corresponding to the inner circumference of the frame 141, r denotes the radius of each of the three inscribed circles 212 inscribed in the circle 211, and d denotes the distance between the centers of the inscribed circles 212. The radius r is set to be equal to the distance d. In this case, 2R≈3.2d. For example, when 2R=54 mm, d=17 mm, as shown in FIG. 21. The frame 141 is expanded to the region 213 between the circle 211 and the inscribed circle 212 shown in FIG. 21, and further expanded to the center of the circle 211 along the boundary line 214 between the inscribed circles 212. The cross section of the portion expanded along the boundary line 214 between the inscribed circles 212 is a square with a width of 3 mm and a height of 3 mm. The central member 142 is positioned at the center of the inscribed circles 212. Each central member 142 is a cylinder with a diameter of 5 mm and a height of 3 mm. Each central member 142 is connected to the central portion of the frame 141 by a corresponding connecting member 143. The cross section of the connecting member 143 is a rectangle with a width of 3 mm and a height of 1.5 mm.

[0055] Figures 22, 23, and 24 show the results of analyzing the vibration of the membrane 13 when the diameters of the central members 142 are 10 mm, 12.5 mm, and 15 mm. The natural frequency of the membrane 13 is 1744.3 Hz when the diameter of the central member 142 is 10 mm as shown in Figure 22, 2133.4 Hz when the diameter of the central member 142 is 12.5 mm as shown in Figure 23, and 2686.2 Hz when the diameter of the central member 142 is 15 mm as shown in Figure 24. The larger the diameter of the central member 142, the higher the natural frequency of the membrane vibration. As described above, changing the diameter of the central member 142 can significantly change the natural frequency of the membrane vibration. Therefore, if a significant change in the natural frequency of the membrane vibration is desired, the third variation is desirable. Note that the example shown in Figure 24 does not include a connecting member 143, but such a case is also within the scope of this patent.

[0056] Fig. 26 schematically shows an example of a support member 14 according to a third variation in accordance with the design method shown in Fig. 25. As shown in Fig. 26, the support member 14 includes a frame 141, four central members 142, and four connecting members 143. The central members 142 are arranged at positions that are equidistant from one another and at the same distance from the center of the support member 14. Each central member 142 is supported relative to the frame 141 by a corresponding connecting member 143.

[0057] In FIG. 25, the radius of the circle 251 corresponding to the inner circumference of the frame 141 is R, the radius of each of the four inscribed circles 252 inscribed in the circle 251 is r, and the distance between the centers of the inscribed circles 252 is d. The radius r is set equal to the distance d. In this case, 2R≈3.2d. For example, when 2R=54 mm, d=15.5 mm, as shown in FIG. 26. The frame 141 is expanded to the region 253 between the circle 251 and the inscribed circle 252 shown in FIG. 25, and further expanded to the center of the circle 251 along the boundary line 254 between the inscribed circles 252. The cross section of the portion expanded along the boundary line 254 between the inscribed circles 252 is a square with a width of 3 mm and a height of 3 mm. The central member 142 is positioned at the center of the inscribed circles 252. Each central member 142 is a cylinder with a diameter of 5 mm and a height of 3 mm. Each central member 142 is connected to the central portion of the frame 15 by a corresponding connecting member 143. The cross section of the connecting member 143 is a rectangle with a width of 3 mm and a height of 1.5 mm.

[0058] Figures 27, 28, and 29 show the results of analyzing the vibration of the membrane 13 when the diameters of the central members 142 are 7.5 mm, 10 mm, and 12.5 mm. The natural frequency of the membrane 13 is 1864.8 Hz when the diameter of the central member 142 is 7.5 mm as shown in Figure 27, 2249.3 Hz when the diameter of the central member 142 is 10 mm as shown in Figure 28, and 2852 Hz when the diameter of the central member 142 is 12.5 mm as shown in Figure 29. The larger the diameter of the central member 142, the higher the natural frequency of the membrane vibration. In this way, the natural frequency of the membrane vibration can be significantly changed by changing the diameter of the central member 142. Therefore, if a significant change in the natural frequency of the membrane vibration is desired, the third variation is desirable.

[0059] The effect of finely adjusting the damping effect by changing the shape of the connecting member 143 is similar to that described above with respect to the first and second variations.

[0060] (Example) Hereinafter, a method for designing the sound absorbing device 10 according to the embodiment will be described.

[0061] The design method for the sound absorbing device 10 includes measuring the Helmholtz resonator characteristics of the surface plate 11. Figures 30A, 30B, and 30C schematically show a structure (Helmholtz resonator) 200 for measuring the Helmholtz resonator characteristics of the surface plate 11. As shown in Figures 30A, 30B, and 30C, the structure 200 includes the surface plate 11, a frame 12, and a back plate 18. The surface plate 11 is connected to the frame 12 so as to close a first open end of the frame 12, and the back plate 18 is connected to the frame 12 so as to close a second open end of the frame 12. The surface plate 11 and the back plate 18 face each other with a length L1 between them. The surface plate 11, the frame 12, and the back plate 18 form an internal space corresponding to the internal space 31 shown in Figure 3. A plurality of frames 12 with different thicknesses L1 are prepared, and the normal incidence sound absorption coefficient of the structure 200 is measured for each frame 12.

[0062] Figure 31 shows a schematic diagram of the structure of the surface plate 11 commonly used in the following examples. As shown in Figure 31, the surface plate 11 has a diameter of 60 mm and a thickness of 1 mm. 61 sound holes 111 are arranged in a honeycomb pattern within a circle 201 with a diameter of 54 mm defined on the surface plate 11. The distance between the center of each side of the regular hexagons (honeycomb regions) 202 that form the honeycomb pattern is 3.1 mm, and the area of ​​the regular hexagons 202 is 33.29 mm. 2 The sound hole 111 has a diameter of 1 mm and an area of ​​0.758 mm 2 Therefore, the aperture ratio is 2.36%. The frame 12 is a cylinder with an inner diameter of 54 mm, an outer diameter of 60 mm, and a thickness of L1. The back plate 18 is a circular flat plate with a diameter of 60 mm.

[0063] Fig. 32 shows the results of measuring the sound absorption characteristics of structure 200, and Fig. 33 shows a plot of the Helmholtz resonance frequency versus the thickness L1 of frame 12. From Fig. 32 and Fig. 33, it can be seen that the Helmholtz resonance frequency depends on the thickness L1 of frame 12 (i.e., the volume of the internal space). Therefore, it is possible to adjust the Helmholtz resonance frequency by adjusting the thickness L1 of frame 12.

[0064] The design method for the sound absorbing device 10 further includes measuring the sound absorption characteristics of the combination of the membrane 13 and the support member 14. Figures 34A, 34B, and 34C schematically show a structure 240 for measuring the sound absorption characteristics of the combination of the membrane 13 and the support member 14. As shown in Figures 34A, 34B, and 34C, the structure 240 includes the membrane 13, the support member 14, a frame 15, and a back plate 16. The combination of the membrane 13 and the support member 14 is connected to the frame 15 to close a first open end of the frame 15, and the back plate 18 is connected to the frame 15 to close a second open end of the frame 15. The combination of the membrane 13 and the support member 14 and the back plate 16 face each other with a length L2 between them. The membrane 13, the support member 14, the frame 15, and the back plate 16 form an interior space corresponding to the interior space 32 shown in Figure 3. A plurality of frames 15 having different thicknesses L2 are prepared, and the normal incident sound absorption coefficient of the structure 240 is measured for each frame 15.

[0065] In the following example, the membrane 13 was made of a 0.2 mm thick hard vinyl chloride film, and attached to the support member 14 with thin double-sided tape. The support member 14 was produced by fused deposition modeling using a 3D printer. The material was ABS (Acrylonitrile Butadiene Styrene), and the layer pitch and density were set to 0.127 mm and solid, respectively, in the 3D printer.

[0066] The design method for the sound absorbing device 10 further includes determining, as a candidate combination of the frame 12 and the frame 15, which is likely to achieve the desired sound absorption characteristics, based on the measurement results of the Helmholtz resonator characteristics of the surface panel 11 and the measurement results of the sound absorption characteristics of the combination of the membrane 13 and the support member 14.

[0067] The design method for the sound absorbing device 10 further includes fabricating a sound absorbing device 10 corresponding to each candidate, measuring the sound absorption characteristics of the sound absorbing device 10 for each candidate, and determining the combination of the frame 12 and the frame 15 that will provide the desired sound absorption characteristics.

[0068] The above-described method for designing the sound absorbing device 10 makes it possible to easily select the combination of the thickness L1 of the frame 12 and the thickness L2 of the frame 15 that maximizes the sound absorbing performance of the sound absorbing device 10.

[0069] Example 1 Example 1 relates to the first embodiment. In Example 1, the support member 14 has the structure shown in FIG. 35. Specifically, the support member 14 includes a frame 141, a central member 142, and four connecting members 143. The connecting members 143 are straight beam members, and their cross sections are rectangular, measuring 3 mm in width and 2 mm in height. The central member 142 is a cylindrical member measuring 20 mm in diameter and 3 mm in height. The frame 141 is a circular member measuring 54 mm in inner diameter, 60 mm in outer diameter, and 3 mm in height. The frame 141, central member 142, and connecting members 143 were integrally molded from ABS using a 3D printer. In addition, to enhance the damping effect, two layers of 0.2 mm-thick hard vinyl chloride film were used as the membrane 13.

[0070] Fig. 36 shows the results of measuring the sound absorption characteristics of the combination of the membrane 13 and support member 14 according to Example 1. The first sound absorption characteristic and the second sound absorption characteristic can be confirmed from Fig. 36. Fig. 37 shows a plot of the natural frequency of the first sound absorption characteristic versus the thickness L2 of the frame 15. Fig. 37 confirms that the natural frequency of the first sound absorption characteristic obtained by the combination of the membrane 13 and support member 14 can be adjusted by adjusting the thickness L2 of the frame 15.

[0071] In the first mode, a combination of the thickness L1 of the frame 12 and the thickness L2 of the frame 15 is determined as a candidate, based on the guideline of roughly matching the natural frequency of the first sound absorption characteristic with the Helmholtz resonance frequency. Figure 38 shows the graphs shown in Figures 34 and 37 together. As shown in Figure 38, when L1 = 49 mm and L2 = 20 mm, the natural frequency of the first sound absorption characteristic roughly matches the Helmholtz resonance frequency. Therefore, the combination of L1 = 49 mm and L2 = 20 mm is determined as a candidate. Further candidates are determined based on this candidate. For example, a frame 15 with L2 = 20 mm is combined with several frames 12 having a thickness L1 close to 49 mm. Specifically, the following combinations are determined as candidates: L1 = 34 mm and L2 = 20 mm, L1 = 39 mm and L2 = 20 mm, L1 = 44 mm and L2 = 20 mm, L1 = 49 mm and L2 = 20 mm, and L1 = 54 mm and L2 = 20 mm. Of these candidates, the one with the closest sound absorption coefficient values ​​for the two peaks and the highest sound absorption coefficient value for the valley between the two peaks is determined as the final combination.

[0072] Figure 39 shows the results of measuring the sound absorption characteristics of sound absorbing device 10 according to Example 1 for the combinations of L1 = 49 mm and L2 = 20 mm. In Figure 39, the solid line shows the sound absorption characteristics of sound absorbing device 10. The sound absorption coefficient peak is separated into two due to the coupling of Helmholtz resonance and the vibration of the combination of membrane 13 and support member 14, and the valley characteristic between the peaks also shows a sound absorption coefficient of 0.7 or more. Compared to sound absorbing device 50 according to the related art, it can be seen that the valley characteristic is significantly suppressed due to the damping effect caused by the viscoelasticity of membrane 13.

[0073] Figure 40 shows the results of measuring the sound absorption characteristics of the sound absorbing device 10 according to Example 1 for each combination of thickness L1 and thickness L2. As shown in Figure 40, when L1 = 44 mm, the valleys are slightly deeper than when L1 = 49 mm, but the sound absorption performance in the high range is improved. The final combination is determined according to the purpose.

[0074] Next, it will be shown that increasing the thickness of the film 13 increases the damping effect.

[0075] FIG. 41 shows the results of measuring the sound absorption characteristics of a combination of membrane 13 and support member 14 when three layers of 0.2 mm-thick rigid vinyl chloride film are used as membrane 13. FIG. 42 shows a plot of the natural frequency of the first sound absorption characteristic versus the thickness L2 of frame 15. FIG. 42 also shows the plot shown in FIG. 37. FIG. 42 confirms that the natural frequency of the first sound absorption characteristic does not change significantly even when the thickness of membrane 13 is increased (when the film is changed from two layers to three layers). This is because the natural frequency of the first sound absorption characteristic is primarily determined by the shapes of central member 142 and connecting member 143 of support member 14. Therefore, by changing the thickness of membrane 13, it is possible to suppress changes in the natural frequency and adjust the damping effect.

[0076] Figure 43 shows the graph shown in Figure 34 together with the graph shown in Figure 42. As shown in Figure 43, when L1 = 54 mm and L2 = 20 mm, the natural frequency of the first sound absorption characteristic roughly matches the Helmholtz resonance frequency.

[0077] Figure 44 shows the measurement results of the sound absorption characteristics of sound absorber 10 for the combination of L1 = 54 mm and L2 = 20 mm, and Figure 45 shows the measurement results of the sound absorption characteristics of sound absorber 10 for the combination of L1 = 49 mm and L2 = 20 mm. In Figures 44 and 45, the solid lines indicate the sound absorption characteristics of sound absorber 10. The sound absorption coefficient peak is separated into two due to the coupling between Helmholtz resonance and the vibration of the combination of membrane 13 and support member 14, and the valley characteristic between the sound absorption coefficient peaks shows a sound absorption coefficient of 0.8 or more. It can be confirmed that the valley characteristic is significantly suppressed due to the damping effect caused by the viscoelasticity of membrane 13, compared to sound absorber 50 of the related art. It was also shown that increasing the thickness of membrane 13 increases the damping effect, thereby increasing the sound absorption coefficient in the valley.

[0078] Fig. 46 shows the specific acoustic impedance of the sound absorbing device 10 according to Example 1. The fact that the value of the real part of the specific acoustic impedance is small in the sound absorption frequency band indicates that a damping effect is being exerted. Fig. 46 confirms that the value of the real part of the specific acoustic impedance is small when the film is triple-layered compared to when the film is double-layered, and that a stronger damping effect is being exerted.

[0079] From the above, it has been shown that by changing the thickness of the film 13, it is possible to adjust the damping effect while suppressing changes in the natural frequency of the first sound absorption characteristic.

[0080] Furthermore, one or more weights 370 were attached to the central member 142 as shown in Figure 47, and the sound absorption characteristics of the combination of the membrane 13 and the support member 14 were measured. The support member 14 had the same structure as that described above with reference to Figure 35. The membrane 13 was made of three layers of 0.2 mm thick hard vinyl chloride film, and was attached to the support member 14.

[0081] Figure 48 shows the results of measuring the sound absorption characteristics of a combination of membrane 13 and support member 14. Figure 48 confirms that the natural frequency of the first sound absorption characteristic decreases as the mass added to central member 142 increases. Therefore, adding mass to central member 142 can be used as a factor for adjusting the natural frequency.

[0082] Furthermore, we verified the change in the natural frequency of the combination of membrane 13 and support member 14 due to changes in the shape of connecting member 143. In this verification, a single sheet of 0.2 mm thick hard vinyl chloride film was used as membrane 13. Four types of support members 14 shown in Figure 49 were used for the verification. The support member 14 shown in the upper left of Figure 49 has four straight connecting members 143 and its cross section is a rectangle with a width of 3.0 mm and a height of 1.5 mm. The support member 14 shown in the upper right of Figure 49 has four straight connecting members 143 and its cross section is a rectangle with a width of 3 mm and a height of 2 mm. The support member 14 shown in the lower left of Figure 49 has two straight connecting members 143 and its cross section is a rectangle with a width of 3 mm and a height of 2 mm. The support member 14 shown in the lower right of Fig. 49 has four connecting members 143, each including straight beam members 1431 and 1432 and a circumferentially extending beam member 1433. The cross sections of beam members 1431 and 1432 are rectangular, measuring 2 mm in width and 2 mm in height, and the cross section of beam member 1433 is rectangular, measuring 12 mm in width and 1 mm in height. When viewed from the Y-axis direction, beam member 1433 has a fan-like shape with an angle θ of 60°.

[0083] Figure 50 shows the results of measuring the sound absorption characteristics of combinations of membranes 13 and support members 14 for the four types of support members 14 shown in Figure 49. Figure 50 confirms that the natural frequency can be lowered by reducing the number of connecting members 143 and by lowering the rigidity of the connecting members 143.

[0084] As described above, the sound absorbing device 10 according to Example 1 can generate sound absorption characteristics with two sound absorption coefficient peaks due to the coupling of Helmholtz resonance and the vibration of the combination of the membrane 13 and the support member 14, and the valley characteristics between the sound absorption coefficient peaks can be suppressed due to the damping effect caused by the viscoelasticity of the membrane 13. As a result, high sound absorption characteristics can be obtained over a wide frequency range. For example, two representative examples of the measurement results described above are as follows:

[0085] When two 0.2 mm thick hard vinyl chloride films are used as membrane 13, the thickness L1 of frame 12 is 49 mm, and the thickness L2 of frame 15 is 20 mm, the frequency band width in which the sound absorption coefficient is 0.7 or higher is 382 Hz (550 Hz to 932 Hz).

[0086] When three layers of 0.3 mm thick hard vinyl chloride film are used as membrane 13, and the thickness L1 of frame 12 is 54 mm and the thickness L2 of frame 15 is 20 mm, the frequency band width where the sound absorption coefficient is 0.7 or higher is 350 Hz (524 Hz to 874 Hz).The frequency band width where the sound absorption coefficient is 0.8 or higher is 292 Hz (551 Hz to 843 Hz), and the sound absorption coefficient of the valley is 0.83.

[0087] As described above, the sound absorbing device 10 according to Example 1 exhibited high sound absorbing performance, demonstrating the appropriateness and superiority of the sound absorbing device 10 according to Example 1.

[0088] It was also shown that the damping effect can be adjusted while suppressing changes in the natural frequency of the first sound absorption characteristic by changing the thickness of the membrane 13. Furthermore, it was shown that the natural frequency of the combination of the membrane 13 and the support member 14 (the natural frequency of the first sound absorption characteristic) can be changed by changing the shape of the connecting member 143 of the support member 14 and by adding mass to the central member 142 of the support member 14.

[0089] <Example 2> Example 2 relates to the second embodiment. In Example 2, the support member 14 has the structure shown in FIG. 51 . Specifically, the support member 14 includes a frame 141, a central member 142, and one connecting member 143. The connecting member 143 is a straight beam member, and its cross section is a rectangle with a width of 3 mm and a height of 2 mm. The central member 142 is a cylindrical member with a diameter of 20 mm and a height of 3 mm. The frame 141 is a circular member with an inner diameter of 54 mm, an outer diameter of 60 mm, and a height of 3 mm. The frame 141, the central member 142, and the connecting member 143 were integrally molded from ABS using a 3D printer. The membrane 13 was made of a hard vinyl chloride film with a thickness of 0.2 mm and attached to the support member 14. In Example 2, the membrane 13 was a single sheet of hard vinyl chloride film with a thickness of 0.2 mm.

[0090] FIG. 52 shows the results of measuring the sound absorption characteristics of the combination of the membrane 13 and support member 14 according to Example 2. The first and second sound absorption characteristics can be seen in FIG. 52. In the second embodiment, the second sound absorption characteristic is utilized. FIG. 53 shows a plot of the natural frequency of the second sound absorption characteristic versus the thickness L2 of the frame 15. It can be seen from FIG. 53 that the natural frequency can be adjusted by adjusting the thickness L2 of the frame 15.

[0091] In the second embodiment, the combination of the thickness L1 of the frame 12 and the thickness L2 of the frame 15 is determined according to the following guidelines.

[0092] Step 1: Compare the Helmholtz resonance frequency and the natural frequency of the second sound absorption characteristic side by side. The Helmholtz resonance frequency is measured using a structure 200 in which a rigid back panel 18 faces the front panel 11, as shown in FIG. 30A. In the sound absorbing device 10, the front panel 11 faces the membrane 13 and support member 14, not the back panel 18. Therefore, the Helmholtz resonance frequency is lower in the sound absorbing device 10 than when measured using the structure 200. When determining candidate combinations of thicknesses L1 and L2, the decrease in the Helmholtz resonance frequency is taken into consideration. For example, as shown in FIG. 54, the Helmholtz resonance frequency and the natural frequency of the second sound absorption characteristic are compared over a range of approximately 100 Hz to determine candidate combinations of thicknesses L1 and L2. In this example, the candidate combinations are determined to be L1 = 39 mm and L2 = 15 mm and L1 = 44 mm and L2 = 25 mm.

[0093] Step 2: Measure the sound absorption characteristics of the sound absorbing device 10 for the candidate combinations of the frame 12 and the frame 15 determined in Step 1. Furthermore, determine further candidates by varying the thickness L1 of the frame 12 while keeping the thickness L2 of the frame 15 fixed, and measure the sound absorption characteristics of the sound absorbing device 10 for each of the further candidates. For example, from the combination of L1 = 39 mm and L2 = 15 mm, the combinations of L1 = 29 mm and L2 = 15 mm and L1 = 34 mm and L2 = 15 mm are determined as further candidates, and from the combination of L1 = 44 mm and L2 = 25 mm, the combinations of L1 = 34 mm and L2 = 25 mm and L1 = 39 mm and L2 = 25 mm are determined as further candidates.

[0094] Step 3: Select the candidate that satisfies the desired conditions as the final combination. The desired conditions are, for example, that the two sound absorption coefficient peaks are approximately equal and that the valley between the sound absorption coefficient peaks is not deep.

[0095] FIG. 55 shows the results of measuring the sound absorption characteristics of sound absorbing device 10 when L2 = 15 mm, and FIG. 56 shows the results of measuring the sound absorption characteristics of sound absorbing device 10 when L2 = 25 mm. As shown in FIG. 55, when L2 = 15 mm, L1 = 29 mm meets the desired condition. With the combination of L1 = 29 mm and L2 = 15 mm, the frequency band where the sound absorption coefficient is 0.8 or higher is 675 Hz to 1297 Hz (width 622 Hz). Also, as shown in FIG. 56, when L = 25 mm, L1 = 39 mm meets the desired condition. With the combination of L1 = 39 mm and L2 = 25 mm, the frequency band where the sound absorption coefficient is 0.8 or higher is 552 Hz to 1125 Hz (width 573 Hz), and the sound absorption coefficient at the valleys is also very high at 0.865. Furthermore, when L1 = 34 mm and L2 = 25 mm are combined, the frequency band where the sound absorption coefficient is 0.8 or higher is 564 Hz to 1179 Hz (width 615 Hz). The sound absorption coefficient in the valleys is lower than when L1 = 39 mm, but the frequency band where the sound absorption coefficient is 0.8 or higher is wider.

[0096] As a result of performing steps 2 and 3, the following combinations are selected as the final combinations: L1 = 29 mm and L2 = 15 mm, L1 = 39 mm and L2 = 25 mm, and L1 = 34 mm and L2 = 25 mm. Figure 57 shows the results of measuring the sound absorption characteristics of sound absorbing device 10 for the combinations of L1 = 29 mm and L2 = 15 mm, L1 = 39 mm and L2 = 25 mm, and L1 = 34 mm and L2 = 25 mm.

[0097] As described above, the sound absorbing device 10 according to Example 2 can generate sound absorption characteristics with two sound absorption coefficient peaks due to the coupling of Helmholtz resonance and the vibration of the combination of the membrane 13 and the support member 14, and the valley characteristics between the sound absorption coefficient peaks can be suppressed due to the damping effect caused by the viscoelasticity of the membrane 13. As a result, high sound absorption characteristics can be obtained over a wide frequency range. For example, two representative examples of the measurement results described above are as follows:

[0098] When the thickness L1 of the frame 12 is 29 mm and the thickness L2 of the frame 15 is 15 mm, the width of the frequency band in which the sound absorption coefficient is 0.8 or more is 622 Hz (675 Hz to 1297 Hz).

[0099] When the thickness L1 of the frame 12 is 39 mm and the thickness L2 of the frame 15 is 25 mm, the frequency band width where the sound absorption coefficient is 0.8 or more is 573 Hz (552 Hz to 1125 Hz). The sound absorption coefficient of the valley is 0.865.

[0100] As described above, the sound absorbing device 10 according to Example 2 exhibited high sound absorbing performance, demonstrating the appropriateness and superiority of the sound absorbing device 10 according to Example 2.

[0101] Furthermore, for the combination of L1 = 34 mm and L2 = 25 mm, there is a slight difference in the value between the two sound absorption coefficient peaks, but the frequency band width where the sound absorption coefficient is 0.8 or higher is 615 Hz, and high sound absorption characteristics are obtained over a wide frequency band.

[0102] Therefore, the final combination is determined according to the purpose.

[0103] Example 3 Example 3 relates to the second embodiment. In Example 3, as shown in FIG. 58, films 13 are provided on both sides of the support member 14. Example 3 is the same as Example 2 except that films 13 are provided on both sides of the support member 14. By providing films 13 on both sides of the support member 14, it is possible to further enhance the damping effect of the films 13 and further suppress the valley characteristics between two sound absorption coefficient peaks. This is demonstrated below through measurement results.

[0104] FIG. 59 shows the results of measuring the sound absorption characteristics of a combination of membrane 13 and support member 14. The first sound absorption characteristic and the second sound absorption characteristic can be confirmed from FIG. 59. FIG. 60 shows a plot of the natural frequency of the second sound absorption characteristic versus the thickness L2 of frame 15. FIG. 60 also shows the natural frequency of the second sound absorption characteristic of Example 2. From FIG. 60, it can be confirmed that the natural frequency of Example 3 is approximately 100 Hz lower than the natural frequency of Example 2. This is because the air between membranes 13 functions as air mass, increasing the overall mass.

[0105] Candidate combinations of the thickness L1 of the frame 12 and the thickness L2 of the frame 15 can be determined according to the same guidelines as those described in relation to Example 2. When the above-described steps 1 and 2 are performed in Example 3, the following combinations are determined as candidates, as shown in Fig. 61 : combinations of L1 = 29 mm and L2 = 10 mm, combinations of L1 = 34 mm and L2 = 10 mm, combinations of L1 = 39 mm and L2 = 10 mm, combinations of L1 = 34 mm and L2 = 15 mm, combinations of L1 = 39 mm and L2 = 15 mm, combinations of L1 = 44 mm and L2 = 15 mm, and combinations of L1 = 49 mm and L2 = 15 mm.

[0106] Figure 62 shows the results of measuring the sound absorption characteristics of sound absorbing device 10 for the combinations of L1 = 29 mm and L2 = 10 mm, L1 = 34 mm and L2 = 10 mm, and L1 = 39 mm and L2 = 10 mm. Figure 63 shows the results of measuring the sound absorption characteristics of sound absorbing device 10 for the combinations of L1 = 34 mm and L2 = 15 mm, L1 = 39 mm and L2 = 15 mm, L1 = 44 mm and L2 = 15 mm, and L1 = 49 mm and L2 = 15 mm.

[0107] As shown in Figure 62, when L2 = 10 mm, L1 = 34 mm satisfies the desired condition that the sound absorption coefficients at the two peaks are roughly equal and the valley does not become deep. When L1 = 34 mm and L2 = 10 mm, the frequency band where the sound absorption coefficient is 0.8 or higher is 680 Hz to 1125 Hz (width 445 Hz). The valley characteristics between the two sound absorption coefficient peaks are significantly suppressed compared to Example 2. Specifically, sound absorption characteristics that can be considered to be substantially unimodal, with a high sound absorption coefficient maintained over a wide frequency band, are obtained.

[0108] As shown in Figure 63, when L2 = 15 mm, L1 = 39 mm or 44 mm meets the desired conditions. When L1 = 15 mm and L2 = 39 mm, the frequency band where the sound absorption coefficient is 0.8 or higher is 646 Hz to 1027 Hz (width 381 Hz). When L1 = 15 mm and L2 = 44 mm, the frequency band where the sound absorption coefficient is 0.8 or higher is 594 Hz to 958 Hz (width 364 Hz).

[0109] Figure 64 shows the results of measuring the sound absorption characteristics of sound absorbing device 10 for the combinations L1 = 34 mm and L2 = 10 mm, L1 = 39 mm and L2 = 15 mm, and L1 = 44 mm and L2 = 15 mm, which satisfy the desired conditions. As shown in Figure 64, in all cases, the valley characteristics between the two sound absorption coefficient peaks are significantly suppressed compared to Example 2, and no valleys are formed. This shows that the damping effect is strengthened by attaching membrane 13 to both sides of support member 14.

[0110] Fig. 65 shows the specific acoustic impedance of the sound absorbing device 10 according to Examples 2 and 3. It can be seen from Fig. 65 that, compared to Example 2, Example 3 has a smaller real part of the specific acoustic impedance, and a stronger damping effect is generated.

[0111] Three representative measurement results according to Example 3 are as follows.

[0112] When L1 = 34 mm and L2 = 10 mm, the width of the frequency band where the sound absorption coefficient is 0.8 or more is 445 Hz (680 Hz to 1125 Hz).

[0113] When L1 = 39 mm and L2 = 15 mm, the width of the frequency band where the sound absorption coefficient is 0.8 or more is 381 Hz (646 Hz to 1027 Hz).

[0114] When L1 = 44 mm and L2 = 15 mm, the width of the frequency band where the sound absorption coefficient is 0.8 or more is 364 Hz (594 Hz to 958 Hz).

[0115] The sound absorbing device 10 of Example 3 has a narrower sound absorption band than the sound absorbing device 10 of Example 2, but no valley characteristics are generated, and high sound absorption characteristics are obtained. This shows that by providing the film 13 on both sides of the support member 14, the damping effect due to the viscoelasticity of the film 13 is further strengthened.

[0116] From the above, in terms of widening the frequency band where the sound absorption coefficient is 0.8 or more, Example 2 in which the membrane 13 is attached to one side of the support member 14 is preferable, and in terms of not generating valley characteristics, Example 3 in which the membrane 13 is attached to both sides of the support member 14 is preferable. Whether the membrane 13 is attached to one side or both sides of the support member 14 can be selected depending on the purpose.

[0117] Example 4 Example 4 relates to the second embodiment. In Example 4, the height of the connecting member 143 included in the support member 14 is made smaller than that of Example 2. The height of the connecting member 143 in Example 2 is 2 mm, whereas the height of the connecting member 143 in Example 4 is 1.5 mm as shown in FIG. 66 . The support member 14 in Example 4 has the same structure as the support member 14 in Example 2 except for the height of the connecting member 143.

[0118] The natural frequency of the second sound absorption characteristic changes only slightly when the height of the connecting member 143 is reduced. As the rigidity of the connecting member 143 decreases, the boundary conditions for membrane support are relaxed, and the damping effect increases. This will be demonstrated below through measurement results.

[0119] FIG. 67 shows the results of measuring the sound absorption characteristics of a combination of membrane 13 and support member 14. The first sound absorption characteristic and the second sound absorption characteristic can be confirmed from FIG. 67. From FIGS. 52 and 67, it can be confirmed that the natural frequency of the second sound absorption characteristic has hardly changed compared to Example 2. The natural frequency of the first sound absorption characteristic is lower compared to Example 2 when the thickness L2 of frame 15, at which the effect of the air spring is reduced, is 20 mm or more. This is because the connecting member 143 becomes softer (the rigidity of connecting member 143 decreases). This loosens the boundary conditions for membrane support, and it is expected that the damping effect will be stronger compared to Example 2.

[0120] Candidate combinations of the thickness L1 of the frame 12 and the thickness L2 of the frame 15 can be determined according to the same guidelines as those explained in relation to Example 2. When the above-described procedure 1 is performed in Example 4, the natural frequency of the combination of the membrane 13 and the support member 14 is almost the same as that in Example 2, and therefore the same combinations as those obtained in Example 2 are determined as candidates.

[0121] Figure 68 shows the results of measuring the sound absorption characteristics of a sound absorbing device when the thickness L2 of the frame 15 is 10 mm. As shown in Figure 68, when L2 = 10 mm, L1 = 24 mm, the desired condition is met where the sound absorption coefficients of the two peaks are roughly equal and the valleys are not deep. When L2 = 10 mm and L1 = 24 mm, the frequency band where the sound absorption coefficient is 0.8 or higher is 790 Hz to 1403 Hz (width 613 Hz).

[0122] Fig. 69 shows the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 4 when the thickness L2 of the frame 15 is 15 mm. As shown in Fig. 69, when L2 = 15 mm, L1 = 32 mm satisfies the desired condition. When L2 = 15 mm and L1 = 32 mm, the frequency band where the sound absorption coefficient is 0.8 or higher is 654 Hz to 1218 Hz (width 564 Hz).

[0123] Fig. 70 shows the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 4 when the thickness L2 of the frame 15 is 20 mm. As shown in Fig. 70, when L2 = 20 mm, L1 = 39 mm satisfies the desired condition. When L2 = 20 mm and L1 = 39 mm, the frequency band where the sound absorption coefficient is 0.8 or higher is 600 Hz to 1100 Hz (width 500 Hz). In this case, a strong damping effect occurs, and no valleys occur.

[0124] Fig. 71 shows the results of measuring the sound absorption characteristics of the sound absorbing device according to Example 4 when the thickness L2 of the frame 15 is 25 mm. As shown in Fig. 71, when L2 = 25 mm, L1 = 39 mm satisfies the desired condition. When L2 = 25 mm and L1 = 39 mm, the frequency band where the sound absorption coefficient is 0.8 or higher is 617 Hz to 1095 Hz (width 478 Hz). In this case, a strong damping effect occurs, and no valleys occur.

[0125] 72 shows the results of measuring the sound absorption characteristics of the sound absorbing device 10 for combinations of thicknesses L1 and L2 that satisfy the desired conditions. Combinations of thicknesses L1 and L2 that satisfy the desired conditions include the combination of L1 = 10 mm and L2 = 24 mm, the combination of L1 = 15 mm and L2 = 32 mm, the combination of L1 = 20 mm and L2 = 39 mm, and the combination of L1 = 25 mm and L2 = 39 mm.

[0126] Figure 73 shows the specific acoustic impedance of the sound absorbing device 10 for the combination of L1 = 15 mm and L2 = 32 mm and the combination of L1 = 20 mm and L2 = 39 mm. It can be seen from Figure 73 that the damping effect is stronger when the combination of L1 = 20 mm and L2 = 39 mm is used than when the combination of L1 = 15 mm and L2 = 32 mm is used.

[0127] As described above, the sound absorbing device 10 of Example 4 has a reduced rigidity of the connecting member 143 of the support member 14 compared to the sound absorbing device 10 of Example 2. The natural frequency of the first sound absorption characteristic of the combination of the membrane 13 and the support member 14 is reduced compared to Example 2 under the condition that L2, at which the effect of the air spring is reduced, is 20 mm or more. This is because the height of the connecting member 143 is reduced, making the connecting member 143 softer, thereby loosening some of the boundary conditions for membrane support. The second sound absorption characteristic of the combination of the membrane 13 and the support member 14 is brought about by membrane vibration, so the natural frequency is almost unchanged compared to Example 2.

[0128] Three representative measurement results according to Example 4 are as follows.

[0129] When L1 = 24 mm and L2 = 10 mm, the width of the frequency band where the sound absorption coefficient is 0.8 or more is 613 Hz (790 Hz to 1403 Hz).

[0130] When L1 = 32 mm and L2 = 15 mm, the width of the frequency band where the sound absorption coefficient is 0.8 or more is 564 Hz (654 Hz to 1218 Hz).

[0131] When L1=39 mm and L2=20 mm, the width of the frequency band where the sound absorption coefficient is 0.8 or more is 500 Hz (600 Hz to 1100 Hz), and no valley characteristics occur.

[0132] When L2 is 15 mm or less, the sound absorption performance is similar to that of Example 2. When L2 is 20 mm or more, no valley characteristics occur, and high sound absorption performance is obtained. In Example 3, the damping effect was strengthened by providing membranes 13 on both sides of the support member 14, but it was confirmed that the damping effect can also be strengthened by reducing the rigidity of the connecting member 143, as in Example 4.

[0133] As shown in the above examples, the sound absorbing device 10 according to the embodiment can absorb sounds in a wide frequency band.

[0134] The shape of the sound absorbing device 10 as viewed in the Y-axis direction is not limited to a circle, but may be a polygon such as a square or a hexagon.

[0135] The characteristic dimensions of the sound absorbing device 10 can be designed to be equal to or less than the wavelength λ of the applicable frequency condition. Preferably, the characteristic dimensions of the sound absorbing device 10 are designed to be equal to or less than λ / 4. Then, the sound absorbing device 10 is used as one unit, with multiple units arranged in a row. A honeycomb arrangement of hexagonal units or a grid arrangement of square units allows the units to be arranged more densely than when circular units are used. In this way, a device in which acoustic devices are arranged in a row at a period equal to or less than the wavelength λ of the upper limit of the applicable frequency is called an acoustic metamaterial. The sound absorbing device 10 is part of an acoustic metamaterial.

[0136] Figures 74 and 75 schematically show a sound absorbing device 100 as an acoustic metamaterial according to an embodiment. As shown in Figures 74 and 75, the sound absorbing device 100 comprises a plurality of sound absorbing units 101 and a plate member 102. The sound absorbing units 101 are arranged in a matrix and fixed to the plate member 102. The sound absorbing device 10 shown in Figure 1 is used as each sound absorbing unit 101. The diameter (maximum dimension in the XZ plane) of the sound absorbing unit 101 is designed to be equal to or less than λ, preferably λ / 4.

[0137] Figures 76 and 77 schematically show a sound absorbing device 40 according to an embodiment. Specifically, Figure 76 shows the external appearance of the sound absorbing device 40, and Figure 77 shows the sound absorbing device 40 in an exploded state. As shown in Figures 76 and 77, the sound absorbing device 40 includes a surface panel 41, a frame 42, a membrane 43, support members 44, a frame 45, and a back panel 46. The surface panel 41, the frame 42, the membrane 43, the support members 44, the frame 45, and the back panel 46 correspond to the surface panel 11, the frame 12, the membrane 13, the support members 14, the frame 15, and the back panel 16 of the sound absorbing device 10 described above, respectively. Here, differences between the sound absorbing device 40 and the sound absorbing device 10 will be described, and descriptions of the same points between the sound absorbing device 40 and the sound absorbing device 10 will be omitted.

[0138] The sound absorbing device 40 is configured to allow adjustment of the distance between the combination of the membrane 43 and the support member 44 and the surface panel 41, as well as the distance between the combination of the membrane 43 and the support member 44 and the back panel 46. An inner peripheral surface 451 of the frame 45 is internally threaded, and a side surface 461 of the back panel 46 is externally threaded, so that the back panel 46 screws into the frame 45. Turning the back panel 46 relative to the frame 45 changes the distance between the combination of the membrane 43 and the support member 44 and the back panel 46. Note that a protrusion may be provided on the back panel 46 to make it easier to turn the back panel 46. An outer peripheral surface 452 of the frame 45 is externally threaded, and an inner peripheral surface 421 of the frame 42 is internally threaded, so that the frame 45 screws into the frame 42. Turning the frame 45 relative to the frame 42 changes the distance between the combination of the membrane 43 and the support member 44 and the surface panel 41.

[0139] Adjusting the distance between the combination of the membrane 43 and the support member 44 and the back panel 46 corresponds to changing the thickness L2 of the frame 15, and adjusting the distance between the combination of the membrane 43 and the support member 44 and the front panel 41 corresponds to changing the thickness L1 of the frame 12. Thus, the sound absorbing characteristics of the sound absorbing device 40 are adjustable.

[0140] If the degree of sealing is reduced due to a gap between the male and female threads, the gap between the components may be protected with tape or a sealant after the distance adjustment.

[0141] 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]

[0142] 10,40...sound absorbing device, 11,41...surface panel, 111...sound hole, 12,42...frame, 13,43...membrane, 14,44...support member, 141...frame, 142...central member, 143...connecting member, 1431, 1432, 1433...beam member, 15,45...frame, 16,46...back panel, 18...back panel, 31,32...internal space, 100...sound absorbing device, 101...sound absorbing unit, 102...plate member.

Claims

1. a surface plate having sound holes; a back plate facing the front plate; a membrane provided between the front panel and the back panel; a support member for supporting the membrane, the support member including: a first frame attached to the membrane; a first member attached to the membrane and positioned inside the first frame; and a connecting member connecting the first frame and the first member; a second frame forming a first space between the surface plate and the membrane; a third frame that forms a second space between the back panel and the membrane; A sound absorbing device comprising:

2. the connecting member supports the first member so as to be vibrable relative to the first frame; a first sound absorption characteristic that is generated when the membrane vibrates in accordance with the vibration of the first member is utilized to reduce sound that enters the first space through the sound hole; 2. The sound absorbing device according to claim 1.

3. The sound absorbing device according to claim 2 , wherein the mass of the first member is adjustable to adjust the natural frequency of the first sound absorbing characteristic.

4. the first frame and the first member are attached to a first portion of the membrane; a second sound absorption characteristic generated by vibration of a second portion of the membrane different from the first portion is utilized to reduce sound entering the first space through the sound hole; 2. The sound absorbing device according to claim 1.

5. 2. The sound absorbing device of claim 1, wherein the connecting member comprises a linear beam member having a first end and a second end, the first end of the beam member being connected to the first frame and the second end of the beam member being connected to the first member.

6. 2. The sound absorbing device of claim 1, wherein the connecting member comprises a first beam member having a straight shape including a first end and a second end, a second beam member having an arc shape including a third end and a fourth end, and a third beam member having a straight shape including a fifth end and a sixth end, and wherein the first end of the first beam member is connected to the first frame, the second end of the first beam member is connected to the third end of the second beam member, the fifth end of the third beam member is connected to the fourth end of the second beam member, and the sixth end of the third beam member is connected to the first member.

7. 10. The sound absorbing device of claim 1, wherein the first member comprises three or more members spaced equidistantly apart from one another and equidistantly apart from a center of the support member.

8. 2. The sound absorbing device of claim 1, wherein the connecting member is attached to the membrane.

9. 2. The sound absorbing device according to claim 1, wherein the support member has a first surface and a second surface opposite to the first surface, and the membrane comprises 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.

10. The sound absorbing device according to claim 1 , wherein the first frame, the first member, and the connecting member are integrally molded.

11. The sound absorbing device according to claim 1 , wherein the second frame and the third frame are configured to adjust the distance between the combination of the membrane and the support member and the surface plate.

12. The sound absorbing device according to claim 1 , wherein the third frame and the back panel are configured to allow adjustment of the distance between the combination of the membrane and the support member and the back panel.

Images