Sound absorption device

Abstract

To provide a sound absorption device capable of absorbing sound at two frequencies in a low-frequency band.SOLUTION: A sound absorption device 10 comprises a membrane 12, a rear plate 15, a hollow member 14, and a support member 13. The rear plate 15 faces the membrane 12. The hollow member 14 is positioned between the membrane 12 and the rear plate 15. The support member 13 supports the membrane 12 and constitutes a vibrating body 11. The support member 13 includes: a ring-shaped frame member 131; an annular member 132 disposed inside the frame member 131; a central member 133 disposed inside the annular member 132; a first beam member 134 connecting the frame member 131 and the annular member 132; and a second beam member 135 connecting the annular member 132 and the central member 133. The frame member 131 is attached to the membrane 12 and the hollow member 14, and the central member 133 is attached to the membrane 12. Attachment of the central member 133 to the membrane 12 may be by adhesion using an adhesive or double-sided tape, or by fixation using magnets.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] There are known sound-absorbing devices that combine Helmholtz resonance with plate vibration. The combination of Helmholtz resonance and plate vibration enables a wide bandwidth of sound absorption characteristics. However, the fabrication of perforated plates, also known as Helmholtz perforated plates, is expensive.

[0003] There is a social need to reduce noise at two frequencies in the frequency band below 200 Hz. The two frequencies include, for example, the fundamental frequency and the noise at twice the fundamental frequency. For example, if the noise is from a power source, the fundamental frequency may be 50 Hz or 60 Hz. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6610684 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a sound absorbing device that can absorb sounds of two frequencies in the low frequency band. [Means for solving the problem]

[0006] A sound absorbing device according to one embodiment comprises a membrane, a back panel, a hollow member, and a support member. The back panel faces the membrane. The hollow member is provided between the membrane and the back panel. The support member supports the membrane. The support member includes an annular frame member, a ring member provided inside the frame member, a central member provided inside the ring member, a first beam member connecting the frame member and the ring member, and a second beam member connecting the ring member and the central member, and the frame member is attached to the membrane and the first hollow member, and the central member is attached to the membrane. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view showing a sound absorbing device according to an embodiment. [Figure 2] 1 is a cross-sectional view showing a sound absorbing device according to an embodiment. [Figure 3] FIG. 2 is a perspective view showing an example of the vibrating body shown in FIG. [Figure 4] FIG. 4 is a perspective view showing the support member shown in FIG. 3. [Figure 5] FIG. 2 is a plan view showing another example of the vibrating body shown in FIG. [Figure 6] FIG. 2 is a diagram showing a vibration model corresponding to the sound absorbing device of FIG. 1. [Figure 7] 1 is a cross-sectional view showing a sound absorbing device according to an embodiment. [Figure 8] FIG. 10 is a perspective view showing a support member (B2) according to the first embodiment. [Figure 9] FIG. 3 is a diagram showing the results of measuring the sound absorption characteristics of the sound absorbing device according to the first example. [Figure 10] FIG. 10 is an enlarged view of a part of FIG. 9. [Figure 11] FIG. 10 is a diagram showing the results of measuring the sound absorption characteristics of the sound absorbing device according to the second embodiment. [Figure 12] FIG. 12 is an enlarged view of a part of FIG. 11. [Figure 13] FIG. 10 is a perspective view showing a support member (B1) according to a third embodiment. [Figure 14] FIG. 10 is a perspective view showing a support member (B3) according to a third embodiment. [Figure 15]FIG. 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to the third embodiment. [Figure 16] FIG. 17 is an enlarged view of a part of FIG. 16. [Figure 17] FIG. 10 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing device according to the fourth embodiment. [Figure 18] FIG. 18 is an enlarged view of a part of FIG. 17. [Figure 19] 1 is a perspective view showing a sound absorbing device according to an embodiment. [Figure 20] FIG. 20 is a perspective view showing a part of the sound absorbing device of FIG. 19. [Figure 21] FIG. 20 is a perspective view showing a part of the sound absorbing device of FIG. 19. [Figure 22] FIG. 20 is a perspective view showing a part of the sound absorbing device of FIG. 19. [Figure 23] FIG. 20 is a graph showing the results of measuring the sound absorption characteristics of the sound absorbing part using the film shown in FIG. 19. [Figure 24] FIG. 7 is a diagram showing vibration velocity transmission characteristics in the two-degree-of-freedom system model shown in FIG. 6. [Figure 25] FIG. 7 is a diagram showing vibration velocity transmission characteristics in the two-degree-of-freedom system model shown in FIG. 6. [Figure 26] FIG. 7 is a diagram showing vibration velocity transmission characteristics in the two-degree-of-freedom system model shown in FIG. 6. [Figure 27] FIG. 7 is a diagram showing vibration velocity transmission characteristics in the two-degree-of-freedom system model shown in FIG. 6. [Figure 28] FIG. 10 is a diagram showing a configuration in which a piezoelectric element is provided on a film according to an embodiment. [Figure 29] FIG. 1 is a perspective view showing an acoustic metamaterial according to an embodiment. [Figure 30] 5A and 5B are diagrams for explaining a fixing means according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment will be described with reference to the drawings.

[0009] Fig. 1 shows a schematic external view of a sound absorbing device 10 according to one embodiment, and Fig. 2 shows a schematic cross section of the sound absorbing device 10. The sound absorbing device 10 is configured to absorb sound generated in an external space. The sound absorbing device 10 is used, for example, to reduce noise.

[0010] As shown in Figures 1 and 2, sound absorbing device 10 includes a vibrating body 11, a hollow member 14, and a back panel 15. In sound absorbing device 10, vibrating body 11 vibrates when subjected to sound pressure. The vibration of vibrating body 11 produces a sound absorption effect at a frequency that corresponds to the structure of vibrating body 11. As will be described later, sound absorbing device 10 is configured so that there are two frequencies at which the sound absorption coefficient reaches a peak value. Below, an example is shown in which each component of sound absorbing device 10 is circular. Instead of a circle, the shape of each component may be a polygon or a figure surrounded by an arbitrary closed curve. The terms cylinder, ring, ring member, and column can be simply read as tube, ring, ring member, and pillar.

[0011] The vibrating body 11 is, for example, disk-shaped overall, and is configured to vibrate in a direction along the central axis of the sound absorbing device 10 (indicated by the dashed line in FIG. 2). The hollow member 14 is a tubular member, for example, a cylindrical member. The cross-sectional shape and cross-sectional area of ​​the hollow member 14 do not necessarily have to be constant. The back plate 15 is, for example, a circular plate. The back plate 15 faces the vibrating body 11, separated by a distance L of the hollow member 14. The length L of the hollow member 14 is the dimension along the central axis of the sound absorbing device 10. The dimension along the central axis of the sound absorbing device 10 is sometimes called the thickness.

[0012] The vibrating body 11, the hollow member 14, and the back plate 15 form an internal space 19. The internal space 19 is a closed space surrounded by the vibrating body 11, the hollow member 14, and the back plate 15. The vibrating body 11 is connected to the hollow member 14 so as to close a first open end of the hollow member 14. The back plate 15 is connected to the hollow member 14 so as to close a second open end of the hollow member 14. Note that the hollow member 14 and the back plate 15 may be molded integrally.

[0013] The vibrating body 11 includes a membrane 12 and a support member 13. The membrane 12 is, for example, a circular thin film. The membrane 12 can be made of, for example, a polymer material such as polyvinyl chloride (PVC) or silicone, or a metal material such as aluminum or copper. The membrane 12 is attached to a portion of the support member 13 and is supported by the support member 13. The support member 13 includes a frame member 131, an annular member 132, a central member 133, beam members 134, and beam members 135. The frame member 131 is, for example, an annular member. The circular member 132 is provided inside the frame member 131, and the beam member 134 connects the frame member 131 and the circular member 132. The beam member 134 supports the circular member 132 so that the circular member 132 can vibrate in a direction along the central axis of the sound absorbing device 10. The central member 133 is provided inside the circular member 132, and the beam member 135 connects the circular member 132 and the central member 133. Beam member 135 supports central member 133 so as to be vibrable in a direction along the central axis of sound absorbing device 10. Central member 133 is, for example, cylindrical. In a planar direction intersecting the central axis of sound absorbing device 10, circular ring member 132 is located between frame member 131 and central member 133, beam member 134 is located between frame member 131 and circular ring member 132, and beam member 135 is located between circular ring member 132 and central member 133.

[0014] The central member 133 is attached to the membrane 12. The central member 133 may be attached to the membrane 12 by adhesive or double-sided tape, or may be fixed using a magnet. The frame member 131 is attached to the membrane 12 and the hollow member 14. Specifically, the frame member 131 includes a first surface and a second surface opposite the first surface, with the first surface of the frame member 131 attached to the membrane 12 and the second surface of the frame member 131 attached to the hollow member 14. The frame member 131 may be attached to the membrane 12 and the hollow member 14 by adhesive or double-sided tape, or may be fixed using a fixing means such as that shown in FIG. 30. In the example shown in FIG. 30, the fixing means includes a frame member 171, a bolt 172, and a nut 173. The frame member 171 includes a first portion having the same diameter as the hollow member 14 and a second portion protruding outward from the first portion. A hole for inserting a bolt 172 is provided in the second portion of the frame member 171. In this example, the back plate 15 has a larger diameter than the hollow member 14, and is provided with holes for inserting bolts 172. By fastening the bolts 172 and nuts 173, the peripheral edge of the membrane 12, the frame member 131, and the hollow member 14 are sandwiched between the frame member 171 and the back plate 15. The annular member 132, the beam members 134, and the beam members 135 may be formed thinner than the frame member 131 and the central member 134 so as not to come into contact with the membrane 12.

[0015] FIG. 3 schematically illustrates an example of a vibrating body 11 including a membrane 12 and a support member 13, and FIG. 4 schematically illustrates the support member 13 viewed from the side where the membrane 12 is provided. In the example illustrated in FIGS. 3 and 4, two beam members 134 and two beam members 135 are provided. There is one or more beam members 134 and 135. Each beam member 134 includes linear beam members 1341 and 1342 and an arc-shaped beam member 1343. A first end of beam member 1341 is connected to frame member 131, a second end of beam member 1341 is connected to a first end of beam member 1343, a first end of beam member 1342 is connected to a second end of beam member 1343, and a second end of beam member 1342 is connected to ring member 132. Each beam member 135 includes linear beam members 1351 and 1352 and an arc-shaped beam member 1353. A first end of beam member 1351 is connected to ring member 132, a second end of beam member 1351 is connected to a first end of beam member 1353, a first end of beam member 1352 is connected to a second end of beam member 1343, and a second end of beam member 1342 is connected to central member 133.

[0016] The sound absorbing device 10 may further include a damping material provided on the beam member to enhance the sound absorbing effect. In the example shown in Fig. 4, the damping material 16 is provided on both the beam member 134 and the beam member 135. The damping material 16 may be provided only on the beam member 134 or only on the beam member 135.

[0017] 3 and 4, the support member 13 has a structure that is symmetrical with respect to the central axis of the sound absorbing device 10. For example, the center of gravity of the frame member 131, the center of gravity of the ring member 132, the center of gravity of the central member 133, the center of gravity of the pair of beam members 134, and the center of gravity of the pair of beam members 135 are all located on the central axis of the sound absorbing device 10. In other examples, the support member 13 may have a structure that is not symmetrical with respect to the central axis of the sound absorbing device 10.

[0018] Fig. 5 shows a schematic diagram of another example of the vibrating body 11 including the membrane 12 and the support member 13. In the example shown in Fig. 5, the beam members 134 and 135 are linear members.

[0019] The beam members 134, 135 may have any shape as long as they can support the ring member 132 and the central member 133 so that they can vibrate. The number of beam members 134 may be one, or three or more. The number of beam members 135 may be one, or three or more. The number of beam members 134 may be different from the number of beam members 135.

[0020] The sound absorbing device 10 having the above-described configuration can absorb or reduce noise at two frequencies in the low-frequency band below 200 Hz. In one example, the sound absorbing device 10 is designed to absorb or reduce fundamental-frequency noise and its harmonics (specifically, noise with a frequency twice the fundamental frequency) generated by a noise source such as an electronic device. If the noise originates from a power source, the fundamental frequency can be 50 Hz or 60 Hz. If the noise originates from a device with a fan, the fundamental frequency is the fan's rotational frequency multiplied by the number of fan blades. For example, if the rotational speed is 600 rpm and the fan has five blades, the fundamental frequency is 50 Hz. Furthermore, since a Helmholtz sound hole plate is not required and the number of components is small, manufacturing costs are low and assembly is easy.

[0021] The vibrating body 11 shown in FIG. 2 can be represented by a simplified two-degree-of-freedom model shown in FIG. 6. The two-degree-of-freedom model shown in FIG. 6 is known as a skyhook two-degree-of-freedom model. In FIG. 6, m1 represents the mass of the annular member 132, k1 is a spring constant representing the rigidity of the beam member 134, m2 represents the mass of the central member 133, k2 is a spring constant representing the rigidity of the beam member 135, k3 is a spring constant representing the combination of the rigidity of the membrane 12 and the air spring in the internal space 19, and c3 is a damping coefficient representing the viscosity of the membrane 12. The mass of the membrane 12 is assumed to be so small that its contribution to vibration is negligible. One or more weights may be attached to the central member 133 to adjust the mass m2. One or more weights may be attached to the annular member 132 to adjust the mass m1.

[0022] Because the structural characteristics of the support member 13 form a two-degree-of-freedom system, the vibration velocity of the central member 133, which has a mass m2 and is correlated with the sound absorption effect, has two resonant frequencies. As a result, the sound absorption effect occurs at two frequencies. Specifically, in the sound absorbing device 10, when sound waves are applied to the membrane 12, the membrane 12 and the central member 133 attached to the membrane 12 vibrate, and the vibration of the central member 133 causes the circular member 132 to vibrate in conjunction with the vibration of the central member 133. The vibration modes are an in-phase drive mode, in which the circular member 132 and the central member 133 vibrate in the same direction, and an out-of-phase drive mode, in which the circular member 132 and the central member 133 vibrate in opposite directions. This results in two frequencies at which the vibration velocity peaks. Because the sound absorption effect is correlated with kinetic energy, two frequencies occur at which the sound absorption coefficient peaks. Hereinafter, the frequencies at which the sound absorption coefficient peaks in the in-phase drive mode and out-of-phase drive mode may also be referred to as sound absorption frequencies.

[0023] Furthermore, a sound absorbing effect is also produced in a membrane vibration mode caused by membrane vibration of the membrane 12. The sound absorbing effect obtained by the membrane vibration mode occurs in a frequency band higher than the two sound absorption frequencies described above.

[0024] The sound absorption frequency of the sound absorbing device 10 can be adjusted, for example, by the following six parameters. (1) Typical dimensions The characteristic dimension is, for example, the diameter of the support member 13. The larger the characteristic dimension, the easier it is to design a lower frequency. (2) Length of the rear air layer The length of the rear air space is the dimension of the internal space 19 in the direction along the central axis of the sound absorbing device 10, and corresponds to the length L of the hollow member 14. Since the air spring (part of the spring constant k3) depends on the length of the rear air space, it is possible to adjust the spring constant k3 by changing the length L of the hollow member 14. (3) Weight attached to central member 133 By changing the number of weights attached to the central member 133, the mass m2 can be adjusted. (4) Weight attached to the ring member 132 By changing the number of weights attached to the circular member 132, the mass m1 can be adjusted. (5) Shape and number of beam members 135 By changing the shape and / or number of the beam members 135, the spring constant k2 can be adjusted. (6) Shape and number of beam members 134 By changing the shape and / or number of the beam members 134, the spring constant k1 can be adjusted.

[0025] By changing these parameters, it is possible to adjust the two sound absorption frequencies at which the sound absorption effect occurs. For example, the parameters are changed to obtain sound absorption effects at 60 Hz and 120 Hz.

[0026] The material of the membrane 12 can also be used as a parameter. The material of the membrane 12 affects the damping coefficient C1 and membrane stiffness (part of the spring constant k3). However, the membrane stiffness is sufficiently small compared to the spring constants k1 and k2, and its contribution to the natural frequency is low compared to the spring constants k1 and k2.

[0027] To demonstrate that a sound absorption effect can be obtained at two frequencies and that the frequencies at which the sound absorption effect is obtained can be adjusted by changing the parameters, the sound absorption performance of the sound absorbing device 10 according to several examples was evaluated. A φ70 acoustic tube capable of measuring the normal incidence sound absorption coefficient in the frequency band of 200 Hz or higher was used to evaluate the sound absorption performance. For this reason, in each example, the sound absorbing device 10 was designed so that the two sound absorption frequencies exceeded 200 Hz. However, as described above, by adjusting the parameters, it is possible to make the two sound absorption frequencies, for example, 60 Hz and 120 Hz.

[0028] Figure 7 shows a schematic diagram of the structure of the sound absorbing device 10 according to each example. As shown in Figure 7, to facilitate parameter adjustments, such as replacement of the support member 13, the central member 133 of the support member 13 is attached to the film 12 using magnets 71 and 72. The magnet 72 is adhered to the central member 133, and the magnet 71 is positioned so that the film 12 is sandwiched between the magnets 71 and 72. An aluminum film (with release paper) with a thickness of 0.08 mm is used as the film 12.

[0029] In the first example, it is shown that a sound absorbing effect can be obtained at two frequencies. In the first example, the length of the back air space is set to 40 mm. That is, a hollow member 14 with L=40 mm is used.

[0030] FIG. 8 schematically shows the structure of the support member 13 according to the first example. The support member 13 shown in FIG. 8 has the same structure as that shown in FIGS. 3 and 4, and therefore its description will be omitted. The frame member 131 has an outer diameter of 60 mm, an inner diameter of 54 mm, and a thickness of 3 mm. The ring member 132 has an outer diameter of 34 mm, an inner diameter of 28 mm, and a thickness of 2 mm. The central member 133 has a diameter of 15 mm and a thickness of 3 mm. The beam member 1343 has an outer diameter of 49 mm, an inner diameter of 39 mm, a central angle of 45 degrees, and a thickness of 1 mm. The beam member 1353 has an outer diameter of 25 mm, an inner diameter of 18 mm, a central angle of 120 degrees, and a thickness of 1 mm. The structure shown in FIG. 8 is referred to as structure B2.

[0031] Fig. 9 shows the results of measuring the sound absorption characteristics of the sound absorbing device 10 according to the first embodiment, and Fig. 10 is an enlarged view of a portion of Fig. 9. Figs. 9 and 10 confirm that the sound absorption coefficient peaks at two frequencies (specifically, near 270 Hz and near 380 Hz). The sound absorption effect near 270 Hz is obtained by the in-phase drive mode, and the sound absorption effect near 380 Hz is obtained by the out-of-phase drive mode. Furthermore, at a frequency near 1400 Hz, a sound absorption effect due to the membrane vibration mode is also observed.

[0032] The second example shows the effect of the back air space on the sound absorption frequency. In the second example, the same membrane 12 and support member 13 as in the first example are used. Measurements were taken while changing the length of the back air space to 20 mm, 30 mm, 40 mm, and 50 mm.

[0033] Fig. 11 shows the results of measuring the sound absorption characteristics of the sound absorbing device 10 according to the second embodiment, and Fig. 12 is an enlarged view of a portion of Fig. 11. From Fig. 11 and Fig. 12, it can be seen that the frequency at which the peak occurs decreases as the rear air space increases. Furthermore, as the rear air space increases, the frequency at which the sound absorption effect due to the membrane vibration mode is obtained also decreases.

[0034] The third example demonstrates the effect of the stiffness of the beam member 134 on the sound absorption frequency. In the third example, the same membrane 12 and hollow member 14 as in the first example were used. Measurements were then performed while varying the stiffness of the beam member 134. The stiffness of the beam member 134 was varied by changing the shape of the arc-shaped beam member 1343 included in the beam member 134. Specifically, a beam member 134 including a beam member 1343 with a central angle of 60 degrees as shown in FIG. 13, a beam member 134 including a beam member 1343 with a central angle of 45 degrees as shown in FIG. 8, and a beam member 134 including a beam member 1343 with a central angle of 30 degrees as shown in FIG. 14 were used. The structure of the beam member 134 shown in FIG. 13 is referred to as Structure B1, and the structure of the beam member 134 shown in FIG. 14 is referred to as Structure B3. Structures B1, B2, and B3 are common to all but the beam member 134. The larger the central angle, the lower the stiffness of the beam member 134.

[0035] Fig. 15 shows the results of measuring the sound absorption characteristics of the sound absorbing device 10 according to the third example, and Fig. 16 is an enlarged view of a portion of Fig. 15. From Figs. 14 and 15, it can be seen that the frequency at which the peak occurs decreases as the rigidity of the beam member 134 decreases. On the other hand, even if the rigidity of the beam member 134 changes, the frequency at which the sound absorption effect due to the membrane vibration mode is obtained remains almost unchanged.

[0036] The fourth example shows the effect of film material on the sound absorption frequency. In the fourth example, an aluminum film with a thickness of 0.08 mm and a copper film with a thickness of 0.07 mm are used as the film 12. The support member 13 and hollow member 14 are the same as those in the first example.

[0037] Fig. 17 shows the results of measuring the sound absorption characteristics of the sound absorbing device 10 according to the fourth embodiment, and Fig. 18 is an enlarged view of a portion of Fig. 17. Figs. 17 and 18 confirm that even if the membrane material is changed, the peak frequency remains almost unchanged between the in-phase drive mode and the out-of-phase drive mode. On the other hand, the frequency at which the sound absorption effect is obtained by the membrane vibration mode changes. In other words, the contribution of the stiffness of the membrane 12 is lower than that of the beam members 134 and 135.

[0038] From the above examples, it can be confirmed that the sound absorbing device 10 according to the embodiment is appropriate and that the two sound absorption frequencies can be changed by adjusting the parameters.

[0039] The sound absorbing device 10 described above can be combined with other sound absorbing devices that use sound absorbing materials, such as fabrics made of aramid fibers.

[0040] 19 is a schematic view showing the appearance of a sound absorbing device 20 according to an embodiment. As shown in FIG. 19, the sound absorbing device 20 includes a sound absorbing portion 21 and a sound absorbing portion 22.

[0041] The sound absorbing section 21 corresponds to the sound absorbing device 10 shown in Figures 1 and 2. That is, the sound absorbing section 21 includes the same components as those shown in Figures 1 and 2, specifically, the vibrating body 11 (membrane 12 and support member 13), the hollow member 14, and the back panel 15.

[0042] The sound absorbing section 22 is provided to surround the sound absorbing section 21. The sound absorbing section 22 includes a membrane 221 and a hollow member 222. The hollow member 222 has a shape in which a cylinder with a smaller diameter is positioned inside a cylinder. The membrane 221 is, for example, a cloth. The cloth used for the membrane 221 can be a cloth containing aramid fiber, for example, polyparaphenylene terephthalamide fiber. It may be a single-material fiber cloth, or a blended fabric containing such fiber. The membrane 221 is connected to the hollow member 222 so as to close the open end of the hollow member 222. The end of the hollow member 222 to which the membrane 221 is not connected is closed. The end of the hollow member 222 to which the membrane 221 is not connected may be closed by the back panel 15. An internal space is formed between the two cylinders by the membrane 221 and the hollow member 222. The internal space is a closed space surrounded by the membrane 221 and the hollow member 222. In order to maintain the shape of the film 221, the film 221 may be sandwiched between punching metal.

[0043] Fig. 20 schematically shows the sound absorbing device 20 with the membrane 221 removed, Fig. 21 schematically shows the sound absorbing device 20 with the membrane 221 and membrane 12 removed, and Fig. 22 schematically shows the sound absorbing device 20 with the membrane 221, membrane 12, and support member 13 removed. As shown in Figs. 20 to 22, the hollow member 222 is located outside the hollow member 14. The hollow member 14 and the hollow member 222 may be integrally molded. The hollow member 222 is provided with partition walls 223 that divide the internal space. If the wavelength of the maximum frequency in the frequency band that is desired to be absorbed by the membrane 221 is λ, the partition walls 223 are arranged so that their representative length is λ / 4.

[0044] Fig. 23 shows the results of measuring the sound absorption characteristics of sound absorbing section 22. As shown in Fig. 23, sound absorbing section 22 using film 221 exhibits a high sound absorption effect at 1.2 KHz or higher. It can also be seen that the sound absorption effect increases as the air space behind sound absorbing section 22 becomes longer.

[0045] The sound absorbing device 20 can simultaneously obtain sound absorption effects for two frequencies in the low frequency band and sound absorption effects for frequencies above 1.2 KHz.

[0046] Next, we will explain a parameter estimation method for the sound absorbing device 10. The parameter estimation method explained below is for estimating parameter values ​​that can achieve desired sound absorption characteristics, and makes it easy to adjust the parameters.

[0047] The sound absorbing device 10 shown in FIGS. 1 and 2 can be expressed by a skyhook type two-degree-of-freedom system model shown in FIG. 6, and the equation of motion can be written as follows:

number

[0048] natural frequency ω n1 ω n1 2 =k1 / m1, and the natural frequency ω n2 ω n2 2 = k2 / m2, and the natural frequency ω n2b ω n2b 2 = k3 / m2 and the mass ratio is α = m2 / m1, the wavelength λ corresponding to the natural frequency ω can be calculated as follows:

number

[0049] The natural frequency ω can be calculated from the wavelength λ according to ω=(√λ / (2π)).

[0050] D=B 2 -4C. D contributes to the difference between the natural frequency of the in-phase drive and the natural frequency of the anti-phase drive.

number

[0051] The first and second terms on the right-hand side correspond to a general two-degree-of-freedom system without k3, and the third term on the right-hand side is the term caused by the skyhook associated with k3. k3< <k1,k2であるので、ω n2b2 The third term, including ω, can be ignored. n1 ω n2 Then, D can be approximated as follows:

number

[0052] The above formula (2) shows that the difference between the natural frequency of the in-phase drive and the natural frequency of the anti-phase drive is the mass ratio α and the natural frequency ω n1 This indicates that it can be adjusted by

[0053] natural frequency ω n1 , ω n2 , ω n2b can be estimated by computer simulation. Specifically, by analyzing the vibrations caused by the annular member 132 and the beam members 134 under the condition that the frame member 131, the central member 133, and the beam members 135 are fixed, ω n1 2 By analyzing the vibration caused by the central member 133 and the beam members 135 under the condition that the frame member 131, the ring member 132, and the beam members 134 are fixed, it is possible to determine ω n2 2 Furthermore, by analyzing the vibrations of the central member 133, the beam members 135, and the membrane 12 under the condition that the frame member 131, the ring member 132, and the beam members 134 are fixed, it is possible to determine ω n2 2 +ω n2b 2 =(k2+k3) / m2 can be determined.

[0054] When the structure of the sound absorbing device 10 according to the first embodiment described above is analyzed, the following analysis results are obtained. ω n1 2 =298Hz ω n2 2 =267Hz ω n2 2 +ω n2b 2=277Hz

[0055] In the above vibration analysis, the air spring was ignored and the mass of the magnet was set to zero.

[0056] Furthermore, the mass ratio α is equal to the ratio between the volume of the central member 133 and the volume of the annular member 132, and is determined as follows. α=m2 / m1 =(7.5 2 π×3) / ((17 2 -14 2 )π×2) =0.9073 In addition, in the vibration analysis, by analyzing the vibrations caused by the annular member 132, the beam member 134, the central member 133, the beam member 135, and the membrane 12 under the condition that the frame member 131 is fixed, the frequency corresponding to the in-phase drive mode is calculated to be 191 Hz, and the frequency corresponding to the out-of-phase drive mode is calculated to be 413 Hz.

[0057] FIG. 24 is a graph plotting the vibration velocity transmission characteristics of x2 in the simple model shown in FIG. 6. The plot also shows the ω n1 2 , ω n2 2 , ω n2 2 +ω n2b 2 We used k1, k2, and k3 calculated from the value of m1 normalized to 1. From Figure 24, we can see that the in-phase drive mode occurs at 192 Hz and the out-of-phase drive mode occurs at 439 Hz.

[0058] The frequencies at which the in-phase and out-of-phase drive modes occur, obtained from the vibration velocity transmission characteristics of x2 using the simplified model, roughly agree with the vibration analysis results above. Therefore, the validity of the simplified model is demonstrated.

[0059] Up to this point, the mass of the air spring and magnet have not been taken into account. However, the mass of the air spring and magnet may be taken into account. For example, assuming that the contribution of the air spring is large, k3 is multiplied by 40. Furthermore, assuming that the magnet mass is twice that of the central member 133, m2 is multiplied by three. After changing k3 and m2 in this way to take the mass of the air spring and magnet into account, and then multiplying k2 by 0.7, the vibration velocity transmission characteristic of x2 shown in Figure 25 is obtained. From Figure 25, it can be seen that the frequencies at which the in-phase drive mode and anti-phase drive mode occur, obtained from the vibration velocity transmission characteristic of x2 using the simplified model, roughly match the results of measuring the sound absorption characteristics of the sound absorbing device 10 according to the first embodiment shown in Figures 9 and 10.

[0060] Figure 26 shows the change in the vibration velocity transmission characteristics of x2 when the influence of the air spring is reduced. In Figure 26, the solid line corresponds to the vibration velocity transmission characteristics of x2 shown in Figure 25, and the dashed line shows the vibration velocity transmission characteristics of x2 obtained when k3 is multiplied by 0.9. Figure 26 confirms that reducing the influence of the air spring (reducing k3) lowers the frequency at which the peak occurs. In other words, it can be confirmed that the influence of the rear air layer can be appropriately evaluated using a simple model.

[0061] Figure 27 shows the change in the vibration velocity transmission characteristics of x2 when the rigidity of beam member 134 is reduced. In Figure 27, the dashed line corresponds to the vibration velocity transmission characteristics of x2 shown in Figure 25, and the solid line shows the vibration velocity transmission characteristics of x2 obtained when k1 is multiplied by 0.4. Figure 27 confirms that when the rigidity of beam member 134 is reduced (k1 is reduced), the frequency at which the peak occurs decreases. In other words, it can be confirmed that the simple model can appropriately evaluate the effect of the rigidity of beam member 134.

[0062] From the above, the validity of the simple model shown in Figure 6 was confirmed. Therefore, it is possible to estimate and evaluate frequency peaks in advance by performing a simulation using the simple model. As a result, parameter adjustment becomes easy. For example, by repeatedly performing a simulation to calculate vibration transmission characteristics using the simple model, parameters that will achieve desired sound absorption characteristics can be identified, and a sound absorbing device is created based on the identified parameters. The sound absorption characteristics of the sound absorbing device are then measured, and the parameters are repeatedly fine-tuned to achieve the desired sound absorption characteristics. In this way, a sound absorbing device with the desired sound absorption characteristics is obtained. Because the parameters that will achieve the desired sound absorption characteristics can be estimated by simulation, it becomes easy to create a sound absorbing device with the desired sound absorption characteristics.

[0063] As described above, the membrane 12 vibrates when it receives sound waves. It is possible to generate electricity by utilizing the vibration of the membrane 12. For example, as shown in FIG. 28, a piezoelectric film 81 serving as a piezoelectric element may be attached to the membrane 12. For example, the piezoelectric film 81 is connected via a conductor to an electric circuit including a full-wave rectifier, and the AC power generated by the piezoelectric film 81 is converted to DC power in the electric circuit and supplied to a load such as a sensor.

[0064] The sound absorbing device 10 and the sound absorbing device 20 can be used as each of the multiple units that make up the acoustic metamaterial.

[0065] Fig. 29 schematically shows an acoustic metamaterial 30 according to an embodiment. As shown in Fig. 29, the acoustic metamaterial 30 includes a plurality of units 31 and a plate member 32. The units 31 are arranged periodically (in a matrix in this example) and fixed to the plate member 32. The sound absorbing device 10 shown in Fig. 1 or the sound absorbing device 20 shown in Fig. 9 is used as each unit 31.

[0066] As described above, the sound absorbing device 10 comprises the membrane 12, the back plate 15 facing the membrane 12, the hollow member 14 provided between the membrane 12 and the back plate 15, and the support member 13 that supports the membrane 12. The support member 13 includes an annular frame member 131, an annular member 132 provided inside the frame member 131, a central member 133 provided inside the circular member 132, beam members 134 connecting the frame member 131 and the circular member 132, and beam members 135 connecting the circular member 132 and the central member 133. The frame member 131 is attached to the membrane 12 and the hollow member 14, and the central member 133 is attached to the membrane 12.

[0067] In the sound absorbing device 10 having the above configuration, a two-degree-of-freedom system is formed by the structure of the support member 13. Therefore, the vibration velocity transmission characteristics of the central member 133, which correlate with the sound absorption effect, have two resonance frequencies, and the sound absorption effect occurs at two frequencies. This makes it possible to obtain sound absorption effects at 60 Hz and 120 Hz, which correspond to power supply noise, for example.

[0068] In addition, the number of components is small, making the structure simple. Furthermore, a Helmholtz tone plate is not required. Therefore, it can be manufactured at low cost.

[0069] 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]

[0070] 10...sound absorbing device, 11...vibrating body, 12...membrane, 13...support member, 131...frame member, 132...annular member, 133...central member, 134, 135...beam member, 1341-1343, 1351-1353...beam member, 14...hollow member, 15...back panel, 16...vibration damping material, 19...internal space, 20...sound absorbing device, 21, 22...sound absorbing section, 30...acoustic metamaterial, 31...unit, 32...plate member, 71, 72...magnet, 81...piezoelectric film, 221...membrane, 222...hollow member, 223...dividing wall.

Claims

1. A membrane and a back plate facing the membrane; a first hollow member provided between the membrane and the back plate; a support member for supporting the membrane, the support member including an annular frame member, a ring member provided inside the frame member, a central member provided inside the ring member, a first beam member connecting the frame member and the ring member, and a second beam member connecting the ring member and the central member, wherein the frame member is attached to the membrane and the first hollow member, and the central member is attached to the membrane; A sound absorbing device comprising:

2. the first beam member supports the ring member so as to be vibrable relative to the frame member; the second beam member supports the central member so as to be vibrable relative to the ring member; 2. The sound absorbing device according to claim 1.

3. the ring member, the first beam member, and the second beam member do not contact the membrane; 2. The sound absorbing device according to claim 1.

4. The sound absorbing device according to claim 1 , further comprising a vibration-damping material provided on the first beam member or the second beam member.

5. The sound absorbing device according to claim 1 , further comprising a piezoelectric element provided on the membrane.

6. a second hollow member; a fabric connected to the second hollow member; Furthermore, an internal space is formed by the second hollow member and the fabric; 2. The sound absorbing device according to claim 1.

7. 7. The sound absorbing device of claim 6, wherein the fabric comprises aramid fibers.

8. 7. The sound absorbing device of claim 6, wherein the fabric comprises polyparaphenylene terephthalamide fibers.

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