Sound absorption structure

Abstract

To provide a sound absorption structure which can obtain large sound absorption effect for a wide frequency range, has a simple structure, can be miniaturized and has a low manufacture cost.SOLUTION: A plurality of resonators 2 are arranged in a plane. The resonator 2 has a hollow box body 3, and an opening part 5 and a neck part 6 are provided in one face 3a of the box body 3. The neck part 6 protrudes from an inner peripheral part of the opening part 5 toward the inside of the box body 3. At least one resonator 2 in the plurality of resonators 2 has a porous body layer 4 arranged inside the box body 3. The porous body layer 4 is arranged in a face 3c facing a face 3a in which the opening part 5 and the neck part 6 are provided with the hollow part 3b interposed therebetween in the box body 3. In at least one resonator 2, a size of the neck part 6 differs from the other resonator 2. In at least 70% of the resonators 2 in the resonators 2 having the porous body layers 4, height of the neck parts 6 is smaller than thickness of the porous body layers 4.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sound absorption structure.

Background Art

[0002] In modern society, countermeasures against noise generated in automobiles, airplanes, railways, construction sites, office buildings, apartment houses, etc. are important issues. In automobiles, in addition to noise derived from engines, new noise sources such as road noise, tire pattern noise, wind noise, and motor noise have emerged with the progress of electrification. In order to provide a quiet and comfortable space for passengers, reduction of in-vehicle noise is required. In addition, in buildings such as office buildings and apartment houses, appropriate sound absorption is required to improve indoor acoustics, such as improving the audibility of human conversations and sounds from audio equipment indoors. In order to solve such problems, sound absorption materials such as urethane foam and glass wool have been conventionally used. On the other hand, these have poor sound absorption performance at low frequencies, and in order to achieve sufficient sound absorption at low frequencies, a member with a large thickness is required. From the viewpoints of reducing fuel consumption and saving space in vehicles, a compact sound absorption member that can well absorb low-frequency noise is increasingly demanded. Therefore, Patent Documents 1 to 2 and Non-Patent Documents 1 to 2 propose a sound absorption structure having a Helmholtz resonator that can exhibit a large sound absorption effect in a small size.

[0003] The sound absorption structure described in Patent Document 1 includes a plate-like member having a plurality of openings, a rigid wall, a back air layer provided between the plate-like member and the rigid wall, and an extension member connected to the openings, and at least an extension portion of the extension member is accommodated in the back air layer.

[0004] The sound absorption member described in Patent Document 2 has a plurality of cavity portions that differ from each other in at least one of shape and size. A plate-like member constituting the wall of the cavity portion included in the plurality of cavity portions is formed with perforations that communicate the inside and the outside of the cavity portion. The surface of the plate-like member includes a first region in which a plurality of perforations are formed and a second region adjacent to the first region in which no perforations are formed.

[0005] The sound-absorbing structure described in Non-Patent Document 1 has a configuration in which a plurality of Helmholtz resonators with necks of different dimensions embedded therein are integrated.

[0006] The sound-absorbing structure described in Non-Patent Document 2 has a configuration in which a plurality of Helmholtz resonators with a circular planar shape are arranged side by side in a plane.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0008]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] According to the configurations described in Patent Documents 1 to 2 and Non-Patent Documents 1 to 2, a certain degree of sound absorption effect can be obtained, but a sound absorption structure that exhibits a greater sound absorption effect is further desired. In addition, in the configuration described in Patent Document 1, the range of frequencies to be sound-absorbed is narrow. In the configuration described in Patent Document 2, since there is no neck portion, the sound absorption effect is small, and in order to widen the range of frequencies to be sound-absorbed, it is necessary to form a large number of perforations, which leads to an increase in size and manufacturing cost. In the configuration described in Non-Patent Document 1, a large number of Helmholtz resonators are required to obtain a large sound absorption effect, resulting in a high manufacturing cost. In the configuration described in Non-Patent Document 2, the range of frequencies to be sound-absorbed is narrow.

[0010] Therefore, an object of the present invention is to provide a sound absorption structure that can obtain a large sound absorption effect over a wide frequency range for low-frequency noise, has a simple configuration, can be thinned and lightened, and has a low manufacturing cost. In particular, it is to provide a sound absorption structure that exhibits high sound absorption characteristics in the frequency band of 500 Hz to 1000 Hz, which is a problem for reducing noise inside an electric vehicle and improving the audibility of human conversations.

Means for Solving the Problems

[0011] In the sound absorption structure of the present invention, a plurality of resonators are arranged side by side in a plane. The resonator has a hollow box body, and an opening and a neck portion are provided on one surface constituting the box body. The neck portion protrudes from the inner peripheral portion of the opening toward the inside of the box body. At least some of the plurality of resonators have a porous body layer disposed inside the box body. The porous body layer is disposed on the surface of the box body that faces the hollow portion with the surface provided with the opening and the neck portion interposed therebetween. At least some of the plurality of resonators have a different neck portion dimension from other resonators. In at least 70% of the resonators having the porous body layer, the height of the neck portion in the direction orthogonal to the surface provided with the opening and the neck portion is smaller than the thickness of the porous body layer.

Effects of the Invention

[0012] According to the present invention, there is provided a sound-absorbing structure that can obtain a large sound-absorbing effect over a wide frequency range against low-frequency noise, has a simple configuration, can be made thin and lightweight, and has a low manufacturing cost. In particular, a sound-absorbing structure that exhibits high sound-absorbing characteristics in the frequency band of 500 Hz to 1000 Hz, which is a problem for reducing noise inside a vehicle of an electric vehicle and improving the audibility of human conversations, can be obtained.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

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Figure 8

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Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1(A) is a perspective view showing a sound-absorbing structure 1 according to an embodiment of the present invention, and FIG. 1(B) is a cross-sectional view thereof. This sound-absorbing structure 1 has a configuration in which a plurality of resonators 2 are arranged side by side in a plane. FIG. 2(A) is an enlarged perspective view of the resonator 2 of the sound-absorbing structure 1, and FIG. 2(B) is an enlarged cross-sectional view thereof. The resonator 2 has a hollow box body 3 and a porous body layer 4 disposed inside the box body 3. An opening 5 and a neck portion 6 are provided on one surface constituting the box body 3, specifically, the top surface 3a located above the drawing, and the resonator 2 constitutes a so-called Helmholtz resonator. The neck portion 6 is a hollow square tube shape protruding from the inner peripheral portion of the opening 5 toward the inside of the box body 3. The porous body layer 4 is disposed so as to overlap the surface (bottom surface) 3c of the box body 3 that faces the surface (top surface) 3a provided with the opening 5 and the neck portion 6 with the hollow portion 3b interposed therebetween. The top surface 3a of the box body 3 and the neck portion 6 are preferably integrally formed. Since the box body 3 and the neck portion 6 exhibit high sound absorption characteristics depending on their shapes, they can be configured with various materials. For example, metal materials such as stainless steel (SUS) and aluminum, plastics (e.g., LDPE (low-density polyethylene), PE (polyethylene), PP (polypropylene), PET (polyethylene terephthalate), PVC (polyvinyl chloride), PLA (polylactic acid), ABS, PC (polycarbonate), composite resins thereof, etc.), wood, etc. can be used. The materials constituting the box body 3 and the neck portion 6 preferably have a Young's modulus of 1 MPa to 250 GPa. By configuring the resonator 2 with a material having such high rigidity, sound waves do not penetrate the members, and acoustic energy can be confined in the box body 3 at the resonance frequency, realizing high sound absorption characteristics. The porous body layer 4 has a flow resistance of 5000 Ns / m (per unit thickness) 4 ~100000 Ns / m 4It is preferably formed of a highly sound-absorbing material. For example, the porous layer 4 is made of various foams such as polyurethane foam, melamine foam, and rubber sponge, non-woven fabric, woven fabric, felt, glass wool, etc. These materials may be made of biomass raw materials. Note that the box body 3 is not limited to a hollow cube or cuboid, and may be any hollow three-dimensional body. The planar shape of the box body 3 may be a polygon other than a quadrilateral, a circle, or other irregular shapes, and the top surface 3a and the bottom surface 3c may be curved surfaces.

[0015] The Helmholtz resonator such as the resonator 2 constituting the sound absorption structure 1 of the present embodiment generally has a resonance frequency f represented by the following formula (1). r exhibits high sound absorption characteristics at.

[0016]

Number

[0017] c represents the speed of sound, s represents the cross-sectional area of the neck constituting the Helmholtz resonator, l represents the length of the neck, and V represents the volume of the resonator. That is, by designing the resonator 2 so as to increase the length of the neck and the volume of the resonator and decrease the cross-sectional area of the neck, the resonance frequency can be lowered to a low frequency, and high sound absorption characteristics at a low frequency can be realized. In particular, when there are restrictions on the space where the sound absorption structure is installed, by adjusting the dimensions of the neck portion, it is possible to lower the resonance frequency while maintaining the dimensions of the entire sound absorption structure 1. Furthermore, by adjusting the dimensions of the neck portions so that the plurality of resonators 2 constituting the sound absorption structure 1 have different resonance frequencies, high sound absorption characteristics can be realized over a wide range of frequencies.

[0018] Based on such a concept, at least some of the plurality of resonators 2 are set such that the height H and width W1 of the neck portion 6 are different from those of the other resonators 2. In the sound absorption structure 1 of the present embodiment, for example, as shown in FIG. 1(B), three types of resonators 2 having different heights H (see FIG. 2(B)) in the direction orthogonal to the top surface 3a where the opening 5 and the neck portion 6 are provided are mixed in the neck portion 6. Further, in the example shown in FIG. 1, resonators 2 having different planar shape sizes of the opening 5 and the neck portion 6 are mixed.

[0019] In addition to the sound absorption effect caused by the intense vibration of the air in the hollow neck portion 6 of the resonator 2 of the sound absorption structure 1, an excellent sound absorption effect is obtained by the action of the porous body layer 4 disposed at a position facing the neck portion 6 inside the box body 3. In particular, in the present embodiment, the porous body layer 4 is disposed so as to overlap the bottom surface 3c of the box body 3 that faces the top surface 3a provided with the opening 5 and the neck portion 6 with the hollow portion 3b interposed therebetween, so that the sound absorption effect is great. For example, compared with the case where the porous body layer 4 is not disposed so as to overlap the bottom surface 3c but is disposed at a position away from the bottom surface 3c and close to the top surface 3a, since the porous body layer 4 overlaps the bottom surface 3c, an especially excellent sound absorption effect is obtained. Due to the action of the porous body layer 4 disposed in this way, even if the height H of the neck portion 6 is somewhat low, the sound absorption property of the sound absorption structure 1 is good. The ability to reduce the height H of the neck portion 6 while ensuring sound absorption contributes to the miniaturization, weight reduction, and ease of manufacture of the sound absorption structure 1. Specifically, since the neck portion 6 is short, it is easy to form by injection molding, laminated molding, or the like. Thus, in order to obtain good sound absorption property of the sound absorption structure 1 even if the height H of the neck portion 6 is somewhat low due to the action of the porous body layer 4, the height H of the neck portion 6 of the resonator 2 is preferably smaller than the thickness T1 of the porous body layer 4. Although it is allowed that the height H of the neck portion 6 of some resonators 2 is larger than the thickness T1 of the porous body layer 4, among a plurality of resonators 2, it is preferable that 70% or more of the resonators 2 having the height H of the neck portion 6 smaller than the thickness T1 of the porous body layer 4 exist, and more preferably 80% or more exist. In order for the sound absorption structure 1 to exhibit sufficient sound absorption characteristics with respect to low-frequency noise of 500 Hz to 1000 Hz and to be thinner than conventional sound absorption materials, the thickness T2 of the resonator 2 is preferably 10 mm or more and 60 mm or less, and more preferably 20 mm or more and 50 mm or less. In order to improve the sound absorption characteristics combining the effects of the porous body layer 4 and the neck portion 6 while maintaining the manufacturability of the neck portion 6, the height H of the neck portion 6 is preferably 1 mm or more and 10 mm or less, and the width W1 of the neck portion 6 is preferably 3 mm or more and 10 mm or less. The width W2 of the resonator is preferably 3 to 10 times the width W1 of the neck portion 6.By setting the width W2 of the resonator within such a range, a sufficient neck portion 6 is formed for the resonator 2 to exhibit high sound absorption characteristics by Helmholtz resonance, and the ratios of the height H and width W1 of the neck portion 6 to the width W2 of the resonator do not become extremely large, resulting in a design that is highly manufacturable.

[0020] In order to ensure the rigidity of the sound absorption structure 1 and the volume inside the box body 3, the plate thickness T of each surface of the box body 3 is preferably 0.5 mm or more and 5 mm or less, and more preferably 1 mm or more and 3 mm or less. And the thickness T1 of the porous body layer 4 is preferably 6 mm or more and not more than the internal height T3 of the box body 3, and more preferably 10 mm or more and T3 or less. Note that the entire inside of the box body 3 may be filled with the porous body layer 4. Here, the internal height T3 of the box body 3 is expressed as T3 = T2 - 2T and is a value depending on the thickness T2 of the resonator 2 and the plate thickness T of the box body 3. Not much complicated work is required for adjusting the thickness T1 of the porous body layer 4. The thickness T1 of the porous body layer 4 of the plurality of resonators 2 may be constant, but the thickness T1 of the porous body layer 4 of some of the plurality of resonators 2 may be different from the thickness T1 of the porous body layer 4 of the other resonators 2.

[0021] The frequency that is the main sound absorption target of the resonator 2 varies depending on the height H in the direction orthogonal to the opening 5 and the top surface 3a where the neck portion 6 is provided, of the neck portion 6. In the sound absorption structure 1 of the present embodiment, since a plurality of types of resonators 2 with different heights H are mixed, a large sound absorption effect can be obtained over a wide frequency band.

[0022] In the sound-absorbing structure 1 of this embodiment, as shown in FIG. 1, since adjacent resonators 2 are in close contact with each other without any gaps, a good sound-absorbing effect can be exerted without leakage throughout the sound-absorbing structure 1. However, as shown in FIG. 3, there may be a gap between adjacent resonators 2, and the gap ΔW between the resonators 2 is preferably 0 mm or more and 5 mm or less. The planar shape of the box body 3 of each resonator 2 is preferably a polygon that can be filled in a plane, such as a quadrilateral, a triangle, or a hexagon. Further, the cross-sectional shape (planar shape) orthogonal to the longitudinal direction of the neck portion 6 is not limited to a square as shown in FIGS. 1 to 2, and may be a circle as shown in FIG. 4(A), a polygon other than a square (for example, an octagon) as shown in FIG. 4(B), a star shape as shown in FIG. 4(C), or the like. The sound-absorbing structure 1 of this embodiment can be manufactured by injection molding, laminated molding, machining, etc. of the above-described materials. Each member constituting the sound-absorbing structure 1 may be integrally molded, or may be joined to each other by adhesion, heat welding, etc. after being individually molded.

[0023] The sound-absorbing structure 1 of the present invention can be used in a wide range of applications for countermeasures against low-frequency noise. For example, by installing the sound-absorbing structure 1 of the present invention in a vehicle, particularly in an automobile, noises such as road noise, tire pattern noise, wind noise, and motor noise propagated inside the vehicle can be reduced, and a comfortable interior space can be realized. Further, by installing the sound-absorbing structure 1 of the present invention on the wall surface or ceiling inside a building such as an office building or an apartment house, excessive reverberation can be suppressed, and the audibility of sounds from conversations and audio equipment can be improved, so that an improvement in indoor acoustics can be expected.

[0024] In the above-described embodiment, the porous body layer 4 is disposed inside the box body 3 of all the resonators 2 of the sound-absorbing structure 1, but the configuration is not limited thereto. As in another embodiment illustrated in FIG. 5, the porous body layer 4 may be disposed only inside the box body 3 of some of the plurality of resonators 2, and the porous body layer 4 may not be disposed inside the box body 3 of the other resonators 2. In particular, it is preferable that the porous body layer 4 is disposed inside the box body 3 of 55% or more of the plurality of resonators 2.

Example

[0025] Specific examples and comparative examples of the sound absorption structure 1 of the present invention will be described below. [Example 1] The sound-absorbing structure 1 of Example 1 of the present invention has substantially the same configuration as that shown in FIG. 1 and has a square planar shape with a length of about 100 mm × a width of about 100 mm. The dimensions of each part of the sound-absorbing structure 1 are described in Table 1. This sound-absorbing structure 1 has a configuration in which nine resonators 2 having a square planar shape with a length of 33.33 mm × a width of 33.33 mm (see FIG. 2(B) for the width W2) are arranged in a 3×3 matrix. The thickness T2 (see FIG. 2(B)) of the resonator 2 and the sound-absorbing structure 1 is 25 mm. An opening 5 having a square planar shape is provided on the top surface 3a of the box body 3, and a hollow square tube-shaped neck portion 6 protruding from the inner peripheral portion of the opening 5 toward the inside of the box body 3 is formed. A porous body layer 4 is disposed so as to overlap the bottom surface 3c of the box body 3 facing the top surface 3a provided with the opening 5 and the neck portion 6 across the hollow portion 3b. The thickness T1 (see FIG. 2(B)) of the porous body layer 4 is 15 mm. The dimensions of the opening 5 and the neck portion 6 are different for each resonator 2. Specifically, the widths of the openings 5 and the widths W1 (see FIG. 2(B)) of the neck portions 6 of the nine resonators 2 (resonators No. 1 to 9) are 5.25 mm, 6.68 mm, 3.58 mm, 5.09 mm, 5.94 mm, 6.96 mm, 8.83 mm, 4.66 mm, and 4.49 mm, respectively. The heights H (see FIG. 2(B)) of the neck portions 6 of the nine resonators 2 (resonators No. 1 to 9) in the direction orthogonal to the top surface 3a provided with the opening 5 and the neck portion 6 are 2.34 mm, 7.73 mm, 2.82 mm, 4.62 mm, 2.35 mm, 1.52 mm, 6.80 mm, 6.65 mm, and 4.22 mm, respectively. Therefore, the ratios of the heights H of the neck portions 6 of the nine resonators 2 (resonators No. 1 to 9) to the thickness T1 of the porous body layer 4 are 0.156, 0.515, 0.188, 0.308, 0.156, 0.102, 0.454, 0.443, and 0.281, respectively. That is, the height H of the neck portion 6 of all the resonators 2 is smaller than the thickness T1 of the porous body layer 4. The sound-absorbing characteristics exhibited by the sound-absorbing structure 1 of this example can be evaluated by the normal incidence sound absorption rate obtained from the transfer matrix method. The normal incidence sound absorption rate α is represented by the following formula (2).

[0026]

Number

[0027] Z air is the characteristic impedance of air, Z all is the impedance of the entire sound-absorbing structure 1. Z all is, as shown in Equation (3), the impedance Z of each resonator i (1 ≦ i < 9) is expressed as follows.

[0028]

Number

[0029] S all is the cross-sectional area of the entire sound-absorbing structure 1, S i represents the cross-sectional area of the i-th resonator. Furthermore, the impedance Z of each resonator i is represented by Equation (4) from the transmission matrix T of the resonator i as follows.

[0030]

Number

[0031] (T i ) 11 ,(T i ) 21 represent the 11-component and 21-component of the transmission matrix, respectively. The transmission matrix T i can be evaluated according to Non-Patent Documents 1 to 2. The relationship between the frequency and the normal incidence sound absorption rate of the sound-absorbing structure 1 of this example is shown in FIG. 6. The average value of the normal incidence sound absorption rate of the sound-absorbing structure 1 of this example at the frequency of 500 Hz to 1000 Hz shown in FIG. 6 is 0.87. Hereinafter, the normal incidence sound absorption rate represented by Equation (2) is simply referred to as the sound absorption rate.

[0032]

Table 1

[0033] [Comparative Example 1] Although not shown, the sound absorption structure 1 of Comparative Example 1 has a configuration similar to the configuration shown in FIG. 1, and the dimensions of each part of the sound absorption structure 1 are described in Table 2. The overall dimensions of the sound absorption structure 1 and the dimensions of the enclosures 3, the openings 5, and the neck portions 6 of the nine resonators 2 (Resonator Nos. 1 to 9) are all the same as the respective dimensions of Example 1. However, none of the resonators 2 of the sound absorption structure 1 of this comparative example have the porous body layer 4. The relationship between the frequency and the sound absorption rate of the sound absorption structure 1 of this comparative example is shown in FIG. 7. The average value of the sound absorption rate of the sound absorption structure 1 of this comparative example at the frequencies of 500 Hz to 1000 Hz shown in FIG. 7 is 0.79.

[0034]

Table 2

[0035] [Comparative Example 2] Although not shown, the sound absorption structure 1 of Comparative Example 2 has substantially the same configuration as that shown in FIG. 1, and the dimensions of each part of the sound absorption structure 1 are described in Table 3. The overall dimensions of the sound absorption structure 1 of this comparative example and the dimensions of the boxes 3 of the nine resonators 2 (Resonator Nos. 1 to 9) are all the same as the respective dimensions of Example 1. However, the dimensions of the openings 5, the neck portions 6, and the porous body layer 4 of the resonators 2 of the sound absorption structure 1 of this comparative example are different from the respective dimensions of Example 1. The thickness T1 of the porous body layer 4 of the resonator 2 of the sound absorption structure 1 of this comparative example is half of the thickness T1 of the porous body layer 4 of Example 1, that is, 7.5 mm. The widths of the openings 5 and the inner diameters of the neck portions 6 of the nine resonators 2 (Resonator Nos. 1 to 9) of this comparative example are the same as the widths of the openings 5 and the inner diameters of the neck portions 6 of the nine resonators 2 of Example 1. The heights H of the neck portions 6 of the nine resonators 2 (Resonator Nos. 1 to 9) of this comparative example are each larger than the heights H of the neck portions 6 of the nine resonators 2 of Example 1, and are 3.47 mm, 14.17 mm, 4.41 mm, 8.00 mm, 3.48 mm, 1.84 mm, 12.33 mm, 12.03 mm, and 7.20 mm. Therefore, the ratios of the heights H of the neck portions 6 of the nine resonators 2 (Resonator Nos. 1 to 9) of this comparative example to the thickness T1 of the porous body layer 4 are 0.463, 1.889, 0.588, 1.067, 0.464, 0.246, 1.645, 1.604, and 0.959, respectively. That is, the heights H of the neck portions 6 of some of the resonators 2 are larger than the thickness T1 of the porous body layer 4. The relationship between the frequency and the sound absorption rate of the sound absorption structure 1 of this comparative example is shown in FIG. 8. The average value of the sound absorption rate of the sound absorption structure 1 of this comparative example at the frequencies of 500 Hz to 1000 Hz shown in FIG. 8 is 0.68.

[0036]

Table 3

[0037] [Comparative Example 3] Although not shown, the sound absorption structure 1 of Comparative Example 3 has a configuration similar to the configuration shown in FIG. 1, and the dimensions of each part of the sound absorption structure 1 are described in Table 4. The sound absorption structure 1 of this comparative example consists of exactly the same nine resonators 2. The overall dimensions of the sound absorption structure 1 of this comparative example and the dimensions of the boxes 3 and the porous layer 4 of the nine resonators 2 (resonators No. 1 to 9) are all the same as the respective dimensions of Example 1. The width of the opening 5 and the width W1 of the inner diameter dimension of the neck portion 6 of all the resonators 2 (resonators No. 1 to 9) of this comparative example are 5.72 mm, and the height H of the neck portion 6 is 4.34 mm. Therefore, the ratio of the height H of the neck portion 6 of all the resonators 2 (resonators No. 1 to 9) of this comparative example to the thickness T1 of the porous layer 4 is 0.289. The height H of the neck portion 6 of the resonator 2 is smaller than the thickness T1 of the porous layer 4. The relationship between the frequency and the sound absorption rate of the sound absorption structure 1 of this comparative example is shown in FIG. 9. The average value of the sound absorption rate of the sound absorption structure 1 of this comparative example at the frequencies of 500 Hz to 1000 Hz shown in FIG. 9 is 0.44.

[0038]

Table 4

[0039] [Example 2] The sound absorption structure 1 of Example 2 of the present invention has a configuration substantially the same as the configuration shown in FIG. 5, and resonators 2 having a porous layer 4 and resonators 2 without a porous layer 4 are mixed. The dimensions of each part of the sound absorption structure 1 are described in Table 5. The cross-sectional shape of the neck portion in this example is circular. Among all the resonators 2 of this sound absorption structure 1, the ratio of the resonators 2 having a porous layer 4 is 77.8%. The relationship between the frequency and the sound absorption rate of the sound absorption structure 1 of this example is shown in FIG. 10. The average value of the sound absorption rate of the sound absorption structure 1 of this example at the frequencies of 500 Hz to 1000 Hz shown in FIG. 10 is 0.875, and the average value of the sound absorption rate of the sound absorption structure 1 of this example at the frequencies of 500 Hz to 700 Hz is 0.835.

[0040]

Table 5

[0041] [Comparative Example 4] The sound absorption structure 1 of Comparative Example 4 compared with Example 2 of the present invention has a box body 3 with the same configuration as each resonator 2 of Example 2, although not shown in the drawings. However, the porous body layer 4 does not exist in all the resonators 2. The dimensions of each part of the sound absorption structure 1 are shown in Table 6. The cross-sectional shape of the neck portion of this comparative example is circular. Among all the resonators 2 of this sound absorption structure 1, the proportion of the resonators 2 having the porous body layer 4 is 0%. The relationship between the frequency and the sound absorption rate of the sound absorption structure 1 of this comparative example is shown in FIG. 11. The average value of the sound absorption rate of the sound absorption structure 1 of this comparative example at frequencies of 500 Hz to 1000 Hz shown in FIG. 11 is 0.81, and the average value of the sound absorption rate of the sound absorption structure 1 of this comparative example at frequencies of 500 Hz to 700 Hz is 0.765.

[0042] [Table 6]

[0043] [Example 3] The sound absorption structure 1 of Example 3 compared with Example 2 of the present invention has a box body 3 with the same configuration as each resonator 2 of Example 2, although not shown in the drawings. And the porous body layer 4 exists in all the resonators 2. The dimensions of each part of the sound absorption structure 1 are shown in Table 7. The cross-sectional shape of the neck portion of this example is circular. Among all the resonators 2 of this sound absorption structure 1, the proportion of the resonators 2 having the porous body layer 4 is 100%. The relationship between the frequency and the sound absorption rate of the sound absorption structure 1 of this example is shown in FIG. 12. The average value of the sound absorption rate of the sound absorption structure 1 of this example at frequencies of 500 Hz to 1000 Hz shown in FIG. 12 is 0.867, and the average value of the sound absorption rate of the sound absorption structure 1 of this example at frequencies of 500 Hz to 700 Hz is 0.818.

[0044] [Table 7]

[0045] [Example 4] The sound-absorbing structure 1 of Example 4 of the present invention has substantially the same configuration as that shown in FIG. 5, and resonators 2 having a porous layer 4 and resonators 2 without the porous layer 4 are mixed. The dimensions of each part of the sound-absorbing structure 1 are shown in Table 8. The cross-sectional shape of the neck part of this example is square. Among all the resonators 2 of this sound-absorbing structure 1, the proportion of the resonators 2 having a porous layer 4 is 77.8%. The relationship between the frequency and the sound absorption rate of the sound-absorbing structure 1 of this example is shown in FIG. 13. The average value of the sound absorption rate of the sound-absorbing structure 1 of this example at a frequency of 500 Hz to 1000 Hz shown in FIG. 13 is 0.872, and the average value of the sound absorption rate of the sound-absorbing structure 1 of this example at a frequency of 500 Hz to 700 Hz is 0.837.

[0046] [Table 8]

[0047] [Comparative Example 5] The sound-absorbing structure 1 of Comparative Example 5 compared with Example 4 of the present invention has a box body 3 having the same configuration as each resonator 2 of Example 4, although not shown, but the porous layer 4 does not exist in all the resonators 2. The dimensions of each part of the sound-absorbing structure 1 are shown in Table 9. The cross-sectional shape of the neck part of this comparative example is square. Among all the resonators 2 of this sound-absorbing structure 1, the proportion of the resonators 2 having a porous layer 4 is 0%. The relationship between the frequency and the sound absorption rate of the sound-absorbing structure 1 of this comparative example is shown in FIG. 14. The average value of the sound absorption rate of the sound-absorbing structure 1 of this comparative example at a frequency of 500 Hz to 1000 Hz shown in FIG. 14 is 0.831, and the average value of the sound absorption rate of the sound-absorbing structure 1 of this comparative example at a frequency of 500 Hz to 700 Hz is 0.790.

[0048] [Table 9]

[0049] [Example 5] The sound-absorbing structure 1 of Example 5, which is compared with Example 4 of the present invention, although not shown in the figure, has a box body 3 with the same configuration as each resonator 2 of Example 4, and a porous body layer 4 exists in all resonators 2. The dimensions of each part of the sound-absorbing structure 1 are shown in Table 10. The cross-sectional shape of the neck part of this example is a square. Among all the resonators 2 of this sound-absorbing structure 1, the proportion of the resonators 2 having the porous body layer 4 is 100%. The relationship between the frequency and the sound absorption rate of the sound-absorbing structure 1 of this example is shown in FIG. 15. The average value of the sound absorption rate of the sound-absorbing structure 1 of this example at the frequencies of 500 Hz to 1000 Hz shown in FIG. 15 is 0.863, and the average value of the sound absorption rate of the sound-absorbing structure 1 of this example at the frequencies of 500 Hz to 700 Hz is 0.817.

[0050]

Table 10

[0051] [Example 6] The sound-absorbing structure 1 of Example 6, which is compared with Example 4 of the present invention, although not shown in the figure, has a box body 3 with the same configuration as each resonator 2 of Example 4. A porous body layer 4 exists in 5 resonators 2, and a porous body layer 4 does not exist in 4 resonators 2. The dimensions of each part of the sound-absorbing structure 1 are shown in Table 11. The cross-sectional shape of the neck part of this example is a square. Among all the resonators 2 of this sound-absorbing structure 1, the proportion of the resonators 2 having the porous body layer 4 is 55.6%. The relationship between the frequency and the sound absorption rate of the sound-absorbing structure 1 of this example is shown in FIG. 16. The average value of the sound absorption rate of the sound-absorbing structure 1 of this example at the frequencies of 500 Hz to 1000 Hz shown in FIG. 16 is 0.870, and the average value of the sound absorption rate of the sound-absorbing structure 1 of this example at the frequencies of 500 Hz to 700 Hz is 0.837.

[0052]

Table 11

[0053] [Results] Compare the sound absorption rates of Examples 1 to 6 and Comparative Examples 1 to 5 of the present invention shown in FIGS. 6 to 16. Referring to FIGS. 6, 10, 12 to 13, and 15 to 16, according to the sound absorption structures 1 of Examples 1 to 6, they show high sound absorption rates over a wide frequency range, and the average value of the sound absorption rate is a high value exceeding 0.8.

[0054] Referring to FIG. 7, in the sound absorption structure 1 of Comparative Example 1, frequencies with high sound absorption rates and frequencies with low sound absorption rates exist alternately, and it cannot show high sound absorption rates over a wide frequency range. And the average value of this sound absorption rate is less than 0.8. In Comparative Example 1, a plurality of resonators 2 with different heights H of the neck portion 6 are provided and show high sound absorption rates at various frequencies. However, since the porous layer 4 does not exist, the variation in the sound absorption rate according to the change in frequency is large and not stable. Therefore, it cannot show high sound absorption rates over the entire wide frequency range, and the sound absorption effect is small at some frequencies.

[0055] Referring to FIG. 8, in the sound absorption structure 1 of Comparative Example 2, locally high sound absorption rates can be obtained at some frequencies, but the sound absorption rates are low in many frequency bands. The average value of this sound absorption rate is less than 0.7. In Comparative Example 2, the height H of the neck portion 6 is too large, and in 4 out of 9 resonators 2 (44.4%), the height H of the neck portion 6 is larger than the thickness T1 of the porous layer 4. As a result, the sound absorption rate is prominently high at some frequencies, but overall, the frequency band with a low sound absorption rate is wide. One of the reasons is that increasing the height H of the neck portion 6 has shifted the resonance frequency of each resonator from the target frequency range. Furthermore, since the thickness T1 of the porous layer is small compared to the height H of the neck portion, the sound absorption rate of each resonator is smaller than that of Example 1, and it is also considered as a cause that it is inferior in broadband characteristics.

[0056] Referring to FIG. 9, in the sound absorption structure 1 of Comparative Example 3, since all nine resonators 2 have the same configuration and the same dimensions, they have the same sound absorption characteristics. As a result, there is only one peak in the sound absorption rate of the sound absorption structure. As the frequency decreases from the peak frequency, the sound absorption rate decreases, and similarly, as the frequency increases from the peak frequency, the sound absorption rate decreases. Therefore, the overall sound absorption rate is low, and a good sound absorption effect can only be achieved at specific points. The average value of the sound absorption rate is 0.44, which is quite small.

[0057] Thus, in the sound absorption structure 1 according to the present invention, since the dimensions of the neck portions 6 of the respective resonators 2 are various, a high sound absorption rate can be obtained over a wide frequency range (for example, 500 Hz to 1000 Hz). Moreover, since the porous body layer 4 is provided on each resonator 2 and is arranged so as to overlap the bottom surface 9c, a large sound absorption effect can be obtained, and the variation in the sound absorption rate accompanying the change in frequency can be made extremely small, and the average value of the sound absorption rate is large. Further, since the sound absorption effect of the porous body layer 4 can be obtained, the neck portion 6 can be shortened while maintaining the sound absorption property, and miniaturization (for example, making the width of the sound absorption structure 1 100 mm or less and the thickness 25 mm or less) and weight reduction (for example, when the box body 3 and the neck portion 6 are made of resin, it is 70 g or less, and when made of metal, it is 160 g or less) and facilitation of manufacturing can be realized. Since a large sound absorption effect can be obtained without increasing the number of resonators 2 too much, there is no need to increase the number of resonators 2 more than necessary, and the number of resonators 2 arranged in a matrix as shown in FIG. 1 can be about nine. Note that the configuration is not limited to the case where the heights H of all the neck portions 6 of the plurality of resonators 2 are different from each other, and the heights H of the neck portions 6 of some of the resonators 2 may be the same.

[0058] Referring to FIG. 10, it can be seen that even in the sound absorption structure 1 of Example 2 in which the porous body layer 4 is provided only on some of the plurality of resonators 2 and not on the remaining resonators 2, a good sound absorption rate can be obtained. FIG. 10 showing the sound absorption rate of the sound absorption structure 1 of Example 2 is compared with FIG. 11 showing the sound absorption rate of the sound absorption structure 1 of Comparative Example 4 which has a box 3 with the same configuration as each resonator 2 of Example 2 but in which the porous body layer 4 does not exist in all the resonators 2, and FIG. 12 showing the sound absorption rate of the sound absorption structure 1 of Example 3 which has a box 3 with the same configuration as each resonator 2 of Example 2 and in which the porous body layer 4 is provided in all the resonators 2. It can be seen that since the resonators 2 not provided with the porous body layer 4 which is a sound absorption material resonate particularly in the low frequency band, when improving the sound absorption rate in the low frequency band, it is effective to configure the porous body layer 4 not to be provided on some of the resonators 2 of the sound absorption structure 1. Referring to FIG. 11, in the sound absorption structure 1 of Comparative Example 4 in which the porous body layer 4 does not exist in all the resonators 2, the dispersion of the frequency response of the sound absorption rate is large and the average value of the sound absorption rate is smaller than that of Example 2. On the other hand, referring to FIG. 12, in the sound absorption structure 1 of Example 3 in which the porous body layer 4 is provided in all the resonators 2, the frequency response of the sound absorption rate is smoothed over the entire frequency band of 500 Hz to 1000 Hz. That is, in Example 3, the average value of the sound absorption rate in the low frequency band is inferior to that of Example 2, but broad characteristics are seen in the low frequency band, and it is considered that a relatively high sound absorption rate is shown even in the frequency bands other than the target frequency band (the frequency band of 500 to 1000 Hz). And preferably, in 70% or more of the resonators 2 having the porous body layer 4, more preferably in 80% or more of the resonators 2, the height H of the neck portion 6 in the direction orthogonal to the top surface 3a provided with the opening portion 5 and the neck portion 6 is smaller than the thickness T1 of the porous body layer 4.

[0059] Similarly, FIG. 13 showing the sound absorption rate of the sound absorption structure 1 of Example 4 in which the porous body layer 4 is provided only on some of the plurality of resonators 2 and not provided on the remaining resonators 2, and the sound absorption structure 1 of Comparative Example 5 having the same structure of the box body 3 as each resonator 2 of Example 4 but having no porous body layer 4 in all resonators 2, and FIG. 15 showing the sound absorption rate of the sound absorption structure 1 of Example 5 having the same structure of the box body 3 as each resonator 2 of Example 4 and having the porous body layer 4 provided in all resonators 2 are compared. As described above, according to Example 4, it can be seen that the sound absorption rate is improved compared to Comparative Example 5, the frequency response of the sound absorption rate is smoothed to some extent, and the maximum value of the sound absorption rate in the low frequency band can be improved. On the other hand, according to Example 5, it can be seen that a relatively high sound absorption rate is obtained in a wide frequency band including the low frequency band and the variation in the sound absorption rate is suppressed to be small.

[0060] Thus, even if the shapes and dimensions of the respective resonators 2 of the sound absorption structure 1 are somewhat different, the sound absorption rate can be improved by providing the porous body layer 4 on at least some of the plurality of resonators 2. In particular, when it is required to smooth the sound absorption rate in a wide frequency band, it can be seen that it is preferable to increase the number of resonators 2 provided with the porous body layer 4. On the other hand, when the smoothing of the sound absorption rate in a wide frequency band is not so required and it is required to improve the average value of the sound absorption rate, the number of resonators 2 provided with the porous body layer 4 may be small. Referring to FIG. 16, by arranging the porous body layer 4 in approximately half (55.6%) of all the resonators 2 of the sound absorption structure 1, the average value of the sound absorption rate is improved, and in particular, it can be seen that the maximum value of the sound absorption rate in the low frequency band (for example, 500 Hz to 700 Hz) is large. That is, at least when the porous body layer 4 is arranged inside the box body 3 of 55% or more of the plurality of resonators 2 of the sound absorption structure 1, it can be said that it is effective in improving the sound absorption rate.

[0061] The present invention may have the following configuration. [1] A plurality of resonators are arranged side by side in a plane, The resonator has a hollow box body, and an opening and a neck portion are provided on one surface constituting the box body. The neck portion protrudes from the inner peripheral portion of the opening toward the inside of the box body. At least some of the plurality of resonators have a porous body layer disposed inside the box body. The porous body layer is disposed on a surface of the box body that faces the hollow portion with the surface provided with the opening and the neck portion interposed therebetween. At least some of the plurality of resonators have a different neck portion dimension from other resonators. In at least 70% of the resonators having the porous body layer, the height of the neck portion in a direction orthogonal to the surface provided with the opening and the neck portion is smaller than the thickness of the porous body layer. A sound absorption structure characterized by this. [2] The sound absorption structure according to [1], wherein the porous body layer is disposed inside the box body of 55% or more of the plurality of resonators. [3] The sound absorption structure according to [1] or [2], wherein the distance between adjacent resonators is 0 mm or more and 5 mm or less. [4] The sound absorption structure according to any one of [1] to [3], wherein the thickness of the porous body layer of the plurality of resonators having the porous body layer is constant. [5] The sound absorption structure according to any one of [1] to [3], wherein at least some of the plurality of resonators having the porous body layer have a different thickness of the porous body layer from other resonators. [6] The sound absorption structure according to any one of [1] to [5], wherein the thickness of the porous body layer is 10 mm or more and not more than the height inside the box body. [7] The sound absorption structure according to any one of [1] to [6], wherein the height of the neck portion in a direction orthogonal to the surface provided with the opening and the neck portion is 1 mm or more and 10 mm or less, and the width of the neck portion is 3 mm or more and 10 mm or less. [8] The sound absorption structure according to any one of [1] to [7], wherein the box body and the neck portion are integrally formed. [9] The sound-absorbing structure according to any one of [1] to [8], wherein the box body and the neck portion are formed of metal or resin.

[10] The porous layer has a flow resistance of 5000 Ns / m 4 or more and 100000 Ns / m 4 or less, and is formed of the following material. The sound-absorbing structure according to any one of [1] to [9].

Explanation of reference numerals

[0062] 1 Sound-absorbing structure 2 Resonator 3 Box body 3a Top surface 3b Hollow portion 3c Bottom surface 4 Porous layer 5 Opening 6 Neck portion H Height of the neck portion W1 Width of the neck portion T1 Thickness of the porous layer T2 Thickness of the resonator W2 Width of the resonator T3 Internal height of the box body T Plate thickness of the box body

Claims

1. A plurality of resonators are arranged side by side in a plane, each of the resonators has a hollow box body, and an opening and a neck portion are provided on one surface constituting the box body. The neck portion protrudes from the inner peripheral portion of the opening toward the inside of the box body. At least some of the plurality of resonators have a porous body layer disposed inside the box body. The porous body layer is disposed on a surface of the box body that faces the hollow portion with the surface provided with the opening and the neck portion interposed therebetween. At least some of the plurality of resonators have a neck portion with dimensions different from those of other resonators. In at least 70% of the resonators having the porous body layer, the height of the neck portion in a direction orthogonal to the surface provided with the opening and the neck portion is smaller than the thickness of the porous body layer. A sound absorption structure characterized by this.

2. The sound absorption structure according to Claim 1, wherein the porous body layer is disposed inside the box body of 55% or more of the plurality of resonators.

3. The sound absorption structure according to Claim 1 or 2, wherein the distance between adjacent resonators is 0 mm or more and 5 mm or less.

4. The sound absorption structure according to Claim 1 or 2, wherein the thickness of the porous body layer of the plurality of resonators having the porous body layer is constant.

5. The sound absorption structure according to Claim 1 or 2, wherein at least some of the plurality of resonators having the porous body layer have a porous body layer with a thickness different from that of other resonators.

6. The sound absorption structure according to Claim 1 or 2, wherein the thickness of the porous body layer is 10 mm or more and not more than the height inside the box body.

7. The sound absorption structure according to Claim 1 or 2, wherein the height of the neck portion in a direction orthogonal to the surface provided with the opening and the neck portion is 1 mm or more and 10 mm or less, and the width of the neck portion is 3 mm or more and 10 mm or less.

8. The sound absorption structure according to Claim 1 or 2, wherein the box body and the neck portion are integrally formed.

9. The sound absorption structure according to Claim 1 or 2, wherein the box body and the neck portion are formed of metal or resin.

10. The porous body layer has a flow resistance of 5000 Ns / m 4 or more and 100000 Ns / m 4 or less, and is formed of the material according to claim 1 or 2, the sound absorption structure.

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