Soundproof structure

Abstract

The present invention provides a soundproof structure capable of reducing transmission of noise from outside a vehicle into a cabin of the vehicle and improving quietness in the cabin. A soundproof structure A according to the present invention is characterized by comprising: a sheet metal B constituting an exterior body of the vehicle; a first member 1 disposed inside the sheet metal B; and a second member 2 which is disposed in a space portion C formed between facing surfaces of the sheet metal B and the first member 1 and which partitions the space portion C in the inward and outward directions, thereby making it possible to block noise from outside the vehicle and effectively reduce entry of noise into the vehicle.

Description

Soundproof structure

[0001] The present invention relates to a soundproof structure.

[0002] Conventionally, in vehicles such as automobiles, special vehicles, construction vehicles, industrial vehicles, railways, and aircraft, noise outside the vehicle such as road noise during traveling (such as friction noise or impact noise between tires and roads, rolling noise, friction noise or impact noise between train wheels and rails), engine noise, or drive motor noise is reduced from being transmitted into the vehicle cabin, and soundproof materials have been used to keep the vehicle cabin quiet.

[0003] As such a soundproof material, Patent Document 1 discloses a polyolefin resin foam having a horizontal burning rate of 100 mm / min or less measured in accordance with ASTM D 1692, an apparent density of 38 kg / m 3 or less, a thickness of 1 to 7 mm, and a tensile elongation of 50% or more, and a sound absorbing layer made of a porous material having a horizontal burning rate of 100 mm / min or less, a thickness of 1 to 50 mm, and an apparent density of 10 to 200 kg / m 3 which is bonded to the resonance layer to form a laminate, and the basis weight of the laminate is 3000 g / m 2 or less, a flame-retardant soundproof material is disclosed.

[0004] Japanese Unexamined Patent Publication No. 2006-240207

[0005] However, the above-mentioned flame-retardant soundproof material cannot sufficiently reduce the noise outside the vehicle and make the vehicle cabin sufficiently quiet, and a soundproof structure with excellent soundproof performance is desired.

[0006] The present invention provides a soundproof structure capable of reducing the transmission of noise outside the vehicle into the vehicle cabin and improving the quietness in the vehicle cabin.

[0007] The soundproof structure of the present invention is characterized by comprising a sheet metal constituting an exterior body of a vehicle, a first member disposed inside the sheet metal, and a second member disposed in a space formed between opposing surfaces of the sheet metal and the first member and partitioning the space in the inner and outer directions.

[0008] In the soundproofing structure of the present invention, a space is formed between the opposing surfaces of a sheet metal constituting the exterior body of a vehicle and a first member disposed inside the sheet metal. A second member is disposed in this space, and the space is divided in an inward and outward direction. Therefore, it is possible to block noise from outside the vehicle and effectively reduce noise entering the vehicle.

[0009] In the above-described soundproofing structure, if the second member has a through-hole that penetrates in the thickness direction, when sound waves caused by noise from outside the vehicle pass through the through-hole of the second member, they vibrate the air in the through-hole portion, and sound can be absorbed by the frictional viscous resistance between the air in the through-hole portion and the wall surface of the through-hole, thus the soundproofing structure has superior soundproofing properties.

[0010] In the above soundproofing structure, if the through-hole of the second member becomes smaller from the outside to the inside, when sound waves caused by noise from outside the vehicle pass through the through-hole of the second member, the frictional viscous resistance between the air in the through-hole portion and the wall surface of the through-hole can be increased, thereby further sound absorption, and the soundproofing structure has superior soundproofing properties.

[0011] In the above soundproofing structure, if the first member does not have through holes that penetrate in the thickness direction, sound waves can be repeatedly reflected and attenuated in the partition formed between the first member and the second member, further reducing the sound waves entering the vehicle interior, and the soundproofing structure has superior soundproofing properties.

[0012] In the above soundproofing structure, if the second member is fixed to a support column protruding from the first member, the distance between the second member and the first member is maintained, and sound waves are attenuated in the partition formed between the first member and the second member, thereby achieving excellent soundproofing performance.

[0013] In the above-described soundproofing structure, if the second member is made of foam, the weight of the soundproofing structure can be reduced, and the soundproofing performance of the soundproofing structure can be further improved by the air layer formed within the second member.

[0014] In the above soundproofing structure, if the foam is a closed-cell foam, the soundproofing performance can be further improved by the closed cells formed within the second member.

[0015] In the above soundproofing structure, the support column has a receiving surface at its tip that receives the second member, and a connecting portion protruding from the receiving surface. When the connecting portion of the support column is fixed in a state where it passes through the second member, the distance between the second member and the first member can be maintained more reliably, and sound waves can be attenuated in the partition formed between the first member and the second member, thereby providing the soundproofing structure with superior soundproofing performance.

[0016] In the above-described soundproofing structure, if the distance between the first member and the second member is 5 to 50 mm, the soundproofing performance of the soundproofing structure can be further improved while reducing the thickness of the soundproofing structure.

[0017] This is a front view of the soundproofing structure of the present invention with the sheet metal omitted. This is a cross-sectional view of the soundproofing structure. This is a graph showing the measurement results of the vertical incidence sound transmission loss measured in Examples 1 to 8 and Comparative Example 1. This is a graph showing the measurement results of the vertical incidence sound transmission loss measured in Examples 9 to 11 and Comparative Example 1. This is a graph showing the measurement results of the vertical incidence sound transmission loss measured in Examples 12 to 14 and Comparative Example 1. This is a graph showing the measurement results of the vertical incidence sound transmission loss measured in Examples 15 to 17 and Comparative Example 1. This is a graph showing the measurement results of the vertical incidence sound transmission loss measured in Examples 18 to 20 and Comparative Example 1.

[0018] An example of the soundproofing structure of the present invention will be described with reference to the drawings. The soundproofing structure A has a sheet metal B that constitutes the exterior body of a vehicle (automobile, special vehicle, construction vehicle, industrial vehicle, railway, aircraft, etc.), a first member 1 disposed inside the sheet metal B, and a second member 2 disposed in a space C formed on the opposing surfaces of the sheet metal B and the first member 1, and partitioning the space C in the inward and outward directions. In the present invention, "outside" refers to the direction outside the vehicle (the direction outside the vehicle's passenger compartment, the direction opposite to the vehicle's passenger compartment), and "inside" refers to the direction towards the passenger compartment. In Figure 2, the left side is the outside (direction outside the vehicle), and the right side is the inside (direction towards the passenger compartment). "Outside the vehicle" refers to the outside of the vehicle's passenger compartment.

[0019] The sheet metal B of soundproofing structure A is a metal plate that constitutes the exterior body of the vehicle and is exposed to the outside. For example, it is a metal plate that makes up the outer parts of the vehicle such as the back door, front door, rear door, quarter panel, fender, roof, underbody, ceiling, side wall, front and rear sections, outer panel, and body.

[0020] The first member 1 is positioned on the inside of the sheet metal B of the soundproof structure A, that is, in the direction toward the passenger compartment. The sheet metal B is usually formed with its outer edge generally curved inward. The first member 1 is positioned to close the opening in the sheet metal B, and the first member 1 constitutes the interior material of the passenger compartment. Alternatively, another member may be positioned further inside the first member 1, and this other member may also serve as the interior material.

[0021] The first member 1 is not particularly limited, but is formed from a synthetic resin molded product and is molded into a desired shape to match the shape of the vehicle interior.

[0022] A space C is formed between the opposing surfaces of the sheet metal B and the first member 1, which is completely closed and forms a sealed space. A sheet-like second member 2 is disposed within space C, and the space C is divided entirely or partially in the inward and outward directions. The outer peripheral edge of the second member 2 is disposed entirely or partially in contact with the inner surface of the sheet metal B or the first member 1, i.e., the inner surface of space C, so that space C is divided entirely or partially into two parts in the inward and outward directions, forming an inner partition C1 and an outer partition C2.

[0023] The second member 2 may be formed from any material, but a molded synthetic resin is preferred. The second member 2 may be composed of foam or non-foam, but it is preferred to be composed of foam, and more preferably of closed-cell foam. When the second member 2 is composed of foam, the soundproofing structure can be made lighter, and the air in the bubbles of the foam can attenuate sound waves caused by noise from outside the vehicle, resulting in a soundproofing structure with superior soundproofing properties. When the second member 2 is composed of closed-cell foam, sound waves caused by noise from outside the vehicle can be attenuated more effectively.

[0024] Furthermore, closed-cell foam refers to foam in which closed cells account for 90% or more of the bubbles contained within the foam. The percentage of closed cells is determined by cutting a sheet of foam in the thickness direction and measuring the percentage of closed cells in any 1 cm section of the cut surface. 2 The cross-section is photographed, and the total number of bubbles and the number of closed bubbles are measured. The percentage of closed bubbles is calculated based on the following formula: Percentage of closed bubbles (%) = 100 × Number of closed bubbles / Total number of bubbles

[0025] The thickness of the second member 2 is preferably 1 to 5 mm, and more preferably 2 to 4 mm. When the thickness of the second member 2 is within the above range, partitions C1 and C2 can be reliably formed between the second member 2 and the first member 1 while ensuring the lightness of the soundproof structure, and the soundproof structure has excellent soundproofing properties.

[0026] On the other hand, multiple support columns 11 of a certain height are provided protruding outward from the inner surface of the first member 1. The tip surfaces of the support columns 11 of the first member 1 are formed as flat receiving surfaces 111 capable of receiving the second member 2, and columnar connecting portions 112 of a certain height are provided protruding outward from the center of the receiving surface 111.

[0027] Furthermore, the connecting portion 112 of the support column 11 of the first member 1 penetrates the sheet-like second member 2, and the second member 2 is held between the enlarged head 112a, which is formed at the tip of the connecting portion 112 and has a larger cross-sectional shape than the connecting portion 112, and the receiving surface 111 of the support column 11, thereby stably fixing the second member 2 on the support column 11 of the first member 1. Therefore, the second member 2 is stably positioned at a distance from the first member 1 equal to the height dimension of the support column 11.

[0028] The second member 2 is supported by the support column 11 of the first member 1, but the second member 2 is not connected (in contact) with the sheet metal B and the first member 1 except for its outer peripheral edge and the support column 11 of the first member 1. The partition C2 formed between the opposing surfaces of the sheet metal B and the second member 2, and the partition C1 formed between the opposing surfaces of the second member 2 and the first member 1, are formed as air layers that are completely filled with air.

[0029] The distance between the first member 1 and the second member 2 is not particularly limited, but 5 to 50 mm is preferred. When the distance between the first member 1 and the second member 2 is within the above range, the soundproofing structure can be made thinner while maintaining the excellent soundproofing performance of the soundproofing structure, and the size of the vehicle's passenger compartment can be increased.

[0030] As shown in Figure 1, the second member 2 has countless through holes 21 that penetrate in the thickness direction, preferably at regular intervals, in the portion other than the portion connected to the connecting portion 112 of the support column 11 of the first member 1. The through holes 21 are formed on the entire surface of the second member 2, and the through holes 21 are formed in a grid pattern (the portion where straight lines drawn vertically and horizontally intersect in a square grid formed by arranging multiple squares vertically and horizontally with adjacent sides sharing each other). By forming the through holes 21 of the second member 2 in a grid pattern, sound waves caused by external noise that enter the space C of the soundproof structure A enter the multiple through holes 21 of the second member 2 almost equally. The sound waves caused by the noise vibrate the air inside the through holes 21, and sound can be effectively absorbed by the frictional viscous resistance between the air in the through holes 21 and the wall surface of the through holes 21. The soundproof structure A exhibits even better soundproofing performance. The through-holes 21 of the second member 2 do not need to be formed in a grid pattern, but may be formed in other forms such as a triangular grid pattern (in a triangular grid formed by arranging multiple equilateral triangles vertically and horizontally with adjacent sides sharing each other, the through-holes 21 are the vertices of each equilateral triangle in the triangular grid). The through-holes 21 of the second member 2 may be formed during the molding of the second member 2, or they may be formed in a non-perforated plate-like body by known means such as punching or drilling.

[0031] The through-hole 21 formed in the second member 2 gradually decreases in size from the outside to the inside. That is, the through-hole 21 is formed such that the opening area (the opening area of ​​the cross-section along the surface direction of the second member 2) gradually decreases from its outer opening end to its inner opening end. By forming the through-hole 21 in this way, which gradually decreases in size from the outside to the inside, the frictional viscous resistance between the air in the through-hole 21 and the wall surface of the through-hole 21 is further increased, allowing for effective sound absorption, and the soundproofing structure has superior soundproofing properties.

[0032] The cross-section of the through-hole 21 of the second member 2 along the surface direction of the second member 2 is not particularly limited and can be a circular shape such as a perfect circle or ellipse, or a polygon such as a triangle or quadrilateral, but a circular shape is preferred because it can more effectively generate frictional viscous resistance between the air in the through-hole 21 and the wall surface of the through-hole 21.

[0033] The distance between adjacent through-holes 21, 21 in the second member 2 is preferably 1 to 50 mm, more preferably 5 to 45 mm, and more preferably 10 to 35 mm. When the distance between adjacent through-holes 21, 21 in the second member 2 is within the above range, sound waves caused by external noise that have entered the soundproof structure A can smoothly enter the through-holes 21, creating frictional viscous resistance between the air in the through-hole 21 portion and the wall surface of the through-hole 21, thereby effectively absorbing sound, and the soundproof structure has superior soundproofing properties. The distance between through-holes 21, 21 refers to the shortest distance (pitch) between the centers P, P of the smallest perfect circles that can surround the opening ends of the through-holes in adjacent through-holes. Adjacent through-holes 21 are defined as two through-holes 21, 21 that are adjacent to each other when the opening end of another through-hole 21 does not lie on the straight line connecting the centers P, P of two through-holes 21, 21.

[0034] The outer opening diameter of the through-hole 21 in the second member 2 is preferably 1 to 15 mm, more preferably 2 to 13 mm, and even more preferably 3 to 10 mm. When the outer opening diameter of the through-hole 21 in the second member 2 is within the above range, the frictional viscous resistance between the air in the through-hole 21 and the wall surface of the through-hole 21 can be generated, effectively absorbing sound, and the soundproofing structure has superior soundproofing properties.

[0035] The inner opening diameter of the through-hole 21 in the second member 2 is preferably 0.5 to 8 mm, more preferably 1 to 6 mm, and even more preferably 2 to 5 mm. When the inner opening diameter of the through-hole 21 in the second member 2 is within the above range, the frictional viscous resistance between the air in the through-hole 21 and the wall surface of the through-hole 21 can be generated, effectively absorbing sound, and the soundproofing structure has even better soundproofing properties.

[0036] The diameter of the opening end of the through hole 21 in the second member 2 refers to the smallest diameter of a perfect circle that can enclose the opening end of the through hole.

[0037] The total ratio of the outer opening end area of ​​the through hole 21 in the second member 2 is preferably 1 to 80%, more preferably 2 to 65%, more preferably 2 to 55%, more preferably 2.5 to 30%, and more preferably 2.6 to 15% of the total area of ​​the outer surface of the second member 2. When the total ratio of the outer opening end area of ​​the through hole 21 in the second member 2 is within the above range, the frictional viscous resistance between the air in the through hole 21 and the wall surface of the through hole 21 can be generated, effectively absorbing sound, and the soundproofing structure has superior soundproofing properties.

[0038] The total ratio of the inner opening end area in the through hole 21 of the second member 2 is preferably 0.5 to 80%, more preferably 0.6 to 65%, more preferably 0.7 to 20%, and more preferably 0.75 to 10% of the total area of ​​the outer surface of the second member 2. When the total ratio of the inner opening end area in the through hole 21 of the second member 2 is within the above range, the frictional viscous resistance between the air in the through hole 21 and the wall surface of the through hole 21 can be generated, effectively absorbing sound, and the soundproofing structure has even better soundproofing properties.

[0039] In the above-described soundproofing structure A, the second member 2 is disposed within a space C formed between the opposing surfaces of the sheet metal B and the first member 1, and the space C is divided in an inward-outward direction into two inner compartments C1 and an outer compartment C2. An air layer is formed throughout the inner compartment C1 and the outer compartment C2.

[0040] Noise is generated outside the vehicle while it is in motion. Examples of noise include friction or impact noise between the tires and the road when the vehicle is traveling on the road, rolling noise, friction noise, or impact noise between the wheels and the tracks when the train is traveling on the tracks, engine noise, and the sound of the electric motors.

[0041] When the sound wave caused by the above noise passes through the sheet metal B of the sound insulation structure A and enters the sound insulation structure A, the sound wave enters the through-hole 21 formed in the second member 2, vibrates the air in the through-hole 21, and is absorbed by the frictional viscous resistance between the air in the portion of the through-hole 21 and the wall surface of the through-hole 21.

[0042] In the case where the through-hole 21 of the second member 2 is formed to gradually decrease from the outside toward the inside, the above frictional viscous resistance can be further increased, and the above sound wave can be more effectively attenuated and absorbed.

[0043] The sound wave that has passed through the second member 2 is attenuated and absorbed by repeated reflection between the opposing surfaces of the first member 1 and the second member 2, since the interior of the partition portion C1 formed between the opposing surfaces of the first member 1 and the second member 2 is filled with air, and also re-enters the through-hole 21 in the second member 2, and is absorbed by the frictional viscous resistance between the air in the portion of the through-hole 21 and the wall surface of the through-hole 21.

[0044] As described above, the sound insulation structure A can reduce the transmission of noise generated outside the vehicle, particularly noise with a frequency of 600 Hz or less (preferably 550 Hz or less, more preferably 500 Hz or less) into the vehicle interior of the vehicle, and can achieve quietness inside the vehicle. The sound insulation structure A can reduce the transmission of noise generated outside the vehicle, particularly noise with a frequency of 100 to 600 Hz (preferably 100 to 550 Hz, more preferably 100 to 500 Hz) into the vehicle interior of the vehicle, and can achieve quietness inside the vehicle.

[0045] In the sound insulation structure A, the first member 1 disposed on the inner side of the sheet metal B can be used as an interior material of the vehicle compartment, and the sound insulation structure can be constructed by utilizing the interior material constituting the vehicle compartment. Therefore, the number of members constituting the sound insulation structure A can be reduced, and the weight of the sound insulation structure A can be reduced.

[0046] Since the sound insulation structure A utilizes the space formed between the sheet metal B and the first member 1, the sound insulation structure A can be made thinner, and a vehicle compartment of a vehicle that has excellent sound insulation performance and a wide space can be formed.

[0047] In the above-described soundproofing structure A, the case in which a through hole 21 is formed in the second member was explained, but the through hole does not necessarily have to be formed in the second member.

[0048] (Examples 1-20) In order to evaluate the sound insulation performance of the above sound insulation structure A, the first member 1 and the second member 2 shown below were prepared and test specimens were made.

[0049] As the first component 1, a circular, non-foamed polypropylene sheet with a diameter of 100 mm and the thickness shown in Table 1 was prepared.

[0050] As the second component 2, a circular polypropylene closed-cell foamed sheet or non-foamed sheet with a diameter of 100 mm and the thickness shown in Table 1 was prepared. The foaming ratio of the second component 2 is shown in Table 1. In the case of the second component being a non-foamed sheet, the foaming ratio is indicated as "1x".

[0051] Four support columns 11 were provided projecting outward from the outer peripheral edge of the outer surface of the first member 1. The tip surfaces of the support columns 11 were formed as receiving surfaces 111 for receiving the second member 2, and connecting portions 112 projected outward from the center of the receiving surface 111. An enlarged head 112a, having a larger cross-sectional shape than the cross-sectional shape of the connecting portion 112, was formed at the tip of the connecting portion 112.

[0052] The connection portions 112 of the four support columns 11 of the first member 1 were penetrated through the second member 2 in the thickness direction. The second member 2 was held and fixed by being sandwiched between the receiving surface 111 of the support column 11 and the enlarged head portion 112a of the connection portion 112 of the support column 11. The first member 1 and the second member 2 were fixed parallel to each other, separated by the height dimension of the support column 11 to its receiving surface 111. The separation dimension between the opposing surfaces of the first member 1 and the second member 2 is shown in the "Air Layer" column of "Partition C1" in Table 1.

[0053] The second member 2 had through-holes 21 formed in a grid pattern, penetrating in both the inward and outward directions. The multiple through-holes 21 were formed at equal intervals in both the vertical and horizontal directions. For through-holes 21, 21 that were adjacent to each other in the vertical and horizontal directions, the distance between the centers of the outer openings of the through-holes is recorded in the "Through-hole distance" column of Table 1. The distance between the centers of the inner openings of the through-holes was the same as the distance between the centers of the outer openings of the through-holes.

[0054] The cross-section of the second member 2 along the planar direction in the through-hole 21 was formed in a circular shape, gradually and continuously decreasing in diameter from the outside to the inside. The peripheral wall surface of the through-hole 21 was formed as a smooth surface. The diameters of the outer and inner opening ends of the through-hole are listed in the "Outer" and "Inner" columns of "Opening End Diameter" under "Through-hole" in Table 1, respectively.

[0055] In the through-hole 21 of the second member 2, the total ratio of the outer opening end area and the total ratio of the inner opening end area are recorded in the "Outer" and "Inner" columns of the "Total Ratio" in the "Through-hole" section of Table 1, respectively.

[0056] (Comparative Example 1) A test specimen was prepared by spot welding a 16 mm thick fibrous material (3M Corporation product name "Thinsulate® sound-absorbing and heat-insulating material TC1503") to the outer surface of the first member 1 of Example 1.

[0057] The normal incidence transmission loss was measured using the above-mentioned test specimen in the following manner, and the results are shown in Figures 3 to 7.

[0058] (Normal incidence sound transmission loss) Using an acoustic tube with an inner diameter of 100 mm, the normal incidence transmission loss was measured at frequencies from 100 to 600 Hz in accordance with ASTM E2611. The measurement device used was the commercially available product "Normal incidence sound absorption coefficient / transmission loss measurement system WinZacMTX" from Nippon Acoustic Engineering Co., Ltd. The measurement results are shown in Figure 3.

[0059] The legends in Figures 3 to 7 describe, in order, the name of the example or comparative example, whether or not the first member is foamed (the thickness of the first member is shown in parentheses), whether or not the second member is foamed (the thickness of the second member and the foaming ratio are shown in parentheses), the distance between the opposing surfaces of the first member 1 and the second member 2 (the thickness of the air layer), and the through-hole distance (the distance between the centers of the outer (inner) opening ends of the through-hole).

[0060] Although the above test specimen does not have a configuration corresponding to the sheet metal B of soundproof structure A, the above test can be equivalent to the degree to which sound waves caused by external noise that have penetrated sheet metal B and entered soundproof structure A are transmitted through the first member, and has a correlation with the soundproofing performance of soundproof structure A. Therefore, the soundproofing performance of soundproof structure A can be evaluated by the above measurement.

[0061]

[0062] This invention can effectively block noise from outside the vehicle and reduce noise entering the vehicle, making it possible to manufacture a vehicle with a quiet interior.

[0063] (Cross-reference of related applications) This application claims priority under Japanese Patent Application No. 2025-68441, filed on 17 April 2025, and the disclosures of this application are incorporated herein by reference to those applications in their entirety.

[0064] 1. First member 11. Support column 2. Second member 21. Through hole 111. Receiving surface 112. Connection part 112a. Enlarged head A. Soundproofing structure B. Sheet metal C. Space C1. Compartment C2. Compartment

Claims

1. A soundproofing structure characterized by comprising: a sheet metal forming the exterior body of a vehicle; a first member disposed inside the sheet metal; and a second member disposed in a space formed between the opposing surfaces of the sheet metal and the first member, and dividing the space in an inward and outward direction.

2. The soundproofing structure according to claim 1, characterized in that the second member has a through hole that penetrates in the thickness direction thereof.

3. The soundproofing structure according to claim 2, characterized in that the through-hole of the second member becomes smaller from the outside to the inside.

4. The soundproofing structure according to claim 1 or 2, characterized in that the first member does not have a through hole formed in the thickness direction thereof.

5. The soundproofing structure according to claim 1 or 2, characterized in that the second member is fixed to a support column protruding from the first member.

6. The soundproofing structure according to claim 1 or 2, characterized in that the second member is made of foam.

7. The soundproofing structure according to claim 6, characterized in that the foam is a closed-cell foam.

8. The soundproofing structure according to claim 5, characterized in that the tip surface of the support column is a receiving surface for receiving the second member, and the support column has a connecting portion that protrudes from the receiving surface and is fixed in a state that penetrates the second member.

9. The soundproofing structure according to claim 1 or 2, characterized in that the distance between the first member and the second member is 5 to 50 mm.

10. The soundproofing structure according to claim 2, characterized in that the distance between adjacent through holes in the second member is 1 to 50 mm.

11. The soundproofing structure according to claim 2, characterized in that, in the through hole of the second member, the outer opening end diameter is 1 to 15 mm, and the inner opening end diameter is 0.5 to 8 mm.

12. The soundproofing structure according to claim 2 or 3, characterized in that, in the through-hole of the second member, the total ratio of the outer opening end area is 1 to 80% of the entire outer surface of the second member, and the total ratio of the inner opening end area is 0.5 to 80% of the entire inner surface of the second member.

13. The soundproofing structure according to claim 5, characterized in that the second member is not connected to the sheet metal and the first member except for its outer peripheral edge and the support column.

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