Soundproof ventilation channel

Abstract

The present invention effectively reduces low-frequency noise caused by the vibration of a peripheral wall of an air passage.　The present invention is a soundproofed air passage that comprises: an air passage that has an open end; and a soundproofing structure for sound emitted from the air passage. The soundproofing structure has a vibration suppression part that is provided to the surface of a peripheral wall that surrounds the air passage. When m and n are natural numbers no greater than 4, λ is the wavelength of sound of a frequency that matches the m-ary natural frequency of the peripheral wall alone, and L1 is the distance of any portion of the air passage from the open end on an imaginary line that passes through the center position of a cross-section that intersects the extension direction of the air passage, the vibration suppression part is within the area in which L1 is at least (4n-3)×λ / 8 but no more than (4n-1)×λ / 8.

Description

[Technical Field]

[0001] The present invention relates to an air passage with a soundproof structure, and more particularly to an air passage with a soundproof structure that has a soundproof structure that suppresses sound emitted from an air passage having an open end. [Background technology]

[0002] In an air passage such as a duct, it is required to reduce noise emitted from the air passage while allowing airflow (wind) to flow. One example of an air passage with a soundproof structure is the duct structure described in Patent Document 1. This duct structure is configured by attaching a soft urethane foam sheet material with a film laminated on one side to an opening provided in a duct body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-156054 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described duct structure, noise passing through the duct body is reduced by having a soft urethane foam sheet material (i.e., sound-absorbing material) absorb sound through the opening of the duct body. However, noise emitted from the duct is not limited to sound passing through the duct, but also includes, for example, sound generated due to vibration of the duct housing. Therefore, in order to sufficiently reduce the noise emitted from the duct, it is necessary to effectively reduce noise caused by duct vibration. However, it is generally difficult to reduce noise caused by vibration using sound-absorbing material provided near the opening of the duct body.

[0005] The present invention has been made in consideration of the above circumstances, and aims to solve the problems of the above-mentioned conventional technology and provide an air passage with a soundproof structure that can effectively reduce noise caused by vibration of the surrounding walls of the air passage. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention has the following configuration. [1] A soundproof ventilation passage having an open end and a soundproofing structure for sound emitted from the ventilation passage, wherein the soundproofing structure has a vibration suppression part provided on the surface of a peripheral wall surrounding the ventilation passage, and wherein m and n are natural numbers less than or equal to 4, λ is the wavelength of sound having a frequency that coincides with the mth-order natural frequency of the peripheral wall alone, and L1 is the distance from the open end of each part of the ventilation passage on a virtual line passing through the center position of the cross section that intersects with the extension direction of the ventilation passage, and the vibration suppression part is located within a range where the distance L1 satisfies the following formula (1). (4n-3) / 8×λ≦L1≦(4n-1) / 8×λ (1) [2] The soundproof ventilation passage described in [1], wherein at least a portion of the vibration suppression portion is provided at a location on the surface of the peripheral wall where the distance L1 is (2n-1) / 4×λ. [3] A soundproof ventilation channel according to [1] or [2], wherein the open end is located at the outlet of the ventilation channel. [4] An air passage with a soundproof structure described in any one of [1] to [3], wherein the air passage is bent, and when the distance along the imaginary line from the opening end to the bending position of the air passage is L2, the distance L2 is less than 5 / 4 × λ, and when the side away from the opening end is the upstream side, the vibration suppression unit is located upstream of the bending position of the air passage. [5] An air passage with a soundproof structure described in any one of [1] to [4], wherein the vibration suppression section includes a vibration-damping material attached to the surface of the peripheral wall. [6] The soundproof structure is an air passage with a soundproof structure described in any one of [1] to [5], which has a sound-absorbing section between the part of the air passage where the vibration suppression section is provided on the peripheral surface of the peripheral wall and the opening end. [7] The air passage is bent, and when the side away from the opening end is considered the upstream side, the vibration suppression section is provided upstream of the bend in the air passage, and the sound absorption section is provided downstream of the bend in the air passage. [6] An air passage with a soundproof structure as described in [6]. [8] An airway with a soundproof structure described in [6] or [7], wherein the sound-absorbing part includes a sound-absorbing material arranged adjacent to the airway, and the surface of the sound-absorbing material facing the airway is exposed to the airway, and the soundproof structure has a covering material that covers all surfaces of the sound-absorbing material other than the surface facing the airway. [9] An air passage with a soundproof structure described in any of [1] to [8], in which a vibration suppression part is provided on the part of the surface of the surrounding wall where the amount of displacement is greatest when the surrounding wall alone vibrates at the mth-order natural frequency.

[10] The soundproof ventilation passage according to [9], wherein the mth-order natural frequency of the peripheral wall alone is the first natural frequency of the peripheral wall alone.

[11] An airway with a soundproof structure as described in [9] or

[10] , wherein when multiple natural numbers correspond to the natural number m, the range in which the distance L1 satisfies formula (1) is determined for each of the multiple natural numbers, and the vibration suppression unit is respectively provided within the determined range for each of the multiple natural numbers.

[12] An air passage with a soundproof structure described in any one of [1] to

[11] , which satisfies the following formula (2), when the mth-order natural frequency of the peripheral wall alone is fa and the mth-order natural frequency of the peripheral wall with a vibration suppression portion provided on the surface is fb. 0.8≦fa / fb≦1.25 (2)

[13] An air passage with a soundproof structure described in any one of [1] to

[12] , in which the vibration suppression part is attached to a part of the outer peripheral surface of the peripheral wall.

[14] The soundproof ventilation passage according to

[13] , wherein the vibration suppression section is a laminate of two or more layers including a layer made of vibration-damping material and a layer made of a vibration shielding plate.

[15] An air passage with a soundproof structure described in any of [1] to

[14] , wherein the vibration suppression part is a two-layer laminate, the laminate having a first layer made of a metal plate and a second layer containing an adhesive and a vibration-damping material, and is attached to the surface of the surrounding wall via the second layer. [Effects of the Invention]

[0007] According to the present invention, an air passage with a soundproof structure is realized that can effectively reduce noise caused by vibration of the peripheral wall of the air passage. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view showing an air passage with a soundproof structure according to an embodiment of the present invention; [Figure 2] 2 is a cross-sectional view taken along the line AA in FIG. 1. [Figure 3] FIG. 2 is a cross-sectional view of a vibration suppressor according to an embodiment of the present invention. [Figure 4] FIG. 4 is a plan view showing the surface of a peripheral wall on which a vibration suppressing portion is provided. [Figure 5] 10A and 10B are diagrams illustrating modified examples of the vibration suppressor. [Figure 6] 10A and 10B are diagrams showing an air passage with a soundproof structure according to another embodiment of the present invention. [Figure 7] 10 is a diagram showing the results of a simulation of sound radiated from a duct in Reference Example 1. FIG. [Figure 8] FIG. 10 is a diagram showing the measurement results of the sound radiated from the duct in Reference Example 1. [Figure 9] FIG. 10 is a diagram showing the results of a simulation performed to analyze the measurement results in Reference Example 1. [Figure 10] 10 is a diagram showing calculation results for the sound transmittance at the duct opening (broken line) and the vibration displacement of the entire duct housing (solid line) in Reference Example 1. FIG. [Figure 11] FIG. 10 is a diagram showing the measurement results of the sound radiated from the duct in Comparative Example 1. [Figure 12] FIG. 4 is a diagram showing the measurement results of the sound radiated from the duct in Example 1. [Figure 13] FIG. 10 is a diagram showing the measurement results of the sound radiated from the duct in Example 2. [Figure 14] FIG. 10 is a plan view showing the arrangement position of the vibration-damping material in Example 3. [Figure 15] FIG. 10 is a diagram showing the measurement results of the sound radiated from the duct in Example 3. [Figure 16] FIG. 10 is a diagram showing the measurement results of the sound radiated from the duct in Example 4. [Figure 17] 10 is a diagram showing the results of a simulation of sound radiated from a duct in Reference Example 2. FIG. [Figure 18] FIG. 10 is a diagram showing the measurement results of the sound radiated from the duct in Comparative Example 2. [Figure 19] FIG. 10 is a diagram showing the measurement results of the sound radiated from the duct in Example 5. [Figure 20] FIG. 13 is a diagram showing the measurement results of the sound radiated from the duct in Example 6. [Figure 21] FIG. 10 is a diagram showing the measurement results of the sound radiated from the duct in Comparative Example 3. [Figure 22] FIG. 13 is a diagram showing the measurement results of the sound radiated from the duct in Example 7. [Figure 23] FIG. 13 is a diagram showing the measurement results of the sound radiated from the duct in Example 8. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The sound-insulating structure-equipped ventilation passage of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0010] It should be noted that the following embodiment is merely an example given to facilitate understanding of the present invention and is not intended to limit the present invention, and that the present invention may be modified or improved from the following embodiment without departing from the spirit of the present invention. Furthermore, the material and shape of each member used to implement the present invention can be set arbitrarily depending on the application of the present invention and the state of the art at the time of implementing the present invention. The present invention also includes equivalents thereof.

[0011] In addition, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower limit and upper limit. In this specification, "orthogonal" and "parallel" include the range of tolerance allowed in the technical field to which the present invention pertains. For example, "orthogonal" and "parallel" mean that the deviation is within a range of less than ±10° from the strict orthogonal or parallel state. The deviation from the strict orthogonal or parallel state is preferably 5° or less, and more preferably 3° or less. In addition, in this specification, the meanings of "same," "identical," and "equal" may include a range of error generally accepted in the technical field to which the present invention belongs. In addition, in this specification, the meanings of "all," "any," and "entirely" include not only 100% but also the range of error generally accepted in the technical field to which the present invention pertains, and may include, for example, 99% or more, 95% or more, or 90% or more.

[0012] Furthermore, in the present invention, "soundproofing" is a concept that includes both sound insulation and sound absorption. Sound insulation means blocking sound, in other words, not allowing sound to pass through. Sound absorption means reducing reflected sound, or more simply, absorbing sound (acoustics). Furthermore, "vibration control" in the present invention means suppressing vibrations of a device to be controlled, and more specifically, reducing or attenuating vibrations by absorbing vibration energy.

[0013] [Example of the configuration of the soundproof ventilation passage of the present invention] The configuration of a soundproof structure-equipped air passage 10 according to one embodiment of the present invention (hereinafter referred to as this embodiment) will be described with reference to FIGS.

[0014] As shown in FIGS. 1 and 2, the soundproof structure-equipped air passage 10 according to this embodiment has an air passage 12 through which air current (wind) flows, and a soundproof structure 20 for preventing sound emitted from the air passage 12.

[0015] (Ventilation channel) The air passage 12 is, for example, an air conditioning duct, and is surrounded on all sides (more specifically, on all four sides) by a peripheral wall 14 that forms the housing of the duct. The use of the air passage 12 is not particularly limited, and may be, for example, air conditioning in a building, air cooling in electrical equipment, or air conditioning in vehicles such as automobiles and airplanes.

[0016] As shown in Fig. 1, the ventilation channel 12 has an open end 16 at its outlet (i.e., gas outlet). The open end 16 is the portion where the ventilation channel 12 connects to the outside of the ventilation channel 12 (external space). The shape of the open end 16 (opening shape) is, for example, rectangular, more specifically, oblong. However, the shape of the open end 16 is not particularly limited and may be circular, elliptical, quadrangle other than rectangular, polygon other than quadrangle, or irregular shape, etc.

[0017] The upstream end of the air passage 12 is connected to a blower or fan (not shown). Here, the upstream side is the upstream side in the direction in which gas (wind) flows through the air passage 12, i.e., the side away from the open end 16.

[0018] 1 and 2, the air passage 12 according to this embodiment is bent in an L shape from the viewpoint of miniaturization and space saving. That is, the extending direction of the air passage 12 changes by approximately 90 degrees midway. Here, the extending direction of the air passage 12 corresponds to the extending direction of an imaginary line I, which will be described later. The bending angle of the air passage 12 is not particularly limited, and may be less than 90 degrees or more than 90 degrees. The air passage 12 may also extend straight without bending.

[0019] The peripheral wall 14 of the air passage 12 is a rectangular tube. In other words, the cross section of each portion of the air passage 12 (strictly speaking, the cross section perpendicular to the extension direction of the air passage 12) is rectangular, more specifically, rectangular. However, the cross section of each portion of the air passage 12 is not particularly limited and may be circular, elliptical, a quadrangle other than a rectangle, a polygon other than a quadrangle, or an irregular shape. In this embodiment, the surface (outer peripheral surface) of the peripheral wall 14 is flat, more specifically, a rectangular flat surface. However, the present invention is not limited to this, and the surface of the peripheral wall 14 may be a curved surface.

[0020] In this embodiment, the peripheral wall 14 is made of a relatively lightweight material, specifically a relatively thin plate material. Examples of materials that can be used to form the peripheral wall 14 include metal materials, resin materials, reinforced plastic materials, and carbon fiber. Examples of metal materials include aluminum, titanium, magnesium, tungsten, iron, steel, chromium, chromium molybdenum, nichrome molybdenum, copper, and alloys such as hot-dip galvanized steel sheet (Steel Galvanized Cold Commercial: SGCC). Examples of resin materials include acrylic resin, polymethyl methacrylate, polycarbonate, polyamide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, ABS resin (acrylonitrile, flame-retardant ABS resin, butadiene, styrene copolymer synthetic resin), polypropylene, triacetylcellulose (TAC), polypropylene (PP), polyethylene (PE), polystyrene (PS), acrylic styrene acrylonitrile (ASA) resin, polyvinyl chloride (PVC) resin, and polylactic acid (PLA) resin. Examples of reinforced plastic materials include carbon fiber reinforced plastics (CFRP) and glass fiber reinforced plastics (GFRP). The peripheral wall 14 may be made of a material such as natural rubber, chloroprene rubber, butyl rubber, EPDM (ethylene propylene diene rubber), silicone rubber, or rubbers containing cross-linked structures of these.

[0021] The peripheral wall 14 is usually made up of a plurality of plates arranged along the extension direction of the air passage 12, and the entire peripheral wall 14 is formed by joining adjacent plates together. The entire peripheral wall 14 may be made of the same material. Alternatively, a portion of the peripheral wall 14 (for example, a portion located downstream of the bending position) may be made of a different material from the other portions, or the same material but with a different thickness.

[0022] (soundproof structure) The soundproof structure 20 is provided to reduce the volume of sound radiated from the entire air passage 12. In this embodiment, the peripheral wall 14 of the air passage 12 is made of thin plastic and metal plates to reduce weight, and therefore the sound radiated from the air passage 12 includes sound caused by vibration of the peripheral wall 14. In this embodiment, the soundproof structure 20 is configured to suppress not only sound emitted from the outlet (i.e., open end 16) of the air passage 12, but also noise caused by vibration of the peripheral wall 14. Specifically, as shown in FIGS. 1 and 2 , the soundproof structure 20 has a vibration suppression section 22 that suppresses vibration of the peripheral wall 14, and a sound absorbing section 30 that absorbs sound passing through the air passage 12.

[0023] <Vibration suppression part> The vibration suppression portion 22 is provided to suppress vibration of the peripheral wall 14 and suppress sound caused by the vibration (i.e., noise emitted from the peripheral wall 14). The vibration suppression portion 22 is provided on the surface of the peripheral wall 14 and includes a vibration-damping material 24 attached to the surface of the peripheral wall 14. The vibration-damping material 24 is a laminate of two or more layers, and in this embodiment, it is a two-layer laminate as shown in FIG. 3. The vibration-damping material 24 has a first layer 26 made of a metal plate and a second layer 28 containing an adhesive and a vibration-damping material, and is attached to the surface of the peripheral wall 14 via the adhesive second layer 28, or more precisely, is bonded.

[0024] The first layer 26 is a layer of plate having a relatively high hardness, specifically a vibration shielding plate, which shields (specifically, reflects) the vibration of the peripheral wall 14 and the sound transmitted through the peripheral wall 14. The hardness of the first layer 26 is expressed as Y×t, where Y and t are the Young's modulus and thickness of the plate material constituting the first layer 26, respectively. 3 The layer that constitutes the first layer 26 is desirably made of metal because it has a large Young's modulus and can be made thin. Examples of metal include aluminum, hot-dip galvanized steel plate (Steel Galvanized Cold Commercial (SGCC)), steel plate, and copper. The plate material that constitutes the first layer 26 is not limited to metal, and may be polycarbonate or acrylic plate.

[0025] The second layer 28 is a layer made of an adhesive and a vibration-damping material, and has a relatively large tan σ, which is an index of viscoelasticity, and is therefore able to absorb vibrations from the peripheral wall 14. The vibration-damping material that makes up the second layer 28 can be a rubber-based material, a resin-based material, a urethane-based material, or the like, and specific examples include butyl-based polymers, chlorinated polyethylene-based polymers, and acrylic-based polymers.

[0026] The laminate constituting the vibration-damping material 24 is not limited to two layers, but may be a laminate of three or more layers.

[0027] As the vibration-damping material 24 having the above-described configuration, for example, a constrained vibration-damping material can be used, and specific examples include Calmoon Sheet from Sekisui Chemical Co., Ltd., Legetrex from Nitto Denko Corporation, Ricocalm from Risho Kogyo Co., Ltd., Hayakawa Rubber Co., Ltd. Hayadamper, and EDM1000 from 3M Corporation.

[0028] The damping material 24 is not limited to a constrained type damping material, but may also be a non-constrained type damping material. The damping material 24 may also be a single-layer damping material, for example, made of damping rubber. Examples of damping materials made of damping rubber include Non-Brene Sheet NS from Hirakata Giken Co., Ltd. The damping material 24 may also be attached by adhesion to the surface of the peripheral wall 14, or may simply be placed on the surface of the peripheral wall 14.

[0029] The damping material 24 is attached to the surface (strictly speaking, the outer peripheral surface) of the peripheral wall 14, which has a rectangular cylindrical shape. More specifically, as shown in Figures 2 and 4, the damping material 24 is attached to the outer peripheral surface of a portion (for example, the upper edge portion) that constitutes one of the four sides of the cross section of the peripheral wall 14. As shown in Figure 4, the damping material 24 has a rectangular shape in plan view, more specifically, a rectangular outer shape. The outer shape of the damping material 24 is not limited to a rectangle, but from the perspective of ease of cutting, a simple shape is preferable, specifically, a quadrangle including a rectangle (rectangle and square), a circle, an ellipse, or a polygon other than a rectangle.

[0030] The damping material 24 is attached to a portion of the outer peripheral surface of the peripheral wall 14. More specifically, as shown in FIG. 4, the damping material 24 is attached only to a portion of the surface of the plate of the peripheral wall 14 to which the damping material 24 is attached (hereinafter referred to as the plate surface). The plate to which the damping material 24 is attached is a portion that forms one of the four sides of the cross section of the peripheral wall 14. Here, if the attachment area of ​​the damping material 24 is S1 and the area of ​​the plate surface is S0, then S1 / S0 × 100 (%) is preferably 25% or more and 50% or less. This numerical range is determined taking into consideration the fluctuation in the frequency of vibration (natural frequency) of the peripheral wall 14 due to the attachment of the damping material 24 while ensuring the vibration damping effect of the damping material 24 (see Examples 7 and 8 described below).

[0031] In this embodiment, from the viewpoint of ease of attachment of the vibration-damping material 24, the vibration-damping material 24 is attached to the outer peripheral surface of the peripheral wall 14 as described above, but this is not limited to this, and the vibration-damping material 24 may also be attached to the inner peripheral surface of the peripheral wall 14.

[0032] In this embodiment, the vibration-damping material 24 is provided as an example of the vibration suppression portion 22, but any structure other than the vibration-damping material 24 may be used as long as it is provided on the surface of the peripheral wall 14 to suppress vibration of the peripheral wall 14. For example, as shown in FIG. 5, a rib 40 protruding from the surface of the peripheral wall 14 may be used as the vibration suppression portion 22. That is, by providing the rib 40, the rigidity of the peripheral wall 14 in the vicinity of the rib 40 is increased, thereby suppressing vibration of the peripheral wall 14 and reducing noise caused by the vibration.

[0033] Furthermore, the vibration of the peripheral wall 14 may be suppressed by locally increasing the rigidity by bending the peripheral wall 14 to provide a bent portion or by beading the peripheral wall 14 to provide a linear raised portion. In this case, the bent portion or the raised portion on the bead corresponds to the vibration suppression portion 22.

[0034] The inventors of the present invention have found that the position on the surface of peripheral wall 14 where vibration suppression portion 22 is provided, more specifically, the attachment position of vibration-damping material 24, affects the amount of vibration suppression of peripheral wall 14. As a result, in this embodiment, in order to effectively reduce noise caused by vibration of peripheral wall 14, vibration suppression portion 22 is provided within a predetermined range on the surface of peripheral wall 14.

[0035] Specifically, when the distance from the opening end 16 on an imaginary line I passing through the center of the air passage 12 is L1, the vibration suppression section 22 is provided within a range in which the distance L1 satisfies the following formula (1). (4n-3) / 8×λ≦L1≦(4n-1) / 8×λ (1) Here, n is a natural number less than or equal to 4.

[0036] The imaginary line I is a line passing through the center position of the cross section of each part of the air passage 12 (the cross section intersecting with the extension direction of the air passage 12), and corresponds to the central axis of the air passage 12. If the cross section shape is a circle, the center position of the cross section is the center of the circle, and if the cross section shape is a polygon including a triangle and a rectangle, the center position is a position equidistant from each vertex of the polygon (in other words, the center of the circumscribing circle). In the following description, when simply referring to "distance," it refers to the distance from the opening end 16 on the imaginary line I unless otherwise specified.

[0037] In the above equation (1), λ is the wavelength of sound of a frequency that matches the mth-order (m is a natural number) natural frequency fa of the peripheral wall 14 alone, and its value is calculated by substituting the natural frequency fa and the speed of sound c0 into the following equation. λ=c0 / fa

[0038] In this embodiment, the wavelength λ is larger than the open end 16 of the air passage 12, and more specifically, is larger than twice the equivalent circle diameter of the open end 16.

[0039] The mth-order natural frequency fa of the peripheral wall 14 alone is the mth-order natural frequency of the peripheral wall 14 when the vibration suppression unit 22 is not provided. Here, m is a natural number equal to or less than 4, and in this embodiment, m=1. In other words, the natural frequency fa is the first natural frequency of the peripheral wall 14 alone, and the wavelength λ in equation (1) is the wavelength of sound having a frequency that coincides with the first natural frequency. Note that the natural frequency fa is determined by the size, thickness, material, and fixing method of the portion (plate material) of the peripheral wall 14 where the vibration suppression unit 22 is provided.

[0040] In this embodiment, the vibration suppression portion 22 is present on the surface of the peripheral wall 14 within the range in which the distance L1 satisfies equation (1), and specifically, the vibration damping material 24 is attached to the outer peripheral surface of the peripheral wall 14 within the above range.

[0041] Incidentally, "the vibration suppression section 22 is present within a range in which the distance L1 satisfies equation (1)" means that in the extension direction of the air passage 12 (in other words, the extension direction on the virtual line I), part or all of the vibration suppression section 22 is located within a range in which the distance L1 satisfies equation (1).

[0042] The number of vibration suppression portions 22, more specifically the number of vibration-damping materials 24 or ribs 40, etc., that are provided within the range in which the distance L1 satisfies formula (1) is not particularly limited, and may be only one within the above range, or two or more.

[0043] The reason why the presence of vibration suppressing portion 22 within the range in which distance L1 satisfies formula (1) makes it possible to effectively reduce noise resulting from vibration of peripheral wall 14 will be explained below.

[0044] At the open end 16 of the air passage 12, the acoustic impedance changes significantly and the degree of change is steep. As a result, sound is reflected near the open end 16, and the degree of reflection increases as the sound frequency decreases. On the other hand, high-frequency sound easily passes through the open end 16. Note that sound reflection at the open end 16 can occur when the wavelength λ of the sound is greater than twice the equivalent circular diameter of the open end 16, in other words, when the sound is low-frequency.

[0045] At open end 16, the phase of the sound changes due to reflection, and this phase change causes the open end (strictly speaking, a position located a distance away from open end 16 that corresponds to the open end correction) to become a node of sound pressure, in other words, an antinode of local particle velocity. In other words, the sound (incident wave) traveling from the upstream side of air passage 12 toward open end 16 and the sound (reflected wave) reflected at open end 16 interfere with each other, forming an acoustic mode (standing wave) near open end 16 of air passage 12.

[0046] The formation of an acoustic mode causes stress to act on various parts of the peripheral wall 14 of the air passage 12. The distribution of stress coincides with the distribution of sound pressure within the air passage 12. That is, at antinode positions within the air passage 12 where sound pressure is high, the stress acting on the peripheral wall 14 increases, making the peripheral wall 14 more likely to vibrate at those positions.

[0047] On the other hand, the open end is the position where the local particle velocity is maximum and corresponds to a node of sound pressure, so the vibration of the peripheral wall 14 is small at that position. Therefore, a position slightly away from the open end, specifically a position a distance from the open end 16 that is approximately (2n-1) / 4×λ, becomes an antinode of sound pressure. At such a position, the vibration of the peripheral wall 14 tends to increase, and the radiated sound caused by the vibration tends to increase.

[0048] Incidentally, due to the effects of sound radiation due to absorption and vibration within the air passage 12, or the loss of sound wave coherence, sound interference decreases with distance from the open end 16. For this reason, among the positions where the antinodes of sound pressure are located, that is, positions where the distance is (2n-1) / 4×λ, positions where the natural number n is smaller are more likely to vibrate.

[0049] On the other hand, there are few cases where the peripheral wall 14 is made of a single plate material, and in most cases the peripheral wall 14 is made up of an array of multiple plate materials. Also, for reasons such as improving rigidity, the thickness of the plate materials (beams, etc.) that make up the peripheral wall 14 may be increased or a support mechanism for the plate materials may be provided. The thicker plate portions and the portions of the peripheral wall 14 that are provided with a support mechanism act as fixed ends during vibration.

[0050] In particular, in the air passage 12 having a bend as in this embodiment, the plate thickness is increased at the bend position, or the plate material is bent at the bend position. Therefore, on the upstream side and downstream side of the bend position, the plate material constituting the peripheral wall 14 becomes independent vibrating plates. Then, the independent upstream and downstream vibrating plates each have a large vibration amount (amount of displacement) at their respective natural frequencies.

[0051] Due to the coupling between the above-mentioned acoustic mode and the behavior (vibration) of the diaphragm in the peripheral wall 14, low-frequency sound is reflected near the open end 16, which makes it easier to form an acoustic mode and, as a result, makes it easier for the peripheral wall 14 to vibrate. The formation of an acoustic mode does not depend on whether or not there is a bend in the air passage 12, and so an acoustic mode can also be formed in an air passage 12 that does not have a bend. Also, even in an air passage 12 that does not have a bend, the vibration amount tends to increase at a position that is a distance from the open end 16 of approximately (2n-1) / 4×λ, i.e., at the antinode of the sound pressure.

[0052] In light of the above, in this embodiment, positions shifted by λ / 8 upstream and downstream from the position where the distance is (2n-1) / 4×λ are identified, i.e., a position where the distance is (4n-3) / 8×λ and a position where the distance is (4n-1) / 8×λ. Then, vibration suppression unit 22 is provided on the surface of peripheral wall 14 so that it exists within a range between the two identified positions, that is, within a range where distance L1 satisfies equation (1). This effectively suppresses vibration of peripheral wall 14, and effectively reduces low-frequency noise caused by the vibration.

[0053] Furthermore, it is preferable that at least a portion of vibration suppression portion 22 (strictly speaking, vibration-damping material 24) is provided at a location on the surface of peripheral wall 14 where distance L1 is (2n-1)×λ / 4. This is because this location corresponds to the position of the antinode of sound pressure in the acoustic mode.

[0054] In this embodiment, the air passage 12 is bent at a position where the distance from the opening end 16 is less than 5 / 4×λ. In other words, when the distance from the opening end 16 to the bending position of the air passage 12 along the imaginary line I is L2, the distance L2 is less than 5 / 4×λ. Here, the bending position of the air passage 12 coincides with the bending position of the imaginary line I.

[0055] 1 and 2, in this embodiment, the vibration suppression unit 22 is provided upstream of the bending position of the air passage 12. In particular, in this embodiment, the distance L2 is less than ¼ × λ, and the antinode of the sound pressure in the acoustic mode is located upstream of the bending position. Therefore, the peripheral wall 14 is more likely to vibrate upstream of the bending position. Therefore, by providing the vibration suppression unit 22 upstream of the bending position, the vibration of the peripheral wall 14 can be more effectively suppressed. As a result, low-frequency sound caused by the vibration of the peripheral wall 14 can be more effectively suppressed.

[0056] From the viewpoint of more effectively suppressing vibration of the peripheral wall 14, it is preferable that the vibration suppression portion 22 is provided at a portion of the surface of the peripheral wall 14 where the amount of displacement is greatest. Here, the portion where the amount of displacement is greatest refers to a portion of the surface of the peripheral wall 14 where the amount of displacement (amount of vibration, or more simply, the amplitude during vibration) is greatest when the peripheral wall 14 vibrates at the mth-order natural frequency of the peripheral wall 14 alone (for example, the first natural frequency). The natural frequency and amplitude during vibration of each peripheral wall 14 can be determined by measurement experiments employing various natural vibration analysis methods (for example, modal analysis in which vibration is excited by an impulse hammer and the amplitude at each position is measured with a displacement meter), or by natural vibration calculations of structural mechanics calculations using the finite element method or the like.

[0057] Furthermore, although the provision of vibration suppression portion 22 on the surface changes the natural frequency of peripheral wall 14, it is preferable that the amount of change be within a certain range. For example, if the m-th order natural frequency of peripheral wall 14 with vibration suppression portion 22 provided on the surface is denoted as fb, it is preferable that natural frequency fb satisfy the following equation (2) in relation to the m-th order natural frequency fa of peripheral wall 14 alone. 0.8≦fa / fb≦1.25 (2) The numerical range shown in equation (2) corresponds to the condition where the natural frequency shifts to the next band in the 1 / 3 octave band evaluation. A shift in the natural frequency to the next band is undesirable from the viewpoint of soundproofing, as it makes it easier to detect changes in sound quality.

[0058] In addition, in the above-described embodiment, m=1, that is, the wavelength λ is calculated from the first natural frequency of the peripheral wall 14 alone, and the range of the distance L1 is derived from the calculated λ and equation (1), and the vibration suppression section 22 is provided on the surface of the peripheral wall 14 within the derived range.

[0059] Meanwhile, since the natural number m includes multiple natural numbers including 1 (specifically, m=1, 2, 3, 4), the range in which distance L1 satisfies formula (1) can be determined for each of the multiple natural numbers m. In this case, vibration suppression units 22 may be provided within the range determined for each natural number. For example, if the natural number m is 1 to 3, as shown in FIG. 6, vibration suppression unit 22A may be provided within the range when m=1, vibration suppression unit 22B may be provided within the range when m=2, and vibration suppression unit 22C may be provided within the range when m=3. FIG. 6 is a diagram showing a soundproof structure-equipped air passage 10x according to a modified example.

[0060] Similarly, the position where the vibration displacement amount is maximum on the surface of peripheral wall 14 (hereinafter referred to as maximum displacement amount position) can be determined for each of a plurality of natural numbers. Therefore, vibration suppression section 22 may be provided at each of the maximum displacement amount positions determined for each natural number.

[0061] <Sound absorption section> The sound absorbing unit 30 is a device or structure that absorbs sound waves. As shown in Fig. 2, the sound absorbing unit 30 of this embodiment is disposed in the air passage 12 between the portion where the vibration suppressing unit 22 is provided on the outer peripheral surface of the peripheral wall 14 and the open end 16.

[0062] More specifically, in this embodiment, the vibration suppression section 22 is provided upstream of the bending position of the air passage 12, and the sound absorbing section 30 is provided downstream of the bending position. This is because, considering that the sound absorbing section 30 functions well at a position in the air passage 12 where the particle velocity is high, it is desirable to place the sound absorbing section 30 near the open end 16 where the particle velocity is high.

[0063] Furthermore, the vibration suppression section 22 is used to suppress vibration of the peripheral wall 14 caused by low-frequency sound reflected at the open end 16, thereby reducing the low-frequency radiated sound resulting from this vibration. In contrast, the sound absorbing section 30 is used to reduce high-frequency sound that passes through the open end 16. The reflection of high-frequency sound at the open end 16 is small, which reduces interference between the incident and reflected waves of high-frequency sound. As a result, vibration of the peripheral wall 14 due to the reflection of high-frequency sound is less likely to occur. For this reason, the sound absorbing section 30 is a more effective means of reducing high-frequency sound than the vibration suppression section 22.

[0064] 2, the sound absorbing section 30 of this embodiment includes a sound absorbing material 32 arranged adjacent to the air passage 12. Specifically, an open portion 18 for exposure (specifically, a through hole) is formed in the peripheral wall 14 of the air passage 12 in a portion located between the bending position of the air passage 12 and the open end 16. The sound absorbing material 32 is arranged along the peripheral wall 14 so that part of its surface (specifically, the surface facing the air passage 12) faces the inside of the air passage 12 through the open portion 18.

[0065] The sound-absorbing material 32 absorbs high-frequency sound propagating through the air passage 12 through the open portion 18. All surfaces of the sound-absorbing material 32 except the surface facing the air passage 12 are covered with the covering material 34. In other words, the sound-absorbing material 32 is housed in a closed space located on the rear side of the sound-absorbing material 32 (the side opposite the air passage 12). By covering and closing the rear side of the sound-absorbing material 32 with the covering material 34 in this manner, it is possible to prevent sound from leaking out from the sound-absorbing material 32.

[0066] As the sound-absorbing material 32, any known sound-absorbing material that absorbs sound by converting sound energy into thermal energy can be used as appropriate. Examples of the sound-absorbing material 32 include foams, foam materials, and nonwoven fabric sound-absorbing materials. Specific examples of foams and foam materials include urethane foam such as Calmflex F from Inoac Corporation and urethane foam from Hikari Corporation, soft urethane foam, ceramic particle sintered materials, phenolic foam, melamine foam, polyamide foam, and the like. Specific examples of nonwoven fabric sound-absorbing materials include microfiber nonwoven fabrics such as Thinsulate from 3M Corporation, polyester nonwoven fabrics (including those with a two-layer structure having a thin, high-density surface nonwoven fabric and a low-density backing nonwoven fabric) such as White Qon from Tokyo Bouon Co., Ltd. and QonPET from Bridgestone KBG, plastic nonwoven fabrics such as acrylic fiber nonwoven fabrics, natural fiber nonwoven fabrics such as wool and felt, metal nonwoven fabrics, and glass nonwoven fabrics. In addition to the above, various known sound-absorbing materials such as sound-absorbing materials made of materials containing minute air particles, specifically sound-absorbing materials made of glass wool, rock wool, and nanofiber fibers, can be used as the sound-absorbing material 32. Examples of nanofiber fibers include silica nanofiber and acrylic nanofiber such as XAI manufactured by Mitsubishi Chemical Corporation. Furthermore, a plate or film with numerous through holes of about 100 μm in diameter, such as a micro-perforated plate, can be used as the sound-absorbing material 32. Sound can be absorbed by such a sound-absorbing material and the space behind it. Examples of micro-perforated plates include aluminum micro-perforated plates such as Suohno manufactured by Daiken Corporation, and polyvinyl chloride resin micro-perforated plates such as DiNoc manufactured by 3M.

[0067] The covering material 34 may be made of the same material as the peripheral wall 14 of the ventilation path 12, or may be made of a different material from the peripheral wall 14. Examples of materials that can be used for the covering material 34 include metal materials, resin materials such as acrylic, ABS resin, and ASA resin, reinforced plastic materials, and carbon fiber. The material that makes up the covering material 34 may also be a plate material, a film material, a sheet material, or the like.

[0068] Furthermore, the sound-absorbing section 30 is not limited to the sound-absorbing material 32, but may include other mechanisms for absorbing sound, such as a plate-shaped or film-shaped sound absorber and a perforated plate sound absorber. A plate-shaped or film-shaped sound absorber resonates when sound of a frequency close to its resonant frequency is incident, and absorbs sound by converting the sound energy into thermal energy through internal losses in the plate or film. A perforated plate sound absorber is a type of resonator-type sound-absorbing structure, and when sound of the same frequency as the resonant frequency hits it, the air in the holes vibrates, and the viscous loss that occurs during this process converts the sound energy into thermal energy.

[0069] Furthermore, the sound absorbing material 32 or other sound absorbing mechanism is not limited to being provided outside the air passage 12 as shown in FIG.

[0070] The soundproof structure-equipped ventilation passage of the present invention has been described above using specific configuration examples, but the above configuration example is merely one example, and other configurations are also possible. For example, in the above-described configuration example, the air passage 12 is bent, but this is not limiting, and the air passage 12 may extend linearly. Even in this case, by providing the vibration suppression portion 22 on the surface of the peripheral wall 14 within a range in which the distance L1 satisfies the formula (1), it is possible to effectively suppress the vibration of the peripheral wall 14 and effectively reduce the low-frequency sound resulting from the vibration.

[0071] Furthermore, in the above-described configuration example, the open end 16 is the outlet of the air passage 12, but this is not limited to this. The open end may be provided at a midpoint of the air passage 12 (i.e., upstream of the outlet). Alternatively, the open end may be the upstream end of the air passage 12, i.e., the end connected to the blower and fan. In these cases, by providing the vibration suppression unit 22 at an appropriate position taking into account the distance from each open end, it is possible to effectively suppress vibration of the peripheral wall 14 and effectively reduce low-frequency noise resulting from that vibration.

[0072] Furthermore, in the above-described configuration example, the sound absorbing section 30 is provided downstream of the bending position of the air passage 12, but the configuration may also be such that the sound absorbing section 30 is not provided. However, if the sound absorbing section 30 is provided, it is possible to muffle (absorb) high-frequency sound passing through the open end 16, thereby more effectively muffling (reducing) sound radiated from the entire air passage 12. In this respect, the above-described configuration example is more effective. [Example]

[0073] The present invention will now be described in more detail with reference to examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. In other words, the scope of the present invention should not be construed as being limited by the following examples.

[0074] Prior to the Examples, as Reference Examples 1 and 2, simulations and measurement experiments were carried out on the sound emitted from a ventilation duct that was not provided with a soundproof structure.

[0075] (Reference example 1) A rectangular straight duct was used as a model of the air passage in Reference Example 1. The straight duct had a rectangular cross section of 14 mm x 60 mm and an open end on the outlet side.

[0076] <Simulation> In Reference Example 1, first, a simulation was performed to determine the sound volume radiated from the open end of the duct in a state where there was no vibration. The finite element method (COMSOL Multiphysics ver. 5.6) was used for the simulation calculation, and one end of the duct was set as the incident boundary for the plane wave, and the other end was set as the open radiation end (open end). In addition, in the simulation, the incident sound volume was set so that the energy was the same at all frequencies.

[0077] Figure 7 shows the radiated sound volume when there is no vibration. As can be seen from Figure 7, the radiated sound volume decreases at low frequencies because the sound is reflected at the open end, but increases as the frequency increases. The frequency at which the long side of the duct cross section (= 60 mm) is half the wavelength (λ / 2) is 2.85 kHz, and the radiated sound volume remains approximately constant at frequencies higher than that.

[0078] At the open end of the duct, there is a sudden change in area from the area inside the duct (cross-sectional area) to the nearly infinite area outside the duct. Therefore, at the open end of the duct, the acoustic impedance, which is inversely proportional to the cross-sectional area, changes suddenly. The larger the acoustic impedance ratio, the higher the sound reflection rate, so the reflection rate at the open end of the duct is high. In reality, however, perfect reflection does not occur due to interference between the ends of the duct in the longitudinal direction, and the shorter the wavelength (i.e., the higher the frequency), the higher the radiated volume. Therefore, the radiated volume for each frequency changes as shown in Figure 7.

[0079] <Measurement experiment> The above-mentioned straight duct with a rectangular cross section was molded from ABS (Acrylonitrile Butadiene Styrene) resin using a 3D printer manufactured by XYZ Printing. The cross section of the molded duct was 14 mm x 60 mm, and the duct length was 500 mm. In addition, to simulate the vibrating part of the duct housing (i.e., the peripheral wall), the thickness of the housing was set to 1.5 mm in the range from 60 mm to 240 mm away from the open end of the duct (i.e., the length range of 180 mm). The thickness of other parts was set to a sufficiently thick 10 mm. As described above, in the measurement experiment of Reference Example 1, a linear duct was created that had a vibration portion of 180 mm×60 mm and a vibration portion of 180 mm×14 mm within the above range.

[0080] A speaker was then placed at one end of the created straight duct (the end farthest from the vibrating part), and white noise was played from the speaker to measure the sound level radiated from the entire duct. The measurement of the sound level (noise volume) radiated from the entire duct was carried out in an anechoic chamber in accordance with known measurement procedures (specifically, ISO 3745:2012). During this measurement, the sound power level (i.e., radiated sound pressure level) was measured, including not only the sound emitted from the duct outlet but also the sound resulting from the duct vibration. The measurement results are shown in Figure 8. As can be seen from FIG. 8, unlike the simulation results shown in FIG. 7, peaks in the radiated sound volume were confirmed not only on the high frequency side but also on the low frequency side, centered in the confirmed range of 600 to 1000 Hz.

[0081] Furthermore, to analyze the above measurement results, a coupled structural acoustics simulation was performed using the finite element method, using a duct model with the same housing material and thickness as in the measurement experiment. In this case, to isolate the causes of radiated sound, the sound volume radiated by duct vibration and the sound volume radiated from the open end of the duct were analyzed separately. The analysis results are shown in Figure 9. As can be seen from Figure 9, at frequencies higher than approximately 1.5 kHz, the volume of sound radiated from the open end of the duct is large, a result consistent with the results shown in Figure 7. On the other hand, in the frequency band below approximately 1.5 kHz, it was found that the sound radiated from the open end becomes smaller, but the volume of sound radiated due to duct vibration becomes larger.

[0082] We also performed calculations to determine the vibration displacement of the entire duct housing. The calculation results are shown in Fig. 10. As can be seen from Figure 10, in the low frequency band where sound transmittance decreases at the open end of the duct (i.e. where sound reflection rate increases), the vibration displacement is about 10 times larger than at the high frequency band. From this result, it can be assumed that the sound radiated from the duct near the open end includes not only sound emitted from the open end, but also sound caused by vibration of the duct housing on the low frequency side. From the above, it was found that in order to effectively suppress sound radiated from a duct, it is necessary to suppress the vibration of the housing in the low frequency band.

[0083] (Comparative Example 1) In Comparative Example 1, a straight duct was fabricated in the same manner as in Reference Example 1. Furthermore, 40 mm-wide open areas (60 mm × 40 mm holes) were provided on two sides of the duct, within a distance of 10 to 50 mm from the open end of the duct. A sound-absorbing material "QonPET" manufactured by Bridgestone KBG Corporation was attached to each open area. The length, thickness, and width of this sound-absorbing material in the duct extension direction were 40 mm, 10 mm, and 60 mm, respectively. In addition, all surfaces of the sound-absorbing material except for the surface facing the duct were covered with a box-shaped body made of 5 mm thick acrylic plate. In other words, a sound-absorbing part with a closed back was installed near the open end of the duct (air passage).

[0084] Then, the sound radiated from the duct was measured using the same procedure as in the measurement experiment of Reference Example 1. The measurement results are shown in Figure 11. Note that in Figures 11 to 16, the measurement results of Reference Example 1 are shown by dashed lines for comparison. As can be seen from Figure 11, the radiated sound is reduced in the high-frequency band by the effect of the sound-absorbing material, but the reduction amount (quantity of silencing) is small in the low-frequency band, and the radiated sound is not reduced at all in the band below 800 Hz in particular. This shows that the silencing effect of the sound-absorbing material is limited. In other words, since the local particle velocity of sound is high near the open end of the duct, the silencing effect of the sound-absorbing material is generally large, but it was found that the sound originating from the vibration of the duct housing due to reflection is difficult to silencing with sound-absorbing material.

[0085] Example 1 In Example 1, the straight duct of Reference Example 1 was used. A vibration-damping material "Calmoon Sheet" manufactured by Sekisui Chemical Co., Ltd. was attached to the entire surface of the vibration portion of the duct, which had a thickness of 1.5 mm. The vibration-damping material had a two-layer structure of SGCC (Steel Galvanized Cold Commercial) steel plate and vibration-damping adhesive rubber, with a total thickness of 1.3 mm. Then, the sound radiated from the duct was measured using the same procedure as in the measurement experiment of Reference Example 1. The measurement results are shown in FIG.

[0086] As can be seen from FIG. 12, in Example 1, the radiated sound on the low frequency side was able to be suppressed overall. More specifically, the natural frequencies of the duct casing (plate material) are 700 Hz, 900 Hz, and 1100 Hz from the low order side (m = 1, 2, 3), and the ¼ times (λ / 4) of the sound wavelength corresponding to each natural frequency is 12.3 cm, 9.5 cm, and 7.5 cm. In the duct casing made in Reference Example 1, the main vibrating part is located within a distance of 6 cm to 24 cm from the open end. Therefore, the antinodes of the amplitude (i.e., antinodes of the sound pressure) corresponding to each of the three wavelengths mentioned above are all included in the above range, and vibration-damping material is provided in that range. For this reason, it is believed that the radiated sound on the low frequency side was able to be effectively silenced, as shown in FIG. 12.

[0087] Example 2 In Example 2, the vibration-damping material "Calmoon Sheet" was attached to the entire vibrating part of the straight duct with sound-absorbing material used in Comparative Example 1 in the same manner as in Example 1, and the sound radiated from the duct was measured. The measurement results are shown in Figure 13. As can be seen from Figure 13, the damping effect of the damping material on low-frequency sounds (more specifically, the vibration damping and sound-absorbing effect) and the sound absorbing effect of the sound-absorbing material on high-frequency sounds were both realized, resulting in a high damping effect across the entire spectrum of radiated sound.

[0088] Example 3 In Example 3, instead of applying the vibration-damping material "Calmoon Sheet" to the entire surface of the vibrating portion of the straight duct in Reference Example 1 (specifically, the vibrating portion of 180 mm x 60 mm), a Calmoon sheet cut to a size of 40 mm x 90 mm was applied. In other words, the vibration-damping material 24 was attached to an area equivalent to 1 / 3 of the entire surface area of ​​the vibrating portion.

[0089] In Example 3, the center position of the damping material 24 in the width direction was aligned with the center position of the duct in the width direction, as shown in Fig. 14. In other words, the damping material 24 was attached to the vibrating portion V of the duct so that the side edges of the damping material 24 were spaced 10 mm apart from the side edges of the duct on both sides of the duct. Also, as shown in Fig. 14, the damping material 24 was set so that the downstream end of the damping material 24 was located 5 mm away from the downstream end (the end closer to the open end) of the vibrating portion V in the extension direction of the duct.

[0090] Then, the sound radiated from the duct was measured using the same procedure as in the measurement experiment of Reference Example 1. The measurement results are shown in Fig. 15. The measurement results of Example 3 will be described later.

[0091] Example 4 In Example 4, the damping material 24 was attached so that its upstream end was located 5 mm away from the upstream end (the end farther from the open end) of the vibrating portion V in the extension direction of the duct. The rest of the duct configuration is the same as in Example 3. Then, sound radiated from the duct was measured using the same procedure as in the measurement experiment of Reference Example 1. The measurement results are shown in FIG. 16. The measurement results of Example 4 will be described later.

[0092] (Measurement results of Examples 2 to 4) In Example 2, the natural frequencies of the vibrating portion (plate) of the duct are 700 Hz, 900 Hz, and 1100 Hz from the low-order side (m = 1, 2, 3), and the ¼ wavelength (λ / 4) of the sound corresponding to each natural frequency is 12.3 cm, 9.5 cm, and 7.5 cm. Here, the vibrating portion (plate) extends from a position 6 cm away from the open end of the duct. Therefore, when viewed from the downstream end of the vibrating portion, the positions where the distance from the open end is λ / 4 (i.e., the antinode positions) for each of the three wavelengths mentioned above are 6.3 cm, 3.5 cm, and 1.8 cm.

[0093] The positions of the antinodes corresponding to the above-mentioned wavelengths are all included in the mounting range of the damping material in Example 3 (that is, the range where the distance from the downstream end of the vibrating part is 0.5 cm to 9.5 cm).

[0094] In Example 4, the positions of the antinodes corresponding to the above-mentioned wavelengths are all outside the attachment range of the damping material (a range of 8.5 cm to 17.5 cm from the downstream end of the vibrating part). Furthermore, for the wavelength λ corresponding to the natural frequency of 700 Hz when m=1, the position at a distance of 3 / 8 λ (= λ / 4 + λ / 8) from the open end is 12.4 cm away from the downstream end of the vibrating part, and is therefore included in the attachment range of the damping material. On the other hand, for the natural frequency of 900 Hz when m=2 and the natural frequency of 1100 Hz when m=3, the position at a distance of 3 / 8 λ from the open end is outside the attachment range of the damping material.

[0095] As described above, in Example 3, in which the damping material is attached at a position λ / 4 away from the open end (i.e., the position of the antinode of the sound pressure), the vibration suppression effect of the damping material is large over a wide frequency band. In particular, in Example 3, a higher sound deadening effect is obtained by placing the damping material at a position in the vibrating part where the vibration displacement is large.

[0096] (Reference example 2) In Reference Example 2, an L-shaped bent duct as shown in Figure 1 was used as a model of the air passage. The cross-sectional shape of this duct is a rectangle measuring 14 mm x 28 mm at the inlet, and a rectangle measuring 14 mm x 60 mm elsewhere. The duct is bent vertically midway. The distance between the bent position and the inlet in the duct (the length corresponding to symbol d in Figure 1) is 180 mm. The height of the part of the duct that rises vertically from the bent position (the length corresponding to symbol h in Figure 1) is 80 mm.

[0097] <Measurement experiment> In the measurement experiment of Reference Example 2, the above-mentioned L-shaped duct was molded from ABS (Acrylonitrile Butadiene Styrene) resin using a 3D printer manufactured by XYZ Printing Co., Ltd. The thickness of the duct housing (i.e., the peripheral wall) was 1.5 mm.

[0098] Then, white noise was applied from the duct inlet, and measurements of duct-propagated sound were carried out using the same procedure as in Reference Example 1. Measurement of the sound emitted from the entire duct (noise volume) was carried out in an anechoic chamber in accordance with known measurement procedures (specifically, ISO 3745:2012). At this time, the acoustic power level (i.e., radiated sound pressure level) was measured, including not only the sound emitted from the duct outlet, but also the sound resulting from vibration of the duct housing.

[0099] <Simulation> In Reference Example 2, an L-shaped duct was modeled using the finite element method (COMSOL MultiPhysics) and acoustic characteristics were calculated. Specifically, similar to Reference Example 1, a calculation model was constructed in which acoustics and structural mechanics were strongly coupled, and the sound radiated from the duct was calculated (simulated). In addition, the above calculation model separately detected the radiated sound caused by the vibration of the duct housing and the propagated sound that propagates through the duct and exits from the duct outlet (open end), and calculated the contribution of each sound for each frequency.

[0100] The simulation results for Reference Example 2 are shown in Figure 17. As can be seen from Figure 17, in the frequency band above approximately 1500 Hz, duct-transmitted sound is the main component. In the frequency band below that, it was found that the contribution of radiated sound caused by vibration of the duct housing is greater than the contribution of duct-transmitted sound.

[0101] Furthermore, in the low-frequency band, as in Reference Example 1, the sound reflection rate at the open end of the duct is high, so an acoustic mode (standing wave) is formed inside the duct, and sound caused by vibration of the duct housing is emitted as radiated sound. In other words, it was presumed that the reflected sound increases the sound pressure inside the duct, making it easier for the housing to vibrate in the part (front section) located upstream of the bend in the duct, which increases the sound pressure of the radiated sound caused by the vibration.

[0102] 17, there is a region in the vicinity of 700 Hz (specifically, the band of 600 to 1200 Hz) where the sound pressure of the radiated sound resulting from vibration increases. As mentioned above, this region is a region where vibration increases.

[0103] Furthermore, in the above-mentioned area, a large amount of radiated sound was confirmed due to vibration at a natural frequency determined by the size, thickness, material, and fixing method of the duct housing (plate material).In addition, judging from the amount of displacement of each part of the duct housing obtained by simulation, it was found that the radiated sound volume caused by the vibration of the housing (plate material) was greater in the part upstream of the bending position in the duct (front stage part).

[0104] Furthermore, if the wavelength corresponding to the natural frequency of the duct housing alone is λ, the distance corresponding to λ / 4 is 12.3 cm when the natural frequency is 700 Hz, and 9.5 cm when the natural frequency is 900 Hz. Here, because the distance from the open end of the duct to the bending position is 8 cm, when the natural frequency is 700 Hz or 900 Hz, the λ / 4 position, i.e., the antinode of the sound pressure, exists on the housing upstream of the bending position. Therefore, it was inferred that the sound pressure antinode is located on the housing upstream of the bending position, and that the radiated sound volume resulting from vibrations caused by sound pressure will also be greater on the housing upstream of the bending position.

[0105] When the sound radiated from the duct of Reference Example 2 was actually measured, it was confirmed that the spectrum of the sound radiated calculated by the simulation was reproduced in the actual measurement results.

[0106] (Comparative Example 2) In Comparative Example 2, the L-shaped duct of Reference Example 2 was used, and a sound-absorbing material "QonPET" manufactured by Bridgestone KBG Corporation was placed at a position connected to the inside of the duct (air passage). The length, thickness, and width of this sound-absorbing material in the duct extension direction were 50 mm, 20 mm, and 60 mm, respectively. The sound-absorbing material was placed at a position 20 mm away from the outlet (open end) of the duct. In addition, all surfaces of the sound-absorbing material other than the surface facing the duct (side and back) were covered with a 3 mm-thick cover made of ABS (Acrylonitrile Butadiene Styrene) resin. In other words, a sound-absorbing part with a closed back was provided in the L-shaped duct.

[0107] Then, the acoustic power level (radiated sound pressure level) of the sound radiated from the duct was measured in the same manner as in Reference Example 2. The measurement results are shown in Fig. 18. In Figs. 18 to 23, the measurement results of Reference Example 2 are shown by dashed lines for comparison. As can be seen from Figure 18, in the frequency band above approximately 1500 Hz, the amount of sound attenuation increased as the frequency increased. On the other hand, the amount of sound attenuation was small on the low frequency side, and in particular in the frequency band below 1000 Hz, almost no sound was attenuated. This is presumably because, as mentioned in Reference Example 2, radiated sound originating from vibrations of the duct housing was dominant on the low frequency side, and the sound-absorbing material located downstream of the bend position was unable to attenuate almost any radiated low-frequency sound.

[0108] Example 5 From the simulation results of Reference Example 2, it was inferred that vibration of the duct housing contributes to radiated sound on the low-frequency side. Therefore, in Example 5, vibration of the duct was suppressed by providing a vibration-damping material to the L-shaped duct of Reference Example 2. Specifically, a vibration-damping material "Calmoon Sheet" manufactured by Sekisui Chemical Co., Ltd. was cut to a predetermined shape, and the vibration-damping material was attached to two wide surfaces located upstream of the bending position in the duct. In this case, the area of ​​the vibration-damping material was set to be the same as each of the two surfaces to which the vibration-damping material was attached, that is, the vibration-damping material was attached to the entire surface of the plate material constituting each of the two surfaces.

[0109] Then, the acoustic power level (radiated sound pressure level) of the sound radiated from the duct was measured using the same procedure as in Reference Example 2. The measurement results are shown in FIG. As can be seen from Figure 19, compared to Comparative Example 2, which used only sound-absorbing material, the amount of sound silencing in the low-frequency band, including the radiated sound that reaches a maximum around 700 Hz (i.e., the radiated sound resulting from vibration of the duct housing), was increased. This reflects the fact that, as already mentioned in the section on Reference Example 2, in the low-frequency band, the radiated sound from the duct is dominated by the vibration sound of the housing. In addition, in the duct of Example 5, the position where the vibration displacement increases due to sound interference is upstream of the bending position, so vibration-damping material was attached to a position upstream of the bending position. This enabled effective silencing of low-frequency vibration sound.

[0110] Example 6 In Example 6, the sound-absorbing material was removed from the duct used in Example 5, and a vibration-damping material, "Calmoon Sheet," was attached to a position upstream of the bend in the duct. Then, the acoustic power level (radiated sound pressure level) of the sound radiated from the duct was measured using the same procedure as in Reference Example 2. The measurement results are shown in Figure 20. As can be seen from FIG. 20, the damping effect of the damping material enabled sound to be silenced across the entire low frequency range without the use of sound absorbing material.

[0111] (Comparative Example 3) In Comparative Example 3, the sound-absorbing material was removed, as in Example 6. Furthermore, in Comparative Example 3, the vibration-damping material attached upstream of the bending position in Example 6 was removed, and instead, vibration-damping material was attached to the entire surface of the duct housing (plate material) located downstream of the bending position. Then, the acoustic power level of the sound radiated from the duct was measured using the same procedure as in Reference Example 2. The measurement results are shown in Figure 21. As can be seen from FIG. 21, the noise reduction on the low frequency side was slight, and compared to Example 6, the frequency band in which noise can be reduced was extremely narrow.

[0112] Example 7 Example 7 was based on the duct structure of Example 6. In Example 7, a Calmoon sheet, which is a vibration-damping material, was attached to the duct housing (plate material) located upstream of the bending position, but the vibration-damping material was attached only to a part of the surface. Specifically, the Calmoon sheet was cut into a rectangular shape measuring 30 mm x 100 mm, and the Calmoon sheet was attached to each of the two surfaces of the duct housing located upstream of the bending position.

[0113] Specifically, the center position of the Karmoon sheet in the width direction was aligned with the center position of the duct in the width direction. The Karmoon sheet was also set so that its edge was located 2 mm upstream of the bending position in the extension direction of the duct. The planar size of the vibrating part of the duct, i.e., the housing (plate) to which the Karmoon sheet is attached, is 60 mm x 180 mm. Therefore, in Example 7, the Karmoon sheet is attached to an area equivalent to 27.8% of the total surface area of ​​the plate.

[0114] Then, the acoustic power level (radiated sound pressure level) of the sound radiated from the duct was measured using the same procedure as in Reference Example 2. The measurement results are shown in FIG. As can be seen from FIG. 22, even with a configuration in which the damping material is attached only to a part of the surface of the plate, it was possible to sufficiently reduce the radiated sound on the low frequency side caused by the vibration of the duct housing.

[0115] In Example 7, the natural frequencies of the duct housing (plate material) were 700 Hz and 900 Hz, and the ¼ times the wavelength (λ / 4) of the sound corresponding to each natural frequency was 12.3 cm and 9.5 cm. Here, the bending position was 8 cm away from the duct outlet (open end), so the positions of the antinodes of the sound pressure λ / 4 away from the outlet were near the bending position, specifically, positions 4.3 mm and 1.5 mm away from the bending position. In Example 7, it was presumed that by attaching the vibration-damping material near the bending position, it was possible to efficiently damp the positions where the vibration displacement was large, and as a result, a significant sound-deadening effect was obtained against the sound caused by vibration.

[0116] Example 8 Example 8 is the same as Example 7, except that the size of the Calmoon sheet is 30 mm x 150 mm. That is, in Example 8, the vibration-damping material is attached to an area equivalent to 46.7% of the surface area of ​​the plate surface. Then, using the same procedure as in Reference Example 2, the acoustic power level (radiated sound pressure level) of the sound radiated from the duct was measured. The results are shown in Figure 23. As can be seen from Figure 23, a sufficient sound-deadening effect was obtained in Example 8 as well.

[0117] The amount of attenuation in each of Reference Example 2, Comparative Example 2, and Examples 5 to 8, which used an L-shaped duct, is shown in Table 1. Here, the amount of attenuation is expressed as the difference between the total volume in Reference Example 2 and the total volume (dBA) obtained by integrating the acoustic power level.

[0118] [Table 1]

[0119] As shown in Table 1, it was found that applying the damping material at a position where the distance from the open end of the duct is λ / 4, i.e., upstream of the bending position, is important for effectively silencing the sound radiated from the duct.

[0120] As explained above, Examples 1 to 8 of the present invention are within the scope of the present invention and have a configuration in which the vibration-damping material is present within a distance from the opening end within a range of λ / 4±λ / 8, so the effects of the present invention are clear. [Explanation of symbols]

[0121] 10,10x soundproof ventilation channels 12 Ventilation channel 14 Peripheral wall 16 Open end 18 Open part 20 Soundproofing 22,22A,22B,22C Vibration suppressor 24 Damping material 26 First Layer 28 Second Layer 30 Sound absorbing section 32 Sound-absorbing material 34 Covering material 40 Ribs I Virtual Line V Vibrating part

Claims

1. An air passage with a soundproof structure, comprising an air passage having an open end and a soundproof structure for sound emitted from the air passage, the soundproof structure has a vibration suppression portion provided on a surface of a peripheral wall surrounding the air passage, Let m and n be natural numbers equal to or less than 4, and let λ be the wavelength of the sound having a frequency that coincides with the m-th natural frequency of the peripheral wall alone, and An airway with a soundproof structure in which all of the vibration suppression parts are located within a range where the distance L1 from the opening end of each part of the airway on a virtual line passing through the center position of a cross section that intersects with the extension direction of the airway satisfies the following formula (1): (4n-3) / 8×λ≦L1≦(4n-1) / 8×λ (1)

2. The soundproof structure-equipped air passage according to claim 1, wherein at least a portion of the vibration suppression portion is provided at a location on the surface of the peripheral wall where the distance L1 is (2n-1) / 4×λ.

3. The air passage with a soundproof structure according to claim 1 or 2, wherein the open end is located at an outlet of the air passage.

4. The ventilation path is bent, When the distance along the virtual line from the opening end to the bending position of the air passage is L2, the distance L2 is less than 5 / 4 × λ, 4. The air passage with soundproof structure according to claim 1, wherein the vibration suppression section is provided upstream of the bending position of the air passage, when the side away from the opening end is defined as the upstream side.

5. The soundproof structure-equipped air passage according to claim 1 , wherein the vibration suppressing portion includes a vibration-damping material attached to a surface of the peripheral wall.

6. 6. The air passage with a soundproof structure according to claim 1, wherein the soundproof structure has a sound absorbing section between the opening end and a portion of the air passage where the vibration suppressing section is provided on the peripheral surface of the peripheral wall.

7. The ventilation path is bent, 7. The air passage with soundproof structure described in claim 6, wherein, when the side away from the opening end is defined as the upstream side, the vibration suppression section is provided upstream of the bending position of the air passage, and the sound absorption section is provided downstream of the bending position of the air passage.

8. the sound absorbing section includes a sound absorbing material disposed adjacent to the air passage, a surface of the sound absorbing material facing the air passage is exposed to the air passage; The air passage with a soundproof structure according to claim 6 or 7, wherein the soundproof structure has a covering material that covers all surfaces of the sound-absorbing material except for a surface facing the air passage.

9. An air passage with a soundproof structure as described in any one of claims 1 to 8, wherein the vibration suppression portion is provided on the surface of the peripheral wall at a portion where the displacement amount is greatest when the peripheral wall alone vibrates at the mth natural frequency.

10. The soundproof structure-equipped air passage according to claim 9 , wherein the mth-order natural frequency of the peripheral wall alone is a first natural frequency of the peripheral wall alone.

11. When a plurality of natural numbers correspond to the natural number m, the range in which the distance L1 satisfies the formula (1) is determined for each of the plurality of natural numbers, The soundproof structure-equipped air passage according to claim 9 or 10, wherein the vibration suppressing portion is provided within the range determined for each of the plurality of natural numbers.

12. 12. An air passage with a soundproof structure as described in any one of claims 1 to 11, which satisfies the following formula (2) when the mth order natural frequency of the peripheral wall alone is fa and the mth order natural frequency of the peripheral wall with the vibration suppression portion provided on the surface is fb. 0.8≦fa / fb≦1.25 (2)

13. The soundproof structure-equipped air passage according to claim 1 , wherein the vibration suppressing portion is attached to a part of an outer peripheral surface of the peripheral wall.

14. 14. The air passage with soundproof structure according to claim 13, wherein the vibration suppressing portion is a laminate of two or more layers including a layer made of a vibration-damping material and a layer made of a vibration-shielding plate.

15. the vibration suppression unit is a two-layer laminate, 15. The soundproof structure-equipped ventilation passage according to claim 1, wherein the laminate has a first layer made of a metal plate and a second layer containing an adhesive and a vibration-damping material, and is attached to the surface of the peripheral wall via the second layer.

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