JP2025123797A - sound-absorbing structure - Google Patents

Abstract

To provide a sound absorption structure without using a member for absorbing sound.SOLUTION: A sound absorption structure includes: a plate-shaped sound absorption plate material 10 for forming an outer shell; and a resonance part 20 having a sound absorption opening 21 which communicates with the outside of the sound absorption plate material and a resonance space S which communicates with the sound absorption opening and is formed inside the sound absorption plate material in a hollow shape. The resonance part includes: a neck part 30 which has the sound absorption opening and extends toward the inside of the sound absorption plate material; a resonance tube part 40 which is a part of the resonance space, whose end on one side communicates with the neck part and forms a resonance tube space Sp extending toward the inside of the sound absorption plate material in a hollow tube shape; and a resonance hollow part 50 which is a part of the resonance space, communicates with at least one of the neck part and the resonance tube part and forms a resonance hollow space Sc expanding inside the sound absorption plate material.SELECTED DRAWING: Figure 3

Description

This disclosure relates to a sound-absorbing structure.

Acoustic metamaterial sound absorbers that include an acoustic resonator array and a sound-absorbing layer are known (see, for example, Patent Document 1). According to Patent Document 1, the sound-absorbing layer is formed from a sound-absorbing material selected from wool, sponge, fiber, cotton, woven metal, cloth, and combinations thereof.

International Publication No. 2018/047153

In a sound-absorbing structure equipped with a sound-absorbing layer such as that described in Patent Document 1, if the sound-absorbing layer deteriorates over time, the sound absorption coefficient of the sound-absorbing layer may decrease, resulting in a decrease in the sound-absorbing performance of the sound-absorbing structure. For this reason, it is desirable for the sound-absorbing structure to be configured without using sound-absorbing materials.

The objective of this disclosure is to provide a sound-absorbing structure that can absorb sound without using sound-absorbing materials.

According to one aspect of the present disclosure,
The sound absorbing structure is
A plate-shaped sound-absorbing board material (10) that forms an outer shell;
a resonance section (20) having a sound-absorbing opening (21) communicating with the outside of the sound-absorbing board material, and a resonance space (S) communicating with the sound-absorbing opening and formed in a hollow shape inside the sound-absorbing board material,
The resonator is
a neck portion (30) having a sound-absorbing opening and extending toward the inside of the sound-absorbing board;
a resonance tube portion (40) that is a part of the resonance space, one end of which is connected to the neck portion and forms a resonance tube space (Sp) that extends in a hollow tubular shape toward the inside of the sound-absorbing board;
and a resonance cavity portion (50) that is a part of the resonance space and communicates with at least one of the neck portion and the resonance tube portion, forming a resonance cavity space (Sc) that expands inside the sound-absorbing board material.

This allows the sound-absorbing structure to absorb sound by resonating in the resonant tube space, and also by resonating in the resonant cavity space. This allows for a wider bandwidth of sound absorption compared to configurations that include only one of the resonant tube section and the resonant cavity section. This makes it possible to provide a sound-absorbing structure that can expand the bandwidth of sound absorption without using sound-absorbing materials.

Note that the reference symbols in parentheses attached to each component indicate an example of the correspondence between that component and the specific components described in the embodiments described below.

1 is a front view of a sound absorbing structure to which a sound absorbing part according to a first embodiment is applied. 1 is a side view of a sound absorbing structure to which a sound absorbing part according to a first embodiment is applied. FIG. 2 is a perspective view of the sound absorbing part according to the first embodiment. FIG. 4 is a cross-sectional view taken along line IV-IV shown in FIG. 4 is a cross-sectional view taken along the line VV in FIG. 3. 6 is a cross-sectional view taken along line VI-VI in FIG. 5A and 5B are diagrams illustrating the sound absorbing performance of the sound absorbing part according to the first embodiment. FIG. 10 is a perspective view of a sound absorbing part according to a second embodiment. 9 is a cross-sectional view taken along line IX-IX in FIG. 8. FIG. 10 is an enlarged view of a portion X shown in FIG. 9 . FIG. 10 is an enlarged view of a resonator tube portion according to a third modified example of the second embodiment. FIG. 10 is an enlarged view of a resonance tube portion according to a fourth modified example of the second embodiment. FIG. 11 is an enlarged view of a resonance tube portion according to a fifth modified example of the second embodiment. FIG. 11 is a perspective view of a sound absorbing part according to a third embodiment. 15 is a cross-sectional view taken along the line XV-XV in FIG. 14. FIG. 10 is a perspective view of a sound absorbing part according to a fourth embodiment. 17 is a cross-sectional view taken along the line XVII-XVII in FIG. 16. 17 is a cross-sectional view taken along line XVIII-XVIII shown in FIG. 16. FIG. 11 is a perspective view of a sound absorbing part according to a fifth embodiment. This is a cross-sectional view taken along the line XX-XX shown in Figure 19. This is a cross-sectional view taken along the line XXI-XXI shown in Figure 19. 13A and 13B are diagrams illustrating the sound absorbing performance of the sound absorbing part according to the fifth embodiment. FIG. 13 is a perspective view of a sound absorbing part according to a sixth embodiment. This is a cross-sectional view taken along line XXIV-XXIV shown in Figure 23. FIG. 13 is an exploded perspective view of a sound absorbing section according to a sixth embodiment, viewed from one side in the first direction. FIG. 13 is an exploded perspective view of a sound absorbing section according to a sixth embodiment, viewed from the other side in the first direction. FIG. 13 is a perspective view of a sound absorbing part according to a seventh embodiment. FIG. 19 is a perspective view of a sound absorbing part according to an eighth embodiment. FIG. 13 is a perspective view of a sound absorbing part according to a ninth embodiment. FIG. 22 is a perspective view of a sound absorbing part according to a tenth embodiment.

Embodiments of the present disclosure will be described below with reference to the drawings. Note that in the following embodiments, parts that are the same as or equivalent to those described in the preceding embodiments will be given the same reference numerals, and their description may be omitted. Furthermore, when only some of the components are described in an embodiment, the components described in the preceding embodiment can be applied to the remaining components. The following embodiments can be partially combined with each other, as long as there is no particular problem with the combination, even if not specifically stated.

(First embodiment)
The sound absorbing section 1 of this embodiment will be described with reference to Figures 1 to 7. In this embodiment, an example will be described in which the sound absorbing section 1 is applied to a sound absorbing structure St shown in Figure 1 and other figures that is used in a vehicle. As shown in Figures 1 and 2, the sound absorbing structure St is configured by combining a plurality of plate-shaped sound absorbing sections 1. The sound absorbing structure St is provided, for example, in a dash panel or door (not shown) that is provided between the interior and exterior of the vehicle cabin.

As shown in FIG. 2 and other figures, the thickness direction of the plate-shaped sound-absorbing unit 1 is defined as the first direction D1. Also, as shown in FIG. 2 and other figures, a predetermined direction along the plate surface of the sound-absorbing unit 1 that is perpendicular to the first direction D1 is defined as the second direction D2, and a direction perpendicular to both the first direction D1 and the second direction D2 is defined as the third direction D3. The sound-absorbing structure St of this embodiment is configured with 25 sound-absorbing units 1, five in each of the second direction D2 and the third direction D3. The sound-absorbing structure St is arranged so that the plate surface of each sound-absorbing unit 1 faces the dash panel or door. Specifically, the sound-absorbing structure St is arranged so that the sound-absorbing opening 21 provided in the first plate surface 11 (described below) of each sound-absorbing unit 1 faces the side where an object that emits sound toward the sound-absorbing structure St is located. For convenience, in FIG. 1 and other figures, reference numerals are assigned to representative ones of the 25 sound-absorbing units 1, and reference numerals for other units are omitted.

The number of sound absorbing sections 1 that make up the sound absorbing structure St is not limited. The sound absorbing structure St may be configured with more than five sound absorbing sections 1 lined up in the second direction D2 or the third direction D3, or may be configured with fewer than five sound absorbing sections 1 lined up. Furthermore, the sound absorbing structure St may be configured with the sound absorbing sections 1 lined up in the first direction D1.

As shown in FIG. 3, the sound absorbing section 1 has a sound absorbing panel 10 and a resonator section 20. The sound absorbing panel 10 forms the outer shell of the sound absorbing section 1. The sound absorbing panel 10 is formed as a plate with a substantially square shape when viewed along the first direction D1 and a panel surface in the first direction D1. That is, the sound absorbing panel 10 is substantially square when viewed in a direction perpendicular to the panel surface, and has a rectangular parallelepiped shape whose size in the first direction D1 is smaller than its sizes in the second direction D2 and the third direction D3. The sound absorbing panel 10 is a member whose mass per unit volume is greater than that of air, and is formed, for example, from resin. The sound absorbing panel 10 in this embodiment is formed from nylon resin.

The sound-absorbing board material 10 has a planar first board surface 11 on one side in the first direction D1, and a planar second board surface 12 on the other side in the first direction D1. Furthermore, the sound-absorbing board material 10 has a sound-absorbing side surface 13 that extends in a planar manner and forms the outer shell of the sound-absorbing board material 10 in a direction different from the first direction D1.

The sound-absorbing structure St of this embodiment is composed of 25 sound-absorbing sections 1 arranged five in each of the second direction D2 and the third direction D3, and the sound-absorbing side surfaces 13 of adjacent sound-absorbing boards 10 are connected without any gaps. Furthermore, the sound-absorbing structure St of this embodiment is composed of 25 sound-absorbing sections 1 arranged five in each of the second direction D2 and the third direction D3, and the sound-absorbing boards 10 are connected so that the first direction D1, which is the thickness direction of each sound-absorbing board 10, is the same direction and does not intersect with each other.

Note that the material of the sound-absorbing board 10 is not limited to nylon resin. The sound-absorbing board 10 may be made of a resin other than nylon resin, or may be made of a material other than resin, such as metal.

The resonator 20 is formed as a hollow space inside the sound-absorbing panel 10, and when sound waves are incident on the sound-absorbing panel 10, the air inside the resonator 20 vibrates, generating Helmholtz resonance. As shown in Figures 3 and 4, the resonator 20 is formed on the first panel surface 11 and has a sound-absorbing opening 21 that communicates with the outside of the sound-absorbing panel 10, and a hollow resonator space S that communicates with the sound-absorbing opening 21 and is filled with air that vibrates when sound waves are incident on it. The resonator 20 has a hollow space inside the resonator space S, and when the sound-absorbing opening 21 communicates with the outside of the sound-absorbing panel 10, air fills the resonator space S.

The resonator section 20 also has a sound-absorbing opening 21 at one end, and a neck section 30 that extends from the first panel surface 11 toward the second panel surface 12, i.e., toward the interior of the sound-absorbing board 10. The resonator section 20 also has a resonator tube section 40 that forms a resonator tube space Sp that extends in a hollow tubular shape toward the interior of the sound-absorbing board 10, and a resonator cavity section 50 that forms a resonator cavity space Sc that expands into a rectangular parallelepiped shape inside the sound-absorbing board 10.

The resonator section 20 is formed by connecting the neck section 30, the resonator tube section 40, and the resonator cavity section 50. This allows the neck space Sn, which is the space formed by the neck section 30, the resonator tube space Sp, which is formed by the resonator tube section 40, and the resonator cavity space Sc, which is formed by the resonator cavity section 50, to be connected. In other words, the resonator space S is made up of the neck space Sn, the resonator tube space Sp, and the resonator cavity space Sc.

As shown in Figures 3 and 4, the neck portion 30 is formed along the first direction D1 from approximately the center of the first panel surface 11 to approximately the center of the sound-absorbing board 10 in the first direction D1. The neck portion 30 has a sound-absorbing opening 21 on one side in the first direction D1, and a cavity-side connecting portion 31 that connects to the resonant cavity 50 on the other side in the first direction D1. The neck portion 30 also has a tube-side connecting portion 32 that connects to the resonant tube 40 between the sound-absorbing opening 21 and the cavity-side connecting portion 31.

The neck portion 30 has a substantially square cross-sectional shape perpendicular to the direction in which the path extends. In other words, the neck portion 30 has a substantially square cross-sectional shape perpendicular to the direction in which the path extends from the sound-absorbing opening 21 toward the cavity-side communicating portion 31. Furthermore, the neck portion 30 has a constant opening area perpendicular to the direction in which the path extends, i.e., the opening area perpendicular to the first direction D1, from the sound-absorbing opening 21 to the cavity-side communicating portion 31.

As shown in FIG. 5, the resonance tube section 40 is formed into a spiral shape by bending like a rectangle whose size increases from the inside to the outside. In this embodiment, the resonance tube section 40 has a spiral shape with three turns. The resonance tube section 40 has a first tube end 41 at the inner end of the spiral shape that communicates with the tube-side connecting section 32 of the neck section 30, and a second tube end 42 at the outer end of the spiral shape that is closed by the sound-absorbing panel 10. The resonance tube section 40 also has multiple bent sections 43 and a resonance tube surface 44 that surrounds the resonance tube space Sp, which is part of the resonance space S through which sound waves propagate.

The resonating tube section 40 is formed around the tube-side connecting section 32 of the neck section 30, with the tube-side connecting section 32 at its center. In other words, the resonating tube section 40 is formed in a position that overlaps with a portion of the neck section 30 in the second direction D2 and the third direction D3. Hereinafter, the first tube end 41 side of the resonating tube section 40 may be referred to as the starting end, and the second tube end 42 may be referred to as the terminal end.

The resonator tube section 40 has a substantially square cross section perpendicular to the direction in which the path extends, from the first tube end 41 to the second tube end 42. Furthermore, the resonator tube section 40 has a constant opening area perpendicular to the direction in which the path extends, i.e., the opening area perpendicular to the direction along the spiral shape, from the first tube end 41 to the second tube end 42. In other words, the opening area of the resonator tube section 40 is constant from the starting end to the ending end. The direction in which the path of the resonator tube section 40 extends is, for example, the direction along the third direction D3 in the cross section of the resonator tube section 40 shown in FIG. 4. The opening area perpendicular to the direction in which the path extends is the opening area in the cross section of the resonator tube section 40 as viewed from the direction along the third direction D3 shown in FIG. 4.

As shown in FIG. 4, the resonant tube section 40 has a constant opening area perpendicular to the direction in which the path extends from the first tube end 41 to the second tube end 42. Furthermore, the size of the opening area of the resonant tube section 40 perpendicular to the direction in which the path extends is approximately equal to the opening area of the neck section 30 perpendicular to the direction in which the path extends. Furthermore, the size of the resonant tube section 40 in this embodiment in the first direction D1 is less than 1/4 of the size in the first direction D1, which is the thickness direction of the sound-absorbing panel 10.

The bent portions 43 are portions that change the extension direction of the resonator tube portion 40. As shown in Figure 5, the resonator tube portion 40 of this embodiment has 12 bent portions 43, and the configuration with these 12 bent portions 43 forms a spiral shape with three turns. Note that in Figure 5, for convenience, a reference number is assigned to one representative of the 12 bent portions 43, and reference numbers for the others are omitted.

When sound waves enter the neck portion 30 through the sound-absorbing opening 21, the first tube end 41 guides the sound waves entering the neck portion 30 into the resonance tube space Sp within the resonance tube portion 40. The sound waves entering the resonance tube space Sp are reflected by the second tube end 42 and the resonance tube surface 44.

As shown in Figures 4 and 6, the resonant cavity 50 is formed in a rectangular parallelepiped shape. In this embodiment, the resonant cavity 50 has approximately equal sizes in the second direction D2 and the third direction D3, and is formed in a rectangular parallelepiped shape that is approximately square when viewed from a direction along the first direction D1.

Furthermore, the resonant cavity 50 is formed so that its size in the first direction D1 is larger than the size of the resonant tube section 40 in the first direction D1. Specifically, the resonant cavity 50 is formed so that its size in the first direction D1 is approximately twice the size of the resonant tube section 40 in the first direction D1. Further, the resonant cavity 50 is formed so that its size in the second direction D2 is larger than the size of the resonant tube section 40 in the second direction D2, and its size in the third direction D3 is larger than the size of the resonant tube section 40 in the third direction D3.

The resonant cavity 50 has a cavity entrance 51 that communicates with the cavity-side connecting portion 31 of the neck 30, and a resonant cavity surface 52 that surrounds the resonant cavity space Sc, which is part of the resonant space S through which sound waves propagate. When sound waves enter the neck 30 through the sound-absorbing opening 21, the cavity entrance 51 guides the sound waves that enter the neck 30 into the resonant cavity space Sc within the resonant cavity 50. The sound waves that enter the resonant cavity space Sc are reflected by the resonant cavity surface 52.

The resonant tube section 40 and the resonant cavity section 50 are formed side by side with a gap in between in the first direction D1, which is the thickness direction of the sound-absorbing board 10.

The sound absorbing section 1 formed as described above is configured so that when sound waves are incident on the sound absorbing section 1, Helmholtz resonance occurs in the resonance tube space Sp and the resonance cavity space Sc. This causes the air in the resonance tube space Sp and the air in the resonance cavity space Sc to resonate at the resonance frequency. We will now explain the Helmholtz resonance that occurs in the resonance tube space Sp and the resonance cavity space Sc.

The length of the resonance tube section 40 in the direction along the spiral shape is greater than the length of the neck section 30 in the first direction D1. Here, the length of the neck section 30 in the first direction D1 is referred to as the neck length, the length of the resonance tube section 40 in the direction along the spiral shape is referred to as the spiral length, the volume of the neck space Sn is referred to as the neck volume, and the volume of the resonance tube space Sp is referred to as the resonance tube volume. A resonance tube section 40 whose opening area perpendicular to the path is formed equal to the opening area perpendicular to the path of the neck section 30 has a resonance tube volume greater than the neck volume.

For this reason, when sound waves are incident on the sound absorbing section 1 and propagate through the sound absorbing opening 21 into the resonance tube space Sp, Helmholtz resonance occurs, and the air in the resonance tube space Sp resonates at a resonance frequency that corresponds to the neck length and resonance tube volume.

Furthermore, the resonant cavity 50 has dimensions in the first direction D1, second direction D2, and third direction D3 that are larger than the dimensions of the resonant tube 40 in the first direction D1, second direction D2, and third direction D3, respectively. Here, the volume of the resonant cavity space Sc is referred to as the resonant cavity volume. When the resonant cavity 50 is formed so that its dimensions in the first direction D1, second direction D2, and third direction D3 are larger than the dimensions of the resonant tube 40 in the first direction D1, second direction D2, and third direction D3, respectively, the resonant cavity volume is larger than the neck volume and the resonant tube volume.

For this reason, when sound waves are incident on the sound absorbing section 1 and propagate through the sound absorbing opening 21 into the resonant cavity space Sc, Helmholtz resonance occurs, causing the air in the resonant cavity space Sc to resonate at a resonant frequency that corresponds to the neck length and volume of the resonant cavity. Therefore, when sound is generated toward the sound absorbing structure St, the sound absorbing section 1 can exert its sound absorbing function by reducing the amplitude of sound waves in frequency bands near the resonant frequencies of the air resonating in the resonant tube space Sp and the resonant cavity space Sc, thereby reducing the volume of the sound.

Specifically, when sound waves propagate from the first tube end 41 through the neck portion 30 into the resonance tube space Sp, Helmholtz resonance occurs in the sound absorbing unit 1, causing the air in the resonance tube space Sp to resonate at a resonance frequency that corresponds to the neck length and resonance tube volume. Furthermore, when sound waves propagate from the cavity entrance 51 through the neck portion 30 into the resonance cavity space Sc, Helmholtz resonance occurs in the sound absorbing unit 1, causing the air in the resonance cavity space Sc to resonate at a resonance frequency that corresponds to the neck length and resonance cavity volume.

When the air resonates in the resonance tube space Sp and the resonance cavity space Sc, this resonance causes the air to vibrate violently, and acoustic energy is converted into heat due to friction and viscous losses that occur in the resonance tube space Sp and the resonance cavity space Sc. This reduces the volume of sound in the frequency band around the resonance frequency when the air resonates at the resonance frequency in the resonance tube space Sp and the resonance cavity space Sc.

As mentioned above, the resonant cavity volume is larger than the resonant tube volume. The resonant frequency of the air that resonates due to Helmholtz resonance decreases as the resonant tube volume of the resonant tube space Sp and the resonant cavity volume of the resonant cavity space Sc increase. Therefore, the resonant frequency at which the air resonates in the resonant tube space Sp and the resonant frequency at which the air resonates in the resonant cavity space Sc are different from each other. Hereinafter, the resonant frequency at which the air resonates in the resonant tube space Sp is also referred to as the resonant tube frequency, and the resonant frequency at which the air resonates in the resonant cavity space Sc is also referred to as the resonant cavity frequency.

A sound absorbing section 1 in which the resonant cavity volume is larger than the resonant tube volume reduces the loudness of sound in the frequency band near the resonance tube frequency, and also reduces the loudness of sound in the frequency band near the resonant cavity frequency. Therefore, compared to a configuration in which the sound absorbing section 1 has only one of the resonance tube section 40 and the resonant cavity section 50, the frequency band of sound that is reduced by the sound absorbing section 1 can be made wider.

Figure 7 shows the results of an experiment conducted to verify the sound absorption performance of the sound absorbing section 1 of this embodiment. The solid line in Figure 7 shows the sound absorption coefficient of the sound absorbing section 1 of this embodiment. The dashed line in Figure 7 shows the sound absorption coefficient of a comparative configuration in which the sound absorbing section 1 of this embodiment does not have the resonating section 20, and the part corresponding to the resonating section 20 is filled with the same material as the sound absorbing panel material 10.

As shown in Figure 7, the comparative configuration exhibits almost no sound absorption performance in any frequency band. In contrast, the sound absorbing section 1 of this embodiment was able to exhibit sound absorption performance for sounds in two frequency bands: near the resonant tube frequency and near the resonant cavity frequency.

In this embodiment, the resonant tube section 40 has an opening area perpendicular to the direction in which the path extends that is approximately equal to the opening area of the neck section 30 perpendicular to the direction in which the path extends, and the size in the first direction D1 is less than one-quarter of the size in the thickness direction of the sound-absorbing board 10. The resonant tube section 40 also has 12 bent sections 43 and is spiral-shaped with three turns. The resonant tube frequency is determined according to the resonant tube volume of the resonant tube section 40 formed in this manner. However, because the resonant tube frequency decreases as the resonant tube volume increases, the shape of the resonant tube section 40 is not limited to this.

In order to correspond to the desired frequency of sound to be reduced, the length of the resonant tube section 40 in the direction in which the path extends, the size of the opening area perpendicular to the direction in which the path extends, the number of turns, etc. can be changed in various ways. For example, the resonant tube section 40 may be formed in a spiral shape in which the diameter increases from the inside to the outside, drawing a circle. The resonant tube section 40 may also be formed in a spiral shape with four or more turns.

In the present invention, the resonance tube volume of the resonance tube section 40, i.e., the length of the path in the resonance tube section 40, contributes more to the resonance frequency of the Helmholtz resonance than the resonance cavity volume of the resonance cavity section 50. Therefore, the resonance frequency can be easily adjusted simply by adjusting the number of turns of the resonance tube section 40.

In addition, the resonant cavity 50 of this embodiment is formed in a rectangular parallelepiped shape with approximately equal sizes in the second direction D2 and the third direction D3. Furthermore, the size of the resonant cavity 50 in the first direction D1 is approximately twice the size of the resonant tube 40 in the first direction D1, and the sizes in the second direction D2 and the third direction D3 are larger than the sizes of the resonant tube 40 in the second direction D2 and the third direction D3. The resonant cavity frequency is determined according to the resonant cavity volume of the resonant cavity 50 formed in this manner. However, because the resonant cavity frequency decreases as the resonant cavity volume increases, the shape of the resonant cavity 50 is not limited to this.

The resonant cavity 50 can be adjusted to various sizes in the first direction D1, second direction D2, and third direction D3 in order to correspond to the desired frequency of sound reduction.

As described above, the sound-absorbing structure St of this embodiment comprises a plate-shaped sound-absorbing board 10 forming an outer shell, a sound-absorbing opening 21 that communicates with the outside of the sound-absorbing board 10, and a resonating portion 20 that has a sound-absorbing opening 21 that communicates with the outside of the sound-absorbing board 10 and a hollow resonance space S that communicates with the sound-absorbing opening 21 and is formed inside the sound-absorbing board 10. The resonating portion 20 includes a neck portion 30 that has the sound-absorbing opening 21 and extends toward the inside of the sound-absorbing board 10, and a resonating tube portion 40 that is part of the resonance space S, one end of which communicates with the neck portion 30 and forms a resonance tube space Sp that extends in a hollow tubular shape toward the inside of the sound-absorbing board 10. The resonating portion 20 further includes a resonating cavity portion 50 that is part of the resonance space S, communicates with the neck portion 30, and forms a resonance cavity space Sc that expands inside the sound-absorbing board 10.

This allows the air to resonate in the resonance tube space Sp, thereby reducing the loudness of sound in a frequency band near the resonance tube frequency, and the air to resonate in the resonance cavity space Sc, thereby reducing the loudness of sound in a frequency band near the resonance cavity frequency. Therefore, the frequency band of sound reduced by the sound absorbing section 1 can be broadened compared to a configuration that includes only one of the resonance tube section 40 and the resonance cavity section 50. Therefore, it is possible to provide a sound absorbing structure St that can expand the frequency band of sound absorption without using sound-absorbing materials.

In particular, the sound-absorbing unit 1 of this embodiment is applied to a sound-absorbing structure St used in a vehicle. When a vehicle is moving, noises caused by the external environment, such as wind noise and road noise, are generated. Furthermore, the vehicle may be equipped with components that generate drive noise, such as fans and inverters. These noises caused by the external environment and the drive noise of these components are perceived as noise by the occupants of the vehicle and can worsen the riding comfort of the occupants. These noises cover a wide range of frequency bands, from low to high. Therefore, it is desirable for the sound-absorbing unit 1 to exhibit sound-absorbing performance across a wide range of frequency bands, from low to high.

Therefore, the sound absorbing unit 1 of this embodiment, which can reduce a wide range of sound frequencies, can easily accommodate situations where sound absorption performance is desired across a wide frequency range, from low to high frequencies.

Furthermore, the above embodiment can achieve the following effects:

(1) In the above embodiment, the resonant tube section 40 has a bent section 43.

This makes it easier to increase the resonance tube volume of the resonance tube section 40 formed inside the sound absorbing section 1. This makes it possible to reduce the resonance tube frequency while preventing the resonance tube section 40 from becoming too large. Therefore, even if the sound absorbing performance required of the sound absorbing section 1 covers a wide frequency range, from low to high, it is possible to reduce sounds across a wide frequency range that are incident on the sound absorbing section 1 without increasing the size of the sound absorbing section 1.

(2) In the above embodiment, the resonant tube portion 40 and the resonant cavity portion 50 are arranged side by side in the first direction D1, which is the direction along the thickness direction of the sound-absorbing board 10.

This allows the dimensions in the second direction D2 and the third direction D3 to be smaller than when the resonance tube section 40 and the resonance cavity section 50 are arranged side by side in the second direction D2 or the third direction D3. This allows the installation area required for the sound-absorbing section 1 to be reduced when installed on a dash panel or door.

(3) In the above embodiment, the sound-absorbing structure St is formed by connecting multiple sound-absorbing sections 1, each of which includes one sound-absorbing board 10, one resonant tube section 40, and one resonant cavity section 50.

By connecting multiple sound absorbing units 1 in this manner, the size of the sound absorbing structure St can be easily adapted to the size of the installation location by adjusting the number of connected sound absorbing units 1.

Second Embodiment
Next, a second embodiment will be described with reference to Figures 8 to 10. In this embodiment, the shape of the resonance tube portion 40 is partially different from that of the first embodiment. The rest of the second embodiment is similar to the first embodiment. Therefore, in this embodiment, differences from the first embodiment will be mainly described, and descriptions of similar portions to the first embodiment may be omitted.

As shown in Figures 8 and 9, the resonator tube section 40 of this embodiment has a stepped section 45 that gradually changes the opening area perpendicular to the direction along the spiral shape of the resonator tube section 40 in a stepped manner. The stepped section 45 is provided at the end of the resonator tube section 40 on the terminal side where the second tube end 42 is formed. The opening area of the stepped section 45, perpendicular to the direction along the spiral shape, gradually decreases from the first tube end 41 side toward the second tube end 42 side in the direction along the spiral shape; specifically, the opening area decreases in a stepped manner. In other words, the opening area of the second tube end 42 of the resonator tube section 40 decreases in a stepped manner from the starting end toward the terminal end. The opening area of the stepped section 45 of this embodiment decreases in two stages from the starting end toward the terminal end.

As shown in Figure 10, the opening area of the stepped section 45 decreases in two stages from the starting end to the terminal end. The portion where the opening area decreases in the first stage is referred to as the first step surface 451, and the portion where the opening area decreases in the second stage is referred to as the second step surface 452. Furthermore, the surface of the resonant tube section 40 that is formed at the portion farthest from the first tube end 41 is referred to as the terminal surface 453. The first step surface 451, second step surface 452, and terminal surface 453 are each perpendicular to the direction along the spiral shape of the resonant tube section 40, and are formed as flat surfaces parallel to the direction perpendicular to the direction along the spiral shape of the resonant tube section 40.

The operation of the sound absorbing unit 1 when the resonance tube 40 has a stepped portion 45 formed in a stepped shape like this will be explained below. When sound waves are incident on the sound absorbing unit 1 whose resonance tube 40 has a stepped portion 45, the sound waves are propagated into the resonance tube 40 via the neck portion 30. The sound waves propagated into the resonance tube 40 are then reflected by the resonance tube surface 44 of the resonance tube 40.

Here, sound waves propagating through the staircase section 45 are reflected at each location within the staircase section 45 where the opening area changes. For example, as in this embodiment, inside the staircase section 45, where the opening area decreases in two steps from the starting end to the ending end, sound waves are reflected at each of the first step surface 451, the second step surface 452, and the ending surface 453. Therefore, three types of sound waves exist in the staircase section 45: sound waves reflected at the first step surface 451, sound waves reflected at the second step surface 452, and sound waves reflected at the ending surface 453. As a result, the air in the resonance tube space Sp resonates with these three types of sound waves, including three resonance tube frequencies.

As a result, the resonance tube section 40 can achieve sound absorption performance for sound waves in frequency bands near the three resonance tube frequencies that are incident on the resonance tube space Sp.

Here, the length along the spiral shape from the first tube end 41 to the first step surface 451 is referred to as the first step length L1, and the length along the spiral shape from the first tube end 41 to the second step surface 452 is referred to as the second step length L2. The length along the spiral shape from the first tube end 41 to the terminal surface 453 is referred to as the terminal length L3. Furthermore, the volume of the resonance tube from the first tube end 41 to the first step surface 451 is referred to as the first tube volume, and the volume of the resonance tube from the first tube end 41 to the second step surface 452 is referred to as the second tube volume. The volume from the first tube end 41 to the terminal surface 453 is the resonance tube volume.

The first step length L1 is shorter than the second step length L2 and the end length L3. Furthermore, the second step length L2 is shorter than the end length L3. In other words, the end length L3 is longer than the first step length L1 and the second step length L2. Therefore, the first tube volume is smaller than the second tube volume and the resonance tube volume. Furthermore, the second tube volume is smaller than the resonance tube volume. In other words, the resonance tube volume is larger than the first tube volume and the second tube volume.

The resonance tube section 40 of this embodiment, configured as described above, has sound absorption performance in three different resonance tube frequency bands based on the differences in the sizes of the first tube volume, second tube volume, and resonance tube volume. Specifically, the resonance tube section 40 exhibits higher sound absorption performance in the resonance tube frequency bands in order of decreasing first tube volume, second tube volume, and resonance tube volume. That is, the resonance tube section 40 exhibits sound absorption performance in the highest of the three resonance tube frequency bands in which it exhibits sound absorption performance due to air resonance caused by sound waves reflected by the first step surface 451. The resonance tube section 40 then exhibits sound absorption performance in the second highest resonance tube frequency band due to air resonance caused by sound waves reflected by the second step surface 452, and exhibits sound absorption performance in the lowest resonance tube frequency band due to air resonance caused by sound waves reflected by the end surface 453.

The length along each spiral shape from the first tube end 41 to the first step surface 451, the second step surface 452, and the terminal surface 453 is set appropriately according to the frequency band in which the required sound absorption performance is obtained in the resonant tube section 40.

Other configurations are the same as those of the first embodiment. The sound absorbing unit 1 of this embodiment can obtain the same effects as those of the first embodiment, which are achieved by a configuration similar to or equivalent to that of the first embodiment.

The sound absorbing section 1 of this embodiment can reflect sound waves propagating within the resonance tube space Sp at the first step surface 451, second step surface 452, and end surface 453 of the staircase section 45, where the opening area of the resonance tube section 40 varies. This allows sound absorption performance to be achieved across multiple frequency bands through air resonance caused by sound waves reflected at the first step surface 451, second step surface 452, and end surface 453. This allows the frequency band of sound reduced by the resonance tube section 40 to be broadened without using sound-absorbing materials.

(First Modification of the Second Embodiment)
In the above-described second embodiment, an example was described in which the opening area of the staircase portion 45, which is perpendicular to the direction along the spiral shape, decreases in a step-like manner from the starting end side to the terminal end side in the direction along the spiral shape, but this is not limited to this.

For example, the stepped portion 45 may have an opening area that increases in a stepped manner in the direction perpendicular to the spiral shape from the starting end to the ending end in the direction along the spiral shape.

(Second Modification of the Second Embodiment)
In the second embodiment described above, an example has been described in which the stepped portion 45 is provided at the end portion on the terminal side of the resonant tube portion 40, but the present invention is not limited to this.

For example, the stepped section 45 may be located approximately in the center between the first tube end 41 and the second tube end 42 of the resonator tube section 40, or at the end closer to the starting end.

(Third Modification of the Second Embodiment)
In the second embodiment described above, the first step surface 451, the second step surface 452, and the end surface 453 are each perpendicular to the direction along the spiral shape, but the present invention is not limited to this.

For example, as shown in FIG. 11, one or more of the first step surface 451, the second step surface 452, and the end surface 453 may be inclined and not perpendicular to the direction along the spiral shape of the resonant tube section 40. Note that FIG. 11 shows an example in which the first step surface 451 is inclined and not perpendicular to the direction along the spiral shape of the resonant tube section 40.

(Fourth Modification of the Second Embodiment)
In the above-described second embodiment, an example was described in which the first step surface 451, the second step surface 452, and the terminal surface 453 are each formed in a planar shape parallel to a direction perpendicular to the direction along the spiral shape, but this is not limited to this.

For example, as shown in FIG. 12, the ends of the first step surface 451, the second step surface 452, and the terminal surface 453 may be curved in a direction perpendicular to the direction along the spiral shape of the resonator tube section 40.

(Fifth Modification of the Second Embodiment)
In the above-described second embodiment, an example was described in which the opening area of the staircase portion 45, which is perpendicular to the direction along the spiral shape, decreases in a step-like manner from the starting end side to the terminal end side in the direction along the spiral shape, but this is not limited to this.

For example, as shown in FIG. 13, the stepped portion 45 may have a plurality of portions in which the opening area perpendicular to the direction along the spiral shape continuously and gradually decreases from the starting end to the ending end in the direction along the spiral shape.

(Third embodiment)
Next, a third embodiment will be described with reference to Figures 14 and 15. In this embodiment, the shape of the resonance tube portion 40 is partially different from that of the first embodiment. The rest of the third embodiment is the same as the first embodiment. Therefore, in this embodiment, differences from the first embodiment will be mainly described, and descriptions of similar portions to the first embodiment may be omitted.

As shown in Figures 14 and 15, the resonance pipe section 40 of this embodiment has a resonance pipe path section 46 that communicates with the outside of the sound-absorbing panel 10 and with the resonance cavity section 50. The resonance pipe path section 46 is formed along the first direction D1. The resonance pipe path section 46 also has a resonance pipe opening section 461 on one side that opens at the first panel surface 11, and a cavity connection section 462 on the other side that communicates with the resonance cavity section 50.

The resonance pipe path section 46 is connected to the resonance pipe section 40 midway between the first pipe end 41 and the second pipe end 42. Specifically, the resonance pipe path section 46 is connected to a portion of the path from the first pipe end 41 to the second pipe end 42 that is closer to the second pipe end 42 than the first pipe end 41.

In this embodiment, the resonance pipe path section 46 is connected at a position where the length from the second tube end section 42 to the resonance pipe path section 46 in the direction along the spiral shape is significantly smaller than the length from the first tube end section 41 to the resonance pipe path section 46 in the direction along the spiral shape. Hereinafter, the portion of the resonance pipe section 40 where the resonance pipe path section 46 is connected is also referred to as the path connection section 463.

The operation of the sound absorbing unit 1 when the resonance tube unit 40 has the resonance tube path 46 will now be described. When sound waves are incident on the sound absorbing unit 1, whose resonance tube unit 40 has the resonance tube path 46, the sound waves propagate into the interior of the resonance tube unit 40 via the sound absorbing opening 21 and the neck portion 30, and also propagate into the interior of the resonance tube unit 40 from the resonance tube opening 461. The sound waves propagating into the interior of the resonance tube unit 40 are then reflected by the second tube end 42 within the resonance tube space Sp of the resonance tube unit 40.

Here, the length from the first pipe end 41 to the path connection portion 463 in the direction along the spiral shape is different from the length from the second pipe end 42 to the path connection portion 463 in the direction along the spiral shape. Furthermore, the volume from the first pipe end 41 to the path connection portion 463 is different from the volume from the second pipe end 42 to the path connection portion 463.

As a result, two types of sound waves exist at the second tube end 42: sound waves that propagate from the sound-absorbing opening 21 into the interior of the resonance tube section 40 and are reflected at the second tube end 42, and sound waves that propagate from the resonance tube opening 461 into the interior of the resonance tube section 40 and are reflected at the second tube end 42. As a result, the air in the resonance tube space Sp resonates with these two types of sound waves, including two resonance tube frequencies.

As a result, the resonance tube section 40 can achieve sound absorption performance for sound waves in frequency bands near two resonance tube frequencies among the sound waves incident on the resonance tube space Sp. Specifically, the resonance tube section 40 exhibits sound absorption performance in a frequency band where the resonance tube frequency of the air caused by sound waves propagating from the sound absorption opening 21 into the interior of the resonance tube section 40 is lower than the resonance tube frequency of the air caused by sound waves propagating from the resonance tube opening 461 into the interior of the resonance tube section 40.

The location of the resonance pipe section 40 where the resonance pipe path section 46 is connected is set appropriately depending on the frequency band in which the required sound absorption performance is to be obtained from the resonance pipe section 40.

Other configurations are the same as those of the first embodiment. The sound absorbing unit 1 of this embodiment can obtain the same effects as those of the first embodiment, which are achieved by a configuration similar to or equivalent to that of the first embodiment.

The sound absorbing section 1 of this embodiment can reflect sound waves propagating from the sound absorbing opening 21 and the resonance tube opening 461 into the resonance tube space Sp at the second tube end 42. This allows sound absorption performance to be achieved across multiple frequency bands through the resonance of the air caused by sound waves propagating from the sound absorbing opening 21 and the resonance tube opening 461. This makes it possible to broaden the frequency band of sound that is reduced by the resonance tube section 40 without using sound-absorbing materials.

(Fourth embodiment)
Next, a fourth embodiment will be described with reference to Figures 16 to 18. In this embodiment, the size of the sound-absorbing board 10 differs from that of the first embodiment, and the positional relationship between the resonance tube portion 40 and the resonance cavity portion 50 differs from that of the first embodiment. Other than this, the fourth embodiment is similar to the first embodiment. Therefore, in this embodiment, differences from the first embodiment will be mainly described, and descriptions of similar portions to the first embodiment may be omitted.

As shown in Figures 16 and 17, the sound-absorbing board 10 of this embodiment has a smaller size in the first direction D1 than the sound-absorbing board 10 of the first embodiment. As shown in Figures 16 and 17, the resonant cavity 50 of this embodiment has a slightly larger size in the first direction D1 than the resonant cavity 50 of the first embodiment.

In contrast to these, the resonance tube section 40 of this embodiment is formed with the same size in the first direction D1 as the resonance tube section 40 of the first embodiment. However, as shown in Figures 16 to 18, the resonance tube section 40 is disposed inside the resonance cavity section 50. That is, the resonance tube section 40 is disposed within the resonance cavity space Sc and is surrounded by the resonance cavity surface 52. The resonance tube section 40 of this embodiment is supported by the neck section 30 by connecting the first tube end section 41 to the tube-side connecting section 32 of the neck section 30.

When sound waves are incident on the sound absorbing section 1 formed as described above, Helmholtz resonance occurs in the resonance tube space Sp and the resonance cavity space Sc, causing the air in the resonance tube space Sp to resonate at the resonance tube frequency and the air in the resonance cavity space Sc to resonate at the resonance cavity frequency. The sound absorbing section 1 then reduces the loudness of sound in the frequency band near the resonance tube resonance frequency, as well as the loudness of sound in the frequency band near the resonance cavity frequency.

In this embodiment, the resonant cavity Sc is provided with a resonant tube 40. Therefore, sound waves entering the resonant cavity Sc are reflected in various directions between the outer periphery of the resonant tube 40 and the resonant cavity surface 52. In other words, sound waves entering the resonant cavity Sc are diffusely reflected within the resonant cavity Sc. The diffusely reflected sound waves within the resonant cavity Sc then cause the air within the resonant cavity Sc to resonate at various frequencies.

As a result, when sound waves are incident on the sound absorbing section 1 and the air in the resonant cavity space Sc resonates, the frequency band of the cavity resonance frequency is wider than when sound waves are not diffusely reflected in the resonant cavity space Sc. Therefore, sound can be absorbed without using sound-absorbing materials, and the frequency band of sound that is reduced can be wider than in a configuration in which the resonant tube section 40 is not placed inside the resonant cavity space 50.

Furthermore, by arranging the resonance tube section 40 inside the resonance cavity section 50, the size of the sound-absorbing board 10 in the first direction D1 can be reduced compared to a configuration in which the resonance tube section 40 is not arranged inside the resonance cavity section 50.

In this embodiment, a configuration in which the entire resonant tube section 40 is disposed inside the resonant cavity section 50 has been described, but a configuration in which only a portion of the resonant tube section 40 is disposed inside the resonant cavity section 50 may also be used.

Fifth Embodiment
Next, a fifth embodiment will be described with reference to Figures 19 to 22. In this embodiment, the size of the sound-absorbing board 10 differs from that of the first embodiment, and the positional relationship between the resonance tube portion 40 and the resonance cavity portion 50 differs from that of the first embodiment. Other than this, the fifth embodiment is similar to the first embodiment. Therefore, in this embodiment, differences from the first embodiment will be mainly described, and descriptions of similar portions to the first embodiment may be omitted.

As shown in Figures 19 and 20, the sound-absorbing board 10 of this embodiment, like the fourth embodiment, has a smaller size in the first direction D1 than the sound-absorbing board 10 of the first embodiment. And as shown in Figures 19 and 20, the resonant cavity 50 of this embodiment, like the fourth embodiment, has a slightly larger size in the first direction D1 than the resonant cavity 50 of the first embodiment. Also, as shown in Figures 19 to 21, the resonant cavity 50 of this embodiment has a cavity protrusion 521 formed on one side in the first direction D1 of the resonant cavity surface 52 surrounding the resonant cavity space Sc that protrudes into the resonant cavity space Sc.

As shown in Figure 21, the hollow protrusion 521 is formed in a spiral shape by bending like a square whose size increases from the inside to the outside. The hollow protrusion 521 has the same number of turns as the resonator tube section 40. In other words, the hollow protrusion 521 has a spiral shape with three turns. However, the winding direction of the hollow protrusion 521 is opposite to the winding direction of the resonator tube section 40. In other words, the hollow protrusion 521 and the resonator tube section 40 are wound in opposite directions along their respective spiral shapes.

The hollow protrusion 521 is formed around the tube side communicating portion 32 of the neck portion 30, with the tube side communicating portion 32 at its center. In other words, the hollow protrusion 521 is formed at a position that overlaps with the resonator tube portion 40 in the second direction D2 and the third direction D3. The hollow protrusion 521 has a substantially square cross section perpendicular to the direction along the spiral shape. The hollow protrusion 521 also has a constant opening area perpendicular to the direction along the spiral shape.

The resonant tube section 40 of this embodiment is formed so that its size in the first direction D1 is slightly smaller than the size of the hollow protrusion 521 in the first direction D1, and its size in the second direction D2 is slightly smaller than the size of the hollow protrusion 521 in the second direction D2. The resonant tube section 40 is disposed in the gap between the spiral-shaped hollow protrusions 521. In other words, the resonant tube section 40 of this embodiment is disposed adjacent to the resonant cavity space Sc, and is partially surrounded by the resonant cavity 50. Specifically, the resonant tube section 40 is surrounded by the resonant cavity 50 except for one side in the first direction D1.

This allows the part of the sound-absorbing board 10 that forms the resonant tube section 40 to be surrounded by the resonant cavity 50, and the part of the sound-absorbing board 10 that forms the resonant cavity 50 to surround the resonant tube section 40 to be shared.

In this embodiment, the resonator tube section 40 is supported by the neck section 30 by connecting the first tube end section 41 to the tube-side connecting section 32 of the neck section 30.

When sound waves are incident on the sound absorbing section 1 formed as described above, Helmholtz resonance occurs in the resonance tube space Sp and the resonance cavity space Sc, causing the air in the resonance tube space Sp to resonate at the resonance tube frequency and the air in the resonance cavity space Sc to resonate at the resonance cavity frequency. The sound absorbing section 1 then reduces the loudness of sound in the frequency band near the resonance tube resonance frequency, as well as the loudness of sound in the frequency band near the resonance cavity frequency.

Here, the resonant cavity 50 of this embodiment has a cavity protrusion 521 that protrudes into the resonant cavity Sc. Therefore, sound waves that enter the resonant cavity Sc are reflected in various directions between the areas where the cavity protrusion 521 is formed and the areas where the cavity protrusion 521 is not formed. In other words, sound waves that enter the resonant cavity Sc are diffusely reflected within the resonant cavity Sc. The diffusely reflected sound waves within the resonant cavity Sc then cause the air within the resonant cavity Sc to resonate at various frequencies.

As a result, when sound waves are incident on the sound absorbing section 1 and the air in the resonant cavity space Sc resonates, the frequency band of the cavity resonance frequency is wider than when sound waves are not diffusely reflected in the resonant cavity space Sc. Therefore, sound can be absorbed without using sound-absorbing materials, and the frequency band of sound that is reduced can be wider than in a configuration in which the resonant cavity section 50 does not have the cavity protrusion 521.

Furthermore, by arranging the resonant tube section 40 in the gap between the spiral-shaped hollow protrusions 521, the size of the sound-absorbing board 10 in the first direction D1 can be reduced compared to a configuration in which the resonant tube section 40 is not arranged in the gap between the spiral-shaped hollow protrusions 521. Furthermore, part of the area forming the resonant tube section 40 of the sound-absorbing board 10 can be shared with part of the area forming the resonant cavity section 50 of the sound-absorbing board 10.

Figure 22 shows the results of a simulation to verify the difference between the frequency band of sound that can be reduced by the sound absorbing section 1 of this embodiment and the frequency band of sound that can be reduced by the sound absorbing section 1 of the first embodiment. Note that the solid line in Figure 22 shows the frequency band of sound that can be reduced by the sound absorbing section 1 of this embodiment and the sound absorption coefficient for each frequency, and the dashed line in Figure 22 shows the frequency band of sound that can be reduced by the sound absorbing section 1 of the first embodiment and the sound absorption coefficient for each frequency.

As shown in Figure 22, the sound absorbing section 1 of this embodiment can reduce a wider frequency band of sound than the sound absorbing section 1 of the first embodiment. Specifically, the sound absorbing section 1 of this embodiment can expand the frequency band in which the sound absorption coefficient is 0.5 or higher by approximately 37% compared to the sound absorbing section 1 of the first embodiment.

In this way, the resonant cavity 50 has a cavity protrusion 521, which diffusely reflects sound waves that enter the resonant cavity space Sc, allowing the sound absorbing unit 1 to reduce a wider frequency band of sound.

Sixth Embodiment
Next, a sixth embodiment will be described with reference to Figures 23 to 26. In this embodiment, the configuration of the sound-absorbing board 10 differs from that of the first embodiment, and the positional relationship between the resonance tube portion 40 and the resonance cavity portion 50 differs from that of the fifth embodiment. Other than this, the sixth embodiment is similar to the fifth embodiment. Therefore, in this embodiment, differences from the fifth embodiment will be mainly described, and descriptions of similar portions to the fifth embodiment may be omitted.

As shown in Figures 23 to 26, the sound-absorbing board 10 of this embodiment has a first board 101, a second board 102, and a third board 103. The sound-absorbing board 10 is formed by stacking the first board 101, the second board 102, and the third board 103. The first board 101 has a first board surface 11 on one side in the first direction D1. The third board 103 has a second board surface 12 on the other side in the first direction D1. The second board 102 is disposed between the first board 101 and the third board 103.

The first plate member 101 has a portion of a neck portion 30 formed approximately at the center, penetrating in the first direction D1. The second plate member 102 has a portion of a neck portion 30 formed approximately at the center, penetrating in the first direction D1. Furthermore, the second plate member 102 has a resonant tube portion 40 formed on one side in the first direction D1, and a portion of a resonant cavity portion 50 formed on the other side in the first direction D1. The second plate member 102 also has a cavity recess 522 formed on the other side in the first direction D1, recessed toward one side in the first direction D1 with respect to the resonant cavity surface 52 surrounding the resonant cavity space Sc. The third plate member 103 has a portion of a resonant cavity portion 50 formed on one side in the first direction D1.

The resonant tube section 40 can be formed, for example, by cutting one side of the second plate member 102 in the first direction D1. The resonant cavity section 50 formed in the second plate member 102 can be formed by cutting the other side of the second plate member 102 in the first direction D1. The resonant cavity section 50 formed in the third plate member 103 can be formed by cutting one side of the third plate member 103 in the first direction D1. The resonant cavity section 50 in this embodiment is formed by combining the second plate member 102 and the third plate member 103.

As shown in Figure 26, the hollow recess 522 is formed in a spiral shape, bent like a square whose size increases from the inside to the outside. The hollow recess 522 has the same number of turns as the resonator tube section 40. In other words, the hollow recess 522 has a spiral shape with three turns. However, the winding direction of the hollow recess 522 is opposite to that of the resonator tube section 40. In other words, the hollow recess 522 and the resonator tube section 40 are wound in opposite directions along their spiral shapes.

The hollow recess 522 is formed around the neck portion 30, centered on the other side of the neck portion 30 in the first direction D1. The hollow recess 522 is formed in a position that does not overlap with the resonator tube portion 40 in the second direction D2 and the third direction D3. The hollow recess 522 has a substantially square cross section perpendicular to the direction along the spiral shape. The hollow recess 522 has a constant opening area perpendicular to the direction along the spiral shape.

In this embodiment, the resonator tube section 40 is formed so that it is located between the hollow recesses 522.

When sound waves are incident on the sound absorbing section 1 formed as described above, Helmholtz resonance occurs in the resonance tube space Sp and the resonance cavity space Sc, causing the air in the resonance tube space Sp to resonate at the resonance tube frequency and the air in the resonance cavity space Sc to resonate at the resonance cavity frequency. The sound absorbing section 1 then reduces the loudness of sound in the frequency band near the resonance tube resonance frequency, as well as the loudness of sound in the frequency band near the resonance cavity frequency.

Here, the resonant cavity 50 of this embodiment has a hollow recess 522 formed by being recessed relative to the resonant cavity surface 52. Therefore, sound waves incident on the resonant cavity Sc are reflected in various directions between the areas of the resonant cavity Sc where the hollow recess 522 is formed and the areas where the hollow recess 522 is not formed. In other words, sound waves incident on the resonant cavity Sc are diffusely reflected within the resonant cavity Sc. As a result, the air within the resonant cavity Sc resonates at various frequencies due to the sound waves diffusely reflected within the resonant cavity Sc.

As a result, when sound waves are incident on the sound absorbing section 1 and the air in the resonant cavity space Sc resonates, the frequency band of the cavity resonance frequency is wider than when sound waves are not diffusely reflected in the resonant cavity space Sc. Therefore, sound can be absorbed without using sound-absorbing materials, and the frequency band of sound that is reduced can be wider than in a configuration in which the resonant cavity section 50 does not have the cavity protrusion 521.

In addition, the sound-absorbing board 10 of this embodiment is formed by laminating a first board 101, a second board 102, and a third board 103. The resonant tube section 40 is formed on one side of the second board 102. The resonant cavity section 50 is formed on the other side of the second board 102 in the first direction D1 and on one side of the third board 103 in the first direction D1.

In this way, by forming the sound-absorbing board 10 in a laminated structure and configuring the resonant tube section 40 and resonant cavity section 50 on one side or the other of the board in the first direction D1, it is possible to easily form the resonant tube section 40 and resonant cavity section 50.

Seventh Embodiment
Next, a seventh embodiment will be described with reference to Fig. 27. In this embodiment, the shape of the sound-absorbing board 10 differs from that of the first embodiment, and the positional relationship between the resonance tube portion 40 and the resonance cavity portion 50 differs from that of the first embodiment. Other than this, the seventh embodiment is similar to the first embodiment. Therefore, in this embodiment, differences from the first embodiment will be mainly described, and descriptions of similar portions to the first embodiment may be omitted.

As shown in FIG. 27 , the sound-absorbing board 10 of this embodiment has a rectangular shape when viewed from a direction along the first direction D1, and is larger in the second direction D2 than in the third direction D3. Furthermore, the size of the sound-absorbing board 10 of this embodiment in the third direction D3 is the same as the size of the sound-absorbing board 10 of the first embodiment in the third direction D3, and is smaller in the first direction D1 than the size of the sound-absorbing board 10 of the first embodiment in the first direction D1. Furthermore, the size of the sound-absorbing board 10 of this embodiment in the second direction D2 is larger than the size of the sound-absorbing board 10 of the first embodiment in the second direction D2. Specifically, the size of the sound-absorbing board 10 of this embodiment in the second direction D2 is approximately twice the size of the sound-absorbing board 10 of the first embodiment in the second direction D2.

Hereinafter, when the sound-absorbing board 10 is divided into two equal parts in the second direction D2, one side in the second direction D2 will be referred to as the first sound-absorbing board 110, and the other side in the second direction D2 will be referred to as the second sound-absorbing board 120.

The first sound-absorbing board 110 has a sound-absorbing opening 21, a neck portion 30, and a resonant tube portion 40. The second sound-absorbing board 120 has a resonant cavity portion 50.

The resonant tube section 40 of this embodiment has a spiral shape with one turn, and the outer end of the spiral shape is connected to the resonant cavity section 50. That is, the second tube end section 42 of the resonant tube section 40 of this embodiment is connected to the cavity inlet section 51 of the resonant cavity section 50.

The resonance tube section 40 and the resonance cavity section 50 are formed side by side in a direction different from the first direction D1, which is the thickness direction of the sound-absorbing board 10. Specifically, the resonance tube section 40 and the resonance cavity section 50 are formed side by side in the third direction D3, which is the larger side of the sound-absorbing board 10, whose size in the third direction D3 is larger than its size in the second direction D2.

In this manner, according to this embodiment, in which the resonant tube section 40 and the resonant cavity section 50 are formed side by side in a direction different from the first direction D1, the size in the first direction D1, which is the direction along the thickness direction of the sound-absorbing board 10, can be reduced.

Eighth Embodiment
Next, an eighth embodiment will be described with reference to Fig. 28. In this embodiment, the shape of the sound-absorbing board 10 differs from that of the first embodiment, and the shapes of the resonance tube portion 40 and the resonance cavity portion 50 differ from those of the first embodiment. Other than this, the eighth embodiment is similar to the first embodiment. Therefore, in this embodiment, differences from the first embodiment will be mainly described, and descriptions of similar portions to the first embodiment may be omitted.

As shown in Figure 28, the sound-absorbing structure St of this embodiment is composed of three sound-absorbing sections 1 connected together. Furthermore, the sound-absorbing board material 10 of this embodiment is formed into a plate shape that has a regular hexagonal shape when viewed from a direction along the first direction D1. That is, the sound-absorbing board material 10 has a substantially regular hexagonal shape when viewed from a direction perpendicular to the board surface, and is a regular hexagonal prism shape whose size in the first direction D1 is smaller than its size in the second direction D2 and the third direction D3.

As shown in Figure 28, the sound absorbing structure St of this embodiment is constructed by connecting three sound absorbing sections 1, and of the six sound absorbing side surfaces 13 that form the outer shell of the regular hexagonal prism shape of the sound absorbing section 1, the sound absorbing side surfaces 13 of adjacent sound absorbing boards 10 are connected without any gaps.

The resonant tube 40 of this embodiment has a spiral shape with one turn. Furthermore, the resonant cavity 50 of this embodiment is formed in a regular hexagonal shape when viewed from the direction along the first direction D1. Specifically, the resonant cavity 50 has approximately equal sizes in the second direction D2 and the third direction D3, and is formed in a hexagonal prism shape that is approximately hexagonal when viewed from the direction along the first direction D1.

The resonant cavity 50 is formed so that its size in the first direction D1 is approximately the same as the size of the resonant tube 40 in the first direction D1. The resonant cavity 50 is also formed so that its size in the second direction D2 is larger than the size of the resonant tube 40 in the second direction D2, and its size in the third direction D3 is larger than the size of the resonant tube 40 in the third direction D3.

Other configurations are the same as those of the first embodiment. The sound absorbing unit 1 of this embodiment can obtain the same effects as those of the first embodiment, which are achieved by a configuration similar to or equivalent to that of the first embodiment.

Ninth Embodiment
Next, a ninth embodiment will be described with reference to Fig. 29. In this embodiment, the shape of the resonance tube portion 40 differs from that of the eighth embodiment. Other than this, the ninth embodiment is similar to the eighth embodiment. Therefore, in this embodiment, differences from the eighth embodiment will be mainly described, and descriptions of similarities with the first embodiment may be omitted.

As shown in FIG. 29 , the sound absorbing structure St of this embodiment, which is formed by connecting three sound absorbing parts 1, has resonance tubes 40 formed in the sound absorbing boards 10 of the three sound absorbing parts 1, each with a different length in the direction in which the path extends. However, in the sound absorbing structure St of this embodiment, which is formed by connecting three sound absorbing parts 1, the resonance cavities 50 formed in the sound absorbing boards 10 of the three sound absorbing parts 1 have the same shape. Furthermore, the resonance tubes 40 of this embodiment have a smaller size in the first direction D1 than the resonance tubes 40 of the eighth embodiment. The resonance cavities 50 of this embodiment have a smaller size in the first direction D1 than the resonance cavities 50 of the eighth embodiment.

By configuring the resonant tube sections 40 in this way so that the lengths of the paths in the direction of extension are different from one another, it is easier to adjust the frequency band of the sound to be reduced compared to a configuration in which the lengths of the paths in the direction of extension of the resonant tube sections 40 are constant.

Other configurations are the same as those of the first embodiment. The sound absorbing unit 1 of this embodiment can obtain the same effects as those of the first embodiment, which are achieved by a configuration similar to or equivalent to that of the first embodiment.

(First Modification of the Ninth Embodiment)
In the above-described ninth embodiment, a configuration has been described in which the lengths of the respective paths of the resonant tube sections 40 formed on the sound-absorbing board material 10 of each of the plurality of sound absorbing sections 1 are different from one another, but the present invention is not limited to this.

For example, the resonant tube sections 40 formed on the sound-absorbing board material 10 of each of the multiple sound absorbing units 1 may have different opening areas in the direction in which the path extends. Alternatively, the resonant tube sections 40 formed on the sound-absorbing board material 10 of each of the multiple sound absorbing units 1 may have different lengths in the direction in which the path extends, and different opening areas in the direction in which the path extends.

(Second Modification of the Ninth Embodiment)
In the above-described ninth embodiment, the resonant cavities 50 formed in the sound-absorbing boards 10 of the three sound-absorbing units 1 are identical in shape to each other. However, the present invention is not limited to this.

For example, the resonant cavities 50 formed in the sound-absorbing board material 10 of each of the three sound-absorbing sections 1 may have different shapes, such as different sizes in the first direction D1.

Tenth Embodiment
Next, a tenth embodiment will be described with reference to Fig. 30. In this embodiment, the shape of the sound-absorbing board 10 differs from that of the first embodiment, and the shapes of the resonance tube portion 40 and the resonance cavity portion 50 also differ from those of the first embodiment. Other than this, the tenth embodiment is similar to the first embodiment. Therefore, in this embodiment, differences from the first embodiment will be mainly described, and descriptions of similar portions to the first embodiment may be omitted.

As shown in Figure 30, the sound-absorbing structure St of this embodiment is composed of three connected sound-absorbing sections 1. Furthermore, the sound-absorbing board material 10 of this embodiment is formed into a plate shape that has an equilateral triangular shape when viewed from a direction along the first direction D1. In other words, the sound-absorbing board material 10 has a substantially equilateral triangular shape when viewed from a direction perpendicular to the board surface.

The sound absorbing structure St of this embodiment, which is constructed by connecting multiple sound absorbing sections 1, has three sound absorbing side surfaces 13 that form the outer shell of a regular triangular prism shape, and of these, portions of the sound absorbing side surfaces 13 of adjacent sound absorbing boards 10 are connected. In the sound absorbing structure St of this embodiment, which is constructed by connecting three sound absorbing sections 1, the sound absorbing boards 10 are connected so that the first direction D1, which is the thickness direction of each sound absorbing board 10, does not intersect with each other.

In the sound-absorbing structure St of this embodiment, one side constituting the sound-absorbing side surface 13 of each of the adjacent sound-absorbing boards 10 is connected to the other, and adhesive G is filled into the gap between the sound-absorbing side surfaces 13 of the adjacent sound-absorbing boards 10, connecting them together with this adhesive G.

The resonant tube 40 of this embodiment has a spiral shape with one turn. Furthermore, the resonant cavity 50 of this embodiment is formed in a triangular shape when viewed along the first direction D1. Specifically, the resonant cavity 50 is formed in a triangular prism shape in which the three sides forming the outer shell of the triangle when viewed along the first direction D1 are of approximately equal lengths, and the shape when viewed along the first direction D1 is approximately an equilateral triangle.

Other configurations are the same as those of the first embodiment. The sound absorbing unit 1 of this embodiment can obtain the same effects as those of the first embodiment, which are achieved by a configuration similar to or equivalent to that of the first embodiment.

The sound-absorbing structure St of this embodiment, in which multiple sound-absorbing boards 10 are connected so that the thickness directions of the individual sound-absorbing boards 10 do not intersect with each other, allows the sound-absorbing structure St to have a curved shape. Therefore, even if the object to which the sound-absorbing structure St is attached has a curved shape rather than a flat shape, the sound-absorbing structure St can be formed to correspond to the shape of the object.

(Other embodiments)
Representative embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments and can be modified in various ways, for example, as follows.

In the above embodiment, an example was described in which the sound absorbing unit 1 has one resonant tube unit 40 and one resonant cavity unit 50, but this is not limited to this.

For example, the sound absorbing section 1 may be configured to have multiple resonant tube sections 40 and multiple resonant cavities 50.

In the above embodiment, an example was described in which the sound absorbing structure St is composed of multiple sound absorbing sections 1 connected together, but this is not limited to this.

The sound-absorbing structure St may be composed of only one sound-absorbing part 1.

It goes without saying that in the above-described embodiments, the elements constituting the embodiments are not necessarily essential unless they are specifically stated as essential or are clearly considered essential in principle.

In the above-described embodiments, when numerical values such as the number, values, amounts, ranges, etc. of components of the embodiments are mentioned, they are not limited to those specific numbers unless expressly stated as essential or unless they are clearly limited to a specific number in principle.

In the above-described embodiments, when referring to the shapes, positional relationships, etc. of components, etc., there is no limitation to those shapes, positional relationships, etc., unless otherwise specified or in principle limited to specific shapes, positional relationships, etc.

10: Sound-absorbing plate material 20: Resonating portion 21: Sound-absorbing opening 30: Neck portion 40: Resonating tube portion 50: Resonating cavity portion S: Resonating space Sc: Resonating cavity space Sp: Resonating tube space

Claims (13)

A sound absorbing structure,
A plate-shaped sound-absorbing board material (10) that forms an outer shell;
a resonance section (20) having a sound-absorbing opening (21) communicating with the outside of the sound-absorbing board material, and a resonance space (S) communicating with the sound-absorbing opening and formed in a hollow shape inside the sound-absorbing board material,
The resonator unit is
a neck portion (30) having the sound-absorbing opening and extending toward the inside of the sound-absorbing board;
a resonance tube portion (40) that is a part of the resonance space, one end of which is connected to the neck portion and forms a resonance tube space (Sp) that extends in a hollow tubular shape toward the inside of the sound-absorbing board;
a resonance cavity portion (50) that is a part of the resonance space and communicates with at least one of the neck portion and the resonance tube portion, and forms a resonance cavity space (Sc) that expands inside the sound-absorbing board material. A sound-absorbing structure as described in claim 1, wherein the resonating tube portion has a bent portion (43) formed by bending. A sound-absorbing structure as described in claim 1, wherein the resonating tube section has a stepped section (45) in which the opening area in a direction perpendicular to the direction of extension from the one end to the other end gradually changes along the extension direction of the resonating tube section. A sound-absorbing structure as described in claim 1, wherein the resonant pipe portion has a resonant pipe path portion (46) that communicates with the outside of the sound-absorbing board material midway from the one end to the other end. The sound-absorbing structure described in claim 1, wherein at least a portion of the resonant tube portion is formed inside the resonant cavity space. The resonant cavity portion has a resonant cavity surface (52) that surrounds the resonant cavity space,
2. The sound-absorbing structure according to claim 1, wherein the resonant cavity surface has at least one of a cavity recess (522) formed recessed relative to the resonant cavity surface and a cavity protrusion (521) protruding toward the resonant cavity space. The sound-absorbing structure according to claim 1, wherein the resonant tube portion and the resonant cavity portion are arranged side by side at a predetermined interval in the thickness direction of the sound-absorbing board material. The sound-absorbing structure according to claim 1, wherein the resonant tube portion and the resonant cavity portion are arranged side by side in a direction different from the thickness direction of the sound-absorbing board material. A sound-absorbing structure according to any one of claims 1 to 7, in which a plurality of sound-absorbing sections (1) are connected together, each comprising one sound-absorbing board, at least one resonant tube section, and at least one resonant cavity section. The sound-absorbing structure according to claim 9, wherein the resonating tube sections of the plurality of sound-absorbing sections differ from one another in at least one of their lengths in the extension direction and their opening areas in the direction perpendicular to the extension direction. The sound-absorbing board has a sound-absorbing side surface (13) that forms an outer shell of the sound-absorbing board and extends in a plane in a direction different from the direction along the board thickness direction of the sound-absorbing board,
The sound absorbing structure according to claim 9 , wherein the sound absorbing portions are formed by connecting the sound absorbing side surfaces of the sound absorbing boards together without any gaps. The sound-absorbing structure according to claim 11, wherein the shape of the sound-absorbing board in the thickness direction of the sound-absorbing board is one of an equilateral triangle, a square, and a regular hexagon. The sound-absorbing structure described in claim 9, wherein the multiple sound-absorbing sections are connected so that the thickness directions of the multiple sound-absorbing boards intersect.