Sound absorber and sound environment adjustment structure

Abstract

To construct a sound absorber capable of easily changing an indoor sound environment, and improve comfort of a room using the sound absorber.SOLUTION: A sound absorber 10 comprises: a self-supporting rectangular frame body 11 with a part of an outside surface serving as a bottom part; a first membrane body 12 closing a first opening 11a on one end side of the frame body 11; a second membrane body 13 closing a second opening 11b on the other end side of the frame body 11; and a sound absorption material 14 made of a porous material, which is arranged inside the frame body 11. The sound absorber is configured to exhibit different sound absorption characteristics depending on whether sound is incident from the first membrane body 12 side or the second membrane body 13 side, and is provided in a room to adjust a sound environment in the room.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a sound absorber and a sound environment adjustment structure for use indoors. [Background technology]

[0002] Conventionally, in order to improve the sound environment in a house, office, etc., sound absorbers have been placed in the room to absorb voices and other sounds (see, for example, Patent Document 1 listed below).

[0003] In Patent Document 1, multiple plate-shaped or block-shaped sound absorbers made of sound-absorbing material are hung from the ceiling so as to surround the periphery of the booth, reducing sound leakage into and out of the booth and suppressing sound reverberation within the booth, making it easier to have conversations within the booth. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-034006 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the sound absorber used in Patent Document 1 is made of one type of sound-absorbing material and has a limited frequency band that it can absorb. Therefore, when it becomes necessary to change the sound environment in the room (such as the frequency band of sound to be absorbed) due to, for example, a change in the use of the room (changing a conference room used for face-to-face meetings into a conference room used for online meetings), it is necessary to remove the sound absorber suspended from the ceiling and replace it with a sound absorber with different sound absorption characteristics (different sound absorption coefficients for each frequency band), making it difficult to change the sound environment in the room.

[0006] The present invention has been made in view of the above points, and its object is to construct a sound absorber that can easily change the sound environment in a room, and to use this sound absorber to improve the comfort of the room. [Means for solving the problem]

[0007] In order to achieve the above object, in the present invention, a sound absorbing body whose sound absorbing characteristics change simply by changing its orientation is used to adjust the sound environment in a room.

[0008] Specifically, the first invention is a sound-absorbing body that is installed in a room and adjusts the sound environment within the room, and is characterized by comprising a rectangular frame body that is self-supporting with part of its outer surface as the bottom, a first membrane body that closes a first opening at one end of the frame body in the depth direction, a second membrane body that closes a second opening at the other end of the frame body in the depth direction, and a sound-absorbing material made of a porous material that is placed inside the frame body, and is configured so that the sound absorption characteristics it exhibits differ depending on whether sound is incident from the first membrane side or the second membrane side.

[0009] In the first invention, the sound absorber is configured such that a rectangular frame body is self-supporting, with a first membrane and a second membrane facing each other horizontally with a sound-absorbing material sandwiched between them, and the sound absorption characteristics it exhibits differ depending on whether the sound is incident from the first membrane side or the second membrane side. In other words, according to the first invention, a sound absorber is configured whose sound absorption characteristics change simply by changing its orientation, and such a sound absorber is installed in a room to adjust the sound environment in the room, so that the comfort of the room can be easily improved simply by changing the orientation of the sound absorber.

[0010] A second invention is characterized in that, in the first invention, the first film body and the second film body are configured to be distinguishable from each other.

[0011] In the second aspect of the present invention, the first film and the second film are configured to be distinguishable from each other, so that the orientation of the sound absorber can be easily changed to an orientation that matches the desired sound absorption characteristics.

[0012] A third invention is characterized in that in the first invention, the first film body and the second film body are made of different materials.

[0013] In the third invention, the first and second membranes are made of different materials, and therefore have different sound transmittances. When sound enters from the membrane side through which sound is easily transmitted, the sound easily enters the sound absorber, and the porous sound-absorbing effect of the sound-absorbing material is exerted. However, when sound enters from the membrane side through which sound is less transmitted, the sound is less likely to enter the sound absorber, and the porous sound-absorbing effect of the sound-absorbing material is hardly exerted, while the membrane vibration of the membrane exerts a membrane-vibration sound-absorbing effect. Porous-type sound absorption tends to have a high sound absorption coefficient from the mid-low to high frequencies, while membrane-vibration-type sound absorption tends to have a high sound absorption coefficient only in a narrow frequency band from the mid-low to mid frequencies. In other words, the sound absorber according to the third invention has different sound absorption coefficients (exhibited sound absorption characteristics) for each frequency band depending on whether the sound is incident from the first membrane side or the second membrane side. In this way, according to the third invention, it is possible to easily construct a sound absorber whose exhibited sound-absorbing characteristics can be changed simply by changing the orientation.

[0014] A fourth invention is characterized in that in the first invention, the first film body is made of woven fabric, and the second film body is made of artificial leather.

[0015] In a fourth aspect of the present invention, the first membrane is made of woven fabric, and the second membrane is made of artificial leather, which has lower breathability than woven fabric. The first membrane made of woven fabric transmits sound easily, while the second membrane made of artificial leather, which has lower breathability than woven fabric, transmits sound less easily than the first membrane. Therefore, in the sound absorber according to the fourth aspect of the present invention, when sound enters from the first membrane side, the sound easily passes through the first membrane and enters the sound absorber, and the porous sound absorption effect of the sound absorbing material is exerted. However, when sound enters from the second membrane side, the sound does not easily enter the sound absorber, and the porous sound absorption effect of the sound absorbing material is hardly exerted, while the membrane vibration of the second membrane exerts a membrane vibration sound absorption effect. Thus, according to the fourth aspect of the present invention, it is easy to construct a sound absorber whose sound absorption characteristics can be changed simply by changing its orientation.

[0016] The fifth invention is characterized in that, in the fourth invention, the sound-absorbing material is formed in a plate shape and is arranged so as to form an air layer between the first and second membrane bodies.

[0017] In the fifth invention, the sound-absorbing material is provided inside the frame so that an air layer is defined between the sound-absorbing material and the two membranes. That is, the sound-absorbing material made of a porous material and having a thickness thinner than the depth dimension of the frame is arranged inside the frame so that an air layer is defined between the two membranes. With this configuration, air layers are formed in front of and behind the sound-absorbing material made of a porous material inside the sound absorber.

[0018] However, the porous-type sound-absorbing effect of a sound-absorbing material made of a porous material tends to be less pronounced the thinner the sound-absorbing material, with the effect being particularly pronounced in the low to mid-low range.On the other hand, tests have shown that a sound absorber in which a sound-absorbing material made of a porous material is abutted against a rigid wall and woven fabric is arranged so as to provide an air layer between the sound-absorbing material and the rigid wall has a lower sound absorption coefficient in the low to mid-low range due to the thinner sound-absorbing material, compared to a sound absorber in which a sound-absorbing material that is thick enough to accommodate the air layer is abutted against the rigid wall and woven fabric is arranged on the opposite side of the sound-absorbing material from the rigid wall.However, it has been found that the sound absorption coefficient in the mid-low to high ranges does not decrease, and is as high as when no air layer is provided. Furthermore, tests were also conducted on a sound absorber in which a thin sound-absorbing material just thin enough to accommodate the air layer was placed against a rigid wall and no woven fabric was placed, and it was found that the sound absorber in which a thin sound-absorbing material just thin enough to accommodate the air layer was placed against a rigid wall and a woven fabric was placed so that an air layer was created between the sound-absorbing material and the sound absorber had a higher sound absorption coefficient in the low-frequency range over a wide frequency range from mid-low to high frequencies than the sound absorber without woven fabric.This result shows that even if the thickness of the sound-absorbing material is thin, if the woven fabric is placed so that an air layer is created between the sound-absorbing material and the sound absorber, the sound absorption coefficient in the low-mid to high frequencies can be maintained at a high level without decreasing.

[0019] Therefore, in the sound absorber of the fifth invention, when the second membrane abuts against or is close to a wall (rigid wall) inside the room and sound is incident from the first membrane, the thickness of the sound absorbing material is thinner than in a sound absorber without an air layer in which a sound absorbing material made of a porous material with the same thickness as the depth dimension of the frame is placed inside the frame, but since the first membrane made of woven fabric is placed so as to create an air layer between it and the sound absorbing material, the sound absorption coefficient in the low range is lower than in a sound absorber without an air layer, but the sound absorption coefficient in the mid-low to high range is about the same as that of a sound absorber without an air layer.

[0020] On the other hand, in the sound absorber of the fifth invention, when the first membrane is in contact with or close to a wall (rigid wall) inside a room and sound is incident from the second membrane, as with the sound absorber without an air layer described above, the second membrane made of artificial leather is less likely to transmit sound and the porous sound absorption effect of the sound absorbing material is hardly exerted. As a result, the membrane vibration type sound absorption effect of the second membrane is exerted, resulting in a high sound absorption coefficient only in a narrow frequency band from the mid-low range to the mid-range. However, compared to the sound absorber without an air layer described above, the tension of the second membrane is reduced, which reduces the natural frequency of the membrane vibration, and therefore the frequency band in which the membrane vibration type sound absorption effect of the second membrane is exerted is also shifted to the lower range.

[0021] Thus, the sound absorbing characteristics exhibited by the sound absorber according to the fifth aspect of the invention also differ depending on whether the sound is incident from the first film side or the second film side, and also differ from the sound absorbing characteristics of a sound absorber without an air layer. Therefore, according to the fifth aspect of the invention, the sound absorbing characteristics of the sound absorber can be easily changed simply by forming an air layer between the sound absorbing material and each of the two films.

[0022] The sixth invention is characterized in that, in the fourth invention, the frame body comprises a first frame material framed in a rectangular shape that forms the first opening, and a second frame material framed in a rectangular shape that forms the second opening, and is formed by joining the first frame material and the second frame material, and the sound-absorbing material is formed in a plate shape and is provided one each in a first space inside the first frame material and a second space inside the second frame material so that an air layer is formed between them.

[0023] In a sixth aspect of the present invention, one sound-absorbing material is provided in each of two spaces inside the two frame members, and the two sound-absorbing materials are provided so that an air layer is formed between them. This configuration results in two sound-absorbing materials made of porous material being provided inside the sound absorber, and an air layer is formed behind the front sound-absorbing material (on the second membrane side of the sound-absorbing material on the first frame member side when sound is incident from the first membrane side, and on the first membrane side of the sound-absorbing material on the second frame member side when sound is incident from the second membrane side). As described above, porous sound absorbers tend to have a high sound absorption coefficient from the mid-low to high frequencies. However, when an air layer is provided between two sound-absorbing materials made of porous material, the thickness of the sound-absorbing material becomes thinner than when no air layer is provided between the two sound-absorbing materials made of porous material, making it difficult to achieve the sound-absorbing effect, and this effect is particularly significant in the low to mid-low frequencies. On the other hand, tests have shown that a sound absorber in which a first sound-absorbing material made of a porous material is placed against a rigid wall, a second sound-absorbing material is placed so that an air layer is formed between the first sound-absorbing material, and a woven fabric is placed on the side of the second sound-absorbing material opposite the air layer has a lower sound absorption coefficient in the low to low-mid ranges due to the thinner sound-absorbing material compared to a sound absorber in which two sound-absorbing materials, each thick enough to accommodate the air layer, are stacked together, one of which is placed against a rigid wall, and the other is placed against the rigid wall opposite the rigid wall, with no air layer between them, but the sound absorption coefficient in the low-mid to high ranges does not decrease and is as high as when no air layer is placed. Tests have also been conducted on a sound absorber with an air layer between the two sound-absorbing materials and no woven fabric, and it was found that the sound absorber with the woven fabric and air layer between the two sound-absorbing materials had a higher sound absorption coefficient in the low range over a wide frequency range from low-mid to high. These results show that even if the thickness of the sound-absorbing material is reduced by creating an air layer between the two sound-absorbing materials, by placing woven fabric on the side of the sound-absorbing material farthest from the rigid wall opposite the rigid wall, the sound absorption coefficient can be maintained high in the mid-low to high ranges without any decrease.

[0024] Therefore, in the sound absorber of the sixth invention, when the second membrane abuts against or is close to a wall (rigid wall) inside the room and sound is incident from the first membrane, the thickness of the sound absorbing material is thinner by the air layer provided between the two sound absorbing materials than in a sound absorber without an air layer in which a sound absorbing material made of a porous material with a thickness equal to the depth dimension of the frame is placed inside the frame, and although the sound absorption coefficient in the low range is lower than in a sound absorber without an air layer, the sound absorption coefficient in the mid-low range to high range is about the same as that of a sound absorber without an air layer due to the presence of the first membrane.

[0025] On the other hand, in the sound absorber of the sixth invention, when the first membrane abuts against or is close to a wall (rigid wall) inside the room and sound is incident from the second membrane, the second membrane made of artificial leather does not easily transmit sound, just like the sound absorber without an air layer described above, and the porous sound absorption effect of the sound absorbing material is hardly exerted.As a result, the membrane vibration sound absorption effect of the second membrane is exerted, and the sound absorption coefficient becomes high only in a narrow frequency band from the mid-low range to the mid range.

[0026] Thus, the sound absorption characteristics exhibited by the sound absorber according to the sixth aspect of the invention also differ depending on whether the sound is incident from the first film side or the second film side, and also differ from the sound absorption characteristics of a sound absorber without an air layer. Therefore, according to the sixth aspect of the invention, the sound absorption characteristics of the sound absorber can be easily changed simply by providing an air layer between two sound-absorbing materials.

[0027] The seventh invention is characterized in that, in the first invention, the frame body comprises a first frame material framed in a rectangular shape that forms the first opening, and a second frame material framed in a rectangular shape that forms the second opening, and is formed by joining the first frame material and the second frame material, and the first film body, together with the first opening, integrally covers the front end face and outer surface of the first frame material on the first opening side, and its peripheral portion is fixed to the back end face or inner surface of the first frame material, and the second film body, together with the second opening, integrally covers the front end face and outer surface of the second frame material on the second opening side, and its peripheral portion is fixed to the back end face or inner surface of the second frame material.

[0028] In the seventh invention, the frame body is constructed from two frame materials (first and second frame materials), and each membrane integrally covers each opening and the front end face and outer surface of each frame material, with its peripheral edge fixed to the back end face or inner surface of each frame material. If the frame body were constructed from a single frame material, blocking each of the frame body's two openings with two membranes would likely result in the membrane's peripheral edge being located on the outer surface of the frame body, which is easily visible, thereby reducing the design of the sound absorber. However, according to the seventh invention, the frame body is constructed from two frame materials, and the two membranes blocking the two openings are configured to cover not only the openings but also the back end face or inner surface of the frame material. With this configuration, when the first and second frame materials are joined together with the first and second membranes fixed to them, the peripheral edges of the first and second membranes are sandwiched between the joint between the first and second frame materials and are not exposed on the outer surface of the frame body, which is easily visible. That is, according to the seventh aspect of the present invention, it is possible to provide a sound absorber with excellent design.

[0029] The eighth invention is a sound environment adjusting structure for adjusting the sound environment in a room, characterized in that a plurality of sound absorbers according to any one of the first to seventh inventions are provided on a shelf installed in the room.

[0030] According to the eighth aspect of the present invention, a plurality of sound absorbers whose sound absorption characteristics change simply by changing their orientation are provided on shelves in a room, and by changing their orientation, the sound environment in the room can be easily adjusted. [Effects of the Invention]

[0031] As explained above, according to the present invention, a sound absorbing body whose sound absorption characteristics change simply by changing its orientation is used to adjust the sound environment in a room, so that a sound absorbing body that can easily change the sound environment in a room can be provided, and the comfort of the room can be improved by using this sound absorbing body. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is an interior view showing an example of a sound environment adjustment structure according to a first embodiment of the present invention. [Figure 2]FIG. 2 is an explanatory diagram for explaining the structure of the sound absorber in the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view of the sound absorber according to the first embodiment. [Figure 4] FIG. 4 is a graph showing the results of a sound absorption performance test carried out in the first embodiment. [Figure 5] FIG. 5 is a cross-sectional view of the sound absorber according to the second embodiment. [Figure 6] FIG. 6 is a cross-sectional view of a sound absorber according to the third embodiment. [Figure 7] FIG. 7 is a graph showing the results of a sound absorption performance test carried out in the third embodiment. [Figure 8] FIG. 8 is a cross-sectional view of the sound absorber according to the fourth embodiment. [Figure 9] FIG. 9 is a graph showing the results of a sound absorption performance test carried out in the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following description of the embodiments is merely exemplary in nature and is not intended to limit the present invention, its applications, or uses.

[0034] First Embodiment of the Invention 1 is an interior view showing a sound environment adjusting structure 1 according to a first embodiment of the present invention. In this first embodiment, as an example of the sound environment adjusting structure 1, a sound absorbing body 10 according to the present invention is provided in a conference room of an office to adjust the sound environment of the conference room.

[0035] A plurality of shelves 2 are installed on a wall W in a conference room shown in Fig. 1. The sound environment adjusting structure 1 of the first embodiment is configured to adjust the sound environment in the conference room by providing a plurality of sound absorbers 10 on the plurality of shelves 2, the sound absorption characteristics of which change simply by changing the orientation of the plurality of sound absorbers 10.

[0036] Here, the change / different sound absorption characteristics means that the sound absorption coefficient changes / differently for each frequency band.

[0037] -Sound absorbing body composition- 2 and 3, the sound absorber 10 includes a frame 11, first and second membranes 12 and 13, and sound absorbing materials 14 (two in the first embodiment). The frame 11 is made up of four plate-like bodies arranged in a rectangular shape, with a first opening 11a at one end in the depth direction being closed by the first membrane 12 and a second opening 11b at the other end being closed by the second membrane 13. The sound absorbing materials 14 (two in the first embodiment) are provided in the internal space inside the frame 11 that is closed by the first and second membranes 12 and 13.

[0038] The sound absorber 10 is self-supporting with part of the outer surface of the frame 11 as its bottom, and is configured so that the first film 12 and the second film 13 are arranged facing each other in the horizontal direction with the sound-absorbing material 14 sandwiched between them. When the sound absorber 10 is installed (self-supporting with part of the outer surface of the frame 11 as its bottom), it has dimensions of approximately 400 to 500 mm in width, 300 to 400 mm in height, and 80 to 111 mm in depth. In this embodiment 1, the sound absorber 10 is formed to have dimensions of 458 mm in width, 318 mm in height, and 100 mm in depth.

[0039] (Frame) In the first embodiment, the frame body 11 is formed by a cylindrical body with a rectangular cross section that is framed in a rectangular shape. In the first embodiment, the frame body 11 is formed by joining first and second frame members 15, 16, each of which is a cylindrical body with a rectangular cross section. The first and second frame members 15, 16 are formed, for example, by framing four rectangular wooden boards (four rectangular plywood boards with a thickness of 12 mm in the first embodiment) into a rectangular shape. The first and second frame members 15, 16 are joined by a plurality of dowels 17. The dowels 17 join the first and second frame members 15, 16 by fitting their ends into dowel holes h formed in the rear end surfaces 15c, 16c of the first and second frame members 15, 16. The back end faces 15c, 16c of the first and second frame members 15, 16 in which the dowel holes h are formed are the end faces opposite the front end faces 15a, 16a on the first and second openings 11a, 11b sides of the two end faces of the frame body 11. The first frame member 15 forms the first opening 11a, and the second frame member 16 forms the second opening 11b.

[0040] (membrane body) The first film 12 and the second film 13 are made of different materials. The first and second films 12, 13 can be made of woven fabric, artificial leather, natural leather, resin film, etc. In this embodiment 1, the first film 12 is made of woven fabric, and the second film 13 is made of artificial leather. In this embodiment 1, by making the first and second films 12, 13 of different materials, the sound absorber 10 is configured to exhibit different sound absorption characteristics depending on whether the sound is incident from the first film 12 side or the second film 13 side.

[0041] Furthermore, the first film 12 and the second film 13 are configured to be distinguishable. In the first embodiment, the colors of the first film 12 and the second film 13 are different enough to be distinguishable. In the first embodiment, the color of the first film 12 is gray, and the color of the second film 13 is black. The method of making the first film 12 and the second film 13 distinguishable is not limited to changing the color. They may be configured to be distinguishable by changing the patterns of the first film 12 and the second film 13, or by marking only one of them. Note that, as in the first embodiment, when the first film 12 and the second film 13 are made of different materials and the surface textures (gloss, unevenness, tactile feel, etc.) are different enough to be distinguishable, there is no need to change the color or pattern or mark them.

[0042] The first film 12 is formed to a size that integrally covers the first opening 11a and the front end surface 15a, outer surface 15b, rear end surface 15c, and at least the rear end portion of the inner surface 15d of the first frame member 15. The first film 12 is wrapped around the first frame member 15 so as to integrally cover the first opening 11a and the front end surface 15a, outer surface 15b, rear end surface 15c, and at least the rear end portion of the inner surface 15d of the first frame member 15, and its peripheral edge is fixed to the inner surface 15d of the first frame member 15 with a stapler, adhesive, or the like. Note that in this embodiment 1, the first film 12 has holes formed therein that correspond to the dowel holes h in the rear end surface 15c of the first frame member 15.

[0043] In addition, in this embodiment 1, the first membrane 12 is made of a rectangular woven fabric with rectangular cutouts formed in the four corners. The cutouts at the four corners of the first membrane 12 are formed by cutting out the portions that will become excess portions so that, when the first membrane 12 is fixed to the first frame member 15, excess portions (portions that do not abut the outer surface 15b) are not generated at the corners of the outer surface 15b of the first frame member 15. In this embodiment 1, at the four corners of the outer surface 15b of the first frame member 15, each of the two sides that form the edges of the cutouts of the first membrane 12 are sewn together.

[0044] The second film 13 is formed in the same manner as the first film 12. Specifically, the second film 13 is formed to a size that integrally covers the front end surface 16a, the outer surface 16b, the rear end surface 16c, and at least the rear end portions of the inner surface 16d of the second frame member 16, together with the second opening 11b. The second film 13 is wrapped around the second frame member 16 so as to integrally cover the second opening 11b and the front end surface 16a, the outer surface 16b, the rear end surface 16c, and at least the rear end portions of the inner surface 16d of the second frame member 16, and its peripheral edge is fixed to the inner surface 16d of the second frame member 16 with a stapler, adhesive, or the like. In this embodiment 1, the second film 13 has holes formed in it that correspond to the dowel holes h in the rear end surface 16c of the second frame member 16.

[0045] In addition, in this embodiment 1, the second membrane 13 is made of rectangular artificial leather with rectangular cutouts formed in the four corners. The cutouts at the four corners of the second membrane 13 are formed in advance to remove excess portions (portions that do not abut the outer surface 16b) from the corners of the outer surface 16b of the second frame member 16 when the second membrane 13 is fixed to the second frame member 16. In this embodiment 1, at the four corners of the outer surface 16b of the second frame member 16, each of the two sides that form the edges of the cutouts of the second membrane 13 are sewn together.

[0046] With the above-described configuration, when the first and second membrane bodies 12, 13 are fixed to the first and second frame members 15, 16 and the first and second frame members 15, 16 are joined with dowels 17, the peripheral portions of the first and second membrane bodies 12, 13 are sandwiched between the joints of the first and second frame members 15, 16 and are not exposed on the outer surface of the frame body 11, where they are easily visible to the public.

[0047] (sound absorbing material) The sound-absorbing material 14 is made of a porous material and is formed in a plate shape. In this embodiment 1, one sound-absorbing material 14 is provided in each of the first space S1 inside the first frame member 15 and the second space S2 inside the second frame member 16. In this embodiment 1, each sound-absorbing material 14 is formed to a thickness of 50 mm and a size equal to the interior dimensions of the first and second frame members 15, 16.

[0048] The porous material constituting the sound-absorbing material 14 is not particularly limited as long as it is a fiber aggregate or resin foam with sound-absorbing properties. A fiber aggregate with sound-absorbing properties has numerous three-dimensionally continuous (interconnected) voids within it, allowing air to pass through the interior and exterior of the aggregate. This fiber aggregate has excellent breathability and soundproofing properties. Examples of such fiber aggregates include woven fabrics (fibrous materials), nonwoven fabrics, wood fiberboard, and inorganic fiberboard. Specific examples include inorganic fiber aggregate materials such as rock wool, glass wool, and soft fibers; and resin fiber aggregate materials such as polyethylene terephthalate (PET) fibers (recycled PET fibers, etc.) and polyester fibers. A resin foam with sound-absorbing properties is an open-cell foam with an open-cell structure in which air bubbles are connected within the foam, allowing air to pass through the interior and exterior of the foam. This foam has excellent breathability and soundproofing properties. Examples of open-cell foams include resin foam materials such as polyurethane foam (urethane foam) and acrylic resin foam (acrylic foam). In the first embodiment, a relatively lightweight polyethylene terephthalate (PET) nonwoven fabric is used as the sound absorbing material 14.

[0049] -How to adjust the sound environment- As shown in Fig. 1, sound absorbers 10 configured as described above are provided by freestanding them on a shelf 2 installed on a wall W of a room, with part of the outer surface of frame body 11 (long side or short side surface of first and second frame members 15, 16) forming the bottom. By freestanding sound absorbers 10 in this way, in each sound absorber 10, first film body 12 and second film body 13 made of different materials are arranged horizontally facing each other with sound-absorbing material 14 sandwiched between them. Then, the orientation of each sound absorber 10 is adjusted.

[0050] Specifically, when the sound absorber 10 is installed with the first film 12 facing the center of the room and the second film 13 facing the wall W, the woven fabric that makes up the first film 12 is relatively breathable and easily transmits sound. Therefore, most of the sound that occurs in the center of the room and enters the first film 12 passes through the first film 12, and the porous sound-absorbing effect of the sound-absorbing material 14 is exerted. Porous sound absorption tends to have a high sound absorption coefficient from the low-midrange to the high-frequency range. Therefore, when the sound absorber 10 is installed with the first film 12 facing the center of the room, sound enters from the first film 12 side, and the porous sound-absorbing effect of the sound-absorbing material 14 increases the sound absorption coefficient over a wide frequency range from the low-midrange to the high-frequency range (160 to 8000 Hz), effectively absorbing the sound.

[0051] On the other hand, if the sound absorber 10 is installed with the second membrane 13 facing the center of the room and the first membrane 12 facing the wall W, the artificial leather that makes up the second membrane 13 has relatively low breathability and is less susceptible to sound transmission than the first membrane 12, so most of the sound that occurs in the middle of the room and enters the second membrane 13 is reflected. As a result, the porous sound absorption effect of the sound absorbing material 14 is hardly exerted, but the sound hits the second membrane 13 and vibrates it, thereby exerting a high membrane vibration sound absorption effect due to the artificial leather that makes up the second membrane 13. Membrane vibration sound absorbers tend to have a high sound absorption coefficient only in a narrow frequency band from the low-mid range to the mid-range. Therefore, if the sound absorber 10 is placed with the second membrane 13 facing the center of the room, sound will enter from the second membrane 13 side, and due to the membrane vibration type sound absorption effect of the second membrane 13, the sound absorption coefficient will be high only in a narrow frequency band from the mid-low range to the mid-range (160 Hz to 315 Hz), and sound will be absorbed most effectively.

[0052] As a result, the orientation of each sound absorber 10 can be changed to match the frequency of the sound that is desired to be reduced among the sounds generated in the room, thereby adjusting the sound environment in the room to a desired state.

[0053] -Sound absorption performance test- In order to confirm that the sound absorption characteristics change when the orientation of the multiple sound absorbers 10 is changed, a sound absorption performance test was conducted with reference to the reverberation room sound absorption coefficient measurement method specified in JIS A 1409:1998.

[0054] Specifically, a large sound-absorbing material 14 measuring 100 mm thick and 1800 mm x 1800 mm was prepared, along with a first membrane 12 (woven fabric) and a second membrane 13 (artificial leather) also of similarly large size. Sound absorber I was fabricated by laminating the sound-absorbing material 14 and the first membrane 12 (woven fabric) in this order on the floor of a reverberation chamber, and sound absorber II was fabricated by laminating the sound-absorbing material 14 and the second membrane 13 (artificial leather) in this order. Sound absorption performance tests were then conducted on each of sound absorbers I and II to measure the sound absorption coefficient in a reverberation chamber. The results are shown in Figure 4.

[0055] As shown in Figure 4, the central frequency (peak central frequency) at which sound absorber I reaches its maximum reverberation room sound absorption coefficient is around 500 Hz, and the reverberation room sound absorption coefficient is 1.0 or higher from 160 Hz to 8000 Hz (from mid-low range to high range), resulting in effective absorption of sound over an extremely wide frequency range from mid-low range (100-300 Hz) to high range (8000 Hz and above). Note that Figure 4 does not show the reverberation room sound absorption coefficient at 8000 Hz for sound absorber I, but the reverberation room sound absorption coefficient at 8000 Hz was also measured in the test, and was found to be 1.06.

[0056] In sound absorber I, sound is incident from the first film 12 side. However, because the woven fabric that makes up first film 12 has relatively high breathability and allows sound to pass through easily, most of the incident sound passes through first film 12 and enters sound absorber 10, where it is absorbed and attenuated by sound-absorbing material 14 (porous sound absorption). Porous sound absorption tends to have a high sound absorption coefficient from the low-midrange to the high-frequency range. Therefore, in sound absorber I, the porous sound-absorbing effect of sound-absorbing material 14 is exerted, and it is thought that the reverberation chamber sound absorption coefficient is high, at 1.0 or more, from the low-midrange to the high-frequency range (160 to 8000 Hz).

[0057] On the other hand, the center frequency (peak center frequency) at which the reverberation room sound absorption coefficient of sound absorber II is maximum is around 200 Hz, and the reverberation room sound absorption coefficient is 0.7 or higher only in a narrow frequency band (160-315 Hz) from the mid-low range (100-300 Hz) to the mid range (300-2000 Hz), resulting in effective sound absorption.

[0058] In sound absorber II, sound enters from the second membrane 13 side. However, because the artificial leather that constitutes second membrane 13 has relatively low breathability and does not allow sound to pass through, most of the incident sound is reflected by second membrane 13 and does not enter sound absorber 10. As a result, the porous sound-absorbing effect of sound-absorbing material 14 in sound absorber 10 is hardly exhibited, while the sound that enters sound absorber 10 is attenuated by hitting second membrane 13 and vibrating it (membrane vibration sound absorption). Membrane vibration sound absorption tends to have a high sound absorption coefficient only in a narrow frequency band from the low-mid to mid-range. Therefore, in sound absorber II, the porous sound-absorbing effect of sound-absorbing material 14 is hardly exhibited, and the membrane vibration sound-absorbing effect of second membrane 13 is exhibited, which is thought to be why the reverberation chamber sound absorption coefficient is 0.7 or higher only in a narrow frequency band from the low-mid to mid-range (160 to 315 Hz).

[0059] From the results of the sound absorption performance tests described above, it can be inferred that sound absorber 10 of embodiment 1 exhibits excellent sound absorption effects (reverberation chamber sound absorption coefficient of 1.0 or more) in an extremely wide frequency range (160 to 8000 Hz) from the low-mid to high ranges for sounds incident from the side of first film 12 made of woven fabric, but exhibits excellent sound absorption effects (reverberation chamber sound absorption coefficient of 0.7 or more) only in a narrow frequency band (160 to 315 Hz) from the low-mid to mid ranges for sounds incident from the side of second film 13 made of artificial leather. In other words, it can be inferred that sound absorber 10 of embodiment 1 exhibits different sound absorption characteristics depending on whether the sound is incident from the side of first film 12 or the side of second film 13.

[0060] -Effects of the first embodiment- In this first embodiment, the sound absorber 10 is configured such that the rectangular frame 11 is self-supporting, and the first film 12 and the second film 13 face each other horizontally with the sound-absorbing material 14 sandwiched between them, so that the sound absorption characteristics that are exhibited differ depending on whether the sound is incident from the first film 12 side or the second film 13 side. In other words, according to this first embodiment, a sound absorber 10 is configured whose sound absorption characteristics that are exhibited change simply by changing its orientation, and such a sound absorber 10 is installed in a room and used to adjust the sound environment in the room, so that the comfort of the room can be easily improved simply by changing the orientation of the sound absorber 10.

[0061] Furthermore, in this embodiment 1, the first film body 12 and the second film body 13 are configured to be distinguishable, so the orientation of the sound absorber 10 can be easily changed to an orientation that corresponds to the desired sound absorption characteristics.

[0062] Furthermore, in this embodiment, the first film 12 and the second film 13 are made of different materials, and therefore have different sound transmittances. When sound enters from the first film 12 side, which is made of woven fabric through which sound easily transmits, the sound easily enters the sound absorber 10, and the porous sound-absorbing effect of the sound-absorbing material 14 is exhibited. However, when sound enters from the second film 13 side, which is made of artificial leather through which sound does not easily transmit, the sound does not easily enter the sound absorber 10, and the porous sound-absorbing effect of the sound-absorbing material 14 is hardly exhibited, while the membrane vibration of the second film 13 exhibits a membrane vibration sound-absorbing effect. Porous-type sound absorption tends to have a high sound absorption coefficient from the low-midrange to the high-frequency range, while membrane vibration-type sound absorption tends to have a high sound absorption coefficient only in a narrow frequency band from the low-midrange to the midrange. In other words, the sound absorber 10 of this embodiment has different sound absorption coefficients (expressed different sound absorption characteristics) for each frequency band depending on whether the sound enters from the first film 12 side or the second film 13 side. In this way, according to the first embodiment, it is possible to easily configure a sound absorber 10 that exhibits different sound absorbing characteristics simply by changing the direction.

[0063] In addition, in this embodiment 1, the frame body 11 is composed of two frame materials (first and second frame materials 15, 16), and each membrane body 12, 13 integrally covers each opening 11a, 11b, the front end faces 15a, 16a, outer surfaces 15b, 16b, rear end faces 15c, 16c, and rear end portions of the inner surfaces 15d, 16d of each frame material 15, 16, and is configured so that the peripheral portions are fixed to the inner surfaces 15d, 16d of each frame material 15, 16. If the frame body 11 is made up of a single frame material, and the two openings 11a, 11b of the frame body 11 are blocked by two membranes 12, 13, respectively, the peripheral portions of the membranes 12, 13 would be positioned on the outer surface of the frame body 11, which is easily visible to the public, and this could reduce the design appeal of the sound absorber 10. However, according to this embodiment 1, the frame body 11 is made up of two frame materials 15, 16, and the two membranes 12, 13 that block the two openings 11a, 11b are configured to cover not only the openings 11a, 11b but also the inner surfaces 15d, 16d of the frame materials 15, 16. According to this configuration, when the first and second frame members 15, 16 are joined together while the first and second membranes 12, 13 are fixed to them, the peripheral edges of the first and second membranes 12, 13 are sandwiched between the joints of the first and second frame members 15, 16 and are not exposed on the outer surface of the frame 11, which is easily visible to the public. In other words, according to this first embodiment, it is possible to provide a sound absorber 10 with excellent design.

[0064] Furthermore, in the sound environment adjusting structure 1 of the first embodiment, a plurality of the sound absorbers 10 are provided on a shelf 2 installed in the conference room to adjust the sound environment in the conference room. With this sound environment adjusting structure 1, the sound environment in the room can be easily adjusted simply by changing the orientation of the sound absorbers 10.

[0065] Second Embodiment of the Invention In the second embodiment, the sound absorber 10 of the first embodiment is partially modified. Specifically, as shown in Fig. 5, in the first embodiment, the first and second films 12 and 13 are formed so that their peripheral edges reach the inner surfaces 15d and 16d of the first and second frame members 15 and 16, whereas in the second embodiment, their peripheral edges reach the outer edges of the rear end faces 15c and 16c of the first and second frame members 15 and 16, respectively, and are fixed to the rear end faces 15c and 16c. This type of sound absorber 10 can also achieve the same effects as the first embodiment.

[0066] Third Embodiment of the Invention The third embodiment is a partial modification of the configuration of the sound absorber 10 of the second embodiment. Specifically, as shown in FIG. 6 , in the third embodiment, the sound absorbing material 14 is provided so that air layers 18, 18 are formed between the first and second films 12, 13, respectively. The third embodiment uses a sound absorbing material 14 that is thinner (e.g., 30 mm thick) than that used in the second embodiment. In the third embodiment, the two sound absorbing materials 14, 14 are provided at the rear sides of the first and second spaces S1, S2, respectively (the rear sides when the first and second films 12, 13 are considered the front sides) so as to abut against each other, and the air layers 18, 18 are formed between the first and second films 12, 13. With this configuration, by forming the air layer 18 inside the sound absorber 10, the thickness of the porous sound absorbing material 14 is thinner than in the first and second embodiments without the air layer 18.

[0067] Incidentally, the thinner the sound-absorbing material 14, the less the porous-type sound-absorbing effect tends to be exerted, with the effect being particularly pronounced in the low to low-midrange frequencies. On the other hand, tests have shown that a sound absorber in which a porous sound-absorbing material is placed against a rigid wall and woven fabric is arranged so as to provide an air layer between the sound-absorbing material and the sound-absorbing material has a lower sound absorption coefficient in the low to low-midrange frequencies due to the thinner sound-absorbing material, compared to a sound absorber in which a sound-absorbing material that is thick enough to accommodate the air layer is placed against a rigid wall and woven fabric is arranged on the opposite side of the sound-absorbing material from the rigid wall, but the sound absorption coefficient in the low-midrange to high ranges does not decrease and is as high as when no air layer is provided. Furthermore, tests were also conducted on a sound absorber in which a thin sound-absorbing material just thin enough to accommodate the air layer was placed against a rigid wall and no woven fabric was placed, and it was found that the sound absorber in which a thin sound-absorbing material just thin enough to accommodate the air layer was placed against a rigid wall and a woven fabric was placed so that an air layer was created between the sound-absorbing material and the sound absorber had a higher sound absorption coefficient over a wide frequency range from mid-low to high frequencies than the sound absorber without woven fabric. These results show that even if the thickness of the sound-absorbing material is thin, if the woven fabric is placed so that an air layer is created between the sound-absorbing material and the sound absorber, the sound absorption coefficient in the mid-low to high frequencies can be maintained at a high level without decreasing.

[0068] Therefore, in the sound absorber 10 of embodiment 3, when the second membrane 13 abuts against or is close to the wall W (rigid wall) and sound is incident from the first membrane 12 side, the thickness of the sound absorbing material 14 is thinner than in the sound absorbers 10 of embodiments 1 and 2 which do not have the air layer 18. However, since the air layer 18 is formed between the first membrane 12 and the sound absorbing material 14, the porous sound absorption effect of the sound absorbing material 14 in the low frequency range is lower than in the sound absorbers 10 of embodiments 1 and 2, but the sound absorption effect in the mid-low to high frequency range is about the same as that of the sound absorber 10 of embodiment 2.

[0069] On the other hand, in the sound absorber 10 of embodiment 3, when the first membrane 12 is in contact with or close to the wall W (rigid wall) and sound is incident from the second membrane 13 side, sound does not easily pass through the second membrane 13 made of artificial leather, just like the sound absorbers 10 of embodiments 1 and 2 which do not have the air layer 18, and when sound is incident from the second membrane 13 side, the porous sound absorption effect of the sound absorbing material 14 is hardly exerted.As a result, the membrane vibration type sound absorption effect of the second membrane 13 is exerted, and the sound absorption coefficient is high only in a narrow frequency band from the mid-low range to the mid range.However, compared to the sound absorbers 10 of embodiments 1 and 2 which do not have the air layer 18, the tension of the second membrane 13 is reduced, and therefore the natural frequency of the membrane vibration is reduced, and the frequency band in which the membrane vibration type sound absorption effect of the second membrane 13 is exerted is also shifted to the lower range.

[0070] Thus, the sound absorption characteristics exhibited by sound absorber 10 of embodiment 3 also differ depending on whether the sound is incident from the first film 12 side or the second film 13 side, and also differ from the sound absorption characteristics of sound absorber 10 of embodiments 1 and 2, which do not have air layer 18. Therefore, according to embodiment 3, the sound absorption characteristics of sound absorber 10 can be easily changed simply by forming air layer 18 between sound absorbing material 14 and the two films 12 and 13.

[0071] -Sound absorption performance test- In order to confirm the change in sound absorption characteristics caused by providing the air layer 18 inside the sound absorber 10, a sound absorption performance test was carried out with reference to the reverberation room sound absorption coefficient measurement method specified in JIS A 1409:1998.

[0072] Specifically, sound absorber III corresponding to sound absorber 10 of embodiment 2 and sound absorber IV corresponding to sound absorber 10 of embodiment 3 were fabricated in a reverberation chamber and placed on the floor, and a sound absorption performance test was conducted on each of sound absorbers III and IV to measure the reverberation chamber sound absorption coefficient. The results are shown in Fig. 7.

[0073] The sound absorber III is made by placing a 100mm high wooden frame made of 100mm x 1800mm boards assembled into a rectangular shape on the floor of the reverberation chamber, placing two 50mm thick sound absorbing materials 14 each measuring 1800mm x 1800mm inside the frame, and then placing an 1800mm x 1800mm first membrane 12 (woven fabric) over the top opening of the wooden frame and fixing it to the frame.

[0074] Sound absorber IV is made by placing a 100mm high wooden frame made of 100mm x 1800mm boards assembled into a rectangular shape on the floor of the reverberation chamber, and inside this frame, multiple crosspieces made of 20mm x 1800mm boards are fixed across one of the opposite sides of the wooden frame, and two 30mm thick sound absorbing materials 14 each measuring 1800mm x 1800mm are placed on top of the crosspieces, and then a first membrane 12 (woven fabric) measuring 1800mm x 1800mm is placed over the top opening of the wooden frame and fixed to the wooden frame.

[0075] As shown in Figure 7, sound absorber III had a reverberation room sound absorption coefficient of 0.9 or higher over the range from 200 Hz to 8000 Hz (from the low-midrange to the high-range), effectively absorbing sounds over an extremely wide frequency range from the low-midrange to the high-range.

[0076] In sound absorber III, sound is incident from the first film 12 side. However, because the woven fabric that makes up first film 12 has relatively high breathability and allows sound to pass through easily, most of the incident sound passes through first film 12 and enters sound absorber 10, where it is absorbed and attenuated by sound-absorbing material 14 (porous sound absorption). Porous sound absorption tends to have a high sound absorption coefficient from the low-midrange to the high-frequency range. Therefore, in sound absorber III, the porous sound-absorbing effect of sound-absorbing material 14 is exerted, and it is thought that the reverberation chamber sound absorption coefficient is high, at 0.9 or more, from the low-midrange to the high-frequency range (200 to 8000 Hz).

[0077] For sound absorber IV, the reverberation chamber sound absorption coefficient is less than 0.9 in the 100 to 250 Hz (low range), which is lower than that of sound absorber III, but the reverberation chamber sound absorption coefficient is 0.9 or higher in the 315 to 8000 Hz (low-mid to high range), resulting in effective absorption of sound over an extremely wide frequency range from low-mid to high, similar to sound absorber III. For sound absorber IV, the thickness of the sound-absorbing material 14 is thinner than that of sound absorber III, but the first film 12 made of woven fabric is arranged so as to provide an air layer 18 between the sound absorber IV and the sound-absorbing material 14. Therefore, although the sound absorption coefficient in the low range (100 to 250 Hz) is lower than that of sound absorber III, the sound absorption coefficient in the low-mid to high range (315 to 8000 Hz) is similar to that of sound absorber III.

[0078] Although no tests were conducted when sound was incident from the second membrane 13 side, it is believed that although the porous sound absorption effect of the sound absorbing material 14 is hardly exerted when sound is incident from the second membrane 13 side, the natural frequency of the membrane vibration caused by the second membrane 13 decreases due to the reduced tension of the second membrane 13 compared to the sound absorber 10 of embodiments 1 and 2 which do not have the air layer 18 described above, and therefore the frequency band in which the membrane vibration type sound absorption effect of the second membrane 13 is exerted also shifts to the lower range.

[0079] From the results of the above sound absorption performance tests, it can be inferred that, by providing air layers 18 between the first and second membranes 12, 13 and the sound-absorbing material 14 inside the sound absorber 10, the sound absorber 10 of embodiment 4 exhibits excellent sound absorption effects (reverberation chamber sound absorption coefficient of 0.9 or more) for sounds incident from the side of the first membrane 12 made of woven fabric in an extremely wide frequency range from the mid-low to high ranges (315 to 8000 Hz), just like the sound absorber 10 of embodiment 2 which does not have air layers 18, and that for sounds incident from the side of the second membrane 13 made of artificial leather, the sound absorber 10 of embodiment 4 exhibits excellent sound absorption effects (reverberation chamber sound absorption coefficient of 0.7 or more) in a narrow frequency range that is shifted toward the lower frequency side compared to the narrow frequency range (160 to 315 Hz) from the mid-low to mid ranges in which the sound absorber 10 of embodiment 2 exhibits excellent sound absorption effects (reverberation chamber sound absorption coefficient of 0.7 or more).

[0080] Therefore, according to the third embodiment, it is possible to configure a sound absorber 10 that exhibits different sound absorbing characteristics depending on whether the sound is incident from the first film 12 side or the second film 13 side. Furthermore, according to the third embodiment, even when a thinner sound absorbing material 14 than that of the first and second embodiments is used, by providing an air layer 18, it is possible to provide a sound absorber 10 that exhibits the same sound absorbing effect as the sound absorbers 10 of the first and second embodiments that use a thicker sound absorbing material 14. In particular, in the range of 500 to 1250 Hz, which corresponds to the frequency of human speech, a sound absorbing effect comparable to that of the sound absorbers 10 of the first and second embodiments can be obtained. In other words, according to the third embodiment, by using a thin sound absorbing material 14, it is possible to provide a sound absorber 10 at an affordable price that exhibits the same sound absorbing effect as the sound absorbers 10 of the first and second embodiments.

[0081] Fourth Embodiment of the Invention The fourth embodiment is a partial modification of the configuration of the sound absorber 10 of the second embodiment. Specifically, as shown in Fig. 8, the fourth embodiment uses two sound absorbing materials 14 that are thinner than those of the second embodiment (for example, 40 mm thick), and the two sound absorbing materials 14 are arranged so that an air layer 19 is formed between them. With this configuration, two sound absorbing materials 14, 14 made of a porous material are provided inside the sound absorber 10, and an air layer 19 is formed behind the front sound absorbing material 14 (on the second film 13 side of the sound absorbing material 14 on the first frame member 15 side when sound is incident from the first film 12 side, and on the first film 12 side of the sound absorbing material 14 on the second frame member 16 side when sound is incident from the second film 13 side).

[0082] Meanwhile, the porous-type sound-absorbing effect of a porous sound-absorbing material tends to be less pronounced as the thickness of the sound-absorbing material 14 becomes thinner, with the effect becoming particularly pronounced in the low to low-mid range. On the other hand, tests have shown that a sound absorber in which a first porous sound-absorbing material is placed against a rigid wall, a second sound-absorbing material is placed so as to create an air layer between the first sound-absorbing material and the second sound-absorbing material, and a woven fabric is placed on the side of the second sound-absorbing material opposite the air layer, has a lower sound absorption coefficient in the low to low-mid ranges due to the thinner sound-absorbing material, compared to a sound absorber in which two sound-absorbing materials, each thick enough to accommodate the air layer, are placed in contact with a rigid wall, and a woven fabric is placed on the other side of the rigid wall, with no air layer between them. However, the sound absorption coefficient in the low-mid range to high ranges does not decrease, and is as high as when no air layer is placed. Furthermore, tests were also conducted on a sound absorber with an air layer between two sound-absorbing materials and no woven fabric placed between them, and it was found that the sound absorber with an air layer between the two sound-absorbing materials and woven fabric placed between them had a higher sound absorption coefficient in the low-frequency range over a wide frequency range from mid-low to high frequencies compared to the sound absorber without woven fabric. These results show that even if the thickness of the sound-absorbing material is reduced by placing an air layer between two sound-absorbing materials, if woven fabric is placed on the side of the sound-absorbing material farthest from the rigid wall, the sound absorption coefficient in the low-mid to high frequencies can be maintained at a high level without decreasing.

[0083] Therefore, in the sound absorber 10 of embodiment 4, when the second membrane 13 abuts against or is close to the wall W (rigid wall) and sound is incident from the first membrane 12 side, the thickness of the sound absorber 14 is thinner by the air layer 18 provided between the two sound absorbers 14, 14 compared to the sound absorbers 10 of embodiments 1 and 2 which do not have the air layer 18, and the sound absorption coefficient in the low range is lower than that of the sound absorbers 10 of embodiments 1 and 2 which do not have the air layer 18. However, due to the presence of the first membrane 12, the sound absorption coefficient in the mid-low to high ranges is approximately the same as that of the sound absorbers 10 of embodiments 1 and 2.

[0084] On the other hand, in the sound absorber 10 of embodiment 4, when the first membrane 12 abuts against or is close to the wall W (rigid wall) and sound is incident from the side of the second membrane 13 that is closer to the air layer 18, sound does not easily pass through the second membrane 13 made of artificial leather, just like the sound absorbers 10 of embodiments 1 and 2 that do not have the air layer 18, and the porous sound absorption effect of the sound absorbing material 14 is hardly exerted.As a result, the membrane vibration sound absorption effect of the second membrane 13 is exerted, and the sound absorption coefficient becomes high only in a narrow frequency band (160 Hz to 315 Hz) from the mid-low range to the mid range.

[0085] Thus, the sound absorption characteristics exhibited by the sound absorber 10 of embodiment 4 also differ depending on whether the sound is incident from the first film 12 side or the second film 13 side, and also differ from the sound absorption characteristics of the sound absorbers 10 of embodiments 1 and 2, which do not have the air layer 18. Therefore, according to embodiment 4, the sound absorption characteristics of the sound absorber 10 can be easily changed simply by providing such an air layer 19 between the two sound-absorbing materials 14.

[0086] -Sound absorption performance test- In order to confirm the change in sound absorption characteristics caused by providing an air layer 18 inside the sound absorber 10 (between the two sound-absorbing materials 14), a sound absorption performance test was conducted with reference to the reverberation room sound absorption coefficient measurement method specified in JIS A 1409:1998.

[0087] Specifically, sound absorber III corresponding to sound absorber 10 of embodiment 2 and sound absorbers V and VI corresponding to sound absorber 10 of embodiment 4 were fabricated in a reverberation chamber and placed on the floor, and a sound absorption performance test was conducted on each of sound absorbers III, V, and VI to measure the reverberation chamber sound absorption coefficient. The results are shown in Fig. 9.

[0088] The sound absorber III is made by placing a 100mm high wooden frame made of 100mm x 1800mm boards assembled into a rectangular shape on the floor of the reverberation chamber, placing two 50mm thick sound absorbing materials 14 each measuring 1800mm x 1800mm inside the frame, and then placing an 1800mm x 1800mm first membrane 12 (woven fabric) over the top opening of the wooden frame and fixing it to the frame.

[0089] The sound absorber V is constructed by placing a 100mm-high wooden frame made of 100mm x 1800mm boards assembled into a rectangular shape on the floor of the reverberation chamber, placing a 40mm-thick, 1800mm x 1800mm sound-absorbing material 14 inside the frame, and then placing multiple 20mm x 1800mm boards on top of that, spanning one opposite side of the frame and fastening it to the frame, placing another 40mm-thick, 1800mm x 1800mm sound-absorbing material 14 on top of the multiple boards, and then covering the top opening of the frame with an 1800mm x 1800mm first membrane 12 (woven fabric) and fastening it to the frame. In other words, the sound absorber V has a 20mm-thick air layer 18 between two 40mm-thick sound-absorbing materials 14, 14.

[0090] Sound absorber VI is constructed by placing a 100mm-tall wooden frame made of 100mm x 1800mm boards assembled into a rectangular shape on the floor of the reverberation chamber, placing 30mm-thick, 1800mm x 1800mm sound-absorbing material 14 inside the frame, and then placing multiple 40mm x 1800mm boards on top of that, spanning one opposite side of the frame and fastening it to the frame, placing another 30mm-thick, 1800mm x 1800mm sound-absorbing material 14 on top of the multiple boards, and then covering the top opening of the frame with an 1800mm x 1800mm first membrane 12 (woven fabric) and fastening it to the frame. In other words, sound absorber VI has a 40mm-thick air layer 18 between two 30mm-thick sound-absorbing materials 14, 14.

[0091] As shown in Figure 9, sound absorber III had a reverberation room sound absorption coefficient of 0.9 or more over the range from 200 Hz to 8000 Hz (from the low-mid range to the high range), which resulted in effective absorption of sounds over an extremely wide frequency range from the low-mid range to the high range.

[0092] In sound absorber III, sound is incident from the first film 12 side. However, because the woven fabric that makes up first film 12 has relatively high breathability and allows sound to pass through easily, most of the incident sound passes through first film 12 and enters sound absorber 10, where it is absorbed and attenuated by sound-absorbing material 14 (porous sound absorption). Porous sound absorption tends to have a high sound absorption coefficient from the low-midrange to the high-frequency range. Therefore, in sound absorber III, the porous sound-absorbing effect of sound-absorbing material 14 is exerted, and it is thought that the reverberation chamber sound absorption coefficient is high, at 0.9 or more, from the low-midrange to the high-frequency range (200 to 8000 Hz).

[0093] For sound absorber V, the reverberation-room sound absorption coefficient was less than 0.9 between 100 and 160 Hz, but was comparable to that of sound absorber III. Furthermore, from 200 to 8000 Hz (low-midrange to high-frequency range), the reverberation-room sound absorption coefficient was 0.9 or greater, resulting in effective absorption of sound across an extremely wide frequency range from low-midrange to high-frequency range, similar to sound absorber III. For sound absorber V, the provision of air layer 18 makes the thickness of sound absorbing material 14 slightly thinner than that of sound absorber III. However, because air layer 18 is only 20 mm thick, it is possible to ensure a sufficient thickness of sound absorbing material 14 to achieve a porous sound absorption effect. Furthermore, by abutting first film 12 against the surface of sound absorbing material 14 opposite air layer 18, it can be inferred that the reverberation-room sound absorption coefficient is comparable to that of sound absorber III across all frequency ranges.

[0094] For sound absorber VI, the reverberation-room sound absorption coefficient is less than 0.9 between 100 and 250 Hz, and is significantly lower than that of sound absorber III in the 160 to 250 Hz (mid-low range). However, from 315 to 8000 Hz (mid-low to high range), the reverberation-room sound absorption coefficient is 0.9 or higher, resulting in effective absorption of sound across an extremely wide frequency range from mid-low to high, similar to sound absorber III. For sound absorber VI, the thickness of the sound-absorbing material 14 is thinner than that of sound absorber III due to the formation of air layer 18, so the porous sound absorption effect is lower than that of sound absorber III in the mid-low range. However, by abutting the first film 12 against the surface of the sound-absorbing material 14 opposite to the air layer 18, it can be estimated that the reverberation-room sound absorption coefficient is as high as that of sound absorber III in the low range and the mid-low to high range.

[0095] Although no tests were conducted on sound absorbers V and VI when sound was incident from the second membrane 13 side, it is believed that the porous sound absorption effect of the sound absorbing material 14 is hardly exerted when sound is incident from the second membrane 13 side, and therefore the formation of the air layer 18 causes almost no change in the sound absorption rate.

[0096] From the results of the above sound absorption performance tests, it can be inferred that, by providing an air layer 18 between the two sound-absorbing materials 14, 14 inside the sound absorber 10, the sound absorber 10 of embodiment 4 exhibits excellent sound absorption effects (reverberation chamber sound absorption coefficient of 0.9 or more) for sounds incident from the first membrane 12 side made of woven fabric in an extremely wide frequency range from the mid-low to high ranges (200 to 8000 Hz for sound absorber V, 315 to 8000 Hz for sound absorber VI), just like the sound absorbers 10 of embodiments 1 and 2 that do not have air layer 18, and that for sounds incident from the second membrane 13 side made of artificial leather, it exhibits excellent sound absorption effects (reverberation chamber sound absorption coefficient of 0.7 or more) only in a narrow frequency range from the mid-low to mid ranges (160 to 315 Hz), just like the sound absorbers 10 of embodiments 1 and 2.

[0097] Therefore, according to the fourth embodiment, it is possible to configure a sound absorber 10 that exhibits different sound absorbing characteristics depending on whether the sound is incident from the first film 12 side or the second film 13 side. Furthermore, according to the fourth embodiment, even when a thinner sound absorbing material 14 than that of the first and second embodiments is used, by providing an air layer 18, it is possible to provide a sound absorber 10 that exhibits the same sound absorbing effect as the sound absorbers 10 of the first and second embodiments that use a thicker sound absorbing material 14. In particular, in the range of 500 to 1250 Hz, which corresponds to the frequency of human speech, a sound absorbing effect comparable to that of the sound absorbers 10 of the first and second embodiments can be obtained. In other words, according to the fourth embodiment, by using a thin sound absorbing material 14, it is possible to provide a sound absorber 10 at an affordable price that exhibits the same sound absorbing effect as the sound absorbers 10 of the first and second embodiments.

[0098] Other Embodiments In embodiment 1, the first and second membranes 12, 13 are formed to a size such that their peripheral edges reach the inner surfaces 15d, 16d of the first and second frame members 15, 16 and are fixed to the inner surfaces 15d, 16d, respectively, while in embodiments 2 to 4, the first and second membranes 12, 13 are formed to a size such that their peripheral edges reach the outer edges of the back end surfaces 15c, 16c of the first and second frame members 15, 16 and are fixed to the back end surfaces 15c, 16c, respectively. The first and second membranes 12, 13 only need to be formed to a size such that their peripheral edges can be sandwiched between the joints of the first and second frame members 15, 16, and may be fixed to either the inner surfaces 15d, 16d or the back end surfaces 15c, 16c of the first and second frame members 15, 16. That is, in the first embodiment, the first and second membranes 12, 13 may be configured as in the second to fourth embodiments, and in the second to fourth embodiments, the first and second membranes 12, 13 may be configured as in the first embodiment.

[0099] In the above embodiments 1 to 3, two sound-absorbing materials 14, 14 are provided in the frame body 11 in abutting contact with each other. However, in embodiments 1 to 3, instead of the two sound-absorbing materials 14, 14, it is also possible to provide one sound-absorbing material 14 having a thickness equivalent to that of the two sound-absorbing materials 14, 14 (80 mm thick, 100 mm thick, etc.).

[0100] In the above-mentioned embodiments 1 to 4, the first and second films 12, 13 are made of different materials, but the first and second films 12, 13 may be made of the same breathable material and the breathability of the first film 12 and the second film 13 may be changed by changing the thickness. With this kind of configuration, it is possible to easily configure a sound absorber 10 that exhibits different sound absorption characteristics simply by changing the orientation, and by placing such a sound absorber 10 in a room and changing its orientation, it is possible to easily adjust the sound environment in the room.

[0101] In the above-described first to fourth embodiments, the first and second frame members 15, 16 constituting the frame body 11 are formed by framing four rectangular wooden boards in a rectangular shape, but the first and second frame members 15, 16 are not limited to the above-described configuration as long as they are self-supporting when frame body 11 is constructed by framing them in a rectangular shape. The first and second frame members 15, 16 may be formed, for example, by arranging two rectangular boards one above the other, with the left and right ends of the two rectangular boards being connected by at least one pillar instead of the boards. [Industrial Applicability]

[0102] The present invention is useful for sound absorbers and sound environment control structures. [Explanation of symbols]

[0103] 1 Sound environment adjustment structure 2 shelves 10 Sound absorber 11 Frame 11a 1st opening 11b 2nd opening 12 First membrane 13 Second membrane 14 Sound-absorbing material 15 1st frame material 15a Front end 15b External surface 15c Back side end 15d inner surface 16 Second frame material 16a Front end 16b External surface 16c Back end 16d inner surface 18 Air Layer 19 Air Layer 21 Sound-insulating film (film material with sound-insulating properties) 23 Plate-shaped member S1 1st space S2 2nd space

Claims

1. A sound absorbing body that is installed in a room and adjusts the sound environment of the room, A rectangular frame body that is self-standing and has a part of its outer surface as a bottom, a first membrane body that closes a first opening at one end side of the frame body in a depth direction; a second membrane body that closes a second opening on the other end side of the frame body in the depth direction; a sound-absorbing material made of a porous material and arranged inside the frame body, The sound absorption characteristics that are exhibited differ depending on whether the sound is incident from the first membrane side or the second membrane side. A sound absorber characterized by:

2. The sound absorber according to claim 1, The first membrane and the second membrane are configured to be distinguishable from each other. A sound absorber characterized by:

3. The sound absorber according to claim 1, The first film and the second film are made of different materials. A sound absorber characterized by:

4. The sound absorber according to claim 1, The first membrane is made of woven fabric, The second film body is made of artificial leather. A sound absorber characterized by:

5. The sound absorber according to claim 4, The sound absorbing material is formed in a plate shape and is provided so as to form an air layer between the first and second membranes. A sound absorber characterized by:

6. The sound absorber according to claim 4, the frame body comprises a first frame material framed in a rectangular shape that forms the first opening, and a second frame material framed in a rectangular shape that forms the second opening, and is formed by joining the first frame material and the second frame material together; The sound absorbing material is formed in a plate shape and is provided in a first space inside the first frame material and in a second space inside the second frame material, one each, so that an air layer is formed between them. A sound absorber characterized by:

7. The sound absorber according to claim 1, the frame body comprises a first frame material framed in a rectangular shape that forms the first opening, and a second frame material framed in a rectangular shape that forms the second opening, and is formed by joining the first frame material and the second frame material together; the first film body integrally covers the front end face and outer surface of the first frame member on the first opening side together with the first opening, and a peripheral edge portion is fixed to the back end face or inner surface of the first frame member, The second film integrally covers the front end face and outer surface of the second frame member on the second opening side together with the second opening, and a peripheral edge portion is fixed to the back end face or inner surface of the second frame member. A sound absorber characterized by:

8. A sound environment adjusting structure for adjusting the sound environment in a room, A plurality of sound absorbers according to any one of claims 1 to 7 are provided on a shelf installed in the room. A sound environment adjustment structure characterized by:

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