JP7523977B2 - Duct structure - Google Patents

Description

The present invention relates to a duct structure to which a soundproofing material is applied to reduce noise in a duct.

Soundproofing materials are sometimes used as a noise countermeasure for ducts through which air for air conditioning flows. A duct structure using this soundproofing material is known from the following Patent Document 1. Specifically, the duct structure described in Patent Document 1 includes an inner tube made of a material that easily transmits sound (sound-transmitting) or a perforated plate, an outer tube made of a material that does not easily transmit sound (sound-insulating), and a soundproofing material (sound-absorbing material) made of rock wool, glass fiber, etc., filled into the annular space formed between the inner tube and the outer tube. This duct structure has the advantage that the sound generated by the air flow flowing inside the inner tube can be reduced by the action of the soundproofing material filled between the inner tube and the outer tube.

Japanese Utility Model Application Publication No. 53-101306 (Figs. 1 and 2)

Here, in ducts through which a relatively large volume of air flows, such as ventilation ducts used in buildings that require large volumes of ventilation, there is a tendency for low-frequency noise caused by duct vibration to increase. For such ducts that generate a lot of low-frequency noise, it is desirable to use soundproofing materials that are effective at reducing low-frequency noise. However, when soundproofing materials made of rock wool or glass fiber (glass wool) are used as in Patent Document 1, while high-frequency noise can be reduced, there is a problem in that low-frequency noise cannot be sufficiently reduced.

The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a duct structure that can effectively reduce low-frequency noise.

In order to solve the above problem, the duct structure of the present invention comprises a duct through which air-conditioned air flows, and a soundproofing material that reduces noise in the duct, the soundproofing material being arranged on the outer peripheral surface of the duct , a plurality of bag bodies that are tubular and extend in the axial direction of the duct and are arranged in the circumferential direction of the duct, a flexible connecting sheet that connects the plurality of bag bodies arranged in the circumferential direction to each other, and a filling material containing a plurality of granular objects filled inside each of the bag bodies in a state that allows them to move relative to each other, the granular objects having a specific gravity of 0.9 to 2.5 and a particle size of 0.5 mm to 6.0 mm (claim 1).

According to the duct structure of the present invention, a bag filled with a filler containing a large number of granular materials is attached to the outer peripheral surface of the duct, so that when vibration occurs in the duct, the granular materials inside the bag collide or rub against each other to generate heat. As a result, the vibration energy is converted into thermal energy, the vibration of the duct is suppressed, and the noise generated by the vibration is reduced. In this case, the range of noise that is easily reduced is thought to vary depending on the specific gravity and particle size of the granular materials. In the present invention, the specific gravity of the granular materials is set to 0.9 to 2.5 and the particle size is set to 0.5 to 6.0 mm, so that low-frequency noise with a frequency of 125 Hz or less can be sufficiently reduced, as will be shown in the embodiment described later. As a result, even in a relatively large-capacity duct where low-frequency noise is likely to occur, the noise can be effectively reduced.

In addition, since the multiple cylindrical bags are connected to each other by a flexible connecting sheet, the multiple bags can be attached to the outer periphery of the duct by wrapping the connecting sheet around the duct. This makes it easy to attach the soundproofing material to the duct, while allowing the multiple bags (within the granular material) to sufficiently reduce low-frequency noise.

Preferably, the filling rate of the filler in the bag is 30% by volume or more and 90% by volume or less (Claim 2).

This configuration allows the relative movement of the granular material inside the bag to be unimpeded, and effectively reduces low-frequency noise generated by the duct through collisions and friction between the granular material.

The material of the filler is not particularly limited, but it is preferable that the filler contains granular matter whose main material is at least one of synthetic resin and synthetic rubber (Claim 3).

Preferably , the soundproofing material further includes a sound insulating layer covering a surface of the connecting sheet ( claim 4 ).

With this configuration, the soundproofing layer on the surface of the connecting sheet can reduce noise in the relatively high frequency range. This provides the effect of reducing noise in both the low and high frequency ranges, further improving the performance of the soundproofing material.

As described above, according to the duct structure of the present invention, low-frequency noise generated from the duct can be effectively reduced.

FIG. 1 is a diagram showing an example of an air conditioning equipment to which the duct structure of the present invention is applied, and is a plan view showing the state in which the air conditioning equipment is installed in the ceiling of a building. FIG. 2 is a cross-sectional view showing the above-mentioned air conditioning equipment installed in the ceiling of a building. 4 is a cross-sectional view showing a state in which soundproofing material is attached to a duct of the above-mentioned air conditioning equipment. FIG. 2 is a side view showing the state in which soundproofing material is attached to the duct of the above-mentioned air conditioning equipment. FIG. FIG. 2 is a cross-sectional view showing the soundproofing material alone. 3 is an enlarged cross-sectional view showing the internal structure of the soundproofing material (granular material filled inside the bag). FIG. FIG. 2 is a plan view showing an experimental air conditioning facility used in a verification experiment to confirm the noise reduction effect of the duct structure of the present invention. 4 is a cross-sectional view showing a state in which soundproofing material is attached to a duct of the above-mentioned experimental air conditioning equipment. FIG. 1A and 1B are graphs showing the measurement results of sound pressure levels at measurement point 1 for each frequency, and FIG. 1B is a graph showing the measurement results of sound pressure levels at measurement point 2 for each frequency. 1A is a graph showing the amount of reduction in sound pressure level at measurement point 1 for each frequency, and FIG. 1B is a graph showing the amount of reduction in sound pressure level at measurement point 2 for each frequency. 1A and 1B are graphs showing the measurement results of vibration acceleration levels at measurement point 1 for each frequency, and FIG. 1B is a graph showing the measurement results of vibration acceleration levels at measurement point 2 for each frequency. 1A and 1B are graphs showing the amount of reduction in vibration acceleration level at measurement point 1 for each frequency, and FIG. 1B is a graph showing the amount of reduction in vibration acceleration level at measurement point 2 for each frequency.

(1) Air Conditioning Equipment Figures 1 and 2 are diagrams showing an example of an air conditioning equipment to which the duct structure of the present invention is applied. The air conditioning equipment 1 shown in these figures is equipment for ventilating a building, and is installed in the space above the ceiling R, i.e., the ceiling space S. The air conditioning equipment 1 includes a fan 2, a chamber 3, and a duct 4. The fan 2 is a blower that compresses and sends out air. The chamber 3 is a volume expansion section for stabilizing the flow of air (air-conditioned air) compressed by the fan 2. The duct 4 is a pipe through which the air introduced into the fan 2 or the air (air-conditioned air) exhausted from the fan 2 flows, and is connected to the fan 2 and the chamber 3, respectively.

The duct 4 has a plurality of duct elements 4a to 4f connected coaxially. Specifically, the duct element 4a is a curved elbow pipe connected to the fan 2 from the upstream side. The duct element 4b is a straight pipe extending straight from the fan 2 to the downstream side and reaching the chamber 3. The duct element 4c is a straight pipe extending straight from the chamber 3 to the downstream side. The duct element 4d is a curved elbow pipe connecting the duct element 4c and the duct element 4e to each other. The duct element 4e is a straight pipe extending straight from the downstream end of the duct element 4d to the downstream side. The duct element 4f is a curved elbow pipe extending from the downstream end of the duct element 4e to the downstream side. The duct 4 in this embodiment is a so-called rectangular duct (angle duct), and each of the duct elements 4a to 4f is formed to have a rectangular cross section. This is to allow the relatively large flow of air compressed by fan 2 to circulate without any hindrance.

(2) Soundproofing Material A soundproofing material 10 shown in Figures 3 to 5 is attached to the outer peripheral surface of the duct 4 (each of the duct elements 4a to 4f). Figures 3 and 4 show the soundproofing material 10 attached to the duct 4, while Figure 5 shows the soundproofing material 10 in a standalone state. The soundproofing material 10 includes a plurality of bags 11, a filler 12 filled inside each bag 11, a flexible connecting sheet 13 connecting each bag 11 to each other, and a sound insulating layer 14 covering the surface of the connecting sheet 13.

5, the direction perpendicular to the paper surface is defined as the first direction X, and the plurality of bags 11 are each formed in a cylindrical shape extending along the first direction X. Also, the direction perpendicular to the first direction X is defined as the second direction Y, and the plurality of bags 11 are arranged so as to be lined up at approximately regular intervals in the second direction Y, and are connected to each other via the connecting sheet 13 so as to maintain their positional relationship. The soundproofing material 10 is attached to the outer circumferential surface of the duct 4 in a state in which the first direction X, which is the extension direction of each bag 11, coincides with the axial direction of the duct 4 (the direction perpendicular to the paper surface in FIG. 3; the left-right direction in FIG. 4). That is, in a state in which the soundproofing material 10 is attached to the duct 4, the plurality of bags 11 are arranged so as to extend along the axial direction of the duct 4 and to be lined up at approximately regular intervals in the circumferential direction of the duct 4. The cross-sectional shape of the cylindrical bag is not particularly limited, and may be, for example, either a cylindrical shape or a square tube shape (rectangle), but the bag 11 in this embodiment is formed to have a cylindrical cross section.

The bag body 11 is formed by, for example, closing both ends of a flexible tubular body made of a resin film by heat welding. The resin film that constitutes the bag body 11 may be, for example, a film made of polyethylene, polypropylene, or polyethylene terephthalate. Of these, polyethylene is preferred because of its flexibility. The bag body 11 has a large number of fine ventilation holes (not shown). The size of the ventilation holes is set so that the granular material 12a (FIG. 6) that constitutes the filling material 12 inside the bag body 11, which will be described later, does not leak out.

The diameter of the bag body 11 is set to a value that is sufficiently small relative to each side of the rectangular cross-section of the duct 4. For example, when a rectangular duct of 500 x 300 mm is used as the duct 4, that is, when a duct with a width W of 500 mm and a height H of 300 mm as shown in Figure 3 is used, it is preferable to set the diameter of the bag body 11 to about 50 mm. In addition, the length of the bag body 11 in this case can be set to, for example, about 400 mm.

The arrangement pitch of the bags 11 (the distance in the second direction Y between the centers of adjacent bags 11) is set to a value such that multiple bags 11 are arranged on each side of the rectangular cross-section of the duct 4. For example, if the arrangement pitch is set to a value smaller than each of 1/2 of the width W and height H of the duct 4 (less than W/2 and less than H/2), multiple (two or more) bags 11 can be arranged on each side of the duct 4. In this embodiment, the arrangement pitch of the bags 11 is set so that six bags 11 are arranged on the long side (side with width W) of the duct 4 and three bags 11 are arranged on the short side (side with height H) of the duct 4 (see FIG. 3).

The filling material 12 is composed of a large number of granular materials 12a as shown in FIG. 6. The granular materials 12a are not bonded to each other and can move freely relative to each other inside the bag body 11. Details of the granular materials 12a will be described later.

The connecting sheet 13 is a strip-shaped sheet made of flexible nonwoven fabric or resin film. The multiple bags 11 are connected to each other via the connecting sheet 13 by bonding each of the multiple bags 11 to the back side of the connecting sheet 13. Specifically, the connecting sheet 13 is arranged so as to be in linear contact with each peripheral surface of the multiple bags 11 arranged in the second direction Y (circumferential direction of the duct 4), and is bonded to each contact portion by means of adhesion or heat welding (or sewing), etc., thereby connecting the bags 11 to each other. The width dimension (dimension in the second direction Y) of the connecting sheet 13 is set to a value one size larger than the outer circumference of the duct 4 (the total dimension of the four sides of the rectangular cross section) so that the connecting sheet 13 can surround the duct 4 with the bag 11 sandwiched between them.

The sound insulation layer 14 is a layered (sheet-shaped) sound insulation material with a predetermined thickness, and includes, for example, a layer of a polymeric material containing PVC (polyvinyl chloride) to which an iron-based filler (iron powder, etc.) has been added. The sound insulation layer 14 is attached to the connecting sheet 13 so as to cover the entire surface of the connecting sheet 13.

When attaching the soundproofing material 10 having the above-mentioned configuration to the duct 4, the connecting sheet 13 is wrapped around the outer periphery of the duct 4 while sandwiching the plurality of bags 11 between the connecting sheet 13 and each side of the duct 4, and the connecting sheet 13 is restrained by a restraining means (not shown) for maintaining this state. As a result, the plurality of bags 11 are held on the outer periphery of the duct 4 in a state in which they are arranged in parallel along the axial direction of the duct 4. In addition, in order to cover the duct 4 over a wide range in the axial direction with the soundproofing material 10, the plurality of soundproofing materials 10 are attached to the duct 4 in a state adjacent to each other in the axial direction (see FIG. 4). As a restraining means for restraining each soundproofing material 10 to the duct 4, for example, a hook that connects the ends of the connecting sheet 13 in the second direction Y can be used. Alternatively, the soundproofing material 10 may be held on the outer periphery of the duct 4 by wrapping an elastic band-like band (e.g., a rubber band) around the connecting sheet 13 surrounding the duct 4.

(3) Details of the granules The numerous granules 12a constituting the filler 12 are independent (not bonded to each other) granules having a specific range of specific gravity and particle size. Specifically, the specific gravity of the granules 12a is set to 0.9 to 2.5 (more preferably 1.2 to 2.2), and the particle size of the granules 12a is set to 0.5 mm to 6.0 mm (more preferably 1.0 mm to 5.0 mm). Note that the particle size in this specification refers to the diameter of a sphere having the same volume as the granules 12a.

The granular material 12a contains at least one of synthetic resin and synthetic rubber as a main material. In other words, the main material of the granular material 12a may be synthetic resin, synthetic rubber, or a mixture of both.

Synthetic resins that can be used as the main material for the granular material 12a include PVC (polyvinyl chloride), PP (polypropylene), LDPE (low density polyethylene), HDPE (high density polyethylene), PS (polystyrene), ABS (acrylonitrile butadiene styrene copolymer) resin, PET (polyethylene terephthalate), soft PVC, olefin-based elastomers, styrene-based elastomers, polyester-based elastomers, urethane-based elastomers, polybutadiene-based elastomers, polyamide-based elastomers, etc.

Synthetic rubbers that can be used as the main material for the granules 12a include styrene butadiene rubber (SBR), butadiene rubber (BR), butyl rubber (IIR), nitrile rubber (NBR), and ethylene propylene rubber (EPDM).

In addition to the main materials as described above, the granular material 12a may contain secondary materials such as plasticizers, specific gravity adjusters, and fiber materials. In this case, the main material refers to the material that has the largest composition ratio among the various components that make up the granular material 12a, and the size of the composition ratio itself does not affect the definition of the main material.

The specific gravity adjusting agent may be, for example, an inorganic filler such as calcium carbonate, talc, aluminum oxide, kaolin, or calcium silicate.

Examples of fiber materials that can be used include organic fibers such as cellulose fibers, paper and pulp, and inorganic fibers such as glass fibers and carbon fibers.

The amount (number) of the granular material 12a configured as described above is adjusted so that the filling rate of the granular material 12a (filler 12) in the bag body 11 is 30 volume % or more and 90 volume % or less (more preferably 40 volume % or more and 80 volume % or less). The granular material 12a filled in the bag body 11 at such a filling rate is not excessively constrained within the bag body 11 and can move relatively freely within the bag body 11. The filling rate refers to the ratio of the volume of the granular material 12a (filler 12) to the maximum volume of the bag body 11.

(4) Effects As described above, the soundproofing material 10 of this embodiment includes the bag 11 placed on the outer peripheral surface of the duct 4, and the filler 12 made of a large number of granular objects 12a filled in a relatively movable state inside the bag 11. With this configuration, it is possible to effectively reduce noise generated from the duct 4 (noise generated due to vibration of the duct 4, air flow within the duct 4, etc.), particularly low-frequency noise.

That is, if the soundproofing material 10 configured as described above is attached to the duct 4, the granular materials 12a inside the bag body 11 collide and rub against each other in response to the vibration of the duct 4, generating heat. As a result, the vibration energy is converted into thermal energy, the vibration of the duct 4 is suppressed, and the noise generated by the vibration is reduced. In this case, the range of noise that is easily reduced is thought to vary depending on the specific gravity and particle size of the granular materials 12a. In the above embodiment, the specific gravity of the granular materials 12a is set to 0.9 to 2.5 and the particle size is set to 0.5 to 6.0 mm, so that low-frequency noise with a frequency of 125 Hz or less can be sufficiently reduced, as shown in the verification experiment described below. As a result, even in a relatively large-capacity duct where low-frequency noise is likely to occur, the noise can be effectively reduced.

In addition, in the above embodiment, the filling rate of the filler 12 (granular material 12a) in the bag body 11 is set to 30 to 90 volume %, so the relative movement of the granular material 12a inside the bag body 11 is not impeded, and low-frequency noise generated from the duct 4 can be effectively reduced by collisions and friction between the granular material 12a.

In addition, in the above embodiment, the multiple cylindrical bags 11 are connected to each other by the flexible connecting sheet 13, so that the multiple bags 11 can be attached together to the outer circumferential surface of the duct 4 by wrapping the connecting sheet 13 around the duct 4. This makes it easier to attach the soundproofing material 10 to the duct 4, while allowing the multiple bags 11 (the granular material 12a inside them) to sufficiently reduce low-frequency noise.

In addition, in the above embodiment, the sound insulation layer 14 is provided on the surface of the connecting sheet 13, and this sound insulation layer 14 can reduce noise in a relatively high frequency range. This can provide the effect of reducing noise in both the low and high frequency ranges, and can further improve the performance of the soundproofing material 10.

(5) Modifications Although the preferred embodiments of the present invention have been described above with reference to FIGS. 1 to 6, the present invention is not limited to the above-described embodiments and various modifications are possible.

For example, in the above embodiment, multiple cylindrical bags 11 are arranged on each side of the duct 4 with a rectangular cross section, but each bag may be a square tube with a rectangular cross section. Also, relatively flat bags with long sides close to the length of each side of the duct 4 may be prepared, and one of these flat bags may be arranged on each side of the duct 4.

In the above embodiment, the multiple bags 11 are connected together with the connecting sheet 13, and then the sound-proofing layer 14 is provided on the surface of the connecting sheet 13. However, if a commercially available sound-proofing sheet material is used as the sound-proofing layer 14, the connecting sheet 13 can be omitted. In other words, the bags 11 may be directly connected together with the sound-proofing sheet material (sound-proofing layer).

In the above embodiment, an aggregate of granular material 12a made mainly of at least one of synthetic resin and synthetic rubber is used as the filler 12 filled into each bag 11, but the granular material may be any granular substance with a specific gravity of 0.9 to 2.5 and a particle size of 0.5 mm to 6.0 mm, and there is no particular limitation on the material. For example, crushed inorganic matter such as minerals may be used as the granular material.

(6) Verification Experiment Next, a verification experiment conducted to confirm the noise reduction effect of the duct structure of the present invention will be described. FIG. 7 is a plan view showing a schematic configuration of an air conditioning system 101 prepared for the verification experiment. The air conditioning system 101 for this experiment is arranged across a reverberation chamber S1 and an anechoic chamber S2 separated by a partition wall W, and includes a fan 102, a joint 103, a duct 104, and an outlet duct 105. The fan 102 is a blower that compresses and sends out air, and is arranged in the reverberation chamber S1. The duct 104 is a pipe through which the air discharged from the fan 102 flows, and includes a plurality of duct elements 104a to 104i arranged in a U-shape in the anechoic chamber S2. The joint 103 connects the duct element 104a on the most upstream side (the side closest to the fan 102) to the fan 102, and is arranged to penetrate the partition wall W. The outlet duct 105 is connected to the duct element 104i on the most downstream side (the side farthest from the fan 102) and is arranged to penetrate the partition wall W.

The fan 102 takes in air from the reverberation chamber S1 and pumps it to the anechoic chamber S2. The pumped air passes through the joint 103 and the duct 104 (duct elements 104a to 104i) before being exhausted from the outlet duct 105 to the reverberation chamber S1.

The duct 104 (each duct element 104a to 104i) is a rectangular duct (square duct) with a rectangular cross section of 500 mm x 300 mm, and has soundproofing material 110 attached to its outer periphery as shown in Figure 8. The soundproofing material 110 comprises a number of bags 111, a filler material 112 filled inside each bag 111, and a flexible connecting sheet 113 that connects each bag 111 to each other.

The bag body 111 is a rectangular tubular bag body having a relatively flat rectangular cross section, and is attached to the outer circumferential surface of the duct 104 with its extension direction coinciding with the axial direction of the duct 104. Specifically, in this verification experiment, a polyethylene bag body having a rectangular cross section of 15 cm x 4.5 cm and a volume of ³⁰⁰⁰ cm3 was used as the bag body 111.

The filler 112 is similar to the filler 12 in the above embodiment (FIGS. 3 to 6) and is composed of a large number of granules 112a. Specifically, in this verification experiment, an aggregate of granules 112a in which a main material made of PVC (polyvinyl chloride) is added with a plurality of secondary materials (plasticizer, specific gravity adjuster, fiber material) was used as the filler 112. More specifically, an aggregate of granules 112a containing 33% by weight of PVC as the main material and 16% by weight of plasticizer, 30% by weight of calcium carbonate (specific gravity adjuster), and 21% by weight of cellulose fiber (fiber material) as secondary materials was used as the filler 112. The specific gravity of the granules 112a with this composition was about 1.75. The particle size of the granules 112a was set to about 2.0 mm (1.93 to 2.07 mm). In addition, the filling rate of the filler 112 (granular material 112a) in the bag body 111 was set to 80% by volume.

The connecting sheet 113 is a strip-shaped sheet that can surround the outer periphery of the duct 4 and maintain that state. A plurality of bags 111 are attached to the back surface of the connecting sheet 113. Specifically, in this verification experiment, a commercially available soundproofing sheet was used as the connecting sheet 113, and each bag 111 was attached to the back surface of the soundproofing sheet with an adhesive. The soundproofing sheet includes a layer of a polymer material containing PVC (polyvinyl chloride) to which an iron-based filler (iron powder, etc.) is added, and is a sheet that can reduce noise mainly in the mid- and high-frequency ranges. Note that restraining means (hooks, rubber bands, etc.) not shown in the figure are added to the connecting sheet 113 so that the connecting sheet 113 can be held in a state surrounding the outer periphery of the duct 4.

An experiment was conducted to measure the noise generated during air conditioning operation (driving the fan 102 to blow air through the duct 104) using an experimental air conditioning system 101 including a duct 104 to which the soundproofing material 110 as described above was applied. The noise was measured at two points, measurement point 1 and measurement point 2 shown in FIG. 7, and both sound pressure level and vibration acceleration level data were obtained as noise data. For the sound pressure level, the sound pressure level was measured at a position 300 mm away from each top surface of the duct 104 (duct elements 104b, 104h) corresponding to measurement points 1 and 2, and for the vibration acceleration level, the acceleration level of the vibration generated on each top surface of the duct 104 (duct elements 104b, 104h) corresponding to measurement points 1 and 2 was measured.

9 and 10 are graphs showing the measurement results of the sound pressure level. Specifically, FIG. 9(a) is a graph showing the measurement results of the sound pressure level at measurement point 1 for each frequency, and FIG. 9(b) is a graph showing the measurement results of the sound pressure level at measurement point 2 for each frequency. The horizontal axis of each graph indicates the center frequency (Hz) of the 1/1 octave band, and the vertical axis indicates the sound pressure level (dB). In addition, the waveform connecting the dots marked with ■ indicates the sound pressure level at each frequency when the soundproofing material 110 (FIG. 8) is used, and the waveform connecting the dots marked with ◆ indicates the sound pressure level at each frequency when the soundproofing material 110 is not used. Then, based on each graph of FIG. 9(a) and (b), the amount of the sound pressure level reduced by the use of the soundproofing material 110 was identified, and each graph of FIG. 10(a) and (b) was obtained. That is, FIG. 10(a) is a graph showing the amount of reduction in sound pressure level obtained at measurement point 1 for each frequency, and FIG. 10(b) is a graph showing the amount of reduction in sound pressure level obtained at measurement point 2 for each frequency.

As shown in the graphs of Figures 9 and 10, the effect of reducing the sound pressure level at all frequencies was confirmed at both measurement points 1 and 2. In this verification experiment, a commercially available sound-proofing sheet capable of reducing noise mainly in the mid- and high-frequency range was used as the connecting sheet 113, so the effect of reducing the sound pressure level in the mid- and high-frequency range above 125 Hz is thought to be mainly due to the action of this sound-proofing sheet (connecting sheet 113). On the other hand, since sound-proofing sheets generally cannot sufficiently reduce noise in the low-frequency range below 125 Hz, if only the sound-proofing sheet is used (if the bag body 111 containing the filling material 112 is omitted), the reduction in the sound pressure level in the low-frequency range below 125 Hz should be relatively small. In contrast, as described above, in this verification experiment, the effect of reducing the sound pressure level was obtained in a wide range of frequencies including the low-frequency range below 125 Hz. This is thought to be the effect of using the bag body 111 containing the filling material 112 (granular material 112a) in addition to the sound-proofing sheet (connecting sheet 113). Rather, in this verification experiment, the frequency at which the sound pressure level reduction was greatest was found to be in the low frequency range below 125 Hz. This suggests that the bag 111 containing the filling material 112 has a very good effect in reducing noise in the low frequency range.

The above can also be confirmed from the measurement results of the vibration acceleration level in Figures 11 and 12. The graphs in Figures 11(a) and 11(b) are graphs in which the vertical axis of each of the graphs in Figures 9(a) and 9(b) is changed from the sound pressure level to the vibration acceleration level, and the graphs in Figures 12(a) and 12(b) are graphs in which the vertical axis of each of the graphs in Figures 10(a) and 10(b) is changed from the reduction in sound pressure level to the reduction in vibration acceleration level. According to the graphs in Figures 11 and 12, when comparing the reduction in vibration acceleration level in the low frequency range below 125 Hz and the reduction in vibration acceleration level in the mid- to high-frequency range below 125 Hz overall, the former is significantly larger than the latter. This also suggests that the bag body 111 containing the filling material 112 (granular material 112a) has an excellent effect of reducing noise in the low frequency range.

In addition to the above verification experiments described with reference to Figs. 7 to 12, an experiment was conducted to measure the noise of a duct of an air conditioning equipment installed in the ceiling of a building (see ceiling S in Fig. 1). Specifically, a soundproofing material containing a bag containing a filler similar to that used in the above verification experiment was attached to the outer peripheral surface of the duct of the air conditioning equipment installed in the ceiling, and the noise generated when the air conditioning equipment was operated in this state was measured in a room on the floor below. Then, the measurement data of the sound pressure level measured in this case was compared with the measurement data of the sound pressure level measured when the soundproofing material was not attached, thereby verifying the noise reduction effect of using the soundproofing material. As a result, it was confirmed that the sound pressure level, especially in the low frequency range, was reduced when the soundproofing material was present compared to when it was not present. For example, the sound pressure level at a frequency of 63 Hz was about 4.5 dB lower when the soundproofing material was present than when it was not present. This also confirmed that the duct structure of the present invention is effective against low frequency noise.

4: Duct 10: Soundproofing material 11: Bag 12: Filler 12a: Granular material 13: Connecting sheet 14: Sound insulation layer 104: Duct 110: Soundproofing material 111: Bag 112: Filler 112a: Granular material 113: Connecting sheet

Claims (4)

The duct through which the air conditioning flows,
and a soundproofing material for reducing noise in the duct;
The soundproofing material is
A plurality of bags arranged on an outer circumferential surface of the duct, each of which has a cylindrical shape extending in an axial direction of the duct and is arranged in a circumferential direction of the duct ;
a flexible connecting sheet that connects the plurality of bags arranged in the circumferential direction to each other;
a filling material including a large number of granular materials filled inside each of the bags in a relatively movable state;
The duct structure , wherein the granular material has a specific gravity of 0.9 to 2.5 and a particle size of 0.5 mm to 6.0 mm. The duct structure according to claim 1,
A duct structure , characterized in that the filling rate of the filler with respect to the bag body is 30 volume % or more and 90 volume % or less. The duct structure according to claim 1 or 2,
A duct structure , characterized in that the filler contains the granular material whose main material is at least one of synthetic resin and synthetic rubber. The duct structure according to claim 1 or 2 ,
The duct structure , wherein the soundproofing material further comprises a sound-insulating layer covering a surface of the connecting sheet.

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