JP2009084857A - Acoustic structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic structure in which a plurality of acoustic chambers are formed of partition walls inside a resin molding, in which holes communicating with the outside are provided one by one in each of the acoustic chambers, and which can absorb sounds with at least two frequencies at acoustic coefficients, not extremely different from each other, even if the holes of the respective acoustic chambers have the same diameter. <P>SOLUTION: Some 9a of the holes 9, which are provided in the acoustic structure 1, are arranged in inside one I of two ranges I and II which divide a section between the center 4 of the acoustic chamber 3 and an outer periphery 6 thereof into two equal parts, so that the sounds with the at least two frequencies can be absorbed. The other holes 9b are arranged in the outside range II. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sound absorbing structure.

Conventionally, as disclosed in Patent Document 1, it is a resin molded body in which a plurality of sound absorbing chambers are formed by partition walls, and each of the sound absorbing chambers is provided with one hole leading to the outside. Sound absorbing structures are known. In this sound absorbing structure, a sound absorbing chamber is constituted by a void layer having a large number of voids, and the sound absorbing chamber is covered with an outer surface layer. The outer surface layer is provided with a hole that allows the sound absorbing chamber to communicate with the outside. In the sound absorbing structure, external sound reaches the sound absorbing chamber through the hole, and Helmholtz resonance occurs in the sound absorbing chamber at that time, thereby causing a predetermined value. The sound of frequency is absorbed.
JP 2002-103492 A

  By the way, in the sound absorbing structure described above, when the diameter and number of holes of each sound absorbing chamber are different, the frequency of the sound absorbed in each sound absorbing chamber changes, so that the sound absorbing structure absorbs sound of multiple frequencies. can do. However, when the diameters of the holes of the sound absorbing chambers are different, a plurality of types of drills must be prepared when the sound absorbing structure is manufactured. Further, when the diameter and number of holes are different, the sound absorption rate of each sound absorption chamber changes.

  Further, in FIG. 12 of Patent Document 1, a state in which the positions of the holes are different in the sound absorbing chamber is shown. However, Patent Document 1 makes it clear which range of each sound absorbing chamber is arranged. It is not intended to clarify how the difference in the positions of the holes affects the frequency of sound absorption in each sound absorbing chamber.

  Accordingly, the present invention has been made in view of the above points, and the object of the present invention is to form a plurality of sound absorbing chambers by partition walls inside the resin molded body, and to each of the sound absorbing chambers. A sound-absorbing structure provided with one hole that communicates with the sound-absorbing structure, wherein the sound-absorbing structure can absorb sound of at least two frequencies even when the diameter of each sound-absorbing chamber is the same. It is to provide.

  The inventors of the present application have studied to confirm the relationship between the frequency of the sound absorbed in the sound absorbing chamber and the position of the hole. As a result, the hole has a second gap between the center and the outer periphery of the sound absorbing chamber. In the case of being arranged in the outer range of the two ranges to be divided, the frequency is low in a state in which the decrease in the sound absorption rate is suppressed as compared with the case where holes of the same diameter are arranged in the inner range. The knowledge that sound can be absorbed was acquired.

  The present invention has been made in view of such knowledge. In the invention of claim 1, a plurality of sound absorbing chambers are formed in the resin molded body by partition walls, and each of the sound absorbing chambers has one hole communicating with the outside. Each of the sound absorbing structures is provided with two ranges in which a part of the hole bisects between the center and the outer periphery of the sound absorbing chamber so that sound of at least two frequencies is absorbed. Is arranged in an inner range, and the remaining portion of the hole is arranged in an outer range of the two ranges.

  According to a second aspect of the present invention, in the sound absorbing structure according to the first aspect, the volume of each of the sound absorbing chambers is the same.

  According to a third aspect of the present invention, in the sound absorbing structure according to the first or second aspect, the cross-sectional shape of each of the sound absorbing chambers is the same polygon.

  According to a fourth aspect of the present invention, in the sound absorbing structure according to any one of the first to third aspects, a connection portion connected to each surface of the resin molded body is formed inside the sound absorbing chamber. Features.

  According to the first aspect of the present invention, even when the diameters of the holes of the respective sound absorbing chambers are the same, in the sound absorbing chamber in which the holes are arranged in the outer range, the holes are arranged in the inner range. Compared with the sound absorption chamber, low frequency sound is absorbed with substantially the same sound absorption rate. For this reason, according to the sound absorbing structure of the present invention, it is possible to absorb sound of at least two frequencies in a state where the sound absorption rate is not extremely different. Moreover, since the diameter of each hole formed in a sound absorption structure can be made the same, when manufacturing a sound absorption structure, all the said holes can be formed with one type of drill. Thereby, the trouble of exchanging a drill is saved, and the production efficiency of the sound absorbing structure is good. Moreover, since the frequency of the sound to be absorbed can be changed by changing the position of the hole, the frequency of the sound absorbed by the sound absorbing structure can be easily adjusted, and the degree of freedom in designing the sound absorbing structure is improved. .

  According to the second aspect of the present invention, since the volume of the sound absorbing chamber is the same, the structure of the sound absorbing structure is simplified, so that the design of the sound absorbing structure is facilitated. Further, since it is not necessary to consider the difference in volume of the sound absorbing chamber when controlling the frequency of the sound to be absorbed, it is possible to absorb sound having a desired frequency simply by changing the position of the hole.

  According to the invention of claim 3, since the cross-sectional shape of the sound absorbing chamber is the same polygon, it is easy to distinguish the outer range and the inner range, so the position of the hole is easy. Can be set to

  According to invention of Claim 4, since the connection part connected with each surface of the said resin molding is formed inside the said sound absorption chamber, the volume of a sound absorption chamber is so absorbed that the sound of a lower frequency is absorbed. Even when this is increased, the rigidity of the sound absorbing chamber is kept high. Further, even when a hollow sound absorbing chamber is formed, unnecessary vibrations generated on the surface of the resin molded body can be suppressed because each surface of the resin molded body is connected by a connecting portion. Therefore, efficient sound absorption is achieved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic view showing a sound absorbing structure 1, (a) is a plan view of the sound absorbing structure 1, and (b) is a cross-sectional view of the sound absorbing structure 1 cut along the line AA in (a). ing. FIG. 2 is an enlarged cross-sectional view showing the inside of a sound absorbing chamber 3 to be described later.

  The sound absorbing structure 1 is a resin molded body in which a plurality of sound absorbing chambers 3 are formed inside by a partition wall 5, and is formed inside the outer surface layer 7 and an outer surface layer 7 that forms an outline of the sound absorbing structure 1. And a void layer constituting the sound absorption chamber 3.

  The outer surface layer 7 is obtained by cooling and solidifying the thermoplastic resin filled in the cavity of the mold by contact with the molding surface, and there is substantially no void in the inside, and it is dense and relatively rigid and strong. Is a high solid layer. For this reason, the outer surface layer 7 reflects incident sound waves.

  The void layer (sound absorbing chamber 3) is a solidified state in which the thermoplastic resin inside the outer surface layer 7 is expanded as a result of expanding the cavity volume when the outer surface layer 7 is formed. The air gap is provided. For this reason, the void layer (sound absorption chamber 3) absorbs (decreases) incident sound waves (sound pressure). Further, in the sound absorbing structure 1, the sound absorbing chambers 3 have the same volume, and the sound absorbing chambers 3 have the same rectangular shape in cross section.

  The surface of the sound absorbing structure 1 is provided with one hole 9 through which each sound absorbing chamber 3 communicates with the outside. This hole 9 is formed by drilling through the outer surface layer 7 of the resin molded body removed from the mold after the outer surface layer 7 and the void layer are formed, and among these holes 9a Is arranged in the inner range I of the two ranges I and II that bisect the center 4 and the outer periphery 6 of the sound absorbing chamber 3, and the remaining holes 9b are arranged in the outer range II. Yes. Moreover, all the holes 9 (9a, 9b) are formed in the same diameter. The outer periphery 6 indicates the periphery of the wall surface of the sound absorbing chamber 3, and the wall surface of the partition wall 5 is included in the wall surface.

  Moreover, as shown in FIG. 2, the connection part 11 connected with each surface of the resin molding is formed in each sound absorption chamber 3.

  In the intake structure 1 having the above-described configuration, when external sound is incident on the sound absorbing chamber 3 through the holes 9, Helmholtz resonance occurs in the sound absorbing chamber 3, and the incident sound is absorbed. At this time, since the hole 9a is arranged in the inner range I and the hole 9b is arranged in the outer range II, the diameter of each hole 9 (9a, 9b) is the same as described above. However, in the sound absorbing chamber 3 in which the hole 9b is formed, a sound having a lower frequency is absorbed in a state in which a decrease in the sound absorption rate is suppressed compared to the sound absorbing chamber 3 in which the hole 9a is formed. For this reason, sound of different frequencies can be absorbed with a sound absorption rate that is not extremely different. Moreover, since all the diameters of the holes 9 formed in the sound absorbing structure 1 are the same, when the sound absorbing structure 1 is manufactured, all the holes 9 can be formed with one kind of drill. Thereby, since the trouble of exchanging the drill can be saved, the manufacturing efficiency of the sound absorbing structure 1 is good. Moreover, since the frequency of the sound to be absorbed can be changed by changing the position of the hole 9, the frequency of the sound absorbed by the sound absorbing structure can be easily adjusted, and the degree of freedom in designing the sound absorbing structure is improved. To do.

  Further, since the volume of each sound absorbing chamber 3 is the same, the structure of the sound absorbing structure is simplified, and the design of the sound absorbing structure is facilitated. Further, since it is not necessary to consider the difference in volume of the sound absorbing chamber 3 in controlling the frequency of the sound to be absorbed, it is possible to absorb sound having a desired frequency simply by changing the position of the hole 9.

  In addition, since the cross-sectional shape of each sound absorbing chamber 3 is the same quadrangle, it is easy to distinguish between the inner range I and the outer range II, so the position of the hole 9 is set. Becomes easier.

  Moreover, since the connection part 11 connected with each surface of the resin molding is formed in the inside of the sound absorption chamber 3, it is a case where the volume of each sound absorption chamber 3 is enlarged in order to absorb the sound of a lower frequency, However, the rigidity of the sound absorbing chamber 3 is kept high.

  In the present embodiment, the sound absorbing chamber 3 has a quadrangular cross section, but may be a polygon other than a quadrangle, such as a triangle, pentagon, or hexagon.

  Further, the sound absorbing chamber 3 of the sound absorbing molded body 1 may be hollow instead of the above-described gap layer. Even in this way, the sound-absorbing molded body 1 exhibits a sound-absorbing function when the incident sound resonates in the cavity. In this case, the resin molded body is formed by closing the mold while blowing air into the parison made of a resin material between the cavities of the blow molding mold to mold the resin molded body, and then removing the mold from the blow molding mold. The sound absorbing molded body 1 is obtained by forming a hole 9 by penetrating the outer surface layer 7 with a drill. Even when the hollow sound absorbing chamber is formed in this way, since the surfaces of the resin molded body are connected by the connecting portion 11, unnecessary vibrations generated on the surface of the resin molded body are suppressed. Therefore, efficient sound absorption is achieved.

  Next, the above-described resin-made sound absorbing structure 1 was manufactured, and the frequency of the sound absorbed in each sound absorbing chamber 3 was confirmed.

  FIG. 3 is a plan view showing the positions of the holes 9 of the sound absorbing structure manufactured in the first embodiment of the present invention.

  In the sound absorbing structure of this embodiment, each sound absorbing chamber 3 has a square shape with vertical and horizontal dimensions of 120 mm × 120 mm. FIG. 3 shows the holes 91 to 98 formed on the surface of the sound absorbing structure by plotting them on one sound absorbing chamber. Each of the sound absorbing chambers 3 in the sound absorbing structure is one of the holes 91 to 98. The diameter of the holes 91 to 98 is all 9 mm.

  The hole 91 is disposed at the center 4 of the sound absorbing chamber 3, and the holes 92 to 94 are formed at positions sequentially displaced from the hole 91 by a predetermined distance in the lateral direction. As a result, the holes 91 to 94 are all disposed in the inner range B out of the two ranges B and C that bisect the space between the center 4 and the outer periphery 6 of the sound absorbing chamber 3 in the lateral direction. It has become. However, when the holes 91 to 94 are arranged in two ranges D and E that bisect the space between the center 4 and the outer periphery 6 of the sound absorbing chamber 3, the holes 91 to 93 are located in the inner range D. On the other hand, the hole 94 is disposed in the outer range E, and the separation distance between the hole 94 and the outer periphery 6 is 15 mm.

  The hole 95 is disposed at the center on the boundary line H of the ranges B and C that bisect the space 4 between the center 4 and the outer periphery 6 of the sound absorbing chamber 3. On the boundary line H, they are arranged at positions shifted sequentially from the hole 95 by a predetermined distance in the lateral direction. When the holes 95 to 98 are arranged in the two ranges D and E that bisect the space between the center 4 and the outer periphery 6 of the sound absorbing chamber, the holes 95 to 97 are arranged in the inner range D. On the other hand, the hole 98 is disposed in the outer range E, and the separation distance between the hole 98 and the outer periphery 6 is 15 mm.

  As for the relationship between the ranges B to E described in this embodiment and the ranges I and II shown in FIG. 1, the range where the ranges B and D overlap corresponds to the range I shown in FIG. The combined range of C and E corresponds to the range II shown in FIG. 1, the holes 91 to 93 and 95 to 97 are arranged in the inner range I in FIG. 1, and the holes 94 and 98 are arranged on the outer side in FIG. It is arranged in the range II.

  And the sound absorption structure which has the said structure was arrange | positioned in the laboratory whose temperature is 25 degreeC, and humidity is 55%, and the frequency of the sound absorbed in each sound absorption chamber was confirmed. 4 to 6 show the results. Table 1 shows the distance from the holes 91 to 98 to the partition wall 5, the frequency of the sound absorbed in each sound absorbing chamber 3, and the sound absorption rate of each sound absorbing chamber 3. In addition, the distance to the outer periphery 6 shown in Table 1 shows the separation distance between the holes 91 to 98 and the corners P (the corners closest to the holes 91 to 98 among the four corners of the sound absorbing chamber 4). ing. This separation distance does not coincide with the shortest distance at which each hole is separated from the outer periphery 6. However, when the separation distance is compared for each of the holes 91 to 94 and the holes 95 to 98, the separation distance is The larger the hole is, the larger the shortest distance is, and the hole is away from the outer periphery 6.

  As shown in FIGS. 4 to 6 and Table 1, it is confirmed that the sound absorbing chamber 3 whose position of the hole 9 is closer to the outer periphery 6 absorbs a lower frequency sound, and the sound absorbing chamber whose position of the hole 9 is closer to the outer periphery 6. It was confirmed that the sound absorption rate gradually decreased by 3. Further, regarding the holes 91 to 94, when the hole position is changed from the hole 93 to the hole 94, the amount of decrease in the sound absorption coefficient is changed from the hole 91 to the hole 92 and from the hole 92 to the hole 93. The amount of decrease in the sound absorption rate when the position of the hole is changed from the hole 97 to the hole 98 is larger from the hole 95 to the hole 96. It is larger than the amount of decrease in the sound absorption coefficient when the hole position is changed from the hole 96 to the hole 97. As a result, it was confirmed that when the holes were formed in the outer ranges C and E, the sound absorption rate was slightly lower than that of the sound absorbing chamber 3 in which the holes were formed in the inner ranges B and D.

  Further, as the second embodiment, a sound absorbing structure having a hollow sound absorbing chamber 3 was manufactured, and an experiment similar to the above was performed.

  FIG. 7 is a plan view showing the positions of the holes 19 of the sound absorbing structure manufactured in the first embodiment of the present invention.

  In this embodiment, the sound absorbing structure is made of brass, and a plurality of hollow sound absorbing chambers 3 are formed by the partition walls 5. As in the first embodiment, each sound absorbing chamber 3 has a square shape with vertical and horizontal dimensions of 120 mm × 120 mm, and communicates with the outside through one of the holes 191 to 198. The arrangement of the holes 191 to 198 is the same as that in the first embodiment. In this embodiment, the diameters of the holes 191 to 198 are 7 mm.

  And the sound absorption structure which has the said structure was arrange | positioned in the laboratory whose temperature is 26 degreeC, and humidity is 51%, and the frequency of the sound absorbed in each sound absorption chamber 3 was confirmed. 8 to 10 show the results. Table 2 shows the distance to the outer periphery 6 of the holes 91 to 98, the frequency of the sound absorbed in each sound absorbing chamber 3, and the sound absorption rate of each sound absorbing chamber 3. In Table 2, as in Table 1, the separation distance between the holes 191 to 198 and the corner P is shown as the distance to the outer periphery 6.

  As shown in FIGS. 8 to 10 and Table 2, as in the first embodiment, it is confirmed that the sound absorbing chamber 3 near the outer periphery 6 absorbs a low frequency sound as in the first embodiment. It was confirmed that the sound absorption rate of the sound absorbing chamber 3 whose position is closer to the outer periphery 6 gradually decreases. Further, regarding the holes 191 to 194, when the hole position is changed from the hole 193 to the hole 194, the amount of decrease in the sound absorption coefficient is changed from the hole 191 to the hole 192 and from the hole 192 to the hole 193. The amount of decrease in the sound absorption coefficient when the position of the hole is changed from the hole 197 to the hole 198 is larger from the hole 195 to the hole 196. It is larger than the amount of decrease in the sound absorption rate when the position of the hole is changed from the hole 196 to the hole 197. As a result, it was confirmed that when the holes were formed in the outer ranges C and E, the sound absorption rate was slightly lower than that of the sound absorbing chamber 3 in which the holes were formed in the inner ranges B and D.

  In addition, a sound absorbing structure made of brass having a sound absorbing chamber 3 in which a hole having a diameter of 3.5 mm or 4.0 mm is formed at the position of the hole 191 is manufactured, and the frequency of sound absorbed in the sound absorbing chamber 3 is manufactured. It was confirmed. As a result, as shown in FIG. 8, the frequency at which the sound absorption coefficient peaks in the sound absorbing chamber 3 in which holes having a diameter of 3.5 mm or 4 mm are formed and the sound absorbing chamber 3 in which holes 198 (diameter 7 mm) are formed. However, it was confirmed that the sound absorption rate is larger in the sound absorption chamber 3 in which the holes 198 are formed. Thereby, it was confirmed that forming the hole in the vicinity of the outer periphery 6 is effective for lowering the frequency of the sound without reducing the sound absorption coefficient. That is, as described in the present embodiment and the first embodiment, when the position of a hole having the same diameter is shifted from the center 4 to the outer periphery 6, the sound absorption coefficient decreases, but the amount of the decrease is centered on the hole. Therefore, shifting the position of the hole closer to the outer periphery 6 is smaller than reducing the diameter of the hole without changing the position of the hole. It was confirmed that it was advantageous to absorb low frequency sound while suppressing a decrease in sound absorption rate.

  In this embodiment, the sound absorbing structure is made of brass. However, in this brass sound absorbing structure as well as the resin sound absorbing structure, the sound is absorbed by the phenomenon that Helmholtz resonance occurs in the sound absorbing chamber. Therefore, it is considered that the sound absorption tendency described in the present embodiment also appears in the same manner in the resin sound absorption structure.

It is the schematic which shows a sound absorption structure. It is sectional drawing which expands and shows the inside of a sound absorption chamber. It is a top view which shows the position of the hole of the sound absorption structure manufactured in 1st Example of this invention. It is a graph which shows the sound absorption characteristic of the sound-absorbing structure manufactured in 1st Example. It is a graph which shows the sound absorption characteristic of the sound-absorbing structure manufactured in 1st Example. It is a graph which shows the relationship between the position of a hole and the frequency of the sound absorbed in a sound absorption chamber in 1st Example. It is a top view which shows the position of the hole of the sound-absorbing structure manufactured in 2nd Example of this invention. It is a graph which shows the sound absorption characteristic of the sound absorption structure manufactured in 2nd Example. It is a graph which shows the sound absorption characteristic of the sound absorption structure manufactured in 2nd Example. It is a graph which shows the relationship between the position of a hole and the frequency of the sound absorbed in a sound absorption chamber in 2nd Example.

Explanation of symbols

1 sound absorbing structure,
3 Sound absorption chamber,
9 holes,
4 center,
6 outer circumference,
11 connection part.

Claims (4)

A plurality of sound absorbing chambers are formed by partition walls inside the resin molded body, and each sound absorbing chamber is a sound absorbing structure provided with one hole leading to the outside,
A part of the hole is disposed in an inner range of two ranges that bisect the center and the outer periphery of the sound absorbing chamber so that sound of at least two frequencies is absorbed. The remaining part is disposed in an outer range of the two ranges, and the sound absorbing structure.   The sound absorbing structure according to claim 1, wherein the sound absorbing chambers have the same volume.   The sound absorbing structure according to claim 1 or 2, wherein a cross-sectional shape of each of the sound absorbing chambers has the same polygonal shape.   The sound absorption structure according to any one of claims 1 to 3, wherein a connection portion connected to each surface of the resin molding is formed inside the sound absorption chamber.

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