JP2005266399A - Resonator type muffling structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resonator-type muffling structure capable of absorbing sounds over a wide frequency range, without increasing the number of chambers. <P>SOLUTION: The resonator muffling structure 1 is equipped with a front wall 10, in which through holes 10a are formed, a rear wall 20, a 1st intermediate wall 31, a 2nd intermediate wall 32, and a flat plate type elastic body 40. The 1st intermediate wall 31 and 2nd intermediate wall 32 have a partition part 31A and a partition part 32A, respectively. The space between the front wall 10 and rear wall 20 is sectioned by the partition part 31A and partition part 31B into a front-wall side space 1a and a rear-wall side space 1b, which form a front-wall side chamber 30a and a rear-wall side chamber 30b sectioned with the elastic body 40. The normal vibration frequency of a vibration system of the elastic body 40 and rear-wall side chamber 30b is nearly equal to the resonance frequency of a resonator, when the elastic body 40 is assumed to be a rigid wall which will not vibrate by sound waves. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a resonator-type sound absorbing structure, and more particularly to a Helmholtz-type resonator-type sound absorbing structure installed on an expressway, a track, or the like.

  In recent years, with the increase in the speed of transportation networks, the problem of noise pollution has become more serious along highways and railway lines. In order to solve this problem, in order to prevent noise from diffusing from highways and railways, noise barriers are installed on both sides of tunnels, roads, railways, and the like. In addition, soundproof walls are also attached to room walls and ceilings.

Japanese Patent Application Laid-Open No. 2003-295866 describes a Helmholtz resonator type sound absorbing structure. The resonator-type sound absorbing structure includes a front wall, a rear wall, and an intermediate wall that connects them, and a space provided between the front wall and the rear wall is partitioned into a plurality of chambers by a partition provided on the intermediate wall. ing. The plurality of chambers have different volumes, and thus can absorb sounds having a plurality of different frequencies. Japanese Patent Application Laid-Open No. 11-338476 describes a Helmholtz type resonator type sound absorbing structure in which an air chamber and a resonance cavity are formed.
JP 2003-295866 A (pages 3 to 5, FIG. 2) Japanese Patent Laid-Open No. 11-338476 (pages 4 to 5, FIG. 1)

  In the resonator type sound absorbing structure described in Japanese Patent Laid-Open No. 2003-295866, one chamber formed in the resonator type sound absorbing structure absorbs sound having one resonance frequency. For this reason, when sound absorption is performed in a wide frequency range, a plurality of chambers having different resonance frequencies must be formed in the resonator type sound absorption structure. On the other hand, when sound absorption is performed in a wide frequency range, the aperture ratio becomes small in a single resonance frequency chamber, which causes a problem that the sound absorption ratio is lowered.

  In the resonator type sound absorbing structure described in Japanese Patent Laid-Open No. 11-338476, one air chamber and one resonance sinus can absorb only sound of one frequency. Problems similar to those of the resonator type sound absorbing structure occur.

  Accordingly, an object of the present invention is to provide a resonator type sound absorbing structure capable of absorbing sound in a wide frequency range without increasing the number of chambers.

To achieve the above object, the present invention includes a front wall 10 in which a plurality of through holes 10a are formed, rear wall 20, 50, 70 disposed opposite to the front wall 10 with a space therebetween, and the front surface. Partitions 31A and 32A for partitioning a portion of the space formed between the wall 10 and the rear walls 20, 50 and 70 on the front wall 10 side into a plurality of front wall spaces 1a. Intermediate walls 31, 31 ′, 32, 62 connecting the front wall 10 and the rear walls 20, 50, 70, and the plurality of through holes 10 a are formed in the front wall side spaces 1 a. In the resonator type sound absorbing structures 1 to 5 formed corresponding to the intermediate walls 31, 31 ', 32, 62 between the front wall 10 and the rear walls 20, 50, 70, The flat plate that separates the plurality of front wall side spaces 1a from the space 1b on the rear wall 20, 50, 70 side The plurality of front wall side spaces 1a are defined by the front wall 10, the intermediate walls 31, 31 ', 32, 62 and the elastic bodies 40, 40'. A plurality of front wall side chambers 30a, 30a ', and a space 1b on the rear wall 20, 50, 70 side is provided along the peripheral edge of the rear wall 20, 50, 70 and faces the front wall 10. The outer peripheral frame and the rear walls 20, 50, 70 and the elastic bodies 40, 40 ', or the partition portions 31A, 32A and the rear walls 20, 50, 70 and the elastic bodies 40, 40'. And the elastic bodies 40, 40 'are vibrated by sound waves that have entered the front wall side chambers 30a, 30a' from the through-hole 10a, and the elastic bodies 40, 40 ' 40 and 40 'are assumed to be rigid walls that are not vibrated by sound waves. Ringing frequency and, and the natural frequency of the vibration system of the substantially matching 'rear wall side chamber 30b, 30b and' elastic body 40, 40, elastic body surface density of 40, 40 'is 126.6694kg / ^{m 2} The following resonator type sound absorbing structure is provided.

  Here, it is preferable that the plurality of front wall side chambers 30a and 30a 'have at least two types of front wall side chambers 30a and 30a' having different volumes.

  The plurality of front wall side chambers 30a and 30a ′ have at least two types of front wall side chambers 30a and 30a ′ having different distances from the front wall 10 to the elastic bodies 40 and 40 ′. Is preferred.

According to the resonator-type sound absorbing structure of the first aspect of the present invention, a flat plate-like space separating the plurality of front wall side spaces from the rear wall side space is provided at the intermediate wall position between the front wall and the rear wall. The elastic body is disposed, and the plurality of front wall side spaces form a plurality of front wall side chambers defined by the front wall, the intermediate wall, and the elastic body, and the space on the rear wall side is formed at the peripheral edge of the rear wall. A rear wall side chamber defined by the outer peripheral frame, the rear wall, and the elastic body that are provided along the front wall and formed by the partition, the rear wall, and the elastic body, and vibrates the elastic body with sound waves. Since the resonance frequency of the resonator when assuming a non-hard wall is substantially equal to the natural frequency of the vibration system of the elastic body and the rear wall side chamber, the surface density of the elastic body is 126.6694 kg / m ² or less. The sound of two frequencies can be absorbed in one front wall side chamber. For this reason, it is not necessary to increase the number of front wall side chambers, and the aperture ratio is not reduced. Therefore, it is possible to absorb a number of different frequencies without reducing the sound absorption rate.

  According to the resonator type sound absorbing structure according to claim 2 of the present invention, the plurality of front wall side chambers have at least two types of front wall side chambers having different volumes from each other. Two times as many sounds with different frequencies can be absorbed.

  According to the resonator type sound absorbing structure according to claim 3 of the present invention, the plurality of front wall side chambers include at least two types of front wall side chambers having different distances from the front wall to the elastic body. It is possible to absorb sounds of different frequencies, twice as many as the type of the front wall side chamber.

  A resonator type sound absorbing structure 1 according to a first embodiment of the present invention will be described with reference to FIGS. The resonator type sound absorbing structure 1 is a Helmholtz type and includes a front wall 10, a rear wall 20, a first intermediate wall 31, a second intermediate wall 32, and a plate-like elastic body 40, as shown in FIG. Yes. In FIG. 1, for convenience of explanation, the front wall 10, the first intermediate wall 31, the second intermediate wall 32, and the elastic body 40 are shown in a state of being separated from each other. As shown in FIG. 2, the structure 1 is configured by joining the front wall 10, the first intermediate wall 31, the elastic body 40, and the second intermediate wall 32 in this order. The second intermediate wall 32 and the rear wall 20 are integrally formed. In addition, about the front-back direction, let the lower left direction of FIG. 1 be the front, and let the upper right direction of FIG. 1 be the back. 2 and 3, the upper direction in the figure is the front and the lower direction in the figure is the rear.

  As shown in FIGS. 1 to 3, the front wall 10 has a planar shape, and a plurality of through holes 10 a having the same diameter are formed in the front wall 10 by pressing. The plurality of through holes 10a are formed one by one corresponding to a plurality of front wall side chambers 30a described later. Since the through hole 10a is formed, sound can enter the plurality of front wall side chambers 30a through the through hole 10a. The front wall 10 is a plate member made of aluminum alloy.

  The rear wall 20 is substantially planar. As shown in FIG. 3, the surface of the rear wall 20 that faces the front wall 10 forms a flat surface at a position that defines a plurality of rear wall spaces 1b to be described later. The thicknesses of the rear wall 20 are different from each other. Therefore, on the surface of the rear wall 20 facing the front wall 10, as shown in FIG. 3, the position in the front-rear direction, that is, the vertical direction in FIG. 3, differs for each of the plurality of rear wall-side spaces 1b. . The rear wall 20 is opposed to the front wall 10 in a parallel positional relationship with a predetermined distance by the presence of the first intermediate wall 31, the elastic body 40, and the second intermediate wall 32 between the rear wall 20 and the front wall 10. Has been.

  The first intermediate wall 31 and the second intermediate wall 32 have substantially the same shape, and are constituted by a partition portion 31A and a partition portion 32A, respectively. The second intermediate wall 32 is integrally connected to the rear wall 20. The partition portion 31A and the partition portion 32A extend from the position of the front wall 10 to the position of the rear wall 20 in the thickness direction of the resonator-type sound absorbing structure 1 with the elastic body 40 interposed therebetween. Existing.

  The first intermediate wall 31 is joined to the front wall 10 at the front end position of the partition portion 31A, and is joined to the elastic body 40 at the rear end position. The second intermediate wall 32 is integrally connected to the rear wall 20 at the rear end position of the partition portion 32A, and is joined to the elastic body 40 at the front end position. Further, by sandwiching the elastic body 40 between the rear end position of the partition portion 31A of the first intermediate wall 31 and the front end position of the partition portion 32A of the second intermediate wall 32, the first intermediate wall 31 and the second intermediate wall 32 are Are joined. The front wall 10, the first intermediate wall 31, the elastic body 40, the second intermediate wall 32, and the rear wall 20 are joined to each other by bolts (not shown) that pass through them.

  As a result of joining in this way, the partition portions 31A and 32A and the elastic body 40 make a part of the space between the front wall 10 and the rear wall 20 on the front wall 10 side a plurality of front wall sides. A plurality of front wall side chambers 30 a are defined by the front wall 10, the elastic body 40, and the partition portion 31 </ b> A of the first intermediate wall 31. Similarly, a part of the space between the front wall 10 and the rear wall 20 on the rear wall 20 side is partitioned into a plurality of rear wall walls 1b, the rear wall 20, the elastic body 40, A plurality of rear wall side chambers 30b are defined by the partition portion 32A of the second intermediate wall 32.

  As described above, the first intermediate wall 31 and the second intermediate wall 32 have substantially the same shape, and each of the front wall side chambers 30a when viewed in a plane perpendicular to the front-rear direction of the resonator type sound absorbing structure 1 is used. The shape of the front end position, the shape of the rear end position, the shape of the front end position of each rear wall side chamber 30b, and the shape of the rear end position are the same. Therefore, when the first intermediate wall 31, the elastic body 40, and the second intermediate wall 32 are joined to each other, the portion of the rear end position of each front wall side chamber 30a and the portion of the front end position of each rear wall side chamber 30b are The elastic bodies 40 are opposed to each other with the elastic bodies 40 in the same positional relationship, and the elastic bodies 40 partition the front wall side chambers 30a and the rear wall side chambers 30b. Each rear wall side chamber 1b prevents the elastic body from vibrating and transmitting noise.

  As shown in FIG. 3, the plurality of front wall side chambers 30 a have different volumes from each other, and are thereby configured to absorb sound having different frequencies for each front wall side chamber 30 a. The first intermediate wall 31 is manufactured by being integrally formed by a die casting method. The second intermediate wall 32 is manufactured by being integrally formed with the rear wall 20 by a die casting method.

The elastic body 40 is made of an elastic body such as a plastic material or a vinyl chloride plate, and has a surface density of 126.6694 kg / m ² or less. Therefore, the elastic body 40 is vibrated by the sound wave that has entered the front wall side chamber 30a from the through hole 10a. Further, the natural frequency of the vibration system of the elastic body 40 and the rear wall side chamber 30b is defined by the rigid wall, the first intermediate wall 31 and the front wall 10 when the elastic body 40 is assumed to be a rigid wall that is not vibrated by sound waves. By setting it close to the resonance frequency of the resonator formed by the virtual front wall side chamber and the through hole 10a of the front wall 10, sound absorption peaks appear at two different frequencies.

  This makes it possible to absorb two different frequency sounds in one front wall side chamber 30a. For this reason, the front wall side chamber 30a has a plurality of types of front wall side chambers 30a having different volumes, but can absorb sounds of different frequencies, twice as many as this type, and reduce the aperture ratio. In the resonator-type sound absorbing structure 1, it is possible to absorb a number of different frequencies.

  In manufacturing the resonator type sound absorbing structure 1, first, the front wall 10, the first intermediate wall 31, the elastic body 40, the rear wall 20 and the second intermediate wall 32 are manufactured. The front wall 10 is manufactured by pressing an aluminum alloy formed into a plate shape having the same shape as the resonator-type sound absorbing structure 1 to be manufactured, and forming a through hole 10a at a predetermined position. The first intermediate wall 31 is manufactured by integrally molding an aluminum alloy by a die casting method. The elastic body 40 is manufactured by cutting a vinyl chloride plate or the like into a plate having the same shape as the resonator type sound absorbing structure 1 to be manufactured. As with the first intermediate wall 31, the rear wall 20 and the second intermediate wall 32 are manufactured by integrally molding an aluminum alloy by a die casting method.

  Next, the resonator-type sound absorbing structure 1 is manufactured by penetrating the front wall 10, the first intermediate wall 31, the elastic body 40, the second intermediate wall 32, and the rear wall 20 with bolts (not shown) and joining them together. To do.

  Since the front wall 10, the rear wall 20, the first intermediate wall 31, and the second intermediate wall 32 are made of aluminum alloy, the recyclability of the resonator type sound absorbing structure 1 can be improved. In addition, the first intermediate wall 31 provided with the partition portions 31A and 32A each having a complicated shape, the second intermediate wall 32, and the rear wall 20 are integrally formed by a die casting method, respectively, so that the front wall 10 and the first intermediate wall Since the resonator-type sound absorbing structure 1 is configured by joining the wall 31, the elastic body 40, the second intermediate wall 32, and the rear wall 20, a plurality of components are provided in the resonator-type sound absorbing structure 1 without going through a complicated process. The hollow front wall side chambers 30a having different volumes can be formed, and the resonator-type sound absorbing structure 1 can be easily manufactured.

  Next, a resonator type sound absorbing structure 2 according to a second embodiment of the present invention will be described with reference to FIGS. In the resonator-type sound absorbing structure 1 according to the first embodiment, one elastic body 40 partitions the plurality of front wall side chambers 30a and the plurality of rear wall side chambers 30b, but the resonance according to the second embodiment. In the container-type sound absorbing structure 2, a small elastic body 40 ′ is provided to partition one front wall side chamber 30 a ′ and one rear wall side chamber 30 b ′ one by one. Therefore, the elastic body 40 'is provided in the same number as the plurality of front wall side chambers 30a'. Further, in the plurality of front wall side chambers 30a ′, the distances from the front wall 10 to the elastic body 40 ′ are different from each other. Further, the surface of the rear wall 50 facing the front wall 10 is flush.

  In the resonator-type sound absorbing structure 1 according to the first embodiment, the elastic body 40 is sandwiched between the rear end position of the partition portion 31A of the first intermediate wall 31 and the front end position of the partition portion A of the second intermediate wall 32. In the resonator-type sound absorbing structure 2 according to the second embodiment, it is formed at the front end position of the partition portion 62A of the second intermediate wall 62 and the partition portion 31A ′ of the first intermediate wall 31 ′. It joins so that it may pinch | interpose with the step part 31B (FIG. 6) made. Except for these, the resonator-type sound absorbing structure 1 according to the first embodiment is the same. 4 to 6, the same members as those in the first embodiment are denoted by the same reference numerals. About the front-back direction, let the left direction of FIG. 4 be front, and let the right direction of FIG. 4 be back. 5 and 6, the upper direction in the figure is the front and the lower direction in the figure is the rear.

  More specifically, as shown in FIG. 4, the resonator type sound absorbing structure 2 includes a front wall 10, a rear wall 50, a first intermediate wall 31 ', a second intermediate wall 62, and a plurality of small plate-like elastic bodies. 40 '. As in FIG. 1, for convenience of explanation, FIG. 4 shows the front wall 10, the first intermediate wall 31 ′, the second intermediate wall 62, and the elastic body 40 ′ in a state of being separated from each other. Actually, as shown in FIG. 5, the resonator-type sound absorbing structure 2 includes a front wall 10, a first intermediate wall 31 ', an elastic body 40', and a second intermediate wall 62 joined together in this order. Composed. In FIG. 4, it seems as if a plurality of elastic bodies 40 ′ are connected to each other as if they were integrated, but each elastic body 40 ′ is not connected to each other, and the number of front wall side chambers 30 a ′ is the same. A corresponding number of elastic bodies 40 'are provided separately and independently.

  As shown in FIG. 6, the first intermediate wall 31 ′ is joined to the front wall 10 at the front end position and is joined to the rear wall 50 at the rear end position. A step portion 31B is provided at a position of the first intermediate wall 31 ′ between the front wall 10 and the rear wall 50. The position where the step portion 31B is provided in the front-rear direction, that is, the vertical direction in FIG. 6, differs for each front wall side chamber 30a ′ defined by the partition portion 31A ′ of the first intermediate wall 31 ′. A front wall side chamber 30a ′ and a rear wall side chamber 30b ′ are defined between the plurality of partition portions 31A ′. From the position of the step portion 31B on the inner peripheral surface of the partition portion 31A ′ that defines them. Further, the portion closer to the rear end forms an enlarged diameter portion 31C, and the portion closer to the front end forms a reduced diameter portion 31D.

  The partition part 62A of the second intermediate part 62 is inserted along the partition part 31A 'from the rear end position of the first intermediate wall 31' along the enlarged diameter part 31C of the first intermediate wall 31 '. By sandwiching the elastic body 40 'preset in 31B between the front end position of the partition 62A of the second intermediate wall 62 and the step 31B of the first intermediate wall 31', the first intermediate wall 31 ', The second intermediate wall 62 is joined. As described above, since the distances from the front wall 10 to the elastic body 40 'are different from each other in the plurality of front wall side chambers 30a', the frequencies absorbed in the plurality of front wall side chambers 30a 'are different from each other. can do. Further, since the elastic body 40 'is provided independently for each front wall side space, the stepped portion 31B can be set for each front wall side space at a desired position suitable for the frequency of sound absorption. It is possible to easily set the frequency for absorbing sound.

  In manufacturing the resonator type sound absorbing structure 2, first, the front wall 10, the first intermediate wall 31 ', the elastic body 40', the rear wall 50, and the second intermediate wall 62 are manufactured. Similar to the first intermediate wall 31 in the first embodiment, the first intermediate wall 31 'is manufactured by integrally molding an aluminum alloy by a die casting method. The elastic body 40 ′ is made of vinyl chloride in a plate shape that is the same shape as the shape of the step portion 31 B of the partition portion 31 A ′ of the first intermediate wall 31 ′ when viewed from the plane perpendicular to the front-rear direction of the resonator-type sound absorbing structure 2. A board etc. are cut and manufactured. The rear wall 50 and the second intermediate wall 62 are manufactured by integrally molding an aluminum alloy by a die casting method, similarly to the rear wall 20 and the second intermediate 32 according to the first embodiment.

  Next, the elastic body 40 ′ is bonded to the step portion 31B of the partition portion 31A ′ of the first intermediate wall 31 ′ using an adhesive. Then, the resonator-type sound absorbing structure 2 is manufactured by penetrating the front wall 10, the first intermediate wall 31 ', and the rear wall 50 with bolts (not shown) and joining them together.

  Next, a resonator type sound absorbing structure 3 according to a third embodiment of the present invention will be described with reference to FIG. In the resonator-type sound absorbing structure 2 according to the second embodiment, the partition portion 31A ′ of the first intermediate wall 31 ′ is provided with the enlarged diameter portion 31C and the reduced diameter portion 31D, and stepped portions are provided at the boundary positions thereof. 31B is provided, but in the resonator-type sound absorbing structure 3 according to the third embodiment, such an enlarged diameter portion 31C and an enlarged diameter portion 31D are not provided, and the first intermediate wall 31 is not provided. A recess 31a for disposing the elastic body 40 'is formed at the rear end position of the "partition 31A". The elastic body 40' set in the recess 31a is formed in the same manner as in the first embodiment. The first intermediate wall 31 ″ is sandwiched between the rear end position of the first intermediate wall 31 ″ and the front end position of the partition portion 32A of the second intermediate wall 32 provided integrally with the rear wall 20.

  Further, the first intermediate wall 31 ″ and the second intermediate wall 32 are joined so that the rear end position of the first intermediate wall 31 ″ and the front end position of the second intermediate wall 32 are in contact with each other. Except for these, the resonator-type sound absorbing structure 2 according to the second embodiment is the same. In FIG. 7, the same members as those in the first and second embodiments are denoted by the same reference numerals. As for the front-rear direction, the upper direction in FIG. 7 is the front and the lower direction in FIG. 7 is the rear.

  In manufacturing the resonator-type sound absorbing structure 3, the elastic body 40 ′ is bonded to the concave portion 31 a with an adhesive, and then the rear wall 20 provided integrally with the second intermediate wall 32, the front wall 10, and the first The resonator-type sound absorbing structure 3 is manufactured by joining the intermediate wall 31 ″ with a bolt (not shown) penetrating the intermediate wall 31 ″. A recess formed at the rear end position of the partition portion 31A ″ of the first intermediate wall 31 ″. Since the elastic body 40 'is disposed on 31a, the elastic body 40' can be easily disposed in the recess 31a.

  Next, a resonator type sound absorbing structure 4 according to a fourth embodiment of the present invention will be described with reference to FIG. The rear wall 20 of the resonator type sound absorbing structure 1 according to the first embodiment has a different thickness for each of the plurality of rear wall side chambers 30b. However, in the resonator type sound absorbing structure 4 according to the fourth embodiment, The thickness of the rear wall 70 is constant, which is different from the resonator type sound absorbing structure 1 according to the first embodiment in this respect.

  Except this point, it is the same as the resonator type sound absorbing structure 1 according to the first embodiment. In FIG. 8, the same members as those in the first embodiment are denoted by the same reference numerals. As for the front-rear direction, the upper direction in FIG. 8 is the front and the lower direction in FIG. 8 is the rear.

  Next, a resonator type sound absorbing structure 5 according to a fifth embodiment of the invention will be described with reference to FIG. The second intermediate wall 32 in the first embodiment has the partition portion 32A, but the second intermediate wall (not shown) in the fifth embodiment does not have the partition portion 32A, and the rear The outer peripheral frame (not shown) is provided integrally with the rear wall 70 along the peripheral edge of the surface wall 70 and extends toward the front wall 10. More specifically, the outer peripheral frame (not shown) is the same as the outer peripheral member of the second intermediate wall 32 in the first embodiment shown in FIG. . The rear end position of the first intermediate wall 31 is joined to the front end position of the outer peripheral frame (not shown) via the elastic body 40. The elastic body 40 is bonded to the rear end position of the first intermediate wall 31 with an adhesive. This is different from the resonator-type sound absorbing structure 1 according to the first embodiment.

  Except this point, it is the same as the resonator type sound absorbing structure 1 according to the first embodiment. In FIG. 9, the same members as those in the first embodiment are denoted by the same reference numerals. Regarding the front-rear direction, the upper direction in FIG. 9 is the front and the lower direction in FIG. 9 is the rear.

  Next, a calculation for obtaining the sound absorption coefficient of the resonator type sound absorbing structure according to the embodiment of the present invention was performed, and a test for the validity of the calculation result was performed. In the calculation and the test, the resonator type sound absorbing structure was assumed to be the resonator type sound absorbing structures 1 to 4 according to the first to fourth embodiments. In the calculation, an equation for deriving the sound absorption coefficient of the resonator type sound absorbing structure in the case of normal incidence was derived. It is assumed that the front wall side chamber is sufficiently dense in the resonator type sound absorbing structure, and the through hole of the front wall and the front wall side chamber are sufficiently small with respect to the wavelength of the sound wave in the frequency band considered by calculation. In this case, the reflected sound can be considered to be flat on average, and it can be considered that the sound wave also travels as a plane wave inside the front wall side chamber. The following analysis when considered in this way is considered as a one-dimensional sound field. In addition, the cross section cut by a plane perpendicular to the front-rear direction of the flat elastic body, the through hole of the front wall, and the front wall side chamber is considered as a circle.

In the calculation for obtaining the sound absorption coefficient of the resonator type sound absorbing structure, the acoustic impedance density Z ₀₋ of the front wall surface is obtained. Here, each symbol is as follows.

ここで、１次モードが支配的な領域を扱うとして、１次モードのみを考える。このとき振動速度v_p ( r )は、

と記述でき、式（１）は次式となる。

ただしjは純虚数、

である。ここで、P_{l 1+}は、

と記述できるので、

である。ただし、

である。式（１０）を式（３）に代入すると、

となるのでZ _l1-は、

となる。ここで、後面壁側室の壁面は剛壁であるので、弾性体の後ろ側の面での音響インピーダンス密度Z _l1+は次式となる。

ここで、kl₂が小さいとすると、

となる。また、

であるので、式（１４）は、

となる。ただし、

である。ここで、

は弾性体と後面壁側室内の空気とを複合した振動系の固有角振動数を表している。 First, the acoustic impedance density _Zl1- on the elastic body surface is _obtained . The equation of motion of the plate-like elastic body can be described by the following expression, where x (r, t) is the displacement of an arbitrary point r on the elastic body at time t.

Here, only the primary mode is considered assuming that the region where the primary mode is dominant is handled. At this time, the vibration speed v _p (r) is

Equation (1) becomes the following equation.

Where j is a pure imaginary number,

It is. Where P _{l 1+} is

Can be described as

It is. However,

It is. Substituting equation (10) into equation (3),

Z _l1-

It becomes. Here, since the wall surface of the rear wall side chamber is a rigid wall, the acoustic impedance density Z _{l1 +} on the rear surface of the elastic body is expressed by the following equation.

Here, if kl ₂ is small,

It becomes. Also,

Therefore, equation (14) is

It becomes. However,

It is. here,

Represents the natural angular frequency of the vibration system that combines the elastic body and the air in the rear wall side room.

ただし、

であり、

は、前面壁の貫通孔部分の空気への付加質量を考慮した管端補正値である。この補正値は、Ｉｎｇａｒｄによると次式により表すことができる。

ただし、

は孔の外部空間側の補正値、

は前面壁側室側の補正値であり、前面壁の貫通孔及び前面壁側室の、前後方向における断面を円形とした今の場合、次式で記述できる。

ここで、P₀₊は、

と表されるので、式(20)は、

となる。よって前面壁の貫通孔１つの音響インピーダンス密度z _hは、

である。したがって

の面積にn個の前面壁側室があるとすると、全体の音響インピーダンス密度Z_0-は、

となる。 Next, the acoustic impedance density Z ₀₋ of the front wall surface is obtained. The equation of motion related to the air in the through hole in the front wall can be described by the following equation if the influence of the sound radiated from the through hole in the front wall is ignored.

However,

And

Is a tube end correction value considering the mass added to the air of the through hole portion of the front wall. This correction value can be expressed by the following equation according to Ingard.

However,

Is the correction value on the outside space side of the hole,

Is a correction value on the front wall side chamber side, and can be described by the following equation in the case where the cross section in the front-rear direction of the through hole of the front wall and the front wall side chamber is circular.

Where P ₀₊ is

Therefore, the equation (20) is

It becomes. Therefore, the acoustic impedance density z _h of one through hole in the front wall is

It is. Therefore

If there are n front wall side chambers in the area, the overall acoustic impedance density Z _0-

It becomes.

と求めることができ、kl₁が十分小さいとすると、

となる。 Here, the relationship between Z ₀₊ and Z _{l 1-} is

If kl ₁ is sufficiently small,

It becomes.

と記述できる。ただし、Z_r 、Z_imはZ_0-の実数部、虚数部であり、次式である。

また、式(32)、式(33)中の

は、

である。 From the above, the acoustic impedance density Z _{0− on the} front wall surface to be finally obtained is calculated using the equations (18), (28), and (30).

Can be described. However, Z _r and Z _im are the real part and imaginary part of Z ₀₋ , and are given by the following equations.

Also, in formula (32) and formula (33)

Is

It is.

であるので、式（３１）を代入し、

により求めることができる。 The sound absorption coefficient α is

Therefore, substituting equation (31),

It can ask for.

Using the above formula, the sound absorption characteristics of the resonator type sound absorbing structure are studied. Here, two resonator type sound absorbing structures having different specifications, namely, the present invention product 1 and the present invention product 2 were examined. The specifications of these product 1 and product 2 are shown in Table 1 below.

The diameter of the front wall through hole is different between the product 1 of the present invention and the product 2 of the present invention, and the opening ratio is 0.79% for the product 1 of the present invention and 2.76% for the product 2 of the present invention. A vinyl chloride plate was used as the flat elastic body. The specifications (material constants) of the vinyl chloride plate are as shown in Table 2 below.

と、弾性体と後面壁側室の振動系の固有振動数

とを一致させるように、板厚を調整した。 The material constants of the vinyl chloride plate shown in Table 2 are values obtained by experiments from frequency response characteristics when the vinyl chloride plate is strip-shaped and subjected to central vibration. However, literature values were used for Poisson's ratio. As the viscous resistance value R of the through hole 10a of the present product 1 and the present product 2, the value calculated from the result of measuring the impedance by the impedance measuring tube 101 for the resonator type sound absorbing structure having the through hole of the same diameter is used. It was. Considering the same as a dynamic vibration absorber, the resonance frequency of the resonator when the elastic body is a rigid wall

And the natural frequency of the vibration system of the elastic body and the rear wall side chamber

The plate thickness was adjusted to match.

When a graph is drawn from the equation of the sound absorption coefficient obtained by the above calculation, it can be seen that a peak where the value of the sound absorption coefficient becomes large appears at two frequency positions. Further, according to Equation (36), in order for the sound absorption coefficient to be a large value, Z _im must be 0 and Z _r must be close to ρC. That is, it can be seen that a high sound absorption coefficient can be obtained when the acoustic impedance density of the resonator type sound absorbing structure matches the characteristic impedance of air.

ではZ_rの値が大きく、吸音率は低くなるため、ピーク値をとらない。それ以外の高周波数、低周波数の２つの周波数付近で吸音率はピーク値をとる。また、Z_rは、式(32)より前面壁の貫通孔部分の抵抗値による成分（第一項）と弾性体の影響を含んだ成分（第二項）の和であることが分かるが、弾性体の損失係数が小さいとき、

付近以外では弾性体の影響は小さく、前面壁の貫通孔部分の抵抗値による成分が大きい。従って、この場合には、従来の共鳴器型吸音構造の場合のZ_rとほぼ同様の値となり、ピーク値をとる周波数における吸音率も従来型の共鳴器と同等となることが分かる。 From the expression of the sound absorption coefficient, it can be seen that there are three frequencies at which Z _im = 0 in the products 1 and 2 of the present invention. When the frequency at these three points is “high frequency”, “medium frequency”, and “low frequency”, the medium frequency

In _Zr, the value of Zr is large and the sound absorption coefficient is low, so the peak value is not taken. Near the other two frequencies, the high frequency and the low frequency, the sound absorption coefficient has a peak value. In addition, _Zr is found to be the sum of the component due to the resistance value of the through hole portion of the front wall (first term) and the component including the influence of the elastic body (second term) from the equation (32). When the loss factor of the elastic body is small,

Outside the vicinity, the influence of the elastic body is small, and the component due to the resistance value of the through hole portion of the front wall is large. Therefore, in this case, substantially the same value as Z _r for a conventional resonator-type sound absorbing structure, sound absorption rate it can be seen that the equivalent to the conventional resonator in the frequency taking the peak value.

  Next, the effect of the material of the elastic body on the sound absorption characteristics will be examined. First, the effect of the loss factor of the elastic body is examined. Here, when the loss factor η is changed from 0.02 to 0.8 for the inventive product 1 and the inventive product 2 (η = 0.02, η = 0.1, η = 0.4, η = 0.8) was calculated and displayed on a graph. In addition, as a comparison with the products 1 and 2 of the present invention, the values calculated for the resonator type sound absorbing structure according to the prior art (prior art 1 and 2) are displayed in a graph. The prior arts 1 and 2 are the same as the products 1 and 2 of the present invention except that the elastic body and the rear wall side chamber are removed from the products 1 and 2 of the present invention and the elastic body is replaced with a rigid wall. is there. The calculation results are as shown in FIG. 10 for the product 1 of the present invention and as shown in FIG. 11 for the product 2 of the present invention.

  From the calculation results shown in FIGS. 10 and 11, it can be seen that by increasing the loss factor for both of the products 1 and 2 of the present invention, the sound absorption rate between peaks is improved and sound is absorbed over a wide frequency range. . It can also be seen that, in the product 2 of the present invention, by increasing the loss coefficient, the peak value of the sound absorption coefficient is also increased, and a large sound absorption coefficient is obtained over a wide frequency range. In the product 1 of the present invention, although the sound absorption coefficient between peaks is improved, the peak value is lowered.

付近で見られるZ_imのピークとディップが小さくなる。また、Z_rは

付近の周波数でのピーク値が低下し、それ以外の周波数においては全体的に上昇する。 When calculating the acoustic impedance density when the loss factor is η = 0.4, by increasing the loss factor,

The Z _im peak and dip seen in the vicinity are smaller. Z _r is

The peak value at a nearby frequency decreases, and increases overall at other frequencies.

If the loss factor is large, the present invention product 1, since the value of Z _r is greater than .rho.c, the peak sound absorption rate is lowered. On the other hand, in the product 2 of the present invention, the frequency at which Z _im takes a value near 0 is relatively wide, and Z _{r at} that time is also a value close to ρC, so that the sound absorption coefficient is high over a wide frequency range. It has become. It can be seen that when the aperture ratio is relatively large, the sound absorption coefficient can be increased over a wide frequency range by increasing the loss factor η of the elastic body. Therefore, the sound absorption rate and the sound absorption frequency can be adjusted by appropriately selecting elastic bodies made of materials having different vibration damping properties.

が一定となるように、ヤング率も同時に変えると考えて計算を行った。表２の密度

を基準として、０．５倍、２倍、１０倍、１００倍として計算を行った。計算結果は図１２に示されるとおりである。 Next, consider the case where the density of the elastic material is changed for the product 1 of the present invention. On this occasion,

The calculation was performed assuming that the Young's modulus was changed at the same time so that was constant. Table 2 Density

Was calculated as 0.5 times, 2 times, 10 times, and 100 times. The calculation result is as shown in FIG.

が低く、剛性（Ｄ）が低い材料ほど、２つのピーク間の周波数が広くなっている。また、密度が高く、剛性も高い材料では弾性体は振動しなくなる。また、１００倍のときの面密度の値を計算すると１２６．６６９４ｋｇ／ｍ^２であり、この値に近づくにつれて２つのピークが互いに近づき、この値を超えて更に大きくなると、最終的に１つのピークとなると考えられる。 As shown in FIG. 12, the density

The lower the stiffness and the lower the stiffness (D), the wider the frequency between the two peaks. In addition, the elastic body does not vibrate with a material having high density and high rigidity. Further, when the value of the surface density at 100 times is calculated, it is 126.6694 kg / m ² , the two peaks approach each other as it approaches this value, and when this value is further increased, one peak is finally obtained. It is thought that it becomes.

  Next, when the natural frequency of the vibration system of the elastic body and the rear wall side chamber is not matched with the resonance frequency of the resonator when the elastic body is assumed to be a rigid wall, only the plate thickness of the elastic body is changed. Consider changes. Based on the plate thickness (h) of the front wall in the case of Table 1, the calculation was performed based on the above-described sound absorption coefficient for 0.5 times, 1 time, 1.5 times, and 2.0 times. The calculation results are as shown in the graph of FIG. In addition, as a comparative example, a graph calculated for the resonator type sound absorbing structure according to the prior art (prior art 1) is displayed in a graph.

  In the 1 × (h × 1) graph shown in FIG. 13, the natural frequency of the vibration system of the elastic body and the rear wall side chamber and the resonance frequency of the resonator when the elastic body is assumed to be a rigid wall are completely shown. The sound absorptivity in the case of coincidence is shown. On the other hand, the 0.5 times (h × 0.5) and 1.5 times (h × 1.5) graphs show the natural frequency and the elastic body of the vibration system of the elastic body and the rear wall side chamber, respectively. The sound absorptivity is shown when the resonance frequency of the resonator is assumed to be slightly deviated from the wall. In the 2.0 times (h × 2.0) graph, the natural frequency of the vibration system of the elastic body and the rear wall side chamber and the resonance frequency of the resonator when the elastic body is assumed to be a rigid wall are large. The sound absorptivity in the case of deviation is shown. Moreover, what was calculated about the resonator type sound absorption structure by a prior art as a comparative example (conventional techniques 1 and 3) was displayed on the graph. In the prior art 1, the elastic body and the rear wall side chamber are removed from the product 1 of the present invention, and the elastic body portion is a rigid wall. In the prior art 3, the elastic body is removed from the product 1 of the present invention. . The rest is the same as the product 1 of the present invention.

  As shown in the graph of FIG. 13, as the plate thickness is increased, the two sound absorption coefficient peaks shift to higher frequencies, and the value of the sound absorption coefficient at the high frequency peak decreases. As the thickness is further increased, the peak on the low frequency side coincides with that obtained by replacing the elastic body with a rigid wall, and the peak on the high frequency side disappears. When the plate thickness is reduced, the peak on the high frequency side is shifted to a higher frequency, and the peak on the lower frequency side is shifted to a lower frequency.

  As the thickness is further reduced, the peak on the low frequency side shifts again to the high frequency side, and finally coincides with the sound absorption coefficient of the resonator composed of one chamber having the total volume of the front wall side chamber and the rear wall side chamber. From these results, the natural frequency of the vibration system of the elastic body and the rear wall side chamber does not necessarily need to completely match the resonance frequency of the resonator when the elastic body is assumed to be a rigid wall, and is close to the resonance frequency. It is thought that it should be designed as Even in the resonator-type sound absorbing structure 5 according to the fifth embodiment as shown in FIG. 9, the spring constant of the rear wall side chamber does not change greatly regardless of the presence or absence of the partition portion of the second intermediate wall. Therefore, it can be seen that sounds of different frequencies, which are twice the number of the types of front wall side chambers 30a having different volumes, can be absorbed.

  Further, as shown in the 0.5 times, 1 times, and 1.5 times graphs of FIG. 13, the natural frequency of the vibration system of the elastic body and the rear wall side chamber and the resonance when the elastic body is assumed to be a rigid wall. If the resonance frequency of the instrument matches or slightly deviates, a high sound absorption coefficient can be obtained at two different frequencies, but as shown in the 2.0 times graph, When the natural frequency of the vibration system of the face wall side chamber and the resonance frequency of the resonator when the elastic body is assumed to be a rigid wall are greatly deviated, the peak of the sound absorption coefficient appears at two frequencies, It can be seen that a good sound absorption rate cannot be obtained at the peak on the high frequency side, and the frequency that can substantially absorb sound is one.

  From this, in order to obtain a good sound absorption coefficient at two different frequencies, the natural frequency of the vibration system of the elastic body and the rear wall side chamber, the resonance frequency of the resonator when the elastic body is assumed to be a rigid wall, and Are substantially equal, that is, assuming that the elastic body is a rigid wall that is not vibrated by sound waves, the resonance frequency of the virtual front wall side chamber defined by the rigid wall, the intermediate wall, and the front wall, and the elastic body It can be seen that the natural frequency of the vibration system of the rear wall side chamber needs to substantially match.

  Next, an experiment was actually performed on the above calculation results, and the validity of the calculation model was verified. As shown in FIG. 14, the normal incident sound absorption coefficient is measured by using the impedance measurement tube 101 (Bruell Care BK4206) by the two-microphone method as a test apparatus, and using the resonator type sound absorption structure 1 according to the present embodiment as an impedance. Measurement was performed by attaching to the end of the measuring tube 101. An FFT analyzer 103 (B & K 3550) connected to the computer 102 is connected to the impedance measuring tube 101.

  The diameter of the impedance measuring tube 101 is φ100 mm, and the thickness of the front wall is 2 mm. The diameter of the through hole in the front wall is 15 mm. When it is assumed that the elastic body is a rigid wall that does not vibrate by sound waves, the resonance frequency of the resonator constituted by the virtual front wall side chamber defined by the rigid wall, the intermediate wall, and the front wall and the through hole in the front wall is 644 Hz. is there. The distance between the front wall and the elastic body is 30 mm, and the distance between the rear wall and the elastic body is 20 mm. As the elastic body, a vinyl chloride plate having a thickness of 1 mm as the vinyl chloride plate shown in Table 2 was used.

は前面壁側室３０ａの半径である。損失係数は、弾性体４０の取付け部などにおいて損失があるため、事前に見積ることが困難であり、実験結果と比較して妥当な値を選んだ。 In the experiment, the sound absorption coefficient of one front wall side chamber 30a was obtained using the impedance measuring tube 101. This is because a plane sound wave is perpendicular to a resonator type sound absorption structure in which a plurality of front wall side chambers having the same aperture ratio are arranged. It can be considered equivalent to the case of incidence. However, since the radiation characteristic from the through hole 10a of the front wall 10 changes between the case of the experiment using the impedance measuring tube 101 and the case of using in the free space, the tube on the incident side is calculated in consideration of comparison with the experiment. The following formula was used as the end correction value.

Is the radius of the front wall side chamber 30a. The loss coefficient is difficult to estimate in advance because there is a loss at the attachment portion of the elastic body 40, and a reasonable value was selected in comparison with the experimental results.

  The test results are as shown in the graph of FIG. As shown in FIG. 15, the calculated value indicating the calculation result and the actually measured value indicating the experimental result were in good agreement, and the validity of the calculation model was confirmed. In addition, as a comparative product 1, a resonator type sound absorbing structure without an elastic body is used, and as a comparative product 2, a damping material of 0.3 mm is bonded to an elastic body with a 1 mm vinyl chloride plate to improve vibration damping. Calculations and experiments were performed in the same manner, but the calculation results and the experimental results were in good agreement, and the validity of the calculation model was confirmed. In addition, the Young's modulus of the elastic body of the comparative product 2 was an average value in a state in which a damping material was attached to a vinyl chloride plate in the same manner as when the material constants in Table 2 were measured.

  The resonator type sound absorbing structure according to the present invention is not limited to the above-described embodiments, and various modifications and improvements can be made within the scope described in the claims. For example, in the present embodiment, the front wall, the rear wall, the first intermediate wall, and the second intermediate wall are made of an aluminum alloy, but may be formed of a metal other than the aluminum alloy (for example, iron) or a resin. In addition, these materials may be appropriately selected and combined, for example, the front wall is made of resin and the first intermediate wall is made of iron.

  Further, in the resonator type sound absorbing structure according to the present embodiment, the rear wall integrally formed with the first intermediate wall and the second intermediate wall is integrally formed by the die casting method, but is integrally formed by another casting method. You may be made to do. The front wall may be formed by casting.

  Further, the front wall and the intermediate wall may be integrally formed by a die casting method. Alternatively, the rear wall may be a plate member, a second intermediate wall having substantially the same shape as the first intermediate wall may be formed, and the rear wall and the second intermediate wall may be separated.

  Moreover, although the elastic body was comprised with elastic bodies, such as a plastic material and a vinyl chloride board, it is not limited to these. The elastic body may be a flat film.

  In the second and third embodiments, the elastic body is bonded to the step portion with an adhesive, but without using the adhesive, the step portion of the first intermediate wall and the front end of the second intermediate wall It may be sandwiched between.

  Further, although the front wall side chambers 30a have different volumes, they may be the same. Moreover, although the front wall 10 has a plurality of through holes 10a having the same diameter, the diameter of the through holes may be different for each front wall side chamber.

  The resonator type sound absorbing structure of the present invention is extremely useful particularly in the field where it is required to absorb a large number of frequencies without reducing the aperture ratio.

The perspective view which shows the front wall, 1st intermediate wall, elastic body, 2nd intermediate wall, and rear surface of the resonator type sound absorption structure by 1st Embodiment. The fragmentary sectional perspective view which shows the resonator type sound absorption structure by 1st Embodiment. Sectional drawing which shows the resonator type sound absorption structure by 1st Embodiment. The perspective view which shows the front wall, 1st intermediate wall, elastic body, 2nd intermediate wall, and rear surface of the resonator type sound absorption structure by 2nd Embodiment. The fragmentary sectional perspective view which shows the resonator type sound absorption structure by 2nd Embodiment. Sectional drawing which shows the resonator type sound absorption structure by 2nd Embodiment. Sectional drawing which shows the resonator type sound absorption structure by 3rd Embodiment. Sectional drawing which shows the resonator type sound absorption structure by 4th Embodiment. Sectional drawing which shows the resonator type sound absorption structure by 5th Embodiment. The graph which shows the calculation result in the case of taking the value of a different loss coefficient about the sound absorption rate of the resonator type sound absorption structure by this Embodiment. The graph which shows the calculation result in the case of taking the value of a different loss coefficient about the sound absorption rate of the resonator type sound absorption structure by this Embodiment. The graph which shows the calculation result in the case of taking the value of a different surface density about the sound absorption coefficient of the resonator type sound absorption structure by this Embodiment. Regarding the sound absorption coefficient of the resonator-type sound absorbing structure according to the present embodiment, the natural frequency of the vibration system of the elastic body and the rear wall side chamber matches the resonance frequency of the resonator when the elastic body is assumed to be a rigid wall. The graph which shows the calculation result when it is. Schematic which shows the test apparatus of the test done in order to examine the validity of the calculation result which calculated | required the sound absorption rate of the resonator type sound absorption structure by this Embodiment. The graph which shows the test result of the test done in order to examine the validity of the calculation result which calculated | required the sound absorption coefficient of the resonator type sound absorption structure by this Embodiment.

Explanation of symbols

1-5 Resonator-type sound absorbing structure 1a Front wall side space 1b Rear wall side space 10 Front wall 10a Through holes 20, 50, 70 Rear walls 31A, 32A Partitions 30a, 30a ′ Front wall side chambers 30b, 30b ′ Rear wall side chambers 31, 31 'First intermediate wall 32, 62 Second intermediate wall 40, 40' Elastic body

Claims (3)

A front wall formed with a plurality of through holes;
A rear wall disposed opposite to the front wall at an interval;
A partition part for partitioning a part on the front wall side into a plurality of front wall side spaces, which is a part of a space formed between the front wall and the rear wall; An intermediate wall that joins the rear wall,
In the resonator-type sound absorbing structure in which the plurality of through holes are formed corresponding to the plurality of front wall side spaces,
At the position of the intermediate wall between the front wall and the rear wall, a plate-like elastic body that separates the plurality of front wall side spaces from the rear wall side space is disposed, and the plurality of front walls The side space forms a plurality of front wall side chambers defined by the front wall, the intermediate wall, and the elastic body, and the space on the rear wall side is provided along the peripheral edge of the rear wall. A rear wall side chamber defined by the outer peripheral frame extending toward the wall, the rear wall, and the elastic body, or by the partition, the rear wall, and the elastic body; Vibrates due to sound waves entering the front wall side chamber from the through hole,
When the elastic body is assumed to be a rigid wall that does not vibrate by sound waves, the resonance frequency of the resonator substantially matches the natural frequency of the vibration system of the elastic body and the rear wall side chamber,
The area density of the elastic body is 126.6694 kg / m ² or less.   2. The resonator type sound absorbing structure according to claim 1, wherein the plurality of front wall side chambers include at least two types of front wall side chambers having different volumes.   2. The resonator type sound absorbing structure according to claim 1, wherein the plurality of front wall side chambers include at least two types of the front wall side chambers having different distances from the front wall to the elastic body.

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