JP2010097148A - Sound absorbing structure, sound absorbing structure group and acoustic room - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve sound absorbing efficiency of a plate-film vibration sound absorbing structure by adding a sound absorbing structure which less impedes original sound absorbing behavior. <P>SOLUTION: A sound absorbing structure 10 includes a vibration object 12. The vibration object 12 is supported by a side face section 111 for composing a case. An air layer is formed inside, by the side face section 111, a bottom face section 112 and vibration object 12. Tube structures 113 and 114 are provided inside the air layer. Tube structures 113 and 114 includes an aperture edge. the inside of the tube structures 113 and 114 is hollow, and air of the air layer may exist. Thereby, if thickness of tube structures 113 and 114 is made thin, its rate of a volume in a whole air layer is made small, and for example, comparing with the case where resistance material of the same volume is provided, influence on the original sound absorbing behavior as the plate-film vibration sound absorbing structure is made small. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for absorbing sound.

Sound absorbing structures that perform plate vibration or membrane vibration are known. Such a sound absorbing structure is hereinafter referred to as a “plate / membrane vibration absorbing structure”. In addition, for the purpose of improving sound absorption efficiency, a technique is also known in which a resistance material (porous material, glass wool, etc.) that resists the movement of gas particles is attached to the inside or opening of a sound absorbing structure. (For example, refer to Patent Document 1 or 2). That is, if a resistance material is added to the region of the gas layer facing the vibrating body having the plate / membrane vibration absorption structure, it may be possible to expect improvement in sound absorption efficiency. In this case, the sound absorption efficiency can be improved by optimally designing the characteristics and quantity of the resistance material.
JP 7-302087 A JP 2003-82839 A

However, when this type of resistance material is provided inside the plate / membrane vibration absorption structure, plate vibration or membrane vibration may be hindered. This is because the plate / membrane vibration absorption structure constitutes a spring mass system in which the vibrating body is a mass component (mass) and the gas layer is a spring component, so that the gas constituting the gas layer by providing a resistance material This is because, as the value decreases, the action of the gas layer as a spring also tends to decrease. This tendency is particularly remarkable when the thickness of the gas layer is small.
Therefore, the present invention aims to improve the sound absorption efficiency of the plate / membrane vibration absorbing structure by adding a sound absorbing structure that is less obstructive to the original sound absorbing action in the plate / membrane vibration absorbing structure. And

The sound absorbing structure according to the present invention is configured to absorb sound from a plate-like or film-like vibrating body and a gas layer that supports the vibrating body in an opening covered by the vibrating body and forms a gas spring facing the vibrating body. It is characterized by comprising a support body sometimes formed and an open or closed tube having an open end, the open end facing a tube structure facing the gas layer.
In the sound absorbing structure according to the present invention, the tube structure may have a length in which a standing wave having a wavelength corresponding to the sound to be absorbed is generated.
In the sound absorbing structure according to the present invention, the support may have a side surface surrounding the gas layer, and at least a part of the side surface may be the tube structure.
In the sound absorbing structure according to the present invention, the tube structure has a resistance region where resistance to movement of gas particles (for example, air molecules) is larger than other regions at a position where the antinode of the particle velocity of the standing wave is generated. It may be a configuration.
The sound absorbing structure according to the present invention may be configured such that the tube structure has a resistance material that prevents movement of gas particles in the resistance region and does not have the resistance material in a region that is not the resistance region.
The sound absorbing structure group according to the present invention includes a combination of a plurality of the sound absorbing structures described above. In this configuration, the sound absorbing structure may be combined with the same type of sound absorbing structure or may be combined with different types of sound absorbing structures.
The sound absorbing structure group according to the present invention may be configured such that at least one of the thickness or volume of the gas layers of the plurality of sound absorbing structures and the length of the open tube or the closed tube is not the same.
The acoustic chamber according to the present invention includes the above-described sound absorbing structure or sound absorbing structure group.

  According to the present invention, it is possible to improve the sound absorption efficiency of the plate / membrane vibration absorption structure by adding a sound absorption structure with less obstruction to the original sound absorption effect in the plate / membrane vibration absorption structure. Become.

[First Embodiment]
FIG. 1 is a diagram showing a configuration of a sound absorbing structure according to the first embodiment of the present invention. The sound absorbing structure 10 is a plate / membrane vibration absorbing structure having a rectangular parallelepiped appearance, and includes a housing 11 and a vibrating body 12. The housing 11 constitutes a side surface and a bottom surface of the sound absorbing structure 10, and the inside thereof is formed hollow. The housing 11 is made of, for example, a synthetic resin such as ABS resin, but may be made of other materials such as metal as long as it has a strength capable of supporting the vibrating body 12. The vibrating body 12 constitutes the upper surface of the sound absorbing structure 10. The “upper surface” here represents the direction of the surface for the sake of convenience, and does not represent the upward direction when the sound absorbing structure 10 is arranged. The sound absorbing structure 10 may be arranged in any orientation as necessary.

  2 is a view showing the housing 11 from the upper surface side, and FIG. 3 is a cross-sectional view of the housing 11 and the vibrating body 12 taken along the line AA in FIG. As shown in these drawings, the housing 11 has an opening on the upper surface side, and includes a side surface portion 111, a bottom surface portion 112, and tubular members 113 and 114. The side surface portion 111 is a member constituting the side surface of the sound absorbing structure 10 and supports the vibrating body 12 at the end portion on the upper surface side. The side surface portion 111 corresponds to an example of a support according to the present invention. In the present embodiment, the height of the side surface portion 111 (the distance from the upper surface side end portion to the lower surface side end portion) is equal to the thickness of the gas layer formed inside the sound absorbing structure 10. The bottom surface portion 112 is a member constituting the bottom surface of the sound absorbing structure 10, and the shape thereof matches the shape of the vibrating body 12. The tubular members 113 and 114 are arranged such that the extending direction (hereinafter referred to as “length direction”) is parallel to the plane formed by the vibrating body 12 and the plane formed by the cut surface (that is, the open end). Is arranged so as to intersect the plane formed by the vibrating body 12. The tubular members 113 and 114 are preferably arranged so as to contact the bottom surface portion 112 and not contact the vibrating body 12. With such an arrangement, it becomes easy to ensure the thickness of the gas layer.

  The tubular members 113 and 114 are hollow and cylindrical members having a predetermined length, and each corresponds to an example of a tube structure according to the present invention. The tubular member 113 is open at both ends and is a so-called open tube. In contrast, the tubular member 114 is a so-called closed tube in which one open end is closed by the side surface portion 111. That is, the tubular members 113 and 114 are configured such that the open ends thereof face the gas layer and the gas layer and the gas can be circulated. The tubular members 113 and 114 are in contact with the bottom surface portion 112, and their diameter is smaller than the height of the side surface portion 111. That is, the tubular members 113 and 114 are separated from the vibrating body 12 with a predetermined interval. Moreover, although the gas with which a gas layer is filled is typically air, and it is assumed that it is air also in this embodiment, it does not prevent other gases. The gas layer refers to a region indicated by hatching in FIG.

  The tubular members 113 and 114 need not be disposed in contact with the side surface portion 111, and may be disposed near the center of the bottom surface portion 112, for example. Further, the open ends of the tubular members 113 and 114 are arranged corresponding to the natural vibration mode of the vibrating body 12. Specifically, the open ends of the tubular members 113 and 114 are disposed at a place where the vibration amplitude (or vibration speed) of the vibrating body 12 is the largest. For example, when the vibrating body 12 vibrates in the primary mode (reference vibration mode), the tubular members 113 and 114 are arranged so that the open ends of the tubular members 113 and 114 are disposed in the region of the substantially central portion of the vibrating body 12. 114 is arranged in the housing 11. By doing in this way, resonance of the same frequency as the vibration of the vibrating body 12 is also easily excited in the tubular members 113 and 114.

The lengths (distance between both ends) of the tubular members 113 and 114 are determined according to the sound to be absorbed. Specifically, when the length of the tubular member 113 that is an open tube is L ₁ , the length of the tubular member 114 that is a closed tube is L _2, and the wavelength of the standing wave corresponding to the sound to be absorbed is λ. , L ₁ and L ₂ satisfy the following expressions (1.1) and (1.2). However, in Formula (1.1) and Formula (1.2), n is an integer of 1 or more.

Note that the actual lengths of the tubular members 113 and 114 need to be determined in consideration of the value of the opening end correction, but are omitted in the equations (1.1) and (1.2). The opening end correction value is determined according to the shapes of the tubular members 113 and 114.
Further, the casing 11 may be one in which the side surface portion 111, the bottom surface portion 112, and the tubular members 113 and 114 are integrally formed. These portions are independent members and are fixed to each other by bonding or the like. It may be a thing.

  The vibrating body 12 is a plate-like or film-like member, is supported by the side surface portion 111, closes the opening on the top surface of the housing 11, and separates the gas layer inside the housing 11 from the external gas. The vibrating body 12 is a plate-like or film-like member, but the thickness is not particularly limited. The vibrating body 12 is made of, for example, a synthetic resin, but may be other materials such as paper, metal, fiber, and the like as long as the vibrating body 12 is elastic to the extent that it is supported by the housing 11 and vibrates. The vibrating body 12 is attached to the housing 11 with an adhesive or a nail.

  The configuration of the sound absorbing structure 10 of the present embodiment is as described above. In this configuration, the sound absorbing structure 10 functions as a plate / membrane vibration absorbing structure. In the sound absorbing structure 10, the gas layer inside the housing 11 functions as a so-called gas spring (air spring). Specifically, when a sound wave in the sound absorbing structure 10 is incident, the vibrating body 12 vibrates, and the sound wave is also incident on the gas layer due to the vibration of the vibrating body 12 to increase the acoustic energy in the gas layer. . This acoustic energy is attenuated by the vibration of the vibrating body 12, the action of the gas layer as a gas spring, and the action of attenuating the vibration caused by the internal resistance of the vibrating body 12 and the gas layer, and is eventually dissipated. That is, the sound absorbing structure 10 forms a spring mass system in which the vibrating body 12 is a mass component (mass) and the gas layer is a spring component.

Each part of the sound absorbing structure 10 of this embodiment is set according to the following conditions.
In general, in a plate / membrane vibration absorbing structure that absorbs sound by a plate-like or membrane-like vibrating body and a gas layer, the sound absorbing frequency is the resonance frequency of the spring mass system due to the mass component of the vibrating body and the spring component of the gas layer. Set by Here, the density of the gas in the gas layer is ρ ₀ (kg / m ³ ), the speed of sound is c ₀ (m / s), the density of the vibrator is ρ (kg / m ³ ), and the thickness of the vibrator is t ( m) When the thickness of the gas layer is L (m), the resonance frequency of the spring mass system is expressed by the following formula (2.1).

Further, in the plate / membrane vibration type sound absorbing structure, when the vibrating body has elasticity and elastically vibrates, a bending system property due to elastic vibration is added. In the field of architectural acoustics, the length of two opposite sides of a rectangular vibrating body is a (m), the length of two sides orthogonal to the two sides is b (m), and the Young's modulus of the vibrating body is E (Pa), where the Poisson's ratio of the vibrating body is σ and the mode order is p and q (positive integers), the resonance frequency of the plate / membrane vibration type sound absorbing structure is obtained by the following equation (2.2). Resonance frequency is used for acoustic design (in the case of peripheral support).

In the present embodiment, parameters are set as follows based on, for example, the equation (2.2) so as to absorb the 160 to 315 Hz band (1/3 octave center frequency).
Gas density ρ ₀ : 1.225 (kg / m ³ )
Speed of sound c ₀ : 340 (m / s)
Density of vibrating body ρ: 940 (kg / m ³ )
Thickness t of vibration body: 0.0017 (m)
Gas layer thickness L: 0.03 (m)
Case length a: 0.1 (m)
Case length b: 0.1 (m)
Young's modulus E of vibrator: 1.0 (GPa)
Poisson's ratio σ: 0.4
Mode order: p = q = 1

  On the other hand, in the equation (2.2), the term of the spring mass system (the first term on the right side, that is, the right side of the equation (2.1)) and the term of the bending system (the second term on the right side) are added. For this reason, the resonance frequency obtained by the equation (2.2) is higher than the resonance frequency of the spring mass system, and it may be difficult to set the peak frequency of sound absorption low. In such a sound absorbing structure, the relationship between the resonance frequency due to the spring mass system and the resonance frequency of the bending system due to the elastic vibration due to the elasticity of the plate or film has not been sufficiently elucidated, and has a high sound absorption effect in the low frequency range. The fact is that no sound absorption structure has been established.

The inventors of the present invention set the value of the fundamental vibration frequency of the bending system to fa (second term on the right side of the equation (2.2)) and the value of the resonance frequency of the spring mass system to fb (right side of the equation (2.2)). In the case of the first term), it has been found that if the above parameters are set so as to satisfy the relationship of the following formula (2.3), a high sound absorption effect can be obtained. As a result, the fundamental vibration of the bending system is coupled with the spring component of the gas layer behind, and a vibration having a large amplitude is excited in the band between the resonance frequency of the spring mass system and the fundamental frequency of the bending system (flexural system resonance). The frequency fa <peak frequency f <spring mass system fundamental frequency fb), and the sound absorption rate increases.

このように、式（２．３）、（２．４）の条件を満足するように各種パラメータを設定することにより、ピーク周波数を低くした吸音構造を構成することができる。 Furthermore, when the above parameter is set to the following formula (2.4), the peak frequency is sufficiently smaller than the resonance frequency of the spring mass system. In this case, it is found that the fundamental frequency of the bending system is sufficiently smaller than the resonance frequency of the spring mass system due to the mode of low-order elastic vibration and is suitable as a sound absorbing structure that absorbs sound having a frequency of 300 (Hz) or less. It was.

Thus, by setting various parameters so as to satisfy the conditions of the expressions (2.3) and (2.4), it is possible to configure a sound absorbing structure with a reduced peak frequency.

  Further, the sound absorbing structure 10 functions as a plate / membrane vibration absorbing structure, and at the same time, the tubular members 113 and 114 function as a resonance tube. The tubular members 113 and 114 convert acoustic energy into thermal energy by generating a standing wave having a predetermined wavelength, and reduce the acoustic energy of the gas layer. That is, the tubular members 113 and 114 absorb the acoustic energy of the gas layer and promote its dissipation, thereby improving the sound absorption efficiency of the sound absorbing structure 10.

  Further, the sound absorbing structure 10 functions as a plate / membrane vibration absorbing structure, and at the same time, the tubular members 113 and 114 function as a resonance tube. The tubular members 113 and 114 convert acoustic energy into thermal energy by generating a standing wave having a predetermined wavelength, and reduce the acoustic energy of the gas layer. Furthermore, since the tubular members 113 and 114 are arranged so that the length direction thereof is parallel to the plane formed by the vibrating body 12, that is, so as not to intersect the thickness direction of the gas layer, the tubular members 113 and 114 have a sufficient thickness for the gas layer. Even when the length cannot be secured, it is easy to secure the length of the tubular members 113 and 114. Therefore, the tubular members 113 and 114 can be resonant tubes having a low resonance frequency based on the formula (1) or the formula (2).

  As described above, the tubular members 113 and 114 absorb the acoustic energy of the gas layer and promote its dissipation, thereby improving the sound absorption efficiency of the sound absorbing structure 10. Furthermore, the tubular members 113 and 114 set the peak of the sound absorption coefficient at a low frequency even when the thickness of the gas layer of the sound absorbing structure 10 is small, and make it possible to improve the sound absorption efficiency in the lower sound range. .

  In the present embodiment, the tubular members 113 and 114 are hollow inside, and a gas in the gas layer may exist. Therefore, if the tubular members 113 and 114 are configured so as to be thin, it is possible to reduce the proportion of the members themselves in the volume of the entire gas layer. Compared with the case where a porous material, glass wool, etc.) are provided, the influence on the sound absorbing action as the original plate / membrane vibration absorbing structure may be reduced. Further, since the tubular members 113 and 114 are not in contact with the vibrating body 12, they do not hinder the vibration of the vibrating body 12.

  Further, the sound absorbing structure 10 can realize a necessary sound absorption rate in a low frequency range by appropriately setting the resonance frequency of the vibrating body 12 and the resonance frequency of the resonance tube. For example, the resonance frequency of the vibration body 12 and the resonance frequency of the resonance tube may be set to the same resonance frequency so that the peak of the sound absorption coefficient of the sound absorbing structure 10 is increased, or the resonance frequency of the vibration body 12 is resonant. The sound absorption rate of the sound absorbing structure 10 may be increased in a wider band as different resonance frequencies that approximate the resonance frequency of the tube. Further, by configuring a plurality of (three or more) resonance tubes so that their resonance frequencies are the same or different from each other, and further combining them, the peak value of the sound absorption coefficient and the expansion of the band can be increased. It is also possible to set appropriately.

[Second Embodiment]
FIG. 4 is a diagram showing a configuration of a sound absorbing structure according to the second embodiment of the present invention. The sound absorbing structure 20 of the present embodiment is characterized in that the side surface is constituted by a tube structure. The sound absorbing structure 20 includes a casing 21 and a vibrating body 22, and the appearance thereof is the same as that of the sound absorbing structure 10 of the first embodiment. The material constituting the sound absorbing structure 20 is the same as that of the sound absorbing structure 10. In the present embodiment, the description of matters that overlap with the first embodiment (terms having a common meaning, etc.) will be omitted as appropriate.

  FIG. 5 is a diagram showing the housing 21 from the upper surface side, and FIG. 6 is a cross-sectional view of the housing 21 and the vibrating body 22 taken along the line BB in FIG. As shown in these drawings, the housing 21 includes an outer surface portion 211, an inner surface portion 212, and a bottom surface portion 213. The outer side surface portion 211 is a member that constitutes the side surface of the sound absorbing structure 20 and is configured to surround four sides of the side surface of the sound absorbing structure 20. The inner side surface portion 212 is a plate-like member provided so as to be parallel to any one of the four sides formed by the outer side surface portion 211, and is configured such that one end thereof is in contact with the outer surface portion 211 and the other end is not in contact with the outer surface portion 211. Has been. The heights of the outer surface portion 211 and the inner surface portion 212 are equal to the thickness of the gas layer formed inside the sound absorbing structure 20. The bottom surface portion 213 is a member constituting the bottom surface of the sound absorbing structure 20, and the shape thereof matches the shape of the vibrating body 12. The vibrating body 22 is the same as the vibrating body 12 of the first embodiment.

  As shown in FIG. 6, the inner side surface portion 212 is in contact with the vibrating body 22 on the upper surface side and is in contact with the bottom surface portion 213 on the bottom surface side. That is, a prismatic air column having a wall surface formed by the vibrator 22, the outer surface portion 211, the inner surface portion 212, and the bottom surface portion 213 is formed between the outer surface portion 211 and the inner surface portion 212. This air column is capable of gas circulation with the gas layer inside the inner side surface portion 212 (near the center of the sound absorbing structure 20) in the opening 212a shown in FIG. That is, each part of the sound absorbing structure 20 provided so as to cover the air column functions as a closed tube with an opening end on the side where the opening 212a is provided. This closed tube corresponds to an example of a tube structure according to the present invention.

  Note that the length of the inner side surface portion 212 (the length in the direction perpendicular to the height direction) is appropriately determined according to the wavelength of the sound to be absorbed. The length of the inner side surface portion 212 may be equal for each side or may be different for each side. Moreover, the partition member 214 as shown in FIG. 7 may be provided to be movable so that the length of the air column can be changed. In FIG. 7, the partition member 214 is configured to be in contact with the vibrating body 22, the outer surface portion 211, the inner surface portion 212, and the bottom surface portion 213, that is, to have the same shape as the cross section of the air column.

The configuration of the sound absorbing structure 20 of the present embodiment is as described above. According to the sound absorbing structure 20, the side surface surrounding the gas layer of the sound absorbing structure 20 can function as a resonance tube.
In the plate / membrane vibration absorption structure, the support for supporting the vibrating body may be hollow for the purpose of reducing the weight. In this case, the present embodiment makes it possible to allow the hollow portion to function as a resonance tube only by providing a gas flow portion (that is, the opening portion 212a) in the hollow support. That is, the sound absorbing structure 20 of the present embodiment can improve the sound absorbing efficiency as compared with the case where the opening 212a is not provided in the sound absorbing structure 20 or when the support is made of a non-hollow columnar member. is there. In other words, it can be said that the sound absorbing structure 20 of the present embodiment can achieve both weight reduction and improvement in sound absorption efficiency.

[Modification]
The present invention can be implemented in a form different from the above-described embodiment. The following modifications are examples of modifications applicable to the present invention. In addition, these modifications may be implemented by appropriately combining each as required. Moreover, in the following description, the description of a configuration common to the configuration described above is omitted as appropriate.

(1) Modification 1
The sound absorbing structure according to the present invention may be configured such that the bottom surface portion 112 (or 213) is omitted instead of the sound absorbing structure 10 (or 20) described above. For example, if the sound absorbing structure 10 (or 20) is attached to a predetermined surface (wall surface or the like), the attachment surface can be used as a substitute for the bottom surface portion. In the sound absorbing structure according to the present invention, if the bottom surface side of the side surface portion 111 (or the outer side surface portion 211 and the inner side surface portion 212) is shaped along the surface to be attached, the gas layer is attached after being attached (that is, during sound absorption). Can be distinguished from the outside, and the inside of the support can function as a gas spring. That is, it is sufficient for the support according to the present invention to form a gas layer at the time of sound absorption (when installed), and at the time of non-absorption of sound such as at the time of sale (when not installed), the gas layer is opened to the outside. The movement may not be hindered.

(2) Modification 2
The specific shape and configuration of the tube structure according to the present invention are not limited to those described above. For example, in the configuration of the first embodiment, the tube structure may be a square tube instead of a round tube (circular tube), or only one of an open tube and a closed tube may be provided. Alternatively, a plurality of pipe structures having different lengths may be provided to improve sound absorption efficiency. In the configuration of the second embodiment, the tube structure may be an open tube with both ends being open ends, or a part of the side surface may not be a tube structure.

  8 and 9 are diagrams showing a modification of the configuration of the second embodiment, that is, the configuration in which the side surface portion has a tube structure. FIG. 8 is a diagram showing a configuration of a case where the side surface portion is not a plurality of tube structures but a single tube structure, and FIG. 9 is a case where a plurality of plate / membrane vibration absorption structures are connected. It is a figure which shows the structure of a body.

  In FIG. 8, the casing 31 includes an outer surface portion 311 and an inner surface portion 312, and the inner surface portion 312 is bent along the shape of the outer surface portion 311. The outer side surface portion 311 and the inner side surface portion 312 are in contact with a vibrating body (not shown) and the bottom surface portion, and the internal space forms a bent prismatic air column. Here, the inner side surface 312 forms an opening 312a. In such a configuration, the length of the air column can be increased as compared with the configuration of the second embodiment, and a lower resonance frequency can be set.

In FIG. 9, the housing 41 includes an outer surface portion 411 and an inner surface portion 412. The outer surface portion 411 and the inner surface portion 412 are in contact with a vibrating body (not shown) and the bottom surface portion. The inner side surface portion 412 forms openings 412a, 412b, 412c and 412d.
FIG. 10 is a diagram showing the gas layer region and the air column region inside the outer surface portion 411 separately. The inner side surface portion 412 divides the region inside the outer side surface portion 411 into seven regions of regions a ₁ , a ₂ , a ₃ , a ₄ , b ₁ , b ₂ , and b ₃ . The regions a _{1 to} a ₄ constitute a gas layer that functions as a gas spring for the opposing vibrating body, and the regions b _{1 to} b ₃ are respectively surrounded by the inner side surface portion 412, the vibrating body, and the bottom surface portion. Constitutes the air column. The sound absorbing structure including the casing 41 can be regarded as a sound absorbing structure group in which four plate / membrane vibration absorbing structures are connected when the regions a _{1 to} a ₄ are viewed as separate gas layers.

The region b ₁ is open to the region a ₁ at the opening 412a. Further, the region b ₃ is open to the region a ₃ at the opening 412c. Accordingly, the regions b ₁ and b ₃ function as closed column air columns and can absorb the acoustic energy of the gas layer that passes through them. The region b ₂ opens to the region a ₂ at the opening 412b and opens to the region a ₄ at the opening 412d. Therefore, the region b ₂ functions as an open column air column and can absorb the acoustic energy of the gas layer that communicates therewith. Here, the gas layer serving area a ₂ and the region a _4, and is configured to be coupled via the air column serving region b ₂ of the open tube.

In this case, since the region b ₂ is an open tube, the phase relationship of vibrations in the openings 412b and 412d is in the case of the reverse phase (when resonating at an odd multiple of λ / 2: (a) and ( c), etc.) and in-phase (resonance at an even multiple of λ / 2: (b) in FIG. 12). Further, the phase relationship of the vibration of the gas layer in the connected regions a ₂ and a ₄ (the phase relationship of the pressure fluctuation in the gas layer) may be in the opposite phase or in the same phase. Therefore, when a plurality of gas layers are connected via an air column, the phase relationship of the vibrations of the plurality of gas layers and the phase relationship of the vibrations of the air column are coupled at a predetermined resonance frequency. Thus, a higher sound absorption rate can be expressed. Specifically, at a predetermined resonant frequency, and resonant and region a ₂ and a ₄ are in phase, and region b ₂ resonates in phase at its opening 412b and 412d resonates (e.g. twice vibrations Thus, if the dimensions, shapes, and the like of the regions a ₂ , a _4, and b ₂ are designed, the regions a ₂ , a _4, and b ₂ are coupled and resonated, so that a higher sound absorption coefficient is exhibited. be able to. Further, resonate in opposite phase and a region a ₂ and a _4, and a region b ₂ is (resonates at e.g. fundamental frequency) resonating in the reverse phase in its opening 412b and 412d manner, region a ₂ and a _If the dimensions, shapes, etc. of ₄ and b ₂ are designed, the regions a ₂ , a ₄ and the region b ₂ are coupled and resonated, so that a higher sound absorption coefficient can be expressed.

The regions a _{1 to} a ₄ may be configured so that they have the same volume, or may be configured so that the volumes are different. The same applies to the regions b _{1 to} b ₃ . In addition, the vibrating bodies facing the regions a _{1 to} a ₄ may be the same member, or may have different thicknesses and materials so that each has a plate / membrane vibration absorption structure with different sound absorption characteristics. .

(3) Modification 3
The tube structure according to the present invention may be made of, for example, a foam material, and further weight reduction may be achieved. In this case, it is sufficient for the open end if gas can be circulated.
FIG. 11 is a diagram showing a tube structure made of a foam material. In the figure, a tube structure 50 is a hollow member having a closed cell portion 51 and an open cell portion 52. The closed cell portion 51 has a closed cell structure, and is a closed tube in which adjacent bubbles (cells) have a structure independent of each other. The open cell portion 52 has an open cell structure, and adjacent bubbles communicate with each other, and gas can be circulated. The open cell portion 52 is provided so as to close the open end of the closed cell portion 51. Therefore, the tube structure 50 is configured so that the gas can flow through the internal hollow region only in the open cell portion 52. That is, the tube structure 50 is a closed tube.
In addition, the tube structure which concerns on this example may have an open cell structure in the position different from FIG. 11, and multiple open cell structures may be provided and an open tube may be comprised.

(4) Modification 4
The tube structure according to the present invention may be provided with a resistance region therein. Here, the resistance region refers to a region in which the resistance to the movement of gas particles is larger than that in other regions. The resistance region can be obtained, for example, by providing a resistance material that prevents the movement of gas particles in the region. The resistance region can also be obtained by roughening the surface of the inner wall of the tube structure and causing the surface to act as a resistance against the movement of gas particles. The resistance region may be a part or all of the inside of the tube structure. In the case where the resistance region is provided in a part of the inside of the tube structure, it is desirable to provide the region at a position where an antinode of the particle velocity of the standing wave is generated.

  12 and 13 are cross-sectional views showing a tube structure in which a resistance region is provided inside. FIG. 12 shows an example when the tube structure is an open tube, and FIG. 13 shows an example when the tube structure is a closed tube. In these figures, the two-dot chain line indicates the distribution of the particle velocity amplitude of the standing wave generated inside the tube structure. FIGS. 12A, 12B, and 12C show the cases of fundamental vibration, double vibration, and triple vibration, respectively. FIGS. 13A, 13B, and 13C show cases of fundamental vibration, triple vibration, and five-fold vibration, respectively.

  In FIG. 12A, the tube structure 60 includes a resistance material 61. The resistance member 61 is provided at and near the position where the antinode of the particle velocity of the standing wave (that is, the node of the sound pressure) occurs. Here, the position where the antinode of the particle velocity occurs is a position where the speed (the absolute value of the amplitude of the vibration velocity) at which the gas particles in the tube structure 60 vibrate is maximized. In the open tube, the antinode position of the particle velocity in the fundamental vibration corresponds to the positions of both open ends. In this case, the antinode position of the particle velocity is actually slightly outside the opening end (opening end correction). Therefore, the resistance material 61 may be provided so as to protrude from the opening end.

On the other hand, in the double vibration or triple vibration, the antinodes of the particle velocity are generated at positions other than the position of the opening end, and as shown in FIGS. 12B and 12C, the resistance material 62 or 63 is provided at that position. Is provided. That is, when the position where the resistance material is provided in the open tube (excluding the position of the opening end) is d ₁ , the position d ₁ can be generalized as the following equation (3.1). Here, the position d ₁ represents a distance from any open end of the tube structure. Moreover, in Formula (3.1), m is an integer greater than or equal to 1, and (lambda) is the value of the wavelength of a standing wave.

Here, the wavelength λ satisfies the relationship shown in the above-described formula (1.1). Therefore, equation (3.1) can be replaced by the following equation (3.2), where L _T is the length of the open tube (distance from one open end to the other open end). However, d ₁ <L _T , that is, n> m.

Similarly, in the closed tube, a resistance material is provided at a position where the antinode of the velocity of the standing wave is generated and in the vicinity thereof. Specifically, the position of the antinode of the velocity in the basic vibration corresponds to the position of the open end. Therefore, the resistance material 71 is provided at such a position. On the other hand, in the double vibration or triple vibration, in addition to the resistance material 71, the resistance material 72 or 73 is provided at the position shown in FIGS. That is, the length of the closed-tube (the distance from the closed end to the open end) is L, when the position where the resistive material in closed tube is provided and d _2, position d ₂ is generally as the following equation (3.3) Can be Here, the position d ₂ represents the distance from the closed end of the tube structure. Moreover, in Formula (3.3), m is an integer greater than or equal to 1, and (lambda) is the value of the wavelength of a standing wave.

Here, the wavelength λ satisfies the relationship shown in the above equation (1.2). Therefore, the formula (3.3) can be replaced with the following formula (3.4). However, d ₂ <L _T , that is, n> m.

As described above, if the resistance material is provided only in a necessary region, the amount of the resistance material can be reduced as compared with the case where the resistance material is provided in the entire inside of the tube structure.
Note that the resistance region may actually be provided only at a position where a significant effect is recognized. That is, the value of m described above can be any integer greater than or equal to 1, but only an appropriate one of them may be selected as appropriate.

(5) Modification 5
In the present invention, the vibrator may have a uniform structure as a whole, or a part of the vibrator may have a mass different from that of the other parts. In this configuration, the part may have a density different from the other parts, or may have the same density as the other parts but a different thickness. Further, the part may have a configuration in which another member is attached by adhesion or the like in order to impart mass. Note that the part is preferably in the center of the vibrating body.

  In FIG. 14, a vibrating body 12 having a square of 100 mm × 100 mm and a thickness of 0.85 mm is fixed to a casing 11 that forms a 10 mm thick air layer having a square bottom of 100 mm × 100 mm. It is a figure which shows the simulation result of the sound absorption rate of the sound absorption structure 10 at the time of changing the surface density of the center part (size 20mm * 20mm, thickness 0.85mm). In the simulation, the sound field of the acoustic chamber in which the sound absorbing structure 10 is arranged is obtained by a finite element method according to JIS A1405-2 (measurement of sound absorption coefficient and impedance by an acoustic tube—part 2: transfer function method), and the transfer function is obtained. The sound absorption characteristic is calculated. Note that in this simulation, a configuration in which the tubular members 113 and 114 are not provided is used for the purpose of excluding the effects of the tubular members 113 and 114 by paying attention to the effect of the mass component of the vibrating body 12.

The configuration of the vibrating body 12 used in the simulation shown in FIG. 14 is as follows. The unit of the surface density and the average density is “g / m ² ”. Further, the surface density of the portion excluding the central portion of the vibrating body 12 is 799 (g / m ² ).
(1) Center area density: 399.5, average density of vibrator: 783
(2) Area density at center: 799, average density of vibrator: 799
(3) Center area density: 1199, average density of vibrator: 815
(4) Area density at center: 1598, average density of vibrators: 831
(5) Area density at center: 2297, average density of vibrator: 863

  As shown in FIG. 14, the sound absorption coefficient is high between 300 to 500 Hz and in the vicinity of 700 Hz. The peak of the sound absorption coefficient near 700 Hz is due to resonance of the spring mass system formed by the mass component of the vibrating body 12 and the spring component of the air layer. In the sound absorption structure of this simulation, the sound is absorbed with the sound absorption coefficient at the resonance frequency of the spring mass system as a peak, and even if the surface density of the central part is increased, the mass of the entire vibrating body 12 does not change greatly. The resonance frequency of the spring mass system does not change greatly.

  On the other hand, the peak of the sound absorption coefficient between 300 and 500 Hz is due to the resonance of the bending system formed by the bending vibration of the vibrating body 12. In the sound absorption structure of this simulation, the sound absorption coefficient at the resonance frequency of the bending system appears as a peak on the low frequency side, and if the surface density of the central part is different, the resonance frequency of the bending system is higher than the resonance frequency of the spring mass system. Also changes significantly. Further, as shown in the figure, the resonance frequency of the bending system decreases as the surface density at the center increases.

  In general, the resonance frequency of the bending system is determined by an equation of motion governing the elastic vibration of the vibrating body 12 and is inversely proportional to the density (and surface density) of the vibrating body 12. In addition, the resonance frequency of the bending system is strongly influenced by the density of the antinodes of natural vibration (when the amplitude is a maximum value). In this simulation, the resonance frequency of the bending system is changed by forming the antinodes of the 1 × 1 natural mode (that is, the central portion) with different surface densities.

  The simulation result shown in FIG. 14 shows that when the surface density of the central portion of the vibrating body 12 is made larger than the surface density of the other portions, the sound absorption coefficient peak on the low sound region side is further lower than the sound absorption peak frequency. It represents moving to. Therefore, if the surface density of the central part is changed, it is possible to move (shift) a part of the frequency at which the sound absorption peak occurs further to the low sound range side or the high sound range side.

  From the above, in the sound absorbing structure according to the present invention, it can be said that the peak frequency of sound absorption can be changed (shifted) by changing the surface density of the central portion. That is, according to the sound absorbing structure according to the present invention, it is possible to absorb a sound having a lower frequency without greatly changing the mass of the entire sound absorbing structure only by changing the mass of the central portion of the vibrating body. Become. As a result, the sound absorbing structure according to the present invention can cope with a change in sound only by changing the mass of the central part of the vibrating body even when the frequency of the sound to be absorbed changes.

(6) Modification 6
The present invention can also be implemented as an acoustic chamber having the above-described sound absorbing structure. Such an acoustic room is an article or a structure provided for listening to musical sounds, such as a speaker or a soundproof room. Further, the present invention may be applied to a wall surface of a vehicle such as a ship, an airplane, or a vehicle, or a wall surface such as a bathroom or a bathtub to constitute an acoustic room. Since the present invention is suitable for application to a place where sound of a specific frequency is generated as noise, when used in such an article or structure, there is a certain effect in suppressing noise.

Diagram showing the structure of sound absorption structure Diagram showing the structure of the housing Sectional drawing which shows structure of housing and vibrating body Diagram showing the structure of sound absorption structure Diagram showing the structure of the housing Sectional drawing which shows structure of housing and vibrating body Diagram showing the structure of the housing Diagram showing the structure of the housing Diagram showing the structure of the housing Diagram showing the structure of the housing Diagram showing tube structure The figure which shows the structure of the tube structure which has the resistance region The figure which shows the structure of the tube structure which has the resistance region The figure which shows the simulation result of the sound absorption rate

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 ... Sound absorption structure 11, 21, 31, 41, 50 ... Housing | casing, 111 ... Side surface part, 112 ... Bottom surface part, 113, 114 ... Pipe structure, 211 ... Outer surface part, 212 ... Inner side surface part, 213 ... Bottom surface Part, 61, 62, 63, 71, 72, 73 ... resistance material

Claims (8)

A plate-like or membrane-like vibrating body;
A supporting body that supports the vibrating body in an opening that is closed by the vibrating body, and that forms a gas layer that forms a gas spring opposite the vibrating body during sound absorption;
A sound-absorbing structure comprising: an open tube or a closed tube having an open end, and the open end facing the gas layer.   The sound absorbing structure according to claim 1, wherein the inside of the tube structure has a length in which a standing wave having a wavelength corresponding to the sound to be absorbed is generated.   The sound absorbing structure according to claim 1, wherein the support has a side surface surrounding the gas layer, and at least a part of the side surface is the tube structure.   The sound absorbing structure according to claim 2, wherein the tube structure has a resistance region where resistance to movement of gas particles is larger than other regions at a position where an antinode of particle velocity of the standing wave occurs.   5. The sound absorbing structure according to claim 4, wherein the tube structure has a resistance material that prevents movement of gas particles in the resistance region, and does not have the resistance material in a region that is not the resistance region.   A sound absorbing structure group comprising a plurality of sound absorbing structures according to claim 1 in combination.   The sound absorbing structure group according to claim 6, wherein at least one of the thickness or volume of the gas layers of the plurality of sound absorbing structures and the length of the open tube or the closed tube is not the same.   An acoustic room comprising the sound absorbing structure according to any one of claims 1 to 5 or the sound absorbing structure group according to claim 6 or 7.

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