JP2012179930A - Sound absorbing body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To absorb sound when a vehicle is travelling and to protect an occupant from impact in the case where an accident occurs to the vehicle.SOLUTION: In the case where an abrupt acceleration occurs in a vehicle, firstly with a case 12, a mass part is shaken much by the inertia based on the law of inertia, and because of this, a fragile part 25 comes into a state in which it is easily broken or is partially broken. After the fragile part 25 has come into the state in which it is broken, the body of an occupant is also shaken by the inertia based on the law of inertia to contact to a sound absorbing body 10. The force applied to the sound absorbing body 10 from the body of an occupant at the time of contacting easily break and crush the fragile part 25 of the case 12. In short, the impact generated at the time when the body of an occupant hits the sound absorbing body 10 is absorbed because the fragile part 25 of the case 12 is broken and crushed at once. The impact applied on the body of an occupant is reduced in magnitude.

Description

  The present invention relates to a sound absorber that absorbs sound.

  As the sound absorber, a plate / membrane vibration type device including a housing having an opening and a plate-like or membrane-like vibrating body provided in the opening and forming an air layer in the housing ( (Hereinafter referred to as “plate sound absorber”) (Patent Document 1). In this type of plate sound absorber, the vibrator elastically vibrates due to the difference between the sound pressure applied from the outside of the vibrator and the sound pressure on the air layer side (ie, the sound pressure difference before and after the vibrator). Thereby, the energy of the sound wave that reaches the sound absorbing body is consumed by the vibration of the vibrating body and the sound is absorbed.

JP 2006-11412 A

  When the sound absorber as described above is mounted on a vehicle such as an automobile, it is possible to absorb noise in the passenger compartment when the vehicle travels. However, assuming that an accident occurs when the occupant is on the vehicle, the occupant may hit the sound absorber and be injured due to an impact at the time of the accident.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a sound absorber that absorbs sound when a vehicle travels and protects the passenger from being injured when the vehicle crashes against the sound absorber. .

  In order to solve the above-described problem, the present invention provides a hollow housing having an opening, a vibrating body provided at a position that closes the opening, and vibrating by sound pressure of a sound wave incident on the housing. And a part of the casing is more easily plastically deformed by an external force than other parts.

  The said structure WHEREIN: It is preferable that the shape of the one part site | part of the said housing | casing is a shape where the cross-sectional secondary moment is small compared with the shape of the said other site | part.

  In the above configuration, it is preferable that a material constituting a part of the casing is a material that is more easily plastically deformed by the external force than a material constituting the other part.

  ADVANTAGE OF THE INVENTION According to this invention, while driving | running | working a vehicle, a passenger | crew can be protected from an impact when an accident generate | occur | produces in a vehicle.

It is a perspective view of a sound absorber concerning an embodiment. It is the longitudinal cross-sectional view seen from the arrow II-II direction of FIG. It is a cross-sectional view of a sound absorber according to a modification. It is a longitudinal cross-sectional view of the sound absorber which concerns on a modification. It is a perspective view of the sound-absorbing body which concerns on a modification. It is the longitudinal cross-sectional view seen from the arrow VI-VI direction in FIG. It is a perspective view of the sound-absorbing body which concerns on a modification. It is a characteristic line figure which shows the sound absorption characteristic in a modification. It is a longitudinal cross-sectional view which shows the Helmholtz type sound absorber which concerns on a modification.

<Configuration of sound absorber>
FIG. 1 is a perspective view of a sound absorber according to an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view as seen from the direction of arrows II-II in FIG. In the drawings, the dimensions of each component may differ from the actual dimensions in order to clearly depict each component. The sound absorber 10 is formed in the casing 12 by a casing 12 that forms a base, a vibrating body 16 that is provided so as to close the opening 15 of the casing 12, and the casing 12 and the vibrating body 16. And an air layer 17. The sound absorber 10 is attached to a predetermined attachment part 100 of a chassis constituting a vehicle such as an automobile by a fixing means such as an adhesive or a screw with the vibrating body 16 facing the vehicle interior. The attachment site 100 of the sound absorber 10 is an area that can be touched by the passenger's body, such as an instrument panel, a door, a pillar, a seat, a rear tray, a sun visor, or a roof in the vehicle interior. The sound absorbing body 10 absorbs noise in the passenger compartment by the sound absorbing action of the vibrating body 16. In addition, when a large acceleration occurs in the vehicle due to an accident or the like, a part of the casing 12 is shocked to prevent the passenger's body from hitting the casing 12 of the sound absorber 10 and being injured. Therefore, it has a structure that is easily deformed and crushed by plastic deformation.

First, the structure related to the sound absorbing action of the sound absorber 10 will be described. The housing 12 is a box-shaped member that is formed of a synthetic resin (for example, ABS resin) and has a rectangular bottom plate 13. A total of four side plates 14 are provided on each of the four sides of the bottom plate 13, and these side plates 14 stand from the bottom side 13. An opening 15 that is rectangular when viewed from above is formed by a side corresponding to the free end of each side plate 14. The vibrating body 16 is formed in a rectangular plate shape from an elastic polymer compound (for example, an olefin copolymer with an inorganic filler), and the periphery thereof is bonded and fixed to the opening 15 of the housing 12. . Inside the sound absorber 10 (behind the vibrating body 16), the vibrating body 16 is fixed to the opening 15 of the housing 12, thereby forming a sealed air layer 17. The vibrating body 16 has relatively low rigidity with respect to the casing 12 other than the vibrating body 16 (low Young's modulus, thin thickness, small cross-sectional moment), or mechanical impedance (8 × ( Bending rigidity x surface density) ^1/2 ) is formed with a relatively low shape / member. Thereby, the vibrating body 16 is more easily vibrated than the housing 12.

  In the sound absorber 10 configured as described above, when a sound wave is incident on the housing 12, the difference between the sound pressure applied from the outside of the vibrating body 16 and the sound pressure on the air layer 17 side (that is, before and after the vibrating body 16). Therefore, the vibrating body 16 elastically vibrates. Thereby, the energy of the sound wave that reaches the sound absorber 10 is consumed by the vibration of the vibrating body 16 and the sound is absorbed. In addition, although the material of the vibrating body 16 is made of synthetic resin, the material of the vibrating body 16 is not limited to synthetic resin, and other materials such as paper, metal, and fiberboard can be used as long as the material generates elastic vibration. There may be. The shape of the vibrating body 16 is not limited to a plate shape, and may be a film shape. In short, the vibrating body 16 is a member of a shape or material that can be repeatedly vibrated by the action of being deformed when a force (sound pressure) is applied and returning to its original state by a restoring force generated by elasticity or tension. Good. Here, the plate shape is a shape having a relatively thin thickness and a two-dimensional extension with respect to a rectangular parallelepiped (solid), and the film shape (film shape, sheet shape) is more than the plate shape. It is relatively thin and generates a restoring force by tension.

  Next, a structure related to the prevention of passenger injury by the sound absorber 10 will be described. On the inner wall surface (the surface on the air layer 17 side) of the four side plates 14 of the housing 12, a notch portion that is continuous over the entire inner periphery of the housing 12 is formed at the substantially central portion in the height direction. Yes. In this cut portion, the thickness of the housing 12 is smaller than the thickness of the other portions and is fragile. Of the side plate 14, the casing 12 on the upper side from the fragile portion 25 has a thickness larger than that on the lower side, and acts as a mass part on which the mass is concentrated more than the lower side.

  Here, when a sudden acceleration occurs in the vehicle, first, the mass portion in the housing 12 is greatly shaken by the inertial force based on the law of inertia, and thus the fragile portion 25 is easily broken. The first phenomenon occurs, or is partially destroyed. In the first phenomenon, for example, after the fragile portion 25 is likely to be destroyed, the occupant's body is also shaken by the inertial force based on the law of inertia and comes into contact with the sound absorber 10. Due to the force applied to the body 10, a second phenomenon occurs in which the housing 12 is easily broken and crushed at the fragile portion 25. That is, the impact when the occupant's body hits the sound absorber 10 is absorbed by the housing 12 being immediately destroyed and crushed by the fragile portion 25, and the magnitude of the impact applied to the occupant's body is reduced. Further, in the first phenomenon, even if the fragile portion 25 is partially destroyed, when the occupant's body subsequently contacts the sound absorber 10, the partially broken housing 12 is further destroyed. The third phenomenon of absorbing the force from the occupant occurs. Thereby, the magnitude | size of the impact given to a passenger | crew's body becomes small. As described above, regardless of whether the inertial force at the time of the accident or the force applied by the occupant is considered as an external force, the housing 12 is easily broken and crushed by the external force, that is, has a portion that is easily plastically deformed. Even if the first and second phenomena or the third phenomenon as described above occur in a very short period of time and a large acceleration occurs in the vehicle due to an accident or the like, the passenger's body is a sound absorber. It is possible to prevent injury from hitting the 10 casings 12.

Finally, conditions for exerting the sound absorbing action of the sound absorber 10 will be described. In general, for a sound absorbing structure that absorbs sound by a plate-like or membrane-like vibrator and an air layer, the frequency to be attenuated depends on the resonance frequency of the spring mass system due to the mass component (mass component) of the vibrator and the spring component of the air layer. Is set. The density of air is ρ ₀ [kg / m ³ ], the speed of sound is c ₀ [m / s], the density of the vibrating body is ρ [kg / m ³ ], the thickness of the vibrating body is t [m], When the thickness is L [m], the resonance frequency of the spring mass system is expressed by the equation (1).

そして、実施形態及び各変形例においては、上記数２の式から１６０〜３１５Ｈｚバンド（１/３オクターブ中心周波数）を吸音するよう、以下のようにパラメータが設定される。
空気の密度ρ₀ ；１．２２５[ｋｇ／ｍ³]
音速ｃ₀ ；３４０[ｍ／ｓ]
振動体の密度ρ ；９４０[ｋｇ／ｍ³]
振動体の厚さｔ ；０．００１７[ｍ]
空気層の厚さＬ ；０．０３[ｍ]
筐体の長さａ ；０．１[ｍ]
筐体の長さｂ ；０．１[ｍ]
振動体のヤング率Ｅ ；１．０[ＧＰａ]
ポアソン比σ ；０．４
モード次数 ；ｐ＝ｑ＝１ In the case of the plate / membrane vibration type sound absorbing structure, when the vibrating body has elasticity and elastically vibrates, the property of a bending system due to elastic vibration is added. In the field of architectural acoustics, the shape of the vibrating body is rectangular, the length of one side is a [m], the length of the other side is b [m], the Young's modulus of the vibrating body is E [Pa], and the Poisson of the vibrating body When the ratio is σ [−] and p and q are positive integers, the resonance frequency of the plate / membrane vibration type sound absorbing structure is obtained by the following formula 2, and the obtained resonance frequency is used for acoustic design. (In the case of peripheral support).

In the embodiment and each modified example, the parameters are set as follows so as to absorb the 160 to 315 Hz band (1/3 octave center frequency) from the equation (2).
Air 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 vibrating body; 0.0017 [m]
Air layer thickness L; 0.03 [m]
Case length a: 0.1 [m]
Case length b: 0.1 [m]
Young's modulus E of vibrating body; 1.0 [GPa]
Poisson's ratio σ: 0.4
Mode order; p = q = 1

On the other hand, in the equation ( ² ), the term of the spring mass system (ρ ₀ c ₀ ² / ρtL) and the term of the bending system (the term added in series after the term of the spring mass system) are added. For this reason, the resonance frequency obtained by the above equation is higher than the resonance frequency of the spring mass system, and it may be difficult to set the frequency at which the sound absorption peak is low.

  In the sound absorber configured as described above, 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 is uniquely determined by Equation 2, but actually Is not fully elucidated, and the actual situation is that the structure of a sound absorber that exhibits high sound absorption in the low frequency range has not been established.

Therefore, as a result of intensive experiments, the inventors have determined that the value of the fundamental vibration frequency of the bending system is fa (= (1 / 2π) · ((p / a) ² + (q / b) ² ) · (π ⁴ Et ³ / (12ρt (1−σ ² ))) ^1/2 ), and when the value of the resonance frequency of the spring mass system is fb (= formula of formula 1), the following formula 3 is satisfied. It was found that the above parameters should be set. As a result, the fundamental vibration of the bending system is coupled with the spring component of the air 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 (the bending system). The resonance frequency fa <sound absorption peak frequency f <spring mass system fundamental frequency fb), and the sound absorption rate increases.

このように、上記した数式３，４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、吸音のピークとなる周波数を低くした吸音体が構成できる。 Furthermore, when the following Expression 4 is set, the frequency of the sound absorption peak is sufficiently smaller than the resonance frequency of the spring mass system. In this case, it was also verified that the fundamental frequency of the bending system is sufficiently smaller than the resonance frequency of the spring mass system due to the low-order elastic vibration mode and is suitable as a sound absorbing structure that absorbs sound having a frequency of 300 [Hz] or less.

In this way, by setting various parameters so as to satisfy the conditions of Equations 3 and 4 described above, it is possible to configure a sound absorber that reduces the frequency at which sound absorption peaks.

The various parameters are parameters for setting the resonance frequency f shown in Equation 2, and include gas density ρ ₀ , sound velocity c 0, vibration body density ρ, vibration body thickness t, gas layer thickness L, , Length a of the case, length b of the case, Young's modulus E of the vibrating body, Poisson's ratio σ, mode order p, q, and the like.

<Modification>
The above-described embodiment may be modified as follows.
<Modification 1>
The structure relating to the prevention of injury to the occupant by the sound absorber 10 is not limited to the above embodiment.
FIG. 3 shows a cross section of the sound absorber 10N according to this modification, that is, a cross section when the sound absorber 10N is cut along a plane parallel to the vibrating body 16. In the sound absorbing body 10N, weak portions 27, which are cut portions extending in the height direction of the housing 12N, are formed at the center and four corners in the longitudinal direction of the four side plates 14N. As a result, when an external force is applied to the housing 12 from a direction perpendicular to the plate surface of the side plate 14N, the housing 12N is broken and crushed in the fragile portion 27 where the stress is concentrated.

<Modification 2>
Further, the structure relating to the prevention of injury to the occupant by the sound absorber 10 may be as follows. In the sound absorber 10B shown in this modification, as shown in FIG. 4, the height direction of each side plate 14B of the housing 12B is cut, and the buffer portion 20B is sandwiched from the upper and lower side plates 14B at this cut portion. ing. The buffer portion 20B is provided so as to continuously go around the four side surfaces of the housing 12B. The buffer portion 20B corresponds to a part of the housing 12 that is easily broken and crushed by an impact. Therefore, the buffer portion 20 </ b> B is made of a material that is easily broken by impact, such as foamed resin or an elastic member, and is less likely to vibrate than the vibrating body 16. That is, the vibration body 16 has a relatively low rigidity with respect to the buffer portion 20B (the Young's modulus is low, the thickness is thin, and the cross-sectional second moment is small), as in the relationship with the casing 12B described above. Alternatively, it is formed of a shape / member having a relatively low mechanical impedance (8 × (bending rigidity × surface density) ^1/2 ).
5 and 6 are a perspective view and a longitudinal sectional view of a sound absorbing body 10C according to another modification. A rectangular hole 14C1 extending in the longitudinal direction of the side plate is formed in the side plate 14C of the housing 12C of the sound absorber 10C so as to be stepped for each side plate 14C. A buffer portion 20C is attached so as to close the hole 14C1. The buffer portion 20C corresponds to a part of the housing 12 that is easily broken and crushed by an impact. Therefore, like the buffer portion 20B, the buffer portion 20C is made of a material that is easily broken by an impact, such as a foamed resin or an elastic member, and is more difficult to vibrate than the vibrating body 16.
FIG. 7 is a perspective view of a sound absorber 10D according to another modification. In the sound absorber 10 </ b> D, the four corners of the housing 12 are configured by buffer portions 20 </ b> D that extend in the height direction of the housing 12. A lower end portion of the buffer portion 20 </ b> D is in contact with the attachment site 100, and an upper end portion thereof is in contact with the vibrating body 16. The buffer portion 20D corresponds to a part of the housing 12 that is easily broken and crushed by an impact. Similarly to the buffer portions 20B and 20C, the buffer portion 20D is made of a material that is easily broken by an impact, such as a foamed resin or an elastic member, and is more difficult to vibrate than the vibrating body 16.
In the sound absorber according to each of the above-described configurations, when a sudden acceleration occurs in the vehicle, the mass part in the housing 12 is greatly shaken by the inertial force based on the law of inertia, thereby destroying the buffer part. The phenomenon that it becomes in the state where it is easy to be done or it is partially destroyed occurs. The body of the occupant is also shaken by the inertial force based on the law of inertia and comes into contact with the sound absorber 10, and the casing 12 is broken at the fragile portion 25 by the external force applied to the sound absorber 10 from the occupant's body at the time of contact. The phenomenon of being crushed occurs. That is, the impact when the occupant's body hits the sound absorbing body 10 is absorbed by the housing 12 being destroyed and crushed by the buffer portion, and the magnitude of the impact applied to the occupant's body is reduced. Thereby, even if a large acceleration occurs in the vehicle due to an accident or the like, it is possible to prevent the passenger's body from hitting the casing 12 of the sound absorber 10 and being injured.

As described in the above embodiment and Modifications 1 and 2, the present invention is a sound absorber that satisfies the condition that a part of the housing 12 is more easily plastically deformed by an external force than the other parts. Good. The condition that the plastic deformation is easy here is, for example, in the configuration of the embodiment or the first modification, when the entire housing 12 is made of the same material, That is, the thickness is smaller than the thickness of other parts. The meaning of the thickness here includes an effective thickness. For example, even if the thickness of a part of the housing 12 and the thickness of the other part are the same as the outer dimensions, the above part of the part is provided with a gap inside or is notched on the outer surface. In other cases, the effective thickness is smaller in some of the above-mentioned parts. . In short, regarding the shape of the housing 12, considering the cross-sectional second moment representing the difficulty of bending with respect to stress, if the condition that the cross-sectional second moment of some parts is smaller than the cross-sectional second moment of other parts is satisfied. Good.
In addition, the condition that plastic deformation is likely to occur in the configuration of the modification 2 is that the material itself that constitutes a part of the housing 12 is more easily plastically deformed by an external force than the material that constitutes the other part. It is that.

<Modification 3>
In the above embodiment, the vibrator is described as having a uniform configuration. However, a part of the vibrator may be formed to have a density different from that of the other part, or a part of the vibrator may have a thickness different from that of the other part. Alternatively, a part of the vibrator may be formed so as to have a mass different from that of the other part. By forming the vibrating body in this way, it is possible to change the vibration conditions in the vibrating body.

  In the sound absorbing body 10, the sound absorbing mechanism is constituted by a spring mass system and a bending system. The inventors conducted experiments on the sound absorption coefficient at the resonance frequency when the surface density of the vibrating body 16 was changed. FIG. 8 shows a vibrating body 16 (size: 100 mm × 100 mm, thickness: 0.85 mm) fixed to the casing 12 having a vertical and horizontal size of 100 mm × 100 mm and a thickness of 10 mm. It is the figure which showed the simulation result of the normal incidence sound absorption coefficient of the sound-absorbing body 10 at the time of changing the surface density of a part (a magnitude | size is 20 mm x 20 mm, thickness 0.85mm). In this simulation, in accordance with JIS A 1405-2 (measurement of sound absorption coefficient and impedance by an acoustic tube—part 2: transfer function method), the sound field of the acoustic chamber in which the sound absorber 10 is arranged is determined by a finite element method. The sound absorption characteristics were calculated from the transfer function.

Specifically, the surface density of the central part is (1) 399.5 [g / m ² ], (2) 799 [g / m ² ], (3) 1199 [g / m ² ], (4) 1598 [g / m ² ], (5) 2297 [g / m ² ], the surface density of the peripheral member is 799 [g / m ² ], and the average density of the vibrator 16 is (1) 783 [g / m ² ]. m ² ], (2) 799 [g / m ² ], (3) 815 [g / m ² ], (4) 831 [g / m ² ], (5) 863 [g / m ² ] This is a simulation result. Looking at the simulation results, the sound absorption rate is high between 300 and 500 [Hz] and in the vicinity of 700 [Hz].

  The high sound absorption rate near 700 [Hz] is due to resonance of the spring mass system formed by the mass of the vibrating body 16 and the spring component of the air layer 17. In the sound absorber 10, 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 portion is increased, the mass of the entire vibrating body 16 does not change greatly. It can be seen that the resonance frequency does not change greatly.

  Moreover, the sound absorption coefficient is increased between 300 and 500 [Hz] because of the resonance of the bending system formed by the bending vibration of the vibrating body 16. In the sound absorber 10, the sound absorption coefficient at the resonance frequency of the bending system appears as a peak on the low frequency range side, and the surface density of the central portion corresponding to the region that becomes the antinode when the vibration body 16 undergoes bending vibration is increased. As a result, it can be seen that only the resonance frequency of the bending system is lowered.

  In general, the resonance frequency of the bending system is determined by an equation of motion that governs elastic vibration of the vibrating body 16 and is inversely proportional to the density (surface density) of the vibrating body 16. The resonance frequency is greatly influenced by the density of the antinodes of natural vibration (when the amplitude is a maximum value). For this reason, in the simulation described above, the region that becomes the antinode of the 1 × 1 eigenmode is formed at different surface densities in the central portion, so that the resonance frequency of the bending system is changed.

  Thus, the simulation results show that when the surface density of the central part is made larger than the surface density of the peripheral part, the peak of the sound absorption coefficient on the low frequency side of the frequency that becomes the peak of sound absorption moves further to the low frequency side. Represents. Therefore, by changing the surface density of the central portion, a part of the frequency at which the sound absorption is peaked can be further moved (shifted) to the low sound region side or the high sound region side.

  In the sound absorber 10 described above, the frequency of the sound absorption sound can be changed (shifted) simply by changing the surface density of the central portion, so that the vibrating body 16 is made of the same material as the sound absorber 10 as a whole. Compared with the case where the sound absorbing sound is changed by increasing the mass of the sound absorber 10 as a whole, the frequency of the sound to be absorbed can be lowered without greatly changing the mass of the sound absorber 10 as a whole.

<Modification 4>
The shape of the housing of the sound absorber 10 is not limited to a rectangular shape, and may be a circular shape or a polygonal shape. Furthermore, the sound absorption coefficient peak value may be increased by filling the air layer 17 of the sound absorber 10 with a porous sound absorbing material (for example, cotton-like fibers such as foamed resin, felt, polyester wool).

<Modification 5>
The sound absorber is not limited to the plate / membrane vibration type but may be a Helmholtz type sound absorber described below.
As shown in FIG. 9, the Helmholtz-type sound absorber 40 includes a rectangular parallelepiped housing 41 having a space formed therein, and a tubular body inserted into an insertion hole 42 drilled in the upper side of the housing 41. Member 43. A sealed space 44 is formed inside the housing 41, and an opening 45 that connects the sealed space 44 and the outside is formed inside the tubular member 43. The tubular member 43 serves as a sound absorbing means according to the present invention.

  The housing | casing 41 is formed in the rectangular parallelepiped shape, for example with FRP (fiber reinforced plastic). For the tubular member 43, for example, a pipe made of vinyl chloride can be used, and the inner surface is roughened so that friction with air is likely to occur. The Helmholtz-type sound absorber 40 acts to attenuate the generated sound by the air in the sealed space 44 that is a small-sized cavity acting as a spring.

  In this sound absorber 40, since the small opening 45 provided in the sealed space 44 communicates with the outside, a one-mass system spring / mass model is formed using the mass of air in the opening 45 as a mass. At the resonance frequency of this system, the air mass in the opening 45 is vibrated by the sound pressure from the outside, and the sound energy is converted into thermal energy by the friction between the peripheral wall of the opening 45 and the air mass. . That is, the sound is attenuated.

Now, the length of the opening 45 is L1, the cross-sectional area of the opening 45 is S, the volume of the air layer 44 is V, the speed of sound is C, and the effective length of the opening 45 is Le (Le≈L1 + 0.8 · S ^1/2 ). Then, the resonance frequency f0 of the sound absorber 40 is f0 = 1 / 2π (C ² S / Le · V) ^1/2 .
From this equation, the resonance frequency f0 can be adjusted by changing the cross-sectional area S or the effective length Le of the opening 45, that is, the inner diameter d or the length L1 of the tubular member 43, thereby reducing sound of different frequencies. I understand that I can do it.
Further, in the structure in which the Helmholtz type sound absorber 40 is attached to the attachment portion 100, the above-described modification examples can be appropriately applied.

DESCRIPTION OF SYMBOLS 10 ... Sound absorption body, 12, 41 ... Housing, 15 ... Opening part, 16 ... Vibrating body, 17 ... Air layer, 20, 21 ... Buffer part, 25, 27. ..Vulnerable part, 43 ... tubular member

Claims (3)

A sound absorber mounted on a vehicle,
A hollow housing with an opening;
A vibrating body that is provided in the opening and vibrates by sound pressure of a sound wave incident on the housing;
A part of the casing is more likely to be plastically deformed by an external force than other parts. The sound absorber according to claim 1,
The shape of a part of the casing is a shape having a small second moment of section as compared to the shape of the other part. The sound absorber according to claim 1,
The sound absorber, wherein a material constituting a part of the housing is more easily plastically deformed by the external force than a material constituting the other part.

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