JP2008191506A - Sound absorbing body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve low frequency performance in a porous type sound absorbing mechanism. <P>SOLUTION: The sound absorbing body of the invention includes: a porous object layer 2; and a film form sound absorbing layer 3 with permeability, which is laminated on a face (a sound source side) of the porous object layer 2. The porous object layer 2 is formed from a glass wool etc. of 25 mm in thickness and 32 kg/m<SP>3</SP>in surface density. The film form sound absorbing layer 3 is formed from a non-organic felt etc. of 3 mm in thickness and 342 g/m<SP>2</SP>in surface density, or 5 mm in thickness and 570 g/m<SP>2</SP>in surface density. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sound absorber, and more particularly to a sound absorber useful for effectively absorbing noise generated from railway vehicles, automobiles, electrical devices, and the like that require space saving.

  In general, three types of sound absorbing mechanisms are known: a resonator type, a plate (membrane) vibration type, and a porous type (for example, see Non-Patent Document 1). Among these sound absorbing mechanisms, the resonator type and the plate (membrane) vibration type are mechanisms that attenuate sound energy based on the fact that the internal structure of the sound absorbing mechanism resonates with sound waves, and are extremely high only in a limited frequency range. It has the feature of showing sound absorption performance. In addition, the porous sound absorbing structure is a mechanism that attenuates sound energy based on the viscous resistance of air passing through the porous body, so it does not have a specific resonance point and has a relatively high sound absorption rate over a wide frequency range. It has the feature of showing.

  On the other hand, in noise countermeasures for railway vehicles, automobiles, electrical equipment, etc., the frequency of generated noise is rarely a constant value, so a wide range of sound absorption performance as seen in porous sound absorption mechanisms is desired. It is rare.

  However, the porous sound absorbing mechanism has a drawback that sound absorption is not performed because the sound energy is not attenuated when air vibration does not occur inside the porous body. In particular, since such a phenomenon appears remarkably in the low frequency sound absorption performance, the porous sound absorption mechanism is generally known to have poor low frequency performance.

  As a method for improving the low-frequency performance of such a porous sound absorbing mechanism, (a) a method of increasing the thickness of the porous body and (b) a method of increasing the density of the porous body are known. .

  However, since there is a tendency to place importance on space efficiency in vehicles and electrical equipment, the method (a) described above is rarely used in practice, and the method (b) described above is ), There is a drawback that the sound absorption effect is small. The influence of the structural parameters of these porous sound absorbing mechanisms on the sound absorbing performance is described in J.6301: 2000 appendix J. Section 4.2 gives a general explanation.

"Architecture and Environmental Acoustics" Kyoritsu Shuppan 1990, Chapter 4

  The present invention has been made paying attention to such points, and has an object to provide a sound absorber that improves low-frequency performance in a porous sound absorbing mechanism and is excellent in space saving.

  The sound absorber according to the first aspect of the present invention includes a porous body layer and a breathable film-like sound absorbing layer laminated on the surface of the porous body layer.

  According to a second aspect of the present invention, in the sound absorber according to the first aspect, the film-like sound absorbing layer is made of any one of a nonwoven fabric, a felt and a woven fabric, or a mixture thereof.

  According to a third aspect of the present invention, in the sound absorbing body according to the second aspect, the fibers constituting the nonwoven fabric, the felt, and the woven material are any of organic materials, inorganic materials, metal materials, or a mixture thereof. It consists of.

  According to a fourth aspect of the present invention, in the sound absorber according to the first aspect, the film-like sound absorbing layer is formed of a film provided with scattered holes.

  According to a fifth aspect of the present invention, in the sound absorber according to the fourth aspect, the base of the film is made of any one of an organic material, an inorganic material and a metal material, or a laminate thereof.

According to a sixth aspect of the present invention, in the sound absorber according to any one of the first aspect to the fifth aspect, the surface density of the film-like sound absorbing layer is set to a low frequency cutoff frequency of the porous body layer. _{When L} and the thickness of the porous body layer are d, the condition of m ≧ f _L × (4π ² × d) / (1.4 × 10 ⁵ ) is satisfied.

  According to the sound absorbing body of the first to seventh aspects of the present invention, the thickness of the porous body layer is almost changed by providing a film-like sound absorbing layer having a suitable air permeability on the surface (sound source side) of the porous body layer. The low frequency performance of the porous sound absorbing mechanism can be improved without any problems. Therefore, according to the sound absorber of the present invention, it has the same thickness as the conventional porous body layer, and can effectively absorb the noise of a wide frequency band from the low frequency region to the high frequency region, It is possible to provide a sound absorber that is suitable for noise reduction in railway vehicles, automobiles, electrical devices, and the like that save space.

  Hereinafter, preferred embodiments of a sound absorber according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a cross-sectional view of a sound absorber according to the present invention. In the figure, a sound absorbing body 1 of the present invention includes a porous body layer 2 made of a porous material, and a membrane-like sound absorbing layer 3 having air permeability laminated on the surface (sound source side) of the porous body layer 2. I have. Here, the porous body layer 2 is laminated on the back side of the film-like sound absorbing layer 3 because the film-like sound absorbing layer 3 part acts as an additional mass, that is, a role of a weight, and the porous body layer 2 is a spring, That is, it acts as a role of an air spring, and performs sound absorption by membrane vibration.

The porous body layer 2 is formed of a material having flame retardancy. Specifically, it is made of glass wool or rock wool having a surface density of 32 kg / m ³ (32K) or a mixture thereof. The porous body layer 2 is preferably formed with a thickness of 1 to 50 mm. Here, the thickness is set to 1 to 50 mm. When the thickness is less than 1 mm, the sound absorption effect due to the vibration of the skeleton portion of the porous body layer 2 is reduced. When the thickness exceeds 50 mm, the vibration as the plate material is reduced. This is because the sound absorbing effect is reduced. In consideration of the strength and space factor as a sound absorber, one having a thickness of 10 to 25 mm is preferable.

  The porous body layer 2 having such a configuration has excellent sound absorption characteristics over a wide range from a low frequency region to a high frequency region, and also has an effective damping property for reducing solid propagation sound and vibration. Demonstrate.

  The film-like sound absorbing layer 3 is formed of a material having moderate air permeability. The film-like sound absorbing layer 3 is preferably formed with a thickness of 3 to 10 mm.

  First, the film-like sound absorbing layer 3 can be formed of any one of a nonwoven fabric, a felt and a woven fabric, or a mixture thereof. The fibers constituting the nonwoven fabric, the felt and the woven fabric are organic materials It can be formed of any one of inorganic materials and metal materials, or a mixture thereof. In this case, the average distance between the fibers is preferably in the range of 20 to 120 μm.

  Here, the relationship between the thickness of the film-like sound absorbing layer (3 to 10 mm) and the average fiber spacing (20 to 120 μm) will be described. Since the sound absorption effect depends on the air flow rate, the fiber spacing should be constant. For example, the greater the thickness of the film-like sound absorbing layer, the greater the sound absorbing effect. If the thickness of the film-like sound absorbing layer is constant, the smaller the fiber spacing, the greater the sound absorbing effect.

  Secondly, the film-like sound absorbing layer 3 can be formed of a film (perforated film) in which scattered holes are provided, and the base of the film is made of an organic material, an inorganic material, and a metal material. It can be formed of any of these or a laminate thereof.

  The film-like sound absorbing layer 3 is preferably integrated with the porous body layer 2 by application of an adhesive or the like in order to improve the degree of freedom of the product form and simplify the construction on site.

  Here, requirements necessary for the film-like sound absorbing layer 3 having air permeability will be described.

  First, when a film having no air permeability is provided on the surface of the porous body layer 2, the sound absorption performance is the same as that in a general film-like sound absorption mechanism, and the high frequency performance is greatly impaired. However, when a film having high air permeability, that is, a film having low viscosity resistance is provided on the surface of the porous body layer 2, the sound absorption performance is almost the same as that of the porous body layer alone. Therefore, “requirements necessary for a film-like sound absorbing layer having moderate air permeability” are considered to be “surface density” and “air flow rate”.

Thus, the surface density of the film-like sound absorbing layer 3 can be estimated from the sound absorbing performance of the porous body layer 2 alone disposed on the back surface (the surface opposite to the sound source side). Specifically, when the thickness was as f _L low-frequency end cut-off frequency of the sound absorbing performance indicated by porous layer 2 is a single d, surface density m of the film-like sound absorbing layer 3 satisfies expression 1 There is a need to.

m ≧ f _L × (4π ² × d) / (1.4 × 10 ⁵ ) (1)
In addition, (1) Formula can be derived | led-out from the formula of the resonant frequency of a film-form sound absorption mechanism.

  Here, since it is difficult to actually measure the air flow rate of the film-like sound absorbing layer 3, the diameter of the opening of the film-like sound absorbing layer 3 is used as a parameter as a value highly correlated with the air flow rate. In addition, as the film-form sound absorption layer 3, it is preferable to use the nonwoven fabric whose average fiber space | interval exists in the range of 20-120 micrometers.

FIG. 2 is an explanatory diagram showing the sound absorption characteristics of the sound absorber in the embodiment of the present invention together with a comparative example. In the figure, the horizontal axis is frequency [Hz], the vertical axis is reverberation chamber method sound absorption [−], and L1 is a conventional sound absorber made of glass wool having a thickness of 25 mm and an area density of 32 kg / m ³ (hereinafter “ L2 is a conventional sound absorber made of glass wool having a thickness of 25 mm and a surface density of 64 kg / m ³ (hereinafter referred to as “Comparative Example 2”), and L3 is a surface having a thickness of 25 mm. An inorganic felt (film-like sound absorbing layer 3) having a thickness of 3 mm and an area density of 342 g / m ² is laminated on the sound source side of glass wool having a density of 32 kg / m ³ (glass wool “porous body layer 2” of Comparative Example 1). L4 is a glass wool having a thickness of 25 mm and a surface density of 32 kg / m ³ (glass wool of “Comparative Example 1“ porous body layer 2 ”). The sound source side is 5mm thick and the surface density is 570g / It shows the respective sound absorption characteristics in the ^two inorganic felt sound absorber of the present invention formed by laminating the (film-like sound absorbing layer 3) (hereinafter referred to as "Example 2".).

From the figure, the cut-off frequency f _L of the porous body layer 2 alone (Comparative Example 1) disposed behind the film-like sound absorbing layer 3 is about 1000 Hz as indicated by L1. From formula 1, it is preferable to use a film having a weight of 282 g / m ² or more as the surface density of the film-like sound absorbing layer 3. As a result, in Examples 1 and 2, as shown by L3 and L4, the sound absorption performance is improved in comparison with Comparative Examples 1 and 2 (L1 and L2) in all frequency bands. When comparing 1 (L1) and Example 2 (L4), it can be seen that the sound absorption coefficient of about 0.3 is improved.

FIG. 3 is an explanatory diagram showing the sound absorption characteristics of the sound absorber together with a comparative example when the thickness of the glass wool is thicker than that shown in FIG. In the figure, the horizontal axis is frequency [Hz], the vertical axis is reverberation chamber method sound absorption [−], and L5 is a conventional sound absorber made of glass wool having a thickness of 50 mm and an area density of 32 kg / m ³ (hereinafter “ Comparative Example 3 ”)), L6 has a thickness of 3 mm on the sound source side of glass wool having a thickness of 50 mm and a surface density of 32 kg / m ³ (glass wool“ porous body layer 2 ”of Comparative Example 3). L7 has a thickness of 50 mm and a surface density of 32 kg / m. The sound absorber of the present invention (hereinafter referred to as “Example 3”) is formed by laminating inorganic felt (film-like sound absorbing layer 3) having a thickness of 342 g / m ² . ^3. An inorganic felt (film-like sound absorbing layer 3) having a thickness of 5 mm and an area density of 570 g / m ² is laminated on the sound source side of No. ³ glass wool (glass wool “porous body layer 2” of Comparative Example 3). Sound absorbers (hereinafter referred to as “Example 4”). It shows the sound characteristics.

From the figure, the cutoff frequency f _L of the porous body layer 2 alone (Comparative Example 3) disposed behind the film-like sound absorbing layer 3 is about 630 Hz as indicated by L5. From formula 1, it is preferable to use a film having a weight of 178 g / m ² or more as the surface density of the film-like sound absorbing layer 3. As a result, in Examples 3 and 4, as indicated by L6 and L7, the sound absorption performance is improved over Comparative Example 3 (L5) in all frequency bands, and in particular, Comparative Example 3 (L5) at 315 Hz. And Example 4 (L7) are compared, it can be seen that the sound absorption coefficient of about 0.2 is improved.

  In addition, when the average fiber space | interval of the inorganic felt as the film-like sound absorption layer 3 used in Examples 1-4 was converted from the measurement result of felt density and fiber diameter, it was in the range of 20-120 micrometers.

  As described above, according to the sound absorber of the present invention, the porous type layer is provided with a film-like sound absorbing layer having a moderate air permeability on the surface (sound source side), so that the porous type layer hardly changes in thickness. The low frequency performance of the sound absorbing mechanism can be improved, and as a result, a sound absorber suitable for noise countermeasures such as railway vehicles, automobiles, and electrical equipment that can save space can be provided.

  In the above-described embodiments, the present invention is described with specific embodiments shown in the drawings. However, the present invention is not limited to these embodiments, and as long as the effects of the present invention are exhibited, You may comprise as follows.

  1stly, in the above-mentioned Example, although the case where inorganic felt was used as a film-like sound absorption layer was described, it replaced with this, Coarse felt, vegetable fiber type felt, animal fiber type felt, synthetic fiber type felt Any of these or a mixture thereof may be used.

  Secondly, in the above-mentioned embodiment, the case where glass wool is used as the porous body layer is described. Instead, inorganic fiber aggregates such as rock wool, cellulose fiber, coarse wool felt, animal hair felt are used. Any of organic fiber aggregates such as PET fiber felt and polyethylene felt, metal fiber aggregates, or a mixture thereof may be used.

Sectional drawing of the sound-absorbing body in the Example of this invention. Explanatory drawing which shows the sound absorption characteristic of the sound absorber in the Example of this invention. Explanatory drawing which shows the sound absorption characteristic of the sound absorber in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sound absorption body 2 ... Porous body layer 3 ... Membrane-like sound absorption layer

Claims (6)

  A sound absorber comprising: a porous body layer; and a breathable film-like sound absorbing layer laminated on the surface of the porous body layer.   The sound absorbing body according to claim 1, wherein the film-like sound absorbing layer is made of any one of a nonwoven fabric, a felt and a woven fabric, or a mixture thereof.   The sound absorber according to claim 2, wherein the fibers constituting the nonwoven fabric, the felt, and the material of the woven fabric are made of an organic material, an inorganic material, a metal material, or a mixture thereof.   The sound absorbing body according to claim 1, wherein the film-like sound absorbing layer is formed of a film provided with scattered holes.   5. The sound absorber according to claim 4, wherein the base of the film is made of any one of an organic material, an inorganic material and a metal material, or a laminate thereof. The surface density of the film-like sound absorbing layer is such that the low frequency cutoff frequency of the porous body layer is f _L and the thickness of the porous body layer is d.
m ≧ f _L × (4π ² × d) / (1.4 × 10 ⁵ )
The sound absorber according to any one of claims 1 to 5, wherein the following condition is satisfied.

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