JPH1136239A - Double reflection sound absorbing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound absorbing effect equal to that in the case of doubling the thickness by providing a second sound wave reflector for reflecting a sound wave focused on a focal point of a first sound wave reflector by use of porous material in a propagation path for a sound wave incident on the first sound wave reflector. SOLUTION: An incident wave and a reflecting wave advance in the opposite directions in the same path to produce an interference position due to the reversed phase relationship depending on the magnitude of wavelength of the sound wave in the advancing path. On the other hand, the polarity of vibration of air particles of both sound waves passed through the porous material 2 is such that the air particles are passed through the porous material 2 which has low density and small penetration loss to cause irregular reflection in multiple. Further the polarity of vibration is weakened and the vibration is changed to the vibration having an arbitrary polarity in the path to be propagated. Accordingly in an interference position of sound waves in the reversed phase relationship, polarities of vibration of sound waves meet each other at random, and the polarities substantially agree with each other to interfere. Thus the surge energy of both sound waves is reduced to expand the frequency band of sound absorption determined according to the thickness of sound absorbing plate of two sound wave reflectors 3, 4 to the lower side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double reflection device capable of obtaining a sound absorbing effect equivalent to doubling the thickness without changing the thickness of a sound absorbing plate comprising a porous material and a reflecting mirror. It relates to a sound absorbing plate.

[0002]

2. Description of the Related Art As one of measures for preventing the diffusion of road traffic noise generated by frictional noise between a road surface and a tire, there is a soundproof wall installed at a road end. However, even if the soundproof wall is installed, the noise of the traveling vehicle passes through the soundproof wall or is diffracted and goes around to the back side of the soundproof wall. The noise that leaks out of the noise barrier is directly radiated from the noise source, is reflected once inside the noise barrier, is reflected again on the surface of the car body, etc. There is noise propagating upwards.

As described above, noise that reaches a sound receiving point is classified into two types: a noise that directly arrives from a noise source and a noise that arrives indirectly by repeating reflection and the like. Often, the ratio of the noise that reaches the sound receiving point exceeds the ratio of the noise that directly reaches the sound receiving point.

If the sound wave reflected inside the soundproof wall is subjected to sound absorption processing without being reflected by the wall surface, the ratio of noise leaking to the outside decreases, and the effect of noise reduction by the soundproof wall increases as a whole. . Improving the sound absorbing performance inside the soundproof wall also relatively increases the sound insulation of the soundproof wall. Therefore, in order to enhance the sound insulation effect of the soundproof wall, it is effective means to provide a high sound absorption function by using a member or structure having a sound absorbing force on the sound source side of the soundproof wall.

[0005] In practice, soundproofing walls installed to prevent the diffusion of road traffic noise are often provided with some countermeasures for sound absorption processing. For example, a metal plate having a slit or a round hole formed on the surface of a soundproof wall is used, and a sound absorbing structure such as a sound absorbing material, an air layer, and a back plate is provided inside the metal plate. Glass wool or a porous material is used as the sound absorbing material, and weather resistance is also devised so as not to be scattered by the wind or penetrated by rain.

[0006]

Various methods have been devised for forcibly attenuating sound waves by using a member or structure having a sound absorbing power, but the frequency range in which sound can be absorbed is as follows.
Since the characteristics and thickness of the sound absorbing material are limited, no matter what kind of sound absorbing material or method is used, in order to absorb sound up to the low frequency range, the thickness of the sound absorbing material or the structure must be increased. There must be.

However, the thickness and height of soundproof walls constructed along roads and railways are severely restricted for safety, landscape, and structural reasons, and the required thickness and height are required. Cannot be increased to a sufficient size. Therefore, when noise diffusion is to be reduced by the noise barrier, there is a problem that the lower the frequency, the more difficult it is to handle.

The present invention has been made in view of the above problems, and has the same sound absorbing effect as that obtained by using a sound absorbing plate having an apparently double thickness without increasing the thickness of a soundproof wall or the like. It is an object of the present invention to provide an obtained double reflection sound absorbing plate.

[0009]

SUMMARY OF THE INVENTION A first sound wave reflecting mirror for reflecting sound waves incident from the front and converging the sound waves to a focal point,
A second sound wave reflecting mirror for reflecting sound waves focused at the focal point of the sound wave reflecting mirror is provided, and a porous material is provided on a propagation path of the sound wave incident on the first sound wave reflecting mirror.

Further, the shape of the second sound wave reflecting mirror may be the first sound wave reflecting mirror.
Depending on the mode of the focal point focused by the reflection of the sound wave reflecting mirror, the shape is cylindrical or spherical.

[0011]

A description will be given of the traveling path of the sound wave in the double reflection sound absorbing plate according to the present invention. The sound wave which has passed through the slit of the surface plate and entered the porous material travels to the first sound wave reflecting mirror at the rear, and the first sound wave reflecting mirror. The sound wave reflected by the sound wave reflecting mirror surface advances to the focal point of the first sound wave reflecting mirror where the second sound wave reflecting mirror is installed, and is reflected again by the second sound wave reflecting mirror surface, but is reflected by the second sound wave reflecting mirror surface Returns to the first sound wave reflecting mirror surface, is reflected once again, and returns to the initial position where the sound wave enters the porous material.

According to the present invention, the first and second two paths, the reflected sound wave being reflected by the reflecting mirror, returning to the point where the sound wave has entered and returning to the point where the sound wave has entered, are returned. By using the sound wave reflecting mirror, the sound wave traveling in the first sound wave reflecting mirror is double-reflected. By doing so, the same effect can be obtained as when the propagation distance of the sound wave within a certain thickness is doubled and the thickness is doubled.

Further, the sound absorption principle of the double reflection sound absorbing plate according to the present invention mainly focuses on reducing the propagation energy of sound waves due to sound wave interference, and efficiently consumes propagation energy as sound waves. is there. First, the reduction of the wave energy of the sound wave due to the sound wave interference will be described.
In order to reduce sound by sound wave interference, the original sound wave and the sound wave of opposite phase and the same sound pressure are merged to make sound wave interference. In the case where the traveling directions of both the sound waves and the sound wave are different from each other, at the confluence, the interference effect of both sound waves is recognized, but the effect of reducing the energy as the wave due to the sound wave interference is not necessarily sufficient. Can not get. This is because the propagation of the sound wave is dependent on the vector as a wave, the frequency and the amplitude are equal, have an opposite phase relationship, and are emitted in a direction in which the propagation direction of the wave front of the sound wave coincides. The energy of the two sound waves as the wave of the two sound waves is significantly reduced due to the interference, and the propagation of the sound waves cannot be continued.

In the double reflection sound absorbing plate according to the present invention, as described above, the incident wave and the reflected wave travel in the same path in opposite directions, respectively. Depending on the size, there is a position where interference occurs in a reverse phase relationship. On the other hand, the directionality of the vibration of the air particles of both sound waves passing through the porous material is such that when the air particles pass through the porous material having a low density and a very small transmission loss, the air particles are multiply irregularly reflected. The directionality of the vibration is gradually weakened, and at each position in the path, the vibration is converted into a vibration having a random direction and propagated. Therefore, at a position where both sound waves interfere with each other in a reversed-phase relationship, the direction of the vibration of the air particles of the sound waves will merge in a random state, and the direction of the vibration of the air particles of the sound waves will substantially match. Since the waves interfere with each other, the wave energy of both sound waves is efficiently reduced.

According to the double reflection sound absorbing plate of the present invention, by using two reflecting mirrors, without increasing the thickness,
The frequency band of sound absorption determined by the thickness of the sound absorbing plate,
It will be possible to expand one octave in the lower direction.

[0016]

【Example】

Embodiment 1 An embodiment of the double reflection sound absorbing plate of the present invention will be described with reference to FIGS. 1, 2, 3, and 4. FIG. FIG. 1 is a sectional view of a double reflection sound absorbing plate according to the present invention, FIG. 2 is a perspective view of the double reflection sound absorbing plate, FIG. 3 is a diagram showing the shape of the first sound wave reflecting mirror 3, and FIG.
FIG. 4 is a view showing the shape of the second sound wave reflecting mirror 4. In FIG. 1, 1 is a surface plate, 2 is a porous material, 3 is a first sound wave reflecting mirror, 4 is a second sound wave reflecting mirror, and 5 is a back plate. Also, O
Is a vertex of the first sound wave reflecting mirror 3, P is a point on the first sound wave reflecting mirror 3, Q is a point on a slit provided on the surface plate 1, R is a point on the second sound wave reflecting mirror 4, and S is a point on the second sound wave reflecting mirror 4. The noise source, F, is the focal point of the first sound wave reflecting mirror 3 and the second sound wave reflecting mirror 4, D is the focal point F of the first and second sound wave reflecting mirrors 3, 4, and the vertex O of the first sound wave reflecting mirror 3. It is assumed that the front surface plate 1 is on the surface including the focal point F, and the back surface plate 5 is on the surface in contact with the vertex O.
The surface plate 1 is provided with a slit-shaped opening. The porous material 2 is a porous acoustic material having a small density and a small transmission loss. As shown in FIG. 3, the first sound wave reflecting mirror 3 is a sound wave reflecting mirror in which a rectangular flat plate is bent into a U-shape to form a paraboloid having a focal point, and the second sound wave reflecting mirror 4 is as shown in FIG. It is a shape of a part of a cylinder obtained by dividing a cylinder vertically, and is a sound wave reflecting mirror for reflecting the sound wave reflected by the first sound wave reflecting mirror 3 again. The axis is attached at a position corresponding to the axis connecting the focal point F of the first sound wave reflecting mirror 3, and the reflection surface may use either side of the unevenness. The back plate 5 is a back surface of a housing for accommodating the double reflection sound absorbing plate according to the present invention, and may be made of the same member integrated with the first sound wave reflecting mirror 3.

The operation will be described below with reference to the sectional view shown in FIG. The sound wave radiated from the front noise source S is assumed to be perpendicularly incident on the surface plate 1. Surface plate 1
The sound wave incident on the point Q on the slit of FIG.
, Is reflected at a point P on the first sound wave reflecting mirror 3, passes through the porous material 2 again, and proceeds toward the focal point F of the first sound wave reflecting mirror 3. The sound wave traveling toward the focal point F of the first sound wave reflecting mirror 3 is reflected at a point R on the second sound wave reflecting mirror 4, but the reflected sound wave follows the path of the traveling sound wave in the opposite direction. In the direction of the point Q on the slit of the surface plate 1 after passing through the porous material 2 and being reflected again at a point P on the first sound wave reflecting mirror 3, passing through the porous material 2 and returning to Heading. That is, the first and third reflections are reflected at a point P on the first sound wave reflecting mirror 3, and the second reflection is reflected at a point R on the second sound wave reflecting mirror 4. A total of three reflections are performed. Will be repeated.

Here, a point P on the first sound wave reflecting mirror 3, a point Q on the slit of the surface plate 1, a point R on the second sound wave reflecting mirror 4, the first sound wave reflecting mirror 3, and the second sound wave reflection. The relationship between the focal point F of the mirror 4 and the distance D between the focal point F of the first and second sound wave reflecting mirrors 3 and 4 and the vertex O of the first sound wave reflecting mirror 3 is represented by a point P
Is a point moving on the paraboloid, so that the relationship of QP + PF = 2D holds. Therefore, the total distance of the path through which the sound wave that has entered the point Q on the slit of the surface plate 1 before returning to the point Q is 2D + 2r ≒ 2D (2D≫2r), where RF = r. The propagation distance of the sound wave until the sound wave incident on the point Q on the slit of the surface plate 1 returns to the point Q again is the first and second propagation distances.
The focal point F of the sound wave reflecting mirrors 3 and 4 and the vertex O of the first sound wave reflecting mirror 3
, That is, twice the distance D between the front plate 1 and the back plate 5.

The sound absorption characteristics when the porous material 2 and the first sound wave reflecting mirror 3 are in close contact with each other are as follows when the distance of sound wave passing through the porous material 2 is 2D (≒ λ / 4). Although there is a difference depending on the material of the porous material 2, a sound wave having a wavelength of a sound wave smaller than 8D (） λ) and having a higher frequency exhibits a high sound absorption characteristic in which the sound absorption coefficient with respect to the frequency is maintained at a substantially constant value. Therefore, doubling the path of the sound wave passing through the porous material 2 means that the range of the sound absorption characteristics is extended to the lower frequency side where the wavelength of the sound wave is long by the expanded amount. Thus, the sound absorbing effect as a sound absorbing plate is greatly improved.

Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. 5, 6, and 7. FIG. FIG. 5 is a perspective view of Embodiment 2 of the double sound wave reflecting plate according to the present invention, FIG. 6 is a diagram showing the first sound wave reflecting mirror 3, and FIG.
FIG. 2 is a diagram showing a second sound wave reflecting mirror 4, and portions common to FIG. 1 are denoted by the same reference numerals. FIG. 6 shows the first sound wave reflecting mirror 3 of Example 1 according to FIG. 1 as a paraboloid of revolution, and FIG. 7 shows the second sound wave reflecting mirror 4 as a hemispherical reflecting mirror. The two sound wave reflecting mirrors 3 and 4 are arranged at positions where the focal point F is shared by one point. The operation of each unit is the same as that of the first embodiment.

Third Embodiment A third embodiment according to the present invention will be described with reference to FIG. FIG.
FIG. 5 is a perspective view of a third embodiment of the double sound wave reflecting plate according to the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals. FIG. 8 shows a porous material 2 made of a porous concrete member having a small density and a small transmission loss, and a first sound wave reflecting mirror 3 made of a concrete member having a sound insulating property and a high reflectance.
And a second sound wave reflecting mirror 4 made of a metal pipe using a convex-side reflecting surface, and has a shape like a concrete block as a whole, and each part is joined. A face plate 1 and a porous material 2, and
The first sound wave reflecting mirror 3 and the back plate 5 are made of the same member integrated with each other, and the operation of each part is the same as that of the first embodiment.

[0022]

According to the present invention, the same sound absorbing effect as when a sound absorbing plate having a thickness twice as large as the thickness is used can be obtained, so that the frequency band on the low frequency side of the noise to be absorbed can be increased by one octave. It can be spread out and becomes highly practical. Therefore, the weight and volume of the sound absorbing plate members required for obtaining the same effect can be greatly reduced, and the economic effect obtained therefor is very large.

Further, the double-reflection sound-absorbing plate according to the present invention provides a sound absorbing function and performance which cannot be obtained by the conventional sound absorbing method. It is also effective when used as a noise reduction measure for noise sources, such as sound absorbing block walls, inner walls of various silencers, and partitions for preventing the diffusion of mechanical noise.

In addition, the present invention can also be applied to reduce noise on walls that reflect sound waves, such as ceilings and walls in factories, inner walls of tunnels, and outer walls of roadside buildings. From the standpoint of environmental conservation, for example, if all of the building structures facing the roads that generate traffic noise have structures that have sound absorbing functions, it is possible to suppress urban noise that is spread over a wide area, and to contaminate with noise. Urban living environment can be reformed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a double reflection sound absorbing plate of the present invention.

FIG. 2 is a perspective view of the first embodiment.

FIG. 3 is a diagram showing a shape of a first sound wave reflecting mirror.

FIG. 4 is a diagram showing a shape of a second sound wave reflecting mirror.

FIG. 5 is a perspective view of a second embodiment.

FIG. 6 is a diagram illustrating a shape of a first sound wave reflecting mirror.

FIG. 7 is a diagram showing a shape of a second sound wave reflecting mirror.

FIG. 8 is a perspective view of a third embodiment.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 surface plate 2 porous material 3 first sound wave reflecting mirror 4 second sound wave reflecting mirror 5 back plate O vertex of first sound wave reflecting mirror P point on first sound wave reflecting mirror Q on slit provided on surface plate 1 Point R Point on second sound wave reflecting mirror S Noise source F Focus of first sound wave reflecting mirror and second sound wave reflecting mirror D Point of focus F of first and second sound wave reflecting mirrors and vertex O of first sound wave reflecting mirror distance

Claims (3)

[Claims] A first sound wave reflecting mirror having a focal point;
A double-reflection sound-absorbing plate, comprising: a second sound-reflecting mirror that reflects sound waves focused at the focal point of the sound-wave reflecting mirror; and a porous material provided on a propagation path of the sound waves incident on the first sound-reflecting mirror. 2. The double reflection sound absorbing plate according to claim 1, wherein said second sound wave reflecting mirror is formed in a cylindrical shape. 3. The double reflection sound absorbing plate according to claim 1, wherein said second sound wave reflecting mirror is spherical.