JPH08166787A - Production of sound absorbing material - Google Patents

Abstract

PURPOSE: To facilitate fabrication and to make it possible to inexpensively obtain a sound absorbing material by blanking and forming acoustic holes at end walls from the inner side of respective Helmholtz resonators by means of punches arranged on the same plane as each other. CONSTITUTION: A resonator forming plate 2 is so formed that the end walls 21a of respective hollow projecting parts 21 exist on the same plane inclined with a mounting plate 1 at the time of forming this resonator forming plate 2 by a vacuum forming method. A stage for forming the respective acoustic holes 3a at these end walls 21a is executed by placing a flat plate on the surfaces (outer surfaces) on the sound source side of the respective end walls 21a and blanking the holes from the inner side of the respective Helmholtz resonators 3 by means of the punches arranged on the same plane as each other. In such a case, a flat plate consisting of timber or rubber, etc., having adequate hardness is usable as the flat plate and, therefore, the extremely inexpensive formation is possible. Since the end walls 21a of the respective hollow projecting parts 21 form the same plane, irregular rugged shapes in appearance are averted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sound absorbing material which is used as a noise countermeasure for a vehicle or the like and which absorbs sound by resonance with a Helmholtz resonator.

[0002]

2. Description of the Related Art A typical conventional example of this type of sound absorbing material is disclosed in JP-A-4-225398.
That is, as shown in a part of FIG. 5, this sound absorbing material includes a large number of Helmholtz resonators having different air column resonance frequencies due to the resonator forming plate 102 attached to the sound source side surface of the mounting plate 101. 103 are arranged, and each Helmholtz resonator 103 resonantly absorbs air-transmitted sound of a predetermined frequency from a sound source. Further, by covering the resonator forming plate 102 on the sound source side of the Helmholtz resonator 103 with a porous layer made of a sound absorbing material, typically non-woven fabric or open-cell plastic, the sound from the resonator forming plate 102 is suppressed. It reduces reflection and improves sound absorption.

In each Helmholtz resonator 103, a sound source side end wall 102a is provided with an acoustic hole 104 for taking in vibration energy of sound. A vacuum forming method is adopted as an inexpensive method for forming the resonator forming plate 102 having a large number of hollow convex portions corresponding to the respective Helmholtz resonators 103. In this forming method, at the same time as forming, the acoustic wave is formed on the end wall 102a. The holes 104 cannot be formed. Therefore, the acoustic hole 104 is opened in a separate process after the resonator forming plate 102 is formed.

Conventionally, in this type of sound absorbing material, in order to make the air column resonance frequencies inside the Helmholtz resonators 103 different from each other, the end wall 1 on the sound source side is arranged.
The height of 02a is variously changed. Therefore, when the acoustic hole 104 is punched and formed in the end wall 102a in the manufacturing process, as shown in FIG. 6, it corresponds to the height of the end wall 102a of each Helmholtz resonator 103 or the position on the plane. A punching die 105 in which a punch 105a is arranged and a pressing die 106 having a projection 106a that presses each end wall 102a from the inside are used. In order to surely punch out the acoustic hole 104, the punching die 105 and The pressing die 106 is required to have extremely high dimensional tolerance. Therefore, the punching die 105 and the pressing die 1
It is inevitable that the production cost of 06 will be high and the product price will be high.

[0005]

SUMMARY OF THE INVENTION The present invention has been made under the circumstances as described above, and its main technical problem is to facilitate punching of acoustic holes in each Helmholtz resonator. , To provide a sound absorbing material at a low cost.

[0006]

As a means for effectively solving the above technical problems, the present invention is directed to a large number of Helmholtz resonance frequencies which are different from each other by a resonator forming plate attached to the sound source side of a mounting plate. Resonators are defined adjacent to each other,
In the production of a sound absorbing material in which acoustic holes are respectively formed in the sound source side end walls of each Helmholtz resonator, the sound source side end walls of a plurality of Helmholtz resonators adjacent to each other intersect the mounting plate in an inclined state. The holes are formed on the same plane, and the end wall is punched from the inside of the Helmholtz resonator while pressing the end wall from the outside to form an acoustic hole.

[0007]

A plurality of Helmholtz resonators adjacent to each other formed by the resonator forming plates are formed with end walls on the sound source side on the same plane intersecting the mounting plate in an inclined state, thereby adjoining Helmholtz resonators. Have different heights (volumes) from each other, and have different natural frequencies (resonance frequencies) of the air columns inside thereof. Since the respective end walls are on the same plane, it is possible to punch from the inside of each Helmholtz resonator with the punches arranged on the same plane when the acoustic hole is formed here. . A suitable flat plate can be used as a means for pressing the end wall during the punching.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing a part of a sound absorbing material manufactured by the manufacturing method of the present invention.
Is a resonator forming plate attached to the surface of the mounting plate 1 on the sound source side. The resonator forming plate 2 has a large number of hollow convex portions 21 having different sizes.
Each of the sound source side end walls 21a is provided with an acoustic hole 3a, whereby a large number of Helmholtz resonators 3 are defined adjacent to the sound source side surface of the mounting plate 1.

The end wall 21a of each hollow convex portion 21 of the resonator forming plate 2 forming the Helmholtz resonator 3 is indicated by II in FIG.
In the cross section shown in FIG. 2 taken along the line II, they are at the same height, but in the cross section shown in FIG.
Since they are formed on the same plane intersecting with each other in an inclined state, the height of each hollow convex portion 21 is sequentially increased in a certain direction. Further, the bottom areas (widths in the plane direction) of the hollow convex portions 21 are also different from each other. Therefore, each hollow convex portion 21 has a different internal volume, and each Helmholtz resonator 3 defined by the hollow convex portion 21 is defined by the internal volume of the hollow convex portion 21 and the hole diameter (area) and length of the acoustic hole 3a. Since the air column resonance frequencies are different from each other, resonance vibration occurs due to the incidence of a sound of a specific frequency, and the resonance absorption of the sound is performed.

In the production of this sound absorbing material, each hollow convex portion 2 is formed when the resonator forming plate 2 is formed by the vacuum forming method.
Since one end wall 21a is formed so as to be located on the same plane inclined with respect to the mounting plate 1, in the step of forming the acoustic holes 3a in each of the end walls 21a, as shown in FIG. The flat plate 4 is applied to the sound source side surface (outer surface) of each end wall 21a, and punched from the inside of each Helmholtz resonator 3 by the punches 5 arranged on the same plane. That is, it is not necessary to use a pressing die having protrusions corresponding to the uneven shape of the resonator forming plate 2 unlike the conventional case,
Since the flat plate 4 made of wood or rubber having an appropriate hardness can be used, the flat plate 4 can be manufactured at an extremely low cost. Further, since the end walls 21a of the hollow convex portions 21 are flush with each other, the appearance does not have an irregular uneven shape.

FIG. 4 shows a sound absorbing material in which the end wall 21a of the hollow convex portion 21 of the resonator forming plate 2 is formed along a plurality of planes having different inclination directions with respect to the mounting plate 1. That is, in the hollow convex portion group 21A on the left side in the drawing, the height of the end wall 21a of each hollow convex portion 21 is gradually increased toward the left side, and the hollow convex portion group 21B at the center in the drawing is each hollow convex portion 21B. The heights of the end walls 21a of the portions 21 are almost the same, and different air column resonance frequencies are set due to the difference in the bottom areas. The hollow convex portion group 21C on the right side in the drawing is each hollow toward the right side. The height of the end wall 21a of the convex portion 21 is gradually increased. And by doing in this way, arrangement | positioning of the Helmholtz resonator 3 of a predetermined resonance frequency can be set arbitrarily.

[0012]

According to the present invention, in order to form Helmholtz resonators having resonance frequencies different from each other, the end wall on the sound source side is formed on the same plane which intersects with the mounting plate in an inclined state. , While pressing the end wall with an appropriate flat plate from the outside, acoustic holes can be punched from the inside of each Helmholtz resonator in the end wall with punches arranged on the same plane. A punching die is not required, processing becomes easy, and a sound absorbing material can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a part of a sound absorbing material manufactured by a manufacturing method of the present invention.

FIG. 2 is a cross-sectional view showing a part of the sound absorbing material, taken along the line II-II in FIG.

FIG. 3 is a schematic explanatory view showing a step of punching and forming an acoustic hole in an end wall on the sound source side of the Helmholtz resonator in the manufacturing method of the present invention.

FIG. 4 is a cross-sectional view showing a sound-absorbing material manufactured by the manufacturing method of the present invention, in which end walls of hollow convex portions are formed along a plurality of planes having different inclination directions.

FIG. 5 is a sectional view showing a part of a sound absorbing material manufactured by a conventional method.

FIG. 6 is a schematic explanatory view showing a punching process of an acoustic hole by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mounting plate 2 Resonator formation plate 21 Hollow convex part 21A, 21B, 21C Hollow convex part group 21a End wall 3 Helmholtz resonator 3a Acoustic hole 4 Flat plate 5 Punch

Claims (1)

[Claims] 1. A plurality of Helmholtz resonators (3) having different resonance frequencies are defined adjacent to each other by a resonator forming plate (2) attached to the sound source side of the mounting plate (1), and each Helmholtz resonator is defined. End wall (21a) on the sound source side of the resonator (3)
In the production of the sound absorbing material in which the acoustic holes (3a) are opened respectively, the sound source side end walls (21a) of a plurality of Helmholtz resonators (3) adjacent to each other intersect the mounting plate (1) in an inclined state. And the step of forming the acoustic hole (3a) by punching the end wall (21a) from the inside of the Helmholtz resonator (3) while pressing the end wall (21a) from the outside. A method of manufacturing a sound absorbing material, comprising: