JPH1124669A - Sound absorbing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound absorbing structure having excellent sound absorbing performance and manufacturable at a low cost. SOLUTION: A sound absorbing material 2 is adhered onto the sound source side surface of a sound insulating plate 1. The sound absorbing material 2 comprises a number of swollen Helmholtz resonators 20A, 20B which consist of two lines of front and rear resonance cases 21A, 21B for forming respective closed cavities 22 with the sound insulating plate 1 and orifice cases 23A, 23B extended along the sound insulating plate 1 from one side walls of each resonance case 21A, 21B to form respective orifices 23a, 23b. The base end of the orifice 23a, 23b within each orifice case 23A, 23B is allowed to communicate with each cavity 22 within the resonance case 21A, 21B, and the top end is opened to the outside by a cut part 24 punched in the sound absorbing material 2 extending over each orifice case 23A, 23B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound absorbing structure which is used for noise reduction of a vehicle or the like and which resonates and absorbs sound using a Helmholtz resonator.

[0002]

2. Description of the Related Art As a soundproof means for an engine room of a vehicle, for example, a number of Helmholtz resonators are arranged on an upper surface (engine side) of a sound insulating plate (under cover) provided below an engine as a sound source. A sound absorbing structure is adopted. That is, as shown in FIG. 4, the sound absorbing structure has a sound absorbing material 200 attached to a sound source side of a sound insulating plate 100, and an orifice hole is formed at the top of a resonance case 202 formed to protrude from the sound absorbing material 200. A large number of Helmholtz resonators 201 having a structure 203 are provided. Each Helmholtz resonator 201 has an internal cavity 2 of a resonance case 202.
02a has a resonance frequency (sound absorption frequency) corresponding to the length of the air column in the inner periphery of the orifice hole 203. According to Helmholtz's resonance theory, a sound in a specific frequency band is taken in from a sound source and resonance absorption is performed. (See, for example, JP-A-4-225398). In this type of sound absorbing structure, the longer the length L of the orifice hole 203 and the larger the volume V of the cavity 202a, the lower the sound absorbing frequency.

[0003]

However, the following problems are pointed out in the above conventional example. (1) Since the orifice hole 203 is formed at the top of the resonance case 202, its length L is equal to the thickness t of the sound absorbing material 200 at the top (about 1 mm), so that the sound absorption frequency can be freely set. Low degree. (2) Since the orifice hole 203 is formed at the top of the resonance case 202, if a foreign substance (for example, water or dust) enters the resonance case 202, the sound absorption frequency changes due to a change in the volume V. If a gap G is provided between the resonance case 202 and the sound insulating plate 100 in order to discharge foreign substances, the sound absorbing performance is reduced. (3) The resonance case 202 is formed by a vacuum forming method, and the orifice hole 203 is formed by punching after the formation of the resonance case 202. However, there is a height difference h between the respective orifice holes 203 due to the difference in the volume V of each resonance case 202. Therefore, high dimensional accuracy is required for the punching device, and the manufacturing cost increases.

Accordingly, a main technical problem to be solved by the present invention is to provide a sound absorbing structure which has excellent sound absorbing performance and can be manufactured at low cost.

[0005]

As a means for effectively solving the above-mentioned technical problems, a sound absorbing structure according to the present invention comprises a sound-insulating plate having a hermetic seal between the sound-insulating plate and the sound-insulating plate. And a plurality of Helmholtz resonators extending from one side of the resonance case along the sound insulating plate and forming an orifice communicating with the cavity. Is attached,
Each orifice of the plurality of Helmholtz resonators is opened to the outside by a cut portion straddling each of the orifice cases. That is, after the plurality of Helmholtz resonators are protruded from the sound absorbing material, the orifices of the plurality of Helmholtz resonators are opened to the outside by forming cut portions extending over the respective orifice cases. Since the length of the orifice in each Helmholtz resonator is determined by the distance from the resonance case to the cut portion, the orifice length varies depending on the position where the resonance case is formed and the position where the cut portion is formed, and an arbitrary sound absorption frequency can be set.

Further, unlike the one in which the orifice is opened at the top of the resonance case, foreign matters such as water and dust hardly enter the resonance case, so that the sound absorption frequency does not change due to the change in the cavity volume of the resonance case. . In this case, by inclining the sound insulating plate so that the open end of the orifice of each Helmholtz resonator faces the lower side, it is possible to reliably prevent foreign matter from entering the resonance case.

[0007]

FIG. 1 shows a preferred embodiment of a sound absorbing structure according to the present invention. In FIG. 1, reference numeral 1 denotes a sound insulating plate made of a synthetic resin material, and reference numeral 2 denotes a sound absorbing material attached to a surface of the sound insulating plate 1 on the sound source side. The sound absorbing material 2 is made of a synthetic resin plate, and has two rows of front and rear resonance cases 21A and 21B defining a closed cavity 22 between the sound absorption board 1 and the resonance cases 21A and 21B.
A large number of Helmholtz resonators 20A and 20B are formed by extending from one side wall 21B along the sound insulating plate 1 and comprising orifice cases 23A and 23B forming orifices 23a and 23b between the sound insulating plate 1 and the sound insulating plate 1, respectively. ing. The base ends of the orifices 23a and 23b inside the orifice cases 23A and 23B are connected to the resonance cases 21A and 2B.
The orifice 1B communicates with each cavity 22, and the tip is open to the outside by a cut portion 24 formed in the sound absorbing material 2 by straddling the orifice cases 23A and 23B.

More specifically, the orifice cases 23A and 23B are parallel to each other, extend in a direction perpendicular to the direction in which the resonance cases 21A and 21B are arranged, and extend from the resonance case 21A in the rear row. The orifice case 23A is a small-volume resonance case 21B in the front row,
It passes between 21B. The rear case 21A has a larger volume than the front case 21B, and the orifice case 23A extending from the rear case 21A has an orifice case 2 extending from the front case 21B.
The orifice cross-sectional area is larger than 3B.

On the other hand, the cutting portion 24 is provided in the orifice case 2
Each of the orifice cases 23A and 23B is formed in a long hole shape extending in a direction perpendicular to the extension direction of the 3A and 23B, that is, in the same direction as the row of the resonance cases 21A and 21B. It is cut to be flush. For this reason, the orifice 23a in the orifice case 23A extending from the large-volume resonance case 21A in the rear row is long, and the small-volume resonance case 21B in the front row is long.
Orifice 23 in orifice case 23B extending from
b is short.

As described above, according to the Helmholtz resonance theory, the resonance frequency (sound absorption frequency) of the Helmholtz resonator increases as the length of the orifice increases and the cavity 2 increases.
2 is lower as the volume is larger. Therefore, in the sound absorbing structure of the embodiment shown in FIG. 1, the sound absorbing frequency of the Helmholtz resonator 20A having the large-volume resonance case 21A and the long orifice 23a is relatively low, and the small-volume resonance case 21B and the short orifice 23b are provided. The sound absorption frequency of the Helmholtz resonator 20B is set relatively high, thereby setting a wide frequency range in which sound can be absorbed. Moreover, the length of the orifices 23a and 23b is sufficiently larger than the thickness of the sound absorbing material 2 and the mass of the air column formed thereby is large, so that the orifices 23a and 23b have excellent sound absorbing performance against incident sound.

As shown in FIG. 2, the sound-absorbing material 2 is formed by, for example, pressing a heat-softened synthetic resin plate against a female mold by vacuum forming.
And after forming the orifice cases 23A and 23B,
In FIG. 2, a portion indicated by a chain line is punched out by a punching device to form a cut portion 24, thereby cutting off the end portions of the orifice cases 23A and 23B extending parallel to each other. Therefore, the resonance cases 21 having different heights are provided.
The need for a punching device having an elaborate punching die as in the case of punching an orifice hole at the tops of A and 21B is eliminated, and the tip of each orifice case 23A and 23B is cut and opened at one time by forming one cut portion 24. You.

The sound absorbing material 2 is provided in the resonance cases 21A, 2A.
1B and the flat plate portion 25 around the orifice cases 23A and 23B are integrally joined to the sound insulating plate 1 by means such as ultrasonic welding or bonding. Thus, the Helmholtz resonator 2 including the cavity 22 defined by the resonance cases 21A and 21B between the sound insulating plate 1 and the orifices 23a and 23b extending from the cavity 22.
0A and 20B are formed.

According to the illustrated embodiment, the resonance case 21
Since A and 21B are opened laterally through orifices 23a and 23b, the structure is such that foreign substances such as water and dust hardly enter the resonance cases 21A and 21B. In this case, as shown in FIG. 3, if the sound insulating plate 1 is inclined by the required angle θ so that the open ends of the orifices 23a and 23b of the Helmholtz resonators 20A and 20B face the lower side,
Foreign matter is less likely to enter the resonance cases 21A and 21B, and the foreign matter that has entered is reliably discharged.
Does not change due to accumulation of foreign matter, and the initial sound absorbing performance is maintained. Accordingly, there is no need to provide a gap between the flat plate portion 25 of the sound absorbing material 2 and the sound insulating plate 1 in order to discharge the foreign matter that has entered, and the resonance cases 21A and 21B are hermetically sealed, thereby improving the sound absorbing performance. be able to.

In FIG. 1, the resonance case 21A,
21A are shown as having substantially the same volume as each other, and the resonance cases 21B and 21B in the front row are also shown as having the same volume. However, these are different volumes and are used as Helmholtz resonators 20A and 20A or 20B and 20B.
Different sound absorption frequencies may be set for the 20Bs. In addition, since the resonance cases 21A, 21A or the resonance cases 21B, 21B are not arranged linearly, different sound absorption frequencies are set by changing the lengths of the orifice cases 23A, 23A or 23B, 23B. You can also.

Further, one cutting portion 2 as shown in FIG.
The plurality of Helmholtz resonators 20A, 20B having the orifices 23a, 23b opened by 4 are grouped into one group, and such Helmholtz resonators 20A, 20B are arranged in a plurality of regions on the sound insulating plate 1. Different sound absorption frequencies can be set for each case.

[0016]

According to the sound absorbing structure of the present invention, the following effects are realized. (1) Since the length of the orifice can be freely set, the sound absorption frequency of the Helmholtz resonator can be set to a wider frequency range as compared with the conventional structure, and the sound absorption performance can be improved. (2) The volume of the cavity does not change because foreign matter does not easily enter the resonance case, and there is no need to provide a gap between the periphery of the resonance case and the sound insulating plate to improve sound absorption performance. . (3) Since the tip of multiple orifices is opened by punching out a common cut section, it does not require a sophisticated punching device such as when punching out orifice holes at the top of resonance cases with different heights, and is manufactured at low cost can do.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a preferred embodiment of a sound absorbing structure according to the present invention.

FIG. 2 is an explanatory diagram showing a manufacturing process of the sound absorbing structure of the embodiment.

FIG. 3 is an explanatory view showing a sound absorbing plate in the sound absorbing structure of the embodiment, which is inclined such that an open end of an orifice of a Helmholtz resonator faces a lower side.

FIG. 4 is a partial cross-sectional view showing a conventional sound absorbing structure.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sound insulating plate 2 sound absorbing material 20 Helmholtz resonator 21A, 21B resonance case 22 cavity 23A, 23B orifice case 23a, 23b orifice 24 cutting part 25 flat part

Claims (2)

[Claims] 1. A resonance case (21A, 21B) for defining a closed cavity (22) between the sound insulation plate (1) and the sound insulation plate (1) on a sound source side surface of the sound insulation plate (1), and the resonance case (21A). 21A, 21B) extending along one side of the sound insulating plate (1) and communicating with the cavity (22).
3a, 23b) orifice case (23A,
23B) and a plurality of Helmholtz resonators (20A,
20B) is affixed with a raised sound absorbing material (2), and the orifices (23a, 23b) of the plurality of Helmholtz resonators (20A, 20B) are cut across the orifice cases (23A, 23B). A sound absorbing structure characterized by being opened to the outside by a part (24). 2. The sound insulation board (1) according to claim 1, wherein each of the sound insulation plates (1) is provided with a respective Helmholtz resonator (20A, 20A).
B) The sound absorbing structure wherein the open ends of the orifices (23a, 23b) are inclined so as to face the lower side.