JP6914004B2 - Noise reduction device - Google Patents

Description

The present invention relates to a noise reduction device that reduces noise propagating in a hollow long body such as a duct or a tunnel.

In a sound field that propagates one-dimensionally, such as air conditioning noise that propagates through a duct and low-frequency noise that propagates inside a tunnel, by arranging an acoustic tube on the wall surface of the duct, it is downstream from that, that is, the noise outlet. Methods for reducing noise propagating to the side have been proposed in Patent Document 1 and Patent Document 2.

In the methods described in Patent Document 1 and Patent Document 2, the noise reduction effect can be obtained at a frequency at which the length of the acoustic tube is equal to 1/4 of the wavelength and at an odd multiple frequency thereof.
Japanese Patent No. 3831263 Japanese Patent No. 5454369

According to the technique described in Patent Document 1, when it is desired to obtain a noise reduction effect for low frequency noise, that is, noise with a long wavelength, an acoustic tube having a long tube length is required, and the noise reduction device becomes large. There was a problem.

Therefore, in Patent Document 2, an attempt has been made to reduce the size of the device by bending a long acoustic tube, but this causes a problem that the structure becomes complicated and the types and numbers of constituent members increase. It becomes. It should be noted that such a problem becomes particularly remarkable in a device in which acoustic tubes of different lengths are combined in order to obtain a noise reduction effect in a wide frequency range.

According to the noise reduction devices described in Patent Document 1 and Patent Document 2, many partition plates are required to form a large number of acoustic tubes having a rectangular cross section, which also complicates the structure and increases the weight of the entire device. Is inviting. As described above, the noise reduction devices described in Patent Document 1 and Patent Document 2 have various problems such as a complicated structure, a large number of types and numbers of constituent members, an increase in weight of the device, and an increase in manufacturing and assembly costs.

The present invention solves the above-mentioned problems, and the noise reduction device according to the present invention is a noise reduction device that reduces noise propagating in a hollow long body, and has a slit portion and one in the slit portion. Noise reduction structures having a cavity that is provided so as to correspond one-to-one and is sealed behind are arranged in pairs on the opposite wall surfaces of the hollow elongated body, and the volume of the space of each cavity is the same. der is, the on both sides of the slit portion partition wall is disposed, said noise reducing structure, the a box-shaped outer shell member one side is open surface, and two L-shaped member, the partition plate member Therefore, the two L-shaped members are characterized in that they have different dimensions from each other.

Further, the noise reduction device according to the present invention is characterized in that the noise reduction structure has an air layer.

The noise reduction device according to the present invention has a structure in which noise reduction structures having slit portions having an acoustic impedance ratio of 0 are arranged in pairs on opposite wall surfaces of the hollow elongated body. According to the noise reduction device according to the present invention, it is possible to reduce the types and numbers of constituent members, simplify the structure, reduce the size and weight of the device, and suppress manufacturing and assembly costs. It will be possible.

It is a figure explaining the principle of the noise reduction apparatus which concerns on embodiment of this invention. It is a figure explaining the noise reduction structure 10 used for the noise reduction apparatus 1 which concerns on 1st Embodiment of this invention. It is a figure which shows the application example to the hollow long body 100 of the noise reduction apparatus 1 which concerns on 1st Embodiment of this invention. It is a figure explaining the manufacturing process example of the noise reduction structure 10 used for the noise reduction apparatus 1 which concerns on 1st Embodiment of this invention. It is a figure explaining the noise reduction structure 10 used for the noise reduction apparatus 1 which concerns on 2nd Embodiment of this invention. It is a horizontal sectional view when the noise reduction apparatus 1 which concerns on 3rd Embodiment of this invention is applied to a hollow elongated body 100. It is a horizontal sectional view when the noise reduction apparatus 1 which concerns on 4th Embodiment of this invention is applied to a hollow elongated body 100. It is a figure which shows the numerical analysis target. It is a figure which shows the result of the numerical analysis. It is a figure explaining the noise reduction structure 10 used for the noise reduction apparatus 1 which concerns on 5th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the principle of the noise reduction method will be described. FIG. 1 is a diagram for explaining the principle of the noise reduction device according to the embodiment of the present invention.

When noise propagates inside a pipeline such as a duct or tunnel (hereinafter, such a pipeline is referred to as "hollow elongated body 100"), the dimensional cross section of the hollow elongated body 100 is less than half of the wavelength of noise. In the case of, the noise propagates one-dimensionally in the pipeline as a plane wave.

FIG. 1A is a perspective view of the hollow elongated body 100. Hereinafter, in the hollow elongated body 100 according to the embodiment in the present specification, a noise source exists on the upstream side, and noise from the noise source is propagated to the downstream side as an example. Further, although the hollow elongated body 100 will be described on the premise that it is installed in the horizontal direction, the installation method of the hollow elongated body 100 is not limited to such an example.

In this hollow elongated body 100, the four wall surfaces forming the hollow elongated body 100 on the upstream side are assumed to be normal wall surfaces, and the two wall surfaces facing each other in the horizontal direction on the downstream side from the dotted line in the perspective view are , It is assumed that it is in an acoustically "soft" state. FIG. 1 (B) is a cross-sectional view of the hollow elongated body 100 of FIG. 1 (A) cut in the horizontal direction.

As shown in FIG. 1, when the wall surfaces facing each other inside the hollow elongated body 100 are acoustically "soft", that is, when the acoustic impedance ratio Z on the surface of the wall surface is 0, the noise propagated from the upstream side. Is known to be reflected upstream and not propagate downstream.

In the present embodiment, the description is based on an example in which two opposing wall surfaces having an acoustic impedance ratio Z on the surface facing each other in the horizontal direction, but the acoustic impedance ratio Z on the surface is 0. The two facing wall surfaces may face each other in the vertical direction.

The existing technology (the technology described in Patent Document 1 and Patent Document 2) has a frequency at which the tube length of the acoustic tube is equal to 1/4 wavelength and an odd multiple frequency thereof, and the acoustic impedance ratio Z at the tube mouth of the acoustic tube is It uses the fact that it becomes 0.

The noise reduction device 1 according to the present invention utilizes a noise reduction structure 10 in which a resonance phenomenon occurs due to a slit structure having a cavity sealed behind as shown in FIG. FIG. 2A is a perspective view of the noise reduction structure 10. 2 (B) is a cross-sectional view of the noise reduction structure 10 of FIG. 2 (A) cut in the horizontal direction.

As shown in FIG. 2, the noise reduction structure 10 used in the noise reduction device 1 according to the present invention is arranged on both sides of a slit portion 50 extending in the vertical direction and the slit portion 50, and is inside the noise reduction structure 10. It is characterized by having a partition wall portion 60 extending to the surface. Here, each dimension of the noise reduction structure 10 functioning as a resonator is represented by a symbol shown in FIG. 2. When each dimension of the noise reduction structure 10 is sufficiently small with respect to the wavelength, the acoustic impedance ratio Z in the slit portion 50 Can be obtained by the following equation (1).

However, f is the frequency of noise, c is the speed of sound, and ρ is the density of the medium (air). Further, V _n is the volume of the space surrounded by the slit portion 50 and the partition wall portion 60 other than the shaded portion in FIG. 2B, and is calculated by the following equation (2) in consideration of end correction. .. The second term in [] in the equation (2) is a term related to end correction. Further, the space in the shaded area in FIG. 2B corresponds to the air layer of the noise reduction structure 10 that functions as a resonator.

Further, V is the volume of the cavity of the noise reduction structure 10 (volume of the air layer), and is calculated by the following equation (3).

Further, S is the area of the slit portion 50 (slit opening) and is calculated by the following equation (4).

The first term r on the right side of the equation (1) is an acoustic resistance such as friction generated between the surface of the partition wall 60 of the noise reduction structure 10 functioning as a resonator and the air. When the partition wall 60 is made of a material having a smooth surface such as metal, the acoustic resistance r becomes an extremely small value, and the acoustic impedance ratio Z at the slit portion 50 opening becomes almost 0 at the resonance frequency f satisfying the following equation.

As shown in FIG. 3, when the two noise reduction structures 10 functioning as such resonators are arranged to face each other along the inner wall of the hollow elongated body 100, the slit slit portions facing each other at the above frequency f Is acoustically "soft", and the noise of frequency f propagating from the upstream side is reflected to the upstream side and does not propagate to the downstream side.

FIG. 3 is a diagram showing an example of application of the noise reduction device 1 according to the first embodiment of the present invention to the hollow elongated body 100. FIG. 3A is a perspective view of the noise reducing device 1 and the hollow elongated body 100, and is a cross-sectional view of the noise reducing device 1 and the hollow elongated body 100 of FIG. 3A as viewed by cutting them in the horizontal direction. ..

Next, the manufacturing process of the noise reduction structure 10 constituting the noise reduction device 1 will be described. FIG. 4 is a diagram illustrating an example of a manufacturing process of the noise reduction structure 10 used in the noise reduction device 1 according to the first embodiment of the present invention.

The outer shell member 20 is a rectangular parallelepiped-shaped box-shaped member in which one of the six surfaces is an opening surface 25. The L-shaped member 30 is a member having an L-shaped cross section and having two surfaces orthogonal to each other.

As shown in FIG. 4, the noise reduction structure 10 can be manufactured by attaching two L-shaped members 30 as described above to the opening surface 25 of the outer shell member 20.

The distance between the two L-shaped members 30 attached to the opening surface 25 of the outer shell member 20 is the slit portion 50. Further, one of the two surfaces of the L-shaped member 30 functions as a partition wall portion 60 of the noise reduction structure 10.

In the method for manufacturing the noise reduction structure 10 as described above, by preparing the outer shell member 20L type member 30 having various dimensions in advance, the noise reduction device 1 capable of easily changing the frequency to be reduced is configured. It becomes possible to do.

As described above, in the noise reduction device 1 according to the present invention, the noise reduction structure 10 having the slit portion 50 having an acoustic impedance ratio of 0 is arranged in pairs on the facing wall surfaces of the hollow elongated body 100. Since it has a structure, according to the noise reduction device 1 according to the present invention, the types and number of constituent members can be reduced, the structure can be simplified, the device can be downsized, and the weight can be reduced. , Manufacturing and assembly costs can be suppressed.

Next, other embodiments of the present invention will be described. The noise reduction device 1 according to the first embodiment described so far exhibits a noise reduction effect at the resonance frequency f determined by the equation (5). The resonance frequency f can be adjusted to the frequency characteristics of noise by adjusting the dimensions W, D, H, a, and l shown in FIG.

However, when the target noise to be reduced by the noise reduction device 1 has a plurality of peak frequencies in the frequency characteristics or has frequency components in a wide band, the noise reduction structure 10 having different resonance frequencies is used. Need to be combined.

Therefore, in the noise reduction device 1 according to the second embodiment of the present invention, the device having a plurality of resonance frequencies is composed of simple and few members. More specifically
In the noise reduction device 1 according to the second embodiment, the noise reduction structure 10 has a rectangular parallelepiped outer shell member 20 (similar to that described above) having one open surface and a single plate-shaped partition plate member. It is composed of 40 and an L-shaped member 30 having different dimensions (similar to that described above).

FIG. 5 is a diagram illustrating a noise reduction structure 10 used in the noise reduction device 1 according to the second embodiment of the present invention.

FIG. 5A is an exploded perspective view of the noise reduction device 1 according to the second embodiment. Further, FIG. 5B is a perspective view of the noise reduction device 1 according to the second embodiment. Further, FIG. 5C is a cross-sectional view of the hollow elongated body 100 to which the noise reduction device 1 is attached according to the second embodiment, as viewed by cutting in the horizontal direction.

As shown in FIGS. 5A and 5B, by attaching two L-shaped members 30 as described above and one partition plate member 40 to the opening surface 25 of the outer shell member 20. , It is possible to manufacture the noise reduction structure 10. In this case, the partition plate member 40 also functions as a partition wall portion 60.

By combining the outer shell member 20, the L-shaped member 30, and the partition plate member 40 as shown in FIG. 5, two slit resonators having space A and space B are configured in one external noise reduction structure 10. can do. In each resonator, _{the acoustic impedance ratio Z of the slit portion 50 becomes almost 0 at the resonance frequencies f 1} and f ₂ , and these are opposed to the wall surface of the hollow elongated body 100 as shown in FIG. 5 (C). By arranging it, the noise reduction effect is exhibited for multiple frequencies.

In the noise reduction device 1 according to the second embodiment as described above, if the position of the partition plate member 40 and the dimensions of the L-shaped member 30 are changed, various outer shell members 20 and the partition plate member 40 having the same dimensions can be used. The noise reduction structure 10 having a resonance frequency can be configured.

FIG. 6 is a horizontal cross-sectional view when the noise reduction device 1 according to the third embodiment of the present invention is applied to the hollow elongated body 100. As shown in FIG. 6, by increasing the number of the partition plate member 40 and the L-shaped member 30, three slit resonators having space A, space B, and space C can be formed, and one outer shell member 20 can be formed. It is possible to construct a noise reduction structure 10 having three or more different resonance frequencies in the structure. In this case, the partition plate member 40 also functions as a partition wall portion 60.

Further, FIG. 7 is a horizontal cross-sectional view when the noise reduction device 1 according to the fourth embodiment of the present invention is applied to the hollow elongated body 100.

In the noise reduction apparatus 1 according to the fourth embodiment of FIG. 7, the noise reducing structures 10 two resonators consisting of the space A and the space C is separated by the partition plate member 40 of the two spaced intervals a _t It has a structure. In this case, the slit between the two resonators is a slit 50 having no air layer behind it. In this case, the partition plate member 40 also functions as a partition wall portion 60.

If such a noise reducing structure 10 and face each other along the inner wall of the hollow elongated body 100 with respect to the frequency interval a _t the cross-sectional dimensions of the hollow elongated body 100 and the partition plate member 40 is equal to or less than a half wavelength The slit portion 50 having no air layer behind it functions as an acoustic tube (space B).

In this case, the dimension D of the outer shell member 20 corresponds to the pipe length of the acoustic tube, in the frequency f _t and its odd multiples of a frequency a quarter of the wavelength is equal to D, the acoustic impedance ratio of the slit portion 50 of the acoustic tube Z becomes 0 and the noise reduction effect is exhibited.

In general, the above _{ft has a frequency higher than the resonance frequency f 1} or f ₂ of the slit resonator (space A and space C in FIG. 6), so that the structure is a combination of the slit resonator and the acoustic tube as shown in FIG. The noise reduction device 1 based on the noise reduction structure 10 can exhibit a noise reduction effect over a wide range of frequencies.

Incidentally, Again, spacing a _t the cross-sectional dimensions and the partition plate of the conduit is for frequencies equal to or less than the half wavelength, the slit having no air layer behind serves as an acoustic tube. The prior art described in Patent Documents 1 and 2 required a large number of dividers to form an acoustic "tube" with a rectangular cross section. On the other hand, in the present invention, these partition plates are unnecessary.
[Example]
In FIG. 6, each dimension of the resonator 1 (space A) is H = 4 m, D = 1.5 m, W = 1.5 m, a = 0.5 m, l = 1 m, and each of the resonator 2 (space C). Assuming that the dimensions are H = 4 m, D = 1.5 m, W = 1 m, a = 0.5 m, l = 0.1 m, the resonance frequency is about 20 Hz for the resonator 1 and about 30 Hz for the resonator 2, respectively. The acoustic impedance ratio Z becomes almost 0 at the slit opening 50 of.

Further, the spacing between the resonator 1 and 2 as a _t = 0.5 m, the slit opening 50 of the acoustic pipe having no cavity behind (space B) is from D = 1.5 m, about 57Hz and odd At double the frequency, the acoustic impedance ratio Z becomes almost 0 at the slit opening 50. (Assuming a speed of sound of 340 m / sec)
Such a noise reduction device is effective at 57 Hz, 30 Hz, and 20 Hz, but in order to be effective at the same frequency in the prior art, the pipe lengths are about 1.5 m, 2.8 m, and 4.3 m, respectively. You will need a tube. For example, even if a long acoustic tube is bent as in the invention described in Patent Document 2, it is inevitable that the device will be complicated.

As described above, the noise reduction device according to the present invention has a structure in which noise reduction structures having slit portions having an acoustic impedance ratio of 0 are arranged in pairs on the facing wall surfaces of the hollow elongated body. According to the noise reduction device according to the present invention, it is possible to reduce the types and numbers of constituent members, simplify the structure, reduce the size and weight of the device, and suppress manufacturing and assembly costs. It becomes possible.

Since the effect of the noise reduction device 1 according to the present invention has been confirmed by numerical analysis, the results are shown below. FIG. 8 is a diagram showing a numerical analysis target, FIG. 8 (A) is a comparison in which a hollow elongated body 100 is arranged, and FIG. 8 (B) is a comparison in which a noise reduction structure 10 is arranged on one side of the hollow elongated body 100. Example 1 and FIG. 8 (C) show Comparative Example 2 in which two noise reduction structures 10 are provided on one side of the hollow elongated body 100, and FIG. 8 (D) shows both sides of the hollow elongated body 100. It is a figure which shows the noise reduction apparatus 1 which concerns on this invention which arranged the noise reduction structure 10 facing each other.

The two-dimensional boundary element method was used as the numerical analysis method. Further, the analysis target is an infinite length duct (hollow long body 100) having a width of 200 mm, a plane sound wave is incident from the upstream side as shown in FIG. 8, and a virtual surface shown by a broken line in the figure is directed toward the downstream side. The sound energy passing through was calculated.

Under the condition that the noise reduction structure 10 as the noise reduction device is arranged as shown in FIGS. 8 (B) to 8 (D), the condition is that the noise reduction structure 10 shown in FIG. 8 (A) is not installed. The amount of reduction of sound energy passing through the virtual surface in the downstream direction, that is, the installation effect of the noise reduction structure 10 was obtained.

The dimensions of the noise reduction structure 10 which is a noise reduction device are W = 150, D = 100, a = 50, and l = 40 (or more unit mm). For two-dimensional analysis, the dimension in the depth direction in the figure was set to H = ∞.

As a comparison target of the noise reduction device 1 according to the present invention in FIG. 8 (D), the noise reduction structure 10 arranged on one side is shown in FIG. 8 (B), and the noise reduction structure 10 is placed on one side. The one arranged in parallel is shown in FIG. 8C.

Numerical analysis is performed for pure tones every 1/27 octave, and the sound energy passing through the obtained virtual surface in the downstream direction is averaged by 9 each centering on the 1/3 octave band center frequency to 1 /. The analysis results were taken in the 3-octave band.

Regarding the obtained analysis results, as described above, "one-sided arrangement" (comparative example 1) and "one-sided parallel arrangement" (comparative example 2) are based on the condition of "no noise reduction structure 10" (FIG. 8 (A)). ), The amount of reduction of the acoustic energy passing through the virtual surface in the downstream direction under the condition of "opposite arrangement" (the present invention) was obtained, and the noise reduction structure 10 effect in the 1/3 octave band was obtained.

FIG. 9 is a diagram showing the results of numerical analysis, and shows the effects of the noise reduction structure 10 in the “one-sided arrangement” (Comparative Example 1), the “one-sided parallel arrangement” (Comparative Example 2), and the “opposed arrangement” (the present invention). Shows the frequency characteristics of.

With reference to FIG. 9, it can be confirmed that the noise reduction effect is obtained mainly in the 400 Hz band close to the resonance frequency under any of the arrangement conditions.

Compared with the "one-sided arrangement" (Comparative Example 1) and the "one-sided parallel arrangement" (Comparative Example 2), the "opposed arrangement" (the present invention) greatly improves the effect near the resonance frequency and obtains the effect. The frequency range is expanding on both the high frequency side and the low frequency side.

Further, the "one-sided parallel arrangement" (Comparative Example 2) uses two noise reduction structures 10 as in the "opposite arrangement" (the present invention), but the effect obtained as compared with the "opposite arrangement" (the present invention). Turns out to be small. Further, in the "one-sided parallel arrangement" (Comparative Example 2), the frequency range in which the effect can be obtained is reduced on the low frequency side as compared with the "one-sided arrangement" (Comparative Example 1).

From the above results, it can be confirmed that the noise reduction device 1 according to the present invention is effective as a noise reduction method as compared with other noise reduction structure 10 arrangement methods.

Next, other embodiments of the present invention will be described. FIG. 10 is a diagram illustrating a noise reduction structure 10 used in the noise reduction device 1 according to the fifth embodiment of the present invention. FIG. 10A shows the noise reduction structure 10 used in the noise reduction device 1 according to the embodiment described so far, and FIG. 10B shows the noise reduction used in the noise reduction device 1 according to the present embodiment. The structure 10 is shown. The noise reduction device 1 according to the fifth embodiment is characterized in that the noise reduction structures 10 shown in FIG. 10B are arranged in pairs on the facing wall surfaces of the hollow elongated body 100.

As shown in FIG. 10A, the noise reduction structure 10 of the noise reduction device 1 according to the embodiment described so far is arranged on both sides of the slit portion 50 and is provided with partition walls 60, and these partition walls are provided. 60 had a length of l in the depth direction.

On the other hand, in the present embodiment, the noise reduction structure 10 of the noise reduction device 1 has a structure in which the partition walls 60 on both sides of the slit portion 50 are omitted. The partition wall portion 60 is omitted, but instead, the plate thickness of the front surface of the noise reduction structure 10 including at least the slit portion 50 has a thickness of l.

_{Due to the plate thickness l, V n} described in the first embodiment is generated also in the noise reduction structure 10 used in the present embodiment. As a result, the noise reduction device 1 according to the fifth embodiment in which the noise reduction structure 10 in which the partition wall portion 60 is omitted can also enjoy the same effect as the noise reduction device 1 described so far. Become.

1 ... Noise reduction device 10 ... Noise reduction structure 20 ... Outer shell member 25 ... Opening surface 30 ... L-shaped member 40 ... Partition plate member 50 ... Slit portion 60 ...・ ・ Partition part 100 ・ ・ ・ Hollow long body

Claims (2)

A noise reduction device that reduces noise propagating in a hollow long body.
A noise reduction structure having a slit portion and a cavity provided in a one-to-one correspondence with the slit portion and sealed behind the slit portion.
Wherein arranged in pairs on opposite walls of the hollow elongate member, Ri volume identical der space of each said cavity,
Partitions are arranged on both sides of the slit.
The noise reduction structure comprises a box-shaped outer shell member having an opening surface on one side, two L-shaped members, and a partition plate member.
A noise reduction device characterized in that the two L-shaped members have different dimensions from each other. The noise reduction device according to claim 1, wherein the noise reduction structure has an air layer.

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