JPH0213602A - Expansion signal reversal wave interference type sound arrester - Google Patents

Abstract

PURPOSE:To attenuate the diffracted sound at the side of sound receiving point and enhance the efficiency of a sound insulation wall by causing interference between the sound wave induced from the inlet pipe of a sound arrester mounted on the upper edge of a sound insulation wall and the signal reversal wave generated by this arrester. CONSTITUTION:A sound wave intake passage 1, a sound wave outlet passage 2, and an expansion room 3 connected to them constitute a sound arrester. A sound absorption plate 4 and a backside air layer 5 are provided in the expansion room 3 to prevent the reflected sound, and a perforated plate 8 and slits 9 are used in the sound wave intake passage 1 and the sound wave outlet passage 2. Then, a part F2 of the reflection diffusing wave generated in the expansion room 3 is used as the sound reduction interference wave on the side of sound receiving point 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a soundproofing device that improves the sound reduction effect of a soundproofing wall.

[Conventional technology]

Conventional sound insulation walls achieve a sound reduction effect by changing the height of the wall, and follow the ancient construction method of stacking wall blocks physically.In modern times, they are one of the few that have been left behind by technological innovation. . Sound insulating walls for roads and railways appeared in the 1960s, and sound-absorbing type sound insulating walls with sound-absorbing materials attached to the wall surface to prevent reflected sound came to be used, but they are mechanically based on ancient architecture. It is no wonder that the perforated sound-absorbing board material was used as an outdoor sound-insulating wall, and this has basically continued unchanged to the present day.

The 1960s was a time when road and railway (hereinafter referred to as "road") noise rapidly became a pollution problem, and in order to overcome emergencies, it was unavoidable to use sound insulation walls borrowed from other fields, but 20 years have passed since that time. As time has passed, the installation of soundproof walls on roads has become commonplace, and even today, when large amounts of national funds are being used, the old-fashioned construction methods continue to be used.

In other words, the first generation sound insulation walls continue in the same state as before, and we are in a situation where we must quickly create second generation products, and pave the way for future technological innovation with third and fourth generation products. is placed in

Conventional sound insulation walls are subject to structural limitations because they are limited by the height of the wall, and construction costs also increase as the square of the wall height. The wind pressure acting on the sound insulating wall is transmitted to the support column, and ultimately the support support and its foundation become fixed-end (lower end) moment proportional to the square of the height of the sound insulating wall. As the sound insulation walls become taller, the pillars and foundations need to be bulkier, and in the case of viaducts, there are restrictions on the load capacity of the bridge itself, the height of the sound insulation walls, etc. Additionally, if it becomes necessary to raise the height of the sound insulating wall due to an increase in traffic volume, etc., noise countermeasures may become impossible if there is no allowance in the allowable stress of the bridge body.

Increasing the height of the sound insulation wall not only increases the construction cost, including the construction cost of the bridge itself, in a squared manner, but also causes pressure fatigue problems due to the sound insulation wall in terms of driving safety, and increases sunlight obstruction.

While the first generation sound insulation walls continue to compete based on height, the second generation
This does not mean that there are no signs of generational products emerging. Some of them are still in the trial construction stage, and it will take time to determine their effectiveness and prepare design materials, and it is unclear whether they will be widely put into practical use. Incorporating technological innovation into sound insulating walls has been a great achievement, and only when five or six such products are created and the base of technological innovation expands will true second-generation products be established.

There are two attempts at new sound insulating wall technology, one of which is a delayed wave interference type sound insulating wall (see Japanese Patent Publication No. 1566/1983). This is based on the same principle as the Quinke tube, and as shown in Figure 5, if you strike a tuning fork with the ROM of the tube and change the path difference between AIR and AnB, the sound may be heard strongly or not at all. arise.

When this path difference is half a wavelength, the sound going to the right and the sound going to the left of the Quinke tube interfere at three points so that the sound disappears, and it is a pure tone (sound frequency is constant) and a standing wave (sound waveform is forward). is equal to the one that comes after it).

However, in the case of noise, it is a complex sound that is composed of many pure tones, and even if one pure tone is extracted, the previous waveform and subsequent waveform are not necessarily equal, and the interference observed in this pure tone is impossible for the noise as a whole. For example 50
Even if the path difference is designed to interfere with the sound of 0H2,
Noise 1: It has 100OHz, 250Hz, Al, N, and 300H2 noises, and since these all enter the tube, some of them are amplified, and this type of noise is considered to have no sound reduction effect. Common. This example can be seen in noise calculations for multiple sound sources, where the distances from each sound source to the sound receiving point are all different, and it is the same as installing a delay circuit for sounds of a specific frequency, but the noise from each sound source This is also clear from the fact that interference effects are not taken into account when synthesizing. The premise of noise calculation is that some things are reduced due to interference, while others are amplified, and that, in terms of plus or minus, it is not a problem that should be considered in practice. As shown in Figure 6, this is an attempt to create a sound detour (11) in the middle of the noise propagation, and through this to cause the wave with a half wavelength to interfere with the wave that comes later. The condition for delaying the previous wave and making it interfere with the following wave is that a sound wave favorable for interference must come later, but we do not know if that is the case or not, or what will come later. This is the property of noise having multiple sound sources. In addition, although multiple delay circuits are provided in the invention, since it is not possible to select a circuit for each frequency component of noise, it is the same whether there is one circuit or multiple circuits, and the above-mentioned sound of a certain frequency will interfere. However, there is a phenomenon of amplification when using a different frequency.

Another attempt at a second-generation sound insulating wall is to attach a sound absorbing material to the top of the sound insulating wall (see Japanese Patent Publication No. 51-46969). Physical phenomena have fundamental laws, and if you ignore them and make judgments based only on small-scale experiments in the laboratory, you may make a big mistake, but according to this invention 1, the cause of the sound reduction is due to the noise on the sound insulation wall. Sound waves diffracted at the edges are absorbed by sound absorbing materials (12)
It is estimated that this is absorbed by the gas, and this has been confirmed through experiments. As shown in Fig. 7, a cylindrical sound absorbing material (12) with a diameter of 8.5 crn is installed on the iron plate fence (13) with a height of 177L, and the sound absorption material (12) is 5KH2 and (j 10KI4Z (7)
Experiments are being conducted using . The frequency of noise that is considered a daily problem is 0.2 to 2KH2, and high frequencies are easily attenuated by the diffraction effect of walls, and low-frequency sounds remain after walls are installed, and processing of this low-frequency sound is a troublesome problem. be.

From the acoustic phase law, if we keep the dimension of the length of the object and the dimension of the sound frequency constant, we can obtain the same result,
For example, if the local noise frequency is 500Hz, 5
In order to obtain the same result as the experimental value of KHz in the field, 10
This meant that a wall of 250 Hz would have to be erected, and a cylindrical sound absorber of 85 c1n would have to be installed on top of it, which would require something twice this size to deal with the 250 Hz local sound. 10
A sound insulating wall with a diameter of 85 or 170 m is also abnormally large, and preferably the size of a Kasagi.In addition, on general expressways, the length of the road is more than 20 m,
It is common to install a sound insulating wall with a height of 3 m to 5 m on one or both sides, but the above experiment was conducted with the sound source closest to the wall, and in reality the sound source is far away from the wall.

In addition, in model experiments, there are always things that do not scale down according to the acoustic phase law, so it is necessary to confirm this on a construction scale.

For example, the thickness of the glass wool fibers used in sound absorbers and the size of the air bubbles have not decreased;
Comparing the results of KI-IZ, the effect drops off rapidly as the experimental frequency decreases, and there is concern about the effectiveness as the frequency drops to the noise frequency band, for example, if 500 H2.

Sound absorber with diameter 8.5 crs in model experiment (12)
If converted to the local size, it will be at least about 1rrL, but in Figure 7, when comparing the sound insulation effect when replacing the iron plate (13) with IWL height with a sound absorbing material (12) with a diameter of 1 rrL, it is found that the sound absorbing material (12) has almost no sound transmission loss, and there is no need to experiment with iron plate (13).
has a better sound insulation effect, which contradicts the experimental judgment of the invention.

Although the above-mentioned method of attaching sound-absorbing material to the upper edge of a sound insulating wall has been experimentally shown to have the potential to reduce sound, many problems may arise when implementing it. In implementation, there are issues of durability as well as soundproofing effects against actual noise sources.

Road structures require durability of 10 to 20 years, and sound-absorbing materials are not exposed to the outside air, but are wrapped in glass wool with a weather-resistant film and have a perforated metal protective plate on the outside. This is the current state of sound-absorbing type sound insulation walls.

However, even if the above two new attempts at soundproofing technology have problems, they are of deep significance for technological innovation.

d) Problems to be Solved by the Invention] It is no exaggeration to say that the current state of soundproofing technology for road noise and railway noise is that the age-old method of dealing with it based on its height continues to prolong.

This invention injects new blood into the classic sound insulation wall technology, and modernizes sound insulation technology against road noise by developing sound insulation technology that is as efficient as possible, rather than just using volume tactics based on height alone. It aims to pave the way for technological innovation.

[Means to solve the problem]

Means for solving the above problem will be explained with reference to FIG. 1, which is an explanatory diagram of the mechanism.

(a) Sound wave intake pipe (1) and sound wave extraction pipe on the sound receiving point side (2)
) is connected to the large-section expansion chamber (3) to form a three-way branch pipe.

(b) Using the wave energy of the traveling wave F1 entering from the intake pipe (1), the above device generates a reaction wave whose sign is opposite to that of the traveling wave F1 (Fl expands from compression, and if Fl expands, it compresses). Generate F2.

(C) The above device is installed near the upper edge of the sound insulation wall, a part of the sound wave FQ that goes around the upper edge of the sound insulation wall from the sound source is taken in through the intake pipe a), and the sign-inverted wave F2 generated by this device is
is used to interfere with the sound wave FO and attenuate the sound energy of the diffracted sound that goes around to the sound receiving point (7).

We are taking technical measures.

[Effect]

Sound is a type of wave, and the changes in its phenomena are expressed by a wave equation.The equation for waves traveling through a pipe can be written as the following equation.

Here, u2 displacement V: Bulk elastic modulus [2 hours,: Density
-) ct) (Backward wave) f9g is a function representing a waveform, where tsu means a traveling wave that moves in the positive direction of X, and g means a backward wave that moves in the negative direction of X.

The sound pressures F and G are F (x-ct)=-v-=-pc2E' (x-c
t) θX G (x-)-c t )==-V""= pC'g'
(x+ct)X Here, f' is the differential function of f (L)) with respect to Z.

On the other hand, the particle velocities F1 and G1 are u1 Fl = -= -c f' (x-ct)t, and the relationship between sound pressure and particle velocity is F=pcF1. G=-PcG1. That is, the sound pressure is proportional to the particle velocity, the sign of the traveling wave does not change, and the sign of the backward wave reverses.

In FIG. 1, when a wave F1 traveling through a pipe reaches a boundary where the cross section changes, part of the wave F1 is reflected (F2) L, and the rest is transmitted (F3). The wave (F3) that has entered the expansion chamber (3) becomes a traveling wave and propagates through the expansion chamber (3), but this hollow body (3) is either infinitely long or there is sound absorption treatment to prevent reflected waves along the way. (In 4 and 5, 4 is a sound absorbing material and 5 is a rear air layer), the reflected wave (or backward wave) in the expansion chamber (3) disappears, and the type of wave in FIG. 1 is Fl.

There are three types: F2 and F3. Note that some of the reflected waves generated at the entrance of the expansion chamber (3) are also distributed to the sound wave intake passage (1), but this and those directed to the extraction passage (2) are collectively referred to as reflected waves ( F2).

The cross-sectional area of the sound wave intake passage (1) is AI, the cross-sectional areas of the extraction passage (2) and the expansion chamber (3) are A2 and A3, and A=Al.
+A2, then from the balance condition of sound pressure and volume velocity (=particle velocity x cross-sectional area) at the entrance of the expansion chamber (3)
F2 = F3 A (FI F2 ) = A3. F3°, and from both equations, -A3 F2=-FI A-)-A3 AF 3 = -FI A+A3. In the above equation, the incident wave (F1) and the transmitted wave (F3
) and the sign of the reflected wave (F2), the transmitted wave (F
3) has the same sign as the incident wave (F1), but the reflected wave (F
2) When the cross-sectional area A3 of the expansion chamber (3) is larger than A,
The sign changes, and if the incident wave (F1) is compression, it becomes a tension wave, and if it is a tension wave, it becomes a compression wave. That is, the sound wave intake passage (1)
By adjusting the cross-sectional area of the take-out passage (2) and the expansion chamber (3), the sign of the reflected wave (F2) can be changed to eliminate the direct wave (FO), and by adjusting the cross-sectional area, the most efficient It is possible to design the amount of reflected waves (F2) generated.

Compared to the direct wave (FO), the reflected wave (F2) from the extraction passage (2) is delayed by the detour. As shown in Figure 4, the direct wave (FO) and reflected wave (F2) have a phase difference e
There are places where it interferes and is partially amplified,
If this phase difference e is small compared to the wavelength, the sounds will interfere so as to cancel each other out as a whole. That is, the wavelength of a low-frequency sound is longer, and the influence of the phase difference e becomes smaller, making it more effective. Instead of delaying the previous wave and causing it to interfere with the wave that comes after, it interferes with its own sign-inverted wave, so it is not affected by the waves that come after.

For high-frequency sounds, the effect of this phase difference increases,
Interference with later waves increases the rate of increase or decrease. Then, the difference between the input and output will be 0 or less. As the frequency increases, various types of attenuation such as attenuation due to bends in the path become large, and since a part of the direct wave (FO) has an intake port (1) in terms of energy, it does not take too much of a detour.

Diffraction attenuation due to sound obstacles such as walls is proportional to 10 times the common logarithm of the sound frequency f (1010g f ), and as the frequency doubles, the three-phone effect becomes larger.
When implementing soundproofing measures using soundproof walls, it is the low-frequency sounds that are inefficient. The device according to the present invention complements this by reducing high-frequency sounds at the height of the sound insulating wall, and lowering low-frequency sounds by increasing the height of the sound insulating wall. This greatly improves the inefficiency of sound reduction effects.

〔Example〕

A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of a soundproofing device according to the present invention, which has one sound wave intake passage (1) and one sound wave extraction passage (2), which are connected to An expansion chamber (3) having a cross section larger than the sum of the cross-sectional areas of both roads is provided. Inside the expansion chamber (3), a sound absorbing material 1) and a back air layer (5) are provided to prevent reflected sound.

Figures 2 and 3 show the sound wave intake passage (1) and the extraction passage (
There is a type that uses a perforated plate (8) or a slit plate (9) for 2), making it difficult to distinguish between the intake passage (1) and the output passage (2), but there is a type that uses the sound source (6) side. Entrance passage (1) part,
The part on the side of the sound receiving point (7) is regarded as the extraction passage (2).
A part (F2) of the reflected and scattered waves generated in the expansion chamber (2) is used as a sound-reducing interference wave on the side of the sound receiving point (7).

〔Effect of the invention〕

The conventional idea is that sound insulation walls for roads and railways achieve a sound reduction effect only by their height, but due to the nature of sound, the first height is good (noise is reduced, but the next 1rrL height is It has the characteristic that the sound reduction effect rapidly decreases, and the more the sound insulation wall becomes damaged, the worse the wall height effect becomes.High frequency noise is attenuated by the wall height effect, and noise in the low frequency band remains.The soundproofing device of the present invention teeth,
This eliminates the bottleneck in dealing with the height of the sound insulation wall and increases the efficiency of the sound insulation wall.

In many areas where noise barriers have already been installed, additional noise countermeasures are required due to the rise in noise levels associated with increasing traffic volume and the needs of roadside residents who are seeking a better environment. If the soundproofing device of the present invention is used in such places, it may be possible to just replace the top of the soundproofing panel with the soundproofing device of the present invention, which eliminates the need to replace the pillars and transfer the load to the road structure itself. Noise countermeasures can be taken without any noise.

The soundproofing device of the present invention is not particularly complex compared to the structure of conventional perforated sound-absorbing panels, and the cost is not particularly different from conventional sound-absorbing panels, so the investment efficiency for soundproofing is very high. There are some expensive ones.

The only way for our country to live is through the development of high-tech technology, and competition is fierce in developing new technologies in each field. The majority of sound insulation walls are used for public works projects, but only in the field of sound insulation walls, old-fashioned construction methods that consume a lot of material and money continue to be used. The technological development according to the present invention is significant for future technological development regarding sound insulating walls, since it challenges and stimulates this.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional side view of a device illustrating a soundproofing mechanism according to the present invention, which is also used as an embodiment of the present invention, Figs. An explanatory diagram of the sound interference situation near the edge, Fig. 5 is a sound interference experimental device using a Quinke tube, Fig. 6 is a schematic side view of a conventional delayed wave interference type soundproofing device, and Fig. 7 is the upper edge of a conventional sound insulating wall. FIG. 2 is a schematic side view of a soundproof wall equipped with a sound absorbing material.

Claims (1)

[Claims] Near the upper edge of the sound insulating wall, there is a structure in which the sound wave intake passage (1) and the sound wave extraction passage (2) are connected to the expansion chamber (3), and the sound wave (F_1) is transmitted from the intake passage (1) to the expansion chamber ( 3) Expansion sign inversion characterized by taking out the sign inversion reflected wave (F_2) generated when entering the room from the extraction passage (2) and making it interfere with the direct wave (F_0) going around the upper edge of the sound insulating wall to obtain a sound reduction effect. Wave interference type soundproofing device.