JPH11256523A - Sound insulating wall - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sound insulating performance by arranging sounding tubes with a wavelength 1/4 of the wavelength of the main component frequency of noise on the upper edge of a sound insulating wall, and installing a sound absorbing object in the vicinity of the openings. SOLUTION: A number of sounding tubes having a wavelength 1/4 of the wavelength of a sound wave forming the component of noise or a wavelength 1/4 of the wavelength of plural sound waves forming the component of noise and having the terminal end closed are arranged side by side. Secondly, a structure where sound absorbing objects are installed near the edges of the openings of the sounding tubes is installed along the upper edge of the sound insulating wall. The array of sounding tubes to which sound absorbing objects are fitted is arbitrary, for example, cylindrical, mushroom-shaped, T-shaped, or inverted- triangular. Thus, as the sound absorbing object is installed, 'negative effect' peculiar to the sounding tube can be reduced, and as the whole frequency band, poise level can be remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soundproof wall provided on a side surface of a highway or a high-speed rail.

[0002]

2. Description of the Related Art Along a highway or a high-speed railway, a noise barrier is provided to control traffic noise. In recent years, due to an increase in the noise level due to an increase in the number of traveling vehicles and an increase in traveling speed, the height of the soundproof wall has been gradually increased. On the other hand, inhabitants along these roads and railroads are obstructed from sunlight and radio waves are obstructed, and drivers and passengers are obstructed from viewing, and comfortable driving is excluded. Road and railroad builders also have a problem that if the height of the soundproofing wall increases, construction costs increase due to wind pressure and weight problems.

[0003] On the other hand, attempts have been made to improve the sound insulation performance while keeping the height of the soundproof wall constant.
At the initial stage, the sound insulation wall surface was made sound absorbing to improve the sound insulation performance. Next, an attempt was made to bend the sound-insulating wall edge to the sound source side to increase the height of the sound-insulating wall equivalently. This is to provide the soundproof wall with a thickness and expect the effect of the thickness. Attempts have also been made to improve the sound insulation performance by attaching a sound absorbing cylindrical object to the edge of the soundproof wall and lowering the sound pressure at the edge, which is currently in practical use. In addition, a quarter-wavelength acoustic tube arranged around the cylinder is attached along the sound-insulating wall edge, or a T-shaped cross-section with acoustic tubes arranged on the top surface to obtain great sound insulation performance. Some do.

In the method of making the surface of the soundproof wall sound absorbing, the thickness of the surface sound absorbing material becomes thicker in a low frequency range, and since there are few materials having a high sound absorbing performance in weather resistant materials, many methods are used. Sound insulation performance cannot be expected. The method of bending the sound-insulating wall edge to the sound source side and equivalently increasing the height of the sound-insulating wall is still used, but the effect of the bending is small, and as a result, the sound-insulating wall as a whole Is tall. In the method of attaching a sound absorbing cylindrical object to the sound insulation wall edge and reducing the sound pressure at the edge to improve the sound insulation performance, the thickness of the sound absorption material and the applicable frequency range are related, and large sound absorption performance can be expected at low frequencies. Absent. 1/4
In the method of attaching the wavelength acoustic tube arranged around the cylinder along the sound insulation wall edge, only the acoustic tube of one depth is used, and the acoustic frequency of the acoustic tube affects the radiation frequency of the tube. At a slightly lower frequency, the sound pressure on the surface of the cylinder becomes extremely high (this is called a negative effect), and the expected sound insulation performance has not been obtained for noise in a wide frequency band. In the case where the cross section is T-shaped and the sound tubes are arranged on the top surface, the length of the sound tubes is designed to resonate with a plurality of frequencies in order to widen the control frequency band.

However, by arranging acoustic tubes having different resonance lengths and having different lengths, the sound insulation performance of the acoustic tube having one length and the other frequency are designed. The negative effects of the sound tubes overlapped,
At present, the sound insulation performance as a whole is decreasing.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and its main purpose is to reduce the frequency slightly lower than the resonance frequency of the acoustic tube by the influence of the radiation impedance of the acoustic tube. In this method, the extremely high sound pressure on the surface of the cylinder is controlled by using a sound absorbing material to improve the sound insulation performance as a soundproof wall.

[0007]

Means for Solving the Problems The present inventor has made intensive studies to solve the above-mentioned problems, and as a result, mounts a sound-absorbing object near each sound tube opening in a sound tube array mounted along the upper edge of the soundproof wall. Thus, the present invention has been completed.

[0008] That is, the present invention is based on a soundproof wall provided with a structure in which a quarter-wavelength acoustic tube is arranged along an upper edge of the soundproof wall with respect to a frequency which is a main component of noise,
In order to further enhance the sound insulation performance, a sound-insulating wall characterized in that a sound-absorbing object is attached near the opening of the acoustic tube.

The present invention will now be described with reference to examples. Fig. 1 shows a commonly used vehicle traffic noise spectrum.
Shown in The noise spectrum behind the conventional simple soundproof wall having a height of 3 m with respect to this noise is experimentally obtained as shown by the square marks in FIG. At this time, the sound source is on the ground 5 m above the soundproof wall, and the sound receiving point is on the ground on the opposite side of the sound source.
m. The noise level for the entire frequency band at that point, that is, the noise level is 77.5 dB when looking at the overall value at the right end of FIG.

On the other hand, the conventional invention "a cylindrical assembly having a length of a quarter of the wavelength of a sound wave which is a main component of noise and having a closed acoustic tube arranged side by side, The height of the sound barrier mounted along the upper edge of the main body (see FIG. 3) is the same as the height of the conventional sound barrier of 3 m, and is replaced with the above sound barrier. The noise spectrum is shown by a circle in FIG. In this case, the value indicated by a circle is 10 dB more than the value indicated by a square near 630 Hz.
This indicates that the noise reduction effect of the cylindrical object is large. The depth of the acoustic tubes arranged on the cylindrical object used at this time is 17 cm, which is almost equal to 1/4 of the wavelength of the sound wave of 500 Hz. The longitudinal section of the acoustic tube is not rectangular, but opens toward the opening. This allows the resonance of this acoustic tube to be 630 instead of 500 Hz.
Hz. However, at around 315 Hz, a sound pressure level higher than the sound pressure level behind the conventional soundproof wall was observed by attaching a cylindrical object. This is what is called the "negative effect" described above. Also 6
A high sound pressure level is also observed around 1250 Hz, which is twice the frequency of 30 Hz. This indicates that the phase of the incident wave at the opening and the phase of the reflected wave reflected at the bottom of the acoustic tube are in phase, and the sound pressure is reduced. It is due to rising.
Due to these effects, the large noise reduction performance around 630 Hz does not work effectively, and when viewed over the entire frequency band, it is 76.2 dB as shown at the right end of FIG. 2, and the effect of the tubular acoustic tube arrangement is 1 Only 3 dB.

Therefore, in order to reduce these negative effects, when a sound absorber is attached near the opening of an acoustic tube arranged in a cylindrical shape as shown in FIG. As a result of measuring the noise spectrum behind the wall, a value indicated by a triangle in FIG. 2 was obtained. As a result, the sound pressure level is slightly higher around 630 Hz,
In the vicinity of 315 Hz and 1250 Hz, the values are smaller than the values indicated by the circles. Especially at 400Hz, 10d
There is a reduction of B or more. The overall evaluation is clear from the overall value at the right end of FIG. 2, which is 1.8 dB greater than that obtained by arranging only the sound tubes, and is 3.1 dB higher than a simple soundproof wall. There was an increase in the sound insulation effect. This is comparable to the effect of raising the sound-insulating wall which is simple and is about 2.5 m. That is, it is equivalent to increasing the height by 2.5 m simply by attaching the cylindrical sound tube array of about 60 cm in diameter with the sound absorbing body attached to the conventional soundproof wall having a height of 3 m. means.

[0012]

[Action] By attaching a sound absorber near the opening of the sound tube of the structure that is configured by the sound tube array and is mounted near the soundproof wall edge, the "negative effect" peculiar to the sound tube can be reduced. The noise level can be greatly reduced in the entire frequency band. The basic structure for mounting the sound absorbing body is not limited to a structure in which the acoustic tubes are arranged in a cylindrical shape, but can be applied to any structure utilizing an acoustic tube arrangement. For example,
Objects using an acoustic tube array, such as a mushroom type as shown in FIG. 5, a T-shaped type as shown in FIG. 6, and an inverted triangular type as shown in FIG. The cross section of the sound-absorbing body to be attached was 70 mm in diameter and 20 mm in wall thickness in this experiment, but it was large enough to show sound absorption performance regardless of the shape of a circle, square, triangle, etc. I just need.

[0013]

As described above, the sound insulating wall according to the present invention has one or more types of 1/4 wavelength acoustic tubes having a frequency that is a main component of noise arranged on the top of a conventional sound insulating wall, and By attaching a sound absorber near the opening, a large insertion loss can be obtained. The sound absorbing material may be any material from a mineral material such as glass wool to a metal material made of aluminum fiber, as long as it can efficiently absorb sound.

[Brief description of the drawings]

FIG. 1 is a spectrum diagram of commonly used automobile traffic noise.

FIG. 2 is a diagram of a noise spectrum behind various soundproof walls.

FIG. 3 shows a cylindrical assembly in which acoustic tubes having a length of の 長 of the wavelength of a sound wave constituting a main component of noise and having a closed end are juxtaposed.
Soundproof wall mounted along the top edge of the wall body

FIG. 4 is a cylindrical assembly in which acoustic tubes each having a length of １ ／ of the wavelength of a sound wave constituting a main component of noise and having a closed end are juxtaposed.
Diagram of a soundproof wall in which an aggregate with sound absorbers attached near the opening of the acoustic tube is attached along the upper edge of the wall main body

FIG. 5 is a diagram in which a structure in which acoustic tubes are arranged in a mushroom type is attached to a soundproof wall edge.

FIG. 6 is a diagram in which a structure in which acoustic tubes are arranged in a T-shape is attached to an edge of a soundproof wall.

FIG. 7 is a diagram in which a structure in which acoustic tubes are arranged in an inverted triangular shape is attached to a soundproof wall edge.

Claims (2)

[Claims] 1. A structure in which a number of acoustic tubes having a length of 1/4 wavelength of a sound wave constituting a noise component and having a closed end are juxtaposed, and near an opening edge of the acoustic tubes. Sound-absorbing wall with a structure with sound-absorbing objects attached to it along the upper edge 2. A structure in which a number of acoustic tubes having a length of 1/4 wavelength of a sound wave of a plurality of frequencies constituting a noise component and having a closed end are juxtaposed. The structure where the sound absorbing object is attached near the opening edge of
Soundproof wall mounted along the upper edge