JP6762129B2 - Sound absorber - Google Patents

Description

The present invention relates to a sound absorbing device using a Helmholtz resonator, which is used as a means for reducing blasting sound in construction of, for example, a mountain tunnel.

In the construction of mountain tunnels, blasting is performed repeatedly on the face side, so it is inevitable that high sound pressure blasting sounds will be generated, and it is necessary to prevent such blasting sounds from leaking to the outside as much as possible. ..

Conventionally, as a means for reducing the bursting sound due to such tunnel construction, a soundproof wall having a plurality of wall portions made of a heavy object having a high sound insulation effect in a low frequency sound range is installed (for example, Patent Documents 1 and 2 below). (Refer to), and in addition to the noise barrier, an acoustic tube with a length corresponding to 1/4 of the wavelength is installed in the tunnel, and the sound wave from the burst sound source in the tunnel mine and the sound wave of the opposite phase returned from the tube body are recorded. A large number of sound absorbers are installed, such as those that reduce sound by interfering with each other (see, for example, Patent Document 2 below), or a rectangular (cubic) box with an opening, and a tubular component inserted into this opening. It is known that the sound is reduced by the Helmholtz resonance action (see, for example, Patent Documents 3 to 5 below).

Japanese Unexamined Patent Publication No. 2006-283545 Japanese Unexamined Patent Publication No. 2011-256609 Japanese Unexamined Patent Publication No. 2015-212790 Japanese Unexamined Patent Publication No. 2014-205215 Japanese Unexamined Patent Publication No. 2014-074328

However, when a plurality of soundproof walls are installed in a tunnel, there is a problem that the construction becomes large-scale, and a high construction cost and a long construction time are required.

In addition, when an acoustic tube with a length corresponding to 1/4 of the wavelength is installed in the tunnel, a long acoustic tube is required to reduce low-frequency components, and the structure is such that the acoustic tube is bent. However, there is a problem that a large installation space is required in the tunnel, and it becomes difficult to secure an installation space for heavy machinery and a passage for workers.

In addition, when a rectangular parallelepiped (cubic) box-shaped Helmholtz resonator is installed in a tunnel pit, each wall surface of the box-shaped Helmholtz resonator vibrates due to the application of extremely large sound pressure due to blasting sound during blasting work. Therefore, the sound absorption performance is lowered, and therefore, it is necessary to use a plate material having high rigidity, which causes a problem of an increase in weight and an increase in construction cost. Moreover, in order to reduce the sound in the low frequency range, it is necessary to lengthen the tubular part inserted into the opening of the box, and therefore it is necessary to increase the supporting strength of the tubular part in the box.

Technical problems, without requiring a large installation space, there the sound absorbing effect by the Helmholtz resonator has high sound-absorbing device lightweight to provide at a low cost.

Serpentine with sound absorbing device, the outer shell opening is opened in the end plates at both ends of the cylindrical portion a bottomed cylindrical shape which is closed by an end plate attached to said end plate, said opening communicating with the interior The outer shell is a diversion of a drum can , and is provided with an acoustic case of a stairwell formed with an orifice having a shaped shape .

By making the outer shell a bottomed cylinder and attaching an acoustic case, the rigidity of the outer shell is increased and it is difficult to vibrate even if a large sound pressure is applied, so excellent sound absorption performance can be achieved. In addition, it is possible to reduce the sound in the low frequency band without increasing the size, and since it is not necessary to manufacture the plate material with high rigidity, it is effective in suppressing the weight increase and reducing the construction cost.

It is a cross-sectional perspective view showing a first embodiment of the sound absorbing device. Is a perspective view showing an outer shell in the first embodiment of the sound absorbing device. It is a cross-sectional perspective view showing an acoustic case in the first embodiment of the sound absorbing device. It is a cross-sectional perspective view showing a second embodiment of the sound absorbing device. It is a cross-sectional perspective view showing a third embodiment of the sound absorbing device. It is a cross-sectional perspective view showing a fourth embodiment of the sound absorbing device. It is a perspective view showing a fifth embodiment of the sound absorbing device. A sixth embodiment of the sound absorbing device is a cross-sectional perspective view showing an example in which a sound absorbing material having air permeability acoustic case. It is a cross-sectional perspective view showing a seventh embodiment of the sound absorbing device. It is a cross-sectional perspective view showing an eighth embodiment of the sound absorbing device. The sound absorbing device is an explanatory view showing an installed state of stacked tunnel underground. It is a graph showing the results of measurement of the sound absorption coefficient of the sound absorbing device. In the test for verifying the sound absorption effect of the sound absorbing device is an explanatory view showing a first installation pattern of the sound absorbing device installed in the tunnel. In the test for verifying the sound absorption effect of the sound absorbing device is an explanatory diagram showing a second installation pattern of the sound absorbing device installed in the tunnel. In the test for verifying the sound absorption effect of the sound absorbing device is an explanatory view showing the positional relationship of the soundproof door and blasting point and the sound absorber and the sound receiving point. It is a diagram which shows the result of the verification test.

For implementation in the form of a sound absorbing device will be described with reference to the drawings. First, FIG. 1 shows the first embodiment, and the sound absorbing device 1 shown in FIG. 1 includes an outer shell 10 and an acoustic case 20 arranged in the outer shell 10.

Specifically, the outer shell 10 is made of, for example, a metal drum can, and as shown in FIG. 2, has a bottomed cylindrical shape in which the cylindrical portion 11 and both ends thereof are closed by end plates 12 and 13. , A rectangular slit-shaped elongated opening 14 is provided in one end plate 12. The shape of the opening 14 is not limited to a rectangular slit shape, and may be a square, a polygon, or a circle.

The acoustic case 20 arranged in the outer shell 10 is made of wood such as plywood, metal or synthetic resin, and as shown in FIG. 3, the outer shell 10 is opened in the end plates 21a and 21b. A rectangular parallelepiped or cubic case body 21 having rectangular elongated communication holes 22 and 23 having the same shape as 14 or larger than the opening 14, and arranged parallel to the end plates 21a and 21b inside the case body 21. The baffle plates 24 and 25 are composed of a plurality of baffle plates 24 and 25, and the baffle plates 24 and 25 are attached to the inside of the case main body 21 in a different shelf shape with their opposite ends separated from the inner surface of the case main body 21. The space is partitioned to form an orifice 20a having a meandering shape between the communication holes 22 and 23. In the illustrated example, two baffle plates are attached, but the number is not limited to two.

Then, in the acoustic case 20, in a state where the communication hole 22 on the upper side in the drawing is aligned with the opening 14 of the outer shell 10, the end plate 21a on the upper side in the drawing is attached to the inner surface of the end plate 12 of the outer shell 10. It is joined by an appropriate means (not shown) such as welding, that is, the upper communication hole 22 in the figure communicates with the external space through the opening 14 of the outer shell 10, and the lower communication hole 23 in the figure is the outer shell 10. And the cavity 10a between the acoustic case 20 and the cavity 10a, in other words, the cavity 10a between the outer shell 10 and the acoustic case 20 communicates with the external space through the meandering orifice 20a inside the acoustic case 20. As a result, the Helmholtz resonator type sound absorbing device 1 is configured.

A large number of sound absorbing devices 1 having the above-described configuration are installed in, for example, in a mountain tunnel, and are used as means for reducing blasting noise generated during excavation of a mountain tunnel. In this case, the sound absorbing devices 1 may be installed side by side so that the openings 14 face upward, may be installed side by side so that the openings 14 face the horizontal direction, or the openings 14 may be installed so as to face the horizontal direction. It may be stacked and installed in.

Here, in general, the resonance frequency of a Helmholtz resonator is basically determined by the air spring action of the internal cavity of the resonator and the mass of the air column in the orifice between the internal cavity and the external space, that is, the internal cavity. The larger the volume and the longer the length of the orifice, the lower the value. Furthermore, the smaller the opening area (aperture ratio) of the end plate, the lower the value. Then, according to the embodiment shown in FIG. 1, since the orifice 20a formed by the acoustic case 20 is sufficiently long enough to be repeatedly meandered by the baffle plates 24 and 25, the opening 14 (communication hole 22) is further increased. , 23) is made into an elongated slit shape, and even if the opening ratio of the end plate is reduced, the viscous resistance value of the orifice can be increased and the sound absorption coefficient can be improved. Therefore, the outer shell 10 is a ready-made drum can having a constant size. Even if it is diverted from, it is effectively ultra-low by lowering the resonance frequency sufficiently and tuning it to 20 Hz or less, which significantly reduces the sound insulation performance of the soundproof door with the infrasound component contained in the sound. The frequency sound can be reduced, and the sound insulation defect of the soundproof door can be compensated.

Further, even if the size of the outer shell 10 is constant, the resonance frequency can be changed by changing the size of the acoustic case 20, the number of baffle plates 24 and 25, or the cross section of the orifice 20a. Since it can be tuned arbitrarily, it is possible to reduce the sound in a wide band by installing a plurality of types of sound absorbing devices 1 having different resonance frequencies.

Further, the energy of blasting sound is extremely large, and at the time of blasting, a large sound pressure is applied to the outer shell 10 of the sound absorbing device 1 installed in the tunnel pit, so that the sound pressure causes vibration (deflection) in the outer shell 10. ), The sound absorption characteristics are impaired and the sound absorption coefficient is lowered. However, according to the illustrated embodiment, since the outer shell 10 has a bottomed cylindrical shape, the cylindrical portion 11 of the outer shell 10 has high rigidity, and the opening 14 for taking in sound waves is provided. In addition to being attached to the opened end plate 12 in a state where the end plates 21a of the case body 21 of the acoustic case 20 are overlapped with each other, the acoustic case 20 is heavier than the tubular acoustic tube in the prior art. Since it is large, the end plate 12 is also difficult to vibrate, and therefore, even if a large sound pressure is applied, the vibration of the outer shell 10 itself is suppressed. Therefore, it is possible to prevent a decrease in the sound absorption coefficient due to the vibration of the outer shell 10 and to achieve excellent sound absorption performance.

Further, for this reason, it is not necessary to manufacture the outer shell 10 from a material having high rigidity, and in the illustrated embodiment, the outer shell 10 is a diversion of a used drum can, so that the manufacturing cost can be reduced.

Since the orifice 20a of the acoustic case 20 is repeatedly meandered by the baffle plates 24 and 25, the acoustic case 20 can be made relatively small even though it has a long orifice 20a inside. By mounting one end plate 21a of the case body 21 on the inner surface of the end plate 12 of the outer shell 10, the mounting strength can be increased.

Moreover, tuning to the low frequency band is realized not only by increasing the volume of the cavity 10a and lowering the spring constant of the air spring, but also by the orifice 20a having a long meandering shape and a relatively small cross-sectional area. Therefore, it is possible to reduce the sound in the low frequency band without increasing the size of the sound absorbing device 1, and it is possible to save the installation space of the sound absorbing device 1.

The sound absorbing device 1 having the above-described configuration can be manufactured as follows. First, a commercially available drum can is prepared as the outer shell 10, and an opening 14 having a length of 6 cm and a width of 30 cm is formed in one of the removable end plates 12 by laser processing. At that time, an open-head drum can can be used as a commercially available drum can. In that case, one end plate 12 can be removed, and the step of cutting 13 of the other end plate can be omitted. Further, when a drum can in which one end plate 12 and the other end plate 13 cannot be easily removed is used, one end plate, for example, the end plate 12 may be cut off in advance.

Next, a commercially available plywood (preferably one having a thickness of about 12 mm) is prepared, eight plate pieces for assembling the acoustic case 20 are cut out, and among these plate pieces, the side plate of the case body 21 is used. The end plate 21a and the end plate 21b, and the baffle plates 24 and 25 are screwed to the sheet pieces to assemble. At that time, due to the difference between the side plate of the case main body 21 and the end plate 21a, the end plate 21b, and the obstruction plates 24 and 25, the longitudinal dimension of these plate pieces and the longitudinal dimension of the side plate Openings having a length of 6 cm and a width of 30 cm having the same dimensions as the openings 14 of the outer shell 10 made of drums are formed alternately in the longitudinal direction.

The acoustic case 20 assembled in this way is inserted into the outer shell 10 made of the drum can from the cut portion of the end plate 13 so that the opening (communication hole 22) of the end plate 21a and the opening 14 of the drum can coincide with each other. The four corners of the acoustic case 20 are screwed from above the end plate 12. Finally, the portion where the end plate 13 is cut off is closed by welding the end plate 13, so that the production of the sound absorbing device 1 is completed.

Further, when the sound absorbing device 1 is installed so that the opening 14 faces upward, the side opposite to the opening 14 of the drum can may be installed on the site even if the end plate 13 is cut off, depending on the installation surface. Since it is closed, it is not always necessary to weld the end plate 13 to close it.

When an open-head drum can is used as the outer shell 10, an opening may be opened in the other end plate 13 instead of the open-head end plate 12. In this case, the acoustic case 20 is positioned so that the opening opened in the end plate 13 coincides with the opening (communication hole 23) of the end plate 21b, and the four corners of the acoustic case 20 are screwed from above the end plate 13. By doing so, the sound absorbing device 1 can be manufactured. In this way, if the end plate 12 having an open head is not used, sound absorption does not have an end plate on the opposite side to the end plate of the drum can having an opening without cutting one end plate of the drum can. The device 1 can be manufactured.

The sound absorbing device 1 having no end plate on the opposite side of the opening 14 of the drum can can suppress the vibration of the end plate constituting the sound absorbing device 1 by resonating with the low frequency sound.

Next, FIG. 4 shows a second embodiment of the sound absorbing device. In this embodiment, the difference from the first embodiment described above is that the acoustic case 20 is arranged outside the outer shell 10, that is, in the acoustic case 20, the communication hole 23 on the lower side in the drawing is the outer shell. In the state of being aligned with the opening 14 of 10, the lower end plate 21b in the drawing is joined to the outer surface of the upper end plate 12 in the drawing in the outer shell 10 by a fitting or an appropriate means (not shown) such as welding. That is, the lower communication hole 23 in the drawing communicates with the cavity 10a in the outer shell 10 through the opening 14 of the outer shell 10, and the upper communication hole 22 in the drawing communicates with the external space. In other words, the cavity 10a, which is the internal space of the outer shell 10, communicates with the external space through the meandering orifice 20a inside the acoustic case 20, thereby forming the Helmholtz resonator type sound absorbing device 1. ..

The configuration of the outer shell 10 and the configuration of the acoustic case 20 are the same as those of FIGS. 2 and 3 described above.

A large number of sound absorbing devices 1 of the second embodiment are also installed in, for example, in a mountain tunnel, and are used as means for reducing blasting noise generated during excavation of a mountain tunnel. In this case, the sound absorbing devices 1 may be installed side by side so that the communication holes 22 of the acoustic case 20 face upward, or the communication holes 22 may be installed side by side so as to face the horizontal direction. 22 may be stacked and installed so as to face the horizontal direction.

According to the embodiment shown in FIG. 4, the orifice 20a formed by the acoustic case 20 is long enough to be repeatedly meandered by the baffle plates 24 and 25, and further, the openings 14 (communication holes 22 and 23). The cross-sectional area of the orifice 20a is set to be small to some extent by forming an elongated slit shape, and the acoustic case 20 is arranged outside the outer shell 10 so that the entire area of the inner cavity 10a of the outer shell 10 is formed. Will form the cavity of the Helmholtz resonator, and its volume will be as large as the volume of the acoustic case 20. Therefore, the resonance frequency (frequency to be reduced) can be set to a lower frequency band as compared with the embodiment shown in FIG.

Further, also in this embodiment, since the outer shell 10 has a bottomed cylindrical shape, the cylindrical portion 11 of the outer shell 10 has high rigidity and the end at which the opening 14 is opened. The plate 12 also has high rigidity because the end plate 21b of the case body 21 of the acoustic case 20 is superposed on the outer surface thereof, so that the outer shell 10 itself has high rigidity even if a large sound pressure is applied. Vibration is suppressed. Therefore, it is possible to prevent a decrease in the sound absorption coefficient due to the vibration of the outer shell 10 and to achieve excellent sound absorption performance, and since the outer shell 10 is a diversion of a used drum can, the manufacturing cost can be reduced. it can.

Although the acoustic case 20 has a long orifice 20a inside, the orifice 20a is repeatedly meandered by the baffle plates 24 and 25, so that the acoustic case 20 can be made relatively small. The mounting strength can be increased by mounting the lower end plate 21b of the case body 21 on the outer surface of the end plate 12 of the outer shell 10 in a state of being overlapped with each other.

Further, as described above, since the acoustic case 20 can be made relatively small, even if the acoustic case 20 is attached to the outside of the outer shell 10, it is possible to suppress the increase in size due to the structure. it can.

Next, FIG. 5 shows a third embodiment of the sound absorbing device. In this embodiment, of the outer shell 10 of the first embodiment described above, the outer surface of the end plate 12 on which the opening 14 is formed is porous, for example, thick felt made of glass wool, rock wool, or the like. A disk-shaped sound absorbing material 30 made of a quality material is attached. The sound absorbing material 30 is provided with an opening 31 corresponding to the opening 14 so as not to block the opening 14 of the outer shell 10.

According to the third embodiment, in addition to the effect of the first embodiment described above, the sound absorbing material 30 made of a porous material attached to the outer surface of the end plate 12 of the outer shell 10 is the outer shell 10. Since the acoustic case 20 has an action of absorbing sound waves in a frequency band higher than the resonance frequency of the Helmholtz resonator, sound reduction in a wide frequency band is possible.

Next, FIG. 6 shows a fourth embodiment of the sound absorbing device. This embodiment is made of a porous material such as a thick felt made of glass wool, rock wool or the like so as to cover the outer surface of the cylindrical portion 11 of the outer shell 10 of the first embodiment described above. A cylindrical sound absorbing material 40 is attached.

In the fourth embodiment, as in the third embodiment described above, the sound absorbing material 40 made of a porous material attached to the cylindrical portion 11 of the outer shell 10 is a Helmholtz resonator using the outer shell 10 and the acoustic case 20. Since it has an absorbing action for sound waves in a frequency band higher than the resonance frequency of, it is possible to reduce sound in a wide frequency band.

Although the acoustic case 20 is attached to the inside of the outer shell 10 in FIG. 6, the acoustic case 20 is attached to the outside of the outer shell 10 as in the second embodiment. Similarly, a cylindrical sound absorbing material 40 can be attached to the outer surface of the cylindrical portion 11 of the outer shell 10.

In the fourth embodiment shown in FIG. 6, the sound absorbing material 30 as shown in FIG. 5 may be attached to the outer surface of the end plate 12 of the outer shell 10. That is, by using the sound absorbing material 30 and the sound absorbing material 40 together, it is possible to improve the efficiency of the absorption action for sound waves in a frequency band higher than the resonance frequency of the Helmholtz resonator, and as a result, the efficiency in a wide frequency band can be improved. Good sound reduction is possible.

Next, FIG. 7 shows a fifth embodiment of the sound absorbing device. In this embodiment, the sound absorbing devices 1 of the first embodiment shown in FIG. 1 are installed side by side so that the openings 14 face upward, or stacked so that the openings 14 face in the horizontal direction. The gaps formed between the outer shells 10 and the outer shells 10 adjacent to each other are filled with a sound absorbing material 50 made of a porous material such as thick felt made of glass wool, rock wool or the like.

Further, in the fifth embodiment as in the third or fourth embodiment described above, the sound absorbing material 50 made of a porous material filled between the outer shells 10 and 10 is the outer shell 10 and the acoustic case. Since it has an action of absorbing sound waves in a frequency band higher than the resonance frequency of the Helmholtz resonator, it is possible to reduce sound in a wide frequency band.

Further, in each of the above-described embodiments, the acoustic case 20 closes one or both of the communication holes 22 and 23 provided in the end plates 21a and 21b, as shown in FIG. 8 as the sixth embodiment. As described above, for example, a breathable sound absorbing material 60 made of thick felt made of glass wool, rock wool or the like may be arranged.

By doing so, it is possible to improve the absorption performance for sound waves in the frequency band near the resonance frequency and to widen the band of the sound absorbing function.

Further, as shown in FIG. 9, in addition to the opening 14 formed in one end plate 12 of the outer shell 10, an opening 15 is also opened in the other end plate 13 of the outer shell 10 so as to show the seventh embodiment. As a configuration in which two acoustic cases 20 are arranged on the outside, one acoustic case 20 is attached to the outer surface of one end plate 12 in the outer shell 10, and the other acoustic case 20 is attached to the outer surface of the other end plate 13. Alternatively, as shown in FIG. 10, as shown in the eighth embodiment, two acoustic cases 20 are arranged in the outer shell 10, and one acoustic case 20 is placed on the inner surface of one end plate 12 in the outer shell 10. By attaching the other acoustic case 20 to the inner surface of the other end plate 13, the cavity 10a in the outer shell 10 communicates with the external space through the orifices 20a and the openings 14 and 15 of both acoustic cases 20. It may be configured.

Then, as shown in FIG. 11, when the sound absorbing device 1 having the configuration shown in FIG. 9 or FIG. 10 is installed in the tunnel T, the sound absorbing devices 1 are stacked so that the openings face in the horizontal direction, thereby providing a sound absorbing area. Is doubled, so that the sound absorption effect can be further enhanced or the installation space can be saved.

FIG. 12 is a diagram showing the result of measuring the sound absorption coefficient of the sound absorbing device 1. Specifically, the vertical incident sound absorption coefficient measured with a 1/6 scale scale model is frequency-converted to 1/1 scale. As a result of the measurement, as shown in FIG. 12, the sound absorption coefficient in the resonance frequency 16 Hz band of the sound absorber Was 0.9, and it was confirmed that high sound absorption performance could be obtained.

Next, as shown in FIGS. 13 and 14, a large number of sound absorbing devices 1 are installed in the tunnel T in two different patterns, and the results of verifying the sound absorbing effect of each of them will be described. In this embodiment, 200 sound absorbing devices 1 are arranged from a position 30 m away from the wellhead (soundproof door) A toward the face B. The cross section of the tunnel T is 88.9 m ² , and the position of the face B due to blasting is 600 m from the soundproof door A.

First, in the first installation pattern shown in FIG. 13, 200 sound absorbing devices 1 were installed in a row in a section of 120 m so that the openings face upward on one side in the width direction of the tunnel T. The installation position was set to a position 1.5 m away from the side wall in order to secure a safety passage.

Further, in the second installation pattern shown in FIG. 14, 200 sound absorbing devices 1 are installed in a row in a section of 60 m so that 100 of the sound absorbing devices 1 are facing upward on both sides in the width direction of the tunnel T. did. The installation position was set to a position 1.5 m away from the side wall in order to secure both sides as safety passages.

As shown in FIG. 15, both the first installation pattern and the second installation pattern are located 20 m outside the soundproof door from the underground sound receiving point P1 provided 300 m from the soundproof door A into the mine. The effect was calculated by measuring the amount of attenuation of the blasting sound propagating to the sound receiving point P2 and comparing with and without the sound absorbing device 1.

As a result, as shown in FIG. 16, a reduction effect of up to about 7 dB was obtained in the resonance frequency 16 Hz band of the sound absorbing device 1. Further, it was found that there was no significant difference in the reduction effect between the first installation pattern and the second installation pattern, that is, the reduction effect did not depend on the installation position of the sound absorbing device 1. Therefore, it was confirmed that the sound absorbing device 1 can be freely installed so as not to interfere with the underground work.

1 Sound absorbing device 10 Outer shell 10a Cavity 11 Cylindrical part 12, 13 End plate 14 Opening 20 Acoustic case 20a Orifice 21 Case body 22, 23 Communication holes 24, 25 Interfering plate 30, 40, 50, 60 Sound absorbing material

Claims (4)

An outer shell that is a bottomed cylinder with both ends of the cylindrical part closed by end plates and has openings in the end plates.
An atrium acoustic case attached to the end plate, which communicates with the opening and forms a meandering orifice inside.
The sound absorbing device is characterized in that the outer shell is a diversion of a drum can . The acoustic case consists of a case body having communication holes at both ends, and a required number of baffle plates installed inside the case body and partitioning the orifice inside the case body into a meandering shape between the communication holes at both ends. The sound absorbing device according to claim 1. The sound absorbing device according to claim 1 or 2 , wherein a porous sound absorbing material is provided on the outer surface of the outer shell. The sound absorbing device according to any one of claims 1 to 3 , wherein a sound absorbing material having air permeability is provided in at least one of the communication holes at both ends of the acoustic case.

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