JP5697130B2 - Ultra-low frequency sound reduction device and soundproof house equipped with the ultra-low frequency sound reduction device - Google Patents

Description

  The present invention relates to a device for reducing ultra-low frequency sound and a soundproof house equipped with the device.

  In recent years, interest in environmental problems related to noise has increased, and regulations (such as prefectural regulations) regarding noise tend to be stricter. For this reason, noise countermeasures such as covering equipment used for construction with a soundproof house are taken at construction sites.

  By the way, in waterworks and subway construction, large vibrating screens are used to separate gravel and soil in excavated mud. In such a device, since the rotation speed of the vibration sieve is about 1000 rpm, an ultra-low frequency sound of about 16 to 17 Hz is generated. This ultra-low frequency sound has a problem that it cannot be silenced by a soundproof wall of a general soundproof house.

  Therefore, it has been proposed to use a sound absorbing wall using a Helmholtz resonator to mute the very low frequency sound (see, for example, Patent Document 1).

JP 2003-253627 A

  By the way, when covering a large vibration sieve with a soundproof house, an opening for carrying earth and sand out of the soundproof house is necessary, and there is a problem that ultra-low frequency sound leaks from this opening.

  Here, the ultra-low frequency sound means a sound of 20 Hz or less. Since ultra-low frequency sound cannot be recognized by human hearing unless the sound pressure is high, it is generally considered that it cannot be heard by human ears. However, the very low frequency sound propagated to the house or the like vibrates the window glass or the joinery. And the secondary noise by this vibration may cause a noise problem. Ultra-low frequency sounds can also cause physiological effects such as headaches, dizziness, and nausea. Furthermore, since a person with good ears can hear an ultra-low frequency sound of about 16 Hz, the ultra-low frequency sound generated from the construction site described above is heard as a temporary noise.

  Thus, it is desired to develop an apparatus that effectively reduces the ultra-low frequency sound generated from the construction site described above. This invention is for solving such a subject, and it aims at providing the soundproof house provided with the apparatus for reducing an ultra-low frequency sound effectively, and its apparatus.

In order to achieve the above object, the invention according to claim 1 is an ultra-low frequency sound reducing device provided in an opening of a soundproof house that covers a sound source that emits ultra-low frequency sound, the ultra low frequency sound reducing device. However, it is provided so as to protrude inside the soundproof house along the edge of the opening, has a cylindrical shape, and is provided integrally with the soundproof house, and the shape expands on the front end side. It is characterized by a cone shape .

The invention according to claim 2 is a soundproof house which covers a sound source emitting ultra-low frequency sound and has an opening, and is characterized in that the ultra-low frequency sound reducing device according to claim 1 is mounted. .
The invention according to claim 3 is characterized in that a belt conveyor for conveying earth and sand from the inside of the soundproof house to the outside is provided through the opening.

  ADVANTAGE OF THE INVENTION According to this invention, the soundproof house provided with the apparatus for effectively reducing a very low frequency sound and its apparatus can be provided.

It is a figure which shows the whole structure of the soundproof house which concerns on embodiment of this invention. It is a figure explaining the structure and installation position of a short pipe type silencer. It is a figure explaining the installation position of a short pipe type silencer. It is a figure which shows the size of a short pipe type silencer. It is the figure which represented the expansion type silencer typically. It is a figure explaining the silencing mechanism of a short pipe type silencer. It is a figure explaining the structure and installation position of a reverse horn type silencer. It is a figure which shows the size of a reverse horn type silencer. It is a block diagram of experimental equipment. It is a perspective view of an experimental model house. (A) is a figure which shows the size of the short pipe type experimental silencer, (B) is a perspective view of the experimental model house. (A) is a figure which shows the size of the reverse horn type | mold experimental silencer, (B) is a perspective view of an experimental model house. It is a perspective view of an experimental vibration sieve. It is a figure explaining the installation position of a microphone. It is a figure which shows the sound pressure spectrum (analysis result by FFT) when not installing a silencer for experiment. It is a figure which shows the sound pressure spectrum (analysis result by FFT) at the time of installing the short pipe type muffler for experiment. It is a figure which shows the sound pressure spectrum (analysis result by FFT) at the time of installing the reverse horn type | mold experimental silencer. It is a figure which shows the sound pressure spectrum (analysis result by 1/3 octave band) when not installing a silencer for experiment. It is a figure which shows the sound pressure spectrum (analysis result by 1/3 octave band) at the time of installing a short pipe type experimental silencer. It is a figure which shows the sound pressure spectrum (analysis result by 1/3 octave band) at the time of installing a reverse horn type experimental silencer. It is a figure which shows the attenuation amount in each measurement point at the time of installing a short pipe type experimental silencer. It is a figure which shows the attenuation amount in each measurement point at the time of installing a reverse horn type experimental silencer. It is a figure which shows distance attenuation | damping when not installing an experimental silencer. It is a figure which shows distance attenuation | damping at the time of installing a short pipe type experimental silencer. It is a figure which shows distance attenuation | damping at the time of installing a reverse horn type experimental silencer. It is a figure which shows the relationship between the frequency and sound pressure in the measurement point P2. It is a figure which shows the relationship between the frequency and sound pressure in the measurement point P3. It is a figure which shows the relationship between the frequency and sound pressure in the measurement point P4. It is a figure which shows the relationship between the frequency in the measurement point P5, and a sound pressure. It is a figure which shows the relationship between the frequency and sound pressure in the measurement point P6. It is a figure which shows the calculation area | region of numerical analysis. It is a figure which shows the sound pressure distribution when not installing an experimental silencer. It is a figure which shows sound pressure distribution at the time of installing a short pipe type experimental silencer. It is a figure which shows the sound pressure distribution at the time of installing a reverse horn type experimental silencer. It is a figure which shows an equal loudness curve.

  Hereinafter, the soundproof house which concerns on embodiment of this invention is demonstrated.

  The soundproof house according to the present embodiment is used at a construction site, and is configured to cover a large vibration sieve used for construction. The soundproof house has an opening for discharging the earth and sand separated by the large vibrating screen to the outside. From the large vibration sieve, an ultra-low frequency sound of about 16 to 17 Hz is generated, and the ultra-low frequency sound leaks from the opening. Therefore, in this embodiment, the silencer which functions as an ultra-low frequency sound reduction apparatus is provided in the opening part of this soundproof house. The silencer is provided so as to protrude inside the soundproof house along the edge of the opening of the soundproof house. Moreover, the shape is cylindrical and is further provided integrally with the soundproof house. In the present embodiment, the silencer can reduce the very low frequency sound leaking from the opening.

  Next, the soundproof house according to the present embodiment will be described in detail with reference to the drawings. As shown in FIG. 1, the soundproof house 1 has a box-like structure, and the size thereof is a side length 12000 mm × depth width 8040 mm × height 9960 mm (see FIG. 2). In addition, the soundproof house 1 includes a wall surface and a ceiling plate by an assembly type sound insulation panel. The size of the soundproof house 1 of this embodiment is merely an example, and does not limit the present invention.

  Two vibration sieves 3 are provided inside the soundproof house 1. This vibration sieve 3 separates the earth and sand generated by excavation from water. In addition, a belt conveyor 4 is provided inside the soundproof house 1 for conveying the separated earth and sand to the outside. The earth and sand transported to the outside of the soundproof house 1 is transported by the transport vehicle 5.

  In addition, an opening 2 for exposing a part of the belt conveyor 4 to the outside of the soundproof house 1 is provided on one side surface which is the depth of the soundproof house 1 (see FIG. 3). That is, the soundproof house 1 has an opening 2 that is always open. The size of the opening 2 is a width of 1992 mm × a height of 996 mm. Note that the size, shape, and position of the opening 2 are merely examples, and do not limit the present invention.

  Since the vibration sieve 3 rotates at a rotation speed of about 1000 rpm, an ultra-low frequency sound of about 16 to 17 Hz is generated. And this very low frequency sound leaks outside from the opening 2. Therefore, in the present embodiment, the silencer 6 is provided in the opening 2 in order to reduce the ultra-low frequency sound.

  As shown in FIG. 2, the silencer 6 is provided so as to protrude inside the soundproof house 1 along the edge of the opening 2, and is provided integrally with the soundproof house 1. The silencer 6 has a quadrangular cylindrical shape with four panels. Note that the shape is not limited to a square cylindrical shape, and may be a cylindrical shape having a constant cross-sectional area such as a triangular cylindrical shape. Further, the silencer 6 is constituted by the same sound insulation panel as the wall surface of the soundproof house 1, thereby reducing the manufacturing cost. In this embodiment, as shown in FIG. 3, the depth of the silencer 6 is 1200 mm (see FIG. 4), but this size is merely an example and does not limit the present invention. In the following description, the shape of the silencer 6 may be referred to as a short tube type.

  Moreover, the depth of the silencer 6 can be set as appropriate. That is, it can be set as appropriate according to restrictions such as the size and shape of the soundproof house 1, the vibration sieve 3, the belt conveyor 4, and the like. Further, when this restriction is not present, it is desirable to determine the depth of the silencer 6 based on the length of the very low frequency sound generated from the vibration sieve 3. Specifically, it is desirable to make the depth of the silencer 6 depend on the wavelength of the ultra-low frequency sound, and to make it 1/4 of the wavelength of the ultra-low frequency sound, and the reduction performance is the highest.

Next, the silencing mechanism by the silencer 6 will be described. The silencer mechanism of the silencer 6 is based on the silencer mechanism of the expansion silencer. FIG. 5 is a side view schematically showing the expansion silencer. As shown in FIG. 5, the silencer B (cross-sectional area S, length l) is connected to the sound source part A via an inlet pipe C (cross-sectional area s, length li), and on the outlet side of the silencer B. Is connected to an outlet pipe D (cross-sectional area s, lo). The silencer B reduces the sound pressure by utilizing the reflection and interference of sound waves generated at the connection portion (change cross section) between the inlet tube C and the outlet tube D.
Here, the difference (insertion loss IL) between the sound pressure at the position X1 (output portion of the inlet pipe C) and the sound pressure at the position X2 (output portion of the outlet pipe D) is:

Is expressed as Here, k is a wavelength constant, k = (2πf) / c, f is the frequency of the very low frequency sound, and c is the speed of sound.
In the present embodiment, the sound output from the inlet pipe C can be regarded as an ultra-low frequency sound from a machine such as the vibration sieve 3 in the soundproof house 1, and the length lo of the outlet pipe D is zero. At (lo = 0), the insertion loss IL can be regarded as an insertion loss of very low frequency sound in the opening 2 of the soundproof house 1.

  On the other hand, when the insertion tube E (cross-sectional area s, length lo1) is provided from the outlet side of the silencer B toward the inside as shown in FIG.

It becomes.
Here, when the insertion pipe is not provided on the inlet side of the silencer B (that is, li1 = 0 in FIG. 6), this silencer mechanism can be applied to the soundproof house 1 of this embodiment, and the output from the inlet pipe C is output. The generated sound can be regarded as a very low frequency sound from a machine such as the vibrating screen 3 in the soundproof house 1.

  Therefore, the insertion loss IL can be increased by providing the insertion tube E. That is, it is possible to reduce the very low frequency sound generated from the sound source.

  The silencer 6 of this embodiment can reduce the ultra-low frequency sound generated from the vibration sieve 3 by using this mechanism. Further, in the present embodiment, the exit pipe D is not provided (that is, in FIG. 6 and Equation 3, lo = lo1), and therefore the length of the insertion pipe E is set to ¼ of the wavelength of the ultra-low frequency sound. In addition, the amount of reduction is the largest.

  Further, as shown in FIGS. 7 and 8, a silencer 7 having a quadrangular pyramid-shaped cylindrical shape whose front end side expands may be provided in the opening 2 of the soundproof house 1. The shape is not limited to a square frustum shape, and may be a pyramid shape such as a triangular frustum shape. In the present embodiment, the depth of the silencer 7 is 1200 mm and the spread angle is 78.7 degrees, but this size is merely an example and does not limit the present invention. In addition, the silencer 7 is provided integrally with the soundproof house 1 as in the above-described silencer 6, and is manufactured by the same sound insulation panel as the wall surface of the soundproof house 1, thereby reducing the manufacturing cost. In the following description, the shape of the silencer 7 may be referred to as an inverted horn type.

  A horn shape used in a speaker or the like can increase sound transmission efficiency by gradually increasing the cross-sectional area in the sound traveling direction (that is, by expanding in the sound traveling direction). In the present embodiment, the transmission of sound is hindered by installing a horn-shaped member in a direction opposite to the sound traveling direction. As a result, the silencer 7 can reduce the ultra-low frequency sound generated from the vibration sieve 3.

  As described above, by installing the silencer 6 and the silencer 7 in the opening 2 of the soundproof house 1, the ultra-low frequency sound generated from the large vibration sieve 3 can be effectively reduced. Moreover, the production cost of the silencer 6 can be reduced by using the same members as the soundproof house 1. Furthermore, since the depth of the silencer 6 and the silencer 7 is about 1 m, it is possible to effectively reduce the very low frequency sound while effectively utilizing the space inside the soundproof house 1.

  The opening 2 provided in the soundproof house 1 may be circular. In this case, since the shape of the silencer is provided along the edge of the opening 2, it has a cylindrical shape or a truncated cone shape. Further, by causing the belt conveyor 4 located in the vicinity of the opening 2 to function as a part of the silencer, and providing sound insulation panels at three places on the upper side and both sides of the opening 2 so as to protrude inward. A silencer may be realized.

[Model experiment]
Next, a model experiment performed to confirm the effectiveness of the present invention will be described.

  First, a block diagram of an apparatus used for a model experiment (hereinafter, also referred to as experimental equipment) will be described with reference to FIG. As shown in FIG. 9, the pink noise reproduced by the CD player 21 was amplified by an amplifier 22 and generated from the speaker 13a of the experimental vibration sieve 13 in the experimental model house 11 installed in the anechoic chamber. The pink noise is collected by the microphone 23 inside and outside the experimental model house 11 and output to the PC 24. Then, frequency analysis was performed on the PC 24 and the result was displayed on a display (not shown). The sampling frequency of the experiment is 2 kHz (c characteristic), the number of sample points is 4096, and the number of averaging is 50 times.

In this model experiment, the following commercially available apparatus was used.
CD player 21: manufactured by TEAC, CD-P1850
・ Amplifier 22: Made by TOA, POWER AMPLIFIER MODEL P300D
Microphone 23: Ono Sokki, MI-1233 (a non-directional 1 / 2-inch measurement condenser microphone)
Microphone preamplifier (not shown): Ono Sokki, MI-3110
Piston phone (microphone configuration): manufactured by Rion, NC-72 (generates sound with a sound pressure level of 114 dB-250 Hz)

  Next, the experimental model house 11 will be specifically described with reference to FIG. The experimental model house 11 was produced on a scale 1/12 that of the actual soundproof house 1. The experimental model house 11 was provided with one opening 12 having a size of 166 × 166 × 83 mm. In addition, the experimental model house 11 has a total of 188 places of 6 mm acrylic plates (2 each of 1000 × 670 mm, 1000 × 830 mm, and 830 × 670 mm) on a steel framework of 1 mm thickness. It was manufactured by screwing with.

  Further, as shown in FIG. 11 and FIG. 12, the opening 12 was provided with a short pipe type experimental silencer 16 and an inverted horn type experimental silencer 17, respectively. In addition, each experimental silencer was made of the same acrylic plate as the experimental model house 11.

  Next, the experimental vibration sieve 13 will be specifically described with reference to FIG. As shown in the figure, the experimental vibration sieve 13 includes a speaker 13a and a model sieve 13b. The model sieve 13b was made of a plywood plate having a thickness of 25 mm. Further, since this experiment is performed in the experimental model house 11 of 1/12 scale, the frequency of the pink noise generated from the speaker 13a is set to 192 Hz.

  Further, in this experiment, the microphone 23 was fixed to the microphone stand so that the center portion had a height of 124.5 mm as shown in FIG. In this experiment, the measurement points are P1, P2, P3, P4, P5, and P6, and the distances from the opening 12 are −50 mm, 166 mm, 249 mm, 332 mm, 415 mm, and 830 mm, respectively.

[Spectrum of sound pressure (analysis result by FFT)]
Next, the spectrum of sound pressure (analysis result by FFT) measured at each measurement point (P1 to P6) under the following three conditions using the above-described experimental equipment will be described.
(1) No experimental silencer installed (2) Short tube type experimental silencer 16 installed (3) Reverse horn type experimental silencer 17 installed

15 to 17 show the sound pressure spectrum (analysis result by FFT) under the conditions (1) to (3). In each figure, the horizontal axis represents frequency (Hz) and the vertical axis represents sound pressure (dB). When attention is paid to the internal sound pressure (sound pressure at the P1 point), peaks are observed at about 180 Hz, 260 Hz, and 340 Hz. These peaks appear at intervals of 80 Hz, and are considered to be due to standing waves generated in the experimental model house 11.
As shown in FIGS. 15 to 17, it is understood that there is an attenuation effect in the entire frequency range when any of the experimental silencer 16 and the experimental silencer 17 is installed inside the opening 12. It was.

[Spectrum of sound pressure (analysis result by octave band)]
Next, the sound pressure spectrum (analysis result by 1/3 octave band) under the three conditions described above is shown in FIGS. In each figure, the horizontal axis represents frequency (Hz) and the vertical axis represents sound pressure (dB).
As shown in FIGS. 18 to 20, it can be seen that even when the experimental silencer 16 and the experimental silencer 17 are installed inside the opening 12, there is an attenuation effect in the entire frequency range. It was.

[Attenuation of ultra-low frequency sound]
Next, the attenuation amount of the very low frequency sound inside and outside the experimental model house 11 will be described. Here, analysis was performed using sound pressures having center frequencies of 160 Hz, 200 Hz, 250 Hz, and 315 Hz, which are close to 192 Hz, which is a control target, among the analysis results of the octave band described above. In the actual soundproof house 1, these center frequencies correspond to 13.3 Hz, 16.7 Hz, 20.8 Hz, and 26.3 Hz, respectively.

  FIG. 21 shows the attenuation at each measurement point (P2 to P6) by the experimental silencer 16. In this figure, the horizontal axis represents frequency (Hz) and the vertical axis represents sound pressure (dB). For each frequency, the left bar graph shows the difference in the sound pressure inside and outside the house without the silencer, the middle bar graph shows the sound pressure difference in the house when the experimental silencer 16 is installed, and the right bar graph Indicates the attenuation amount of the very low frequency sound by the experimental silencer 16. As shown in FIG. 21, it was found that an attenuation effect of about 5 dB can be obtained in the entire frequency region.

  FIG. 22 shows the attenuation at each measurement point (P2 to P6) by the experimental silencer 17. In this figure, the horizontal axis represents frequency (Hz) and the vertical axis represents sound pressure (dB). For each frequency, the left bar graph shows the difference in the sound pressure inside and outside the house without the silencer, the middle bar graph shows the sound pressure difference in the house when the experimental silencer 17 is installed, and the right bar graph. Indicates the attenuation amount of the very low frequency sound by the experimental silencer 17. As shown in FIG. 22, it was found that an attenuation effect of about 4 dB can be obtained in the entire frequency region.

  Further, as shown in FIGS. 21 and 22, it was found that the experimental silencer 16 has a higher attenuation effect (about 1 dB) (about 1 dB in the figure) than the experimental silencer 17.

[Distance attenuation]
Next, distance attenuation of very low frequency sound will be described.
FIG. 23 shows the sound pressure at each measurement point (P2 to P6) for each frequency when the silencer is not used. FIG. 24 shows the sound pressure at each measurement point (P2 to P6) for each frequency when the experimental silencer 16 is attached. Furthermore, FIG. 25 has shown the sound pressure of each measurement point (P2-P6) at the time of attaching the experimental silencer 17 for every frequency. In each figure, the horizontal axis is the distance (mm) from the opening 12, and the vertical axis is the sound pressure (dB).

  As shown in these figures, since the slopes of the graphs are similar in each figure, the attenuation effect by the experimental silencer 16 and the experimental silencer 17 may not be related to the distance from the opening 12. all right.

[External sound pressure comparison]
Next, the comparison result of the sound pressure of the experimental model house 11 will be described.
FIG. 26 shows the relationship between the frequency and the sound pressure at the measurement point P2 for each of the above three conditions. Similarly, FIG. 27 shows measurement point P3, FIG. 28 shows measurement point P4, FIG. 29 shows measurement point P5, and FIG. 30 shows the relationship between frequency and sound pressure at measurement point P6. In each figure, the horizontal axis is frequency (Hz) and the vertical axis is sound pressure (dB).

  As shown in these figures, it was found that the attenuation effect by the experimental silencer 16 and the experimental silencer 17 can be obtained at any distance and frequency band.

  As explained above, the effect of the soundproof house 1 according to the embodiment of the present invention could be confirmed by this experiment.

[Numerical analysis]
Next, numerical analysis performed to confirm the effectiveness of the present invention will be described. In this analysis, the effectiveness of the present invention was confirmed by solving the Helmholtz equation within the range of discretization error using acoustic finite elements and boundary elements.

Here, the Helmholtz equation will be described.
A differential equation governing wave propagation phenomena such as electromagnetic waves, sound, and pressure is generally expressed by the following wave equation.

  Here, p (x, t) represents a scalar potential at a point x in the medium at time t, and c represents a wave propagation velocity. When the vibration of the medium is a steady-state vibration with a small amplitude, that is, when a signal in which the time dependency of p (x, t) is harmonically oscillated at the angular frequency ω is displayed in a complex manner,

It becomes. When this (Equation 5) is differentiated twice at time t,

It becomes. Substituting (Equation 5) and (Equation 6) into (Equation 4),

It becomes. And from (Equation 7)

The relationship is guided. This (Equation 8) is expressed as follows using wave number k = (ω / c).

  The equation (9) obtained in this way is called the Helmholtz equation.

  Next, calculation conditions in this analysis will be described. FIG. 31 shows the calculation area of this analysis. In the figure, the left side shows the internal area of the experimental model house 11, and the right side shows the external area outside the soundproof house 1. In this analysis, two sound sources were provided inside the experimental model house 11, and 192 Hz sound waves were generated from each sound source.

32 to 34 respectively show the sound pressures under the following conditions: (1) no silencer, (2) experimental silencer 16 installed, and (3) experimental silencer 17 installed. Distribution is shown.
As shown in FIGS. 32 and 33, it was found that the attenuation effect of about 8.5 dB can be obtained by installing the experimental silencer 16.
Further, as shown in FIGS. 32 and 34, it was found that an attenuation effect of about 7 dB can be obtained by installing the experimental silencer 17.

  Further, when comparing the above-described model experiment and numerical analysis, in any case, it was found that the amount of attenuation was larger when the experimental silencer 16 was installed.

  As described above, according to the present embodiment, by installing the silencer 6 and the silencer 7 in the opening 2 of the soundproof house 1, the ultra-low frequency sound generated from the large vibration sieve 3 is effectively reduced. be able to. Moreover, the production cost of the silencer 6 can be reduced by using the same members as the soundproof house 1. Furthermore, since the depth of the silencer 6 and the silencer 7 is about 1 m, it is possible to effectively reduce the very low frequency sound while effectively utilizing the space inside the soundproof house 1.

  In addition, a person with good ears can listen to the ultra-low frequency sound that the soundproof house 1 of the present embodiment is intended to reduce. However, by installing the muffler of the present embodiment in the soundproof house, the soundproof house 1 is extremely low. When the frequency sound is reduced by about several dB, the auditory attenuation becomes large (see the equal loudness curve in FIG. 35).

  Further, the silencer 6 and the silencer 7 according to the present embodiment may be used together with other silencers provided inside and outside the soundproof house 1 so as to further reduce the very low frequency sound.

  The present invention is not limited to the above-described embodiment, and it goes without saying that various improvements and modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Soundproof house 2 Opening part 3 Vibration part 6 Silencer 7 Silencer

Claims (3)

An ultra-low frequency sound reduction device provided at the opening of a soundproof house that covers a sound source that emits ultra-low frequency sound,
The ultra-low frequency sound reduction device is provided to protrude inside the soundproof house along the edge of the opening, has a cylindrical shape, and is provided integrally with the soundproof house,
The said shape is a cone shape which the front end side expands. The very low frequency sound reduction apparatus characterized by the above-mentioned.   A soundproof house that covers a sound source emitting ultra-low frequency sound and has an opening,
  The ultra-low frequency sound reduction device according to claim 1 is mounted.
  Soundproof house characterized by that.   The soundproof house according to claim 2, wherein a belt conveyor that conveys earth and sand from the inside of the soundproof house to the outside is provided through the opening.

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