JP2007324388A - Low-frequency sound absorbing material and transformer sound-proofing system employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve sound absorbing characteristics of a low-frequency sound absorbing material in frequency bands of 100-200 Hz. <P>SOLUTION: This low-frequency sound absorbing material 1 is provided with a coating film 2 consisting of a silicone-based resin having a thickness of about 50 μm and a surface density of 0.68-0.78 kg/m<SP>2</SP>or 1.75-1.85 kg/m<SP>2</SP>; and a porous layer 3 consisting of a glass wool (density: 32 kg/m<SP>3</SP>) laminated on the back surface side of the coating film 2. The low-frequency sound absorbing material 1 employing the coating film 2 of type F' or type S is placed on a floor 51 of a metallic (made of steel sheet) casing 5 for accommodating the transformer so that the porous layer 3 may face the floor 51. According to the transformer sound proofing system having this structure, noises of about 4.0 dB can be reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a low-frequency sound-absorbing material and a transformer soundproofing system using the same, and in particular, to control noise of an apartment housing that generates frequency noise twice, four times, and six times the commercial frequency. The present invention relates to a low-frequency sound absorbing material that can be used and a transformer soundproofing system using the same.

  In recent years, in an urban area, since houses, buildings, condominiums, and the like are built in an overcrowded state, noise generated from a collective housing transformer installed in the vicinity of the condominiums and the like may have a significant impact on the lives of residents.

  For this reason, noise reduction measures are desired for collective housing transformers from the viewpoint of preserving the living environment of residents.

  Conventionally, as a noise reduction means of this type of transformer, the transformer is completely sealed with a soundproof wall such as a soundproof tank made of steel plate or concrete, or a soundproof wall having an open part in part. Is known (see, for example, Patent Document 1).

  However, in the soundproof wall having such a configuration, since the sound generated from the transformer for the apartment house is reflected in the noise barrier, the noise generated from the transformer for the apartment house cannot be effectively absorbed, As a result, there is a difficulty that the propagation of noise to the surroundings cannot be suppressed.

  For this reason, attempts have been made to cover the surroundings of a transformer for apartment buildings with a noise barrier made of low-frequency sound absorbing material such as glass wool, but such a noise barrier is generated from a transformer for apartment buildings. However, there was a problem that the prevailing noise could not be reduced sufficiently. That is, when a transformer for apartment buildings generates prevailing noise twice, four times, six times the commercial frequency such as 100 Hz, 200 Hz, and 300 Hz during operation, such a transformer for apartment buildings has a frequency band of about 300 Hz. Even if it is covered with a low-frequency sound absorbing material that absorbs noise, there is a problem in that it cannot sufficiently absorb noise in the frequency bands of 100 Hz and 200 Hz. Therefore, in order to perform noise control of an apartment housing transformer, it is desired to improve the sound absorption characteristics of the low frequency sound absorbing material in the frequency bands of 100 Hz and 200 Hz. In addition, since multi-family housing transformers are installed outdoors, if there is a structure that reflects sound around multi-family housing transformers, the response from the structure may vary depending on the installation environment of multi-family housing transformers. There is a problem that the sound is concentrated in a specific place, for example, an apartment existing around a transformer for an apartment house, and the noise level in the apartment increases. Therefore, it is desired to reduce the noise level generated from the collective housing transformer to a predetermined value.

Japanese Patent Laying-Open No. 2003-45726 (paragraph “0002”)

  The present invention controls frequency noise that is twice, four times, and six times the commercial frequency generated during operation of an apartment housing transformer, and can reduce the noise level around the housing transformer. An object of the present invention is to provide a high frequency sound absorbing material and a transformer soundproofing system using the same.

The low-frequency sound-absorbing material according to the first aspect of the present invention is a film made of a resin mainly composed of silicone having a surface density of 0.68 to 0.78 kg / m ² or 1.75 to 1.85 kg / m ^2. And a porous body layer laminated on the surface opposite to the sound source side of the film.

  According to a second aspect of the present invention, in the low-frequency sound absorbing material according to the first aspect, the porous body layer is made of glass wool.

  The transformer soundproofing system according to the third aspect of the present invention includes a housing that houses the transformer, and the low-frequency sound absorbing material according to the first or second embodiment is a porous body on the floor surface in the housing. The layer is placed with the floor side facing.

  According to a fourth aspect of the present invention, there is provided a housing that accommodates the transformer, and the low-frequency sound absorbing material of the first embodiment or the second embodiment has a porous body layer on the floor surface side on the floor surface in the housing. The soundproof panel is placed on the outside of the housing so as to surround the housing so as to surround the housing.

  According to a fifth aspect of the present invention, in the transformer soundproofing system according to the fourth aspect, the soundproofing panel includes the low frequency sound absorbing material according to the first aspect or the second aspect, and the outer surface of the low frequency sound absorbing material. And a metal protective layer which is in contact with the sound source side of the waterproof layer and has a property of transmitting sound.

  According to a sixth aspect of the present invention, in the transformer soundproofing system according to the fifth aspect, the protective layer is made of a punching metal or an expanded metal.

According to the low frequency sound absorbing material of the first to sixth aspects of the present invention and the transformer soundproofing system using the same, the surface density of the coating film of the low frequency sound absorbing material is 0.68 to 0.78 kg / m ^2. Alternatively, by setting the pressure to 1.75 to 1.85 kg / m ² , the peak frequency of the sound absorption coefficient of the low frequency sound absorbing material can be shifted to the low frequency band side, and the sound absorption coefficient in the 200 Hz frequency band can be improved. In addition, a low-frequency sound-absorbing material having a coating surface density of 0.68 to 0.78 kg / m ² or 1.75 to 1.85 kg / m ² is installed on the floor surface of the housing as the back rigid wall layer. As a result, it is possible to reduce the prevailing noise and to suppress the propagation of the noise to the vicinity of the apartment.

Hereinafter, preferred embodiments to which a low-frequency sound absorbing material of the present invention and a transformer soundproofing system using the same are applied will be described with reference to the drawings.
[Example 1]
FIG. 1 shows a cross-sectional view of a low-frequency sound absorbing material in the present invention.

In the figure, a low-frequency sound absorbing material 1 of the present invention is composed of a sheet-like laminate that is tuned according to the acoustic characteristics of a transformer to be described later. Specifically, the surface density is 0.68 to 0.78 kg / m ² or 1.75 to 1.85 kg / m ² , and the film 2 made of silicone resin and the sound source side of the film 2 (opposite the transformer) And a porous body layer 3 laminated on the opposite surface (hereinafter referred to as “rear surface”).

Here, the film 2 made of a silicone resin is used because, as will be described later, the film 2 made of a silicone resin does not change the sound absorption coefficient even in a high temperature atmosphere of 60 ° C. to 80 ° C. This is because the appearance does not deteriorate. The reason why the surface density of the film 2 is set to 0.68 to 0.78 kg / m ² or 1.75 to 1.85 kg / m ² is due to the film made of a silicone resin at the density as described later. This is because the peak frequency can be shifted to the low frequency band side. The thickness of the film 2 is about 50 μm.

The porous body layer 3 is formed of a material having flame retardancy. Specifically, it is formed of glass wool having a density of 32 kg / m ³ . In addition, the thickness of the porous body layer 3 is 1-50 mm, desirably about 10-25 mm.

  Here, the porous body layer 3 is laminated on the coating 2 because the coating 2 portion functions as an additional mass, that is, a weight, and the porous body layer 3 functions as a spring, that is, an air spring. This is to cause sound absorption by vibration.

  The coating 2 is integrated with the porous body layer 3 by adhesion, silicone graft reaction, or the like in order to improve the degree of freedom of the product form and simplify the construction on site.

  Next, the film | membrane suitable as the low frequency sound-absorbing material 1 of this invention is demonstrated.

  FIG. 2 shows the thickness, target heat resistance temperature, surface density, and the like of four types of test materials selected as candidates for the film 2 of the low-frequency sound absorbing material 1 of the present invention. Here, as each test material, a material obtained by punching a film formed in a sheet shape into a circle (diameter 90 mm) is used.

  FIG. 3 shows the results of measuring the sound absorption coefficient using the normal incident tube sound absorption coefficient for the four types of test materials shown in FIG. Here, the sound absorption coefficient of the normal incidence tube was measured based on JIS A1405: 1998 “Acoustic-Measurement of sound absorption coefficient and impedance by impedance tube—Standing wave ratio method”.

  In addition, it has been confirmed in the test of “transformer propagation sound frequency characteristics” separately conducted by the present applicant that the prevailing noise of the transformer is 100 Hz, 200 Hz, and 300 Hz. Moreover, since the frequency characteristic of the noise which a transformer produces changes with models, it is preferable to select the thing in the range of 200-300 Hz or 100-200 Hz as a peak frequency of a sound absorption coefficient.

From FIG. 3, the peak frequency of the sound absorption coefficient of the type F film made of silicone resin with a surface density of 0.65 kg / m ² is 315 Hz, and the surface density is 1.00 kg / m ² and the urethane resin. The peak frequency of the sound absorption coefficient of the type L film consisting of 400 Hz is 400 Hz, whereas the peak frequency of the sound absorption coefficient of the type S film consisting of a silicone resin with a surface density of 1.80 kg / m ² is 200 Hz. In addition, it can be seen that the peak frequency of the sound absorption coefficient of the type F ′ film made of silicone resin with a surface density of 0.73 kg / m ² is 250 Hz.

Here, in the present invention, the surface density of the type F ′ film is set to 0.68 to 0.78 kg / m ² because the sound absorption coefficient at 300 Hz decreases when the surface density is less than 0.68 kg / m ^2. In other words, if it exceeds 0.78 kg / m ² , the sound absorption rate at 200 Hz is lowered. Further, the surface density of the film type S was set to 1.75~1.85kg / m ^2, the surface density of 200Hz exceeds or 1.85 kg / m ² less than 1.75 kg / m ² This is because the sound absorptance of the sound is reduced.

From the above, the peak frequency of the sound absorption coefficient is reduced to the low frequency band side by using a film made of a silicone resin having an areal density of 0.68 to 0.78 kg / m ² or 1.75 to 1.85 kg / m ^2. And a sound absorption coefficient in a frequency band of 200 Hz can be improved.

Next, type F ′, type S, and type F samples made of silicone resin were selected as the coating 2, and heat resistance characteristic evaluation, outdoor environment evaluation, and acoustic characteristic evaluation were performed on these samples.
[Evaluation of heat resistance]
First, for heat resistance evaluation, after heating for 60 days at 60 ° C. and 80 ° C. using a thermostat, the appearance of the samples before and after heating was confirmed for the samples of type F ′, type S and type F. Also in the sample, there was no damage such as melting or missing due to heating. Further, when the sound absorption coefficient was measured by the normal incidence method for each sample before and after heating, no change in the sound absorption coefficient due to heating was observed in any sample.
[Outdoor environmental evaluation]
Next, for outdoor environment evaluation, a soundproof panel described later was prepared using a type F sample, and a predetermined test was performed. Specifically, a porous body layer made of glass wool having a thickness of 25 mm is provided on the sound source side of a type F film made of silicone resin and having an areal density of 0.65 kg / m ² , and a thickness of 50 mm is provided on the back side. A low-frequency sound-absorbing material (hereinafter referred to as “outdoor environment evaluation sample (25F50)”) in which porous layers made of glass wool are laminated is prepared with a standard size (length 607 mm × width 910 mm × thickness 75 mm) The outdoor environment evaluation sample (25F50) is bound in a bag with an outdoor protective film (Asahi Glass fluorine film) with a thickness of 21 μm, and further stored in a soundproof panel with a regular size (length 610 mm × width 920 mm × thickness 80 mm). Installed in the environment.

  The soundproofing panel was removed after 3 months from the installation, and the sound absorption coefficient was measured by the normal incidence method to confirm the presence or absence of characteristic deterioration. In this test, type F is used as the film sample, but this type F sample is the same as the type F ′ sample in that it is a silicone-based resin, that is, type F and type F. Since only the surface density of the film is different from ′, it can be considered that an outdoor environment evaluation test using the same material (silicone resin) is performed.

Thus, when the outdoor environment evaluation sample (25F50) was taken out of the outdoor protective film and its appearance was confirmed, no external water permeation or change in appearance due to ultraviolet light was observed. Further, when the sound absorption coefficient of the film was measured by the normal incidence method, the sound absorption coefficient at the peak frequency was 0.87, and no sign of characteristic deterioration was observed. Furthermore, the appearance of the outdoor protective film (fluorine film) was confirmed, and no fading or penetrating injury was observed.
[Evaluation of acoustic characteristics]
Finally, for the acoustic characteristic evaluation, the surface density is 0.68 to 0.78 kg / m ² and the type F ′ made of silicone resin and the surface density is 1.75 to 1.85 kg / m ² and the silicone type is used. Four types of soundproofing panels were created using two types of samples made of resin, and the sound absorption rate was measured by the reverberation chamber method while changing the arrangement of the porous body layers (glass wool) on the sound source side and back side. did. Here, as the four types of samples, first, a low-frequency sound absorbing material (hereinafter referred to as “first acoustic characteristics”) in which a porous body layer made of glass wool having a thickness of 25 mm is laminated on both sides of a type F ′ film. An evaluation sample (25F′25) ”) is prepared in a 2 × 3 plate size (607 mm × 910 mm), and secondly, a porous body made of glass wool having a thickness of 50 mm on the back side of the type F ′ film. A low-frequency sound-absorbing material (hereinafter referred to as “second acoustic characteristic evaluation sample (F′50)”) having a laminated structure was prepared in a 2 × 3 plate size (607 mm × 910 mm). 2 × 3 plate size (607 mm × 910 mm) of a low-frequency sound-absorbing material (hereinafter referred to as “third acoustic characteristic evaluation sample (25S25)”) in which porous layers made of glass wool having a thickness of 25 mm are laminated on both sides ), And fourth, A low-frequency sound-absorbing material (hereinafter referred to as “fourth acoustic characteristic evaluation sample (S50)”) in which a porous layer made of glass wool having a thickness of 50 mm is laminated on the back side of the film of type S is a 2 × 3 plate size. (607 mm × 910 mm), and the reverberation chamber sound absorption coefficient of these four types of samples was measured based on JIS A1509: 1998 “Measurement method of sound absorption coefficient of reverberation chamber method”. In the measurement, the measurement was carried out using 18 regular sound absorbing materials (total area 9.9 m ² ).

  FIG. 4 shows the measurement results of the reverberation chamber method sound absorption coefficient of the first to fourth acoustic characteristic evaluation samples. From the figure, the first acoustic characteristic evaluation sample (25F'25) in which glass wool is arranged on both sides (sound source side and back side) of the film 2 has a peak at 500 Hz, and both sides of the film 2 (sound source side and back side). It can be seen that the third acoustic characteristic evaluation sample (25S25) in which glass wool is disposed on the top has a peak at 400 Hz and has excellent sound absorption characteristics in a wide band (particularly in a frequency band of 1000 Hz or more). In contrast, the second acoustic characteristic evaluation sample (F′50) and the fourth acoustic characteristic evaluation sample (S50) in which the sound source side of the film 2 is exposed are concentrated on the low frequency band side and the sound absorption coefficient is increased. I understand that Therefore, since the prevailing noise from the transformer is 100, 200, and 300 Hz, the sound absorbing material in these frequency regions is a low frequency type in which the peak frequency of the coating 2 is shifted to the low frequency band side. No. 2 acoustic characteristic evaluation sample (F′50) is suitable, and when the 100 Hz component is high in the noise generated from the transformer, the peak frequency of the film 2 is shifted to the low frequency band side. It can be said that the acoustic characteristic evaluation sample (S50) is suitable.

Considering the above sound absorption coefficient measurement results and heat-resistant temperature, the film 2 of the low frequency sound absorbing material 1 of the present invention has a surface density of 0.68 to 0.78 kg / m ² and is made of a silicone resin. It can be said that a film of type S, or a film of type S made of a silicone resin having a surface density of 1.75 to 1.85 kg / m ² is preferable.
[Example 2]
Next, a transformer soundproofing system using the low frequency sound absorbing material 1 of the present invention will be described.

  5 (a) is a perspective view of a housing that houses the transformer, FIG. 5 (b) is a front view of a state in which the low-frequency sound-absorbing material 1 of the present invention is installed on the floor in the housing, and FIG. 5 (c). FIG. 5 shows a cross-sectional view along the line AA in FIG.

  In FIG. 5A, a metal (steel plate) housing 5 that houses a transformer (not shown) has a rectangular parallelepiped shape, and doors 5a and 5b are provided on the front surface thereof. Here, since the floor surface of the casing is made of metal (steel plate), the low-frequency sound-absorbing material 1 according to the present invention has a function as a back rigid wall layer.

  On the floor surface 51 of the casing 5 having such a configuration, as shown in FIG. 5B, a low-frequency sound absorbing material (second acoustic characteristic evaluation) using the above-described type F ′ or type S film 2 is used. A sample (F′50) or a fourth acoustic characteristic evaluation sample (low frequency sound absorbing material corresponding to S50) 1 is placed with the porous body layer 3 facing the floor 51. Here, the low frequency sound absorbing material is placed. It is preferable to use the material 1 having an area equal to covering almost the entire surface of the floor 51. In this embodiment, since the three-phase trunk cable 6 is present, the low-frequency sound absorbing material 1 is rectangular. The first and second low-frequency sound absorbing materials 1a and 1b divided into two are used, that is, in this embodiment, the three-phase trunk cable 6 is directed upward from the lower position of the housing 5. As shown in FIG. 5 (c), the first and second are set up because of the installation. The low-frequency sound absorbing materials 1a and 1b are placed on the floor surface 51 so as to sandwich the main cable 6 between the first and second low-frequency sound absorbing materials 1a and 1b. Shows a transformer.

According to the transformer soundproofing system having such a configuration, as described later, the noise of about 4.0 dB can be reduced by installing the low frequency sound absorbing material 1 on the floor surface 51 of the casing 5.
[Example 3]
Next, another transformer soundproofing system using the low frequency sound absorbing material 1 of the present invention will be described.

  FIG. 6 is a plan view showing the state of the transformer installation part before installing the soundproof panel.

  In the figure, a housing 5 that houses a transformer is surrounded by a rigid wall 8 made of, for example, a concrete wall having a thickness of about 200 mm. Here, the rigid wall on the back side of the housing is located at a position about 150 mm away from the back surface of the housing 5, and the rigid wall on the left side of the housing is located about 290 mm away from the left side of the housing 5. These rigid walls are erected so as to be parallel to the wall surface of the housing 5 at positions separated from the right side surface of the housing 5 by about 430 mm, and are arranged so as to have a U-shape as viewed from above. The horizontal width of the housing 5 is about 1300 mm, and the vertical width is about 1100 mm.

  In such a transformer installation environment, when complaints about noise occur from residents such as condominiums living in a position about 20 m away from the front of the housing 5 in the figure (hereinafter referred to as “high noise point”) P There is. This is probably because the sound generated from the transformer reverberates by the rigid wall on the left side of the housing and reaches the high noise point P.

  FIG. 7 is a plan view showing a state of a transformer installation part after installing a soundproof panel of the present invention which will be described later. In the figure, parts common to those in FIG. 6 are denoted by the same reference numerals and detailed description thereof is omitted.

  In FIG. 7, first, the soundproof panel 9 shown in FIG. 8 is arranged on the sound source side (transformer side) of the rigid wall 8 in parallel with the wall surface of each rigid wall.

  As shown in FIG. 9, the soundproof panel 9 is a low-frequency sound absorbing material (second acoustic characteristic evaluation sample (F′50) or fourth acoustic characteristic evaluation sample) using the type F ′ or type S film 2 described above. (Low-frequency sound absorbing material corresponding to (S50)) low-frequency sound absorbing material) 1, a waterproof layer 10 made of a fluorine film covering the outer surface of the low-frequency sound absorbing material 1, and the sound source side of the waterproof layer 10; And a protective layer 11 made of a punching metal or an expanded metal. The waterproof layer 10 and the protective layer 11 covering these low-frequency sound absorbing materials 1 are housed in a U-shaped stainless steel panel frame member 12, for example. It is unitized by the body 13 being attached.

  The dimensions of the soundproof panel 9 are 610 mm in length, 920 mm in width, and 55 mm in height, and the dimensions of the low frequency sound absorbing material 1 are 607 mm in length, 910 mm in width, and 55 mm in height. By using the unit type soundproof panel 9 having such a configuration, it is possible to mount the unit in a short time in the field, and the deterioration of the characteristics is reduced in an outdoor environment.

  FIG. 10 is an explanatory diagram when the installation conditions of the soundproof panel and the low frequency sound absorbing material are changed. Here, under condition 1, six soundproof panels 9 are arranged in two rows on the rigid walls 8 on the back side and both side surfaces of the housing, respectively, and furthermore, low-frequency sound absorption on the floor surface 51 in the housing 5. Material 1 is installed. In Condition 2, in Condition 1, the low frequency sound absorbing material 1 in the housing 5 is cut. In the condition 3, in the condition 2, all the soundproof panels 9 are cut.

  Under the installation conditions of such a soundproof panel and a low-frequency sound absorbing material, a sound pressure level value (F characteristic) of 200 Hz was measured using a “Rion normal sound level meter NL-22”. Note that the measurement point was set at a position 1 m away from the center of the front of the transformer (enclosure) at a height of 1 m above the ground. In addition, the measurement was performed at a height of 1 m above the ground at the high noise point P.

  FIG. 11 shows a sound pressure level value (F characteristic) of 200 Hz in type F ′ and type S obtained by such a measuring method.

  From the figure, it is possible to reduce the noise of 200 Hz by installing a low-frequency sound absorbing material on the floor of the cabinet 5, and to install a soundproof panel around the cabinet that houses the transformer. Thus, it is possible to further reduce the 200 Hz dominant noise. Specifically, first, a remarkable reduction effect exceeding 10 dB is recognized on the front surface of the housing 5. Second, even when the installation conditions of the soundproof panel and the low-frequency sound absorbing material are changed, the same tendency is observed for both the type F ′ and the type S. Third, when the condition 1 and the condition 2 are compared, it can be seen that a noise reduction effect of 2.3 to 4.5 dB can be obtained by installing a low-frequency sound absorbing material inside the housing 5. Fourth, it can be seen that the noise reduction effect is generally high for Type S. Fifth, a sound pressure level of 200 Hz at the high noise point P is recognized to be 3.7 to 5.2 dB for Type F ′ and 7.6 to 9.1 dB for Type S.

  The present invention can be changed and modified as follows within the scope of the claims.

  1stly, in the above-mentioned Example, although the low frequency sound-absorbing material is arrange | positioned only in the trunk line cable side of the housing which accommodates a transformer, it is preferable to install also on the floor surface by the side of a branch cable.

  Secondly, in the above-described embodiments, the transformer for an apartment house is described. However, the same effects as those of the present invention can be achieved even when applied to a cubicle type high-voltage power receiving facility that accommodates the transformer.

Sectional drawing of the low frequency sound-absorbing material in the 1st Example of this invention. Explanatory drawing which shows the target heat-resistant temperature, surface density, etc. of four types of test materials selected as a candidate of the film | membrane of a low frequency sound-absorbing material. Explanatory drawing which shows the measurement result of the sound absorption coefficient in four types of test materials. Explanatory drawing which shows the measurement result of the reverberation room method sound absorption coefficient in four types of acoustic characteristic evaluation samples. It is explanatory drawing of the transformer sound-insulation system in 2nd Example of this invention, A part (a) is a perspective view of the housing which stores a transformer, A part (b) is a low frequency sound absorption on the floor surface in a housing The front view of the state which installed the material, and a part figure (c) is sectional drawing which follows the AA line of part figure (b). The top view which shows the condition of the transformer installation part before installing a soundproof panel. The top view which shows the condition of the transformer installation part after installing a soundproof panel. The front view of a soundproof panel. Explanatory drawing which shows the assembly condition of a soundproof panel. Explanatory drawing at the time of changing the installation conditions of a soundproof panel and a low frequency sound-absorbing material. Explanatory drawing which shows the sound pressure level value (F characteristic) of 200 Hz in the soundproof panel of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Low frequency sound-absorbing material 2 ... Film | membrane 3 ... Porous body layer 5 ... Housing 51 ... Floor surface 9 ... Soundproof panel

Claims (6)

A film made of a resin mainly composed of silicone having a surface density of 0.68 to 0.78 kg / m ² or 1.75 to 1.85 kg / m ² , and a layer opposite to the sound source side of the film. A low-frequency sound-absorbing material comprising a porous body layer.   The low-frequency sound-absorbing material according to claim 1, wherein the porous body layer is made of glass wool. With a housing to house the transformer,
The transformer soundproofing system, wherein the low-frequency sound-absorbing material according to claim 1 or 2 is placed on the floor surface of the enclosure with the porous body layer facing the floor surface side. . With a housing to house the transformer,
The low-frequency sound-absorbing material according to claim 1 or 2 is placed on the floor surface in the enclosure with the porous body layer facing the floor surface side.
A transformer soundproofing system, wherein a soundproofing panel is provided on the outside of the housing so as to surround the housing so as to surround the housing.     The soundproof panel is in contact with a low frequency sound absorbing material according to claim 1 or 2, a waterproof layer covering an outer surface of the low frequency sound absorbing material, and a sound source side of the waterproof layer, and transmits sound. The transformer soundproofing system according to claim 4, further comprising a protective layer made of metal having 6. The transformer soundproofing system according to claim 5, wherein the protective layer is made of a punching metal or an expanded metal.

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