JP7053389B2 - Noise reduction method and attic structure - Google Patents

Description

The present invention relates to a noise reduction method for reducing noise from the attic and an attic structure.

A soundproofing device has been proposed in which a sound absorbing material is erected behind the ceiling for soundproofing and soundproofing between adjacent rooms when the inside of a building such as a tenant building is partitioned by a partition wall up to the ceiling (Patent Document 1). ). The soundproofing device of Patent Document 1 is installed behind the ceiling above the partition wall.

On the other hand, if low-frequency noise is generated from equipment such as fans, air conditioners, and ducts installed in the so-called space behind the ceiling between the ceiling and the floor on the upper floor, go to the room under the equipment. Noise reduction may be required. In such a case, it is common to install a sound absorbing material on the equipment itself, not on the sound insulating device between the adjacent rooms. However, such measures against low-frequency sound have a large construction load, and the low-frequency sound cannot be significantly reduced.

Japanese Unexamined Patent Publication No. 8-222289

Therefore, an object of the present invention is to provide a noise reduction method and an attic structure for reducing noise from the attic.

The present invention has been made to solve at least a part of the above-mentioned problems, and can be realized as the following aspects or application examples.

[1] One aspect of the noise reduction method according to the present invention is
Measure the sound pressure level according to the frequency in the room with a sound level meter,
Set the set frequency you want to reduce based on the measurement result by the sound level meter, and set it.
Find the position in the horizontal plane behind the ceiling where the particle velocity of the set frequency is maximized.
It is characterized in that a sound absorbing material extending in the width direction of the attic and the height direction of the attic is installed in at least one of the positions.

According to one aspect of the noise reduction method, the noise from the ceiling can be reduced by installing the sound absorbing material at an appropriate position behind the ceiling.

[2] In one aspect of the noise reduction method,
Two parallel walls facing each other are arranged behind the ceiling.
The position can be obtained from the result of measuring the sound pressure level of the set frequency with the sound level meter at a plurality of points between the two walls.

According to one aspect of the noise reduction method, the sound absorbing material can be installed at an appropriate position based on the measurement results of the sound pressure levels at a plurality of places between two parallel walls facing each other behind the ceiling.

[3] In one aspect of the noise reduction method,
Two parallel walls facing each other are arranged behind the ceiling.
The position can be determined as a position at a distance from one of the two walls toward the other, which is an odd multiple of a quarter wavelength of the set frequency.

According to one aspect of the noise reduction method, the sound absorbing material can be installed at an appropriate position based on the wavelength of the set frequency.

[4] In one aspect of the noise reduction method,
Two parallel walls facing each other are arranged behind the ceiling.
The position is an odd multiple of 1 / 2n (n is a natural number) of the distance from one of the walls to the other when the distance between the two walls coincides with or approximates the length of the wavelength of the set frequency. It can be obtained as a position.

According to one aspect of the noise reduction method, the sound absorbing material can be installed at an appropriate position when the distance between two opposing walls behind the ceiling matches or approximates the wavelength of a standing wave.

According to one aspect of the attic structure, noise from the attic to the room can be reduced by the sound absorbing material provided in the attic.

[ 5 ] One aspect of the attic structure according to the present invention is
At least one of the positions where the horizontal distance from one of the two parallel walls behind the ceiling to the other is an odd multiple of 1/2 n (n is a natural number) of the distance between the two walls. It is characterized by having a sound absorbing material extending in the width direction of the ceiling and the height of the ceiling above the location.

According to one aspect of the attic structure, noise from the attic to the room can be reduced by the sound absorbing material provided in the attic.

[ 6 ] In one aspect of the attic structure,
The sound absorbing material can be a structure containing a breathable porous sound absorbing material.

According to one aspect of the attic structure, noise from the attic to the room can be reduced by the sound absorbing material including the porous sound absorbing material having a breathability.

According to the present invention, it is possible to provide a noise reduction method for reducing noise from the ceiling. Further, according to the present invention, it is possible to provide an attic structure that reduces noise from the attic.

It is a flowchart of the noise reduction method which concerns on this embodiment. It is a vertical sectional view of the measurement target room and the ceiling of the noise reduction method which concerns on this embodiment. It is a top view of the measurement target room of the noise reduction method which concerns on this embodiment. It is a top view of the ceiling of the construction target of the noise reduction method which concerns on this embodiment. It is a vertical cross-sectional view of the ceiling of the construction target of the noise reduction method which concerns on this embodiment, and is the figure explaining the relationship between a standing wave and a particle velocity. It is a vertical sectional view of the ceiling which shows the installation state of the sound absorbing material of the noise reduction method which concerns on this embodiment. It is a top view of the ceiling which shows the installation state of the sound absorbing material of the noise reduction method which concerns on this embodiment. It is a measurement result of the sound pressure level in a room in Example 1. It is a sound pressure distribution in a room in Example 1. It is a sound pressure distribution of the ceiling before construction in Example 1. It is a measurement result of the sound pressure level in a room after construction in Example 1. It is the sound pressure distribution in the room after the construction in Example 1.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unreasonably limit the content of the present invention described in the claims. Moreover, not all of the configurations described below are essential constituent requirements of the present invention.

In the noise reduction method according to the embodiment of the present invention, the sound pressure level according to the frequency in the room is measured by a sound level meter, the set frequency to be reduced is set based on the measurement result by the sound level meter, and the set frequency is set. A sound absorbing material extending in the width direction of the ceiling and the height of the ceiling is installed in at least one of the positions in the horizontal plane of the ceiling where the particle velocity of the ceiling is maximized. And.

1. 1. Noise Reduction Method The noise reduction method according to the present embodiment will be described with reference to FIGS. 1 to 7. 1 is a flowchart of a noise reduction method according to the present embodiment, FIG. 2 is a vertical sectional view of a measurement target chamber 10 and a ceiling back 20, FIG. 3 is a plan view of the measurement target chamber 10, and FIG. 4 is a plan view. It is a plan view of the ceiling back 20 to be constructed, FIG. 5 is a vertical sectional view of the ceiling back 20 to be constructed, and is a diagram explaining the relationship between the steady wave Sw and the particle velocity, and FIG. 6 is a sound absorbing material 40. , 41 is a vertical sectional view of the ceiling back 20 showing the installation state, and FIG. 7 is a plan view of the ceiling back 20 showing the installation state of the sound absorbing materials 40 and 41.

As shown in FIG. 1, the noise reduction method according to the present embodiment includes an indoor measurement step (S10), a setting step (S20), a position determination step (S30), and an installation step (S40). According to one aspect of the noise reduction method, the noise from the attic 20 can be reduced by installing the sound absorbing materials 40 and 41 at appropriate positions in the attic 20. The noise reduction method can be performed by installing the sound absorbing materials 40 and 41 at appropriate positions of the ceiling 20 above the measurement target room 10. Hereinafter, each step will be described in detail.

S10: The indoor measurement step is a step of measuring the sound pressure level according to the frequency in the room with a sound level meter. By measuring the sound pressure level in the room, it is possible to obtain the measurement result used for estimating or specifying the frequency of the noise in question.

As shown in FIG. 2, the “indoor” is the inside of the measurement target room 10 in which noise is a problem. As shown in FIGS. 2 and 3, the measurement target chamber 10 is, for example, a space formed by walls 11, 12, 13, 14 arranged on all sides, a ceiling 15, and a floor 16. In the present embodiment, the measurement target room 10 is one room, but the measurement target room 10 may be a set of two or more rooms in the building.

As shown in FIGS. 2 and 4, there is an attic 20 above the measurement target chamber 10. The attic 20 is a space surrounded by walls 21, 22, 23, 24 arranged on all sides, the ceiling 15 of the measurement target room 10, and the floor 25 on the upper floor. If there is no upper floor, a roof may be used instead of the floor 25.
The walls 21, 22, 23, 24 need not be arranged so as to completely block all sides, but include at least two parallel walls 21 and 22 facing each other. The attic 20 can be substantially rectangular in plan view. The wall 21 and the wall 22 face each other at both ends in the longitudinal direction of the ceiling 20 in a plan view. The wall 23 and the wall 24 face each other at both ends of the ceiling 20 in the lateral direction in a plan view. In the present embodiment, the walls 21 and 22 in the longitudinal direction of the attic 20 will be described, but instead of the two walls 21 and 22, two parallel walls 23 and 24 in the lateral direction of the attic 20 may be used. ..

Equipment 30 can be arranged behind the ceiling 20. The equipment 30 is, for example, a fan, an air conditioner, a duct, or the like, and the equipment 30 behind the ceiling 20 may be a source of noise in terms of indoor noise problems. Of the noise generated by the equipment 30, so-called low frequency sound of 20 Hz to 100 Hz tends to be a problem. In the noise reduction method according to the present embodiment, it is possible to reduce the noise corresponding to the dominant frequency component of the low frequency sound generated in the ceiling 20 in particular.

As the sound level meter, a commercially available sound level meter capable of frequency analysis of noise can be adopted. The sound level meter can measure the sound pressure level according to the frequency by, for example, 1/3 octave band analysis. In order to accurately set the frequency to be reduced, it is preferable to use a highly accurate bandpass filter, for example, a 1/3 octave band filter is preferable to a 1/1 octave band filter. According to the 1/3 octave band analysis, it is possible to measure the sound pressure level for each band in which one octave of the frequency is divided into three. The measurement result can be expressed as the sound pressure level of the center frequency of the 1/3 octave band.

The sound pressure level in the measurement target room 10 can be measured by a sound level meter at a plurality of places in the room, for example, at the positions of the square points in FIGS. 2 and 3. The measurement positions of FIGS. 2 and 3 are located in the horizontal plane of the height H2 lower than the total height H1 of the measurement target chamber 10, for example, at equal intervals of 0.5 m from the wall 11 to the wall 12 and 0.5 m from the wall 13 to the wall 14. It is arranged at equal intervals.

In this embodiment, an example showing an excellent sound pressure level of the set frequency at all the measurement positions in the fourth row from the wall 21 to the wall 23 in FIGS. 2 and 3 will be described.

S20: The setting step is a step of setting a set frequency to be reduced based on the measurement result by the sound level meter in the indoor measurement step (S10). The measurement result by the sound level meter is the sound pressure level according to the frequency at each measurement position. For example, the horizontal axis is the center frequency (unit is Hz) and the vertical axis is the sound pressure level (unit is dB). Create a broken line graph for each measurement position.

Since the noise in question indicates an excellent sound pressure level in this measurement result, the frequency indicating this excellent sound pressure level is set as a set frequency to be reduced. The set frequency is the center frequency of the bandpass filter of the sound level meter. The set frequency can be a low frequency sound of 100 Hz or less.

S30: The step of finding the position is a step of finding the positions A1 and A2 in the horizontal plane of the ceiling back 20 where the particle velocity of the set frequency set in the setting step (S20) is maximized. The "maximum particle velocity" of the set frequency includes those estimated to have the maximum particle velocity of the set frequency.

The step (S30) for determining the position can be carried out by the following two methods (1), (2) and (3).

(1) Measurement of sound pressure level behind the ceiling The sound pressure level of the set frequency at multiple locations between the two walls 21 and 22 at positions A1 and A2 in the horizontal plane of the ceiling 20 shown in FIG. 4 is measured by a sound level meter. It can be obtained from the measurement results. As a result, the sound absorbing materials 40, 41 (FIGS. 6 and 7) are placed at appropriate positions A1 and A2 based on the measurement results of the sound pressure levels at a plurality of locations between the two parallel walls 21 and 22 facing each other in the attic 20. Can be installed in. Appropriate positions A1 and A2 of the sound absorbing materials 40 and 41 are positions in the measurement target chamber 10 that are excellent in noise reduction effect.

From the result of measuring the sound pressure level in the ceiling 20, the position where the sound pressure level is minimized may be obtained as the positions A1 and A2 where the sound absorbing materials 40 and 41 are installed. The minimum sound pressure level means the maximum particle velocity at the set frequency. Therefore, the position where the sound pressure level is minimized can be obtained as the positions A1 and A2 by measuring the sound pressure level at a plurality of places in the ceiling 20 using a sound level meter. When the positions A1 and A2 are obtained from the measurement result of the sound pressure level by the sound level meter, the sound level meter used in the indoor measurement step (S10) can be used.

As shown by the black circles in FIG. 4, the measurement position by the sound level meter is at a predetermined interval from the wall 21 of the ceiling 20 to the facing wall 22, for example, every 0.5 m, and is in the horizontal plane of the height H4 from the ceiling 15. Can be set to. In FIG. 4, the measurement points are obtained for the wall 21 and the wall 22 which are parallel walls facing each other in the longitudinal direction of the ceiling back 20, but the measurement points may be obtained for the walls 23 and 24 in the lateral direction, and the measurement points may be obtained in the longitudinal direction. And may be measured in both the lateral direction. It is preferable to set the measurement position while avoiding the equipment 30.

In the present embodiment, the measurement position is targeted at the "longitudinal direction" of the attic 20, because the particle velocity is increased in the longitudinal direction of the attic 20 by performing the indoor measurement step (S10) in the entire area of the measurement target chamber 10. This is due to the estimation that there is a maximum position. Further, considering the wavelength of the low frequency sound and the distance L1 in the longitudinal direction, it is considered that the antinodes of the particle velocities of a plurality of standing waves are formed in the longitudinal direction. The distance L1 is the distance between two parallel walls 21 and 22 facing each other.

(2) Calculate the distance from the wall The wavelengths of the set frequencies of the positions A1 and A2 of one of the ceiling back 20 shown in FIG. 5 from one of the parallel walls 21 and 22 facing the ceiling back 20 toward the other. It can be obtained as a position at a distance L2 and L3 which is an odd multiple of 1/4 of. As a result, the sound absorbing materials 40 and 41 can be installed at appropriate positions based on the wavelength of the set frequency. In the present embodiment, the two walls 21 and 22 facing each other in the longitudinal direction of the ceiling 20 will be described, but the two walls 23 and 24 facing each other in the lateral direction may be used.

From the results of experiments by the inventors, it is inferred that a noise problem may occur when a standing wave Sw is generated in the ceiling 20 at a set frequency. Therefore, as shown in FIG. 5, when the wavelength of the set frequency to be reduced and the distance between the walls 21 and 22 of the attic 20 match or are close to each other, the standing wave Sw of the set frequency is the attic 20. It can be estimated that it has occurred. The positions of the antinodes B1 and B2 of the standing wave Sw are located at a distance L2 and L3, which is an odd multiple of 1/4 of the wavelength of the standing wave Sw, from one wall 21, and are the desired positions A1 and A2. It is estimated that the particle velocity of the set frequency at the positions A1 and A2 thus obtained becomes maximum.

Since the positions A1 and A2 correspond to the positions of the antinodes B1 and B2 of the standing wave Sw, the sound absorbing materials 40 and 41 can be arranged at the position where the particle velocity of the set frequency is maximized, so that the noise is efficiently reduced. It can be reduced.

In the present embodiment, the distance from the wall 21 to the wall 23 is targeted for the same reason as in (1) above, and the longitudinal direction is taken into consideration when the wavelength of the low frequency sound and the longitudinal distance L1 are taken into consideration. This is because it is considered that antinodes B1 and B2 of particle velocities of a plurality of standing waves Sw are formed.

The step (S30) for determining the position may be performed by combining the above (1) and the above (2). For example, when the positions A1 and A2 obtained in the above (1) and the positions A1 and A2 obtained in the above (2) match or approximate, it is obtained by either the above (1) or the above (2). Positions A1 and A2 may be adopted.

(3) Calculation based on wall spacing The set frequency is the distance L1 which is the distance between the two opposing walls 21 and 22 of the ceiling back 20 at the positions A1 and A2 in one horizontal plane of the ceiling back 20 shown in FIG. When it matches or approximates the length of the wavelength, it can be obtained as a position that is an odd multiple of 1 / 2n (n is a natural number) of the distance L1 from one wall 21 toward the other wall 22. As a result, the sound absorbing materials 40 and 41 can be installed at appropriate positions when the distance L1 between the walls 21 and 22 of the ceiling 20 matches or approximates the wavelength of the standing wave Sw. The reason why the case where the distance L1 and the length of the wavelength are close to each other is included is to consider that there is a bandwidth of the bandpass filter of the sound level meter. In the present embodiment, the distance L1 will be described, but instead of the distance L1, the full width W1 which is the distance between the two walls 23 and 24 facing each other in the lateral direction may be used. Since the odd multiple of 1 / 2n (n is a natural number) of the distance L1 is the distance inside the ceiling 20, the distance L1 is not exceeded. This is the same when the distance L1 is the full width W1.

Since the set frequency usually has a width in the band by the bandpass filter, the process can be simplified by directly calculating from the distance L1 of the ceiling 20 and obtaining the positions A1 and A2. In order to estimate that the distance L1 coincides with the wavelength of the standing wave Sw considered to be generated in the attic 20, it is premised that the distance L1 and the length of the set frequency match or approximate.

1-4. Installation process S40: In the installation process, sound absorbing materials 40, 41 extending in the width direction of the attic 20 and the height direction of the attic 20 in at least one of the positions A1 and A2 determined in the position determination step (S30). To install. Even when there are multiple positions A1 and A2, installing the sound absorbing materials 40 and 41 at at least one position has the effect of reducing noise, and installing the sound absorbing materials 40 and 41 at all of the plurality of positions A1 and A2. By doing so, the noise reduction effect can be obtained.

As shown in FIGS. 6 and 7, two sound absorbing materials 40 and 41 (shaded areas) can be installed at positions A1 and A2 of the attic 20. The sound absorbing materials 40 and 41 have the same width and height as the total width W1 and the total height H3 of the attic 20, and the thickness of the sound absorbing materials 40 and 41 can have, for example, 50 mm to 200 mm. The thickness of the sound absorbing materials 40 and 41 may be different depending on the material.

The sound absorbing materials 40 and 41 have a rectangular plate shape. A plurality of plate-shaped sound absorbing materials 40, 41 may be arranged in the lateral direction. By preparing a plurality of sets of a pair of hanging bolts 50 and arranging them side by side along both sides of the sound absorbing materials 40 and 41 in the lateral direction of the ceiling 20, the sound absorbing materials 40 and 41 are supported by being sandwiched by the hanging bolts 50. Can be done. Both ends of the hanging bolt 50 are connected to the ceiling 15 and the floor 25 on the upper floor. For example, the hanging bolt 50 may be hung from the floor 25 on the upper floor in order to hang the ceiling 15.

According to the noise reduction method of the present embodiment, the noise from the ceiling 20 in the measurement target room 10 can be efficiently reduced.

2. 2. Attic structure As shown in FIGS. 6 and 7, the attic structure 60 according to the present embodiment reduces the horizontal distance from one of the two opposing parallel walls 21 and 22 of the attic 20 to the other. The sound absorbing materials 40 and 41 extending in the width direction of the attic 20 and the height direction of the attic 20 are provided at one or more of the positions A1 and A2 which are odd multiples of the 1/4 wavelength of the set frequency to be set. In the present embodiment, the case where the distance L1 and the wavelength of the set frequency match or are close to each other will be described, but when the full width W1 and the wavelength of the set frequency match or are close to each other, the two walls in the lateral direction will be described. It may be 23 or 24.

It is preferable to install the sound absorbing materials 40 and 41 at two locations as shown in FIGS. 6 and 7 in order to obtain an excellent noise reducing effect, but for example, the noise reducing effect can be obtained with only one sound absorbing material 40. be able to.

The sound absorbing materials 40 and 41 can be a structure including a porous sound absorbing material having a breathability. Examples of the breathable porous sound absorbing material include fiber-based materials such as glass wool and rock wool, and foam-based materials using polymers such as urethane.

It is considered appropriate that the sound absorbing materials 40 and 41 have a flow resistance of 10,000 N · s / m ⁴ and a thickness of 100 mm. When the glass wool is used as the sound absorbing materials 40 and 41, the thickness can be 100 mm at 32 kg / m ³ , for example.

3. 3. Attic structure according to the modified example The attic structure 60 according to the modified example is the embodiment of 2 above when the distance L1 between the facing walls 21 and 22 of the attic 20 matches the length of the wavelength of the stationary wave Sw. Since it is the same as the ceiling structure 60, it will be described with reference to FIGS. 5 to 7.

As shown in FIG. 5, when the wavelength of the standing wave Sw coincides with the distance L1, the positions of the horizontal distances L2 and L3 from the wall 21 to the wall 22 are the positions of the antinodes of the particle velocity of the standing wave Sw. The distance L2 corresponds to the distance from the wall 21 to 1/4 of the wavelength of the standing wave Sw, and the distance L3 corresponds to the distance from the wall 21 to 3/4 of the wavelength of the standing wave Sw.

As shown in FIGS. 6 and 7, in the ceiling back structure 60 according to the modified example, the horizontal distances L2 and L3 from one of the parallel walls 21 and 22 facing in the longitudinal direction of the ceiling back 20 to the other are walls. The sound absorbing materials 40 and 41 extending in the width direction of the ceiling back 20 and the height direction of the ceiling back 20 are provided in at least one of the position A1 of 1/4 of the distance L1 and the position A2 of 3/4 of the distance between 21 and 22. You may. By doing so, it is possible to reduce the noise from the ceiling 20 to the inside of the measurement target room 10 by the sound absorbing materials 40 and 41 provided in the ceiling 20.

As the materials and sizes of the sound absorbing materials 40 and 41, the same materials and sizes as those of the ceiling structure 60 according to the embodiment can be adopted.

The sound pressure level according to the frequency was measured with a sound level meter in the measurement target chamber 10 having the shapes shown in FIGS. 2 and 3. The measurement target chamber 10 had a total length (distance L1) × total width W1 × total height H1 of 6.6 m × 2.2 m × 2.51 m. The attic 20 had the same shape as the measurement target room 10 in a plan view, and the total height was 1.3 m. Equipment 30 was arranged behind the ceiling 20. As the sound level meter, NA-28 manufactured by Rion Co., Ltd. with a 1/3 octave band filter function was used. The height H2 at the measurement position of the measurement target chamber 10 was 1.5 m. The measurement positions of the measurement target chamber 10 were 63 points in the horizontal plane at intervals of 0.5 m. The measurement results at the measurement positions Pt1 and Pt2 by the sound level meter are shown in FIG. The horizontal axis of FIG. 8 is the center frequency (unit: Hz), and the vertical axis is the sound pressure level (unit: dB).

In FIG. 8, the sound pressure level of 50 Hz was predominant at the measurement position Pt2. Based on the measurement results of this sound level meter, it was predicted that the noise in question was at a frequency of 50 Hz, and the frequency was set as a setting frequency at which 50 Hz was desired to be reduced.

Further, a sound pressure distribution in the 50 Hz band was created from the measurement results by the sound level meter, and this is shown in FIG. FIG. 9 corresponds to the plan view of the measurement target chamber 10, and the left side of FIG. 9 corresponds to the wall 11 and the right side corresponds to the wall 12. There were measurement positions with sound pressure levels of 60 dB to 65 dB at positions 2 m and 5 m from the wall 11. There was a tendency to have sound pressure levels close to each other along the width direction of the measurement target chamber 10.

The sound pressure level of 50 Hz, which is the set frequency, was measured using a sound level meter at the measurement position of the black square point in the longitudinal direction of the ceiling 20 in FIG. The measurement result is shown in FIG. In FIG. 10, the horizontal axis is the distance from the wall 21 of the ceiling 20 to the measurement position (unit is m), and the vertical axis is the sound pressure level (unit is dB).

From the measurement results of FIG. 10, the sound pressure level was the smallest at the measurement positions Pt3 and Pt4 (FIG. 4) 2 m and 5 m from the wall 21. That is, the particle velocity at the set frequency of 50 Hz was the maximum at the horizontal measurement positions Pt3 and Pt4 of the attic 20. Further, since the wavelength of the set frequency of 50 Hz is 6.8 m, the horizontal distances L2 and L3, which are odd times 1/4 of 6.8 m from the wall 21 to the wall 22, are 1.7 m and 5.1 m. Become. Since the distance L1 between the walls 21 and 22 was 6.6 m, when the distance L1 was divided into four equal parts, the distance L2 from the wall 21 was 1.65 m (6.6 / 4), and the distance from the wall 21 was 1. The distance L3 was 4.95 m (3 × 6.6 / 4).

Positions A1 and A2 shown in FIGS. 4 and 5 are set to 1.7 m and 5.1 m from the wall 21, and at positions A1 and A2, the width direction of the attic 20 and the ceiling as shown in FIGS. 6 and 7. Sound absorbing materials 40 and 41 extending in the height direction of the back 20 were installed. The sound absorbing materials 40 and 41 were arranged vertically side by side so as to have a length of 2.2 m and a height of 1.3 m using glass wool 32 kg / m ³ having a thickness of 100 mm.

After the construction of the sound absorbing materials 40 and 41, the sound pressure level was measured using a sound level meter at the measurement position in the second row from the wall 14 of the measurement target chamber 10. The measurement result at the measurement position Pt2 is shown in FIG. The horizontal axis of FIG. 11 is the center frequency (unit is Hz), the vertical axis is the sound pressure level (unit is dB), the broken line is the measurement result before the sound absorbing materials 40 and 41 are installed, and the solid line is the sound absorbing material. It is a measurement result after construction of materials 40 and 41. The measurement results at the measurement positions in the second row from the wall 14 are shown in FIG. The horizontal axis of FIG. 12 is the distance from the wall 11 (unit is m), the vertical axis is the sound pressure level (unit is Hz), and the broken line is the measurement result before the sound absorbing materials 40 and 41 are installed. The solid line is the measurement result after the sound absorbing materials 40 and 41 are installed.

According to FIG. 11, in the band having a center frequency of 50 Hz, the sound pressure level after the construction was reduced by about 11 dB as compared with that before the construction. According to FIG. 12, the sound pressure level in the band of the center frequency of 50 Hz after the construction was reduced in the entire longitudinal direction of the measurement target chamber 10 as compared with that before the construction.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the present invention includes substantially the same configurations as those described in the embodiments (eg, configurations with the same function, method, and result, or configurations with the same purpose and effect). The present invention also includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. Further, the present invention includes a configuration having the same action and effect as the configuration described in the embodiment or a configuration capable of achieving the same object. Further, the present invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

10 ... Measurement target room, 11, 12, 13, 14 ... Wall, 15 ... Ceiling, 16 ... Floor, 20 ... Ceiling back 21,22,23,24 ... Wall, 25 ... Floor, 30 ... Equipment, 40, 41 ... Sound absorbing material, 50 ... Suspension bolt, 60 ... Ceiling structure, A1, A2 ... Position, B1, B2 ... Belly, H1 ... Overall height, H2 ... Height, H3 ... Overall height, H4 ... Height, L1, L2 L3 ... Distance, Pt1, Pt2, Pt3, Pt4 ... Measurement position, Sw ... Constant wave, W1 ... Full width

Claims (6)

Measure the sound pressure level according to the frequency in the room with a sound level meter,
Set the set frequency you want to reduce based on the measurement result by the sound level meter, and set it.
Find the position in the horizontal plane behind the ceiling where the particle velocity of the set frequency is maximized.
A noise reduction method comprising installing a sound absorbing material extending in the width direction of the attic and the height direction of the attic at at least one of the positions. In claim 1,
Two parallel walls facing each other are arranged behind the ceiling.
A noise reduction method, characterized in that the position is obtained from the result of measuring the sound pressure level of the set frequency at a plurality of points between the two walls by the sound level meter. In claim 1,
Two parallel walls facing each other are arranged behind the ceiling.
A noise reduction method, characterized in that the position is determined as a position at a distance that is an odd multiple of 1/4 of the wavelength of the set frequency from one of the two walls toward the other. In claim 1,
Two parallel walls facing each other are arranged behind the ceiling.
When the distance between the two walls is close to the wavelength of the set frequency, the position is determined as an odd multiple of 1 / 2n (n is a natural number) of the distance from one of the walls to the other. A noise reduction method characterized by. At least one of the positions where the horizontal distance from one of the two parallel walls behind the ceiling to the other is an odd multiple of 1/2 n (n is a natural number) of the distance between the two walls. A ceiling-back structure characterized by having a sound-absorbing material extending in the width direction of the ceiling back and the height direction of the ceiling back above the location. In claim 5 ,
The attic structure is characterized in that the sound absorbing material is a structure containing a breathable porous sound absorbing material.

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