JP2006313055A - Silencer for ventilating air duct - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silencer for a ventilating air duct that provides higher silencing performance and suppresses the generation of wind noise without changing the appearance size. <P>SOLUTION: The silencer for a ventilating air duct is disposed at some midpoint along the ventilating air duct and silences noise passing through the ventilating air duct. The silencer has a square-barrel-shaped casing 4 having an opening end 2a facing toward an upstream ventilating air duct 3a and the other opening end 2b facing toward a downstream ventilating air duct 3b. A first noise absorbing member 5a and a second noise absorbing member 5b each made up of a noise absorbing material 7 and a porous plate 6 are provided on opposing inner walls of the casing 4 in a direction from the upstream side to the downstream side of the passage, with a space interposed therebetween. The first noise absorbing member 5a is greater in thickness than the second noise absorbing member 5b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a splitter-type ventilation wind tunnel silencer that silences noise generated from a ventilation fan or the like that is interposed in the ventilation wind tunnel and passes through the ventilation wind tunnel.

  As a conventional example of this type of splitter-type ventilation wind tunnel silencer, a noise absorbing member having a uniform thickness is provided on opposing inner walls of a casing interposed in the middle of the ventilation wind tunnel to reduce noise (Japanese Patent No. 3059057). No. publication).

Japanese Patent No. 3059057

  Incidentally, in the silencer for a splitter type ventilation wind tunnel as described in Patent Document 1, it is necessary to increase the amount of the sound absorbing material in order to improve the silencing performance. Specifically, it is necessary to increase the thickness of the sound absorbing material or to increase the length of the sound absorbing material. However, in the former case, the interval between the sound absorbing members facing each other becomes narrow. This means that the cross section of the flow path is narrowed, resulting in an increase in flow rate. As a result, there arises a problem that wind noise (self-noise) increases. In the latter case, when the total length of the silencer is restricted from the viewpoint of installation space, there is a problem that the length of the sound absorbing member cannot be sufficiently secured and desired performance characteristics cannot be obtained. Therefore, there has been a demand for a silencer for a ventilation wind tunnel having the same external dimensions, high noise reduction performance, and low generation of wind noise.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a silencer for a ventilation wind tunnel having a high noise reduction performance and a low occurrence of wind noise in a silencer having the same external dimensions. Is to provide.

  In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention is a ventilation wind tunnel silencer that is interposed in the ventilation wind tunnel and silences noise passing through the ventilation wind tunnel. A square cylindrical casing facing the side ventilation wind tunnel and the other open end facing the downstream ventilation wind tunnel, and a plurality of sound absorbing members each composed of a sound absorbing material and a perforated plate are provided on opposing inner walls of the casing. The members are provided at intervals in the flow path direction, and the thickness of the plurality of sound absorbing members is gradually reduced from the upstream side toward the downstream side.

  With the above configuration, the sound reduction performance is improved by increasing the thickness of the upstream sound absorbing member. On the other hand, when the thickness of the upstream side sound absorbing member is increased, the cross section of the flow path is narrowed, resulting in an increase in flow velocity and an increase in wind noise. However, since the thickness of the downstream sound absorbing member is small and there is a gap between the upstream sound absorbing member and the downstream sound absorbing member, the flow passage area is rapidly expanded, and a vortex is generated in this portion to generate wind noise. It is considered that the wind noise is reduced by reducing the energy. As a result, in the silencer having the same external dimensions, it is possible to realize a ventilation wind tunnel silencer that has high silencing performance and generates less wind noise.

  The invention according to claim 2 is the silencer for a ventilation wind tunnel according to claim 1, wherein the plurality of sound absorbing members are located on the first sound absorbing member located on the upstream side of the flow path and on the downstream side of the flow path. The thickness of the first sound absorbing member is larger than the thickness of the second sound absorbing member.

  As described above, even if the plurality of sound absorbing members are constituted by the first sound absorbing member and the second sound absorbing member, the same operations and effects as those of the first aspect can be obtained.

  The invention described in claim 3 is the silencer for a ventilation wind tunnel according to claim 2, wherein the external dimensions are the same, and one sound absorbing member is provided on each opposing inner wall in the casing. The filling amount of the sound absorbing material is equal to the sum of the filling amount of the sound absorbing material filled in the first sound absorbing member and the filling amount of the sound absorbing material filled in the second sound absorbing member, and the one When assuming a silencer in which the length of the sound absorbing member in the flow path direction is equal to the total length of the first sound absorbing member and the second sound absorbing member in the flow path direction, the thickness of the sound absorbing member in the silencer Is t3 [mm], the thickness of the first sound absorbing member is t1 [mm], and the thickness of the second sound absorbing member is t2 [mm], t3 = (t1 + t2) / 2 is satisfied. To do.

  With the above-described configuration, it is possible to realize a ventilation wind tunnel silencer with high noise reduction performance and less wind noise generation under the same amount of sound absorbing material.

  The invention according to claim 4 is the silencer for a ventilation wind tunnel according to claim 2 or 3, wherein the length of the first sound absorbing member in the flow path direction and the flow path direction of the second sound absorbing member. It is characterized by being equal to the length of.

  The invention according to claim 5 is the silencer for a ventilation wind tunnel according to any one of claims 2 to 4, wherein a distance between the first sound absorbing member and the second sound absorbing member is 10 to 300 [mm]. It is characterized by being.

With the above configuration, the sound reduction performance can be improved. The reason why the distance between the first sound absorbing member and the second sound absorbing member is limited to 10 to 300 [mm] is as follows.
That is, if it is less than 10 [mm], there is no effect outside the effective frequency band, and in the range exceeding 300 mm, the application of the noise to be reduced in the silencer for a ventilation wind tunnel according to the present invention is applied. This is because two valleys are generated in the frequency band of 63 to 8000 [Hz], which is in the range, and the performance characteristics as a silencer remain uneasy.

  According to the present invention, it is possible to realize a splitter-type ventilation wind tunnel silencer that has a high silencing performance and generates less wind noise under the same outer dimensions of the silencer.

  Hereinafter, a splitter type silencer for a ventilation wind tunnel according to the present invention will be described in detail based on embodiments. Note that the present invention is not limited to the following embodiments.

(Embodiment 1)
1 is a perspective view of a silencer for a ventilation wind tunnel according to Embodiment 1, FIG. 2 is a cross-sectional view of the silencer for a ventilation wind tunnel, and FIG. 3 is a sectional view taken along the line BB in FIG. 4 is a cross-sectional view taken along the line CC in FIG. The silencer 1 is a silencer for a ventilation wind tunnel in an underground building such as a road ventilator. The silencer 1 is provided in the middle of a ventilation wind tunnel that communicates a machine room in which a blower or the like is stored with the outside. It is a silencer that reduces noise. This silencer 1 for a ventilation wind tunnel has a casing 4 with one opening end 2a facing the upstream ventilation wind tunnel 3a (see FIG. 2) and the other opening end 2b facing the downstream ventilation wind tunnel 3b (see FIG. 2). . The casing 4 is formed in a rectangular tube shape having a height H, a length L, and a width W, and is made of, for example, a galvanized steel plate. A first sound absorbing member 5a and a second sound absorbing member 5b are provided on the inner walls facing each other in the casing 4 in this order from the upstream side to the downstream side of the flow path with a predetermined interval L3. Yes. The first sound-absorbing member 5a and the second sound-absorbing member 5b are filled in the perforated plate 6 and the perforated plate 6 in which a large number of holes 6b are formed in the flat portion 6a projecting inward of the casing 4 and parallel to the flow path. It is comprised from the sound-absorbing material 7 (for example, water-repellent glass wool). The perforated plate 6 is made of, for example, a galvanized steel plate.

What should be noted here is that the thickness t1 (see FIG. 3) of the first sound absorbing member 5a is set larger than the thickness t2 (see FIG. 4) of the second sound absorbing member 5b. Compared with a silencer such as the conventional example having the same dimensions (the same filling amount of the sound absorbing material 7) and having one sound absorbing member provided on each of the opposing inner walls in the casing 4 due to such a configuration, The sound reduction performance is improved and wind noise is reduced. This point is proved by the experiment result of the present inventor in Example 1 described later.
In the silencer for a ventilation wind tunnel according to the present embodiment, it is preferable to set the interval L3 in the range of 10 to 300 [mm]. Thereby, in the silencer for ventilation wind tunnel according to the present embodiment, there is an effect that a stable sound reduction performance is obtained in the frequency band (63 to 8000 [Hz]) of noise to be reduced. This point is proved by the experiment result of the present inventor in Example 2 described later.

  In the present embodiment, the length L1 (see FIG. 2) of the first sound absorbing member 5a and the length L2 (see FIG. 2) of the second sound absorbing member 5a are set equal to each other. It is not limited to this, and the length L1 may be larger or smaller than the length L2.

(Other matters)
In the above example, two sound absorbing members are provided in the flow path direction, but the present invention is not limited to this, and three or more sound absorbing members are provided, and the thickness of each sound absorbing member is set upstream of the flow path. You may comprise so that it may become small sequentially toward the downstream from the side.

(Experimental example 1)
The silencer according to the above embodiment, which is set to the following dimensions (hereinafter referred to as the present invention), and the silencer provided with the single sound absorbing member shown in FIG. 6 (hereinafter referred to as Comparative Example 1). The sound reduction performance test was conducted under the following conditions.

-Dimensions of the present invention (see FIG. 5)
Total length L = 1800 [mm], length L1 of first sound absorbing member 5a = 810 [mm], length L2 of second sound absorbing member 5b = 810 [mm], interval L3 = 88 [mm], open end and sound absorbing The distance L4 between the members 5a and 5b is 44 [mm], the thickness t1 of the first sound absorbing member 5a is 215 [mm], and the thickness t2 of the second sound absorbing member 5b is 175 [mm]. That is, the average thickness of the entire sound absorbing member was the same as in Comparative Example 1 shown below.

-Dimensions of Comparative Example 1 (see FIG. 6)
The total length L = 1800 [mm], the length L1 of the sound absorbing member 50 = 1620 [mm], and the thickness t3 of the sound absorbing member 50 = 200 [mm].

-Experiment conditions It experimented about flow velocity: 0 [m / s], 3 [m / s], 5 [m / s], and 7 [m / s].
Center frequency of measurement object: 63 [Hz], 125 [Hz], 250 [Hz], 500 [Hz], 1K [Hz], 2K [Hz], 4K [Hz], 8K [Hz]
Measurement items: pressure loss (hereinafter abbreviated as pressure loss) [Pa], sound reduction performance [dB], wind noise volume [dB]

Experimental results The experimental results are shown in Tables 1 to 5 and FIGS. Table 1 shows measured values of sound reduction performance and pressure loss related to the present invention, Table 2 shows measured values of wind noise related to the present invention, and Table 3 shows sound reduced performance related to Comparative Example 1. Table 4 shows measured values of wind noise for Comparative Example 1, and Table 5 compares the sound reduction performance of the present invention and Comparative Example 1. It is. 7 is a graph comparing the sound reduction performance of the present invention and Comparative Example 1 when using a wind speed of 5 [m / s], and FIG. 8 is a graph showing measured values of wind noise relating to the present invention. 9 is a graph showing measured values of pressure loss related to the present invention, FIG. 10 is a graph showing measured values of wind noise regarding Comparative Example 1, and FIG. 11 shows measured values of pressure loss related to Comparative Example 1. It is a graph to show. In Tables 2, 4 and 8 and 10, the average value (OA) is also shown.

[Examination of experimental results]
As apparent from Table 1 and FIG. 7, it is recognized that the present invention has a greater sound reduction performance in all frequency bands than Comparative Example 1. Further, as is clear from Table 1, it can be seen that the magnitude of wind noise generation is almost the same between the present invention and Comparative Example 1. As a result, in the silencer having the same outer dimensions, the present invention means that a silencer with high noise reduction performance and less wind noise can be realized.

The reason why such a result was obtained is considered as follows.
That is, in the present invention, the sound reduction performance is improved by increasing the thickness of the first sound absorbing member. On the other hand, when the thickness of the first sound absorbing member 5a is increased, the cross section of the flow path is narrowed, resulting in an increase in flow velocity and an increase in wind noise. However, since the thickness of the second sound absorbing member 5b is small and there is an interval between the first sound absorbing member 5a and the second sound absorbing member 5b, the flow path area is rapidly expanded, and a vortex is generated in this portion and the wind is cut. It is considered that the wind noise is reduced by reducing the sound energy. In addition, since the thickness of the 2nd sound absorption member 5b is small, since the flow-path cross section in the part is large, the flow velocity becomes small and generation | occurrence | production of a wind noise is small.
Therefore, the present invention can be suitably applied to a silencer in which the size of the entire silencer is regulated from the installation location or the like and a high sound reduction performance is required.

(Experimental example 2)
As shown in FIG. 12, the silencer (hereinafter referred to as Comparative Example 3) is the same as that of Comparative Example 1 except that the total length L and the length L of the sound absorbing member 50 are different. An experiment similar to that described above was performed for a silencer (hereinafter referred to as Comparative Example 4) having the same overall length L as in Example 3 and having the central portion of the sound absorbing member recessed to increase the sound absorption area.

-Dimensions of Comparative Example 3 (see FIG. 12)
The total length L is 1500 [mm], the length L1 of the sound absorbing member 50 is 1282 [mm], and the thickness t3 of the sound absorbing member 50 is 225 [mm].

-Dimensions of Comparative Example 4 (see FIG. 13)
Total length L = 1500 [mm], sound absorbing member length L1 = 1282 [mm], sound absorbing member thickness t3 = 225 [mm], interval between recesses t4 = 100 [mm], bottom surface of recess and casing outer wall The interval t5 = 50 [mm].

Experimental conditions Same as Experimental Example 1.

Experimental results The experimental results are shown in Table 6 and FIG. Table 1 shows the sound reduction performance and pressure loss of Comparative Example 3 and Comparative Example 4 when the wind speed is 3 m / sec. FIG. 14 is a graph comparing the sound reduction performance of Comparative Example 3 and Comparative Example 4 when the wind speed is 3 m / sec.

[Examination of experimental results]
As apparent from Table 6 and FIG. 14, it is understood that the noise reduction performance tends to be worse in Comparative Example 4 than in Comparative Example 3. Further, as is apparent from Table 1, it is understood that the pressure loss is almost the same. As a result, if the central portion of the sound absorbing member is recessed to increase the sound absorbing area, the sound reducing performance is deteriorated.

(Experimental example 3)
As shown in FIG. 15, the silencer (hereinafter referred to as Comparative Example 5 and Comparative Example 5A) is the same as that of Comparative Example 1 except that the total length L and the length L1 of the sound absorbing member 50 are different. As shown, when two comparative examples 5 (comparative example 5A) were connected in series (hereinafter referred to as comparative example 6), an experiment similar to the above was performed.

-Dimensions of Comparative Example 5 (Comparative Example 5A) (see FIG. 15)
The total length L is 750 [mm], the length L1 of the sound absorbing member 50 is 640 [mm], and the thickness t3 of the sound absorbing member is 225 [mm].

Experimental conditions Same as Experimental Example 1.

Experimental results The experimental results are shown in Table 7 and FIG. Table 7 shows the sound reduction performance and pressure loss of Comparative Example 5 (Comparative Example 5A) and Comparative Example 6 when the wind speed is 3 m / sec. FIG. 17 is a graph comparing the sound reduction performance of Comparative Example 5 (Comparative Example 5A) and Comparative Example 6 when the wind speed is 3 m / sec.

[Examination of experimental results]
As apparent from Table 7 and FIG. 17, the sum of the sound reduction performance values of Comparative Example 5 does not match the sound reduction performance value of Comparative Example 6. In other words, when the same silencer is used alone or when two stages are connected in series, the sum of the sound reduction performance when used alone is different from the sound reduction performance when two stages are connected in series. It was.

  Further, as apparent from Table 7 and FIG. 17, when the sound reduction performance of Comparative Example 6 and Comparative Example 3 having the same dimensions as Comparative Example 6 are compared, they are almost the same in the frequency band of 125 to 500 [Hz]. It is recognized that it has performance. Here, paying attention to the pressure loss, the latter is about 70% of the former in the total of the pressure loss of Comparative Example 5 (in the case of a single unit) and the pressure loss of Comparative Example 6 (in the case of two-stage series). Is recognized.

(Examination of Experimental Examples 1 to 3 above)
From Experimental Example 2, if the central portion of the sound absorbing member is recessed, the sound reduction performance deteriorates. On the other hand, from Experimental Example 3, it is considered that when the sound absorbing member is completely separated and a certain interval is provided between the two sound absorbing members, some change occurs in the characteristics of the sound reduction performance. However, if the separated and non-separated thicknesses are the same, they have almost the same performance in the frequency band of 125 to 500 [Hz]. Therefore, the present inventor completely separates the sound absorbing member to leave a certain distance between the two sound absorbing members, and sets the thickness t1 of the first sound absorbing member 5a on the upstream side to the thickness t2 of the second sound absorbing member 5b. By reaching a larger configuration of the present invention and performing Experimental Example 1, the effect of improving the sound reduction performance and reducing the wind noise has been proved.

The inventor calculated the optimum range of the distance L3 between the first sound absorbing member 5a and the second sound absorbing member 5b based on the following principle.
Specifically, the optimum range of the interval L3 was calculated by applying the principle of sound reduction by the hollow silencer shown in FIG.
First, the principle of sound reduction by the hollow silencer will be described. FIG. 18 is a diagram illustrating the principle of the hollow silencer. This hollow silencer expands the cross section in the middle of the duct to form the hollow portion 50, so that the hollow portion 50 functions as an acoustic filter by changing the cross section at two locations. It is assumed that it is attenuated when passing.
Here, in FIG. 18, the cross section of the upstream duct 51a is S1 [mm], the cross section of the cavity 50 is S2 [mm], the cross section of the downstream duct 51b is S3 [mm], and S1 = S3. Then, attenuation R [dB] is calculated | required with the following formula | equation ("Architecture and environmental acoustics" written by Junichi Maekawa Kyoritsu Shuppan Co., Ltd. P124 reference).

Where m = S2 / S1, k = 2π / λ (where λ is the wavelength)

  Here, the silencer for the ventilation wind tunnel having the same structure as the silencer for the ventilation wind tunnel according to the present invention, except that the thickness t1 of the first sound absorbing member 5a shown in FIG. 19 is equal to the thickness t2 of the second sound absorbing member 5b. (Hereinafter referred to as Reference Example 1) and the above-described hollow silencer were compared. In FIG. 19, reference numeral 100 is a passage defined by the opposing first sound absorbing members 5a and 5a, reference numeral 101 is a space between the first sound absorbing member 5a and the second sound absorbing member 5b, and reference numeral 102 is opposite. This is a passage defined by the second sound absorbing members 5b and 5b. Reference sign S1 ′ is a cross section of the passage 100, reference sign S2 ′ is a cross section of the space 101, and reference sign S3 ′ is a cross section of the passage 102.

  Comparing the structure of Reference Example 1 and the structure of FIG. 18, the cross section S1 ′ corresponds to the cross section S1, the cross section S2 ′ corresponds to the cross section S2, the cross section S3 ′ corresponds to the cross section S3, and the interval L3 corresponds to L. In Reference Example 1 shown in FIG. 19, there are cross-sectional changes on the upstream side and the downstream side of the space portion 101, respectively, and the structure is similar to the hollow silencer shown in FIG. 18. Therefore, it can be inferred that Reference Example 1 shown in FIG. 19 has a sound reduction characteristic similar to the sound reduction performance of the hollow silencer. Therefore, the present inventor sets the interval L3 (corresponding to L) to 10 [mm], 20 [mm], 100 [mm], 300 [mm], and 600 [mm] for the reference example 1 shown in FIG. For each set value, the frequency f is 63 [Hz], 125 [Hz], 250 [Hz], 500 [Hz], 1000 [Hz], 2000 [Hz], 4000 [Hz], and 8000 [Hz]. Since the volume reduction R [dB] when changed to [Hz] was calculated based on the first equation, the results are shown in Table 9 and FIG. The wavelength λ was obtained from each of the above frequencies, k was calculated by substituting the value of each wavelength λ into k = 2π / λ, and this k was applied to the first equation. Table 8 shows k corresponding to each frequency.

[Examination of experimental results]
The sound reduction characteristics of the hollow silencer structure are such that the volume reduction increases as the cross-sectional area ratio m increases, and the number of valleys of the curve decreases as the interval L decreases, which is applicable to a wide frequency band. It is known to be advantageous because it can. Therefore, considering the optimum range of the interval L from the graph of FIG. 20, it is understood that L is preferably set to 10 to 300 mm. This is because if it is less than 10 [mm], there is no effect outside the effective frequency band, and in the range exceeding 300 mm, the application of the noise to be reduced in the silencer for a ventilation wind tunnel according to the present invention is applied. This is because two valleys are generated in the frequency band of 63 to 8000 [Hz], which is in the range, and the performance characteristics as a silencer remain uneasy.

  Thus, in Reference Example 1 shown in FIG. 19, in order to improve the sound reduction performance, the interval L is preferably set to 10 to 300 mm.

[Examination of whether or not the optimum range (10 to 300 mm) of the interval L applied in Reference Example 1 shown in FIG. 19 is applicable to the silencer for a ventilation wind tunnel according to the present invention]
In the silencer for a ventilation wind tunnel according to the present invention, the thickness t1 of the first sound absorbing member 5a is larger than the thickness t2 of the second sound absorbing member 5b, while the reference example 1 shown in FIG. 19 is the thickness t1 of the first sound absorbing member 5a. And the thickness t2 of the second sound absorbing member 5b is different.
Accordingly, in the ventilation wind tunnel silencer according to the present invention, whether or not the optimum range (10 to 300 mm) of the interval L applied in Reference Example 1 shown in FIG.

  (1) If the thickness of the second sound absorbing member 5b is set smaller than the thickness of the first sound absorbing member 5a as in the present invention (corresponding to the cross section S1 ′> the cross section S3 ′), Even if the cross-sectional change on the upstream side of the cavity is the same, the cross-sectional change on the downstream side is small, so that the function of the acoustic filter is lowered, and the peak value of the sound reduction is considered to be slightly reduced. However, it is considered that the acoustic filter function is caused by the change in the cross section at two locations, and therefore, it is considered that the general tendency of the sound reduction performance shown in FIG. Therefore, it is considered that the optimum range (10 to 300 mm) of the interval L applied in Reference Example 1 shown in FIG. 19 also applies to the silencer for a ventilation wind tunnel according to the present invention.

  (2) If the thickness of the second sound absorbing member 5b is set to be smaller than the thickness of the first sound absorbing member 5a, the volume reduction is slightly reduced as described above, but the cross section S3 ′ of the passage 102 becomes larger. Since the generation of wind noise at 102 can be suppressed, noise can be reduced as a whole silencer for a ventilation wind tunnel according to the present invention.

  (3) For reference, in Experimental Example 2, the structure in which the recess is provided (Comparative Example 4) has a result that the sound reduction performance is worse than the structure in which the recess is not provided (Comparative Example 3). It was. Based on the principle of the cavity-type silencer, the structure in which this recess is provided is because the cavity is formed by providing the recess, so that the sound reduction performance is improved, and is considered to be inconsistent with Experimental Example 2. However, the cavity silencer has a structure in which a cavity is formed in the middle of the duct, and there is no sound absorbing member on the inner wall of the cavity. On the other hand, in Experimental Example 2, a recess is formed in a part of the sound absorbing member, and the sound absorbing member exists on the inner wall of the cavity formed by the recess. Moreover, even if the sound absorption area is increased by the formation of the concave portion, the amount of the sound absorbing material at the corresponding portion is reduced, so that the sound reduction performance is lowered from the viewpoint of reducing the amount of the sound absorbing material. Accordingly, it is considered that the sound reduction performance is lowered as a result of the decrease in the sound reduction performance due to the decrease in the amount of the sound absorbing material in the recess than the increase in the sound reduction performance due to the formation of the hollow portion. Therefore, it is added that the principle of the hollow silencer and the experimental example 2 are not contradictory.

  The present invention can be applied as a silencer for a ventilation wind tunnel in an underground building such as an expressway ventilation station.

1 is a perspective view of a silencer for a ventilation wind tunnel according to Embodiment 1. FIG. 2 is a cross-sectional view of the silencer for a ventilation wind tunnel according to the first embodiment. It is arrow BB sectional drawing of FIG. It is CC sectional view taken on the line of FIG. 1 is a sectional view of the present invention related to Example 1. FIG. 6 is a sectional view of Comparative Example 1. FIG. It is the graph which compared the sound reduction performance of this invention and the comparative example 1. FIG. It is a graph which shows the measured value of the wind noise regarding this invention. It is a graph which shows the measured value of the pressure loss regarding this invention. 10 is a graph showing measured values of wind noise regarding Comparative Example 1. 6 is a graph showing measured pressure loss values for Comparative Example 1. 10 is a cross-sectional view of Comparative Example 3. FIG. 10 is a cross-sectional view of Comparative Example 4. FIG. It is the graph which compared the sound reduction performance of the comparative example 3 and the comparative example 4 in the case of a wind speed of 3 m / sec. 10 is a cross-sectional view of Comparative Example 5. FIG. It is sectional drawing of the comparative example 6. FIG. It is the graph which compared the sound reduction performance of the comparative example 5 and the comparative example 6 in the case of a wind speed of 3 m / sec. It is a figure for demonstrating the principle of sound reduction by a cavity type silencer. Except that the thickness t1 of the first sound absorbing member 5a is equal to the thickness t2 of the second sound absorbing member 5b, a ventilation wind tunnel silencer having the same structure as the ventilation wind tunnel silencer according to the present invention (hereinafter referred to as reference example 1) It is a sectional view showing a simplified structure. It is a graph which shows the relationship between the frequency when the space | interval L3 is changed about the reference example 1 shown in FIG. 19, and a volume reduction.

Explanation of symbols

1: silencer 2a, 2b: open end 4: casing 5a: first sound absorbing member 5b: second sound absorbing member 6: perforated plate 7: sound absorbing material t1: thickness of first sound absorbing member t2: thickness of second sound absorbing member L3 :interval

Claims (5)

In a silencer for a ventilation wind tunnel that is interposed in the middle of a ventilation wind tunnel and silences noise passing through the ventilation wind tunnel,
One open end faces the upstream ventilation wind tunnel, and the other open end has a rectangular tubular casing facing the downstream ventilation wind tunnel. The opposing inner walls of the casing are respectively made of a sound absorbing material and a porous plate. A plurality of configured sound absorbing members are provided at intervals in the flow path direction,
The silencer for a ventilation wind tunnel, wherein the thickness of the plurality of sound absorbing members is gradually reduced from the upstream side to the downstream side of the flow path.   The plurality of sound absorbing members are composed of a first sound absorbing member located on the upstream side of the flow path and a second sound absorbing member located on the downstream side of the flow path, and the thickness of the first sound absorbing member is the thickness of the second sound absorbing member. The silencer for a ventilation wind tunnel according to claim 1, which is larger.   A silencer having the same outer dimensions and one sound absorbing member provided on each of the opposing inner walls of the casing, wherein the amount of sound absorbing material filled is the amount of sound absorbing material filled in the first sound absorbing member. And the length of the one sound absorbing member in the flow path direction is equal to the sum of the filling amounts of the sound absorbing material and the flow direction of the first sound absorbing member and the second sound absorbing member. Assuming a silencer equal to the sum of the length of the sound absorber, the thickness of the sound absorbing member in the silencer is t3 [mm], the thickness of the first sound absorbing member is t1 [mm], and the thickness of the second sound absorbing member is The silencer for a ventilation wind tunnel according to claim 2, wherein t3 = (t1 + t2) / 2 is satisfied when t2 [mm] is satisfied.   The silencer for a ventilation wind tunnel according to claim 2 or 3, wherein a length of the first sound absorbing member in the flow path direction is equal to a length of the second sound absorbing member in the flow path direction.   The silencer for ventilation wind tunnels in any one of Claims 2 thru | or 4 whose space | interval of a 1st sound absorption member and a 2nd sound absorption member is 10-300 [mm].