JPH0346715B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an air supply duct for a building air conditioner or various smoke evacuation devices, and particularly relates to an air supply duct for reducing noise in a connecting pipe or a branch pipe portion of the duct. This invention relates to a silencer for air ducts.

[Conventional technology] Conventionally, in order to muffle the sound of an air supply duct, the lining was lined with a sound absorbing material such as glass wool, or the canceling effect of the phase shift of noise waves caused by the difference in the internal and external paths of a right-angled elbow was used. Therefore, measures were taken to muffle the sound by increasing the number of elbows.

[Problems to be Solved by the Invention] However, although the porous sound-absorbing material for lining can reduce high-frequency noise, it has a low sound-absorbing effect on low-frequency noise and cannot eliminate it.

Furthermore, even if the number of elbows is increased to enhance the canceling effect of the right-angle elbows mentioned above, regardless of whether it is necessary for the route, if the duct is bent with elbows only for noise reduction, it will become a detour and an emergency. In some cases, this was not possible due to the bulk and piping space constraints. The noise reduction effect of the elbow itself is
Even if a right-angled elbow is obtained, the effect is said to be low if it has curvature.

The present invention was made in view of the problems of such conventional silencers, and eliminates the need for special installation space or minimizes the need for special installation space in the connecting pipe or branch pipe portion of the duct, and eliminates noise in the low frequency range. It is an object of the present invention to provide a noise reduction device for an air supply duct that can extremely effectively reduce noise.

[Means for Solving the Invention] The present invention has been completed in accordance with the above-mentioned objects, and a resonance tube or a resonance chamber is compactly provided in a connecting pipe or a branch pipe portion of an air supply duct.
(1) One or more resonant cylinders with one end open and the other end closed and having a depth of approximately one-fourth of the target noise wavelength are built into the connecting pipe or branch pipe of the duct, and the open end of the resonant cylinder is installed in the air passage. (Claim 1), (2)
The air supply duct according to claim 1, wherein the sounding tube has a hollow section with a small-diameter through-hole formed in the tube wall, and is also provided with a resonance chamber that resonates at or near the target noise frequency. (Claim No. 2), (3)
The gist of the present invention is a silencing device for an air supply duct according to claim 1 or 2 (claim 3), wherein the connecting pipe is an elbow.

[Function] As a result of the above, in the air duct silencer of the present invention, the air in the resonance tube or resonance chamber resonates with the target noise frequency component of the noise propagating in the duct and vibrates violently, converting sound energy into heat. to attenuate the noise.

[Example] Hereinafter, an example will be described with reference to the drawings. In FIGS. 1 and 2, 1 in the figure is a silencer for an air supply duct according to the present invention, and the silencer 1 of this example is
is formed in the connecting pipe 2 of the duct, and the connecting pipe 2 is
In this example, a right-angled elbow made of a galvanized iron plate has air supply openings 3, 3 opened in two orthogonal directions, and a bent inner periphery 4 between both openings is connected by a hypotenuse, and three resonance cylinders 5 are connected.
a, 5b, and 5c are built-in, and the open end of the resonance cylinder is made to face the air passage of the connecting pipe.

The resonance cylinders 5a to 5c of this example are formed by folding a galvanized iron plate 6 several times in an O-shape to form three wedge-shaped resonance cylinders with one end open and the other end closed at each valley part.
In this example, the connecting pipe 2, which is an elbow, is fixedly built in with its plate surface erected over the entire height between the upper and lower inner surfaces 7 and 8.

Here, the depth l1 to l3 of each resonant cylinder is formed to be one-fourth of the target noise wavelength to be reduced.
In this example, the first resonance tube 4a is 111 cm (l1 in the figure, target noise frequency 75Hz), and the second resonance tube 4b is 64 cm (l1 in the figure).
2, 130Hz), and the third resonator cylinder 4c is 36cm (l in the figure).
3. 230Hz).

The target noise wavelength is generally one with a large noise component, such as the rotating sound of a fan, but it is also set to a target wavelength depending on individual problems such as resonance of surrounding members (not shown) of the duct.

Then, the open ends 9 of the resonance cylinders 5a to 5c
In this example, the opening directions are aligned and they face the air passage 10 in the connecting pipe.

Next, the embodiments shown in Figs. 3 and 4 will be explained. Like the above embodiments, these have a resonant tube built into the duct connecting pipe (elbow in this example), but the difference is that: In the embodiment shown in FIG. 3, the shape of the resonator cylinders 5a to 5d is replaced with the wedge shape described above and has a rectangular cross section, each having a depth of approximately one-fourth of the target noise wavelength, and four resonant cylinders are arranged in parallel in the order of wavelength. As a result, the open ends 9 of these resonant cylinders are arranged in a stepwise manner.

On the other hand, the resonance tubes 5a to 5 of the embodiment shown in FIG.
E has a trapezoidal cross section with the opening end face as the hypotenuse, and is of course formed according to the target noise wavelength, and five of them are arranged in parallel in the order of wavelength, and their opening ends 9 are aligned diagonally in a straight line. It should be noted that the resonant tubes of both embodiments share the entire or partial wall of the resonant tube with an adjacent resonant tube.

Next, in the embodiment shown in FIG. 5, similar to the embodiment shown in FIG. 2, the iron plate 6 is folded several times in a Z-shape inside the connecting pipe 2 of the duct, which is an elbow, to form a wedge-shaped resonance tube 5a in the valley.
5c (target noise wavelength and cylinder depth are the same as resonant cylinders 5a to 5c in FIG. A small diameter through hole 11 is provided near the opening end 9 of the
... is opened and communicated with the hollow part 13 ... formed in the wedge-shaped cylinder wall 12 ... to resonate at the target noise frequency (in this example, each corresponds to the target value of the communicating resonant cylinder) or a value in the vicinity thereof. Resonance chambers 14a to 14c
It is particularly different in that it has a . In the figure, reference numerals 15 are partition walls of the resonance chambers, which are arranged and fixed at predetermined positions after calculating the volume of the resonance chambers, thereby tightly partitioning the resonance chambers 14a to 14c from the remaining hollow portions 16 in the cylindrical wall.

Here, the dimensional relationship of the resonance chamber is determined by the target noise frequency to be reduced, namely, the volume of the hollow part is V, the cross-sectional area of the through hole is s, and the effective length of the neck of the through hole is l. , the mass of air per unit volume is ρ, the bulk elastic modulus is k, the resistance per unit area of the neck of the hole is r, and the velocity of air movement at the neck of the hole is v. Sound pressure (P×e jωt
The inertial force of the air inside the neck of the through-hole (slρ ×
dv/dt), the frictional resistance of the neck (srv), and the compression reaction force of the hollow air ((s ² k/V)∫vdt), P x e to the jωt power = slρ x dv /dt +srv + (s ² К/V)∫vdt, so solve this to find the impedance Z
is Z=sp/v=sr+j{ωslρ−s ² К/(ωV)}, and if we set the imaginary part in the middle bracket to 0 and rearrange it for ω, we find the resonant frequency f (where k=
ρc ² ; c is the speed of sound, which is approximately 334 m/sec), and f=ω(2π) = {c/(2π)}×SQR{s/(lV)} is obtained. Note that if l → 0 here, it can be expressed as f={c/(2π)}×SQR{d/V} (d is the diameter of the through hole).

Therefore, the dimensional relationship of each resonance chamber in this example is, for example, 75
If the diameter of the through hole 11 in the first resonance chamber 14a whose target frequency is Hz is set to 1 cm, the volume of the hollow portion 13 will be 5027 cm ³ (if it is cubic, each side is 17.1 cm). Of course, these dimensional relationships can be changed in various ways while satisfying the above conditions. For example, if the diameter of the small-diameter through hole is 5 cm, the volume of the hollow portion is over 25,000 cm ³ .

Similarly, if the diameter of the through hole is 1 cm in the second resonance chamber 14b with the target frequency of 130 Hz, the volume of the hollow part is
3rd resonance chamber 1 with a target value of 1673cm ³ and 230Hz
When the diameter of the hole is 1 cm in 4c, the volume of the hollow part is 535 cm ³
It is.

Next, in the embodiment shown in FIG. 6, the branch pipe 1 of the duct
7 (in this example, it is a Y-tube made of galvanized iron plate, and the orthogonal cross-sectional shape of each path is square or circular, etc.) is different from the above-mentioned embodiments in that the resonance tubes 5a to 5d are built in (incorporated in the connecting tube). Of course, the depth of each resonant cylinder 5a to 5d is approximately one-fourth of the target noise wavelength, and its open end 9
... is made to face the air passage 10 of the branch pipe. Note that 18 in the figure is a bottom plate at the closed end of the resonance cylinder.

Further, in the embodiment shown in FIG. 7, hollow portions 13 are provided with small-diameter through holes 11 in the cylinder walls 12 of the resonance cylinders 5a to 5d built in the branch pipe 17.
This example differs from the example shown in FIG. 5 in that resonance chambers 14a to 14d are additionally provided to form a target noise frequency and resonate at a value at or near the target noise frequency.

On the other hand, in the embodiment shown in FIG.
(in this example, the elbow), there are three resonant cylinders 5a to 5c each having a cylinder depth (l1 to l3 in the figure) approximately one-fourth of the target noise wavelength and having one end open and the other end closed.
The opening end 9 of the connecting pipe is made to face the air passage 10 of the connecting pipe, and each of the resonant cylinders 5a to 5c is built into a curved shape.

Note that common items in each embodiment are given the same numbers in the drawings, and some explanations are omitted.

The illustrated example is as described above, but in carrying out the present invention, the shape of the resonance tube can of course be made into various shapes such as cylindrical or prismatic. Depending on the situation, one or more can be provided, and for example, it is also possible to partition the inside of the elbow into a parallel grid shape to form a large number of resonant cylinders. Furthermore, when the resonance cylinder is built into a connecting pipe or a branch pipe of a duct, the closed end and the like may protrude out of the pipe to some extent as long as there is no problem in terms of space.

In addition to the illustrated elbow, the connecting pipe of the duct may be a straight connecting pipe with a different diameter or a U-shaped return connecting pipe, and even if it is an elbow, the bending angle etc. may be arbitrary. On the other hand, various types of branch pipes, such as a Y-tube shown in the figure, a T-shape, a cross-shape branch, and the like can be used.

Furthermore, such a silencer may also be equipped with a sound absorbing material such as glass wool or rock wool, and examples of where to install it are, for example, in the case of the elbow shown in Fig. 2, on the oblique side of the bent inner circumference, It can be installed slightly closer to the inner periphery of the upper and lower inner surfaces, or it can be inserted into the bottom of the resonance cylinder (the depth of the cylinder is determined with this in mind), or the cylinder wall itself can be made of these sound-absorbing materials. It is also possible. Furthermore, when a hollow part is formed between the cylinder walls of each resonant cylinder as in the embodiment shown in FIGS. It can be filled with sound absorbing materials such as

In addition, when installing a resonance chamber together with a resonance cylinder,
The target noise frequency may be slightly shifted from the target value of the communicating resonant tube to make the resonance bimodal.

Further, although not shown, it is desirable to cover the connection pipe or branch pipe of the duct with the resonance tube or resonance chamber with a heat insulating material such as glass wool to keep the temperature-controlled air warm and prevent condensation.

Although the embodiment is configured as described above, the present invention includes a resonance cylinder, a duct, a connecting pipe, a branch pipe, an air passage, an elbow, an open end of a resonance cylinder, a small diameter through hole, a hollow part, It goes without saying that the specific structure, shape, dimensions, material, number, arrangement, and functions of the cylinder wall, resonance chamber, and elbow can be changed in various ways, and are not limited to those illustrated and explained above. do not have.

[Effects of the Invention] The air duct silencing device of the present invention has the following effects since it is constructed as per the gist of the invention.

In other words, the connection pipe or branch pipe of the air supply duct has a built-in resonant cylinder having a depth of approximately one-fourth of the target noise wavelength, so it has an effective silencing range that extends to the low frequency range and also has a depth of approximately one-fourth of the target noise wavelength. It is possible to provide an air duct silencing device that can set one or more noise frequencies and attenuate them intensively, can obtain a high silencing effect with a simple means, and is highly practical. can.

Since the resonance cylinder is built into the connection pipe or branch pipe of the air supply duct, it is not bulky and there is no waste of space, and there are no restrictions when deciding the connection part or branch part of the duct where it is installed. is extremely small and does not cause strain on the piping.

Furthermore, in the muffler according to claim 2, the resonant cylinder is provided with a resonance chamber that resonates at or near the target noise frequency by forming a hollow part with a small-diameter through hole in the cylinder wall. Therefore, it is possible to dramatically improve the silencing effect through the combination of the resonance cylinder and the resonance chamber formed in the cylinder wall.

[Brief explanation of drawings]

The drawings show embodiments, and FIG. 1 is a perspective view of a silencer of the present invention in which a resonance tube is built into the connecting pipe of an air supply duct, FIG. 2 is a cross-sectional view of the same device, and FIGS. 3 to 8 The figures each show other embodiments of the muffler of the present invention, and Figs. 3 and 4 are cross-sectional views of the muffler in which the shape of the resonance tube built into the connecting pipe of the air duct is changed, and Fig. Figure 5 is a cross-sectional view of this muffling device, which has a resonance chamber built into the cylinder wall of a resonator cylinder built into the connecting pipe of the air supply duct, and Figure 6 is a cross-sectional view of the muffler, which has a resonance chamber built into the branch pipe of the air supply duct. Fig. 7 is a cross-sectional view of the device, and Fig. 7 is a cross-sectional view of the silencing device in which a resonance chamber is attached to the wall of a resonant cylinder built into a branch pipe of the air duct, and Fig. 8 is a cross-sectional view of the silencer with a resonance chamber attached to the cylinder wall of the resonant tube built into the branch pipe of the air duct. FIG. 2 is a cross-sectional view of the muffler incorporating a built-in resonator cylinder. DESCRIPTION OF SYMBOLS 1... Air duct silencer, 2... Duct connection pipe, 5, 5a to e... Resonance tube, 9... Open end of resonance tube, 10... Air passage, 11... Small diameter through hole, 12... Cylinder wall, 13 ...Hollow part, 14, 14a to e... Resonance chamber, 17... Branch pipe of duct.

Claims (1)

[Scope of Claims] 1. One or more resonant cylinders having one end open and the other end closed and having a depth of approximately one-fourth of the target noise wavelength are built into the connecting pipe or branch pipe of the duct, and the above-mentioned resonant cylinder is built into the air passage. A silencing device for an air duct, characterized in that the open end of a cylinder is made face-to-face. 2. The air supply according to claim 1, wherein the resonance cylinder is provided with a resonance chamber that resonates at or near the target noise frequency by forming a hollow part with a small-diameter through hole in the cylinder wall. Duct silencer. 3. The air duct silencer according to claim 1 or 2, wherein the connecting pipe is an elbow.