JPH01296040A - Noise damping device using resonance for air supply duct - Google Patents

Abstract

PURPOSE:To effectively damp the low frequency noise without requiring any special physical space by having the swelling on the opposing inner surfaces of a duct to form a resonating constriction of a length half of the wave length of the noise, and disposing resonating chambers on the fore and aft ends of said constriction which resonate at or near the noise frequency. CONSTITUTION:The duct 2 made of zinc-coated sheet metal has a rectangular section configuration, and a swelling plate 5 of the same material which is curved at the fore and aft ends is fitted to the inner sides of it over the entire height to form a swelling section 6. The length of the straight portion 8 of the swelling plate 5 excluding the curved sections 7 is half of the wave length of the targeted noise to be damped. Resonating chambers 4 are formed in the upper and lower levels in the fore and aft ends of the right and left hand side swelling sections 6 (eight locations altogether). Hollow spaces 11 are formed by partioning the space delimited by the duct outer sheet metal 9 and th swelling plate 5 over the entire height with inner walls 10, and a small hole 12 is opened to the resonating constriction 3 in the fore and aft parts of the straight section 8 of the swelling plate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air duct in a building air conditioner or various smoke evacuation devices, and particularly relates to a resonance muffling device for an air duct to reduce noise. Regarding.

[Prior art] Conventionally, in order to muffle the noise of an air supply duct, the inner circumferential surface of the duct was lined with a porous sound-absorbing material such as glass wool (lined duct), or the cross section was abruptly cut in the middle of the duct. A cavity-type muffler was used that attenuated the permeation of sweat toward the front of the duct by reflecting the noise waves at the discontinuous boundary surface.

[Problem to be solved by the invention] However, although the porous sound-absorbing material of the lining reduct can reduce high-frequency noise, it has a low sound-absorbing effect on low-frequency noise.
This cannot be removed.

On the other hand, in order to improve the attenuation (Iff) of a cavity type muffler, it is necessary to increase the cross-sectional expansion ratio (for example,
0x) It is bulky and may not be adopted due to space constraints.

The present invention was made in view of the problems of such conventional duct silencers, and is capable of attenuating the resonance of air ducts without taking up any special installation space and extremely effectively attenuating low frequency noise. The purpose is to provide a silencer.

[Means for Solving the Problems] The present invention has been completed in accordance with the above-mentioned object, that is, the present invention has been accomplished by bulging the opposing inner surfaces of the duct so that the target noise wavelength is approximately 2
At the same time, a hollow part is formed at the front and rear ends of the bulge part and communicated with the resonance bottleneck through a small diameter hole. A resonance muffling device for an air supply duct, characterized in that it is equipped with a resonance chamber that resonates at or near a frequency (Claim 1)
, and instead of the resonant bottleneck in which the opposing inner surface of the duct is bulged out, an intermediate partition plate along the air supply direction is integrally built into the duct, and the partition plate or the inner surface of the duct opposing the partition plate is bulged out. The object of the present invention is to provide a resonant silencer 21 for an air supply duct according to claim 1 (claim 2) in which a plurality of resonant bottlenecks having different target noise wavelengths are formed.

[Function] Result 1 In the resonant device of the air supply duct of the present invention, the air in the resonant bottle resonates with the one frequency component of the noise propagating in the duct, and the peak occurs at the front and rear ends of the bottleneck. Vibrating violently, the energy of [) is converted into frictional heat and dissipated, and the air in the resonant chamber also resonates at the front and rear ends of the bottleneck where the amplitude is maximum, thereby attenuating the noise ff.

[Example] Hereinafter, an example will be explained with reference to the drawings (first, see Figs. 1 and 2). In these figures, 1 is a resonance muffling device for an air supply duct according to the present invention, and the muffling device l The opposing inner surfaces of the duct 2 are bulged to form a resonance bottleneck 3, and resonance chambers 4 are also provided at the front and rear ends of the resonance bottle.

The duct 2 in this example is made of a galvanized iron plate and has a rectangular cross section, and is expanded by attaching curved bulging plates 5, 5 of the same quality at the front and rear ends over the entire height of the left and right inner surfaces in the middle of the longitudinal direction. It forms a protrusion 6.6.

Here, the bulging plate 5 is formed so that the #N rear length of the f plate portion 8 excluding the curved portion 7.7 is half of the noise wavelength aimed at reducing. Then, it is 223 am (UA middle view, target noise frequency fi75H).As a result, the left and right bulges 6
, 6 is formed with a resonant bottleneck 3 having a length of 1/2 of the noise wavelength of 11.

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 peripheral members (not shown) of the duct 2.

On the other hand, the wood example resonance chamber 4... has the left and right bulges 6.6 (
The space between the outer peripheral iron plate 9 of the duct and the bulging plate 5 is made up of the front and rear inner walls 10 and 10 to the full height. The hollow parts 11 are formed by densely dividing the parts, and small-diameter through holes 12 are formed at the front and rear ends of the bulging plate part 8 to form the resonant bottleneck 3.
It communicates with

Here, the dimensional relationship of the resonance chamber 4 is such that the Il
It is determined by the target noise 1'f frequency, uJJ, the volume of the hollow part 11 is V, the cross-sectional area of the through hole 12 is S, the effective length of the neck of the through hole is determined, and the quality of the air per medium body is determined by Similarly, let ρ be the bulk elastic modulus, let r be the resistance per unit area of the through hole 5111, and let V be the dynamic velocity M of the air at the neck of the through hole, and let the changing outdoor sound pressure (jω of PXe be The inertial force of the air in the perforated part (S ρXdv/dt) against the force of
Considering the balance of x/V) fv dt), 6 Pxe multiplied by jω = supX dv/ dt+s r
Since it can be expressed as v + (32x/V) fv dt, solving this gives impedance 2 as Z = s p / v = s r + j (ω5fLp-s” pt/ (ωV)
), and if we rearrange ω with the imaginary part in the curly brackets as 0 and find the resonance frequency af, we get (here =/)C2;C
The speed of sound is approximately 334 m/see).

f=ω/(2π) = (c/ (2r))x 5QR(s/ (JIV
)) get. In addition, if we set intersection → 0 here, then f = (
It can be expressed as c/(2π)) x 5QR(d/V) (d is the diameter of the through hole).

Therefore, the dimensional relationship of each part of the resonance chamber in this example with the target frequency being 75H7 is 1. For example, if the diameter d of the through hole 12 is 1 cm, the volume of the hollow part 11 is 5027 cm' (if it is cubic, each side is 17.1 cm). ).Of course, these dimensional relationships can be changed in various ways to satisfy the L equation. 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'.

Next, the embodiment shown in No. 31211 will be described. The resonance canceling 1f device 211' of this embodiment has an intermediate partition plate 13 built in the duct 2 along the air supply direction, and a bulge 6 on the inner surface of the duct. . . . facing the partition plate bulge 6
° It is equipped with...

This embodiment differs from the previous embodiment in that three resonant bottlenecks 3a, 3b, and 3c having different noise wavelengths are formed in the two divided air supply paths 14, 14. The lengths of these resonant bottlenecks in this example are 223 mm, the first bottleneck 3a being the same as in the previous example.
c m (Fig. 1.1'l sweating frequency 751 (z)
, the second bottleneck 3b is 128 cm (text 2 in the figure, 130 Hz)
), and the third bottleneck 3C is 72 cm (UA'tj 3, 230H1). Note that the same numbers as in the above embodiments are given to the same points in the figure, and the explanation is omitted.

Although not shown in the drawings, the l&1 exit portion can be formed on all four circumferences of the duct, and in the case of a cylindrical duct, a resonant bottleneck can be formed by bulging the entire circumference or any opposing surface. Furthermore, it is of course possible to partition the cross section of the duct into a vertical and horizontal cross shape, a parallel cross shape, or an O shape, regardless of the number of intermediate partition plates. Furthermore, for example, as in the silencing device shown in the embodiments of FIGS. 1 and 2, it is also possible to have a plurality of resonant channels of the same length stacked one above the other, or to arrange them side by side on the left and right.

On the other hand, the target noise frequency of the resonance chamber may be slightly shifted from the one value of the resonance bottleneck to make the resonance bimodal.

In addition, such a resonance muffling device may also be equipped with a sound-absorbing material such as glass wool or rock wool, and examples of its installation location include, for example, the upper and lower surfaces when the left and right inner surfaces of the duct are bulged out, or It is also possible to form the protrusion itself from these sound absorbing materials and arrange it between the front and rear resonance chambers.

Although the embodiments have been configured as described above, the present invention can be applied to a duct, an opposing inner surface of a duct, a resonant bottleneck, a resonant bottleneck,
The specific shape, structure, material, dimensions, fi number, arrangement, and relationship thereof of the bulging part, hollow part, small-diameter through hole, resonance chamber, intermediate partition plate, etc. can be changed variously, and the above implementation is possible. Needless to say, this is not limited to this example.

[9. Effect of light] The resonant noise device of the air supply duct of the present invention bulges the opposing inner surface of the duct to generate l-1 noise rf fI! A resonant bottleneck having a length of approximately half of bc is formed, and a hollow part is formed at the front and rear ends of the bulged part and communicated with the resonance bottle through a small diameter hole, so that the front and rear ends of the resonant bottleneck are connected to each other. Because it has a resonance chamber on the side that resonates at or near the target noise frequency,
It has an effective Ff range that extends to the low frequency range, and can set the target noise frequency and attenuate it intensively, and is also placed in conjunction with the resonance bottleneck and the maximum position of the bottleneck circular vibration amplitude. By using a resonance chamber in combination with a heavy pipe, the aerosol extinguishing effect can be dramatically improved.

Furthermore, in the resonant silencer according to claim 2, instead of the resonant bottleneck in which the opposing inner surfaces of the duct are bulged, an intermediate partition plate along the air supply direction is integrally or integrally built into the duct. In addition, the partition plate or the inner surface of the duct facing the partition plate is bulged to form a plurality of resonance bottlenecks with different target noise wavelengths, so it is possible to set a plurality of target noise frequencies and attenuate them at the same time, resulting in a silencing effect. Not only can the noise attenuation characteristic curve be multi-peaked, it is possible to further increase the silencing effect for these intermediate frequency noises as well.

In addition, the resonant silencing device of the present invention, as described in [2], bulges out the opposing inner surface of the duct or an intermediate partition plate built into the duct to form a resonant bottleneck, and forms a hollow part in the outer bulge. Since a resonance chamber is provided, there is no need to extremely expand the external shape of the duct, and it can be compactly stored inside the duct, and can be installed at the piping location a without taking up much installation space.

[Brief explanation of the drawing]

The drawings show embodiments, and FIG. 1 is a perspective view of a resonant silencer for an air supply duct according to the present invention, FIG. 2 is a cross-sectional view of the silencer, and FIG. 3 is another embodiment of the silencer. Horizontal Pfi showing
ini diagram. 1, l' 4...Resonance chamber...Resonance of air supply duct 6,6゛...Bulging part silencer
11...Hollow part 2...Duct 12...Small diameter through hole 3.3
a to 3b 13-...Intermediate partition plate...Resonance bottleneck

Claims (2)

[Claims] (1) The opposing inner surfaces of the duct are bulged to form a resonant bottleneck approximately half the length of the target noise wavelength, and a hollow part is formed at the front and rear ends of the bulge, and the resonant bottleneck is formed through a small-diameter through hole. 1. A resonant muffling device for an air supply duct, characterized in that a resonant chamber that resonates at or near a target noise frequency is provided at the front and rear end sides of the resonant bottleneck in communication with the resonant bottleneck. (2) Instead of the resonant bottleneck that bulges out the opposing inner surface of the duct, an intermediate partition plate along the air supply direction is integrally built into the duct, and the partition plate or the inner surface of the duct opposing the partition plate is expanded. 2. A resonant silencing device for an air supply duct according to claim 1, wherein a plurality of resonant bottlenecks having different target noise wavelengths are formed.