RU2225484C1 - Sound-absorbing structure - Google Patents

Abstract

FIELD: construction unit production, particularly for industrial and civil buildings having inner noise sources. SUBSTANCE: sound-absorbing structure having multicellular frame with ribs and cross-bars comprises rectangular panel array. Each panel has cells with channels. Ribs and cross-bars form inlet orifice of each channel. Channel height and length are selected from the following equations: h(x) = h•e^-δx; L = ln[h(e^δAo-1)/0,1A_o]/δ, where h is panel thickness, δ is slope factor, A_o is inlet dimension of cell rib, L is channel length, h(x) is current channel height, x is current coordinate. EFFECT: increased sound absorption factor in low frequency region, increased technological effectiveness, possibility of sound absorption with sound energy propagation in any direction; possibility of inlet acoustic impedance matching with medium resistance. 8 dwg

Description

The invention relates to the production of building products and is intended for use in the construction of industrial and civil buildings with internal noise sources. The invention can also be used to make additional sound absorption in a room with increased requirements for acoustics, as well as in channels, ducts, shafts to reduce noise propagating through them.

Known sound-absorbing panel made of porous material mainly for sheathing the inner surface of walling does not have the necessary sound-absorbing properties in the low and high frequencies. (USSR author's certificate No. 344087, IPC: E 04 C 2/46, published. 1972, Bull. No. 21).

Sound-absorbing structures based on fibrous sound-absorbing materials are known (I.I. Bogolepov, Industrial soundproofing, - L .: Sudostroenie, 1986, p. 301-303; Handbook of technical acoustics, - L .: Sudostroenie, 1980, p. 320).

The disadvantage of such sound-absorbing structures is their low efficiency in the low-frequency range, as well as the need for their location at some distance from the acoustically rigid wall, which requires additional fasteners and the selection of this distance.

The second significant drawback of such sound-absorbing structures when they are located directly on the wall is the need to design panels of several layers with different packing densities.

Known sound-absorbing panel, the surface of which is made in the form of wedges (triangular prisms) of sound-absorbing materials. (II Bogolepov, Industrial isolation, - L .: Shipbuilding, 1986, p.336, Fig. 9.14).

The disadvantage of this sound-absorbing panel is its large thickness, as well as the complexity of manufacturing the surface in the form of wedges and the need to optimize the size of these wedges.

Known sound-absorbing structure containing a multi-cell frame with ribs and cross members. (USSR author's certificate No. 787589, IPC: E 04 B 1/82, published. 1980, Bull. No. 46).

The disadvantage of this design is its bulkiness and narrowness of use, because it is intended for use in a known direction of noise and is practically unsuitable for industrial and civil buildings.

This invention eliminates these disadvantages of analogues and prototype.

The technical result of the invention is to increase the absorption coefficient in the low frequency region, manufacturability, the possibility of sound absorption in any direction of the flow of sound energy, matching the acoustic input impedance with the wave impedance of the medium.

The technical result is achieved by the fact that the sound-absorbing structure containing a multi-cell frame with ribs and cross-pieces contains a set of rectangular panels, cells with channels are made in each panel, the edges and cross-sections of the cell serve as the inlet of each channel, and the height and length of each channel are selected from the conditions

h (x) = h · e ^-δx ; ; L = ln [h (eδ ^A0 -1) / 0,1A ₀ ] / δ,

where h is the panel thickness, δ is the channel slope coefficient, A ₀ is the input cell edge size, L is the channel length, h (x) is the current channel height, x is the current coordinate.

The invention is illustrated in figures 1-8.

Figure 1 shows a fragment of the panel, where 1 is the channel, 2 is the wall of sound-absorbing material, 3 is the wall of the room, A ₀ is the input size of the cell edge, B ₀ is the input size of the cell cross member, d is the transverse size of the cell edges and cross ( channel walls).

Figure 2 shows the geometry of the channels of the sound-absorbing structure, where h is the panel thickness (channel height), x is the current coordinate from the beginning of the channel, L is the channel length, 6 is the channel slope coefficient.

Figure 3 shows the dependence of the sound absorption coefficient α of the structure on the length of the channel L. The curves correspond to L = 0.2; 0.3; 0.4 m, A ₀ B ₀ = _0.1 m; h = 01m; d = 0.01m.

Figure 4 shows the dependence of the sound absorption coefficient of the structure on its thickness h. The curves correspond to A ₀ = 0.05 m; B = 0.1 m; L = 0.3 m at h = 0.1 m; h = 0.15 m and h = 0.2 m

Figure 5 shows the dependence of the sound absorption coefficient α of the structure from A ₀ - the input size of the cell edge at h = 0.1 m; L = 0.2 m; d = 0.01 m; At ₀ = 0.1 m. The curves correspond to A ₀ = 0.025; 0.05 and 0.075 m.

Figure 6 shows the dependence of the sound absorption coefficient α of the structure on the input size of the cell cross member B _about . The input size of the cell edge A ₀ = 0.1 m; h = 0.1 m; d = 0.01 m; L = 0.2 m at B ₀ = 0.025; 0.05 m; 0.075 m.

7 shows the dependence of the sound absorption coefficient α of the structure with parameters A ₀ = B ₀ = 0.1 m; L = 0.4 m from the sound absorption coefficient α _st on the channel walls. The curves correspond to the values of α _article = 0.01; 0.05 and 0.1.

Fig. 8 shows curves for comparing the effectiveness of the invention (curve 4) with a structure equal to it by the mass of a layer of sound-absorbing material with a thickness of 0.02 m adjacent to a rigid wall (curve 5) and spaced from the wall at a distance of 0.08 m (curve 6).

Consider the operation and principle of operation of the sound-absorbing structure.

In order for a sound-absorbing structure to be highly efficient, two conditions must be met: it must have high internal absorption of sound energy, and the input impedance of the structure must be consistent with the medium wave impedance. For a design based on fibrous sound-absorbing materials (ZPM), such coordination is usually achieved either by spacing the ZPM layer from the rigid wall onto which this structure is fixed, or by constructing a structure from a large number of ZPM layers with a packing density that is insignificant for the outer layer and increases uniformly as you approach the hard wall. A variable average density of space filling with sound-absorbing material is also realized with the help of triangular prisms (wedges) from ZPM of constant density installed on the wall of the room close to each other with their bases and turned with sharp ends towards the incident sound wave. This design, in particular, is generally accepted in the processing of walls, ceilings and floors of damped measuring chambers.

Effective sound absorption and matching of acoustic impedances allows the present invention with the internal channels of the cells in which the acoustic impedance gradually increases as the sound wave moves from the wide part of the channel 1 to the narrow part with the simultaneous absorption of sound energy on its walls 2 made of a thin layer of ZPM , the design is located on the wall of the room 3 (figure 1).

The inlet of the channel has dimensions A ₀ · B ₀ , and the input dimension of the cell cross-section B _about does not change along the length of the channel. The thickness of the channel walls made of ZPM is d, the total thickness of the structure is equal to h. In this case, the walls are curved according to the law h (x) = he ^-δx (Fig. 2).

Provided A _0, B _{0 0} ≤ λ / 6, wherein λ ₀ - sound wavelength in the air, the wave front propagating along the channel, and flat throughout the perpendicular axis. The practically appropriate length of channel 1 is determined from the condition that by the end of its cross section decreases by 10 times. This condition allows you to determine the length of the channel 1 (figure 2) from the condition

L = ln [h (e ^-δA0 -1) / 0,1A ₀ ] / δ,

where h is the panel thickness, δ is the channel slope coefficient, A _{0 is the} input cell edge size, L is the channel length, h (x) is the current channel height, x is the current coordinate.

For example, in the case of A ₀ = 0.1 m; h = 0.15 m; L≈0.4 m at δ = 6 m ^-1 , L≈0.3 m at δ = 10 m ^-1 and 1≈0.2 m at δ = 25 m ^-1 .

The length of the curved wall of the channels L at the indicated values of δ is equal to 0.43 m; 0.35 m; 0.28 m instead of L = 0.4 m; 0.3 m; 0.2 m respectively.

Figure 3 shows the frequency characteristics of the sound absorption coefficient α depending on the geometric parameters of the structure. It can be seen that to a noticeable decrease in the frequency of the first maximum of the design efficiency, starting from which the value of α approaches the limiting value of α≈1, only the increase in the channel length L leads (Fig. 3). This is due to the fact that the phase incursion of the sound wave over the channel length, necessary for acoustic matching of its input impedance, takes place at a longer sound wavelength. A slight decrease in the frequency also gives an increase in the thickness h of the structure (Fig. 4), leading for a given length L of the channel to increase its real length L _p . The efficiency itself increases with decreasing size A ₀ , the channel inlet (Fig. 3) and little depends on the size B ₀ (Fig. 6), since in the first case a smoother change in the channel cross-section occurs, entailing a decrease in the coefficient reflections of a sound wave from a design. A certain increase in efficiency is also observed with a decrease in the wall thickness d (without changing the sound absorption coefficient α _st on them), since the channel has a larger value of the local sound absorption coefficient than the ends of the walls.

In addition, an excessive decrease in the sound absorption coefficient α _st on the channel walls (Fig. 7), along with an increase in the maximum (resonance) values of the total loss coefficient α, leads to a decrease in its average value due to antiresonance efficiency dips. An increase in α _st smooths the frequency response of α, thereby increasing its average value while decreasing the maximum.

Smooth narrowing of the channels 1 significantly reduces the reflection of sound waves from the structure with the simultaneous concentration of sound energy in the narrow part of the channels 1, where the energy is intensively absorbed on the walls 2, because they are made of sound-absorbing material, as well as in sound-absorbing material located in the end part of the channel 1. The curved shape of the channels 1 allows to increase their length, which increases the efficiency of the structure with its small thickness h.

Fig. 8 compares the effectiveness of this design and its equal in weight layer of sound-absorbing material directly adjacent to the rigid wall and spaced from it at a distance of 0.08 m. The proposed design provides a sound absorption coefficient close to α≈1, starting with significantly more low frequencies. Thus, the proposed design with matched acoustic impedance has much better sound absorption in the low-frequency region. This is its main advantage over sound absorbers having a layered structure.

Since the direction of the flow of sound energy is not known in advance, the sound-absorbing structure is assembled from panels (a fragment of the panel is shown in Fig. 1) oriented in different directions. For a vertical wall, these will be, for example, directions up, left, down, right. By changing the orientation of the panels or rows, get the maximum coefficient of sound absorption. This design of the sound-absorbing structure leads to a consistent acoustic impedance and allows you to effectively suppress noise in the low-frequency region for any direction of the flow of sound energy.

Claims (1)

A sound-absorbing structure containing a multi-cell frame with ribs and cross-pieces, characterized in that it contains a set of rectangular panels, cells with channels are made in each panel, the edges and cross-sections of the cell are the inlet of each channel, and the height and length of each channel are selected from the conditions h (x) = h · e ^-δx ; L = ln [h (e ^δAo -1) / 0.1A _о ] / δ, where h is the thickness of the panel; δ is the slope coefficient of the channel; And _o is the input size of the cell edge; L is the length of the channel; h (x) is the current channel height; x is the current coordinate.

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