A Scalable Microperforated Panel Sound Absorbing Structure and Design Method

Abstract

The present invention relates to a telescopic microperforated panel sound-absorbing structure, which is formed by connecting a plurality of microperforated panel sound absorbers in series. The diameters of the plurality of microperforated panel sound absorbers form a telescopic microperforated panel sound-absorbing structure in a decreasing form. By telescoping the microperforated panel sound absorbers, the volume of the back cavity and the distance between each microperforated panel are changed, thereby changing the structural resonance frequency and absorbing noises of different frequencies. The present invention designs a telescopic microperforated panel sound-absorbing structure, and by stretching and contracting the structure, the depth of the back cavity and the distance between the microperforated panels are changed, so as to achieve the absorption of noises of different frequencies by the structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of medium and low frequency vibration and noise reduction, and particularly relates to a telescopic micro-perforated panel sound absorption structure and a design method thereof. Background Art

[0002] The theory of the micro-perforated panel sound absorption structure was proposed by the famous acoustics expert, Academician Ma Dayou in China in the 20th century. This structure can generate a sound resistance that matches the atmospheric sound resistance only by making micro-holes on the original panel. At the same time, the acoustic mass is also small, and it can consume sound energy without adding any sound damping material. However, the disadvantage of the single-layer micro-perforated panel structure is that the sound absorption frequency band is relatively narrow, and it is difficult to meet the actual application in the face of a complex noise environment.

[0003] Traditional sound absorption materials and structures can only have good sound absorption effects within a specific frequency range. Once the structure is fixed, the corresponding sound absorption frequency band is also fixed. In the face of the complex noise environment in reality, when the environment changes, the traditional sound absorption materials and structures lose their good sound absorption effects, which results in the disadvantage of low reuse rate. Problems such as the low reuse rate of the structure restrict the practical application of conventional sound absorption materials and structures. Therefore, it is necessary to design an adjustable sound absorption structure in the face of a complex noise environment. Summary of the Invention

[0004] In order to solve the above problems, the present invention designs a telescopic micro-perforated panel sound absorption structure. By stretching and contracting the structure, the depth of the back cavity and the distance between the micro-perforated panels are changed, so as to realize the absorption of noises with different frequencies by the structure.

[0005] The present invention is realized through the following technical solutions.

[0006] A telescopic micro-perforated panel sound absorption structure is composed of a plurality of micro-perforated panel sound absorbers connected in series. The diameters of the plurality of micro-perforated panel sound absorbers form a telescopic micro-perforated panel sound absorption structure in a decreasing form. The micro-perforated panel sound absorber includes a micro-perforated panel, a bottom rigid wall, and an outer rigid wall. The outer rigid wall is a hollow cylinder. A back cavity is formed between the micro-perforated panel, the bottom rigid wall, and the outer rigid wall. Except for the micro-perforated panel sound absorber with the smallest diameter, an opening is provided on the bottom rigid wall of each micro-perforated panel sound absorber for docking with the micro-perforated panel of the next micro-perforated panel sound absorber, so that the next micro-perforated panel sound absorber and this micro-perforated panel sound absorber form a telescopic structure. By stretching and contracting the micro-perforated panel sound absorber, the volume of the back cavity and the distance between each micro-perforated panel are changed, thereby changing the structural resonance frequency and absorbing noises with different frequencies.

[0007] Furthermore, except for the diameters, the plurality of micro-perforated panel sound absorbers adopt micro-perforated panels, bottom rigid walls, and outer rigid walls with the same parameters.

[0008] Furthermore, the thicknesses of the micro-perforated plates, the bottom rigid walls, and the outer rigid walls of several of the micro-perforated panel absorbers are all 1 mm.

[0009] Furthermore, the micro-perforated plate is a rigid panel.

[0010] Furthermore, there are four micro-perforated panel absorbers, and the four micro-perforated panel absorbers are connected in series to form a telescopic micro-perforated panel absorption structure.

[0011] A design method for a telescopic micro-perforated panel absorption structure, characterized by comprising the following steps:

[0012] In the first step, according to the micro-perforated plate theory of Academician Ma Dayou and computer simulation to verify the feasibility of the model, the absorption coefficient of the micro-perforated panel absorber at normal incidence is:

[0013]

[0014] For the micro-perforated plate, its acoustic impedance rate is:

[0015] Z = R + jωM (2)

[0016] Obtain its relative acoustic impedance:

[0017] r + jωm = (R + jωM) / ρc (3)

[0018] Among them, the acoustic resistance r and the acoustic mass m are respectively:

[0019]

[0020]

[0021] And the perforated plate constant

[0022]

[0023] In the above formulas, t is the plate thickness, d is the perforation diameter, both in mm, p is the perforation rate, f is the sound frequency, and the acoustic impedance rate of the cavity behind the plate is

[0024] Z D = jρc cot(ωD / c) (7)

[0025] Using the impedance transfer method to gradually deduce layer by layer from the last layer forward, finally obtain the impedance transfer formula at the pipe orifice, and apply it to the analysis and calculation of the acoustic characteristics of the micro-perforated plate structure. The calculation process is as follows. The acoustic impedance of the single-layer micro-perforated plate structure is composed of the acoustic impedance of the micro-perforations and the acoustic impedance of the cavity. Therefore, the acoustic impedance of the fourth-layer micro-perforated plate structure can be denoted as:

[0026]

[0027] The acoustic impedance of the third and fourth layers of the micro-perforated panel structure is:

[0028]

[0029] The total acoustic impedance of the second, third, and fourth layers is:

[0030]

[0031] The total acoustic impedance of the four-layer micro-perforated panel structure is:

[0032]

[0033] Where Z ai are the acoustic impedances of the micropores in the i-th layer respectively, and D i is the depth of the back cavity of the i-th layer; ρ and c are the density and sound speed of air respectively;

[0034] The sound absorption coefficient of the micro-perforated absorber reaches the maximum value at resonance, and the maximum sound absorption coefficient value is:

[0035]

[0036] The resonance frequency f 0 satisfies:

[0037] 2πf 0 m - cot(2πf 0 D / c) = 0 (13)

[0038] As can be seen from the above theory, by changing the depth of the back cavity, the acoustic impedance of the structure can be changed, and the change in acoustic impedance causes the change in the sound absorption coefficient and resonance frequency;

[0039] In the second step, based on the variation law of the above-mentioned structure acoustic impedance with the back cavity depth, a telescopic micro-perforated panel sound absorption structure is designed. By telescoping, the overall back cavity depth of the structure is changed, that is, its acoustic impedance is changed, so as to achieve the absorption of noises with different frequencies; facing different application scenarios, a suitable sound absorption effect is achieved by stretching or contracting.

[0040] Compared with the prior art, the advantages of the present invention are:

[0041] 1. The telescopic micro-perforated panel sound absorption structure described in the invention can be aimed at noises with different frequencies, and the resonance frequency is changed by telescoping the structure to achieve the best absorption of noises;

[0042] 2. Compared with the series connection of traditional micro-perforated panel absorbers, the telescopic micro-perforated panel sound absorption structure described in the invention can achieve a higher sound absorption coefficient and has a wider sound absorption frequency band;

[0043] 3. Compared with the series connection of several micro-perforated panel absorbers with equal diameters, when the proposed telescopic micro-perforated panel absorption structure is used in occasions with low noise reduction requirements, in the fully contracted state, the structure occupies a small space and can meet the absorption requirements.

[0044] 4. The proposed telescopic micro-perforated panel absorption structure is simple to manufacture and operate, and has broad application prospects in the field of noise reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is the front view schematic diagram of the overall structure of the present invention;

[0046] Figure 2 is the three-dimensional schematic diagram of the overall structure of the present invention;

[0047] Figure 3 is the absorption coefficient diagram of the present invention in the fully stretched state;

[0048] Figure 4 is the cross-sectional schematic diagram of the structure when the fourth-layer micro-perforated panel of the present invention shrinks by 10 mm;

[0049] Figure 5 is the cross-sectional schematic diagram of the structure when the third-layer micro-perforated panel of the present invention shrinks by 10 mm:

[0050] Figure 6 is the cross-sectional schematic diagram of the structure when the second-layer micro-perforated panel of the present invention shrinks by 10 mm;

[0051] Figure 7 is the absorption coefficient comparison diagram of three contraction cases of the present invention;

[0052] Figure 8 is the absorption effect of random cases during the contraction process of the present invention;

[0053] Figure 9 is the absorption effect of the present invention when it expands and contracts irregularly;

[0054] In the figure: 1. Micro-perforated panel, 2. Bottom rigid wall, 3. Outer rigid wall, 4. Back cavity. DETAILED DESCRIPTION OF THE INVENTION

[0055] The present invention will be further described below in conjunction with the drawings and specific embodiments, but it is not intended to limit the present invention.

[0056] As Figure 1 and Figure 2As shown in the figure, a telescopic micro-perforated panel sound-absorbing structure is composed of a number of micro-perforated panel sound absorbers connected in series. The diameters of a number of the micro-perforated panel sound absorbers form a telescopic micro-perforated panel sound-absorbing structure in a decreasing form. The micro-perforated panel sound absorber includes a micro-perforated panel 1, a bottom rigid wall 2, and an outer rigid wall 3. The outer rigid wall 3 is a hollow cylinder. A back cavity 4 is formed between the micro-perforated panel 1, the bottom rigid wall 2, and the outer rigid wall 3. Except for the micro-perforated panel sound absorber with the smallest diameter, an opening for docking with the micro-perforated panel 1 of the next micro-perforated panel sound absorber is provided on the bottom rigid wall 2 of each micro-perforated panel sound absorber, so that the next micro-perforated panel sound absorber and this micro-perforated panel sound absorber form a telescopic structure. By telescoping the micro-perforated panel sound absorber, the volume of the back cavity 4 and the distance between each micro-perforated panel 1 are changed, thereby changing the structural resonance frequency and absorbing noises of different frequencies.

[0057] Further, except for the diameters, a number of the micro-perforated panel sound absorbers adopt micro-perforated panels 1, bottom rigid walls 2, and outer rigid walls 3 with the same parameters.

[0058] Further, the thicknesses of the micro-perforated panels 1, bottom rigid walls 2, and outer rigid walls 3 of a number of the micro-perforated panel sound absorbers are all 1 mm.

[0059] Further, the micro-perforated panel 1 is a rigid panel.

[0060] Further, there are four micro-perforated panel sound absorbers, and the four micro-perforated panel sound absorbers are connected in series to form a telescopic micro-perforated panel sound-absorbing structure.

[0061] A design method for a telescopic micro-perforated panel sound-absorbing structure is characterized by including the following steps:

[0062] In the first step, according to the micro-perforated panel theory of Academician Ma Dayou and computer simulation to verify the feasibility of the model, the sound absorption coefficient of the micro-perforated panel sound absorber at normal incidence is:

[0063]

[0064] For the micro-perforated panel, its acoustic impedance rate is:

[0065] Z = R + jωM (2)

[0066] Its relative acoustic impedance is obtained:

[0067] r + jωm = (R + jωM) / ρc (3)

[0068] Among them, the acoustic resistance r and the acoustic mass m are respectively:

[0069]

[0070]

[0071] And the perforated plate constant

[0072]

[0073] In the above formulas, t is the plate thickness, d is the perforation diameter, both in mm, p is the perforation rate, f is the sound frequency, and the acoustic impedance rate of the cavity behind the plate is:

[0074] Z D = jρc cot(ωD / c) (7)

[0075] Using the impedance transfer method, gradually deduce layer by layer from the last layer forward. Finally, the impedance transfer formula at the pipe orifice is obtained and applied to the analysis and calculation of the acoustic characteristics of the micro-perforated plate structure. The calculation process is as follows. The acoustic impedance of the single-layer micro-perforated plate structure is composed of the acoustic impedance of the micro-perforations and the acoustic impedance of the cavity. Therefore, the acoustic impedance of the fourth-layer micro-perforated plate structure can be denoted as:

[0076]

[0077] The acoustic impedance of the third-layer and fourth-layer micro-perforated plate structures is:

[0078]

[0079] The total acoustic impedance of the second, third, and fourth layers is:

[0080]

[0081] The total acoustic impedance of the four-layer micro-perforated plate structure is:

[0082]

[0083] Where Z ai are the acoustic impedances of the micropores in the i-th layer respectively, and D i is the depth of the cavity in the i-th layer; ρ and c are the density and sound speed of air respectively;

[0084] The sound absorption coefficient of the micro-perforated absorber reaches the maximum value at resonance, and the maximum sound absorption coefficient value is:

[0085]

[0086] The resonance frequency f 0 Satisfies:

[0087] 2πf 0 m - cot(2πf 0 D / c) = 0 (13)

[0088] As can be seen from the above theory, by changing the depth of the back cavity, the acoustic impedance of the structure can be changed, and the change in acoustic impedance causes the change in the sound absorption coefficient and the resonance frequency;

[0089] In the second step, based on the variation law of the above-mentioned acoustic impedance of the structure with the depth of the back cavity, a telescopic micro-perforated panel sound absorption structure is designed. By telescoping, the overall depth of the back cavity of the structure is changed, that is, its acoustic impedance is changed, so as to achieve the absorption of noise at different frequencies; in the face of different application scenarios, a suitable sound absorption effect is achieved by stretching or contracting.

[0090] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention. For those skilled in the art, it should be realized that all the equivalent replacements and obvious changes made by using the description and illustration content of the present invention should be included in the protection scope of the present invention.

Claims

1. A telescopic micro-perforated panel sound absorption structure, characterized in that, it is composed of a number of micro-perforated panel sound absorbers connected in series. The diameters of a number of the micro-perforated panel sound absorbers form a telescopic micro-perforated panel sound absorption structure in a decreasing form. The micro-perforated panel sound absorber includes a micro-perforated panel (1), a bottom rigid wall (2), and an outer rigid wall (3). The outer rigid wall (3) is a hollow cylinder. A back cavity (4) is formed between the micro-perforated panel (1), the bottom rigid wall (2), and the outer rigid wall (3); except for the micro-perforated panel sound absorber with the smallest diameter, an opening for docking with the micro-perforated panel (1) of the next micro-perforated panel sound absorber is provided on the bottom rigid wall (2) of each micro-perforated panel sound absorber, so that the next micro-perforated panel sound absorber and this micro-perforated panel sound absorber form a telescopic structure. By telescoping the micro-perforated panel sound absorber, the volume of the back cavity (4) and the distance between each micro-perforated panel (1) are changed, thereby changing the structural resonance frequency and absorbing noises of different frequencies; A number of the micro-perforated panel sound absorbers use micro-perforated panels (1), bottom rigid walls (2), and outer rigid walls (3) with the same parameters except for the diameters; The design method of the telescopic micro-perforated panel sound absorption structure includes the following steps: The first step is to verify the feasibility of the model according to the micro-perforated panel theory of Academician Ma Dayou and computer simulation. The sound absorption coefficient of the micro-perforated panel sound absorber under normal incidence is: For the micro-perforated panel, its acoustic impedance rate is: Z = R + jωM (2) The relative acoustic impedance is obtained: r + jωm = (R + jωM) / ρc (3) Among them, the acoustic resistance r and the acoustic mass m are respectively: And the perforated plate constant In the above formulas, t is the plate thickness, d is the perforation diameter, and the units are both mm, p is the perforation rate, f is the sound frequency, and the acoustic impedance rate of the back cavity behind the plate is: Z D = jρc cot(ωD / c) (7) Using the impedance transfer method, gradually deduce forward layer by layer from the last layer. Finally, the impedance transfer formula at the pipe orifice is obtained and applied to the analysis and calculation of the acoustic characteristics of the micro-perforated panel structure. The calculation process is as follows. The acoustic impedance of the single-layer micro-perforated panel structure is composed of the acoustic impedance of the micro-perforations and the acoustic impedance of the cavity. Therefore, the acoustic impedance of the fourth-layer micro-perforated panel structure can be recorded as: The acoustic impedance of the third and fourth-layer micro-perforated panel structures is: The total acoustic impedance of the second, third, and fourth layers is: The total acoustic impedance of the four-layer micro-perforated panel structure is: where Z ai is the acoustic impedance of the i-th layer of micropores, D i is the depth of the i-th back cavity; ρ and c are the density and sound velocity of air respectively; The sound absorption coefficient of the micro-perforated sound absorber reaches the maximum value at resonance, and the maximum sound absorption coefficient value is: Resonant frequency f 0 Satisfy: 2πf 0 m - cot(2πf 0 D / c) = 0 (13) It can be seen from the above theory that by changing the depth of the back cavity, the acoustic impedance of the structure can be changed, and the change in the acoustic impedance causes changes in the sound absorption coefficient and the resonance frequency; The second step is to design a telescopic micro-perforated panel sound absorption structure based on the above variation law of the structural acoustic impedance with the back cavity depth. By telescoping, the overall back cavity depth of the structure is changed, that is, its acoustic impedance is changed, so as to achieve the absorption of noises of different frequencies; in the face of different application scenarios, a suitable sound absorption effect is achieved by stretching or contracting.

2. The telescopic micro-perforated panel sound absorption structure according to claim 1, characterized in that, the thicknesses of the micro-perforated panels (1), the bottom rigid walls (2), and the outer rigid walls (3) of a number of the micro-perforated panel sound absorbers are all 1 mm.

3. The scalable micro-perforated panel sound absorption structure according to claim 1, characterized in that, the micro-perforated panel (1) is a rigid panel.

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