Nested micro-perforated plate low-frequency sound absorption structure with robustness for oblique incidence sound waves

Abstract

The invention discloses a nested micro-perforated plate low-frequency sound absorption structure with robustness for oblique incident sound waves, and the structure comprises an outer layer sound absorber which is composed of an outer layer micro-perforated plate and an outer layer back cavity, and the outer layer back cavity is a cavity defined by the outer layer micro-perforated plate and rigid walls and rigid backs around the outer layer micro-perforated plate; the inner-layer sound absorber is composed of an inner-layer micro-perforated plate and an inner-layer back cavity, the inner-layer back cavity is a cavity defined by the inner-layer micro-perforated plate, the four rigid walls around the inner-layer micro-perforated plate and the rigid backing, the inner portion and the bottom of the back cavity of the outer-layer sound absorber share the same rigid backing, and gaps are formed between the other four outer-layer rigid walls and the four inner-layer rigid walls. The second micro-perforated plate sound absorber is arranged in the back cavity of the first micro-perforated plate sound absorber instead of being connected in series behind the first back cavity, and gaps are reserved around the second micro-perforated plate sound absorber, so that sound wave propagation paths in the back cavity of the outer-layer sound absorber and the number of the sound absorbers are increased under the condition that the overall thickness of the structure is not increased; meanwhile, the influence of incident angle changes on the length of a sound wave propagation path in a back cavity of the sound absorber of the outer layer micro-perforated plate is reduced, so that the sound absorber has a good low-frequency broadband sound absorption effect, the influence of the incident angle changes on the whole sound absorption characteristic is small, and the sound absorber has a good robust sound absorption effect on sound waves of different incident angles.

Description

Technical Field

[0001] The invention relates to the technical field of noise control, in particular to a nested micro-perforated plate low-frequency sound absorption structure which is robust against oblique incident sound waves. Background Art

[0002] Noise pollution has many harmful effects, including hearing loss, cardiovascular disease, sleep disturbance, etc. Long-term exposure to noise can also shorten the service life of buildings and machinery. Therefore, the importance of sound absorption and noise reduction technology is self-evident. The use of sound-absorbing materials is currently recognized as an effective means of noise reduction.

[0003] The micro-perforated plate proposed by Ma Dayou in 1975 is a porous sound-absorbing material with many advantages in terms of sound absorption characteristics, flow resistance, moisture resistance, corrosion resistance, sanitation and cleanliness. Its structure is simple, and the basic acoustic unit has only two parts: the micro-perforated plate and the back cavity. However, the sound absorption performance of a single-layer micro-perforated plate sound absorber in practical applications is relatively limited, and its sound absorption frequency band is relatively narrow, mainly concentrated in the medium and high frequency ranges. In order to make the single-layer micro-perforated plate sound absorber have good sound absorption performance in the low frequency range, it is often necessary to increase the depth of the back cavity. In occasions with limited space, this method seems to be somewhat inadequate.

[0004] The double-layer serial micro-perforated plate sound absorption structure proposed by Ma Dayou at the same time has significantly improved the low-frequency sound absorption performance and sound absorption bandwidth compared to the single-layer micro-perforated plate sound absorber, but it still essentially increases the overall thickness of the structure and has the same problem in occasions with limited space; in addition, noise is usually composed of sound waves with various incident angles, and the double-layer serial micro-perforated plate sound absorption structure has a large change in sound absorption performance under different sound wave incident conditions, and its low-frequency sound absorption performance will deteriorate with the increase of the incident angle, and it is not robust. Specifically, as the incident angle of the sound wave increases, its effective sound absorption frequency band gradually moves to high frequency, and the peak of the sound absorption coefficient curve gradually decreases, so the sound absorption performance in the low-frequency range deteriorates. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a nested micro-perforated plate low-frequency sound absorption structure that is robust against obliquely incident sound waves. The present invention places the second micro-perforated plate sound absorber inside the back cavity of the first micro-perforated plate sound absorber, rather than being connected in series behind the first back cavity, and leaving gaps around it, so as to increase the sound wave propagation path and the number of sound absorbers in the back cavity of the outer sound absorber without increasing the overall thickness of the structure, and at the same time reduce the influence of the change of the incident angle on the length of the sound wave propagation path in the back cavity of the outer micro-perforated plate sound absorber. Therefore, the present invention not only has good low-frequency broadband sound absorption effect, but also the overall sound absorption characteristics are less affected by the change of the sound wave incident angle, that is, it presents a good robust sound absorption effect for sound waves with different incident angles.

[0006] The present invention aims to solve the problems of insufficient low-frequency sound absorption performance and space limitation of a single-layer micro-perforated plate sound absorber, while improving the robustness of the sound absorption performance under oblique incidence conditions.

[0007] In order to achieve the above objectives, the present invention proposes a nested micro-perforated plate low-frequency sound absorption structure that is robust against oblique incident sound waves, the structure comprising: An outer sound absorber, which is composed of an outer micro-perforated plate and an outer back cavity, wherein the outer back cavity is an air layer surrounded by the outer micro-perforated plate and four rigid walls around it and a rigid backing; At least one inner sound absorber is composed of an inner micro-perforated plate and an inner back cavity. The inner back cavity is an air layer surrounded by the inner micro-perforated plate and four rigid walls and a rigid backing around it. Inside the back cavity of the outer sound absorber, the bottom shares the same rigid backing, and gaps are formed between the other four outer rigid walls and the four inner rigid walls.

[0008] Preferably, the inner layer sound absorber is composed of one or more inner layer micro-perforated plate sound absorbers nested in sequence.

[0009] Preferably, the shape of the inner sound absorber is one of rectangular, trapezoidal or cylindrical.

[0010] Preferably, the total thickness of the low-frequency sound absorbing structure is determined by the outer layer sound absorber, and the inner layer sound absorber serves to increase the propagation path of sound waves in the back cavity of the outer layer sound absorber and the number of sound absorbers, so as to improve the low-frequency sound absorption performance and expand the effective sound absorption frequency band without increasing the thickness of the overall structure.

[0011] Preferably, the effective sound absorption band of the low-frequency sound absorption structure is less affected by changes in the sound wave incident angle, that is, it exhibits a good robust sound absorption effect for sound waves with different incident angles, and the peak of the sound absorption coefficient curve increases with the increase of the sound wave incident angle.

[0012] Preferably, the above structure can design the structural parameters of the inner and outer micro-perforated plates, the inner and outer back cavity depths, and the number or shape of the nested inner layer sound absorbers according to requirements to achieve low-frequency broadband absorption of noises of different frequencies.

[0013] The advantages of the present invention are: 1. The total thickness of the nested micro-perforated plate low-frequency sound absorption structure, which is robust under oblique incidence conditions, is determined only by the outer layer of sound absorbers. The inner layer of sound absorbers increases the propagation path of sound waves in the back cavity of the outer layer of sound absorbers and the number of sound absorbers, so as to improve the low-frequency sound absorption performance and expand the effective sound absorption frequency band without increasing the thickness of the overall structure. The back cavity space of the outer layer of sound absorbers is fully utilized, thereby meeting some occasions where the sound absorption space is limited.

[0014] 2. The nested micro-perforated plate low-frequency sound absorption structure is robust under oblique incidence conditions. The effective sound absorption frequency band is less affected by the change of the sound wave incident angle, and the peak of the sound absorption coefficient curve increases with the increase of the sound wave incident angle. Therefore, the sound absorption performance has good robustness under oblique incidence conditions and has practical value in many occasions.

[0015] 3. The nested micro-perforated plate low-frequency sound absorption structure is robust under oblique incidence conditions. The structural parameters of the inner and outer micro-perforated plates, the inner and outer back cavity depths, and the number or shape of the nested inner layer sound absorbers can be designed according to the needs. The sound absorbers with different sound absorption frequency bands can be coupled to achieve wide-band absorption of noises of different frequencies, which has high flexibility.

[0016] 4. The nested micro-perforated plate low-frequency sound absorption structure, which is robust under oblique incidence conditions, has the advantages of simple structure, environmental protection, and convenient processing, and has broad application prospects in the field of noise reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a cross-sectional schematic diagram of the low-frequency sound absorption structure of nested micro-perforated plates having robustness under oblique incidence conditions of the present invention.

[0018] Figure 2 is a cross-sectional schematic diagram of an inner layer micro-perforated plate sound absorber structure with different shapes embedded in it, where Figure 2 (a) is a cross-sectional schematic diagram of the trapezoidal inner micro-perforated plate sound absorption structure. Figure 2 (b) is a schematic cross-sectional view of the cylindrical inner micro-perforated plate sound absorption structure.

[0019] Figure 3 It is a cross-sectional schematic diagram of the three-layer nested micro-perforated plate low-frequency sound absorption structure of the present invention.

[0020] Figure 4 This is a comparison chart of the sound absorption coefficients of a double-layer nested micro-perforated plate sound absorption structure and a traditional double-layer series micro-perforated plate sound absorption structure.

[0021] 1- outer microperforated plate, 2- outer back cavity, 3- inner microperforated plate, 4- inner back cavity, 5- rigid backing, 6- inner rigid wall, 7- outer rigid wall, P in-incident sound wave, θ -Angle of incidence of the sound wave. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention. Example 1

[0023] Figure 1It is a cross-sectional schematic diagram of a nested micro-perforated plate low-frequency sound absorbing structure that is robust against obliquely incident sound waves, which is composed of an outer sound absorber consisting of an outer micro-perforated plate 1 and an outer back cavity 2, and an inner sound absorber consisting of an inner micro-perforated plate 3 and an inner back cavity 4, which are nested in sequence, wherein the outer back cavity 2 is an air layer surrounded by the micro-perforated plate 1 and its four surrounding rigid walls 6 and a rigid backing 5, and the inner back cavity 4 is an air layer surrounded by the micro-perforated plate 3 and its four surrounding rigid walls 7 and a rigid backing 5. The inner sound absorber is placed inside the back cavity 2 of the outer sound absorber, and the bottom shares the same rigid backing 5, and gaps are formed between the remaining four outer rigid walls 6 and the four inner rigid walls 7.

[0024] The outer micro-perforated plate 1 in Example 1 has a hole diameter of 0.1-1 mm, a plate thickness of 0.2-2 mm, a perforation rate of 0.1%-19.6%, and a depth of 20-100 mm of the outer back cavity 2. The outer micro-perforated plate and the outer back cavity 2 determine the total thickness of the sound absorbing structure.

[0025] The pore size of the inner micro-perforated plate 3 is 0.1-1 mm, the plate thickness is 0.2-2 mm, the perforation rate is 0.1%-19.6%, the depth of the inner back cavity 4 is 10-90 mm, and the depth of the inner back cavity 4 must be less than the depth of the outer back cavity 2. The inner micro-perforated plate 3 and the inner back cavity 4 increase the number of micro-perforated plate layers and the sound wave propagation path to expand the effective sound absorption frequency band and improve the low-frequency sound absorption performance, but do not increase the total thickness of the sound absorption structure.

[0026] The outer sound absorber composed of the outer micro-perforated plate 1 and the outer back cavity 2 shares the same rigid backing 5 with the inner sound absorber composed of the inner micro-perforated plate 3 and the inner back cavity 4. Gaps are formed between the other four outer rigid walls 7 and the four inner rigid walls 6. The maximum gap between the inner rigid wall 6 and the outer rigid wall 7 is 20% to 50% of the side length of the rigid backing 5, which increases the propagation path of sound waves to improve the low-frequency sound absorption performance of the structure. Example 2

[0027] Figure 2 , Figure 3 Three extended embodiments of the structure described in the invention are described below. Figure 2 (a) is a trapezoidal nested micro-perforated plate sound absorption structure. Figure 2 (b) is a cylindrical nested micro-perforated plate sound absorption structure. Figure 3 It is a three-layer nested micro-perforated plate sound absorption structure. The present invention includes but is not limited to these three implementations. The embedded inner layer sound absorption body structure is highly flexible and can be expanded in many ways to meet the absorption needs of noises of different frequencies in various occasions. Example 3

[0028] Figure 4This is a comparison chart of the sound absorption coefficients of the double-layer nested micro-perforated plate sound absorption structure shown in Example 1 and the traditional double-layer series micro-perforated plate sound absorption structure under plane wave incidence and oblique incidence conditions. The total thickness of the two structures is the same, and the values ​​of each parameter are as follows: Double-layer nested micro-perforated plate sound absorption structure: the aperture of the outer micro-perforated plate 1 is 0.3mm, the plate thickness is 1mm, the perforation rate is 2.5%, and the depth of the outer back cavity 2 is 50mm; the aperture of the inner micro-perforated plate 3 is 0.3mm, the plate thickness is 1mm, the perforation rate is 2%, and the depth of the inner back cavity 4 is 45mm; the side length of the rigid backing 5 is 50mm, and the bottom side length of the inner rigid wall 6 is 33mm.

[0029] Double-layer series micro-perforated plate sound absorption structure: the first layer of micro-perforated plate has a hole diameter of 0.3mm, a plate thickness of 1mm, a perforation rate of 2.5%, and a back cavity depth of 28mm; the second layer of micro-perforated plate has a hole diameter of 0.3mm, a plate thickness of 1mm, a perforation rate of 2%, and a back cavity depth of 22mm.

[0030] Figure 4 The results show that the double-layer nested micro-perforated plate sound absorption structure of Example 1 has better low-frequency sound absorption performance than the traditional double-layer series micro-perforated plate sound absorption structure at the same total thickness, and exhibits good robust sound absorption performance for oblique incident sound waves at different incident angles.

[0031] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A nested micro-perforated plate low-frequency sound absorption structure with robustness against oblique incident sound waves, characterized in that: The structure comprises: An outer sound absorber, which is composed of an outer micro-perforated plate and an outer back cavity, wherein the outer back cavity is a cavity surrounded by the outer micro-perforated plate and four rigid walls around it and a rigid backing; At least one inner layer sound absorber is composed of an inner layer micro-perforated plate and an inner layer back cavity. The inner layer back cavity is a cavity surrounded by the inner micro-perforated plate and four rigid walls and a rigid backing around it. Inside the back cavity of the outer layer sound absorber, the bottom shares the same rigid backing, and gaps are formed between the other four outer layer rigid walls and the four inner layer rigid walls.

2. The nested micro-perforated plate low-frequency sound absorption structure with robustness against oblique incident sound waves according to claim 1, characterized in that: The inner layer sound absorber is composed of one or more inner layer micro-perforated plate sound absorbers nested in sequence.

3. The nested micro-perforated plate low-frequency sound absorption structure with robustness against oblique incident sound waves according to claim 1 or 2, characterized in that: The shape of the inner sound absorber is one of a rectangle, a trapezoid or a cylinder.

4. The nested micro-perforated plate low-frequency sound absorption structure having robustness against oblique incident sound waves according to claim 1, characterized in that: The total thickness of the low-frequency sound absorbing structure is determined by the outer layer sound absorbing body, and the inner layer sound absorbing body serves to increase the propagation path of the sound wave in the back cavity of the outer layer sound absorbing body and the number of sound absorbing bodies, so as to improve the low-frequency sound absorbing performance and expand the effective sound absorbing frequency band without increasing the thickness of the overall structure.

5. The nested micro-perforated plate low-frequency sound absorption structure having robustness against oblique incident sound waves according to claim 1, characterized in that: The effective sound absorption band of the low-frequency sound absorption structure is less affected by changes in the sound wave incident angle, that is, it exhibits a good robust sound absorption effect for sound waves with different incident angles, and the peak of the sound absorption coefficient curve increases with the increase of the sound wave incident angle.

6. The nested micro-perforated plate low-frequency sound absorption structure having robustness against oblique incident sound waves according to claim 1, characterized in that: The structure can design the structural parameters of the inner and outer micro-perforated plates, the inner and outer back cavity depths, and the number or shape of the nested inner layer sound absorbers according to requirements, so as to achieve low-frequency and wide-band absorption of noises of different frequencies.

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