Device and method for implementing low-frequency broadband sound absorption in a small space acoustic test box

Abstract

The application discloses a device for realizing low-frequency wideband sound absorption of a small-space acoustic test box, which comprises a box body, and a composite sound absorption layer is arranged on the inner wall of the box body, characterized in that the composite sound absorption layer comprises multiple air layers for sequentially propagating sound, a micro-slit plate is arranged on the sound input side of each air layer, and a porous sound absorption material and a bottom closed flat plate are arranged on the sound output side of the air layer for finally propagating sound. The size of the small-space acoustic test box is optimized by calculating the normal frequency distribution, the degeneration of low-frequency vibration modes is avoided, and the irregular distribution of low-frequency normal vibration mode frequencies is optimized. The low-frequency sound dyeing and comb filter effect in the small-space acoustic test box are reduced, and a high-fidelity sound test signal acquisition environment is realized.

Description

Technical Field

[0001] This invention belongs to the field of sound absorption technology, specifically relating to a device and its manufacturing method for achieving low-frequency broadband sound absorption in a small-space acoustic testing box. Background Technology

[0002] The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art.

[0003] In small spaces such as small acoustic test chambers, the number of excitations of normal modes of vibration is small, their distribution is uneven, and they are prone to degeneracy. This leads to the amplification or reduction of the sound waves of the normal mode frequency components, producing a comb filtering effect. This causes severe distortion of the sound signal received by the acoustic sensor, resulting in a large error in acoustic detection.

[0004] Current solutions and technologies mainly include porous sound-absorbing material sound absorption technology and thin plate resonant structure sound absorption technology. However, they have the following defects, which prevent them from being applied in small spaces such as small acoustic test boxes.

[0005] 1) Sound absorption technology using porous sound-absorbing materials

[0006] Porous fiber sound-absorbing materials, such as ultrafine glass wool and melamine foam, have poor sound absorption performance for low-frequency noise but good performance for mid-to-high frequency noise. For porous granular sound-absorbing materials, the particle size is related to the sound absorption frequency band distribution. Small-sized porous granular sound-absorbing materials are mainly effective for mid-to-high frequency sound absorption but poor for low-frequency sound absorption, while large-sized porous granular sound-absorbing materials are effective for mid-to-low frequency sound absorption but poor for mid-to-high frequency sound absorption. However, the test chamber is a small space, and large-sized porous granular sound-absorbing materials have too low a space utilization rate, making them difficult to apply.

[0007] 2) Microporous resonant structure sound absorption technology

[0008] Microporous resonant structures can achieve low-frequency resonant absorption, but they have strong frequency selectivity and a narrow frequency range for the absorption resonance peak distribution, making it impossible to achieve broadband absorption. Furthermore, achieving low-frequency resonant absorption requires a large cavity depth, resulting in low space utilization.

[0009] In small spaces such as small acoustic test chambers, the number of excitations of normal modes of vibration is small and they are prone to degeneracy, which leads to the enhancement or reduction of the sound waves of the normal frequency components, causing distortion of the acquired sound signal. This mainly leads to the following two problems.

[0010] 1. Sound coloration problem: The superposition of certain reflected sound and direct sound causes certain frequency components of the direct sound to be enhanced, resulting in a deterioration of sound quality and producing audible distortion in tone and timbre.

[0011] 2. Comb Filtering Effect: The effect of delayed reflected sound on the frequency response of sound is commonly referred to as the comb filtering effect. The comb filtering effect significantly interferes with the detection of continuous product noise with a certain broadband energy distribution. Its linear spectrum appears as a comb, fluctuating up and down. The smaller the room size, the smaller the interval between reflected and direct sound. The larger the frequency peak-to-peak value and node spacing produced by the comb filtering effect, the more obvious the interference with the sound signal. Figure 1 As shown. Summary of the Invention

[0012] Therefore, the technical problem to be solved by the present invention is how to broaden the bandwidth of the resonance absorption peak.

[0013] To address the aforementioned technical problems, this invention provides a device for achieving low-frequency broadband sound absorption in a small-space acoustic testing chamber. The device includes a chamber housing, the inner wall of which is provided with a composite sound-absorbing layer. This composite sound-absorbing layer comprises multiple air layers that sequentially propagate sound. Each air layer has a micro-slit plate on its sound input side, and the final air layer propagating sound has a porous sound-absorbing material on its sound output side. The porous sound-absorbing material has a bottom sealed plate on its sound output side.

[0014] The normal vibration frequency distribution within the box satisfies the following formula:

[0015] ;

[0016] in, It is the Nth normal mode frequency. If the calculation results show that the values ​​of multiple normal modes are very close, then a significant resonance of that frequency will occur in the enclosure, making the sound pressure level of that frequency significantly higher or lower than the sound pressure level of the sound source signal in the free field space. This is the degeneracy of the normal modes. c0 is the speed of sound, which is generally taken as 340m / s at normal temperature and pressure. , , It is any positive integer not less than 0; , , The rigid walls of the box form the length, width, and height of a rectangular space;

[0017] The composite sound-absorbing layer satisfies the following formula:

[0018] ;

[0019] in, The value is the center frequency of the resonant absorption peak of the composite sound-absorbing layer, and the value substituted is the degenerate normal vibration frequency that occurs within the box. c is the speed of sound, 340 m / s; P is the perforation rate of the micro-slit plate; t is the thickness of the micro-slit plate. B is the width of the micro-slit plate, and L is the center-to-center distance between the micro-slits.

[0020] In one embodiment of the present invention, the spacing between adjacent seams of the micro-slit plate is 50-100 mm, and the seam length is determined by calculation based on the required perforation rate P.

[0021] In one embodiment of the present invention, the micro-slit width on the micro-slit plate is 6-20mm.

[0022] In one embodiment of the present invention, the perforation rate P of the micro-slit plate is between 0.1% and 15%.

[0023] In one embodiment of the present invention, the micro-slit board is a wooden board or a metal board.

[0024] In one embodiment of the present invention, the porous sound-absorbing material is a folded flame-retardant sound-absorbing cloth or ultrafine glass wool.

[0025] In one embodiment of the present invention, the total thickness of the composite sound-absorbing layer is 0.1m-0.3m.

[0026] In one embodiment of the present invention, the composite sound-absorbing layer comprises 2-4 air layers.

[0027] In one embodiment of the present invention, the sound output side of the porous sound-absorbing material is provided with a solid back plate, a grid is provided between two adjacent micro-slit plates, and a grid frame is provided between adjacent micro-slit plates and the back plate.

[0028] The present invention also provides another technical solution: a method for achieving low-frequency broadband sound absorption in a small space acoustic test box. By calculating the normal frequency distribution of the small space acoustic test box and optimizing its size, the degeneracy of low-frequency vibration modes is avoided, the irregular distribution of low-frequency normal vibration mode frequencies is improved, sound coloration and comb filtering effects are reduced, and sound signal distortion is reduced.

[0029] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0030] 1) The device for achieving low-frequency broadband sound absorption in a small space acoustic test box disclosed in this invention optimizes the length-width-height ratio by calculating the frequency distribution and number of normal vibration modes in a small space, reducing the degeneracy of low-frequency normal vibration modes and avoiding comb filtering effects, thereby reducing the distortion of sound signals.

[0031] 2) The device for achieving low-frequency broadband sound absorption in a small-space acoustic test box disclosed in this invention, in order to enable the micro-slit sound-absorbing resonant cavity in the composite sound-absorbing layer to have good sound absorption performance in a wide frequency range, combines resonators. According to the frequency range where the normal vibration mode distribution degenerates, two or more layers of micro-slit plates with specific perforation ratio and slit width are selected and combined with square grid and back plate to form a multi-layer coupled resonant micro-slit plate sound absorption structure. It can achieve two or more resonant absorption peaks and obtain a high sound absorption coefficient in multiple octave bands. It solves the problem of low-frequency normal vibration mode degeneracy that cannot be avoided even after size ratio optimization, as well as the resulting comb filtering effect and sound coloration problem. Attached Figure Description

[0032] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0033] Figure 1 A schematic diagram illustrating the relationship between the frequency peak-to-peak value and node spacing generated by comb filtering and their interference with the audio signal;

[0034] Figure 2 This is a schematic diagram of the exterior of the housing disclosed in this invention;

[0035] Figure 3 This is a cross-sectional view of the composite sound-absorbing layer disclosed in this invention;

[0036] Figure 4 This is a planar schematic diagram of the composite sound-absorbing layer disclosed in this invention.

[0037] Among them, 1. Box body; 21. Air layer; 22. Micro-slit board; 23. Porous sound-absorbing material; 24. Bottom closed flat plate; 25. Grille frame. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0039] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation for this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. In this disclosure, terms such as “upper,” “lower,” “left,” “right,” “front,” “rear,” “vertical,” “horizontal,” “side,” “bottom,” etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are merely relational terms determined for the convenience of describing the structural relationships of the components or elements of this disclosure, and do not specifically refer to any component or element in this disclosure, nor should they be construed as limiting this disclosure. In this disclosure, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this disclosure based on the specific circumstances, and they should not be construed as limitations on this disclosure.

[0040] The following is a preferred embodiment used to illustrate the present invention, but it is not intended to limit the scope of the invention.

[0041] Example 1

[0042] See Figures 2 to 4As shown in the illustration, a device for achieving low-frequency broadband sound absorption in a small-space acoustic testing box includes a box 1 with internal dimensions of 1.5m * 1.6m * 2.2m. The degenerate frequencies of its normal vibrations are 155Hz and 347Hz. The inner wall of the box 1 is provided with a composite sound-absorbing layer, which includes two air layers 21 that propagate sound sequentially. Each air layer 21 has a micro-slit plate 22 on its sound input side, and a porous sound-absorbing material 23 on the sound output side of the last air layer 21. The porous sound-absorbing material has a bottom sealing layer on its sound output side. The closed plate 24 has a grid 25 between adjacent micro-slit plates 22 and a grid frame 25 between adjacent micro-slit plates 22 and the bottom closed plate 24. The total thickness of the composite sound-absorbing layer is 300mm. The composite sound-absorbing layer includes two air layers. The thicknesses of the two micro-slit plates arranged sequentially along the sound propagation direction are 1mm and 3mm, respectively. The thicknesses of the two air layers arranged sequentially along the sound propagation direction are 300mm and 200mm, respectively. The micro-slit widths on the two micro-slit plates arranged sequentially along the sound propagation direction are 10mm and 15mm, respectively. The perforation rates of the two micro-slit plates arranged sequentially along the sound propagation direction are 2% and 6.3%, respectively. The micro-slit plates are aluminum micro-slit metal plates. The thickness of the porous sound-absorbing material is 200mm, and the porous sound-absorbing material is folded flame-retardant sound-absorbing cloth. The bottom closed plate 24 is a steel plate.

[0043] The normal frequencies within the acoustic test chamber were calculated, and the distribution of normal vibration frequencies below 400Hz is shown in the table below, where the degenerate frequencies are 155 and 347 Hz, respectively:

[0044]

[0045] To reduce the sound coloration and comb filtering effect caused by the degeneracy of low-frequency vibration modes, the resonant absorption peaks of the composite sound-absorbing layer in this embodiment are calculated to be 107Hz and 348Hz, respectively. The theoretically calculated sound absorption bandwidth Ω when the sound absorption coefficient drops to half of the peak value is 1.36 octaves (f1=66Hz, f2=180Hz) and 2.67 octaves (f1=138Hz, f2=876Hz).

[0046] Example 2

[0047] The rest is the same as in Embodiment 1, except that the internal dimensions of the aforementioned box 1 are 1.8m*2.0m*2.4m, and the frequencies of its normal vibration below 400Hz, after degeneracy, are 170Hz, 207Hz, 272Hz, 283Hz, 292Hz, 296Hz, 317Hz, 330Hz, 354Hz, 360Hz, 364Hz, 381Hz, and 393Hz, respectively. The total thickness of the aforementioned composite sound-absorbing layer is 0.2m, and the aforementioned composite sound-absorbing layer includes two aforementioned air layers. The thicknesses of the two aforementioned micro-slit plates arranged sequentially along the sound propagation direction are 1mm and 3mm, respectively, and the thicknesses of the two aforementioned air layers arranged sequentially along the sound propagation direction are 0.2m and 0.18m, respectively. The width of the micro-slits on the aforementioned micro-slit plates is 10mm. The perforation rates of the two micro-slit plates arranged sequentially along the sound propagation direction are 0.8% and 4.0%, respectively. The two micro-slit plates are stainless steel and aluminum plates, respectively. The thickness of the porous sound-absorbing material is 150 mm, and the porous sound-absorbing material is ultrafine glass wool. The bottom sealing plate is a wooden board.

[0048] The normal modes within the acoustic test chamber were calculated, and the distribution of normal vibration frequencies below 400Hz is shown in the table below. The frequencies that are degenerate are 170, 207, 272, 283, 292, 296, 317, 354, 360, 364, 381, and 393.

[0049]

[0050] To reduce the sound coloration and comb filtering effect caused by the degeneracy of low-frequency vibration modes, the resonant absorption peaks of the composite sound-absorbing layer in this embodiment are calculated to be 87Hz and 225Hz, respectively. The sound absorption bandwidth Ω when the absorption coefficient drops to half of the peak value is 0.83 octaves (f1=72Hz, f2=128Hz) and 1.96 octaves (f1=135Hz, f2=525Hz), respectively.

[0051] Example 3

[0052] The rest is the same as in Embodiment 1, except that the internal dimensions of the aforementioned box 1 are 1.2m*1.5m*2.0m, and the frequencies of normal vibration below 400Hz that are degenerate are 142Hz, 283Hz, 317Hz, 340Hz, and 368Hz, respectively. The total thickness of the aforementioned composite sound-absorbing layer is 0.25m. The aforementioned composite sound-absorbing layer includes three aforementioned air layers. The thicknesses of the three aforementioned micro-slit plates arranged sequentially along the sound propagation direction are 0.8mm, 1.0mm, and 1.0mm, respectively. The thicknesses of the three aforementioned air layers arranged sequentially along the sound propagation direction are 0.25m, 0.2m, and 0.15m, respectively. The micropores on the aforementioned micro-slit plates are micro-slits, and the width of the aforementioned micro-slits is 10mm. The perforation rates of the three micro-slit plates arranged sequentially along the sound propagation direction are 1%, 5%, and 15%, respectively. The micro-slit plates are stainless steel plates, stainless steel plates, and aluminum plates, respectively. The thickness of the porous sound-absorbing material is 0.15 μm, and the porous sound-absorbing material is ultrafine glass wool.

[0053] The normal modes within the acoustic test chamber were calculated, and the distribution of normal vibration frequencies below 400Hz is shown in the table below. The frequencies that are degenerate are 142, 283, 317, 340, and 368 Hz.

[0054]

[0055] To reduce the sound coloration and comb filtering effect caused by the degeneracy of low-frequency vibration modes, the resonant absorption peaks of the composite sound-absorbing layer in this embodiment are calculated to be 88Hz, 239Hz, and 773Hz, respectively. The sound absorption bandwidths Ω when the resonant absorption coefficient drops to half of the peak value are 0.95 octaves (f1=63Hz, f2=122Hz), 1.95 octaves (f1=121Hz, f2=470Hz), and 3.85 octaves (f1=203Hz, f2=2935Hz).

[0056] Example 4

[0057] The rest is the same as in Embodiment 1, except that the internal dimensions of the box 1 are 1.4m*1.6m*2.2m, and the frequencies of normal vibration below 400Hz that are degenerate are 255Hz, 332Hz, and 394Hz, respectively. The total thickness of the composite sound-absorbing layer is 0.3m. The composite sound-absorbing layer includes three air layers. The thicknesses of the three micro-slit plates arranged sequentially along the sound propagation direction are 3mm, 1mm, and 1mm, respectively. The thicknesses of the three air layers arranged sequentially along the sound propagation direction are 0.3m, 0.2m, and 0.15m, respectively. The micropores on the micro-slit plates are micro-slits, and the widths of the three micro-slits arranged sequentially along the sound propagation direction are 5mm, 10mm, and 10mm, respectively. The perforation rates of the aforementioned micro-slit panels are 1.5%, 3.0%, and 15.0% respectively. The three aforementioned micro-slit panels arranged in sequence along the sound propagation direction are wood, aluminum, and stainless steel respectively. The thickness of the aforementioned porous sound-absorbing material is 150mm, and the aforementioned porous sound-absorbing material is ultrafine glass wool.

[0058] The normal frequencies within the acoustic test chamber were calculated, and the distribution of normal vibration frequencies below 400Hz is shown in the table below, where the degenerate frequencies are 252, 298, and 319.

[0059]

[0060] To reduce the sound coloration and comb filtering effect caused by the degeneracy of low-frequency vibration modes, the resonant absorption peaks of the composite sound-absorbing layer in this embodiment are calculated to be 78Hz, 185Hz, and 481Hz, respectively. The sound absorption bandwidths Ω when the resonant absorption coefficient drops to half of the peak value are 1.01 octaves (f1=54.8Hz, f2=110Hz), 1.56 octaves (f1=108Hz, f2=317Hz), and 3.15 octaves (f1=161Hz, f2=1434Hz).

[0061] Example 5

[0062] The rest is the same as in Example 4, except that the thicknesses of the three micro-slit plates arranged sequentially along the sound propagation direction are 0.8mm, 0.8mm, and 1mm, respectively; the thicknesses of the three air layers arranged sequentially along the sound propagation direction are 0.3m, 0.25m, and 0.18m, respectively; the micropores on the three micro-slit plates arranged sequentially along the sound propagation direction are micro-slits, and the slit widths of the micro-slits are 5mm, 10mm, and 10mm, respectively; the perforation rates of the three micro-slit plates arranged sequentially along the sound propagation direction are 1%, 2.5%, and 15%, respectively; the three micro-slit plates arranged sequentially along the sound propagation direction are stainless steel, aluminum, and aluminum plates, respectively; the thickness of the porous sound-absorbing material is 150mm; and the porous sound-absorbing material is ultrafine glass wool.

[0063] Example 6

[0064] The rest is the same as in Example 5, except that the thickness of the air layer is 0.3m, 0.2m, and 0.1m respectively, the micro-slit plate is stainless steel plate, aluminum plate, and aluminum plate respectively, the thickness of the porous sound-absorbing material is 100mm, and the porous sound-absorbing material is ultrafine glass wool.

[0065] Comparative Example 1

[0066] Chinese invention patent with publication number CN113539224A discloses a low-frequency broadband composite flat panel sound-absorbing structure.

[0067] Comparative Example 2

[0068] Chinese utility model patent with publication number CN113628604A discloses a spatially bent porous superstructure with adjustable sound absorption frequency band and low-frequency broadband sound absorption.

[0069] The following is a comparison of the technical effects of the present invention and the prior art:

[0070]

[0071] As can be seen from the table above, the resonant absorption peak bandwidth of the device for achieving low-frequency broadband sound absorption in the small-space acoustic test box of the present invention has been greatly broadened.

[0072] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, is provided. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for achieving low-frequency broadband sound absorption in a small-space acoustic testing box, comprising a box body, wherein the inner wall of the box body is provided with a composite sound-absorbing layer, characterized in that... The composite sound-absorbing layer comprises multiple air layers that propagate sound sequentially. Each air layer has a micro-slit plate on its sound input side, and the last air layer to propagate sound has a porous sound-absorbing material on its sound output side. The porous sound-absorbing material has a bottom closed plate on its sound output side. The normal vibration frequency distribution within the box satisfies the following formula: ； in, It is the Nth normal mode frequency. If the calculation results show that the values ​​of multiple normal modes are very close, then a significant resonance of this frequency will occur in the enclosure, making the sound pressure level of this frequency significantly higher or lower than the sound pressure level of the sound source signal in the free field space. This is the degeneracy of the normal modes; c0 is the speed of sound, which is taken as 340m / s at normal temperature and pressure. It is any positive integer not less than 0; The rigid walls of the box form the length, width, and height of a rectangular space; The composite sound-absorbing layer satisfies the following formula: ； in, The value is the center frequency of the resonant absorption peak of the composite sound-absorbing layer, and the value substituted is the degenerate normal vibration frequency that occurs within the box. c is the speed of sound, 340 m / s; P is the perforation rate of the micro-slit plate; t is the thickness of the micro-slit plate; b is the width of the micro-slit plate; B is the center-to-center distance of the micro-slits; L is the thickness of the micro-slit plate from the bottom closed plate. By calculating the frequency distribution and number of normal vibration modes in a small space, the length-width-height ratio of the enclosure is optimized. The spacing between adjacent seams of the micro-slit plate is calculated to be 50-100mm using the formula. The width of the micro-slits on the micro-slit plate is 6-20mm. The perforation rate P of the micro-slit plate is 0.1% to 15%. Based on the frequency range where the normal vibration mode distribution exhibits degeneracy, two or more layers of the micro-slit plate with specific perforation rates and seam widths are selected to form a multi-layer coupled resonant micro-slit plate sound absorption structure with the bottom closed plate, thereby achieving two or more resonant absorption peaks and obtaining a high sound absorption coefficient within multiple octave bands.

2. The device for achieving low-frequency broadband sound absorption in a small-space acoustic testing box according to claim 1, characterized in that, The micro-slotted board is made of wood or metal.

3. The device for achieving low-frequency broadband sound absorption in a small-space acoustic testing box according to claim 1, characterized in that, The porous sound-absorbing material is a folded flame-retardant sound-absorbing cloth or ultra-fine glass wool.

4. The device for achieving low-frequency broadband sound absorption in a small-space acoustic testing box according to claim 1, characterized in that, The total thickness of the composite sound-absorbing layer is 0.1m-0.3m.

5. The device for achieving low-frequency broadband sound absorption in a small-space acoustic testing box according to claim 1, characterized in that, The composite sound-absorbing layer comprises 2-4 air layers.

6. The device for achieving low-frequency broadband sound absorption in a small-space acoustic testing box according to claim 1, characterized in that, The sound output side of the porous sound-absorbing material is provided with a solid back plate, and a grid is provided between two adjacent micro-slit plates, and a grid frame is provided between adjacent micro-slit plates and the back plate.

7. A method for achieving low-frequency broadband sound absorption in a small-space acoustic testing box, characterized in that, By calculating the optimized dimensions of the normal frequency distribution of the device for low-frequency broadband sound absorption in the small space acoustic test box according to any one of claims 1 to 6, the degeneracy of low-frequency vibration modes is avoided, the irregular distribution of low-frequency normal vibration mode frequencies is improved, sound coloration and comb filtering effects are reduced, and sound signal distortion is reduced.

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