A low frequency broadband absorber

Abstract

The application discloses a low-frequency broadband sound absorber, which comprises a resonator, the outer part of the resonator is covered with a porous material layer, one side of the porous material layer is connected with a rigid backing, and the side opposite to the rigid backing is an incident surface; the resonator comprises an inner shell and an outer shell, the inner shell is located inside the outer shell; a first opening is arranged at the center of one side of the outer shell close to the sound wave incident surface, a second opening is arranged at the center of one side of the inner shell close to the rigid backing, and the first opening and the second opening are oppositely arranged. The application can efficiently absorb sound waves in a wide band range of low-frequency waves, and the high-efficiency absorption effect is hardly affected by the sound wave incident angle.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of acoustics, and relates to a sound absorption structure, in particular to a low-frequency broadband sound absorber. BACKGROUND

[0002] Traditional sound absorption materials include porous material layers, micro-perforated panels, etc., which usually have good sound absorption performance in the medium and high frequency bands, but when facing low-frequency sound waves, a huge structural thickness is often needed to have a better absorption effect, which affects the application of sound absorption materials in the field of low-frequency noise reduction.

[0003] The emergence of acoustic metamaterials has opened up new avenues for low-frequency sound absorption. Acoustic metamaterials can achieve high-efficiency sound absorption with a thickness much smaller than the wavelength, which makes this type of material have broad application prospects in dealing with low-frequency sound absorption problems. However, due to the sound absorption principle of the resonator, the sound absorption frequency band of most existing low-frequency sound absorbers is relatively narrow. The main method to expand the sound absorption frequency band at present is to combine multiple sound absorbers with different working frequencies. However, this combination method makes the sound absorption structure too complex and large, increasing the manufacturing cost in actual application.

[0004] To solve the above problems, recent research has proposed the following improvement measures for porous material layers: adding hard inclusions in the porous material layer. The emergence of bound modes due to the interaction between the porous material layer and the outer wall of the inclusion greatly enhances the sound absorption effect of the porous material layer in the medium and low frequency bands, but the high absorption peak is often discretely distributed in the medium and low frequency range, which is not conducive to achieving wideband sound absorption. SUMMARY

[0005] In order to overcome the deficiencies in the prior art, the present application provides a low-frequency broadband sound absorber which can efficiently absorb sound waves in a wide frequency range in the low-frequency band through a single structural unit with a small volume, and the high-efficiency absorption effect is almost not affected by the incident angle of the sound wave.

[0006] To solve the above technical problems, the present application provides the following technical solutions:

[0007] A low-frequency broadband sound absorber includes a resonator, the resonator is externally covered with a porous material layer, one side of the porous material layer is connected with a rigid backing, and the side opposite to the rigid backing is an incident surface.

[0008] According to the present application, the resonator includes an inner shell and an outer shell, the inner shell is located inside the outer shell, preferably, the cross sections of the inner shell and the outer shell are rectangular, for example, square, and preferably, the inner shell and the outer shell are arranged concentrically.

[0009] According to the present application, the cross section of the porous material layer is a hollow rectangle, and the hollow part accommodates the resonator, preferably, the porous material layer is arranged concentrically with the resonator;

[0010] Preferably, the interior of the inner shell is a hollow resonant cavity, and the outer wall of the inner shell and the inner wall of the outer shell constitute another hollow resonant cavity.

[0011] According to the present application, the first opening is arranged at the center of one side of the outer shell close to the sound wave incidence surface, and the second opening is arranged at the center of one side of the inner shell close to the rigid backing, and the first opening and the second opening are arranged oppositely, preferably, the width of the first opening and the second opening is the same, both being w .

[0012] According to the present application, a long pipe is connected to the second opening, preferably, the long pipe is arranged in the interior of the inner shell, preferably, the width of the long pipe is the same as the width of the second opening, both being w , and the length of the long pipe is l ;

[0013] According to the present application, the cross section of the inner shell and the outer shell is preferably a concentric square with the same wall thickness, both being t ;

[0014] Preferably, the side length of the outer shell is a 1, the side length of the inner shell is a 2, and the width of the channel (i.e. the vertical distance) between the inner wall of the inner shell and the outer wall of the outer shell is c , c = ( a 1- a 2- t *2) / 2; preferably, the width of the porous material layer is L , and the thickness of the porous material layer is D .

[0015] Preferably, the side length a 1 of the outer shell is 50-70 mm, and the side length a 2 of the inner shell is 25-50 mm; preferably, the width of the channel c ≥ 4 mm, the width L of the porous material layer is 80-150 mm, and the thickness D of the porous material layer is 80-150 mm; preferably, the wall thickness t of the inner shell and the outer shell is 1-3 mm;

[0016] Preferably, the width w of the first opening, the second opening and the long pipe is 2-10 mm, and the length of the long pipe isl 0-25 mm.

[0017] According to the present application, the side length of the outer shell a 1 is 60 mm, the side length of the inner shell a 2 is 43 mm, the wall thickness of the inner shell and the outer shell t is 2 mm, the channel width between the inner wall of the inner shell and the outer wall of the outer shell c is 6.5 mm.

[0018] Preferably, the width of the first opening, the second opening and the long pipe w is 3 mm, the length of the long pipe l is 14 mm.

[0019] Preferably, the width of the porous material layer is L 120 mm, and the thickness is D 90 mm.

[0020] Preferably, the acoustic impedance of the resonator is greater than 300 times the acoustic impedance of the background medium and above.

[0021] Preferably, the resonator is made of plastic or metal, and the porous material layer is made of sound-absorbing sponge.

[0022] Preferably, the equivalent porosity of the sound-absorbing sponge is 0.95, the tortuosity factor is 1.42, the flow resistivity is 8900 Nsm -4 , the viscous characteristic length is 180 μm, and the thermal characteristic length is 360 μm.

[0023] According to the present application, the sound absorption coefficient of the resonator (1) A can be expressed as Formula One:

[0024] Formula One

[0025] wherein, r is the sound pressure reflection coefficient, is the resonant frequency, is the loss factor of the structure, is the leakage factor.

[0026] According to the present application, the sound absorption coefficient of the sound absorber to the sound in the wide frequency band of 289-1112 Hz is higher than 0.8, and the corresponding wavelength is 1.19-0.31 m, and the wavelength of the low-frequency noise reaches 13 times the thickness of the sound absorber structure.

[0027] The present application also provides the use of the above-mentioned sound absorber for absorbing low-frequency sound waves.

[0028] According to the present application, the sound absorber is arranged in a house, a sound insulation device or a train for absorbing low-frequency sound waves in the environment.

[0029] Advantages

[0030] The low-frequency broadband sound absorber of the present application only uses a single structural unit, that is, it can achieve high-efficiency absorption of sound waves in a broadband range of low-frequency wave bands, and the high-efficiency absorption effect is hardly affected by the incident angle of sound waves. The designed absorber thickness is only about 1 / 13 of the wavelength of sound waves, and the occupied space volume is small, which has broad application prospects in the field of low-frequency noise reduction. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a low-frequency broadband sound absorber structure diagram in the present application;

[0032] Figure 2 It is the sound absorption spectrum simulation result of the present application embodiment 1 with the side length of the resonator internal shell changes; a 2;

[0033] Figure 3 It is the sound absorption spectrum simulation result of the present application embodiment 1 with the length of the resonator long pipe changes; l 2;

[0034] Figure 4 It is the sound absorption spectrum simulation result of the present application embodiment 1 with the side length of the resonator external shell changes; a 1;

[0035] Figure 5 It is the sound absorption spectrum simulation result of the present application embodiment 1 with the width of the resonator first opening, second opening and long pipe changes; w 2;

[0036] Figure 6 It is the comparison diagram of the experimental result and the simulation result of the present application embodiment 1 selected 3D printing plastic sample and sound absorbing sponge;

[0037] Figure 7 It is the simulation result diagram of the present application embodiment 1 at different sound wave incident angles;

[0038] Figure 8 It is the simulation result diagram of the present application embodiment 1 at random sound wave incident angles.

[0039] In the figure, 1-resonator, 2-porous material layer, 3-rigid backing, 4-internal shell, 5-external shell, 6-first opening, 7-second opening, 8-long pipe. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below with reference to specific accompanying drawings and embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0041] Example 1

[0042] like Figure 1 The image shows a cross-sectional view of a low-frequency broadband sound absorber, which includes a resonator 1. The resonator 1 is covered with a porous material layer 2. One side of the porous material layer 2 is the sound wave incident surface, and a rigid backing 3 is connected to the outer side of the porous material layer 2 opposite to the sound wave incident surface.

[0043] The resonator 1 includes a double-layered hollow rectangular shell: an inner shell 4 and an outer shell 5. The inner shell 4 and the outer shell 5 are arranged concentrically. The hollow cavity of the inner shell 4 can be used as a resonant cavity, hereinafter referred to as the inner resonant cavity. The cavity formed by the inner wall of the inner shell 4 and the outer wall of the outer shell 5 is used as another resonant cavity, hereinafter referred to as the outer resonant cavity.

[0044] In this embodiment, both the inner shell 4 and the outer shell 5 are square, and both have a thickness of [missing information]. t The outer shell 5 has a side length of 5. a 1. The side length of the inner shell 4 is a 2. The width (i.e., vertical distance) of the channel between the inner wall of the inner shell 4 and the outer wall of the outer shell 5 is: c = ( a 1- a 2- t *2) / 2, the outer shell 5 has a first opening 6 at its center on the side opposite to the sound wave incident surface, and the inner shell 4 has a second opening 7 at its center near the rigid backing 3. The first opening 6 and the second opening 7 are positioned opposite each other, and both have a width of w A long pipe 8 is connected to the second opening 7, and the width of the long pipe 8 is also... w , length is l .

[0045] The porous material layer 2 tightly wraps the resonator 1, and the width of the porous material layer 2 is... L Thickness is D The porous material layer 2 is a rectangle concentric with the resonator 1.

[0046] When the frequency is f sound waves along y axial direction (i.e., from the incident surface of the sound wave) θ Angular incident on absorber (initial) θAt the angle of 0° (i.e. normal incidence), a part of the sound wave enters the absorber and is absorbed, and a part of the sound wave is reflected. Due to the effect of the rigid backing 3, the sound wave cannot be transmitted, and thus the sound absorption coefficient of the absorber can be defined as A = 1 – | r | 2 wherein r is the amplitude of the reflected sound wave.

[0047] When the sound wave passes through the outer porous material layer 2, the effect between the porous material layer 2 and the outer wall of the resonator 1 and the rigid backing 3 leads to the emergence of a bound mode, which enhances the sound absorption of the porous material layer 2 in the low and medium frequency wave band.

[0048] In addition, the design of the opening on the inner shell 4 and the outer shell 5 makes the resonator 1 have the following two resonance modes, and the resonance occurs in the inner resonance cavity of the inner shell 4 and the outer resonance cavity between the inner shell 4 and the outer shell 5.

[0049] In the resonant system of the present embodiment, the inner wall thermal viscosity effect of the resonator 1 and the loss effect of the porous material layer 2 wrapped therearound provide a structural loss factor , and the loss factor is related to the material and thickness of the porous material layer 2; and the open resonant system (the inner resonance cavity and the outer resonance cavity) without loss provides a leakage factor , and the loss factor and the leakage factor are related to the structure and material of the corresponding resonator 1, and the corresponding relationship is obtained by numerical simulation.

[0050] According to the coupling mode theory, the quality factor of the resonant system can be calculated by the resonance frequency and the resonance half-bandwidth , i.e. . When the system loss is not considered (i.e. ), the leakage factor of the resonant system is the quality factor of the system, i.e. , and thus the loss factor of the system can be obtained from the quality factor considering the loss, i.e. .

[0051] The sound absorption coefficient A of the resonator 1 can be represented by Formula One:

[0052] ……Formula One

[0053] As can be seen from Formula One, near the resonance frequency, the stronger the coupling between the loss factor and the leakage factor , the greater the sound absorption coefficient of the resonator 1.

[0054] The embodiment finds that, in the case of keeping the size of the outer wall of the resonator 1 unchanged, i.e. without changing the bound mode absorption (the structure and relative position of the three of the porous material layer 2, the outer wall of the resonator 1 and the rigid backing 3) and the leakage factor , the loss factor of the structure and the frequency position of the two resonance peaks can be adjusted by adjusting the width of the first opening 6 and the second opening 7, the width and length of the long pipe 8, and the side length of the inner shell 4 (i.e. the passage width between the outer wall of the inner shell 4 and the inner wall of the outer shell 5), so that the two resonance peaks are distributed on both sides of the bound mode absorption peak, and the strong coupling between the loss factor and the leakage factor is achieved in a wide frequency band, so that the sound absorption in a wide frequency band is achieved.

[0055] The resonator 1 and the rigid backing 3 are made of a material with an acoustic impedance much larger than that of air, such as plastic or metal, and the porous material layer 2 is made of a porous material such as sound-absorbing sponge.

[0056] The outer porous material layer 2 is equivalent to a uniform equivalent fluid according to the Johnson-Champoux-Allard (JCA) model, and the equivalent density ρ e and the equivalent bulk modulus K e are calculated by Formulas Two and Three respectively:

[0057] Formula Two

[0058] Formula Three

[0059] In Formulas Two and Three, ω is the angular frequency, ρ 0 is the air density, η is the air dynamic viscosity, P 0 is the air pressure, γ is the adiabatic constant, P r is the Prandtl number, is the equivalent porosity, is the tortuosity factor, σ is the flow resistivity, is the viscous characteristic length, is the thermal characteristic length.

[0060] In the embodiment, is set to 0.95, the tortuosity factor is 1.42, the flow resistivity σ is 8900 Nsm -4 , the viscous characteristic length 180 μm, thermal characteristic length It is 360 μm, of which , , .

[0061] In this invention, the side length of the inner shell 4 a 2. The length of the long pipe 8 l , Side length of outer shell 5 a 1. Width of the first opening 6, the second opening 7, and the long pipe 8 w All can be flexibly adjusted to adapt to specific requirements in practice. In the simulation experiment conducted in this embodiment, the following settings are provided. a 2 = 43 mm, l = 14 mm, a 1 = 60 mm w = 3 mm, shell thickness is all t = 2 mm, therefore the width of the channel between the two shell layers is 6.5 mm, and the width of the porous material layer 2 is... L It is 120 mm thick. D The value is 90 mm. When one of the factors is measured, such as... a 2 pairs of loss factors When considering the influence of the frequency positions of the two resonance peaks, other factors remain unchanged at the above values.

[0062] Figure 2 This is the sound absorption spectrum of the sound absorber prepared according to the above conditions in this embodiment. The horizontal axis is the frequency of the incident sound wave, and the vertical axis is the side length of the inner shell 4. a 2. The depth of its color represents the magnitude of its sound absorption coefficient, which is determined by... Figure 2 It can be seen that the sound absorption coefficient has a stable dark gray region around the 615 Hz frequency. A ≈0.85, this is the confined mode absorption caused by the interaction between the porous material layer 2 and the outer wall of the resonator 1 and the rigid backing 3. This absorption peak is denoted as P 2. Mark the area on the diagram with a white dashed line. P There are two dark black regions on either side of 2, which are the two resonance absorption peaks, denoted as . P 1 (left) and P 3 (right), marked with a white double-dotted line and a dotted-dotted line.

[0063] along with a 2. Resonance peak increases from 25 mm to 50 mm. P The resonant frequency of 1 gradually decreases from 550 Hz to around 220 Hz, and its sound absorption coefficient decreases slightly. P 3 follow a2, the resonance frequency first decreases to 900 Hz and then gradually increases, the absorption coefficient reaches the maximum value near 900 Hz, and the high absorption bandwidth is relatively wide, when a 2= 43 mm, P 1, P 3 are symmetrically distributed on P 2, at this time, the best sound absorption effect can be achieved.

[0064] Figures 3-5 The sound absorption coefficients of the sound absorber with the length of the long pipe 8 being l , the side length of the external shell 5 being a 1, the width of the first opening 6, the second opening 7 and the long pipe 8 being w changed are shown in the following table (in other conditions unchanged, only the length l , a 1, w of the long pipe 8 is changed), the marks of the three peaks are consistent with Figure 2 .

[0065] As can be seen from Figure 3 , the frequencies of the resonance peaks P 1 and P 3 both decrease with the increase of l , but the speeds of the two peak frequencies decreasing are obviously different. With l increasing from 0 to 25 mm, the resonance frequency of the resonance peak P 1 decreases from 360 Hz to 300 Hz, while the frequency of P 3 decreases from 1210 Hz to 860 Hz, and the absorption coefficients of the two peaks basically do not change with l , when l = 14 mm, P 1, P 3 are symmetrically distributed on P 2, at this time, the best sound absorption effect can be achieved.

[0066] As shown in Figure 4 , with a 1 increasing from 50 mm to 70 mm, the resonance frequency of the resonance peak P 1 gradually increases from 200 Hz to 300 Hz, while the resonance frequency of P 3 decreases at a relatively fast rate from 1500 Hz to 770 Hz, and the absorption coefficients of the two resonance peaks both slightly increase with a 1 increasing, when a 1 is 60 mm, P 1, P 3 are symmetrically distributed on POn both sides of 2, the optimal sound absorption effect can be achieved. Furthermore, the change in the size of the outer wall of resonator 1 affects the absorption of the bound mode, thus... P The frequency of 2 decreased from 650 Hz to 550 Hz, and its absorption coefficient decreased slightly.

[0067] Figure 5 The data shows that the resonance peaks P 1 and P The frequency of 3 all follows w The frequency increases with increasing frequency, but the rates of increase for the two peak frequencies differ significantly. w As the diameter increases from 2 mm to 10 mm, the resonance peak... P The resonant frequency of 1 increases from 300 Hz to 400 Hz, while P As the frequency of peak 3 increases from 840 Hz to 1360 Hz, the absorption coefficients of the two peaks increase accordingly. w It increases slightly with the increase, when w When it is 3 mm, P 1, P 3 Symmetrical distribution in P On both sides of 2, the best sound absorption effect can be achieved.

[0068] from Figures 2-5 As can be seen from this, the absorption frequency of the low-frequency broadband sound absorber in this embodiment is flexibly adjustable by adjusting the geometric parameters of the internal double-layer rectangular acoustic resonator. a 2, l，a 1, w The frequencies of the two resonance peaks can be adjusted to make them symmetrically distributed on both sides of the bound mode absorption peak, thereby achieving wideband acoustic absorption.

[0069] right Figure 1 The low-frequency broadband sound absorber was simulated and experimentally measured. The optimal parameters were set as follows: the four sides of the internal shell were set to... a 2 = 43 mm, long pipe 8 mm l = 14 mm, side length of outer shell 5 a 1 = 60 mm, the width of the first opening 6, the second opening 7, and the long pipe 8 w = 3 mm, width of the channel between the two shell layers c = 6.5 mm.

[0070] During the experimental measurement, an internal resonator sample was printed using 3D printing technology, and a high-density polyurethane foam was used as the outer wrapping layer. The experimental measurement was carried out in a waveguide with a cross-section of 120 mm × 120 mm.

[0071] See Figure 6, where represents the sound absorption spectrum of the corresponding low-frequency broadband sound absorber, with the horizontal axis representing the frequency of the incident sound wave and the vertical axis representing the sound absorption coefficient. In this embodiment, simulation results show that the absorption coefficient is higher than 0.8 in the wide frequency range of 289-1112 Hz. The experimental results are roughly similar to the simulation results, which further proves that the structure of this embodiment can achieve efficient sound absorption in the low-frequency broadband range.

[0072] Simulation calculations were performed on this invention, with the incident angle of the sound wave set as follows: θ = 0°, 30°, 60°, see Figure 7 As shown in the results, the sound absorption spectrum under different sound wave incident angles demonstrates that the sound absorber in this embodiment exhibits good sound absorption performance for sound waves at different incident angles. Subsequently, based on the randomness of sound wave incident in reality, simulation calculations were performed on the structure, defining the sound absorption coefficient as... A rand The calculation method is shown in Formula 4:

[0073] ...Formula 4

[0074] in, A ( θ ) represents the structure at different sound wave incident angles θ The corresponding sound absorption coefficient is shown in the following figure. Figure 8 As shown in the simulation results, the sound absorber of this embodiment also exhibits good sound absorption performance for sound waves with random incident angles. These results also demonstrate that the efficient sound absorption effect of the low-frequency broadband sound absorber of this embodiment across a wide operating range is unaffected by the incident angle of the sound wave, which has broad application prospects in the field of low-frequency noise reduction.

[0075] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-frequency broadband sound absorber, characterized in that, Includes a resonator (1), the resonator (1) is covered with a porous material layer (2), one side of the porous material layer (2) is connected to a rigid backing (3), and the side opposite to the rigid backing (3) is the incident surface. The resonator (1) includes an inner shell (4) and an outer shell (5), the inner shell (4) being located inside the outer shell (5); the cross-sections of the inner shell (4) and the outer shell (5) are rectangular, and the inner shell (4) and the outer shell (5) are concentrically arranged; the interior of the inner shell (4) is a first hollow resonant cavity, and the outer wall of the inner shell (4) and the inner wall of the outer shell (5) constitute a second hollow resonant cavity; The outer shell (5) has a first opening (6) at the center of the side near the sound wave incident surface, and the inner shell (4) has a second opening (7) at the center of the side near the rigid backing (3). The first opening (6) and the second opening (7) are arranged opposite to each other. A long pipe (8) is connected to the second opening (7), and the long pipe (8) is located inside the inner shell (4); The width of the long pipe (8) is the same as the width of the first opening (6) and the second opening (7), which is w .

2. The low-frequency broadband sound absorber according to claim 1, characterized in that, The cross-sections of the inner shell (4) and the outer shell (5) are square.

3. The low-frequency broadband sound absorber according to claim 1, characterized in that, The cross-section of the porous material layer (2) is a hollow rectangle, which accommodates the resonator (1), and the porous material layer (2) and the resonator (1) are arranged concentrically.

4. The low-frequency broadband sound absorber according to claim 1, characterized in that, The inner shell (4) and the outer shell (5) have concentric square cross-sections and the same wall thickness. t .

5. The low-frequency broadband sound absorber according to claim 4, characterized in that, The side length of the outer shell (5) is a 1. The side length of the inner shell (4) is a 2. The width of the channel between the inner wall of the inner shell (4) and the outer wall of the outer shell (5) is c , c =( a 1- a 2- t *2) / 2; the width of the porous material layer (2) is L Thickness is D .

6. The low-frequency broadband sound absorber according to claim 5, characterized in that, The side length of the outer shell (5) a 1 is 50-70 mm, the side length of the inner shell (4) a 2 is 25-50 mm.

7. The low-frequency broadband sound absorber according to claim 5, characterized in that, The channel width c ≥4 mm, the width of the porous material layer (2) L 80-150 mm in diameter, thickness D The wall thickness of the inner shell (4) and the outer shell (5) is 80-150 mm. t 1-32 mm; The width of the first opening (6), the second opening (7), and the long pipe (8) w The length of the long pipe (8) is 2-10 mm. l It is 0-25 mm.

8. The low-frequency broadband sound absorber according to claim 5, characterized in that, The side length of the outer shell (5) a 1 is 60 mm, and the side length of the inner shell (4) is a 2 is 43 mm, the wall thickness of the inner shell (4) and the outer shell (5) is t Both are 2 mm, and the channel width between the inner wall of the inner shell (4) and the outer wall of the outer shell (5) is 2 mm. c It is 6.5 mm.

9. The low-frequency broadband sound absorber according to claim 7, characterized in that, The width of the first opening (6), the second opening (7), and the long pipe (8) w The length of the long pipe (8) is 3 mm. l It is 14 mm.

10. The low-frequency broadband sound absorber according to claim 5, characterized in that, The width of the porous material layer (2) is L It is 120 mm thick. D It is 90 mm.

11. The low-frequency broadband sound absorber according to any one of claims 1-4, characterized in that, The acoustic impedance of the resonator (1) is 300 times or more greater than the acoustic impedance of the background medium.

12. The low-frequency broadband sound absorber according to any one of claims 1-4, characterized in that, The resonator (1) is made of plastic or metal, and the porous material layer (2) is made of sound-absorbing sponge.

13. The low-frequency broadband sound absorber according to claim 12, characterized in that, The sound-absorbing sponge has an equivalent porosity of 0.95, a tortuosity of 1.42, and a flow resistance of 8900 Nsm. -4 The viscous feature length is 180 μm. The thermal feature length is 360 μm.

14. The low-frequency broadband sound absorber according to any one of claims 1-4, characterized in that, The sound absorption coefficient of the resonator (1) A Calculate according to Formula 1: ...Formula 1 in, r The sound pressure reflection coefficient is... f The frequency of the incident wavelength, The resonant frequency, This is the loss factor of the sound absorber. This is a leakage factor.

15. The low-frequency broadband sound absorber according to any one of claims 1-4, characterized in that, The sound absorber has an absorption coefficient higher than 0.8 for a wide frequency band of sound in the range of 289-1112 Hz, corresponding to wavelengths of 1.187-0.308 m. The wavelength of low-frequency noise is up to 13 times the thickness of the sound absorber structure.

16. Use of the low-frequency broadband sound absorber according to any one of claims 1 to 15 for absorbing low-frequency sound waves.

17. Use of the low-frequency broadband sound absorber according to any one of claims 1 to 15, installed in a residence, soundproofing facility or train, for absorbing low-frequency sound waves in the environment.

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