COMPOSITE SOUND-ABSORBING DEVICE WITH BUILT IN RESONANT CAVITY
The composite sound-absorbing device of the present invention includes a perforated board having a number of first pores thereon, a back board and side boards, the perforated board, back board and side boards forming a closed cavity, wherein: at least one or more of the resonant cavities being located within the closed cavity; at least one or more of second pores being located on the resonant cavities; at least one of the second pores being connected with the closed cavity; the resonant cavity having a volume of V=10 mm3 −1×1010 mm3, having a thickness of 0.05 mm-10 mm, the second pores having an aperture of d′=0.05-100 mm, with a perforation rate σ′=0.01%-30%. The present invention is beneficial to improve the effect of sound-absorbing and expand the frequency band of sound-absorbing.
The present invention relates to a composite sound-absorbing device and more particularly relates to a composite sound-absorbing device with built-in resonant cavity.
BACKGROUND OF THE INVENTIONIn noise control engineering, many types of sound-absorbing material and structures are used, which can be roughly divided into porous sound-absorbing materials and resonant sound-absorbing materials according to their acoustical principles. For example, fiber materials and plaster materials, among others, fall into the category of porous sound-absorbing materials, while resonant sound-absorbing structure of thin board, resonant sound-absorbing structure of membrane and resonant sound-absorbing structure of perforated board fall into the category of resonant sound-absorbing materials. In 1975, Dah-You Maa published an article titled “Theory and Design of Microperforated board Sound-absorbing Structure” published in Science in China and in 2000 “Theory of Micro slit Absorbers” in Chinese Journal of Acoustics, wherein Maa expanded the application range of resonant sound-absorbing structure.
Although resonant sound-absorbing structure of perforated board, resonant sound-absorbing structure of microperforated board and double layer microperforated sound-absorbing structure are superior to porous sound-absorbing material in terms of sound absorption characteristics, flow resistance, anti-moisture, anti-corrosion and hygiene, they still cannot meet some practical needs of noise control engineering, especially when dealing with low frequency noise within strictly limited space for sound absorption. For as to common resonant sound-absorbing structure, the depth of cavity has to be increased greatly to absorb more low frequency sound, which is almost impossible to realize in practice. Applicant has searched G10K with a special emphasis on G10k 11/172 and found out “The Bundle Type Perforated board Resonant Sound-absorbing Device” with patent number of CN ZL00100641.X and “Muffler with Multi Insert Pipe Parallel Connected Structure” with patent number of CN ZL00264613.7.
The bundle type perforated board resonant sound-absorbing device features a bundle type perforated board resonant sound-absorbing structure, which is consisted of a perforated board, a bottom board and side board (forming a closed cavity) and a bundle of tubes. The diameter of the tubes is equal to that of the pores on the perforated board and the length of these tubs is not restrained by the cavity depth of the perforated board resonant sound-absorbing device. The tubes can either be longer or shorter than the cavity depth so as to tune resonance frequency and alter sound absorption coefficient. This sound-absorbing structure is designed on the basis of the sound-absorbing principle of coupling resonance to increase its sound absorption coefficient, acoustic impedance and to enhance the sound-absorbing effect of low frequency sound. However this structure absorbs only sound within low and medium frequency band, which band is not wide enough. The length of those flexible tubes is critical in that if the tubes are not long enough, the sound-absorbing performance would be greatly affected, i.e., greatly degrading sound-absorbing effect. Therefore longer tubes have to be used to ensure good sound-absorbing performance. Accordingly cavity has to be deeper correspondingly. However longer tubes and deeper cavities are not beneficial to expand the application range of this structure. It is further compounded by the fact that the tubes being wire like, this structure cannot give full play the coupling resonance effect of tube cavity. Moreover, the length of the tubes contributes less to the consumption of acoustic energy.
The muffler with multi insert pipe parallel connected structure described in ZL00264613.7 is designed for the intake system for internal combustion engine of automobiles and that it includes an intake pipe and two or four resonant cavities arranged in parallel. The resonant cavities are arranged in a casing. Each of the resonant cavities is connected to a radial-direction pore axially arranged on the intake pipe, through conduct pipes. The size of the radial-direction pore and the conduct pipes is designed to match with the intake noise spectrum of the internal combustion engine. This muffler is not only able to greatly reduce the intake noise but also increase the power of the internal combustion engine. Moreover, it is compact in size.
Therefore, it has been a long-time effort internationally in the field of acoustics and noise control engineering to invent a device, which can effectively absorb low frequency sound and has a wide sound-absorbing frequency band to replace or improve conventional sound-absorbing structure which is deficient in absorbing low frequency sound. To this end, this invention proposes a composite sound-absorbing device with built-in resonant cavity. This device is realized based on several principles, namely by combining acoustic scattering inside the resonant cavity, sound elimination of small pores and the coupling resonance of multiple resonant cavities, to increase sound absorption coefficient and expand sound frequency band.
SUMMARY OF THE INVENTIONThe purpose of the present invention is to overcome the defect of the above sound-absorbing structure used in current noise control engineering that it cannot absorb enough sound with low and medium frequency by providing a composite sound-absorbing structure with built-in resonant cavity.
According to the present invention, a composite sound-absorbing device with a built-in resonant cavity, includes: a perforated board having a number of first pores thereon, a back board and side boards, the perforated board, back board and side boards forming a closed cavity, wherein: at least one or more of the resonant cavities being located within the closed cavity; at least one or more of second pores being located on the resonant cavities; and at least one of the second pores being connected with the closed cavity; the resonant cavity having a volume of V=10 mm3-1×1010 mm3, the thickness of the wall thereof being 0.05 mm-10 mm, the second pores having an aperture of d′=0.05-100 mm, with a perforation rate σ′=0.01%-30%.
In the composite sound-absorbing device of the present invention, the resonant cavity is in a shape of sphere, ellipsoid or polyhedron.
Furthermore, in the composite sound-absorbing device of the present invention, the second pores are connected to the closed cavity directly, or are connected to the closed cavity via tubes. Moreover, in the composite sound-absorbing device of the present invention, when the number of the resonant cavities is more than one, they are located within the closed cavity directly or fixed separately within the closed cavity partitioned by a number of partition boards.
Preferably, in the composite sound-absorbing device of the present invention, the first or second pores are connected to one end of the tubes and the tubes are located within the closed cavity for increasing acoustical impedance. Preferably, in the composite sound-absorbing device of the invention, the other end of the tubes on the second pores are connected to the closed cavity, the second pores on another resonant cavity or the first pores on the perforated board.
Preferably, in the composite sound-absorbing device of the present invention, the tubes are made of metal, glass, plastic or rubber; when the tubes are made of rubber, they are connected to the first pores or second pores via binding, or they are connected to the first pores via a first transition joint at the ends of the tubes, or they are connected to the second pores via a second transition joint at the ends of the tubes; when the tubes are made of metal, glass or plastic, they are connected to the first pores or second pores via binding, welding, thread connection or injection, or they are connected to the first pores via a first transition joint at the ends of the tubes, or they are connected to the second pores via a second transition joint at the ends of the tubes.
Preferably, in the composite sound absorptive device of the present invention, the perforated board has a thickness of 0.5-10 mm, the diameter of the first pores on the perforated board d is 0.1-5 mm, with a perforation rate of 0.1%-30%. Furthermore, the first pores on the perforated board are arranged regularly in a shape of triangle or square or irregularly. Moreover; the closed cavity has a depth D of 10-2000 mm, and is in a shape of cylinder composed by one side board or a polyhedron composed by a plurality of side boards.
Preferably, in the composite sound-absorbing device of the present invention, the back side of said perforated board is coated with a layer of porous sound-absorbing material, the layer of porous sound-absorbing material being located within the closed cavity, with a thickness of 0.1 mm-200 mm.
In the above technical solutions, the perforated board can be iron board, steel board, copper board, corrosion resistant board, aluminum board, plastic board, glass board, PVC board, PE board or wood board.
In the above technical solutions, the resonant cavity can be made of metal, glass, ceramics, rubber, plastic or fiber. The length L of the tubes is 1-5000 mm. The diameter of the tubes is 0.1-100 mm.
The present composite sound-absorbing device with built-in resonant cavity comprises a perforated board with a plurality of pores, a back board, side board(s) and multiple resonant cavities. The resonant cavities are small cavities placed in a closed cavity. The resonant cavities are used to scatter sound, connect with the closed cavity and increase acoustic impedance. When a sound wave reaches the resonant cavities, the air inside the cavity vibrates back and forth. Due to viscous damping, part of the acoustic energy is converted into heat energy and is lost. By using the principle of Helmholtz resonator, the pores on the wall of the resonant cavities increase acoustic impedance of the perforated board, sufficiently consume the acoustic energy and so enhance sound absorption. The fact that the resonant cavity being hollow increases acoustic resistance of the present sound-absorbing device. At the same time, the resonant cavities are connected with the closed cavity serially so as to realize multiple cavities' coupled resonance, thereby expanding the frequency band of sound absorption consequently. Furthermore, the size of each of the resonant cavities can be different from each other and the size of each of the second pores can be different from each other in order to tune the resonant frequency and alter sound absorption coefficient under different frequencies. The present invention utilizes the resonant cavity to scatter sound in the closed cavity and utilizes the second pores to increase acoustic impedance and consume acoustic energy. In addition, the present invention modulates formant and sound-absorbing frequency band based on the principle of multiple-cavity coupled resonance. Therefore, the present invention increases acoustic impedance, improves sound quality and the effect of sound absorption and expands sound-absorbing frequency band.
Major technical features of the present invention include: the resonant cavity is connected with the closed cavity via second pores to realize coupling resonance among cavities and so expand sound-absorbing frequency band. In addition, there is no limitation imposed on the number of the pores on the resonant cavity, thus increasing acoustic impedance of the sound-absorbing device. The number of the pores and the diameter of the pores can be adjusted as required to increase or reduce the acoustic impedance and thus to increase sound absorption coefficient. The tubes connecting to the resonant cavities increase the thickness of the pores on the resonant cavities, which is not only to the benefit of increasing acoustic impedance but also realizes coupling resonance by connecting the tubes with resonant cavities. Moreover, the present invention advantageously can increase sound absorption coefficient, expand sound-absorbing frequency band and cause the sound absorption frequency band to shift towards low frequency band, so it is beneficial to absorb sound with low frequency. With the coupled resonance of the resonant cavities and the closed cavity, it can be regarded that sound absorption is carried out in a double-deck structure within the same and one cavity. In the meantime, the capacity of the rear cavity is reduced. Therefore, the present invention is suitable to the situations where space for sound absorption is strictly limited. Moreover, in order to expand the frequency range of noise elimination of the present composite sound-absorbing device, each of the resonant cavities can be different from each other in size and shape, and each of the second pores can be different from each other in size and shape, which is beneficial for the present invention to be used in different sound elimination situations. The acoustic scattering on the surfaces of the resonant cavities allows the sound wave to reach to every resonant cavity in the rear cavity and pushes the air in the second pores to vibrate back and forth, thereby consuming acoustic energy sufficiently and being beneficial to absorb sound by using the space of the rear cavity.
The advantages of the invention lie in that, by arranging a plurality of resonant cavities in the limited space of the rear cavity, the present invention makes full use of the principles of acoustic scattering, pores' acoustic impedance consuming acoustic energy and sound absorption by multi-cavity coupled resonance, as well as the modulation features of the size of the cavities and the pores to formant and sound-absorbing frequency band, thus increasing sound absorption coefficient, enhancing the absorption of low and medium frequency noise and expanding sound-absorbing frequency band.
In the following, the present invention will be described in details with reference to the accompanying drawings and embodiments.
Embodiment OneReferring to
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An experiment was conducted to test low and medium frequency sound muffling mechanism of the composite sound-absorbing device with built-in resonant cavity by using a standing wave meter. In the experiment, the low and medium frequency sound absorption coefficient of a perforated board, a perforated board whose cavity is provided with sphere without pores and a composite sound-absorbing device with built-in resonant cavity are measured to verify that multiple cavities coupling is beneficial to increase sound absorption coefficient. Other parameters of resonant sound-absorbing structures employed in the experiment are listed as follows:
Parameters of the perforated board: the pores are arranged in the pattern of a square, with the diameter of the pores being 1.7 mm, the center to center spacing of the pores being 7 mm, the thickness of the perforated board being 0.7 mm and the depth of the closed cavity being 50 mm.
Parameters of the perforated board whose cavity is provided with sphere without pores: the pores are arranged in the pattern of a square, with the diameter of the pores being 1.7 mm, the center to center spacing of the pores being 7 mm, the thickness of the perforated board being 0.7 mm. Four plastic hollow spheres without pores are placed in the closed cavity, with the thickness of the wall of the sphere being 0.4 mm and the volume V of the sphere being 3.35×104 mm3. The spheres are arranged in the closed cavity freely, with the depth of the closed cavity being 50 mm.
Referring to
In the experiment, four composite sound-absorbing devices with built-in resonant cavity according to the present invention are separately provided with nine, seven, four and one resonant cavity inside the closed cavity. The experiment tests the low and medium frequency sound muffling mechanism by using a standing wave meter to verify the impact of the number of resonant cavities on sound absorption coefficient and the frequency band of sound absorption. The other parameters of the resonant sound-absorbing structures employed in the experiment are listed as follows:
Parameters of the perforated board: the pores, with a diameter of 1.7 mm, are arranged in a pattern of square, with the center to center spacing of the pores being 7 mm, the thickness of the board being 0.7 mm and the depth of the closed cavity being 100 mm. From
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A comparison experiment is conducted to verify the sound muffling mechanism of low and medium frequency sound of the composite sound-absorbing device according to the present invention and the perforated board with tubes by using a standing wave meter. In the experiment, the low and medium sound absorption coefficient of the perforated board, the perforated board with tubes and the composite sound-absorbing device with built-in cavities are measured respectively to determine the effect of resonant cavities provided in the perforated board sound-absorbing structure. The other parameters of the resonant sound-absorbing structure are listed as follows:
Parameters of the perforated board: the pores are arranged in a pattern of square, with the diameter of the pores being 1.7 mm, the center to center spacing of the pores being 7 mm, the thickness of the wall of the perforated board being 0.7 mm and the depth of the cavity being 50 mm.
Parameters of the perforated board with tubes: the pores are arranged in a pattern of square, with the diameter of the pores being 1.1 mm, the center to center spacing of the pores being 7 mm, the thickness of the wall of the perforated board being 0.7 mm, the length of the tubes being 8.5 mm and the diameter of the tubes being 1.1 mm. The tubes are welded on the pores on the perforated board. The depth of the cavity is 50 mm.
As shown in
Referring to
To conclude, the composite sound-absorbing device with built-in resonant cavity according to the present invention makes full use of the acoustic scattering on the surface of the resonant cavity, acoustic impedance of the second pores on the resonant cavity and the modulation to the sound-absorbing formant and sound-absorbing frequency band by resonant cavities' coupling and etc., to absorb sound, wherein its sound-absorbing frequency band is wider, sound absorption coefficient is bigger and so the absorption effect of low and medium frequency noise is improved, when compared with conventional perforated board resonant sound-absorbing structure. Moreover, the present device is compact, economical and practical. It is clear from the above comparison experiments that the sound-absorbing effect of the present device is obviously superior to the perforated board resonant sound-absorbing device and as the number of the resonant cavities increases, the sound frequency band becomes wider and the formant of major sound-absorbing frequency becomes higher and gradually evolves into two formants, which is similar to the double layer microperforated board sound-absorbing structure. The number of resonant cavities and the pores on the resonant cavities is crucial to the present device, and if the number of the resonant cavities is not enough, the sound-absorbing effect would be greatly reduced.
It should be noted that the present invention is not necessarily limited to the foregoing embodiments, which can be further modified in various ways within the scope of the invention as defined in the appended claim.
Claims
1. A composite sound-absorbing device with built-in resonant cavity, including: a perforated board having a number of first pores thereon, a back board and side boards, said perforated board, back board and side boards forming a closed cavity, wherein: at least one or more independent said resonant cavities being located within said closed cavity randomly; said resonant cavities being in a shape of sphere, ellipsoid or polyhedron; at least one or more of second pores being located on said resonant cavities; and at least one of said second pores being connected with said closed cavity;
- said resonant cavity having a volume of V=10 mm3-1×1010 mm3, the thickness of the wall of the cavity being 0.05 mm-10 mm, said second pores having an aperture of d′=0.05-100 mm, with a perforation rate σ′=0.01%-30%.
2. The composite sound-absorbing device of claim 1, wherein the number of said resonant cavities is more than one, which are located within said closed cavity directly or fixed within said closed cavity separately partitioned by a number of partition boards.
3. (canceled)
4. The composite sound-absorbing device of claim 1, wherein said second pores are connected to said closed cavity directly.
5. The composite sound-absorbing device of claim 1, wherein said second pores are connected to said closed cavity via tubes.
6. The composite sound-absorbing device of claim 1, wherein said first or second pores are connected to one end of said tubes and said tubes are located within said closed cavity for increasing acoustical impedance.
7. The composite sound-absorbing device of claim 6, wherein the other end of said tubes on said second pores are connected to said closed cavity, said second pores on another resonant cavity or said first pores on said perforated board.
8. The composite sound-absorbing device of claim 6, wherein said tubes are made of metal, glass, plastic or rubber, with a length of 1-5000 mm and diameter of 0.1-100 mm;
- when said tubes are made of rubber, they are connected to said first pores or second pores via binding, or they are connected to said first pores via a first transition joint at the ends of said tubes, or they are connected to said second pores via a second transition joint at the ends of said tubes;
- when said tubes are made of metal, glass or plastic, they are connected to said first pores or second pores via binding, welding, thread connection or injection, or they are connected to said first pores via a first transition joint at the ends of said tubes, or they are connected to said second pores via a second transition joint at the ends of said tubes.
9. The composite sound absorptive device of claim 1, wherein said perforated board has a thickness of 0.5-10 mm, the diameter of said first pores on said perforated board d being 0.1-5 mm, with a perforation rate of 6′=0.1%-30%; said closed cavity having a depth of D=10-2000 mm, and said closed cavity having a shape of cylinder composed by one side board or polyhedron composed by a plurality of side boards;
- said first pores on said perforated board are arranged in a shape of regular triangle or square or are arranged irregularly.
10. The composite sound-absorbing device of claim 1, wherein the back side of said perforated board is coated with a layer of porous sound-absorbing material, said layer of porous sound-absorbing material being located within said closed cavity, with a thickness of 0.1 mm-200 mm.
Type: Application
Filed: Oct 14, 2010
Publication Date: Oct 4, 2012
Inventor: Jun Yang (Beijing)
Application Number: 13/515,148