The sound absorption material shall be connected with the surrounding sound transmission mediumAcoustic characteristic impedanceMatching, so that the sound energy enters the sound absorbing material without reflection, and most of the incident sound energy is absorbed.
The material that can absorb the incident sound energy by its own porosity, film effect or resonance effect is one of the components of ultrasonic inspection equipment.
In the application mode of sound absorption materials, resonance sound absorption structure or gradual transition layer structure is usually used.In order to increase the internal loss of materials, fillers containing a large number of bubbles or metal beads are generally mixed in the materials.
Sound absorbing materials are often used to improve the acoustic performance of structures such as sound insulation and decoupling between the elements of the transducer array, sound absorption block on the back of the transducer, sound elimination covering treatment of the interior wall and components of the liquid filled transducer cavity, sound absorption veneer on the interior wall of the anechoic tank, etc.
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Acoustical materials can be divided into:
① Porous materials that attenuate sound waves by many small open channels from the surface to the inside, mainly absorb medium and high frequency sound waves, various organic or inorganic fibers and their products with fibrous aggregation structure, as well as open cell foamed plastics with porous structure andExpanded perlite products。
② Flexible materials absorbing sound by resonance (such as closed cell foam plastics, absorbing medium frequency), membrane materials (such as plastic film or cloth, canvas, lacquer cloth and artificial leather, absorbing low and medium frequency), plate materials (such as plywoodHard fibre board、Asbestos cement boardandplasterboard, absorbing low frequencies) and perforated plates (made by punching holes on various plate-like materials or metal plates, absorbing intermediate frequencies).[1]
The above materials can be used together to expand the sound absorption range and improveSound absorption coefficient。Decorate withSound-absorbing boardStick to the wall orsuspended ceilingThe combination of porous materials and perforated plates or membrane materials installed on the wall, or even floating cloud suspension, can improve the indoor sound quality and control noise.porous material In addition to absorbing air sound, it can also reduce the vibration caused by solid sound and air sound in empty rooms.Filling porous materials into the composite structure composed of various plate-like materials can improvesound insulationAbility and reduce the weight of the structure.
yesIncident soundA material that can absorb.Sound absorbing materials are mainly used to control and adjust indoorreverberation time , eliminate echo to improve indoor hearing conditions;It is used to reduce noise in noisy places to improve living environment and working conditions (seeSound absorption and noise reduction）；It is also widely used to reduceVentilation and air conditioning pipelineNoise.[1]
(2) Structural characteristics: there should be a large number of micropores and gaps in the material, and these micropores should be as small as possible and evenly distributed in the material.The micropores inside the material should be interconnected rather than closed, and individual bubbles and closed gaps will not absorb sound.The micropores are open to the outside, so that sound waves can easily enter the micropores.
(3) The sound absorption characteristics are mainly high frequency. The factors affecting the sound absorption performance are mainly the flow resistance of the material, pores, structural factors, thickness, unit weight, and the influence of the underlying conditions.[2]
Perforated asbestos cement, gypsum boardHard fibre boardPlywood, steel plate and aluminum plate can be used as perforated panel resonance sound absorption structure, which has large absorption near its structural resonance frequency and is suitable for intermediate frequency.
2. Film sound absorption structure
It includes leather, artificial leather, plastic film and other materials, which are impermeable, soft, elastic under tension and other characteristics, and absorb the incident sound energy near the resonance frequency. The resonance frequency is usually in the range of 200~1000HZ, and the maximum sound absorption coefficient is about 0.3~0.4. It is generally regarded as the sound absorption material in the medium frequency range.If it is filled in the cavity behind the filmporous material At this time, the sound absorption characteristics depend on the types of membrane and porous materials and the installation method of the membrane.[3]
3. Thin plate sound absorption structure
PlywoodHard fibre board, gypsum board, asbestos cement board and other boards are fixed on the frame around, together with the closed air layer behind the board, forming a vibration system. Its resonance frequency is mostly 80~300HZ, and its sound absorption coefficient is about 0.2~0.5, which can be used as a low-frequency sound absorption structure.The main factors determining the sound absorption performance of the thin plate sound absorption structure are:
(1) The influence of the mass m of the thin plate increases the weight per unit area of the plate, which can generally make its resonance frequency move to low frequency.The selection of low quality, impermeable materials such as leather is conducive to the resonance frequency moving to the high-frequency direction.
(2) The influence of the thickness of the air layer behind changes the thickness of the air layer as well as the quality of the plate, and the resonance frequency will also change.Filling in the air layerporous material The sound absorption coefficient near the resonance frequency can be improved.
(3) The influence of the structure of the keel behind the plate and the installation method of the plate Because the thin plate sound absorption structure has a certain low frequency sound absorption ability, but poor sound absorption for the middle and high frequencies, it has a strong reflection ability in the middle and high frequencies.It can increase the diffusion of indoor sound energy.By changing the installation method of keel structure, various forms of reflective surface, diffusion surface and sound absorption diffusion structure are designed.[2]
5. Special sound absorption structure
(1) Curtain
Curtain is a fabric with ventilation performance, which hasporous material Because of its thin sound absorption material, it can not achieve great sound absorption effect.If it is used as a curtain and installed at a certain distance from the wall or window opening, just as the air layer is set behind the porous material, it can have a certain sound absorption effect in the middle and high frequencies.When it is hung at odd times of 1/4 wavelength from the wall, it can obtain high sound absorption at corresponding frequency.
(2) Space absorber
The sound absorption material is made into a spatial cube, such as a flat, spherical, conical pyramid or column, so that it can absorb sound waves on many sides. Under the same projection area, it is equivalent to increasing the effective sound absorption area and edge effect. In addition to the diffraction effect of sound waves, the actual sound absorption effect is greatly improved, and its high-frequency sound absorption coefficient can reach 1.40. In actual use,According to different use locations and requirements, various forms of sound absorbers hanging from the ceiling can be designed.[2]
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According to the design requirements of building materials and the characteristics of sound absorption materials, the selection and design of materials and shapes are carried out.The commonly used sound absorbing materials in construction include foam plastic, urea formaldehyde foam plastic, industrialfelt、Foam glass、Glass wool、Slag wool, asphalt slag woolcementExpanded perlite board, gypsum mortar (mixed with cement andglass fibre）、cement mortar, brick (clean water wall surface), cork board, etc., each kind of sound absorption material has requirements for its thickness, unit weight, sound absorption coefficient at various frequencies and installation conditions, and shall comply with the corresponding specifications.The installation effect must be considered for the sound absorption materials used in buildings.[4]
Installation position
When installing sound absorbing materials in buildings, they should be installed on the surfaces that are most likely to contact sound waves and have many reflections, and the uniformity of distribution should also be considered, instead of concentrating on the ceiling and walls.Most sound-absorbing materials have low strength. In addition to attention during installation and operation, waterproof, anti-corrosion, mothproof and other issues should also be considered.Use materials with high sound absorption coefficient as far as possible, so as to use less materials to achieve better results.[4]
Material selection
The materials used as sound absorption materials shall be non flammable, non moth eaten and mildew resistant, pollution resistant and low moisture absorption materials.Due to the porous nature of the material, it is easy to absorb moisture, and the size is easy to deform, so pay attention to expansion during installation.
Decorative properties of materials
Sound absorbing materials are installed on the surface of buildings.Therefore, the coordination and decoration between the belt and the building should be considered in the design and installation.When using decorative paint, pay attention not to block the pores to avoid reducing the sound absorption effect.
Material structure characteristics
Some porous materials are used as sound absorption materials, and the name of the page is the same -porous material However, the pore characteristics are completely different.Thermal insulation materialIt is required to have closed and unconnected pores, while sound absorbing materials are required to have open and connected pores. The more such pores, the better the sound absorption effect. On the contrary, the worse the thermal insulation effect.In addition, sound absorption andSound insulation materialDifferences.
The sound absorption material has poor sound insulation performance due to its light weight, porosity and looseness. According to the acoustic principle, the greater the density of the material (kg/m ³), the more difficult it is to vibrate, and the better the sound insulation effect.Dense and heavy clay brickreinforced concreteThe sound insulation effect of such materials is good, but the sound absorption effect is poor.[4]
