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The sound absorbing material should be connected with the surrounding sound transmitting medium
Acoustic characteristic impedance
Matching, so that the sound energy does not reflect into the sound absorption material, and the incident sound energy is mostly absorbed.
A material that absorbs incident sound energy by its porosity, film action, or resonance action, one of the components of an ultrasonic inspection device.
- Chinese name
- Sound absorbing material
- Foreign name
- sound-absorbing material
- Generic type
- Organic fiber materials, inorganic fiber materials
- serve
- Strong absorption of sound energy, reduce noise performance
- structure
- Resonant sound absorption structure or gradual transition layer structure
- characteristic
- There are a lot of pores and gaps inside
In the application of sound absorbing materials, resonant sound absorbing structures or gradual transition layer structures are usually adopted. In order to improve the internal loss of the material, the filler containing a large number of bubbles is generally mixed into the material or the metal microbeads are added.
Sound absorbing materials are often used to improve the acoustic performance of the transducer array, such as sound insulation decoupling between the various elements of the transducer array, sound absorption block on the back of the transducer, sound suppression covering treatment of the interior walls and components of the liquid filled transducer chamber, and sound absorption veneer of the inner wall of the silencer sink.
Sound absorbing materials are divided into:
(1) A porous material that attenuates sound waves by many small open channels from the surface to the interior, mainly absorbing medium and high frequency sound waves, various organic or inorganic fibers and their products with fibrous aggregation structures, and open-porosity foam and porous structures
Expanded perlite products
.
② Flexible materials that absorb sound by resonance (such as closed-cell foam, absorbing intermediate frequency), membrane-like materials (such as plastic film or cloth, canvas, varnished cloth and artificial leather, absorbing low intermediate frequency), plate-like materials (such as plywood,
hardboard
,
Asbestos cement board
and
plasterboard
Absorb low frequency) and perforated plate (made of various plate-like materials or metal plates by punching holes to absorb medium frequency).
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The composite use of the above materials can expand the sound absorption range and improve
Absorption coefficient
. Decorate with
Acoustic panel
Attached or
Suspended ceiling
The combination of porous materials and perforated plates or membrane materials is installed on the wall, and even the use of floating cloud suspension can improve the indoor sound quality and control noise.
Porous material
In addition to absorbing air sound, it can also weaken the vibration caused by solid sound and empty room air sound. It can be improved by filling the porous material into the composite structure composed of various plate materials
Sound insulation
Capacity and structural weight reduction.
right
Incoming sound
A material capable of absorption. Sound absorbing materials are mainly used to control and adjust indoor
Reverberation time
, eliminate echoes to improve indoor listening conditions; Used to reduce noise in noisy places to improve the living environment and working conditions (see
Sound absorption and noise reduction
); Also widely used for lowering
Ventilation and air-conditioning duct
The noise.
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Material classification and characteristics
(1)
Porous sound absorbing material
The types include: organic fiber materials, ramie cotton felt, inorganic fiber materials, glass wool, rock wool, mineral wool, urea-formaldehyde foam, polyurethane foam, etc.
Polyvinyl chloride
and
Styrofoam
Not belong to
Porous material
, for earthquake protection,
Thermal insulation material
More suitable.
(2) Structural characteristics: there should be a large number of micropores and gaps inside the material, and these micropores should be as small as possible and evenly distributed inside the material. The microholes inside the material should be connected to each other, rather than closed, and separate bubbles and closed gaps do not absorb sound. The pores open outwards, allowing sound waves to easily enter the pores.
(3) The sound absorption characteristics are mainly high frequency, and the factors affecting the sound absorption performance are mainly the flow resistance of the material, pores, structural factors, thickness, bulk density, and the influence of the underlying conditions.
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Material structure
1, perforated plate resonance sound absorption structure
Using perforated asbestos cement, gypsum board,
hardboard
Plywood, steel plate, aluminum plate, can be used as a perforated plate resonance sound absorption structure, near the resonance frequency of its structure, there is a large absorption, suitable for medium frequency.
2, film sound absorption structure
Including leather, artificial leather, plastic film and other materials, with airtight, soft, elastic and other properties when tensioning, absorb the incident sound energy near the resonance frequency, the resonance frequency is usually in the range of 200 ~ 1000HZ, the maximum sound absorption coefficient is about 0.3 ~ 0.4, generally as a medium frequency range of sound absorption materials. If you fill the cavity behind the membrane
Porous material
At this time, the sound absorption characteristics depend on the type of film and porous material and the device method of the film.
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3, thin sheet sound absorption structure
Put plywood,
hardboard
Gypsum board, asbestos cement board and other panels are fixed around the frame, together with the closed air layer behind the board, forming a vibration system, its resonance frequency is mostly 80 ~ 300HZ, its sound absorption coefficient is about 0.2 ~ 0.5, can be used as a low frequency sound absorption structure. The main factors that determine the sound absorption performance of thin plate sound absorption structure are:
(1) The influence of thin plate mass m increases the weight per unit area of the plate, which can generally make its resonance frequency move to the low frequency. The selection of small quality, non-breathable materials such as leather, is conducive to the resonance frequency to move in the high frequency direction.
(2) The influence of the thickness of the air layer behind changing the thickness of the air layer is the same as changing the quality of the plate, the resonance frequency will also change. Fill in the air layer
Porous material
The sound absorption coefficient near the resonance frequency can be improved.
(3) The influence of the keel structure and the installation mode of the plate because the sound absorption structure of the thin plate has a certain low frequency sound absorption ability, and the sound absorption of the middle and high frequency is poor, so it has a strong reflection ability at the middle and high frequency. Can increase indoor acoustic energy diffusion. By changing the keel structure and different installation methods, various forms of reflective surface, diffusion surface and sound absorption -- diffusion structure are designed.
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5, special sound absorption structure
(1) Curtain
Curtain is a textile with ventilation performance, with
Porous material
The sound absorption characteristics, because the thin itself is used as a sound absorption material, it can not get a large sound absorption effect. If it is used as a curtain and installed at a certain distance from the wall or window hole, just as the air layer is set behind the porous material, it can have a certain sound absorption effect in the middle and high frequency. When it is hung at an odd multiple distance of 1/4 wavelength from the wall, high sound absorption of the corresponding frequency can be obtained.
(2) Spatial sound absorber
The sound absorption material is made into a cube of space such as: flat shape, spherical shape, conical pyramid shape or column shape, so that it absorbs sound waves on many sides, in the case of the same projected area, it is equivalent to increasing the effective sound absorption area and edge effect, coupled with the diffraction effect of sound waves, greatly improving the actual sound absorption effect, 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 absorption can be designed from the ceiling hanging down.
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According to the design requirements of building materials and the characteristics of sound absorbing materials, the selection and design of materials and shapes are carried out. The sound absorbing materials commonly used in construction are foam, urea-formaldehyde foam, and industrial
felt
,
Foam glass
,
Glass wool
,
Mineral wool
Asphalt slag cotton,
cement
Expanded perlite board, gypsum mortar (cement and
Glass fibre
),
Cement mortar
Brick (clean wall), cork board, etc., each sound absorption material has requirements for its thickness, volume weight, sound absorption coefficient at each frequency and installation, and the corresponding specifications should be implemented. The application of sound absorption materials in construction must consider the installation effect.
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The installation of sound absorbing materials in the building should be installed on the surface that is most easily exposed to sound waves and has more reflections, and the uniformity of distribution should also be considered, and it is not necessary to concentrate on the ceiling and walls. Most of the sound absorption materials have low strength, in addition to the installation operation should pay attention to, should also consider waterproof, anti-corrosion, anti-moth and other issues. As far as possible, use materials with a high sound absorption coefficient in order to use less materials to achieve better results.
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Materials used as sound absorbing materials should be as far as possible to choose non-flammable, not easy to moth mold, pollution resistance, low moisture absorption materials. Due to the porosity of the material is easy to absorb moisture and the size is easy to be deformed, so pay attention to the expansion problem when installing.
Sound absorbing materials are mounted on the surface of the building. Therefore, in the design and installation should be considered with its coordination with the building and decorative. When using decorative paint, be careful not to plug the fine holes, so as not to reduce the sound absorption effect.
Some porous materials are used as sound absorbing materials, the name of the page is the same -
Porous material
However, it is completely different in stomatal characteristics.
Thermal insulation material
It is required to have closed pores that are not interconnected, and the sound absorbing material is required to have pores that are open and connected with each other, and the more the porosity, the better the sound absorption effect, on the contrary, the worse the thermal insulation effect. In addition, also clear sound absorption and
Sound insulating material
The difference.
The sound absorbing material is light, porous and loose, and the sound insulation performance is not good, according to the acoustic principle, the density of the material (kg/m³) is larger, the more difficult to vibrate, the better the sound insulation effect. As dense and heavy as clay bricks,
Reinforced concrete
The sound insulation effect of such materials is better, but the sound absorption effect is not good.
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