There are many types of sound absorbing materials and sound absorbing structures. In terms of sound absorption mechanism, sound energy is generally converted into other forms of energy (mainly heat energy), but in terms of physical processes, it varies from material to material. This difference is mainly caused by the structural form of the material itself. Whether it is a sound absorbing material or a sound absorbing structure, their primary use is in their acoustic properties, that is sound absorbing ability. However, in actual selection, the specific requirements of the use occasion must also be met. For example, when selecting sound absorbing materials for construction, it is necessary to meet the requirements of building regulations and architectural arts. Therefore, it is necessary to further conduct comprehensive evaluation from other aspects. In general, this evaluation should include both its functional and sensory qualities.
In addition, many granular materials and their products, such as clay acoustic absorbing bricks, expanded perlite sound absorbing panels and some foam materials that have been produced in China at present. Among these foam materials, polystyrene, polyvinyl chloride, polyurethane formate foam, urethane foam, phenolic foam, and the like have been produced in China. The structural feature of the porous sound absorbing material is that there are many fine gaps and connected bubbles inside the material. In fiber materials, there is a complex connection between fibers and fibers. This kind of joint makes this material have many tiny gaps, which are the decisive factors for the good sound absorption properties of fiber materials; in addition to fiber materials, all kinds of porous materials and their products are almost all in materials. There are connected bubbles. Obviously, although there are bubbles in the material, most of these bubbles are single closed closed cells, and a class of materials without aeration properties cannot be classified as porous sound absorbing materials from structure to mechanism.
Porous sound absorbing materials have a special important position in sound absorbing materials. Therefore, the research on it has attracted wide interest and has obtained a lot of research results. Qualitatively speaking, the sound absorbing effect of the porous sound absorbing material is firstly caused by the internal vibration of the material or the vibration of the air in the micropores under the excitation of the sound waves, so that the air and the solid ribs are relatively moved. Due to the viscosity of the air, a corresponding viscous resistance is formed in the gap or the micropores, so that the acoustic energy is continuously converted into heat energy; secondly, the continuous heat exchange between the air and the pore walls and the fibers during the adiabatic compression of the air This causes heat loss, which also converts acoustic energy into heat. These two factors are the main cause of the attenuation of acoustic energy when sound waves are incident on the surface of the porous sound absorbing material. Strictly speaking, the fibers constituting the porous sound absorbing material and the pore walls themselves will also generate some vibration under the action of sound waves. In addition, the elastic waves propagating inside must also be taken into account. However, these effects are generally considered to be secondary and therefore negligible.
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