In the indoor sound quality design, the Sound Absorptive Tiles and sound absorption structure is widely used, the main purpose is: to control the room reverberation time, so that the room has a good sound quality; eliminate echo, trembling echo, sound focus and other acoustic defects: Sound noise reduction; pipe silence. The size of the material and structure of the sound absorption capacity is usually expressed by the sound absorption coefficient a, sound absorption coefficient a is defined in the first chapter of the first chapter. Generally, the sound absorption coefficient a ≥ 0.2 material called sound-absorbing materia
Although the sound-absorbing material and structure of many types, but in accordance with the sound absorption mechanism, commonly used sound-absorbing material and structure can be divided into two kinds of fire, that is, porous sound-absorbing material and resonant sound absorption structure.
The same sound-absorbing material and structure have different sound absorption coefficients for different frequencies of sound waves. Usually the use of 125Hz, 250Hz, 500Hz, 1000Hz, 2000Hz, 4000Hz six frequency of sound absorption coefficient to represent the material and structure of the sound absorption frequency characteristics. The arithmetic mean of the sound absorption coefficients at four frequencies of 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz is called the noise reduction coefficient (NRC), which is used to roughly compute and select the sound absorptive material at the time of noise reduction.
There are many kinds of sound-absorbing materials and sound-absorbing structures. According to their sound absorption mechanism, it can be divided into three categories,Sound Absorptive Tiles namely, porous sound-absorbing material, resonant sound-absorbing structure and composite sound-absorbing structure, Ceiling structure and so on.
Porous Sound Absorptive Tiles is characterized by a large number of internal and external connectivity of the pores and bubbles, when the sound waves into which the air can cause air vibration. Due to the viscous resistance of the air, the friction between the air and the hole wall,Sound Absorptive Tiles a considerable part of the sound energy into heat and loss. In addition, when the air adiabatic compression, the air and the hole wall between the continuous heat exchange, due to heat conduction, will make part of the sound energy into heat.
Some insulation materials, such as polystyrene and some polyvinyl chloride foam, also have a large number of bubbles inside, but most of them are single closed, non-connected, so the sound absorption is not good. So that the surface of the wall rough, such as the practice of cement nap, and did not improve its permeability, and therefore can not improve its sound absorption coefficient.
The factors that affect the sound absorption performance of the porous sound-absorbing material mainly have the air flow resistance, porosity,Sound Absorptive Tiles apparent density and structural factor of the material, in which the structural factor is the physical quantity determined by the structural properties of the porous material. In addition, the material thickness, the conditions behind, the surface layer and environmental conditions and other factors will also affect its sound absorption characteristics.
The porous Sound Absorptive Tiles comprises a fibrous material and a particulate material. Fiber materials are: glass wool, ultra-fine glass wool, mineral wool and other inorganic fibers and their carpets, board products, cotton, wool, lin and other organic fiber fabric. Granular materials are expanded perlite, microporous brick and other plates, block products.
Porous sound-absorbing materials generally have good high-frequency sound absorption performance, the sound absorption mechanism is not because the surface roughness, but because the porous material has a large number of internal and external connectivity of the tiny gaps or bubbles. In general, the sound absorption capacity of the porous material is related to its thickness and bulk density. As shown in Figure 10-15, with the increase of the thickness, the middle and low frequency sound absorption coefficient increased significantly, the high frequency did not change much. Thickness unchanged, increase the density can also improve the low-frequency sound absorption coefficient, but smaller than the effect of increasing the thickness. In the case of the same material, when the thickness is not limited, the porous material is loosened.