What are the factors affecting the sound absorption coefficient of porous sound-absorbing materials ? The main factors influencing the sound absorption coefficient of porous sound-absorbing materials are flow resistance, thickness of sound-absorbing material, bulk density or void ratio of sound-absorbing material, humidity and temperature, influence of air layer after material, and effect of material facing. The following Xiaobian detailed look at it.
Porous sound-absorbing material
What are the factors that affect the sound absorption coefficient of porous sound-absorbing materials?
1, flow resistance
The flow resistance Rl is a parameter for evaluating the effect of the sound-absorbing material or the sound-absorbing structure on the viscometric performance of the air. Flow resistance is defined as the ratio of the static pressure difference and the flow velocity on both sides of the material when the micro-air flow is stably flowing through the material.
Flow resistance is related to the viscosity of air, the thickness or density of materials or structures. Generally, the flow resistance of the sound-absorbing material or the sound-absorbing structure is controlled within a proper range. The material or structure with a large sound-absorption coefficient has a relatively large flow resistance, and an excessive flow resistance will affect the structure of the ventilation system and the like. Normal operation, so the flow resistance must be considered in the sound absorption design.
2, the thickness of the material
A large number of tests have proved that the thickness of the sound absorption material determines the size and frequency range of the sound absorption coefficient. Increase the thickness can increase the sound absorption coefficient, especially increase the sound absorption coefficient. The same material, different thickness, different sound absorption coefficient and absorption frequency characteristics; different materials, sound absorption coefficient and absorption frequency characteristics are also very different, specific selection can refer to the relevant acoustic manual.
1 When the material is thin, increase the thickness, the material's low-frequency sound absorption performance will be greatly improved, but the impact of high-frequency sound absorption performance is less.
2 When the thickness increases to a certain degree, the thickness of the material is increased again, and the slope of the increase in the sound absorption coefficient will gradually decrease.
3 The first resonant frequency of the porous material is approximately inversely proportional to the thickness of the sound absorbing material. As the thickness increases, the sound absorption performance at low frequencies increases, the peak value of the sound absorption coefficient shifts toward the low frequency, and the thickness doubles. The peak value of the sound absorption coefficient will shift one octave toward the low frequency.
Porous sound-absorbing material
3, the bulk density or porosity of the material
The bulk density of the material refers to the weight per unit volume after the sound-absorbing material is shaped. Sometimes described by porosity. Porosity refers to the ratio of the volume of air in the porous sound-absorbing material to the total volume of the material. The bulk density or porosity of the material is different, which has a significant effect on the sound absorption coefficient and frequency characteristics of the sound-absorbing material.
Under normal circumstances, dense, large-capacity materials, its low-frequency sound absorption performance, high-frequency sound absorption performance is poor; on the contrary, soft, low bulk density material, its low-frequency sound absorption performance is poor, and high-frequency sound absorption performance is good . Therefore, in the specific design and selection, the bulk density of the material should be reasonably selected in conjunction with the acoustic characteristics of the space to be treated. Generally for the same material, when the thickness is constant, increasing the bulk density can improve the sound absorption performance of the low-middle frequency, but the change caused by the increase in thickness is smaller. For each of the different porous sound-absorbing materials, there is generally an ideal range of the bulk density. In this range, the sound-absorbing performance of the material is good, and if the bulk density is too low or too high, the sound-absorbing performance of the material is not improved.
4, humidity and temperature
Humidity also has a very significant effect on the sound absorption properties of porous materials. With the increase of the water content in the pores, the pores are blocked, the air in the sound-absorbing material no longer communicates, the void ratio decreases, the sound-absorbing performance decreases, and the sound-absorbing frequency characteristics also change. Therefore, in some areas with large water content, ultra-fine glass wool felts with moisture-proof effect should be reasonably selected to meet the needs of the use of wet climates and underground projects in the south.
The temperature also has a certain influence on the porous sound-absorbing material. When the temperature drops, the low frequency sound absorption performance increases; when the temperature rises, the low frequency sound absorption performance drops, so in the project, the influence of the temperature factor should also draw attention.
Porous sound-absorbing material
5. Influence of air layer after material
In the actual engineering structure, in order to improve the low-frequency sound absorption performance of the sound-absorbing material, a certain thickness of air layer is usually reserved behind the sound-absorbing material. The existence of the air layer is equivalent to the use of a layer of air as a sound-absorbing material after the sound-absorbing material, or, equivalently, a sound-absorbing structure.
6, the effect of material decoration
In the actual project, in order to protect the porous sound-absorbing material from being deformed and polluting the environment, metal mesh, glass cloth, and perforated plates with large perforation ratios are generally used as packaging protective surfaces; in addition, some environments require painting of the surface, etc. These will all affect the sound absorption properties of the sound absorption material to varying degrees. When the perforation rate of the covering material (the ratio of the perforation area to the total area of ​​the covering surface) exceeds 20%, this effect is negligible.
What are the factors that affect the sound absorption coefficient of the porous sound-absorbing material ? Here is a brief introduction to it. We hope to help you. For more information, please visit this website. Stay tuned.
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