Flow resistance is one of the basic parameters of porous sound absorbing materials. It is an important factor in determining the sound absorption efficiency of materials. It is the quality index of sound absorbing materials. In foreign countries, the sound absorption materials are more developed, such as the Japanese Industrial Standard (JIS). There is a product flow resistance regulation (JIS6306) to control the stability of product performance. In China, we only apply it as a theoretical value, and finally can be applied to the actual development and production of sound absorbing materials. Some manufacturers of sound absorbing materials also use the sound absorption coefficient of early reverberation or standing wave tube detection, which has a certain gap with the actual performance of the product. For example, the same thickness and bulk density of fiberglass board is not a batch does not mean the same suction. Sound coefficient, different thickness and bulk density, under the same flow resistance value, the sound absorption coefficient is the same. The detection of flow resistance was as early as 64 years and 82 years at the Institute of Physics, China Academy of Building Research. Professor Hu Junmin published the "Measurement of Flow Resistance of Acoustic Materials", "Flow Resistance Control of Sound Absorption Properties of Mineral Fiber Boards", and "Polyporation". The surface treatment of sound-absorbing panels, and many other papers.
Flow resistance is the resistance of the air mass through the material gap. In a steady state of gas flow, the ratio of the pressure difference (ΔP) on both sides of the material to the line velocity (U) through the material is defined as the flow resistance (R) of the material in Rayleigh.
There are many ways to test the flow resistance. The easiest is the flow resistance measurement system designed by LLBeranek according to the principle of water tank.
Second, the flow resistance value detection can contribute to the development of sound-absorbing panels
1. The flow resistance value detection can reasonably control the fiber thickness and effectively study the material mechanism.
Porous sound absorbing material, its sound absorption mechanism is mainly due to the vibration of air particles caused by sound waves, friction and viscous resistance in the micropores of the material, so that the sound energy is converted into heat energy, so that the sound energy is absorbed. The porosity of the material is manifested by the presence of a large number of micropores inside the material which should be interpenetrating and should not be hermetic. It can also be said that the size of the micropores, the thickness of the fibers and the sound absorption coefficient, and the sound absorption spectrum have a direct relationship. In the domestic glass fiber sound absorbing panel manufacturers, the fiber filaments of the new nozzles are thinner and longer. The fiber spun from the wear will become thicker, not more than double the thickness of a batch. After the flow resistance test, the fine sound absorption coefficient of the fiber filament is large. (At the same time, it has a certain relationship with the amount of glue and the order, and it needs to be studied.) Reasonable control of the flow resistance of the material is a fundamental task in the development of sound-absorbing sheet machine.
2. The flow resistance value detection can reasonably control the thickness and bulk density and reduce the cost.
Through the detection of the flow resistance value, the thickness and bulk density of the plate can be determined, so that the plate can achieve the best sound absorption performance of different requirements, which can reduce the large-scale and repeated measurement work of the standing wave tube, and reduce the blindness to a certain extent and meaning. Effectively speed up the product development process, and also reduce the material production cost. For example, when the 10mm thickness fiberglass board can properly control the flow resistance, it can achieve the sound absorption with different bulk density of 20mm, which reduces the material production cost and saves the cost. The decoration space of the plate is of great significance for the rapid entry of new materials into the market and acceptance by users.
3. The flow resistance value detection can reasonably control the surface layer and improve the decorative effect.
The surface treatment of porous fiber sound absorbing panels is an important part of modern architectural decoration. The sound absorption performance of the sheet depends on the porosity of the sheet itself. This porosity is manifested by a large number of micropores in the material, which is the gas permeability or the flow resistance of the material. Without the surface treatment, the decorative effect will be reduced and it will not be People accept no market. The surface layer can improve the sound absorption coefficient of the material through the reasonable control of the flow resistance, especially the low and medium frequencies, to achieve the desired decorative effect. Unreasonable flow resistance values ​​will reduce the sound absorption coefficient of the sheet and affect the overall performance of the sheet. (Please refer to Professor Hu Junmin's article "Surface treatment of porous sound-absorbing panels".) 4. Flow resistance detection can reasonably control high, medium and low frequencies to meet the needs of different places.
In the practical application of the project, there should be sound-absorbing materials with different frequencies to adapt to the needs of different places. Some materials in China only have comprehensive sound absorption coefficient. The materials in the special frequency bands are not clear, and the reverberation or standing wave tube detection takes time. And capital, flow resistance detection can quickly solve these problems, especially the manufacturer's research and development materials are easy to control, fast, thus greatly reducing the test workload; the material's sound absorption spectrum can also be controlled by adjusting the material flow resistance and Quantify to ensure the needs of different places.
Third, flow resistance detection has important significance for the production quality monitoring of sound-absorbing panels.
At present, the domestic sound-absorbing sheet market is more chaotic. Some of the plates are only the sound absorption of reverberation and standing wave tube detection a few years ago. There is a certain difference between the actual sound absorption and the actual sound absorption of the material. The user does not understand architectural acoustics too much. Affecting the overall sound absorption effect, especially the sound absorbing materials of various frequencies are more uncertain, and the manufacturer can not control the quality of different batches of materials. If the manufacturer uses the flow resistance value to reasonably control the materials, the quality of each batch can be guaranteed and adapted. Market demand. Flow resistance detection is accurate, fast, simple and easy to operate for manufacturers.
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