Why is the earth so quiet on a snowy night? In auditoriums, conference rooms, music rooms, you can often see that sound-absorbing panels are installed on the walls, the purpose of which is to eliminate external interference and reduce human interference in the outside world. There are many small holes on the surface of the sound absorbing panel. When the sound enters the small holes, it will be randomly reflected in the inner wall of the structure, which is a little like a sponge, as long as most of the energy of the sound wave is consumed and converted into heat energy to achieve the sound insulation effect.
When it snows, the ground, buildings and trees are often covered with a layer of snow. Snow is different from ice, snow is not a solid, on the contrary, snowflakes are collected together in a sparse manner, with many small gaps in the middle, which is a bit like the structure of a sound-absorbing panel. This gap creates a sound absorbing effect on sound waves, especially at frequencies above 600 Hz. This is the reason for the unusually quiet land on a snowy night.
The principle of sound absorption of sound-absorbing materials is also the same. Sound-absorbing materials are mainly divided into microporous and fibrous. There is no significant difference between the two materials. This is a channel made up of tiny holes. connected or innumerable fibers criss-cross together, forming innumerable small gaps), but once the sound enters, it cannot exit, because the channel is too chaotic, and the sound drills many small holes in it. countless little slots), but once the sound enters, it cannot exit because the sound is too long, the sound drills inside, and it is constantly consumed in the process. Energy, sound-absorbing principle of sound-absorbing materials is the same.
Metal foam production methods include powder metallurgy and electroplating. In the first case, the metal foam is prepared by adding a blowing agent to the molten metal, and in the second case, the metal foam is converted into polyurethane foam by electroplating.
Sound waves passing through the pores of the metal foam are absorbed and repeatedly reflected in the pore skeleton, and part of the sound energy is lost in the form of heat, which leads to a decrease in sound intensity. By changing the shape, size and pore distribution of the metal foam, it can have a better sound absorption capacity.