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How Do Soundproof Cotton Work?

Aug 28, 2018

Fiber porous sound insulation materials, such as polyester fiber cotton insulation cotton, centrifugal glass wool, rock wool, mineral wool, plant fiber spraying, etc., the sound insulation mechanism is that there are a large number of tiny connected pores inside the material, and sound waves can penetrate deep into the material along these pores. The friction with the material converts the acoustic energy into heat. The sound insulation property of the porous sound insulation material is that the sound insulation coefficient is gradually increased as the frequency is increased, which means that the low frequency absorption has no high frequency absorption. The necessary conditions for sound insulation of porous materials are: the material has a large number of voids, the voids communicate with each other, and the pores penetrate deep into the material. One of the misconceptions is that the material with a rough surface has sound insulation properties, but it is not. For example, the brushed cement and the surface of the stone are basically not soundproof. The second misunderstanding is that materials with a large number of holes inside the material, such as polyphenylene, polyethylene, closed-cell polyurethane, etc., have good sound insulation properties. In fact, these materials cannot penetrate into the material due to the lack of connectivity of the internal holes. Internal vibration friction, so the sound insulation coefficient is small.

A perforated plate with an air layer on the wall or ceiling, even if the material itself has poor sound insulation, the structure also has sound insulation properties, such as perforated gypsum board, wood board, metal plate, and even slit sound insulation brick. This type of sound insulation is called Helmholtz resonance sound insulation. The sound insulation principle is similar to the acoustic resonance of a thermos bottle. The external space of the material is connected to the internal cavity through a narrow bottleneck. When the sound wave is incident, at the resonant frequency, the air and the inside of the neck. The intense resonance between the spaces consumes acoustic energy. The Helmholtz resonance absorption is characterized by a large sound insulation coefficient only at the resonance frequency.

The film or sheet can also be sound-insulated when there is a cavity in the wall or ceiling, such as a wooden board, a ceiling made of a metal sheet or a wall panel, etc. The sound-insulating mechanism of this structure is thin-plate resonance sound insulation. At the resonance frequency, the acoustic energy is largely absorbed due to the severe vibration of the thin plate. Thin plate resonance absorption mostly has good sound insulation performance at low frequencies.

Explain the principle of sound insulation in general: the principle of sound insulation is to leave a channel for the sound to enter (a channel composed of numerous tiny holes that are connected together, or a mixture of countless fibers intertwined to form numerous small gaps) but sound Once you get in, you can't get out. Because the passage is too long, the sound is drilled in and out. The left and right collisions gradually consume energy in this process, which plays a role in sound insulation.