The application of sound-absorbing cotton in interior parts

Recently, the topic of car sound insulation has been very hot. After more and more friends around me have done full-car sound insulation, many car owners are considering sound insulation modification. The reason is simple, after experiencing it, you naturally know what you need. Driving pleasure, how can a noisy car environment give you a quiet environment? It is still necessary."With the advent of automobiles, people's pace of life has been accelerating. As the most common tool of modern transportation, automobiles have an important impact on people's lives. People's functional needs for automobiles are also gradually increasing. On the basis of safety and speed, they require more comfortable space. During car travel, the noise is relatively large, affecting the health of passengers. Therefore, car noise has also become one of the important standards for the mechanical performance and comfort of automobiles."
Generation and main control methods of automobile noise

Automobile noise includes comprehensive noise of various types of noise, mainly divided into external and internal noise.

External noise mainly comes from the noise radiated from various parts of the automobile to the external space, mainly including engine noise, exhaust and tire noise, and braking and transmission system noise, etc.

Internal noise mainly refers to the noise from outside the car that is transmitted to the inside of the car through multiple paths, as well as the noise radiated into the car by the vibration of various parts of the car during vibration. These noise sound waves, under the influence of the acoustic characteristics of the car's interior space, will form a complex reverberation sound field, ultimately forming the noise inside the car.

The sources of automobile noise can be mainly divided into engine noise, body resonance noise, tire noise, chassis noise, wind noise, and cabin resonance noise, etc.

Currently, there are two main methods for noise control in automotive technology: active control and passive control.

Active control refers to adding additional energy during noise control to control noise. This control method is also called active control.
Passive noise control technology is mainly divided into three aspects: first, eliminating and weakening the source noise; second, controlling the propagation path of noise and reducing solid transmission; finally, protecting passengers from noise. The sound absorption and sound insulation methods in automotive interior materials are passive noise control.

Factors affecting the sound absorption effect of sound-absorbing cotton in automotive interiors

(1) Material flow resistance

Sound-absorbing cotton is a porous sound-absorbing material. When sound waves cause vibration in the air, the physical parameters of the air permeability of the sound-absorbing cotton will cause a small amount of air to pass through the pores of the porous material. At this time, the ratio between the static pressure difference on both sides of the material and the air flow velocity is the flow resistance of the material. The number, size, and degree of mutual connection of the micropores inside the absorbing material will all affect the size of the flow resistance. The size of the flow resistance has an important impact on the sound absorption effect of the material. A certain thickness of porous material should correspond to a reasonable flow resistance value. Too high or too low will affect the sound absorption performance of the material. Therefore, it is necessary to adjust the flow resistance of the material and control the flow resistance value within a scientific range to maximize its effect.

(2) Porosity

The ratio between the air volume of the porous material and the total volume of the material is the porosity, usually expressed as a percentage. Usually, the porosity of porous sound-absorbing materials is around 70%, and some are as high as 90%. The pores of the porous material should be small and evenly distributed, increasing the ligament area inside the material and promoting noise absorption.

(3) Influence of material thickness

For the same porous sound-absorbing material with a certain thickness, the sound absorption coefficient is relatively low in the low-frequency range, while the sound absorption coefficient increases rapidly with the increase in frequency. When it reaches the high-frequency range, the change in the sound absorption coefficient is not obvious. However, if the thickness of the material continues to increase, the effect of absorbing high-frequency noise will not increase significantly, while the increase in thickness has a greater impact on the low-frequency sound absorption coefficient. Experiments have shown that for the same type of porous material, when the stacking density is the same, the product of thickness and frequency has a decisive effect on the sound absorption coefficient. When the thickness of the material is doubled, the frequency spectrum curve moves one octave towards the low frequency.

(4) Influence of air layer behind porous material

The thickness of the air layer behind the porous material has an important impact on its sound absorption function. When there is a certain space between the porous material and the rigid wall, a certain cavity will appear on the back of the material, increasing the effective thickness of the material and having a certain impact on its low-frequency noise absorption function. When the thickness and stacking density of the porous material are certain, the influence of the change in the air layer is relatively large. When the thickness of the air layer is an odd multiple of 1/4 wavelength, the sound absorption coefficient reaches the maximum value.

(5) Influence of changes in external operating conditions

First, the influence and change of temperature will cause changes in the speed of sound and wavelength, and will also cause changes in flow resistance due to air viscosity, affecting the sound absorption function of the material. Usually, when the temperature increases, the high-frequency sound absorption frequency curve shifts towards high frequency; second, the influence of humidity. Porous materials absorb moisture, causing changes in the nature of the material, reducing the porosity of the material, and affecting the sound absorption performance.

Application of sound-absorbing cotton in automotive interiors

(1) Application of sound-absorbing materials

With the increasing demand for automobiles, noise control in the car has become one of the important contents in automobile product research and development. At present, most of the sound-absorbing materials used in automobiles are porous materials, such as asbestos, glass wool, slag wool, bamboo fiber composite materials, and felt, etc. Porous sound-absorbing materials mainly absorb mid-frequency and high-frequency noise. Through measurement research and relevant experiments, it is known that appropriately increasing the thickness and specific gravity of the material and reasonably designing the sound absorption structure, the sound-absorbing material can also absorb a certain amount of low-frequency noise.