Most sound-absorbing materials and sound-absorbing materials are porous materials, such as slag wool and blankets. The sound absorption mechanism is that the sound waves penetrate into the pores of the material, and the pores are mostly open pores that are interpenetrated inside, and are subject to friction and viscous drag of air molecules. As well as mechanically vibrating the fine fibers so that acoustic energy is converted into heat energy. The sound absorption coefficient of such a porous sound-absorbing material generally increases gradually from low frequency to high frequency, so sound absorption effects at high frequencies and intermediate frequencies are good. The following small series for everyone to introduce sound-absorbing materials related knowledge.
Sound-absorbing material principle
The sound originates from the vibration of the object. It causes the vibration of the adjacent air to form sound waves and propagates around in the air medium.
When the sound is transmitted to the surface of the component material, a part of the acoustic energy is reflected, a part penetrates the material, and a part is attenuated due to the vibration of the component material and the friction of the sound in the propagating medium. The acoustic energy is converted into heat energy and the acoustic energy is lost. That is, the sound is usually absorbed by the material.
Sound absorption coefficient
The sound absorption performance of the material is expressed by the sound absorption coefficient α. Α is the sum of the loss factor E/E0 and the transmission coefficient E/E0.
The sound absorption performance of a material is related to the structure and thickness of the material and the surface characteristics of the material, as well as the direction and frequency of the incident sound.
Sound-absorbing material applications
First, the control of indoor sound quality in the architectural field
In general, the larger the volume of the room, the longer the reverberation time and the poorer the speech intelligibility. In order to ensure speech intelligibility, it is necessary to do sound absorption indoors to control the reverberation time. Such as auditoriums, classrooms, stadiums, and cinemas.
For music buildings, the reverberation time is longer than that for a certain fullness, but it cannot be too long. Sound absorption control can be used.
In the hall building, in order to prevent acoustic defects such as echo, acoustic feedback, and acoustic focusing, sound absorption is often used on the rear wall, the railings on the second floor, the side wall surface, and the local area.
Second, sound absorption and noise reduction
In workshops, factories, and large open spaces (airport halls, offices, exhibition halls, etc.), due to the sound of reverberation, the noise will be 10-15dB higher than the same sound source outdoors. By arranging the sound-absorbing material indoors, the reverberation sound can be absorbed and the noise in the room can be reduced.
Acoustic noise reduction can get up to 10-15dB of noise reduction. Noise reduction amount = 10 lg (A0/A1). The less the indoor sound absorption is when no sound-absorbing material is added, the greater the amount of sound absorption in the room after the sound-absorbing material is added, and the better the noise reduction effect.
Third, the air conditioning system
The causes of noise in buildings are various, and the noise generated in the operation of air-conditioning systems occupies a considerable proportion. How to reduce the noise generated during the operation of the HVAC system is particularly important for sound-absorbing materials research to improve the acoustic environment in buildings.
1. Ways and methods for noise reduction in HVAC system
1.1 System Design Concept
With the constant emergence of some new technologies, new processes, and new materials in the air conditioning field, we can achieve the purpose of noise reduction in system operation through various methods. Noise control techniques often used include sound-absorbing cotton, sound-absorbing cotton, sound insulation felt, acoustic felt, sound-absorbing panels, and other sound-absorbing materials, which are mainly controlled and processed on the basis of noise sources, noise transmission paths and acceptance points.
Air conditioning systems, especially central air conditioning systems, are a large and complex system. The pros and cons of the system design directly affect the performance of the system. To use a fan with high efficiency and low noise, make its working point at or near the efficiency point of the fan. When the air volume of the system is constant, the safety factor for selecting the pressure head of the fan should not be too large. If necessary, the blower and the return fan are used together to bear the total resistance of the system. Under conditions permitting, increase the temperature difference of air supply to reduce the air volume of the fan, thus reducing the peripheral speed of the fan impeller, and the noise generated by the fan will also be reduced.
1.2 Design and Selection of Sound Absorbing Materials
In the noise reduction process, sound-absorbing materials are needed. The design and installation of soundproofing materials is an important measure to control the flow of airborne noise through the barriers such as pipelines. A sound insulation cotton with good performance can reduce airflow noise by 20-40dB. According to the amount of noise reduction, aerodynamic performance, and environment required by the noise source, different types of mufflers are selected. According to the requirements of the aerodynamic performance of the noise source, consider the aerodynamic performance of the sound-absorbing cotton, and control the resistance loss of the sound-damping cotton so that the equipment can work within the normal working range. When designing sound-absorbing materials, the effects of noise generated by the muffler on regenerative noise should be taken into consideration, so that the noise level of the muffler air regenerative regeneration is lower than the permissible noise level of the environment. The main noise source in the operation of the HVAC system is the medium-low frequency-dominated fan. , The use of resistive or impedance composite sound insulation board can play a good noise reduction effect.
1.3 Vibration Isolation Measures
1.4 Noise Control of Equipment Room
1.5 Avoiding Noise by Improper Construction
2. Existing problems and countermeasures
2.1 Design and Management Issues of HVAC Systems
2.2 Development, promotion and application of new technologies, new processes, and new materials
Encourage the development of new technologies, new processes, and new materials, and actively apply them to practical projects. If the conditions permit, vigorously develop low-temperature air supply technology, promote the use of composite material ventilation ducts, new sound-absorbing and sound insulation materials (such as plant cellulose) in the project.
The above is Xiaobian's introduction to sound-absorbing materials. More practical knowledge, please pay attention to Qijia information.
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