Ventilation duct muffler is the principle of resistive sound absorption and noise reduction with good effect on medium and high frequency broadband characteristics, the principle of resistant noise reduction with good effect on low, medium frequency and pulsation characteristics, as well as micro perforated muffler and impedance composite muffler. Muffler is a device that uses the principles of sound absorption, reflection and interference to reduce the air flow noise in ventilation and air conditioning system. According to different silencing principles, it can be divided into resistance, resistance, resonance type and compound type.
The resistive muffler uses the sound absorption function of sound-absorbing materials to eliminate noise. The structure is to fix the sound-absorbing material on the inner wall of the pipe where the air flow flows, or arrange it in the pipe or shell in a certain way to form a resistive muffler. The sound-absorbing material can partially absorb the sound energy incident on it. The reason why sound energy can be absorbed is due to the porosity and looseness of sound-absorbing materials. When sound waves enter the pores, the air and materials in the pores produce small vibration due to friction and viscous resistance. A considerable part of sound energy is converted into heat energy and absorbed.
It has good effect on high-frequency and intermediate frequency noise, but poor silencing performance on low-frequency noise.
1. Tubular muffler
Tubular muffler is a simple muffler, which is only pasted with a layer of sound-absorbing material around the inner circumference of the pipe wall, so it is also called "pipe lining". It is characterized by convenient manufacture and low resistance, but it is only suitable for small air ducts, and the diameter is generally no more than 400mm. The tubular muffler only has a certain silencing effect on medium and high frequency sound absorption. Poor performance at low frequencies.
2. Plate and format Silencers
The tubular muffler has poor low-frequency performance and is easy to pass through the medium and high rate noise. Moreover, when the pipe section area is large, it will affect the silencing effect of high-frequency noise. This is because the high-frequency sound wave (short wavelength) propagates in a narrow beam in the pipe. When the pipe area is large, the contact between the sound wave and the sound-absorbing material on the pipe wall is reduced, so that the silencing amount of high-frequency sound is reduced, Therefore, for the air duct with large section, the section can be divided into several grids, which are chip and format silencers. The plate muffler is widely used and has simple structure. The format muffler shall ensure that the useful sectional area is not less than the air duct section, so the volume is large, and the size of each grid should be controlled at 200mm × About 200mm. The spacing between the plates of the plate muffler is generally in the range of 100 ~ 200mm. When the spacing between the plates increases, the silencing amount will decrease accordingly.