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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.

阻性消聲器利用吸聲材料的吸聲作用而消聲的。其構造是把吸聲材料固定在氣流流動的管道內壁，或按一定方式排列在管道或殼體內構成阻性消聲器，吸聲材料能夠把入射在其上的聲能部分地吸收掉。聲能之所以能被吸收，是由于吸聲材料的多孔性和松散性。當聲波進入孔隙，引起孔隙中的空氣和材料產生微小的振動，由于摩擦和粘滯阻力。使相當一部分聲能化為熱 能而被吸收掉。

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.

它對于高頻和中頻噪聲效果較好，但對低頻噪聲消聲性能較差。

It has good effect on high-frequency and intermediate frequency noise, but poor silencing performance on low-frequency noise.

1、管式消聲器

1. Tubular muffler

管式消聲器是一種簡單的消聲器，它僅在管壁內周貼上一層吸聲材料，故又稱“管襯”。特點是制作方便，阻力小，但只適用于較小的風道，直徑一般不大于400mm風管。管式消聲器僅對中、高頻率吸聲有一定的消聲作用。對低頻性能很差。

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、片式和格式消聲器

2. Plate and format Silencers

管式消聲器對低頻性能很差，對中、高額率噪聲又易直通，并且當管道段面積較大時，會影響對高頻噪聲的消聲效果，這是由于高頻聲波（波長短）在管內以窄束傳播，當管道面積較大時，聲波與管壁吸聲材料接觸減少，從而使高頻聲的消聲量減少，因此對斷面較大的風管可將斷面分成幾個格子，這就是片式及格式消聲器。片式消聲器應用廣泛，構造簡單，格式消聲器要保證有用斷面積不小于風道斷面，因而體積較大，每格的尺寸宜控制在200mm×200mm左右。片式消聲器的片間距一般在100~200mm的范圍內，片間距增 大時，消聲量會相應地下降。

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.