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.

阻性消声器利用吸声材料的吸声作用而消声的。其构造是把吸声材料固定在气流流动的管道内壁，或按一定方式排列在管道或壳体内构成阻性消声器，吸声材料能够把入射在其上的声能部分地吸收掉。声能之所以能被吸收，是由于吸声材料的多孔性和松散性。当声波进入孔隙，引起孔隙中的空气和材料产生微小的振动，由于摩擦和粘滞阻力。使相当一部分声能化为热 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.

它对于高频和中频噪声效果较好，但对低频噪声消声性能较差。

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

1、管式消声器

1. Tubular muffler

管式消声器是一种简单的消声器，它仅在管壁内周贴上一层吸声材料，故又称“管衬”。特点是制作方便，阻力小，但只适用于较小的风道，直径一般不大于400mm风管。管式消声器仅对中、高频率吸声有一定的消声作用。对低频性能很差。

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、片式和格式消声器

2. Plate and format Silencers

管式消声器对低频性能很差，对中、高额率噪声又易直通，并且当管道段面积较大时，会影响对高频噪声的消声效果，这是由于高频声波（波长短）在管内以窄束传播，当管道面积较大时，声波与管壁吸声材料接触减少，从而使高频声的消声量减少，因此对断面较大的风管可将断面分成几个格子，这就是片式及格式消声器。片式消声器应用广泛，构造简单，格式消声器要保证有用断面积不小于风道断面，因而体积较大，每格的尺寸宜控制在200mm×200mm左右。片式消声器的片间距一般在100~200mm的范围内，片间距增 大时，消声量会相应地下降。

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.