1、 Resistance muffler
The resistance muffler uses the sound absorption function of sound absorbing materials to eliminate noise. Its structure is to fix the sound absorbing material on the inner wall of the pipe with air flow, 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 is absorbed is the porosity and porosity of sound absorbing materials. When the sound wave enters the pore, the air and material in the pore will produce tiny vibration due to friction and viscous resistance. A considerable part of sound energy is converted into heat energy and absorbed.
It has good noise reduction effect on high-frequency and intermediate frequency noise, but poor noise reduction effect on low-frequency noise.
1. Pipe muffler
The tubular muffler is a simple muffler. It only sticks a layer of sound absorbing material on the inner edge of the pipe wall, so it is also called "pipe lining". It is characterized by convenient manufacturing and small resistance, but it is only applicable to small air ducts, and the diameter generally does not exceed 400mm. The tubular muffler has a certain sound attenuation effect only for medium and high frequency sound absorption. Poor performance at low frequencies.
2. Plate and format muffler
管式消聲器低頻性能差，易通過中、高速率噪聲。此外，當管道截面面積較大時，會影響高頻噪聲的消聲效果。這是因為高頻聲波(短波長)在管道中以窄束傳播。管面積大時,聲波之間的聯系和管壁上的吸聲材料降低,這樣沉默的高頻聲音降低,因此,空氣管的很大部分,部分可分為幾個網格,芯片和格式消音器。片狀消聲器應用廣泛，結構簡單。格式消聲器的有效截面積不得小于風管的截面積，因此體積較大，每個格網的尺寸應控制在200mm × 200mm左右。板式消聲器的板間間距一般在100 ~ 200mm范圍內。當板間距加大時，消聲量相應減小。
The tubular muffler has poor low frequency performance and is easy to pass through medium and high speed noise. In addition, when the pipe section area is large, it will affect the noise reduction effect of high-frequency noise. This is because high-frequency sound waves (short wavelengths) travel in narrow beams in the pipe. When the pipe area is large, the connection between sound waves and the sound absorbing material on the pipe wall will be reduced, so the silent high-frequency sound will be reduced. Therefore, a large part of the air pipe can be divided into several grids, chips and format silencers. The sheet muffler is widely used and simple in structure. The effective sectional area of the format muffler shall not be less than the sectional area of the air duct, so the volume is large, and the size of each grid shall be controlled within 200mm × About 200mm. The spacing between plates of plate muffler is generally 100~200mm. When the plate spacing increases, the noise reduction amount decreases accordingly.
2、 Resonant muffler
The absorption capacity of sound absorbing materials to low-frequency noise is usually very low. It is not economical to improve the sound absorption effect only by increasing the thickness of the sound absorption material. In order to improve the sound absorption effect of low-frequency noise, resonant muffler is usually used. The resonant muffler is in the form that the nozzle is connected with the resonant cavity, and the air column at the small hole forms an elastic resonant system with the air in the cavity. When the frequency of the external noise is the same as the natural frequency of the resonance system, the air column in the hole will resonate and rub violently with the hole wall, which can consume sound energy, so as to achieve the purpose of noise elimination