1. Ventilation duct resistance muffler: It absorbs sound energy and reduces noise by absorbing sound data inside the box. It is commonly used to eliminate high and intermediate frequency noise. However, it is not suitable for high temperature, high humidity and high speed because of the structure.

　　2、抗式消声器：是经过改动截面来消声的。我们常用的消声静压箱都是这个原理。普通降低中、低频噪音，对风系统没有详细的请求。

　　2. Reactor muffler: It is muffled by changing cross section. This is the principle of our commonly used silencing static pressure box. Normally, there is no detailed request for wind system to reduce medium and low frequency noise. 

　　3、阻抗复合式：当然是分离二者的构造原理。能够消弭低中高频噪音。但是对风系统的请求同阻式消声器关于普通的民用空调通风系统，我个人以为选用阻抗复合消声器为好。阻性消声用具有良好的中高频消声性能。按气流通道几何外形不同，可分为直管式、片式、折板式、迷宫式、蜂窝式、声流式、障板式、弯头式等。

　　3. Impedance Compound: Of course, it is the construction principle of separating the two. It can eliminate low, medium and high frequency noise. But for the requirement of the air system, I personally think it is better to choose the impedance compound muffler for the ordinary civil air conditioning and ventilation system. Resistive silencer has good performance of medium and high frequency noise elimination. According to the geometrical shape of airflow passage, it can be divided into straight tube type, sheet type, folded plate type, labyrinth type, honeycomb type, acoustic flow type, baffle type, elbow type, etc.

　　抗性消声器适用于消弭中低频噪声或窄带噪声。按其作用原理不同，可分为扩张式、共振腔式和干预式等多种型式。阻抗复合式消声器，有共振腔、扩张室、穿孔屏等声学滤波器件，综合了阻性消声器良好的中高频消声特性和阻抗性消声器较好的低频消声特性，因而其消声频带宽，它是常用的规范消声器系列之一。

　　Resistant mufflers are suitable for eliminating medium and low frequency noise or narrowband noise. According to its different principles, it can be divided into expansion type, resonant cavity type and intervention type. Impedance compound muffler has resonant cavity, expansion chamber, perforated screen and other acoustic filters. It combines the good middle and high frequency muffler characteristics and the good low frequency muffler characteristics of impedance muffler. Therefore, its muffling frequency bandwidth is one of the most commonly used standard muffler series.

　　适合风速为6～8米/秒，高可到达8～12米，可单独运用，也可串联运用。消声效果：低频10～15dB/m，中频15～25dB/m，高频25～30dB/m，均匀阻力系数为0.4。依据《空气调理》，消声弯头、消声静压箱均属于消声器的一种。消声器是一种既能允许气流经过，又能有效地阻止或削弱声能向外传播的安装。

　　Suitable for wind speed of 6-8 m/s, up to 8-12 m, can be used alone or in series. Acoustic attenuation effect: low frequency 10-15 dB/m, medium frequency 15-25 dB/m, high frequency 25-30 dB/m, uniform resistance coefficient 0.4. According to Air Conditioning, muffler elbow and muffler static pressure box belong to one kind of muffler. Muffler is a kind of installation which can not only allow air to pass through, but also effectively prevent or weaken the sound energy to spread outward.