It is divided into two parts: one part is related to the periodic rotation of the engine, which is called order sound; The other part is the tail gas flow, which produces a sound called air flow in the air, while the attractive sound waves pursued by the modified exhaust are all order sounds. In order to highlight the scale, it is necessary to reduce the sound of airflow. The usual method is to use sound-absorbing cotton, make the exhaust pipe thicker and reduce the velocity of exhaust gas, thus reducing the airflow.