It is divided into two parts: one part is related to the periodic rotation of the engine and is called infrasound; The other part is the exhaust flow, which produces a sound called air flow in the air, and the enchanting sound waves pursued by modified exhaust are all infrasound. To highlight the musical scale, it is necessary to reduce the sound of the airflow. The usual method is to use sound-absorbing cotton, thicken the exhaust pipe, and reduce the exhaust velocity, thus reducing the airflow.
