The main use of porous sound-absorbing materials to reduce noise. The sound-absorbing material is fixed on the inner wall of the airflow channel or arranged in a pipeline in a certain manner to form a resistive muffler. When the sound wave enters the resistive muffler, a part of the sound energy is rubbed in the pores of the porous material to be converted into thermal energy to be dissipated, which weakens the sound wave passing through the muffler. A resistive muffler is like a purely resistive electrical circuit, and the sound-absorbing material is similar to a resistor. Therefore, people call this muffler a resistive muffler. The resistive muffler has a good effect on the middle and high frequencies and has a poor effect on the low frequencies.