The double 3.75 "end muffler is T-304 Stainless Steel TIG welded, with limited service life, stainless steel mesh wrapped hole core and high-quality glass fiber packaging. The resistance loss of the muffler can generally be expressed by negative pressure difference and resistance coefficient. Considering that the cross sections of the inlet and outlet of the muffler are different and the air velocity is equal, so the dynamic pressure is the same, and the resistance loss only depends on the change of negative pressure. The negative pressure difference is defined as the negative pressure difference between the inlet and outlet of the muffler, and the negative pressure difference is defined as the dynamic pressure ratio on the end face of the measuring point. The smaller the negative pressure difference and resistance coefficient, the smaller the resistance loss of the muffler.