... gas not arise the dustperforation muffler has small resistance loss. Checke 1,Mufflers Type WX, consisting of zincification(or allumium ... because of different perforation and double-layer perforation. This muffler can eliminate noise in low frequency; in middle frequency. ... contioners and ventilating pipes.3,perforation muffler has small resistance loss. Checked, the muffler has a resistance 0.7-3mmH20 ...