... Efficient Duct mufflersize 4" miniDuct mufflerFine structure ,Practical, Strong,Appearance perfectMaterials1.Up and down the cover Spinning, punching2.Level 1 ... fan, air compressor, boiler vent, generators, water pumps and other vent noise larger equipment)3.gas flow path or ... exhaust system,reduce the noise device,Prevent noise pollution4.Simple structure, practical5.Sound-absorbing effect:85%6.Easy ...