outlet 18 can be permanently attached to the housing 12 such as by welding crimping etc again with the desire of forming a gas tight connection it is foreseeable that the outlet 18 could be adapted for removal instead of the inlet 16 or both the inlet 16 and outlet 18 could be removable so that the silencer cartridge unit 14 can be removed from either end 22 and 24 of the housing 12 the silencer cartridge unit 14 including its core wall 26 absorptive media 30 outer wall 38 and end walls 39 is a unit separate from the silencer housing 12 as a result of the core wall 26 enclosure 28 absorptive media 30 outer wall 38 and end walls 39 not being secured to the housing 12 as such the housing 12 can be installed as an essentially permanent component of the air flow system in which it is used whereas the silencer cartridge unit 14 can be manufactured as a disposable unit and simply replaced when its attenuation properties or overall condition degrades as may result from wear damage or accumulation of debris and particles from the air stream aging corrosion scaling and decomposition from weathering and corrosive agents in the air stream etc none of which is visible or otherwise readily apparent from the exterior of the silencer housing 12 the.