The use of
fiber metal or similarly high flow resistance and high acoustic transparency material as a liner for traditional acoustically absorptive media in a dissipative
muffler exhibits improved
low frequency sound attenuation, reduces backpressure, and eliminates media entrainment or "blow-out" phenomenon which results in longer
muffler life. The same class of materials may also be used to fashion an element that provides linear
occlusion inside an otherwise line-of-
sight type of
muffler, where the occluding element provides improved impedance-matching
acoustic absorption. Disclosed embodiments providing linear
occlusion minimize traditional increases in muffler backpressure by incorporating
helical, conical, and annular members in mufflers with round ducts. To maximize attenuation, a muffler according to the invention may feature both a
fiber metal fill liner and a
fiber metal linear
occlusion element. Further, the liner that connects the inlet and outlet ports of the muffler may feature an offset,
elbow, or turn that would simultaneously allow it to provide means for linear occlusion.