A muffler is described for muffling both positive power and compression brake type engine retarders. The muffler includes an outer shell defining an internal volume. A first, inner, perforated wall is spaced from the outer shell and defines a first, annular, volume therebetween. A first volume of packing material is positioned within the annular volume. An inlet tube is oriented within the internal volume. In certain embodiments, the inner perforated wall circumscribes at least a portion of the inlet tube, and extends a distance of at least 25% of the axial length of the outer wall. Both single and dual muffler systems are described. Methods of use and operation are also provided.