An exhaust silencing device comprises an outer tube that is pinched down to form a series of annular chambers around a coaxial inner gas flow tube and has openings connecting the chambers to provide for some secondary gas flow parallel to primary flow through the tube. The device and is shown in conjunction...http://www.google.com/patents/US4744440?utm_source=gb-gplus-sharePatent US4744440 - Exhaust gas silencing device
