A muffler for internal combustion engines in which the structure cancels sound waves by interference. The gases generally flow in one direction through the muffler with intermittant flow reversal occurring only upon acceleration. The muffler is formed with a plurality of longitudinal chambers divided by reflection walls. Edge echo openings in the reflection walls permit limited gas entry into the chambers. A plurality of helical members surrounded by a large open tube and pierced by a small open tube channel all of the gases through a bulkhead wall which divides the muffler housing into two volumetrically generally equal portions.
