A muffler of simplified construction which compensates for variations in exhaust gas pressure and flow rate in order to eliminate back pressure from the muffler has a chamber in the form of a closed loop path having a given cross-sectional area. An inlet to the chamber and an outlet from the chamber are provided for the exhaust gas. A plurality of objects, such as hollow metal balls, dimensioned to substantially encompass the cross-sectional area of the closed loop path are movable around the path in response to force exerted by the exhaust gas. The spacing among the objects as they move around the path varies to compensate for changes in the exhaust gas pressure and flow rate, thus eliminating back pressure to an engine from the muffler.
