MUFFLER

PURPOSE:To effectively attenuate noise even if the frequency of the generated noise varies, by installing a partitioning wall in a shiftable manner in a body and changing the position by operating a motor. CONSTITUTION:A muffler 6 is constituted by assembling partitioning walls 62-64 and a movable wall 65 alternately in superposed state on a fixed wall 61 having an edge wall, 61a fixed on an intake pipe 3 and a cylinder part 61b, and these parts can be shifted by motors 62M-65M. A rotary shaft 7 is connected with the rotary shaft of a motor 7M, and shutters 72-75 are fitted on the rotary shaft 7 so as to be slidable in the axis line direction. When the motors 62M-65M are operated, and the partitioning walls 62-64 and the movable wall 65 are shifted, also the shutter plates 72-75 shift along the rotary shaft 7. Since the frequency which is effectively attenuated by the muffler 6 is determined according to the capacity of the inside space, in particular the distance of the inner wall of the space, the noise having the frequency after variation is effectively attenuated by shifting the partitioning walls 62-64 and the movable wall 65, when the frequency of the noise generated from a noise source varied.