. . "Noise from pneumatic rock drills shape and exit noise of an exhaust muffler"@en . . . . . . "Studies were made to determine the effect of the shape of a pneumatic-rock-drill exhaust muffler on its efficiency, and the origin and reduction of exit noise from the mufflers. The report describes the investigation of rock-drill noise abatement."@en . . . . "Noise from pneumatic rock drills : shape and exit noise of an exhaust muffler"@en . . . . .