U.S. Bureau of Mines Makes a Compact Retrofit Muffler for Rock Drills.
Visnapuu-A; Martin-JR; Lay-SE; Schwaneke-AE
Eng and Min J 1978 Oct; 179(10):90-94
Some new drills are supplied with integral muffling, but a large number of older drills still in service have no mufflers. The retrofit muffler described here is an excellent way of reducing the exhaust-air noise of standard rotary percussion drills and other unmuffled pneumatic drilling systems.
Eng. and Min. J., V. 179, No. 10, October 1978, PP. 90-94