Book Description

"One-third octave spectrum analyses of the exhaust noise produced by a medium sized pneumatic rock drill were obtained during free recriprocation to determine the most troublesome bands of noise. Noise reduction techniques were then used to design exhaust mufflers which would reduce the level of the exhaust noise to an acceptable level with a minimum increase in back pressure. The prototype mufflers evaluated included an expansion chamber, a resonator, and various modified expansion chambers. One of the modified expansion chambers tested provided very good attenuation reducing the exhaust noise from 113 dBA to 87 dBA at the operator's ear position. It caused only a slight increase in the back pressure and no detrimental effect on drill performance. The resonator muffler did not provide acceptable attenuation of the exhaust noise. Muffler development progressed under the assumption that icing would not be a problem. However, the icing characteristics of the final prototype muffler were studied and a possible method to prevent icing is suggested"--Abstract, leaf ii.