Pneumatic muffler noise.

Sixty-five commercial pneumatic mufflers in the size range of 1/8 to 3/8-inch American Standard Taper Pipe Thread (NPT) were evaluated for noise level as a function of air supply pressure and back pressure. Also, typical directivity pattern and spectral content were determined. A rating system has been devised, as well as individual prediction formulas, to rank order the mufflers and provide a capability of calculating expected noise levels for a given supply pressure. As this study reveals, noise reductions in excess of 40 dBA may be achieved by employing an efficient pneumatic muffler.