CASE-HISTORY - NOISE-CONTROL IN AIRPLANE MANUFACTURING

In an airplane factory, noise from riveting produces short-duration, h igh-amplitude sounds with high-level components at frequencies where t he human ear is most sensitive. High-pressure air exhausted from air-p owered tools is another prevalent noise source in airplane manufacture and repair and can be a major contributor to a worker's daily exposur e to noise. Control of the impulsive sound of riveting without affecti ng production was achieved by developing a new way to apply constraine d-layer damping pads to the skin of an aluminum panel. A pad is held a gainst a panel by a vacuum pressure of about 90 kPa. The time-average, A-weighted sound level at a position representative of the ear of the operator of a riveting hammer was reduced by about 5.5 dB by applicat ion of the damping pads. Compressed-air tool-exhaust noise was reduced by multi-cavity mufflers consisting of reactive (tuned), resistive, a nd dispersive elements. The total 8-hour-average. A-weighted sound lev el was reduced from approximately 93 dB to approximately 85 dB at the location of a worker exposed to the noise from tools powered by compre ssed air. (C) 1996 Institute of Noise Control Engineering.