Airborne noise control

R. D. Berendt and G. E. Winder, A Guide to Airborne, Impact, and Structure Rome Noise Control in Multifamily Dwellings, U.S. Department of Housing and Urban Development, Washington, D.C., 1963. 

In addition, depending on the type of chemicals and type of exposure, the respiratory tract should also be protected against inhalation of airborne contaminants, which can be in the form of particles, vapors or gases. Also, hearing protectors should not be forgotten. The need to use hearing protectors starts when the noise level, in spite of engineering control measures, exceeds the national limit value, which is 90 or 85 dB in many countries (Korhonen 1997). 

The most commonly used materials for control of noise in industry are sound-absorbing and barrier materials for airborne sound, and vibration isolators and dampers for structureborne sound. Selection of materials is often affected by factors other than acoustics. Factors include ... 

Noise is airborne sound energy within a broad range of frequencies that has the potential to cause either discomfort or injury to people working in the area. Specifically, noise needs to be controlled in order to ... 

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