ABSTRACT
When machinery with moving parts and parts in collision is run, sound is produced. This chapter focuses on the nature of sound and of hearing, how sound is measured, the levels of sound that cause hearing loss, and the means for protecting hearing. The greater the amplitude of the sound, the greater is its ability to cause damage to hearing. For purposes of analysis, the range of human hearing is divided into octave bands, eight ranges in each of which the highest frequency is twice the lowest frequency. Loss of hearing in the high-frequency range makes it difficult to distinguish words that differ only in the terminal consonant. The effectiveness of hearing protection can be estimated by determining the quietest sound audible with the protection off and in place at each of a range of frequencies.
