General Acoustical Theory
Practically speaking, noise is any sound that is considered excessive or annoying. From a technical standpoint, noise is a pressure wave as detected by the ear. The ear distinguishes both the frequency (pitch) and the intensity or magnitude.
Generally, of two noise sources of equal magnitude but different frequency, the higher frequency noise will be perceived to be more undesirable. Fortunately, these higher frequency noise sources are also more readily treated with various control measures.
The human ear is amazingly versatile, able to pick up very faint whispers of sound on the one hand, to a deafening noise over a hundred million times greater. Being such a finely tuned instrument, it is also very susceptible to gradual erosion of this phenomenal range by surprisingly low levels of noise. Also, potentially dangerous fatigue and mental stupor can affect the body, as well as the ears, from being “bombarded” with sound pressure waves.
Comparative studies of urban and rural cultures around the world have shown that a lifetime of exposure to a generally higher background level of noise, even if this background noise is not extremely high, will cause the same amount of hearing loss caused by shorter exposure to a higher noise level.