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The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 10 1/10 (approximately 1.26) or root-power ratio of 10 1/20 (approximately 1.12). [1] [2]
Environmental noise regulations usually specify a maximum outdoor noise level of 60 to 65 dB(A), while occupational safety organizations recommend that the maximum exposure to noise is 40 hours per week at 85 to 90 dB(A). For every additional 3 dB(A), the maximum exposure time is reduced by a factor 2, e.g. 20 hours per week at 88 dB(A).
NIHL can be either permanent or temporary, called a threshold shift. Unsafe levels of noise can be as little as 70 dB (about twice as loud as normal conversation) if there is prolonged (24-hour) or continuous exposure. 125 dB (a loud rock concert is ~120 dB) is the pain level; sounds above this level cause instant and permanent ear damage.
Of these 65 million acquired the condition during childhood. [15] At birth ~3 per 1000 in developed countries and more than 6 per 1000 in developing countries have hearing problems. [15] Hearing loss increases with age. In those between 20 and 35 rates of hearing loss are 3% while in those 44 to 55 it is 11% and in those 65 to 85 it is 43%. [8]
Mild hearing loss is thresholds of 25–45 dB; moderate hearing loss is thresholds of 45–65 dB; severe hearing loss is thresholds of 65–85 dB; and profound hearing loss thresholds are greater than 85 dB. Tinnitus occurring in only one ear should prompt the clinician to initiate further evaluation for other etiologies.
One definition of signal-to-noise ratio is the ratio of the power of a signal (meaningful input) to the power of background noise (meaningless or unwanted input): =, where P is average power.
To determine noise levels, sounds are measured day and night and then averaged. If an area hits that 65 decibel level or higher, mitigation measures need to be taken.
PTS is measured in decibels. TTS (Temporary Threshold Shift) is a temporary change of the hearing threshold the hearing loss that will be recovered after a few hours to couple of days. Also called auditory fatigue. TTS is also measured in decibels. In addition to hearing loss, other external symptoms of an acoustic trauma can be: Tinnitus [10 ...