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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).
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]
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]
The ear can be exposed to short periods of sound in excess of 120 dB without permanent harm — albeit with discomfort and possibly pain — but long term exposure to sound levels over 85 dB(A) can cause permanent hearing loss. [31] There are two basic types of NIHL: NIHL caused by acoustic trauma; NIHL that gradually develops.
This is a list of roots, suffixes, and prefixes used in medical terminology, their meanings, and their etymologies. Most of them are combining forms in Neo-Latin and hence international scientific vocabulary. There are a few general rules about how they combine.
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.
Audiometry (from Latin audīre 'to hear' and metria 'to measure') is a branch of audiology and the science of measuring hearing acuity for variations in sound intensity and pitch and for tonal purity, involving thresholds and differing frequencies. [1]
Transmission loss (TL) in general describes the accumulated decrease in intensity of a waveform energy as a wave propagates outwards from a source, or as it propagates through a certain area or through a certain type of structure. It is a terminology frequently used in radio communication, twisted pair systems (PTSN, Ethernet, etc), optics and ...