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Hearing loss may be caused by a number of factors, including: genetics, ageing, exposure to noise, some infections, birth complications, trauma to the ear, and certain medications or toxins.Use of the terms "hearing impaired," "deaf-mute," or "deaf and dumb" to describe deaf and hard of hearing people is discouraged by advocacy organizations as they are offensive to many deaf and hard of hearing people.There are many qualities of human hearing besides frequency range and amplitude that can't easily be measured quantitatively.But for many practical purposes, normative hearing is defined by a frequency versus amplitude graph, or audiogram, charting sensitivity thresholds of hearing at defined frequencies.Human hearing extends in frequency from 20-20,000 Hz, and in amplitude from 0 d B to 130 d B or more.0 d B does not represent absence of sound, but rather the softest sound an average unimpaired human ear can hear; some people can hear down to -5 or even -10 d B. But the ear doesn't hear all frequencies equally well; hearing sensitivity peaks around 3000 Hz.If one is exposed to loud sound (including music) at high levels or for extended durations (85 d B A or greater), then hearing loss will occur.
As 3 d B represents a doubling of intensity of sound, duration of exposure must be cut in half to maintain the same energy dose.
For workplace noise regulation, the "safe" daily exposure amount at 85 d B A, known as an exposure action value, is 8 hours, while the "safe" exposure at 91 d B(A) is only 2 hours.
Different standards use exposure action values between 80d BA and 90d BA.
Common sources of damaging noise levels include car stereos, children's toys, motor vehicles, crowds, lawn and maintenance equipment, power tools, gun use, musical instruments, and even hair dryers.
Noise damage is cumulative; all sources of damage must be considered to assess risk.
Hearing loss due to noise may be temporary, called a 'temporary threshold shift', a reduced sensitivity to sound over a wide frequency range resulting from exposure to a brief but very loud noise like a gunshot, firecracker, jet engine, jackhammer, etc.