Noise And Our Hearing
The inner ear of humans (and other vertebrates) contains a snail-shaped structure called a cochlea that is lined with thousands of microscopic hairs. When sound vibrations enter the cochlea, they cause the tiny hairs to move back and forth. If strong vibrations blast into the cochlea, the hairs can be flattened and damaged. The damage usually results in some degree of hearing loss.
Sound is measured in decibels (dB). Zero dB represents the quietest sound that a healthy human can hear. One hundred dB equals a noise that is 10 billion times as intense as one dB. Brief exposure to more than 110 dB can damage ears immediately; prolonged exposure to more than 85 dB can damage ears gradually.
Examples of decibel-level sounds that one may encounter in modern life are as follows:
- quiet library or soft whisper—30 dB
- normal conversation—50-60 dB
- busy traffic or noisy restaurant—70 dB
- subways, heavy city traffic, alarm clock at 2 ft (61 cm), or factory noise—80 dB
- noise in industrial plants, or call centers—90 dB
- train traveling 45 mi (28 km) per hour—93 dB
- chain saw, stereo headphones, night club or pneumatic drill—100 dB
- loudest sound that can be tolerated by the human ear—about 120 dB
- sound at a rock concert in front of speakers, sandblasting, or thunderclap—120 dB
- gunshot blast or jet plane—140 dB
- automobile drag race—171 dB
- sound at a rocket launching pad—180 dB
As noted, the most powerful sounds we encounter include jets taking off, loud amplified music, gun shots, and chain saws. Just a single exposure to these sounds can damage our ears.
We also damage our ears if we are exposed to noises that are less loud, but that are heard more often. For example, office workers who daily endure noise from telephones and loud machines may suffer some hearing loss over time. Workers in loud factories also experience hearing loss.
We can even hurt our hearing when we play. Motorboats, motorcycles, and snowmobiles all make loud noises likely to hurt our ears. Playing loud music on a personal stereo can also damage hearing. If someone near you can hear the music you are playing on your personal stereo, you are probably causing noise pollution for them and hearing loss for yourself.
Noise hurts more than our hearing. When we are exposed to loud noise, our bodies react as if we were in danger. Physiological responses to noise include increased heart rate, stress, eye conditions, muscle tension, elevated cholesterol levels and hormone secretion, and of course high blood pressure; even migraines can be induced by noise. Noise also impairs concentration. Studies have shown that children's learning and achievement can be also be affected by exposure to noise. Noise over 55 decibels can disrupt sleep and produce aggression if it is uninvited and persists long enough. While such a situation might be acceptable for a short time, millions of people around the world live with excessive noise every day and night.
A noise level of 75 decibels generates high levels of stress in most people. Tinnitus, or ringing in the ear, may occur at 80 decibels. The 100 decibels regularly encountered in night clubs can cause ear damage after only fifteen minutes. Noise can also induce mental states that lead to suicide and homicide. In Great Britain, anti-noise campaigners are keeping a count of the number of crime-related deaths that occur each year traceable to a response to noise.
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