There are many definitions of noise, some technical and some philosophical. A common definition for noise is any loud, irritating, surprising, or unwanted sound made by humans, animals, nature, or machines. However, what is music to one person's ears might be noise to someone else and music along with parties can be a problem in crowded residential areas. For the most part, noise pollution is any unwanted sound or any sound that interferes with hearing, causes stress, or disrupts one's life. The source of most outdoor noise comes from construction and transportation systems, including the noise from motor vehicles, aircraft, and railroads. For instance, a commercial jet preparing to land and flying over a residential area may likely produce noise pollution to these residents. Sound is measured either in dynes, watts, or decibels. Usually 80 decibels (db) is the level at which sound becomes physically painful; thus, it is often denoted as noise. Note that decibels are logarithmic; that is, a ten decibel (db) increase represents a doubling of sound energy.
The sensitivity and discrimination of one's hearing is remarkable. Normally, humans can hear sounds between 16 and 20,000 hertz (hz). A young child whose hearing has not yet been damaged by excess noise can hear the whine of a mosquito's wings at the window when less than one quadrillionth of a watt per square centimeter is reaching the eardrum.
The sensory cell's microvilli are flexible and resilient, but only up to a point. They can bend and then spring back up, but they die if they are smashed down too hard or too often. Prolonged exposure to sounds above about 90 decibels can flatten some of the microvilli permanently, and their function will be lost. By age thirty years, most Americans have lost five decibels of sensitivity and cannot hear anything above 16,000 hertz; by age sixty-five, the sensitivity reduction is 40 decibels for most people, and all sounds above 8,000 hertz are lost. By contrast, in the African country of Sudan, where the environment is very quiet, even 70-year-olds have insignificant hearing loss.
Noises come from many sources. Traffic is generally the most omnipresent noise in the city. Cars, trucks, and buses create a roar that permeates nearly everywhere. Around airports, jets thunder overhead, stopping conversation, rattling dishes, sometimes even cracking walls. Jackhammers rattle in the streets; sirens pierce the air; motorcycles, lawn mowers, snow blowers, and chain saws create an infernal din; and music from radios, televisions, and loudspeakers fill the air everywhere.
Every year since 1973, the U.S. Department of Housing and Urban Development has conducted a survey to find out what city residents dislike about their environment. Every year the same factor has been near or at the top of the list as most objectionable. It is not crime, pollution, or congestion; it is noise—something that affects every person every day.
The U.S. Census Bureau stated that based on its 2009 American Housing Survey about 25.4 million people in the United States—out of a total of about 111.8 million households,—reported being upset or irritated by street noise or heavy traffic. A study by the World Health Organization found that environmental noise in Western Europe caused annoyance in many people, but it also caused much more serious medical conditions such as cardiovascular disease, cognitive impairment, sleep disturbances, and tinnitus.
It has been known for a long time that prolonged exposure to noises, such as loud music or the roar of machinery, can result in hearing loss. Evidence now suggests that noise-related stress also causes a wide range of psychological and physiological problems, ranging from irritability to heart disease. An increasing number of people are affected by noise in their environment. By the age of 40, nearly everyone in the United States has suffered hearing deterioration in the higher frequencies. An estimated 10% of Americans (30 million people) suffer serious hearing loss, and the lives of at least another 80 million people are significantly disrupted by noise.
Extremely loud sounds—above 130 decibels, the level of a loud rock band or music heard through earphones at a high setting—actually can rip out the sensory microvilli, causing aberrant nerve signals that the brain interprets as a high-pitched whine or whistle. Many people experience ringing ears after exposure to very loud noises. Coffee, aspirin, certain antibiotics, and fever also can cause ringing sensations, but they usually are temporary.
One of the symptoms of noise pollution is hearing loss and related problems. For instance, a persistent ringing is called tinnitus. It has been estimated that 94% of the people in the United States suffer from some degree of tinnitus. For most people, the ringing is noticeable only in a very quiet environment, and they rarely are in a place that is quiet enough to hear it. About 35 out of 1,000 people have tinnitus severe enough to for it to interfere with their lives. Sometimes the ringing becomes so loud that it is unendurable, resembling the shrieking brakes on a subway train. Unfortunately, there is not yet a treatment for this distressing disorder. One of the first charges to the Environmental Protection Agency (EPA) when it was founded in 1970 was to study noise pollution and to recommend ways to reduce the noise in one's environment. Standards have since been promulgated for noise reduction in automobiles, trucks, buses, motorcycles, mopeds, refrigeration units, power lawnmowers, construction equipment, airplanes, and many other noise-producing devices and machines. The EPA has considered ordering that noise warnings be placed on power tools, radios, chain saws, and other household equipment. The Occupational Safety and Health Administration (OSHA) also has set standards for noise in the workplace that have considerably reduced noise-related hearing losses.
Whether self-inflicted or just part of everyday living noise can cause temporary or permanent deafness. When one is around noise for long periods of time, the risk of deafness is increased. For instance, train engineers, automobile mechanics, and construction workers are at increased risk for being hearing impaired, as are musicians in musical bands or listeners of their music. The most dangerous noise is that to which people voluntarily subject themselves while listening to music. In-ear headphones commonly used with portable media devices may reduce noise pollution for others but cause negative health problems in the wearer at volumes over 50 decibels.
Another problem caused by noise is decreased efficiency at work. Medical research has proven that the efficiency of a worker decreases as more noise is introduced. Most workers are disturbed by noise, which can affect their concentration at performing their jobs. The first and foremost effect of noise is a decrease in the efficiency in working. Research has proved that human efficiency increases with noise reduction. Fatigue is another problem caused by noise. Because people are adversely affected by noise, they often take more time to complete their tasks, which leads to fatigue.
Stress levels are usually higher for people working around noise. Continued stress can lead to such medical conditions as anxiety, high blood pressure (hypertension), depression, and other such problems. If noise continues for long periods, it can eventually lead to mental illness and damage to the nervous system.
Treatment for temporary or reversible hearing loss from noise pollution may be as simple as removing the source of the noise. However, permanent hearing loss may require hearing devices or hearing implants. Hearing aids help to make sounds louder by amplifying the sound waves that enter the ear. Although they do not restore hearing, they may help a person to function and communicate more easily. Hearing implants are devices that are worn outside or inside the ear. A cochlear implant is a type of implantable hearing device.
An audiologist can help to determine whether one's hearing has been compromised by noise pollution. Such a visit should be the first step to diagnosing and treating hearing loss. This medical professional will assist in determining the extent of hearing loss through a comprehensive hearing evaluation. If hearing loss is found, the audiologist may recommend various aids such as a change in lifestyle, hearing aids or other assistive listening devices, or surgery.
It is difficult to totally eliminate noise from busy society, but it can be reduced to more tolerable levels. Noises can be reduced by using white noise machines that play soothing sounds such as raindrops falling on a roof. Music at comfortable levels can also be played on a music device (such as an iPod) or a stereo in order to drown out irritating noises. White noise is also helpful when irritating noises in the night make it difficult to sleep. Meditation can also help to reduce stress levels caused by noise pollution.
Noise can be prevented, or at least reduced, by the use of devices, laws, materials, and technology. Devices such as noise barriers can reduce roadway noise that occurs next to residential neighborhoods. Tees planted along busy roads, for instance, can block much of the noise that can otherwise impinge on people living nearby. Another solution for reducing road noise is limiting vehicle speeds on roads and highways, along with improving the texture of roadway surfaces, limiting the movement of heavy vehicles, improving tire design, and the use of traffic control systems that reduce the amount of braking and acceleration. Computer models are often designed to consider such factors when building new roads or making improvements on existing ones. These models take into account local topography, meteorological conditions, and population densities, to name a few.
For aircraft, engines are developed so they run more quiet than in the past. In addition, computer models are run to find the flight path than interferes the least with residential communities.
See also Clean Air Act (1963, 1970, 1977, 1990) ; Environmental Protection Agency (EPA ; Occupational Safety and Health Administration ; World Health Organization .
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Better Hearing Institute, 1444 I St. NW, Ste. 700, Washington, D.C., 20005, (202) 449-1100, Fax: (202) 216-9646, email@example.com, http://www.betterhearing.org .
Environmental Protection Agency, 1200 Pennsylvania Ave. NW, Washington, DC, 20460, (202) 272-0167, http://water.epa.gov .
National Hearing Conservation Association, 3030 W 81st Ave., Westminster, CO, 80031, (303) 224-9022, Fax: (303) 458-0002, nhcaoffice@hearingconservation. org, http://www.hearingconservation.org .
William P. Cunningham
Revised by William A. Atkins, BB, BS, MBA