Noise
Noise refers to unwanted or unintended sounds that disrupt other auditory experiences. It can manifest in various contexts, including acoustics, where it is recognized as sounds audible to the human ear or perceived through vibrations. The United States Environmental Protection Agency classifies noise pollution as sounds that interfere with normal activities like sleeping or conversing, often originating from sources such as traffic, construction, or sporting events. Noise levels are measured in decibels (dB), with different sounds ranging from a quiet whisper at about 30 dB to a jet aircraft at around 140 dB. Regulations regarding acceptable noise levels vary across communities, reflecting local preferences and the impact of noise on daily life.
In addition to acoustic noise, electronic noise also plays a significant role; it refers to unwanted electrical energy that disrupts signals, often encountered in radio and television technology. This interference can arise from various sources, including thermal movements in conductors or atmospheric conditions. Notably, certain scientific findings suggest that human-created noise can affect wildlife, particularly marine life, which relies on sound for communication. Overall, noise, whether auditory or electrical, can significantly influence both human activities and natural environments.
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Noise
Noise is an undesired or unintended sound or signal that interferes with other sounds or signals. There are several classifications of noise depending on the medium. In acoustics, noise is a sound disruption audible to the human ear or perceived through vibration. Electrical noise is a fluctuation or disturbance in an electrical signal. In radio transmissions, this interference is called static; in older television sets, it is known as snow.
Acoustic Noise
Sounds are vibrations that travel through air or another medium and are heard when they are perceived by a receptor, such as the human ear. Sound waves are constantly being generated by many sources on the planet. When these sounds fall within acceptable levels, they usually go unnoticed or are incorporated as part of the background of daily life.
An unwanted sound or one that is so loud as to be disturbing is called noise. In its definition of noise pollution, the United States Environmental Protection Agency (EPA) classifies an unwanted sound as one that "interferes with normal activities such as sleeping, conversation, or disrupts or diminishes one’s quality of life." Such noise can originate from road traffic, aircraft, construction, sporting events, businesses, and many other sources.
One of the ways to gauge noise is by decibel level (dB), a measure of a sound's intensity. The sound of a quiet whisper, for example, has a decibel level of about 30. A vacuum cleaner or hair dryer is about 70 dB; city traffic about 80 dB; a chainsaw about 100 dB; and a jet aircraft about 140 dB. The average human pain threshold is about 110 dB, although the EPA has classified sounds above 65 dB as "annoying." The decibel level of noise is also a relative measure of an impact on a community. Traffic and aircraft noise are more common in a larger city and would be more tolerated, while even the engine hum of one plane might meet with resistance in a rural community.
EPA guidelines set during the 1970s state the average acceptable level for aircraft noise in residential communities is 55 dB. The Federal Aviation Administration (FAA) has set an average level of 65 dB. These numbers are taken into consideration when airport construction or expansion plans are formulated. To lessen noise from highway traffic, the Federal Highway Administration has constructed noise barriers to shield nearby homes. These barriers have been found to lower the noise rate by 10 to 15 dB.
Local noise regulations vary across the country and are often tailored to fit the desires of the community. Car alarms, emergency vehicle sirens, and construction work may be an annoyance to city residents, but regulating that noise involves lessening its impact, not eliminating it. In rural communities, industrial noise or noise from vehicles such as snowmobiles or watercraft may prompt a zoning change or a call to ban recreational activity.
While there is limited data on the effect of noise on animals and wildlife, some scientists have found that human-generated sounds do impact certain forms of marine life. The noise produced by shipping activity in the oceans interferes with the ability of whales to communicate and locate each other across distances. This noise pollution poses a serious threat to the animals and prompted the International Maritime Organization to set new guidelines for ship propellers in 2013.
Electronic Noise
Electronic noise is not generated by sound waves but is unwanted electrical energy that interferes with reception and disrupts a signal. Such energy is common and can come from internal or external sources. Internal sources can be fixed through engineering means, while external interference can only be reduced by moving the receiver.
Thermal noise is a form of internal interference caused by the random movement of electrons as they interact with charged atoms in a conductor. Since particles are more active at higher temperatures, the potential for noise is greater under those conditions. Shot noise is the random movement of electrons in an electrical current. Transit-time noise is interference that is more common at higher frequencies.
External noise can be caused by atmospheric factors, such as thunderstorms or interference from electrical devices or power lines. This disruption becomes audible as a crackling noise called static and is more common at lower frequencies, such as on the AM radio dial. Interference from some man-made sources, such as aviation signals or two-way radios, can cause noise at higher frequencies. On televisions made before digital capability, the electrical disruption left a random pattern on the screen called snow. In the United States, a conversion to digital broadcast technology in 2009 all but eliminated this effect.
Some of the external electronic noise comes from the sun, which emits a constant stream of energy along a wide range of frequencies. This energy can cause disruptions in radio and television communications, and increases as the sun becomes more active. A small amount of electrical interference originates from outside our solar system. Distant stars and galaxies are also energy sources, which occasionally produce disruptions that find their way to Earth. Some radio and TV noise is even the signature left over from the birth of the universe. About 1 percent of electronic interference on Earth comes from background radiation from the big bang, which is believed to have created the universe about 13.7 billion years ago.
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