Image noise is random variation of brightness or color information in images, is an aspect of electronic noise. It can be produced by the circuitry of a scanner or digital camera. Image noise can originate in film grain and in the unavoidable shot noise of an ideal photon detector. Image noise is an undesirable by-product of image capture; the original meaning of "noise" was "unwanted signal". By analogy, unwanted electrical fluctuations are called "noise". Image noise can range from imperceptible specks on a digital photograph taken in good light, to optical and radioastronomical images that are entirely noise, from which a small amount of information can be derived by sophisticated processing; such a noise level would be unacceptable in a photograph since it would be impossible to determine the subject. Principal sources of Gaussian noise in digital images arise during acquisition; the sensor has inherent noise due to the level of illumination and its own temperature, the electronic circuits connected to the sensor inject their own share of electronic circuit noise.
A typical model of image noise is Gaussian, independent at each pixel, independent of the signal intensity, caused by Johnson–Nyquist noise, including that which comes from the reset noise of capacitors. Amplifier noise is a major part of the "read noise" of an image sensor, that is, of the constant noise level in dark areas of the image. In color cameras where more amplification is used in the blue color channel than in the green or red channel, there can be more noise in the blue channel. At higher exposures, image sensor noise is dominated by shot noise, not Gaussian and not independent of signal intensity. There are many Gaussian denoising algorithms. Fat-tail distributed or "impulsive" noise is sometimes called spike noise. An image containing salt-and-pepper noise will have dark pixels in bright regions and bright pixels in dark regions; this type of noise can be caused by analog-to-digital converter errors, bit errors in transmission, etc. It can be eliminated by using dark frame subtraction, median filtering, combined median and mean filtering and interpolating around dark/bright pixels.
Dead pixels in an LCD monitor produce a non-random, display. The dominant noise in the darker parts of an image from an image sensor is that caused by statistical quantum fluctuations, that is, variation in the number of photons sensed at a given exposure level; this noise is known as photon shot noise. Shot noise has a root-mean-square value proportional to the square root of the image intensity, the noises at different pixels are independent of one another. Shot noise follows a Poisson distribution, which except at low intensity levels approximates a Gaussian distribution. In addition to photon shot noise, there can be additional shot noise from the dark leakage current in the image sensor. Dark current is greatest at "hot pixels" within the image sensor; the variable dark charge of normal and hot pixels can be subtracted off, leaving only the shot noise, or random component, of the leakage. If dark-frame subtraction is not done, or if the exposure time is long enough that the hot pixel charge exceeds the linear charge capacity, the noise will be more than just shot noise, hot pixels appear as salt-and-pepper noise.
The noise caused by quantizing the pixels of a sensed image to a number of discrete levels is known as quantization noise. It has an uniform distribution. Though it can be signal dependent, it will be signal independent if other noise sources are big enough to cause dithering, or if dithering is explicitly applied; the grain of photographic film is a signal-dependent noise, with similar statistical distribution to shot noise. If film grains are uniformly distributed, if each grain has an equal and independent probability of developing to a dark silver grain after absorbing photons the number of such dark grains in an area will be random with a binomial distribution. In areas where the probability is low, this distribution will be close to the classic Poisson distribution of shot noise. A simple Gaussian distribution is used as an adequately accurate model. Film grain is regarded as a nearly isotropic noise source, its effect is made worse by the distribution of silver halide grains in the film being random.
Some noise sources show up with a significant orientation in images. For example, image sensors are sometimes subject to row column noise. A common source of periodic noise in an image is from electrical or electromechanical interference during the image capturing process. An image affected by periodic noise will look like a repeating pattern has been added on top of the original image. In the frequency domain this type of noise can be seen as discrete spikes. Significant reduction of this noise can be achieved by applying notch filters in the frequency domain; the following images illustrate an image affected by periodic noise, the result of reducing the noise using frequency domain filtering. Note that the filtered image still has some noise on the borders. Further filtering could reduce this border noise, however it may reduce some of the fine details in the image; the trade-off between noise reduction and preserving fine details is application specific. For example if the fine details on the castle are not considered important, further low pass filtering c
Atmospheric noise is radio noise caused by natural atmospheric processes lightning discharges in thunderstorms. On a worldwide scale, there are about 40 lightning flashes per second – ≈3.5 million lightning discharges per day. In 1925, AT&T Bell Laboratories started investigating the sources of noise in its transatlantic radio telephone service. Karl Jansky, a 22-year-old researcher, undertook the task. By 1930, a radio antenna for a wavelength of 14.6 meters was constructed in Holmdel, NJ, to measure the noise in all directions. Jansky recognized three sources of radio noise; the first source was local thunderstorms. The second source was weaker noise from more distant thunderstorms; the third source was a still weaker hiss that turned out to be galactic noise from the center of the Milky Way. Jansky's research made him the father of radio astronomy. Atmospheric noise is radio noise caused by natural atmospheric processes lightning discharges in thunderstorms, it is caused by cloud-to-ground flashes as the current is much stronger than that of cloud-to-cloud flashes.
On a worldwide scale, 3.5 million lightning flashes occur daily. This is about 40 lightning flashes per second; the sum of all these lightning flashes results in atmospheric noise. It can be observed, with a radio receiver, in the form of a combination of white noise and impulse noise; the power-sum varies with nearness of thunderstorm centers. Although lightning has a broad-spectrum emission, its noise power increases with decreasing frequency. Therefore, at low frequency and low frequency, atmospheric noise dominates, while at high frequency, man-made noise dominates in urban areas. From 1960s to 1980s, a worldwide effort was made to measure variations. Results have been documented in CCIR Report 322. CCIR 322 provided seasonal world maps showing the expected values of the atmospheric noise figure Fa at 1 MHz during four hour blocks of the day. Another set of charts relates the Fa at 1 MHz to other frequencies. CCIR Report 322 has been superseded by ITU P.372 publication. Atmospheric noise and variation is used to generate high quality random numbers.
Random numbers have interesting applications in the security domain. Radio atmospheric Singh, Big Bang: The Origin of the Universe, Harper Perennial, ISBN 978-0-00-716221-5 Spaulding, Arthur D..
Noise is unwanted sound judged to be unpleasant, loud or disruptive to hearing. From a physics standpoint, noise is indistinguishable from sound, as both are vibrations through a medium, such as air or water; the difference arises when the brain perceives a sound. Acoustic noise is any deliberate or unintended. In contrast, noise in electronics may not be audible to the human ear and may require instruments for detection. In audio engineering, noise can refer to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as a hiss; this signal noise is measured using A-weighting or ITU-R 468 weighting. In experimental sciences, noise can refer to any random fluctuations of data that hinders perception of a signal. Sound is measured based on the frequency of a sound wave. Amplitude measures; the energy in a sound wave is measured in decibels, the measure of loudness, or intensity of a sound. Decibels are expressed in a logarithmic scale. On the other hand, pitch is measured in hertz.
The main instrument to measure sounds in the air is the Sound Level Meter. There are many different varieties of instruments that are used to measure noise - Noise Dosimeters are used in occupational environments, noise monitors are used to measure environmental noise and noise pollution, smartphone-based sound level meter applications are being used to crowdsource and map recreational and community noise. A-weighting is applied to a sound spectrum to represent the sound that humans are capable of hearing at each frequency. Sound pressure is thus expressed in terms of dBA. 0 dBA is the softest level that a person can hear. Normal speaking voices are around 65 dBA. A rock concert can be about 120 dBA. In audio and broadcast systems, audio noise refers to the residual low-level sound, heard in quiet periods of program; this variation from the expected pure sound or silence can be caused by the audio recording equipment, the instrument, or ambient noise in the recording room. In audio engineering it can refer either to the acoustic noise from loudspeakers or to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as'hiss'.
This signal noise is measured using A-weighting or ITU-R 468 weighting Noise is generated deliberately and used as a test signal for audio recording and reproduction equipment. White noise is energy randomly spread across a wide frequency band containing all notes from high to low, it is called "white" noise as it is analogous to "white" light which contains all the colors of the visible spectrum. Environmental noise is the accumulation of all noise present in a specified environment; the principal sources of environmental noise are surface motor vehicles, aircraft and industrial sources. These noise sources expose millions of people to noise pollution that creates not only annoyance, but significant health consequences such as elevated incidence of hearing loss and cardiovascular disease. There are a variety of mitigation strategies and controls available to reduce sound levels including source intensity reduction, land-use planning strategies, noise barriers and sound baffles, time of day use regimens, vehicle operational controls and architectural acoustics design measures.
Certain geographic areas or specific occupations may be at a higher risk of being exposed to high levels of noise. Noise regulation includes statutes or guidelines relating to sound transmission established by national, state or provincial and municipal levels of government. Environmental noise is governed by laws and standards which set maximum recommended levels of noise for specific land uses, such as residential areas, areas of outstanding natural beauty, or schools; these standards specify measurement using a weighting filter, most A-weighting. In 1972, the Noise Control Act was passed to promote a healthy living environment for all Americans, where noise does not pose a threat to human health; this policy's main objectives were: establish coordination of research in the area of noise control, establish federal standards on noise emission for commercial products, promote public awareness about noise emission and reduction. The Quiet Communities Act of 1978 promotes noise control programs at the state and local level and developed a research program on noise control.
Both laws authorized the Environmental Protection Agency to study the effects of noise and evaluate regulations regarding noise control. The National Institute for Occupational Safety and Health provides recommendation on noise exposure in the workplace. In 1972, NIOSH published a document outlining recommended standards relating to the occupational exposure to noise, with the purpose of reducing the risk of developing permanent hearing loss related to exposure at work; this publication set the recommended exposure limit of noise in an occupation setting to 85 dBA for 8 hours using a 3-dB exchange rate. However, in 1973 the Occupational Safety and Health Administration maintained the requirement of an 8-hour average of 90 dBA; the following year, OSHA required employers to provide a hearing conservation program to workers exposed to 85 dBA average 8-hour workdays. The European Environment Agency regulates noise control and surveillance within the European Union
The Kelvin scale is an absolute thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin is the base unit of temperature in the International System of Units; until 2018, the kelvin was defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. In other words, it was defined such that the triple point of water is 273.16 K. On 16 November 2018, a new definition was adopted, in terms of a fixed value of the Boltzmann constant. For legal metrology purposes, the new definition will come into force on 20 May 2019; the Kelvin scale is named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin, who wrote of the need for an "absolute thermometric scale". Unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to or written as a degree; the kelvin is the primary unit of temperature measurement in the physical sciences, but is used in conjunction with the degree Celsius, which has the same magnitude.
The definition implies that absolute zero is equivalent to −273.15 °C. In 1848, William Thomson, made Lord Kelvin, wrote in his paper, On an Absolute Thermometric Scale, of the need for a scale whereby "infinite cold" was the scale's null point, which used the degree Celsius for its unit increment. Kelvin calculated; this absolute scale is known today as the Kelvin thermodynamic temperature scale. Kelvin's value of "−273" was the negative reciprocal of 0.00366—the accepted expansion coefficient of gas per degree Celsius relative to the ice point, giving a remarkable consistency to the accepted value. In 1954, Resolution 3 of the 10th General Conference on Weights and Measures gave the Kelvin scale its modern definition by designating the triple point of water as its second defining point and assigned its temperature to 273.16 kelvins. In 1967/1968, Resolution 3 of the 13th CGPM renamed the unit increment of thermodynamic temperature "kelvin", symbol K, replacing "degree Kelvin", symbol °K. Furthermore, feeling it useful to more explicitly define the magnitude of the unit increment, the 13th CGPM held in Resolution 4 that "The kelvin, unit of thermodynamic temperature, is equal to the fraction 1/273.16 of the thermodynamic temperature of the triple point of water."In 2005, the Comité International des Poids et Mesures, a committee of the CGPM, affirmed that for the purposes of delineating the temperature of the triple point of water, the definition of the Kelvin thermodynamic temperature scale would refer to water having an isotopic composition specified as Vienna Standard Mean Ocean Water.
In 2018, Resolution A of the 26th CGPM adopted a significant redefinition of SI base units which included redefining the Kelvin in terms of a fixed value for the Boltzmann constant of 1.380649×10−23 J/K. When spelled out or spoken, the unit is pluralised using the same grammatical rules as for other SI units such as the volt or ohm; when reference is made to the "Kelvin scale", the word "kelvin"—which is a noun—functions adjectivally to modify the noun "scale" and is capitalized. As with most other SI unit symbols there is a space between the kelvin symbol. Before the 13th CGPM in 1967–1968, the unit kelvin was called a "degree", the same as with the other temperature scales at the time, it was distinguished from the other scales with either the adjective suffix "Kelvin" or with "absolute" and its symbol was °K. The latter term, the unit's official name from 1948 until 1954, was ambiguous since it could be interpreted as referring to the Rankine scale. Before the 13th CGPM, the plural form was "degrees absolute".
The 13th CGPM changed the unit name to "kelvin". The omission of "degree" indicates that it is not relative to an arbitrary reference point like the Celsius and Fahrenheit scales, but rather an absolute unit of measure which can be manipulated algebraically. In science and engineering, degrees Celsius and kelvins are used in the same article, where absolute temperatures are given in degrees Celsius, but temperature intervals are given in kelvins. E.g. "its measured value was 0.01028 °C with an uncertainty of 60 µK." This practice is permissible because the degree Celsius is a special name for the kelvin for use in expressing relative temperatures, the magnitude of the degree Celsius is equal to that of the kelvin. Notwithstanding that the official endorsement provided by Resolution 3 of the 13th CGPM states "a temperature interval may be expressed in degrees Celsius", the practice of using both °C and K is widespread throughout the scientific world; the use of SI prefixed forms of the degree Celsius to express a temperature interval has not been adopted.
In 2005 the CIPM embarked on a programme to redefine the kelvin using a more experimentally rigorous methodology. In particular, the committee proposed redefining the kelvin such that Boltzmann's constant takes the exact value 1.3806505×10−23 J/K. The committee had hoped tha
Noise pollution known as environmental noise or sound pollution, is the propagation of noise with harmful impact on the activity of human or animal life. The source of outdoor noise worldwide is caused by machines and propagation systems. Poor urban planning may give rise to noise pollution, side-by-side industrial and residential buildings can result in noise pollution in the residential areas; some of the main sources of noise in residential areas include loud music, transportation noise, lawn care maintenance, nearby construction, or young people yelling. Noise pollution associated with household electricity generators is an emerging environmental degradation in many developing nations; the average noise level of 97.60 dB obtained exceeded the WHO value of 50 dB allowed for residential areas. Research suggests that noise pollution is the highest in low-income and racial minority neighborhoods. Documented problems associated with urban environment noise go back as far as ancient Rome. High noise levels can contribute to cardiovascular effects in humans and an increased incidence of coronary artery disease.
In animals, noise can increase the risk of death by altering predator or prey detection and avoidance, interfere with reproduction and navigation, contribute to permanent hearing loss. While the elderly may have cardiac problems due to noise, according to the World Health Organization, children are vulnerable to noise, the effects that noise has on children may be permanent. Noise poses a serious threat to a child’s physical and psychological health, may negatively interfere with a child's learning and behavior. Noise pollution affects both behavior. Unwanted sound can damage physiological health. Noise pollution can cause hypertension, high stress levels, hearing loss, sleep disturbances, other harmful effects. Sound becomes unwanted when it either interferes with normal activities such as sleep or conversation, or disrupts or diminishes one's quality of life. Noise-induced hearing loss can be caused by prolonged exposure to noise levels above 85 A-weighted, decibels. A comparison of Maaban tribesmen, who were insignificantly exposed to transportation or industrial noise, to a typical U.
S. population showed that chronic exposure to moderately high levels of environmental noise contributes to hearing loss. Noise exposure in the workplace can contribute to noise-induced hearing loss and other health issues. Occupational hearing loss is one of the most common work-related illnesses in the U. S. and worldwide. Less addressed is. Indeed, tolerance for noise is independent of decibel levels. However, Murray Schafer's soundscape research was groundbreaking in this regard. In his eponymous work, he makes compelling arguments about how humans relate to noise on a subjective level, how such subjectivity is conditioned by culture, he notes that sound is an expression of power, as such, material culture tend to have louder engines not only for safety reasons, but for expressions of power by dominating the soundscape with a particular sound. Other key research in this area can be seen in Fong's comparative analysis of soundscape differences between Bangkok and Los Angeles, California, US. Based on Schafer's research, Fong's study showed how soundscapes differ based on the level of urban development in the area.
He found. Fong's important findings tie not only soundscape appreciation to our subjective views of sound, but demonstrates how different sounds of the soundscape are indicative of class differences in urban environments. Noise pollution can have negative affects on children on the autistic spectrum; those with Autism Spectrum Disorder can have hyperacusis, an abnormal sensitivity to sound. People with ASD that experience hyperacusis may have unpleasant emotions, such as fear and anxiety, sensations in noisy environments with loud sounds; this can cause individuals with ASD to avoid environments with noise pollution which can cause isolation and negatively impact their quality of life. Sudden explosive noises typical of high-performance car exhausts and car alarms are types of noise pollution that can affect individuals with ASD. Noise can have a detrimental effect on animals, increasing the risk of death by changing the delicate balance in predator or prey detection and avoidance, interfering the use of the sounds in communication in relation to reproduction and in navigation.
These effects may alter more interactions within a community through indirect effects. Acoustic overexposure can lead to permanent loss of hearing. European robins living in urban environments are more to sing at night in places with high levels of noise pollution during the day, suggesting that they sing at night because it is quieter, their message can propagate through the environment more clearly; the same study showed that daytime noise was a stronger predictor of nocturnal singing than night-time light pollution, to which the phenomenon is attributed. Anthropogenic noise reduced the species richness of birds found in Neoptropical urban parks. Zebra finches become less faithful to their partners; this could alter a population's evolutionary trajectory by selecting traits, sapping resources devoted to other activities and thus leading to profound genetic and evolutionary consequences. Underwater noise pollution due to human activities is prevalent in the sea. Cargo ships generate high levels of noise due to diesel engines.
This noise pollutio
Architectural acoustics is the science and engineering of achieving a good sound within a building and is a branch of acoustical engineering. The first application of modern scientific methods to architectural acoustics was carried out by Wallace Sabine in the Fogg Museum lecture room who applied his new found knowledge to the design of Symphony Hall, Boston. Architectural acoustics can be about achieving good speech intelligibility in a theatre, restaurant or railway station, enhancing the quality of music in a concert hall or recording studio, or suppressing noise to make offices and homes more productive and pleasant places to work and live in. Architectural acoustic design is done by acoustic consultants; this science analyzes noise transmission from building exterior envelope to vice versa. The main noise paths are roofs, walls, windows and penetrations. Sufficient control ensures space functionality and is required based on building use and local municipal codes. An example would be providing a suitable design for a home, to be constructed close to a high volume roadway, or under the flight path of a major airport, or of the airport itself.
The science of limiting and/or controlling noise transmission from one building space to another to ensure space functionality and speech privacy. The typical sound paths are ceilings, room partitions, acoustic ceiling panels, windows, flanking and other penetrations. Technical solutions depend on the source of the noise and the path of acoustic transmission, for example noise by steps or noise by flow vibrations. An example would be providing suitable party wall design in an apartment complex to minimize the mutual disturbance due to noise by residents in adjacent apartments; this is the science of controlling a room's surfaces based on sound absorbing and reflecting properties. Excessive reverberation time, which can be calculated, can lead to poor speech intelligibility. Sound reflections create standing waves that produce natural resonances that can be heard as a pleasant sensation or an annoying one. Reflective surfaces can be angled and coordinated to provide good coverage of sound for a listener in a concert hall or music recital space.
To illustrate this concept consider the difference between a modern large office meeting room or lecture theater and a traditional classroom with all hard surfaces. Interior building surfaces finishes. Ideal acoustical panels are those without a face or finish material that interferes with the acoustical infill or substrate. Fabric covered. Perforated metal shows sound absorbing qualities. Finish material is used to cover over the acoustical substrate. Mineral fiber board, or Micore, is a used acoustical substrate. Finish materials consist of fabric, wood or acoustical tile. Fabric can be wrapped around substrates to create what is referred to as a "pre-fabricated panel" and provides good noise absorption if laid onto a wall. Prefabricated panels are limited to the size of the substrate ranging from 2 by 4 feet to 4 by 10 feet. Fabric retained in a wall-mounted perimeter track system, is referred to as "on-site acoustical wall panels"; this is constructed by framing the perimeter track into shape, infilling the acoustical substrate and stretching and tucking the fabric into the perimeter frame system.
On-site wall panels can be constructed to accommodate door frames, baseboard, or any other intrusion. Large panels can be created on ceilings with this method. Wood finishes can consist of punched or routed slots and provide a natural look to the interior space, although acoustical absorption may not be great. There are four ways to solve workplace sound problems -- the ABCDs. A = Absorb B = Block C = Cover-up D = Diffuse Building services noise control is the science of controlling noise produced by: ACMV systems in buildings, termed HVAC in North America Elevators Electrical generators positioned within or attached to a building Any other building service infrastructure component that emits sound. Inadequate control may lead to elevated sound levels within the space which can be annoying and reduce speech intelligibility. Typical improvements are vibration isolation of mechanical equipment, sound traps in ductwork. Sound masking can be created by adjusting HVAC noise to a predetermined level.
Acoustic transmission Noise health effects Noise mitigation Noise Reduction Coefficient Noise regulation Noise and harshness Room acoustics Sound transmission class Wallace Clement Sabine Acoustical Society of America American Institute of Architects National Council of Acoustical Consultants Institute of Acoustics Speech Privacy Calculator Optimum sizes for small rooms Concert Hall Acoustics Everything You Always Wanted to Know About Concert Hall Acoustics An on-line version of an exhibition on concert hall acoustics shown at the South Bank Centre, London
Noise control or noise mitigation is a set of strategies to reduce noise pollution or to reduce the impact of that noise, whether outdoors or indoors. The main areas of noise mitigation or abatement are: transportation noise control, architectural design, urban planning through zoning codes, occupational noise control. Roadway noise and aircraft noise are the most pervasive sources of environmental noise. Social activities may generate noise levels that affect the health of populations residing in or occupying areas, both indoor and outdoor, near entertainment venues that feature amplified sounds and music that present significant challenges for effective noise mitigation strategies. Multiple techniques have been developed to address interior sound levels, many of which are encouraged by local building codes. In the best case of project designs, planners are encouraged to work with design engineers to examine trade-offs of roadway design and architectural design; these techniques include design of exterior walls, party walls, floor and ceiling assemblies.
Many of these techniques rely upon material science applications of constructing sound baffles or using sound-absorbing liners for interior spaces. Industrial noise control is a subset of interior architectural control of noise, with emphasis on specific methods of sound isolation from industrial machinery and for protection of workers at their task stations. Sound masking is the active addition of noise to reduce the annoyance of certain sounds. Organizations each have their own standards, recommendations/guidelines, directives for what levels of noise workers are permitted to be around before noise controls must be put into place. OSHA's requirements state that when workers are exposed to noise levels above 90 A-weighted decibels in 8-hour time-weighted averages, administrative controls and/or new engineering controls must be implemented in the workplace. OSHA requires that impulse noises and impact noises must be controlled to prevent these noises reaching past 140 dB peak sound pressure levels.
MSHA requires that administrative and/or engineering controls must be implemented in the workplace when miners are exposed to levels above 90 dBA TWA. If noise levels exceed 115 dBA, miners are required to wear hearing protection. MSHA, requires that noise levels be reduced below 115 dB TWA. Measuring noise levels for noise control decision making must integrate all noises from 90dBA to 140 dBA; the FRA recommends that worker exposure to noise should be reduced when their noise exposure exceeds 90 dBA for an 8-hour TWA. Noise measurements must integrate all noises, including intermittent, continuous and impulse noises between 80 dBA to 140 dBA; the DoD suggests that noise levels be controlled through engineering controls. The DoD requires that all steady-state noises be reduced to levels below 85 dBA and that impulse noises be reduced below 140 dB peak SPL. Time Weighted Average exposures are not considered for the DoD's requirements; the European Parliament and Council directive require noise levels to be reduced or eliminated using administrative and engineering controls.
This directive requires lower exposure action levels of 80 dBA for 8 hours with 135 dB peak SPL, along with upper exposure action levels of 85 dBA for 8 hours with 137 peak dBSPL. Exposure limits are 87 dBA for 8 hours with peak levels of 140 peak dBSPL. An effective model for noise control is the source and receiver model by Bolt and Ingard. Hazardous noise can be controlled by reducing the noise output at its source, minimizing the noise as it travels along a path to the listener, providing equipment to the listener or receiver to attenuate the noise. A variety of measures aim to reduce hazardous noise at its source. Programs such as Buy Quiet and the National Institute for Occupational Safety and Health Prevention through design promote research and design of quiet equipment and renovation and replacement of older hazardous equipment with modern technologies. Physical materials, such as foam, absorb sound and walls to provide a sound barrier that modifies existing systems that decrease hazardous noise at the source.
The principle of noise reduction through pathway modifications applies to the alteration of direct and indirect pathways for noise. Noise that travels across reflective surfaces, such as smooth floors, can be hazardous. Pathway alterations include sound dampening enclosures for loud equipment and isolation chambers from which workers can remotely control equipment while removed from noise; these methods prevent sound from traveling along a path to other listener. In the industrial or commercial setting, workers must comply with the appropriate Hearing conservation program. Administrative controls, such as the restriction of personnel in noisy areas, prevents unnecessary noise exposure. Personal protective equipment such as foam ear plugs or ear muffs to attenuate sound provide a last line of defense for the listener. Sound insulation: prevent the transmission of noise by the introduction of a mass barrier. Common materials have high-density properties such as brick, thick glass, metal etc. Sound absorption: a porous material which acts as a ‘noise sponge’ by converting the sound energy into heat within the material.
Common sound absorption materials include decoupled lead-based tiles, open cell foams and fiberglass Vibration damping: applicable for large vibrating surfaces. The damping mechanism works by extracting the vibration energy from the thin sheet and dissipating it as heat. A co