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Ear Muffs
Earmuffs are accessories designed to cover a person's ears either for warmth or for hearing protection. Both types of earmuff consist of a thermoplastic or metal head-band that fits over the top or back of the head, and a cushion or cup at each end to usually cover both ears. Hearing protection earmuffs are a type of personal protective equipment. Cold weather History Thermal earmuffs were invented by Chester Greenwood of Farmington, Maine in 1873, when he was 15. He reportedly conceived the idea while ice skating, and asked his grandmother to sew tufts of fur between loops of wire. His patent was for improved ear protectors, which he and his local employees manufactured in the Farmington area for nearly 60 years. Earmuffs vs. hats Thermal earmuffs are worn for protection from the cold. Because the ears extend from the sides of the head to gather sound waves, they have a high skin surface-area-to-volume ratio, and very little muscle tissue, causing them to be one of the fir ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
494th Fighter Squadron Homecoming 151008-F-ER377-203
494th may refer to: * 494th Bombardment Squadron, inactive United States Air Force unit * 494th Bombardment Wing, inactive United States Air Force unit * 494th Fighter Squadron (494 FS), part of the 48th Fighter Wing at RAF Lakenheath, England See also * 494 (number) * 494 (other) * 494, the year 494 (CDXCIV) of the Julian calendar * 494 BC {{mil-unit-dis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Headphones
Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an audio source privately, in contrast to a loudspeaker, which emits sound into the open air for anyone nearby to hear. Headphones are also known as earphones or, colloquially, cans. Circumaural (around the ear) and supra-aural (over the ear) headphones use a band over the top of the head to hold the drivers in place. Another type, known as earbuds or earpieces, consists of individual units that plug into the user's ear canal; within that category have been developed cordless air buds using wireless technology. A third type are bone conduction headphones, which typically wrap around the back of the head and rest in front of the ear canal, leaving the ear canal open. In the context of telecommunication, a headset is a combination of a hea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earplug
An earplug is a device that is inserted in the ear canal to protect the user's ears from loud noises, intrusion of water, foreign bodies, dust or excessive wind. Earplugs may be used as well to improve sleep quality or focus in noisy environments. Since they reduce the sound volume, earplugs may prevent hearing loss and tinnitus (ringing of the ears), in some cases. US Occupational Safety and Health Administration requires hearing conservation programs which include the provision of hearing protection devices (HPDs). But this does not mean that OSHA considers HPDs to be effective. History The first recorded mention of the use of earplugs is in the Greek tale ''Odyssey,'' wherein Odysseus's crew is warned about the Siren (mythology), Sirens that sing from an island they will sail past. Circe, their hostess, tells them of the Sirens' bewitching song that makes men drive their boats ashore and perish. She advised Odysseus to fashion earplugs for his men from beeswax so they would n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NIOSH наушники En
The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury, illness, disability, and death. Its functions include gathering information, conducting scientific research both in the laboratory and in the field, and translating the knowledge gained into products and services.About NIOSH National Institute for Occupational Safety and Health. Among NIOSH's programs are determination of s for toxic chemicals and other hazards, field research such as the |
Active Noise Control
Active noise control (ANC), also known as noise cancellation (NC), or active noise reduction (ANR), is a method for reducing unwanted sound by the addition of a second sound specifically designed to cancel the first. The concept was first developed in the late 1930s; later developmental work that began in the 1950s eventually resulted in commercial airline headsets with the technology becoming available in the late 1980s. The technology is also used in road vehicles, mobile telephones, earbuds, and headphones. Explanation Sound is a pressure wave, which consists of alternating periods of compression and rarefaction. A noise-cancellation speaker emits a sound wave with the same amplitude but with an inverted phase (also known as antiphase) relative to the original sound. The waves combine to form a new wave, in a process called interference, and effectively cancel each other out – an effect which is called destructive interference. Modern active noise control is gen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decibel
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a Power, root-power, and field quantities, power or root-power quantity on a logarithmic scale. Two signals whose level (logarithmic quantity), levels differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 101/20 (approximately ). The strict original usage above only expresses a relative change. However, the word decibel has since also been used for expressing an Absolute scale, absolute value that is relative to some fixed reference value, in which case the dB symbol is often suffixed with letter codes that indicate the reference value. For example, for the reference value of 1 volt, a common suffix is "#Voltage, V" (e.g., "20 dBV"). As it originated from a need to express power ratios, two principal types of scaling of the decibel are used to provide consistency depending on whether the scaling refer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microphone
A microphone, colloquially called a mic (), or mike, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, sound recording, two-way radios, megaphones, and radio and television broadcasting. They are also used in computers and other electronic devices, such as mobile phones, for recording sounds, speech recognition, Voice over IP, VoIP, and other purposes, such as Ultrasonic transducer, ultrasonic sensors or knock sensors. Several types of microphone are used today, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. The most common are the dynamic microphone, which uses a coil of wire suspended in a magnetic field; the condenser microphone, which uses the vibrating Diaphragm (acoustics), diaphragm as a capacitor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Attenuation
In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a Transmission medium, medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates. Hearing protection device, Hearing protectors help reduce Sound power, acoustic flux from flowing into the ears. This phenomenon is called acoustic attenuation and is measured in decibels (dBs). In electrical engineering and telecommunications, attenuation affects the Wave propagation, propagation of waves and signals in electrical circuits, in optical fibers, and in air. Attenuator (electronics), Electrical attenuators and optical attenuators are commonly manufactured components in this field. Background In many cases, attenuation is an exponential function of the path length through the medium. In optics and in chemical spectroscopy, this is known as the Beer–Lambert law. In engineering, attenu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earplug
An earplug is a device that is inserted in the ear canal to protect the user's ears from loud noises, intrusion of water, foreign bodies, dust or excessive wind. Earplugs may be used as well to improve sleep quality or focus in noisy environments. Since they reduce the sound volume, earplugs may prevent hearing loss and tinnitus (ringing of the ears), in some cases. US Occupational Safety and Health Administration requires hearing conservation programs which include the provision of hearing protection devices (HPDs). But this does not mean that OSHA considers HPDs to be effective. History The first recorded mention of the use of earplugs is in the Greek tale ''Odyssey,'' wherein Odysseus's crew is warned about the Siren (mythology), Sirens that sing from an island they will sail past. Circe, their hostess, tells them of the Sirens' bewitching song that makes men drive their boats ashore and perish. She advised Odysseus to fashion earplugs for his men from beeswax so they would n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
A-weighting
A-weighting is a form of frequency weighting and the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. A-weighting is applied to instrument-measured sound levels in an effort to account for the relative loudness perceived by the human ear, as the ear is less sensitive to low audio frequencies. It is employed by arithmetically adding a table of values, listed by octave or third-octave bands, to the measured sound pressure levels in dB. The resulting octave band measurements are usually added (logarithmic method) to provide a single A-weighted value describing the sound; the units are written as dB(A). Other weighting sets of values – B, C, D and now Z – are discussed below. The curves were originally defined for use at different average sound levels, but A-weighting, though originally intended only for the measurement of low-level sounds (aro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Occupational Safety And Health
Occupational safety and health (OSH) or occupational health and safety (OHS) is a multidisciplinary field concerned with the safety, health, and welfare of people at work (i.e., while performing duties required by one's occupation). OSH is related to the fields of occupational medicine and occupational hygiene and aligns with workplace health promotion initiatives. OSH also protects all the general public who may be affected by the occupational environment. According to the official estimates of the United Nations, the '' WHO/ ILO'' ''Joint Estimate of the Work-related Burden of Disease and Injury'', almost 2 million people die each year due to exposure to occupational risk factors. Globally, more than 2.78 million people die annually as a result of workplace-related accidents or diseases, corresponding to one death every fifteen seconds. There are an additional 374 million non-fatal work-related injuries annually. It is estimated that the economic burden of o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
