Earmuffs
- This article is about earmuffs that covers a person's ears. “Earmuffs” may also refer to the “earmuff convention” in Common Lisp.
Earmuffs, also known as earmuffles, are objects designed to cover a person's ears for protection. They consist of a thermoplastic or metal head-band, that fits over the top of the head, and a pad at each end, to cover the external ears.
Chester Greenwood invented the earmuff in 1873, at the age of 15.[1][2] He reportedly came up with the idea while ice skating, and had his grandmother sew tufts of fur between loops of wire.[3] He was awarded patent #188,292 on March 13, 1877. He manufactured these ear protectors, providing jobs for people in the Farmington Maine area, for nearly 60 years.[1][4]
Modern earmuffs come in two basic kinds:
- Thermal earmuffs, worn in cold environments to keep a person's ears warm.
- Acoustic earmuffs, also known as ear defenders: cups lined with sound-deadening material, like thermal earmuffs and headphones in appearance, which are worn as hearing protection. These may be carried on a head-band or clipped onto the sides of a hard hat, for use on construction sites. Some manufacturers combine headphones with ear defenders, allowing the wearer to listen to music, communication or other audio source and also enjoy protection or isolation from ambient noise. For extra sound attenuation, earplugs can also be used in conjunction with earmuffs.[5]
Ear defenders protect the wearer from extreme noises. The head band and outer covering is usually made from a hard thermoplastic or metal. The protection usually comes from acoustic foam - this absorbs sound waves by increasing air resistance, thus reducing the amplitude of the waves. The energy is transformed into heat. Some ear defenders employ active sound protection, in which a microphone mounted in the headset picks up ambient sounds and transmits them through a dynamic range compression circuit to earphones inside. By virtue of the dynamic compression, the headset can be adjusted to allow the wearer to hear sounds at ordinary volumes normally, while attenuating louder sounds.
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[edit] Hearing Protection
If people are exposed to excessively loud environments (90 dB or more), ear protectors are necessary to prevent ear damage. They should be worn whenever power tools, loud yard equipment, or unsuppressed firearms are used. The table below shows how easy it is to exceed the maximum exposure levels. Even at sound levels below the level of possible damage, hearing protection will reduce fatigue from frequent exposure to sound.
| Level of noise (dB(A)) | Maximum daily exposure time |
|---|---|
| 85 | 8 Hours |
| 91 | 2 Hours |
| 97 | 30 Minutes |
| 103 | 7 Minutes |
[edit] See also
[edit] References
- ^ a b Maine Secretary of State Kid's Page - Famous People
- ^ Chester Greenwood - Earmuffs
- ^ Dec. 4, 1858: It Was Very Cold the Day Chester Greenwood Was Born
- ^ Earmuff History - Invention of Earmuffs
- ^ Stephenson, Carol Merry. "Choosing the Hearing Protection That's Right For You". http://www.cdc.gov/niosh/topics/noise/abouthlp/chooseprotection.html. Retrieved 2009-07-30.
[edit] External links
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