There are several different types of commonly used headphones. The particular needs of the listener determine the choice of headphone. The need for portability indicates smaller, lighter headphones but can mean a compromise in fidelity. Headphones used as part of a home hi-fi do not have the same design constraints and can be larger and heavier. Generally, headphone form factors can be divided into four separate categories: circumaural, supra-aural, earbud, and in-ear.
Circumaural headphones (sometimes called full size headphones) have circular or ellipsoid earpads that encompass the ears. Because these headphones completely surround the ear, circumaural headphones can be designed to fully seal against the head to attenuate any intrusive external noise. Because of their size, circumaural headphones can be heavy and there are some sets which weigh over 500 grams (1 lb). Ergonomic headband and earpad design is required to reduce discomfort resulting from weight.
Supra-aural headphones have pads that sit on top of the ears, rather than around them. They were commonly bundled with personal stereos during the 1980s. This type of headphone generally tends to be smaller and more lightweight than circumaural headphones, resulting in less attenuation of outside noise.
Circumaural and supra-aural headphones can both also be further differentiated by the type of earcups:
Open-back headphones have the back of the earcups open. This leaks more sound out of the headphone and also lets more ambient sounds into the headphone, but gives a more natural or speaker-like sound and more spacious "soundscape" - the perception of distance from the source.
Closed-back styles have the back of the earcups closed. Depending on the model they may block 8-32db of ambient noise, but have a smaller soundscape, giving the wearer a perception that the sound is coming from within their head.
Among audio professionals, earbuds and earphones refer to very small headphones that are fitted directly in the outer ear, facing but not inserted in the ear canal; they have no band or other arrangement to fit over the head. (However, many consumer-quality in-ear-canal systems are also called earbuds by their manufacturers.) The outer-ear earphones are portable and convenient, but many people consider them to be uncomfortable and prone to falling out.
In-ear headphones, like earbuds, are small and without headband, but are inserted in the ear canal itself. They are sometimes known as canalphones. Price and quality range from relatively inexpensive to very high; the better ones are called in-ear monitors (IEMs) and are used by audio engineers and musicians as well as audiophiles. Canalphones offer portability similar to earbuds, block out much environmental noise by obstructing the ear canals, and are far less prone to falling out. When used for casual portable use they block out sounds which can be important for safety (e.g., approaching vehicles). Universal canalphones provide one or more stock silicone rubber, elastomer, or foam sleeves to fit various ear canals, for correct placement and best noise isolation.
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