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Headphones (also known as earphones, earbuds, stereophones, headsets, or by the slang term cans) are a pair of transducers that receive an electrical signal from a media player or receiver and use speakers placed in close proximity to the ears (hence the name earphone/headphones) to convert the signal into audible sound waves. In the context of telecommunication, the term headset is also commonly understood to refer to a combination of headphones and microphone used for two-way communication, for example with a mobile phone.
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Headphones may be used to prevent other people from hearing the sound either for privacy or to prevent disturbance, as in listening in a public library. They can also provide a level of sound quality that could only be matched by speakers costing a great deal more than the headphones. This is especially true in the bass (low frequency) region, where loudspeaker-listening room interactions normally cause resonant modes, so that even with the best speakers, a listener in a given place hears some bass notes too loudly and others too softly. Good headphones, with a good seal to the ear, can have an extremely flat low-frequency response down to 20 Hz within 3dB. (Marketed claims such as 'frequency response 4 Hz to 20 kHz' are usually overstatements: the product's response at frequencies lower than 20 Hz is typically very small.) Headphones of the 'closed back' type are also used to exclude external sounds, particularly in sound recording studios and in noisy environments. Headphones can also be useful for videogames that use 3D positional audio, allowing players to better judge the position of an off-screen sound source (such as the footsteps of an opponent).

Headphones are normally attached to an audio device through a connector, the so-called jack plug. The two common connectors are 1/4" and 3.5 mm plugs. Headphones designed for home stereo systems and recording studios use the older 1/4" connector. Sony introduced the 3.5 mm connector in 1979, adapting the older monophonic 3.5 mm connector for use with its Walkman personal stereo. (headphones) Advantages of the smaller connector include lower bulk, weight and cost. This smaller connector is more prevalent today due to the popularity of portable music devices, although aftermarket headphones sometimes include an adapter for compatibility with the larger connector. In the professional world, only 1/4" is used, although professional headphones often come with an adapter to 3.5 mm. .