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Headphones (or head-phones in the early days of telephony and radio) are a pair of small listening devices that are designed to be worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound in the user's ear. Headphones are designed to allow a single user to listen to an audio source privately, in contrast to a loudspeaker, which emits sound into the open air, allowing anyone nearby to listen. Headphones are also known as earspeakers, earphones〔(【引用サイトリンク】title=earphone )〕 or, colloquially, cans.〔Stanley R. Alten ''Audio Basics'' Cengage 2011 ISBN 0-495-91356-1 page 63〕 Circumaural and supra-aural headphones use a band over the top of the head to hold the speakers in place. The other type, known as earbuds or earphones〔 consist of individual units that plug into the user's ear canal. In the context of telecommunication, a headset is a combination of headphone and microphone. Headphones either connect directly to a signal source such as an audio amplifier, radio, CD player, portable media player, mobile phone, video game consoles, electronic musical instrument, or use wireless technology such as bluetooth or FM radio. Early headphones were first used by radio pioneers (crystal sets) and also by radio telephone and telegraph operators allowing a better audio reception without distubing others around. Initially the audio quality was mediocre and a step forward was the invention of high fidelity headphones. Headphones are made in a range of different audio reproduction quality capabilities. Headsets designed for telephone use typically cannot reproduce sound with the high fidelity of expensive units designed for music listening by audiophiles. Headphones that use cables typically have either a 1/4 inch (6.35mm) or 1/8 inch (3.5mm) phone jack for plugging the headphones into the audio source. As of 2015, most headphones are amplified by a headphone amplifier, either an integrated amplifier (e.g., in an iPod) or a standalone unit. == History == Headphones originated from the earpiece, and were the only way to listen to electrical audio signals before amplifiers were developed. The first truly successful set was developed in 1910 by Nathaniel Baldwin, who made them by hand in his kitchen and sold them to the United States Navy.〔(【引用サイトリンク】title=Howeth: Chapter XI (1963) )〕〔(Utah History To Go. ''Ruin Followed Riches for a Utah Genius'' (Will Bagley for the Salt Lake Tribune, July 8, 2001) )〕 Some very sensitive headphones, such as those manufactured by Brandes around 1919, were commonly used for early radio work. These early headphones used moving iron drivers, with either single ended or balanced armatures. The requirement for high sensitivity meant that no damping was used, thus the sound quality was crude. These early models lacked padding, and often produced excessive clamping forces on the wearer's head. Their impedance varied; headphones used in telegraph and telephone work had an impedance of 75 ohms. Those used with early wireless radio had to be more sensitive and were made with more turns of finer wire. Impedance of 1000 to 2000 ohms was common, which suited both crystal sets and triode receivers. In early powered radios, the headphone was part of the vacuum tube's plate circuit and carried dangerous voltages. It was normally connected directly to the positive high voltage battery terminal, and the other battery terminal was securely grounded. The use of bare electrical connections meant that users could be shocked if they touched the bare headphone connections while adjusting an uncomfortable headset. In 1943, John C. Koss, an audiophile and jazz musician from Milwaukee, produced the first stereo headphones. Previously, headphones were used only by telephone and radio operators, and individuals in similar industries. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「headphones」の詳細全文を読む スポンサード リンク
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