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 headphone and microphone.

Headphones connect to a signal source such as an audio amplifier, radio, CD player, portable media player, mobile phone, video game console, or electronic musical instrument, either directly using a cord, or using wireless technology such as Bluetooth, DECT or FM radio. The first headphones were developed in the late 19th century for use by switchboard operators, to keep their hands free. Initially, the audio quality was mediocre and a step forward was the invention of high fidelity headphones.

Headphones exhibit 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 (6.4 mm) or 1⁄8 inch (3.2 mm) phone jack for plugging the headphones into the audio source. Some headphones are wireless, using Bluetooth connectivity to receive the audio signal by radio waves from source devices like cellphones and digital players. As a result of the Walkman effect, beginning in the 1980s, headphones started to be used in public places such as sidewalks, grocery stores, and public transit. Headphones are also used by people in various professional contexts, such as audio engineers mixing sound for live concerts or sound recordings and disc jockeys (DJs), who use headphones to cue up the next song without the audience hearing, aircraft pilots and call center employees. The latter two types of employees use headphones with an integrated microphone.

Headphones grew out of the need to free up a person's hands when operating a telephone. By the 1880s, soon after the invention of the telephone, telephone switchboard operators began to use head apparatuses to mount the telephone receiver. The receiver was mounted on the head by a clamp which held it next to the ear. The head mount freed the switchboard operator's hands, so that they could easily connect the wires of the telephone callers and receivers. The head-mounted telephone receiver in the singular form was called a headphone. These head-mounted phone receivers, unlike modern headphones, only had one earpiece.

By the 1890s a listening device with two earpieces was developed by the British company Electrophone. The device created a listening system through the phone lines that allowed the customer to connect into live feeds of performances at theaters and opera houses across London. Subscribers to the service could listen to the performance through a pair of massive earphones that connected below the chin and were held by a long rod.

French engineer Ernest Mercadier in 1891 patented a set of in-ear headphones. The German company Siemens Brothers at this time was also selling headpieces for telephone operators which had two earpieces, although placed outside the ear. The Siemens Brothers headpieces looked similar to modern headphones. The majority of headgear used by telephone operators continued to have only one earpiece.

Headphones appeared in the emerging field of wireless telegraphy, which was the beginning stage of radio broadcasting. Some early wireless telegraph developers chose to use the telephone receiver's speaker as the detector for the electrical signal of the wireless receiving circuit. By 1902 wireless telegraph innovators, such as Lee de Forest, were using two jointly head-mounted telephone receivers to hear the signal of the receiving circuit. The two head-mounted telephone receivers were called in the singular form head telephones. By 1908 the headpiece began to be written simply as head phones, and a year later the compound word headphones began to be used.

One of the earliest companies to make headphones for wireless operators was the Holtzer-Cabot Company in 1909. They were also makers of head receivers for telephone operators and normal telephone receivers for the home. Another early manufacturer of headphones was Nathaniel Baldwin. He was the first major supplier of headsets to the U.S. Navy. In 1910, motivated by his inability to hear sermons during Sunday service, he invented a prototype telephone headset. He offered it for testing to the navy, which promptly ordered 100 of them. Wireless Specialty Apparatus Co., in partnership with Baldwin Radio Company, set up a manufacturing facility in Utah to fulfill orders. These early headphones used moving iron drivers, with either single-ended or balanced armatures. The common single-ended type used voice coils wound around the poles of a permanent magnet, which were positioned close to a flexible steel diaphragm. The audio current through the coils varied the magnetic field of the magnet, exerting a varying force on the diaphragm, causing it to vibrate, creating sound waves. The requirement for high sensitivity meant that no damping was used, so the frequency response of the diaphragm had large peaks due to resonance, resulting in poor sound quality. These early models lacked padding, and were often uncomfortable to wear for long periods. Their impedance varied; headphones used in telegraph and telephone work had an impedance of 75 ohms. Those used with early wireless radio had more turns of finer wire to increase sensitivity. Impedances of 1,000 to 2,000 ohms was common, which suited both crystal sets and triode receivers. Some very sensitive headphones, such as those manufactured by Brandes around 1919, were commonly used for early radio work.