Applications
Headphones may be used both with fixed equipment such as CD or DVD players, home theater, personal computers and with portable devices (e.g. digital audio player/mp3 player, mobile phone, etc.). Cordless headphones are not connected via a wire, receiving a radio or infrared signal encoded using a radio or infrared transmission link, like FM, Bluetooth or Wi-Fi. These are powered receiver systems of which the headphone is only a component. Cordless headphones are used with events such as a Silent disco or Silent Gig.
In the professional audio sector headphones are used in live situations by disc jockeys with a DJ mixer and sound engineers for monitoring signal sources. In radio studios, DJs use a pair of headphones when talking to the microphone while the speakers are turned off, to eliminate acoustic feedback and monitor their own voice. In studio recordings, musicians and singers use headphones to play along to a backing track. In the military, audio signals of many varieties are monitored using headphones.
Wired headphones are attached to an audio source. The most common connectors are 6.35mm (¼″) and 3.5mm phone connectors. The larger 6.35mm connector tending to be found on fixed location home or professional equipment. Sony introduced the smaller, and now widely used, 3.5mm "minijack" stereo connector in 1979, adapting the older monophonic 3.5mm connector for use with its Walkman portable stereo tape player. The 3.5mm connector remains the common connector for portable application today. Adapters are available for converting between 6.35mm and 3.5mm devices.
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