Headphones can 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 do not need to be 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 actually made of powered receiver systems of which the headphone is only a component, these types of cordless headphones are being used more frequently 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 1/4″ and 3.5 mm stereophonic jack plugs and sockets. The older 1/4″ standard is used on professional equipment, and is often used on fixed equipment. Sony introduced the smaller, cheaper, and now widely-used, 3.5 mm “mini” stereo connector in 1979, adapting the older monophonic 3.5 mm connector for use with its Walkman portable stereo tape player. Adapters are available for converting between 1/4″ and 3.5 mm devices.
