Proprietary interfaces using both four- and five-conductor versions exist, where the extra conductors are used to supply power for accessories.
Many different configurations of these phone plugs were used, some accommodating five or more conductors, with several tip profiles.
Of these many varieties, only the two-conductor version with a rounded tip profile was compatible between different manufacturers, and this was the design that was at first adopted for use with microphones, electric guitars, headphones, loudspeakers, and many other items of audio equipment.
It is cylindrical in shape, typically with two, three, four and, recently, five contacts.
Three-contact versions are known as TRS connectors, where T stands for "tip", R stands for "ring" and S stands for "sleeve".
The three-conductor (TRS for Tip-Ring-Shield) versions are capable of handling balanced line signals and are used in professional audio installations.