The more technical term for an audio jack is a TRS connector. TRS stands for tip-ring-sleeve, and these refer to the basic components of the connector. The tip carries the left-hand channel of a stereo signal or the signal line for an unbalanced mono signal. The ring, which is usually in between two black-colored insulating rings, carries the right-hand channel of a stereo signal. Finally the sleeve, which is the rest of the audio jack's plug, is usually the ground.
Audio jacks that only need to carry mono signals, such as those used for electric musical instruments, only have a tip-sleeve (TS) configuration with one black-colored insulating ring in between. Consumer audio headphones and earphones use the typical tip-ring-sleeve design. There is another kind of audio jack that has a tip-ring-ring-sleeve (TRRS) configuration. These are used for special headsets that have an attached microphone and a radio push-to-transmit (or push-to-talk) feature. Each tip, ring and sleeve component has its own wire terminal counterpart inside the housing. It is important therefore to match the right kind of wire with the audio jack configuration.
1. Use a single conductor wire for a mono audio jack.
A single conductor wire has only one central wire wrapped in its own insulation, and meshed around this insulation are the shielding wires. The central wire should be soldered to the tip wire terminal, and the thin shielding wires should be grouped and twisted together (for easier soldering) and then soldered to the ground/sleeve terminal.
2. Use a 2 conductor wire for a stereo audio jack.
In a 2 conductor wire, there are actually two central wires, each with its own insulation. The insulations are color-coded so that you can establish a distinction between which wire would carry the right or left-channel signal. Solder the left-channel wire to the tip wire terminal, the right-channel wire to the ring terminal, and again the shielding wire goes to the ground/sleeve terminal.
3. Use a 4 conductor wire for a TRRS audio jack.
In a TRRS audio jack, the tip carries the microphone signal, the first ring carries the headphone signal, the second ring carries the push-to-transmit signal and finally the sleeve is still used for the ground. The wire terminals in a generic TRRS audio jack are symmetrically arranged in a circle in the housing. Usually numbers are stamped on each terminal to distinguish what terminal leads to which component. Meanwhile, the wires in a four conductor wire are correspondingly color coded. The white wire comes from the microphone and should be soldered to terminal 1. The blue wire comes from the headphones and must connect to terminal 2. The red wire comes from the push-to-transmit button and must connect to terminal 3. Finally the black wire functions as the ground and connects to terminal 4.
Headsets that use the TRRS configuration of an audio jack are usually the ones used by aviation and emergency services personnel. This configuration is also used for wiring voice-activated intercoms.