What is a 3.5mm Headphone Jack?

According to connector naming convention, a 1/8-inch (3.5mm) headphone jack is an audio socket that accepts a 3.5mm male pin or audio plug. The term “headphone jack” is commonly used to mean the male plug as well as the female socket. This jack is a smaller version of the original 1/4-inch (6.35mm) socket, which also remains in widespread use. A third, even smaller standard is the 3/32-inch (2.5mm) jack, found on many cellphone headsets.

The ubiquitous 3.5mm headphone jack or socket is standard on most handheld electronics with limited space, such as cell phones, personal digital assistants (PDAs), digital audio players and vidcams. Netbooks and laptops also use this configuration, as do internal desktop audio cards. Advanced sound cards geared towards recording music often feature a separate patch bay with a full-sized headphone jack and inputs for musical instruments and microphones.

An alternate name for the male pin at the end of the headphone wire is a TRS connector, short for Tip, Ring, Sleeve. This describes the actual construction by naming the contact points on the pin or plug. A stereo headphone plug has two colored insulating rings on the pin’s shaft, with the Ring in between. The Ring handles the right audio channel, while the Tip handles the left. A mono earphone plug has only one insulating ring with the single-channel audio handled by the Tip. The Sleeve typically serves as the ground.

Headsets with a built-in microphone make use of a 3.5mm headphone jack by reconfiguring the way the tip or plug is used. A mixed stereo signal can be sent to the Tip in a single audio channel, for example, while the Ring can be used for the microphone’s signal, though there are more configurations and signals can also be balanced or unbalanced, depending.

A video signal can also be sent through a 3.5mm headphone jack, common on vidcam equipment. The device’s 3.5mm output port is used with a cable that features a 3.5mm plug on one end, and 1/4-inch (6.35mm) RCA connectors or plugs on the other. If the device sends discreet stereo channels plus video, there will be three RCA connectors: one red (audio right), one white (audio left) and one yellow (composite video). Running the connector cable from the vidcam to Line-In RCA ports on a television will allow viewing the camera's contents on the TV.

While earbuds and lightweight headphones designed for personal electronics are normally quite adequate, adapters are available to use with 1/4-inch pins which feature a female 1/4-inch socket on one end, and a male 3.5mm pin on the other. These 3.5mm adapters will allow one to use standard headphones with the smaller jack. The opposite type of adapter is also available, with a 3.5mm female socket on one end, and a 1/4-inch pin on the other. This allows 3.5mm headphones to be used in jacks made for larger headphones.

This size jack has become a versatile port on contemporary personal electronics. Inexpensive adapters and converter cables of all types are available at local or online electronic retailers.