A phone connector, also known as an audio jack or a headphone jack, is a family of electrical coupling generally used for analog audio signals. The standard specifies that a plug (known as a male connector) is connected to a female connector (known as a female jack).

The headphone jack was developed in the 19th century for use in telephone plug-board and is still widely used. The phone plug has a cylindrical shape with a ridged tip that holds it in place. It generally has 2, 3, 4 and, sometimes, 5 contacts in its initial audio configuration,

Three-connection versions are also called TRS connectors, where T stands for “tip”,  R for “ring”, and S for “sleeve”.

Ring contacts usually have the same diameter as the sleeve, the long shank. Similarly, versions with two, four, and five contacts are known as TS, TRRS and TRRRS connectors, respectively.

The outer diameter of the sleeve connector is 6.35 mm (1⁄4 inches). The mini connector comes with a diameter of 3.5 mm (0.14 inch), while the micro connector’s diameter is pegged at 2.5 mm (0.098 inches).

What Are the Types of Headphone Jacks?

The 3.5mm Headphone Jack

Most people are familiar with the 3.5mm headphone type. It’s the standard size most smartphone jacks use and other media devices. You’ll realize that other devices, from desktop computers, portable compact disc players make use of this jack type to connect headphones.

Most of today’s 3.5mm headphone jacks have in-built controls and microphones. These are specially built for use with a smartphone, allowing you to answer incoming and outgoing calls, change the volume, and skip music tracks without taking the phone out of your pocket.

You might also find 3.5mm jacks that can only produce sound via one speaker, so you won’t be able to enjoy listening to your favorite music in stereo.

The 2.5mm Headphone Jack

As implied by the name, the 2.5mm headphone jack is a smaller version of the typical headphone jack. It’s often used by smaller devices and also some smartphones. This is quite similar to the 3.55mm in every aspect, but with a slightly smaller frame.

Most 2.5mm headphone jacks also come with the standard controls built into your smartphone. The devices that use 2.5mm jacks have become quite unusual. The advantage here is that 3.5mm adapters can be purchased to ensure that your 2.5mm jack remains relevant.

The 6.3mm Headphone Jack

Headphones with a 6.3 jack socket are few and far between nowadays. The 6.3 jack socket is only found in professional music equipment, old microphones, and metal detectors.

Wiring Standards

It gets slightly tricky when it comes to the wiring caliber of headphone jacks. In this section, we discuss the 2.5, 3.5, and 6.35mm headphone plugs/jacks in terms of how they are connected and the different signals they can send.

Tip, Ring & Sleeve

To know what the audio jack and connector wiring are, we need to first understand the different number of poles on the plug and jack and the internal cables that transmit sound from the cable.

The poles/conductors are known as tips, rings, and sleeves. These designations refer only to the position where the conductors are outlined in a socket/plug.

The tip is located at the tip of the connector. The rings are electrically insulated and wrap around the circumference of the plug in the middle of the plug length. The sleeve lies toward the base of the plug.

With each headphone sockets, the electrically conductive plug has a housing with a larger diameter underneath. This housing isn’t there to only mark the end of the plug and intercept damage, but also to accommodate the electrical connection linking the signal wires in the cable of the headphone and the independent poles in the connector.

The corresponding conductors inside of the connectors are connected to the signal wires in the audio/headphone cord to transport the audio signal from one place to another successfully. This path runs from the audio device to the headphones, in the case of headphones.

While providing a tubular shield within the cable instead of a single wire, the sleeve of the plug is usually connected to electrical ground. The shield supplies some suppression of electromagnetic intrusion in the signal wires, while the ground provides a zero potential for the other signal wires to which reference can be made.

TS (Tip-Sleeve)

In terms of a TS connector, the sleeve serves as the ground and simultaneously as a return line for the audio signal. The TS is not commonly used for headphones because it’s not capable of transmitting a stereo audio signal.

TRS (Tip-Ring-Sleeve)

The TRS plug is much more regular as it allows stereo audio. However, a rare circumstance (at least for headphones) is that the TRS carries a balanced mono signal.

Unbalanced Stereo TRS

Unbalanced stereo wiring is very common with wired headphones. It allows the left and right passage of the stereo audio signal to be transmitted to the matching sides of the headphones (or the corresponding earphones).

The term, “unbalanced”, signifies that the correct audio signal is sent over one line only. This process is fine, although the signal may be vulnerable to electromagnetic and radio frequency intervention, and a cable with a longer length may reduce the signal.

Concerning unbalanced stereo audio, two separate unbalanced signals are transmitted through the cable. The left channel’s audio signal is conveyed on the tip (with the sleeve serving as the return path), while the right channel’s audio signal is carried on the ring (with the sleeve substituting as the return path).

The tip is connected to a wire leading to the positive (+) terminal of the left driver coil of the headphone; the ring is connected to a wire leading to the positive terminal of the right driver. The sleeve is connected to a wire leading to the two negatives (-) driver coil’s terminals.

Balanced Mono TRS

Balanced TRS cables are seldom used for headphones because they’re not stereo-compatible.

Relatively, they’re frequently used to connect the single left and right channel outputs to studio monitors and as patch panel cable to direct balanced signals in a music or broadcast studio.

Connecting headphones to a balanced output (such as the left channel output of an audio link) would dispatch uniform signals with contrasting polarities to the headphone drivers. And the derived sound would be quite terrible. A balanced TRS is wired in the same way as a 3-pin XLR output, with the tip being pin 1, the ring pin 2, and sleeve pin 3.

TRRS (Tip-Ring-Ring-Sleeve)

TRRS headphone connectors are what we commonly find in consumer quality headsets and earphones with in-built microphones. With 4 poles, this plug can effectively transmit a stereo headphone signal and a mono microphone signal with a common ground.

There are two grades that we see in TRRS cables: CTIA and OMTP:

CTIA Standard for TRRS

CTIA is the new grade and has been taken on by practically all consumer-quality audio equipment manufacturers since 2015. Manufacturers of smartphones, laptops, and tablets have switched from the old OMTP standard. So, the headsets and headphones with in-built microphones available on the market today are wired with the CTIA for compatibility reasons.

OMTP Standard for TRRS

OMTP is the older standard, which may be the cabling scheme in an older audio device or headphones that you own.

Note that not all headsets make use of the TRRS connector. A lot of professional broadcast headsets utilize a completely separate connector for headphones & microphone to enhance versatility.

Computer and video game headphones often use different types of USB for connection. Older landline desk phones often make use of RJ9 (RJ10/RJ22). Headphones and headsets built for newer iPods are connected via Lightning connectors.

Other Headphone/Audio Jack Types

Various types of jacks are also used for connection to certain audio devices. These include the following:

The RCA Jack

This audio jack is used for the connection of media players to a stereo system. It’s being in existence for decades and is still regarded as an integral part of a high-quality home sound system and even for professional use. The RCA jack isn’t a standard on telephones because it’s unsuitable and is also not found in consumer-class desktop computers, but it can be installed if desired.

The MIDI Cable

This audio jack technically isn’t a “socket” in a certain sense. It’s predominantly used for the connection of electronic musical instruments such as keyboards – computer or other sound systems.

The MIDI cable can be grouped as one of the previous generations of cables. This is because most electronic musical instruments have moved on to the use of USB cables as the primary means of connecting an audio device.

USB

A USB connector is the abbreviation for “universal serial bus” and is used in linking to a computer port.  Most items that you utilize on a computer, such as your keyboard, mouse, and printer, connect to the computer with a USB connector.  Educational headphones that use a USB port are usually plug-and-play devices, which means that once they’re plugged in, your computer downloads and activates the relevant drivers.  When finished, your headphones are typically set as your new sound source.

Closing Remarks

Headphone jacks might become less common in the future with the development of wireless headphones, but there’s no denying the fact that this is among the most authentic means of connecting headphones to other audio devices. Thanks to their robust and very reliable design, they’ll remain an indispensable accessory for audio systems for decades to come.