How Do Headphone Jacks And Plugs Work? (+ Wiring Diagrams)


It’s easy to simply plug your headphones (and other devices) into their proper jacks or ports and have them work… until it’s not. Learning how headphone jacks and plugs work electrically will help tremendously in our comprehension of signal flow and device compatibility while also improving our troubleshooting skills.

How do headphone jacks and plugs work? Headphone plugs (male) plug into headphone jacks (female) to establish an electrical connection that allows audio signals to flow. Though the purpose is the same, the size; specific wiring; inclusion of a microphone; connection quality, and compatibility differ from jack to jack; plug to plug, and plug to jack.

In this article, we’ll look at the inner workings of these various sizes, wirings and qualities of headphone jacks to better understand how they work in general as well as how they work in tandem with headphone plugs.

Related article: How Do Headphone Jacks And Plugs Work? (+ Wiring Diagrams)


The Difference Between A Headphone Jack And A Headphone Plug

When most people discuss headphone jacks, they mean both the female port connectors and the male connectors at the end of the headphone cables.

However, technically speaking, the headphone jack is the female port and the headphone plug is the male connector. This is the case with any phone-style connector (having tip, ring and sleeve connectors).

These are headphone plugs:

6.35mm, 3.5mm and 2.5mm TRS Audio Plugs

This is a headphone jack:

3.5mm TRRS Headphone Jack (Macbook Air 2015)

The same difference can be applied to microphone connectors. To learn more, check out my article What Is The Difference Between A Microphone Plug And Jack?

With that primer in terminology, let’s get into the bulk of this article.


How Do Headphone Jacks And Plugs Connect?

Let’s begin by stating that not all headphone jacks and plugs are compatible.

In order for a headphone jack and plug to connect properly and have an optimal signal flow, they must match in the following ways:

  • Be the same size
  • Have the same wiring schematic

Note that there is some leeway in wiring compatibility. Note, too, that just because a plug fits in a jack doesn’t necessarily mean it’s compatible. We’ll touch on these issues later in this article in the section on the headphone jack and plug compatibility.

Essentially, headphone jacks and plugs are single connectors that have multiple (2-5) conductors within their design. In order for a headphone plug to work with a headphone jack, the conductors must be properly aligned in the correct format to transfer the proper audio signal(s).

It’s important to note that headphones are transducers and are inherently analog devices. Analog audio signals are simply AC (alternating current) voltages. These signals are carried via electrically conductive wires.

The wires within a headphone cable are internally matched to the individual conductors of a cable’s plug. The audio source’s jack also has individual conductors that are wired to carry specific signals.

The idea is to make contact between the jack and plug conductors to allow the analog audio signals to flow from the source through the cable and to the appropriate headphone drivers according to the wiring schemes.

In the vast majority of cases, we cannot actually see the physical connection between a headphone plug and jack without deconstructing the jack. The following is a simplified cross-sectional diagram of a jack-plug connection:

So that’s the basic idea of how headphone jacks and plugs work. They simply act as conductive connections that allow electrical current to flow from one place to another (from the audio source to the headphone drivers).

In this article, we’ll talk more about the sizes and wiring standards for headphone jacks/plugs and look into compatibility.


Headphone Jack/Plug Sizes

Let’s begin by discussing the various headphone jack and plug sizes. They are:

  • 2.5mm
  • 3.5mm
  • 4.4mm
  • 6.35mm

2.5mm (3/32 in)

The 2.5mm headphone jack/plug is not very common but worth mentioning here for thoroughness.

This headphone plug/jack still gets used regularly in two-way radios (walky-talkies) and some video cameras.

2.5mm headphone connections are typical unbalanced mono TS (tip-sleeve) or unbalanced stereo TRS (tip-ring-sleeve) connectors.

3.5mm (1/8 in)

The 3.5mm headphone jack/plug is the most common for wired headphones.

This is the jack found on older smartphones; in laptops and tablets; and in some audio mixing consoles and field recorders.

3.5mm headphone connections are often either unbalanced stereo TRS (tip-ring-sleeve) or unbalanced stereo plus a microphone TRRS (tip-ring-ring-sleeve) connectors.

4.4mm

The 4.4mm is a relatively new headphone jack/plug.

The standard 4.4mm is named the Pentaconn and is found in some HiFi products, particularly from Sony.

Sony is featured in My New Microphone’s Top 13 Best Headphone Brands In The World.

The Pentaconn standard is wired as balanced stereo with a TRRRS (tip-ring-ring-ring-sleeve) connector.

6.35mm (1/4 in)

The 6.35mm “quarter-inch” jack and plug are what you’ll typically find when connecting electric musical instruments. The plugs/jacks used for instruments are often unbalanced and wired as TS (tip-sleeve).

However, the 6.35mm jack is also used for headphones, though it is typically wired as unbalanced stereo TRS (tip-ring-sleeve).

The 6.35mm headphone jack/plug is found in many audio interfaces, headphone amplifiers, mixing consoles and recording devices.

Size Adapters

Of the 4 sizes mentioned above, the 3.5mm (1/8″) and 6.35mm (1/4″) phone connectors are the most common.

Fortunately, there are adapters to effectively convert between jack/plug sizes. These adapters even come as jack-to-jack or plug-to-plug in addition to the straight jack-to-plug and plug-to-jack adapters.

For a detailed article on headphone jack and plug sizes, check out My New Microphone’s post titled Differences Between 2.5mm, 3.5mm & 6.35mm Headphone Jacks.


Headphone Jack/Plug Wirings

In the section on headphone jack/plug size, I briefly mentioned the tip, ring and sleeve connections. These terms refer to the different conductors on the connectors themselves that have their own wires with the headphone cable and carry their own audio line.

In this section, we’ll explore the wiring standards used in headphone jacks and plugs and get into how they connect with one another and effectively transfer audio signals from the audio source to the headphone drivers.

Stereo Vs. Mono Audio

Most headphones are wired to accept stereo audio since stereo is the standard for music.

However, some headphones and particularly headset only require mono audio and are designed in that fashion.

In order to carry mono, a headphone connector must have at least 2 conductors: 1 signal wire and one return wire (which also typically acts as ground). This is most simply done via a TS (tip-sleeve) connection.

Stereo audio requires at least 3 conductors: a left channel audio signal wire; a right channel audio signal wire, and a common ground/return wire.

Note that mono and stereo headphones may have more than their necessary conductors for microphone integration or balanced signal transfer.

Balanced Vs. Unbalanced Audio

Most headphones utilize unbalanced audio, though there are exceptions.

Unbalanced audio is wired as having one signal wire and one return wire. The return wire often doubles as a ground wire. These two conductive wires complete a circuit and allow an audio signal to “travel” from a sound source to a headphone driver.

Unbalanced audio is fine for carrying audio through short cable lengths (like those in headphone cables) but will degrade signals, particularly in the high-end, through any significant length.

Balanced audio is wired as having two signal wires: one to carry the signal in positive polarity and the other to carry the signal in negative polarity.

Having equal but opposite signals on the two wires effectively double the voltage swing in a connected headphone driver, leading to a stronger signal transfer. As one wire “pushes” current at one side of the driver, the other wire “pulls” current from the other side of driver within the circuit.

Balanced audio inputs effectively sum the differences between the two signal wires via a differential amplifier, allowing for a stronger signal with excellent protection against any interference or noise common to both conductors. It is, therefore, common for long cable runs and for situations where clean audio with low noise is required.

Microphones, for example, output relatively low-level audio signals that are more susceptible to electromagnetic interference (the induced noise will be more noticeable compared to a mic level signal than a line level signal). Therefore, professional microphones all utilize balanced lines to carry their signals.

It’s important to note that stereo headphones require two different unbalanced or balanced audio signals: one for each driver.

With that primer, let’s get into the various wiring schemes of headphone jacks and plugs.

TS (Tip-Sleeve)

The TS is the most basic phone connector. It allows a mono audio signal to be carried via the signal wire (tip) and the return/ground wire (sleeve).

To lay the conductors of the TS connector out simply:

  • Tip: signal wire
  • Sleeve: return wire and ground

The TS can be connected to a single headphone driver (in one-sided designs) or be split to reach to separate drivers.

Unbalanced Mono Headphones Signal Flow

TS headphone plugs and jacks are generally only found in 2.5mm connectors. Note that 6.35mm TS “patch cable” connectors are common for electric instruments, particularly electric guitar and bass guitar.

TRS (Tip-Ring-Sleeve)

TRS is common in headphone jacks/plugs as a carrier of unbalanced stereo audio.

The unbalanced TRS connector is wired as follows:

  • Tip: left channel audio signal wire
  • Ring: right channel audio signal wire
  • Sleeve: common return wire and ground

In this configuration, the sleeve wiring is split at the Y in the cable and connects to both drivers.

Unbalanced Stereo Headphones Signal Flow

The TRS unbalanced stereo wiring scheme is used in 2.5mm, 3.5mm and 6.35mm headphones jacks/plugs and is common in professional headphones.

Note that another common wiring standard for TRS jacks/plugs is balanced mono though this is never really used in headphone design. The balanced mono TRS is typically used in professional audio patch bays and in studio monitor and loudspeaker hookups.

TRRS (Tip-Ring-Ring-Sleeve)

The TRRS is another very common headphone jack/plug connector. It has gained popularity with the rise of headphones that include a microphone in their design.

Many of our digital devices (smartphones, laptops, tablets) have 3.5mm TRRS jacks to accommodate these headphone+microphone devices and headsets.

The TRRS wiring is mostly used in 3.5mm headphone connectors and typically follows the AHJ (American Headset Jack) standard set forth by the CTIA (Cellular Telecommunications and Internet Association). Let’s have a look at this standard.

CTIA Standard

  • Tip: left channel audio signal wire
  • Ring: right channel audio signal wire
  • Ring: common return wire and ground
  • Sleeve: microphone audio wire

In these headphones, the common return (second ring) splits three ways and connects to the microphone element and both headphone drivers.

An older standard worth mentioning is the OMTP. It is very similar except for one major switch.

OMTP Standard

  • Tip: left channel audio signal wire
  • Ring: right channel audio signal wire
  • Ring: microphone audio wire
  • Sleeve: common return wire and ground

In this standard, the sleeve also splits three ways and connects to the microphone element and both headphone drivers.

Unbalanced Stereo Headphones WIth Microphone Signal Flow

TRRRS (Tip-Ring-Ring-Ring-Sleeve)

The TRRRS connector is used in the rare 4.4mm Pentaconn connector.

This specialized headphone jack/plug carries balanced stereo to compatible headphones and is wired as follows:

  • Tip: left channel audio (positive polarity)
  • Ring: left channel audio (negative polarity)
  • Ring: right channel audio (positive polarity)
  • Ring: right channel audio (negative polarity)
  • Sleeve: ground

If we recall the description of balanced audio, we know that there is no need for a return wire since we have a positive polarity and negative polarity wire to connect to the headphone driver.

Balanced Stereo Headphones Signal Flow

There is no common return wire in the 4.4mm TRRRS Pentaconn standard which improves clarity by minimizing crosstalk due to the lack of a common return. The balanced audio is also stronger due to the nature of balanced versus unbalanced audio.

For a detailed read on the various wiring schemes of headphone audio, check out my article An In-Depth Look Into How Headphone Cables Carry Audio.


Headphone Jack And Plug Compatibility

At the beginning of this article, I mentioned that headphone jacks and plug may be compatible even if their conductors do not match up. I also stated that headphone jacks and plugs may not be compatible even if they are the same size.

Let’s clear some of this confusion by looking at specific examples:

Compatibility Between TRS & TRRS Jacks/Plugs

Imagine a scenario where we have a pair the following:

  • Headphones with a 3.5mm TRS plug
  • Headphones with a microphone and 3.5mm TRRS plug
  • Smartphone with a 3.5mm TRRS jack

The smartphone will certainly have a TRRS jack since it is designed as an input and output device, capable of accepting a microphone and outputting a headphone signal. Let’s assume for this example that it uses the CTIA standard mentioned previously.

Once again, the CTIA standard is:

  • Tip: left channel audio signal wire
  • Ring: right channel audio signal wire
  • Ring: common return wire and ground
  • Sleeve: microphone audio wire

So then, we know that the 3.5mm TRRS headphones+microphone (assuming CTIA standard) is compatible with the headphone jack because the wiring schemes match and the sizes are the same.

However, when we plug out basic unbalanced stereo 3.5mm TRS headphones into the smartphone, they work just fine. Why is that?

Well, the tip and ring of the TRS plug and the TRRS jack match up perfectly. The ground/return wire also connects. The sleeve of the TRRS jack which is designed to accept the mic signal is simply shorted to the ground wire of the TRS plug of the headphone.

Of course, this isn’t a perfect connection but they remain compatible nonetheless.

Incompatibility Between TRRS (CTIA) & TRRS (OMTP) Jacks/Plugs

It’s important to know the difference between the older OMTP standard and the newer CTIA standard for unbalanced stereo headphones + unbalanced microphone signals.

Though the tip and first ring are fully compatible (left and right headphone audio), the common return and mic signal wire (on the second ring and sleeve) are incompatible, making the OMTP and CTIA standards incompatible with one another.

Size Adapters

There are plenty of size adapters on the market to adapt the plug of your headphones to fit an intended jack.

The most common adapters are 3.5mm TRS to 6.35mm TRS and 6.35mm TRS to 3.5mm TRS but there are plenty of others on the market.

Wiring Adapters

There are some wiring adapters that help to improve connectivity between headphones plugs and jacks that do not have exactly the same connections (the aforementioned imperfect TRS plug to TRRS jack, for example).


Using Headphone Jacks To Connect Devices Other Than Headphones

Sometimes it’s possible to connect devices other than headphones to headphone jacks. Let’s further our discussion.

Speakers

Most speakers are designed with relatively low impedance and to accept speaker level signals and, therefore, will not work properly being connected to a headphone out.

However, there are plenty of handheld/mobile speakers designed to connect to the headphone output of smartphones, laptops, etc.

The JBL Charge 3 (link to check the price on Amazon) is a Bluetooth speaker that has a wired input that can easily accept signal from a headphone output.

JBL Charge 3

JBL is featured in My New Microphone’s:
Top 11 Best Home Speaker Brands You Should Know And Use
Top 11 Best Subwoofer Brands (Car, PA, Home & Studio)
Top 11 Best PA Loudspeaker Brands You Should Know And Use
Top 10 Best Loudspeaker Brands (Overall) On The Market Today

Aux Inputs

You’ve likely done this before when you connected a smartphone to a car’s auxiliary input. Many home sound system amps also have aux inputs that can be used to accept headphone level signals.

To learn more about the differences between headphone jacks and auxiliary outputs, check out my article Are AUX (Auxiliary) Connectors & Headphone Jacks The Same?

Microphones

Microphones can connect via specific headphone jacks designed to accept mic signals. The TRRS headphone jacks we discussed early are capable of accepting microphones that connect via 3.5mm phone connectors.

To read about a few of my recommended TRRS microphones, check out my article Top 4 Best External Microphones For Android Smartphones.

Related article: How Do Microphones Work? (A Helpful Illustrated Guide)


Is aux the same as headphone jack? Aux cables/connectors are designed to be a universal 3.5mm TRS connection while headphone plugs/jacks come in a variety of sizes and are designed to carry signals from a sound source to a pair of headphones. Note that aux outputs can often drive headphones just fine (though not always) while headphone outputs will typically drive aux inputs just fine.

How do headphone cables work? Headphone cables are designed to connect headphone drivers to their intended sound source by completing a circuit between the source and the driver. In other words, they allow the audio signals (AC voltages) to pass through the transducer elements of headphones that convert the signals into sound waves.

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