Differences Between 2.5mm, 3.5mm & 6.35mm Headphone Jacks


Although the popularity of wireless headphones continues to increase, wired headphones and their associated headphone jacks are still used regularly. There are a few different headphone jack sizes we should be aware of when using our wired headphones. These sizes are 2.5mm (3/32″), 3.5mm (1/8″) and 6.35mm (1/4″).

What are the differences between 2.5mm, 3.5mm & 6.35mm headphone jacks? The primary, most obvious difference is size. The numbers given refer to the diameter of the jack but the lengths of the connectors are also different. Certain applications have certain standard sizes. In terms of wiring, there are various standards that can be applied to each size jack.

So in this article, we’ll talk about the nuanced differences between headphone jacks along with the similarities these jacks share.


A Primer On Jacks And Plugs

Before we get started, let’s first understand the difference between a headphone jack and a headphone plug.

The headphone jack is the receptacle and the headphone plug is inserted into the jack. In other words, the headphone jack is the female connector and the headphone plug is the male connector.

To better understand, if your headphones are permanently wired, the end of the cable features a plug. Your audio player, smartphone, laptop, etc. has a headphone jack that you plug your headphones into.

Headphone Plug
Headphone jack of an iPhone 6S (above) and a headphone plug (below)

Note that when people say “headphone jack,” they sometimes are referring to the plug. This primer is not only to distinguish between the two but also to ensure clarity in the remainder of this article when we discuss jacks and plugs together.


The Size Difference

The most obvious difference between 2.5mm, 3.5mm and 6.35mm headphone jacks is in the name itself: the size of the jack and its associated plug.

The quoted size refers to the diameter of the jack/plug and each size has its own length(s) as well. Here are the specified dimensions for each headphone jack size:

Plug DiameterPlug Length
2.5mm11mm
0.43"
3.5mm (~1/8")14mm - 17mm
0.55" - 0.69"
6.35mm (1/4")30mm - 31mm
1.18" - 1.22"

As we can see from the table above, there isn’t always a set standard for the lengths of the specific plug sizes. Though 2.5mm connectors are nearly all regulated to be 11mm in length, 3.5mm and 6.35mm plugs have some variation.

3.5mm plugs are usually 14mm long but can, in some instances, be as long as 17mm and still be considered standard. 15mm and 17mm are used in video applications, though 17mm is quite rare. 3.5mm headphone jacks are typically designed to receive either 15mm or 17mm plugs.

6.35mm or 1/4″ plugs are a bit more standardized and have a smaller range in length between 30mm – 31mm (1.18″ – 1.22″). This small difference is not overly critical when it comes to proper connectivity between quarter-inch plugs and jacks.

The vast majority of wired headphones have 3.5mm-diameter 15mm length TRS or TRRS connectors. These work perfectly will most consumer audio devices (portable music players, smartphones, laptops, tablets, etc.). Professional headphone amps typically have 1/4″ TRS jacks and so many pro headphones come with a 3.5mm-to-6.35mm adapter.

Let’s get into the different sizes in more detail here:

The 6.35mm (1/4″) Plug & Jack

If you’ve ever played an electric guitar or bass through an amplifier, you’ve used a 6.35 (1/4″) TS “patch” cable. This patch connection has the same dimensions as the 1/4″ headphone plug/jack. However, the headphone jack typically uses an extra pole/conductor in its connector, making it a TRS (tip-ring-sleeve) rather than a TS (tip-sleeve).

The 6.35mm is relatively bulky and is generally reserved for professional headphones and other professional audio devices. These devices include but are not limited to headphone amplifiers, audio interfaces, digital-to-analog converters, mixing consoles and field recorders.

Here is a picture of a 6.35mm (1/4″) TRS headphone plug:

6.35mm (1/4″) Headphone Plug

Here is an example of a simple one-channel headphone amp with a 1/4″ (6.35mm) headphone jack to the right of its front face:

Schiit Magni 3 Heresy Headphone Amp With 6.35mm (1/4″) Headphone Jack

The 3.5mm (1/8″) Plug & Jack

Most analog wired headphones today have 3.5mm (1/8″) plugs. The 3.5mm connector is also used in auxiliary “aux” audio connections commonly found in automobile audio consoles, mixing consoles, and other consumer products.

Note that, due to smartphone manufacturers abandoning the headphone jack, lighting and USB-C digital headphone connectors are becoming common as are wireless Bluetooth headphones.

3.5mm headphone jacks are found in portable audio players, laptops, smartphones, tablets, field recorders, mixing consoles, and many other audio devices. Headphones typically used TRS 3-pole 3.5mm connectors while headphones with a microphone will utilize TRRS 4-pole 3.5mm connectors.

Here is a picture of a 3.5mm TRS and a 3.5mm TRRS headphone plug:

3.5mm (1/8″) TRS Plug (left) – 3.5mm (1/8″) TRRS Plug (right)

And here’s a picture of my MacBook Air’s 3.5mm headphone jack (the computer I’m using to write this article!):

Macbook Air 13-inch Early 2015 3.5mm Headphone Jack

The 2.5mm Plug & Jack

The 2.5mm (3/32″) connector is less common in pro audio applications. However, it still gets used regularly in two-way radios (walky-talkies) and some video cameras.

Here is a picture of a 2.5mm TRS headphone plug:

2.5mm (3/32″) TRS Plug

And here is a picture of a two-way radio that has a 2.5mm headphone jack:

Tait TP93/94 Speaker Microphone with 2.5mm Headphone Jack

Headphone Jacks Are Not Only For Headphones

These connectors are often referred to as headphone jacks and, in many instances, they are used for headphones hence the name. If a jack is specifically meant for headphones, it’s often referred to as a headphone jack. However, the 2.5mm, 3.5mm and 6.35mm connectors mentioned above are used for much more than just headphones.

Because there are plenty of other uses for these jacks that do not include headphones, it’s sometimes better to refer to them generically as “audio jacks”.

For example, these audio jacks can be used in the following applications:

  • Microphones
  • Headsets (headphones + microphone)
  • Audio in/auxiliary
  • Audio out/auxiliary
  • Electric musical instruments (electric guitar, electric bass guitar, keyboards, etc.)
  • Loudspeakers
  • Studio monitors
  • Studio patch bays

It’s important to remember that not all plugs and jacks are used exclusively for headphones.


Wiring Standards

Things get a bit tricky when it comes to wiring standards of headphone jacks. In this section, we’ll discuss the 2.5mm, 3.5mm and 6.35mm headphone plugs/jacks in terms of the way they connect and the various signals they are capable of sending.

Tip, Ring & Sleeve

To understand the wiring of audio jacks and plugs, we must understand the different pole-counts at the plug and jack as well as the internal wires that carry audio from the cable.

The poles/conductors are best-known as tips, rings, and sleeves. These labels simply refer to the location the conductors are designed in a jack/plug.

The tip is at the tip of the plug; the rings are electrically isolated and wrap around the plug’s circumference in the middle of its length, and the sleeve is toward the base of the connector.

We notice in each of the headphone connections that the electrically conductive plug has a larger-diameter housing below it. This housing isn’t only to mark the end of the connector and prevent damage but is also put there to house the electrical connection between the signal wires in the headphone cable and the individual poles in the plug connector.

If we took apart an audio plug, it would look similar to this:

The coinciding conductors on the interior of the connectors attach to the signal wires in the audio/headphone cable to effectively move the audio signal from one place to another. In the case of headphones, this path is from the audio device to the headphones.

The sleeve of the connector is typically connected to electrical ground while also providing a tubular shield within the cable rather than a single wire. The shield provides some rejection of electromagnetic interference in the signal wires while having it grounded provides a zero-potential for the other signal wires to be referenced against.

TS (Tip-Sleeve)

In the case of a TS connector, the sleeve acts as the ground and also as a return for the audio signal. When used for headphones, the wiring is as follows:

  • Tip: Mono headphone signal
  • Sleeve: Ground & mono headphone signal return

More generally, the TS connector is wired with:

  • Tip: Signal
  • Sleeve: Ground & return

The TS is not often used for headphones since it is not capable of carrying a stereo audio signal.

TRS (Tip-Ring-Sleeve)

The TRS connector is much more common because it allows for stereo audio. That being said, a much more rare circumstance (for headphones, at least) is the TRS carrying a balanced mono signal.

Unbalanced Stereo TRS:

The unbalanced stereo wiring is the most common in wired headphones. It allows the left and right channels of the stereo audio signal to be carried to their coinciding sides of headphones (or their corresponding earbuds).

Unbalanced stereo TRS is generally wired as:

  • Tip: Left headphone signal
  • Ring: Right headphone signal
  • Sleeve: Ground/returns

The term “unbalanced” means that the proper audio signal is sent along one wire only. This method is fine, though the signal may be susceptible to electromagnetic and radio frequency interference and a longer cable length may degrade the signal.

In the case of unbalanced stereo audio, there are two separate unbalanced signals being carried through the cable. The left channel audio signal is carried on the tip (with the sleeve acting as the return) while the right channel audio signal is carried on the ring (with the sleeve acting as the return).

The tip connects to a wire that goes to the positive (+) lead of the left headphone driver coil; the ring connects to a wire that goes to the positive lead of the right driver. The sleeve connects to a wire that goes to both negative (-) terminals of the driver coil. This wire usually has a solder joint in the “Y” or in the earpiece where ground wire from the plug splits into separate wires that are connected to the negative terminals of the driver coils.

Balanced Mono TRS:

Balanced TRS cables are rarely ever used for headphones since they are not stereo.

Rather, they are often used for connecting individual left channel and right channel outputs to studio monitors and as patch bay cable to route balanced signals around a music or broadcast studio.

For your information, balanced TRS is wired like this:

  • Tip: Positive polarity headphone signal
  • Ring: Negative polarity headphone signal
  • Sleeve: Ground

Connecting a pair of headphones to a balanced output (like the left channel output of an audio interface, for example), would send equal signals with opposite polarities to the headphone’s drivers and the resulting sound would be quite awful.

As an aside, balanced TRS is wired in the same fashion as 3-pin XLR with tip bring pin 1; ring bring pin 2, and sleeve being pin 3.

TRRS (Tip-Ring-Ring-Sleeve)

TRRS headphone plugs are what we’ll often find with consumer-grade headsets and the earbuds that have built-in microphones. With 4 poles, this connector can effectively carry a stereo headphone signal and a mono microphone signal with a common ground.

There are two standards we see with TRRS cables: CTIA and OMTP:

CTIA Standard For TRRS

  • Tip: Left headphone
  • Ring: Right headphone
  • Ring: Ground
  • Sleeve: Microphone

CTIA is the new standard and has been adopted by practically all producers of consumer-grade audio devices since 2015. Smartphone, laptop and tablet manufacturers have switched over from the old OMTP standard and so the headsets and headphones with built-in microphones on the market today are also wired with the CTIA for compatibility.

OMTP Standard For TRRS

For your information, here is the older OMTP standard that may be the wiring scheme in an older audio device or pair of headphones you own.

  • Tip: Left headphone
  • Ring: Right headphone
  • Ring: Microphone
  • Sleeve: Ground

It’s important to note that not all headsets use the TRRS connection. In fact, many professional broadcasting headsets use completely different connectors for the headphones and the microphone for improved versatility.

Computer and video game headsets will often use various USB types to connect. Older, fixed-line desk phones often use RJ9 (RJ10 or RJ22). Headphones and headsets designed for newer iPods connect via Lightning connectors.

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

TRRRS gives us 5 poles to work with but is rare in 2.5mm, 3.5mm and 6.35mm connectors. Rather the TRRRS design is combined with the relatively unfamiliar 4.4mm connector, which we’ll get to shortly.

The TRRRS has great potential for various wiring schemes. A proper wiring design for the TRRRS headphone plug/jack is:

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

Again, we’ll discuss this in more detail when we touch on the 4.4mm audio jack.


Other Headphone Connectors

As briefly mentioned above, not all headphones utilize the 2.5mm, 3.5mm or 6.35mm connectors. There are plenty of other options out there. Here are a few:

Lightning

When Apple did away with the headphone jack on their iPhones, a whole new range of headphones came out that utilized the Lightning connector (the charging port of iPhone since the iPhone 5).

Pictured below are Apple’s Earpods with Lightning connector (link to check the price on Amazon):

Apple Earpods with Lightning Connector

The lightning port can be used for headphones, headsets, and microphones, too. Check out My New Microphone’s Top 4 Best External (Lightning) Microphones For iPhone Audio for more info.

USB

Following Apple’s lead, many other smartphone manufacturers have ditched the headphone jack. This has opened up a new market for USB-C headphones.

Here is a picture of consumer-grade Lewder In-Ear Headphones (link to check the price on Amazon):

Headphones with USB-C connector

There are also many headsets out there that utilize USB-A as their connector. The Logitech H390 headset (link to check the price on Amazon) is one such example:

XLR

Some professional headphones and headsets utilize XLR to make their connection. Many of these headphones/headsets have detachable cables that offer a variety of connections to choose from, including XLR.


The 4.4mm Audio Jack

4.4mm TRRRS Audio Jack

As discussed previously, there is also a lesser-known 4.4mm headphone jack.

The 4.4mm Pentaconn is a relatively new balanced plug that sits somewhere between a 3.5mm headphone jack and a high-end XLR. It is typically 5-pole TRRRS and is currently used in professional audio and the telecommunication industries.

The TRRRS has great potential for various wiring schemes. This is the most common in terms of headphones:

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

So with the 4.4mm TRRRS connector, we get two balanced channels for a balanced stereo signal. Balanced audio is less susceptible to electromagnetic and radio frequency interference, signal degradation and headphone cross-talk making it a quiet, more effective way of carrying stereo audio to your headphones.

Of course, there are many that would argue that balanced headphone connections like the 4.4mm TRRRS are not worth the extra cost and provide minimal enhancement over unbalanced stereo. However, the science of balanced vs. unbalanced audio is clear. The question then becomes, is the extra cost worth it to you?


Adapters

Fortunately, there are adapters for pretty much any change in connector you could want.


Wireless & Bluetooth Headphones

Let’s bring our discussion back to Apple’s decision on getting rid of the headphone jack in their smartphones. This seemingly big move was not done lightly. There had to be an alternative other than the Lightning cable to prompt such a big choice. That alternative was wireless headphones and, more specifically, Bluetooth headphone technology.

Wireless headphones work with a transmitter and receiver. The transmitter emits the source audio wirelessly and the receiver, which is built into the headphones, picks up the audio to convert it into sound.

These wireless audio signals are encoded, which means they are carried within another signal rather than being transmitted as audio waves. The wireless signals are often in the radio-frequency or infrared frequency range. Note that encoding must take place or else the audio signal would simply be propagated as audible sound.

So a more accurate description would be that the transmitter takes the audio signal, encodes it, and sends it to the receiver wirelessly. The receiver then decodes the wireless signal to access the audio signal, amplifies the audio signal, and converts the audio into sound.

With that said, let’s quickly run through the wireless headphone connections.

Radio Frequency Wireless Headphone Connection

RF wireless headphones, as the name suggests, utilize radio frequencies to transmit audio signals wirelessly. The range of frequencies is typically either in the very high frequency/VHF (30 MHz – 300 MHz) or in the ultra high frequency/UHF (300 MHz – 3 GHz) range.

Wireless headphone manufacturers will generally design their products to work in a specific and small range of radio frequencies.

RF signals typically travel 15m to 100m and do not require line-of-sight between the transmitter and receiver to function properly.

With RF wireless headphones, we can have as many headphones listening to the same RF channel as you’d like.

Unfortunately, RF is susceptible to interference and static when listening. Low-level noise and a relative lack of bass are also often present in RF wireless headphone signals.

Bluetooth Wireless Headphone Connection

Bluetooth is an international digital wireless standard. It encodes and transmits digital audio rather than analog audio (like most RF and IR wireless systems). Bluetooth actually works with RF frequencies in a band of 79 different frequencies centred on 2.45 GHz.

Bluetooth can connect to 8 different devices simultaneously with no interference. Each connection changes frequencies 1600 times per second to ensure this.

Infrared Wireless Headphone Connection

Infrared wireless headphones transmit audio encoded in infrared waves (frequency range from 300 GHz – 430 THz).

IR wireless provides a cleaner signal than RF at the expense of being reliant on line-of-sight.

This is similar to how a TV remote control interacts with a television.


Related Questions

What is the difference between a headphone jack and audio out? A headphone jack outputs audio (typically unbalanced stereo) that is meant for headphones. Audio outs commonly output balanced or unbalanced mono signals which would not drive headphones properly and may not have the proper output voltage or impedance for optimal compatibility with headphones.

Can speakers be plugged into a headphone jack? Although you can, it is not advised unless the speakers are stereo and designed to accept the voltage and impedance levels of the headphone out. Plugging a speaker designed to accept speaker level audio may not yield the best results when plugged into a headphone output. In some cases, it may even damage the jack and the output circuit.

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