All About Jack Headphones You Need To Know

The current 3.5mm headphone jack is becoming rarer as phones gradually ditch this headphone port, and wireless headphones are growing at breakneck speed. However, few people know that the headphone jack port has been around for nearly 100 years and will probably continue soon.

1. History of the headphone jack

Headphone jacks had appeared since the late 19th century for use on telephone switchboards in the past when employees had to plug and unplug to connect phone signals. Then they needed a device that could be easily plugged in to connect the currents carrying the audio signal quickly, easily unplugged, and switched.

In the 19th century, the headphone jack was a 1/4-inch (6.35mm) jack, still commonly found in today’s professional audio equipment. The current popular 3.5mm headphone jack first appeared in the 50s with compact radios running on semiconductor circuits.

The push that made the 3.5mm jack so popular was the Sony Walkman, which shaped and changed the world of portable audio with many cassettes and mini-CDs following. Since then, almost everyone has had a 3.5mm jack headset.

2. Variants of a phone headphone jack

The 2.5mm jack is the sub-miniature jack that appeared in the early 2000s on phones, especially Nokia and Motorola. However, this port went into oblivion after a while because the 3.5mm port still appears on more home audio devices and more firmly than the 2.5mm port on phones.

There was also a brief time when the headset port through the Mini USB port like the HTC Dream or the ExtUSB port on many HTC models. However, this is a very short time and quite troublesome when each brand has its charging port and a separate headphone port.

Currently, manufacturers are producing headphones using the new USB-C port, but there are also many different problems, and it isn’t easy to replace the 3.5mm port.

3. USB-C port on headphones: future or inconvenient

The USB-C port is trying to replace the 3.5mm port on high-end phones, as phone companies are racing to see which phones are lighter and thinner. However, currently, the problem of USB-C ports is very troublesome when there are so many different standards.

There are two popular USB-C audio outputs available today:

– Output digital signal to DAC/Amp on headphones to decode audio

– Output analog signal similar to 3.5mm port using DAC/Amp

Good luck; look at the USB-C port and know which headphones use which decoding. And also depends on your phone support; digital or analog audio output is quite complex. Not to mention the noise problems when a port has too many pins connected, many different features.

4. Why does the 3.5mm jack have 1 bar, 2 bar, and 3 bar?

Previously, audio-only had one channel (mono) and only needed a 1-line signal to divide the signal head and ground end. This end is commonly referred to as the TS jack (1 bar) and is still commonly used in pro-audio.

When stereo (2 channels left, right) as a present was introduced, the headphone jack also had to be changed to carry the audio signal of 2 channels. The 2-bar (3-inch) jack was born properly called TRS (Tip, Ring, Sleeve). The sleeve at the end of the jack is grounded (GRND: Ground), and the Ring and Tip will carry the audio signal of the two channels. The ring between the two bars carries the signal on the right, and the tip part of the jack carries the signal on the left channel.

Then the need to use mobile phones led to the need to integrate the microphone directly on the headset cord. The solution is very simple: divide one more line into three lines to carry a separate microphone line signal. The 3-bar jack is now called TRRS (Tip, Ring, Ring, Sleeve).

However, there is a small problem when there are two different mic jacks, OMTP and CTIA. Nokia, Samsung, and Sony Ericsson use OMTP. Meanwhile, Apple, HTC, LG, and others (later Nokia and Samsung) use CTIA as the standard.

These two standards are quite similar and can be plugged in and played because the part that carries the audio signal is the same. The difference between OMTP and CTIA is that the ground and microphone are reversed. So to talk to control playback, increase or decrease the volume, you need to see what standard the phone or jack uses carefully.

5. Uses other than the audio of the 3.5mm jack

Some Sony headphones use the TRRRS jack (4 bars). The third Ring part allows the company to add a microphone line to use for active noise cancellation. The phone or the Walkman player will receive information from the two microphone clusters for noise cancellation, so the headset does not need a battery or the ability to handle noise directly from the channel like Bose or AKG.

Another variation of the CTIA player is that it is possible to output the image signal on the TV when using the video signal instead of the traditional microphone on the TRRS. Nokia N95 for a 3.5mm wire can output image signals on TVs and control assemblies directly on the wire.

FM Radio is also a feature that can be used with a headset cord. At this point, the headphone cord will act as a radio antenna. Those of you who remember the old phones and music players will also know this feature.

6. Jack balanced often found on music players

Audio players often find on music players balanced 2.5mm or 4.4mm ports. Many of you still do not know how this jack is different from the single-ended 3.5 jack. You need to understand, with single-ended, that each headset channel has only one signal wire, and the other is cool with no signal. Whereas Balanced will be separated, each channel will have two wires carrying the same signal but in reverse phase. When it arrives at the headset, the reverse signal will be inverted to reduce noise. That is to reduce common-mode noise. It can be roughly understood as noise caused by RFI waves leading to signal changes during transmission.

You will see the signal of two channels on the picture, but the opposite phase is denoted L+, L- (left), and R+, R- (right).

The balanced ports commonly found on Astell&Kern players are 2.5mm TRRS. Same as on previous Nokia headsets. You can see that all four parts carry the signal.

Sony’s 4.4mm balanced head not long ago is TRRRS (3 Ring because it has 4 bars). The wiring structure will be slightly different with the 2.5mm end with the addition of ground wire.

In theory, a balanced port ensures more signal accuracy than a single-ended one. However, whether it is better or not depends a lot on the amplifier circuit of the music player, amp.

7. Why Pro-Audio and audiophiles will continue to use 3.5mm jack headphones

With audiophiles because will continue to care about sound quality and compatibility with high-end audio equipment.

In addition to sound quality, Pro-Audio also cares about latency and connection stability in a professional environment. Today’s best codec in terms of latency is AptX Low Latency, with latency as low as 32ms (1 frame delay in a 30fps video). For pre-recorded content, it’s fairly easy to deal with this delay. However, for live content such as games, video calls, live TV, or live stage live sound, this is quite important and requires the stability of wired headphones. On Android 10, users have an additional Low Latency Audio Codec (LLAC) with the same latency as aptX LL at about 30ms.

So wired headphones and a 3.5mm jack will continue to exist and develop but will probably serve a certain set of users. The trend will still favor wireless headphones and especially True-Wireless with the leading position belonging to AirPods.

8. The meaning and use of the circles on the headphone jack

When you look at the headphone jack, you’ll see circles (maybe different colors). So what is the effect of these circles?

Technically, these rings are insulators to separate the jack body into different parts, also known as pins. Each jack will need at least two pins (the jack body will have a separator ring): 1 pin is responsible for signal transmission, and the other is ground for anti-interference.

The pin designs are divided into several types:

– 1 loop (2 batteries): mono sound

– 2 loops (3 pins): stereo with the left channel, right channel, and ground

– 3 loops (4 pins): stereo with the left channel, right channel, microphone, and ground

The 4.4mm balanced jack has become more popular on music players and portable DAC/amp devices in recent years. This jack standard has many advantages over the 2.5mm balanced jack on older Astell&Kern music players thanks to the larger, stronger, and more durable jack, better contact with the female jack.

The 2.5mm and 4.4mm balanced jacks only differ in size; the circuit is the same: the circuit diagram will divide the signal into left + left – and Right+ and Right- for two channels, the last pin is the ground pin.