Connecting

Wired

Jack

Normally a headphone is connected with a jack.
As a jack is TRS (tip, ring, sleeve); you have three wires, the signal for the left and right channel and a common ground for both drivers.

 

The ¼ inch (6.35mm) TRS jack is the standard.

As it is about as thick as a mobile, for portable gear a 3.5 mm connector is used.

 

Symmetrical

An alternative is to connect the headphone with 4 wires, a separate + and – for each driver.
This is called “balanced” in the headphone world.

This has nothing to do with a balanced connection as we know from connecting two pieces of gear e.g. a pre-amp and a power amp using a XLR.
XLR is a 3 wire connection, a hot, a cold and a common ground.
At the receiver there is a differential amp removing all common noise.


In case of a headphone, having 2 wires for the left and 2 for the right, is identical to how we connect out speakers to an amp. Nothing “balanced” about this symmetrical connection but it does allow for amplifier topologies like indeed a balanced amp.

 

In this example you have an amp driving the + and an amp using the inverse to drive the - channel. You can't do this push-pull using a common ground.

 

To change from TRS to TRRS a common solution is a 4 pin XLR.

 

A mini TRRS jack is another option

 

 

Benefits

The question is do you really benefit from going “balanced”.
Obvious you won’t get more silence (rejection of common noise) as the connection is not balanced.
In fact you might get a bit more distortion as instead of driving each channel with 1 amp, you drive each channel with 2 amps. This will increase distortion.
However as you do use 2 amps for a single driver, it will certainly provide much more power.

 

Some even advocate the opposite, a balanced headphone amp is inferior to a single ended one.

Benchmark does not offer voltage-balanced headphone outputs on any of its products. The reason for this is that a voltage-balanced interface serves no useful purpose when driving headphones. The truth is that a conventional single-ended headphone drive is technically superior to a balanced drive.

AUDIO MYTH - BALANCED HEADPHONE AMPLIFIERS ARE BETTER

 

Headroom BUDA balanced headphone amp

 

 

USB-C

More and more manufacturers of mobiles starts dropping het 3.5 headphone jack.
Another trend is replacing the micro USB connector with a USB-C connector.

You can connect a dongle (DAC with headphone out) to the USB-C.

 

Moshi 24 bit / 192 kHz USB DAC - € 25.00

 

 

This is what one expects, a digital bus hence a DAC to convert the digital to analog.

 

Google USB-C Digital to 3.5 mm headphone adapter - $12

 

A DAC at $12

I’m afraid its performance lives up to its price tag.

An inside view.

Analog USB-C

The 24 pins USB-C allows for analog audio!

The device must set the bus in Alternate mode to obtain this.

Obvious, USB-C is the most analog sounding digital bus!

Wireless

A wireless headphone allows you to move freely.
A wireless headphone is an all in one solution.
Sound quality depends not on the drivers only but on the inbuilt DAC and amp as well.

Any wired headphone can be turned into a wireless one using a portable receiver.

Infrared

Infrared (IR) is light hence it almost free of interference (WIFi etc)
The downside is that sender and receiver must literally see each other.
Infrared is in general limited to 10 m.

Sennheiser Set 900 infrared headphone

Radio Frequency

Wireless headphones often use a RF (Radio Frequency) transmitter.
The advantage is its long range (up to 100 m) and sender and receiver don’t have to be in the same room like in case of IR.
RF transmitters often use the 2.4 MHz  band.
This might cause interference with WiFi.

Sennheiser Flex 5000 $199

Base/docking station with optical and analog input.

Receiver with headphone out turns any wired headphone in a "wireless" one.

Added 2017

Bluetooth

Bluetooth is the most popular protocol to connect a headphone wireless.

A big advantage is low power consumption.
This is crucial as beside the Bluetooth receiver the battery also powers the built-in DAC and amp. The sender is often a mobile phone. Being frugal on power improves battery life.

 

Bluetooth audio is not lossless.

Detailed information about Bluetooth and its audio codecs can be found here.

 

Portable Bluetooth receivers brings the convenience of  wireless to any wired headphone.
This is covered in more detail here.

 

At first glance I was a bit puzzled, how to wear this?
Hopefully not on your head!

It is a Bluetooth reciever specially made for the Ultrasone Perfomance serie.

 

Although wireless, wireless headphones use wires to connect the left and right driver.

Novero Rockaway bluetooth headphone

 

In case of in-ears you have a neckband.

True wireless headphones

Today you can get True wireless headphones, They have a wireless connection between left and right earbud.

Check user experience before you buy because some models do have problems maintaining the connection between the 2 earbuds.

 

Onkyo W800 BT
$299.99

WiFi

As WiFi is a very popular protocol and is not handicapped by limited bandwidth and range like Bluetooth.

It looks like the ideal protocol to connect a headphone wireless.
Unfortunately, power consumption is high compared with Bluetooth resulting in a limited battery live.
The Koss Striva is the only WiFi enabled headphone known to me.

It is no longer in production.

References
  1. Balanced Drive vs. Unbalanced Drive - Headroom
  2. AUDIO MYTH - BALANCED HEADPHONE AMPLIFIERS ARE BETTER - Benchmark Media 2016
  3. Balanced audio - Wikipedia
  4. Headphone Connectors & Pins - DIY audio blog
  5. How Do Headphone Jacks And Plugs Work? - mynewmicrophone.com