I don’t get the difference….
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When it comes to audio, balanced is a more complicated way of doing things, but it gets rid of noise and interference, while allowing for more power. How it works depends on which piece of gear you’re talking about. There’s basically one definition that applies to electronics like the DAC (digital-to-analog converter) and the amplifier; and a slightly different definition when it comes to the headphones themselves.
Let’s start with the electronics. A simple unbalanced connection from the DAC to the amplifier uses RCA cables, which have 1 signal wire (max 2 volts) and 1 ground wire each. XLR balanced cables have 3 wires per cable; 2 for signal (so max 4 volts) that cancel each other out at the amplifier (so no ground), and a shield wire to absorb interference. If there’s some interference on one of those signal wires for the XLR, it “cancels out” with the other at the amplifier for a cleaner signal. 4 volts instead of 2 also allows you to use a longer cable without the signal dropping off.
So now that you have a balanced signal coming into the amplifier, let’s talk about the headphones… Simple unbalanced headphones have a signal wire going to each ear cup, and a Y-shaped shared ground wire. (3.5mm and 6.35mm connectors are 3-pole.) This shared ground can cause a tiny bit of the signal to “bleed over” from one side to the other, called crosstalk. If you try to send a signal to just the right channel, 99% will come out the right side while 1% comes out the left and your brain interprets that as a slightly narrower soundstage.
Balanced headphones have 2 signal wires going to each ear cup. Here, the signals are slightly different. They’re close, so they basically cancel each other out at the driver (and don’t need a ground), but the difference between them is what causes the driver to move and generate sound. There is no crosstalk because there is no shared ground wire. (XLR headphone connectors are 4-pole. 4.4mm “penta-conn” connectors are 5-pole and have a shield wire like the XLR electronics connectors. It’s confusing.)
When hi-fi equipment says it has a “truly balanced circuit” it means balanced inputs and outputs so there’s no ground wire anywhere in the chain.
I’ll try to give a reasonably simple explanation …
Normal “unbalanced” audio, such as used by pretty much all of your consumer audio gear consists of two wires: the ground wire, and the signal wire. The actual “signal” as measured by the receiver, is the difference between ground and the signal line.
As the signal travels down the wire, it gets exposed to electrical noise in the environment, and like an antenna, picks some of it up. By the time the signal reaches its destination, `signal` becomes `signal + noise`.
There are various ways to combat this, such as turning the ground wire into a hollow tube called a “shield”, and encasing the signal wire inside of the tube, to protect it against noise. Signal strength, impedance, endpoint termination, and other factors can also be taken into account.
I think AT&T invented balanced audio back in the day. Basically, at the source, you transmit *three* wires: ground, +signal, and -signal. This can be done through a simple transformer, or via active electronics.
At the receiving end, the receiver takes the difference between `+signal` and `-signal`, ignoring ground. This is your audio signal. Again, this can be done with a simple transformer or via active circuitry.
What makes this clever is that as the wires pass through any zone of electrical noise, that noise gets added to both wires equally. So the receiver receives `+signal+noise` and `-signal+noise`. When the receiver takes the difference, the noise cancels itself out.
In fact, the wires are typically twisted just to make sure that both wires are equally exposed to the noise. Microphone cables actually have two `+signal` and two `-signal` wires, all alternating and twisted, to make *sure* they all get an equal dose of the noise.
Fun fact: ethernet cables, such as Cat-5 and beyond, have four pairs of signal wires (and no ground at all), and each pair is twisted at a different rate to make sure they don’t transmit signals to each other (crosstalk). For this reason, you can’t just wire an ethernet cable randomly, you actually have to pay attention to which wire goes to which pin on the connector.
Another fun fact: not too long ago, someone realized that if the ground wire in unbalanced audio is not connected directly to the actual ground, but instead is connected with the same termination resistance as the signal wire, you get the same advantage as balanced audio. We may be seeing a change in wiring standards in the not too distant future.
Source: used to be the chief operator of a radio station.
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