What's the difference between balanced and unbalanced cables, and which should you use?
Cables come in balanced and unbalanced varieties, and it's important that you buy the right one. If you don't, you will potentially be introducing noise into your PA system.
An unbalanced cable has two wires inside the cable: a signal wire in the centre of the cable with a ground wire surrounding it.
The ground wire carries some of the audio signal and also acts as a shield to the main signal wire, protecting it partially from interference from lights, transformers and radio signals. However the ground wire can act as an aerial and pick up some noise!
Examples of unbalanced cables are a standard TS (tip-sleeve) guitar cable and a standard RCA cable.
Unbalanced cables are best used in short lengths up to 6 metres. If you need to use an unbalanced cable over a longer length you can use a DI box.
A balanced cable has three wires in the cable, two signals wires surrounded by a ground wire.
The same signal is sent down both signal wires, but one is sent with the polarity reversed. Any noise or interference the cable picks up along the way forms a peak. The reversed-polarity copy of the signal sent down the second wire carries it as a negative peak. When the signal arrives the negative peaks cancel out the positive peaks and the result is a clean signal with any noise cancelled out.
Balanced cables are therefore best for longer runs of up to 30 meters, but you can use a balanced cable at any length if you are concerned about noise.
Examples of balanced cables are XLR microphone cables and those used to connect mixer to amps. Balanced jack cables will be TRS (tip-ring-sleeve).
If you are sending a signal which is unbalanced at source, you will get no benefit from using a balanced cable beyond that. So the equipment you are connecting your balanced cable into (e.g. mixer) must be capable of producing a balanced signal.
If you use an unbalanced cable to send a signal which was balanced at source it won't cause any problems, but the signal will be susceptible to noise.