HOW BALANCED WIRING REJECTS NOISE?

Signal Connections on an analog audio system may be either balanced or unbalanced.

An unbalanced (two conductor system) connection relies on a two conductor cable. The central conductor (core) carries live (hot) signal and the other is cold (- ve) which is connected to the ground. This conductor can give less protection against an electromagnetic interference to the wanted signal.

So normally unbalanced wiring is not recommended in audio wiring.

Professional equipment solves this problem for getting increased immunity to electromagnetic induction.

In balanced wiring, instead of 2 conductor system,3 conductors are used. They are often labeled (for convenience) as ‘+’ for live or hot and ‘-‘ or return or cold (since audio is an alternating current, there is no constant polarity). The two wires are twisted closely together in a single cable, so the interference radiated into the cable gets picked up equally by both wires.

When you take voltage differences between wires you can see that the noise is cancelled.

Find the diagram below which depicts the technical aspects in detail,