Within Pro Audio, recording and PA applications there is only one standard protocol for passing un-amplified or pre-amplified analogue signals, which is referred to as ‘Line Level’. However, Line Level comes in one of two varieties, namely Balanced or Unbalanced.
A single core screened cable generally carries an unbalanced line level connection. The screening around the core, which carries the signal, provides the earth connection and protects the core from unwanted interference or noise. However, within long cable throws it is possible for noise to penetrate the screen and to become superimposed upon the signal, carried by the core.
Unbalance line level operates at a signal strength of -10dBu. Typical connectors are ¼” Jack or Phono connections.
To counter the issue broached above, wherein noise may be superimposed upon signals carried by long unbalanced cabling, one may use balanced connections providing the products within a particular system support this protocol.
Balanced cabling uses a twin core screened cable. As in an unbalanced lead the screen offers a certain degree of protection against unwanted noise, which may be superimposed upon the signal carried by the core. However, within a balanced signal there are two component parts that carry the signal, a positive connection and a negative connection, which are precisely 180 degrees out of phase.
Upon transmission within a balanced system the signal is split into two components, one remains untouched (positive) whereas the other (negative) is phase shifted by 180 degrees. Upon receipt, the negative component receives another 180-degree phase shift and at this point is recombined with the positive signal. As a result any noise, which may have been superimposed upon both the positive and negative components of the signal within the cable, becomes completely phase cancelled leaving a ‘clean’ signal with a far higher Signal to Noise Ratio than would otherwise be the case if using unbalanced connections.
Balanced signals also have a higher signal strength, at +4dBu, than unbalanced signals, which operate at a standard –10dBu. Typical connections are either XLR or ¼” TRS (Tip, Ring, Sleeve) Jacks. Note that within XLR’s, pin one is the screen, pin 2 positive and pin 3 negative whereas on a TRS Jack the sleeve connects to the screen, the tip is positive and the ring negative.
Examples of mixers that have balanced outputs:
Examples or power amplifiers or active speaker cabs that have balanced inputs:
It is therefore apparent that is far more preferable to use balanced connections, particularly over long cable throws, to unbalanced providing the products used within a given system support this protocol.
Note: Screened cabling must never be used as speaker cabling, since it extremely inefficient at carrying the high power levels generally delivered by power amplifies. The effect of using screened cables for speakers is normally twofold, firstly reduced output due to the resistivity of the cabling and secondly cables failing as they burn out – speaker cables use much thicker wiring designed to efficiently pass high power, unlike screened cabling.