Lexikon Symmetrischer Anschluß specifications

Category : Lexicon

With the balanced connection, an audio signal is transmitted via a pair of wires, which acts as a forward and return line (this forms an electrical circuit). As a result, the transmission becomes independent of the level of the signal ground. Further advantages result if the impedances of the forward and return lines are made equal and the two wires are twisted together. In addition, the wire pair can also be surrounded with a shield. A transmission designed in this way offers a very high noise immunity, and is suitable for longer distances (several hundred meters).

Full symmetry is achieved when the signal that is exactly inverse to the forward signal is present on the return line. However, this is not absolutely necessary to achieve good noise immunity. The decisive factor is rather the symmetry of the impedances, which ensures that disturbances in the forward and return conductors couple in equally strongly, and thus fall out again in the receiver by forming a difference.

In the case of symmetrical transmission, the forward conductor is often called "Hot" or marked with the plus sign. The return conductor is then "Cold" or bears the minus sign. A possible shield is usually connected to the housing mass of the connected devices.

The connectors used for balanced transmission are the 3-pin XLR connector and, to a lesser extent, the 1/4" jack connector. The XLR connector uses pin 1 for shielding, pin 2 for "Hot" and pin 3 for "Cold" as standard. The following applies to the jack plug: sleeve = shielding, tip = Hot, ring = Cold.

Symmetrical transmission is found above all when the high immunity to interference and the insensitivity to differences in the ground level are required, which is especially the case with longer cable lengths and high quality requirements. Such requirements occur in professional sound engineering, such as studio technology, event technology, and when installing sound engineering systems in larger buildings, e.g. concert halls or broadcasting stations. In the Hi-fi sector, balanced connections are the exception, even if they would offer a good way to avoid hum loops.