The XLR plug is the standard for pro audio and video applications. The plug itself is an electrical connector by design. Not unlike the more well-known RCA connector, which used regularly with home audio and video electronics, the XLR connector is different in several important ways.
Originally designed and manufactured by James h. Cannon, the connector was originally called the “Cannon X,” and later the “Canon XL” and finally the “XLR” after the addition of the latch (XL) and rubber compound (XLR) which surrounds the connectors.
The 3-pin XLR is the most widely used, and is the standard as a balanced audio connector for professional microphones and connections between equipment. Other configurations are also widely used including the 4-pin XLR4, for Clear-Com and Telex intercom headsets and DC power connection for film and video cameras. The XLR5 connector is the standard for DMX512 digital lighting control and also is used for dual element microphones and dual channel intercom headsets. XLR6 is the standard connection for dual channel intercom belt-packs.
There are several now obselete configurations with additonal pins including the XLR-LNE mains power connector, which was identified by its red insulation and shrouded pins, and has now been replace by the Neutrik PowerCon connector. XLR3 connectors were at one time also used extensively on 2-conductor loudspeaker cables, with either pin 2 or 3 as live (depending on the manufacturer) and pin 1 as the earthly return. However, this turned out to be dangerous to equipment and has since been replaced by the Neutrik Speakon connector.
XLRF connectors are made to connect the ground pin first, before the other pins make contact while the XLRM is being inserted. Due to the fact that the ground connection is made before the signal lines make contact, XLR’s can be plugged and unplugged without interference from external signals, a common problem with RCA connections. Even nowadays there is discrepancy between various manufacturers between whether pin 2 is udes as the normal input and pin 3 as the inverting input or vice versa, but this reflects nothing more than their own pre-existing standards before any standards existed. Pin 1 is always the ground, or earthly return pin, and is often connected to the internal shell or case.
Lastly, the XLRM male connector is used for output and the XLRF plug is used for input. So, for example vocal microphones will have a XLRM connector . Signal cables will have XLRM at one end and an XLRF connector at the other. Mixers and other multi-track recording equipment components will have XLRF inputs, and XLRM returns to stage, or out to other components.
XLR connectors are the standard in the professional audio and recording industry. “Balanced” XLR cables help reduce noise and interference, especially over long runs. Quality in XLR cables varies greatly depending on the manufacturer, but for professional use please check out Canare, Mogami and Neutrik.
Recently, the advent of USB microphones that connect directly to a PC or MAC have gained popularity. So far, USB microphones are primarily intended to be used as studio microphones, and live stage vocal microphones continue to use the standard XLR connections.
