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 ubiquitous RCA plug , 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. the connector was first called the “Cannon X,” and after the addition of a latch the “Cannon XL” and finally the “XLR” after having a rubber compound added to 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 widely used configurations of the XLR plug is the 4-pin XLR4, used with Clear-Com and Telex intercom headsets and as DC power connectors for video and film cameras. XLR5 is the standard for DMX512 digital lighting control as well as 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 additional 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. Until recently, XLR3 connectors were also widely used with 2-conductor loudspeaker cables, with either pin 2 or 3 as live (varies 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 However, this turned out to be dangerous to equipment and has since been replaced by the Neutrik Speakon connector.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. There is some discrepancy between various manufacturers between swapping pin 2 (normal input) and pin 3 (inverting input), but this reflects nothing more than their own pre-existing standards before any standards existed. Pin 1 is exclusively the earthly return or ground pin, and often soldered to the internal shell or case.
Lastly, the XLRM male connector is used for output and the XLRF plug is used for input. So, a microphone for example will have the XLRM connector. Signal cables will have XLRM at one end and an XLRF connector at the other. Mixing boards and various multi-track recording equipment pieces typically have XLRF inputs and XLRM returns which lead back to the stage, or to other components.
XLR connectors have been the standard in the professional recording and audio industry. XLR plugs are typically referred to as “balanced” and help reduce noise interference, especially over long spans. 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.