The XLR connector is the standard for professional audio and video applications. The plug itself is an electrical connector by design. Like the more ubiquitous RCA plug, which is 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 adding a latch, the “Cannon XL” and finally the “XLR” after adding a rubber compound 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 film and video cameras. XLR5 is the standard for DMX512 digital lighting control, as well as two-element microphones and two-channel talkback headsets. XLR6 is the standard connection for dual channel intercom beltpacks.
There are several now obsolete configurations with additional pins, including the XLR-LNE mains power connector, which was identified by its red insulation and covered pins, and has now been replaced by the Neutrik PowerCon connector. Until recently, XLR3 connectors were also widely used with 2-conductor speaker cables, with pin 2 or 3 as hot (varies by manufacturer) and pin 1 as ground return. However, it turned out to be dangerous to equipment and has since been replaced by the Neutrik Speakon connector.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 inserted. Due to the fact that the ground connection is made before the signal lines make contact, XLRs can be connected and disconnected without interference from external signals, a common problem with RCA connections. There is some discrepancy between various manufacturers between the swapping of pin 2 (normal input) and pin 3 (inverting input), but this reflects nothing more than their own pre-existing standards before standards existed. Pin 1 is exclusively the ground or ground return pin and is often soldered to the internal case or casing.
Lastly, the XLRM male connector is used for output and the XLRF connector is used for input. So a microphone for example will have the XLRM connector. The signal cables will have XLRM on one end and an XLRF connector on the other. Mixing consoles and various multitrack recording equipment often have XLRF inputs and XLRM returns that lead to the stage or other components.
XLR connectors have long been the standard in the professional audio and recording industry. XLR plugs are generally referred to as “balanced” and help reduce noise interference, especially on long runs. The quality of XLR cables varies widely by manufacturer, but for professional use, check out Canare, Mogami, and Neutrik.
Recently, the advent of USB microphones that plug directly into a PC or MAC has gained popularity. Until now, USB microphones are primarily intended for use as studio microphones, with live stage vocal microphones continuing to use the standard XLR connections.