History of the XLR Connector

The origin of the XLR connector was the Cannon X Series connector. It was fitting the demands of the audio community except the missing latch. Cannon rearranged the pins and added a latch. The new connector was called Cannon XL Series (X Series with Latch). Later the female version was changed to put the contacts in a resilient rubber compound. The connector was then called Cannon XLR Series.
This connector soon became the industry's standard and nearly every connector manufacturer copied the Cannon connector. It became a AES standard in 1982 with the pin assignment: 1: shield/ground, 2: hot pin, 3: cold pin. It has needed a long period of time until the pin 2 / pin 3 confusion was finished (Is it really finished yet?).

New AES-Standard: AES14-1992 (r1998) AES standard for professional audio equipment, application of connectors, part 1, XLR-type polarity and gender [1999-03-05 printing].

Soon XLR connectors with more pins and special purposes were developed.

Since the AES standard AES 3-1992 the three-pin XLR connector is also the standard connector for AES/EBU digital connections (electronically balanced, impedance 110 ohms).