XLR 3-Pin

The XLR connector was invented by James H. Cannon, founder of Cannon Electric in Los Angeles. Cannon's original X Series connector gained a locking latch around 1950, creating the "XL" line, and around 1955 gained a synthetic rubber (neoprene) insulator on its female contacts, giving rise to the "XLR" part-number prefix that became the connector's common name. The company later became ITT Cannon.

Though it began as a Cannon Electric trademark, other manufacturers eventually produced compatible connectors and XLR became a generic industry term. Its three-pin, balanced-signal design suited it to broadcast and professional audio equipment, and it remains the standard connector for microphones, balanced line-level audio, and DMX lighting control decades later.

The 48-volt phantom power standard used to power condenser microphones over the same XLR cable as the audio signal traces back to Neumann in the 1960s. Neumann needed a power source for its new KM 84 small-diaphragm condenser microphone, developed for Norwegian Broadcasting (NRK); NRK's studios already ran 48-volt supplies for backup lighting, and that voltage was adopted for the microphone design. It was later formalized in the German DIN 45596 standard, and 48V phantom power (P48) remains the industry standard today.

Because Pins 2 and 3 both carry the same 48V relative to Pin 1's ground, phantom power doesn't interfere with the balanced audio signal riding on those same two pins -- the microphone's internal transformer blocks the DC while passing the AC audio signal through.