Beyond headphones, there's a line out for connecting it to a sound system, and a line in and microphone jack for adding external sound to the set.

ENGADGET

Murray said that technical difficulties prevented the microphone from picking up sound, the drill steel was blocking the microphone, and a line broke.

CNN: Camera lowered into mine cavity shows 'survivable space'

You hear him (via the microphone he's wearing) shout an audible at the line and listen as his breath swells.

FORBES: Magazine Article