[ben1040]

I flew some overseas trips on Delta 767s in the late 1990s that still had the tube headphones. I was pretty intrigued by the concept, you could hold your hand up to the tube holes in the arm rest and hear the music echo off your hand.

Either on the headphones themselves or in the little overwrap bag there was a note to leave them on the aircraft when you deplane, because they (obviously) wouldn’t work elsewhere.