MJ uses T20 FOSTEX semi-open vintage headphones.
This is a FOSTEX T20.It's a legendary model used by Michael Jackson, for example, in We Are the World.It's a semi-open type.It's re-cableable and can also be balanced (GND) connected.The ear pads were replaced about six months ago with thick, fluffy ones.I'll also include an adapter to convert the 6.35mm jack to 3.5mm.However, it doesn't produce much sound when used with a smartphone.