The SR-003MK2 is a 5-pin PRO bias type in-the-ear earspeaker, and can be used by connecting to a driver unit having 5-pin PRO bias output socket. The redesigned ear canal type structure of the SR-003 enables you to enjoy excellent electrostatic sound quality without covering your ears. The SR-003MK2 connects to STAX driver units or adapters equipped with 5-pin type PRO bias output.