alt Hacker Newsnot only can electromagnet voice coils (speakers or microphones), be used as either a speaker or a microphone (transducer), they can even be used as both at the same time using a DC-coupled circulator / isolator:
not only can electromagnet voice coils (speakers or microphones), be used as either a speaker or a microphone (transducer), they can even be used as both at the same time using a DC-coupled circulator / isolator: