Okay I hate to go all science-y on you, but they're kinda both, but mostly mics. They receive the soundwaves hitting your ear, much like a microphone. However, the reason our voices sound ever-so-slightly different (and a large reason why we hate the sound of our own voices) is is because of "bone conduction", wherein the sound from your larynx (voice box) is conducted to your inner ear directly via your skull bones, making your voice sound just that tiny bit deeper to you. So they KINDA act as speakers, too, if you really loosen your interpretation.
Caption this Meme
