As another reply mentioned, I gave a speech in the morning assembly once. I could, in some way, listen to myself speak through the speakers in real time and I didn't stutter at all. I gave a speech two years ago in front of my classroom where I was friends with literally everyone but still I stuttered a lot. In the assembly speech, I did know many of them, so that may have been a helpful factor, but I didn't know around 50% of the audience at all and yet I didn't stutter.