Well, that is what they claim. But, think about it. People have been speaking in public for 1,000s of years in crowds like this. It didn't even look that that big of a crowd. Speakers CAN speak loud enough to be heard pretty well just by projecting their voice.
What did people do before electronic microphones? They projected their voice. It is really quite simple. Actors, Opera singers do it all the time.
That is why I think that the repeating stunt is some kind of “group bonding” technique. See comments above about Jim Jones supposedly doing this.
I thought a very clever group of conservatives did this as a joke on liberals. Really! What was that uniform way of flapping their hands?