The whole point of a live sound system is to take a sound, turn it into a signal, then boost it WAY up so speakers can turn it back into a much louder sound. Then, a large audience can hear the original sound and we have a show.
Of course, this is way over simplified, and there are a TON of parts in that system! But the way we turn sound into signal, and signal into sound, is with a transducer. Technically, a transducer is something that takes one form of energy and turns it into another form of energy. For us, it's acoustic sound into electrical signal, and then back into sound.
For the first part of this process, we use a microphone. This takes a sound wave and uses a diaphragm to turn it into a signal. We then can route that signal through the rest of the audio system and it will eventually come out the other end, which are the speakers.
And in the same way that a microphone turns the sound into signal, a speaker turns the signal into sound. These two transducers are the key to the whole system working, and are also the most difficult to sound good. That’s why high-quality microphones and speakers are really expensive!
Obviously, not every venue can afford that. But, lucky for us, even the quality of inexpensive speakers has gotten SO much better with modern audio technology. And this means that we're able to have good sound almost anywhere. You just need a good mix!