Or “Do I need a mixer?”
A mixer combines the audio signals from more than one microphone and adjusts their volume. It can also combine other audio signals (“sources”) like sound from your computer, DVD audio or music from an MP3 player. How do you decide when you need one?
If you’re using a professional sound system you need a mixer. If you have more than one audio source you need one. If you want to adjust the volume of your audio sources you need one.
One exception is if you’re plugging a single microphone into a house sound system. A microphone usually plugs directly into the wall, and you can adjust volume with controls on the wall. Even then technically you are using a mixer, it’s just built into the system. That’s why you might not see a separate “mixer” charge on the order.
It’s possible you’ll receive a quote with a bigger mixer than you need. Count up the number of “sources” (Microphones, computers with audio, etc.) then add at least two (in case of last minute needs). Your mixer should have at least this many “channels”. If you receive a quote for a mixer with many more channels (say, 16 instead of 4) then you may be able to switch to a less expensive model.