This basic single speaker is great for public address within a medium radius. Pair it with a microphone to complete the package.
You can also get a pair for dance music within a small hall.
The speaker has the ability to connect to your phone through bluetooth, or you can plug in a USB drive or even an SD card with MP3's on it to play music.
If you need something larger, especially for an outdoor space, consider the Loud Outdoor Sound System.