1. Active speaker 2. Class AB amplifier 3. Rechargeable battery 4. Microphone priority switch 5. USB/SD card player 12'' ... USB SD MP3 Wireless Portable PA Speaker System AK12-203Portable PA System Features:1. USB ... *Room, outside(especially suitable dancing, gymnastics, demonstration's loud-speaker, recorded, play) *Teaching, Conference, classroom, military training, ...