Using Android device as a loudspeaker I have a class of 100 students, and I have an idea to use my mobile as a loudspeaker so I don't have to shout.

Alternatively, it should work like an amplifier system. The difference is that the input is the mobile, the amplifier is the mobile and the output is a USB speaker connected to it.

Is it possible to do that?
You can use a microphone app like Microphone by Gaz Davidson.

There is a lag, but then again your phone isn't a full blown stereo mixer.