Now let's make a simple intercom. When you finish wiring, set the slide switch up and speak into the LS1.
Rotate the control volume clockwise slowly. Your voice through the speaker should get louder. Don't rotate the control volume too much, or an acoustic feedback (howling) may result.
Set the slide switch down. Now the LS1 and the speaker LS2 switch their function-speak into the speaker, and you hear your voice through LS1.
The LS1 and the slide switch works as master station of an intercom, and the speaker LS2 works as the remote station. This system is used in the household intercoms in your home.