A cappella
A barbershop group has 4 people. The name of this genre came from the tradition that when many men gathered in a barbershop they would sing with no musical instruments. A barbershop quartet has four male voices or four female voices.  Mixed barbershop quartets are also possible, usually with two male and two female voices.  The voices parts are called bass, baritone, lead, and tenor. In music in the barbershop style, the melody (the "tune") is sung by the lead part.