Love barbershop music.  It's normally performed by a quartet.
It's famous for it's ringing chords, produced by singing a combination of notes that are perfectly tuned.
One of the things I really love about the sound is the harmony and the use of what's called "snakes" or "swipes".
It was developed by African Americans in the late nineteenth century.
So many things were influenced by African-Americans.  They constitute 1/3 largest racial and ethnic group in the United States.
When Edison's phonograph grew in popularity, the music genre did too.
Edison is described as one of the greatest American inventors.  He had an interesting middle name of Alva.