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.
African Americans
African Americans (also referred to as Black Americans or Afro-Americans) are an ethnic group of Americans with total or partial ancestry from any of the black racial groups of Africa. The term typically refers to descendants of enslaved black people who are from the United States.
African Americans constitute the third largest racial and ethnic group in the United States (after White Americans and Hispanic and Latino Americans). Most African Americans are descendants of enslaved peoples within the boundaries of the present United States. On average
usually sung by the tenor or baritone, except for an infrequent note or two to avoid awkward voice leading, in tags or codas, or when some appropriate embellishment can be created. One characteristic feature of barbershop harmony is the use of what is known as "snakes" and "swipes". This is when a chord is altered by a change in one or more non-melodic voices. Occasional passages may be sung by fewer than four voice parts.
Barbershop music is generally performed by either a barbershop quartet,