Roman said a chord is “locked” when the four parts are sung precisely on pitch, with identical vowel sounds. When that happens, overtones — extra notes — are created even though they're not actually being sung.
Music Central director Mark Winn said barbershop harmony produces an unmistakable sound.
Both local groups are members of the Barbershop Harmony Society.
The original organization was formed in Tulsa in 1938 following an impromptu songfest on the rooftop of a downtown hotel, reviving an American art form that began in the 1800s.
OK Chorale became the third chapter to join.
Pinkson said OK Chorale, originally known as the Singing Sooners, once had a membership of about 100. Membership now stands at about 60, with ages ranging from 11 to 93.
Gov. Mary Fallin proclaimed the week of April 7-14 as Barbershop Harmony Week in Oklahoma.
The April 27 concert will include western, patriotic and gospel music, a medley of songs from “The Music Man,” and old standards such as “My Wild Irish Rose” and “By the Old Mill Stream.”
Ricky Bugher, 60, has been singing barbershop music for 28 years. He recently brought his grandson, Levi Saylor, 11, into the chorus.
When done right, Bugher said, barbershop harmony is like no other kind of singing.
“People don't know what it is they like about it — but they like it.”