Full, rich sound - without instrumental accompaniment or studio gimmicks - is the striking impression you get from The Heart of Carolina Chorus.

Representing the Durham-Chapel Hill chapter of the Barbershop Harmony Society, the all-male group is composed of basses, baritones, lead or second tenors, and tenors or first tenors.

"We have to create the instrumental sound to make a cappella sound like it is more than it is," director Chris Slacke said as his singers ran through the Frank Sinatra/Michael Buble tune "Come Fly with Me" during a recent rehearsal

"Let it grow and expand," he instructed. "When you hit the note, put some tension on it."

Barbershop quartets are all about balance and blend.

The four vocalists each play a specific role, working together to form chords, with the melody mostly in the second tenor, Slacke said. The goal is something called "the overtone," or fifth voice, also known as the harmonic.

"When it locks, it creates the harmonic," said tenor Matthew Gorman. "You can't help but smile when you hear chords."

The Heart of Carolina Chorus' 32 members come from a broad spectrum and include salesmen, medical doctors and retired clergy.

Assistant director Chris Boveroux of Chapel Hill, who has been singing in choirs since the fourth grade and plans to pursue a graduate degree in choral music, is "dedicated to making good music while also having fun."

Joe Simpson of Durham sings bass, and has been a member since 2007.

"I'm immersed, addicted, and enjoy it as a central part of life," he said. "I've made some great friends and have learned a huge amount."

The Barbershop Harmony Society was founded by Owen C. Cash in 1938. With headquarters in Nashville, Tenn., nearly 30,000 men from the United States and Canada were members as of 2007, according to its Web site.

The Durham-Chapel Hill chorus formed in 2005. It disbanded in 2008 and reorganized in September of 2009, and placed first in its division in an October competition.

"When we came off the stage at Myrtle Beach, my wife was sobbing," said Jack McCallus, chapter president. "She never heard us before."

The Heart of Carolina Chorus performs next at Emerald Pond, a retirement community in Durham, 7:30 p.m. Feb. 24 The performance is open to the public.

A fundraiser is also planned in Durham for March to help a young English girl with a genetic disorder that affects lipid metabolism. Her father has barbershop connections, and the family needs help paying her medical bills at Duke. For more information, visit helpmillie.co.uk.

The chorus rehearses on Thursday evenings at Blacknall Presbyterian Church in Durham.

Slacke said there also is an RTP group based out of Raleigh, and that some members sing in both groups.

For more information, Slacke may be reached at 919-730-3342.