If you hear a group of female voices singing in distinctively sweet and sonorous harmony this week, don’t be surprised. Just sit back and let the music ring.

Chances are you’ll be enjoying championship-level vocalizing from participants in the 67th annual Sweet Adelines International convention and competition, which will be in town this week for five days of performances. More than 5,000 a cappella vocalists from as far away as Scandinavia and Africa are expected.

"There’s about 30 choruses competing from all over the world, and there will be about 50 quartets as well," said Christina Smith, assistant director of Hono­lulu Blend Show Chorus, a local chapter of Sweet Adelines. "And all the regional winners come in, and they compete for the big award, the international award. This is big time."

Sweet Adelines are women who specialize in a four-part-harmony style of singing originally popularized by men’s barbershop quartets. Aside from the generally good-humored nature of the songs, the style is characterized by a bright, vibrant and full sonority created by a unique blend of voices singing in a mathematically precise tuning. Done properly, the four voices produce not just four notes, but a particularly resonant effect called an overtone.

"In barbershop the tenor is very light on the top, and the bass is very broad on the bottom, like a foundation," Smith said. "And the idea is to ‘lock and ring’ the chords, and when you lock and ring, you get an overtone. If you’re not in tune, or if you’ve got any issues with balance or anything like that, you won’t ring the chords. Basically, on the competition side of it, whoever rings the most chords wins."

Honolulu Blend is one of two Sweet Adelines groups in Hawaii. Na Leo Lani, led by Vera Egge, has been performing in Hawaii for 38 years. Smith formed Hono­lulu Blend in 2007, and the group now has about 25 members and has become quite proficient in ringing the chords, winning a regional championship last year against teams from California. The group is coached by Bonnie McKibben, an internationally recognized Sweet Adeline singer who also coaches the local men’s barbershop quartet organization, the Sounds of Aloha Chorus.

Her group won’t be competing at this convention — it’s been invited to a tourney next year for the top five small choruses in the world — but it will still get recognition by performing as a warm-up to the competition for small and midsize choruses at 6 p.m. Tuesday.

"We’re the mic testers," Smith said. "It’s very much a place of honor. And because this is our home and where we all live, and internationally it seems we’re progressing really fast and really well, we’re being allowed to do this with our director. So we’re very lucky, very lucky to get onto the international stage and have a practice before we do it for real next year."