A cappella band Six Appeal will perform their classics in Beijing on Friday. [Photo provided to China Daily]

In 2012, they won the National Harmony Sweepstakes Championship, an annual competition in the US.

"When Six Appeal was very new, I always believed that it could be a professional ensemble. There were several a cappella groups at that time that showed us that it could be done, and were an inspiration to us from the very beginning," says Roll, of groups such as Naturally 7, The Real Group and The Swingle Singers, among others.

The real trick to a cappella singing, Roll says, is that you have to make it seem easy.

"No audience wants to feel as though the music is out of control. That is the first step. The second step is to create new music. It's one thing to mimic a song that everybody knows. There are hundreds of a cappella groups that can mimic. What makes a group special is to add artistry to the music. The third step is to set yourselves apart. Find what makes your group special," Roll says.

It took several years for Six Appeal to have a style of their own. They describe their sound as "vibrant, dynamic and eclectic". Beyond music, they believe that their shows should be fun.

"We want the audience to feel relaxed, playful and surprised over and over again throughout our show, and be thoroughly entertained on every level," Roll says.

One of the biggest challenges for Six Appeal is presenting music in a voice-only format to listeners who are not accustomed to a cappella. But it also comes as one of a cappella's biggest rewards, "when you see an audience member recognize a song", says Roll.

"They'll either start singing along, or have an amazed look on their face for the rest of the show," he adds.

Now, with about 120 shows a year, the group is considering taking in a seventh member－maybe even a woman.

If you go

7:30 pm, Friday. Art& Education Center for the Performing Arts, Tsinghua University, Haidian district, Beijing. 010-6278-1984.