Closing your eyes, it's hard to imagine that all those sounds are coming from the human voice.

But with the five-man a cappella group Rockapella, that's exactly the case. And much of that is thanks to Jeff Thacher, who does the "mouth drums."

"I am the percussion instrument," Thacher explained.

Rockapella will bring its sound to the Utah Symphony next weekend when they join with conductor Keith Lockhart for a concert. "We so look forward to it," Thacher said, "because every time we play Utah, we meet with a great response of people. They really seem to enjoy what we have to offer. And of course, if you put that with something really interesting and different, like an orchestra and an a cappella group together, then you can't lose."

Thacher said the group has just come off of a "deliciously fun tour" with the Boston Pops (also with Lockhart), which included performances at Ravinia, Tanglewood, Symphony Hall in Boston and the Fourth of July celebration at the Boston Esplanade — which he said was "quite something."

"It's half a million people — and that's probably just what's on the grass, not counting the TV broadcast. You have professional cameras shooting you for TV, so it's this swirling bit of entertainment with a lot of really high security."

The program played on the tour, he said, was similar to the program scheduled for Salt Lake City. It's a mix of several original songs, arrangements of other songs and two additional songs that were created exclusively for the orchestral shows — fun 1960s and '70s songs, such as "Rock the Boat," "Shambala" and "Here Comes the Sun," with an overall '70s theme.

"There's a little give and take between each group," Thacher said, "but each group has something that the other doesn't, so it works out nicely. We also do a few things on our own, so the audience gets a feel for what we're about, then we do things together with the orchestra, and of course, the orchestra does things on their own."

Recently, Rockapella has become known for appearing on the PBS children's program "Carmen Sandiego" for five years. For a time, he said, the group's voices were also heard in "the homes of America" with a well-known Folgers TV ad, as well as national morning shows and "countless" local TV appearances.

"We're quite comfortable in front of the camera," Thacher said, "in fact, perhaps too comfortable sometimes. But I think Rockapella translates well between live and camera and studio, so we're sort of the Swiss army knife of music."

Thacher has been with the group since 1993. None of the current singers — Thacher, Scott Leonard, Kevin Wright, John Brown, and George Baldi — was part of the original group, however. "We've always had great musicians in the group, but we've evolved into a much more dynamic touring act. We tour America and Asia, and we have our own original material on our albums. And as that developed, our group became more and more defined, and groovy — to use a slightly outdated word.

"It definitely locked into this very rhythmic, high-power, high-energy sound that was there to some degree beforehand, but I think it really came into its own in, I'd say, the late '90s, early 2000s."

If you go

What: Rockapella, Utah Symphony

Where: Abravanel Hall, 123 S. West Temple

When: Friday and Saturday, 8 p.m.

How much: $20-$50

Phone: 355-2787 or 888-451-2787