WILLIAMSTOWN -- Over the low thrum of the bass, the shimmer of the dulcimer and the rhythm of strumming guitar, voices sing softly in three-part harmony.

Wintergreen -- Alice Spatz on double bass, Larry Spatz on guitar and Jared Polens on hammered dulcimer -- has played together for 24 years.

The folk trio will perform at the Williamstown Rural Lands Foundation at Sheep Hill on Saturday, March 8, and at the Berkshire Music School next Saturday, March 15, to celebrate the first new album they have recorded in almost a decade.

They came together over Irish music. In 1990, the Sterling and Francine Clark Art Institute had an Irish exhibit and wanted an evening of Irish music, Alice explained. She and Larry had played together for many years, with their son, Gregory, who appears on the new album, along with his wife, Caridwen Irving-Spatz, and local musicians Rick Leab, Tony Pisano and Aaron Marcus.

The Spatzes knew Polens from the Wild Oats co-op in Williamstown, where he worked then, and the three of them got together to play the Clark concert -- and they loved the sound they made.

The way the dulcimer rings reminds Alice of a harp or a harpsichord, she said, and it changed the way she and Larry play together.

Larry, a clinical chemist at Berkshire Medical Center, had taught himself to play the guitar in high school, after years of studying piano. He would go down to Greenwich Village, to Washington Square, in the 1950s -- as the folk boom was just beginning. He would listen to Pete Seeger and Leadbelly recordings and learn, he said, by listening and doing.

Polens, now kitchen manager at the Berkshire Food Project in North Adams, began his musical explorations with mountain dulcimer, with plucked strings. He first played a hammered dulcimer at a folk festival in the early ‘80s, he said, trying out someone else's instrument, "and that was it" -- he was hooked. He had sung a cappella in a Berkshire group called Northern Spy, and he played in Southwind, when it was the house band for a regular Pittsfield contra dance.

He began to sing with the hammered dulcimer only when Wintergreen began playing together, he said.

"And he's playing all his complicated counter-rhythms and countermelodies," Alice said.

She teaches at the Berkshire Music School, and composes classical music, as well as folk tunes. She grew up singing traditional music with her mother and grandmother, she said. And she had played mandolin, autoharp and guitar in her younger days, but when her children were in school, she discovered the double bass.

"It did to me what the hammered dulcimer did to Jared," she said.

She had a close encounter with a double bass, playing near one in a group -- and she started laughing spontaneously, she said. The sound of it touched her.

Wintergreen plays a mix of traditional American, Irish, English music -- "Eclectic is the right term," Larry said -- from the light to the solemn, from waltzing with bears and swinging on a star to Civil War music and Woody Guthrie ballads. They have collected songs and music from the Underground Railroad.

Alice has written tunes about old milltowns and about the Constitution Oak in Lanesborough, an enormous red oak on Bald Hill that has been growing, she said, for more than 300 years. A state forester told her that it might have been standing when John Adams signed the Constitution.

She has even written a tune inspired by a Berkshire Eagle story.

When judge Jack Downing started Soldier On to work with local veterans, Alice said, he said he could no longer serve as a judge -- "he said ‘we're all bound together in our brokenness,' " she recalled, and the idea stayed with her.

"We do our arrangements as we go," Polens said. "We don't write our arrangements -- not like bluegrass."

Larry added, "Alice and Jared can spontaneously --"

"Combust?" Polens suggested.

"Harmonize," Larry said. "You sing something and one of them can put a countermelody to that."

They improvise from long practice. They play all through the county, Polens said, and around it, from Williams College to the Troy Music Hall, to Windsor Lake in North Adams, to folk festivals in Boston. And in 1995, they traveled to Germany, to Pittsfield's sister city in Bavaria -- where they saw themselves advertised as "American country music," but the crowds loved their sound all the same.

But then, the three musicians asked each other, what exactly is folk music -- Gospel, Appalachian ballads, contra-dance jigs, French-Canadian reels, Swedish dance tunes ?

"It's anything anybody sings," Larry said. "There's no firm definition. You say it's music handed down in an oral tradition -- but then Bob Dylan and Woody Guthrie come along" and write their own music, "and that doesn't work."

A music student of Alice's, Paul Graubard, once told her that he loved Klezmer and Irish music because they were both the saddest and the happiest he had ever heard.

Polens recalled traveling in Ireland, meeting musicians in pubs and playing late into the night.

Maybe a folk song is the kind of song people play together in a fiddle jam in the small hours -- or the kind of song longtime friends sing together, their three voices rising firmly: "You'd better rosin up your bow before it's time to go."

If you go ...

What: Wintergreen in concert to celebrate new album

Where: Sheep Hill, 671 Cold Spring Road, Route 7, Williamstown

When: 2 p.m. Saturday, March 8

Where: Berkshire Music School, 30 Wendell Ave., Pittsfield

When: 3 p.m. Saturday, March 15

Admission: Free

Information: wrlf.org, wintergreentrio.com, berkshiremusicschool.org