Behind every great fiddler ...

Bob Childs lifts a naked, pale piece of maple wood up to the window. "We're looking for shapes," he says.

Only one shape is obvious to the untrained eye: This skinny slab looks like a violin. There are no strings, no scroll, no body, even – but there is nothing else these plump curves could become.

This, the back of the violin, represents a week's work. With a one-inch brass plane that works like a vegetable peeler, Mr. Childs has scraped away every flat spot on the surface. Each time he carves, he leaves an edge so tiny that he can't see it.

So Childs needs the sun. He tilts the wood toward the window, then away, like he's rocking a small baby with one hand. The light will catch the edges and cast shadows that act like a topographical map, telling Childs where a cut may need to be deepened or an edge softened. When the afternoon light finally falls in the right place, the back of Childs's newest violin looks like a glimmering lake. Sun and shadows dance, and he knows if the sound will be good.

His precise intuition makes him the go-to guy for New England folk-fiddlers and symphony players alike. His reputation allows him a rather unusual business model: Unlike many makers, who often leave their instruments in shops, Childs has never sold a violin on consignment. He crafts each $16,000 instrument with a person in mind – who they are, how they play, what sound they need.

He gets new customers by referrals from old ones. And he's collected the oldest and best of them in a band called Childsplay – 30 players, each a Childs violin owner, who descend on Cambridge, Mass., once a year from around the country and, occasionally, from abroad. They travel less for the chance to perform than to see Childs, reunite with friends for a week of rehearsals and a month of concerts – and to try out one another's fiddles.

In this way, Childs's work is less a business than a musical family, held together by a laid-back patriarch who otherwise labors quietly, far from the limelight – except for the annual Childsplay concert, a folk music love-fest at which Childs is, naturally, the center of attention.

The tradition stretches back to a 1988 night in Childs's living room, where he collected some customers-cum-friends; each played a song. "I loved that concert because it was such a demonstration of Bob's caring for each person that he had built an instrument for," says Mary Lea, Childs's first customer. "[H]e was a mother hen with his chicks."

The group quickly grew into a proper band: Today, it has a website, childsplay.org, and just released its fourth CD. Though the players stay the same from year to year (Childs, who makes five or six fiddles a year, has closed membership in the group), the featured folk tradition changes. In their solo lives, musicians usually specialize in one genre, from old-time Appalachian to Celtic-sounding Cape Breton fiddling, and play center stage.With a grace often missing from family reunions, the Childsplay fiddlers surrender the limelight to a few featured players and focus on what Childs thinks makes his band unique among folk groups – meticulously layered rhythm and harmony, like the great symphonies of the classical world.

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Some fiddlers start as classical musicians; they may keep up the concertos or abandon them for a world of reels, jigs, and airs. It can be a difficult switch: Classical players learn by reading music, but folk players learn by ear. That process is integral to the sense of community many fiddlers love: open your case, pick up your instrument, and jam with whomever's around. To do that, you have to give up the stability of the printed page – and the fear that playing without it can inspire. You have to play, Childs says, from a different place.

"I have a friend ...[whose] conclusion was when you play classical music, because you're reading notes, you're playing from the outside in," he says. "When you're playing fiddle music, you're playing from the inside out."

Childs didn't play until he was 18. "I fell in love with it so much that I almost didn't finish college," he says. He learned by ear and took his fiddle to Maine, where he made furniture after college. When the instrument needed repair, he took it to Ivie Mann, a luthier in his 70s who'd never left the state. Mr. Mann invited Childs to be his first student. Skeptical, Childs took up the study part time, eventually spending 10 years learning the craft. Unlike many modern American makers, who usually study in one of the country's four violinmaking schools, Childs learned the old-fashioned way, as an apprentice in small shops. His training included repair work, which meant he got to disassemble some of the most sought-after violins and make patterns he still uses today.

But the profession's two cruelest characteristics – perfection and isolation – soon bothered him. Though essentially nothing about the way good violins are made has changed since Stradivarius, the craft is exhaustively exacting. Childs wasn't certain he'd reach its standards for perfection. He also wasn't certain that he wanted to: It required toiling in quiet solitude, and he sometimes felt lonely.

So he quit. He started painting classes and began a search for his roots; Childs had been given up for adoption as an infant, shuttled between foster homes, and finally adopted when he was 3. Though he remembers little of that time, the mystery nagged him. In his early 30s, he began a search for his birth mother. During the search, he had a gripping dream that changed everything about violins for him. In the dream, Childs wanted to visit an unknown country, but he was stopped by a border guard who took him into a small room, dark and empty but for a table with a violin. A guard told Childs to pick up the violin; he obeyed. Inlaid into the back, was an image of a small boy crying," he remembers.

For the first time, he realized making violins was more than a living for him: The craft, he says, helped him express experiences "that don't necessarily have language."

After that, his fiddles changed: Their tone was more even, their voice more consistent. Players who bought his early instruments and traded up as he improved didn't feel the need to any longer. And Childs found an answer for the isolation: He got a doctorate, one night class at a time, in psychology, and opened a psychotherapy practice. In some sense it isn't all that different from making violins. He listens for things without language and whittles away until a patient, like an instrument, finds a hidden voice.

"It's a trick for trees to give up their secrets," Childs says. He needs customers to describe "the sound they hear in their head when they're playing." He, in turn, describes how the planks of wood he lays in front of them will sound when fashioned into an instrument. To do this, he pinches a two-foot piece of spruce between his left thumb and fingers and holds another in his right. Gently, he strikes one piece against the other, and the room rings. "We're listening for a bell-like sound, where it doesn't just go 'thud,' " he explains. Each person has to find the right ring. When it works, it's almost magical.

"It's not that it's the perfect fiddle everybody wants to play," says Hanneke Cassel, a folk player. "But it's the right fiddle for me. It made me sound more like what I sound like."

Childs gets it right every time – only one of 140 customers ultimately disliked his new instrument – because he knows violins are best made like music: from the inside out.