There's a patch of grass named for Harry Bertoia in the centre of the sprawling Huntington Library and Botanical Gardens complex in San Marino, California. It was there that I first encountered the Italian-American designer and artist's sounding sculptures—in this case, a set of 19-foot high beryllium rods topped with thick copper caps. The appearance was striking, geometric but natural, swaying in the wind like pond reeds. What was even more remarkable was the sound it made. As those caps and rods collided, the sculpture produced an immense roar, somewhere between the rush of a river and a gust of wind. The sculpture looked both futuristic and archaic, like a relic from a civilization that could have existed thousands of years in the future or the past.

That towering sounding sculpture is just one of tens of thousands that Harry Bertoia, who is best known for his modernist furniture, produced from the early 1960s until his death in 1978. Bertoia was a prolific and preternaturally talented sculptor, able to bend and mold metal as if it were wet clay. But the impact and power of his sculptures went beyond just appearance and feel. Like that piece at the Huntington, many were designed with sound in mind. Bertoia called this style Sonambient. These bespoke instruments sound unlike anything else made at the time—or today, for that matter.

Bertoia once put the sounds of his sculptures to wax, and called his record label Sonambient—years before Brian Eno ever used the term 'ambient' for music—but it's only in the past few years that the full scope of his work has been recognized. Thanks to an exhaustive reissue package from Important Records in 2016, and an ongoing effort to curate and release new Bertoia recordings by Important and the Bertoia estate, this visionary artist is earning his place among the 20th century experimental music greats.

Encompassing design, sculpture, acoustic sound art and experimental electronic music, Bertoia's body of work fuses modernism, futurism, minimalism and naturalism in a way that few other artists have. Even if Bertoia's art isn't electronic, its use of reverb, decay, volume and physicality in non-musical ways shares ideas with electroacoustic traditions, as well as electronic music. There isn't a world of difference in feeling those vibrations go through the floor and into your body from the bassweight of dubstep, or from the core-shaking frequencies of experimental drone artists.

Bertoia's sound sculptures have been used in contemporary recordings by the likes of Lee Ranaldo and Robert Aiki Aubrey Lowe. Japanese composer and musician Ryuichi Sakamoto cited Bertoia's sound sculptures as a major influence on his 2017 album, async, and recordings of Sakamoto playing the sculptures—made as part of a program at the New York Museum Of Design And Arts—appeared on that LP. Lowe, meanwhile, made his own album of Sonambient music, released last year on Demdike Stare's DDS label. Lowe found inspiration in the overtones, singing over the instruments to create a ghostly chorus. It's easy to imagine the vibrating metal reeds adding atmosphere or shading to a composition by Sakamoto.

Born Arieto Bertoia in Italy in 1915, Harry Bertoia moved with his father to Detroit when he was 15. He enrolled in a technical high school where he learned to make jewelry, and his handiwork earned him a scholarship at the Cranbrook Academy Of Art, where Bertoia fell in with designers like Florence Knoll and Charles and Ray Eames. Soon the Knoll company hired Bertoia to design modernist furniture, and it was then that his eye for intricate geometric patterns and natural-looking contours came to life.

Some of the furniture that Bertoia designed for Knoll became almost as famous as the legendary Eames chair. His "diamond chair," with its swooping lattices of metal and inviting round shape, remains his best-known creation. Still in production today, the chair provided Bertoia with the money to explore more abstract and creative work. Knoll encouraged his extracurricular activities, sometimes showing his sculptures alongside furniture in their showroom. Architectural sculpture commissions started rolling in as Bertoia's attention turned towards artistic and less-functional pieces, such as the metal trees and bushes that are starting to fetch higher prices today.

Many of Bertoia's sculptures mimic forms of nature. His vivid childhood memories of the Italian countryside, particularly fields of wheat, informed his designs. He began to make upright sculptures of rods that could sway and bend with the gentlest of force. It was when the rods started colliding that Bertoia had his eureka moment. They produced a sound that felt immense and monolithic, both hushed and impossibly loud, like the music of the Earth itself. He began to develop all sorts of instruments, from abstract sculptures to giant gongs, able to produce a range of sounds from the beautiful to the terrifying, and ranging in stature from miniature to massive.

For decades, Bertoia's own collection of his sculptures has sat in a big red barn in Allentown, Pennsylvania. The barn's high walls gave the already impressive sound of the sculptures an incredible natural reverb. He preferred to work in isolation, surrounded by nature. Bertoia would use this barn as a concert hall of sorts, walking between sculptures and activating them at particular times, creating an orchestra of otherworldly tones and bright resonance that rang out into the cavernous space around them.

Struck by the sounds he was getting from his sculptures and keen to share them with the world, Bertoia tried recording them for posterity. He released his first album on his Sonambient label in 1970. That record remained a one-off until his diagnosis with lung cancer, likely caused by decades of metalwork, in 1976. He hastily recorded over ten albums' worth of material, with a glut of records seeing release shortly after his death in 1978.

The Sonambient records languished in obscurity until recently, with only a little-known—and badly transferred—reissue by Japanese label P.S.F. in the late '90s. To celebrate 100 years since Bertoia's birth, the American experimental label Important Records released an 11-CD box set of all the Sonambient records in 2016, remastered from the original tapes. Previously unreleased recordings have also started to trickle out. The first features a previously unheard composition by Bertoia on one side, while the other side contains a piece recorded by his brother, Oreste, who was Harry's unwavering patron throughout his life.

Bertoia's recordings have an incredible dynamism that represents the raw power of nature, held together with a control that reaffirms the influence of man, a triumph of modernist thought and design. The sound of the sculptures reflected Bertoia's core philosophy. He tried to capture the beauty of the natural world with his complex array of metal structures. His work grappled with the non-musical modes of the Italian futurists, but where those artists sought to imitate mechanism and machinery, Bertoia's work revered a pre-industrial state of nature.

Though Bertoia's sculptures aren't as widely known as the work of some of his contemporaries (Alexander Calder, Donald Judd), they often make obsessives out of anyone lucky enough to hear and see them. James Elkind is one of those people. His Lost City Arts antiques store, on the edge of SoHo in New York City, has one of the biggest and most accessible collections of Bertoia's work outside the barn in Allentown. The shop hosts pieces, sounding and otherwise, that sell from anywhere between $40,000 and $300,000.

Elkind has been collecting Bertoia for almost two decades, from sounding sculptures to stately bronze bushes to the weeping willow tree that takes up one whole corner of the store, its thin metal rods draped down in a beautiful sweeping curve. Seeing sculptures like these in person is when you really start to understand Bertoia's incredible skill for craftsmanship and metalwork. Elkind told me that you could tell that certain pieces were not the work of his studio assistants, because "no one else could do exactly what he did." He also told me that, even taking studio assistants into consideration, Bertoia made his sculptures at an incomprehensible rate—at least one or two per day—if you average them out over the years that he was working.

At the entrance of Lost City Arts stands a six-foot tall gong that represents one of Bertoia's other ventures into the world of sound art, one that engages with traditional musical instruments. But it's no ordinary gong. Hollow and made from oxidized copper, the "monumental" gong has a gorgeous, stony appearance, as if it were carved from the wall of some mythical cave. Bertoia designed a special mallet himself, too, wrapped in suede, which softens the impact and makes even that tool feel like a product of the natural world. Hitting the gong, like playing the sounding sculptures in person, is an experience in resonance and decay.

Despite the imposing nature of some of Bertoia's gongs (a one-tonne, ten-foot wide gong hangs above his gravesite in Pennsylvania), it was the sculptures that didn't resemble instruments that made the most breathtaking sounds. Until recently, to hear them you'd have to visit a museum exhibiting his works, or the barn in Allentown, where master tapes and old copies of the Sonambient records sat for decades, under the care of the surviving Bertoia family.

The entire collection of Bertoia's master tapes now sits in the home of Important Records founder John Brien, about an hour's drive north of Boston. Walking into the room is like entering a shrine to Bertoia. There are framed pictures of him everywhere. His catalogue of tapes takes up an entire wall. A hefty (and carefully restored) tape console is installed solely to play back Bertoia's archives.

It's a sign of how large this project has become for Brien. When I arrived on a cloudy February afternoon, he had almost finished making his way through all of the master tapes, but a plan for what—and how much—to release was still a foggy notion. It had only been a few years since he discovered Bertoia, and now his life was consumed by him.

"Around five years ago, I pulled a photo of Harry out of a furniture catalogue. It was a picture of someone working on something they deeply care about," he explained. "But it was Discogs that recommended me his albums. I had no idea they existed. People had the records, but it took me a while to get to the bottom of that. There aren't a lot of them."

Bertoia's son Val found a trove of unsold records hidden in the barn. They were sun-damaged and warped, but they were the real thing, and their discovery caused a minor hubbub in the experimental music and sound art world. Val first gave the records to the RRR label. This connected Val to Massachusetts-based distributor Forced Exposure, which began selling the records directly to consumers. Seeing the prices start to rise, Val started selling the records himself, and it was at this point that some reissue campaigns started and fizzled.

"There were incredible overtones in the music," Brien told me of his first experience listening to the records. "I compare it to La Monte Young's Well-Tuned Piano, or singing Tibetan bowls, [and] bells. If there's anything with rich harmonic overtones, I get immersed really quickly. And Bertoia's music is just absolutely perfect. "

On all his albums, Bertoia created pieces, between ten and 20 minutes, with movements like symphonies. There was no known notation system, though Brien attests to the existence of multiple run-throughs of each work, hinting at some level of composition. Some pieces feature startling booms, jarring left turns or slow-burn crescendos; all have peaks and valleys of volume that make them unusually dynamic. Whether you consider it music or sound art, it's singular material.

"When different groups came into the Sonambient barn, they heard different things," Bertoia's daughter Celia, who now runs his estate and foundation, told me over the phone. "A group of nuns came one time, and they said, 'Oh, it sounds like the singing of hymns of a church.' Another gentleman was an airplane pilot and he thought it sounded like jets taking off. It meant something different to each person who heard it."

Buoyed by reactions like these, Bertoia sought to bring his sound art to as many ears as possible. "It was important to Harry to get his work out so people could experience it," Celia said. "He was pretty determined to see those recordings come to fruition."

All of the Sonambient albums have a similar approach: Bertoia would run through the barn, playing upwards of 20 sculptures for one piece. But the recordings that sit unreleased in the archives reveal other, more precise approaches, including a number of recordings simply labelled "experimental" that Bertoia seemed less interested in preserving. (Many were taped over or erased.) These experimental recordings focus on a single sculpture or type of sound, droning in a more focused way that reveals new layers and nuances in the sounding sculptures.

Sitting in Brien's studio listening to some of the experimental tapes, I was struck by how different they sounded. They were unmistakably Bertoia, but the atmosphere was different, more focused and almost monk-like. Some tapes hint at other forms of composition and experimentation. On other tapes, the music is reversed, creating a whole different kind of sound. And there's even what Brien describes as a "five-part opus," establishing a narrative structure in music that otherwise seemed to resist it.

Despite the loud, roaring sound emanating through the room, I was struck by the fleeting nature of Bertoia's art, as his sounds boom and fade into silence. The sound was stored on ephemeral media, too, largely kept on master tapes that were never digitally transferred. If these tapes weren't found at just the right time, they would have slowly degraded and been lost forever.

The beauty of Bertoia's sounding sculptures is that they could be played by anyone. When he was still alive, he encouraged visitors to play with the sculptures, and the family followed suit for a while after his death. Over the years, other artists have been invited to play and create with the sculptures, too.

But as Bertoia's work undergoes a critical reevaluation, access to his sound sculptures is shrinking. Bertoia's son Val no longer lets visitors to the barn play the instruments, and more of them are appearing in auction houses, likely to end up at museums where—for conservation reasons—people almost certainly would not be allowed to touch them. Most people I spoke to expressed concern that pieces held and exhibited by museums would only be on visual display and not for touching, which only allows them to tell half their story.

"It would make Harry crazy when he saw the exhibition sculptures with a big sign saying 'do not touch,'" Celia told me. "That was the whole thing—you had to see the visual, hear the auditory, and if you were in the Sonambient barn with the wood floor, you would even feel the vibrations right through the floor coming up your body. It was very important to him."

But Brien is doing his bit—he took the recordings of Bertoia playing on his sculptures and made them into an interactive installation that exhibited at Unsound Kraków last year. And thanks to Important Records, more of Bertoia's own recordings are on their way, while various installations around the world offer glimpses into Bertoia's universe of brass, copper and beryllium. And there's always that patch of grass in the Huntington, where the nine-foot sounding sculpture stands as an imposing monument to Bertoia's vision, one where mankind and the natural world lived in harmony, each basking in, and reacting to, the other's beauty and power.

Harry Bertoia Sonambient Mix

A 16-minute mix created by Important Records that features segments from each track of the 11-CD boxset, Complete Sonambient Collection.