Bertoia was a pioneer in using sound as sculptural material. He first noticed the aural qualities of vibrating metal in his wire works in the late 1950s, but began to create sound-based sculptures in earnest during the later 1960s. The Sonambient classification includes gongs, singing bars, and tonals, as well as the recordings Bertoia made using these sounding sculptures. No two Sonambient artworks are exactly the same, which is a particularly astounding fact in the case of tonals, which number in the hundreds.
Bertoia coined the word Sonambient in order to convey the unique properties of his sounding sculptures. The term connotes the use of sculpture to create an ambient sonic environment and is closely associated with the performances enacted in his barn studio. The term, however, has also led to some confusion in the titling and categorization of Bertoia’s sound-based sculptures. Sonambient is sometimes used as a shorthand for the tonals, and frequently appears as a modifier for Bertoia’s home studio (the Sonambient Barn) or the works that were placed inside the studio on his property in Barto, Pennsylvania. These pieces carry added art historical significance in that Bertoia personally activated or recorded them as a group. But it should be noted that the individual works remain untitled sculptures, and the artist frequently rotated sculptures in and out of the Barn until his death in 1978. The Harry Bertoia Catalogue Raisonné uses the term Sonambient as a general classification to refer to the entirety of Bertoia's work, including the recordings, that was primarily concerned with how sculpture could be used to create an ambient sound environment.
The largest group of works included in the Sonambient category are what Bertoia referred to as sounding sculptures, which are comprised of three types: tonals, gongs, and singing bars. Tonals, composed of vertical rods welded to a base and loose at their tops, were the first sounding sculpture Bertoia realized and became the most prevalent type. They range from six inches to twenty feet in height, and, with the exception of one limited edition series from 1977, each is unique in form, materials, and configurations. Bertoia placed the rods in single rows and grouped them in rectangular or circular layouts, usually on a solid metal plate. The rods can be perpendicular to their metal base or angled, and sometimes there are multiple groups of rods in a single work. The artist also employed different metals to produce a variety of tones. Variances were further amplified by leaving the tops unadorned or by adding pieces of metal in shapes resembling plant buds, cattails, or cylinders. Compelling sculptural forms when static, the tonals can be activated by moving the rods to produce distinctive sounds and resonances. In the late 1960s, Bertoia began creating gongs, large sculptures made either with a solid metal plate or a double wall of two sheets welded at the edges. Many gongs also have incisions and were shaped in order to produce particular sounds. Gongs were struck or stroked with mallets Bertoia made specifically to accompany his sculptural instruments. Singing bars, introduced in the early 1970s, are the least common type of sounding sculpture. Composed of thick metal rods, singing bars are suspended in closely hung pairs that reverberate off each other when set in motion.
Alongside his musically inclined brother, Oreste, Bertoia often “played” the sounding sculptures in the Barn that served as his home studio. He made numerous recordings of the sounding sculptures, producing eleven Sonambient LPs that are now also available as CDs and digital files. Jeffrey and Miriam Eger also made a film titled Sonambients in 1971. Shot over the course of two days in February, the short documentary features Bertoia playing his sculptures in the barn and his reflections on the origins of the Sonambient works.