Free The Sound Book: The Science of the Sonic Wonders of the World by Trevor Cox

Luray Caverns in Virginia contains the Great Stalacpipe Organ, which entertains visitors and occasionally accompanies brides marching down the subterranean isle.
    Andrew Campbell, the tinsmith from the town of Luray, discovered the cave back in the late nineteenth century. A report by the Smithsonian Institution in 1880 commented, “There is probably no other cave in the world more completely and profusely decorated with stalactite and stalagmite ornamentation.” 21 When I visited, a year after my trip to Wayland’s Smithy, I was amazed by the number of formations. They seemed to cover every surface. The curators have lit the cave with bright lights, giving visitors the impression that they’re walking around a film set.
    The organ is toward the end of the tour. In the middle of the cathedral cavern, among a forest of cave formations, sits an item that superficially resembles a regular church organ. But when a key is pressed, instead of compressed air blowing through an organ pipe, a small rubber plunger taps a stalactite, which rings and makes a note. The current instrument uses stalactites covering 1.4 hectares (3.5 acres) of the cavern. “It is the largest natural musical instrument in the world,” the tour guide proudly announced in a staccato Virginia twang so rapid that every other sentence was unintelligible.
    With each key connected to a different cave formation, the organ can play thirty-seven different notes. A magazine article from 1957 reports, “Visitors stand enthralled as melody and chords play all round them. No twinkly tunes these, but full-throated music rolling through the cavern.” 22 Apparently I heard a rendition of “A Mighty Fortress Is Our God,” a sixteenth-century hymn by Martin Luther, but I struggled to pick out any semblance of a tune. It was my own fault; I stood very close to the stalactite that plays the musical note B-flat to get a good view of how it worked. But this meant that the volume balance between the different notes was awry. The cave formations playing the notes are strung out over such a large area that many were too distant and quiet. From where I stood, the music appeared to have only five notes, and it was more like a piece of avant-garde experimental music than a hymn.
    In the middle of the cavern the balance between notes is better, and the reverberance of the cave adds an ethereal quality to the music. A combination of the natural ring of the stalactites and reverberance in the cavern means that notes start and end vaguely. By standing close to one stalactite, I could examine the quality of one note in detail. It reminded me of a metallic gong or church bell.
    The Great Stalacpipe Organ was the brainchild of Leland W. Sprinkle, an electronic engineer whose day job was at the Pentagon. While visiting the cavern, Sprinkle heard a tour guide hit a cave formation with a rubber hammer, and he was inspired to make the instrument. 23 He then spent three years armed with a small hammer and a tuning fork, searching for good cave formations. When he tapped a stalactite, it would ring with the cave formation’s natural resonant frequency. So his task was to find stalactites that produced a beautiful ringing tone and also had a natural resonant frequency close to a note in a musical scale. As Sprinkle discovered, the most visually impressive formations often failed to produce a sound that lived up to their appearance. Only two formations were naturally in tune, so others had to be altered. Sprinkle used an angle grinder to shorten these stalactites, thereby raising the natural frequencies of the cave formations, and eventually he produced a scale of notes that were in tune.
    Sprinkle certainly did not spend a long time worrying about appearance. The Stalacpipe Organ looks as if a cowboy electrician botched the cave’s wiring. The mechanisms are crudely bolted onto neighboring cave formations and walls, and wires hang loosely and without