Deep inside Virginia’s Luray Caverns, a song rises above the steady drip-drip-drip of water echoing upon limestone. The tune emanates not from an cellphone ignored by a visiting tourist, but from an acoustical oddity: the Great Stalacpipe Organ.

Technically, this stalacpipe organ is not an organ at all, but a percussion instrument known as a lithophone. Instead of blowing air through pipes, it operates by rhythmically striking 37 different stalactites scattered across the 3.5-acre cave. The stalacpipe organ is so big that the Guinness Book of World Records has crowned it the world’s largest instrument.

For that, you can thank Mother Nature, time and a particularly creative mathematician.

Vibration formation

The story of the Great Stalacpipe Organ begins more than 400 million years ago.

At the time, the Appalachian Mountains — where the Luray Caverns now reside — were an ancient sea floor. As years passed, marine sediments formed a layer of limestone known as dolomite nearly 100 feet thick.

A few tectonic shifts later, the nearly watertight rock chambers elevated to an area known to locals as “Cave Hill.” Atop the hill, a relatively horizontal surface allowed rainwater to slowly seep into the ground below.

The water became rich in carbonic acid as it percolated through decaying soil. Over time, the now giant chambers of Luray Caverns formed, as the acidified water dissolved the limestone away. Only when the large volumes of water dissipated through the cavern’s lower fissures could Mother Nature’s interior design process begin.

As the atmosphere inside changed, water droplets rich in calcium carbonate and carbon dioxide dripped through the cave at a slow enough rate to release carbon dioxide into the air. The calcium carbonate collects on adjacent surfaces. Water droplet depositions on the ceiling eventually formed stalactites. Droplets that fell to the floor slowly formed stalagmites.

Since stalactites hang freely from cave ceilings, they vibrate when struck. The formations are, in essence, Mother Nature’s tuning forks.

An idea is sparked

Millions of people have toured Luray Caverns since its discovery in 1878, including Leland Sprinkle, an electronics engineer and mathematician who worked at the Pentagon in Arlington, Virginia.

Sprinkle and his son visited the caverns in 1954. At the time, guides tapped the cave’s stalactites to demonstrate how different sizes would give off different tones. That demonstration inspired Sprinkle, who was also a musician, to create the Great Stalacpipe Organ.

Take a 360 tour of the Luray Caverns Stalacpipe

“The most amazing thing is that he went to our management to ask to attempt this project, and they allowed him to do this,” said John Shaffer, director of public relations at Luray Caverns. “He spent virtually every weekend during that period prospecting for stalactites that could be perfectly tuned.”

Ultimately, Sprinkle spent three years constructing the organ. He selected 37 stalactites for their pitch, sanded all but two down to perfect their tone and then attached a rubber mallet device, measuring more than a foot long, next to each stalactite. Whenever a musician strikes a key, a corresponding note on a stalactite sounds.

Archaeoacoustic scientist David Lubman, who studies the acoustics of caves and religious sites and founded DL Acoustics in Westminster, CA, is not surprised Luray Caverns became home to the Great Stalacpipe Organ.

“It’s no coincidence that people would think to put an organ in a reverberant cave, because those are the acoustics,” he said.

Lubman likened the porous rock textures of Luray Caverns to foam or carpet lining the walls of a recording studio. The porous textures absorb enough sound to reduce confusing repetition of notes, but still allow tones to travel through the cave and back to the Cathedral Room where the organ is located.

Today, the instrument plays songs for more than 400,000 tourists a year.

How it works

Deep in the Luray Caverns, Larry Moyer, operations manager for the Great Stalacpipe Organ remarked on the peculiarity of turning a cave into an instrument. “You’re standing inside the organ right now. There’s notes all around you.”

To play the organ, a musician sits at a console that resembles an upright piano with four stacked keyboards. When a player strikes a key, it sends an electric signal to a mechanical device tucked into a stone staircase hidden in the cave. The device transfers that command to a corresponding rubber mallet, which taps on the stalactite of the same note.