Andy Cavatorta

The Gravity Harps are a kinetic sculpture and musical instrument featured at MoMA, on Björk's Biophilia album, and taken around the world on her tour.

They are the result of a year-long collaboration between Björk and me in which we explored new possibilities combining music and forces of nature.

Many new vectors and potentials were explored in this process. Many trailheads were uncovered. Below are documented the many possibilities uncovered on the way to the Gravity Harps.

Björk originally asked me to consider a musical Foucault pendulum. It's a lovely idea. But how can we make music with pendulums?

The Marinas were three pendulums with three monocord string instruments that were plucked at or near the nadir of each pendulum's swing.

Each pendulum had the same period. But they could be started and stopped in different phases, creating different patterns. And their pluckers could be adjusted to pluck a short distance from the nadir, creating asymmetrical rhythms.

These were hypnotic like a fireplace. Everybody in the room would stop talking and quietly watch and listen.

What happens when our real-time feelings about music become part of an AI?

In The Inner, an AI generates music and uses the emotional responses of a human listener for training and feedback. It's an intelligent machine that requires a human mind as one of its components. It's also a collaboration that requires no volition on the part of the human — just listen and feel.

The system should learn to create optimal music for each person that is completely unique. And these optima may reflect and reveal essential aspects of the listener. It could even have therapeutic use in the diagnosis or classification of brain conditions.

These early explorations foretold a musical world that could not be expressed with a typical keyboard.

There were so many timbres; so many pitches that weren't on a piano keyboard.

I designed several new universal keyboards inspired by the work of Bosanquet, Fokker, and Carlos. These new keyboards included not just pitches but timbres and an exotic musical pantheon of intervals and harmonies. I will make time to share the digital versions of these if enough people ask.

Can we play music with rain?

This experiment created a sort of precise rain. Each droplet's location and timing were controlled by software. These raindrops fell on the strings of a Celtic harp, playing them softly.

But the raindrops had so many nondeterministic properties that added randomness to their paths. They had different shapes that caught the air differently. They exited the nozzle at different angles. They drifted a bit in the slightest breeze — even indoors.

I added salt to the water to increase the surface tension of the droplets. I added needles to the edges of the nozzles to guide the droplets into one predictable path.

But my lesson was that randomness is an intrinsic part of some forces of nature.

Seth Hunter's delightful SoundForms project inspired me to try to make music with real water ripples.

This experiment used a physical ripple tank, a camera, the OpenCV library, some bowed string samples I'd recorded, and a lot of code written in Python.

This resulted in a wonderful interactive project. It was great for exploring unexpected outcomes.

One walking machine weaves a musical fabric. The other plays it mechanically like a music box and unweaves it on spools. The two machines wander around with this tension of time and music between them.

When Björk told me that she wanted to embed a gamelan in a keyboard instrument, I got very excited. I designed a number of physical keyboard instruments that held the variety of instruments from a Balinese gamelan. Gangsas, barungs, trompongs, sarons, demuns, slentems. It was a little nuts.

Björk soon told me that her plans were much more modest and less full of cultural appropriation. But not before I created two 2010-style, iPad-ready mockups that put that wide variety of timbres at a player's fingertips.

Click the image below for a web version tuned in Balinese pelog tuning. The white spaces at the bottom of each key damp the sound. This is an important part of note-shaping in gamelan music.

They need a few seconds to load fully.

At the beginning of this project, Biophilia was to be an IMAX film. I was designing large set pieces to build and film in a disused power plant outside of Reykjavík. I produced and documented concepts in Boston and sent them to Björk in Reykjavík. Here's the video with the early pendulum concept.

The next phase of the design process for the IMAX film was a ring of 38 pendulums that would swing in complex patterns to play the song Solstice.

Björk could perform within the ring of swinging pendulums or carefully walk among them.

We were designing and prototyping The Pendulum Ring around the clock — creating the harps, the mechanisms, the software, the sound.

Our friends at Hypersonic.cc created our first tests of a motion system. It taught us that there will be no way to fake the freely swinging motion. Even when the math looks perfect, the eye can tell.

These projects resulted in so much software and so many simulations.

The video capture below shows custom simulation software used to choreograph the pendulums to play the music.

When we got the word that the Pendulum Ring would have to go on tour, we all started having nightmares. To make this beast robust and easy to dis/assemble required a complete redesign, reengineering, and new prototypes.

In a long lunch meeting with Björk, we designed a much smaller and simpler instrument.

This new design would require a novel, circular harp design that could be rotated to precise positions and plucked as it passes the nadir of the pendulum swing.

Every big project is an iceberg. Much of what makes it work isn't visible to the audience.

The Gravity Harps have a suite of software for composing, improvising, performing, and calibrating.

The assembly and calibration of the Gravity Harps is still an all-day affair. It is always fraught with unexpected troubles that need to be fixed before the clock runs out.

Here is a little peek at the process.