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Gravity Harps for Björk


The Gravity Harps use the Earth’s gravity to create music. Gravity sets the rhythms and stores the energy. Robotic technologies provide initial energy and synchronization.

They were used on Björk’s Biophilia album and in the live shows on tour around the world.

The Gravity Harps are the product of a collaboration between Björk and me. Björk had a vision for a musical version of The Foucault Pendulum. She had a harp-like timbre in mind. And she’d already written a beautiful, floating song for it, with an unusual scale and freely drifting time signatures.

As I prototyped harps and other physical parts, I worked on how to play the drifting time signatures with one big pendulum. I turned the puzzle around and around like a Rubik’s Cube. But the physics of pendulums was working against me. Near the tops of their swings, the pendulums’ kinetic energy is almost completely gone, having been temporarily converted into gravitational potential energy. Too slow and too weak to reliably play strings.

But the challenges did all get solved. Here is a bit of the evolution of the Gravity Harps.

Design 1: The Marinas
This original concept was named after Mihaeko Schroedinger, whose help was indispensable.

Design 2: The Celestial Sinusoid
The song is called Solstice, so I wrapped the line of pendulums into a circle, to create patterns that echo celestial cycles.

The Wooden Prototype

CAD Drawings for full scale version

Design 3: The Gravity Ring
But Björk wanted each pendulum to play only one note, so that the patterns of motion echoed the patterns of the song. An instrument shaped like a song! I liked it.

I wrote this simulator to figure out how to do it. Click the image below to open it.

Prototype harps made from fiberglass, spruce and aluminum.

Design 4: The Gravity Harps
The final design which met all of the new criteria was the Gravity Harps. Four pendulums with circular harps on the bottom which can be turned to play different strings as they swing.

Our second prototype harp was made of fiberglass, walnut, spruce and all the epoxy we could find. This is the harp Bjork used on the new album. Here is Mihaeko putting the strings on for the first time.

Mihaeko with Harp

And here is it under computer control:

Our third prototype harp was made of walnut, spruce and a custom composite of epoxy and veneer.

harp prototype 3

Here is the final version in Manchester

Gravity Harps in Manchester

Special thanks to (chronologically):
Mihaeko Schroedinger
Karl Biewald
Doug Ruuska
James Patten
Ryan Wistort


15 replies »

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  1. Thank you so much for this detailed post about a great and interisting project. It sounds like a good idea to make a model por my physycs class, anyways, I hope to hear more about you and new things like this in the future. Thank you in advance.

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