Cymatics, seeing sound

In 1787 a Leipzig lawyer with a sideline in physics published a short book with a long title. Ernst Chladni's Entdeckungen über die Theorie des Klanges, Discoveries on the Theory of Sound, described an experiment anyone can repeat. Take a thin metal plate, hold it at the center, scatter fine sand across it, and draw a violin bow down one edge. The plate sings at one pitch, the sand jumps, and within a second or two it settles into a figure: crossed lines, rings, stars, a lattice of curves. Change the pitch and the figure changes with it.

Chladni took the plates on the road. He showed them across Europe for two decades, and in 1809 he published a French edition, the Traité d'acoustique, after demonstrating the figures in Paris. The French Academy of Sciences then put up a prize for a mathematical theory of what he had found. Sophie Germain won it in 1816, on her third attempt, and her work on the elasticity of vibrating plates is where the modern theory begins.

What the sand is doing

The figure is a map of stillness. A plate driven at one of its resonant frequencies divides itself into regions that swing up while their neighbors swing down. Between those regions run nodal lines, where the plate does not move at all. A grain of sand on a moving region is thrown into the air and lands a little to one side, again and again, until it reaches a place where nothing throws it. So the grains walk to the nodes and stop. The figure shows you the lines the plate is not vibrating along.

Michael Faraday cleared up a puzzle in this picture in 1831. Very fine powder does the opposite of sand and gathers at the centers of the moving regions. Faraday showed that the air just above the plate is being pumped by the vibration, and the small currents it makes carry the lightest particles toward the points of greatest motion. In the same paper he described a second class of figures, in liquids. A dish of water shaken up and down at a steady rate grows a standing pattern of ripples on its surface, and the ripples oscillate at half the driving frequency. Those are Faraday waves. Stéphane Douady mapped them carefully in 1990, frequency against amplitude, and the crystalline lattices you see in cymatics videos, where a speaker drives a shallow tray of water under a hard light, are this instability on camera.

Both effects are now solved problems. In 2015 a group at National Chiao Tung University in Taiwan reconstructed Chladni's figures from a theoretical model of the plate and matched them against real experiments across a wide range of frequencies. The rule that falls out is the one Chladni had noticed by ear: more nodal lines means a higher pitch, and the figures of one plate form a family that climbs with frequency. But the shape depends just as much on the size, thickness, stiffness and mounting of the plate. The same note draws a different figure on a different plate. There is no geometry that belongs to 432 hertz or to 528 hertz. There is only the geometry of this plate at that pitch.

One more thing the figures need is a single steady tone. A sine wave gives the plate one mode to settle into. Music does not. A chord excites several modes at once, a drum hit excites all of them for a moment, and the sand never settles into anything. The clean mandalas in the videos are made with test tones, not with songs.

Hans Jenny and the word

The word cymatics dates from 1967, when the Swiss physician Hans Jenny published Kymatik in Basel, from the Greek kyma, wave. Jenny built a device he called a tonoscope, which let a person sing into a membrane and watch powder or liquid respond, and over more than a decade he photographed hundreds of figures in sand, lycopodium spores, water and glycerine. The photographs are beautiful and still in print. Jenny also wrote that the figures revealed a formative principle at work throughout nature, and it is that second claim, not the first, that sound healing culture took up and ran with.

Here is the line we hold. A Chladni figure is evidence that a plate has resonant modes. A Faraday pattern is evidence that a vibrated liquid surface goes unstable in an orderly way. Neither is evidence that a frequency can heal, rearrange the water in your cells, or carry a sacred shape. Your body is not a thin plate held at the center, and the pictures made on one say nothing about what a tone does inside a person. When a video shows a mandala forming in a tray of water at a named frequency and offers it as proof of a therapeutic effect, it is showing you physics and calling it medicine.

The figure shows you where the plate is still. It does not show you what the sound does to you.

Why AVA does not use a plate

We were tempted. Set a tray of water on the bed, light it hard from the side, point a camera at it, project the feed. It looks like magic and it is honest physics. We did not do it, for two reasons. The first is the one above about tones and songs: a tray shows one steady frequency well and a full mix badly, and a piece of music with bass, chords and a voice at once turns the surface to mud. The second is the line we hold. We did not want to hand guests a picture that reads as proof of something the research has not shown.

So the light on AVA comes from the signal itself. The same audio that feeds the 33 transducers is analyzed as it plays, band by band, from the 41 hertz zone at the feet to the 880 hertz zone at the head, along with the size of each hit and the slow drift of the overall level. Those numbers drive generative software, and the software draws what the projector puts on the wall and ceiling. Nothing is filmed. When the bass drops, the image opens because the number for that band grew, and you feel the same number in your legs in the same instant. That is the link cymatics points at, taken without the plate.

Chladni's sand still moves the way it did in 1787, and an hour with a plate and a bow is worth having. Come to the room at 29 Nassau Ave for the other half: sound you can feel in five zones of the body, and light that moves because the sound did.