an installation by Aernoudt Jacobs

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photography by Aneil Karia


Everyone knows that sound needs a medium to propagate sound waves. There is no sound in a vacuum. In space there is no sound, absolute silence will never exist for us either. Silence is a relative phenomenon, an ideal state.
What would happen if there was no vacuum in space? What would be the sound in space like? It is probably a good thing that there is no sound propagation in space. The species on earth would have certainly evolved with a different set of ears.

Heliophone is an installation which turns sunlight into sound. In order to create this installation, Aernoudt Jacobs researched the ‘photo-acoustic principle’ as discovered by Alexander Graham Bell at the end of the 19th century. Bell proved that a strong light source can be converted into an acoustic wave and, moreover that any material comes with a sonority that will be revealed by hitting it with a strong periodically interrupted beam of light. The inventions of Bell led a.o. to the predecessor of the wireless telephone, and now indeed also to Heliophone. The basic principle of Heliophone is simple: energy from the sun is transformed into sound without electronic amplification. In the design, however, Jacobs combines an array of traditional and cutting-edge technologies. The installation follows the trajectory of the sun, catching the sunlight and focusing it, via a parabolic lens, onto one point. There, a rotating disk chops the light up into small fragments. A photo-acoustic cell further transforms the light fragments into sound, made audible by a large horn.

Heliophone is a sound piece for the sun; the loudness and tonality of the installation correlates with the intensity of the sun. With the installation, the notion of 'environmental sounds' gains an entirely different meaning. Heliophone can be seen as a prolongation of Jacobs' field recording work where he hunts and grasps for sound phenomena in materials and ephemerals.
(Aernoudt Jacobs - WMMNA interview, 11/06/2015)


Concept: Aernoudt Jacobs
Co-Production:Overtoon, STUK
Executive Production: Overtoon
Supported: IWT CICI grant 2015, Innoviris Grant 2018-2019
Scientific research:KU Leuven, Laboratory for Acoustics; Christ Glorieux, Bert Roozen, Monika Rychtarikova, Bert Verstraeten, Jonas Doevenspeck, Kristof Peeters (optics calculations of the CPC)
Technical and Mechanical Realisation: Dennis Pohl, Culture Crew, iMAL Fablab, Glass workshop KU Leuven
CPC version 2018-2019: Sven De Troy (Sirris)
Photography: Aneil Karia
Many thanks to: Julie Vandenbroucke, the crew at STUK Leuven


September-October 2015: Heliophone & Photo-acoustic Prototypes (solo show), STUK, Leuven, Belgium
July-October 2016: WEATHER OR NOT (group show), MU Gallery, Eindhoven, The Netherlands
April-September 2017: Musical Instruments Museum, Brussels (in the frame of the exhibition: Ou sont les Sons ? Where are Sounds?



INTERVIEW (about PHOTOPHON, the precursor)
Exploring the almost-impossibilities between art and science By Harold Schellinx



1. Alexander Graham Bell

HELIOPHONE is based on intensive research of the ‘photo-acoustic principle’ that was discovered at the end of the 19th century by Alexander Graham Bell. According to this principle, a strong light source can be converted into an acoustic wave due to absorption and thermal excitation. Besides this, Bell’s research shows that any material comes with a sonority that will be revealed by hitting it with a strong periodically interupted beam of light. To validate his discoveries Bell used candlelight, sunlight, and electricity in the form of batteries to amplify sound. The device that Bell invented from these discoveries was the predecessor of the wireless telephone. This device, called the Photophone, used a beam of sunlight to transmit voice over a certain distance..

2. Heliophone

The basic principle of HELIOPHONE is simple: transforming the energy of the sun into a sound without electronic amplification. Sunlight provides enough energy to produce sounds. However, behind this simple premise, a complex installation that bridges different technologies from the past and the present is hidden.
A custom-made heliophonic sculpture is playing variable tones. This tone is created directly from the sun’s energy, from which the position is meticulously tracked around the polar axis. The sunlight is captured into a parabolic sun catcher. The parabolic shape (CPC or Compound Parabolic Concentrator) concentrates incoming sunlight into a very tiny spot, and a rotating disc chops this light into small fragments. The resulting light fragments are transformed into sound from the photo-acoustic cell that is connected to a large catenoidal horn.

The CPC is a very efficient light collector. At a predefined acceptance angle, every incomming ray of sunlight will be reflected and concentrated into one focal point. The basic shape of a CPC consist of 2 tilted parabola segments. In our design it is a cylindrical shape.

The photo-acoustic cell, which is the 'heart' of the installation, has been re-engineered from Bell's notes to be able to produce specific frequencies. The scientific and optics research has been done in collaboration with the Acoustics Lab at KU Leuven.

The engineering consisted of redesigning two main elements: adapting the original cavity to a Helmholtz resonator and by carefully tuning the photo-acoustic cell to the large horn. Both elements are tuned around a fundamental frequency which is extremely sensitive and becomes an audible tone as soon as rays of sunlight are tunneled through a rotating disc. This crucial element is now able to produce sound without electronics. It is a kind of a Helmhotz tone generator that produces sound from sunlight with Bell's photo-acoustic theories. As an installation HELIOPHONE creates a novel way of generating sounds and the energy for producing the sounds is freely available.

With HELIOPHONE, I intend to provide a certain kind of musicality, though in the form of a single well-tuned tone that is activated by an ephemeral kinetic installation, not of a playable instrument. The tonality of the installation has a constant shift in time and will have a changing vibrating micro-tonal structure that correlates constantly with the brightness of the sun.
The structure of the tone is defined by the slits in the chopper. The shape and the rythm of the slits has been designed to provide a distinct character.

The tone is put into relation with the acoustic environment. At times it will locally emerge and at other times the tone will be erased and absorbed into the environment. Heliophone drafts a tone into the sonic fingerprint of the environment.

With the installation I’m interested in achieving a sonic event from ephemeral phenomena. I am attracted by the idea that sounds around us can be created with light. The conclusion that can be made from Bell’s notes and research is that any material has a sonority if you project a strong periodically interupted light-beam onto it. We know that every material has a resonant frequency but also every material can be ‘activated’ with light and this sound has a direct correlation to its resonant frequencies. The shape of materials will also have an impact, but this remains a side effect. The activation of frequencies by light is quite an important revelation because it touches the world of sounds in its very essence. The sun radiates an exceedingly amount of energy, of which only a very tiny amount is more than enough to produce sounds. Sounds can emerge without any direct physical contact. Sounds from materials around us can be revealed with light.

Reading Graham Bell's notes, these particular excerpts sparked me to dig further into his research on the photo-acoustic principles:

"… A continuous increase in the loudness of the sound was observed upon moving the receiver gradually from the violet into the ultra-red the point of maximum sound lay very far out in the ultra-red. Beyond this point the sound began to decrease, and then stopped so suddenly that a very slight motion of the receiver made all the difference between almost maximum sound and complete silence."

"… the nature of the rays that produce sonorous effects in different substances depends upon the nature of the substances that are exposed to the beam, and that the sounds are in every ease due to those rays of the spectrum that are absorbed by the body." “Of course the ear cannot for one moment compete with the eye in the examination of the visible part of the spectrum; but in the invisible part beyond the red, where the eye is useless, the ear is invaluable.”

In 2018-19, Heliophone will be updated. The parabolic lens, which is the heart of the installation that focusses light into a tiny spot has been re-engineered and re-produced to optimise efficiency in light concentration.
The original CPC was casted from aluminium in 2015. The surface accuracy was not consistent for our needs. This meant that the efficiency of the CPC was not up to par.
We looked into alternative production methods that could give a more consistent result and also a more ecologic production method. We produced a new CPC with the a relative new technology called ISF (incremental sheet metal forming). The technology enables higher precision. It is a technique where a sheet is formed into the final workpiece by a series of small incremental deformations. The sheet was formed by a round tipped tool. The tool, which was attached to a robot arm, indents into the sheet by about 1 mm and follows a contour of the CPC part. It then indents further and draws the next contour for the part into the sheet and continues to do this until the full part is formed. After this the elements are cutted with a water jet cutter.

>> Further recommended readings :

1. Converting sunlight into audible sound by means of the photoacoustic effect: The Heliophone on The Journal of the Acoustical Society of America
2. The Photophone patent
3. Excerpt from Chamber's Encyclopedia