~CYMATIC SYNTHESIS OF A SERIES OF BELLS
Stephen Barrass
Faculty of Arts and Design
University of Canberra
ABSTRACT
Frequency analysis and additive synthesis are the conventional
way to reproduce sounds in signal processing. However,
digital fabrication provides an alternative way to reproduce
sounds by geometrical reproduction of acoustics. This paper
proposes cymatic synthesis by geometricalreproduction as an
alternative to signal processing as a way to design sounds. IN
the other direction, cymatic synthesis can also be used to
design geometric shapes from sounds. The potential of
cymatic synthesis was explored through an experiment to
produce a recursive series of bells, where the geometry of each
bell is constructed from the spectral profile of the previous bell
in the series. The knowledge gained from these experiments is
captured in a process model with modular stages of SHAPE,
SOUND, XFORM and PROFILE. Based on the results of the
first experiment, we have designed further XFORM mappings
that are more directly cymatic than the spectral profile. The
substitution of alternative XFORM mappings demonstrates the
modularity and generality of the process diagram. These
mappings also demonstrate the creative and generative
potential of cymatic synthesis.
1. INTRODUCTION
The Fourier analysis of sound into frequency
components, and the resynthesis of the sound from sine
tones, is a common process in signal processing. A
similar process has recently become common in digital
fabrication, where an object is scanned in 3D and then
remeshed to 3D print a reproduction. Initially, digital
reproductions could only be printed in plastic, but the
range of materials now includes ceramics, glass, and
metals such as stainless steel, bronze, and brass. This
diversification of materials also brings a diversification
of acoustical properties, and the resonance of metal
underpins the invention of early musical instruments
such as gongs, bells and singing bowls. The size and
shape of these acoustic objects affect the pitch, timbre,
duration of ringing, loudness, and other aspects of the
way it sounds. The digital fabrication of an acoustic
object is also a way to reproduce the sound that it
makes. In cymatic experiments the effect of the shape of
an object on is acoustical resonance is made visible, by
for example, patterns of grains sprinkled on the surface
of a metal plate attached to a speaker, or ripples on the
surface of water in a bowl placed on the speaker. These
cymatic experiments raise the question of whether the
sound recording of an object could contain enough
information to reconstruct the geometry of the object?
Or would it produce a class of objects that all have the
same acoustics? If the sound of an object is used to
construct another object, does that object produce a
different sound or the same sound as the original object?
Speculating further, what would happen if we then
recorded the sound from the new object and fabricated
Tim Barrass
Independent Artist
Melbourne
yet another object from that sound? This recursive
process would generate an interleaved series of shapes
and sounds, as shown in Figure. 1. The question then
becomes - where will it end?
Figure 1. A recursive series of shapes and sounds
In this paper we propose that "cymatic synthesis" by the
geometrical reproduction of a sound through digital
fabrication can be an alternative to frequency analysis
and additive synthesis. The questions raised by cymatic
synthesis could, perhaps, be answered by a
computational simulation using finite mesh modelling.
However, the simulation of complex objects is
computationally demanding, and involves many
simplifications and assumptions. In this paper we
explore digital fabrication as an alternative method for
understanding and designing the acoustics of complex
3D objects.
2. BACKGROUND
In the 17th Century, Galileo Galilei noticed strange marks
appeared on a metal plate that he was chiselling
whenever the plate produced a harmonic whistling
sound. A century later Ernst Chiadni described the
vibration patterns produced by sprinkling sand on a
metal plate and bowing it with a violin bow. In the
1960's Hans Jenny coined the word cymatics to describe
his study of the modal vibrations of sound waves in 2D
plates [1] Today, cymatics is often used to teach
acoustics in science classes, through simple experiments
with corn-starch on a speaker as shown in Figure 2.
Figure 2. Cornstarch solution under the influence of sine
wave vibration: Photo - Collin Cunningham
18 2013 ICMCide
