Operation Manual

22 Parameters
Figure 8: Contour plot corresponding to normal mode [1,1] and [3,2] of a plate.
nodal line of a mode (a line where amplitude of the motion associated with a mode is zero) does
not allow the transfer energy to that specific mode and its corresponding partial will not be excited.
The effect will not be as pronounced but will still exist as the excitation point is moved around the
nodal lines which explains how the excitation point influences the relative amplitude of the partials
and therefore the tone.
4.2.2 Coupling of Resonators
One of the key features of Chromaphone is that it allows one to couple objects together, in other
words to take into account the interaction between objects as opposed to simply feeding the signal
from one object to the other. This is very interesting because this interaction between components
results into a new object which, while being related to its original elements, behaves and sounds
differently. In fact, musical instruments are based on combinations of objects such as a string and
a soundboard for a guitar, a bar and a tube in the case of a vibraphone or a skin and a column of air
in a drum.
The coupling of objects results in a bidirectional transfer of energy between the objects. In
physical terms, the amount of exchange is determined by the relative value of the mechanical
impedance of the different objects. The impedance is a notion which measures how much an
object opposes motion when subjected to a force. It is a frequency domain function as the response
of an object can vary greatly with frequency. For example the amplitude of the motion of an object
will be much greater when excited at a resonance frequency.
In simpler terms, the effect of coupling can be understood by considering how rigid one object
is compared to the other which determines how much energy can be transferred from the first object
to the second one. Let’s imagine a string attached to a very stiff sound board. While some energy
will be transmitted to the sound board through the bridge, it will not greatly affect the motion