Flute acoustics: measurement, modelling and design - School of ...

8 CHAPTER 1. INTRODUCTION
‘in-tune’ instrument is difficult to define.
A flute plays notes close in frequency to the impedance minima in its impedance spectrum.
How close depends on several factors, including the impedance of the player’s face
and embouchure, and the frequency of other impedance minima. In order to approximate
the frequency-dependence of a typical player’s embouchure, we asked professional and semiprofessional
flute players to play notes on the flute without aiming to play the note in tune, but
rather to aim for the best sound. We then compared the tunings obtained in this way to those
measured on the impedance spectrum, and used the difference in a correction factor.
1.7 SOFTWARE IMPLEMENTATION: GOALS AND LIMITATIONS
What are the requirements of the software program that is the practical aim of this thesis?
The maker should be able easily to enter, store and retrieve flute data in a familiar form. The
interface should additionally show a schematic diagram of the instrument for a quick overview
of the flute design and for comparison to existing designs.
The software should calculate and display the acoustic parameters of interest (tuning, timbre
and playability) for a couple of dozen important notes reasonably quickly—within a minute
at most on an inexpensive computer. This condition is important, since the flute maker should
be able to make iterative changes to a design and see the effect of each change without having
to wait an inordinate amount of time. This limits the software models available to us and has
implications for the software implementation. It would be useful as a design aid if the software
has the facility to plot the magnitude of the pressure and flow waves along the flute for any fingering,
as these give insight into the contribution of each tone hole to the tuning of a particular
note and help with the correct placement of register holes.
The software program C was used to produce the impedance model. Some of the code
used in the impedance model of Botros et al. (2006) is inherited and used in this thesis. The
command line input to the C program is an XML file describing the flute geometry, and a file
containing fingering information. The program outputs the impedance spectra for each fingering.
A related software tool outputs the pressure and flow magnitudes along the flute.
The software interface was written using Java. Java is an object-oriented programming language
developed by Sun Microsystems. One of the main advantages of Java is that it is platform
independent: provided the user has a Java Runtime Environment (JRE) installed on their machine,
the code will run. JREs are available for all major operating systems.
1.8 GUIDE TO THE THESIS
In Chapter 2 the relevant literature is surveyed, important formulae are quoted or derived and
existing flute models are compared. Next, an impedance spectrometer is made and carefully
calibrated (Chapter 3) so as to measure the input impedance of wind instruments quickly and
with a high degree of accuracy. The impedance characteristics of finger holes, such as are used
on recorders, classical flutes and clarinets, are measured in Chapter 4 and fit-formulae are derived.
Databases of impedance spectra for modern and classical flutes and a modern clarinet
are assembled (Chapter 5). Possible effects on impedance spectra of the material used for flute