Material Influence on the Sound of Brasses

Currently the question how the wall material does have influence on acoustical systems containing resonant air columns has become one of the major hot topics in acoustics. Basic research done at different places is giving strong evidence that such an influence does exist. This research is driven by musical acousticians as wind instruments are without any doubt the acoustical systems which are concerned most. A better understanding of the factors related to sound quality and playability of brass wind instruments is one of the goals of the proposed project. The focus will be set on a combination of material science and acoustics with the aim of characterizing different modern and historic brass materials with respect to acoustically relevant properties. Another goal is to acquire the knowledge necessary to remanufacture brass wind instruments which resemble the sound and other qualities of historical instruments from the Renaissance period as close as possible. Only few of those instruments have survived and most of them can no longer be played for conservation reasons. A revival of early music can be observed not only in Austria which creates a strong demand for such instruments to play the rediscovered music the most authentic way. The proposed research project includes the study of material influences on the vibrational behavior of instruments and the attempt to identify and quantify the acoustically most relevant mechanical parameters. In a next step, the effect of different vibration modes and deflection shapes on the quality of the radiated sound, on the intonation and on the playability will be studied. Another part of the work will consist of archival research upon the manuscripts that contain additional information on historical brass making techniques and used materials and of acoustical analysis of surviving historical instruments in order to define sound quality targets for remanufacturing them. A full documentation of the acoustical, metallurgical and geometrical properties of the surviving 16th century trombones will be made.

Makers consider the vibrational behaviour of brass wind instruments as a crucial aspect of their design. A principal objective of this work was to investigate how specific materials and processing techniques relate to the sound and playability of brasses, specifically of sixteenth-century trombones, and how to reconstruct them for purposes of historical performance. Experiments revealed that small differences in wall thickness could significantly impact structural resonances. Process parameters such as annealing time, annealing temperature and rate of deformation can be adjusted in order to control the relative stiffness of the material. It was demonstrated that bells made from a carbon-fiber-reinforced composite were much stiffer than brass, which was assessed by musicians as a strongly enhanced responsiveness without any degradation in intonation. Physical modelling was applied to study the interaction between structural vibrations and the oscillating air column. However, it was determined that theoretical models could not fully account for all claims made by players. Partially this is due to the fact that subjective assessments usually are not based on unbiased blindfold experiments and partially it is due to inaccuracies and oversimplifications of the used theoretical models. Nevertheless, the application of computer modelling and optimization can no longer be neglected in the design and construction of wind instruments which changes the way makers will work in future. In order to bridge the remaining gap between theory and practice in playing and making, it is essential to listen to musicians and makers but to also scrutinize their claims and observations using empirical methods like blindfold tests and statistics. Statistical tests have been applied here to the responses given by numerous makers of tubas, trombones, horns and trumpets who had been asked to assess certain instruments or experimental modifications. It could be shown with statistical significance that instruments with thin walls and uniform wall thickness in combination with a high degree of hardness are consistently assessed as being of superior acoustical quality. Furthermore, the addition of mass at specific points on brass wind instruments has been consistently noted and often judged as a significant modification of playing properties. Thin-walled instruments, which vibrate strongly, are assessed by musicians as having a decreased sound volume, a brighter sound timbre, increased responsiveness, an improved lipping range with associated tonal flexibility. Without any doubt, one of the principal achievements of this project is the development of a comprehensive practical and theoretical framework for the historically informed reproduction of sixteenth-century trombones. The validity of this framework has been proven practically by providing musicians with two reconstructed instruments resembling the originals in both appearance and acoustics.