Wall properties of brass instruments

• Main Author: Watkinson, Peter Stuart
• Published: University of Surrey 1981
• Subjects: 534; Acoustics & noise analysis
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291377

The content of this thesis splits into two distinct areas, investigating the effect of material and its condition on the properties of brass instruments. Firstly, acoustic losses in tubes are studied. A method for deducing losses from impedance and transfer function measurements is developed and applied to a number of tubes having different internal wall finishes. The cases studied are considered representative of the wall finishes found in brass instruments, both in factory condition, and after having been used for some time and not cleaned. Results show that a build-up of deposit on the inside of the tube causes the most significant increase in attenuation of sound propagating down the tube, whereas the results for smooth and roughened tubes are very close to theoretical predictions. An attempt is made to extend the theory to measurements on actual instruments but success is limited due to the flared portions of tubing. Secondly, the vibration properties of trombone and trumpet bells are studied. A Finite Element package is used to model the bells and a post-processor program written to model the acoustic excitation and thus predict the forms of vibration. These calculated responses are compared with some results from experiments performed in conjunction with Southampton University. The finite element model is also used to indicate the properties of the bell structure which are implicit in determining its mechanical response; supports (stays), material of construction, wall thickness, rim size and asymmetries in geometry. It is difficult to give these properties musical significance though some results show that in certain circumstances, they do contribute to an instrument's musical characteristics.