The lips of a brass player form a complex mechanical oscillator which has a non-harmonic set of resonance frequencies. In order for the lips to create a note when a player starts to play a brass instrument there must be interactions between the mechanical resonances of the lips, the fluid dynamics of the air passing between the lips, and the acoustic pressures which surrounding the lips. In this thesis studies are made of these interactions utilising an artificial lip and mouth to perform experimental measurements and Lattice Boltzmann fluids simulations to study the flow of air between the lips. By taking mechanical response measurements of the artificial lips, the mechanical resonances of the lips has been examined. The effects of both air flow between the lips and the presence of acoustic resonators, both in the form of an instrument on the downstream side of the lips and the mouth cavity on the up-stream side of the lips have been studied. Results of these measurements have shown that the lips of a brass player can behave in either of two lip reed operating regimes (inward or outward striking), depending on the relationship between the resonance frequency of the lips and that of the resonator. The behaviour of the lips during the transition between inward and outward striking regimes has been studied in order that improved models of the lip reed can be constructed. Numerical simulations of the flow in a pipe with a constriction which is based on the shape of a players lips both with and without a mouthpiece downstream of the lips have provided information on how the jet formation by the lips occurs. By using the data from these simulations the size of the forces which lead to the inward and outward striking behaviour of the lips have been estimated and a clearer picture of the physics behind the operation of a brass players lips obtained.

In this thesis, the basic theory describing wave propagation in tubes of varying cross-section is outlined, together with a review of how the time domain technique of APR can be used to measure the input impulse response of a tubular object, such as the vocal tract, from which the bore profile can be calculated using the layer peeling algorithm. Experimental measurements of the human vocal tract during the phonation (imitation of) for five non-nasalised vowels [a, e, i, o, u] are presented, using recent enhancements to the APR technique (MLS excitation signals and virtual DC tube method) for a single subject, together with optimisation of the APR technique for vocal tract measurement and its application in a group study using adults and children. To validate the results obtained using the APR technique, a comparative study with an accepted ‘gold standard’ imaging technique (MRI) is presented, using the same subject, a voice professional, in both studies. The results from this study show reasonable overall agreement between the APR and MRI data, with the limited resolution of the acoustic technique tending to broaden features and underestimate cross sectional areas, particularly in the region of the pharynx and glottis. Protocols and supplementary documentation required by scientific, clinical and ethical review bodies for the use of human volunteers in research trials are documented. From this study a data corpus of vocal tract measurements is gathered, using the techniques of APR and MRI, in adult males, adult females and children. In concluding, limitations of the APR technique for vocal tract measurement are discussed and potential improvements are proposed.

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