Sound zone reproduction facilitates listeners wishing to consume personal audio content within the same acoustic enclosure by filtering loudspeaker signals to create constructive and destructive interference in different spatial regions. Published solutions to the sound zone problem are derived from areas such as sound field synthesis and beamforming. The first contribution of this thesis is a comparative study of multi-point approaches. A new metric of planarity is adopted to analyse the spatial distribution of energy in the target zone, and the well-established metrics of acoustic contrast and control effort are also used. Simulations and experimental results demonstrate the advantages and disadvantages of the approaches. Energy cancellation produces good acoustic contrast but allows very little control over the target sound field; synthesis-derived approaches precisely control the target sound field but produce less contrast. Motivated by the limitations of the existing optimization methods, the central contribution of this thesis is a proposed optimization cost function ‘planarity control’, which maximizes the acoustic contrast between the zones while controlling sound field planarity by projecting the target zone energy into a spatial domain. Planarity control is shown to achieve good contrast and high target zone planarity over a large frequency range. The method also has potential for reproducing stereophonic material in the context of sound zones. The remaining contributions consider two further practical concerns. First, judicious choice of the regularization parameter is shown to have a significant effect on the contrast, effort and robustness. Second, attention is given to the problem of optimally positioning the loudspeakers via a numerical framework and objective function. The simulation and experimental results presented in this thesis represent a significant addition to the literature and will influence the future choices of control methods, regularization and loudspeaker placement for personal audio. Future systems may incorporate 3D rendering and listener tracking.

This thesis documents the development of a novel fibre optic hydrophone, for the characterisation of medical ultrasound transducers and the measurement of ultrasound induced temperature rises. The transduction mechanism of the hydrophone is based on the detection of acoustically and thermally induced changes in the optical thickness of a Fabry-Perot interferometer deposited at the tip of a single mode optical fibre. The interferometer comprises a layer of Parylene-C sandwiched between two thin gold mirrors. The design of the sensor was optimised using a numerical model of the interferometer transfer function. Through the use of vacuum deposition techniques, a fabrication procedure has been developed which enables batch production of the sensors. A self contained sensor interrogation system has also been developed. The system uses a rapidly tuneable laser developed originally for the telecoms industry to interrogate the sensor and make acoustic and thermal measurement, Control of the system is achieved via a PC using software written in Labview 8.0.

No description available.

No description available.

No description available.

The separation of waves in acoustic waveguides can be used to infer information from various acoustic systems. When applied to musical wind instruments, it allows novel techniques for in-depth investigation of the physics of the instrument, including the extraction of playing information in wind instruments, bore reconstruction and impedance measurement. Although a few approaches to this problem can be found in the literature, little attention has been given to the calibration of the system and above all to the assessment of its performance. The proposed methodology is based on a frequency-domain optimisation of a small set of parameters that best describe the system. The nonlinear optimisation problem that arises is formulated in order to exploit the considerable amount of a-priori knowledge given by the theory of propagation in ducts. The resulting cost surface is typically characterised by several local minima; however, the initial guess given by the nominal values for the parameters ensures the convergence to the desired solution. The main feature of the optimisation approach is that it can be applied in system and does not require any special calibration apparatus. As a consequence, it is also possible to track slow variations in the propagation due to changes in temperature and humidity of the medium during normal operation. A procedure for the assessment of a wave separation algorithm is also proposed; this shows that, under the same conditions, the optimisation approach improves the performance of the system. Finally, the proposed frequency-domain optimisation is also suitable for other applications such as in-air direction of arrival estimation. Preliminary results on these applications are also presented.

No description available.

No description available.

No description available.

Loudspeaker research has been carried out for many years and some of the latest developments involve a panel to produce the sound. Using panels to produce sound offers many possible advantages – for example, it is possible to create sound using a window or a house wall. However, to make these new sound devices feasible, it is necessary to investigate further the exact frequency response of these drivers, how they compare with traditional technologies and how efficient they are. This research has been focussed on the optimisation of gel-type panel drivers and their performance under different conditions. Gel-based drivers have their structure based on soft rubber type materials (gel), and that same gel transfers the vibrations from the driver to the panel. In addition, this thesis covers the development of design tools necessary to predict and improve the gel-based drivers performance. Consequently, a Finite Element Analysis package was employed to enable the simulation of the gel-based drivers. Laser Doppler vibrometer measurements to validate the process were also carried out. Other factors investigated included gel hardness, driver position on the panel, panel material and overall frequency response compared to conventional loudspeaker technology.