Bibliography: p. 199-207. Electronic publication; full text available in PDF format; abstract in HTML format. Describes the basis of a theoretical and experimental project, directed at the design and evaluation of a practical active noise control system suitable for a single light engine aircraft. The performance of virtual sensors were evaluated both analytically and experimentally in progressively more complex environments to identify their capabilities and limitations. Electronic reproduction.[Australia] :Australian Digital Theses Program,2001.

In this thesis, we are interested in processing noisy speech signals that are meant to be heard by humans, and hence we approach the noise-suppression problem from a perceptual perspective. We develop a noise-suppression paradigm that is based on a model of the human auditory system, where we process signals in a way that is natural to the human ear. Under this paradigm, we transform an audio signal in to a perceptual domain, and processes the signal in this perceptual domain. This approach allows us to reduce the background noise and the audible artifacts that are seen in traditional noise-suppression algorithms, while preserving the quality of the processed speech. We develop a single- and dual-microphone algorithm based on this perceptual paradigm, and conduct subjecting tests to show that this approach outperforms traditional noise-suppression techniques. Moreover, we investigate the cause of audible artifacts that are generated as a result of suppressing the noise in noisy signals, and introduce constraints on the noise-suppression gain such that these artifacts are reduced.

Wave scattering by arrays of cylinders has received special attention by many authors and analytical solutions have been derived. The investigation of optical and acoustical analogies to the problem of interaction of water waves with rigid and flexible cylinder arrays is the main focus of this thesis. In acoustics, a sound may be attenuated while it propagates through a layer of bubbly liquid. In fact, if the natural frequency of the bubbles is in the range of the wave periods, the attenuation becomes more evident. The ultimate objective of the research described herein is to determine if this phenomenon may also be found in the interaction between water waves and arrays of flexible cylinders. In a first approach, arrays of rigid cylinders are studied in shallow water. The array is treated as an effective medium, which allows for the definition of reflection and transmission coefficients for the array, and theories from Hu and Chan (2005) associated with the Fabry-Perot interferometer are compared against direct computations of wave scattering using the commercial code WAMIT. Reflection and transmission coefficients from WAMIT are evaluated by applying a Maximum Likelihood Method. The results from WAMIT were found to be in good agreement with those obtained from the effective medium theory. Due to observed inconsistencies for short wave periods and small incident angles, the effective width of the medium is defined and corrected. For the case of a flexible cylinder, generalized modes corresponding to deformations of the cylinder's surface are formulated and added to WAMIT's subroutine. Equations of motion are derived from the theory of vibration for thin shells and mass and stiffness matrices are defined. The objective is to maximize wave attenuation from the array of flexible cylinders. Therefore, the natural periods of the "breathing" mode for these cylinders is set in the range of the studied wave periods. Then, material properties, as well as mass and stiffness matrices, are chosen to achieve this effect.

Computer aided auto-construction of various types of folded horns and acoustic analysis of coupled horn and driver systems are presented in this thesis. A new procedure is developed for auto construction of folded horn shapes. Linear graph modeling technique is employed for specification of horn driver output in terms of diaphragm velocity or throat pressure. In the final phase of the design procedure, acoustic analysis of folded horns is carried by means of finite element analysis. A commercial software package MSC.ACTRAN is used to calculate directivity patterns and resulting acoustic pressure in the free field. Horn geometry consisting of linear, exponential, hyperbolic and tractrix shapes is automatically constructed by parallel working of Delphi and finite element analysis program. The enclosure bordering the horn contours are considered rigid in the analyses. Maximum number of folding is limited to two. This study is made possible to evaluate the performance of these four types of horn contours for a specified range of frequencies.

D. Tech. Mechanical Engineering. / The level and quality of vibration experienced by motor vehicle occupants are issues of increasing concern and will probably be among the major challenges of the automotive industry in the twenty-first century. The vibration behaviour of door panels that enclose the passenger cabin can affect low-frequency noise in the cabin. This thesis presents the theory necessary for the development and simulation of a vibroacoustic door mount system and, thereafter, investigates its potential. Compared to the existing design, a perceivable noise reduction of 6.15 dB(A) was achieved by using the proposed sensitivity analysis procedure.

This dissertation describes two possible methods for the calibration of an ultrasound tomography system developed at University of Manitoba's Electromagnetic Imaging Laboratory for imaging with the contrast-source inversion algorithm. The calibration techniques are adapted from existing procedures employed for microwave tomography. A theoretical model of these calibration principles is developed in order to provide a rationale for the effectiveness of the proposed procedures. The applicability of such an imaging algorithm and calibration methods in the context of ultrasound are discussed. Also presented are 2D and 3D finite-difference time-domain update equations for the simulation of acoustic wave propagation in inhomogeneous media. Details regarding the application of an absorbing boundary-condition, point-source modelling and the treatment of penetrable objects are included in this document.

Thesis (D.Tech.: Electronic Engineering)-Dept. of Electronic Engineering, Durban University of Technology, 2007 vii, 150 leaves / Detecting and minimising distortion in audio signals is an important aspect of sound engineering. Distortion of a signal passing through an audio system may be caused by a number of factors and it is necessary to detect these effects for optimal sound. The problem is of interest to users and operators of high quality audio equipment and transmission facilities. The objective of this thesis was the development of techniques for the blind identification of distortion in a high quality audio signal using digital signal processing techniques. The techniques developed are based on digital signal processing techniques and statistical analysis of a recorded audio signal, which is treated as a random, non-stationary signal.

This dissertation describes two possible methods for the calibration of an ultrasound tomography system developed at University of Manitoba's Electromagnetic Imaging Laboratory for imaging with the contrast-source inversion algorithm. The calibration techniques are adapted from existing procedures employed for microwave tomography. A theoretical model of these calibration principles is developed in order to provide a rationale for the effectiveness of the proposed procedures. The applicability of such an imaging algorithm and calibration methods in the context of ultrasound are discussed. Also presented are 2D and 3D finite-difference time-domain update equations for the simulation of acoustic wave propagation in inhomogeneous media. Details regarding the application of an absorbing boundary-condition, point-source modelling and the treatment of penetrable objects are included in this document.

Bibliography: p. 199-207. Describes the basis of a theoretical and experimental project, directed at the design and evaluation of a practical active noise control system suitable for a single light engine aircraft. The performance of virtual sensors were evaluated both analytically and experimentally in progressively more complex environments to identify their capabilities and limitations.

Αυτή η εργασία ασχολείται και αναλύει τα χαρακτηριστικά του συστήματος Controlled Acoustical Bass System (C.A.B.S.), το οποίο είναι ένα σύστημα βελτίωσης της ακουστικής κλειστών χώρων σε χαμηλές συχνότητες, χρησιμοποιώντας πολλαπλά ηχεία και μια τεχνική διόρθωσης βασισμένη στην ανάλυση του ηχητικού πεδίου στο χρόνο. Πριν όμως προχωρήσουμε σε οποιαδήποτε ανάλυση, θα πρέπει πρώτα από όλα να ορίσουμε πιο ακριβώς είναι το πρόβλημα που δημιουργείται στις χαμηλές συχνότητες σε κλειστούς χώρους, καθώς και ποίες μέθοδοι χρησιμοποιούνται για να το αντιμετωπίσουν. / -