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.

Performance of the buildings has always been a concern for the architects. With the enhancements in the technology, it is possible to measure, analyze and evaluate the performance of an architectural design before it is built via simulation tools developed. With the evaluation of the analysis performance of the concerned space can be upgraded if simulation tools are employed throughout the design process. However, even though the simulation tools are developed for the acoustical simulation and performance analysis, it is not always simple to integrate the simulation tools to whole design process because of both specific knowledge required for the usage of the tools and the nature of the acoustical simulation tools. Within the scope of the thesis, a simulation tool, which does not require advanced knowledge on acoustics and which provides rapid feedbacks about the performance of the design for the enhancement of the performance is developed using method of image sources.

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.

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.

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.

De nos jours, le béton est le matériau de construction le plus utilisé dans le monde en raison de ses performances mécaniques, sa facilité de mise en oeuvre, son coût compétitif et sa « recyclabilité ». Toutefois, compte tenu de son caractère fragile en terme mécanique et de sa faible résistance à la traction, il est souvent renforcé par des armatures métalliques qui lui confèrent une bonne ténacité et une meilleure aptitude à supporter les efforts de traction. Ce composite béton-armature ne peut cependant assurer efficacement son rôle que si les deux composants sont étroitement liés l’un à l’autre. C’est donc dans la qualité de l’adhérence que réside l’efficacité du transfert des efforts entre les deux matériaux. Or, dès la mise en place des ouvrages en béton armé et pendant toute la durée de leur exploitation, différentes actions et agents agresseurs peuvent modifier la qualité de cette adhérence. Il peut s’agir de phénomènes naturels comme le gel/dégel et l’action du dioxyde de carbone atmosphérique, ou des sollicitations accidentelles comme l’incendie ou encore l’action de certains agents spécifiques comme les chlorures et les sulfates. Notre objectif dans cette thèse est de qualifier les modifications d’adhérence qui résultent de quatre types de sollicitations couramment rencontrées dans la vie des ouvrages en béton armé: l’effet des températures élevées, l’effet de la carbonatation, l’effet des cycles gel/dégel, l’effet de la corrosion. Nous évaluons la qualité de l’adhérence par la mesure de la résistance à l’arrachement et par l’analyse du comportement résiduel sous sollicitation mécanique. La technique d’émission acoustique est utilisée pour localiser en temps réel, l’endommagement du matériau sous sollicitation. Les applications de notre étude concernent non seulement les armatures et inserts classiques du béton armé mais aussi les nombreux dispositifs constructifs des structures mixtes acier – béton qui utilisent les liaisons par goujons pour relier les deux matériaux. / Nowadays, concrete is the most used construction material in the world because of its mechanical performances, its ability to be molded or cast, its competitive cost and its recyclability. However, concrete has a low ductility and a relatively low tensile strength compared to other construction materials. Therefore, concrete is often reinforced by steel rebars to improve the ductility and tensile strength. Nevertheless, to make reinforced concrete being highly efficient material, the two components need to be correctly bonded each to other. The bond quality the efficiency of the force transfer between rebar and concrete surrounding ensures. In fact, since the casting of concrete and during the service life of reinforced concrete structure, various actions such corrosion action, freeze/thaw attack and chemical attack etc. may affect the bond quality. The objective of this PhD research work is to qualify the changes of adhesion property causing by four types of action which frequently takes place in the service life of reinforced concrete structures: the effect of high temperatures, the effect of carbonation, the effect of cycles freeze/thaw, the effect of corrosion. The concrete-rebar bond quality is evaluated by doing pull-out tests under static mechanical action and measuring the bond strength and analyzing residual behaviour. Moreover, the acoustic emission technique is used to locate the cracks and evaluate the cracking evolution in real time. The founding of this study can be also extended to apply to other concrete-steel structures like composite structures in which headed studs are used to connect steel profiles to concrete.

No description available.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

The hearing and understanding problems of the people with high frequency hearing loss are covered within the scope of this thesis. For overcoming these problems, two main studies, developing hearing loss simulation (HLS) and applying new frequency lowering methods (FLMs) were carried out. HLS was developed with the suprathreshold effects and new FLMs were applied with different combinations of the FLMs. For evaluating the studies, modified rhyme test (MRT) and speech intelligibility index (SII) were used as subjective and objective measures, respectively. Before both of the studies, offline studies were carried out for specifying the significant parameters and values for using in MRT. For the HLS study, twelve hearing impaired subjects listened to unprocessed sounds and thirty six normal hearing subjects listened to simulated sounds. In the evaluation of the HLS, both measures gave similar and consistent results for both unprocessed and simulated sounds. In FLMs study, hearing impaired subjects were simulated and normal hearing subjects listened to frequency lowered sounds with the specified methods, parameters and values. All FLMs were compared with the standard method of hearing aids (amplification) for five different noisy environments. FLMs satisfied 83% success of higher speech intelligibility improvement than amplification in all cases. As a conclusion, the necessity of using subject-specific FLMs was shown to achieve higher intelligibility than with amplification only. Accordingly, a methodology for selection of the values of parameters for different noisy environments and for different audiograms was developed.