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This thesis is a contribution towards developing cost-effective ways for reducing outdoor traffic noise in outdoor environments by exploiting the interaction between sound travelling directly to a listener from the source and sound reflected by the intervening ground . Sound propagation over different kinds of porous, rough and mixed impedance ground surfaces have been studied experimentally and numerically. Measurements of short-range acoustic level difference spectra over outdoor ground surfaces and artificially-created surfaces outdoors and in the laboratory have been compared with predictions to establish suitable impedance models. Sound propagation over mixed impedance ground having single or multiple impedance discontinuities has also been studied . Acoustic transmission loss through vegetation, crops and hedges has been investigated. • The phenomenon of sound diffraction and periodicity due to rough periodic ground surfaces has been explored through artificially created rough surfaces in the laboratory and outdoors. The phenomenon of surface wave propagation over rough hard surfaces and porous surfaces has been explored through laboratory experiments. Measured data indoors and outdoors have been used to validate numerical (BEM and FEM), empirical and analytical (MST) prediction techniques. The validated numerical methods have been used to make predictions at scales suitable for attenuating traffic noise by means of carefully designed ground treatments. The work has also been extended to railway and tramway noise. It has been found that replacing hard ground with porous ground, introducing single or multiple impedance discontinuities, growing vegetation and introducing low height roughness can all contribute between 3 and 15 dB additional attenuation of traffic noise. In respect of replacing hard ground by porous ground, it is concluded that the ground with lowest flow resistivity i.e. grassland left untouched and allowed to grow wild gives the best attenuation performance. However, dividing a single width of soft ground into alternating strips of hard and soft surfaces does not improve the insertion loss. The overall width of the soft surface is the main factor. Cultivating crops over porous ground can enhance the attenuation but the effect is not very significant for A-weighted levels as most of additional attenuation occurs at higher frequencies above 3 kHz. A 0.3 m high and at least 3 m wide lattice structure design is found to be very useful for traffic noise attenuation since it offers greater insertion loss than the same width and height of parallel low walls and the resulting attenuation is azimuthal angle independent. It has been shown also that the potentially negative effect on insertion loss due to propagation of roughness-induced surface waves over rough surfaces can be reduced by introducing sound absorbing material in between the walls.

Adaptive feedback cancellers in hearing aids can produce unpleasant sounding nonlinear distortion artefacts (entrainment) in response to periodic or tonal inputs, including music. The aim of this study was to determine the ability of different objective metrics to predict mean quality judgments made by normal and hearing impaired listeners for music processed by hearing aid adaptive feedback cancellation. The metrics tested consisted of 'cognitive' parameters from perceptually-based audio quality models established in the literature and four new cognitive parameters described by the authors of this study. Neural networks were used to map between the values of cognitive parameters and a subjective scale of perceived quality. Network training data consisted of cognitive parameter values obtained from different excerpts of orchestral music processed by a model of a hearing aid adaptive canceller, and corresponding subjective ratings of sound quality. An optimal combination of cognitive parameters to use as network inputs was found using an extended Fourier amplitude sensitivity test (EFAST) (Saltelli et al., 1999). In an initial experiment, audio quality models were trained and validated using mean subjective ratings obtained from 26 normal hearing subjects. In a second experiment, quality model training and validation was performed using mean subjective ratings obtained from 13 subjects with cochlear hearing loss. Cognitive parameters used in the second experiment featured modifications based on subject pure-tone hearing threshold loss data to account for effects of reduced cochlear compression, frequency resolution and temporal resolution. Experimental results suggest that it possible to produce relatively accurate predictions of mean subjective quality ratings from normal and hearing impaired subjects of audio samples degraded by entrainment distortion, using perceptually-based models. This was evidenced by measured correlation scores between predicted and measured subjective ratings in excess of p=O.93. For both the normal and hearing impaired data, the most salient cognitive parameters consist of measures related to distortion loudness and the proportion of aperiodic power present in the processed signal (the latter being quantified by a new parameter, 'YINparam', which is described by the author). Cognitive parameters modelling normal hearing ears were found to be an accurate predictor of quality ratings from hearing impaired subjects; however, modifications of cognitive parameters, based on pure tone threshold data, which were used to account for supra threshold hearing loss effects did not generally improve ability to predict quality ratings from hearing impaired subjects.

Ground-borne vibration induced by railway system is a major environmental concern in urban areas. Many researches, usually based on numerical modelling, have been conducted to study this problem. Numerical modelling usually makes many simplifying assumptions to reduce the complexity of the problem. One commonly used assumption is that soil properties are constant with depth. However, various studies in the field of geotechnical engineering have shown that soil properties change with depth due to the effect of increasing confining stress. Ground-borne vibration is hence unrealistically simulated if constant soil properties are assumed throughout a half space or a soil layer. This research focused on studying the soil non-homogeneity effects due to the variation of soil properties with depth on surface and underground railway induced ground-borne vibration. It also explored the use of physical modelling as an alternative of numerical modelling to simulate this problem. The study was performed using physical modelling in a geotechnical centrifuge and by conducting numerical simulations of the tests. The advantage of conducting centrifuge tests on scaled models is that the soil behaviour, which greatly depends on the stress field, is realistically simulated because the in-situ stress field is replicated within the model. Two series of centrifuge tests were conducted to simulate ground-borne vibration from surface and underground railways. To obtain a better understanding of the experiment results, corresponding numerical models were developed to simulate the two series of tests. Boundary effects due to the presence of the centrifuge container on the two series of measurement results were investigated first. The numerical models were then used to examine the soil non-homogeneity effects. Two cases were simulated in each of the numerical models. One assumed that the properties of model soil were uniform. The other case accounted for the variation of dynamic soil properties with depth. The findings from this study suggest that centrifuge modelling is a useful method to study railway induced ground-borne vibration. Reliable and consistent measurement results can be obtained in the centrifuge. This study also addressed an important issue, boundary effects due to presence of the centrifuge container for the tests. The boundary can significantly affect the behaviour of the models, causing fluctuation in the plots of frequency response functions (FRFs) and amplifying model responses. Comparison of the experimental and numerical results demonstrated that the homogeneous models are able to give good estimates of the model behaviour at one location either at the free surface or the interior, depending on the selection of material parameters. However, in order to obtain good estimates of the whole behaviour of the models, it is important to account for the variation of soil properties with depth when studying railway induced ground-borne vibration.

Profile structures were previously introduced to improve the performance of noise barriers. Subsequent researches on reactive surfaces have shown that these surfaces improve the performance of the profile barriers at certain frequency ranges. This thesis details an investigation into prediction, measurement and the reduction mechanism of profile Schroeder diffuser barriers.

This study demonstrates how aircraft noise can be translated into a form of landing charge. The objectives of the thesis were to develop noise landi'ng charges for six of the major airports in England and to determine what the implication it has on passengers' choice of airports. An airport choice model is developed distinguished by three market types: long-haul international scheduled, short-haul international scheduled and charter international. Modelling of airport choice was also carried out for passengers from the Greater London and South East areas. The best results are obtained using difference in access time, logarithmic difference in frequencies and weighted differences in fare variables. There is consistency in the access time coefficients for all three markets. Airport choice for international scheduled and charter passengers for the Greater London and other South East areas also show consistency in access time amongst different passenger groups in choosing airports. The implication of the noise charge particularly at Gatwick and Heathrow for the short and long haul markets reveal that the fare coefficients are sensitive and are subject to doubt. However Brooke et al (1994) acknowledge that exact fare details are difficult to obtain. Therefore it is a difficult task to produce accurate fare coefficients with published fare details that do not take into account discounts received by passengers. This is reflected in this study by observing the fact that high number of passengers change airports, when it may be argued that the noise charges are moderate. The sensitivity of the implications of the noise charge determined in this study have depended highly on the fare coefficients. This study has demonstrated the importance and perhaps the over reliance of depending on a single parameter for the evaluation of the implications of the noise charge.