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published_or_final_version / Mechanical Engineering / Master / Master of Science in Engineering

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The sound transmission loss of a range of plywood panels was measured to investigate the influence of the orthotropic stiffness of the plywood panels. The plywood panels were tested as single and also double leaf partitions, with a range of stud configurations. A new method was developed for predicting the sound transmission loss of single leaf partitions with both orthotropic and frequency dependent stiffness values. The sound transmission loss was evaluated for two significantly different sample sizes. The observed influence of the sample size on the measured sound transmission loss was profound. The construction of the partition was shown to significantly affect the influence of the sample size on the sound transmission loss. A qualitative analysis based on existing published research of the contributing factors is presented, and methods for adjusting the results for the small sample size for comparison with the large results were developed. The influence of a range of acoustic treatments of lightweight plywood partitions was investigated. The treatments involved internal viscoelastic materials and decoupled mass loaded barriers in various arrangements. The attachment between the treatment and the plywood panel was found to influence the sound transmission loss significantly. A prediction method based on published models was modified to allow the influence of the treatments to be included. Reasonable agreement was achieved between the predicted and measured results for a wide range of samples. A prediction method was developed that accounts for the influence of orthotropic, frequency dependent material parameters. This method utilised an adaptive, numerical integration method to solve an analytical formulation for the sound transmission loss. The influence of the finite sample size was accounted for using an expression for the finite panel radiation impedance. The finite panel radiation impedance was predicted analytically and an approximation was also presented. The presence of a significant source room niche was accounted for by applying an appropriate limit to the integration range of the angle of incidence. The prediction methods developed are compared with the measured transmission loss results from both the small and large test facilities. Good agreement was seen for some of the predicted results. Generally the agreement within the coincidence region was worse than for the rest of the transmission loss curve. The inclusion of orthotropic and frequency dependent stiffness values significantly improved the agreement within the coincidence region.

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Globally, the ever increasing consumer interest in multichannel audio is a major factor driving the research intent in soundfield reconstruction and compression. The popularity of the well commercialized 5.1 surround sound system and its 6-Channel audio has been strongly supported by the advent of powerful storage medium, DVD, as well as the use of efficient telecommunication techniques. However, this popularity has also revealed potential problems in the development of soundfield systems. Firstly, currently available soundfield systems have rather poor compatibility with irregular speaker arrangements. Secondly, bandwidth requirement is dramatically increased for multichannel audio representation with good temporal and spatial fidelity. This master???s thesis addresses these two major issues in soundfield systems. It introduces a new approach to analyze and sysnthesize soundfield, and compares this approach with currently popular systems. To facilitate this comparison, the behavior of soundfield has been reviewed from both physical and psychoacoustic perspectives, along with an extensive study of past and present soundfield systems and multichannel audio compression algorithms. The 1th order High Spatial Resolution (HSR) soundfield recording and reproduction has been implemented in this project, and subjectively evaluated using a series of MUSHRA tests to finalize the comparison.

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This thesis represents the development and evaluation of a theory for sound transmission analysis by sound intensimetry. In the context of this study sound transmission analysis is understood to embrace the following: (1) The measurement of sound reduction indices. (2) Diagnostic analysis of sound transmission through panels and structures. The sound intensity method is examined against the theoretical background of the classic two-room method which forms the basis of currently used international standards. The flanking problem, which is one of the principle limiting factors in the use of the classic method, is analyzed. The standard formulation of the intensity method is expanded to account for leakage error, boundary interference effects and calibration mismatch. It is shown that the commonly observed low-frequency discrepancy between intensity and classic method results is resolved by application of the Waterhouse correction. Sound absorption by the test object on the receiving side is shown to cause an error which increases with the flanking factor and with the fraction of the receiving room absorption located on the surface of the test object. Guidelines are developed for the assessment and control of absorption error in practical situations. Using the common mode rejection index as a performance rating for sound intensity meters, the measurement of sound transmission in reactive fields is investigated. Derivation of a formula for the reactivity near the surface of a transmitting panel surrounded by a flanking structure in a reverberant field, leads to the development of a theoretical framework and criteria for the planning and evaluation of test arrangements for sound transmission analysis. Guidelines are given for the calculation of minimum receiving room absorption and the microphone spacing required in practical situations. A study of the characteristic properties of sound intensity fields in diffuse and non-diffuse environments is used as a basis in formulating a new method of measuring directional diffusivity. Based on the relationship between reactivity and the degree of directional balance in a sound intensity field, this method involves spatial averaging of the pressure level and determination of the magnitude of the total intensity vector at the point under consideration. A direct-reading diffusivity meter has been developed and employed in assessing diffusivity in practical situations. The effect of a lack of directional diffusivity on the accuracy of sound transmission analysis in reactive fields is examined. Criteria for calculating minimum diffusivity requirements in the source and receiving room are developed and evaluated experimentally. / Thesis (Ph.D.)-University of Natal, 1985.