Theoretical investigation of sound reduction by finite barriers.

Noise pollution in factories has become a major problem which has been highlighted in recent years. This thesis attempts to construct a model which will predict sound attenuation by finite barriers within enclosures, thus simulating factory conditions.The research uses the classical Kirchhoff-Fresnel diffraction theory outlined in Bom and Wolf1 to develop a model by which the barriers' surface is divided into elements. Using Babinet's Principle, sound attenuation was predicted for a finite barrier in free space. The sound source was assumed to be a point source of monotonic frequency.The free space environment served as a basic theoretical model where computer programs compared the zero and first-order models. This comparison showed that the first-order model was the more productive and identified the optimum element size to give an accuracy within the precision grade of measurement.After validating the theory, the model was adapted to predict insertion loss, using a finite barrier in contact with the ground. There is much contemporary literature for this model but little research has been undertaken in predicting sound losses due to finite barriers within enclosures.A further extension to the research was to place the barrier in a flat room, where reflections of the sound waves from the roof as well as the floor were included. This model also allowed the effect on insertion loss to be examined by increasing the aspect ratio of width/height of the barrier.Finally, side walls were introduced into the model to see if they have any significant effect on insertion loss as compared to the flat room model.