The design of resonant absorbers.

The purpose of this project was to investigate the acoustic performance of a range of resonant absorbers as typically used in automotive applications. A literature review considering sources of exhaust noise, muffler types and components, sound measurement, and prediction techniques was undertaken. Test facilities were constructed that allowed testing of muffler systems with either an engine or a speaker as the source of excitation. This enabled measurements made with a speaker to be compared to those made with an engine, the latter including flow, temperature and pressure effects. A number of different muffler systems were tested and their acoustic performance predicted using a scattering matrix technique. Comparing measured and predicted results allowed assessment of the accuracy of the predictions, the performance of various muffler components and the reliability of measurements. The model adequately predicted muffler performance for all muffler systems tested apart from those containing Helmholtz resonators. This was attributed to pressure and flow effects not included in the model. Using the modelling procedure presented, muffler systems can be quickly designed and optimised