Model development for auralization of interior tyre noise

Abstract: Increasing competition has set pressure on the product development process to reduce development time and costs. Computer Aided Engineering (CAE) has been used to decrease development times by facilitating early predictions of product performances and qualities. Especially in early phases of product development, models with sufficient accuracy can provide valuable decision supports in order to pass legislations and fulfill customer expectations. Acoustic performance and sound quality are essential parts of the perceived product functionality and quality. A powerful method in product sound development is to combine recordings and simulations into auralizations. Interior vehicle noise is an important factor in the perceived product quality where tyre noise is a dominant source. The objective of this licentiate thesis was to lay the foundation for an auralization model of interior tyre noise. The aim of the model is to use the results from for example FEM simulations of tyre/road interaction and filter it through experimentally measured transfer functions into the cabin of the car. By varying compounds, components and road profiles in simulations, tyre noise can be auralized in different cars in an early design phase. Tyre noise predictions and auralizations are relevant both in tyre and car development. The vibrations generated by the tyre/road interaction are transferred through the hubs of the car and into the cabin as structure borne sound. The hub acts as the coupling element and describes the boundary condition for the rim. In paper I, the mechanical mobility of a hub was measured in 6-DOF. Measurement results showed good multiple coherences, reciprocities and low random errors in the frequency range 0-300 Hz. The measured mobilities will be used to transform operational forces and moments into velocities and will be implemented as boundary conditions in FEM simulations. For auralizations of the air-borne tyre noise contribution, knowledge of the required accuracy in positioning of sources and receivers is essential. In Paper II, variations in perceived sound caused by displacements of source and listening positions were assessed to find the smallest displacement giving a just audible differences. In addition, binaural transmissibility functions were measured from a loudspeaker near a wheel to an artificial head inside the car. Results showed that the accuracy in the positioning of the source and the receiver needed to be smaller than 2 cm to avoid audible differences. In order to generalize auralizations of interior tyre noise, audible variations in specimens of nominally identical products need to be known. In Paper III, variations in perceived interior sound between tyres of different brands and specimens of nominally identical cars were assessed. The differences between five nominally identical cars were found to be two to three times larger than the difference between two tyre models