Abstract:
Consideration of interior noise and vibration levels, during the development of a new motor car, has tended to concentrate on the use of structural modal surveys, combined with the measurement of sound-pressure levels in the fully trimmed car. However, there is increasing pressure to reduce development lead times, as well as to provide an improved level of refinement. The work described here uses the finite-element method to predict interior noise levels. A finite-element model of the acoustic cavity of a Rover Metro-R6 has been generated, and frequency response functions of the vibration of the vehicle structure are applied as a forcing function to the boundary. This enables noise transfer functions to be predicted at locations within the cavity such as the driver's ear, in order to identify any problem areas. Boundary impedance is included in the model to represent the presence of carpet and seats. The impedance values were obtained using the two microphone impedance tube method [ASTM Standard E1050-86]. Experimental noise transfer functions results were found, using a vibration. These showed good agreement with the predicted values. The boundary element method was also used to investigate panel contribution. [Work supported by Rover Group, UK.]