A Study of Sound Source Characteristics for Vehicle Airborne Transfer Function Measurement

Transfer function measurements are the basis for construction of conventional test based source-path-receiver model of a vehicle. Interior noise of a vehicle can be synthesized using source excitation (both acceleration at source and near source sound pressure level) and its corresponding transfer function (Vibro-Acoustic Transfer Function (VATF) and Acoustic Transfer Function (ATF) respectively) to the interior of vehicle. Ideally ATF should be linear and independent of sound source, dependent only on size of air cavities, body structure and its material characteristics in between receiver and source location. But practically because of the type of excitation signal used to excite the sound source and characteristics of sound source itself, there is a possibility of variations in amplitude of acoustic transfer function. This paper discusses about characterization procedure of two different sources which are studied based on the sound propagation inside hemi-anechoic chamber with unique method of response microphone locations at known distances from sound source. Based on the measurement inside hemi-anechoic chamber, a detailed analyses procedure on how to check the degree of dependency of response function with respect to different types of source excitation signal and how to arrive the appropriate source excitation signal to be used for vehicle airborne transfer function measurement are discussed. Finally a case study on the degree of correlation achieved between synthesized and actual measured interior noise of a vehicle are highlighted in this paper.