Structure-Borne Noise Measures and Their Correlation to Sound Radiation over a Broad Range of Frequencies

Structure-borne noise within vehicle structures is often transmitted in a multi-dimensional manner and thus the vibro-acoustic model(s) of automotive powertrain or chassis must incorporate longitudinal and transverse (flexural) motions as well as their couplings. In this article, we employ the continuous system theory to model a typical vibration isolator (say the engine mounting system) and a compliant receiver that could simulate the body structure. The powertrain source is however assumed to be rigid, and both harmonic force and moment excitations are considered. Our analysis is limited to a linear time-invariant system, and the frequency domain based mobility method is utilized to synthesize the overall system. Contributions of both in-plane and flexural motions to structure-borne and radiated noise are incorporated. Two examples are considered to illustrate the methodology. First, multi-dimensional transmissibility and effectiveness terms are analytically and comparatively evaluated along with vibration power-based measures for an inverted ‘L’ beam receiver and selected source configurations. Further, free field sound pressures are calculated and correlated with structure-borne power transmitted to the receiver. Second, sound measurements and predictions for an experimental inverted ‘L’ plate receiver demonstrate that a rank order based on free field sound pressures may be regarded as a measure of structure-borne noise reduction. Measured insertion losses for sound pressure match well with those computed.