In order to optimise the vibro-acoustic behaviour of panel-like structures in a more systematic way, accurate structural models are needed. However, at the frequencies of relevance to the vibro-acoustic problem, the mode shapes are very complex, requiring a high spatial resolution in the measurement procedure.
The large number of required transducers and their mass loading effects limit the applicability of accelerometer testing.
In recent years, optical measuring methods have been proposed. Direct electronic (ESPI) imaging, using strobed continuous laser illumination, or more recently, pulsed laser illumination, have lately created the possibility to bring the holographic testing approach to the level of industrial applicability for modal analysis procedures.
The present paper discusses the various critical elements of a holographic ESPI modal testing system. Next to the optical parts, the integration with the modal analysis procedures, including the integration of geometry and response information, are discussed. Special attention is paid to the modal parameter extraction of the large DOF number data, for which a special data reduction scheme was developed. The paper furthermore discusses test results obtained on a car panel in a vibro-acoustic set-up. The measurement data are used to predict interior noise.