Obtaining a scaled modal model of panel type structures using acoustic excitation

For a modal analysis, in general, a structural excitation is used. This means : performing a hammer excitation or attaching shakers to the structure. One of the typical problems with shaker excitation, especially for light-weight components, is that its dynamic characteristics, the effect of the attachment (additional mass and rotational stiffness), can have a disturbing effect on the measured modal characteristics. In this paper, it will be shown that an accurate modal model can be extracted from measurements of an acoustic - contactless - excitation. The conclusion that eigenfrequencies, modeshapes and damping can be found correctly, can be taken from a comparison with a finite element model. A typical problem of acoustic excitation is to obtain the correct scaling of the modes. A method is proposed to calculate accurately the modal mass from this kind of excitation. This means that the whole model can be known and transfer functions with non-measured structural DOFs as input can be correctly synthesized. This shows that acoustic excitation can be a useful tool when one wants to minimize the disturbing effect of the shakers attachment and still wants an accurate model.