Characterisation of a resonating system by mean of electrical impedance measurements

In recent years the use of affordable alternatives to impact hammer measurements to assess musical instruments and systems with complex resonating behaviour has emerged. By using small electro-dynamic exciters, standard methodologies such as sine-sweep measurements and real time spectral analysis together with pink-noise have shown positive results to quickly and economically characterise both the mechanical and the mechano-acoustical responses of musical instruments and resonating plates.

This investigation tries to expand on the theory behind the coupling of an exciter and a resonating structure. Electrical impedance measurements will be performed at the terminals of an exciter placed in different positions of an unknown soundboard. The interaction between the actuator and the plate will be interpreted drawing from the models describing the coupling between an electro-dynamic transducer and a vented enclosure. Accordingly, a lumped element model will be presented and discussed. The goal is to estimate which is the minimum number of measurements needed to characterise the first ten modes of an unknown structure. A criterion to select the correct size and power handling capability of the exciter used to sense will also be discussed.