Abstract
A technique developed to carry out experimental acoustic modal analysis using commercially available structural modal analysis software is described. This uses a finite difference calculation to determine the spatial variation in pressure. In order that the resulting function exhibits the same nodes and antinodes as the actual pressure distribution at resonance, a second-order finite difference calculation is performed to obtain the second spatial derivative. This is implemented in practice using a three side-by-side microphone probe with an analogue differential amplifier.
The technique is verified by measuring the natural frequencies and mode shapes of a bare rectangular office. These results are compared with analytical calculations and output from a finite element model. The results show very good agreement for all modes in the frequency range of interest.
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