In this paper, the acoustical modal analysis of a rectangular shallow cavity is performed. It is shown that a suitable choice for the acoustical excitation is the volume acceleration and, for the acoustical response, the sound pressure. When using a Finite Element model and an analytical model, it is shown that the computed Frequency Response Functions must be multiplied by the mass density of the air to yield units of Pascal per unit volume acceleration (m~3/s~2), which are straightforward to obtain experimentally. In the experiments, two types of excitation devices were used. The first utilizes a shaker-driven piston which thrusts against a thin rubber membrane stretched flush to one of the cavity side walls, covering a cylindrical hole. The other actuator was built based upon a research report developed in an EEC project (Brite-EuRam II: PIANO). This acoustic actuator has a high impedance (higher than any practical surrounding impedance) so that the impedance of the cavity does not need to be considered in the calibration factor relating the microphone signal and the source strength. A good agreement was obtained in the comparisons between experimental, analytical and numerical Frequency Response Functions and modes.
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