When setting up an electrostatic-structural and acoustic calculation, consider the following hints and recommendations:
A prestress analysis is required before the linear perturbation harmonic analysis.
The voltage constraint needs to be deleted in the prestressed coupled-field harmonic analysis.
The acoustic mesh should be fine enough to properly capture the pressure waves.
To account for deformations resulting from the coupled-field static analysis, use element morphing to morph the mesh in the acoustic fluid.