| 1. A diaphragm assembly comprising:
at least two piezoelectric diaphragm members arranged in a stacking direction, each piezoelectric diaphragm member comprising
at least a piezoelectric material; an interface layer situated between adjacent piezoelectric diaphragm members, the interface
layer in the stacking direction being displaceable and either incompressible or resilient and configured to transmit the force
applied by the displacement of a first of the piezoelectric diaphragm members on a first side of the interface layer to a
second of the piezoelectric diaphragm members on a second side of the interface layer;
wherein the interface layer comprises a gas.
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