Abstract: An omnidirectional acoustic sensor has an air-backed diaphragm in a unit which has a central axis and is mounted so as to be responsive to acoustic pressure waves. A piezoelectric ceramic disc is attached to each face of the diaphragm. This combination forms a sensor unit whose acoustical and capacitive sensitivities are relatively independent of varying static pressure. The ceramic discs and diaphragm are each of a preselected size such that the ratio of disc diameter to diaphragm diameter is not greater than about 0.8. The sensor assembly further includes collar-like support means from which the diaphragm is supported. The sensor unit has a radius of zero stress, with the diaphragm being connected to the support means radially outwardly of the radius of zero stress. The ceramic discs lie within that radius of zero stress. In the preferred configuration the diaphragm and support means are the same piece of material.