Abstract: A hydrophone comprising an acoustical reflector constituted by a sealed, flexible and deformable container containing two rigid parallel plates separated by lattice sheets of interlaced filaments and at least one piezoelectric transducer with a thin flexible blade fixed at its periphery to a rigid annular support. The reflector and the transducer are entirely embedded in a common synthetic resin layer having a thickness of several millimeters which secures them together and maintains the transducer in proximity to the front face of the acoustical reflector. The layer of resin has a reduced thickness of the order of 1 mm facing the transducer.