A hydrophone, comprising: a rectangular-shape transduction element of two end sensing faces, a damping shell or wrapping, a rigid tubular housing, a first sound-permeable seal, a second sound-permeable seal and wires; wherein the first sound-permeable seal covers one open end of the rigid tubular housing, the second sound-permeable seal covers the other open end of the rigid tubular housing, and the rectangular-shape transduction element is connected to an external load via wires through either or both sound-permeable seals; wherein both the first and second sound-permeable seals (130, 140) serve to waterproof the rectangular-shape transduction element from external environment while allowing the acoustic signal in water to transmit through them to the rectangular-shape transduction element; characterized in that the rectangular-shape transduction element is made of lead based relaxor element solid solution piezoelectric single crystal polarized in a crystal direction and having either or crystal direction as the sensing direction, the latter being also the axial direction of the transduction element; wherein said relaxor single crystal comprises solid solutions of lead zinc niobate-lead titanate, lead magnesium niobate-lead titanate, lead magnesium niobate-lead zirconate titanate, lead indium niobate-lead magnesium niobate-lead titanate, or derivative compositions thereof; wherein the damping shell or wrapping is applied over all side faces of the rectangular-shape transduction element except both end sensing faces; wherein the rigid tubular housing sleeves the wrapped rectangular-shape transduction element so that the damping shell or wrapping helps to damp out rubbing noise produced by the friction between the rectangular-shape transduction element and a bore surface of the rigid tubular housing; wherein said rectangular-shape transduction element receives the acoustic signal via its both end sensing faces and converts the acoustic signal to an electric signal and outputs the electric signal to the external load. wherein the first sound-permeable seal covers one open end of the rigid tubular housing, the second sound-permeable seal covers the other open end of the rigid tubular housing, and the rectangular-shape transduction element is connected to an external load via wires through either or both sound-permeable seals; wherein both the first and second sound-permeable seals (130, 140) serve to waterproof the rectangular-shape transduction element from external environment while allowing the acoustic signal in water to transmit through them to the rectangular-shape transduction element; characterized in that the rectangular-shape transduction element is made of lead based relaxor element solid solution piezoelectric single crystal polarized in a crystal direction and having either or crystal direction as the sensing direction, the latter being also the axial direction of the transduction element; wherein said relaxor single crystal comprises solid solutions of lead zinc niobate-lead titanate, lead magnesium niobate-lead titanate, lead magnesium niobate-lead zirconate titanate, lead indium niobate-lead magnesium niobate-lead titanate, or derivative compositions thereof; wherein the damping shell or wrapping is applied over all side faces of the rectangular-shape transduction element except both end sensing faces; wherein the rigid tubular housing sleeves the wrapped rectangular-shape transduction element so that the damping shell or wrapping helps to damp out rubbing noise produced by the friction between the rectangular-shape transduction element and a bore surface of the rigid tubular housing; wherein said rectangular-shape transduction element receives the acoustic signal via its both end sensing faces and converts the acoustic signal to an electric signal and outputs the electric signal to the external load.