An underwater sound projector adapted to produce time-harmonic waveforms, comprising: a housing; an electro-magnetic force generator comprising: a stator rigidly connected to the housing and having an inner open space; at least two stationary coils (550a, 550b) physically connected to the stator and located in said inner open space; at least four stationary permanent magnets (560a, 560b) physically connected to the stator and located in said inner open space; and two moving armatures (530a, 530b), located in said inner open space and configured to linearly move in said inner open space along a common axis; and two pistons (512a, 512b), connected to said moving armatures, each piston positioned on each one of two opposite sides of the electro-magnetic force generator; wherein the structure of the stator, the location and orientation, in the inner open space, of the stationary coils, of the stationary permanent magnet and of the two moving armatures, and the magnetic fields generated by the permanent magnets and by the coils are symmetric with respect to a plane perpendicular to said axis and passing for the geometric center of the electromagnetic-force generator, so that the two moving armatures and the two pistons are symmetrically actuated and the respective accelerations are cancelled in a virtual node located in the center of the electromagnetic-force generator; the underwater sound projector being characterized in that: the projector further comprises means to finely adjust a static position of the moving armatures and of the two pistons, said means comprising a feedback control system configured to superimpose a DC bias on a AC drive signal applied to each coil associated with each piston-armature assembly. a housing; an electro-magnetic force generator comprising: a stator rigidly connected to the housing and having an inner open space; at least two stationary coils (550a, 550b) physically connected to the stator and located in said inner open space; at least four stationary permanent magnets (560a, 560b) physically connected to the stator and located in said inner open space; and two moving armatures (530a, 530b), located in said inner open space and configured to linearly move in said inner open space along a common axis; and two pistons (512a, 512b), connected to said moving armatures, each piston positioned on each one of two opposite sides of the electro-magnetic force generator; wherein the structure of the stator, the location and orientation, in the inner open space, of the stationary coils, of the stationary permanent magnet and of the two moving armatures, and the magnetic fields generated by the permanent magnets and by the coils are symmetric with respect to a plane perpendicular to said axis and passing for the geometric center of the electromagnetic-force generator, so that the two moving armatures and the two pistons are symmetrically actuated and the respective accelerations are cancelled in a virtual node located in the center of the electromagnetic-force generator; the underwater sound projector being characterized in that: the projector further comprises means to finely adjust a static position of the moving armatures and of the two pistons, said means comprising a feedback control system configured to superimpose a DC bias on a AC drive signal applied to each coil associated with each piston-armature assembly. a stator rigidly connected to the housing and having an inner open space; at least two stationary coils (550a, 550b) physically connected to the stator and located in said inner open space; at least four stationary permanent magnets (560a, 560b) physically connected to the stator and located in said inner open space; and two moving armatures (530a, 530b), located in said inner open space and configured to linearly move in said inner open space along a common axis; and two pistons (512a, 512b), connected to said moving armatures, each piston positioned on each one of two opposite sides of the electro-magnetic force generator; wherein the structure of the stator, the location and orientation, in the inner open space, of the stationary coils, of the stationary permanent magnet and of the two moving armatures, and the magnetic fields generated by the permanent magnets and by the coils are symmetric with respect to a plane perpendicular to said axis and passing for the geometric center of the electromagnetic-force generator, so that the two moving armatures and the two pistons are symmetrically actuated and the respective accelerations are cancelled in a virtual node located in the center of the electromagnetic-force generator; the underwater sound projector being characterized in that: the projector further comprises means to finely adjust a static position of the moving armatures and of the two pistons, said means comprising a feedback control system configured to superimpose a DC bias on a AC drive signal applied to each coil associated with each piston-armature assembly.