Abstract: An experimental investigation of the pressure field distribution produced by a piane circular piston in water were carried out applying two receivers of different size. A transducer of 46-mm-diam and 1,O-MHz center frequency was used as a transmitter. The PVdF needle hydrophone of l mm diameter was the first receiver, whereas the second one bad a diameter equal to that of the source. All experiments were performed using a high precision computer-controlled tank facility.