The mutual radiation impedance, which acts among transducer elements vibrating in the medium, is one of the most important factors for considering the interaction of recent high-power and low-frequency sonar arrays and active acoustic control. The mutual radiation impedance is numerically obtained from an equation of directional functions. When the amplitude of one of two transducer elements is changed, the total and individual power output become quadratic curves with minimum peaks as a function of amplitude. This minimum peak of the total power output curve means that there is the most effective vibrating velocity amplitude for the additional or the secondary source to minimize the total power output from the original or the primary source. The measurement of the acoustic intensity from the underwater array made of piezorubber sheet visualizes the phenomena of the total power output reduction. Near-field 3-D maps of the active intensity l and the reactive intensity Q show some interesting patterns of energy flow in the vicinity of transducers especially in low-frequency regions.