To calculate the transmitting characteristicsof sonar arrays, taking into account the acoustic interactions between the transducers and the finite size of the array, a computer model has been developed. The method applies to arbitrary-shaped arrays with piston transducers. The acoustic mutual impedance matrix between the transducers is first computed, and comparison with analytical results in a special case is presented. Then, some results on arrays containing 8 and 32 transducers are shown. For a densely packed array of circular pistons with diameter equal to λ/4 at the resonance, the acoustic interactions may have large effects on the pressure and velocity distributions on the surface of the array.