The paper reports a study of a radiating acoustic system in the form of an array of coaxial piezoceramic shells. Three methods of shell excitation are discussed. In one, each shell is driven by its own electric generator. In the second, all shells are electrically connected in parallel and driven by a single common generator. In the third, the shells are series-connected and also driven by a single common generator. It is shown that, with the second and third excitation methods, the sells are electrically coupled over the circuits, and this can have a significant detrimental effect on the energy efficiency and the directivity of the acoustic system.