A steel coil cutting apparatus that overcomes these and other problems has an automated arm having a free end. The power efficient capacitive load driving device can be used to drive one or more acoustic transducers of a parametric audio system with low distortion and a flat frequency response. The pipe-shaped members are joined to each other, forming a single unit, and join parts that join adjacent pipe-shaped members to each other are at least 70% as long as the pipe-shaped members themselves. The active area has a first width and the usable emitter formation area has a second width, where the second width is at least as large as the first width. The retaining arm includes a proximate end and an exterior surface.