An acoustic standing wave is utilized to separate components from a multi-component fluid, such as oil from an oil-water mixture, or cells entrained in a fluid, in a fluid flow scheme with an acoustophoresis device. For example, the flow scheme and device allows for trapping of the oil as the oil coalesces, agglomerates, and becomes more buoyant than the water. A driver and controller for the acoustophoretic device accommodate variable loading as the components are separated, thereby improving separation efficiency.