At least embodiment is directed to an earpiece comprising a housing; and a field responsive fluid, where the field responsive fluid is in the housing, where the housing is part of the earpiece, and where the earpiece is configured to vary a field to vary an acoustical property of the field responsive fluid. A voltage generator includes a low voltage high speed generator, a low voltage to high voltage high speed level translator, and a high voltage driver. A swapping technique is selected from gain-swapping and a combination of bit-swapping and gain-swapping based on two index values such that the difference between the maximum mean square error and the minimum mean square error is minimized and the gain factor constraints are met. The first refresh rate corresponds to a maximum refresh rate. The selection part selects examination conditions corresponding to the detected position based on the association information.