This paper presents the design considerations and performance capabilities of a modified series combination of passive and active elements as a system for vibration control. The investigated primary model consists of a main mass and a randomly excited support. The performance measures, which considered to be minimal, are the main mass acceleration and the relative displacement between the mass and the system support. The operation of the modified system depends essentially on an implemented ideal filtration process in the proposed combination. This process is realized in two different ways: Cl) by the use of an ideal low pass filter CLPF), C23 by the use of an ideal high pass filter CHPF). Additionally, this process controls the flow of the command signal of the combined system which operates the active element. Thereby, the modified system has the property of operating either as a combined system or as a classical passive system. The stochastic optimal control theory in addition to a graphical criterion are well posed together in order to determine the effective cut-off frequency for any of the implemented ideal filters. The pertinent results are compared with those of the combined system. In contrast, they are found to be more encouraging, superior, and compatible with the requirements of many actual engineering applications.