On the standard deviation of change-in-impedance due to fuzzy subsystems

The effects of attached multiple subsystems of uncertain properties on the behavior of a main system are investigated by modeling the natural frequencies of the subsystems as random points in the frequency domain. Both the mean and the standard deviation of the change-in-impedance, attributable to the subsystems, are computed without the usual assumption of ''modal overlap.'' It is shown that the standard deviation, which has been overlooked by most authors on this subject, can sometimes be greater than the mean. Thus the knowledge of the mean alone is inadequate to make engineering decisions. (C) 1997 Acoustical Society of America.