Measurement of point moment mobility in the presence of non-zero cross mobility

One of the main difficulties in measuring moment mobility is that of generating a moment which is pure and of sufficient power. Measurement systems have been proposed which consist of a pair of matched shakers, a shaker-lever system or an actuator to a design by Petersson. All have been used to directly measure moment mobility and results are encouraging in conditions where the cross mobility is small or zero. Otherwise there is a discrepancy between the measured and true mobility which is a function of the ratio between the unwanted vertical force and applied moment and of the cross mobility at the receiver point. This error is discussed theoretically and a correction term introduced to enable point moment mobility to be measured directly. (C) 1997 Elsevier Science Ltd.