The structure‐borne sound characteristics of a commonly found fan installation were examined through measurements and further analyses in the frequency range up to 500 Hz. The focus was to determine the prediction improvements by including the rotational degrees of freedom. Free velocities of the fan were measured in five degrees of freedom (in‐plane rotation or twisting motion were neglected), while fan mobilities were measured and foundation mobilities were predicted in three degrees of freedom: a translational and two rotational, those resulting in bending motion. The two in‐plane translations were considered by transforming their motion to rotations resulting in moment excitations on the foundation. Measurements were also made of the corresponding isolators’ stiffness values. Comparisons are made with power measurements of the complete system. It was found that an unsatisfactory moment excitation resulted in one of the rotational degrees of freedom while employing a twin shaker arrangement when determining the fans’ mobilities. Therefore, a source signal filtering technique was applied to improve the measurement. Comparisons are made with the originally measured mobilities. [This work has been supported by the Swedish Council for Building Research (BFR) through Contract 950192‐8 and the Swedish Research Council for Engineering Sciences (TFR) through Contract 95‐160.]