Locating cracks using sensor information is central to structural health monitoring. Experimental validation of algorithms for crack localization is often difficult because the test structure has to be damaged and it is difficult to try different crack sizes and locations without having a large number of specimens. Analytical procedures can be tested, however, by using mass modifications that are easy to control and do not produce permanent changes. In this work we report results of an experiment where an added mass was localized in an aluminum beam. The tests were carried out to validate a null space strategy known as the dynamic damage locating vector approach (dDLV). Emphasis is placed on testing the merit of a recently developed approach intended to promote robustness against modeling error.