A new measurement procedure to obtain transmissibilities for application in a two-step transfer path analysis is presented. In the proposed method an external excitation, for instance by means of a non-instrumented hammer, is used to bring the structure into vibration. The resulting response is then used to estimate the transmissibilities. In most cases the transmissibilities thus determined are of a better quality as compared to the conventionally determined transmissibilities obtained during machine operation, i.e. in conventional operational transfer path analysis procedures. The reason of this is that when a structure is excited by hammer strokes, its responses are largely independent from each other, whilst vibrations induced by machine operation are in general not.
Subsequently the transmissibilities are applied in a transfer path analysis (TPA) like approach. It was found that the identification of the transfer paths were better as compared to the identification transfer paths by means of a conventional operational transfer path analysis.
The advantages of the method are illustrated by means of an experiment on a small gearbox.
Additionally, a procedure to determine the number of significant transmission paths is proposed which is based upon a singular value decomposition of the response matrix.
In the application discussed in the paper the number of significant structural transmission paths could be estimated by means of this procedure, as well as
the order of magnitude of the strength of the acoustic path relative to that of the structural transmission paths.