This paper investigates a method called spectral decomposition and is presented as an alternate approach to determine the system frequency response functions of turbomachinery. Spectral decomposition is a method that is based on the principals established by the acoustic similarity laws to determine the spectral characteristics of a source function. The decomposition process was originally implemented to investigate the isolated acoustic source spectra of fans specifically excluding structureborne sources; however, this paper focuses on using the method for the purpose of characterizing the system response functions associated with rotating machinery. During this investigation, static impact test data was acquired on a large industrial motor to characterize the frequency response functions of the motor/compressor system. Spectral decomposition results are then calculated using the motor operational structureborne data and compared to the results of the static impact test. This paper shows that the spectral decomposition is a viable option to use in place of the static impact test results where qualitative frequency response functions are desired.