The article presents the possibility of an innovative use of spectral analysis to control the quality of joints welded using the multispot projection welding method. The tests discussed in the article included the analysis of welding machine and welding fixtures frequency. The analysis consisted in the impulse-based excitation of vibrations in the entire system (including the welding machine and elements subjected to welding) and the recording of the object response using an acceleration sensor. The results were afterwards subjected to spectral analysis using the Fourier transform. As a result, it was possible to identify the effect of the lack of a weld on the free vibration frequencies of the entire system. Related quality control was performed by comparing the free vibration frequency spectrum of reference elements with that of elements not containing a metallic joint between them. The acquisition and analysis of measurement data were carried out in the LabView environment. The test results confirmed the possibility of using spectral analysis to control the quality of the projection welding process.