The railway bed is a source of powerful vibrations. These vibrations are a source of waste energy suitable for conversion into electrical energy. To build the adequate generator-harvester, it is necessary to choose the most effective oscillation frequencies within the spectrum of the railway track. Two types of piezoelectric transducers are compared in the paper: flexural beam-type transducer and disk bimorph transducer of the umbrella-type. Using these transdusers, and the vibrometer-phonendoscope, the frequency spectrum of a real railway embankment is obtained. Examples of spectra are given, and also the most effective frequency is estimated from 10 different measurement results.