Abstract: The present invention is directed to a method of calculating the impedance of a material behind the section of a casing. An acoustic excitation pulse is directed towards a section of the casing, resulting in a return waveform having a reverberation segment and an initial reflection segment. The return waveform is analyzed to choose a resonance frequency indicative of the casing's nominal thickness. The return waveform is bandpass filtered about the chosen frequency. A time window of the reverberation segment is selected, and the energy content in the time window of the filtered reverberation segment is calculated. Both the bandpass filter and time windows are selected based on the chosen resonance frequency, thereby removing variations in the thickness of the casing. The energy content calculation produces a cementation signal indicative of the impedance of the cement behind the section of the casing. The impedance value is indicative of the cement quality.