Abstract Mechanical and electrical relaxation processes are compared on identical superionic glasses in which the glassy matrix AgPO 3 was doped with various kinds of salt dopant. It was found that the same values characterize the a.c. conductivity as well as the mechanical spectra. Above T≈10K there are two different activated contributions to the acoustic absorption: one, dominant at high temperatures/low frequencies is characterized by a linear decrease of the activation energy as the salt dopant is increased; the second, dominant at intermediate temperatures/frequencies is characterized by activation energy values one order of magnitude smaller. At the same time the log–log representation of the experimental a.c. conductivity vs. frequency shows a double power law behaviour. Two different relaxing processes can account for the activation energy values and for the double power law behaviour of the a.c. conductivity.