Mechanical and electrical relaxation processes are compared on identical superionic glasses in which the glassy matrix AgPO3 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 approximate to 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.