  In this investigation an holographic description of the deconfined phase
transition of scalar and tensor glueballs is presented within the so called
hard-wall model. The spectra of these bound states of gluons have been
calculated from the linearized Einstein equations for a graviton propagating
from a thermal $AdS_5$ space to an AdS Black-Hole. In this framework, the
deconfined phase is reached via a two steps mechanism. We propose that the
transition between the AdS thermal sector to the BH is described via a first
order phase transition, with discontinuous masses at the critical temperature,
which has been determined by Herzog's method of regulating the free energy
densities. Then, the glueball masses diverge with increasing $T$ in the BH
phase and thus lead to deconfined states \`a la Hagedorn.
