  The properties of the quark-gluon plasma(QGP) in the presence of baryon
chemical potential are studied using the Field Correlator Method(FCM). At low
densities the QGP thermodynamics with the colormagnetic confinement and the
Polyakov line interaction is in good agreement with lattice data,and the speed
of sound satisfies $C_s^2\leq \frac13$,but in the intermediate range of
densities the speed of sound displays a singular behaviour and one needs
density modifications of the Polyakov line interaction to avoid instabilities.
In particular for $\mu_q >0.5$ GeV there exists a region in the $(\mu, T)$
plane where $C^2_s$ violates the conformal limit. This behaviour is strongly
connected to the properties of the Polyakov loop and its density dependence.
