Based on joint feedback controls, the stabilization issue of a serially connected vibrating strings system is presented. Suppose that the two ends of the strings system are clamped and the vertical force of strings is continuous at interior nodes while the transversal displacement is discontinuous. The vertical force of strings at interior nodes are observed and the compensators are derived from the observation values. Then the feedback controllers are arranged at interior nodes to stabilize this system. Through a detailed spectral analysis, this closed loop system is proved to be asymptotically stable and there exists a sequence of (generalized) eigenvectors of the system that forms a Riesz basis with parentheses for the state space under certain conditions. Hence the spectrum-determined-growth (SDG) condition holds.