We use here HUM (cf. Lions l9r–ll0r) to study the Neumann controllability of a two-dimensional hybrid system membrane with strings on general convex polygon domains (cf. Lee and You l1r, Littman l11r for a related version of this model). This system is governed by utt − Δu e 0 in \Omega \times (0,T), \ \rho u _{tt} - \beta {\partial^2 u \over \partial \tau^2}+ {\partial u \over \partial \nu} = 0 on \Gamma_1 \times (0,T), {\partial u \over \partial \nu} = g_2 on Γ2 × (0,T), u e 0 on Γ3 × (0,T)s u(Aj) e 0 if A_j \in {\overline \Gamma}_1 \ \backslash \ {\overline \Gamma}_2 and 0 \lt t \lt T, \ {\partial u \over \partial \tau_{j+1}} (A_j)=d_j if ej ⊂ Γ2 and ej+1 ⊂ Γ1, 0<t<T, and {\partial \over \partial \tau_j} (A_j)=d_j if ej ⊂ Γ1 and ej+1 ⊂ Γ2, 0<t<T (see Sec. 1 for notations). An inverse inequality of the energy has been derived when Ω satisfies certain geometric conditions and T is sufficiently large. As a consequence, an exact control in (H^1 (0,T; L^2(\Gamma_2))^\prime \times \prod \limits_{A_j \in {\overline \Gamma}_1\cap{\overline \Gamma}_2} (H^1(0,T))^\prime or L^2(0,T;L^2(\Gamma_2)) \times \prod \limits_{A_j \in {\overline \Gamma}_1\cap{\overline \Gamma}_2} L^2(0,T) is respectively obtained. Some other interesting properties (such as the uniqueness of the solution and a Carleman type inequality) of the above problems are also presented.