The exchange-striction mechanism, where parallel or antiparallel alignment of an ion's spin with its neighbour leads to displacements away from or towards the neighbour which can add up to a net electric polarisation if the ions carry different charges, is thought to be the underlying mechanism behind the magnetically induced ferroelectricity in BiMn2O5 and other RMn2O5 (R=rare earth, Y, Bi). In BiMn2O5 in particular, a high field spin-flop transition was found to be accompanied by a flip of the electric polarisation, illustrating their close affinity. This proposal seeks to measure the magnon spectrum in a powder sample as a first step to determining the spin Hamiltonian governing the magnetic behaviour, including the spin-flop transition, and also to determine the changes in the lattice dynamics with the magnetoelectric ordering.