An example apparatus comprises a drive coil energizable by a drive signal, at least one permanent magnet, and at least one magnetic return path element for flux induced by the drive signal, the magnetic return path element, such as a balanced armature, being configured to provide a variable reluctance, so as to reduce nonlinearities in a displacement versus drive signal relationship. Modifying the reluctance versus flux properties of the magnetic return path of a transducer, e.g. the armature of a balanced armature device, allows compensation for nonlinearity arising in another part of the apparatus.