Abstract
The magnetoelectric effect (ME) is considered in the frame of a general classification of electric and magnetic properties of anisotropic solids. The role of coexistence of ME, piezoelectric effect (PE) and piezomagnetic effect (PM) in the theory of elastic waves is described. A new acoustic resonance is predicted. The resonance is due to the ME, PE and PM simultaneously. This phenomenon takes place in systems where ME, PE and PM exist separately in different coupled subsystems.