S1 is heard when the AV values close (when the ventricles are filled). S2 is heard when the aortic and pulmonic valves close (when the ventricles have emptied their blood into the aorta and pulmonary arteries). S2 is heard best over the RSB, 2nd ICS and LSB, 2nd ICS. S1 and S2 are heard equally over Erb's point (LSB, 3rd ICS). S1 is louder at the LSB, 4th ICS and over the apex (fifth ICS, LMCL).
RSB 2nd ICS - over the aortic valve
LSB 2nd ICS - over the pulmonic valve
Erb's point - S1 and S2 equal
LSB 4th ICS - tricuspid valve
LSB LMCL - mitral valve
Ape To Man (APETM) - aortic, pulmonic, Erb's point, tricupid, mitral
Isn't all this in your basic health assessment textbook?