Abstract: A metal base assembly for speaker that combines with a magnetic circuit to produce a fluctuating magnetic field which drives an acoustic diaphragm into vibration to produce a warning alarm. The metal base assembly comprises a top pad, a middle pad, a bottom plate, positioning rivets, a magnetic plate and a metal plate. The positioning rivets couple the top pad, the middle pad and the bottom plate together forming the metal base assembly with a recess cavity for accommodating the magnetic plate and the metal plate. Under influence of a magnetic force generated by a circular magnetic field generator, an acoustic diaphragm inside the speaker is made to vibrate rapidly producing a high tone warning alarm.