Working principle of electromagnetic buzzer:
　　The AC signal is wrapped on the core column of the support through the wire wound on the support to generate an alternating magnetic flux. The alternating magnetic flux and the constant magnetic flux of the magnetic ring are superimposed to make the molybdenum sheet vibrate at a given AC signal frequency and sound in cooperation with the resonant cavity. The response curve of the whole frequency and sound pressure of the product is directly related to the gap value, the natural vibration frequency of molybdenum sheet (which can be roughly refracted into the thickness of small molybdenum sheet), the frequency of shell (Helmholtz resonance cavity), the magnetic strength of magnetic ring and the wire diameter of enamelled wire.