It provides a permanent magnetic field for the coils in it, and the rapid alternating direction of the current causes the cone to vibrate back and forth, and then the audio signal comes out of the speaker.
Waxay bixisaa beer joogto ah magnetic for gariiradda in afhayeenka, si degdeg ah talantaalli ah jihada of hadda wuxuu keenaa koorta birqaya iyo dib u, ka dibna signalka audio soo baxay afhayeenka.