Magnet for Electro acoustic field

Sintered neodymium magnet are widely used in speaker, it provides a permanent magnetic field for the speaker coil, which is embedded in the paper of the speaker cone. When theaudio signal flows throw the speaker coil, it generates a small magnetic field. This small magnetic field is repelled to the permanent magnetic field. Thus the paper cone moves away from or closer towards the back of the speaker. Hence as the strength of the audio signal wiggles the paper cone wiggles back and forth, and you get sound waves that match the audio signal.