This is a simple way to made a Speaker from 12 volt Relay .
1- 12 Volt relay.
2- Plastic dish.
3- Strong magnet.
4- Audio Amplifier.
Connect The input of Audio Amp. to PC or any media player audio output.
Connect the output of Audio Amplifier to 12 volt relay coil and fellow the below video.
Note that the Audio Amp. used TDA1557 Chip shown in attached Data sheet.