Solenoid must be familiar to you if you are electrician, mechanic or had physics Major ever. The solenoid is a basic device used in your car to start it, it is also used in earphones, microphone, speaker, DC motors, many of door locks and many more things. It works on simple physics and is very easy to understand. One basic model can be made at home too.
A solenoid is a simple device which uses the most basic laws of electromagnetism. Its construction includes an insulated copper wire rolled over a metallic cylindrical core in the helical form.
Its basic function is to control and channel the magnetic field produced by the varying electric current. In the case of the speaker, this further helps to move the rod on which the wire is wound, this movement changes the kinetic energy of the air particles in t and hence the air pressure. These changes in air pressure help the membrane attached vibrate. And vibrations produce sounds. This is how the solenoid works in your car’s speaker. You can read more about here.