How stuff works: Speakers
Speakers work on the principle of electromagnetism and magnetic attraction and repulsion.
" When an electric current is passed through a conductor, it behaves as a magnet (temporary). This phenomena is known as a electromagnetism and the magnet so produced is called electromagnet".
Current carrying coil behaving as a magnet
Basic constituents of a speaker
- Permanent magnet
- Electromagnet coil (voice coil)
- Cone assembly
There's a permanent magnet which is fixed (at the apex of the cone shaped diaphragm). A conductive coil is placed in the magnet's magnetic field. The electromagnetic coil is attached with the cone shaped diaphragm and is free to move (actually vibrate).
Mechanism at a glance
- Electrical audio signal (alternating) is passed through the conductor coil making it a temporary magnet.
- The alternating current changes the magnetic polarity of the conductor coil.
- Continuous attraction and repulsion of conductor coil by permanent magnet creates a to and fro (vibrational) motion of coil.
- The diaphragm vibrates with coil, pushing air, and makes sound (sound waves).
The Mechanism Explained
The input fed to the speaker is ELECTRICAL AUDIO SIGNAL which is modulated (frequency) such that the output be a sound wave. The electrical audio signal oscillates with fixed frequencies which when converted to mechanical vibrations would produce sound waves.
When this current flows through the conductor coil, due to electromagnetism the coil becomes a magnet with north and south poles respectively. The permanent magnet attracts or repels (depending upon the orientation) this newly formed electromagnet (for sake of convenience, let's say it attracts). As the current changes (polarity), the polarity of the electromagnet (coil) also changes (north becomes south and vice- versa). Now, the permanent magnet starts repelling (as per our assumption of attraction initially) the coil. The attraction - repulsion - attraction - repulsion causes a to and fro motion of the coil. The polarity changes are real quick, so it's not literally motion but vibration. The cone shaped diaphragm being attached to the coil, also vibrates. And as it vibrates, it forces the air near it to vibrate. The vibrations hence produced in air lie in the sound wave frequency range and that's why we are able to hear the sound coming from the speaker.
A Simple Electromagnetic Speaker
Ultra Thin Electrostatic Speakers
So, that is basically all the physics behind your old pair of speakers. This has been the working mechanism for years now. But these days we see flat panelled electrostatic speakers. They don't have an electromagnet, instead, they have conductive diaphragms trapped between electrostatic field of changing polarity which makes the diaphragms move back and forth leading to sound production.