Every audio speaker uses permanent magnets whether the speaker is in your car, in your stereo, your earphones or your smartphone. Permanent magnets provide the force that makes the component in the speaker that creates the sound, moves.
What is sound and how is it created?
Sound is created when an object vibrates i.e. moves. The vibration or movement causes air molecules to move to result in waves of varying pressure known as sound waves.
If you are in contact with the same air as the object, the waves will hit your eardrum which also moves and you hear the sound. If the vibration is fast, the pitch of the sound is high and if the vibration is slow the pitch of the sound is low.
What’s in a speaker?
Now we know how sound is created the most basic concept for a speaker is moving a surface back and forth which will make waves of pressure in the air.
Modern speakers come in all shapes and sizes and obviously contain many more components than just a vibrating piece of material, but at their core, they remain surprisingly simple devices.
In order to convert an electrical signal into a sound speakers use a type of electromagnet called a voice coil, a permanent magnet and a cone usually made from paper or plastic plus wiring, circuitry and casing.
How does a speaker create sound?
As referred to above, the movement of the cone in a speaker is what creates sound. The cone itself is moved by the interaction of the magnetic fields produced by the electromagnetic voice coil and the permanent magnet.
The permanent magnet generates a consistent magnetic field while the voice coil can be turned on and off by passing an electrical current through it.
When current is passed through a voice coil it produces a magnetic field of either north or south polarity, depending on the direction of the current. If the current is reversed so is the polarity of the electromagnet.
The strength of the field can also be altered by altering the current passed through the coil.
Inside a speaker, the voice coil is connected to the cone and placed in front of a permanent magnet which is fixed in position. When current is passed through the coil of the the polarity direction of its magnetic field is rapidly changed.
This means that the electromagnet is either attracted to or repelled by the permanent magnet moving it, and therefore the cone, back and forth. The cone amplifies the vibrations created by the movement of the voice coil pushing sound waves out of the speaker and into the surrounding air.
To create an audible sound the current passing through the voice coil must be manipulated hundreds of times per second.
To accurately reproduce the different frequencies of a piece of music high-end speakers usually have different sized cones dedicated to high, medium and low pitches.
Build Your Own Basic Speaker
A speaker can be made out of almost anything. If you want to have a little fun and learn a thing or two about how a speaker is made there is no better way than to have a go at making your own out of readily available items. Here’s what you need:
- A Styrofoam or paper cup (a Mcdonald’s or Starbucks coffee cup is fine)
- A 20mm x 3mm neodymium disc magnet
- A headphone jack. You could cut one off the end of an old pair of headphones or earphones
- Approximately one metre of thin copper wire
- Tape
- Alligator clips with wire
- A device to plug your speaker into such as a radio
- Two ice lolly sticks or strips of thick card
Step 1
Take the copper wire and wind it into a coil, winding it around a number of times. The finished coil should but slightly smaller in diameter than the base of the cup. Remember to leave both ends of the copper wire easily accessible.
Step 2
Turn the cup upside down and tape your coil to the bottom.
Step 3
Next, strip some of the insulating coating from the cord of the headphone jack to expose the copper wires.
Step 4
Attach the alligator clips to each end of the coiled wire and to each of the copper wires coming from the headphone jack.
Step 5
Next, tape the ice lolly sticks or card over the coil to create a frame to fix the neodymium magnet too.
Step 6
Fix the neodymium to the stick or card frame. You can do this using superglue or tape.
Step 7
Now plug your headphone jack into your audio device and see if it plays! Alternatively you can follow this really great Instructables tutorial.
