magnetism blog: how speakers work

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Katelyn Miller
Magnetism Blog
How do speakers work?

On the front of a loudspeaker there is a fabric, plastic, paper, or lightweight metal cone. The outer part of the cone is fastened to the outer part of the loudspeaker's circular metal rim. The inner part is attached to an iron coil that sits just in front of a permanent magnet. When you hook up the loudspeaker to a stereo, electrical signals feed through the speaker cables into the coil. This turns the coil into a temporary magnet or electromagnet. As the electricity flows back and forth in the cables, the electromagnet either attracts or repels the permanent magnet. This moves the coil back and forward, pulling and pushing the loudspeaker cone. Like a drum skin vibrating back and forth, the moving cone pumps sounds out into the air.

Loudspeakers will play loudly when the cone vibrates a large amount, or softly when it moves a small amount. Banging a drum skin really hard makes the skin vibrate a greater distance and produce a louder sound. In the same way, sending a bigger pulse of electricity into a loudspeaker makes the cone move further and generates a louder noise. Quieter sounds are made by smaller pulses of electricity.

It's not just the moving cone that determines how a speaker sounds. Most speakers are made out of wood or plastic to improve the sound quality. You probably know that a guitar's wooden body amplifies the sound the strings make by a process called sympathetic resonance. As the strings vibrate, they make the air around them vibrate too. That starts the air vibrating inside the guitar body in sympathy—and this is what makes the sound loud enough to hear. A loudspeaker case works in exactly the same way. Without the resonance of the case, you'd hardly hear a guitar or a loudspeaker at all.

crosssection of fridge magent

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