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How loudspeakers turn electricity into sound?

How many times every day do you hear recorded music on the radios on TV, in stores, in elevators—even in the street? You’d never hear music at all if it weren’t for loudspeakers: electric sound-making machines. Most of the music we hear around us is played back with big loudspeakers attached to stereos or tiny earbud headphones. Radios, televisions, computers, cellular phones, intercoms, and talking toys are just some of the electric gadgets that make sounds with loudspeakers. But what exactly are loudspeakers and how do they work?


How loudspeakers turn electricity into sound?

When things shake about, or vibrate, they make the sounds we can hear in the world around us. Sound is invisible most of the time, but sometimes you can actually see it! If you thump a kettle-drum with a stick, you can see the tight drum skin moving up and down very quickly for some time afterward—pumping sound waves into the air. Loudspeakers work in a similar way.

At the front of a loudspeaker, there is a fabric, plastic, paper, or lightweight metal cone (sometimes called a diaphragm) not unlike a drum skin (colored gray in our picture). The outer part of the cone is fastened to the outer part of the loudspeaker’s circular metal rim. The inner part is fixed to an iron coil (sometimes called the voice coil, colored orange in the diagram) that sits just in front of a permanent magnet (sometimes called the field magnet, and colored yellow). When you hook up the loudspeaker to a stereo, electrical signals feed through the speaker cables (red) 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