What is Speaker and how does it work ?

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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?

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.

Loudspeakers will play loud when the cone vibrates a large amount, or soft when it moves a small amount. Why? Think about drums.

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.

We can reach the same conclusion by thinking about energy. The laws of physics tell us that we can't make energy out of thin air.

So if we want to make a loud sound (one that carries lots of energy), we need to create a vibration with lots of energy in the first place (in other words, hit something really hard).

Some drums have pedals on them that make the skin tighter or looser. If the skin is tight, it vibrates more quickly when you bang the drum and produces a higher-pitched sound; if the skin is loose, the opposite happens and you get a much lower note.

A similar thing happens in a loudspeaker. Bigger speakers with large cones (known as woofers) move more slowly than smaller speakers with smaller cones (known as tweeters)—so they are better for producing lower frequencies.

Any speaker can produce a wide range of different sound frequencies by moving back and forth quickly (for higher notes) or slowly (for lower notes).

Speakers that need to produce high-frequency sounds (or ultrasound, well beyond the range of human hearing) sometimes use piezoelectric transducers, based on vibrating crystals, instead of the traditional magnetic coil setup.

Often referred to as crystal loudspeakers or just "buzzers," they're also used to produce piercing sounds in things like telephone ringers and smoke alarms, where the effectiveness of the alert is much more important than its quality.

Diaphragm (cone): Moves in and out to push air and make sound.

Dust cap (dome): Protects the voice coil from dust and dirt.

Surround: A piece of elastic rubber, foam, or textile that flexibly fastens the diaphragm to the basket (outer frame).

Basket: The sturdy metal framework around which the speaker is built.

Spider (suspension): A flexible, corrugated support that holds the voice coil in place, while allowing it to move freely.