Big, little, simple, complex, cheap, expensive... speakers come in all flavors. They all start from the same basics, and knowing these basics can help you make an informed decision on what to buy.

The purpose of a speaker is to compress and rarefy the air in order to create pressure waves that your ears interpret as sound. They do not, as is often said, "move air." If a speaker is moving air, it is horribly broken.

How they go about this compression and rarefaction varies somewhat, but most speakers have a few basic components.

It starts with a transducer, or "Driver." A transducer is anything that converts one form of energy into another. In the case of speakers, the drivers convert electrical signals from your receiver/amp into movement of the cone. This is what compresses and rarefies the air. In the simplest of speakers, there's just a single cone doing all the work.

Asking a single driver to reproduce the entire frequency range is like making every vehicle in the world a Geo Metro. Sure, for some people it would be fine. Small, good gas mileage. Cheap to run. But would they really work as a bus? Can you picture a Geo pulling cargo containers? In other words, every driver has a frequency range that it can do well, but above and below that range, it's going to falter.

This is why most speakers have more than one driver. Splitting up the labor, as it were. In the most basic of these forms is a speaker with a tweeter and a woofer.

A tweeter is a driver that specializes in high frequency sounds. Cymbals are in this range, as are the high notes from a flute or piano. Also, every instrument and sound has "overtones" that give that sound its color or timbre. These are often in the tweeter's range as well.

A woofer is tasked with the low frequency sounds; boom boom bass and so on.

One of the tasks of a speaker designer is finding the right match of drivers so that the tweeter doesn't have to reproduce something too low for its range, and the woofer doesn't have to create too high a sound for its range.

If the speaker designer wants, he can add in a mid-range driver that slots in between these two.

Many speakers have multiple drivers, often reproducing the same frequencies. On many tower speakers, for example, you could have two 6-inch woofers. These won't work exactly like a single 12-inch woofer, but they'll be similar and because they're smaller they have their own strengths.

In reality, you can design a fantastic speaker with just a single tweeter and woofer. One of the best speakers I've ever reviewed were Acoustic Energy AE1 MkIII SE (image at the top). These small bookshelf speakers were amazing (and at $5k a pair, the better have been), and had just a single 1.5-inch ring-radiator tweeter and a 4.33-inch aluminum cone woofer.

Nearly all bookshelf speakers with small woofers, though, need a subwoofer. This is a large woofer in its own box tasked with nothing but the lowest frequencies. They're often self-powered. Even if you don't crank them up, a subwoofer will make any system sound better. Also, by unloading the hard to reproduce bass sounds to a dedicated speaker, your main speakers don't have to work as hard, and neither does your receiver/amp. This means more volume and clarity from your current system.

In Part 2 we'll get into what to look, I mean listen, for when you're shopping.