2-Way
This design uses 2 drivers: a tweeter and a midrange/woofer to produce sound. This design can be just as clear as a 3-way design on the highs. Any speaker that lists it has 1 tweeter with 1 woofer is actually using the midrange/woofer design.

The 2-Way setup is most commonly found in bookshelf speakers. There are 2-way tower speakers out there and many towers use a second mid/woofer or a dedicated bass driver (woofer) of similar size to the midrange to help produce more bass. The latter is more of a 2.5-way design as the midrange driver is still a mid/woofer design.

3-way
This design uses 3 drivers: a tweeter, midrange, and woofer to produce sound. This is the most practical application for speaker design as all the drivers can be made at the size they sound their best. Tweeters always remain small, midranges can be 3-6 inches, and woofers can go as large as 18 inches. This allows for a lot more bass response than most 2-way designs.

Variants
Alternate designs of direct radiating speakers offer multiple tweeters, midranges, and woofers to better steer sound, fill in gaps in the spectrum, or simply to produce more sound. Most alternate designs will use multiple midranges and woofers. Designs using multiple tweeters are typically used with THX speaker designs.

Drivers
Speaker cones come in many different shapes and materials. Use of exotic material mixtures to create drivers is common among high-end speaker manufactures, but there are some qualities that you should look for that pertain to all.

Tweeters
These are among the most varying types of drivers out there. The best sounding version of the tweeter is the dome tweeter.

Using a dome to control the dispersion of sound from the tweeter offers a smoother, more consistent sound across the listening environment than a cone. Most tweeters made today are liquid cooled which allows them to play loud and reliably for extended periods. Most domes are made using some type of metal or fabric.

A fabric dome will sound softer and a metal dome brighter. The surround of the tweeter greatly effects the dispersion pattern as well, and there are many variants. In the end what you're looking for in a tweeter is a quality driver that has a nice sound. Any non-dome tweeter should be looked upon with skepticism.

Horn Drivers
Klipsh speakers offer horn enclosed tweeters that make for an extremely efficient design as far as energy consumption is concerned. Klipsh speakers played a big role back in the 50s and 60s bringing quality speakers to the home.

Back then amplifiers had very little power compared to today's standards and speakers needed to help with the amplification of sound in any way possible. Enter the horn driver.

The horn driver is what made a Klipsh speaker able to play at louder volume levels with less power. The horn enclosure is wrapped around the tweeter in order to amplify the sound that the tweeter emits. As more amplification became available the reason for horn driven speakers was no longer there. Non-horn enclosed speakers became a reality, and played at the same sound levels with a softer, less harsh sound than horns usually emit.

Klipsh has accomplished a lot in the 90s to take the harshness out of their horn designed speakers and are really worth listening to.

Due to their efficiency, horn driven speakers will play louder with less power than standard speakers. To match speakers together in your system you should either use all horn speakers or none at all.

Midranges
These drivers create most of the sound you will actually hear by producing all but the very high or very low sounds. Good midranges tend to come in sizes ranging from 3 to 6 inches.

More and more speaker makers are using a midrange/woofer along with a dedicated woofer or multiple woofers to produce better upper bass sound. Many great speakers are made that use both midrange or mid/woof designs.

You'll want to look for a high quality driver that uses rubber and not foam for the cone surrounds. Foam can deteriorate over time, which shortens the life of your speakers. You'll also want non-paper material for the cone structure, as paper is less durable and not as rigid as plastics and metals. As always, there are exceptions to the rule, but these are great guidelines to start with when auditioning speakers.

Woofers
The woofer is where you'll find many different configurations. The basic assumptions with woofers are that they need to be able to handle all your bass, but this is simply not true. All you need the woofer to do is handle the upper bass frequencies that a powered subwoofer does not. The subwoofer takes charge of the most demanding low frequencies freeing your main speaker's woofers from the burden. You should look for the same qualities as that of the midrange. Non-foam surrounds and a rigid cone material will make for a long lasting driver.

Sound qualities you want to look for in a woofer is the ability to play relatively low while sounding smooth and unstressed. You'll want to ward away from speakers with a muddy sound as these can dirty the overall sound your system produces. The bass should have great presence and clear refinement that enables you to hear the subtle details of the low frequencies.

Many tower speakers can produce enough bass that you may think you don't need a sub. These are the speakers worth taking looking at. If the speakers can handle serious low frequencies then you won't have to worry about their drivers stressing to handle the upper bass frequencies.

To Sub or Not to Sub
You can purchase speakers with built-in powered subwoofer, but you may want to stray away from these designs for a couple of reasons.

The first reason is that you can't optimally place your speakers for both highs and lows. The low frequencies that subwoofers produce sound better and louder closer to a wall while the high frequencies of the other drivers produce a better sound-stage placed farther out into the room. Putting a subwoofer out in the middle of the room requires the sub to be set at higher volume level to attain the same sound a sub placed close to a wall would produce.

The second reason is that having all your eggs in one basket isn't a good idea. If one part of the speaker malfunctions in some way, or you simply want new speakers, you'll be forced to buy another expensive set of speakers that come with built-in subs or a separate sub to go with your new speakers. It simply isn't cost effective.

Built-in subs cause speaker placement issues and lack of flexibility. Getting a dedicated powered subwoofer with a good set of speakers is your best bet for the future.

The Enclosure
The enclosure of a speaker plays as big a role on the sound your speakers produce as the drivers do. The goal of an enclosure is to be as solid as possible, not interfere with the sound of the high frequency drivers, and to use the cabinet's volume to increase the bass produced by the woofers. The size of the enclosure greatly increases the amount of bass that the woofers emit. Bad enclosures can make your speakers sound boxy, and can affect the imaging qualities tremendously.

The inside of the box should have plenty of internal damping (the cotton-like fuzzy stuff) to absorb the internal sound waves high frequency drivers produce. The absorbent material is invisible to low-frequency sound waves allowing the woofer to use the entire volume of the enclosure to produce more bass.

There should also be a lot of internal bracing, which makes the enclosure extremely solid. The more solid the enclosure the more likely the enclosure will not interfere with the sound. A good test to measure the quality of the enclosure is to knock on the side and top of the speaker enclosure. The sound should be the equivalent of knocking on solid piece of wood or a rock. If knocking on the enclosure gives off a hollow sound the enclosure design is really second rate and you should look at different speakers.

Connections
Speaker connections help the power from the amplifier flow freely into the speaker. Speakers with high quality binding posts offer the most secure connections and a larger metal connection area for your speaker wire to rest against.

Spring clips offer a second rate solution with very little connection area for the speaker cable to transfer the signal. They can affect the sound quality of your speakers by blocking the flow of electrical power from the amp.

Binding posts, combined with quality speaker cables, will eliminate any possibility of your speaker's connection degrading your sound. (See the "Cables" section for more info on connections.)

What You'll find Out There
Amazingly, a well-designed tower using mid/woofs can produce the same amount of bass produced by traditional 3-way designs that use a large dedicated woofer. You'll find a lot more 2-2.5 way speakers using smaller drivers to drive the bass.

With the popularity of powered subwoofers you'll see less and less of the traditional large woofers in speaker designs. Small woofer designs slim down the cabinet size making the speaker enclosure sleeker, less garish to look at, and easier to place.

Direct speakers come in all different shapes and sizes. You should audition as many as you can and also compare them against reflecting radiating speaker designs to find out which type of sound you like best.

Overall Speaker Performance
Great speakers will make a world of difference on the impact your home theater has. You'll want speakers that you don't hear at all. Instead, you want to be enveloped in a sound field that seems to defy the laws of physics by going beyond the boundaries of the speakers.

While watching a movie in a dim room you should only hear the sounds around you a not be able to pinpoint the exact location of the speakers themselves. Great home theater speakers pull you in with their dazzling sound so much that you'll stop listening to the speakers and become entranced in the movie itself.

In short... you will never hear great speakers.