Loudspeakers may be the most critical pieces of stereo equipment you will purchase. They are the last link in the chain of sound. No matter how much money you spend on the rest of your equipment, if you've bought the wrong speakers, the sound of your system will be disappointing.

Most speakers are priced per pair, but make sure you clarify this when you are quoted a price.

Features

Speaker drivers are designed to handle a particular range of frequencies. The tweeter handles the upper-end of the scale, the treble, and can be considered the soprano of the speaker drivers. It's the smallest driver and can be as small as an inch in diameter. The larger driver is the woofer, which reproduces the bass and lower frequencies and puts the thump into the music. Woofers range from five inches to more than a foot in diameter.

An electronic crossover network inside the speaker cabinet directs the sound frequencies to the appropriate drive -- the treble to the tweeter and bass to the woofer.

Most speaker enclosures are two-way, meaning they include both a tweeter and a woofer. Three-way speakers include a tweeter, woofer and a mid-range driver that reproduces a broad range of sound between highs and lows (middle frequencies often include vocals).

A full-range speaker has a single driver that is designed to reproduce almost all audible sound. Its frequency range is generally not as wide as that of two- or three-way speakers. Full-range speakers are used most often in compact, less expensive systems.

Size and location

Speakers come in many shapes and sizes and use varying types of technology to reproduce sound.

The three most common sizes of speakers are:

• Floor or tower speakers, often at least three feet tall and designed to sit on the floor without any stand or support
• Bookshelf, designed to sit on a tabletop, floor stand, or bookshelf
• In-wall, smaller speakers built inside a wall with only the grille visible

Many people believe that the larger the speaker, the better the quality. But modern technology has made it possible to create an excellent sounding speaker in a small enclosure. The only limitation that size places on a speaker is in bass response. Low-frequency signals require a certain amount of space to reproduce the long bass wave accurately.

Speakers should be positioned in a room so the tweeters -- the drivers delivering the highest frequencies - are at ear-level, as high frequencies are extremely directional. This is why tweeters are usually mounted at the top of the speaker's cabinet.

A popular way to address the problem of space for bass sound is the satellite subwoofer. A pair of very small two-way speakers produces the high- and mid-range frequencies, and a single a low-frequency speaker produces bass. Low bass frequencies are relatively non-directional; the bass seems to come from nowhere and everywhere at once. So you can place a subwoofer in a corner, or anywhere out of the way, such as behind furniture.

Sometimes a subwoofer has its own amplifier, making it an active or powered subwoofer. Most subwoofers connect directly to the amplifier, and are called passive subwoofers.

Materials

Speaker drivers can be composed of varying types of materials. Tweeters are usually fabric but may be metal, which allows for an almost microscopic tweeter. Mid-range and woofer drivers used to be made of paper, but often now are composed of a synthetic polymer called polypropylene.

Purchase

The size and shape of your room, along with some acoustic and technical considerations, will determine the size and type of your speakers.

Stores design sound rooms to ensure that their speakers will sound very good, and you probably will notice a difference when you get your speakers home. Sound is severely affected by the physical properties of the space that contains its waves.

Try this simple test. Clap your hands around a room, first in the middle, then near a wall. How much echo is there? A large amount of echo will reduce the effectiveness of most speakers.

Before you spend a lot of money on speakers, you may want to make your room acoustically "warmer" by adding carpeting, upholstery, curtains and wall hangings to cut down the echo. Many audiophile companies make echo-absorbing products, such as small "pillows" that can be placed in corners to absorb some of the excess echo.

Consider the size of your room. Larger rooms require bigger and/or more powerful speakers to compensate for the increased echo that a big room produces. Smaller rooms with a lot of carpeting and upholstery don't require large, powerful speakers.

When considering which speakers to buy, bring music you are familiar with, then position yourself at the apex of an equilateral triangle between the two speakers. The perfect position between them, where they sound best, is the sweet spot. Many speakers have a wider sweet spot, or soundstage, and some are more particular or precise. The kind of speaker you decide to purchase depends on how you are usually positioned in a room when you listen to music.

Another consideration in buying speakers is their efficiency; that is, how much power is required to produce clear sound? Any decent speaker will sound impressive when the volume is cranked up, but you rarely listen to music this way. After you've heard the speakers with the volume high, ask to have the volume lowered. When low, is the sound still as full? Or is it thin and tinny, or muddy and thick? How a speaker reproduces sound at low volume is the best test.

Now move left and right. How significantly does the sound change? This test enables you to determine how wide the speakers' soundstage is. Compare different sets of speakers. Ask the salesperson to play the "best" speakers and compare them to those you are considering.

Some high-end stores understand the differences between their sound rooms and your sound room and will allow you to audition the speakers in your home before committing to an actual purchase.

Connections

Before you hook up your speakers, turn down the volume of your amplifier or receiver and turn the power off. You need to turn the volume down because you don't want a sudden jolt to travel to the speaker when you turn it on. Always turn the volume down on an amplifier or receiver before you turn it on, then adjust the volume.

Choose appropriate speaker wire, which consists of two insulated wires -- positive and negative. One side is differentiated from the other by color, printing, striping, ribbing or some other simple means.

As mentioned in the introduction, speaker wire conducts an electrical signal. Resistance causes electrical signals to dissipate over long runs. The thicker the wire, the more efficiently the signal is transmitted, and the better your speakers will sound, especially over longer speaker wire lengths. Speaker wire comes in many varieties, measured in gauges. The lower the gauge, the thicker the cable. The highest-gauge speaker cable you should consider using is 18 gauge, sometimes called zip cord. Many people use standard power cord, called lamp cord, which is usually 16 gauge. If you are using higher-grade components, use 12 gauge or lower.

Measure the distance between the back of the amplifier to the back of the speaker, taking into account the wall and floor over which the speaker wire extends. Use a tape measure or the wire itself to measure this distance, then add about a foot to be safe, and cut the wire. Split the two wires apart, creating a double or forked end. Strip the insulation off the ends of the wire exposing about an inch of the bare copper strands. Twist the bare wires into a solid end. Repeat the process on the other end of the wire.

On the back of your speaker you'll see two terminals, usually red and black plugs or steel screw-top terminals. One of these terminals will be marked with a plus sign (+) "red" or a minus sign (-) "black." The speaker terminals on the back of your amplifier are similarly marked for the left and right speaker.

When hooking up the speaker cable from the amplifier to the speaker terminal, match positive-to- positive, negative-to-negative, for both left and right speakers. It doesn't matter which side of the wire you use to connect plus-to-plus or minus-to-minus, as long as you are consistent. If you used the ribbed side to match plus-to-plus on the right speaker, do the same on the left speaker.

Crossing the speaker leads will put your speakers "out of phase," and you will have reduced bass.

Speaker terminals differ from speaker to speaker and from receiver to receiver. The speaker instructions will show you how speaker cables should attach to the speaker terminals.

Accessories

Bare speaker wire attached to a speaker terminal may not be the best way to attach a speaker. The bare wire can oxidize over time, ruining both the wire and the terminal. Many manufacturers suggest that speaker ends be terminated with an attached accessory plug. There are two types of speaker terminals: banana plugs and spade plugs that are designed to fit around a speaker terminal post.

If you wish to run speakers into several rooms but your receiver has only one pair of speaker terminals, you may want to buy a speaker switcher box. This device has a number of speaker outputs, and a number of switches controlling each set of attached speakers. Simply run the main speaker wire into the box, then run pairs of speaker wires from the box to your various sets of speakers. By switching the controls on the box, you can choose which of the speakers to listen to. Be careful, however, not to overload the receiver. It is generally a good idea not to run more than two pairs of speakers simultaneously.

Floor-standing speakers placed on a wood floor can resonate. Isolate the speaker with speaker spikes that fit into the bottom, and lift it off the floor, thereby limiting the speaker's contact with the floor. Worried about damaging a wood floor? Put pennies underneath the spikes.

If you've bought bookshelf speakers and decide to stand them on the floor, get speaker stands to raise them to ear level. Many speaker manufacturers design stands to aesthetically match their speakers. Accessory manufacturers also make speaker stands to fit every taste in interior decor.

You can attach bookshelf speakers to a wall with a variety of wall mounts that can be purchased at most hardware stores.