Successful business presentations, multimedia applications, and MIDI work demand external high-fidelity stereo speakers. Although you can use standard stereo speakers, they are often too big to fit on or near your desk. Smaller bookshelf speakers are better.

Sound cards offer little or none of the amplification needed to drive external speakers. Although some sound cards have small 4-watt amplifiers, they are not powerful enough to drive quality speakers. Also, conventional speakers sitting near your display can create magnetic interference, which can distort colors and objects onscreen or jumble the data recorded on nearby floppy disks or other magnetic media.

To solve these problems, computer speakers need to be small, efficient, and self-powered. Also, they should be provided with magnetic shielding, either in the form of added layers of insulation in the speaker cabinet or electronic cancellation of the magnetic distortion.

Quality sound depends on quality speakers. A 16-bit audio adapter might provide better sound to computer speakers, but even an 8-bit adapter sounds good from a good speaker. Conversely, an inexpensive speaker makes both 8-bit and 16-bit adapter cards sound tinny.

Now dozens of models of PC speakers are on the market, ranging from inexpensive minispeakers from Sony, Creative, and LabTech to larger self-powered models from prestigious audio companies such as Bose, Cambridge Sound Works, Klipsch, Monsoon, and Altec Lansing.

Many of the medium- to higher-end speaker systems even include subwoofers to provide additional bass response. To evaluate speakers, it helps to know the jargon. Speakers are measured by three criteria:

• Frequency response. A measurement of the range of high and low sounds a speaker can reproduce. The ideal range is 20Hz–20KHz, the range of human hearing. No speaker system reproduces this range perfectly. In fact, few people hear sounds above 18KHz.

An exceptional speaker might cover a range of 30Hz–23,000Hz, and lesser models might cover only 100Hz–20,000Hz. Frequency response is the most deceptive specification because identically rated speakers can sound completely different.

• Total Harmonic Distortion (THD). An expression of the amount of distortion or noise created by amplifying the signal. Simply put, distortion is the difference between the sound sent to the speaker and the sound you hear. The amount of distortion is measured in percentages.

An acceptable level of distortion is less than .1% (one-tenth of 1%). For some CD-quality recording equipment, a common standard is .05%, but some speakers have a distortion of 10% or more. Headphones often have a distortion of about 2% or less.

• Watts. Usually stated as watts per channel, this is the amount of amplification available to drive the speakers. Check that the company means "per channel" (or RMS) and not total power. Many audio adapters have built-in amplifiers, providing up to 8 watts per channel (most provide 4 watts).

This wattage is not enough to provide rich sound, however, which is why many speakers have built-in amplifiers. With the flick of a switch or the press of a button, these speakers amplify the signals they receive from the audio adapter. If you do not want to amplify the sound, you typically leave the speaker switch set to "direct." In most cases, you'll want to amplify the signal.

Inexpensive PC speakers sometimes use batteries to power the amplifiers. Because these speakers require so much power, you might want to invest in an AC adapter or purchase speakers that use AC power. With an AC adapter, you won't have to buy new batteries every few weeks.

If your speakers didn't come with an AC adapter, you can pick one up from your local Radio Shack or hardware store. Be sure that the adapter you purchase matches your speakers in voltage and polarity; most third-party adapters are multiple voltage, featuring interchangeable tips and reversible polarity.

You can control the volume and other sound attributes of your speakers in various ways, depending on their complexity and cost. Typically, each speaker has a volume knob, although some share a single volume control. If one speaker is farther away than the other, you might want to adjust the volume accordingly.

Many computer speakers include a dynamic bass boost (DBB) switch. This button provides a more powerful bass and clearer treble, regardless of the volume setting. Other speakers have separate bass and treble boost switches or a three-band equalizer to control low, middle, and high frequencies.

When you rely on your audio adapter's power rather than your speakers' built-in amplifier, the volume and dynamic bass boost controls have no effect. Your speakers are at the mercy of the adapter's power. For best audio quality, adjust the master volume on the sound card near the high end and use the volume control on powered speakers to adjust the volume.

Otherwise, your speakers will try to amplify any distortions coming from the low-power input from the PC's audio adapter. A 1/8'' stereo minijack connects from the audio adapter's output jack to one of the speakers. The speaker then splits the signal and feeds through a separate cable from the first speaker to the second one (often referred to as the "satellite speaker").

Before purchasing a set of speakers, check that the cables between the speakers are long enough for your computer setup. For example, a tower case sitting alongside your desk might require longer speaker wires than a desktop computer.

Beware of speakers that have a tardy built-in sleep feature. Such speakers, which save electricity by turning themselves off when they are not in use, might have the annoying habit of clipping the first part of a sound after a period of inactivity.

Speakers that are USB based will not be capable of playing CD music unless the CD-ROM drive can perform digital audio extraction. Check your drive's specifications for information. Headphones are an option when you can't afford a premium set of speakers. Headphones also provide privacy and enable you to play your PC audio as loud as you like.

For best results with newer sound cards that support four speakers or more, check the properties sheet for the audio adapter and set whether you're using headphones, stereo speakers, or a larger number of speakers. Make sure that speakers are placed properly.

If you use a subwoofer, put it on the floor for better bass sound and to reduce EMI interference with other devices. How can you tell whether wireless satellite speakers are causing interference? Watch your monitor; frequencies as high as 2KHz can interfere with your video display. Move the speakers away from the monitor and check the display again.

Theater and Surround Sound

If you're a serious gamer or DVD movie lover, you won't be content with ordinary stereophonic sound. Most audio adapters now support front and rear speakers, and many of the best audio adapters also support Dolby-compatible 4.1 and 5.1 speaker setups.

To ensure you get the sound you expect from four or more speakers, check the following:

• Use the properties sheet for your audio adapter to properly describe your speaker setup. This includes selecting the number of speakers you are using, setting options for 3D environmental audio and positional sound such as reverb, and setting up your subwoofer if present.

• Make sure you use the correct cabling between your speakers and audio adapter. If you are planning to use AC3/Dolby speaker setups, such as 4.1, 5.1, 6.1, or 7.1, be sure you use the correct S/PDIF connection and configuration. This varies from audio adapter to audio adapter; check the vendor's Web site for details.

• Make sure you have placed your speakers correctly. In some cases you can adjust the audio adapter's properties to improve sound quality, but sometimes you might need to move the speakers themselves.

• Make sure you have connected your speakers to the proper jacks. Mixing up left and right or front and rear causes poor sound quality.

Speaker Setups

The simplest audio configuration available today is stereo, which uses two speakers placed to overlap sound. Most audio adapters now support at least four speakers, but depending on the audio adapter, settings, and sound output options in the program, the rear speakers might simply mirror the front speakers' output, or you might have four distinct sound streams.

4-point surround sound uses four speakers plus a subwoofer to surround you with music and gaming sound effects; the four speakers are placed around the listener, and the subwoofer is usually placed near a wall or in the corner to amplify its low-frequency sound. The subwoofer in such setups is not on a separate circuit but is controlled by the same signals sent to the other speakers.

5.1 Surround sound, also referred to as Dolby Digital or DTS Surround sound, uses five speakers plus a subwoofer. The fifth speaker is placed between the front two speakers to fill in any missing sound caused by incorrect speaker placement. The subwoofer is independently controlled. This is the preferred sound system for use with DVD movies.

Most lower-cost audio adapters lack support for 5.1 Surround sound. Some of the latest sound cards support 6.1 and 7.1 Surround sound. The 6.1 configuration resembles the 5.1 Surround setup but adds a middle speaker along with a subwoofer. 7.1 Surround sound uses left-middle and right-middle speakers to flank the listener, along with a subwoofer.