No matter how good your audio adapter is, it's useless unless you have speakers or headphones to listen to the audio it produces. Computer speakers span the range from $10 pairs of small satellites to $500+ sets of up to nine speakers that are appropriate for a home theater system.
As is true of displays and input devices, personal preference is the most important factor in choosing speakers. Speakers that render a Bach concerto superbly may not be the best choice for playing a first-person shooter game like Unreal Tournament. For that matter, speakers that one person considers perfect for the Bach concerto (or the UT game), another person may consider mediocre. For that reason, we strongly suggest that you listen to speakers before you buy them, particularly if you're buying an expensive set.
Here are the important characteristics of speakers:
Speaker sets are designated by the total number of satellite speakers, followed by a period and a "1" if the set includes a subwoofer. Choose a speaker set configuration that your audio adapter supports. For example, there is no point to buying a 7.1 speaker set if your audio adapter supports at most a 5.1 configuration.
The price of a speaker set has little bearing on the number of speakers in the set. For example, there are $75 7.1 speaker sets available, and $500 2.0 sets. We recommend that you decide on the number of speakers according to your budget. If you have $75 to spend, for example, you're much better off buying a decent 2.1 speaker set than a cheesy 7.1 speaker set.
Only 2.0, 2.1, 4.1, 5.1, and 7.1 sets are common; 6.1 and 8.1 speaker sets are rare. If your sound card supports a 6.1 or 8.1 configuration those with a rear center channel output buya 5.1 or 7.1 speaker set and add an individual center-channel speaker to fill out the configuration.
Frequency response is the range of sound frequencies that the speaker can reproduce. The values provided for most speakers are meaningless, because they do not specify how flat that response is. For example, professional studio-monitor speakers may provide 20 Hz to 20 kHz response at 1 dB. Expensive home audio speakers may provide 20 Hz to 20 kHz response at 3 dB, and 40 Hz to 18 kHz response at 1dB. Computer speakers may claim 20 Hz to 20 kHz response, but may rate that response at 10 dB or more, which makes the specification meaningless. A reduction of about 3 dB halves volume, which means that sounds below 100 Hz or above 10 kHz are nearly inaudible with many cheap computer speakers. The only sure measure of adequate frequency response is that the speakers sound good to you, particularly for low bass and high treble sounds.
Manufacturers use two means to specify output power. Peak power, which specifies the maximum wattage the amplifier can deliver instantaneously, is deceptive and should be disregarded. RMS power (Root Mean Square), a more accurate measure, specifies the wattage that the amplifier can deliver continuously. Listening to music at normal volume levels requires less than one watt. Home audio systems usually provide 100 watts per channel or more, which allows them to respond instantaneously to transient high amplitude peaks in the music, particularly in bass notes, extending the dynamic range of the sound. The range of computer speakers is hampered by their small amplifiers, but computer speakers also use small drivers that cannot move much air, so their lack of power is not really important. Typical dual-speaker sets provide 4 to 8 watts RMS per channel, which is adequate for normal sound reproduction. Typical subwoofers provide 15 to 40 watts, which, combined with the typical 5" driver, is adequate to provide flat bass response down to 60 Hz or so (although subwoofers often misleadingly claim response to 20 Hz). Headphones are not amplified, but use the line-level output of the audio adapter.
Most 2.0 sets place the amplifier in one speaker, which has connections for Line-in (from the audio adapter), Speaker (to the other speaker), and DC Power (to a power brick). Many speakers also provide an output for a subwoofer. Sets that include a subwoofer usually put the amplifier in the subwoofer, which has connections for the other speakers in the set. Some sets also provide a second Line-in jack. This jack is quite useful if you want to connect both your PC and a separate line-level audio source, such as a CD player or another PC, to the amplified speakers, allowing you to listen to either source separately or both together. An increasing number of high-end speakers particularly six-channel Dolby Digital 5.1 systems provide direct digital inputs via a Digital DIN connector, an S/PDIF connector, or both.