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Publisher18.1 Speaker and Headphone Characteristics
Here
are the important characteristics of speakers:
Computer speakers are sold in sets. Two-piece sets include two small
speakers intended to sit on your desk or attach to your monitor.
Three-piece sets add a subwoofer, which resides under the desk and
provides enhanced bass response. Four-piece sets include four small
speakers, and are useful primarily to gamers who have a 3D-capable
sound card installed. Five-piece sets add a subwoofer to that
arrangement. Six-piece sets include a subwoofer, a center-channel
speaker, and four satellites, and are intended for PC-based
home-theater applications. Most headphones use only two speakers, one
per ear, but some use two horizontally offset speakers per ear to
provide true four-channel support.
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 1 dB. Computer speakers may claim 20 Hz to 20 kHz
response, but may rate that response at 10 dB or more, which makes
the specification effectively meaningless. A reduction of about 3 dB
halves volume, which means sounds lower than 100 Hz or higher than 10
kHz are nearly inaudible with many 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 continually. Listening to music at
normal volume levels requires less than a 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 anyway, so their lack of power is not really important.
Typical dual-speaker sets provide 4 to 8 watts of RMS Power per
channel, which is adequate for normal sound reproduction. Typical
subwoofers provide 15 to 40 watts, which, combined with the typical
5-inch 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 sound card.
Most computer speakers place the amplifier in one speaker, which has
connections for Line-in (from the sound card), Speaker (to the other
speaker), and DC Power (to a power brick). Many speakers also provide
an output for a subwoofer. Some speakers also provide a second
Line-in jack. This 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 speakersparticularly six-channel Dolby Digital 5.1
systemsprovide direct digital inputs via a Digital DIN
connector, an SP/DIF connector, or both.
