Hardware Reference
In-Depth Information
WhaT arE DBs, anyWay?
The following is a gross oversimplification, and we're sure
we'll hear about it from people who know more than we do
about sound, but here goes.
The dB scale is logarithmic, which means that an increase of
about 3 dB doubles the sound level. For example, if a power
supply produces 30 dB and a CPU cooler also produces 30
dB, running both at the same time doubles the sound level
to 33 dB (not 60 dB). Doubling the sound level again by run-
ning four 30 dB devices simultaneously increases the overall
sound level by 3 dB again, to 36 dB. Running 8 such devices
doubles the sound level to 39 dB, 16 takes it to 42 dB, and
so on.
Sound is measured and specified in deciBels—a tenth of a
Bel—which is abbreviated dB. (Some components specify
Bels; multiply by 10 to get dB.) Because humans perceive
identical sound levels at different frequencies as having
different loudness, various weighting schemes are used. The
most common, A-weighting, is abbreviated as dB(A). There
are also dB(B) and dB(C) scales, but those are not commonly
used.
However, because of the way humans perceive sound, a
1 dB difference is barely perceptible; a 3 dB difference is
noticeable, but a sound must be about 10 dB louder to be
perceived as “twice as loud.” For example, if one computer
produces 40 dB and another 30 dB, the first computer actu-
ally produces about 10 times the sound level of the second
PC, but to human ears it “sounds” only twice as loud.
A sound level of 0 dB is defined as the threshold of hearing,
a sound level that is just barely perceptible in the absence of
any other sound. Here are some reference points:
• 20 dB—a very quiet library or church; rural background
noise at night; the quietest possible PC with moving
parts
• 25 dB—a whispered conversation; a very quiet PC
• 30 dB—suburban background noise at night; a quiet
PC
• 40 dB—a quiet conversation; a standard PC
• 50 dB—normal household noise; a normal conversa-
tion at 1 meter; a loud PC
• 60 dB—office conversation; a loud gaming PC or server
PC components differ dramatically in sound levels. For
example, a very quiet hard drive might produce 25 dB, while
another model produces 30 dB or more. At idle, a standard
400W power supply might produce 40 dB, a quieter model
30 dB (half as “loud”), and a specialty quiet model only 20
dB (half as “loud” again). The same differences exist among
other noise-producing components, such as CPU coolers,
supplemental case fans, optical drives, and so on. Merely by
choosing the quietest standard PC components rather than
noisier alternatives, you can reduce the noise level of your
PC noticeably.
Choose a quiet case
Inexpensive cases are designed with little thought to noise abatement.
Better cases incorporate numerous design features that reduce noise, in-
cluding large, slow-spinning exhaust fans, sound-absorbing composite
panels, rubber shock mounts for drives that isolate vibration, and so on.
We cover case considerations thoroughly in the next chapter.
Choose a quiet power supply
In most systems, the power supply is potentially the first or second largest
noise source, so minimizing power supply noise is critical. Here are a few
tips:
• At the first level, choose a noise-reduced power supply, such as the
models we recommend in the next chapter. Such power supplies cost
little or no more than competing models of equivalent capacity and
quality but are noticeably quieter. A system that uses one of these
power supplies can be quiet enough to be unobtrusive in a normal
residential environment.
