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FANLESS CASES
A steady trickle of fanless cases have tempted silence-seeking PC users over
the past decade. The basic concept with almost all fanless cases is simple:
Turn the external casing into a big heatsink which conducts the heat from hot
components by direct contact or via heatpipes, then disspiate it into the air
with natural convection. Most often, the case is made from aluminum, which is
a better conductor of heat than steel. Some of these cases have been massive
and heavy, like the now discontinued Zalman
TNN series, in order to accommodate the high thermal characteristics of
powerful gaming components. Others have taken the minimalist approach, using
cooler running components so that there's less heat to dissipate, allowing for
a smaller, less costly product.
Today, CPUs with extremely low thermal design power (TDP) that run under 10W
at idle, and automated dynamic clock/voltage features (like AMD Cool'n'Quiet
or Intel SpeedStep) make passive cooling relatively easy, at least with some
CPUs and big heatsinks. In combination with higher performance motherboard-integrated video cards, a completely fanless PC is a lot more practical than
in the past. However, fanless operation of a higher power system (such as the
typical gaming rig) still remains a challenge. Fanless devotees should be aware
that components such as the voltage regulation module on the motherboard, and
similar power electronics in video cards are designed with the expectation of
at least some airflow across them. Even in a very low power system, eliminating
all forced airflow usually shortens component life.
The small Coolermaster TC-100 is a sensible passively cooled case:
It's only meant for low-thermal mini-ITX motherboards. |
Spinning hard drives and electronic noise from power components
have also been challenges for fanless systems.
The best approach to quieting a HDD is to mechanically decouple it from the
case so that its vibrations don't excite the large thin panels of the case and
cause noise. This means "float" mounting the HDD in an elastic suspension
or soft rubber bushings or grommets. In a conventional case, the loss of cooling
via conduction can be compensated with directed airflow from quiet fans. But
in a passively cooled case, this is much more difficult. The increased availability
of high performance, silent, solid state drives at much more affordable prices
— in combination with inexpensive high capacity network attached storage
— has made HDD noise much less of a problem in recent years.
The high pitched whining and squealing of power electronics has usually been
masked in the past by the whooshing and whining of high speed fans, but in a
system without fans, such electronic noise can become quite annoying. While
this type of noise can usually be avoided by staying with high quality components,
it is sometimes caused by interactions between power circuitry and a particular
component or combination of components. In such cases, trial and error replacement
of offending parts is the only solution for DYI builders — other than re-introducing
a whooshing fan.
ALUMINUM
The Aluminum Myth - Some favor aluminum cases, citing an ability to
better cool components mounted within. This is a myth. No heat producing component
benefit in any significant way from being inside an aluminum case — unless
the components have some kind of direct conduction path to the case panels,
a feature usually found only in a few cases meant to be fanlessly cooled. The
only heat producing devices that are normally mounted in direct contact with
a case are the drives, particularly the hard drives; the difference between
aluminum and steel in this application is insignificant, because HDDs produce so little heat (typically <10W).
The Aluminum Drawback - One consistent acoustic property seems difficult
to avoid: Aluminum cases tend to pick up hard drive and fan vibrations more
readily than steel cases, and make a more audible humming or buzzing
sound. This quality is related to the density of aluminum: It
has only about 30% of the density of the cheaper, more commonly used steel.
Hence, an aluminum panel is lighter and more easily turns vibration from a mechancially couple device like a HDD or fan into noise, like a sounding board in a musical instrument. Internally applied panel damping materials (especially the heavier kinds) can damp the resonance down fairly effectively, but vibration-induced noise can be difficult and expensive
to eliminate entirely. Internal supporting cross braces that effectively divide
the large panels into smaller ones also help quite a lot because smaller panels
are more rigid, stiffer, and less prone to lower frequency vibration than larger
ones.
This does not mean aluminum cases cannot be used to make a silent computer,
just that there are disadvantages with them when compared to similarly constructed
steel cases. Regardless, many aluminum cases certainly look nice, and some can
be made very quiet.
Aluminum / Steel Combo - Some case makers have sought to combine the
desirable look of aluminum with the sturdiness of steel by using a front facia
or bezel made of aluminum on a steel chassis. The Silverstone
GD05 and the Coolermaster Sileo 500
are examples of hybrid cases.
Silverstone Fortress FT02: This well-built aluminum / steel case
shows no signs of the dreaded Aluminum Hum. |
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