On Sun, 31 Aug 2003 05:37:03 -0500, David Maynard
wrote:

kony wrote:
On Sat, 30 Aug 2003 21:49:12 GMT, TC wrote:



/\/\/\/\
Actually .. the ducted fan is state of the art.


Nope, Gateway, Compaq and others have been using passive coolers and
ducts since the Pentium 1 days.

True. Different designs, however.

The CPU runs hotter as a result,
then and today.

Not so. It is not 'because' of the ducted design. It because their design goal,
regardless of the chosen cooling method, is proper operation within the
temperature specs and not 'the coolest we can get it'.

The issue is not one of achieving "the coolest we can get it", but
rather noise/heat ratio, that a duct impedes exhaust, making the rear
fan noiser at the same exhaust flow rate. To keep the CPU at the same
(high) operating temp as in the Dell ducted system, a good active
cooler's fan can run at low enough RPM, low enough turbulence, that
what litte noise it creates, being buffered by the enclosure, is less
audible than the increase in ducted exhaust fan noise. Running the
rear fan at higher RPM is necessitated by the duct, else there is more
heat buildup in the system.

The total system heat generation can be considered constant so the
total airflow through the system must also remain the same else the
Dell system runs hotter in more areas than just the CPU. Lower air
intake into the system will then result in hotter air entering the
heatsink.

Proper operation within the temperature spec (instead of lowest
possible CPU temp) is the notion that allows using a low-RPM fan on
the heatsink instead of the noisey fans most people compare to the
Dell ducted system. If we are considering a custom-designed OEM
cooling system it has to be compared to an active cooling stategy with
similar forethought, not just a cheap/junk $5 'sink with a
tornado-speed fan on top.


Ductwork is merely cheaper than a high-quality
heatsink,

Again, not necessarily so. Depends on the overall design.

There are a lot of variables involved with design, production, parts,
but in general a high-volume production piece of plastic should be
less costly than a second fan and more elaborate heatsink. There can
be exceptions but practically we can only consider the ducted systems
being used by OEMs, not theorectical, nonexistant systems. A ducted
cooling system does tend to be the best noise/heat ratio if there are
budget constraints, at least for an OEM who can buy in bulk.

In other words, it can be the best budget-optimized solution for an
OEM, but optimizing as much as possible for cooling or noise, a ducted
passive 'sink cooling system cannot attain as low a noise/heat ratio.
Combining the two strategies, having a duct AND an active cooler,
would be the choice for lowest temps but again the duct necessitates
an increase in noise else *something* will run hotter, and of course
it will tend to be the most expensive alternative.


which would keep the CPU cooler AND be as quiet.

Simply not possible. HSF assembly gets it's air from and discharges it's hot air
into the case, which then needs to be ventilated more than if that hot air were
immediately expelled (as it is in the ducted design). The result is more fans
(or fan speeds) and more noise for the equivalent cooling.

It is possible with a high-quality active cooler. Even though some
heated air is recirculated the primary source of audible noise in an
optimized configuration is the rear fan, which is less efficient with
a duct on it. By optimizing both methods there might be similar
noise/heat ratios, but then the ducted system is more dependent on
preservation of the chassis airflow model.

The other
benefit is that these systems are being shipped, sometimes great
distances under less-than-ideal conditions, so reduced heatsink weight
as on the Dells is reducing the chance of RMA due to socket or CPU
damage.

Odds are the 'passive' (it's not really passive; the fan is just located
differently) heatsink is as massive, perhaps more, than one with the fan mounted
on it. It depends on the design if removal of the fan compensates but it isn't a
foregone conclusion.

Passive 'sinks are usually less densely populated with fins and have a
greater percentage of weight at their base, which is less leveraged
force against the socket or retention mechanism.




Proper fan selection is crucial to achieve low noise on an active
heatsink, but so it was also when Dell built their ducted system.

True. The point is, by ducting the hot CPU air directly out of the case, rather
than mixing it in as a HS mounted one does, there is less work needed to cool
the system.

Possibly, not not necessarily, and work is not always directly related
to _audible_ noise. Increasing the work done by a single fan by
having it create a suction through a duct, requires higher RPM, enough
so that the fan is no longer as quiet as the audible sum of [that fan
at lower RPM & turbulence, same airflow rate without duct] + [fan on
heatsink keeping CPU at same temp].

We could argue that a highly optimized (per system) duct be used, but
it would then need be compared to an optimized active 'sink, and the
optimized duct would be even less forgiving of user modifications to
the system, which must be considered on a PC.


Dave