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1 2 3 NextDecember 20, 2004 by Peter Scott
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Peter Scott is a computer consultant who works with computers much of the day in a quiet home office environment, an eco-inspired earth house with amazing acoustics. He writes from Auckland, New Zealand about his efforts to quiet a noisy P4 2.66A box. His article is another saga of experimentation and inventiveness that seem to be requisite for a successful PC silencing project. Peter also shows us yet another variant of the HDD anti-vibration decoupling suspension technique we espouse; he would probably say it's part and parcel of Kiwi make-do ingenuity. It's also reminiscent of the first year of SPCR when DIY project article submissions were the norm, not the exception. I expect this article will inspire those who live in places where the latest "silent" gear is not available.
Mike Chin, Editor / Publisher of SPCR
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I approached the task of quieting this noisy office PC by tackling
each of the four noise sources in turn. It turned
into quite an incremental approach, chipping a bit of noise off here and bit
there, until no one source really stood out and the overall noise level was
very tame. It took several weeks, surprisingly.
Firstly I ordered an all copper heatsink, the Thermaltake Golf 325, which
was available locally for a reasonable price. My criteria for the CPU cooler
were:
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must be able to fit 80mm fan,
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no more than NZ$50 and
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be efficient enough
to run on a slow fan.
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It's shown below complete with some homemade rubber fan
mounts.
I ditched the supplied Thermaltake Smartfan
because it has a real growl of a rumble at any speed. I guess its strength would be in overclocking, etc., as it spins up to
4500 rpm. I couldn't locate any NZ sources of either Papst or Panaflo L1 fans,
but did track down a supply of 80mm SilenX thermistor controlled fans. These
are quiet, and seem to have good build quality, but more about these later.
So with the parts arrived, I gutted the box, and set about improving the ventilation
into this particular case. Something you might know about NZers is that we
do things on a shoestring, using bits of whatever we have around. The case
has survived a number of upgrades, and, due to its vintage, was in serious need
for some more air flow. I enlarged the lower front air holes, and created
air holes at the upper rear where none previously existed. In hindsight I
should have cut these out completely and used wire grids, but I was being
cautious about RF pollution. Note the soft silicone rubber mounts, and sundry
other case holes taped over to preserve the thermal chimney effect.
As for the PSU, I couldn't locate a NZ source of Seasonic or
Nexus gear, and thought I'd have a go at modifying the existing PSU. After taking
the top off the PSU and fitting one of the SilenX fans using the supplied
silicone mounts, I figured the thermistor should go near the heatsinks but
out of the main airflow. After firing the modified PSU up, initially it ran quietly but
the new fan quickly rev'd up due to the inherently warm
environment of a 65% (in)efficient switching PSU.
For all the manufacturers
raves about silence, the SilenX fan certainly didn't sound too silent to me. It was only
after reading some more that it dawned upon me that so called silent fans
aren't really that much more quiet for a given airflow, they just
tend to run slower and hence more quietly. (See graph at www.cpemma.co.uk)
The SilenX 80mm starts off at about 1400 rpm and tops out at around 2400 rpm.
So I sorted through my old fan collection (which comprised mostly of a bunch
of plain old garden variety case fans) and basically tested each one for a)
starting reliably at 5v, b) absence of vibration and "rumble", and c) decent
airflow at 12V.
After concluding that the SilenX themistor wasn't really much use, with a quick
snip it was lopped off. I determined with a multimeter that it has about
11K ohms resistance when cold, and about 1K when hot. So I soldered on a 10K resistor and
— lo! — a permanently silent, albeit low airflow fan.
Unsatisfied by this lack
of control, I found a simple fan controller circuit on the web (www.cpemma.co.uk/ef.html)
which has only 5 parts. I threw that little circuit together, and mounted
it on an empty PCI slot hatch. Our local electronic parts retailer had these
rows of header pins which when you snip a pair off and solder them onto the
circuit board, fit most fan socket connectors quite nicely. Here's the finished
result.
The fan voltage varies between 5V and 11.3V, and it will cope with
40W of fans! The cable pair at left is the incoming 12V power which comes
from a Molex adapter.
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