helmut said:
hello all,
I built a pentium D 3.0ghz system in july(winter over here) and its been
running quiet with standard intel fan but now summer is coming, ambient
temps are rising and the cpu fan has sped up and sounds like a turbine.. I
know that that its the cpu fan because i stuck my finger in it to stop it
and silence prevailed,except for the hard drives and gfx card fan which are
very quiet in comparison. I also blew all the dust off but still noisy. So I
want to fit a 3rd party silent fan but aren't sure as to what is meant by
silent..theres a lot of hype around. Do they mean silent when the cpu is
cool or silent at max load..
The system has 2 gig ram and is rarely at max load.
I'm just looking for some genereal info on whats what.
thanks.
There is a discussion of decibel levels here:
http://en.wikipedia.org/wiki/Decibels
Acoustic noise is subject to masking. If something in your computer
case is louder than your CPU fan, then that other noise source will
drown it out. So your computer cannot be quieter than the worst
noise source in the case. The fan on your graphics card, or seek
noise from the hard drive, may continue to be a distraction, even
if you buy a very good CPU heatsink/fan. Hearing is logarithmic,
so battling noise is a pretty hopeless proposition. (On my computer,
the rear fan is louder than the CPU fan, and I cannot hear the CPU
fan as a result.)
The type of noise also makes a difference. The device measuring
the noise, may be "A" weighted. If the noise is a "tone" at
a fixed frequency, the measured value will be low, yet the noise
will be an irritating one. The methods used to make the noise
measurements, make a dB rating useless as a performance metric.
(In fact, you can only compare dB readings from reviews made
by the same web site. No two web sites measure noise exactly
the same way.)
One unavoidable noise source, is the computer case fan. You need
good airflow through the computer case, and that means you'll have
at least one fan sitting close to the outside of the computer.
Good airflow is necessary, to keep your disk drive cool, and
give it a long operating life. So you cannot dispense with all
fans.
In terms of general principles:
1) Buy a heatsink with a footprint larger than the socket area.
2) Select a heatsink where the fins are not too tightly spaced.
While a tight spacing allows many square inches of surface to
be packaged in a small space, it also raises the resistance to
airflow (arrestance). Some heatsinks are designed to be used
with high pressure fans (a fan like one found in a vacuum
cleaner). So there is a relationship between the heatsink
design, and the designer's expectation of what fan will be
used. A high pressure fan is more likely to be noisy.
You don't want a design from the good ole days, that used
a fan running at 55dB.
3) A copper base is a good choice, as it promotes spreading of
the central heat source, to all of the fins. The degree of
heat spreading is proportional to the base thickness. Even
with the presence of heatpipes, the base still have to be
thick enough, to transport the heat to the heatpipe.
4) Fins can be aluminum or copper. Aluminum is a better choice
for fins, as it keeps the weight of the top of the heatsink
to a reasonable level. Motherboards do have a limit as to
how heavy a heatsink that should be attached.
5) Heatpipes are very good at moving the heat from the base
plate, to the fins. They are a virtual perfect transport
mechanism (as long as the fluid is present in the heat pipe,
and the pressure inside is adjusted for the desired operating
temperature range).
6) A large, low speed fan, is the best cooling source. Small
fans are noisier. Due to the precision of the bearings,
buying too large a fan, can drive the noise level up again.
7) Directed air flow (ducting) can sometimes help cooling
performance.
Heatsink performance is measured as a thermal resistance. The
units are degrees C per Watt of heat. A value of 0.2 C/W for example,
along with a 90W max power processor, would give 0.2 * 90 = 18 degrees
C rise above the computer case internal air temperature. If the
internal air in the case was 32C, the processor temperature
would be 32+18 = 50C.
If you buy a heatsink with a theta_R of 0.2 or less, you can adjust
the fan operating speed, to trade off noise and cooling performance.
An example of a heatsink that is optimized for quiet operation, is
the Typhoon. It comes with a low speed fan, so even if the fan runs
at full speed, you will hardly hear it.
Thermaltake Big Typhoon $44
http://www.newegg.com/Product/Product.asp?Item=N82E16835106061
Notice the fin spacing on this one:
Scythe SCNJ-1000 Ninja heatsink
http://www.silentpcreview.com/article251-page2.html
The fin spacing might be a little bit tighter on this one. The
fan mounting (in the center of the unit), is not the best,
because if you have a fan blade right next to the fins, the
local turbulence can make it noisier.
Sunbeam Tuniq Tower 120
http://www.ocia.net/reviews/tuniq/page1.shtml
Some coolers are silent enough, that the users claim they leave
them running at full speed. There are a ton of reviews out there,
and with a couple days research, you should be able to find
some good candidates. (Make sure the heatsink supports your
motherboard socket type, whether it is S478 or LGA775. You'll
also have to compare the dimensions of the heatsink, to the
available space inside your computer case.)
Paul
